| 1. |
- Kanne, Thomas, et al.
(author)
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Double Nanowires for Hybrid Quantum Devices
- 2022
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In: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 32:9
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Journal article (peer-reviewed)abstract
- Parallel 1D semiconductor channels connected by a superconducting strip constitute the core platform in several recent quantum device proposals that rely, for example, on Andreev processes or topological effects. In order to realize these proposals, the actual material systems must have high crystalline purity, and the coupling between the different elements should be controllable in terms of their interfaces and geometry. A strategy for synthesizing double InAs nanowires by the vapor-liquid-solid mechanism using III-V molecular beam epitaxy is presented. A superconducting layer is deposited onto nanowires without breaking the vacuum, ensuring pristine interfaces between the superconductor and the two semiconductor nanowires. The method allows for a high yield of merged as well as separate parallel nanowires with full or half-shell superconductor coatings. Their utility in complex quantum devices by electron transport measurements is demonstrated.
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| 2. |
- Lindberg, Caroline, et al.
(author)
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Silver as Seed-Particle Material for GaAs Nanowires - Dictating Crystal Phase and Growth Direction by Substrate Orientation
- 2016
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 16:4, s. 2181-2188
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Journal article (peer-reviewed)abstract
- Here we investigate the feasibility of silver as seed-particle material to synthesize GaAs nanowires and show that both crystal phase and growth direction can be controlled by choice of substrate orientation. A (111)B substrate orientation can be used to form vertically aligned wurtzite GaAs nanowires and a (100) substrate orientation to form vertically aligned zinc blende GaAs nanowires. A 45-50% yield of vertical nanowire growth is achieved on the (100) substrate orientation without employing any type of surface modification or nucleation strategy to promote a vertical growth direction. In addition, photoluminescence measurements reveal that the photon emission from the silver seeded wurtzite GaAs nanowires is characterized by a single and narrow emission peak at 1.52 eV.
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| 3. |
- Mårtensson, Erik K., et al.
(author)
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Understanding GaAs Nanowire Growth in the Ag-Au Seed Materials System
- 2018
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In: Crystal Growth and Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; , s. 6702-6712
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Journal article (peer-reviewed)abstract
- The integration of III-V semiconductors with Si in device fabrication is facilitated by the use of nanoscale structures such as nanowires. Nanowires are predominantly grown using Au seed particles; however, the seed material is known to affect the nanowire growth and properties. Here we present growth of GaAs nanowires using three different seed particle materials: Au, Ag, and a AgAu alloy. By comparing the results from the different seeds, we found that the growths of Au- and AgAu-seeded nanowires were in general very similar, with homogeneous and vertical nanowires observed in both cases. The Ag-seeded growths instead revealed a lower yield of vertical nanowires with large variations in lengths. Different Ga-concentrations were measured in the different seed particles, which suggested that the Au and the AgAu seed particles were liquid during growth, whereas Ag particles were solid. The chemical potential of Ga was however found to be similar for all three seed materials. We propose that the Ga concentrations are determined by the chemical potential of Ga, which in turn explains why Ag-seeded nanowire growth proceeds with a solid particle. Overall, this study shows that varying the seed material can be a powerful tool to gain a deeper understanding of particle assisted nanowire growth.
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| 4. |
- Tanta, Rawa, et al.
(author)
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Micro-Raman spectroscopy for the detection of stacking fault density in InAs and GaAs nanowires
- 2017
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In: Physical Review B. - 2469-9950. ; 96:16
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Journal article (peer-reviewed)abstract
- We investigate the relation between crystal stacking faults in individual wurtzite InAs and GaAs nanowires and the intensity of the forbidden longitudinal optical (LO) phonon mode in the Raman spectra. Micro-Raman spectroscopy and transmission electron microscopy are combined on the same individual nanowires to evaluate the LO mode intensity as a function of the stacking fault density. A clear increase in the LO mode intensity was observed when the stacking fault density was increased. Our results confirm the utility of Raman spectroscopy as a powerful tool for detecting crystal defects in nanowires.
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| 5. |
- Thelander, Claes, et al.
(author)
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Gold nanoparticle single electron transistor with carbon nanotube leads
- 2001
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 79:13, s. 2106-2108
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Journal article (peer-reviewed)abstract
- We have used carbon nanotubes to electrically contact a 7 nm gold particle by scanning-probe manipulation. The result was a single-electron transistor showing a periodic modulation of the current as a function of gate voltage for temperatures up to ∼200 K, with the particle responsible for the main features of the electron transport. This interpretation could be verified when the particle was removed and the two nanotubes were moved into electrical contact.
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| 6. |
- Utko, P., et al.
(author)
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Coupling between electronic and vibrational excitations in carbon nanotubes filled with C(60) fullerenes
- 2011
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In: Acta Physica Polonica A. - 0587-4246. ; 120:5, s. 839-841
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Journal article (peer-reviewed)abstract
- We investigate the low-temperature electron transport through C60 peapods, which are carbon nanotubes encapsulating C60 fullerenes. We find that the temperature dependence of the Coulomb blockade oscillations in peapod quantum dots deviates from conventional Breit–Wigner behavior, showing signatures of the Franck–Condon blockade of conductance. This indicates the presence of a coupling between electronic states and vibrational excitations. Unlike for suspended empty nanotubes, these are not intrinsic vibrational modes of the tube but mechanical vibrations of the encapsulated fullerenes that affect the electronic transport. Fullerene peapods thus emerge as a new class of nanoelectromechanical systems.
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| 7. |
- Utko, Pawel, et al.
(author)
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Nanoelectromechanical coupling in fullerene peapods probed by resonant electrical transport experiments
- 2010
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 1
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Journal article (peer-reviewed)abstract
- Fullerene peapods, which are carbon nanotubes encapsulating fullerene molecules, can offer enhanced functionality with respect to empty nanotubes. Their prospective applications include, for example, data storage devices, single-electron transistors and spin-qubit arrays for quantum computing. However, the present incomplete understanding of how a nanotube is affected by entrapped fullerenes is an obstacle for peapods to reach their full potential in nanoscale electronic applications. In this paper, we investigate the effect of C60 fullerenes on low-temperature electron transport through peapod quantum dots. Compared with empty nanotubes, we find an abnormal temperature dependence of Coulomb blockade oscillations, indicating the presence of a nanoelectromechanical coupling between electronic states of the nanotube and mechanical vibrations of fullerenes. This provides a method to detect the C60 presence and to probe the interplay between electrical and mechanical excitations in peapods, which thus emerge as a new class of nanoelectromechanical systems.
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| 8. |
- Whiticar, Alexander M., et al.
(author)
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Annealing of Au, Ag and Au-Ag alloy nanoparticle arrays on GaAs (100) and (111)B
- 2017
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In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:20
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Journal article (peer-reviewed)abstract
- Metal nanoparticles (NPs), in particular gold NPs, are often used in the fabrication process of semiconductor nanowires. Besides being able to induce the 1D crystallization of new material, it is highly beneficial if the NPs can be used to dictate the position and diameter of the final nanowire structure. To achieve well-defined NP arrays of varying diameter and pitch distances for nanowire growth, it is necessary to understand and control the effect that a pre-growth annealing process may have on the pre-defined NP arrays. Recently, it has been demonstrated that silver (Ag) may be an alternative to using gold (Au) NPs as seed for particle-seeded nanowire fabrication. This work brings light onto the effect of annealing of Au, Ag and Au-Ag alloy metal NP arrays in two commonly used epitaxial systems, the molecular beam epitaxy (MBE) and the metalorganic vapor phase epitaxy (MOVPE). The metal NP arrays are fabricated with the aid of electron beam lithography on GaAs 100 and 111B wafers and the evolution of the NPs with respect to shape, size and position on the surfaces is studied after annealing using scanning electron microscopy. We find that while the Au NP arrays are found to be stable when annealed up to 600 °C in a MOVPE system, a diameter and pitch dependent splitting of the particles is seen for annealing in a MBE system. The Ag NP arrays are found to be less stable, with smaller diameters (≤50 nm) dissolving during the annealing process in both epitaxial systems. In general, the mobility of the NPs is observed to differ between the two the GaAs 100 and 111B surfaces. Finally, our observations on the effect of annealing on Au-Ag alloy NP arrays suggest that these NP can withstand necessary annealing conditions for a complete de-oxidation of GaAs surfaces in both MOVPE and MBE.
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