| 1. |
- Balitskii, Olexiy A., et al.
(författare)
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Tuning the Localized Surface Plasmon Resonance in Cu2-xSe Nanocrystals by Postsynthetic Ligand Exchange
- 2014
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 6:20, s. 17770-17775
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Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles exhibiting localized surface plasmon resonances (LSPR) are valuable tools traditionally used in a wide field of applications including sensing, imaging, biodiagnostics and medical therapy. Plasmonics in semiconductor nanocrystals is of special interest because of the tunability of the carrier densities in semiconductors, and the possibility to couple the plasmonic resonances to quantum confined excitonic transitions. Here, colloidal Cu2-xSe nanocrystals were synthesized, whose composition was shown by Rutherford backscattering analysis and electron dispersive X-ray spectroscopy, to exhibit Cu deficiency. The latter results in p-type doping causing LSPRs, in the present case around a wavelength of 1100 nm, closely matching the indirect band gap of Cu2-xSe. By partial exchange of the organic ligands to specific electron trapping or donating species the LSPR is fine-tuned to exhibit blue or red shifts, in total up to 200 nm. This tuning not only provides a convenient tool for post synthetic adjustments of LSPRs to specific target wavelength but the sensitive dependence of the resonance wavelength on surface charges makes these nanocrystals also interesting for sensing applications, to detect analytes dressed by functional groups.
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| 2. |
- Chamard, Virginie, et al.
(författare)
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Evidence of stacking-fault distribution along an InAs nanowire using micro-focused coherent X-ray diffraction
- 2008
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Ingår i: Journal of Applied Crystallography. - 1600-5767. ; 41:Part 2, s. 272-280
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Tidskriftsartikel (refereegranskat)abstract
- InAs nanowire samples grown by metal-organic chemical vapor deposition present a significant amount of wurtzite structure, while the zincblende lattice is known to be the stable crystal structure for the bulk material. The question of the wurtzite distribution in the sample is addressed using phase-sensitive coherent X-ray diffraction with a micro-focused beam at a synchrotron source. The simultaneous investigation of the wurtzite 10 (1) over bar0, 10 (2) over bar0, 10 (3) over bar0 reflections performed on a bunch of single wires shows unambiguously that the wurtzite contribution is a result of stacking faults distributed along the wire. Additional simulations lead to adjustments of the wire structural parameters, such as the wurtzite content, the strain distribution, the wire diameters and their respective orientations.
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| 3. |
- 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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| 4. |
- Keplinger, Mario, et al.
(författare)
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Core-shell nanowires: From the ensemble to single-wire characterization
- 2010
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 268:3-4, s. 316-319
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Konferensbidrag (refereegranskat)abstract
- Recent investigations of core-shell nanowires using synchrotron radiation techniques deduced the average structural parameters of heterostructure core-shell nanowires. Here, we report on first results and discuss the problems arising when measuring such complex nanostructures by using nanofocusing X-ray techniques. InAs/IAsP core-shell nanowires exhibit a certain bending, the origin of which is described using finite element simulations assuming a displacement of the core, and a gradient in the chemical composition of the wire's shell. (C) 2009 Elsevier B.V. All rights reserved.
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| 5. |
- Keplinger, Mario, et al.
(författare)
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Structural Investigations of Core-shell Nanowires Using Grazing Incidence X-ray Diffraction.
- 2009
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 9:5, s. 1877-1882
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Tidskriftsartikel (refereegranskat)abstract
- The fabrication of core-shell structures is crucial for many nanowire device concepts. For the proper tailoring of their electronic properties, control of structural parameters such as shape, size, diameter of core and shell, their chemical composition, and information on their strain fields is mandatory. Using synchrotron X-ray diffraction studies and finite element simulations, we determined the chemical composition, dimensions, and strain distribution for series of InAs/InAsP core-shell wires grown on Si(111) with systematically varied growth parameters. In particular we detect initiation of plastic relaxation of these structures with increasing shell thickness and/or increasing phosphorus content. We establish a phase diagram, defining the region of parameters leading to pseudomorphic nanowire growth. This is important to avoid extended defects which are detrimental for their electronic properties.
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| 6. |
- Keplinger, Mario, et al.
(författare)
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X-ray diffraction strain analysis of a single axial InAs1-xPx nanowire segment.
- 2015
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Ingår i: Journal of Synchrotron Radiation. - 1600-5775. ; 22:Pt 1, s. 59-66
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Tidskriftsartikel (refereegranskat)abstract
- The spatial strain distribution in and around a single axial InAs1-xPx hetero-segment in an InAs nanowire was analyzed using nano-focused X-ray diffraction. In connection with finite-element-method simulations a detailed quantitative picture of the nanowire's inhomogeneous strain state was achieved. This allows for a detailed understanding of how the variation of the nanowire's and hetero-segment's dimensions affect the strain in its core region and in the region close to the nanowire's side facets. Moreover, ensemble-averaging high-resolution diffraction experiments were used to determine statistical information on the distribution of wurtzite and zinc-blende crystal polytypes in the nanowires.
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| 7. |
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| 8. |
- Kriegner, Dominik, et al.
(författare)
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Unit Cell Structure of Crystal Polytypes in InAs and InSb Nanowires
- 2011
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 11:4, s. 1483-1489
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Tidskriftsartikel (refereegranskat)abstract
- The atomic distances in hexagonal polytypes of III-V compound semiconductors differ from the values expected from simply a change of the stacking sequence of (111) lattice planes. While these changes were difficult to quantify so far, we accurately determine the lattice parameters of zinc blende, wurtzite, and 4H polytypes for InAs and InSb nanowires, using X-ray diffraction and transmission electron microscopy. The results are compared to density functional theory calculations. Experiment and theory show that the occurrence of hexagonal bilayers tend to strech the distances of atomic layers parallel to the c-axis and to reduce the in-plane distances compared to those in zinc blende. The change of the lattice parameters scales linearly with the hexagonality of the polytype, defined as the fraction of bilayers with hexagonal character within one unit cell.
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| 9. |
- Mandl, Bernhard, et al.
(författare)
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Au-free epitaxial growth of InAs nanowires
- 2006
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 6:8, s. 1817-1821
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Tidskriftsartikel (refereegranskat)abstract
- III-V nanowires have been fabricated by metal-organic vapor-phase epitaxy without using Au or other metal particles as a catalyst. Instead, prior to growth, a thin SiOx layer is deposited on the substrates. Wires form on various III-V substrates as well as on Si. They are nontapered in thickness and exhibit a hexagonal cross-section. From high-resolution X-ray diffraction, the epitaxial relation between wires and substrates is demonstrated and their crystal structure is determined.
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| 10. |
- Mandl, Bernhard, et al.
(författare)
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Crystal structure control in Au-free self-seeded InSb wire growth.
- 2011
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 22:14
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Tidskriftsartikel (refereegranskat)abstract
- In this work we demonstrate experimentally the dependence of InSb crystal structure on the ratio of Sb to In atoms at the growth front. Epitaxial InSb wires are grown by a self-seeded particle assisted growth technique on several different III-V substrates. Detailed investigations of growth parameters and post-growth energy dispersive x-ray spectroscopy indicate that the seed particles initially consist of In and incorporate up to 20 at.% Sb during growth. By applying this technique we demonstrate the formation of zinc-blende, 4H and wurtzite structure in the InSb wires (identified by transmission electron microscopy and synchrotron x-ray diffraction), and correlate this sequential change in crystal structure to the increasing Sb/In ratio at the particle-wire interface. The low ionicity of InSb and the large diameter of the wire structures studied in this work are entirely outside the parameters for which polytype formation is predicted by current models of particle seeded wire growth, suggesting that the V/III ratio at the interface determines crystal structure in a manner well beyond current understanding. These results therefore provide important insight into the relationship between the particle composition and the crystal structure, and demonstrate the potential to selectively tune the crystal structure in other III-V compound materials as well.
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