| 1. |
- Gustafsson, Anders, et al.
(författare)
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A cathodoluminescence study of the influence of the seed particle preparation method on the optical properties of GaAs nanowires.
- 2012
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 23:26
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Tidskriftsartikel (refereegranskat)abstract
- Cathodoluminescence at 8 K is used to compare the optical properties of AlGaAs-capped GaAs nanowires, grown by metal-organic vapour phase epitaxy and seeded by gold particles prepared by different methods. Six different methods were used to fabricate and deposit gold seed particles onto GaAs substrates: colloid particles, aerosol particles and particles defined by electron beam lithography. The nanowires were grown with and without an in situ annealing step prior to the nanowire growth. The morphology showed no significant differences between the nanowires. The emissions from ensembles of nanowires have the same peak position, irrespective of seed particle type. Without the in situ annealing step prior to the nanowire growth, there are significant differences in the emission intensity and emission patterns from nanowires grown from different seed particles. When an in situ annealing step is included, all the resulting nanowires show identical optical emission intensity and emission patterns. This shows the importance of using an in situ annealing step prior to growth. This study demonstrates that different preparation methods for gold seed particles can be used to produce GaAs nanowires with highly similar optical properties. The choice of particle preparation method to be used can therefore be based on availability and cost.
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| 2. |
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| 3. |
- Hillerich, Karla, et al.
(författare)
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Cu particle seeded InP InAs axial nanowire heterostructures
- 2013
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Ingår i: Physica Status Solidi. Rapid Research Letters. - : Wiley. - 1862-6254. ; 7:10, s. 850-854
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the epitaxial growth of alternating InP-InAs nanowire heterostructures using Cu seed particles in MOVPE. We observe extraordinary early stages in the formation of InAs segments, e.g. three-dimensional nucleation instead of step-flow growth. Furthermore, InAs segments of thin nanowires exhibit extended 4H crystal structure.
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| 4. |
- Hillerich, Karla, et al.
(författare)
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Epitaxial InP nanowire growth from Cu seed particles
- 2011
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 315:1, s. 134-137
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Konferensbidrag (refereegranskat)abstract
- Cu-seeded epitaxial growth of vertically aligned InP nanowires is reported for the first time. The nanowires were grown at temperatures between 290 and 420 degrees C by metal-organic vapor phase epitaxy (MOVPE) from particles formed from Cu thin films. In the temperature range of 340-370 degrees C high yields of vertically aligned nanowires could be achieved. The nanowire crystal structure and the particle composition were investigated by TEM and XEDS. The nanowires showed a zinc blende structure and a post-growth particle composition of 64 at% Cu and 36 at% In. (C) 2010 Elsevier B.V. All rights reserved.
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| 5. |
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| 6. |
- Hillerich, Karla
(författare)
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Influence of Seed Particle Material, Preparation, and Dynamics on Nanowire Growth
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Semiconducting nanowires have attracted scientific attention for more than 20 years due to their potential applications in electronic devices, as sensors, and in solid state lighting. These applications require high quality nanowires to begin with. Achieving such good control over the growth of nanowires is not trivial and requires profound understanding of the underlying processes. In this thesis, nanowires of different materials and combinations thereof have been grown with the help of seed particles by metal-organic vapor phase epitaxy (MOVPE). The focus of the investigations lies on the influence of several seed particle properties on nanowire growth. First, we compared six particle preparation and deposition methods for the most common seed particle material – gold - and their influence on the growth of GaAs nanowires. We observed only small differences, mainly in incubation times, which did not have a significant effect on the nanowire length after some growth time, though. The optical properties, however, varied between nanowires seeded by different particle types. Further, copper as seed particle material for growth of InP nanowires and InP-InAs heterostructures was investigated. The aim was to get a deeper understanding of which properties or combination of properties determine a “good” seed particle material. InP nanowire growth from Cu particles differs a lot from nanowire growth from Au seed particles in terms of temperature range and precursor molar fractions. Furthermore, growth from two types of particles – Cu-rich and In-rich – occurs simultaneously at low V/III ratios. The investigations of InP-InAs heterostructures showed that it is indeed possible to grow straight heterostructures, but we observed unusual layer formation of the InAs segments. Finally, we used the possibility of in situ TEM to investigate nanowire growth at the IBM T.J. Watson Research Center. We combined group IV and group III/V materials and investigated the particle dynamics that may lead to kinking. In addition, we investigated the instantaneous kinetics of GaP growth.
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| 7. |
- Hillerich, Karla, et al.
(författare)
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Simultaneous growth mechanisms for Cu-seeded InP nanowires
- 2012
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Ingår i: Nano Reseach. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 5:5, s. 297-306
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Tidskriftsartikel (refereegranskat)abstract
- We report on epitaxial growth of InP nanowires (NWs) from Cu seed particles by metal-organic vapor phase epitaxy (MOVPE). Vertically-aligned straight nanowires can be achieved in a limited temperature range between 340 A degrees C and 370 A degrees C as reported earlier. In this paper we present the effect of the V/III ratio on nanowire morphology, growth rate, and particle configuration at a growth temperature of 350 A degrees C. Two regimes can be observed in the investigated range of molar fractions. At high V/III ratios nanowires grow from a solid Cu2In particle. At low V/III ratios, nanowire growth from two particle types occurs simultaneously: Growth from solid Cu2In particles, and significantly faster growth from In-rich particles. We discuss a possible growth mechanism relying on a dynamic interplay between vapor-liquid-solid (VLS) and vapor-solid-solid (VSS) growth. Our results bring us one step closer to the replacement of Au as seed particle material as well as towards a deeper understanding of particle-assisted nanowire growth.
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| 8. |
- Hillerich, Karla, et al.
(författare)
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Strategies To Control Morphology in Hybrid Group III-V/Group IV Heterostructure Nanowires.
- 2013
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 13:3, s. 903-908
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Tidskriftsartikel (refereegranskat)abstract
- By combining in situ and ex situ transmission electron microscopy measurements, we examine the factors that control the morphology of "hybrid" nanowires that include group III-V and group IV materials. We focus on one materials pair, GaP/Si, for which we use a wide range of growth parameters. We show through video imaging that nanowire morphology depends on growth conditions, but that a general pattern emerges where either single kinks or inclined defects form some distance after the heterointerface. We show that pure Si nanowires can be made to exhibit the same kinks and defects by changing their droplet volume. From this we derive a model where droplet geometry drives growth morphology and discuss optimization strategies. We finally discuss morphology control for material pairs where the second material kinks immediately at the heterointerface and show that an interlayer between segments can enable the growth of unkinked hybrid nanowires.
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| 9. |
- Jacobsson, Daniel, et al.
(författare)
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Phase Transformation in Radially Merged Wurtzite GaAs Nanowires.
- 2015
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 15:10, s. 4795-4803
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Tidskriftsartikel (refereegranskat)abstract
- III-V Nanowires (NWs) grown with metal-organic chemical vapor deposition commonly show a polytypic crystal structure, allowing growth of structures not found in the bulk counterpart. In this paper we studied the radial overgrowth of pure wurtzite (WZ) GaAs nanowires and characterized the samples with high resolution X-ray diffraction (XRD) to reveal the crystal structure of the grown material. In particular, we investigated what happens when adjacent WZ NWs radially merge with each other by analyzing the evolution of XRD peaks for different amounts of radial overgrowth and merging. By preparing cross-sectional lamella samples we also analyzed the local crystal structure of partly merged NWs by transmission electron microscopy. Once individual NWs start to merge, the crystal structure of the merged segments is transformed progressively from initial pure WZ to a mixed WZ/ZB structure. The merging process is then modeled using a simple combinatorial approach, which predicts that merging of two or more WZ NWs will result in a mixed crystal structure containing WZ, ZB, and 4H. The existence large and relaxed segments of 4H structure within the merged NWs was confirmed by XRD, allowing us to accurately determine the lattice parameters of GaAs 4H. We compare the measured WZ and 4H unit cells with an ideal tetrahedron and find that both the polytypes are elongated in the c-axis and compressed in the a-axis compared to the geometrically converted cubic ZB unit cell.
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| 10. |
- Lehmann, Sebastian, et al.
(författare)
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III/V Nanodrähte
- 2013
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Ingår i: DGKK.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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