Tags:
SMN
Publications
-
-
-
Whitlow, Harry James; Nagy, Gyula; Frost, Robert J.W.; Toyen, Donruedee; Bose, Deepanwita & McLaughlin, Aaron
[Show all 11 contributors for this article]
(2026).
Ion microprobe determination of ex vivo trace element molarities: the LINAEUS code suite.
Journal of Analytical Atomic Spectrometry.
ISSN 0267-9477.
doi:
10.1039/d5ja00505a.
Full text in Research Archive
Show summary
MeV-ion based analytical methods such as Particle Induced X-ray Emission (PIXE) using a MeV ion microprobe in conjunction with analysis codes such as GeoPIXE represent powerful methods for analysis of trace elements in biomedical samples. In order to make the method truly quantitative for thin biological samples, knowledge of the local composition and thickness is required. Here the development and application of the LINAEUS code package, a complementary companion code to the GeoPIXE code, are described. This provides regional major element (C, H, N and O) composition and thickness data from Elastic Backscattering Spectrometry (EBS) and Off-Axis Scanning Transmission Ion Microscopy (OA-STIM) measurements. The program suite employs the same dynamic analysis method as used in GeoPIXE. LINAEUS incorporates a tissue region detection procedure based on spatial correlation to mitigate bias due to void regions without tissue corresponding to blood vessels, etc. The results for healthy murine small-intestine tissue showed no differences in the C, H, N and O contents but did show differences in thickness that were attributed to morphological distortion during drying of the tissue section. The molarity of trace elements (S, Cl, K, Ca and Fe) exhibited differences between tissue regions. Ca “hot-spots” (10–30 µm regions with much enhanced Ca levels) reported in other simian tissue samples were observed. These could not be attributed to mineralisation and their origin remains unclear.
-
Lábár, János L.; Cora, Ildikó; Pécz, Béla; Azarov, Alexander & Kuznetsov, Andrej
(2026).
Local deformations quantified with the common sublattice method.
Nanoscale.
ISSN 2040-3364.
18(4),
p. 2264–2276.
doi:
10.1039/d5nr03934g.
Full text in Research Archive
Show summary
Measurement of strain in epitaxial layers frequently faces the problem of localizing “perfectly” unstrained regions to use as a reference for the whole structure. Here, we develop a method for deducing such references in the unstrained substrate (with one crystal structure) to determine the local lattice deformations in the layer (with another crystal structure). The method works if there is a common sublattice in the layer and the substrate, so that the deviations from it may be used to interrelate the experimentally recorded data. The proof-of-concept is obtained using samples of cubic γ-Ga2O3 layers on a monoclinic β-Ga2O3 substrate, confirming that the new method overcomes several limitations of HRTEM-based methods. The precision of the method is ∼0.5% in strain values.
-
Mubaiwa, Praise Tinotenda; Sabatino, Marisa Di; Khromov, Sergey; Nybrodahl, Marthe; Azarov, Alexander & Safarian, Jafar
(2026).
Challenges and Practices in the Analysis of Silicon Kerf from the PV Industry by Combinatorial Analytical Methods.
Materials.
19(3),
p. 541–541.
doi:
10.3390/ma19030541.
Full text in Research Archive
Show summary
Exploitation of waste streams has gained prominence not only in sustainable use of resources but also as a potential source of raw materials. Silicon kerf is one such waste stream and its recycling has been quite topical in recent years. In the present study, the characterization of different industrial kerf samples was carried out using several techniques. The average metallic impurity concentration was approximately 400 ppmw with average particle size (D50) of 3.5 µm and surface area of approximately 33 m2/g. The inhomogeneity of kerf was shown to pose challenges like potential isotope interferences during analysis as well as being susceptible to high uncertainties and relative standard deviation (RSD). Remedies and best practices were recommended for successful characterization of such inhomogeneous materials.
-
Titov, Andrei; Klevtsov, Anton; Fedorenko, Elizaveta; Azarov, Alexander; Kuznetsov, Andrej & Karaseov, Platon
(2025).
Density and fractality of collision cascades in α-Ga2O3.
Applied Physics Letters.
ISSN 0003-6951.
127(15).
doi:
10.1063/5.0288966.
Full text in Research Archive
Show summary
Control over radiation defect generation is essential while applying ion-beam technology to materials. In this work, we study disorder formation in rhombohedral polymorph of gallium oxide (α-Ga2O3) as a function of the bombarding ion mass. As such, we discriminate the impact of the collision cascades density, specifically its impact on the surface amorphization rates in α-Ga2O3. Importantly, along with collecting experimental data, we calculated collision cascades parameters using different algorithms based on the binary collision approximation predicting disorder accumulation trends observed in the experiments. Furthermore, we showed that collision cascades in α-Ga2O3 can be modeled within a fractal geometry framework, correlating fractal dimension with the collision cascade density. These results enhance the understanding of radiation defects in Ga2O3 polymorphs, applicable in the development of the ion beam technology in these interesting materials.
-
Azarov, Alexander; Fernandez, Javier Garcia; Zhao, Junlei; He, Ru; Park, Ji-Hyeon & Jeon, Dae-Woo
[Show all 9 contributors for this article]
(2025).
Phase glides and self-organization of atomically abrupt interfaces out of stochastic disorder in α-Ga2O3.
Nature Communications.
16.
doi:
10.1038/s41467-025-58516-9.
Full text in Research Archive
Show summary
Disorder-induced ordering and remarkably high radiation tolerance in γ-phase of gallium oxide is a recent spectacular discovery at the intersection of the fundamental physics and electronic applications. Importantly, by far, these data were collected with initial samples in form of the thermodynamically stable β-phase of this material. Here, we investigate these phenomena starting from metastable α-phase and explain radically new trend occurring in the system. We argue that in contrast to that in β-to-γ disorder-induced transitions, the O sublattice in α-phase exhibits hexagonal close-packed structure, so that to activate α-to-γ transformation significant structural rearrangements are required in both Ga and O sublattices. Moreover, consistent with theoretical predictions, α-to-γ phase transformation requires accumulation of the substantial tensile strain to initiate otherwise impossible lattice glides. Thus, we explain the experimentally observed trends in term of the combination of disorder and strain governed process. Finally, we demonstrate atomically abrupt α/γ interfaces paradoxically self-organized out of the stochastic disorder.
-
-
-
-
Abdullaev, Azat; Sekerbayev, Kairolla; Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Chauhan, Vinay S. & Utegulov, Zhandos
[Show all 7 contributors for this article]
(2024).
Thermal conductivity of double polymorph Ga2O3 structures.
APL Materials.
12(8).
doi:
10.1063/5.0213985.
Full text in Research Archive
Show summary
Recently discovered double gamma/beta (γ/β) polymorph Ga2O3 structures constitute a class of novel materials providing an option to modulate functional properties across interfaces without changing the chemical compositions of materials, in contrast to that in conventional heterostructures. In this work, for the first time, we investigate thermal transport in such homo-interface structures as an example of their physical properties. In particular, the cross-plane thermal conductivity (k) was measured by femtosecond laser-based time-domain thermoreflectance with MHz modulation rates, effectively obtaining depth profiles of the thermal conductivity across the γ-/β-Ga2O3 structures. In this way, the thermal conductivity of γ-Ga2O3 ranging from 1.84 to 2.11 W m−1 K−1 was found to be independent of the initial β-substrates orientations, in accordance with the cubic spinel structure of the γ-phase and consistently with the molecular dynamics simulation data. In turn, the thermal conductivity of monoclinic β-Ga2O3 showed a distinct anisotropy, with values ranging from 10 W m−1 K−1 for [−201] to 20 Wm−1 K−1 for [010] orientations. Thus, for double γ-/β-Ga2O3 polymorph structures formed on [010] β-substrates, there is an order of magnitude difference in thermal conductivity across the γ/β interface, which can potentially be exploited in thermal energy conversion applications.
-
-
Slusar, Tetiana; Azarov, Alexander; Galeckas, Augustinas; Hallén, Anders; Ju, Jung Jin & Moon, Kiwon
[Show all 7 contributors for this article]
(2024).
Er:LiNbO3 Quantum Memory Platform Optimized with Dynamic Defect Annealing.
Advanced Optical Materials.
doi:
10.1002/adom.202401374.
Full text in Research Archive
Show summary
Lithium niobate (LiNbO3) exhibits poor radiation resistance when conventionally implanted with Er at room temperature. To repair the structural disorder, high-temperature post-implantation anneals are typically required; however, such treatments can cause sample cracking and dopant redistribution, which are incompatible with device applications. The optimized approach is proposed by performing implants at elevated but acceptably low temperatures to in situ minimize the structural defects generated in the collision cascades, via so-called “dynamic defect annealing”. Thus, a gradual increase in Er optical activity is shown as a function of irradiation temperature in the range of 25–450 °C, in striking correlation with a decreasing trend for the residual disorder. The impact of moderate post-implantation anneals is also investigated by comparing the results of anneals of samples implanted at 25 °C and 450 °C. This comparison further confirms the higher optical activation of Er and lower residual structural disorder when the material is initially implanted at elevated temperatures. Based on these data, it is concluded that the use of dynamic defect annealing during the Er implantation of LiNbO3 is a promising strategy for optimizing it as a quantum memory platform, resolving otherwise inevitable trade-offs.
-
Klevtsov, Anton; Karaseov, Platon; Azarov, Alexander; Karabeshkin, Konstantin; Fedorenko, Elizaveta & Titov, Andrei
[Show all 7 contributors for this article]
(2024).
Non-linear effects in α-Ga2O3 radiation phenomena.
APL Materials.
12(11).
doi:
10.1063/5.0235497.
Full text in Research Archive
Show summary
The rhombohedral phase of gallium oxide (α-Ga2O3) is of interest because of its highest bandgap among the rest of the Ga2O3 polymorphs, making it particularly attractive in applications. However, even though the ion beam processing is routinely used in device technology, the understanding of radiation phenomena in α-Ga2O3 is not mature. Here, we study non-linear effects for radiation disorder formation in α-Ga2O3 by varying both the defect generation rate and the density of collision cascades, enabled by comparing monoatomic and cluster ion implants, also applying systematic variations of ion fluxes. In particular, we show that the collision cascade density governs the surface amorphization rates, also affected by the ion flux variations. These trends are explained in terms of the non-linear in-cascade and inter-cascade defect interactions occurring during ballistic and dynamic defect annealing stages. As such, these data reveal new physics of the radiation phenomena in α-Ga2O3 and may be applicable for more predictive ion beam processing of α-Ga2O3-based devices.
-
Polyakov, Alexander Y.; Vasilev, Anton A.; Kochkova, Anastasiia I.; Shchemerov, Ivan V.; Yakimov, Eugene B. & Miakonkikh, Andrej V.
[Show all 17 contributors for this article]
(2024).
Proton damage effects in double polymorph γ/β-Ga2O3 diodes.
Journal of Materials Chemistry C.
ISSN 2050-7526.
12,
p. 1020–1029.
doi:
10.1039/d3tc04171a.
Full text in Research Archive
Show summary
Double polymorph γ/β-Ga2O3 structures remain crystalline upon unprecedentedly high crystal disorder levels where other semiconductors lose their long-range symmetry and, eventually, become amorphous. However, it is unclear if this radiation tolerance translates to device-like operation, where much lower levels of damage degrade the performance. In this work, we fabricated conducting double polymorph γ/β-Ga2O3 structures using ion implantation and subsequent hydrogenation of the top γ-Ga2O3 layer, instead of conventional impurity doping which is limited by γ-Ga2O3 stability tradeoffs. While not a direct comparison, these structures exhibited much higher radiation tolerance compared to conventional Schottky diodes made of β-Ga2O3. Specifically, using 1.1 MeV proton irradiation at fluences of 1014–1015 cm−2, conventional β-Ga2O3 diodes became unfunctional, while double polymorph γ/β-Ga2O3 diodes remained operational. The centers supplying electrons in γ-Ga2O3 were characterized by prominent DX-like persistent photocapacitance. For samples implanted with Ga+ and Si+ to produce the β → γ transition, annealed at 600 °C and plasma hydrogenated, the net donor concentration was ∼1012 cm−3, with dominant electron traps near EC − 0.65–0.7 eV and photocapacitance and photocurrent spectra determined by deep acceptors with optical ionization thresholds 1.3 eV, 2 eV, 2.3 eV and 2.8 eV. Irradiation with 1 MeV protons increased the net donor density of these conducting γ/β-Ga2O3 structures, with carrier creation rates of (1.5–4.4) × 10−2 cm−2, in sharp contrast to the carrier removal rates of 150–200 cm−1 under identical conditions in the original β-Ga2O3 films.
-
-
Chen, Xingqian; Li, Haozhen; Chen, Wei; Mei, Zengxia; Azarov, Alexander & Kuznetsov, Andrej
[Show all 7 contributors for this article]
(2024).
Interstitial Doping of SnO2 Film with Li for Indium-Free Transparent Conductor.
Chinese Physics Letters.
ISSN 0256-307X.
41(3).
doi:
10.1088/0256-307X/41/3/037305.
Full text in Research Archive
Show summary
SnO2 films exhibit significant potential as cost-effective and high electron mobility substitutes for In2O3 films. In this study, Li is incorporated into the interstitial site of the SnO2 lattice resulting in an exceptionally low resistivity of 2.028 × 10−3 Ω⋅cm along with a high carrier concentration of 1.398 × 1020 cm−3 and carrier mobility of 22.02 cm2/V⋅s. Intriguingly, Lii readily forms in amorphous structures but faces challenges in crystalline formations. Furthermore, it has been experimentally confirmed that Lii acts as a shallow donor in SnO2 with an ionization energy ΔED1 of −0.4 eV, indicating spontaneous occurrence of Lii ionization.
-
Azarov, Alexander; Galeckas, Augustinas; Wendler, Elke; Monakhov, Eduard & Kuznetsov, Andrej
(2024).
Inverse dynamic defect annealing in ZnO.
Applied Physics Letters.
ISSN 0003-6951.
124(4).
doi:
10.1063/5.0184669.
Full text in Research Archive
Show summary
Radiation tolerance of semiconductors depends on the dynamic defect annealing efficiency during irradiation. Consequently, it matters at what temperature one keeps the sample during irradiation, so that elevated temperatures typically result in lower remaining disorder. In the present work, we observed an opposite trend for the nitrogen ion implants into zinc oxide. Combining ion channeling technique, x-ray diffraction, and photoluminescence spectroscopy, we demonstrate that the interaction of nitrogen with radiation defects promotes an inverse dynamic annealing process, so that the increase in irradiation temperature leads to a more efficient defect formation. As a result, the residual radiation disorder is maximized at 650 °C and this state is characterized by the appearance of prominent optical signatures associated with zinc interstitials and strongly reduced strain accumulation as compared to the samples implanted at lower temperatures. However, for higher implantation temperatures, the impact of the inverse annealing decreases correlating with the surface degradation and loss of nitrogen.
-
-
Azarov, Alexander; Galeckas, Augustinas; Cora, Ildikó; Fogarassy, Zsolt; Venkatachalapathy, Vishnukanthan & Monakhov, Eduard
[Show all 7 contributors for this article]
(2024).
Optical Activity and Phase Transformations in γ/β Ga2O3 Bilayers Under Annealing.
Advanced Optical Materials.
doi:
10.1002/adom.202401325.
Full text in Research Archive
Show summary
Gallium oxide (Ga2O3) can be crystallized in several polymorphs exhibiting different physical properties. In this work, polymorphic structures consisting of the cubic defective spinel (γ) film on the top of the monoclinic (β) substrate are fabricated by disorder-induced ordering, known to be a practical way to stack these polymorphs together. Such bilayer structures are annealed to investigate optical properties and phase transformations. Specifically, photoluminescence and diffuse reflectance spectroscopy are combined with transmission electron microscopy, Rutherford backscattering/channeling spectrometry and X-ray diffraction to monitor the evolutions. As a result, a two-stage annealing kinetics is observed in γ/β Ga2O3 bilayers associated with the epitaxial γ-to-β regrowth at the interface at temperatures below 700 °C and a non-planar γ-to-β phase transformation starting at higher temperatures. Thus, the present data enhance understanding of the polymorphism in Ga2O3, interconnecting the phase transformation kinetics with the evolution of the optical properties.
-
Fernandez, Javier Garcia; Kjeldby, Snorre Braathen; Zeng, L. J.; Azarov, Alexander; Pokle, Anuj & Nguyen, Phuong Dan
[Show all 10 contributors for this article]
(2024).
In situ atomic-resolution study of transformations in double polymorph γ/β-Ga2O3 structures.
Materials Advances.
5,
p. 3824–3831.
doi:
10.1039/D3MA01011B.
Full text in Research Archive
Show summary
Disorder-induced formation of metastable Ga2O3 polymorphs as well as the recovery of the stable state upon annealing attract attention because of the fundamental novelty and rapidly increasing interest in the use of Ga2O3 in practical applications. In this study, double polymorph γ/β-Ga2O3 structures fabricated by the radiation-induced disorder approach were used as a starting point for systematic in situ annealing electron microscopy experiments. We show that, under the conditions of the TEM in situ annealing, double γ/β-Ga2O3 polymorph structures remained stable up to 300 °C, when onsets of the γ-to-β transformation become traceable, leading to a prominent γ- and β-mixture already at 500 °C. Interestingly, the recrystallization of the β-Ga2O3 occurs throughout the whole γ-film and the preferential alignments at the newly emerging γ/β-interfaces are different from that of the initial γ/β-interface formed as a result of the disorder-induced ordering. The alignments of the two polymorphs are maintained as a function of temperature – with a reduction in the volumetric ratio of γ-domains for increasing annealing temperature. Finally, at 1100 °C, γ-Ga2O3 fully transforms into β-Ga2O3, without dominating crystallographic relationships or preferred orientations, indicating that energy barriers are not any longer implied limiting factors, because of a sufficiently high thermal energy supply. Thus, these TEM in situ measurements enable a new level of accuracy for assessing polymorphic transformations in Ga2O3.
-
Kurbanova, B.; Chakraborty, D.; Abdullaev, A.; Shamatova, A.; Makukha, O. & Belarouci, A.
[Show all 11 contributors for this article]
(2024).
Multiscale phonon thermal transport in nano-porous silicon.
Applied Physics Letters.
ISSN 0003-6951.
124(25).
doi:
10.1063/5.0205455.
Full text in Research Archive
Show summary
We performed a comprehensive multi-scale phonon-mediated thermal transport study of nano-porous silicon (np-Si) films with average porosities in the range of = 30%–70%. This depth-resolved thermal characterization involves a combination of optical methods, including femtosecond laser-based time-domain thermo-reflectance (TDTR) with MHz modulation rates, opto-thermal micro-Raman spectroscopy, and continuum laser wave-based frequency domain thermo-reflectance (FDTR) with kHz modulation rates probing depths of studied samples over 0.5–1.2, 2–3.2, and 23–34 μm, respectively. We revealed a systematic decrease in thermal conductivity ( ) with the rise of , i.e., with the lowering of the Si crystalline phase volumetric fraction. These data were used to validate our semi-classical phonon Monte Carlo and finite element mesh simulations of heat conduction, taking into account disordered geometry configurations with various and pore size, as well as laser-induced temperature distributions, respectively. At high , the decrease in is additionally influenced by the disordering of the crystal structure, as evidenced by the near-surface sensitive TDTR and Rutherford backscattering spectroscopy measurements. Importantly, the values measured by FDTR over larger depths inside np-Si were found to be anisotropic and lower than those detected by the near-surface sensitive TDTR and Raman thermal probes. This finding is supported by the cross-sectional scanning electron microscopy image indicating enhanced distribution over these micrometer-scale probed depths. Our study opens an avenue for nano-to-micrometer scale thermal depth profiling of porous semiconducting media with inhomogeneous porosity distributions applicable for efficient thermoelectric and thermal management.
-
-
Mubaiwa, Praise Tinotenda; Garshol, Askh; Azarov, Alexander & Safarian, Jafar
(2024).
Silicon Kerf Recovery via Acid Leaching Followed by Melting at Elevated Temperatures.
Recycling.
ISSN 2313-4321.
9(4).
doi:
10.3390/recycling9040066.
Full text in Research Archive
Show summary
The aim of this work was to study the purification of silicon kerf loss waste (KLW) by a combination of single-acid leaching followed by inductive melting at high temperatures with an addition of fluidized bed reactor (FBR) silicon granules. The KLW indicated an average particle size (D50) of approximately 1.6 µm, and a BET surface area of 30.4 m2/g. Acid leaching by 1 M HCl indicated significant removal of impurities such as Ni (77%), Fe (91%) and P (75%). The combined two-stage treatment resulted in significant removal of the major impurities: Al (78%), Ni (79%), Ca (85%), P (92%) and Fe (99%). The general material loss during melting decreased with an increasing amount of FBR silicon granules which aided in the melting process and indicated better melting. It was observed that the melting behavior of the samples improved as the temperature increased, with complete melting being observed throughout the crucibles at the highest temperature (1800 °C) used, even without any additives. At lower temperatures (1600 °C–1700 °C) and lower FBR-Si (<30 wt.%) additions, the melting was incomplete, with patches of molten silicon and a lot of surface oxidation as confirmed by both visual observation and electron microscopy. In addition, it was indicated that more reactive and volatile elements (Ga, Mg and P) compared to silicon are partially removed in the melting process (51–87%), while the less reactive elements end up in the final silicon melt. It was concluded that if optimized, the combined treatment of single-acid leaching and inductive melting with the addition of granular FBR silicon has great potential for the recycling of KLW to solar cells and similar applications. Moreover, the application of higher melting temperatures is accompanied by a higher silicon yield of the process, and the involved mechanisms are presented.
-
Azarov, Alexander; Galeckas, Augustinas; Mikhaylov, Alexey; Nikolskaya, Alena; Tetelbaum, David & Korolev, Dmitry
[Show all 8 contributors for this article]
(2024).
Defect evolution and nitrogen incorporation in ion-implanted β-Ga2O3.
Applied Physics Letters.
ISSN 0003-6951.
125(19).
doi:
10.1063/5.0239899.
Full text in Research Archive
Show summary
Nitrogen plays an important role in the Ga2O3-based device fabrication since it demonstrates a deep acceptor behavior and it can be used as a compensation impurity. In the present work, we introduced N into the monoclinic β-Ga2O3 single crystals by ion implantation using different dose-rates. The thermal evolution of the structural and optical properties of the implanted samples was studied by combining Rutherford backscattering/channeling spectrometry and x-ray diffraction with photoluminescence spectroscopy. We demonstrate that crystal disorder in N-implanted β-Ga2O3 is a strong function of ion flux even for room temperature implantation. Unlike other implanted species, the defect annealing kinetics for N exhibit a distinct two-stage behavior, where the low-temperature stage (<400 °C) is characterized by a rapid defect annealing, whereas the radiation defects exhibit a very slow evolution at the elevated temperatures (>400 °C). These trends are discussed in the framework of the disorder stabilization induced by the incorporation of the implanted N atoms into the Ga2O3 lattice. The obtained results can be used to better understand the interaction between N and intrinsic defects as well as to push forward the development of β-Ga2O3-based electronic devices.
-
Arslan, H.; Aulika, I.; Sarakovskis, A.; Bikse, L.; Zubkins, M. & Azarov, Alexander
[Show all 8 contributors for this article]
(2023).
Reactive pulsed direct current magnetron sputtering deposition of semiconducting yttrium oxide thin film in ultralow oxygen atmosphere: A spectroscopic and structural investigation of growth dynamics.
Vacuum.
ISSN 0042-207X.
211,
p. 1–11.
doi:
10.1016/j.vacuum.2023.111942.
Full text in Research Archive
Show summary
An experimental investigation was conducted to explore spectroscopic and structural characterization of semiconducting yttrium oxide thin film deposited at 623 K (±5K) utilizing reactive pulsed direct current magnetron sputtering. Based on the results obtained from both x-ray diffraction and transmission electron microscope measurements, yttrium monoxide is very likely formed in the transition region between β-Y2O3 and α-Y2O3, and accompanied by the crystalline Y2O3. Resulting from either the low energy separation between 4d and 5s orbitals and/or different spin states of the corresponding orbitals’ sublevels, the stability of monoxide is most presumably self-limited by the size of the crystal in thermodynamic terms. This behavior develops a distortion in the structure of the crystal compared to the metal oxide cubic structure and it also effectuates the arrangement in nanocrystalline/amorphous phase. In addition to this, spectroscopic ellipsometry denotes that the semiconducting yttrium oxide has the dominant, mostly amorphous, formation character over crystalline Y2O3. Our purpose, by means of the current findings, is to advance the understanding of formation kinetics/conditions of yttrium with an unusual valency (2+).
-
Polyakov, Alexander Y.; Yakimov, Eugene B.; Nikolaev, Vladimir I.; Pechnikov, Alexei I.; Miakonkikh, Andrej V. & Azarov, Alexander
[Show all 12 contributors for this article]
(2023).
Impact of Hydrogen Plasma on Electrical Properties and Deep Trap Spectra in Ga2O3 Polymorphs.
Crystals.
13(9),
p. 1–25.
doi:
10.3390/cryst13091400.
Full text in Research Archive
Show summary
In this study, the results of hydrogen plasma treatments of β-Ga2O3, α-Ga2O3, κ-Ga2O3 and γ-Ga2O3 polymorphs are analyzed. For all polymorphs, the results strongly suggest an interplay between donor-like hydrogen configurations and acceptor complexes formed by hydrogen with gallium vacancies. A strong anisotropy of hydrogen plasma effects in the most thermodynamically stable β-Ga2O3 are explained by its low-symmetry monoclinic crystal structure. For the metastable, α-, κ- and γ-polymorphs, it is shown that the net result of hydrogenation is often a strong increase in the density of centers supplying electrons in the near-surface regions. These centers are responsible for prominent, persistent photocapacitance and photocurrent effects.
-
Polyakov, A.Y.; Kochkova, A.I.; Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Miakonkikh, A.V. & Vasilev, A.A.
[Show all 11 contributors for this article]
(2023).
Tuning electrical properties in Ga2O3 polymorphs induced with ion beams.
Journal of Applied Physics.
ISSN 0021-8979.
133(9),
p. 095701-1–095701-9.
doi:
10.1063/5.0133181.
Full text in Research Archive
Show summary
Ion beam fabrication of metastable polymorphs of Ga2O3, assisted by the controllable accumulation of the disorder in the lattice, is an interesting alternative to conventional deposition techniques. However, the adjustability of the electrical properties in such films is unexplored. In this work, we investigated two strategies for tuning the electron concentration in the ion beam created metastable κ-polymorph: adding silicon donors by ion implantation and adding hydrogen via plasma treatments. Importantly, all heat treatments were limited to ≤600 °C, set by the thermal stability of the ion beam fabricated polymorph. Under these conditions, silicon doping did not change the high resistive state caused by the iron acceptors in the initial wafer and residual defects accumulated upon the implants. Conversely, treating samples in a hydrogen plasma converted the ion beam fabricated κ-polymorph to n-type, with a net donor density in the low 1012 cm−3 range and dominating deep traps near 0.6 eV below the conduction band. The mechanism explaining this n-type conductivity change may be due to hydrogen forming shallow donor complexes with gallium vacancies and/or possibly passivating a fraction of the iron acceptors responsible for the high resistivity in the initial wafers.
-
Macková, Anna; Jagerová, Adéla; Lalik, Ondrej; Mikšová, Romana; Poustka, David & Mistrík, Jan
[Show all 12 contributors for this article]
(2023).
Combined Au/Ag nanoparticle creation in ZnO nanopillars by ion implantation for optical response modulation and photocatalysis.
Applied Surface Science.
ISSN 0169-4332.
610,
p. 1–13.
doi:
10.1016/j.apsusc.2022.155556.
Full text in Research Archive
Show summary
ZnO nanopillars were implanted with Au-400 keV and Ag-252 keV ions with ion fluences from 1 × 1015 cm−2 to 1 × 1016 cm−2. We compared ZnO nanopillars solely implanted with Au-ions and dually-implanted with Au and Ag-ions. Rutherford Back-Scattering spectrometry (RBS) confirmed Ag and Au embedded in ZnO nanopillar layers in a reasonable agreement with theoretical calculations. A decreasing thickness of the ZnO nanopillar layer was evidenced with the increasing ion implantation fluences. Spectroscopic Ellipsometry (SE) showed a decrease of refractive index in the nanopillar parts with embedded Au, Ag-ions. XRD discovered vertical domain size decreasing with the proceeding radiation damage accumulated in ZnO nanopillars which effect was preferably ascribed to Au-ions. SE and diffuse reflectance spectroscopy (DRS) showed optical activity of the created nanoparticles at wavelength range 500 – 600 nm and 430 – 700 nm for the Au-implanted and Au, Ag-implanted ZnO nanopillars, respectively. Photoluminescence (PL) features linked to ZnO deep level emission appear substantially enhanced due to plasmonic interaction with metal nanoparticles created by Ag, Au-implantation. Photocatalytic activity seems to be more influenced by the nanoparticles presented in the layer rather than the surface morphology. Dual implantation with Ag, Au-ions enhanced optical activity to a larger extent without significant morphology deterioration as compared to the solely Au-ion implanted nanopillars.
-
Nowak, M.; Mulewska, K.; Azarov, Alexander; Kurpaska, L. & Ustrzycka, A.
(2023).
A peridynamic elasto-plastic damage model for ion-irradiated materials.
International Journal of Mechanical Sciences.
ISSN 0020-7403.
237,
p. 1–19.
doi:
10.1016/j.ijmecsci.2022.107806.
Full text in Research Archive
Show summary
This study presents the novel peridynamic constitutive relations formulated in order to predict the plastic deformation and damage evolution in irradiated materials. The plastic behaviour of the material in which radiation induced defects contribute to the defined peridynamic porosity is described by the Gurson–Tvergaard–Needleman (GTN) yield criterion with irradiation hardening. The definition of peridynamic porosity is proposed as a volume of discontinuities created in the volume of peridynamic particles. The new constitutive relations for irradiation hardening based on the dilatational part of elastic strain energy are formulated. The physical relevance of coupling the porosity with the nonlinear irradiation hardening is discussed. The expressions for the yield function, kinetics of evolution of radiation induced porosity, irradiation hardening and plastic flow rule are derived in terms of the peridynamics variables. The peridynamic predictions are calibrated based on the experimental data obtained during the advanced experimental campaigns dedicated to irradiated materials to verify the validity of the proposed constitutive model. Ion irradiation campaigns were carried out to mimic the effects of neutron irradiation. A series of indentation experiments were conducted to elucidate the effects of material structure modification and assess the hardening effect originating from radiation defects.
-
Polyakov, A.Y.; Kuznetsov, Andrej; Azarov, Alexander; Miakonkikh, A.V.; Chernykh, A.V. & Vasilev, A.A.
[Show all 10 contributors for this article]
(2023).
The effects of hydrogenation on the properties of heavy ion irradiated β-Ga2O3.
Journal of materials science. Materials in electronics.
ISSN 0957-4522.
34(15).
doi:
10.1007/s10854-023-10628-y.
Full text in Research Archive
Show summary
Defects created in lightly Sn-doped (2 × 1016 cm−3) (010)-oriented bulk β-Ga2O3 implanted with 1.2 MeV, 3 × 1015 cm−2 197Au+ ions before and after treatment in hydrogen plasmas at 330 °C were studied by X-ray measurements, Rutherford backscattering spectra, capacitance–voltage, current–voltage, admittance spectra and deep level transient spectroscopy. Au implantation creates defects that produce total depletion of carriers in the top 1.5 µm and introduces electron traps with energy levels at Ec-0.7 eV, Ec-1.05 eV, Ec-0.45 eV, and deep acceptors with optical ionization thresholds near 1.3 eV, 2.3 eV and 3.1 eV, similar to the centers dominating the spectra of deep traps in β-Ga2O3. Hydrogen plasma treatment greatly enhances the photocurrent and photo-capacitance and decreases the width of the insulating layer produced by Au implantation. The results can be explained by hydrogen passivation of the triply charged Ga vacancies and doubly charged split Ga vacancies acceptors in the implanted region, returning part of this region to n-type conductivity.
-
Wyszkowska, E.; Mieszczynski, C.; Kurpaska, Ł.; Azarov, Alexander; Jóźwik, I. & Kosińska, A.
[Show all 11 contributors for this article]
(2023).
Tuning heterogeneous ion-radiation damage by composition in NixFe1−x binary single crystals.
Nanoscale.
ISSN 2040-3364.
15,
p. 4870–4881.
doi:
10.1039/d2nr06178c.
Full text in Research Archive
Show summary
Radiation-induced heterogeneous damage is the single largest source of failures seen in structural components in nuclear power reactors. Single crystal materials without grain boundaries, show considerable promise for overcoming this problem. In this work, such heterogeneous damage was further overcome in NixFe1−x single crystal alloys via a simple strategy of fine-tuning the composition. [001] NixFe1−x (x = 0, 0.38 and 0.62 at%) single crystals prepared using the Bridgman method were irradiated over a wide fluence range (4 × 1013 to 4 × 1015 ions per cm2). The irradiation-induced defect evolution was studied using Rutherford backscattering/channeling spectrometry, Monte Carlo simulations, transmission electron microscopy and nanoindentation. The results indicate an increased radiation tolerance of Ni0.38Fe0.62 compared to pure Ni and Ni0.62Fe0.38. The structural analysis performed by transmission electron microscopy revealed that defects tend to agglomerate at one place in Ni and Ni0.62Fe0.38, while in Ni0.38Fe0.62 no defect accumulation zone (characteristic damage peak) has been captured either at low or high fluence. Moreover, we found that the hardness change with the increase of Fe content is due to different arrangements of Fe atoms in the crystal structure, which influences the obtained mechanical properties of NixFe1−x in the pristine state and after ion implantation.
-
Azarov, Alexander; Fernández, Javier García; Zhao, Junlei; Djurabekova, Flyura; He, Huan & He, Ru
[Show all 13 contributors for this article]
(2023).
Universal radiation tolerant semiconductor.
Nature Communications.
14,
p. 1–8.
doi:
10.1038/s41467-023-40588-0.
Full text in Research Archive
Show summary
Abstract Radiation tolerance is determined as the ability of crystalline materials to withstand the accumulation of the radiation induced disorder. Nevertheless, for sufficiently high fluences, in all by far known semiconductors it ends up with either very high disorder levels or amorphization. Here we show that gamma/beta (γ/β) double polymorph Ga 2 O 3 structures exhibit remarkably high radiation tolerance. Specifically, for room temperature experiments, they tolerate a disorder equivalent to hundreds of displacements per atom, without severe degradations of crystallinity; in comparison with, e.g., Si amorphizable already with the lattice atoms displaced just once. We explain this behavior by an interesting combination of the Ga- and O- sublattice properties in γ-Ga 2 O 3 . In particular, O-sublattice exhibits a strong recrystallization trend to recover the face-centered-cubic stacking despite the stronger displacement of O atoms compared to Ga during the active periods of cascades. Notably, we also explained the origin of the β-to-γ Ga 2 O 3 transformation, as a function of the increased disorder in β-Ga 2 O 3 and studied the phenomena as a function of the chemical nature of the implanted atoms. As a result, we conclude that γ/β double polymorph Ga 2 O 3 structures, in terms of their radiation tolerance properties, benchmark a class of universal radiation tolerant semiconductors.
-
Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Lee, In-Hwan & Kuznetsov, Andrej
(2023).
Thermal versus radiation-assisted defect annealing in β-Ga2O3.
Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films.
ISSN 0734-2101.
41(2).
doi:
10.1116/6.0002388.
Full text in Research Archive
Show summary
Gallium oxide (Ga2O3) exhibits complex behavior under ion irradiation since ion-induced disorder affects not only the functional properties but can provoke polymorphic transformations in Ga2O3. A conventional way used to minimize the lattice disorder is by doing postirradiation anneals. An alternative approach is to prevent the disorder accumulation from the beginning, by doing implants at elevated temperatures, so that a significant fraction of the disorder dynamically anneals out in radiation-assisted processes. Here, we use these two approaches for the minimization of radiation disorder in monoclinic β-Ga2O3 implanted to a dose below the threshold required for the polymorphic transformations. The results obtained by a combination of channeling and x-ray diffraction techniques revealed that implants at 300 °C effectively suppress the defect formation in β-Ga2O3. On the other hand, in order to reach similar crystalline quality in the samples implanted at room temperature, postirradiation anneals in excess of 900 °C are necessary.
-
Zaborowska, A.; Kurpaska, L.; Wyszkowska, E.; Azarov, Alexander; Turek, M. & Kosińska, A.
[Show all 8 contributors for this article]
(2023).
High versus low energy ion irradiation impact on functional properties of PLD-grown alumina coatings.
Nuclear Instruments and Methods in Physics Reseach B.
ISSN 0168-583X.
540,
p. 24–29.
doi:
10.1016/j.nimb.2023.03.027.
Full text in Research Archive
Show summary
It is well known that ion irradiation can be successfully used to reproduce microstructural features triggered by neutron irradiation. Even though the irradiation process brings many benefits, it is also associated with several drawbacks. For example, the penetration depth of the ion in the material is very limited. This is particularly important for energies below MeV, ultimately reducing the number of available irradiation facilities. In addition to that, extracting information exclusively from the modified volume may be challenging. Therefore, extreme caution must be taken when interpreting obtained data. Our work aims to compare the findings of nanomechanical studies already conducted separately on thin amorphous ceramic coatings irradiated with ions of different energies, hence layers of different thicknesses. In this work, we show that in some instances, the 10% rule may be obeyed. In order to prove our finding, we compared results obtained for ion irradiated (with two energies: 0.25 and 1.2 MeV up to 25dpa) alumina coating system. Mechanical properties of pristine and ion-irradiated specimens were studied by nanoindentation technique. Interestingly, the qualitative relationship between nanohardness and irradiation damage level is very similar, regardless of the energy used. The presented work proves that for some materials (e.g., hard coatings), the qualitative assessment of the mechanical changes using nanoindentation might be feasible even for shallow implantation depths.
-
Azarov, Alexander; Park, Ji-Hyeon; Jeon, Dae-Woo & Kuznetsov, Andrej
(2023).
High mobility of intrinsic defects in α-Ga2O3.
Applied Physics Letters.
ISSN 0003-6951.
122(18),
p. 182104-1–182104-4.
doi:
10.1063/5.0149870.
Full text in Research Archive
Show summary
Migration properties of the intrinsic defects were investigated in α-Ga2O3 by controllable introduction of the lattice disorder with ion irradiation and monitoring its evolution as a function of ion dose, flux, and temperature. Already the dose dependence acquired at room temperature suggested prominently high mobility of intrinsic defects in α-Ga2O3, since we observed two distinct disordered regions—near the surface and in the bulk—instead of a Gaussian shape following the ballistic defects production process. Moreover, the disorder accumulation has shown to be highly sensitive to the variation of the ion flux and temperature, known in the literature as the dose-rate effect. Therefore, by monitoring the process as a function of the flux and temperature, we observed such dose-rate effect in α-Ga2O3 with an activation energy of 0.33 ± 0.04 eV, which we attributed to the migration barrier of the intrinsic defects in the Ga sublattice, from where we collected the experimental data. By setting these results in the context of the theoretical data available in the literature, we argued that this energy may be attributed to the migration activation of the Ga self-interstitials in α-Ga2O3.
-
Mieszczynski, Cyprian; Jozwik, Przemyslaw; Skrobas, Kazimierz; Stefanska-Skrobas, Kamila; Ratajczak, Renata & Jagielski, Jacek
[Show all 11 contributors for this article]
(2023).
Combining MD-LAMMPS and MC-McChasy2 codes for dislocation simulations of Ni single crystal structure.
Nuclear Instruments and Methods in Physics Reseach B.
ISSN 0168-583X.
540,
p. 38–44.
doi:
10.1016/j.nimb.2023.04.010.
Full text in Research Archive
Show summary
The unique capability of the new version of the McChasy code (called McChasy2) is to provide the possibility to simulate experimental energy spectra delivered by Rutherford Backscattering Spectrometry in channeling direction (RBS/C) using large atomic structures (ca. 108 atoms). Ni-based alloys are nowadays one of the most studied and promising materials that can be used in the power generation sector and in general for high-temperature applications because of their radiation resistance and proof against harsh environmental conditions. In this work, we present recent results of investigations regarding simulations of extended structural defects (edge dislocations and loops) developed in the directions typically observed in the fcc systems that are formed inside nickel-based single-crystal alloys. The extended defect models are created using ATOMSK and the Molecular Dynamics (MD)-LAMMPS thermalization process. The models are then used to create virtual samples and fit experimental RBS/C spectra.
-
Wyszkowska, E.; Mieszczynski, C.; Kurpaska, Ł.; Azarov, Alexander; Chromiński, W. & Jóźwik, I.
[Show all 13 contributors for this article]
(2023).
The Fe addition as an effective treatment for improving the radiation resistance of fcc NixFe1-x single-crystal alloys.
Journal of Nuclear Materials.
ISSN 0022-3115.
584,
p. 1–12.
doi:
10.1016/j.jnucmat.2023.154565.
Full text in Research Archive
Show summary
In this work, five different compositions of fcc Ni and NixFe1-x single crystal alloys namely Ni, Ni0.88Fe0.12, Ni0.77Fe0.23, Ni0.62Fe0.38, Ni0.38Fe0.62 were irradiated by 1.5 MeV 58Ni ions at room temperature in a wide fluence range (4 × 1013 to 4 × 1015 ions/cm2). The role of Fe addition on the radiation resistance of the NixFe1-x single crystals was studied by transmission electron microscopy (TEM), ion channeling technique (RBS/C) and nanoindentation techniques. The Multi-Step Damage Accumulation analysis revealed the cross-sections for damage formation significantly decreases for Ni0.38Fe0.62 and Ni0.62Fe0.38 as compared to that in pure Ni single crystal, which is consistent with RBS/C and TEM results. The results of nanoindentation show that Ni0.62Fe0.38 alloy possesses the highest hardness (2.96 GPa) among the other compositions in a pristine state. To interpret this result, hybrid Monte Carlo/ Molecular dynamics simulations were used to check the presence of the ordered crystal phase structure for NixFe1-x binary alloys. The simulation results have shown that depending on the iron content, we deal with different amounts of FeNi3 (L12) phase. This result revealed that in Ni0.62Fe0.38 alloy, nanoprecipitate FeNi3 (L12) phase (around 20%) is formed inside the disordered matrix, which could be one of the main reasons for the high hardness of this alloy before irradiation.
Additionally, we have found adding iron reduced the number and size of the defects (as a result of ion irradiation) in NixFe1-x because the Fe element is more stable than Ni, which results from the electron configuration of both elements in the excited state. Therefore, the more iron in the material, the fewer defects are created.
-
Azarov, Alexander; Galeckas, Augustinas; Ling, Francis Chi-Chung & Kuznetsov, Andrej
(2022).
Tuning defect-related optical bands by channeling implants in semiconductors.
Journal of Physics D: Applied Physics.
ISSN 0022-3727.
56(3).
doi:
10.1088/1361-6463/aca778.
Full text in Research Archive
Show summary
Abstract Ion implantation is an excellent method to introduce defects into semiconductors, extending their functionalities in a controllable way. Herein, we investigated an option to use crystallographically aligned implants as an additional route to control the balance between optically active defects, selecting ZnO as a test material. The optical data were correlated with the structural analysis confirming the formation of different dominating crystalline defects in samples implanted along and off [0001] direction. Specifically, we demonstrated that different proportions in the contents of the extended and point defects in the initial as-implanted states of these samples, lead to prominent variations in the defect-related luminescence upon annealing. As such, we conclude that channeling implants may have an added value in the functionalization of defects in semiconductors, e.g. to tune specific spectral contents in the defect-related emission bands.
-
Kjeldby, Snorre Braathen; Azarov, Alexander; Nguyen, Phuong Dan; Venkatachalapathy, Vishnukanthan; Mikšová, R. & MacKová, A.
[Show all 9 contributors for this article]
(2022).
Radiation-induced defect accumulation and annealing in Si-implanted gallium oxide.
Journal of Applied Physics.
ISSN 0021-8979.
131(12).
doi:
10.1063/5.0083858.
Full text in Research Archive
Show summary
Defect accumulation and annealing phenomena in Si-implanted monoclinic gallium oxide (β-Ga 2 O 3 ) wafers, having [Formula: see text], (010), and (001) orientations, were studied by Rutherford backscattering spectrometry in channeling mode (RBS/c), x-ray diffraction (XRD), and (scanning) transmission electron microscopy [(S)TEM]. Initially, the samples with different surface orientations were implanted with 300 keV 28 Si + -ions, applying fluences in the range of 1 × 10 14 –2 × 10 16 Si/cm 2 , unveiling interesting disorder accumulation kinetics. In particular, the RBS/c, XRD, and (S)TEM combined data suggested that the radiation disorder buildup in Si-implanted β-Ga 2 O 3 is accompanied by significant strain accumulation, assisting crystalline-to-crystalline phase transitions instead of amorphization. Selected samples having [Formula: see text] orientation were subjected to isochronal (30 min) anneals in the range of 300–1300 °C in air. Systematic RBS/c and XRD characterization of these samples suggested complex structural transformations, which occurred as a function of the fluence and the temperature. Moreover, a detailed (S)TEM analysis of the sample implanted with 2 × 10 16 Si/cm 2 and annealed at 1100 °C was enhanced by applying dispersive x-ray and electron energy-loss spectroscopies. The analysis revealed silicon agglomerations in the form of silicon dioxide particles. Signal from silicon was also detected outside of the agglomerates, likely occurring as substitutional Si on Ga sites.
-
Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Karaseov, Platon; Titov, Andrei; Karabeshkin, Konstantin & Struchkov, Andrei
[Show all 7 contributors for this article]
(2022).
Interplay of the disorder and strain in gallium oxide.
Scientific Reports.
12(1).
doi:
10.1038/s41598-022-19191-8.
Full text in Research Archive
Show summary
Abstract Ion irradiation is a powerful tool to tune properties of semiconductors and, in particular, of gallium oxide (Ga 2 O 3 ) which is a promising ultra-wide bandgap semiconductor exhibiting phase instability for high enough strain/disorder levels. In the present paper we observed an interesting interplay between the disorder and strain in monoclinic β-Ga 2 O 3 single crystals by comparing atomic and cluster ion irradiations as well as atomic ions co-implants. The results obtained by a combination of the channeling technique, X-ray diffraction and theoretical calculations show that the disorder accumulation in β-Ga 2 O 3 exhibits superlinear behavior as a function of the collision cascade density. Moreover, the level of strain in the implanted region can be engineered by changing the disorder conditions in the near surface layer. The results can be used for better understanding of the radiation effects in β-Ga 2 O 3 and imply that disorder/strain interplay provides an additional degree of freedom to maintain desirable strain in Ga 2 O 3 , potentially applicable to modify the rate of the polymorphic transitions in this material.
-
Adeojo, Samuel; Malherbe, Johan; Azarov, Alexander; Odutemowo, Opeyemi; Njoroge, Eric & Abdelbagi, Hesham
[Show all 8 contributors for this article]
(2022).
Effects of implantation temperature and annealing on structural evolution and migration of Se into glassy carbon.
Solid State Sciences.
ISSN 1293-2558.
129.
doi:
10.1016/j.solidstatesciences.2022.106914.
Full text in Research Archive
Show summary
The use of glassy carbon (GC) as a future nuclear waste storage material depends on its capability to retain all radioactive fission products found in spent nuclear fuels. Selenium (79Se) is found in trace amounts in uranium ores, spent, and reprocessed nuclear fuel. This work investigates the effects of implantation temperature and annealing on the structural evolution and migration of Se implanted GC. To achieve these objectives, 150 keV Se+ was implanted into GC samples separately at room temperature (RT) and 200 °C to a fluence of 1 × 1016 cm−2. Some of the as-implanted samples were annealed at 1000, 1100 and 1200 °C for 5h and characterised by transmission electron microscopy (TEM), Raman spectroscopy, and secondary ion mass spectrometry (SIMS). Both TEM and Raman spectroscopy showed that implantation caused defects in the GC structures, with more defects in the RT as-implanted sample. Annealing caused the healing of both sample types but retained some radiation damage. No migration of Se atoms was observed in the RT and 200 °C as-implanted samples. However, a different migration behaviour was seen after annealing the RT and 200 °C samples up to 1200 °C, attributed to the trapping and de-trapping of Se atoms in different amounts of defect induced by implantation.
-
Titov, A.I.; Karabeshkin, K.V.; Struchkov, A.I.; Nikolaev, V.I.; Azarov, Alexander & Gogova, D.S.
[Show all 7 contributors for this article]
(2022).
Comparative study of radiation tolerance of GaN and Ga2O3 polymorphs.
Vacuum.
ISSN 0042-207X.
200.
doi:
10.1016/j.vacuum.2022.111005.
Full text in Research Archive
Show summary
The mechanisms of ion-induced defect formation and physical characteristics promoting radiation tolerance of wide and ultra-wide bandgap semiconductors are not well-studied and understood. In contrast to gallium nitride (GaN), gallium oxide (Ga2O3) can be crystallized in several polymorphs having different crystal structures and physical properties. In the preset paper, the damage buildup in wurtzite GaN as well as in corundum (α-) and monoclinic (β-) Ga2O3 polymorphs bombarded at room temperature with 40 keV P+ ions is studied by Rutherford backscattering/channeling spectrometry. We demonstrate that ion-beam-induced damage formation in Ga2O3 is different from that observed in GaN and dramatically depends on the polymorph type. Both Ga2O3 polymorphs cannot be rendered amorphous and exhibit considerably higher damage saturation at ∼90% of the full amorphization as compared to that of GaN. Intriguing enough the metastable α-Ga2O3 demonstrates considerably higher radiation resistance as compared to the most thermodynamically stable β-Ga2O3 polymorph. Furthermore, our results indicate that the sample surface and dynamic annealing play a significant role in the ion-induced damage formation processes in all Ga-based compounds studied.
-
Azarov, Alexander; Bazioti, Kalliopi; Venkatachalapathy, Vishnukanthan; Ponniah, Vajeeston; Monakhov, Eduard & Kuznetsov, Andrej
(2022).
Disorder-Induced Ordering in Gallium Oxide Polymorphs.
Physical Review Letters.
ISSN 0031-9007.
128(1).
doi:
10.1103/PhysRevLett.128.015704.
Full text in Research Archive
Show summary
olymorphs are common in nature and can be stabilized by applying external pressure in materials. The pressure and strain can also be induced by the gradually accumulated radiation disorder. However, in semiconductors, the radiation disorder accumulation typically results in the amorphization instead of engaging polymorphism. By studying these phenomena in gallium oxide we found that the amorphization may be prominently suppressed by the monoclinic to orthorhombic phase transition. Utilizing this discovery, a highly oriented single-phase orthorhombic film on the top of the monoclinic gallium oxide substrate was fabricated. Exploring this system, a novel mode of the lateral polymorphic regrowth, not previously observed in solids, was detected. In combination, these data envisage a new direction of research on polymorphs in Ga2O3 and, potentially, for similar polymorphic families in other materials.
-
Macková, Anna; Malinský, Petr; Jagerová, Adéla; Mikšová, Romana; Lalik, Ondrej & Nekvindová, Pavla
[Show all 14 contributors for this article]
(2022).
Energetic Au ion beam implantation of ZnO nanopillars for optical response modulation.
Journal of Physics D: Applied Physics.
ISSN 0022-3727.
55(215101).
doi:
10.1088/1361-6463/ac5486.
Full text in Research Archive
Show summary
Abstract Nanopillars of ZnO were implanted with Au-400 keV ions at various ion fluences from 1 × 10 15 cm −2 to 1 × 10 16 cm −2 and subsequently annealed at 750 °C for 15 min in order to reduce the implantation damage and to support Au nanoparticle (NP) aggregation. It was found that implantation-induced effects and thermal effects influence the Au NP coalescence as well as the quality of the ZnO nanopillars. Rutherford Back-Scattering spectrometry (RBS) showed the broader Au-depth profiles than it was theoretically predicted, but the Au-concentration maximum agrees well with prediction taking into account the effective ZnO layer density. The implantation at the higher fluences induced the morphology modification of the nanopillar layer evidenced by RBS and scanning electron microscopy (SEM). An indirect evidence of this effect was given by optical ellipsometry due to gradual refractive index changes in the ZnO nanopillars with the increased Au-ion fluence. Optical characterization of the Au-implanted and annealed nanopillars performed by means of photoluminescence (PL) and diffuse-reflectance spectroscopy (DRS) evidenced the surface plasmon resonance (SPR) activity of the embedded Au NPs. The SPR-enhanced scattering and PL emission observed in the spectral range 500–650 nm are ascribed to Au NPs or more complex Au-clusters. In addition, the ellipsometry measurements of extinction coefficient are found to corroborate well results from DRS, both indicating increase of SPR effect with the increase of Au-ion fluence and after the post-annealing.
-
Titov, A.I.; Karabeshkin, K.V.; Struchkov, A.I.; Karaseov, P.A. & Azarov, Alexander
(2022).
Radiation tolerance of GaN: The balance between radiation-stimulated defect annealing and defect stabilization by implanted atoms.
Journal of Physics D: Applied Physics.
ISSN 0022-3727.
55(17).
doi:
10.1088/1361-6463/ac4a38.
Full text in Research Archive
Show summary
Abstract Realization of radiation-hard electronic devices that are able to work in harsh environments requires deep understanding of the processes of defect formation/evolution occurring in semiconductors bombarded by energetic particles. In the present work we address such intriguing radiation phenomenon as high radiation tolerance of GaN and analyze structural disorder, employing advanced co-irradiation schemes where low and high energy implants with different ions have been used. Channeling analysis revealed that the interplay between radiation-stimulated defect annealing and defect stabilization by implanted atoms dominates defect formation in the crystal bulk. Furthermore, the balance between these two processes depends on implanted species. In particular, strong damage enhancement leading to the complete GaN bulk amorphization was observed for the samples pre-implanted with fluorine ions, whereas the co-irradiation of the samples pre-implanted with such elements as neon, phosphorus and argon leads to a decrease of the bulk damage.
-
Aarseth, Bjørn Lupton; Granerød, Cecilie Skjold; Galeckas, Augustinas; Azarov, Alexander; Nguyen, Phuong Dan & Prytz, Øystein
[Show all 7 contributors for this article]
(2021).
Formation and functionalization of Ge-nanoparticles in ZnO.
Nanotechnology.
ISSN 0957-4484.
32(50).
doi:
10.1088/1361-6528/ac264a.
Full text in Research Archive
Show summary
Semiconductor nanocrystals are often proposed as a viable route to improve solar energy conversion in photovoltaics and photoelectrochemical systems. Embedding the nanocrystals in, e.g. a transparent and conducting electrode of a solar cell will promote the photon absorption and subsequent transfer of the generated charge carriers from the nanocrystal, and thereby enhance the function of the electrode. This can be accomplished by embedding a semiconducting nanocrystal with a small bandgap in a transparent conducting oxide (TCO), which is commonly utilized as electrode in new generation solar cells. Here, we demonstrate the incorporation, formation, and functionalization of germanium (Ge) nanocrystals in zinc oxide utilizing ion implantation, where post implantation annealing at 800 °C results in diamond cubic Ge nanocrystals with sizes between 2 and 20 nm. Photoluminecence spectra show a distinct emission around 0.7 eV arising from the Ge nanocrystals, and with additional emission features up to 1.15 eV due to quantum confinement, demonstrating a novel functionalization and tunability of the TCO electrode.
-
Zaborowska, A.; Kurpaska, L.; Clozel, M.; Olivier, E.J.; O'Connell, J.H. & Vanazzi, M.
[Show all 13 contributors for this article]
(2021).
Absolute radiation tolerance of amorphous alumina coatings at room temperature.
Ceramics International.
ISSN 0272-8842.
47,
p. 34740–34750.
doi:
10.1016/j.ceramint.2021.09.013.
Full text in Research Archive
Show summary
In this study structural and mechanical properties of a 1 μm thick Al2O3 coating, deposited on 316L stainless steel by Pulsed Laser Deposition (PLD), subjected to high energy ion irradiation were assessed. Mechanical properties of pristine and ion-modified specimens were investigated using the nanoindentation technique. A comprehensive characterization combining Transmission Electron Microscopy and Grazing-Incidence X-ray Diffraction provided deep insight into the structure of the tested material at the nano- and micro-scale. Variation in the local atomic ordering of the irradiated zone at different doses was investigated using a reduced distribution function analysis obtained from electron diffraction data. Findings from nanoindentation measurements revealed a slight reduction in hardness of all irradiated layers. At the same time TEM examination indicated that the irradiated layer remained amorphous over the whole dpa range. No evidence of crystallization, void formation or element segregation was observed up to the highest implanted dose. Reported mechanical and structural findings were critically compared with each other pointing to the conclusion that under given irradiation conditions, over the whole range of doses used, alumina coatings exhibit excellent radiation resistance. Obtained data strongly suggest that investigated material may be considered as a promising candidate for next-generation nuclear reactors, especially LFR-type, where high corrosion protection is one of the highest prerogatives to be met.
-
Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Vines, Lasse; Monakhov, Eduard; Lee, In-Hwan & Kuznetsov, Andrej
(2021).
Activation energy of silicon diffusion in gallium oxide: Roles of the mediating defects charge states and phase modification.
Applied Physics Letters.
ISSN 0003-6951.
119(18).
doi:
10.1063/5.0070045.
Full text in Research Archive
Show summary
Silicon (Si) is an efficient n-type dopant in gallium oxide (Ga2O3)—an ultra-wide bandgap semiconductor promising in a number of applications. However, in spite of the technological importance for device fabrication, the activation energy for Si diffusion in Ga2O3 is missing in the literature. In the present work, we do such measurements in ion implanted monoclinic β-Ga2O3 samples employing anneals in air ambient, also admitting the influence of potential ion beam induced phase modifications on diffusion. Importantly, we show that Si diffusion in β-Ga2O3 fits with the concentration dependent diffusion model, involving neutral and single negatively charged point defects to mediate the process; so that we assumed gallium vacancies in the corresponding charge states to assist Si diffusion in β-Ga2O3 with activation energies of 3.2 ± 0.3 and 5.4 ± 0.4 eV, respectively. Moreover, we also found that a preexisting phase modified surface layer efficiently suppressed Si diffusion in β-Ga2O3 for temperatures up to 1000 °C.
-
Nyborg, Martin; Azarov, Alexander; Bergum, Kristin & Monakhov, Eduard
(2021).
Deposition and characterization of lithium doped direct current magnetron sputtered Cu2O films.
Thin Solid Films.
ISSN 0040-6090.
722(31),
p. 1–5.
doi:
10.1016/j.tsf.2021.138573.
Full text in Research Archive
-
Zhu, Mengyi; Wu, Guixuan; Azarov, Alexander; Monakhov, Eduard; Tang, Kai & Müller, Michael
[Show all 7 contributors for this article]
(2021).
Effects of La2O3 Addition into CaO-SiO2 Slag: Structural Evolution and Impurity Separation from Si-Sn Alloy.
Metallurgical and Materials Transactions B.
ISSN 1073-5615.
52B(5),
p. 3045–3063.
doi:
10.1007/s11663-021-02232-4.
Full text in Research Archive
Show summary
Boron (B) and phosphorus (P) are the most problematic impurities to be removed in the production of solar-grade silicon by the metallurgical process. In this work, the distribution of B and P between CaO-(La2O3)-SiO2 slags and Si-10 mass pct Sn melt was experimentally studied. B distribution coefficient increased from 2.93 in binary CaO-SiO2 slag to 3.33 and 3.65 with 2 and 10 mass pct La2O3 additions, respectively. In the followed acid-leaching experiments, the slag-treated Si-Sn alloys exhibited higher B and P removal than that of the initial alloy without slag treatment. Molecular dynamics simulations were performed to study the effect of La2O3 addition on the slag structural and transport properties. A novel oxygen classification method was proposed to distinguish the different structural roles of La and Ca in the CaO-La2O3-SiO2 system. It was found that La3+ prefers to stay in the depolymerized region, mostly connects with 6-7 non-bridging oxygen, and requires a weak charge compensation with Ca2+. Possible silicothermic reduction was evaluated to discuss the slag chemistry and the mass transfer between slag and metal phase. A thermodynamic model was derived to theoretically study the alloying effect on impurity distribution in slag refining where positive interaction coefficient and high alloying concentration were found most beneficial to improve the impurity removal.
-
Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Monakhov, Eduard & Kuznetsov, Andrej
(2021).
Dominating migration barrier for intrinsic defects in gallium oxide: Dose-rate effect measurements.
Applied Physics Letters.
ISSN 0003-6951.
118(23).
doi:
10.1063/5.0051047.
Full text in Research Archive
Show summary
Ion bombardment provides an opportunity to study basic properties of intrinsic defects in materials since the radiation-induced disorder accumulation depends on the balance between defect generation and migration rates. In particular, variation of such parameters as irradiation temperature and ion flux, known in the literature as dose-rate effect, interconnects the macroscopically measured lattice disorder with the migration barrier of the dominating defects. In this work, we measured the dose-rate effect in monoclinic gallium oxide (β-Ga2O3) and extracted its activation energy of 0.8 ± 0.1 eV in the range of 25–250 °C. Taking into account that the measurements were performed in the Ga-sublattice and considering 0.8 ± 0.1 eV in the context of theoretical data, we interpreted it as the migration barrier for Ga vacancies in β-Ga2O3, limiting the process. Additionally, we observed and took into account an interesting form of the lattice relaxation due to radiation-induced disorder buildup, interpreted in terms of the compressive strain accumulation, potentially trigging phase transitions in Ga2O3 lattice.
-
Cieślik, I.; Duchna, M.; Płociński, T.; Wyszkowska, E.; Azarov, Alexander & Zieniuk, M.
(2020).
Ion irradiation effect on the microstructure of Inconel 625 obtained by Selective Laser Melting and by the metallurgical process.
Surface & Coatings Technology.
ISSN 0257-8972.
396.
doi:
10.1016/j.surfcoat.2020.125952.
Full text in Research Archive
-
Ellingsen, Josef Gert Åsheim; Venkatachalapathy, Vishnukanthan; Azarov, Alexander; Nilsen, Ola & Kuznetsov, Andrej
(2020).
Al incorporation during metal organic chemical vapour deposition of aluminium zinc oxide.
Thin Solid Films.
ISSN 0040-6090.
709.
doi:
10.1016/j.tsf.2020.138245.
Full text in Research Archive
Show summary
Aluminium zinc oxide (AZO) is a promising transparent conductive oxide this is difficult to fabricate by metal-organic chemical vapour deposition (MOCVD) because of prereactions between the precursors for Al and oxygen. One way of reducing prereactions is to use separate injectors. In this work, we investigated the effect of separate injectors and various flow configurations on the MOCVD fabrication of AZO using diethyl zinc (DEZn), tert-butanol (tBuOH), and trimethyl aluminium (TMAl) precursors. X-ray diffraction revealed that the resulting films maintained a purely wurtzite ZnO structure, and that the Al incorporation changed the c lattice parameters from 5.207 to 5.181 Å in agreement with theoretical models of mixing on the Zn sub-lattice. This indicates that Al was mainly incorporated onto the Zn sub-lattice. The maximum Al concentration was 6 × 1021 cm . The Al concentration was directly influenced by the TMAl flow rates, but the incorporation efficiency of Al also depended on the O/Zn balance as determined by the tBuOH supply and the total flow rate through the TMAl+DEZn injector. The tBuOH supply decreased the incorporation efficiency, while it increased for higher total flow in the TMAl+DEZn injector although both changes nominally increases the O/Zn balance. This dual, but contradicting, dependency on the O/Zn suggested that the incorporation efficiency depended not only on precursor supply, but also on the chemical stability of the Al species present at the growth interface. The concept of a reaction depth of TMAl was introduced to discuss the observed trends, and a qualitative model was suggested to explain how the Al-species present at the growth interface are determined by the relative depths of the reaction depth and the boundary layer. These findings illustrate the limits of the O/Zn parameter when using separate injectors because the properties of the boundary layer can affect Al incorporation during MOCVD growth. This should be relevant for MOCVD growth of other compound semiconductor systems that are grown using separate injectors.
-
Zhu, Mengyi; Azarov, Alexander; Monakhov, Eduard; Tang, Kai & Safarian, Jafar
(2020).
Phosphorus separation from metallurgical-grade silicon by magnesium alloying and acid leaching.
Separation and Purification Technology.
ISSN 1383-5866.
240.
doi:
10.1016/j.seppur.2020.116614.
Full text in Research Archive
Show summary
In this paper, the separation of phosphorus from metallurgical-grade silicon was investigated based on an Mg alloying and HCl leaching approach. Experimental results show that P concentration was reduced from initial 15.1 ppmw to 0.2 ppmw with also large extent removal of metallic impurities by two times Mg alloying-leaching purification. The mechanism of enhanced P separation is clarified owing to the strong affinity between Mg and P, which is validated by SIMS elemental mapping. A two-parameter analytical model was developed to predict the P removal degree based on the variables of alloying metal concentration and interaction coefficient between alloying metal and P. The model is validated with experimental results and the interaction coefficient ε^P_{Mg In Si} was obtained as −10.8. This approach can be applied to model the removal of impurity which follows Gulliver-Scheil solidification from other binary alloying systems. Furthermore, in order to study the effect of applied alloying-leaching operation times, a model was proposed which establishes the mathematical relationships among key processing variables like initial and target P concentrations, the amount of the alloying metal, and the process operation times.
-
Azarov, Alexander; Galeckas, Augustinas; Venkatachalapathy, Vishnukanthan; Mei, Zengxia; Du, Xiaolong & Monakhov, Eduard
[Show all 7 contributors for this article]
(2020).
Acceptor complex signatures in oxygen-rich ZnO thin films implanted with chlorine ions.
Journal of Applied Physics.
ISSN 0021-8979.
128.
doi:
10.1063/5.0021089.
Full text in Research Archive
Show summary
Spectroscopic identification of defects and impurities is crucial for understanding doping asymmetry issues in ZnO and, therefore, realization of true ZnO-based bipolar devices. Chlorine (Cl) is an amphoteric impurity in ZnO exhibiting acceptor behavior in the interstitial configuration and donor action once on substitutional oxygen sites (ClO). In its turn, the incorporation of Cl atoms depends on the material growth conditions and a ClO fraction should be suppressed in O-rich materials. In the present work, Cl ions were implanted into ZnO thin films synthesized under O-rich conditions. In contrast to a negligible effect of Cl incorporation to electrical conductivity, photoluminescence measurements revealed dramatic developments of optical properties with a strong acceptor-like spectral signature emerging after 900 °C anneals. We discuss the origins of a new excitonic I* line (3.355 eV) induced by Cl-implantation and propose two alternative defect models based on shallow acceptor and shallow donor complexes.
-
Azarov, Alexander; Galeckas, Augustinas; Mieszczyński, Cyprian; Hallen, Anders & Kuznetsov, Andrej
(2020).
Effects of annealing on photoluminescence and defect interplay in ZnO bombarded by heavy ions: Crucial role of the ion dose.
Journal of Applied Physics.
ISSN 0021-8979.
127.
doi:
10.1063/1.5134011.
Full text in Research Archive
Show summary
Bombardment of ZnO with heavy ions generating dense collision cascades is of particular interest because of the formation of nontrivial damage distribution involving a defected layer located between the surface and the bulk damage regions, as seen by Rutherford backscattering spectroscopy in the channeling mode. By correlating photoluminescence and channeling data, we demonstrate that the thermal evolution of defects in wurtzite ZnO single crystals implanted with Cd ions strongly depends on the implanted dose. Specifically, the ion dose has a profound effect on the optical response in the spectral range between the near-band-edge emission and deep-level emission bands. The interplay between interstitial and vacancy type defects during annealing is discussed in relation to the evolution of the multipeak damage distribution.
-
Kjeldstad, Torunn; Thøgersen, Annett; Stange, Marit Synnøve Sæverud; Azarov, Alexander; Monakhov, Eduard & Galeckas, Augustinas
(2019).
Monitoring selective etching of self-assembled nanostructured a-Si:Al films.
Nanotechnology.
ISSN 0957-4484.
30(13),
p. 1–5.
doi:
10.1088/1361-6528/aafb86.
Full text in Research Archive
Show summary
Nanoporous and nanowire structures based on silicon (Si) have a well recognized potential in a number of applications such as photovoltaics, energy storage and thermoelectricity. The immiscibility of Si and aluminum (Al) may be utilized to produce a thin film of vertically aligned Al nanowires of 5 nm diameter within an amorphous silicon matrix (a-Si), providing a cheap and scalable fabrication method for sub 5 nm size Si nanostructures. In this work we study functionalization of these structures by removal of the Al nanowires. The nanowires have been etched by an aqueous solution of HCl, which results in a structure of vertically aligned nanochannels in a-Si with admixture of SiO x . The removal of Al nanowires has been monitored by several electron microscopy techniques, x-ray diffraction, Rutherford backscattering spectroscopy, and optical reflectance. We have established that optical reflectance measurements can reliably identify the complete removal of Al, confirmed by other techniques. This provides a robust and relatively simple method for controlling the nano-fabrication process on a macroscopic scale.
-
Azarov, Alexander; Aarseth, Bjørn Lupton; Vines, Lasse; Hallen, Anders; Monakhov, Eduard & Kuznetsov, Andrej
(2019).
Defect annealing kinetics in ZnO implanted with Zn substituting elements: Zn interstitials and Li redistribution.
Journal of Applied Physics.
ISSN 0021-8979.
125(7).
doi:
10.1063/1.5083226.
Full text in Research Archive
Show summary
It is known that the behavior of residual Li in ion implanted ZnO depends on the preferential localization of the implants, in particular, forming characteristic Li depleted or Li pile-up regions for Zn or O sublattice occupation of the implants due to the corresponding excess generation of Zn and O interstitials in accordance with the so-called “+1 model.” However, the present study reveals that conditions for the radiation damage annealing introduce additional complexity into the interpretation of the Li redistribution trends. Specifically, four implants residing predominantly in the Zn-sublattice, but exhibiting different lattice recovery routes, were considered. Analyzing Li redistribution trends in these samples, it is clearly shown that Li behavior depends on the defect annealing kinetics which is a strong function of the implanted fluence and ion species. Thus, Li depleted and Li pile-up regions (or even combinations of the two) were observed and correlated with the defect evolution in the samples. It is discussed how the observed Li redistribution trends can be used for better understanding a thermal evolution of point defects in ZnO and, in particular, energetics and migration properties of Zn interstitials.
-
Olsen, Vegard Skiftestad; Bazioti, Kalliopi; Baldissera, Gustavo; Azarov, Alexander; Prytz, Øystein & Persson, Clas
[Show all 9 contributors for this article]
(2019).
Effects of Substrate and Post-Deposition Annealing on Structural and Optical Properties of (ZnO)1-x(GaN)x Films.
Physica status solidi (b).
ISSN 0370-1972.
256(6).
doi:
10.1002/pssb.201800529.
Full text in Research Archive
Show summary
The structural and optical properties of magnetron sputtered thin films of (ZnO)1−x(GaN)x deposited on zinc oxide, sapphire, and silicon oxide are studied as a function of strain accumulation and post‐deposition anneals at 600–800 °C. For the experimental conditions studied, we found that different amounts of tensile strain accumulated in the samples practically does not affect the strong bandbowing effect, that is, optical bandgap, observed in the as‐deposited alloys. In its turn, post‐deposition annealing results in a reduction of the tensile strain and dislocation density in the films, as measured by both X‐ray diffraction and transmission electron microscopy, corroborating an increase in the crystal quality. In addition, the grain size is found to increase with annealing temperature, for example, mean values of 20 nm up to 50 nm were measured for the alloys with x = 0.15. Meanwhile, the full‐width at half maximum of the (0002) X‐ray diffraction reflection increases with annealing temperature, but with only a small increase in bandgap energies for the x = 0.15 sample. However, this observation was explained combining the experimental data and first‐principles calculations based on density functional theory, showing that the increase in the amount of Ga‐N bonds lowers the total energy of the system. As such, we conclude that the thermal treatments increase the Ga‐N ordering, resulting in several contributions or a widening of the diffraction peaks.
-
-
Azarov, Alexander & Kuznetsov, Andrej
(2019).
Energetics, migration and trapping of Zn interstitials in ZnO.
Journal of Physics D: Applied Physics.
ISSN 0022-3727.
52(48).
doi:
10.1088/1361-6463/ab3eab.
Full text in Research Archive
Show summary
Zn interstitial (Zni) is one of the fundamental intrinsic defects in ZnO and prominently affects the physical properties of the material. Here, the energetics and migration properties of Zni have been studied in ion implanted ZnO using a new approach based on the Li marker diffusion. Specifically, ZnO single crystals were implanted with 3.2 keV/amu B and BF2 ions and the release of Zni from the implanted regions during annealing was correlated with the advance of the characteristic Li depleted region into the bulk of the samples. Using this methodology, we calculate the activation energy of 1.45 eV to govern the process for B implants. Assuming that the migration energy of Zni to be of ~0.6 eV, as discussed previously in literature, a barrier for releasing Zni from the implanted region may be estimated as ~0.8–0.9 eV. Meanwhile, in the BF2 implanted samples, the migration of Zni is less efficient, as interpreted from the Li redistribution features in these samples; in particular, it is argued that Zni may be trapped by defect complexes related to the presence of F.
-
-
Bazioti, Kalliopi; Azarov, Alexander; Johansen, Klaus Magnus H; Svensson, Bengt Gunnar; Vines, Lasse & Kuznetsov, Andrej
[Show all 7 contributors for this article]
(2019).
Role of Nitrogen in Defect Evolution in Zinc Oxide: STEM−EELS
Nanoscale Investigations.
The Journal of Physical Chemistry Letters.
10(16),
p. 4725–4730.
doi:
10.1021/acs.jpclett.9b01472.
Full text in Research Archive
Show summary
Direct evidence of the formation of nitrogen molecules (N2) after ion implantion of ZnO has been revealed by an atomically resolved scanning transmission electron microscopy (STEM)–electron energy-loss spectroscopy (EELS) investigation. Taking advantage of the possibility of using multiple detectors simultaneously in aberration-corrected STEM, we utilize the detailed correlation between the atomic structure and chemical identification to develop a model explaining the formation and evolution of different defect types and their interaction with N. In particular, the formation of zinc vacancy (VZn) clusters filled with N2 after heat treatment at 650 °C was observed, clearly indicating that N has not been stabilized in the O substitution site, thus limiting p-type doping. Previous results showing an exceptional thermal stability of vacancy clusters only for the case of N-doped ZnO are supported. Furthermore, VZn–N2 stabilization leads to suppression of VZn–Zni recombination; hence, the highly mobile Zn interstitials preferentially condense on the basal planes promoting formation of extended defects (basal stacking faults and stacking mismatched boundaries). The terminations of these defects provide energetically favorable sites for further N2 trapping as a way to reduce local strain fields.
-
-
Azarov, Alexander; Wendler, Elke; Monakhov, Edouard & Svensson, Bengt Gunnar
(2018).
Defect stabilization and reverse annealing in ZnO implanted with nitrogen at room and cryogenic temperature.
Journal of Applied Physics.
ISSN 0021-8979.
123(10).
doi:
10.1063/1.5022152.
Full text in Research Archive
Show summary
Despite the fact that nitrogen is a potential acceptor dopant and one of the most studied elements in ZnO, lacking understanding of associated defects and their thermal evolution limits realization of reliable p-type doping of ZnO. Here, we use ion implantation to introduce N at room temperature (RT) and 15 K in ZnO samples with/without a pre-existing buried disorder layer formed by Ag ion bombardment aligned along the [0001] direction. The buried layer contains a high concentration of extended defects, which act as traps for migrating point defects. Channeling analysis shows that reverse annealing occurs in all the N implanted samples during post-implant heat treatment above 600 °C with strong non-linear additive damage accumulation in the co-implanted samples. The reverse annealing effect is less stable in the RT co-implanted sample and the data suggest that a high local concentration of intrinsic point defects, like Zn interstitials, promotes the stability of the N-defect clusters responsible for the reverse annealing. This suggestion is also corroborated by enhanced and defect-mediated Ag outdiffusion at 1100 °C in the RT co-implanted samples.
-
-
Galeckas, Augustinas; Carvalho, Patricia Almeida; Ma, Quanbao; Azarov, Alexander; Hovden, Sigurd Slettemark & Thøgersen, Annett
[Show all 13 contributors for this article]
(2018).
Optical and microstructural investigation of heavy B-doping effects in sublimation-grown 3C-SiC.
Materials Science Forum.
ISSN 0255-5476.
924,
p. 221–224.
doi:
10.4028/www.scientific.net/MSF.924.221.
Full text in Research Archive
Show summary
In this work, a complementary microstructural and optical approach is used to define processing conditions favorable for the formation of deep boron-related acceptor centers that may provide a pathway for achieving an intermediate band behavior in highly B-doped 3C-SiC. The crystallinity, boron solubility and precipitation mechanisms in sublimation-grown 3C-SiC crystals implanted to 1-3 at.% B concentrations were investigated by STEM. The revealed defect formation and boron precipitation trends upon thermal treatment in the range 1100-2000°C have been cross-correlated with the optical characterization results provided by imaging PL spectroscopy. We discuss optical activity of the implanted B ions in terms of both shallow acceptors and deep D-centers, a complex formed by a boron atom and a carbon vacancy, and associate the observed spectral developments upon annealing with the strong temperature dependence of the D-center formation efficiency, which is further enhanced by the presence of implantation-induced defects.
-
-
-
Venkatachalapathy, Vishnukanthan; Galeckas, Augustinas; Azarov, Alexander; Vines, Lasse & Kuznetsov, Andrej
(2018).
Phase stability and strain accumulation in CdO as a function of Cd/O supply during MOVPE synthesis.
Superlattices and Microstructures.
ISSN 0749-6036.
120,
p. 569–577.
doi:
10.1016/j.spmi.2018.06.017.
Full text in Research Archive
-
Schifano, Ramon; Riise, Heine Nygard; Domagala, J.; Azarov, Alexander; Ratajczak, R. & Monakhov, Edouard
[Show all 11 contributors for this article]
(2017).
Comparison of the structural properties of Zn-face and O-face single crystal homoepitaxial ZnO epilayers grown by RF-magnetron sputtering.
Journal of Applied Physics.
ISSN 0021-8979.
121(1).
doi:
10.1063/1.4973342.
Full text in Research Archive
Show summary
Homoepitaxial ZnO growth is demonstrated from conventional RF-sputtering at 400 °C on both Zn and O polar faces of hydrothermally grown ZnO substrates. A minimum yield for the Rutherford backscattering and channeling spectrum, χmin, equal to ∼3% and ∼12% and a full width at half maximum of the 00.2 diffraction peak rocking curve of (70 ± 10) arc sec and (1400 ± 100) arc sec have been found for samples grown on the Zn and O face, respectively. The structural characteristics of the film deposited on the Zn face are comparable with those of epilayers grown by more complex techniques like molecular beam epitaxy. In contrast, the film simultaneously deposited on the O-face exhibits an inferior crystalline structure ∼0.7% strained in the c-direction and a higher atomic number contrast compared with the substrate, as revealed by high angle annular dark field imaging measurements. These differences between the Zn- and O-face films are discussed in detail and associated with the different growth mechanisms prevailing on the two surfaces. © 2016 AIP Publishing
-
View all works in NVA
-
Bazioti, Kalliopi; Azarov, Alexander; Vines, Lasse; Prytz, Øystein & Kuznetsov, Andrej
(2026).
Fundamental insights into polymorphism and defect evolution in ion-irradiated semiconductors by employing atomic-scale Transmission Electron Microscopy.
Full text in Research Archive
-
-
-
Azarov, Alexander; Slusar, Tetiana; Galeckas, Augustinas; Moon, Kiwon; Hallen, Anders & Kuznetsov, Andrej
(2024).
Dynamic defect annealing in Er implanted LiNbO3.
Full text in Research Archive
-
-
-
Azarov, Alexander; Park, Ji-Hyeon; Jeon, Dae-Woo; Monakhov, Eduard & Kuznetsov, Andrej
(2023).
Defect migration energies in Ga2O3 polymorphs measured by variations of temperature and flux under irradiation.
Full text in Research Archive
-
-
Azarov, Alexander; Bazioti, Kalliopi; Venkatachalapathy, Vishnukanthan; Vajeeston, Ponniah; Monakhov, Eduard & Kuznetsov, Andrej
(2022).
Disorder-induced ordering in Ga2O3 polymorphs.
Full text in Research Archive
-
Azarov, Alexander; Bazioti, Kalliopi; Venkatachalapathy, Vishnukanthan; Vajeeston, Ponniah; Monakhov, Eduard & Kuznetsov, Andrej
(2022).
Ion-beam-induced phase transitions in gallium oxide: impact of the implantation temperature.
Full text in Research Archive
-
-
-
Kjeldby, Snorre Braathen; Azarov, Alexander; Aarholt, Thomas; Prytz, Øystein & Vines, Lasse
(2021).
Defect-annealing in Si+-implanted β-Ga2O3.
Full text in Research Archive
-
Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Monakhov, Eduard & Kuznetsov, Andrej
(2021).
Dose-rate effect in β-Ga2O3.
Full text in Research Archive
-
Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Monakhov, Eduard & Kuznetsov, Andrej
(2021).
Dominating migration barrier for intrinsic defects in gallium oxide at and above room temperature.
Full text in Research Archive
-
-
Azarov, Alexander; Venkatachalapathy, Vishnukanthan; Monakhov, Eduard & Kuznetsov, Andrej
(2021).
Radiation defect dynamics in β-Ga2O3: ion flux vs irradiation temperature.
Full text in Research Archive
-
Azarov, Alexander; Hoseinpur, Arman; Safarian, Jafar & Monakhov, Eduard
(2021).
Impurity analysis in Al-Si alloys by SIMS: the role of the primary beam.
Full text in Research Archive
-
-
-
Azarov, Alexander; Galeckas, Augustinas; Mieszczyński, Cyprian; Hallen, Anders & Kuznetsov, Andrej
(2019).
Effects of annealing on photoluminescence and defect interplay in ZnO bombarded with heavy ions: crucial role of the ion dose.
Full text in Research Archive
-
Bazioti, Kalliopi; Olsen, Vegard Skiftestad; Azarov, Alexander; Kuznetsov, Andrej; Vines, Lasse & Prytz, Øystein
(2019).
Defect formation and thermal evolution in ZnO-based structures (Highlight talk).
Full text in Research Archive
-
-
Bazioti, Kalliopi; Azarov, Alexander; Svensson, Bengt Gunnar & Prytz, Øystein
(2018).
An aberration-corrected (S)TEM study of N-induced defects in ZnO: formation and thermal evolution.
Full text in Research Archive
-
Bazioti, Kalliopi; Azarov, Alexander; Svensson, Bengt Gunnar & Prytz, Øystein
(2018).
(S)TEM characterization and thermal evolution of ion-induced defects in ZnO.
Full text in Research Archive
-
-
Ayedh, Hussein Mohammed Hussein; Azarov, Alexander; Galeckas, Augustinas; Svensson, Bengt Gunnar & Monakhov, Edouard
(2017).
DLTS study of the interstitial carbon–oxygen complex in
proton irradiated p-type Si.
Full text in Research Archive
View all works in NVA
Published
Aug. 17, 2016 11:57 AM
- Last modified
Sep. 8, 2016 10:44 AM