类金刚石薄膜的激光损伤特性及工艺优化

采用脉冲真空电弧沉积(PVAD)技术制备了类金刚石(DLC)薄膜,并对其抗激光损伤特性进行了研究,优化了制备工艺.对DLC薄膜激光损伤阈值(LIDT)的测试结果表明,随着厚度的增加,薄膜的LIDT开始呈下降趋势,当厚度达到100nm以上时,则趋于一个稳定值.正交实验结果的处理和分析表明,在所给定的工艺参数范围内,主回路电压是影响DLC膜抗激光损伤性能的最主要因素,基片温度、清洗时间和脉冲频率则影响较小.为得到较好的抗激光损伤能力,采用PVAD技术制备DLC薄膜的最佳工艺参数为:清洗时间20 min、基片温度150℃、脉冲频率5 Hz、主回路电压150 V.退火处理会使DLC薄膜的激光损伤阈值明显提高.     

不同技术制备DLC膜的激光损伤特性研究

随着高能量大功率激光器的发展和激光元件的广泛应用,用于红外窗口表面增透保护的类金刚石薄膜(DLC)的抗激光损伤特性成为评价薄膜质量优劣的一个重要指标。然而,不同的制备方法和技术沉积的DLC薄膜具有各异的微观结构,从而具有不同的抗激光损伤特性。本文采用脉冲真空电弧(PVAD)和非平衡磁控溅射(UBMS)技术沉积了DLC膜,对两种DLC膜抗激光损伤特性进行了研究,测试结果表明,两种技术沉积的DLC薄膜激光损伤阈值分别0.6 J/cm2和0.3 J/cm2,PVAD技术比UBMS技术沉积的DLC薄膜具有更高的抗激光损伤阈值。基于实验研究了薄膜光学常数和表面形态,分析了两种技术制备DLC膜激光损伤特性差异的主要原因。结果表明,采用UBMS技术沉积的DLC膜具有较小的折射率和较大的消光系数,薄膜表面存在较多的疵病和缺陷,这些是其激光损伤阈值较低的主要原因。     

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。     

不锈钢衬底两面同时液相电沉积类金刚石薄膜及其沉积机理研究

为了利用液相电沉积技术实现在金属衬底表面全方位电沉积类金刚石(DLC)薄膜,采用不同尺度的不锈钢片作为衬底,在表面电沉积了DLC薄膜,利用X射线光电子能谱、Raman光谱和扫描电子显微镜分别对衬底两面薄膜的化学成分、微观结构和表面形貌进行了分析。结果显示:对于尺度大于石墨阳极的不锈钢衬底,仅在衬底正对着阳极的一面实现了DLC薄膜的沉积;而对于尺度小于阳极的不锈钢衬底,在衬底两面都有DLC薄膜沉积,且两面薄膜结构相似,形貌相近。利用准静态电场理论对实验结果进行了解释,提出在金属衬底表面实现液相电沉积DLC薄膜的前提条件是存在垂直于衬底表面的电场分量,为进一步实现在复杂形状的导电性衬底表面沉积DLC薄膜提供了理论依据。     

节瘤缺陷对薄膜热力损伤的有限元分析

在多层介质薄膜中,节瘤缺陷是影响薄膜激光损伤的关键因素。为了理解节瘤缺陷对薄膜激光损伤的影响,以热传导理论为依据,通过有限元方法模拟了多层介质薄膜中的节瘤缺陷在激光辐照下的热力响应,分析了节瘤缺陷的大小和深度对热力响应的灵敏度。发现大而浅的节瘤缺陷有较高的热力响应灵敏度,因此,消除直径较大的膜层表面附近的缺陷有助于提高薄膜抗激光损伤的能力。     

DLC膜在磨损、表面改性及力电耦合作用下损伤特性

为评价超薄类金刚石（DLC）膜在使用过程中的安全状况，利用原子力显微镜（AFM）的多模式功能，从磨损、表面改性、力电失效3个方面对DLC膜进行了试验研究．研究结果表明：相同法向力作用在不同厚度薄膜的磨损深度不同；对DLC膜的形貌和电学特性进行比较发现，磨损区域导电性比未磨损区域强；在厚度为64．09nm薄膜施加正向25V电场作用下，当针尖作用在表面的压力超过一定临界压力（375nN）之后，薄膜发生击穿，形成凹坑。     

金刚石薄膜抗激光破坏研究

介绍了金刚石优异的光学和力学特性,对金刚石薄膜在从紫外到红外波段以及不同脉宽激光参数下的激光损伤行为和损伤阈值进行了评述。分析了不同激光工作参数对金刚石薄膜的激光损伤机理,认为石墨化导致晶格失稳是金刚石薄膜激光损伤的主要原因。金刚石薄膜石墨化有两种方式:垂直表面向体层方向石墨化和平行表面按分层的方式逐层石墨化。     

中频磁控溅射沉积DLC/TiAlN复合薄膜的结构与性能研究

采用中频非平衡磁控溅射沉积工艺,并施加霍尔离子源辅助沉积,在高速钢W18Cr4V及单晶硅基体上制备了梯度过渡的DIE/TiAlN复合薄膜.利用扫描电镜(SEM)、X射线光电子能谱仪(XPS)、显微硬度计、摩擦磨损仪等分析检测仪器对DLC/TiAlN复合薄膜的表面形貌、晶体结构、显微硬度、耐磨性等性能进行了检测分析.实验及分析结果表明:DLC/TrAlN薄膜平均膜厚为1.1μm,由于薄膜中的Al含量较多,使得复合薄膜的表面比DLC薄膜的表面要粗糙一些;通过对复合薄膜表层的XPS分析可知,ID/IG为2.63.由XPS深层剖析可知,DLC/TiAlN薄膜表层结构与DLC薄膜基本相同,里层则与TiAlN薄膜相似.在梯度过渡膜中,复合膜层之间的界面呈现为渐变过程,结合的非常好.DLC/TiAlN薄膜的显微硬度为2030 HV左右.与DLC薄膜显微硬度接近,低于TiAlN薄膜的显微硬度.但是DLC/TiAlN薄膜的耐磨性要好于TiAlN薄膜和DLC薄膜;DLC/TiAlN薄膜的耐腐蚀性能略好于DLC薄膜.     

类金刚石薄膜的激光损伤特性测试与分析

使用脉宽12ns，波长1064nm调Q Nd：YAG激光器对真空阴极电弧沉积（VCAD）法制备的类金刚石薄膜进行抗激光损伤测试，结果表明，VCAD法镀制的薄膜抗激光损伤阈值为0．6J／cm^2。通过对热冲击效应的数值计算，得到了光斑中心的温度场和薄膜表面的应力场分布。研究表明，热应力在类金刚石薄膜的破坏过程中起主导作用，脉冲电弧沉积的DIE薄膜的激光损伤主要源于应力破坏。     

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.     

Effect of defects on long-pulse laser-induced damage of two kinds of optical thin films

In order to study the effect of defects on the laser-induced damage of different optical thin films, we carried out damage experiments on two kinds of thin films with a 1 ms long-pulse laser. Surface-defect and subsurface-defect damage models were used to explain the damage morphology. The two-dimensional finite element method was applied to calculate the temperature and thermal-stress fields of these two films. The results show that damages of the two films are due to surface and subsurface defects, respectively. Furthermore, the different dominant defects for thin films of different structures are discussed.     

Multiscale analysis of the laser-induced damage threshold in optical coatings

We have investigated the influence of laser beam size on laser-induced damage threshold (LIDT) in the case of single- and multiple-shot irradiation. The study was performed on hafnia thin films deposited with various technologies (evaporation, sputtering, with or without ion assistance). LIDT measurements were carried out at 1064 nm and 12 ns with a spot size ranging from a few tens to a few hundreds of micrometers, in 1-on-1 and R-on-1 modes. These measurements were compared with simulations obtained with the statistical theory of laser-induced damage caused by initiating inclusions. We show how to obtain information on the initiating defect properties and the related physical damage mechanisms with a multiscale study. Under certain conditions, it is possible with this method to discriminate different defects, estimate their densities, and follow the evolution of the defects under multiple irradiation. The different metrology implications of our approach, particularly for obtaining a functional LIDT of optical components are discussed.     

Coupling effect of multi-wavelength lasers in damage performance of beam splitters at 355 nm and 1064 nm

The coupling effect between a 355 nm laser and a 1064 nm laser in damage initiation and morphology formation was investigated on beam splitters. When extra 1064 nm pulse energy was low, 355 nm laser-induced damage thresholds (LIDTs) increased because of laser conditioning, and when 1064 nm pulse energy was high enough, 355 nm LIDTs decreased. Damage morphologies were also studied to explore the damage mechanism at respective wavelengths. For the entirely different electric field intensity distributions, 355 nm laser-induced damages were mainly from nanometer-sized absorbers at upper interfaces, while initiators for the 1064 nm laser were located at substrate-coating interface or substrate subsurface. Under simultaneous illumination, the sensitive defects were still the precursors, and damages also showed the representative damage characteristics induced by a single laser, namely, 355 nm laser-induced small pits and 1064 nm laser-induced large delamination. Further studies also showed that, although the 1064 nm laser fluence was kept unchanged, delamination area grew with the increase of pits, which were induced by the 355 nm laser. A possible mechanism was proposed to interpret the delamination area growth phenomenon.     

类金刚石薄膜的紫外辐照研究

对射频等离子体方法制备的类金刚石（以下简称DLC）薄膜样品进行了紫外辐照，采用电阻率，Raman光谱及红外光谱研究了紫外光（以下简称UV）辐照对DLC薄膜结构与特征的影响，Raman光谱表明：紫外光对DLC薄膜中SP^3C-H键的破坏作用非常明显，红外（IR）光谱结果进一步验证了这一结果，经UV辐照后，DLC薄膜的电阻率呈变小趋势，这说明薄膜被强烈氧化，最后呈现石墨化趋势。     

等离子体基脉冲偏压沉积DLC膜的氢分布和氢含量

用核反应分析方法,对等离子体基脉冲偏压沉积DLC膜的氢分布和氢含量进行了较系统的研究.结果表明,用等离子体基脉冲偏压沉积技术可获得较低氢含量的DLC膜;其氢含量范围约为6at％～17at％,且氢沿膜厚是均匀分布的,随等离子体密度及离化率降低,DLC膜的氢含量增加,荷能离子对生长表面的轰击具有较强的析氢作用,工作气体中引入氢气促进DLC膜中氢的析出.     

Stress and strain in DLC films induced by electron bombardment

Radiation induced stress and strain have been investigated in amorphous hydrogenated DLC films after their exposure to high-energy (12 MeV) electrons, produced in the medical linear accelerator. DLC structures of different hydrogen contents and thickness, deposited from acetylene gas onto Si<111> wafers in the two-chamber plasmotron system were used in this investigation.Optically levered laser technique was used to measure the radius of curvature of the investigated DLC films and residual stress in the film was determined. Surface morphology of DLC films was defined by AFM “Nanotop-206”. Microhardness measurements were performed using MTS Nanoindenter G200. Bonding structure of the DLC films was analysed using the Raman scattering spectroscopy.It was found that the bombardment of DLC films with high-energy electrons introduced additional residual stress in all investigated samples. However, stress saturation tendency was observed after some fractions of the irradiation. Radiation induced stress was lower in the samples with well-organized networking structure, depending on technological conditions of the film growth. Significant deterioration of the mechanical properties of DLC films after their bombardment with high-energy electrons was not observed. Radiation induced changes in irradiated DLC films are discussed on the basis of the results of measurements.     

Synthesis of functional diamond-like carbon nanocomposite films containing titanium dioxide nanoparticles

Synthesis of diamond-like carbon (DLC) films with UV-induced-hydrophilicity function was studied by inductively-coupled plasma (ICP) chemical vapor deposition. Titanium tetraisopropoxide (TTIP) and oxygen gases were employed as the precursors to deposit diamond-like nanocomposite films containing titanium dioxide (TiO₂) nanoparticles. X-ray diffraction and high-resolution transmission electron microscopy revealed that TiO₂ nanocrystallites were formed in the DLC films when oxygen concentration was higher than TTIP concentration during deposition. The DLC nanocomposite film was hydrophobic without ultraviolet (UV) irradiation, and became highly hydrophilic under UV irradiation, exhibiting the self-cleaning effect. A very broad peak centered at 1580 cm^− 1 was observed in the Raman spectra confirming the formation of DLC films. The hardness of the film was about 8 GPa with a stress of 3 GPa. ICP was essential in forming the photocatalytic TiO₂ nanoparticles in the DLC matrix.