首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The effect of ion-beam milling (IBM) on the electrical properties of vacancy-doped mercury cadmium telluride (MCT) p-Hg1−x Cd x Te (x ∼ 0.22) has been studied. The samples were prepared by thermal annealing of molecular beam epitaxy (MBE)-grown heterostructures and the films and single crystals grown by liquid-phase epitaxy (LPE). The etching of samples by IBM resulted in the formation of donor centers. In MBE-grown heterostructures (but not in LPE-grown samples), the concentration of these centers reached ∼1017 cm−3. It is established that the appearance of a high concentration of donor centers in the heterostructures is caused by the IBM-induced activation of neutral defects formed during epitaxial growth. The probable nature of defects is discussed.  相似文献   

2.
Crystals with the sillenite structure, grown in an oxygen-free (argon) atmosphere, are investigated by the ac photovoltage method. It is found that the photoconductivity in red light is sharply higher (by two orders of magnitude) than in crystals grown in the presence of oxygen. Such crystals can be used in interferometric devices. Pis’ma Zh. Tekh. Fiz. 23, 28–33 (September 12, 1997)  相似文献   

3.
Potassium dihydrogen phosphate (KDP) single crystals doped with molybdate (MoO4 2−) were grown via the conventional temperature cooling and rapid growth methods, respectively. MoO4 2− made KDP crystals tapering for conventional temperature cooling method. When KDP crystals were grown by rapid growth method, MoO4 2− could induce liquid inclusions and simultaneous crystals. The measurement on growth rates indicated that MoO4 2− broadened the dead zone and decreased the growth rate of (100) face of KDP crystals. The growth kinetic analysis in terms of two-dimensional nucleus and screw dislocation models implied that the energetic parameter γ/kT decreased with an increase of MoO4 2− concentration. The influence of MoO4 2− growth steps on (100) face of KDP crystal was observed through ex situ AFM technique. It gave evidence that MoO4 2− could postpone the step bunching and make the step edge curving and knaggy to reduce the edge free energy, which was in agreement with the growth kinetics calculations. Additionally, the poisoned mechanism of MoO4 2− and Fe3+ on step morphologies was detailed contrasted. The interaction process was discussed according to electro negativity analysis, which indicated MoO4 2− (actually were HMoO4 and H2MoO4) could be absorbed onto (100) face through charge-assisted hydrogen bonds and caused more Mo element distributed in prismatic sector.  相似文献   

4.
Silicon nanowires (NWs) and vertical nanowire-based Si/Ge heterostructures are expected to be building blocks for future devices, e.g. field-effect transistors or thermoelectric elements. In principle two approaches can be applied to synthesise these NWs: the ‘bottom-up’ and the ‘top-down’ approach. The most common method for the former is the vapour-liquid-solid (VLS) mechanism which can also be applied to grow NWs by molecular beam epitaxy (MBE). Although MBE allows a precise growth control under highly reproducible conditions, the general nature of the growth process via a eutectic droplet prevents the synthesis of heterostructures with sharp interfaces and high Ge concentrations. We compare the VLS NW growth with two different top-down methods: The first is a combination of colloidal lithography and metal-assisted wet chemical etching, which is an inexpensive and fast method and results in large arrays of homogenous Si NWs with adjustable diameters down to 50 nm. The second top-down method combines the growth of Si/Ge superlattices by MBE with electron beam lithography and reactive ion etching. Again, large and homogeneous arrays of NWs were created, this time with a diameter of 40 nm and the Si/Ge superlattice inside.  相似文献   

5.
Single crystals of NaClO3 and NaBrO3 are grown from their aqueous solutions at a constant temperature of 35°C by slow evaporation by using good quality seed crystals. Systematic microhardness studies are made on as-grown faces of these crystals at various loads. Typical cracks are observed at the corners of the impressions in NaClO3 whereas in addition to the cracks at the corners microcracks also appeared in NaBrO3 crystals around the impressions. The impressions formed in NaBrO3 are not very clear as in NaClO3, a possible mechanism for it is discussed. The work hardening index number(n) for both these crystals is around 1.6 suggesting that these are moderately harder samples. The hardness studies point out that NaBrO3 is harder than NaClO3H ≈ 100 kg/mm 2,this could be due to strong inter ionic forces acting between Na-Br in NaBrO3 crystals. Using Gilman’s empirical relation, hardness values are calculated from the values of elastic constants (C 44) and are found to be close to the experimental results.  相似文献   

6.
The synthesis of semiconductor nanowires is more and more interested to the applications for building blocks of the innovative nano-sized devices and circuits, but the research and fabrication of these nanowires are also holding a number of difficulties and challenges. Among many different kinds of semiconductor nanowires, Ga2O3 is increasingly grown for many promising applications in nano-device production, namely nanowire LED and Laser. So far there are many synthesizing methods of semiconductor nanowires, among them the vapor–liquid–solid (VLS) method is simple, cheap and popular. However, when we use the VLS method for nanowire growth, various technological problems exist. This paper aims at investigating some influences of the growth technological conditions and Au metal catalyst on the morphology of Ga2O3 nanowire grown by VLS on GaAs substrate. The main considering factors include the different growing temperatures and times, the effects of Au diffusion, Au droplets formation, Au cluster islands formation, and gas volume of the growing tube/ampoule at the 10−1 torr low air pressure. The obtained experimental results regarding the structural properties of nanowires under these effects investigated by scanning electron microscopy, field emission scanning electron microscopy, high angle annular dark field and bright field, scanning transmission electron microscopy, energy-dispersive X-ray techniques, and focus ion beam are presented and discussed.  相似文献   

7.
Thermally stimulated currents and anisotropic electrical conductivity are studied in GeS layered crystals prepared by the Bridgman-Stockbarger, Pizzarello, and sublimation techniques. All the crystals arep-type, regardless of the growth technique, owing to the presence of Ge vacancies. The conductivity anisotropy in the melt-grown crystals is high compared to the vapor-grown GeS. The anisotropy rises exponentially with temperature. The concentrations and ionization energies of traps in GeS crystals are determined from thermally stimulated current curves. The spectral response of the photocurrent through the crystals prepared by sublimation, whose structural perfection is higher than that of the melt-grown crystals, is governed by the spectral dependence of the absorption coefficient forad ≪ 1 (near-edge region) and by the spectral dependence of reflectivity for αd > 1 (high-α region). Regardless of the growth technique, the 293-K photocurrent spectra of GeS crystals show strongly polarized peaks at 1.65 (Ea) and 1.78 eV (Eb), which are due to the Λ 1 v → Λ 1 c and Δ 2 v → Δ 2 c optical transitions. The low-temperature photoresponse athv < 1.7 eV is due to absorption by Si impurity.  相似文献   

8.
ZnO single crystals with thickness up to 12 mm, 2 inches in “diameter” and weight of about 150 g have been grown from KOH, NaOH, and K2CO3 based hydrothermal solutions on the seeds of (0001) orientation. The addition of LiOH up to 3.0–4.5 mol/L allowed to decrease the growth rate of ZnO crystals along the 〈0001〉 crystallographic direction. For positive and negative monohedra, it was achieved 0.12 and 0.01 mm/day, respectively, at temperature 340 °С and ΔТ = 10 °С. The best ZnO etching agent was found to be the solutions 25 mol% HCl + 3 mol% NH4F at room temperature, and etching time 5 min. The dislocation density of ZnO crystals varied from 240 cm−2 to 3,200 cm−2 in the case of growth rates 0.04 mm/day to 0.11 mm/day, respectively. It was also found that ZnO crystals grown are stable in air, oxygen, nitrogen, and argon atmosphere as well as in vacuum at the temperatures up to 1,000 °C under thermal treatment during 4 h.  相似文献   

9.
3C-SiC nanowires and nanocones were grown by pyrolysing mixture of acid-treated oil palm empty fruit bunch fibres and rice husk ash (RHA), which acted as carbon and silicon source, respectively. The effects of different RHA amounts and pyrolysis temperature were studied. When the amount of RHA was increased to 80 % of the mixture, there was a change in the morphology from nanowires to nanocones. Overall, it was found that 40 % of RHA in the mixture was the ideal amount in growing the nanowires with the maximum yield and with the least amount of impurities. When the pyrolysis temperature was raised, there was an increase in the amount, diameter and length of the nanowires. The proposed main growth mechanism for the SiC nanowires were combination of solid-state reaction and vapour–solid mechanisms, with some nanowires grown under vapour–liquid–solid (VLS) mechanism induced by trace metals as well. The growth of the nanocones could also be related to VLS mechanism.  相似文献   

10.
Magnesium oxide (MgO) whiskers (with diameters of about 60–80 nm) formed on the surface of bulk polycrystalline MgB2 superconductor at a relative low temperature (720 °C) during in situ sintering process. The reaction between Mg and B powders begins at a temperature below melting point of Mg and maintains till about 750 °C. The residual Mg powders evaporate and react with trace oxygen to form MgO vapor as the temperature exceeds the melting temperature of Mg and a low supersaturation is required for the growth of MgO whiskers. The preformed MgB2 and MgO crystals act as substrates and the melted Mg powders on the surface of them serve as catalysts during the growth process of MgO whiskers. The growth process of MgO whiskers is dominated by a self-catalytic vapor–liquid–solid (VLS) mechanism.  相似文献   

11.
Germanium nanowires were grown on Au coated Si substrates at 380 °C in a high vacuum (5 × 10− 5 Torr) by e-beam evaporation of Germanium (Ge). The morphology observation by a field emission scanning electron microscope (FESEM) shows that the grown nanowires are randomly oriented with an average length and diameter of 600 nm and 120 nm respectively for a deposition time of 60 min. The nanowire growth rate was measured to be ∼ 10 nm/min. Transmission electron microscope (TEM) studies revealed that the Ge nanowires were single crystalline in nature and further energy dispersive X-ray analysis (EDAX) has shown that the tip of the grown nanowires was capped with Au nanoparticles, this shows that the growth of the Ge nanowires occurs by the vapour liquid solid (VLS) mechanism. HRTEM studies on the grown Ge nanowire show that they are single crystalline in nature and the growth direction was identified to be along [110].  相似文献   

12.
Vapor growth of In-doped PbTe crystals by the sublimation–condensation and vapor–liquid–solid (VLS) processes is examined. Well-faceted Pb1 – x In x Te crystals with x = 0.04–0.06 are prepared by the sublimation method. The effects of the charge composition on the facial development and growth rate in the range 0 x 0.02 are discussed. The growth process at x 0.02 is shown to follow the VLS mechanism. Bulk Pb1 – x In x Te crystals with x 0.05 are grown by a vertical VLS process. The crystal composition is shown to depend significantly on the rate of ampule translation through the temperature field of the furnace and the separation between the evaporation and condensation zones. The longitudinal indium profiles in the crystals are correlated with growth kinetics.  相似文献   

13.
M. Lei 《Materials Letters》2009,63(22):1928-1930
Zinc gallate (ZnGa2O4) nanowires were directly grown on the amorphous carbon-coated silicon substrates using a facile chemical vapor deposition method without any metal catalysts. The growth mechanism can be attributed to a self-organization vapor-liquid-solid (VLS) process. The amorphous carbon layer plays an important role in the nucleation and growth process of the ZnGa2O4 nanowires. The photoluminescence (PL) of the nanowires shows a broad, strong green emission band centered at 532 nm and a weak UV emission band at 381 nm, which can be attributed to a large amount of ionized oxygen vacancies and the combination of Ga3+ ions with free electrons in coordinated oxygen vacancies, respectively.  相似文献   

14.
《Materials Letters》2003,57(16-17):2413-2416
Ga-polarity GaN thin films were grown on sapphire (0001) substrates by rf-plasma assisted molecular beam epitaxy (MBE) using a double buffer layer, which consisted of an intermediate-temperature GaN buffer layer (ITBL) grown at 690 °C and a conventional AlN buffer layer deposited at 740 °C. Raman scattering spectra showed that the E2 (high) mode of GaN film grown on conventional AlN buffer layer is at about 570 cm−1, and shifts to 568 cm−1 when an ITBL was used. This indicates that the ITBL leads to the relaxation of residual strain in GaN film caused by mismatches in the lattice constants and coefficients of thermal expansion between the GaN epilayer and the sapphire substrate. Compared to the GaN film grown on the conventional AlN buffer layer, the GaN film grown on an ITBL shows higher Hall mobility and substantial reduction in the flicker noise levels with a Hooge parameter of 3.87×10−4, which is believed to be, to date, the lowest reported for GaN material. These results imply that the quality of Ga-polarity GaN films grown by MBE can be significantly improved by using an ITBL in addition to the conventional low-temperature AlN buffer layer.  相似文献   

15.
Dislocation etching of GaSe single crystals was investigated by using a dilute chromic-sulphuric acid mixture, when conical etch pits were revealed on the (0001) surfaces. At the apices of spiral growth hills, bunches of spiral dislocations were revealed, proving that it is not a single screw dislocation of large Burgers vector, but a bunch of co-operating screw dislocations that were responsible for the spiral growth formations of large step-height. In the case of GaSe crystals, grown by vapour transport methods, dislocation densities of 102 to 106 cm−2 were found. The Bridgman crystals investigated were completely free from non-basal dislocations.  相似文献   

16.
Single crystals of strontium oxalate have been grown by using strontium chloride and oxalic acid in agar–agar gel media at ambient temperature. Different methods for growing crystals were adopted. The optimum conditions were employed in each method by varying concentration of gel and reactants, and gel setting time etc. Transparent prismatic bi-pyramidal platy-shaped and spherulite crystals were obtained in various methods. The grown crystals were characterized with the help of FT–IR studies and monoclinic system of crystals were supported with lattice parameters a = 9·67628 ?, b = 6·7175 ?, c = 8·6812 ?, b\boldsymbol{\beta} = 113·566°^{\boldsymbol\circ}, and V = 521·84 ?3 calculated from X-ray diffractogram.  相似文献   

17.
Abstract

Conditions of growing C60 films deposited from the gas‐dynamic vapor flow on different substrates [layered GaSe substrates with inactive surface, AIIBVI (CdS, CdSe) crystals, silicon substrates of (1 1 1) orientations, porous Si substrate] are studied. The condensate structure and growth mechanisms for different substrate are compared. It is shown that the high‐quality epitaxial films of the fullerenes can be prepared by using GaSe layered crystals as substrates.  相似文献   

18.
It is shown that GaN films can be grown by molecular-beam epitaxy with plasma activation of the nitrogen by a magnetron rf discharge in a specially constructed coaxial source with capacitive coupling. A growth rate of ∼0.1 μm/h is obtained on GaAs and sapphire substrates, and ways are found for optimizing the design of the plasma source in order to increase the growth rate. The electrophysical and luminescence properties of undoped epitaxial films are investigated at temperatures ranging all the way to room temperature. Pis’ma Zh. Tekh. Fiz. 24, 30–35 (June 26, 1998)  相似文献   

19.
The doping process in GaP core–shell nanowire pn‐junctions using different precursors is evaluated by mapping the nanowires' electrostatic potential distribution by means of off‐axis electron holography. Three precursors, triethyltin (TESn), ditertiarybutylselenide, and silane are investigated for n‐type doping of nanowire shells; among them, TESn is shown to be the most efficient precursor. Off‐axis electron holography reveals higher electrostatic potentials in the regions of nanowire cores grown by the vapor–liquid–solid (VLS) mechanism (axial growth) than the regions grown parasitically by the vapor–solid (VS) mechanism (radial growth), attributed to different incorporation efficiency between VLS and VS of unintentional p‐type carbon doping originating from the trimethylgallium precursor. This study shows that off‐axis electron holography of doped nanowires is unique in terms of the ability to map the electrostatic potential and thereby the active dopant distribution with high spatial resolution.  相似文献   

20.
Single crystals of sodium bromate are grown at various supersaturations ranging from 3% to 8%. Surface studies have been carried out on as-grown and etched (111) faces of these crystals. Typical and systematically oriented growth hillocks are observed almost on all the faces. Further dislocation studies are made to understand the growth history of these crystals. These studies suggest that the crystals grow by 2D-growth mechanism. In addition to this, studies are also conducted on the formation of overgrowths and inclusions in these crystals.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号