| 1. |
- Kindlund, Hanna, et al.
(author)
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Kinetic Engineering of Wurtzite and Zinc-Blende AlSb Shells on InAs Nanowires
- 2018
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:9, s. 5775-5781
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Journal article (peer-reviewed)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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| 2. |
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| 3. |
- Birch, J., et al.
(author)
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Structural characterization of precious-mean quasiperiodic Mo/V single-crystal superlattices grown by dual-target magnetron sputtering
- 1990
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In: Physical Review B. - 1098-0121. ; 41:15, s. 10398-10407
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Journal article (peer-reviewed)abstract
- A class of quasiperiodic superlattice structures, which can be generated by the concurrent inflation rule A→AmB and B→A (where m=positive integer), has been studied both theoretically and experimentally. Given that the ratios between the thicknesses of the two superlattice building blocks, A and B, are chosen to be γ(m)=[m+(m2+4)1/2]/2 (known as the ‘‘precious means’’), then the x-ray- and electron-diffraction peak positions are analytically found to be located at the wave vectors q=2πΛ−1r[γ(m)]k, where r and k are integers and Λ is an average superlattice wavelength. The analytically obtained results have been compared to experimental results from single-crystalline Mo/V superlattice structures, generated with m=1, 2, and 3. The superlattices were grown by dual-target dc-magnetron sputtering on MgO(001) substrates kept at 700 °C. X-ray diffraction (XRD) and selected-area electron diffraction (SAED) showed that the analytical model mentioned above predicts the peak positions of the experimental XRD and SAED spectra with a very high accuracy. Furthermore, numerical calculations of the diffraction intensities based on a kinematical model of diffraction showed good agreement with the experimental data for all three cases. In addition to a direct verification of the quasiperiodic modulation, both conventional and high-resolution cross-sectional transmission electron microscopy (XTEM) showed that the superlattices are of high crystalline quality with sharp interfaces. Based on lattice resolution images, the width of the interfaces was determined to be less than two (002) lattice-plane spacings (≊0.31 nm).
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| 4. |
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| 5. |
- Bovin, JO, et al.
(author)
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Imaging of atomic clouds outside the surfaces of gold crystals by electron microscopy
- 1985
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 317, s. 47-49
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Journal article (peer-reviewed)abstract
- The structure of small metal crystals has been intensively examined by high-resolution electron microscopy (HREM). In particular, multiply-twinned gold and silver crystals have been characterized using the profile-imaging method1,2 at atomic resolution, and reconstructed metal surfaces observed2. Crystal structure images of large gold clusters consisting of 55 gold atoms arranged in a cubeoctahedron have been recorded3 using 2.5 Å resolution, and crystal growth, row by row, on a {111} surface has been documented4 using a low-light-level silicon-intensified target television (TV) camera and video system with an on-line image processor. Direct imaging of rearrangements of atomic columns on extended gold surface5 established that profile imaging can provide information about surface self-diffusion. The motion of surface atoms, recorded with a real-time video tape-recorder (VTR) system, and the formation of surface atom steps on {100} surfaces, although not {111}, has also been reported recently6. Dynamic HREM observations at TV rate showing defect motion in gold7 and CdTe (refs. 8, 9) has given information on ‘in-lattice’ rearrangements of columns of atoms. We report here surface profile images recorded with the electron beam along the 〈110〉 direction with spatial resolution of ∼2.0 Å which reveal changes in occupancy of the atom columns often within periods of less than 0.1 s. Surfaces with several adjacent atom columns involved in rapid structural changes frequently interacted with a cloud of atoms extending out to 9 Å off the crystal and changes in shape and density of the clouds were recorded. Although these clouds have already been described6,10, the present work is the first to analyse these events properly and to describe them in detail. The motion of atomic columns and the existence of atom clouds revealed here may have important consequences for crystal growth, surface science and catalysis studies.
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| 6. |
- Carlsson, N, et al.
(author)
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IMPROVED SIZE HOMOGENEITY OF INP-ON-GAINP STRANSKI-KRASTANOW ISLANDS BY GROWTH ON A THIN GAP INTERFACE LAYER
- 1995
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 156:1-2, s. 23-29
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Journal article (peer-reviewed)abstract
- Coherent InP nano-sized islands, embedded into GaInP, have been grown by metal-organic vapour phase epitaxy using the Stranski-Krastanow growth mode. Photoluminescence, atomic force microscopy and transmission electron microscopy studies show that the insertion of a thin ∼ 4 monolayer thick GaP layer affects the critical thickness of the subsequently deposited two-dimensional InP wetting layer, increasing it from ∼ 1.5 monolayers (without an inserted GaP layer) to ∼ 2.5 monolayers (with an inserted GaP layer). We demonstrate that the inserted GaP layer affects also the island formation. The bimodal size distribution of Stranski-Krastanow islands, typical for low InP coverages, can be overcome without island coalescence by deposition on top of the thin GaP layer, where a coverage of InP of about 3.5–4.5 monolayers results in the formation of almost only the larger, fully developed, pyramidal islands. Annealing experiments at growth temperature of 580°C show that these islands (base area ≈ 40 × 50 nm2, height ≈ 10–15 nm, surface density ≈ (1−2) × 109 cm−2) are rather stable in a time-scale over several minutes before they slowly undergo an Ostwald ripening process.
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| 7. |
- Chen, Wei, et al.
(author)
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Crystal field, phonon coupling and emission shift of Mn2+ in ZnS:Mn nanoparticles
- 2001
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89, s. 1120-1129
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Journal article (peer-reviewed)abstract
- The Mn2+ emission wavelengths are at 591, 588, 581 and 570 nm, respectively, for the similar to 10, similar to4.5, similar to3.5 nm sized nanoparticles and the ZnS:Mn nanoparticles formed in an ultrastable zeolite-Y. To reveal the cause for the shift, the crystal field and phonon coupling were investigated. The results show that the predominant factor for the shift is the phonon coupling, whose strength is size dependent and is determined by both the size confinement and the surface modification of the nanoparticles. Although the crystal field strength decreases with the decreasing of the particle size, its change has little contribution to the emission shift of Mn2+ in ZnS:Mn nanoparticles. (C) 2001 American Institute of Physics.
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| 8. |
- Chen, W, et al.
(author)
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Pressure dependence of Mn2+ fluorescence in ZnS:Mn2+ nanoparticles
- 2000
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In: Journal of Luminescence. - 0022-2313. ; 91:3-4, s. 139-145
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Journal article (peer-reviewed)abstract
- The photoluminescence of Mn2+ in ZnS : Mn2+ nanoparticles with an average size of 4.5 nm has been measured under hydrostatic pressure from 0 to 6 GPa. The emission position is red-shifted at a rate of −33.3±0.6 meV/GPa, which is in good agreement with the calculated value of −30.4 meV/GPa using the crystal field theory.
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| 9. |
- Chen, W, et al.
(author)
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Size dependence of Eu2+ fluorescence in ZnS:Eu2+ nanoparticles
- 2001
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89:5, s. 2671-2675
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Journal article (peer-reviewed)abstract
- The emission bands of the 4.2, 3.2 and 2.6 nm sized ZnS:Eu2+ nanoparticles are peaking at 670, 580 and 520 nm, respectively. The emission of the 4.2 nm sized nanoparticles originates from the recombination of the Eu2+-bound exciton, while the emission of the 3.2 and 2.6 nm sized nanoparticles is from the Eu2+ intra-ion transition of 4f(6)5d(1)(t(2g))-4f(7). Possible mechanisms for the size dependence of the 4f(6)5d(1)(t(2g))-4f(7) transition of Eu2+ in ZnS:Eu2+ nanoparticles were investigated, and it was concluded that the decreases in the electron-phonon coupling and in crystal field strength upon a decrease in size are the two major factors responsible for the shift. (C) 2001 American Institute of Physics.
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