激光辐照对类金刚石薄膜改性及损伤研究

介绍了激光损伤的检测及损伤阈值的测量方法.讨论激光辐照对类金刚石结构和性质的影响规律.并论述不同工作参数的激光对类金刚石薄膜的激光破坏行为及其损伤阈值.在此基础上分析类金刚石薄膜激光损伤的机理.还从物理特性及制备技术方面着手,比较分析金刚石及类金刚石薄膜各自的优缺点和实际应用状况,并提出类金刚石薄膜的应用前景和有待进一步研究的问题.     

纳秒激光辐照对类金刚石薄膜的损伤及改性

利用Nd:YAG纳秒激光(波长分别为355、532和1 064 nm)辐照由电子束蒸发技术制备的类金刚石(DLC)薄膜,通过光学显微镜、光学轮廓仪和拉曼光谱仪等分析了辐照后的薄膜样品,结果表明:不同波长的单脉冲激光辐照时,DLC膜的激光损伤阈值不同;同一波长的多脉冲激光辐照时,损伤阈值低于单脉冲辐照阈值;脉冲激光辐照对DLC膜具有改性作用,受辐照薄膜区域表层发生了石墨化、剥落和气化效应,致使DLC膜表面出现了隆起和弹坑,隆起高度和弹坑深度与激光能量密度大小和脉冲个数有关.     

非平衡磁控溅射类金刚石薄膜的激光损伤过程研究

类金刚石薄膜是一种很好的红外窗口表面增透保护材料,随着对其抗激光损伤特性研究的不断深入,越来越多的研究者都将研究的重点放在了如何提高其激光损伤阈值上。然而,不同沉积方法制备的薄膜由于其微观结构存在的差异,必然会导致破坏的过程有所不同。本文采用非平衡磁控溅射技术沉积的薄膜,对其损伤过程进行了深入的研究。结果表明：在不同的激光能量下,DLC薄膜出现不同的损伤形态,而这些与薄膜的缺陷、内应力以及薄膜与衬底的结合力密切相关。     

CVD金刚石薄膜的成核机理研究

利用热丝化学气相沉积 ,在预沉积无定形碳的硅镜面基底及表面研磨预处理的铜基底上 ,实现了金刚石薄膜的沉积 ,并由此讨论了金刚石的成核机理。研究表明 ,无定形碳是金刚石成核的前驱态 ;成核密度不仅与基底材料有关 ,更主要由基底的表面状态决定 ,基底表面状态的设计是改善成核密度的最有效的方法。     

CVD金刚石薄膜的成核机制

已有许多有效的方法来提高ＣＶＤ金刚石薄膜的成核密度，但成核机理仍有很多问题，本文简要介绍作者在这方面的一些工作。     

金刚石薄膜研究的进展

一、概况金刚石墨膜可以充分发挥金刚石优异的性能,可广泛应用于力学、热学、电子学、光学等多项尖端技术领域,如刀具、集成电路和激光的散热片,红外窗口、高温半导体等,是一种很有发展前途的新型的功能材料。由于在许多不同材料上可以以气相沉积金刚石薄膜,这种涂覆技术的进展更激起了大家的兴趣,具有各种形态和不同物理性质的金刚石薄膜已经获得成功,在某些情况下,已经确定了生产金刚石涂层零件的技术     

激光拉曼光谱在CVD金刚石薄膜质量表征中的应用

激光拉曼光谱是一种优异的，灵敏的，应用广泛的无损表征技术，对于评估碳物质质量及其键合状态，也是有效的手段。     

激光低温沉积金刚石膜

用ＸｅＣｌ紫外与ＣＯ２红外复合激光化学气相沉积方法，在３４０℃硅衬底上沉积成高纯金刚石膜。     

金刚石薄膜的应用

简要介绍了金刚石薄膜的发展史，着重叙述了金刚石膜在机械、光学、声学和半导体方面的一些应用，指出了金刚石膜在今后的研究和商品过程中所要遇到的一些问题。     

在短脉冲激光作用下薄膜的损伤机制

计算了不同材料的能带带隙、初始电子密度、激光波长和激光脉宽等参效对薄膜的抗激光损伤闭值的影响,研究了在不同脉冲宽度激光作用下多光子离化和雪崩离化两种损伤机制的竞争．结果表明,在以平均电子能量不变为特征的雪崩电离的建立期间,光电离速度影响初始电子的浓度,从而影响雪崩电离和光电离之间的竞争．激光脉冲的宽度越大,雪崩电离对电子发展的贡献越大,而多光子离化的贡献越小．     

Effect of polyvinyl butyral on the microstructure and laser damage threshold of antireflective silica films

Silica antireflective films modified by polyvinyl butyral (PVB) were deposited on fused silica substrates by sol-gel process. The effects of PVB on the microstructure and laser damage threshold (LIDT) of films were investigated. The results of the nano particle analyzer and scanning probe microscope revealed that PVB molecules surrounded silica particles and controlled the particle growth, which resulted in a stable sol with uniformly distributed silica particles. Therefore, the films deposited from these modified sols possessed more uniform microstructures than the films without PVB. The adhesive-resistance test indicated that the strength of the modified silica films increased due to the bond reaction between PVB molecules and silica particles. The introduction of PVB into silica sols had also increased the LIDT of films. The LIDT of films increased from 30.0 J/cm² to 40.1 J/cm² after 1.0 wt.% PVB was added. The increase in LIDT was attributed to the increased strength and uniform microstructures of films as an effect of the PVB modification.     

Adhesion improvement of diamond films on cemented carbides with copper implant layer

The deposition of diamond films on cemented carbides is strongly influenced by the catalytic effect of cobalt under typical deposition conditions. Decreasing the content of Co on the surface of the cemented carbide is often used for the diamond film deposition. But the leaching of Co from the WC-Co substrate leads to a mechanical weak surface, often causing poor adhesion. In this paper we adopt a copper implant layer to improve the mechanical properties of the Co leached substrate. The copper implant layer is prepared with vaporization. The diamond films are grown by microwave plasma chemical vapor deposition from the CH₄/H₂ gas mixture. The morphology and the quality of the diamond films have been characterized by scanning electron microscopy and Raman spectroscopy. A Rockwell apparatus has evaluated the adhesion of the diamond on the substrate. The results indicate that the diamond films have good adhesion to the cemented carbide substrate due to the recovery of the mechanical properties of the Co depleted substrate after the copper implantation and less graphite formation between the substrate and the diamond film.     

Laser-assisted vibrational control of precursor molecules in diamond synthesis

Control of chemical reactions is the essence of chemistry, producing designed outcomes while suppressing unwanted side products. Laser-assisted molecular vibrational control has been demonstrated to be a potential approach to influencing the outcome of a chemical reaction. In this article, we reviewed recent progress in the laser control of diamond synthesis through vibrational excitation of precursor molecules in a laser-assisted combustion chemical vapor deposition process. Significantly promoted diamond deposition rate (139 μm/h) and crystalline quality were achieved by resonantly exciting the Q-branch (ΔJ = 0) of the CH₂-wagging mode (v₇ mode 949.3 cm⁻¹) of C₂H₄ molecules. Resonant excitation of the fundamental vibrational modes is more effective in promoting diamond growth than random vibrational excitation. Control of diamond crystallographic orientation was also realized by resonantly exciting the R branch (ΔJ = 1) of the CH₂-wagging mode of C₂H₄ molecules and resulted in the preferential growth of {1 0 0}-oriented diamond crystals. Nitrogen-doped diamond films with a nitrogen concentration of 1.5 × 10²⁰ atoms/cm³ were synthesized by resonantly exciting the rotational–vibrational transition (J = 5 → J′ = 6, K = 0) of the N–H wagging mode (v₂ mode) in ammonia molecules. The findings demonstrate the feasibility of laser-assisted vibrational control in steering chemical reactions and controlling reaction outcomes.     

Effect of B/C ratio on the physical properties of highly boron-doped diamond films

Highly boron-doped diamond films were deposited on silicon substrate by hot filament chemical vapor deposition in a gas mixture of hydrogen and methane. The chemical bonding states, surface texture, and electrical resistivity of these films were analyzed by X-ray photoelectron spectroscopy, scan electron microscope, and four-point probe method. It was found that boron dopants play an important role in the texture and chemical bonding states of the diamond films. An appropriate concentration of boron dopants (B/C ratio of 10 000 ppm) can simultaneously improve crystal quality and reduce resistivity of the diamond films. The minimum resistivity of diamond films reaches 1.12 × 10⁻² Ω cm, which is applicable as electrodes.     

Hydrogen induced microstructural variation in diamond and diamond like carbon thin films

Hydrogen plays a crucial role in the growth of micro-crystalline diamond (MCD) and diamond like carbon (DLC) thin films grown by plasma assisted chemical vapour deposition (PACVD) processes. It selectively etches graphite phase and helps in stabilizing the diamond phase. The presence of various hydrocarbon species in the plasma and their reaction with atomic, excited or molecular hydrogen on the substrate surface decide the mechanism of diamond nucleation and growth. Several mechanisms have been proposed but the process is still not well understood. Control of hydrogen and other deposition parameters in the PACVD process leads to deposition of yet another class of materials called diamond like carbon. By varying the concentration of hydrogen it is possible to produce purely amorphous carbon films on the one hand and amorphous hydrogenated carbon films (with as high as 60% hydrogen) on the other. Very hard, optically transparent and electrically insulating films characterize the diamond like behaviour. The proportion of hydrogen and its bonding with carbon or hydrogen in the film can be varied to obtain very hard to very soft films which could be optically transparent or opaque. The microstructure of these films have been investigated by a large number of techniques. The results show interesting situations. This paper reviews the work on the role of hydrogen on the growth, structure and properties of MCD and DLC thin films.     

The mechanism of persistent photoconductivity induced by minority carrier trapping effect in ultraviolet photo-detector made of polycrystalline diamond film

Performances of long persistent photoconductivity, high responsivity and high photoconductive gain were observed in a metal-semiconductor-metal ultraviolet photo-detector fabricated on a microcrystalline diamond film. Charge-based deep level transient spectroscopy measurement confirmed that a shallow level with activation energy of 0.21 eV and capture cross section of 9.9 × 10⁻²⁰ cm² is presented in the band gap of the diamond film. The shallow level may not act as effective recombination center due to the so small activation energy according to Schockly-Read-Hall statistics. The persistent photoconductivity relaxation fits in with the so called “barrier-limited recombination” model, which may be a minority carrier trapping effect related recombination process. The photo-induced minority carriers (electrons in this paper) may be trapped by the shallow level during light irradiation process and then de-trap slowly via thermal excitation or tunneling effect after removing the light source, which contributes to the persistent photoconductivity. The trapping effect can also reduce the probability of carrier recombination, resulting in the high responsivity and the high gain.     

金刚石膜紫外光电导探测器及性能

用化学气相沉积法生长金刚石膜,在此膜上制作紫外光电探测器,并作了性能测试。该器件是叉指式电极结构,可以减小电极间隙,减少光激发载流子的损失,提高器件的响应灵敏度。表面处理可除去金刚石膜的低电阻表面层,提高器件对紫外光的探测性能。测试表明,用金刚石制作的器件对波长小于２２５ｎｍ的紫外光的响应比可见光高４个量级。     

Laser induced plasma in the formation of surface-microstructured silicon

The plasma induced by femtosecond laser pulses irradiated on silicon surface has been investigated by optical emission spectroscopy. The plasma emission spectra show strong dependence on the structuring ambient gas species and pressure. Among the four ambient gases (SF₆, N₂, air and vacuum), the plasma obtained in sulfur hexafluoride (SF₆) shows the strongest signals. The emission intensities increase initially with the gas pressure, and achieve strongest at the pressure of about 70 kPa, then decrease as the pressure further increases. The stronger plasma emission signals indicate stronger reactions, resulting in sharper sample morphology, which provides an insight into the reaction process.