Daya Dhungana | University of Lyon (original) (raw)

Papers by Daya Dhungana

Nanotechnology

Integrating self-catalyzed InAs nanowires on Si(111) is an important step toward building vertica... more Integrating self-catalyzed InAs nanowires on Si(111) is an important step toward building vertical gate-all-around transistors. The CMOS compatibility and the nanowire aspect ratio are two crucial parameters to consider. In this work, we optimize the InAs nanowire morphology by changing the growth mode from Vapor-Solid to Vapor-Liquid-Solid in a CMOS compatible process. We study the key role of the Hydrogen surface preparation on nanowire growths and bound it to a change of the chemical potential and adatoms diffusion length on the substrate. We transfer the optimized process to patterned wafers and adapt both the surface preparation and the growth conditions. Once group III and V fluxes are balances, aspect ratio can be improved by increasing the system kinetics. Overall, we propose a method for large scale integration of CMOS compatible InAs nanowire on silicon and highlight the major role of kinetics on the growth mechanism.

Nanoscale Horizons

Buffering silicene with a stanene interlayer proves to be effective in breaking its strong intera... more Buffering silicene with a stanene interlayer proves to be effective in breaking its strong interaction with the supporting Ag(111) substrate. Unprecedented optothermal response of silicene discloses new applications in thermoelectrics and plasmonics.

InAs and Bi1-xSbx nanowires with their distinct material properites hold promises for nanoelec- t... more InAs and Bi1-xSbx nanowires with their distinct material properites hold promises for nanoelec- tronics and quantum computing. While the high electron mobility of InAs is interesting for na- noelectronics applications, the 3D topological insulator behaviour of Bi1-xSbx can be used for the realization of Majorana Fermions based qubit devices. In both the cases improving the quality of the nanoscale material is mandatory and is the primary goal of the thesis, where we study CMOS compatible InAs nanowire integration on Silicon and where we develop a new nanoscale topological insulator. For a full CMOS compatiblity, the growth of InAs on Silicon requires to be self-catalyzed, fully vertical and uniform without crossing the thermal budge of 450 °C. These CMOS standards, combined with the high lattice mismatch of InAs with Silicon, prevented the integration of InAs nanowires for nanoelectronics devices. In this thesis, two new surface preparations of the Silicon were studied involving in-...

The synthesis of new Xenes and their potential applications prototypes have achieved significant ... more The synthesis of new Xenes and their potential applications prototypes have achieved significant milestones so far. However, to date the realization of Xene heterostructures in analogy with the well-known van der Waals heterostructures remains an unresolved issue. Here, we introduce a Xene heterostructure concept based on the epitaxial combination of silicene and stanene on Ag(111), and demonstrate how one Xene layer enables another Xene layer of different nature to grow on top. We synthesized single-phase (4 x 4) silicene using stanene as a template, and managed to grow stanene on top of silicene on the other way around. In both heterostructures <em>in situ</em> and <em>ex situ</em> probes confirm layer-by-layer growth without intercalations and intermixing. Modelling via Density Functional Theory (DFT) shows that the atomic layers in the heterostructures are strongly interacting and hexagonal symmetry conservation in each individual layer is sequence-select...

Grâce a leur proprietes uniques, les nanofils d'InAs et de Bi1-xSbx sont important pour les d... more Grâce a leur proprietes uniques, les nanofils d'InAs et de Bi1-xSbx sont important pour les domaines de la nanoelectronique et de l'informatique quantique. Alors que la mobilite electronique de l'InAs est interessante pour les nanoelectroniques; l'aspect isolant topologique du Bi1-xSbx peut etre utilise pour la realisation de Qubits bases sur les fermions de Majorana. Dans les deux cas, l'amelioration de la qualite du materiau est obligatoire et ceci est l'objectif principal cette these ou` nous etudions l'integration des nanofils InAs sur silicium (compatibles CMOS) et ou nous developpons un nouvel isolant topologique nanometrique: le Bi1-xSbx. Pour une compatibilite CMOS complete, la croissance d'InAs sur Silicium necessite d'etre auto- catalysee, entierement verticale et uniforme sans depasser la limite thermique de 450 ° C. Ces normes CMOS, combinees a la difference de parametre de maille entre l'InAs et le silicium, ont empeche l'inte...

Advanced Functional Materials, 2021

The synthesis of new Xenes and their potential applications prototypes have achieved significant ... more The synthesis of new Xenes and their potential applications prototypes have achieved significant milestones so far. However, to date the realization of Xene heterostructures in analogy with the well known van der Waals heterostructures remains an unresolved issue. Here, a Xene heterostructure concept based on the epitaxial combination of silicene and stanene on Ag(111) is introduced, and how one Xene layer enables another Xene layer of a different nature to grow on top is demonstrated. Single-phase (4 × 4) silicene is synthesized using stanene as a template, and stanene is grown on top of silicene on the other way around. In both heterostructures, in situ and ex situ probes confirm layer-by-layer growth without intercalations and intermixing. Modeling via density functional theory shows that the atomic layers in the heterostructures are strongly interacting, and hexagonal symmetry conservation in each individual layer is sequence selective. The results provide a substantial step toward currently missing Xene heterostructures and may inspire new paths for atomic-scale materials engineering.

ACS Applied Materials & Interfaces, 2021

Bismuth−antimony alloy (Bi 1 − x Sb x) is the first reported 3D topological insulator (TI). Among... more Bismuth−antimony alloy (Bi 1 − x Sb x) is the first reported 3D topological insulator (TI). Among many TIs reported to date, it remains the most promising for spintronic applications thanks to its large conductivity, its colossal spin Hall angle, and the possibility to build low-current spin-orbit-torque magnetoresistive random access memories. Nevertheless, the 2D integration of TIs on industrial standards is lacking. In this work, we report the integration of high-quality rhombohedral BiSb(0001) topological insulators on a cubic GaAs(001) substrate. We demonstrate a clear epitaxial relationship at the interface, a fully relaxed TI layer, and the growth of a rhombohedral matrix on top of the cubic substrate. The antimony composition of the Bi 1 − x Sb x layer is perfectly controlled and covers almost the whole TI window. For optimized growth conditions, the sample generates a semiconductor band structure at room temperature in the bulk and exhibits metallic surface states at 77 K.

Microfluidics and Nanofluidics, 2017

Anisotropic carbonyl iron-PolyDiMethylSiloxane (PDMS) composites were developed and implemented i... more Anisotropic carbonyl iron-PolyDiMethylSiloxane (PDMS) composites were developed and implemented in microfluidic devices to serve as magnetic flux concentrators. These original materials provide technological solutions for heterogeneous integration with PDMS. Besides microfabrication advantages, they offer interesting modular magnetic properties. Applying an external magnetic field during the PDMS reticulation leads to the formation of 1D-agglomerates of magnetic particles, organized in the non-magnetic polymer matrix. This induces an increase of susceptibility as compared to composites with randomly dispersed particles. In this report, we explored the gain in reachable magnetophoretic forces in operating microfluidic devices, from the study of magnetic micro-beads motion injected in the microchannel. We show that even at relatively large distances from the magnetically-functionalized channel wall, the anisotropic composite leads to a factor two increase in the magnetophoretic force. Finally, further investigations based on finite element description suggest that the measured benefit of anisotropic composite polymers does not only rely on the global susceptibility increase but also on the local magnetic field gradients originating from the microstructure.

Microfluidics and Nanofluidics, 2019

Nano Research, 2018

A CMOS compatible process is presented in order to grow self-catalyzed InAs nanowires on silicon ... more A CMOS compatible process is presented in order to grow self-catalyzed InAs nanowires on silicon by molecular beam epitaxy. The crucial step of this process is a new in-situ surface preparation under hydrogen (gas or plasma) during the substrate degassing combined with an in-situ arsenic annealing prior to growth. Morphological and structural characterizations of the InAs nanowires are presented and growth mechanisms are discussed in detail. The major influence of surface termination is exposed both experimentally and theoretically using statistics on ensemble of nanowires and density functional theory (DFT) calculations. The differences observed between Molecular Beam Epitaxy (MBE) and Metal Organic Vapor Phase Epitaxy (MOVPE) growth of InAs nanowires can be explained by these different surfaces terminations. The transition between a vapor solid (VS) and a vapor liquid solid (VLS) growth mechanism is presented. Optimized growth conditions lead to very high aspect ratio nanowires (up to 50 nm in diameter and 3 micron in length) without passing the 410 °C thermal limit, which makes the whole process CMOS compatible. Overall, our results suggest a new method for surface preparation and a possible tuning of the growth mechanism using different surface terminations.

2016 IEEE Nanotechnology Materials and Devices Conference (NMDC), 2016

III-V nanowires gained general interest due to their unique properties such as high mobility, dir... more III-V nanowires gained general interest due to their unique properties such as high mobility, direct band gap and wide coverage of the solar spectrum. They provided advances in the fields of optoelectronics, nanoelectronics and energy applications. Recently, the focus has been shifted towards the self-catalyzed growth of these nanowires on silicon since gold produces detrimental mid-gap states in silicon. However, the lattice mismatch and the presence of native oxide hinders the growth of vertical and uniform nanowires arrays on silicon (Si). In this context, different surface preparation methods have been developed in order to remove the native oxide present on the Si(111) substrates. Chemical treatment with HydroFluoric acid (HF), in situ H2 Plasma, and in situ high temperature annealing are considered.

AIP Advances, 2016

Here we report on the influence of anisotropic microstructure on the performances of magnetically... more Here we report on the influence of anisotropic microstructure on the performances of magnetically soft micro-patterns intended to integrate microfluidic systems. These micro-patterns are made of a composite obtained by mixing carbonyl iron particles with polydimethylsiloxane, which offers practical integration advantages. We investigated a wide range of magnetic particle loadings, from 10wt% to 83wt%, reaching magnetization as high as 630 kA/m. A homogeneous field was applied during the polymer's cross-linking phase so that to obtain a 1D arrangement of the particles in the solidified polymer, along the field direction. Here we present the results obtained for square-based micro-pillars prepared under a magnetic field applied along one of its diagonal. We assessed the magnetic anisotropy owing to the particles' spatial arrangement by comparing the magnetization processes along the two diagonals of the micro-pillar's base. The magnetic susceptibilities along the two directions differ from a factor greater than three. The results can be described in terms of high aspect ratio and porous magnetic agglomerates.

Nanotechnology

Integrating self-catalyzed InAs nanowires on Si(111) is an important step toward building vertica... more Integrating self-catalyzed InAs nanowires on Si(111) is an important step toward building vertical gate-all-around transistors. The CMOS compatibility and the nanowire aspect ratio are two crucial parameters to consider. In this work, we optimize the InAs nanowire morphology by changing the growth mode from Vapor-Solid to Vapor-Liquid-Solid in a CMOS compatible process. We study the key role of the Hydrogen surface preparation on nanowire growths and bound it to a change of the chemical potential and adatoms diffusion length on the substrate. We transfer the optimized process to patterned wafers and adapt both the surface preparation and the growth conditions. Once group III and V fluxes are balances, aspect ratio can be improved by increasing the system kinetics. Overall, we propose a method for large scale integration of CMOS compatible InAs nanowire on silicon and highlight the major role of kinetics on the growth mechanism.

Nanoscale Horizons

Buffering silicene with a stanene interlayer proves to be effective in breaking its strong intera... more Buffering silicene with a stanene interlayer proves to be effective in breaking its strong interaction with the supporting Ag(111) substrate. Unprecedented optothermal response of silicene discloses new applications in thermoelectrics and plasmonics.

InAs and Bi1-xSbx nanowires with their distinct material properites hold promises for nanoelec- t... more InAs and Bi1-xSbx nanowires with their distinct material properites hold promises for nanoelec- tronics and quantum computing. While the high electron mobility of InAs is interesting for na- noelectronics applications, the 3D topological insulator behaviour of Bi1-xSbx can be used for the realization of Majorana Fermions based qubit devices. In both the cases improving the quality of the nanoscale material is mandatory and is the primary goal of the thesis, where we study CMOS compatible InAs nanowire integration on Silicon and where we develop a new nanoscale topological insulator. For a full CMOS compatiblity, the growth of InAs on Silicon requires to be self-catalyzed, fully vertical and uniform without crossing the thermal budge of 450 °C. These CMOS standards, combined with the high lattice mismatch of InAs with Silicon, prevented the integration of InAs nanowires for nanoelectronics devices. In this thesis, two new surface preparations of the Silicon were studied involving in-...

The synthesis of new Xenes and their potential applications prototypes have achieved significant ... more The synthesis of new Xenes and their potential applications prototypes have achieved significant milestones so far. However, to date the realization of Xene heterostructures in analogy with the well-known van der Waals heterostructures remains an unresolved issue. Here, we introduce a Xene heterostructure concept based on the epitaxial combination of silicene and stanene on Ag(111), and demonstrate how one Xene layer enables another Xene layer of different nature to grow on top. We synthesized single-phase (4 x 4) silicene using stanene as a template, and managed to grow stanene on top of silicene on the other way around. In both heterostructures <em>in situ</em> and <em>ex situ</em> probes confirm layer-by-layer growth without intercalations and intermixing. Modelling via Density Functional Theory (DFT) shows that the atomic layers in the heterostructures are strongly interacting and hexagonal symmetry conservation in each individual layer is sequence-select...

Grâce a leur proprietes uniques, les nanofils d'InAs et de Bi1-xSbx sont important pour les d... more Grâce a leur proprietes uniques, les nanofils d'InAs et de Bi1-xSbx sont important pour les domaines de la nanoelectronique et de l'informatique quantique. Alors que la mobilite electronique de l'InAs est interessante pour les nanoelectroniques; l'aspect isolant topologique du Bi1-xSbx peut etre utilise pour la realisation de Qubits bases sur les fermions de Majorana. Dans les deux cas, l'amelioration de la qualite du materiau est obligatoire et ceci est l'objectif principal cette these ou` nous etudions l'integration des nanofils InAs sur silicium (compatibles CMOS) et ou nous developpons un nouvel isolant topologique nanometrique: le Bi1-xSbx. Pour une compatibilite CMOS complete, la croissance d'InAs sur Silicium necessite d'etre auto- catalysee, entierement verticale et uniforme sans depasser la limite thermique de 450 ° C. Ces normes CMOS, combinees a la difference de parametre de maille entre l'InAs et le silicium, ont empeche l'inte...

Advanced Functional Materials, 2021

The synthesis of new Xenes and their potential applications prototypes have achieved significant ... more The synthesis of new Xenes and their potential applications prototypes have achieved significant milestones so far. However, to date the realization of Xene heterostructures in analogy with the well known van der Waals heterostructures remains an unresolved issue. Here, a Xene heterostructure concept based on the epitaxial combination of silicene and stanene on Ag(111) is introduced, and how one Xene layer enables another Xene layer of a different nature to grow on top is demonstrated. Single-phase (4 × 4) silicene is synthesized using stanene as a template, and stanene is grown on top of silicene on the other way around. In both heterostructures, in situ and ex situ probes confirm layer-by-layer growth without intercalations and intermixing. Modeling via density functional theory shows that the atomic layers in the heterostructures are strongly interacting, and hexagonal symmetry conservation in each individual layer is sequence selective. The results provide a substantial step toward currently missing Xene heterostructures and may inspire new paths for atomic-scale materials engineering.

ACS Applied Materials & Interfaces, 2021

Bismuth−antimony alloy (Bi 1 − x Sb x) is the first reported 3D topological insulator (TI). Among... more Bismuth−antimony alloy (Bi 1 − x Sb x) is the first reported 3D topological insulator (TI). Among many TIs reported to date, it remains the most promising for spintronic applications thanks to its large conductivity, its colossal spin Hall angle, and the possibility to build low-current spin-orbit-torque magnetoresistive random access memories. Nevertheless, the 2D integration of TIs on industrial standards is lacking. In this work, we report the integration of high-quality rhombohedral BiSb(0001) topological insulators on a cubic GaAs(001) substrate. We demonstrate a clear epitaxial relationship at the interface, a fully relaxed TI layer, and the growth of a rhombohedral matrix on top of the cubic substrate. The antimony composition of the Bi 1 − x Sb x layer is perfectly controlled and covers almost the whole TI window. For optimized growth conditions, the sample generates a semiconductor band structure at room temperature in the bulk and exhibits metallic surface states at 77 K.

Microfluidics and Nanofluidics, 2017

Anisotropic carbonyl iron-PolyDiMethylSiloxane (PDMS) composites were developed and implemented i... more Anisotropic carbonyl iron-PolyDiMethylSiloxane (PDMS) composites were developed and implemented in microfluidic devices to serve as magnetic flux concentrators. These original materials provide technological solutions for heterogeneous integration with PDMS. Besides microfabrication advantages, they offer interesting modular magnetic properties. Applying an external magnetic field during the PDMS reticulation leads to the formation of 1D-agglomerates of magnetic particles, organized in the non-magnetic polymer matrix. This induces an increase of susceptibility as compared to composites with randomly dispersed particles. In this report, we explored the gain in reachable magnetophoretic forces in operating microfluidic devices, from the study of magnetic micro-beads motion injected in the microchannel. We show that even at relatively large distances from the magnetically-functionalized channel wall, the anisotropic composite leads to a factor two increase in the magnetophoretic force. Finally, further investigations based on finite element description suggest that the measured benefit of anisotropic composite polymers does not only rely on the global susceptibility increase but also on the local magnetic field gradients originating from the microstructure.

Microfluidics and Nanofluidics, 2019

Nano Research, 2018

A CMOS compatible process is presented in order to grow self-catalyzed InAs nanowires on silicon ... more A CMOS compatible process is presented in order to grow self-catalyzed InAs nanowires on silicon by molecular beam epitaxy. The crucial step of this process is a new in-situ surface preparation under hydrogen (gas or plasma) during the substrate degassing combined with an in-situ arsenic annealing prior to growth. Morphological and structural characterizations of the InAs nanowires are presented and growth mechanisms are discussed in detail. The major influence of surface termination is exposed both experimentally and theoretically using statistics on ensemble of nanowires and density functional theory (DFT) calculations. The differences observed between Molecular Beam Epitaxy (MBE) and Metal Organic Vapor Phase Epitaxy (MOVPE) growth of InAs nanowires can be explained by these different surfaces terminations. The transition between a vapor solid (VS) and a vapor liquid solid (VLS) growth mechanism is presented. Optimized growth conditions lead to very high aspect ratio nanowires (up to 50 nm in diameter and 3 micron in length) without passing the 410 °C thermal limit, which makes the whole process CMOS compatible. Overall, our results suggest a new method for surface preparation and a possible tuning of the growth mechanism using different surface terminations.

2016 IEEE Nanotechnology Materials and Devices Conference (NMDC), 2016

III-V nanowires gained general interest due to their unique properties such as high mobility, dir... more III-V nanowires gained general interest due to their unique properties such as high mobility, direct band gap and wide coverage of the solar spectrum. They provided advances in the fields of optoelectronics, nanoelectronics and energy applications. Recently, the focus has been shifted towards the self-catalyzed growth of these nanowires on silicon since gold produces detrimental mid-gap states in silicon. However, the lattice mismatch and the presence of native oxide hinders the growth of vertical and uniform nanowires arrays on silicon (Si). In this context, different surface preparation methods have been developed in order to remove the native oxide present on the Si(111) substrates. Chemical treatment with HydroFluoric acid (HF), in situ H2 Plasma, and in situ high temperature annealing are considered.

AIP Advances, 2016

Here we report on the influence of anisotropic microstructure on the performances of magnetically... more Here we report on the influence of anisotropic microstructure on the performances of magnetically soft micro-patterns intended to integrate microfluidic systems. These micro-patterns are made of a composite obtained by mixing carbonyl iron particles with polydimethylsiloxane, which offers practical integration advantages. We investigated a wide range of magnetic particle loadings, from 10wt% to 83wt%, reaching magnetization as high as 630 kA/m. A homogeneous field was applied during the polymer's cross-linking phase so that to obtain a 1D arrangement of the particles in the solidified polymer, along the field direction. Here we present the results obtained for square-based micro-pillars prepared under a magnetic field applied along one of its diagonal. We assessed the magnetic anisotropy owing to the particles' spatial arrangement by comparing the magnetization processes along the two diagonals of the micro-pillar's base. The magnetic susceptibilities along the two directions differ from a factor greater than three. The results can be described in terms of high aspect ratio and porous magnetic agglomerates.