连续激光荧光光谱对酚醛邻叠氮萘醌分子光分解的研究

用连续激光荧光光谱研究了感光高分子酚醛邻叠氮萘醌与激光相互作用的物理化学过程,发现了光化学反应的中间体分子及产物分子的荧光特征,提出了研究分子光分解宏观规律的激光荧光衰减法,得到了分子光分解的数学规律。     

刻蚀AlN缓冲层对硅衬底N极性n-GaN表面粗化的影响

研究了等离子体刻蚀AlN缓冲层对硅衬底N极性n-GaN表面粗化行为的影响. 实验结果表明, 表面AlN缓冲层的状态对N极性n-GaN的粗化行为影响很大, 采用等离子体刻蚀去除一部分表面AlN缓冲层即可以有效提高N极性n-GaN在KOH溶液中的粗化效果, AlN缓冲层未经任何刻蚀处理的样品粗化速度过慢, 被刻蚀完全去除AlN缓冲层的样品容易出现粗化过头的现象. 经X射线光电子能谱分析可知, 等离子体刻蚀能够提高样品表面AlN缓冲层Al 2p的电子结合能, 使得样品表面费米能级向导带底靠近, 原子含量测试表明样品表面产生了大量的N空位, N空位提供电子, 使得材料表面费米能级升高, 这降低了KOH溶液和样品表面之间的肖特基势垒, 从而有利于表面粗化的进行. 通过等离子体刻蚀掉表面部分AlN缓冲层, 改善了N极性n-GaN在KOH溶液中的粗化效果, 明显提升了对应发光二级管器件的出光功率.     

激光表面处理技术综述

<正> 材料表面处理的传统方法有渗碳、涂层、非晶化、加工硬化、冲击硬化、真空气相沉积、化学气相沉积等。而用激光对材料表面实施各种处理,则是一门新兴的处理技术,通过处理不仅可以改善材料表面的机械性能、物理性能以满足各种不同的使用要求,而且与传统的方法相比有很多优点。用激光进行材料表面处理的方法主要有以下几种:     

6H-SiC单晶的激光刻蚀及光谱分析

激光微加工是半导体精密加工的一个有效方法。对于碳化硅(SiC)单晶,使用紫外波段激光可以获得对入射能量最大的吸收效率。使用355 nm全固态激光器对6H-SiC单晶进行刻蚀。同时将样品置于不同的介质下以探究最优加工条件。使用拉曼光谱表征激光刻蚀后的SiC表面。刻蚀后表面主要由无定形硅及纳米晶石墨组成,对于空气下刻蚀的SiC晶片,无定形硅主要分布于刻蚀坑的周围,刻蚀坑内较少。而在液体下刻蚀的样品,无定形硅的空间分布相反。通过分析残留在表面的物质,在另一角度研究了激光刻蚀的反应机理。对于液体辅助的激光加工,以往的研究主要关注液层的厚度及粘度,对液体还原性的研究很少。为确定液体还原性的影响,使用共聚焦激光扫描显微镜及能量色散谱检测了不同液体辅助加工样品的表面形貌及氧含量。结果表明,液体还原性在激光刻蚀过程中有着较大的影响,使用有着还原性的液体作为介质可以有效减少表面氧化并获得更规则的表面形貌。     

单晶铁金属表面污染物的激光烧蚀机理

激光惯性约束核聚变装置中要求光学元件能够承受极高的激光通量,因此对装置内部洁净度有很高的要求.研究表明装置内部的颗粒污染物主要来源于装置内的机械结构件,杂散光作用下机械结构件表面的损伤将产生颗粒污染物.精密金属构件的激光诱导损伤问题是制约高功率激光装置超洁净制造的重要因素.由于机械结构件表面不可避免地存在污染物,因此本文基于传统的分子动力学能量耦合方式,模拟了激光与表面吸附污染物单晶铁的相互作用过程,探讨了铁材料在激光作用下的烧蚀行为,并分析了激光加载方式和激光能量密度对铁材料烧蚀的作用情况,对比研究了材料表面有无污染物对材料烧蚀的影响情况.研究表明：激光作用下铁材料表面原子在污染物原子的剧烈碰撞下呈现出不同的运动状态;激光能量瞬时加载时更容易烧蚀铁材料;当激光能量密度低于0.0064 J/cm²时,将去除铁材料表面的污染物并不会对铁材料产生烧蚀现象,进一步分析表明铁材料表面吸附污染物时更容易被激光烧蚀.研究结果可为提高高功率激光装置的内部洁净度、实现系统超洁净控制提供理论依据.     

6H-SiC单晶的激光刻蚀及光谱分析（英文）

激光微加工是半导体精密加工的一个有效方法。对于碳化硅(SiC)单晶,使用紫外波段激光可以获得对入射能量最大的吸收效率。使用355nm全固态激光器对6H-SiC单晶进行刻蚀。同时将样品置于不同的介质下以探究最优加工条件。使用拉曼光谱表征激光刻蚀后的SiC表面。刻蚀后表面主要由无定形硅及纳米晶石墨组成,对于空气下刻蚀的SiC晶片,无定形硅主要分布于刻蚀坑的周围,刻蚀坑内较少。而在液体下刻蚀的样品,无定形硅的空间分布相反。通过分析残留在表面的物质,在另一角度研究了激光刻蚀的反应机理。对于液体辅助的激光加工,以往的研究主要关注液层的厚度及粘度,对液体还原性的研究很少。为确定液体还原性的影响,使用共聚焦激光扫描显微镜及能量色散谱检测了不同液体辅助加工样品的表面形貌及氧含量。结果表明,液体还原性在激光刻蚀过程中有着较大的影响,使用有着还原性的液体作为介质可以有效减少表面氧化并获得更规则的表面形貌。     

激光等离子体光谱分析技术的发展现状

综述了近几年来应用激光等离子体光谱分析技术在不同领域所取得的研究成果,包括利用激光诱导击穿光谱学(LIBS)和激光诱导等离子体光谱学(LIPS)方法对固体样品(如金属合金、土壤、混凝土、矿物、化石、药品等)、液体样品(溶液、纯净水、液体喷射流等)和气体样品(大气、纯净气体、水蒸气和气溶胶等)中物质成分和相关特性的分析研究,以及在其他方面的研究应用;讨论了影响检测性能的因素,如激光波长、脉冲能量、功率密度、环境气氛、外加电场、样品表面涂层以及样品材料性能等对分析精确度和检出限的影响;对一些改进的实验装置及方法也进行了简单介绍。激光等离子体光谱分析技术的发展,为许多科学和应用研究创造了方便和快捷的有利条件,对科技进步有深远影响。     

光斑尺寸对连续激光辐照铝合金温度响应影响研究

为了探究不同光斑尺寸连续激光辐照6 061铝合金的温度响应及热致损伤问题,基于ANSYS有限元软件建立了激光辐照下的三维物理模型;使用不同的激光参数进行激光辐照实验,根据所采集的温度和前表面散射光强度数据,反演计算了靶材在激光辐照过程中吸收率的动态变化;最后,利用优化后的模型分析了不同光斑尺寸下,激光辐照靶材的温升特点。研究结果表明:在1 000 W/cm~2的激光辐照条件下,材料的吸收率随着温度的升高而升高;由于激光加载的局域化特征,横向热扩散影响纵向温升,光斑足够大时该影响变小,这与其热扩散长度有关;对于4 mm厚的6 061铝合金材料,当光斑尺寸大于10 cm时,光斑影响可以忽略,靶材背表面发生熔融损伤时间阈值保持2.6 s不变。     

工程陶瓷表面抗激光损伤能力研究

实验研究了纳秒激光辐照下不同材料的工程陶瓷表面的抗激光损伤能力,并与不锈钢、铝合金等金属材料进行了对比.结果表明,不同材料的工程陶瓷表面抗激光损伤特性不同;氧化铝陶瓷的损伤阈值最高,氮化硅陶瓷的损伤阈值较低.与金属材料相比较,工程陶瓷表面损伤阈值比不锈钢和铝合金高.由于材料的熔点和热传导率等热力学特性不同,不同的陶瓷材料具有不同的损伤阈值和损伤形貌.理论分析了不同材料抗激光损伤阈值的差异;陶瓷材料的吸收系数远远小于金属材料,吸收系数通过影响能量沉积区域和有效热扩散速率影响材料温度的演化过程,最终影响着材料的激光损伤阈值和损伤特性.实验结果为高功率激光装置中对抗激光损伤能力要求较高的机械支撑材料的选择提供了指导.     

激光驱动薄膜产生等离子体射流的条件分析

 以聚乙烯薄膜材料为研究对象,从实验物态方程出发,对强激光驱动薄膜材料时影响激光在薄膜后表面形成等离子体射流的主要因素,包括激光强度、波长、脉宽、气库膜材料及厚度,进行了理论和数值分析。研究表明,到达薄膜后表面的冲击波强度足够高时,能够产生气态或等离子体射流,否则卸载过程仍然为凝聚态;对于聚乙烯材料,形成等离子体射流的基本条件是到达薄膜后表面的冲击波强度达到约80 GPa以上;采用短波长、较高功率密度、较长激光脉宽的激光驱动具有低汽化温度、低电离阈值的薄靶,更容易实现等离子体射流。     

Study of temperature dependence and angular distribution of poly(9,9-dioctylfluorene) polymer films deposited by matrix-assisted pulsed laser evaporation (MAPLE)

Poly(9,9-dioctylfluorene) (PFO) polymer films were deposited by matrix-assisted pulsed laser evaporation (MAPLE) technique. The polymer was diluted (0.5 wt%) in tetrahydrofuran and, once cooled to liquid nitrogen temperature, it was irradiated with a KrF excimer laser. 10,000 laser pulses were used to deposit PFO films on 〈1 0 0〉 Si substrates at different temperatures (−16, 30, 50 and 70 °C). One PFO film was deposited with 16,000 laser pulses at a substrate temperature of 50 °C. The morphology, optical and structural properties of the films were investigated by SEM, AFM, PL and FTIR spectroscopy. SEM inspection showed different characteristic features on the film surface, like deflated balloons, droplets and entangled polymer filaments. The roughness of the films was, at least partially, controlled by substrate heating, which however had the effect to reduce the deposition rate. The increase of the laser pulse number modified the target composition and increased the surface roughness. The angular distribution of the material ejected from the target confirmed the forward ejection of the target material. PFO films presented negligible modification of the chemical structure respect to the bulk material.     

Oxygen reduction activity of N-doped carbon-based films prepared by pulsed laser deposition

Carbon-based films with nitrogen species on their surface were prepared on a glassy carbon (GC) substrate for application as a non-platinum cathode catalyst for polymer electrolyte fuel cells. Cobalt and carbon were deposited in the presence of N₂ gas using a pulsed laser deposition method and then the metal Co was removed by HCl-washing treatment. Oxygen reduction reaction (ORR) activity was electrochemically determined using a rotating disk electrode system in which the film samples on the GC substrate were replaceable. The ORR activity increased with the temperature of the GC substrate during deposition. A carbon-based film prepared at 600 °C in the presence of N₂ at 66.7 Pa showed the highest ORR activity among the tested samples (0.66 V vs. NHE). This film was composed of amorphous carbons doped with pyridine type nitrogen atoms on its surface.     

液晶显示用取向材料聚甲基丙烯酸肉桂酰氧基乙酯的光控取向研究

通过实验研究了光聚合物材料聚甲基丙烯酸肉桂酰氧基乙酯（ＣＥＭＣ）的光化学反应过程, 以及对液晶材料ＬＣ－６７１０Ａ 的取向能力． 通过原子力显微镜（ＡＦＭ）观察了取向层表面在光化学反应前后的变化, 测量了光控取向膜液晶盒中液晶分子的预倾角及单面光控取向扭曲向列液晶显示器（ＴＮＬＣＤ）的电光特性和时间响应特性曲线, 研究了液晶分子排列取向的机理．     

脉冲激光诱导金属薄膜电离的分子动力学模拟

采用分子动力学方法模拟研究了激光诱导金属薄膜的电离过程,对激光等离子体形成早期原子的运动轨迹、薄膜表面的温度变化以及原子的电离特性进行了详细分析,并探究了脉冲激光参数对原子电离过程的影响.结果表明,在激光照射过程中,薄膜表面先熔化而后又气化,气化的原子继续吸收激光能量继而电离.激光的峰值功率密度越大,原子电离速率越快,电离数目越多,薄膜表面的温度越高.脉冲宽度越小,原子电离速率越快,薄膜表面的温度越高,但原子的电离数目先增加后减小.     

UV-laser-assisted liquid phase fluorination of PMMA

Polymethylmethacrylate (PMMA) substrate was covered with liquid 1,2,3,5-tetrafluorobenzene by spin coating. Then the sample was irradiated by a KrF-excimer laser (λ = 248 nm). Thus, fluorine is released from the fluorine-containing precursor diffusing into the polymeric substrate material where it is expected to substitute the hydrogen atoms of the polymeric molecule and form a water-repellent (hydrophobic) fluorinated polymer. After drying out the polymeric substrate, the sample surface was investigated by SEM, EDX, XPS and contact angle measurement method in order to determine the fluorine content and the wettability of the treated polymeric surface as well as the substitution sites inside the polymeric molecule. The measurements indicate some chemically bonded fluorine at the top of the sample layer. A UV-photochemical fluorination mechanism is proposed based on the XPS spectra evaluation.     

Effect of substrate curvature on thickness distribution of polydimethylsiloxane thin film in spin coating process

The polymer spin coating is critical in flexible electronic manufaction and micro-electro-mechanical system(MEMS)devices due to its simple operation, and uniformly coated layers. Some researchers focus on the effects of spin coating parameters such as wafer rotating speed, the viscosity of the coating liquid and solvent evaporation on final film thickness.In this work, the influence of substrate curvature on film thickness distribution is considered. A new parameter which represents the edge bead effect ratio(re) is proposed to investigate the influence factor of edge bead effect. Several operation parameters including the curvature of the substrate and the wafer-spin speed are taken into account to study the effects on the film thickness uniformity and edge-bead ratio. The morphologies and film thickness values of the spin-coated PDMS films under various substrate curvatures and coating speeds are measured with laser confocal microscopy. According to the results, both the convex and concave substrate will help to reduce the edge-bead effect significantly and thin film with better surface morphology can be obtained at high spin speed. Additionally, the relationship between the edge-bead ratio and the thin film thickness is like parabolic curve instead of linear dependence. This work may contribute to the mass production of flexible electronic devices.     

Solvent-related effects in MAPLE mechanism

To study the role of the solvent and of the laser fluence in the matrix-assisted pulsed laser evaporation (MAPLE) process, we used a soft polymer (polydimethylsiloxane—PDMS) as “sensing surface” and toluene as solvent. Thin films of the PDMS polymer were placed in the position of the growing film, while a frozen toluene target was irradiated with an ArF laser at the conventional fluences used in MAPLE depositions (60–250 mJ/cm²). Apart the absence of solute, the MAPLE typical experimental conditions for the deposition of thin organic layers were tested. The effects on the PDMS films of the toluene target ablation, at different fluences, were studied using atomic force microscopy and contact angles measurements. The results were compared with the effects produced on similar PDMS films by four different treatments (exposure to a drop of the solvent, to saturated toluene vapors and to plasma sources of two different powers). From this comparative study, it appears that depending on the MAPLE experimental conditions: (1) the MAPLE process may be “semidry” rather than purely dry (namely the solvent is likely to be present in the deposition environment near the growing film), (2) the solvent, if sufficiently volatile, is in form of vapor molecules (neutral, ionized and probably dissociated) rather than in liquid phase near the substrate and (3) at relatively high laser fluences (>150 mJ/cm²), the formation of an intense plasma plume results which can damage/affect a soft substrate as well as a growing polymer film.     

Theoretical study on line source laser-induced surface acoustic waves in two-layer structure in ablative regime

The generation of ultrasound in film–substrate system by a laser line source is studied in the case of ablation mechanism, which can be realized by adding a liquid layer at the excitation point. The time domain displacement can be yielded by the numerical jointed inversed Laplace–Fourier transformation technique. The typical surface acoustic waves (SAW) of two layer structures, slow film on fast substrate and fast film on slow substrate, are obtained and the effect of the propagation distance and the thickness of the film on the SAW are given.     

Changes in morphology and optical properties of silver island films on transparent dielectric substrates under exposure to laser radiation

The influence of a single nanosecond laser pulse on the morphology of an island silver film was studied. It is shown that, during the pulse time span, the islands can change their shape from an arbitrary one to nearly spheroidal. The islands change their shape due to diffusion of silver atoms on the islands’ surface (self-diffusion), as well as on the substrate surface.     

Liquids microprinting through a novel film-free femtosecond laser based technique

Laser-induced forward transfer (LIFT) is a high resolution microprinting technique in which small amounts of material are transferred from a previously prepared donor thin film to a receptor substrate. The application of LIFT to liquid donor films allows depositing complex and fragile materials in solution or suspension without compromising the integrity of the deposited material. However, the main drawback of LIFT is the preparation of the donor material in thin film form, being difficult to obtain reproducible thin films with thickness uniformity and good stability.In this work we present a laser microprinting technique that is able to overcome the drawbacks associated with the preparation of the liquid film, allowing the deposition of well-defined uniform microdroplets with high reproducibility and resolution. The droplet transfer mechanism relies on the highly localized absorption of strongly focused femtosecond laser pulses underneath the free surface of the liquid contained in a reservoir.An analysis of the influence of laser pulse energy on the morphology of the printed droplets is carried out, revealing a clear correlation between the printed droplet dimensions and the laser pulse energy. Such correlation is interpreted in terms of the dynamics of the liquid displaced by a laser-generated cavitation bubble close to the free surface of the liquid. Finally, the feasibility of the technique for the production of miniaturized biosensors is tested.