硬质合金YG8衬底直接沉积金刚石薄膜的探讨

在硬质合金衬底上直接沉积金刚石薄膜．总是伴随着石墨化过程．钴是促进石墨生长的积极因素。由于衬底温度决定氢原子的活性和钴的扩散方式．因而它是金刚石形核和生长的关键条件。在合适的衬底温度下，金刚石能形成均匀连续的薄膜。     

甲烷—氢气体系金刚石生长的热力学相图分析

低压金刚石的生长实验自八十年代至今已取得了很大成功。但采用合理的计算方法定量化地预测出金刚石生长条件在国内外还是一个新的课题。本文根据非平衡热力学耦合理论模型绘制了甲烷－氢气体系金刚石生长投影相图，并收集了１９８２－１９９７年大量的实验结果，经比较相一致，并讨论了氢原子在金刚石生长过程中的作用。计算得到的相图与经典平衡相图有本质不同，有金刚石生长区，因而可以合理解决金刚石低压下连续生长而石墨被腐蚀的实验事实与经典平衡热力学之间的矛盾。本文的计算结果可以为ＣＶＤ金刚石生长实验提供定量化的压力条件的选择和优化实验条件。     

激光熔覆复合涂层中金刚石的形态转变对涂层性能的影响

采用半导体激光器在45#钢基体上制备金刚石复合涂层, 熔覆层材料为铁基粉末2Cr13和人造金刚石微粉的混合粉末, 熔覆设备使用2 kW光纤耦合半导体激光器。利用扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)对涂层的显微组织、元素分布和相结构进行分析; 并采用摩擦磨损试验机对涂层的摩擦磨损性能进行了测试。结果表明: 该复合涂层中的金刚石在激光的作用下发生了形态转变, 一部分完全碳化形成石墨; 另一部分不完全碳化形成石墨并残留小部分金刚石相。XRD分析涂层的相组成可知, 该涂层主要由硬质相Fe0.64Ni0.36、金刚石、FexCy、过饱和固溶体Cr和石墨等组成。由于涂层中金刚石及石墨的存在, 使得涂层具有优异的耐磨性能, 涂层的耐磨性相比未添加金刚石涂层提高了近60%, 涂层的磨损机制以磨粒磨损为主。     

低压气相生长金刚石薄膜成核机理的研究

本文论述了低压气相生长金刚石薄膜中活性原子团ＣＨ＿３和原子态氢在金刚石成核运动中的作用以及衬底材料性能对成核的影响，认为活性基ＣＨ＿３是生长金刚石的主要活性物质，它们在衬底表面的吸附、碰撞、聚集等构成了成核运动，原子氢在成核运动中的主要作用是参与ＣＨ＿３的脱氢反应和石墨相碳原子团的刻蚀反应，并且还有稳定ＣＨ＿３中ＳＰ￣３杂化轨道的作用。衬底材料性能对成核的影响在于晶格失配而导致的错配位错和晶格畸变所引起的界面势垒和晶核弹性能的增加。最后讨论了金刚石薄膜与衬底之间是否存在过渡层问题，认为过渡层不是金刚石唯一的成核区，它的存在与生长条件密切相关，并且解释了关于过渡层实验研究中遇到的相互矛盾的结论。     

用于场发射阴极的磁控溅射金刚石薄膜的研究

用激光拉曼谱和原子力显微镜等现状分析手段研究了磁控溅射石墨靶制备的薄膜的结构和特性。结果表明：薄膜由金刚石相和石墨相组成，它们的相对含量取决于制备工艺参数，特别是沉积时的基体温度的影响尤为明显。薄膜表面呈现为密度很高的微尖锥，这为制造大面积场发射平板显示器的阴极提供了广阔的前景。     

C60,石墨,金刚石和非晶碳的电子结构研究

Ｃ＿（６０）、石墨、金刚石和非晶碳的电子结构研究王永瑞，邹　骐，吴自勤（上海交通大学材料科学系，上海２０００３０）（中国科学技术大学基础物理中心，合肥　２３００２６）自从Ｋｒａｔｓｃｈｍｅｒ￣［１］等发现了制备Ｃ＿（６０）的新方法以来，这种具有独特性...     

预处理对不锈钢表面沉积类金刚石薄膜的影响

类金刚石碳(diamond-like carbon，DLC)薄膜具有非常优异的力学、电学、光学等性能，因此在许多领域有着巨大的应用前景，在世界范围内形成了研究类金刚石碳薄膜的热潮。但目前在铁质材料上沉积类金刚石碳薄膜存在一个很大的问题：由于铁对碳氢化合物的分解及石墨相的形成有很强的催化作用，降低了薄膜的各项性能。     

钼酸铵在流动床反应室中的热解作用

本文研究了用空气作流动介质，在流动床反应室中钼酸铵的热分解，热解过程中释放的氨蒸汽直接引入ＨＣｌ溶液，通过监控测量在处理过程中随时间，温度变化对ＨＣｌ溶液的ＰＨ值的变化。计算处理过程的热分解度α。研究发现，整个分解过程的动力学与“幂函数定律”模型相符得很好，测得的总的反应活化能Ｅ和速率常数Ｋ分别为在１６．３ＫＪ．ｍｏｌ＾－１和１．２４×１０＾－３秒＾－１活化能的数据表明过程受表面控制，研究结果指出     

脉冲激光沉积类金刚石膜技术

脉冲激光沉积(PLD)技术制备类金刚石(DLC)薄膜存在着金刚石相含量较低、石墨颗粒多、薄膜与衬底附着力差、膜内应力大等技术难题,为此,研究人员研究出了多种技术措施,如通过引入背景气体、超快激光、偏压、磁场以及加热等措施提高了薄膜金刚石相含量;采用金刚石或丙酮靶材、减小单脉冲能量等措施减少了石墨颗粒;采用间歇沉积、真空退火、超快激光等措施减少了膜内应力;合理没计过渡层改善了膜与衬底间的附着力等.这些技术有力地推动了脉冲激光沉积技术的发展.     

多脉冲激光修整青铜金刚石砂轮的表面变质层

对脉冲激光修整青铜金刚石砂轮石墨变质层进行了理论研究,当激光功率密度为1.68×10~8~3.359×10~8 W/cm~2时,对金刚石表面的温度演化进行了数值仿真。研究结果表明,金刚石达到石墨化温度的时间约为435~440ns,金刚石的石墨化程度较低。提出了水柱流辅助脉冲光纤激光修整青铜金刚石砂轮的新方法,降低了金刚石的石墨化程度。     

金刚石簿膜生长技术

本文回顾了低压合成金刚石的历史,对各种金刚石薄膜的生长方法进行了简要的对比。低压条件下金刚石处于亚稳态而石墨处于稳定相,本文重点介绍了低压条件下抑制石墨形成促进金刚石生长的关键因素。对金刚石在不同衬底上的成核状况,衬底的表面状况对成核的影响,生长过程中原子氢的作用,以及衬底温度的影响等作了概括,提出了目前阶段金刚石薄膜研究中所要解决的问题。     

Ultrafast Direct Ablative Patterning of HOPG by Single Laser Pulses to Produce Graphene Ribbons

Ultrafast, single step and direct patterning of highly oriented pyrolytic graphite (HOPG) is achieved through pulsed laser interference ablation using a near field transmitting phase mask. Periodic arrays of lines are patterned on the HOPG surface over large areas by spatially modulating the laser intensity through the mask. Thus patterned surface serve as a source for multi and few layer graphene ribbons for transferring onto desired substrates using polydimethylsiloxane as transferring agent. The transferred regions are contained with few layer graphene (5–6 layers) ribbons as well as thick graphitic ribbons (30–40 nm), with widths ～1 μm and lengths of several micrometers. Raman, TEM and electrical measurements have confirmed that the transferred ribbons are highly crystalline in nature. Using combinations of shadow and transmitting phase masks, other patterns such as checker boards and diamond‐shaped pits are produced.     

硅基氮化镓异质结材料与多晶金刚石集成生长研究

在50.8 mm(2英寸)硅基氮化镓异质结半导体材料上采用低压等离子体化学气相沉积方法淀积100 nm厚度的氮化硅材料,然后采用微波等离子体化学气相沉积设备在氮化硅层上方实现多晶金刚石材料的外延生长.采用氮化硅作为过渡层和保护层有效调控了材料应力,保护了氮化镓基材料在多晶外延过程中被氢等离子体刻蚀,使得外延前后氮化物异...     

Current-voltage characteristics of thin film and bulk diamondtreated in hydrogen plasma

It is shown that the electrical properties of thin film and bulk diamond can be systematically altered by hydrogen plasma treatment under controlled conditions. The concentration of electrically active hydrogen introduced in diamond can be determined from the current-voltage characteristics of hydrogenated samples containing traps. Hydrogen passivation of deep traps in diamond is clearly demonstrated     

Growth and Isolation of Large Area Boron‐Doped Nanocrystalline Diamond Sheets: A Route toward Diamond‐on‐Graphene Heterojunction

Many material device applications would benefit from thin diamond coatings, but current growth techniques, such as chemical vapor deposition (CVD) or atomic layer deposition require high substrate and gas‐phase temperatures that would destroy the device being coated. The development of freestanding, thin boron‐doped diamond nanosheets grown on tantalum foil substrates via microwave plasma‐assisted CVD is reported. These diamond sheets (measuring up to 4 × 5 mm in planar area, and 300–600 nm in thickness) are removed from the substrate using mechanical exfoliation and then transferred to other substrates, including Si/SiO₂ and graphene. The electronic properties of the resulting diamond nanosheets and their dependence on the free‐standing growth, the mechanical exfoliation and transfer processes, and ultimately on their composition are characterized. To validate this, a prototypical diamond nanosheet–graphene field effect transistor‐like (DNGfet) device is developed and its electronic transport properties are studied as a function of temperature. The resulting DNGfet device exhibits thermally activated transport (thermionic conductance) above 50 K. Below 50 K a transition to variable range hopping is observed. These findings demonstrate the first step towards a low‐temperature diamond‐based transistor.     

Non-equilibrium thermodynamics and the vapor phase preparation of diamond for electronic applications

Bulk diamond is unstable relative to bulk graphite except at high pressure and temperature. In spite of this, well crystallized diamond has been grown using numerous CVD methods, many of which have in common the production of atomic hydrogen and hydrocarbon radicals in regimes where solid carbon is expected to be a stable product. Several fundamentally different points of view have emerged in the effort to explain why well crystallized diamond, and not graphite or vitreous carbon, is observed in these experiments. One of the earliest argues that graphite is “etched” by atomic hydrogen at a rate higher than diamond and hence diamond is kinetically stable with respect to graphite. If diamond formation is kinetically controlled the deposition mechanism is critical and much debate has centered on the mechanism and species involved. Alternatively it can be argued that at the growth interface, diamond surfaces are stabilized by termination with hydrogen. If this is correct, and bulk reorganization ignored, then it is shown that a global understanding of the parameters important to the growth of diamond can be obtained without detailed kinetic analyses. Thus it is argued that single crystal diamond films of arbitrarily high purity and perfection are theoretically possible by CVD in spite of the bulk instability of diamond. It is also suggested that general principles exist which might be applied to the growth of other well crystallized metastable phases-notably cubic boron nitride.     

晶体硅中氢钝化硼的机理

利用量子化学近似计算方法MNDO和红外光谱法研究了晶体硅中氢和硼的相互作用.结果表明,原子氢束缚在离代位硼原子约1.25A的球面能谷中,可绕硼转动,形成一个动态的硼-氢复合体,从而钝化硼.B-H对的动态性质导致对应的1875cm~(-1)红外吸收峰的宽化,这种状态可保持到10K.     

High temperature DC and RF performance of p-type diamond MESFET:comparison with n-type GaAs MESFET

The DC and RF performance of a p-type diamond MESFET is simulated and compared with the simulated performance of an n-type GaAs MESFET over the operating temperature range, 300-923 K. Power performance of a diamond MESFET is shown to improve with increasing temperature and to exceed that of a GaAs MESFET when operated at temperatures higher than 550 and At 923 K the simulated diamond MESFET produces about 0.8 W/mm of output power for an operating frequency of 5 GHz. Small signal current gain for a diamond MESFET is also found to increase with temperature. The cut-off frequency, f_T, of a diamond MESFET at 923 K is comparable with that of a GaAs MESFET at room temperature. It is concluded that there are microwave power applications of MESFET's in p-type diamond but otherwise conventional design is limited to high temperature     

Single‐Atom Engineering of Directional Charge Transfer Channels and Active Sites for Photocatalytic Hydrogen Evolution

Efficiency of layered photocatalysts such as graphitic carbon nitride (g‐CN) is still too low due to the poor utilization of photoexcited‐charge carriers. The major drawback is that the weak van der Waals force among g‐CN layers is unfavorable for the charge transfer between the adjacent layers and the intrinsically π‐conjugated planes with inefficient random in‐plane charge migration. Herein, an atomically dispersed Pd layered photocatalyst with both bridged sites of adjacent layers and surface‐sites of g‐CN is demonstrated, providing directional charge‐transfer channels and targeting active sites for photocatalytic water reduction. Both theoretical prediction and empirical characterizations are conducted to achieve the successful synthesis of single‐atom engineered Pd/g‐CN hybrid and the excellent separation of charge transfer as well as the efficient photocatalytic hydrogen evolution, much better than that of the optimized Pt/g‐CN benchmark. The finding in this work provides a rational way for tailoring the performance and engineering of single‐atomic noble metal.