| 1. |
- Barcena, L. T., et al.
(author)
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Control of oscillatory thermocapillary convection with local heating
- 2006
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 286:2, s. 502-511
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Journal article (peer-reviewed)abstract
- In this experimental work, a proportional feedback control was applied to attenuate an oscillatory thermocapillary flow in an open cylindrical container (annular configuration) filled with silicon oil with high Prandt1 number (Pr = 14 at 25 degrees C). The control was realized by locally heating the free surface with two point source heaters strategically positioned in different azimuthal positions. The heaters were actuated using the local temperature signals fed back from paired sensors. It is suggested that the shortcoming of the control performance accompanied with the amplification of the harmonic frequency components is due to the coupling of the fundamental and the harmonic modes caused by the local control. A remedy is demonstrated to validate the suggestion, where the coupling can be attenuated by increasing the azimuthal length of the actuation region.
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| 2. |
- Baruah, S., et al.
(author)
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pH-dependent growth of zinc oxide nanorods
- 2009
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In: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 311:8, s. 2549-2554
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Journal article (peer-reviewed)abstract
- Here we study the effect of pH variation on the dimension and morphology of zinc oxide (ZnO) nanorods grown through hydrothermal process at temperatures less than 100 °C. ZnO nanorods were grown on pre-seeded glass substrates using zinc nitrate hexahydrate as the source of Zn ions and hexamethylenetetramine as the source of hydroxyl ions. The pH of the reaction bath was found to change gradually from 6.4 to 7.3 in 5 h during the growth process. The growth of the ZnO nanorods was observed to be faster, both laterally and longitudinally, when the growth solution was in basic conditions. However, flower petal like ZnO nanostructures were obtained when the growth process was initiated in basic condition (pH 8–12), indicating that initial acidic conditions were required to obtain nanorods with well-defined hexagonal facets. ZnO is known to erode in acidic condition and the final dimension of the nanorods is determined by a competition between crystal growth and etching. ZnO nanorods of different dimensions, both laterally (diameters ranging from 220 nm to 1 μm) and longitudinally (lengths ranging from 1 to 5.6 μm) were successfully synthesized using the same concentration of zinc nitrate and hexamine in the reaction bath and the same growth duration of 5 h simply through appropriate control of the pH of the reactant solution between 6 and 7.3.
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| 3. |
- Bi, Zhaoxia
(author)
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Low-temperature MOCVD growth of InN buffer layers with indium pre-deposition technology
- 2007
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 300:1, s. 123-126
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Journal article (peer-reviewed)abstract
- Cubic-InN was grown at a low temperature of 350 degrees C using our home-made low-pressure metal-organic chemical vapor deposition (MOCVD). The technology of indium pre-deposition was applied, that is, a layer of indium was deposited on the sapphire surface with a precursor of trimethylindium (TMI) before the growth of InN. Both X-ray diffraction (XRD) and X-ray photoelectron (XPS) spectra show that the pre-deposited indium is able to promote the growth of InN, and meanwhile, suppress the indium aggregation in the grown layer. Atomic force microscopy (AFM) images indicate that the nucleation of InN becomes easier with the pre-deposition of indium. It is proposed that the pre-deposited indium can seed the growth of InN, just like the vapor-liquid-solid (VLS) fabrication of InN whiskers with indium nanoparticles. (c) 2006 Elsevier B.V. All rights reserved.
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| 4. |
- Bohnen, T., et al.
(author)
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ScAlN nanowires : A cathodoluminescence study
- 2009
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In: JOURNAL OF CRYSTAL GROWTH. - : Elsevier BV. - 0022-0248. ; 311:11, s. 3147-3151
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Journal article (peer-reviewed)abstract
- Wurtzite ScAlN nanowires, grown on a scandium nitride (ScN) thin film by hydride vapor phase epitaxy (HVPE), were analyzed by energy dispersive analysis of X-rays (EDX), CL, high resolution transmission electron spectroscopy (HRTEM), and scanning electron microscopy (SEM). The wires were grown along the [0 0 0 1] axis, had an average length of 1 mu m, a diameter between 50 and 150 run, and a ScAlN composition with a 95:5 Al:Sc ratio. Cathodoluminescence studies on the individual wires showed a sharp emission near 2.4 eV, originating from the Sc atoms in the aluminum nitride (AlN) matrix. The formation of such a semiconducting ScAlN alloy could present a new alternative to InAlN for optoelectronic applications operating in the 200-550 nm range.
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| 5. |
- Borg, Mattias, et al.
(author)
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Characterization of GaSb nanowires grown by MOVPE
- 2008
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In: Journal of Chrystal Growth. - : Elsevier BV. - 0022-0248. ; 310:23, s. 5119-5122
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Conference paper (peer-reviewed)abstract
- We report the growth and characterization of GaSb nanowires grown by MOVPE. The structural properties of the nanowires are investigated by the means of transmission electron microscopy, X-ray diffraction and single nanowire photoluminescence. The measurements confirm a high material quality in the GaSb nanowires. Also, a back-gated nanowire transistor structure is used to extract values for the polarity and resistivity of the GaSb. Finally, a simple kinetic model is presented to explain the non-linear time dependence of the GaSb nanowire growth. (C) 2008 Elsevier B.V. All rights reserved.
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| 6. |
- Borg, Mattias, et al.
(author)
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GaAs/GaSb nanowire heterostructures grown by MOVPE
- 2008
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 310:18, s. 4115-4121
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Journal article (peer-reviewed)abstract
- We report Au-assisted growth of GaAs/GaSb nanowire heterostructures on GaAs(1 1 1)B-substrates by metal-organic vapor phase epitaxy. The growth is studied at various precursor molar fractions and temperatures, in order to optimize the growth conditions for the GaSb nanowire segment. In contrast to most other III-V nanowire systems, the GaSb nanowire growth is Group V-limited under most conditions. We found that depending on the TMSb molar fraction, the seed particle is either supersaturated AuGa or AuGa2 during GaSb growth. The high Ga content in the particle gives a characteristic diameter increase between the GaAs and GaSb segment. From TEM and XEDS measurements we conclude that the GaSb nanowire growth occurs along either the AuGa-GaSb or AuGa2-GaSb pseudo-binaries of the Au-Ga-Sb ternary phase diagram. Finally, the GaSb nanowires exhibit untapered radial growth on the {1 (1) over bar 0} side facets. (C) 2008 Elsevier B.V. All rights reserved.
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| 7. |
- Ciechonski, Rafal, et al.
(author)
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Structural instabilities in growth of SiC crystals
- 2005
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 275:1-2, s. e461-e466
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Journal article (peer-reviewed)abstract
- Misoriented grains, which may occur on the growth front of 6H–SiC boules have been studied in relation to their appearance during sublimation growth. The effect was obtained by applying growth conditions at which the source powder was gradually approaching graphitisation and the vapour becoming C-rich. The high off-orientation of the grains is demonstrated through etching in molten KOH and transmission light optical microscopy. Micropipes propagating in the single crystal area and facing the misoriented grain have been studied, and it is shown that they may either be terminated at the grain or their propagation is altered to be parallel with the grain boundary. It has been found that the polytype of the grains may switch from 6H to 4H, which is explained by the change of the Si/C ratio in the vapour.
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| 8. |
- Codato, Simone, et al.
(author)
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Ga assisted in situ etching of AlGaInAs and InGaAsP multi quantum well structures using tertiarybutylchloride
- 2005
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 282:1-2, s. 7-17
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Journal article (peer-reviewed)abstract
- In this work, we present Studies on the in situ etching (ISE) technique using tertiarybutylchloride (TBCl) as etchant precursor in a metal organic vapour phase epitaxy (MOVPE) reactor. Experiments were made in PH3 and PH3-free environments at low pressures (50-100 mbar) and in a low-temperature regime (545-600 degrees C). In particular, the combination of standard reactive ion etching (RIE) and ISE for the realization of suitable mesa structures for device applications has been systematically investigated. In our etching experiments InP, InGaAsP and Al-containing multi quantum wells (MQWs) have been used as etching targets. Particular efforts were devoted to the etching of Al-containing structures. For this material, the addition of trimethylgallium (TMGa) during the etching resulted to be of key importance in providing good surface morphology and etching of the MQW structure. The role of Ga species in the etching mechanisms will be discussed. The dependence of surface morphology and mesa shape on etching conditions, in particular, temperature, chlorine concentration, gallium concentration and etching time, will be described.
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| 9. |
- da Silva, A. F., et al.
(author)
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Electronic and optical properties of wurztzie and zinc-blende TlN and AlN
- 2005
-
In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 281:1, s. 151-160
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Journal article (peer-reviewed)abstract
- We present calculations of the band structure, density of states and the real and imaginary parts of the dielectric functions in intrinsic TIN and AlN, both for wurtzite and the zinc-blende polytypes. They are based on the local density approximation (LDA) within the density functional theory (DFT), employing the first-principles, full-potential linearized augmented plane wave (FPLAPW) method. We correct the band gap of the AlN by using a quasi-particle method proposed by Bechstedt and Del Sole. The calculated energy gaps, lattice constants and dielectric constants for AlN are in good agreement with available experimental values while for TIN there is no experimental investigation.
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| 10. |
- Darakchieva, Vanya, et al.
(author)
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Effect of anisotropic strain on phonons in a-plane and c-plane GaN layers
- 2007
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In: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 300:1, s. 233-238
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Journal article (peer-reviewed)abstract
- We have studied phonons in two types of anisotropically strained GaN films: c-plane GaN films grown on a-plane sapphire and a-plane GaN films grown on r-plane sapphire. The anisotropic strain in the films is determined by high-resolution X-ray diffraction (HRXRD) in different measuring geometries and the phonon parameters have been assessed by generalized infrared spectroscopic ellipsometry (GIRSE). The effect of strain anisotropy on GaN phonon frequencies is presented and the phonon deformation potentials aA1 (TO), bA1 (TO), cE1 (TO) and cE1 (LO) are determined. © 2006 Elsevier B.V. All rights reserved.
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