高速生长CVD金刚石单晶及应用

文章简要地介绍了近年来国内外CVD金刚石单晶的高速生长和应用进展.实验中采用微波等离子体化学气相沉积(CVD)方法,同质外延高速生长金刚石单晶,通过改变反应腔压强、反应气氛(在CH4／H2中引入氮气N2、二氧化碳CO2、氧气O2、)等,调制单晶生长速率、质量、颜色、表面粗糙度、光谱等特性.利用高温氢等离子体进行退火,可使金刚石单晶的颜色有很大的改善.研制了CVD金刚石单晶刀具,用于金属材料的曲面镜面加工.     

人造大单晶金刚石的合成技术进展及主要应用

随着宝石级金刚石合成技术的不断进步,最好的人造金刚石其品级已经超过了天然金刚石.文章简单介绍了大单晶金刚石高温高压合成技术和CVD合成技术近年来的进展,大单晶金刚石的主要应用以及市场前景.     

单晶质CVD金刚石的特性及其制作切削工具的应用

阐述单晶质CVD金刚石作切削工具所应考虑的力学与热学性质。元素6公司进行的研究试验表明，单晶质CVD金刚石切削工具在加工强度高质量轻的结构材料如金属基体复合材料（MMCs）等方面具有广阔发展前景。CVD金刚石镀覆工具在现代飞机制造业中加工碳纤维增强塑料（CFPs）和CFP-金属复合材料已显示出其重要作用。在汽车工业中用单晶金刚石镀覆刀片高效高精度车削含硅铝合金（Al—SillCu2Fe）材料的试验取得了良好的效果。     

CVD金刚石薄膜技术发展现状及展望(下)

简要描述了CVD金刚石薄膜技术的发展历程。介绍了纳米特别是超纳米金刚石膜、CVD金刚石大单晶的技术特点及其应用。超纳米金刚石膜在MEMS(微机电系统)、电化学和生物医学上的应用和CVD金刚石大单晶是当前的研究热点。简言之,金刚石的发展向着更大或者更小的方向深入进行,即"非大即小"。     

CVD金刚石薄膜技术发展现状及展望(上)

简要描述了CVD金刚石薄膜技术的发展历程.介绍了纳米特别是超纳米金刚石膜、CVD金刚石大单晶的技术特点及其应用.超纳米金刚石膜在MEMS(微机电系统)、电化学和生物医学上的应用和CVD金刚石大单晶是当前的研究热点.简言之,金刚石的发展向着更大或者更小的方向深入进行,即“非大即小”.     

CVD金刚石切削工具

阐述金刚石切削工具在机加工中的重要作用和CVD金刚石的优异性能以及CVD金刚石切削工具的形式.对CVD金刚石薄膜切削工具和CVD金刚石厚膜切削工具的特点和应用范围进行了分析对比,并指出存在问题和发展前景.     

CVD金刚石技术和应用

通过大量文献资料和有关网页,叙述了近年来国内外化学气相沉积金刚石的制备、加工和应用技术研究的进展、商业化现状等.文章列举了大量图片和数据,试图展示近几年CVD金刚石有关方面的信息.文章显示,CVD金刚石技术研究和商业开发虽然都取得了长足的进步,但仍然有巨大的发展空间,特别是在传统的金刚石无法涉足的一些高技术应用领域.     

单晶CVD金刚石作为功能材料的应用

阐述单晶CVD金刚石的发展、特性及应用.分析了单晶CVD金刚石在工业与技术应用方面的优越性.目前其重要应用领域主要包括:半导体器件;微波技术;监测器件与检测系统;光纤通讯以及光信息存储技术等.     

CVD金刚石技术和应用(下)

通过大量文献资料和有关网页,叙述了近年来国内外化学气相沉积金刚石的制备、加工和应用技术研究的进展、商业化现状等.文章列举了大量图片和数据,试图展示近几年CVD金刚石有关方面的信息.文章显示,CVD金刚石技术研究和商业开发虽然都取得了长足的进步,但仍然有巨大的发展空间,特别是在传统的金刚石无法涉足的一些高技术应用领域.     

说说金刚石在功能应用方面的那些事

金刚石在工业和科学技术领域中,概括地说,是用作工程材料和功能材料的。文章仅就金刚石在医学、微电子机械系统、光学、检测器和传感器、声学、磁性录音系统、场发射显示器、电子信息、热学、高温高频半导体材料和电化学与辐射探测学等方面的应用,做了简要的阐述。认为从所提供的不多信息中,可初略地感觉金刚石其功能应用的端倪。为使金刚石功能应用的美好未来早日展现在人们的面前,提出了一马当先,比别人多想几步;马上行动,成功源于行动和立马做第一个吃螃蟹人的理念。     

Pulse thermometers based on synthetic single crystal boron-doped diamonds

A time delay of electrical resistance of boron-doped semiconductor diamond sensor at heating pulses was investigated. We used a symmetric scheme with 2 equivalent 2 × 2 × 1.5 mm³ single crystal elements connected via thermal conductive electrical insulating glue. One of elements served as pulse heater and the other one as a sensor. About 40 ms characteristic time delay of diamond sensor was achieved. It is supposed, that using smaller crystals for sensors and by optimization of their electrical and heat conductivity properties, a regular value of time delay less than 1 ms will be attained. The potential application of diamond thermometers for temperature control in combustion engines is shown.     

The effect of CO2 on the high-rate homoepitaxial growth of CVD single crystal diamonds

In this paper, we report the effect of gaseous carbon dioxide (CO₂) introduced in the typical reaction atmosphere of CH₄/H₂/N₂ (60/500/1.8 in sccm) on the growth rate, morphology and optical properties of homoepitaxy single crystal diamonds (SCDs) by microwave plasma chemical vapor deposition. The additional carbonaceous sources supplied by CO₂ are favorable to increase the growth rate, and meanwhile, the oxygen related species generated would enhance the etching effect not only to eliminate the non-diamond phase of SCD but also to decrease the growth rate. The appropriate addition of CO₂ can increase the high growth rate, decrease the surface roughness, and reduce the concentration of N-incorporation. It is demonstrated that adding CO₂ strongly affects the contents of various reaction species in plasma, which would determine the growth features of CVD SCDs.     

The influence of recess depth and crystallographic orientation of seed sides on homoepitaxial growth of CVD single crystal diamonds

Microwave plasma chemical vapor deposition (MPCVD) has gained increasing attention as a feasible and effective way to produce large, high-quality, single-crystal diamonds. However, the growth of polycrystalline diamond on the periphery of the seed crystal and the cracking generated by the internal stress during the growing process lead to significant decline of the quality and integrity of the CVD diamond, thus increasing the difficulty of synthesizing large diamond layers. Although optimized growth parameters and refined substrate holders have been employed by some researchers to improve the periphery quality of CVD diamond layers, more research needs to be done in this area. In this study, we used a specially designed substrate holder with a circular recess, in which the seed crystal was placed. By designing substrate holders with different recess depths and a seed crystal with different side-surface crystallographic orientations, we aimed to determine the influence of the recess depths and the crystallographic orientation of seed sides on the growth quality according to polarizing microscope, laser Raman spectroscopy, UV fluorescence imaging, and photoluminescence (PL) mapping measurements. The results demonstrate that as the recess depth increases, the amount of polycrystalline diamonds and the internal stress on the periphery are controlled effectively. The crystalline quality is improved, and the growth rate is decreased. In addition, compared to the periphery with {100} seed sides, the periphery with {110} seed sides displays better crystalline quality, lower internal stress, and fewer polycrystalline diamonds after growth, which is probably due to the intrinsic nature of the growth steps propagating on the {100} diamond surface and the effect of nitrogen atoms on the growing process in the diamond lattice.     

Photochemical attachment of amine-layers on H-terminated undoped single crystalline CVD diamonds

The initial nucleation and growth characteristics of amine layers photochemically attached from 10-amino-dec-1-ene molecules protected with tri-fluoroacetic acid group to H-terminated undoped single crystal CVD diamond surfaces are characterized by tapping and contact mode atomic force microscopy (AFM) and scanning tunneling microscopy (STM) with nanometer resolution. The diamond is atomically flat which allows attributing variations of tunneling currents in STM to amine grafted surface areas. Island formation and growth of islands with increasing photochemical attachment time is revealed by these experiments. This results support the growth model, where hydrogen cleavage reactions from the diamond surface by amine molecules bonded to diamond is the major growth mechanism. These reactions might be initiated by UV light illumination of pyrolysis of organic peroxides in the presence of the adsorbate, which are proposed to break H–C bonds to create surface dangling bonds. It occurs at the periphery of islands which gives rise to island growth.     

Elastic anomalies in ZrTiO4 single crystal

Elastic properties of ZrTiO₄ single crystal have been investigated by ultrasonic and piezoelectric resonance method. The elastic stiffness C^E₄₄ softens around the Tl (normal-incommensurate transition temperature), whereas C₁₁and C₁₂show only small abrupt jumps.     

Structure image of single crystal of polyethylene

High-resolution electron macroscopic images of lamellar single crystal of polyethylene (PE) have been successfully obtained using high-resolution electron microscopy (HREM), although so far the feasibility of obtaining HREM images from such a radiation sensitive polymer is still drastically questioned. The HREM images with a clear two-dimensional periodic structure reported here were recorded in a transmission electron microscope operated at 200 kV. The images consisted of lattice fringes derived from the 〈001〉 zone, and the structure images of different lattice fringes were resolved. To our knowledge, this is the first time that such clear structure images of PE have been reported at a molecular level.     

Charge transport in high mobility single crystal diamond

Time of Flight (TOF) measurements using conventional laser TOF and α-particle TOF setups have been carried out on high quality CVD diamond samples to study the electron and drift mobility and to compare them with the mobility data for IIA diamond. The measured mobilities for all samples investigated are in the range 2000–2250 cm²/Vs for holes and 2200–2750 cm²/Vs for electrons, thus close to the theoretical prediction as well as to IIa diamond mobility values. The charge transient profile measured in the laser TOF measurements is influenced by the electric field profile in the sample, which might be changed based on the charge trapping at low electric fields applied, depending on the surface atomic termination. The temperature dependence of the drift mobility indicates that at room temperature the scattering on acoustic phonons is the main dominant scattering mechanism and the contribution of other types of carrier scattering mechanism is negligible.     

Raman scattering in CsTiOAsO4, single crystal

The longitudinal (LO) and transverse (TO) A₁ vibrational modes have been measured between 30-1200 cm^-1 as a function of temperature (30-1240 K) for CsTiOAsO₄ (CTA). The frequencies for all corresponding Raman components shifted to lower frequencies on increasing the temperature, however, there is no typical soft-mode like behavior observed in the measured frequency range. The relative intensities of the low frequency bands increase substantially with increasing temperature due to high mobility of Cs⁺ ion. Transition to higher symmetry structure was noticed above 940K and the corresponding changes in the phonon spectra were observed.     

Nanoscale anisotropic plastic deformation in single crystal GaN

Elasto-plastic mechanical deformation behaviors of c-plane (0001) and nonpolar GaN single crystals are studied using nanoindentation, cathodoluminescence, and transmission electron microscopy. Nanoindentation tests show that c-plane GaN is less susceptible to plastic deformation and has higher hardness and Young''s modulus than the nonpolar GaN. Cathodoluminescence and transmission electron microscopy characterizations of indent-induced plastic deformation reveal that there are two primary slip systems for the c-plane GaN, while there is only one most favorable slip system for the nonplane GaN. We suggest that the anisotropic elasto-plastic mechanical properties of GaN are relative to its anisotropic plastic deformation behavior.PACS: 62.20.fq; 81.05.Ea; 61.72.Lk.