| 1. |
- Bernal, Ximena E., et al.
(författare)
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Empowering Latina scientists
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 363:6429, s. 825-826
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Paschoal Jr., Waldomiro, 1977-, et al.
(författare)
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Magnetoresistance in Mn ion-implanted GaAs:Zn nanowires
- 2014
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Ingår i: Applied Physics Letters. - New York : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 104:15
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the magnetoresistance (MR) in a series of Zn doped (p-type) GaAs nanowires implanted with different Mn concentrations. The nanowires with the lowest Mn concentration (~0.0001%) exhibit a low resistance of a few kΩ at 300K and a 4% positive MR at 1.6K, which can be well described by invoking a spin-split subband model. In contrast, nanowires with the highest Mn concentration (4%) display a large resistance of several MΩ at 300K and a large negative MR of 85% at 1.6K. The large negative MR is interpreted in terms of spin-dependent hopping in a complex magnetic nanowire landscape of magnetic polarons, separated by intermediate regions of Mn impurity spins. Sweeping the magnetic field back and forth for the 4% sample reveals a hysteresis that indicates the presence of a weak ferromagnetic phase. We propose co-doping with Zn to be a promising way to reach the goal of realizing ferromagnetic Ga1-xMnxAs nanowires for future nanospintronics. © 2014 AIP Publishing LLC.
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| 3. |
- Johannes, A., et al.
(författare)
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Enhanced sputtering and incorporation of Mn in implanted GaAs and ZnO nanowires
- 2014
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Ingår i: Journal of Physics D: Applied Physics. - Bristol : IOP Publishing. - 1361-6463 .- 0022-3727. ; 47:39
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Tidskriftsartikel (refereegranskat)abstract
- We simulated and experimentally investigated the sputter yield of ZnO and GaAs nanowires, which were implanted with energetic Mn ions at room temperature. The resulting thinning of the nanowires and the dopant concentration with increasing Mn ion fluency were measured by accurate scanning electron microscopy (SEM) and nano-x-Ray Fluorescence (nanoXRF) quantification, respectively. We observed a clearly enhanced sputter yield for the irradiated nanowires compared to bulk, which is also corroborated by iradina simulations. These show a maximum if the ion range matches the nanowire diameter. As a consequence of the erosion thinning of the nanowire, the incorporation of the Mn dopants is also enhanced and increases non-linearly with increasing ion fluency.
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| 4. |
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| 5. |
- Dick Thelander, Kimberly, et al.
(författare)
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Growth of GaP nanotree structures by sequential seeding of 1D nanowires
- 2004
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 272:1-4, s. 131-137
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Tidskriftsartikel (refereegranskat)abstract
- Complex nanostructures are becoming increasingly important for the development of nanoscale devices and functional nanomaterials. Precise control of size and morphology of these structures is critical to their fabrication and exploitation. We have developed a method for stepwise growth of tree-like nanostructures via the vapour liquid-solid (VLS) growth mode, demonstrated for III-V semiconductor materials. This method uses the initial seeding of nanowires by catalytic aerosol nanoparticles to form the trunk, followed by sequential seeding of branching structures. Here we present a detailed study of the growth of these complex structures using Gap. Diameter of each level of nanowires is directly determined by seed particle diameters, and number of branches is determined by seed particle density. Growth rate is shown to increase with temperature to a maximum corresponding to the temperature of complete decomposition of the Group-III precursor material, and subsequently decrease due to competition with bulk growth. Growth rate also depends on flow of the Group-III precursor, but not on the Group-V precursor. Finally, there is a relationship between the number of branches and their growth rate, suggesting that material diffusion plays a role in nanowire branch growth. (C) 2004 Elsevier B.V. All rights reserved.
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| 6. |
- Jurgilaitis, Andrius, et al.
(författare)
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Time-Resolved X-ray Diffraction Investigation of the Modified Phonon Dispersion in InSb Nanowires
- 2014
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Ingår i: Nano letters (Print). - Washington, DC : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 14:2, s. 541-546
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Tidskriftsartikel (refereegranskat)abstract
- The modified phonon dispersion is of importance for understanding the origin of the reduced heat conductivity in nanowires. We have measured the phonon dispersion for 50 nm diameter InSb (111) nanowires using time-resolved X-ray diffraction. By comparing the sound speed of the bulk (3880 m/s) and that of a classical thin rod (3600 m/s) to our measurement (2880 m/s), we conclude that the origin of the reduced sound speed and thereby to the reduced heat conductivity is that the C44 elastic constant is reduced by 35% compared to the bulk material. © 2014 American Chemical Society.
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| 7. |
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| 8. |
- Seifert, Werner, et al.
(författare)
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Growth of one-dimensional nanostructures in MOVPE
- 2004
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 272:1-4, s. 211-220
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Tidskriftsartikel (refereegranskat)abstract
- The use of metal organic vapor-phase epitaxy (MOVPE) for growth of one-dimensional nanostructures in the material systems GaAs, GaP, InAs and InP is investigated. Some kinetic effects are discussed, especially the general finding that in MOVPE thinner whiskers grow faster than thicker whiskers. Effects of growth temperature on growth rate and shape of the whiskers, the effects of different growth directions on the perfection of the materials and the possibilities to grow heterostructures in axial and lateral directions are reported. Ways to overcome the randomness in whisker growth by controlled seeding of the Au particles and by using lithography for site control are demonstrated.
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| 9. |
- Seifner, Michael S., et al.
(författare)
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Interface Dynamics in Ag–Cu3P Nanoparticle Heterostructures
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126.
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Tidskriftsartikel (refereegranskat)abstract
- Earth-abundant transition metal phosphides are promising materials for energy-related applications. Specifically, copper(I) phosphide is such a material and shows excellent photocatalytic activity. Currently, there are substantial research efforts to synthesize well-defined metal–semiconductor nanoparticle heterostructures to enhance the photocatalytic performance by an efficient separation of charge carriers. The involved crystal facets and heterointerfaces have a major impact on the efficiency of a heterostructured photocatalyst, which points out the importance of synthesizing potential photocatalysts in a controlled manner and characterizing their structural and morphological properties in detail. In this study, we investigated the interface dynamics occurring around the synthesis of Ag–Cu3P nanoparticle heterostructures by a chemical reaction between Ag–Cu nanoparticle heterostructures and phosphine in an environmental transmission electron microscope. The major product of the Cu–Cu3P phase transformation using Ag–Cu nanoparticle heterostructures with a defined interface as a template preserved the initially present Ag{111} facet of the heterointerface. After the complete transformation, corner truncation of the faceted Cu3P phase led to a physical transformation of the nanoparticle heterostructure. In some cases, the structural rearrangement toward an energetically more favorable heterointerface has been observed and analyzed in detail at the atomic level. The herein-reported results will help better understand dynamic processes in Ag–Cu3P nanoparticle heterostructures and enable facet-engineered surface and heterointerface design to tailor their physical properties.
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| 10. |
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| 11. |
- Adolph, David, 1971, et al.
(författare)
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Hybrid ZnO/GaN distributed Bragg reflectors grown by plasma-assisted molecular beam epitaxy
- 2016
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Ingår i: APL Materials. - : AIP Publishing. - 2166-532X. ; 4:8, s. 086106-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate crack-free ZnO/GaN distributed Bragg reflectors (DBRs) grown by hybrid plasma-assisted molecular beam epitaxy using the same growth chamber for continuous growth of both ZnO and GaN without exposure to air. This is the first time these ZnO/GaN DBRs have been demonstrated. The Bragg reflectors consisted up to 20 periods as shown with cross-sectional transmission electron microscopy. The maximum achieved reflectance was 77% with a 32 nm wide stopband centered at 500 nm. Growth along both (0001) and (000-1) directions was investigated. Low temperaturegrowth as well as two-step low/high-temperature deposition was carried out where the latter method improved the DBR reflectance. Samples grown along the (0001) direction yielded a better surface morphology as revealed by scanningelectron microscopy and atomic force microscopy. Reciprocal space maps showed that ZnO(000-1)/GaN reflectors are relaxed whereas the ZnO(0001)/GaN DBRs are strained. The ability to n-type dope ZnO and GaN makes the ZnO(0001)/GaNDBRs interesting for various optoelectronic cavity structures.
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| 12. |
- Aspegren, Markus, et al.
(författare)
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Perfect Zeeman Anisotropy in Rotationally Symmetric Quantum Dots with Strong Spin-Orbit Interaction
- 2024
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Ingår i: Nano Letters. - 1530-6984. ; 24:26, s. 7927-7933
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Tidskriftsartikel (refereegranskat)abstract
- In nanoscale structures with rotational symmetry, such as quantum rings, the orbital motion of electrons combined with a spin-orbit interaction can produce a very strong and anisotropic Zeeman effect. Since symmetry is sensitive to electric fields, ring-like geometries provide an opportunity to manipulate magnetic properties over an exceptionally wide range. In this work, we show that it is possible to form rotationally symmetric confinement potentials inside a semiconductor quantum dot, resulting in electron orbitals with large orbital angular momentum and strong spin−orbit interactions. We find complete suppression of Zeeman spin splitting for magnetic fields applied in the quantum dot plane, similar to the expected behavior of an ideal quantum ring. Spin splitting reappears as orbital interactions are activated with symmetry-breaking electric fields. For two valence electrons, representing a common basis for spin-qubits, we find that modulating the rotational symmetry may offer new prospects for realizing tunable protection and interaction of spin-orbital states.
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| 13. |
- Barker, David, et al.
(författare)
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Experimental Verification of the Work Fluctuation-Dissipation Relation for Information-to-Work Conversion
- 2022
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Ingår i: Physical Review Letters. - 0031-9007. ; 128:4
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Tidskriftsartikel (refereegranskat)abstract
- We study experimentally work fluctuations in a Szilard engine that extracts work from information encoded as the occupancy of an electron level in a semiconductor quantum dot. We show that as the average work extracted per bit of information increases toward the Landauer limit Formula Presented, the work fluctuations decrease in accordance with the work fluctuation-dissipation relation. We compare the results to a protocol without measurement and feedback and show that when no information is used, the work output and fluctuations vanish simultaneously, contrasting the information-to-energy conversion case where increasing amount of work is produced with decreasing fluctuations. Our study highlights the importance of fluctuations in the design of information-to-work conversion processes.
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| 14. |
- Behrle, Raphael, et al.
(författare)
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Electrical and Structural Properties of Si1−xGex Nanowires Prepared from a Single-Source Precursor
- 2023
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 13:4
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Tidskriftsartikel (refereegranskat)abstract
- Si1−xGex nanowires (NWs) were prepared by gold-supported chemical vapor deposition (CVD) using a single-source precursor with preformed Si–Ge bonds. Besides the tamed reactivity of the precursor, the approach reduces the process parameters associated with the control of decomposition characteristics and the dosing of individual precursors. The group IV alloy NWs are single crystalline with a constant diameter along their axis. During the wire growth by low pressure CVD, an Au-containing surface layer on the NWs forms by surface diffusion from the substrate, which can be removed by a combination of oxidation and etching. The electrical properties of the Si1−xGex/Au core-shell NWs are compared to the Si1−xGex NWs after Au removal. Core–shell NWs show signatures of metal-like behavior, while the purely semiconducting NWs reveal typical signatures of intrinsic Si1−xGex. The synthesized materials should be of high interest for applications in nano- and quantum-electronics.
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| 15. |
- Borgström, Magnus, et al.
(författare)
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Precursor evaluation for in situ InP nanowire doping
- 2008
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 19:44
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Tidskriftsartikel (refereegranskat)abstract
- The use of tetraethyltin (TESn) and dimethylzinc (DMZn) as in situ n- and p-dopant precursors during particle-assisted growth of InP nanowires is reported. Gate voltage dependent transport measurements demonstrate that the nanowires can be predictably synthesized as either n- or p-type. These doped nanowires can be characterized based on their electric field response and we find that n- type doping scales over a range from 10(17) to 10(19) cm(-3) with increasing input TESn dopant molar fraction. On the other hand, the p-type doping using DMZn saturates at low levels, probably related to a strong increase in nanowire growth rate with increasing DMZn molar fractions. By optimizing growth conditions with respect to tapering, axial pn-junctions exhibiting rectifying behavior were fabricated. The pn-junctions can be operated as light emitting diodes.
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| 16. |
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| 17. |
- Chen, I. Ju, et al.
(författare)
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Conduction Band Offset and Polarization Effects in InAs Nanowire Polytype Junctions
- 2017
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 17:2, s. 902-908
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Tidskriftsartikel (refereegranskat)abstract
- Although zinc-blende (ZB) and wurtzite (WZ) structures differ only in the atomic stacking sequence, mixing of crystal phases can strongly affect the electronic properties, a problem particularly common to bottom up-grown nanostructures. A lack of understanding of the nature of electronic transport at crystal phase junctions thus severely limits our ability to develop functional nanowire devices. In this work we investigated electron transport in InAs nanowires with designed mixing of crystal structures, ZB/WZ/ZB, by temperature-dependent electrical measurements. The WZ inclusion gives rise to an energy barrier in the conduction band. Interpreting the experimental result in terms of thermionic emission and using a drift-diffusion model, we extracted values for the WZ/ZB band offset, 135 ± 10 meV, and interface sheet polarization charge density on the order of 10-3 C/m2. The extracted polarization charge density is 1-2 orders of magnitude smaller than previous experimental results, but in good agreement with first principle calculation of spontaneous polarization in WZ InAs. When the WZ length is reduced below 20 nm, an effective barrier lowering is observed, indicating the increasing importance of tunneling transport. Finally, we found that band-bending at ZB/WZ junctions can lead to bound electron states within an enclosed WZ segment of sufficient length, evidenced by our observation of Coulomb blockade at low temperature. These findings provide critical input for modeling and designing the electronic properties of novel functional devices, such as nanowire transistors, where crystal polytypes are commonly found.
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| 18. |
- Dahl, Magnus, et al.
(författare)
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Sb Incorporation in Wurtzite and Zinc Blende InAs1-xSbx Branches on InAs Template Nanowires
- 2018
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Ingår i: Small. - : Wiley. - 1613-6810. ; 14:11
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Tidskriftsartikel (refereegranskat)abstract
- The physical properties of material largely depend on their crystal structure. Nanowire growth is an important method for attaining metastable crystal structures in III-V semiconductors, giving access to advantageous electronic and surface properties. Antimonides are an exception, as growing metastable wurtzite structure has proven to be challenging. As a result, the properties of these materials remain unknown. One promising means of accessing wurtzite antimonides is to use a wurtzite template to facilitate their growth. Here, a template technique using branched nanowire growth for realizing wurtzite antimonide material is demonstrated. On wurtzite InAs trunks, InAs1-xSbx branch nanowires at different Sb vapor phase compositions are grown. For comparison, branches on zinc blende nanowire trunks are also grown under identical conditions. Studying the crystal structure and the material composition of the grown branches at different xv shows that the Sb incorporation is higher in zinc blende than in wurtzite. Branches grown on wurtzite trunks are usually correlated with stacking defects in the trunk, leading to the emergence of a zinc blende segment of higher Sb content growing parallel to the wurtzite structure within a branch. However, the average amount of Sb incorporated within the branch is determined by the vapor phase composition.
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| 19. |
- Davtyan, Arman, et al.
(författare)
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Characterization of individual stacking faults in a wurtzite GaAs nanowire by nanobeam X-ray diffraction
- 2017
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495. ; 24:5, s. 981-990
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Tidskriftsartikel (refereegranskat)abstract
- Coherent X-ray diffraction was used to measure the type, quantity and the relative distances between stacking faults along the growth direction of two individual wurtzite GaAs nanowires grown by metalorganic vapour epitaxy. The presented approach is based on the general property of the Patterson function, which is the autocorrelation of the electron density as well as the Fourier transformation of the diffracted intensity distribution of an object. Partial Patterson functions were extracted from the diffracted intensity measured along the direction in the vicinity of the wurtzite Bragg peak. The maxima of the Patterson function encode both the distances between the fault planes and the type of the fault planes with the sensitivity of a single atomic bilayer. The positions of the fault planes are deduced from the positions and shapes of the maxima of the Patterson function and they are in excellent agreement with the positions found with transmission electron microscopy of the same nanowire.The application of the synchrotron-radiation-based coherent nanobeam X-ray diffraction method to study the type, quantity and the exact distances in between stacking faults in single GaAs nanowires is demonstrated.
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| 20. |
- Dick, Kimberly A.
(författare)
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Gas-phase materials synthesis in environmental transmission electron microscopy
- 2023
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Ingår i: MRS Bulletin. - 0883-7694. ; 48:8, s. 833-841
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Forskningsöversikt (refereegranskat)abstract
- Gas-phase transmission electron microscopy is an essential tool for elucidating the mechanisms involved in the synthesis of functional materials. Here, we review the latest developments in understanding the growth of novel nanostructural materials afforded by following the process in situ in electron microscopes. Particular focus is on investigations of catalyzed growth of one-dimensional carbon-based and semiconductor nanostructures, while other types of nanocrystal and epitaxial crystal growth are briefly addressed. Also discussed are how these methods have been employed to answer critical questions about the growth mechanisms as well as to bring insight into the relationships between synthesis parameters and materials properties. Graphical abstract: [Figure not available: see fulltext.]
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| 21. |
- Escobar Steinvall, Simon, et al.
(författare)
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Visualizing the Mechanism Switching in High-Temperature Au-Catalyzed InAs Nanowire Growth
- 2023
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Ingår i: Crystal Growth and Design. - 1528-7483. ; 23:9, s. 6228-6232
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Tidskriftsartikel (refereegranskat)abstract
- We use environmental transmission electron microscopy to observe in situ the switch from an axial vapor-liquid-solid (VLS) growth mechanism in Au-catalyzed InAs nanowires toward a radial vapor-solid (VS) one, dominated by layers nucleating at the triple-phase line. At elevated temperatures, in addition to high V/III ratios, the affinity for In in the Au catalyst will be greater than that of In in InAs, which in turn reduces the driving force and probability for nucleation at the liquid-solid interface. Consequently, with increased temperature, the catalyst particle stops acting as a sink for incoming material and the decomposition of precursors away from the catalyst increases, making radial vapor-solid growth the dominating growth mechanism. It is further observed that the growth proceeds through multistep propagation rather than a layer-by-layer propagation under these conditions.
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| 22. |
- Fan, Dingxun, et al.
(författare)
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Schottky barrier and contact resistance of InSb nanowire field-effect transistors
- 2016
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 27:27
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Tidskriftsartikel (refereegranskat)abstract
- Understanding of the electrical contact properties of semiconductor nanowire (NW) field-effect transistors (FETs) plays a crucial role in the use of semiconducting NWs as building blocks for future nanoelectronic devices and in the study of fundamental physics problems. Here, we report on a study of the contact properties of Ti/Au, a widely used contact metal combination, when contacting individual InSb NWs via both two-probe and four-probe transport measurements. We show that a Schottky barrier of height is present at the metal-InSb NW interfaces and its effective height is gate-tunable. The contact resistance () in the InSb NWFETs is also analyzed by magnetotransport measurements at low temperatures. It is found that in the on-state exhibits a pronounced magnetic field-dependent feature, namely it is increased strongly with increasing magnetic field after an onset field . A qualitative picture that takes into account magnetic depopulation of subbands in the NWs is provided to explain the observation. Our results provide solid experimental evidence for the presence of a Schottky barrier at Ti/Au-InSb NW interfaces and can be used as a basis for design and fabrication of novel InSb NW-based nanoelectronic devices and quantum devices.
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| 23. |
- Geijselaers, Irene, et al.
(författare)
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Radial band bending at wurtzite–zinc-blende–GaAs interfaces
- 2018
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Ingår i: Nano Futures. - : IOP Publishing. - 2399-1984. ; 2:3
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Tidskriftsartikel (refereegranskat)abstract
- The band offset between wurtzite (wz) and zinc-blende (zb) GaAs is an important fundamental parameter in polytype heterostructure engineering. Since the interface has a type-II band alignment, it is reasonably straightforward to measure the band offset using photoluminescence (PL) e.g. on nanowires containing heterostructures between wz and zb GaAs. It has, however, been found that the transition energy in such heterostructures depends on the diameter of the nanowires which introduces uncertainties in the determined value of the band offset. In order to extract a more accurate value and to further elucidate the diameter-dependent behavior of the transition energy we have performed PL studies on a large set of GaAs nanowires. Those nanowires have different diameters and contain one wz–GaAs segment embedded in otherwise zb–GaAs. We have also studied the effect of a passivating capping layer of AlAs on the determined band offset. We find that our data is well explained by a diameter-dependent radial band bending in the nanowires. Combining modeling of the band bending with the experimental data we extract a band offset of about 125 meV and a p-type doping concentration of 1016 cm−3. Our results will improve the accuracy of future modeling of the electronic properties of wz–zb GaAs heterostructures and other engineered polytypic materials.
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| 24. |
- Gómez, Víctor J., et al.
(författare)
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Growth selectivity control of InAs shells on crystal phase engineered GaAs nanowires
- 2022
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Ingår i: Nanoscale Advances. - : Royal Society of Chemistry (RSC). - 2516-0230. ; 4:16, s. 3330-3341
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Tidskriftsartikel (refereegranskat)abstract
- In this work we demonstrate a two-fold selectivity control of InAs shells grown on crystal phase and morphology engineered GaAs nanowire (NW) core templates. This selectivity occurs driven by differences in surface energies of the NW core facets. The occurrence of the different facets itself is controlled by either forming different crystal phases or additional tuning of the core NW morphology. First, in order to study the crystal phase selectivity, GaAs NW cores with an engineered crystal phase in the axial direction were employed. A crystal phase selective growth of InAs on GaAs was found for high growth rates and short growth times. Secondly, the facet-dependant selectivity of InAs growth was studied on crystal phase controlled GaAs cores which were additionally morphology-tuned by homoepitaxial overgrowth. Following this route, the original hexagonal cores with {110} sidewalls were converted into triangular truncated NWs with ridges and predominantly {112}B facets. By precisely tuning the growth parameters, the growth of InAs is promoted over the ridges and reduced over the {112}B facets with indications of also preserving the crystal phase selectivity. In all cases (different crystal phase and facet termination), selectivity is lost for extended growth times, thus, limiting the total thickness of the shell grown under selective conditions. To overcome this issue we propose a 2-step growth approach, combining a high growth rate step followed by a low growth rate step. The control over the thickness of the InAs shells while maintaining the selectivity is demonstrated by means of a detailed transmission electron microscopy analysis. This proposed 2-step growth approach enables new functionalities in 1-D structures formed by using bottom-up techniques, with a high degree of control over shell thickness and deposition selectivity.
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| 25. |
- Gorji, Sepideh, et al.
(författare)
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Self-catalyzed MBE grown GaAs/GaAsxSb1-x core-shell nanowires in ZB and WZ crystal structures
- 2013
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 24:40
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the growth of self-catalyzed GaAs/GaAsxSb1-x core-shell nanowires directly on Si(111) substrates by molecular beam epitaxy. The compositions of the GaAsxSb1-x shells are tuned in a wide range where the Sb-content is varied from 10 to similar to 70%, covering the miscibility gap. In addition, the GaAsxSb1-x shells are grown on both zinc blende (ZB) and wurtzite (WZ) crystal structures. Morphological and structural characterizations of the grown nanowires indicate successful transfer of the GaAs core crystal structure to the GaAsxSb1-x shells for both ZB and WZ nanowires, with slower shell growth rate on the WZ segments.
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| 26. |
- Haldar, Subhomoy, et al.
(författare)
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Energetics of Microwaves Probed by Double Quantum Dot Absorption
- 2023
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Ingår i: Physical Review Letters. - 0031-9007. ; 130:8
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Tidskriftsartikel (refereegranskat)abstract
- We explore the energetics of microwaves interacting with a double quantum dot photodiode and show wave-particle aspects in photon-assisted tunneling. The experiments show that the single-photon energy sets the relevant absorption energy in a weak-drive limit, which contrasts the strong-drive limit where the wave amplitude determines the relevant-energy scale and opens up microwave-induced bias triangles. The threshold condition between these two regimes is set by the fine-structure constant of the system. The energetics are determined here with the detuning conditions of the double dot system and stopping-potential measurements that constitute a microwave version of the photoelectric effect.
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| 27. |
- Hallberg, Robert T., et al.
(författare)
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Nanowire morphology and particle phase control by tuning the in concentration of the foreign metal nanoparticle
- 2018
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 30:5
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Tidskriftsartikel (refereegranskat)abstract
- Controllable particle assisted growth (PAG) of III-V nanowires is today almost exclusively done with Au, Ga or In nanoparticles, whereas other metals often yield nanowires with uncontrolled growth directions. To improve the control of the initial growth direction in PAG, independent of choice of metal, we propose to initiate nanowire growth from a group-III-rich foreign metal particle. For III-V nanowire growth, the group III concentration of the particle can be made to increase or decrease with the relative supply of group III and group V material, which can be used to promote the liquid phase that is necessary for vapor-liquid-solid growth. In this paper, 30 nm Pd nanoparticles are used to develop growth conditions for In-rich PAG of InAs nanowires. The particle size evolution for different growth times and V/III ratios is correlated with changes in nanowire density and morphology. In addition, we demonstrate In-rich Co, Pd, Pt and Rh nanoparticles and optimized In-rich PAG from Au and Pd seeds. The Au and Pd seeded nanowires are remarkably similar and by tuning the particle composition we trigger a morphological change. The vertical nanowire morphology is associated with In-rich nanoparticles that contain a liquid phase. The curly nanowire morphology, with random growth directions have an In concentration less than or equal to that of the most In rich compound of the seed metal-In system.
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| 28. |
- Havir, Harald, et al.
(författare)
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Quantum dot source-drain transport response at microwave frequencies
- 2023
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Ingår i: Physical Review B. - 2469-9950. ; 108:20
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Tidskriftsartikel (refereegranskat)abstract
- Quantum dots are frequently used as charge-sensitive devices in low-temperature experiments to probe electric charge in mesoscopic conductors where the current running through the quantum dot is modulated by the nearby charge environment. Recent experiments have operated these detectors using reflectometry measurements up to gigahertz frequencies rather than probing the low-frequency current through the dot. In this work, we use an on-chip coplanar waveguide resonator to measure the source-drain transport response of two quantum dots at a frequency of 6 GHz, further increasing the bandwidth limit for charge detection. Similar to that in the low-frequency domain, the response is here predominantly dissipative. For large tunnel coupling, the response is still governed by the low-frequency conductance, in line with Landauer-Büttiker theory. For smaller couplings, our devices showcase two regimes where the high-frequency response deviates from the low-frequency limit and Landauer-Büttiker theory: When the photon energy exceeds the quantum dot resonance linewidth, degeneracy-dependent plateaus emerge. These are reproduced by sequential tunneling calculations. In the other case with large asymmetry in the tunnel couplings, the high-frequency response is two orders of magnitude larger than the low-frequency conductance G, favoring the high-frequency readout.
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| 29. |
- Hjort, Martin, et al.
(författare)
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Crystal Structure Induced Preferential Surface Alloying of Sb on Wurtzite/Zinc Blende GaAs Nanowires
- 2017
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 17:6, s. 3634-3640
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Tidskriftsartikel (refereegranskat)abstract
- We study the surface diffusion and alloying of Sb into GaAs nanowires (NWs) with controlled axial stacking of wurtzite (Wz) and zinc blende (Zb) crystal phases. Using atomically resolved scanning tunneling microscopy, we find that Sb preferentially incorporates into the surface layer of the {110}-terminated Zb segments rather than the {1120}-terminated Wz segments. Density functional theory calculations verify the higher surface incorporation rate into the Zb phase and find that it is related to differences in the energy barrier of the Sb-for-As exchange reaction on the two surfaces. These findings demonstrate a simple processing-free route to compositional engineering at the monolayer level along NWs.
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| 30. |
- Hjort, Martin, et al.
(författare)
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Electronic and Structural Differences between Wurtzite and Zinc Blende InAs Nanowire Surfaces: Experiment and Theory
- 2014
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 8:12, s. 12346-12355
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Tidskriftsartikel (refereegranskat)abstract
- We determine the detailed differences in geometry and band structure between wurtzite (Wz) and zinc blende (Zb) InAs nanowire (NW) surfaces using scanning tunneling microscopy/spectroscopy and photoemission electron microscopy. By establishing unreconstructed and defect-free surface facets for both Wz and Zb, we can reliably measure differences between valence and conduction band edges, the local vacuum levels, and geometric relaxations to the few-millielectronvolt and few-picometer levels, respectively. Surface and bulk density functional theory calculations agree well with the experimental findings and are used to interpret the results, allowing us to obtain information on both surface and bulk electronic structure. We can thus exclude several previously proposed explanations for the observed differences in conductivity of Wz-Zb NW devices. Instead, fundamental structural differences at the atomic scale and nanoscale that we observed between NW surface facets can explain the device behavior.
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| 31. |
- Hu, Tianyi, et al.
(författare)
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Direct Observation of Liquid–Solid Two-Phase Seed Particle-Assisted Kinking in GaP Nanowire Growth
- 2023
-
Ingår i: Small Structures. - 2688-4062. ; 4:9
-
Tidskriftsartikel (refereegranskat)abstract
- In the last decades, the metal-assisted growth approach of semiconductor nanowires (NWs) has shown its potential in controlling crystal properties, such as crystal structure, composition, and morphology. Recently, literature reports have shown successful semiconductor NW growth with multiphase seed particles under growth conditions. Exploring alternative metal seeds and the mechanisms for growing semiconductor NWs is an exciting research field aiming to improve the control over the crystal growth process. Herein, the gallium phosphide (GaP) NW growth using Cu as seed particles inside an environmental transmission electron microscope is studied. In particular, the transformations of the Cu-rich seed particles during the nucleation and growth of GaP NWs are observed. The supply of a relatively high amount of Ga atoms by the precursor mixture led to a solid Cu-rich seed particle core covered by a liquid phase. Different growth dynamics within the two-phase seed particle resulted in local competition in NW growth. As a result, the GaP NW kinked into another growth direction by forming a new interface at the NW growth front. The generated results enable insights into fundamental processes occurring in the seed particle during growth, creating leverage points for controlling the NW morphology.
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| 32. |
- Jacobsson, Daniel, et al.
(författare)
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Interface dynamics and crystal phase switching in GaAs nanowires
- 2016
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 531:7594, s. 317-322
-
Tidskriftsartikel (refereegranskat)abstract
- Controlled formation of non-equilibrium crystal structures is one of the most important challenges in crystal growth. Catalytically grown nanowires are ideal systems for studying the fundamental physics of phase selection, and could lead to new electronic applications based on the engineering of crystal phases. Here we image gallium arsenide (GaAs) nanowires during growth as they switch between phases as a result of varying growth conditions. We find clear differences between the growth dynamics of the phases, including differences in interface morphology, step flow and catalyst geometry. We explain these differences, and the phase selection, using a model that relates the catalyst volume, the contact angle at the trijunction (the point at which solid, liquid and vapour meet) and the nucleation site of each new layer of GaAs. This model allows us to predict the conditions under which each phase should be observed, and use these predictions to design GaAs heterostructures. These results could apply to phase selection in other nanowire systems.
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| 33. |
- Jash, Asmita, et al.
(författare)
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Excitonic Dynamics at the Type-II Polytype Interface of InP Platelets
- 2023
-
Ingår i: ACS Photonics. - 2330-4022. ; 10:9, s. 3143-3148
-
Tidskriftsartikel (refereegranskat)abstract
- Indirect excitons are the focus of intense research due to the opportunity of studying degenerate quantum gases and liquids in an excitonic system. To realize such systems, it is highly advantageous to have as little scattering as possible. A polytype type-II interface is formed between wurtzite and zincblende InP due to the band alignment. Electrons gather on the zincblende and holes on the wurtzite side of the interface. Therefore, electrons and holes that are spatially separated by the interface form indirect excitons with aligned dipoles. This polytype type-II interface is perfectly flat, which limits scattering. Here we report that repulsive interaction between the indirect excitons is the driving force behind the long-range transport of indirect excitons along the interface at high exciton densities. This is indicative of less scattering than in conventional type-II heterostructures. The spatial separation of the charge carriers across the interface leads to a low recombination rate of the indirect excitons since the overlap of the electron-hole wavefunction at the interface is small. Emission from the long-lived indirect excitons can be detected even after 40 μs. Our studies have been performed by using spatially and temporally resolved photoluminescence at the low temperature.
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| 34. |
- Jash, Asmita, et al.
(författare)
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Time-resolved photoluminescence studies of single interface wurtzite/zincblende heterostructured InP nanowires
- 2022
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 120:11
-
Tidskriftsartikel (refereegranskat)abstract
- The interface between wurtzite and zinc blende InP has been identified as type-II, where electrons gather on the zinc blende side and holes on the wurtzite side of the interface. The photoluminescence resulting from recombination across the interface is expected to be long-lived and to exhibit non-exponential decay of emission intensity after pulsed excitation. We verify this prediction using time-resolved photoluminescence spectroscopy on nanowires containing a single heterostructure between a single segment of wurtzite and zinc blende. We find that a significant intensity of type-II emission remains even more than 30 ns after excitation. The decay of the emission intensity is also non-exponential and considerably longer than the exponential decay of the wurtzite InP segment (260 ps). Our results are consistent with the expected photoluminescence characteristics of a type-II interface between the two polytypes. We also find that the lifetime becomes shorter if we create an electron gas at the interface by n-type doping the entire wurtzite segment of the nanowire. This is expected since there are many electrons that a given hole can recombine with, in contrast to the undoped case.
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| 35. |
- Jünger, Christian, et al.
(författare)
-
Intermediate states in Andreev bound state fusion
- 2023
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Ingår i: Communications Physics. - 2399-3650. ; 6:1
-
Tidskriftsartikel (refereegranskat)abstract
- Hybridization is one of the most fundamental quantum mechanical phenomena, with the text book example of binding two hydrogen atoms in a hydrogen molecule. Here we report tunnel spectroscopy experiments illustrating the hybridization of another type of discrete quantum states, namely of superconducting subgap states that form in segments of a semiconducting nanowire in contact with superconducting reservoirs. We discuss a collection of intermediate states with unique (tunnel) spectroscopic fingerprints in the process of merging well-known individual bound states, hybridized by a central quantum dot and eventually coherently linking the reservoirs, carrying a Josephson current. These coupled and fused Andreev bound states can be seen as superconducting analogues to atomic and molecular single electron states in nature, and explain a variety of recent bound state spectra, with specific fingerprints that will have to be winnowed in future Majorana fusion experiments.
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| 36. |
- Jünger, Christian, et al.
(författare)
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Magnetic-Field-Independent Subgap States in Hybrid Rashba Nanowires
- 2020
-
Ingår i: Physical Review Letters. - 0031-9007. ; 125:1
-
Tidskriftsartikel (refereegranskat)abstract
- Subgap states in semiconducting-superconducting nanowire hybrid devices are controversially discussed as potential topologically nontrivial quantum states. One source of ambiguity is the lack of an energetically and spatially well defined tunnel spectrometer. Here, we use quantum dots directly integrated into the nanowire during the growth process to perform tunnel spectroscopy of discrete subgap states in a long nanowire segment. In addition to subgap states with a standard magnetic field dependence, we find topologically trivial subgap states that are independent of the external magnetic field, i.e., that are pinned to a constant energy as a function of field. We explain this effect qualitatively and quantitatively by taking into account the strong spin-orbit interaction in the nanowire, which can lead to a decoupling of Andreev bound states from the field due to a spatial spin texture of the confined eigenstates. This result constitutes an important step forward in the research on superconducting subgap states in nanowires, such as Majorana bound states.
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| 37. |
- Jünger, Christian, et al.
(författare)
-
Spectroscopy of the superconducting proximity effect in nanowires using integrated quantum dots
- 2019
-
Ingår i: Communications Physics. - : Springer Science and Business Media LLC. - 2399-3650. ; 2:1
-
Tidskriftsartikel (refereegranskat)abstract
- The superconducting proximity effect has recently attracted a renewed interest as the basis of topologically nontrivial states in materials with a large spin–orbit interaction, with protected boundary states useful for quantum information technologies. However, spectroscopy of these states is challenging because of the limited control of conventional tunnel barriers. Here we report electronic spectroscopy measurements of the proximity gap in a semiconducting indium arsenide nanowire segment coupled to a superconductor, using quantum dots formed deterministically during the crystal growth. We extract characteristic parameters describing the proximity gap, which is suppressed for lower electron densities and fully developed for larger ones. This gate-tunable transition of the proximity effect can be understood as a transition from the long to the short junction regime of subgap bound states in the NW segment. Our device architecture opens up the way to systematic, quantitative spectroscopy studies of subgap states, such as Majorana-bound states.
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| 38. |
- Khan, Waqar, et al.
(författare)
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Efficient and continuous microwave photoconversion in hybrid cavity-semiconductor nanowire double quantum dot diodes
- 2021
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
-
Tidskriftsartikel (refereegranskat)abstract
- Converting incoming photons to electrical current is the key operation principle of optical photodetectors and it enables a host of emerging quantum information technologies. The leading approach for continuous and efficient detection in the optical domain builds on semiconductor photodiodes. However, there is a paucity of efficient and continuous photon detectors in the microwave regime, because photon energies are four to five orders of magnitude lower therein and conventional photodiodes do not have that sensitivity. Here we tackle this gap and demonstrate how microwave photons can be efficiently and continuously converted to electrical current in a high-quality, semiconducting nanowire double quantum dot resonantly coupled to a cavity. In particular, in our photodiode device, an absorbed photon gives rise to a single electron tunneling through the double dot, with a conversion efficiency reaching 6%.
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| 39. |
- Kindlund, Hanna, et al.
(författare)
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Kinetic Engineering of Wurtzite and Zinc-Blende AlSb Shells on InAs Nanowires
- 2018
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:9, s. 5775-5781
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Tidskriftsartikel (refereegranskat)abstract
- Using AlSb as the model system, we demonstrate that kinetic limitations can lead to the preferential growth of wurtzite (WZ) AlSb shells rather than the thermodynamically stable zinc-blende (ZB) AlSb and that the WZ and ZB relative thickness can be tuned by a careful control of the deposition parameters. We report selective heteroepitaxial radial growth of AlSb deposited by metal-organic vapor phase epitaxy (MOVPE) on InAs nanowire core templates with engineered lengths of axial WZ and ZB segments. AlSb shell thickness, crystal phase, nanostructure, and composition are investigated as a function of the shell growth temperature, Ts, using scanning electron microscopy, transmission electron microscopy, electron tomography, and energy-dispersive X-ray spectroscopy. We find that ZB- and WZ-structured AlSb shells grow heteroepitaxially around the ZB and WZ segments of the InAs core, respectively. Surprisingly, at 390 < Ts < 450 °C, the WZ-AlSb shells are thicker than the ZB-AlSb shells, and their thickness increases with decreasing Ts. In comparison, the ZB-AlSb shell thicknesses increase slightly with increasing Ts. We find that the increased thickness of the WZ-AlSb shells is due to the formation and enhanced deposition on {112-0} facets rather than on the more commonly grown {101-0} sidewall facets. Overall, these results, which are in direct contrast with previous reports suggesting that heteroepitaxial radial growth of III-antimonides is always favored on the ZB-structure facets, indicate that the growth of WZ-AlSb is preferred over the thermodynamically stable ZB-AlSb at lower growth temperatures. We attribute this behavior to kinetic limitations of MOVPE of AlSb on ZB and WZ phases of InAs.
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| 40. |
- Knutsson, Johan Valentin, et al.
(författare)
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Electronic Structure Changes Due to Crystal Phase Switching at the Atomic Scale Limit
- 2017
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 11:10, s. 10519-10528
-
Tidskriftsartikel (refereegranskat)abstract
- The perfect switching between crystal phases with different electronic structure in III-V nanowires allows for the design of superstructures with quantum wells only a single atomic layer wide. However, it has only been indirectly inferred how the electronic structure will vary down to the smallest possible crystal segments. We use low-temperature scanning tunneling microscopy and spectroscopy to directly probe the electronic structure of Zinc blende (Zb) segments in Wurtzite (Wz) InAs nanowires with atomic-scale precision. We find that the major features in the band structure change abruptly down to a single atomic layer level. Distinct Zb electronic structure signatures are observed on both the conduction and valence band sides for the smallest possible Zb segment: a single InAs bilayer. We find evidence of confined states in the region of both single and double bilayer Zb segments indicative of the formation of crystal segment quantum wells due to the smaller band gap of Zb as compared to Wz. In contrast to the internal electronic structure of the nanowire, surface states located in the band gap were found to be only weakly influenced by the presence of the smallest Zb segments. Our findings directly demonstrate the feasibility of crystal phase switching for the ultimate limit of atomistic band structure engineering of quantum confined structures. Further, it indicates that band gap values obtained for the bulk are reasonable to use even for the smallest crystal segments. However, we also find that the suppression of surface and interface states could be necessary in the use of this effect for engineering of future electronic devices.
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| 41. |
- Lehmann, Sebastian, et al.
(författare)
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Simultaneous Growth of Pure Wurtzite and Zinc Blende Nanowires
- 2019
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 19:4, s. 2723-2730
-
Tidskriftsartikel (refereegranskat)abstract
- The opportunity to engineer III-V nanowires in wurtzite and zinc blende crystal structure allows for exploring properties not conventionally available in the bulk form as well as opening the opportunity for use of additional degrees of freedom in device fabrication. However, the fundamental understanding of the nature of polytypism in III-V nanowire growth is still lacking key ingredients to be able to connect the results of modeling and experiments. Here we show InP nanowires of both pure wurtzite and pure zinc blende grown simultaneously on the same InP [100]-oriented substrate. We find wurtzite nanowires to grow along «111»B and zinc blende counterparts along «111»A. Further, we discuss the nucleation, growth, and polytypism of our nanowires against the background of existing theory. Our results demonstrate, first, that the crystal growth conditions for wurtzite and zinc blende nanowire growth are not mutually exclusive and, second, that the interface energies predominantly determine the crystal structure of the nanowires.
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| 42. |
- Lindberg, Caroline, et al.
(författare)
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Silver as Seed-Particle Material for GaAs Nanowires - Dictating Crystal Phase and Growth Direction by Substrate Orientation
- 2016
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 16:4, s. 2181-2188
-
Tidskriftsartikel (refereegranskat)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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| 43. |
- Liu, Yi, et al.
(författare)
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Self-selective formation of ordered 1D and 2D GaBi structures on wurtzite GaAs nanowire surfaces
- 2021
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
-
Tidskriftsartikel (refereegranskat)abstract
- Scaling down material synthesis to crystalline structures only few atoms in size and precisely positioned in device configurations remains highly challenging, but is crucial for new applications e.g., in quantum computing. We propose to use the sidewall facets of larger III–V semiconductor nanowires (NWs), with controllable axial stacking of different crystal phases, as templates for site-selective growth of ordered few atoms 1D and 2D structures. We demonstrate this concept of self-selective growth by Bi deposition and incorporation into the surfaces of GaAs NWs to form GaBi structures. Using low temperature scanning tunneling microscopy (STM), we observe the crystal structure dependent self-selective growth process, where ordered 1D GaBi atomic chains and 2D islands are alloyed into surfaces of the wurtzite (Wz) { 11 2 ¯ 0 } crystal facets. The formation and lateral extension of these surface structures are controlled by the crystal structure and surface morphology uniquely found in NWs. This allows versatile high precision design of structures with predicted novel topological nature, by using the ability of NW heterostructure variations over orders of magnitude in dimensions with atomic-scale precision as well as controllably positioning in larger device structures.
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| 44. |
- Maliakkal, Carina B., et al.
(författare)
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In situ analysis of catalyst composition during gold catalyzed GaAs nanowire growth
- 2019
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10:1
-
Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowires offer the opportunity to incorporate novel structures and functionality into electronic and optoelectronic devices. A clear understanding of the nanowire growth mechanism is essential for well-controlled growth of structures with desired properties, but the understanding is currently limited by a lack of empirical measurements of important parameters during growth, such as catalyst particle composition. However, this is difficult to accurately determine by investigating post-growth. We report direct in situ measurement of the catalyst composition during nanowire growth for the first time. We study Au-seeded GaAs nanowires inside an electron microscope as they grow and measure the catalyst composition using X-ray energy dispersive spectroscopy. The Ga content in the catalyst during growth increases with both temperature and Ga precursor flux.
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| 45. |
- Maliakkal, Carina B., et al.
(författare)
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Independent Control of Nucleation and Layer Growth in Nanowires
- 2020
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 14:4, s. 3868-3875
-
Tidskriftsartikel (refereegranskat)abstract
- Control of the crystallization process is central to developing nanomaterials with atomic precision to meet the demands of electronic and quantum technology applications. Semiconductor nanowires grown by the vapor-liquid-solid process are a promising material system in which the ability to form components with structure and composition not achievable in bulk is well-established. Here, we use in situ TEM imaging of Au-catalyzed GaAs nanowire growth to understand the processes by which the growth dynamics are connected to the experimental parameters. We find that two sequential steps in the crystallization process - nucleation and layer growth - can occur on similar time scales and can be controlled independently using different growth parameters. Importantly, the layer growth process contributes significantly to the growth time for all conditions and will play a major role in determining material properties such as compositional uniformity, dopant density, and impurity incorporation. The results are understood through theoretical simulations correlating the growth dynamics, liquid droplet, and experimental parameters. The key insights discussed here are not restricted to Au-catalyzed GaAs nanowire growth but can be extended to most compound nanowire growths in which the different growth species has very different solubility in the catalyst particle.
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| 46. |
- Maliakkal, Carina B., et al.
(författare)
-
Post-nucleation evolution of the liquid-solid interface in nanowire growth
- 2022
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 33:10
-
Tidskriftsartikel (refereegranskat)abstract
- We study using in situ transmission electron microscopy the birth of GaAs nanowires from liquid Au-Ga catalysts on amorphous substrates. Lattice-resolved observations of the starting stages of growth are reported here for the first time. It reveals how the initial nanostructure evolves into a nanowire growing in a zincblende 111 or the equivalent wurtzite0001 direction. This growth direction(s) is what is typically observed in most III-V and II-VI nanowires. However, the reason for this preferential nanowire growth along this direction is still a dilemma. Based on the videos recorded shortly after the nucleation of nanowires, we argue that the lower catalyst droplet-nanowire interface energy of the {111} facet when zincblende (or the equivalent {0001} facet in wurtzite) is the reason for this direction selectivity in nanowires.
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| 47. |
- Maliakkal, Carina B., et al.
(författare)
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Vapor-solid-solid growth dynamics in GaAs nanowires
- 2021
-
Ingår i: Nanoscale Advances. - : Royal Society of Chemistry (RSC). - 2516-0230. ; 3:20, s. 5928-5940
-
Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowires are promising material systems for coming-of-age nanotechnology. The usage of the vapor-solid-solid (VSS) route, where the catalyst used for promoting axial growth of nanowires is a solid, offers certain advantages compared to the common vapor-liquid-solid (VLS) route (using a liquid catalyst). The VSS growth of group-IV elemental nanowires has been investigated by other groupsin situduring growth in a transmission electron microscope (TEM). Though it is known that compound nanowire growth has different dynamics compared to elemental semiconductors, the layer growth dynamics of VSS growth of compound nanowires have not been studied yet. Here we investigate for the first time controlled VSS growth of compound nanowires byin situmicroscopy, using Au-seeded GaAs as a model system. The ledge-flow growth kinetics and dynamics at the wire-catalyst interface are studied and compared for liquid and solid catalysts under similar growth conditions. Here the temperature and thermal history of the system are manipulated to control the catalyst phase. In the first experiment discussed here we reduce the growth temperature in steps to solidify the initially liquid catalyst, and compare the dynamics between VLS and VSS growth observed at slightly different temperatures. In the second experiment we exploit thermal hysteresis of the system to obtain both VLS and VSS at the same temperature. The VSS growth rate is comparable or slightly slower than the VLS growth rate. Unlike in the VLS case, during VSS growth we frequently observe that a new layer starts before the previous layer is completely grown,i.e., ‘multilayer growth’. Understanding the VSS growth mode enables better control of nanowire properties by widening the range of usable nanowire growth parameters.
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| 48. |
- Marnauza, Mikelis, et al.
(författare)
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In situ observations of size effects in GaAs nanowire growth
- 2022
-
Ingår i: Nanoscale Horizons. - : Royal Society of Chemistry (RSC). - 2055-6756 .- 2055-6764. ; 8:2, s. 291-296
-
Tidskriftsartikel (refereegranskat)abstract
- Lateral dimensions of III-V nanowires are known to affect the growth dynamics and crystal structure. Investigations into size effects have in the past relied on theoretical models and post growth observations, which only give a limited insight into the growth dynamics. Here we show the first experimental investigation into how nanowire diameter affects the growth dynamics by growing Au-seeded GaAs nanowires in an environmental transmission electron microscope. This was done by recording videos of nanowires during growth and analysing the Ga-limited incubation time and As-limited step-flow time. Our data show that the incubation time is stable across the investigated diameter range aside from a sharp increase for the smallest diameter, whereas the step-flow time is observed to steadily increase across the diameter range. We show using a simple model that this can be explained by the increasing vapour pressure in the droplet. In addition to the existing understanding of nanowire growth at small dimensions being limited by nucleation this work provides experimental evidence that growth is also limited by the inability to finish the step-flow process.
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| 49. |
- Martensson, Erik K., et al.
(författare)
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Simulation of GaAs Nanowire Growth and Crystal Structure
- 2019
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 19:2, s. 1197-1203
-
Tidskriftsartikel (refereegranskat)abstract
- Growing GaAs nanowires with well-defined crystal structures is a challenging task, but may be required for the fabrication of future devices. In terms of crystal phase selection, the connection between theory and experiment is limited, leaving experimentalists with a trial and error approach to achieve the desired crystal structures. In this work, we present a modeling approach designed to provide the missing connection, combining classical nucleation theory, stochastic simulation, and mass transport through the seed particle. The main input parameters for the model are the flows of the growth species and the temperature of the process, giving the simulations the same flexibility as experimental growth. The output of the model can also be directly compared to experimental observables, such as crystal structure of each bilayer throughout the length of the nanowire and the composition of the seed particle. The model thus enables for observed experimental trends to be directly explored theoretically. Here, we use the model to simulate nanowire growth with varying As flows, and our results match experimental trends with a good agreement. By analyzing the data from our simulation, we find theoretical explanations for these experimental results, providing new insights into how the crystal structure is affected by the experimental parameters available for growth.
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| 50. |
- Mousavi, S. Fatemeh, et al.
(författare)
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Atomic Hydrogen Annealing of Graphene on InAs Surfaces and Nanowires : Interface and Morphology Control for Optoelectronics and Quantum Technologies
- 2022
-
Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 5:12, s. 17919-17927
-
Tidskriftsartikel (refereegranskat)abstract
- Folding two-dimensional graphene around one-dimensional III-V nanowires yields a new class of hybrid nanomaterials combining their excellent complementary properties. However, important for high-quality electrical and optical performance, needed in many applications, are well-controlled oxide-free interfaces and a tight folding morphology. To improve the interface chemistry between the graphene and InAs, we annealed the samples in atomic hydrogen. Using surface-sensitive imaging, we found that the III-V native oxides in the interface can be reduced at temperatures that maintain the graphene and the III-V nanostructures. Transferring both single- and multilayer graphene flakes onto InAs NWs, we found that single layers fold tightly around the NWs, while the multilayers fold weakly with a decline of only a few degrees. Annealing in atomic hydrogen further tightens the folding. Together, this indicates that high-quality morphological and chemical control of this hybrid material system is possible, opening for future devices for quantum technologies and optoelectronics.
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