Synthesis of nano-sized SiC precipitates in Si by simultaneous dual-beam implantation of C+ and Si+ ions

Nanometer-sized SiC precipitates were synthesized in situ in Si by simultaneous implantation of two ion beams of C⁺ and Si⁺ ions. The results of simultaneous dual-beam implantation are compared with those of sequential dual-beam ion implantation and of single-beam C⁺ ion implantation. Remarkable differences are observed regarding the content and the crystal quality of SiC precipitates as well as the defect structure of the Si substrate. The SiC precipitation during dual-beam synthesis is found to depend on the ion energy of the second beam and on the implantation mode, simultaneous or sequential. For suitable implantation conditions, simultaneous dual-beam synthesis can improve the in situ SiC formation in comparison to the single-beam synthesis. A higher density of SiC precipitates with better crystal quality was observed, whereas their size was not changed. The second ion beam enables a shift in the dynamic equilibrium of constructive and destructive processes for SiC formation. A model is proposed assuming that SiC precipitation preferentially proceeds in regions with vacancy defects. The implantation process itself creates vacancy-dominated and also interstitial-dominated regions. The balance of the local point-defect composition is shifted under the second ion beam. In this way, the conditions for SiC precipitation can be modified. Received: 18 February 2002 / Accepted: 17 May 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +49-351/260-3411, E-mail: koegler@fz-rossendorf.de     

Novel technique for hetero-epitaxial diamond film growth on cubic boron nitride from iron carbide at high temperature and high pressure

Cubic boron nitride (c-BN) crystals about 0.1–0.3 mmin dimension were treated with iron carbide powders (high purity 99%) with size of 80–100 mesh at a high temperature of 1620 K and a high pressure of 5.2 GPa. It was found that hetero-epitaxial diamond films have been grown on the c-BN from iron carbide. The formation of dia-mond films on the cubic boron nitride can be confirmed by laser Raman spectra, face scan of elements and reflective high-energy electron diffraction. It was suggested that diamond films could be epitaxially formed on the c-BN through decomposition of iron carbide. This approach provides a possible and very effective way to realize hetero-epitaxial growth of homogeneous and large-area diamond films on c-BN, which is different from the conventional technique using a chemical vapor deposition method. Received: 20 December 2000 / Accepted: 9 January 2001 / Published online: 28 February 2001     

pH and temperature dependence of particle size in Pb1−xFexS nanoparticle films

The growth mechanism of Pb_1−xFe_xS nanoparticle films in chemical deposition is discussed. Grain growth for the Pb_1−xFe_xS films with increasing temperature of the chemical bath is observed to be due to the phenomenon of coalescence and formation of bigger particles at higher pH is possibly due to aggregation.     

Preparation of nano-hydroxyapatite particles with different morphology and their response to highly malignant melanoma cells in vitro

To investigate the effects of nano-hydroxyapatite (HA) particles with different morphology on highly malignant melanoma cells, three kinds of HA particles with different morphology were synthesized and co-cultured with highly malignant melanoma cells using phosphate-buffered saline (PBS) as control. A precipitation method with or without citric acid addition as surfactant was used to produce rod-like hydroxyapatite (HA) particles with nano- and micron size, respectively, and a novel oil-in-water emulsion method was employed to prepare ellipse-like nano-HA particles. Particle morphology and size distribution of the as prepared HA powders were characterized by transmission electron microscope (TEM) and dynamic light scattering technique. The nano- and micron HA particles with different morphology were co-cultured with highly malignant melanoma cells. Immunofluorescence analysis and MTT assay were employed to evaluate morphological change of nucleolus and proliferation of tumour cells, respectively. To compare the effects of HA particles on cell response, the PBS without HA particles was used as control. The experiment results indicated that particle nanoscale effect rather than particle morphology of HA was more effective for the inhibition on highly malignant melanoma cells proliferation.     

Effects of Al and Ti/Cu on Synthesis of Type-IIa Diamond Crystals in Ni70Mn25Co5-C System at HPHT

High-quality type-Ⅱa gem diamond crystals are successfully synthesized in a NiToMn25Co5-C system by temperature gradient method （TGM） at about 5.5 GPa and 1560 K. Al and Ti/Cu are used as nitrogen getters respectively. While nitrogen getter Al or Ti/Cu is added into the synthesis system, some inclusions and caves tend to be introduced into the crystals. When Al is added into the solvent alloy, we would hardly gain high-quality type-Ⅱa diamond crystals with nitrogen concentration Nc 〈 1 ppm because of the reversible reaction of Al and N at high pressure and high temperature （HPHT）. Piowever, when Ti/Cu is added into the solvent alloy, high-quality type-Ⅱa diamond crystals with Nc 〈 1 ppm can be grown by decreasing the growth rate of diamonds.     

A highly effective method for synthesizing hybrid Pt-CdSe nanocomposite

Hybrid Pt-CdSe nanocomposite was fabricated by a two-step chemical route. Cadmium selenide (CdSe) quantum rods (QRs) were prepared by a one-pot approach with tunable size. After ligand exchange, CdSe QRs were loaded with monodisperse 1.9 nm Pt nanopaticles in aqueous solution. Transmission electron microscopy (TEM) revealed the morphology of the Pt-CdSe nanostructure, and the decreased photoluminescence (PL) intensity demonstrated that electron and hole separation can be enhanced after loading Pt on CdSe QRs. X-ray photoelectron energy spectrum (XPS) was applied to confirm the existence of Pt and detect the Pt mass concentration of 3%.     

Spontaneous growth of arsenic oxide micro-crystals on chemically etched MnAs surfaces

Micrometer-size crystals are observed to grow spontaneously on chemically etched MnAs surfaces. The wet chemical etching leaves a nearly exclusive pile of amorphous arsenic on the surface when the MnAs layer is etched incompletely. Using Raman spectroscopy, we identify that these micro-crystals are the arsenolite crystal of arsenic oxides. The manganese in the MnAs layer is oxidized by the hydrogen peroxide in the etch solution to MnO₂, which then works as the catalyst for the rapid oxidation and crystallization of the amorphous arsenic. Received: 14 November 2002 / Accepted: 18 November 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. Fax: +49-30/20377-515, E-mail: takagaki@pdi-berlin.de     

Hetero-Epitaxial Diamond Single Crystal Growth on Surface of cBN Single Crystals at High Pressure and High Temperature

We report a new diamond synthesis process in which cubic boron nitride single crystals are used as seeds, FesoNi20 alloy powder is used as catalyst/solvent and natural flake-like graphite is used as the carbon source. The samples are investigated using laser Raman spectra and x-ray diffraction （XRD）. Morphology of the sample is observed by a scanning electron microscope （SEM）. Based on the measurement results, we conclude that diamond single crystals have grown on the cBN crystal seeds under the conditions of high temperature 1230℃ and high pressure 4.8 GPa. This work provides an original method for synthesis of high quality hereto-semiconductor with cBN and diamond single crystals, and paves the way for future development.     

Effect of Carbon Source with Different Graphitization Degrees on the Synthesis of Diamond

Using three kinds of graphites with different graphitization degrees as carbon source and Fe-Ni alloy powder as catalyst, the synthesis of diamond crystals is performed in a cubic anvil high-pressure and high-temperature apparatus （SPD-6 × 1200）. Diamond crystals with perfect hexoctahedron shape are successfully synthesized at pressure from 5.0 to 5.5GPa and at temperature from 1570 to 1770K. The synthetic conditions, nucleation, morphology, inclusion and granularity of diamond crystals are studied. The temperature and pressure increase with the increase of the graphitization degree of graphite. The quantity of nucleation and granularity ofdiamonds decreases with the increase of graphitization degree of graphite under the same synthesis conditions. Moreover, according to the results of the M6ssbauer spectrum, the composition of inclusions is mainly Fe3 C and Fe-Ni alloy phases in diamond crystals synthesized with three kinds of graphites.     

Growth of High-Quality Decagonal Al-Cu-Co Quasicrystals from Ternary Melt

By changing the initial elements, we obtain high-quality samples of Al-Cu-Co decagonal quasicrystals with a wide range of composition. The sizes of the samples are typically several centimetres in length and 2-3 mm in diameter. These samples are identified to be decagonal single grains by powder x-ray diffraction method, and the composition is homogeneous confirmed by EDX and chemical method.     

Multidimensional magnesium oxide nanostructures with cone-shaped branching

Branching structures in nanometer level are of great importance in developing nanoscale science and functional electrical devices. In this letter, multidimensional magnesium oxide structures with cone-shaped branching have been mass-produced using a simple chemical vapor deposition method. The dominant structures in the product include two-dimensional ‘+’, ‘T’, or ‘Γ’ assemblies, and three-dimensional complex configurations. The results presented here enrich the nanoscale community with new basic materials for the fabrication of functional electrical and chemical sensing devices.     

Dependence of Limited Growth Rate of High-Quality Gem Diamond on Growth Conditions

The growth rate of diamond has been investigated for a long time and researchers have been attempting to enhance the growth rate of high-quality gem diamond infinitely. However, it has been found according to previous research results that the quality of diamond is debased with the increase of growth rate. Thus, under specific conditions, the growth rate of high-quality diamond cannot exceed a limited value that is called the limited growth rate of diamond. We synthesize a series of type Ib gem diamonds by temperature gradient method under high pressure and high temperature （HPHT） using the as-grown {100} face. The dependence of limited growth rate on growth conditions is studied. The results show that the limited growth rate increases when synthetic temperature decreases, also when growth time is prolonged.     

Structural Feature and Solute Trapping of Rapidly Grown Ni3Sn Intermetallic Compound

The rapid dendritic growth of primary Ni3Sn phase in undercooled Ni-30.9%Sn-5%Ge alloy is investigated by using the glass fluxing technique. The dendritic growth velocity of Ni3Sn compound is measured as a function of undercooling, and a velocity of 2.47m/s is achieved at the maximum undercooling of 251 K （0.17TL）. The addition of the Ge element reduces its growth velocity as compared with the binary Ni75Sn25 alloy. During rapid solidification, the Ni3Sn compound behaves like a normal solid solution and it displays a morphological transition of ＂coarse dendrite-equiaxed grain-vermicular structure＂ with the increase of undereooling. Significant solute trapping of Ge atoms occurs in the whole undercooling range.     

Chiral Symmetry Breaking During Growing Process of NaClO3 Crystal under Direct-Current Electric Field

We investigate the influence of dc electric field on chiral symmetry breaking during the growing process of NaClO3 crystal. Nucleation and growth of NaClO3 are completed from an aqueous solution by a fast cooling temperature technology. A pair of polarization microscopes are used to identify a distribution of chiral crystals. Experimental results indicate that the dc electric field has an effect on distribution of chirality, but the direction of the dc electric field is not sensitive to the chiral autocatalysis and selectivity, i.e. the nature convection driving by the gravity does not play an important role on a thin layer of NaClO3 solution. The experimental phenomena may be elucidated by the ECSN mechanism.     

Finite Element Analysis of Convection in Growth Cell for Diamond Growth Using Ni-Based Solvent

Thermal-electricaJ-fluid coupled finite element analyses are performed in the model of the growth cell in a high-pressure and high-temperature （HPHT） cubic apparatus in which the large diamond crystal can be grown by using Ni-based solvent with temperature gradient method （TGM）. The convection in the Ni-based solvent with different thicknesses at 1700-1800 K is simulated by finite element method （FEM）. The experiments of diamond crystal growth are also carried out by using Ni-based solvent at 5.7GPa and 1700-1800K in a China-type cubic high pressure apparatus （CHPA）. The simulation results show that the Rayleigh number in the solvent is enhanced obviously with the increasing solvent thickness. Good quality diamond single crystal cannot be grown if the Rayleigh number in the solvent is too high.     

Fabrication of MgO nanobelts using a halide source and their structural characterization

MgO nanobelts have been fabricated by chemical vapor deposition using MgCl₃ as starting material. The products consist of a large quantity of belt-like nanostructures with typical lengths in the range of several tens to several hundreds of micrometers; some of them even have lengths on the order of a millimeter. The typical thickness and width-to-thickness ratio of the MgO nanobelts are in the range of 20 to 100 nm and about 5 to 10, respectively. The size and morphology of the MgO nanobelts were measured by transmission electron microscopy. Investigations of X-ray diffraction patterns and using high-resolution transmission electron microscopy indicate that the nanobelts have a cubic structure and are single-crystalline. Received: 23 August 2001 / Accepted: 27 August 2001 / Published online: 2 October 2001     

Sealing of bore-holes in Si crystals by epitaxial overgrowth below 560° C

Liquid phase epitaxy (LPE) is applied to seal small bore-holes (diameter 250–400 m) in Si crystals by lateral overgrowth. The overgrowth layers have a typical thickness of 20 m, are mechanically stable and gas-tight. Using Ga as solvent for the LPE process the overgrowth can be performed at temperatures as low as 560°C.     

Emission characteristics, crystalline phase and composition of vapor-transport-equilibrated Er:LiNbO3 crystal codoped with 6 mol% MgO

Polarized downconversion, 980-nm-upconversion and near-infrared emission characteristics of vapor-transport-equilibrated (VTEed) bulk Er (0.4 mol%)/MgO (6 mol%)-codoped LiNbO₃ crystals were investigated. The downconversion and upconversion visible emissions display similar VTE effects including the drop of emission intensity and the weakening of polarization dependence. At 0.98 and 1.5 μm regions, the VTE has a weak effect on the emission intensity, but a strong effect on the spectral shape. The crystalline phases in these bulk Er/Mg-codoped VTE crystals are determined by comparing their infrared emission characteristics with those of pure ErNbO₄ powder and locally Er-doped MgO (4.5 mol%):LiNbO₃ crystal. The results show that the Er³⁺ ions present in these bulk Er/Mg-codoped VTE crystals as a mixture of Er:LiNbO₃ and ErNbO₄ phases. The percentages of the ErNbO₄ phase contained in these VTE crystals were evaluated from the 1531 and 1536 nm characteristic absorption areas. The contents of constituent elements were determined by chemical analysis.     

Surface Structure of Large Synthetic Diamonds by High Temperature and High Pressure

With NiMnCo and FeCoNi alloys as solvent metals, large single-crystal diamonds of about 3mm across are grown by temperature gradient method （TGM） under high temperature and high pressure （HPHT）. Although both {100} and {111} surfaces are developed by a layer growth mechanism, some different characteristic patterns are seen clearly on the different surfaces, no matter whether NiMnCo or FeCoNi alloys are taken as the solvent metals. For {100} surface, it seems to have been melted or etched greatly, no dendritic patterns to be found, and only a large number of growth hillocks are dispersed net-likely; while for {111} surface, it often seems to be more smooth-faced, no etched or melted traces are present even when a lot of depressed trigonal growth layers. This distinct difference between {111} and {100} surfaces is considered to be related to the difference of surface-atom distribution of different surfaces, and {111} surfaces should be more difficult to be etched and more steady than {100} surfaces.     

Optical behaviour of VTE treated near stoichiometric LiNbO3 crystals

Near stoichiometric LiNbO₃ crystal wafers of thickness up to 2 mm were prepared by vapour transport equilibration technique (VTE) at various process temperatures. Crystals were characterised by measurement of the UV absorption edge, refractive index, second harmonic generation (SHG) efficiency, and conoscopy pattern analysis. The comparison of VTE treated crystals show that the blue shift in cut off wavelength occurred with the increasing process temperature (i.e. increasing Li/Nb ratio). The refractive indices were found decreasing with increasing process temperature of VTE samples. The SHG efficiency increases in the range of 1.98-2.3 times for the VTE processed samples with respected to congruent crystals. Conoscopy pattern reveals the optical homogeneity of the VTE treated crystal.