Table of Content

15 August 2004, Volume 33 Issue 4

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Recent Development for UV and Deep-UV Nonlinear Optical Crystals

2004, 33(4):  455-464. 

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Coherent light sources in the deep and vacuum UV (DUV and VUV) spectral regions become more important with the development of photolithography, laser micro-machining as well as laser spectroscopy. The review will briefly introduce how to use the anionic group theory to develop new borate-based DUV and VUV nonlinear optical crystals. Meanwhile, The basic linear and nonlinear optical properties of these borate-based crystals are systemically reviewed. Moreover, some typical examples to produce DUV and VUV harmonic generation and their applications are given.

Wavelength Tunable Optical Parametric Oscillator Based on Periodically Poled Lithium Niobate

2004, 33(4):  465-470. 

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We report wavelength tunable quasi-phase-matching (QPM)optical parametric oscillators (OPOs) based on periodically poled lithium niobate (PPLN) pumped by an acousto-optically Q-switched CW-diode-end-pumped Nd:YVO4 laser. Widely wavelength tunable outputs have been obtained by using temperature tuning, angle tuning and grating period tuning. The analysis of comparison about these tuning methods is given in this paper which is helpful to realize widely, rapidly and continuously tunable coherent sources.

Crystal Surface Structure and Its Growth Units of Anionic Coordination Polyhedra

2004, 33(4):  471-474. 

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The relationship between the crystallographic orientation of anionic coordination polyhedra and the surface structures was discussed in this paper. It is suggested that the surface structures show the locus formed by the combination of growth units of anionic coordination polyhedra on different surfaces during crystal growth. Therefore the growth mechanism could be studied and the crystal orientation determined by means of the surface structures in crystals.

Anionic Coordination Polyhedron Growth Units and Crystal Morphology

2004, 33(4):  475-478. 

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Based on the theoretical model of anionic coordination po1yhedron growth units,this paper discussed the relationship between the crystal morphology and the orientation of anionic coordination polyhedra in the isomer (rutile,brookite and anatase)and allomer (rutile and cassiterite;corundum,hematite and ilmenite). It was found that the crystal habits of these crystals were related to the stability of combination of anionic coordination polyhedron growth units with different faces.The combination of the vertexes is the best stable,the edge second and the face third.Furthermore,the morphology of polar crystals ZnS and ZnO was also interpreted in the viewpoint of anionic coordination polyhedron growth units.

New Insights into Chiral Symmetry Breaking in Crystal Growth of NaClO3

2004, 33(4):  479-485. 

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The topic on spontaneous chiral symmetry breaking in unstirred crystallization was studied from aqueous solution of NaClO3. A sodium chlorate solution was prepared by dissolving the A.R. of the NaClO3 powder in distilled water. A solubility of NaClO3 solution was measured by both Mach-Zehnder interferometry and a weight technique. Total of 11545 chiral crystals were identified by the polarizers. The crystals were grown on spontaneous nucleation from the 90 runs of experiments with different pH value in solution. An experimental results indicated that the pH value in solution could influence the distribution of the crystal chirality of NaClO3. The effect of pH might be explained by stochastic kinetics and embryos coagulation secondary nucleation (ECSN) qualitatively.

Crystal Structure of a New Assembly of Three Complex-[Co(dmg)2Cl2]3·[Co(dmg)2Cl(OH)]· [Co(dmg)(phen)]·(H2O)4

2004, 33(4):  486-489. 

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A new assemble crystal[Co(H2dmg)2Cl2]3·[Co(H2dmg)2Cl(OH)]·[Co(Hdmg)(phen)]·(H2O)4 (H2dmg＝dimethylglyoxime, phen＝1,10-Phenanthroline) was synthesized and its structure was determined by X-ray diffraction method. The five central Co2+ ions and relevant ligands form a unit which piles up in space.The space group is P-1,cell parameters a=1.3738nm,b=1.4396nm,c=1.8656nm. Molecular structure and spectroscopic properties of the complex were also discussed in this article.

Crystal Structure of Sodium Lanthanum Borate Na3La2(BO3)3

2004, 33(4):  490-495. 

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Single crystal of Na3La2(BO3)3 was grown from the high temperature solution by employing Na2CO3-H3BO3-NaF as fluxes. The structure was established by single-crystal X-ray diffraction method. The compound crystallizes in the orthorhombic system, space group Amm2 (No.38) with a=0.51580(10) nm, b=1.1350(2) nm, c=0.73230(15) nm, α=β=γ=90°, V=0.42871(15) nm, and Z=2. Its three-dimensional network structure is formed by isolated BO3 triangles held together by the Na(1)O6, Na(2)O8, Na(3)O6, and La(1)O9 polyhedra. The relationship between the structure and optical second harmonic generation (SHG) effect of Na3La2(BO3)3 crystal was also discussed.

Formation of Silicon Carbon Nitride Crystals and Aligned Silicon Carbon Nitride Microrods by Microwave Plasma Chemical Vapor Deposition

2004, 33(4):  496-499. 

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Silicon carbon nitride (SiCN) crystals and silicon carbon nitride aligned microrods were synthesized on Si wafer by the novel microwave plasma chemical vapor deposition (MPCVD) system with CH4, H2, N2 and additional Si column as sources. The morphologies of the films were investigated by field emission scanning electron microscopy (SEM). The chemical bonding states of the SiCN crystals and the SiCN microrods were characterized by X-ray photoelectron spectroscopies (XPS) and Raman backscattering microscopies, suggesting that the films are multibonding structures. The X-ray diffraction spectra (XRD) revealed the SiCN crystals and microrods might possess a new hexagonal phase.

Mathematical Modeling as a Tool for Thermal Unit Constructing for Large Optical Crystal Growing Part Ⅱ- Technique and Results of Radiativeconductive Heat Exchange Calculations for CaF2Ф 400mm Crystal Growing

Ju.Linhart;Myron Pankevich

2004, 33(4):  500-509. 

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Growth of large size fluoride crystals was based on the results of calculations and experimental research of thermal exchange in furnace heating units. Boundary conditions in containers of complicated configurations and two-dimensional task for temperature fields calculations in a growing crystal in different stages of technological process were solved. We presented here concrete data on temperature fields configurations and their transformation in process of crystal growth. All calculations were done using spectral and temperature dependence of optical characteristics of crystals, melt, container materials and also temperature dependence of their thermo-physical values.The results could be used in technological processes developments and in a design and construction of growth furnaces and containers. To this time these results contain the most precise data on temperature fields forming in fluorides crystal growth processes and systems.

A Heat Transfer Analysis for SiC Single Crystal Growth by PVT Method

2004, 33(4):  510-515. 

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A heat transfer analysis for PVT growth of SiC was performed to optimize the growth conditions, aiming at obtaining better quality crystals. The analysis was focused on the heat transfer between the furnace lid and the crucible lid to which the seed was attached. It was found that the thermal shielding condition above the crucible lid, i.e. the hole shape and size in the graphite felt, plays an important role in determining the temperature uniformity on the crucible lid. The total radiation resistance and the heat transfer amount between the crucible lid and the furnace lid can be calculated using the simplified model presented in this paper for different positions of the crucible and different shapes and diameters of the hole in the graphite felt. The factors affecting the heat transfer amount between the crucible lid and the furnace lid were discussed. Besides, the feasibility of dynamic modification of the heat transfer conditions of the crucible lid was discussed.

Nucleation Process of Hexadecly Hydrogen Maleate(HHM) Crystals in Supersaturated Solution

2004, 33(4):  516-519. 

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In this article, the nucleation process of hexadecly hydrogen maleate (HHM) crystals in supersaturated solution were studied and toluene was used as dissolvent. The nucleation rate indicated by inducement temporal hour was measured. Solid-liquid surface tension, nucleation free energy, critical nucleation radius were calculated according to classical nucleation theory. It can be presumed that the nucleation rate of HHM will increase with the rise of temperature and supersaturated ratio, when toluene used as dissolvent. And the property of dissolvent will change the nucleation rate.

Luminescence Properties of Lu2SiO5:Ce Crystals Grown by Czochralski Method

2004, 33(4):  520-523. 

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Lu2SiO5:e crystals with dimension of φ50mm×60mm were grown by Czochralski method from an inductively heated iridium crucible. The crystal structure was examined by XRD and confirmed to be monoclinic symmetry. Its optical transmission, UV-excited, X-ray excited emission and light yield were measured at room temperature. The results show that the emission spectra exhibit doublet structure peaking at 403nm and 420nm,which can be attributed to the transition of the Ce3+ ions at Lu site from the lowest 5d level to the two 4f ground states,5d′→5F5/2 and 5d′→5F7/2.The decay time tested under gamma ray excitation is 41ns.The best light yield is 32000P/MeV.

Up-conversion of Er3+ Ions in Er3+/Yb3+ Co-doped YVO4 and LiNbO3 Crystals

2004, 33(4):  524-530. 

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The Judd-Ofelt parameters Ωλ(λ=2,4,6) have been calculated for Er3+ ions in Er3+/Yb3+ co-doped LiNbO3 and YVO4 crystals at room temperature, together with the radiative transition probabilities, non-radiative transition probabilities and resonant transition probabilities of Er3+ ions. Taking into account the energy transfer from Yb3+ to Er3+, the rate equations are given for Er3+ ions. We have obtained from a solution of the rate equations that Er3+/Yb3 co-doped YVO4 crystal is more efficient for up-converted 550nm Er3+ emission than Er3+/Yb3+ co-doped LiNbO3 crystal, which is consistent with our observation.

Investigation on Elastic Strain Energy in Quantum Dots

2004, 33(4):  531-534. 

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In this paper, we calculated the elastic strain and elastic strain energy inside the semiconductor quantum dots by using the finite element programming package ANSYS 6.0. The values of elastic strain and strain energy in the three shapes of quantum dots were calculated, and led to the conclusion that the pyramid island structure of quantum dots is the most stable shape in the three shapes under thermal-equilibrium condition.

Non-stoichiometry Related Deep Level Defects in Semi-insulating InP

2004, 33(4):  535-538. 

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Semi-insulating (SI) InP materials have been prepared under different stoichiometric conditions, including Fe-doping in indium-rich melt and high temperature annealing undoped wafer in phosphorus and iron phosphide ambients. Deep level defects related with non-stoichiometry have been detected in the SI-InP samples. A close relationship between the material quality of electrical property and native deep defects has been revealed by a comprehensive study of defects in as-grown Fe-doped and annealed undoped SI-InP materials. Fe-doped SI-InP material with low carrier mobility and poor thermal stability contains a high concentration of deep defects with energy levels in the range of 0.1-0.4eV. The suppression of the defects by high temperature annealing undoped InP leads to the manufacture of high quality SI-InP with high mobility and good electrical uniformity. A technology for the growth of high quality SI-InP through stoichiometry control has been proposed based on the results.

Metal-organic Vapor Phase Epitaxy Growth and Characterization of InAlGaN Epilayers

2004, 33(4):  539-544. 

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In order to improve crystal quality for growth of quaternary InAlGaN, a series of InAlGaN films were grown on GaN buffer layer under different growth temperatures and carrier gases by low-pressure metal-organic vapor phase epitaxy. Energy dispersive spectroscopy (EDS) was employed to measure the chemical composition of the quaternary, high resolution X-ray diffraction (HRXRD) and photoluminescence (PL) technique were used to characterize structural and optical properties of the epilayers, respectively. The PL spectra of InAlGaN show with and without the broad-deep level emission when only N2 and a N2+H2 mixture were used as carrier gas, respectively. At pressure of 1.01×104 Pa and with mixed gases of nitrogen and hydrogen as carrier gas, different alloy compositions of the films were obtained by changing the growth temperature while keeping the fluxes of precursors of indium (In), aluminum (Al), gallium (Ga) and nitrogen (N2) constant. A combination of HRXRD and PL measurements enable us to explore the relative optimum growth parameters-growth temperature between 850℃ and 870℃,using mixed gas of N2+H2 as carrier gas.

Studies of the Heteroepitaxial SiC Films on the Si Substrates

2004, 33(4):  545-548. 

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High-quality SiC films were successfully prepared on Si(111) substrates by low pressure metal-organic chemical vapor deposition (LP-MOCVD). The mechanism of the heteroepitaxial SiC films on the Si substrates was studied. Many researchers supported that the initiative stage was the Si out-diffusion from the Si substrates. But from the experimental results of heteroepitaxial SiC films grown on the Si substrate and Al2O3 substrate, respectively,it is found that the dominant transport process during the growth of SiC films on the Si substrates, is the C in-diffusion rather than Si out-diffusion. In addition,the results show that the reaction rate will become faster with the increase of the SiH4 flux,but the crystallization will be weakened.

A Practical Ⅲ-Ⅴ Group Semiconductor Material Growth Model Concerning to the Mass Production in Turbo-Disc MOCVD Reactor

2004, 33(4):  549-552. 

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A practical Ⅲ-Ⅴ group semiconductor material growth model was obtained, when the Ⅲ-Ⅴ group materials growth was investigated under MOCVD mass flow control growth process. This model is based on the molecular dynamics and chemical kinetics, etc.The Turbo-Disc growth model was formalized specified after the Turbo-Disc heat and transfer flow model was applied in the boundary layer. The relation between the inlet reactant parameters(IPs) and the boundary layer growth parameters is directly connected in this growth model. This theoretical model was found to be useful in explaining the matched GaInP/GaAs , the ternary-alloy growth. The calculations are consistent with the GaInP/GaAs epitaxial experiment results. This model is very efficient for the mass production to get the matched ternary-alloy epitaxial layers.

Recent Developments of Piezoelectric Crystals for SAW Applications

2004, 33(4):  553-558. 

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Recent developments of piezocrystals, Li2B4O7, Sr3Ga2Ge4O14, LiNbO3 and LiTaO3 in our laboratory were reported in this paper. Li2B4O7 single crystals of 3 to 4 inches in diameter have been grown successfully by the modified vertical Bridgman method and mass production of large size Li2B4O7 crystals has been realized. Sr3Ga2Ge4O14 (SGG) crystal is a novel piezoelectric crystal with the largest piezoelectric constants among the langasite family. Bridgman growth of SGG crystal up to 2 inches in diameter has been reported and its piezoelectric properties have been measured. In order to improve the yield of SAW devices, pyro-free LiNbO3 and LiTaO3 wafers were prepared by chemical reduction at 700℃ and 450℃ respectively under a mixed atmosphere of CO2 and H2. Bridgman growth of LiNbO3 crystals was also investigated and some new phenomena were observed.

K3V5O14-a New IR Nonlinear Optical Material

2004, 33(4):  559-561. 

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Oxides and chalcopyrites semiconductor materials have infrared laser properties noticed in the infrared region, but their application was restricted due to their disadvantages.K3V5O14 crystal belongs to the space group P31m.K3V5O14 has a wide transparency wavelength range and powder double-frequency studies show that its SHG signal is about 20 times larger than that of KDP.This paper reports a new synthesis method and research work for crystal conditions on the K3V5O14.The results show that K3V5O14 is a new promising nonlinear optical material in the infrared region.

Numerical Simulation on Thermal Field in Thermal Anisotropic Crucible Used in Bridgman Method

2004, 33(4):  562-566. 

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The combinations of crucibles with different thermal properties were investigated. If the anisotropic material is used for making single layer crucible, it is preferable for the material larger thermal conductivity along transverse direction, small thermal conductivity along longitudinal direction or having comparative thermal conductivity along longitudinal direction to the crystal and its melt. It is unfavorable for material with small thermal conductivity along transverse direction and large thermal conductivity along longitudinal direction. For composite crucible, the conductivity of the two materials should be very close.

Study of the Preparation and Mechanism of Producing Pores on Tiny Porous HAp-ZrO2 Biocomposite

2004, 33(4):  567-570. 

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In this paper, the authors studied the preparation and the mechanism of producing pores on tiny porous HAp based biomaterial.At first, the multiplex powder was moulded by cold pressing and isostatic pressing; then, the samples were sintered at 1200℃ for about 3h in air and the tiny porous HAp-ZrO2 composites with different pores were obtained. When the moulding pressure, sintering temperature and keeping temperature time are all the same, the flexural strength of the composite is becoming lower with the increase of additive and nano-zirconia contents. But the lowest value of flexural strength is still about 23MPa which is much higher than that of the porous hydroxyapatite in literatures. The added quantity of additive and nano-zirconia is the key factor which influences the diameter and ratio of pores in the composite. Other factors, such as moulding mode, sintering temperature and the time of keeping temperature, can influence them too.

Choice of Thermal Isotropic Crucible in Bridgman Method

2004, 33(4):  571-574. 

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The combinations of crucibles with different thermal properties were investigated. If the isotropic material is used for making crucible, the material having comparative thermal conductivity to the crystal and its melt or having larger thermal conductivity should be preferable.The material with small thermal conductivity is unfavorable. If the material is strong enough, thinner wall crucible will be good for crystal growth.

Relationship of Valence Electron Structure and Mechanical Properties on Fe3Al after Order Degree Intercepted

2004, 33(4):  575-580. 

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Based on the empirical electron theory (EET) of solids and molecules, the glide energies of two structures (D03-type and B2-type) of Fe3Al were calculated firstly. The result shows the glide energy of B2-type Fe3Al is less than that of D03-type Fe3Al. When the less work is done, the B2-type Fe3Al can preferentially slip. It predicts B2 structure has better ductility than D03 structure, then Fe3Al is processed by order degree interception, the results indicate a Fe3Al with an imperfectly ordered B2 structure after orderdegree intercepted has improved machinability properties deeply, the hardness and compressive strength decrease simultaneously. According to the study, relationships of valence electron structures of two structures and mechanical properties have been set up.The results obtained well conform to the experimental data.

Room Temperature Absorption and Emission Spectra of Nd3+:Gd3Ga5O12 Crystal

2004, 33(4):  581-585. 

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The HAP SSL crystal Nd3+:d3Ga5O12(Nd3+:GG) was grown by the Czochralski method. The absorption and emission spectra of Nd3+:GG crystal at room temperature were studied. The relationship between the energy level scheme and the emission spectra was analyzed. The absorption, emission cross-section and fluorescence lifetime are estimated as 4.32×10-20cm-2,2.3×10-19cm-2, 240μs, respectively. From the oscillator strengths of the absorption transitions the Judd-offelt intensity parameters were evaluated.The spectroscopic parameters of Nd3+:GG and Nd3+:AG crystal were compared, and the Nd3+:GG crystal has many advantages over Nd3+:YAG.

Photorefraction-resistance Property of Mg-doped Near Stoichiometric Lithium Niobate Crystals

2004, 33(4):  586-590. 

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With the help of vapor transport equilibrium technique, we obtained three near stoichiometric lithium niobate crystals with the doping concentration of Mg near the second threshold. These crystals show, up to now, the best resistant ability against laser induced optical damage:no laser beam distortion was observed under a light intensity of 26 MW/cm2, and only a Δn of 4.6×10-7 was measured by two-beam holographic recording.

Optical and Scintillating Properties of Large-size PbWO4 Crystal Grown by Modified Bridgman Method

2004, 33(4):  591-595. 

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In this paper, we presented the study of large-size Y3+-doped PbWO4 crystal grown using a modified Bridgman method for the CMS experiment at the Large Hadron Collider at CERN. The optical and scintillation properties of the crystal were given, including photo-luminescence and X-ray stimulated luminescence spectra, longitudinal and transverse transmittance spectra, light yield, and radiation hardness. The measurement results indicate that the crystal has very highlight yield values (>13 pe/MeV), fast scintillation within 100ns, and the radiation hardness close to the need for CMS-ECAL End Cap crystals. A good consistency is shown among the same batch of crystals.

Growth and Characteristics of Cr:iSrAlF6 Crystal

2004, 33(4):  596-600. 

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High quality Cr:iSrAlF6 (abbreviated as Cr:iSAF) crystals were grown by Bridgman method and their laser performance are reported in this paper. The starting materials were treated using a solid fluorinating agent to remove oxides and water. The size of Cr:LiSrAlF6 crystals, which were grown in a small temperature gradient at a slow growth rate, is up to 20mm in diameter and 130mm in length. 1-15mol; homogeneous Cr3+ doping concentration can be realized. From the XRD spectrum of Cr:iSAF, the lattice parameters are figured out to be a=0.502nm and c=0.967nm. The absorption spectrum of Cr:iSAF was measured and the causes bringing about the absorptions were discussed. Flashlamp-pumped Cr:iSAF laser action was realized. The slope efficiency of flashlamp-pumping is up to 5.85;.

Effect of Abrasive Particles in Slurry on the Wear Resistance of Alumina-reinforced Y-TZP Composites

2004, 33(4):  601-604. 

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The effect of the properties of abrasive particles in slurry, including the morphology and hardness, on the wear resistance of alumina-reinforced yttria-stabilized zirconia polycrystals (3Y-TZP/10wt;Al2O3, 10ADZ) was investigated in 5;NaOH slurry containing different abrasive particles using a pin-on-plate tribometer. The results showed that the wear resistance of ADZ ceramic depends on the properties of the abrasive particles. As expected, the wear resistance is increased with hardness of abrasive particles decreasing, but it is also influenced by the other, more subtle differences in the morphology, that is, the sharper the abrasive particle the higher wear rate. The main wear mechanism of ADZ in SiO2 particle slurry is plastic deformation and microploughing, but the removal of material is controlled by brittle fracture in the Al2O3 slurry.

Search for New Optical Crystals by the Chemical Bond Method

2004, 33(4):  605-612. 

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From the chemical bond viewpoint, dielectric properties of some practical materials with various crystal structures were quantitatively studied. The correlation between constituent chemical bonds and dielectric properties of these crystals was analyzed using the proposed chemical bond method. Furthermore, on the basis of the chemical bond method a combination method was presented for the quantitative determination of dielectric properties of materials with a similar crystal structure. From the current work, we may derive structural information concerning the nonlinearity origin of optical crystals, which is helpful for the nonlinear optical crystal engineering.

Synthesis of Nanopowders of Titanium Nitride by in-situ Nitridation of Titanium Oxide

2004, 33(4):  613-617. 

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The TiN nanopowder was prepared by in-situ nitridation using TiO2 nanopowder as starting material. The crystalline characteristics, morphology and composition of the TiN nanopowders were investigated by XRD patterns, TEM and chemical analysis. The results indicate that TiN nanopowders are obtained with an average diameter of about 40nm and 80nm by nitridation at 1000℃ and 1100℃ for 5h respectively, and their contents of TiN are 95.40; and 98.37;. When nitridation time reduced to 2h at 1000℃ the content of TiN is only 58.36;. The results reveal that the nitridation temperature and time play important roles on synthesizing the TiN nanopowders. The higher temperature and longer nitridation time are beneficial to form the high purity titanium nitride powders, and prolonging nitridation time is more beneficial to obtain high purity particles with a smaller diameter compared with elevating temperature.

Preparation and Characterization of Sheet Nano-zinc Oxide Single Crystal

2004, 33(4):  618-623. 

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This paper presented a two-step method to prepare sheet nano-zinc oxide single crystals(SNOSC).The precursor of SNOSC was first made by homogeneous precipitation method (HPM), using zinc chloride and alkali zinc carbonate as the raw materials and carbamide as the precipitant. Then the SNOSC was obtained by the thermal decomposition of the precursor. The prepared SNOSC is colorless and transparent with a hexagonal, pentagonal, rectangular or an irregular form, as examined by IR spectra and SEM. The single crystal is 30-600μm in diameter and 30-60nm in thickness . The important factors to the preparation are the ratio of reaction materials, the concentration of carbamide (1:) and the reaction temperature (70-85℃). In addition, the content of ethanol ranging 10;-40; appears favorable for the formation of the precursor of SNOSC.

Influence of Sintering Technique on Mechanical Properties and Microstructure of CNTs/HAp Composite

2004, 33(4):  624-628. 

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In this paper, the influence of different sintering technique on mechanical properties and microstructure of CNTs/HAp composite was studied. The mechanical properties of CNTs/HAp composite sintered in vacuum is more higher than that in Ar or N2. The increasing range of fracture toughness is the biggest. The maximum is 2.2 MPa·m1/2 which is higher than that of the pure hydroxyapatite. We found that the composite is very pure by XRD and IR. After sintered in vacuum at 1100℃, CNTs/HAp composite has less pore and more thin grain , at the same time, the diameter of CNTs will be enlarged. After sintered in Ar or N2 at 1100℃,the CNTs in composite can easily be preserved in its primitive shape but the composite is more porous and grains are bigger.

Study of Glow Discharge Effect on Alignment Growth of Carbon Nanotubes by Negative Bias-enhanced Hot Filament Chemical Vapor Deposition

2004, 33(4):  629-633. 

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Carbon nanotubes were synthesized on silicon substrates coated with NiFe films of different thickness by negative bias-enhanced hot filament chemical vapor deposition at different negative bias and pressure, and their growth was investigated by scanning electron microscopy. It was found that the bent and aligned carbon nanotubes are respectively grown without and with glow discharge, indicating that glow discharge plays an important role for alignment growth of carbon nanotubes. Due to occurrence of glow discharge, a strong electric filed is established near the substrate, where its strength relative to the field without glow discharge can be enhanced two order of the magnitude. In the work, the effect of glow discharge on alignment growth of carbon nanotubes was studied in detail.

Microwave-assisted Synthesis of Rutile Titania Nanoparticles from TiOCl2 Aqueous Solution

2004, 33(4):  634-637. 

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Rutile TiO2 nanoparticles of controled size were prepared by a very simple forced hydrolysis from TiOCl2 aqueous solution using microwave irradiation. The products were analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The TiO2 particles produced from the present route have spherical structure. The influence of heating power on TiOCl2 solution hydrolytic process was studied and a possible nucleation mechanism of rutile TiO2 nanoparticles was discussed.

Study on Formation Mechanism of Bamboo-structured Carbon Nanotubes

2004, 33(4):  638-643. 

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In the process of preparation of carbon nanotubes(CNTs) by chemical vapor deposition(CVD), bamboo-structured CNTs can be catalytically synthesized from nitric gas environment. However, the formation mechanism of the bamboo-structured CNTs has not been well understood. In the work, the state change of the catalyst particle in the process of growing CNTs by CVD is analyzed, and a new mechanism of forming the bamboo-structured CNTs is put forward after the diffusion of carbon atoms in different states of the catalyst particle is analyzed.

Study on the Relationship between Nano-silicon Microstructure and the Reactive Gas Flux during the Process of Preparation

2004, 33(4):  644-646. 

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Nano-silicon particles were prepared using LICVD technique. The transform discipline of nano-silicon microstructure was studied at different parameters. The effect mechanism of parameters was studied. The results show that in the conditions of constant laser power density and reactive gas components, with the increase of the reactive gas flux, the microstructures of nano-silicon particles are dramatically different, the grain size becoming smaller gradually and the amorphous phase increasing.

Observation of Fractal Geometry in Lithium Niobate Crystal

2004, 33(4):  647-650. 

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We investigated both a true grown interface of lithium niobate crystal and a etch pit pattern on axial c surface of lithium niobate crystal. We observed the fractal pattern that demonstrates all of the geometric characters of Sierpinski gasket (triangle). The fractal dimension of grown interface and etching pit pattern in lithium niobate crystal have been calculated to be ln3/ln2≈1.58. It is suggested that an etching potential plays a key role in the formation of fractal geometry in the etch pit pattern.

Theoretical Study of the Molecular Structure and Spectroscopic Properties for Y2O3-doped ZrO2 Complexes

2004, 33(4):  651-656. 

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This work constitutes a study guided to the design of the molecular geometry and the growth process of zirconia gels aided by computer-based calculations (density functional theory). The geometric parameters, spectroscopic properties and Mulliken charge population of zirconium complexes are explored. Theoretical calculations show that the reduced crystallite size of doped-zirconia powder is attributed to the slow oxolation reaction rate because of the reduced intergranular attraction force. Moreover, vibration spectra analysis shows that the order of precursor and the second-phase dopant will apparently reduce the characteristic spectrum of monoclinic-phase zirconia. Our theoretical results are relatively in good accordance with the experimental results.

Study on Effect of Growth Atmosphere and Rate on Preparation of Rutile (TiO2) Single Crystal

2004, 33(4):  657-661. 

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The effect of growth atmosphere and rate on the preparation of rutile single crystal in the flame fusion method was mainly studied in this paper. The annealed result in air was compared with it in oxygen. Swing curve and transmissivity of the sample were measured. It was made clear that crystal growth is influenced by chamber atmosphere, temperature at the liquid-solid interface and growth rate, and that the chamber atmosphere is an essential factor on whether crystal could be formed or not. To form a perfect crystal it's a necessary condition that the partial pressure of oxygen at the liquid-solid interface is higher than its decomposed pressure. The role of annealing is to relieve thermal stress formed in crystal growth. However, the more important role of annealing is the oxidization reaction to eliminate oxygen vacancies .The annealing time could be considerably shortened in oxygen. The crystal grown in the optimal experimental condition has good perfection and it's transmissivity is 70-72;, close to commercial crystal.

Effects of Discharge Power on Silicon-based Films Fabricated by VHF-PECVD

2004, 33(4):  662-666. 

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A series of silicon-based samples were fabricated by the very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) technique at various discharge powers. The results show that the transition zone occures at different discharge power for silane concentration (SC=[SiH4]/[SiH4+H2]) of 4; and 6;. Furthermore, the dark conductivity also shows different changes with the increase of the crystalline volume fraction, indicating a different relationship between the structural and electrical properties for the samples prepared at different discharge power for the different SC. In addition, the microstructure measurements of the film characterized by scanning electronic microscopy show the evident ‘cauliflower-like' surface morphology and columnar structure.

Photoresponse of TiO2 Thin Films Deposited by DC Reactive Magnetron Sputtering

2004, 33(4):  667-669. 

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TiO2 thin films were prepared by DC reactive magnetron sputtering on ITO surface which deposited on glass substrates. The structure of TiO2 thin films was studied by Raman spectrum and the absorption spectra. The photoresponses of TiO2 thin films were investigated in virtue of photocurrent. The photoresponse time is less than 100s when photocurrent reaches 96; of the maximum and the photocurrent decays to dark current within 200s.The sensitivity and stability of the photoresponse indicate that it is possible for TiO2 thin films to be a new UV detector material.

Hydrothermal Synthesis of MnxZn1-xO Microcrystal

2004, 33(4):  670-673. 

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MnxZn1-xO crystal was synthesized by hydrothermal method in this work. The experimental parameters for hydrothermal synthesis were:mineralizer concentration 3mol·L-1KOH, the fill factor 35;, temperature 430℃, Zn(OH)2 doped with MnO2 used as precursor, and the reaction time 24 hours. The Mn concentration in crystal was determined by X-ray EDS. The atomic percentage of Mn in crystal increases as the concentration of MnO2 in precursor increased. The maximum atomic percentage for Mn is over 2;. The morphology shows characteristics of hexagonal prism of pure ZnO crystal. The exposed faces are hexagonal faces m{1010}, hexagonal cone faces p{1011}, negative polar faces {0001}and positive polar faces{0001}. The diameters of the crystals are 50-200μm,the heights are 20-100μm.

Analysis of Residual Stress Distribution in DC Arc Plasma Jet CVD High Quality Diamond Films by Raman Spectroscopy

2004, 33(4):  674-678. 

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Diamond films were deposited on molybdenum substrates (φ60mm) by a 100kW DC arc plasma jet CVD apparatus under different process parameters. The diamond films were characterized by scanning electron microscopy (SEM), Raman spectroscopy (laser excitation wavelength:488 nm) and X-ray diffraction. The results show that in the process of DC arc plasma jet CVD diamond film deposition, the internal stress increases from the center to the edge, and the stress mode is compressive. This demonstrates a significant inhomogeneity of stress in diamond films. Both methane concentration and substrate temperature influence the internal stress in diamond films. The trend is that internal stress increases with the increase of methane concentration and substrate temperature.

Further Study on Improvement of Adhesive Force of Diamond Films with Si Substrates by Ion Bombardment

2004, 33(4):  679-682. 

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Owing to the large surface energy difference of diamond with silicon, the diamond nucleation on the mirror-polished silicon surface is difficult when diamond films are prepared by chemical vapor deposition. However, the nucleation can be enhanced by a negative substrate bias, indicating that the adhesive force of diamond nuclei on Si surface is improved. The ion bombardment results in a production of micro-defects(pits)on Si substrate surface and therefore the contact area of diamond film with Si surface is enlarged. Based on these results, the influence of ion bombardment on Si surface with the negative bias was analyzed and the effect of ion bombardment on the adhesive force between diamond film and Si substrate was theoretically studied.

Design of Crystalline Structure for Crack-free Self-standing Diamond Film by DC Plasma Jet

2004, 33(4):  683-689. 

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Crack patterns in self-standing diamond film were observed as network-shape pattern, river-shape and circle-shape pattern, depending on growth temperature. Fracture mechanism was firstly studied by atomic force microscope (AFM) on the fractured section. Both intergranular fracture and transgranular fracture were found by this technique. Transgranular fracture was easy to observe in network-shape pattern, and intergranular fracture was found in circle-shape pattern. The river-shape pattern seemed to result from the combination of inter- and trans-granular fracture. X-ray diffraction (XRD) test was done on all of growth side, nucleation side and fractured section of the film body. Corresponding to XRD results, transgranular fracture took place in the film with (111)-crystalline surface being dominant in all of the three detected surfaces. Intergranular fracture occurred in the film with (220)-crystalline surface being dominant in all of the three detected surfaces. Raman test showed that the intrinsic stress was in the range of several tens MPa to several hundreds MPa. Micro-Raman test on fractured section indicated that there was the distribution of stress in the film body. Also by micro-Raman, testing along the crack path indicated that crystalline structure with few defects was benefit for blocking the propagation of crack. A mechanical model was set up to analyze the effect of dominant surface on fracture strength. Based on the experimental results and mechanical analysis, crack-free self-standing diamond films with 2mm in thickness and 120mm in diameter were successfully grown by controlling the crystalline structure of the films.

Formation of Epitaxial Platinum Films on Ceramics-(100) Single Crystal Substrates

2004, 33(4):  690-693. 

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Thin platinum (Pt) films were prepared on single-crystal substrates MgAl2O4 (100) (MAO) and SrTiO3 (100) (STO) by a facing-target sputtering technique. The films prepared at higher substrate temperature (Ts= 700℃) were grown epitaxially with (200) orientation on SrTiO3 (100) and MgAl2O4 (100). Different from the lower resistivity of Pt/STO film, Pt/MAO film shows a very higher resistivity and the temperature dependence of the resistance exhibits insulator behavior because of the pinhole formation. We also grew epitaxial Pt (50 nm)/La0.67Ca0.33MnO3 (50nm)/STO structure, indicating that Pt is a good electrode for devices involving colossal magnetoresistance materials.