Frode Sneve Strand

• Strand, Frode Sneve; Cooil, Simon Phillip; Campbell, Quinn T.; Flounders, John J.; Røst, Håkon & Åsland, Anna Cecilie [Show all 16 contributors for this article] (2025). Direct Observation of 2DEG States in Shallow Si:Sb δ-Layers. Journal of Physical Chemistry C. ISSN 1932-7447. 129(2), p. 1339–1347. doi: 10.1021/acs.jpcc.4c07331. Full text in Research Archive Show summary

  We investigate the electronic structure of high-density layers of Sb dopants in a silicon host, so-called Si:Sb δ-layers. We show that, in spite of the known challenges in producing highly confined Sb δ-layers, sufficient confinement is created such that the lowest conduction band states (Γ states, studied in depth in other silicon δ-layers), become occupied and can be observed using angle-resolved photoemission spectroscopy. The electronic structure of the Si:Sb δ-layers closely resembles that of Si:P systems, where the observed conduction band is near-parabolic and slightly anisotropic in the k∥ plane. The observed Γ state extends ∼1 nm in the out-of-plane direction, which is slightly wider than the 1/3 monolayer thick dopant distribution. This is caused by a small segregation of the dopant layer, which is nevertheless minimal when comparing with earlier published attempts. Our results serve to demonstrate that Sb is still a feasible dopant alternative for use in the semiconductor δ-layer platform, providing similar electronic functionality to Si:P systems. Additionally, it has the advantages of being less expensive, more controllable, safer to handle, and more compatible with industrial patterning techniques. Si:Sb is therefore a viable platform for emerging quantum device applications.

• Røst, Håkon; Tosi, Ezequiel; Strand, Frode Sneve; Åsland, Anna Cecilie; Lacovig, Paolo & Lizzit, Silvano [Show all 7 contributors for this article] (2023). Probing the Atomic Arrangement of Subsurface Dopants in a Silicon Quantum Device Platform. ACS Applied Materials & Interfaces. ISSN 1944-8244. 15(18), p. 22637–22643. doi: 10.1021/acsami.2c23011. Full text in Research Archive Show summary

  High-density structures of subsurface phosphorus dopants in silicon continue to garner interest as a silicon-based quantum computer platform; however, a much-needed confirmation of their dopant arrangement has been lacking. In this work, we take advantage of the chemical specificity of X-ray photoelectron diffraction to obtain the precise structural configuration of P dopants in subsurface Si:P δ-layers. The growth of δ-layer systems with different levels of doping is carefully studied and verified using X-ray photoelectron spectroscopy and low-energy electron diffraction. Subsequent diffraction measurements reveal that in all cases, the subsurface dopants primarily substitute with Si atoms from the host material. Furthermore, no signs of carrier-inhibiting P–P dimerization can be observed. Our observations not only settle a nearly decade-long debate about the dopant arrangement but also demonstrate how X-ray photoelectron diffraction is surprisingly well suited for studying subsurface dopant structure. This work thus provides valuable input for an updated understanding of the behavior of Si:P δ-layers and the modeling of their derived quantum devices.

• Røst, Håkon Ivarssønn; Reed, Benjamen P.; Strand, Frode Sneve; Durk, Joseph A.; Evans, D. Andrew & Grubišić-Čabo, Antonija [Show all 18 contributors for this article] (2021). A Simplified Method for Patterning Graphene on Dielectric Layers. ACS Applied Materials & Interfaces. ISSN 1944-8244. 13(31), p. 37510–37516. doi: 10.1021/acsami.1c09987. Full text in Research Archive Show summary

  The large-scale formation of patterned, quasi-freestanding graphene structures supported on a dielectric has so far been limited by the need to transfer the graphene onto a suitable substrate and contamination from the associated processing steps. We report μm scale, few-layer graphene structures formed at moderate temperatures (600–700 °C) and supported directly on an interfacial dielectric formed by oxidizing Si layers at the graphene/substrate interface. We show that the thickness of this underlying dielectric support can be tailored further by an additional Si intercalation of the graphene prior to oxidation. This produces quasi-freestanding, patterned graphene on dielectric SiO2 with a tunable thickness on demand, thus facilitating a new pathway to integrated graphene microelectronics.

• Røst, Håkon Ivarssønn; Chellappan, Rajesh Kumar; Strand, Frode Sneve; Grubišić-Čabo, Antonija; Reed, Benjamen P. & Prieto, Mauricio J. [Show all 16 contributors for this article] (2021). Low-Temperature Growth of Graphene on a Semiconductor. Journal of Physical Chemistry C. ISSN 1932-7447. 125(7), p. 4243–4252. doi: 10.1021/acs.jpcc.0c10870. Full text in Research Archive Show summary

  The industrial realization of graphene has so far been limited by challenges related to the quality, reproducibility, and high process temperatures required to manufacture graphene on suitable substrates. We demonstrate that epitaxial graphene can be grown on transition-metal-treated 6H-SiC(0001) surfaces, with an onset of graphitization starting around 450–500 °C. From the chemical reaction between SiC and thin films of Fe or Ru, sp3 carbon is liberated from the SiC crystal and converted to sp2 carbon at the surface. The quality of the graphene is demonstrated by using angle-resolved photoemission spectroscopy and low-energy electron diffraction. Furthermore, the orientation and placement of the graphene layers relative to the SiC substrate are verified by using angle-resolved absorption spectroscopy and energy-dependent photoelectron spectroscopy, respectively. With subsequent thermal treatments to higher temperatures, a steerable diffusion of the metal layers into the bulk SiC is achieved. The result is graphene supported on magnetic silicide or optionally, directly on semiconductor, at temperatures ideal for further large-scale processing into graphene-based device structures.

• Hu, Jinbang; Strand, Frode Sneve; Chellappan, Rajesh Kumar; Zhang, Zhengde; Shen, Kongchao & Hu, JinPing [Show all 13 contributors for this article] (2020). Direct Synthesis of Semimetal Phthalocyanines on a Surface with Insights into Interfacial Properties. The Journal of Physical Chemistry Letters. 124(15), p. 8247–8256. doi: 10.1021/acs.jpcc.0c00895. Full text in Research Archive
• Holt, Ann Julie; Mahatha, Sanjoy K.; Stan, Raluca-Maria; Strand, Frode Sneve; Nyborg, Thomas & Curcio, Davide [Show all 12 contributors for this article] (2020). Observation and origin of the [delta] manifold in Si:P [delta] layers. Physical review B (PRB). ISSN 2469-9950. 101(12). doi: 10.1103/PhysRevB.101.121402. Full text in Research Archive

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• Stalsberg, Marte Pedersen; Strand, Frode Sneve; Cooil, Simon Phillip; Campbell, Quinn T.; Flounders, John J. & Røst, Håkon Ivarssønn [Show all 10 contributors for this article] (2024). A 2D electron gas by shallow Sb doping in Si for use in Quantum Devices. Full text in Research Archive
• Tosi, Ezequiel; Strand, Frode Sneve; Åsland, Anna Cecilie; Lacovig, Paolo; Lizzit, Silvano & Wells, Justin William (2023). Probing the Atomic Arrangement of Sub-Surface Dopants in a Silicon Quantum Device Platform. Full text in Research Archive Show summary

  Recently, efforts to realize a silicon-based, CMOS-compatible quantum computer have been intensifying. Central to its development are so-called Si:P δ-layers: i.e., ultra-sharp layers of phosphorus atoms placed beneath the silicon surface. Until recently, one key property has remained elusive: the arrangement of the P dopants within the δ-layer. The answer to this question is of crucial importance, as the dopant arrangement will directly impact the energy separation (i.e., valley-splitting) of the supported quantum well states. In this talk, we will demonstrate how the local neighborhood around encapsulated dopants in a bulk semiconductor can be directly probed using X-ray photoelectron diffraction (XPD). By utilizing subtle core level energy shifts that are concomitant with the coordination of a dopant, chemically specific diffractive images can be formed. Through comparison with XPD simulations that are derived from models of the local atomic environment around the dopants, the true dopant atom placement can be ascertained. Typically, XPD is only used as a probe of surface structure. We demonstrate here that – under the right conditions, it also can be used to determine the local arrangement of sub-surface atoms. Therefore, XPD is well suited for solving the long-standing mystery of the Si:P δ-layer structure.

• Røst, Håkon; Tosi, Ezequiel; Strand, Frode Sneve; Åsland, Anna Cecilie; Lacovig, Paolo & Lizzit, Silvano [Show all 7 contributors for this article] (2023). Determining the Arrangement of Subsurface Dopants in a Silicon Quantum Device Platform. Full text in Research Archive
• Stalsberg, Marte Pedersen; Strand, Frode Sneve; Cooil, Simon Phillip; Campbell, Quinn T.; Flounders, John J. & Røst, Håkon Ivarssønn [Show all 10 contributors for this article] (2023). Atomically Sharp and High-Density Sb Doping in Si for use in Quantum Devices. Full text in Research Archive

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