纳米结构超硬材料的机遇与挑战

经过几十年的研究和发展，纳米结构金刚石和立方氮化硼已相继被成功制备，其高硬度和强韧性充分表明纳米力学增强机制是制备超强超硬材料的有效途径。目前纳米结构超硬材料的研究仍处于起步阶段，高温高压相转变的路径与机制、复杂中间相的结构与产生的条件、热力学条件对晶粒生长和微结构(孪晶和堆垛层错等)形成的作用，以及超硬材料的纳米结构对力学性能和强化机制的影响等尚未完全揭示出来。为此，文章对近年来在相关领域的研究进行综述，总结了设计与寻找超硬材料的一般策略与原则，概括了典型的纳米微结构对超硬材料力学与热稳定性的影响，归纳了纳米结构超硬材料的高温高压相变与转化机制，并对当前的研究进展和潜在应用进行了归纳与展望。     

β—C3N4—一种新型的超硬材料

对于一种硬度可能超过金刚石的新型超硬材料β－Ｃ３Ｎ４的研究已经成国际上材料科学研究的一个热点，文章综述了目前国际上研究β－Ｃ３Ｎ４材料的现状及所得的一些进展。     

超纳米金刚石薄膜结构相变的第一原理分子动力学研究

纳米金刚石薄膜的结构相变非常复杂,对稳定性和物理性质又尤为重要。本文用第一性原理分子动力学模拟研究了超纳米金刚石薄膜的结构相变和表面重构。研究发现,纳米金刚石的表面碳团簇通过断开（111）面的σ键,形成具有碳六元环结构的石墨碎片;内部原子sp3杂化向sp2杂化转化的发生是从（111）面上成对C原子向石墨相转化时形成π键的过程中获得了能量,驱动石墨的转变由表层向心部逐渐进行。转变过程中存在一种洋葱状富勒烯和金刚石结构共存的过渡相——Bucky-diamond,表面悬空键的消除和表层的富勒烯外壳最大限度地降低了表面能和系统总能量,Bucky-Diamond结构稳定存在。     

金刚石镶嵌非晶碳膜表面形貌对场致电子发射的影响

用微波等离子体化学气相沉积设备，在经过不同研磨预处理的金属钼衬底上沉积出了表面形貌有较大差异的金刚石镶嵌非晶碳膜，分别用扫描电子显微镜（ＳＥＭ）、金相显微镜和Ｘ射线衍射谱（ＸＲＤ）以及Ｒａｍａｎ光谱对样品进行了分析测试．研究了各样品的场致电子发射特性，结果发现薄膜表面由大量镶嵌有金刚石小晶粒的非晶碳球组成，在我们的实验范围内，薄膜表面非晶碳球尺寸越小，场致电子发射效果越好     

复合超硬材料的高压合成与研究

复合超硬材料作为一种性能优异的结构材料,被越来越广泛地应用于切削加工、油气钻探等领域.目前大部分复合超硬材料是通过高温高压方法制备.本文主要介绍了近年来复合超硬材料的高压合成与研究取得的成果和进展,重点包括纳米、亚微米、微米聚晶金刚石与立方氮化硼、立方相氮化硅-金刚石超硬复合材料以及金刚石-立方氮化硼超硬合金(复合)材料等,这些新型的复合超硬材料已经被成功合成,各种性能检测表明这些复合超硬材料的硬度、热稳定性等主要性能已明显超越传统超硬材料,可成为有广阔应用前景的新一代复合超硬材料.文中还介绍了近些年研究复合超硬材料出现的一些新的思路、方法与途径,并对复合超硬材料的进一步研究做出了展望.     

微波ECR全方位离子注入制备类金刚石碳膜的结构及摩擦学性能研究

利用微波ECR全方位离子注入技术，在单晶硅（100）衬底上制备类金刚石薄膜.分析结果表明，所制备的类金刚石碳膜具有典型的类金刚石结构特征，薄膜均匀、致密，表面粗糙度小，摩擦系数小.其中，薄膜的结构和性能与氢流量比关系密切，随氢流量比的增加，薄膜的沉积速率减小，表面粗糙度降低，且生成sp³键更加趋向于金刚石结构，表面能 更低，从而使摩擦系数大幅降低. 关键词： 全方位离子注入 类金刚石碳膜 拉曼光谱 摩擦磨损     

CH基团与金刚石(111)面的碰撞反应及其对碳膜生长的影响

等离子体增强化学气相沉积技术中的碳膜选择性自组装机理是高性能碳膜制备过程中的挑战性基础课题.采用经典分子动力学方法,模拟了不同能量(1.625-65 eV)的CH基团在清洁金刚石和吸氢金刚石(111)面上的轰击行为,获得了吸附、反弹、反应等各类事件的发生概率,并据此探讨了含氢碳膜制备过程中CH基团的贡献.结果表明,随着入射能量的增加,CH基团对薄膜生长的贡献由单纯的吸附、反弹机理向反应、吸附混合机理转变,其中最主要的反应过程是释放一个或两个氢原子的反应,而释放氢分子的反应则很少发生.这些反应不仅使薄膜生长过程更均匀、薄膜表面更平整,还降低了薄膜的氢含量.生长机理的转变导致低能量条件下所成薄膜中的多数碳原子都包含一个氢原子作为配位原子,而高能量条件下的薄膜中的碳原子则很少有氢原子作为配位原子.另外,通过分析sp~3-C和sp~2-C数目的变化,研究了CH基团对金刚石基底的破坏作用.     

MPCVD金刚石的Raman光谱分析

用微波等离子体化学气相淀积法（MPCVD）在Si基片上生长了金刚石薄膜，通过对其进行Raman光谱分析，一次表征了金刚石的结构，纯度及应力状况等材料性能，同时并研究了生长过程中微波功率与金刚石性质的关系。研究表明，微波等离子体化学气相溶积法生长的金刚石薄膜，除了金刚石成分的生长外，还会有部分非金刚石成分的生长，金刚石的纯度与微波功率的关系不明显，另外此种方法生长的金刚石薄膜主要表现为张应力。     

“超硬”材料及其研究现状

 由于生产、生活中常要进行切、割、钻、削等各种加工,人们总是在不断寻找更硬的材料来制作加工工具。要说当今世界上最硬的材料,谁都会说是金刚石。金刚石在莫氏硬度表上占首位,其硬度值为10。金刚石不仅硬度高,在室温下还具有良好的导热率,在用它工作时,工作面上昕产生的热能迅速散发,因而金刚石可在多种加工(如切削、研磨、抛光等)上供人选用。     

氮对类金刚石薄膜的微观结构内应力与附着力的影响

采用原子力显微镜(AFM)、俄歇电子能谱(AES)和显微压痕分析等手段对射频等离子体增强化学气相沉积法制备的掺氮类金刚石(DLC：N)薄膜的微观结构和力学性能进行了研究.结果表明,随着含氮量的增加,DLC薄膜的AFM表面形貌中出现了几十纳米的颗粒,原子侧向力显微镜和AES分析表明这种纳米颗粒是x大于0.126的非晶氮化碳CN_x结构.这种非晶DLC/CN_x的纳米复合结构,减小了薄膜的内应力,从而提高了薄膜与衬底的附着力. 关键词： 类金刚石碳膜 微观结构 附着特性     

高压及热处理对氮碳薄膜激光诱导荧光效率的影响

 应用激光激发荧光光谱实验对经热处理后及高压条件下的氮碳薄膜荧光光谱进行了测量分析。实验显示,热处理效应和高压效应均导致薄膜荧光效率降低,前者表现为不可恢复,后者为可恢复即卸压后荧光效率的恢复,表明导致荧光光谱效率降低的微观机制不同,为氮碳薄膜荧光模型提供了新的实验证据。     

高压及热处理对氮碳薄膜激光诱导荧光效应的影响

应用激光激发荧光光谱实验对经热处理后及高压条件下的氮碳薄膜荧光光谱进行了测量分析。实验显示,热处理效应和高压效应均导致薄膜荧光疚降有者表现为不可恢复,后者为可恢复即卸压后荧光效率的恢复,表明导致荧光光谱效率低的微观机制不同,为氮碳薄膜荧光模型提供了新的实验证据。     

CRYSTALLINE CARBON NITRIDE THIN FILMS DEPOSITED BY MICROWAVE PLASMA CHEMICAL VAPOR DEPOSITION

The crystalline carbon nitride thin films have been prepared on Si (100) substrates using microwave plasma chemical vapor deposition technique. The experimental X-ray diffraction pattern of the films prepared contain all the strong peaks of α-C₃N₄ and β-C₃N₄, but most of the peaks are overlapped.The films are composed of α-C₃N₄ and β-C₃N₄. The N/C atomic ratio is close to the stoichiometric value 1.33. X-ray photoelectron spectroscopic analysis indicated that the binding energies of C 1s and N 1s are 286.43eV and 399.08 eV respectively. The shifts are attributed to the polarization of C-N bond. Both observed Raman and Fourier transform infrared spectra were compared with the theoretical calculations. The results support the existence of C-N covalent bond in α- and β-C₃N₄ mixture.     

人工合成金刚石研究进展

1796年英国科学家S．Tennant的精确燃烧实验，首次揭示金刚石是由纯碳构成的宝石，从此人类开始了漫长的人工合成金刚石的探索．金刚石通常只能在极端条件下形成，因此，合成技术的突破是人类合成水平提高的一个重要标志，文章对这一领域一些重要工作做了简单回顾，也讨论了作者在合成金刚石方面的工作．我们在440℃的低温条件下，用碱金属(Li，Na，K)还原超临界CO2，得到透明、大尺寸的金刚石晶体，首次实现了金刚石燃烧实验的逆过程，即把低能、直线型CO2分子变成了碳-碳四面体连接的金刚石，开辟了人工合成金刚石的新途径．也讨论了它与天然金刚石起源之间的可能联系．     

Growth of preferentially-oriented AlN films on amorphous substrate by pulsed laser deposition

Preferentially-oriented aluminum nitride (AlN) films are grown directly on natively-oxidized Si (100) substrate by pulsed laser deposition (PLD) in nitrogen (N₂) environment. The AlN preferential orientation changes from (002) to (100) with increasing N₂ pressure. Such different behaviors are discussed in terms of deposition-rate-dependent preferential orientation, kinetic energy of depositing species and confinement of laser plume. Finally, sample deposited at 0.9 Pa is proved to have the highest (002) peak intensity, the lowest FWHM value, the highest deposition rate and a relatively low RMS roughness (1.138 nm), showing the optimal growth condition for c-axis-oriented AlN growth at this N₂ pressure.     

Diamond and cubic boron nitride under high pressure: Raman scattering,equation of state and high pressure scale

Abstract

The development of the diamond-anvil cell has stimulated Raman-scattering investigation of vibrational modes in covalent crystals. The linear pressure coefficient reported for diamond by Hanfland et at' (2.90 ± 0.05 cm-¹/GPa) agrees to within mutual experimental error with the result of Boppard et aL² (2.87±0.01 cm-¹/GPa). As to cubic boron nitride, the only work by Sanjurjo ef aL3 reports 3.45 ± 0.07 cm-¹/GPa for LO- and 3.39 ± 0.08 cm-¹/GPa for TO- modes. Since no compressibility data are availablel^1?3, the mode Griineisen parameter γ = ‐ δ In γ/δ is defined as y = K/Y·dv/aP and depends on the bulk modulus K and the calibration of the ruby scale. The above papers report y= 0.96 and y=0.95±O.O3fordiamondand γ_Lo=1.21,γTo=1.51 forBN.     

Surface modification of titanium membrane by chemical vapor deposition and its electrochemical self-cleaning

Membrane separation is applied widely in many fields, while concentration polarization and membrane fouling, limiting its promotion and application greatly, are the bottlenecks in membrane application. Among which, membrane fouling is irreversible, membrane must be periodically cleaned or even replaced to restore permeability. Membrane cleaning has become one of the key issues in membrane separation areas. Considering incomparable electrochemical advantages of boron-doped diamond (BDD) film electrode over conventional electrode, a new composite membrane Ti/BDD, made by depositing CVD (chemical vapor deposition) boron-doped diamond film on titanium(Ti) membrane to modify porous titanium surface, that can be cleaned electrochemically is proposed. Feasibility of its preparation and application is discussed in this paper. Results shows that based on the unique electrochemical properties of diamond, cleaning level of this composite Ti/BDD membrane is significantly increased, making membrane life and efficiency improved prominently.     

Field emission properties and surface structure of nickel containing amorphous carbon

Nickel containing amorphous carbon (a-C:Ni) films have been deposited by filtered cathodic vacuum arc (FCVA) technique by introducing pure nickel into the graphite target. The field electron emission property of a-C:Ni was improved when compared to that of pure tetrahedral amorphous carbon (ta-C) by FCVA. The emission threshold field of a-C:Ni film is about 5 V μm⁻¹, whilst the threshold field of the ta-C film is about 13 V μm⁻¹. Raman spectroscopy suggests that the sp² clusters in the carbon film increase both in size and number when Ni is introduced. However, the emission was found to degrade to threshold fields beyond 20 V μm⁻¹ after the a-C:Ni film was left in ambient for a week. This observation is attributed to surface absorption of oxygen on the a-C:Ni film, as determined by X-ray Photoelectron Spectroscopy.     

Effects of ion implantation on yellow luminescence in unintentional doped n-type GaN

The effects of Si, O, C and N ion implantation with different implantation doses on yellow luminescence (YL) of GaN have been investigated. The as-grown GaN samples used in the work were of unintentional doped n-type, and the photoluminescence (PL) spectra of samples had strong YL. The experimental results showed that YL of ion implanted samples exhibited marked reductions compared to samples with no implantation, while the near band edge (NBE) emissions were reduced to a lesser extent. The deep-level centers associated with YL may be produced in GaN films by O and C ion implantation, and identities of these deep-level centers were analyzed. It was also found that the dose dependence of YL was analogous with the one of the intensity ratios of YL to the near band edge (NBE) emission (I _YL /I _NBE ) for ion implanted samples. The possible reason for this comparability has been proposed.      

Vacancy profiles and clustering in light-ion-implanted GaN and ZnO

We present experimental results obtained in H-implanted GaN and He- and Li-implanted ZnO. The ion energies were varied in the range 100-850 keV, and the implantation fluences in the range 5 × 10¹³ to 1 × 10¹⁸ cm⁻². In addition, conventional and flash anneals at temperatures 500-1400 °C were performed on the ZnO samples. The data obtained with a slow positron beam show that vacancy clusters are formed in as-implanted samples with fluences above 1 × 10¹⁷ cm⁻². Below this value only single vacancies are detected after implantation, but vacancy clusters can be formed and subsequently dissociated by thermal annealings.