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Hommedal, Ylva Knausgård; Bathen, Marianne Etzelmüller; Reinertsen, Vilde Mari; Johansen, Klaus Magnus H; Vines, Lasse & Frodason, Ymir Kalmann
(2024).
Theoretical modeling of defect diffusion in wide bandgap semiconductors.
Journal of Applied Physics.
ISSN 0021-8979.
135.
doi:
10.1063/5.0205866.
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Since the 1940s, it has been known that diffusion in crystalline solids occurs due to lattice defects. The diffusion of defects can have a great impact on the processing and heat treatment of materials as the microstructural changes caused by diffusion can influence the material qualities and properties. It is, therefore, vital to be able to control the diffusion. This implies that we need a deep understanding of the interactions between impurities, matrix atoms, and intrinsic defects. The role of density functional theory (DFT) calculations in solid-state diffusion studies has become considerable. The main parameters to obtain in defect diffusion studies with DFT are formation energies, binding energies, and migration barriers. In particular, the utilization of the nudged elastic band and the dimer methods has improved the accuracy of these parameters. In systematic diffusion studies, the combination of experimentally obtained results and theoretical predictions can reveal information about the atomic diffusion processes. The combination of the theoretical predictions and the experimental results gives a unique opportunity to compare parameters found from the different methods and gain knowledge about atomic migration. In this Perspective paper, we present case studies on defect diffusion in wide bandgap semiconductors. The case studies cover examples from the three diffusion models: free diffusion, trap-limited diffusion, and reaction diffusion. We focus on the role of DFT in these studies combined with results obtained with the experimental techniques secondary ion mass spectrometry and deep-level transient spectroscopy combined with diffusion simulations.
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Kang, Xiaolan; Reinertsen, Vilde Mari; Both, Kevin Gregor; Galeckas, Augustinas; Aarholt, Thomas & Prytz, Øystein
[Show all 9 contributors for this article]
(2022).
Galvanic Restructuring of Exsolved Nanoparticles for Plasmonic and Electrocatalytic Energy Conversion.
Small.
ISSN 1613-6810.
18(29).
doi:
10.1002/smll.202201106.
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There is a growing need to control and tune nanoparticles (NPs) to increase their stability and effectiveness, especially for photo- and electrochemical energy conversion applications. Exsolved particles are well anchored and can be re-shaped without changing their initial location and structural arrangement. However, this usually involves lengthy treatments and use of toxic gases. Here, the galvanic replacement/deposition method is used, which is simpler, safer, and leads to a wealth of new hybrid nanostructures with a higher degree of tailorability. The produced NiAu bimetallic nanostructures supported on SrTiO3 display exceptional activity in plasmon-assisted photoelectrochemical (PEC) water oxidation reactions. In situ scanning transmission electron microscopy is used to visualize the structural evolution of the plasmonic bimetallic structures, while theoretical simulations provide mechanistic insight and correlate the surface plasmon resonance effects with structural features and enhanced PEC performance. The versatility of this concept in shifting catalytic modes to the hydrogen evolution reaction is demonstrated by preparing hybrid NiPt bimetallic NPs of low Pt loadings on highly reduced SrTiO3 supports. This powerful methodology enables the design of supported bimetallic nanomaterials with tunable morphology and catalytic functionalities through minimal engineering.
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Thøgersen, Annett; Jensen, Ingvild Julie Thue; Belle, Branson Delano; Stange, Marit Synnøve Sæverud; Reinertsen, Vilde Mari & Kjeldstad, Torunn
[Show all 9 contributors for this article]
(2022).
Plasmonic properties of aluminium nanowires in amorphous silicon.
Journal of Physics: Condensed Matter.
ISSN 0953-8984.
35(6),
p. 1–10.
doi:
10.1088/1361-648X/aca30e.
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Plasmonic structures can help enhance optical activity in the ultraviolet (UV) region and therefore enhancing photocatalytic reactions and the detection of organic and biological species. Most plasmonic structures are composed of Ag or Au. However, producing structures small enough for optical activity in the UV region has proved difficult. In this study, we demonstrate that aluminium nanowires are an excellent alternative. We investigated the plasmonic properties of the Al nanowires as well as the optoelectronic properties of the surrounding a − Si matrix by combining scanning transmission electron microscopy imaging, electron energy loss spectroscopy and electrodynamic modelling. We have found that the Al nanowires have distinct plasmonic modes in the UV and far UV region, from 0.75 eV to 13 eV. In addition, simulated results found that the size and spacing of the Al nanowires, as well as the embedding material were shown to have a large impact on the type of surface plasmon energies that can be generated in the material. Using electromagnetic modelling, we have identified the modes and illustrated how they could be tuned further.
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Both, Kevin Gregor; Reinertsen, Vilde Mari; Aarholt, Thomas; Jensen, Ingvild Julie Thue; Neagu, Dragos & Prytz, Øystein
[Show all 8 contributors for this article]
(2022).
Ni-doped A-site excess SrTiO3 thin films modified with Au nanoparticles by a thermodynamically-driven restructuring for plasmonic activity.
Catalysis Today.
ISSN 0920-5861.
413.
doi:
10.1016/j.cattod.2022.11.011.
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Plasmonically active nanoparticles offer a promising pathway to extend the absorption range of photocatalysts. While not necessarily catalytically active themselves, these particles allow the absorption of lower energy photons in wide band gap photocatalysts. Here, we present A-site excess SrTiO3 thin films, doped with Ni, where through a subsequent exsolution process we created well-socketed Ni nanoparticles in the surface of SrTiO3. These were galvanically replaced by Au, resulting in well-socketed Au nanoparticles with variable size on the surface, depending on the galvanic replacement time. Photoelectrochemical measurements and electron energy loss spectroscopy revealed the improved photoresponse of the thin films by plasmonic activity of the nanoparticles. The energy of the plasmon peak suggests that the main improvement results from the injection of hot charge carriers. Our study opens new avenues for the design and synthesis of the next generation of photocatalytic materials.
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Karjalainen, Antti; Weiser, Philip Michael; Makkonen, I.; Reinertsen, Vilde Mari; Vines, Lasse & Tuomisto, Filip
(2021).
Interplay of vacancies, hydrogen, and electrical compensation in irradiated and annealed n-type β-Ga2O3.
Journal of Applied Physics.
ISSN 0021-8979.
129(16).
doi:
10.1063/5.0042518.
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Positron annihilation spectroscopy, Fourier transform-infrared absorption spectroscopy, and secondary ion mass spectrometry have been used to study the behavior of gallium vacancy-related defects and hydrogen in deuterium (D) implanted and subsequently annealed β-Ga2O3 single crystals. The data suggest the implantation generates a plethora of VGa-related species, including VGa1- and VGa2-type defects. The latter’s contribution to the positron signal was enhanced after an anneal at 300 ∘C, which is driven by the passivation of VibGa by hydrogen as seen from infrared measurements. Subsequent annealing near 600 ∘C returns the positron signal to levels similar to those in the as-received samples, which suggests that split VGa-like defects are still present in the sample. The almost complete removal of the VibGa-2D vibrational line, the appearance of new weak O-D lines in the same spectral region, and the lack of D out-diffusion from the samples suggest that the 600 ∘C anneal promotes the formation of either D-containing, IR-inactive complexes or defect complexes between VibGa-2D and other implantation-induced defects. The degree of electrical compensation is found to be governed by the interactions between the Ga vacancies and hydrogen.
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Reinertsen, Vilde Mari; Weiser, Philip Michael; Frodason, Ymir Kalmann; Bathen, Marianne Etzelmüller; Vines, Lasse & Johansen, Klaus Magnus H
(2020).
Anisotropic and trap-limited diffusion of hydrogen/deuterium in monoclinic gallium oxide single crystals.
Applied Physics Letters.
ISSN 0003-6951.
117.
doi:
10.1063/5.0027333.
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The effect of lattice anisotropy on the diffusion of hydrogen (H)/deuterium (2H) in b-Ga2O3 was investigated using secondary ion mass spectrometry (SIMS) and hybrid-functional calculations. Concentration-depth profiles of 2H-implanted single crystals show that 2H can diffuse along the direction perpendicular to the (010) surface at temperatures as low as 300 degC, whereas diffusion along the direction perpendicular to the (-201) surface occurs only around 500 degC. For both directions, the evolution of the 2H concentration–depth profiles after heat treatments can be modeled by trap-limited diffusion. Moreover, the traps can be present in the as-received crystals or created during ion
implantation. Comparison of the experimentally obtained binding energy for 2H to the trap (2.3+/-0.2 eV) with the binding energies determined from first-principles calculations suggests that intrinsic point defects (e.g., VGa^ib) or defect complexes (e.g., VGa(2)VO(2)) are excellent candidates for the trap and will play a crucial role in the diffusion of H or 2H in b-Ga2O3.
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Kang, Xiaolan; Reinertsen, Vilde Mari; Both, Kevin Gregor; Galeckas, Augustinas; Aarholt, Thomas & Prytz, Øystein
[Show all 9 contributors for this article]
(2022).
Galvanic Restructuring of Exsolved Nanoparticles for Plasmonic and Electrocatalytic Energy Conversion (Small 29/2022 Inside back cover feature).
18(29),
p. 2270156–2270156.
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Aarholt, Thomas; Both, Kevin Gregor; Reinertsen, Vilde Mari & Prytz, Øystein
(2021).
Surface plasmon investigations by STEM-EELS mapping of Au/Ni nanoparticles on STO.
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Metallic nanoparticles have traditionally had sharp absorption peaks between 1 and 5 eV due to the
excitation of surface plasmons. Localized surface plasmon resonance (LSPR) is the coherent oscillation
of quasi-free electrons excited by the electromagnetic fields of a photon or fast electron1,2. Since the
absorption peak energies are in the range of visible light, surface plasmons present a potential pathway
for absorbing energy to drive photoelectrochemical reactions or contribute to photovoltaic applications.
For driving photoelectrochemical reactions, one difficulty is placing photoactive nanoparticles near the
catalyst responsible for a chosen reaction, for example, water splitting. The ideal semiconductor for water
splitting has a bandgap of 1.9 – 2.3 eV, although semiconductors in this range are seldom stable during
photocatalytic water splitting3. Utilizing plasmonics in wide bandgap semiconductors is a promising
alternative, avoiding the stability issue3. In this work, we present a STEM-EELS study of Au nanoparticles
created by galvanic replacement of Ni nanoparticles grown by exsolution of a PLD-deposited thin-film of
A-site excess strontium titanate (Sr1.07Ti 0.93Ni0.07O 3-δ) (STO). STO is an indirect, wide bandgap (3.2
eV) perovskite, studied as a promising photocatalyst for water splitting 4. Ni can easily substitute the Ti
in the STO, making it a suitable candidate for exsolution, while Au cannot substitute Ti5. Simultaneously,
Ni nanoparticles barely show any plasmonic activities, while Au particles are second only to Ag
nanoparticles6. The presented manufacturing technique results in nanoparticles of gold and nickel
freestanding, but socketed, on the surface and embedded in the bulk, with diameters between 50 and 100
nm, which are well-suited for plasmonic applications.
As a starting point, STEM-EELS was performed with a monochromated 300kV STEM probe with ZeroLoss Peak (ZLP) full-width at half-maximum of 110 meV on an FEI Titan G2. A peculiarly shaped gold
nanocluster was studied. After removing the ZLP, the spectrum image was linearly fitted with Gaussians
centered at 1.46, 1.95, and 2.40 eV. The 2.40 eV peak is a well-known Au surface plasmon, whereas the
remaining two are investigated in conjunction with modeling approaches. An RGB composite of the fit
results can be seen in figure 1. Spectra extracted from the coloured regions can be seen in figure 2.
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Reinertsen, Vilde Mari
(2025).
Theory and modelling of plasmonic response in nanoparticles for plasmonically enhanced photocatalysis.
Universitetet i Oslo.
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The field of photocatalysis is a promising field in which researchers aim to improve the catalysis of important chemical reactions. The improvement is focused on making the catalysis greener by utilizing the abundant energy from the sun. The first photocatalysts were semiconductors in which the band gap enables the material to absorb light and the excited charge carriers contribute in chemical reactions. However, these materials have not yet reached an efficiency which makes them industrially realizable. The lack in efficiency has different sources and one of them is low absorption of sunlight. In plasmonically enhanced photocatalysis, this issue is handled by exploiting the remarkable light interaction of some metal nanoparticles. These materials have material properties which enable visual light to excite localized surface plasmon resonances on the metal nanoparticles that creates a very strong local field near the particles, making extinction cross sections of the particles many times larger than their geometrical cross sections. These features, combined with a multiple of interesting surface plasmon decay mechanisms, are properties of plasmonic metal nanoparticles that enable them to both catalyze chemical reactions themselves and enhance semiconductor photocatalysts. In this work, we have investigated the plasmonic response of nanoparticles in scalable systems with electromagnetic calculations, i.e., surface plasmon simulations. By combining these simulations with transmission electron microscope measurements and a theoretical foundation, we have identified surface plasmon modes in complex systems and investigated the surface plasmons’ dependencies on material properties, geometry, size, environment and interaction. These insights bring these systems a step closer to industrial realization.
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Pedersen, Benedicte Allum; Vines, Lasse; Kjeldby, Snorre Braathen & Reinertsen, Vilde Mari
(2022).
Positioning and control of single-photon emitters in SiC-based nanostructures for quantum applications.
Universitetet i Oslo.
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Published
Sep. 5, 2022 3:15 PM
- Last modified
Feb. 27, 2023 2:10 PM
