硫化锌窗口上CVD法制备金刚石膜的研究进展

金刚石具有优异的红外透过性能,可作为硫化锌红外窗口的保护膜。但由于CVD金刚石的沉积过程会刻蚀硫化锌衬底,导致在窗口表面直接生长金刚石膜比较困难。本文主要综述了近年来通过添加过渡层沉积金刚石薄膜的方法和光学焊接金刚石厚膜的方法来增强硫化锌窗口的性能,并介绍了CVD金刚石膜的光学应用及其目前所存在的问题,最后对未来CVD金刚石膜发展的方向作出了展望。     

光学窗口用低应力类金刚石薄膜

类金刚石(DLC)薄膜自身具备较好的光学性能,从而在红外光学窗口具有极大的应用前景,但其残余应力决定了薄膜的稳定性。基于射频磁控溅射技术,在双面抛光Si (100)基底上,采用射频功率350 W、本底真空2.0×10^-7Pa、溅射气压7.1×10^-3Pa、氩气流量50 mL/min等工艺,沉积厚度为2.5785μm、残余应力为0.9 GPa的DLC薄膜,膜基结合力良好。Raman光谱测试显示薄膜具备DLC薄膜特性。轮廓仪测试的S_q为0.957 nm,样品表层较为平滑。利用剥离法,用3M胶带检测薄膜附着力等级达到3B,未出现薄膜脱离现象。     

金刚石-硫化锌复合窗口的弹性应变研究

对于金刚石－硫化锌复合红外光学窗口，结构中存在的热应力和挠曲度的大小对其可靠性有很大的影响。利用弹性应变模型研究了在光学焊接中不同粘接温度和金刚石厚度下金刚石－硫化锌复合窗口将发生的最大应力、曲率和衬底到边缘的挠曲率。计算结果表明，当膜厚在极值附近时，复合结构明显弯曲、ZnS表面的应力极大；如何粘接温度较高，复合结构将严重变形，ZnS中所受的应力可能会超过其自身的断裂强度。当对金刚石－硫化锌复合红外窗口设计时，了解结构中存在的热应力和挠曲度的大小是很有用的。     

空间光学窗口的热光学灵敏度分析

在试验测点温度值的基础上，利用Zernike多项式拟合出玻璃表面的温度分布，对特定的周向、径向、轴向温差和温度水平，进行窗口外玻璃热弹性分析，把节点的热变形拟合为Zernike多项式并代入ZEMAX软件求得系统波前误差的RMS。分析结果表明，在温度变化相同时，窗口外玻璃的周向温差对系统波差影响最大。     

光学元件检测技术的研究

介绍了光学非球面加工精磨阶段和抛光阶段的检测技术、柱面镜面形的测量方法、超高精度球面面形的测量方法和光学元件参数的高精度测量技术。     

CVD金刚石的高温氧化及其保护

化学气相沉积(CVD)金刚石具有优异的机械、光学和热学性能,成为高速长波红外窗口的首选材料,但是当高速飞行时,由于空气动力加热会产生很高的温度而使其迅速遭受氧化,甚至完全失效.简要概述了CVD金刚石高温氧化现象及机理、抗氧化保护的最新研究进展.     

由红外透过谱确定金刚石膜的光学常数及相关因素

结合金刚石膜的具体情况,考虑到色散效应、膜的微结构、表面粗糙度及样品中自由载流子和C-H的吸收等多种因素对红外透过谱的影响,在无吸收单层膜透过率模型的基础上进行了修正,给出了自支撑金刚石薄膜透过率的数学模型.并对不同制备方法和工艺参数下沉积的金刚石膜的红外透过谱用Levenberg-Mar-quardt算法进行非线性最小二乘拟合,从而确定出样品的红外光学常数和其它影响透过率的因素.这些结果对正确分析金刚石薄膜的红外光学性质是很重要的.     

遗传算法用于衍射光学元件的优化设计

提出了一种基于遗传算法的衍射光学元件优化设计方法;在衍射光学元件设计中遗传算法运行参数对遗传算法性能有一定的影响:采用较大的群体规模,遗传算法越容易获得最优解;交叉算子越大,遗传算法全局搜索能力越强;选择算子对遗传算法的影响不是太大;如果要进一步提高解的精度,可选取较大的终止代数。数值计算结果表明,用遗传算法优化设计的衍射光学元件,其误差小于 5.2%,衍射效率达到 91.2%。遗传算法很适合衍射光学元件的优化设计。     

MPCVD制备纳米金刚石真空窗口的研究

微波等离子体化学气相沉积装置用于制备纳米金刚石膜和纳米金刚石真空窗口,气源为H₂、CH₄、Ar和少量O₂。扫描电镜、拉曼光谱、X射线衍射仪、原子力显微镜用于表征和分析纳米金刚石膜,自制的漏气率测量装置测出纳米金刚石真空窗口漏气率。结果表明:金刚石膜厚20μm、表面平均粗糙度Ra=34.6 nm,平均晶粒尺寸35 nm,金刚石窗口漏气率为2.78×10^-9Pa·m³/s。     

用激光法合成纳米金刚石

使脉冲激光与石墨粉在空气中相互作用,并对其氧化提纯．对产物进行的显微激光拉曼光谱（Raman）与高分辨电子显微镜（HRTEM）分析表明,产物中含大量纳米金刚石颗粒,其尺寸为5nm左右,且具有较多的晶体缺陷和残余内应力．提出了石墨转变为金刚石纳米晶的机理：在脉冲激光产生的高温高压的条件下,具有石墨结构的原子团发生快速滑移切变,形成立方金刚石晶核,碳等离子体中高化学活性的碳粒子集团使金刚石晶核迅速长大,形成金刚石微晶．     

新型光学纤维材料的研究

介绍了各类新型光学纤维即红外光学纤维、聚合物光学纤维、液芯光学纤维、激光光学纤维及传感光学纤维材料及其研究进展。     

CVD金刚石膜中黑色缺陷的存在形式

采用光学显微镜在透射光、反射光和侧光模式下研究了多晶CVD金刚石厚膜中黑色缺陷的存在形式,利用X射线光电子能谱、拉曼光谱研究了黑色缺陷的组成成分。结果表明:晶界处的裂隙或者孔洞和晶粒内部的结晶缺陷是金刚石膜内部黑色缺陷的存在形式之一。     

法拉第滤光器在法拉第激光器领域研究进展

法拉第激光器是一种利用法拉第反常色散原子滤光器作为选频元件的新型外腔半导体激光器,原理上法拉第激光的输出波长随着激光二极管驱动电流及工作温度的变化,始终与原子跃迁谱线相对应,可以将激光频率有效地锁定至原子跃迁谱线,实现窄线宽的激光输出信号,并且短期与长期频率稳定性均较好。本文详细介绍了自1845年法拉第旋光效应提出以来,法拉第反常色散原子滤光器的发展历程,法拉第激光器的工作机理、发展历程以及性能优越性,并结合国内外的研究进展,介绍了法拉第激光发展各个阶段的技术瓶颈及相应的解决办法,同时展望了法拉第激光器未来在量子领域特别是量子精密测量领域的重要价值。     

Ⅱb型金刚石单晶的制备和半导体特性研究进展

Ⅱb型金刚石由于具有极佳的半导体性能，适合于制造高性能电力电子器件，可以在更高的温度和恶劣的环境下正常工作，是一种有发展前途的高温、大功率半导体材料。本文从结构、合成方法、半导体特性和应用等方面阐述了Ⅱb型半导体金刚石的研究现状，在此基础上提出了今后的研究方向。     

Formation and characterization of diamond crystals synthesized by microwave plasma CVD system

Abstract

Diamond crystals have been successfully synthesized on (100) Si wafer using microwave plasma CVD. The growth was conditioned in a flowing system in which the parameters, such as CH₄/H₂ ratio, pressure, temperature and microwave power were varied. Cubo‐octahedra or tetrakaidecahedra are the equilibrium shape of diamond single crystals obtained under all conditions and are therefore the basic unit for the formation of polycrystalline diamond films, mostly through repetitive twinning and secondary growth of diamond crystals on {100} habit planes of cubo‐octahedra. Both X‐ray diffraction and Raman spectroscopy were used to facilitate the analysis of the diamond crystallinity and purity. These qualities are similar to those of natural diamonds.     

Ion irradiation-induced modifications of diamond nanorods synthesised by microwave plasma chemical vapour deposition

Diamond nanorods (DNRs) synthesised by the high methane content in argon rich microwave plasma chemical vapour deposition (MPCVD) have been implanted with nitrogen ions. The nanorods were characterised by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The DNRs consist of single-crystalline diamond cores of 3–5?nm in diameter and several tens of nanometres in length. For purification from non-diamond contents, hydrogen plasma etching of DNRs was performed. Structural modifications of etched DNRs were studied after irradiating with 50?keV nitrogen ions under the fluence of 5?×?10¹⁴, 1?×?10¹⁵, 5?×?10¹⁵ and 1?×?10¹⁶?ions?cm^?2. Nitrogen-ion implantation changes the carbon–carbon bonding and structural state of the nanocrystalline diamond (NCD). Raman spectroscopy was used to study the structure before and after ion irradiation, indicating the coexistence of diamond and graphite in the samples. The results indicated the increase in graphitic and sp²-related content, at the expense of decrease in diamond crystallinity, for ion implantation dose of 5?×?10^15?cm^?2 and higher. The method proves valuable for the formation of hybrid nanostructures with controlled fractions of sp³–sp² bonding.     

全固态飞秒光学频率梳研究进展及展望

自1999年至今,光学频率梳（Optical Frequency Comb,OFC）经历了二十多年的快速发展。基于飞秒激光的光学频率梳在频率计量学、超快光谱学、光学频率标准、阿秒脉冲的产生、多脉冲时域合成等众多前沿研究领域中发挥了不可替代的作用。特别是继飞秒钛宝石激光频率梳、飞秒光纤激光频率梳之后,基于二极管激光直接泵浦的全固态飞秒激光频率梳由于兼具钛宝石激光噪声低、重复频率高,光纤激光结构紧凑、电光效率高的共同优势,引起了许多研究组的兴趣,并取得系列有意义的进展。本文综述了全固态光学频率梳的发展和已取得的典型应用,并结合笔者所在课题组取得的研究成果,对全固态光学频率梳未来的发展方向进行展望,为促进全固态飞秒锁模振荡器的发展提供借鉴。     

Analysis of femtosecond laser surface patterning on bulk single-crystalline diamond

Preliminary work is reported on 2-D and 3-D microstructures written directly with a Yb:YAG 1026?nm femtosecond (fs) laser on bulk chemical vapour deposition (CVD) single-crystalline diamond. Smooth graphitic lines and other structures were written on the surface of a CVD diamond sample with a thickness of 0.7?mm under low laser fluences. This capability opens up the opportunity for making electronic devices and micro-electromechanical structures on diamond substrates. The fabrication process was optimised through testing a range of laser energies at a 100?kHz repetition rate with sub-500?fs pulses. These graphitic lines and structures have been characterised using optical microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. Using these analysis techniques, the formation of sp² and sp³ bonds is explored and the ratio between sp² and sp³ bonds after fs laser patterning is quantified. We present the early findings from this study and characterise the relationship between the graphitic line formation and the different fs laser exposure conditions.     

Structural and optical properties of ultrananocrystalline diamond / InGaAs/GaAs quantum dot structures

The combination of the unique properties of ultrananocrystalline diamond (UNCD) films and of semiconductor quantum dot (QD) structures could significantly improve the performance of different electronic and optoelectronic devices, where e.g. good thermal management and advanced mechanical parameters are required. In the current work quantum dot InGaAs/GaAs heterostructures have been grown by molecular beam epitaxy (MBE) with different densities between 1.6 × 10¹⁰ cm^− 2 and 1.6 × 10¹¹ cm^− 2 controlled by the substrate temperature in the range between 490 and 515 °C. These structures were overgrown with UNCD by microwave plasma chemical vapor deposition (MWCVD) using methane/nitrogen mixtures at 570 °C. Scanning electron microscopy (SEM) reveals that without ultrasonic pretreatment the diamond nucleation density on QD structures is low and only separate islands of UNCD are deposited, while after pretreatment thin closed films are formed. From the cross-section SEM images a growth rate of ca. 3 nm/min is estimated which is very close to that on silicon at the same deposition conditions. The UNCD coatings exhibit a morphology consisting of two types of structures as shown by atomic force microscopy (AFM). The first one includes nodules with diameters between 180 and 350 nm varying with the density of the underlying QDs; the second is formed by a kind of granular substructure of these nodules with diameters of about 40 nm for all QD densities. The optical properties were investigated by photoluminescence (PL) spectroscopy before and after the deposition of UNCD. The PL signals of QD structures overgrown with UNCD, although with decreased intensity, remain almost unchanged with respect to the peak positions and widths, revealing that the UNCD/QD structures retain the optical properties of uncoated InGaAs/GaAs quantum dots.