Heidi Potts | Ecole Polytechnique Federale de Lausanne (original) (raw)
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Papers by Heidi Potts
Nano letters, Jan 20, 2015
GaAs nanowire arrays on silicon offer great perspectives in the optoelectronics and solar cell in... more GaAs nanowire arrays on silicon offer great perspectives in the optoelectronics and solar cell industry. To fulfil this potential, gold-free growth in predetermined positions should be achieved. Ga-assisted growth of GaAs nanowires in the form of array has been shown to be challenging and difficult to reproduce. In this work we provide some of the key elements for obtaining a high yield of GaAs nanowires on patterned Si in a reproducible way: contact angle and pinning of the Ga droplet inside the apertures achieved by the modification of the surface properties of the nanoscale areas exposed to growth. As an example, an amorphous silicon layer between the crystalline substrate and the oxide mask results in a contact angle around 90o, leading to a high yield of vertical nanowires. Another example for tuning the contact angle is anticipated, native oxide with controlled thickness. This work opens new perspectives for the rational and reproducible growth of GaAs nanowire arrays on silicon.
Physical Review Letters, 2011
We use 75 As nuclear magnetic resonance (NMR) to investigate the local electronic properties of B... more We use 75 As nuclear magnetic resonance (NMR) to investigate the local electronic properties of Ba(Fe1−xRux)2As2 (x = 0.23). We find two phase transitions, to antiferromagnetism at TN ≈ 60 K and to superconductivity at TC ≈ 15 K. Below TN , our data show that the system is fully magnetic, with a commensurate antiferromagnetic structure and a moment of 0.4 µB/Fe. The spin-lattice relaxation rate 1/ 75 T1 is large in the magnetic state, indicating a high density of itinerant electrons induced by Ru doping. On cooling below TC, 1/ 75 T1 on the magnetic sites falls sharply, providing unambiguous evidence for the microscopic coexistence of antiferromagnetism and superconductivity. In the iron-based superconductors, superconductivity (SC) is achieved on suppressing a long-ranged antiferromagnetic order [1] by doping or pressure. At this phase boundary, much attention has been drawn to the question of whether SC may coexist with antiferromagnetism (AFM). Proposals for possible coexisting phases have included commensurate [2] and incommensurate [3-5] magnetic structures, competition between AFM and SC , and variations in the size of the ordered moment or the pairing symmetry . No consensus has yet been reached on the pairing mechanism or the possible phenomena arising from the interplay of AFM and SC. For most materials, local-probe studies on high quality samples are required as a matter of urgency to distinguish the key properties of microscopic coexistence from any form of phase separation.
Crystal Growth & Design, 2015
ABSTRACT Ga-assisted growth of GaAs nanowires on silicon provides a path for integrating high-pur... more ABSTRACT Ga-assisted growth of GaAs nanowires on silicon provides a path for integrating high-purity III–Vs on silicon. The nature of the oxide on the silicon surface has been shown to impact the overall possibility of nanowire growth and their orientation with the substrate. In this work, we show that not only the exact thickness, but also the nature of the native oxide determines the feasibility of nanowire growth. During the course of formation of the native oxide, the surface energy varies and results in a different contact angle of Ga droplets. We find that, only for a contact angle around 90° (i.e., oxide thickness ∼0.9 nm), nanowires grow perpendicularly to the silicon substrate. This native oxide engineering is the first step toward controlling the self-assembly process, determining mainly the nanowire density and orientation.
Nano letters, Jan 20, 2015
GaAs nanowire arrays on silicon offer great perspectives in the optoelectronics and solar cell in... more GaAs nanowire arrays on silicon offer great perspectives in the optoelectronics and solar cell industry. To fulfil this potential, gold-free growth in predetermined positions should be achieved. Ga-assisted growth of GaAs nanowires in the form of array has been shown to be challenging and difficult to reproduce. In this work we provide some of the key elements for obtaining a high yield of GaAs nanowires on patterned Si in a reproducible way: contact angle and pinning of the Ga droplet inside the apertures achieved by the modification of the surface properties of the nanoscale areas exposed to growth. As an example, an amorphous silicon layer between the crystalline substrate and the oxide mask results in a contact angle around 90o, leading to a high yield of vertical nanowires. Another example for tuning the contact angle is anticipated, native oxide with controlled thickness. This work opens new perspectives for the rational and reproducible growth of GaAs nanowire arrays on silicon.
Physical Review Letters, 2011
We use 75 As nuclear magnetic resonance (NMR) to investigate the local electronic properties of B... more We use 75 As nuclear magnetic resonance (NMR) to investigate the local electronic properties of Ba(Fe1−xRux)2As2 (x = 0.23). We find two phase transitions, to antiferromagnetism at TN ≈ 60 K and to superconductivity at TC ≈ 15 K. Below TN , our data show that the system is fully magnetic, with a commensurate antiferromagnetic structure and a moment of 0.4 µB/Fe. The spin-lattice relaxation rate 1/ 75 T1 is large in the magnetic state, indicating a high density of itinerant electrons induced by Ru doping. On cooling below TC, 1/ 75 T1 on the magnetic sites falls sharply, providing unambiguous evidence for the microscopic coexistence of antiferromagnetism and superconductivity. In the iron-based superconductors, superconductivity (SC) is achieved on suppressing a long-ranged antiferromagnetic order [1] by doping or pressure. At this phase boundary, much attention has been drawn to the question of whether SC may coexist with antiferromagnetism (AFM). Proposals for possible coexisting phases have included commensurate [2] and incommensurate [3-5] magnetic structures, competition between AFM and SC , and variations in the size of the ordered moment or the pairing symmetry . No consensus has yet been reached on the pairing mechanism or the possible phenomena arising from the interplay of AFM and SC. For most materials, local-probe studies on high quality samples are required as a matter of urgency to distinguish the key properties of microscopic coexistence from any form of phase separation.
Crystal Growth & Design, 2015
ABSTRACT Ga-assisted growth of GaAs nanowires on silicon provides a path for integrating high-pur... more ABSTRACT Ga-assisted growth of GaAs nanowires on silicon provides a path for integrating high-purity III–Vs on silicon. The nature of the oxide on the silicon surface has been shown to impact the overall possibility of nanowire growth and their orientation with the substrate. In this work, we show that not only the exact thickness, but also the nature of the native oxide determines the feasibility of nanowire growth. During the course of formation of the native oxide, the surface energy varies and results in a different contact angle of Ga droplets. We find that, only for a contact angle around 90° (i.e., oxide thickness ∼0.9 nm), nanowires grow perpendicularly to the silicon substrate. This native oxide engineering is the first step toward controlling the self-assembly process, determining mainly the nanowire density and orientation.