Optoacoustic technique for thickness measurement of submicron metal coatings

The new nondestructive method for thickness measurement of submicron metal coatings on transparent substrate is developed. The method is based on the optoacoustic (OA) transformation in the system, where the coating is covered by an optically transparent liquid. Theoretical treatment of the problem consists of two steps. At the first step laser-induced thermal field in the system is calculated, taking into account the large thermal conductivity of the metal film and partial heat diffusion into the liquid. At the second step the system of wave equations for scalar potential of vibration velocities is solved. Heat sources, determined at the first step, are free form of wave equations. Three chrome coatings of different thickness (approximately 0.2, 0.3, and 0.6 μm) deposited on the quartz substrate are tested experimentally. Two different organic liquids (acetone and ethanol) are used to cover chrome coatings. Nanosecond diode-pumped Nd:YAG laser operated at the main harmonic is used to perform OA transformation (laser pulse duration is τ _L = 12 ns, the laser energy is about 0.2 mJ). Two detection modes are used. In forward mode laser pulse irradiates the film from the side of the substrate and in backward mode—from the side of the liquid. Detection of induced ultrasonic pulses is performed by the wide-band piezoelectric transducer in the liquid in both cases. The thickness of the coatings is determined by the least squares fitting of the theoretical dependencies of spectral transfer functions of OA transformation to experimental data. It is demonstrated, that the developed technique can be used for measurement of metal coatings thickness within the range from 50 nm to 5 μm with the error about 50 nm.     

基于铝浸润层的超薄银透明导电薄膜研究北大核心CSCD

超薄银薄膜具有高柔韧性和优良的光电性能,是用于透明导电电极的潜在材料。通过电阻热蒸发技术以金属铝作为浸润层制备超薄银透明导电薄膜。引入铝浸润层降低银薄膜的阈值厚度,使银薄膜在K9玻璃基底上以尽可能低的厚度达到连续。对不同厚度铝浸润层上银薄膜方块电阻进行测试,经SEM图像验证后得出,1 nm铝浸润层对银薄膜具有较好的浸润效果。随后采用相同的工艺在1 nm铝浸润层上制备了不同厚度的银薄膜,透过率和方阻测试结果表明,1 nm铝浸润层上制备的10 nm银薄膜方阻值可达到13Ω/,其在0.4μm~2.5μm波段内透过率可达到50%以上。     

Thickness optimization of Mo films for Cu（InGa）Se2 solar cell applications

Mo thin films are deposited on soda lime glass (SLG) substrates using DC magnetron sputtering. The Mo film thicknesses are varied from 0.08 μm to 1.5 μm to gain a better understanding of the growth process of the film. The residual stresses and the structural properties of these films are investigated, with attention paid particularly to the film thickness dependence of these properties. Residual stress decreases and yields a typical tensile-to-compressive stress transition with the increase of film thickness at the first stages of film growth. The stress tends to be stable with the further increase of film thickness. Using the Mo film with an optimum thickness of 1 μm as the back contact, the Cu(InGa)Se2 solar cell can reach a conversion efficiency of 13.15%.     

用干涉方法测量薄膜应力

基于基片弯曲法和牛顿环的基本原理,使用He-Ne激光器、扩束镜、凸透镜和带分光镜的移测显微镜,搭建了薄膜应力测量装置.采用直流溅射法制备了厚度为30~144 nm的银薄膜,衬底采用厚度为0.15 mm、直径为18 mm的圆形玻璃片.实验发现,薄膜厚度对银薄膜的内应力有显著的影响,在薄膜厚度很小时,随着薄膜厚度的增加,应力迅速增大,达到最大值后,随着厚度的继续增加,薄膜应力下降较快并趋于稳定值.     

Influence of thermal diffusion on the laser ablation of thin polymer films

The laser ablation of a photosensitive triazene polymer was investigated with a ns XeCl excimer laser over a broad range of thicknesses (10–400 nm). We found that the ablation threshold fluence increased dramatically with decreasing film thickness for films thinner than 50 nm. Ablation on substrates with different thermal properties (sapphire, fused silica, PMMA) was investigated as well, and a clear influence of the substrate material was obtained. A mathematical model combining thermal diffusion and absorption effects was used to explain the experimental data. The model is in good agreement with the experimental data and shows that heat diffusion into the substrate plays a crucial role for the ablation process of very thin films. PACS 52.38.Mf; 44.05.+e; 81.05.Lg     

基于带电粒子活化法开展的SGⅡ-U皮秒激光质子加速实验研究

基于带电粒子活化测谱方法在SGⅡ-U装置上开展了皮秒激光靶背鞘场机制质子加速实验研究,对靶参数进行了优化.利用带电粒子活化测谱方法测量了相同激光条件、不同Cu薄膜靶厚度情况下靶背鞘场加速质子的最高截止能量、角分布、总产额以及激光能量到质子的转化效率等关键参数.实验发现,SGⅡ-U皮秒激光靶背鞘场加速机制的最佳Cu薄膜靶厚度为10 μm,对应质子最高能量接近40 MeV,质子（>4 MeV）总产额约4×10¹²个,激光能量到质子的转化效率约2%.薄膜靶更厚或者更薄都会降低加速质子的最高截止能量;当靶厚减薄至1 μm时,皮秒激光的预脉冲开始对靶背鞘场产生显著影响,质子最高截止能量急剧下降,高能质子束斑呈现空心结构;而当靶厚增加至35 μm时,虽然质子束的能量有所降低,但是质子束斑的均匀性更好.     

Microstructure parameters and optical properties of cadmium ferrite thin films of variable thickness

CdFe₂O₄ thin films of different thicknesses were deposited onto glass substrates by the thermal evaporation technique. Their structural characteristics were studied by X-ray diffraction (XRD). The microstructure parameters, crystallite size, and microstrain were calculated. It is observed that both the crystallite size increases and microstrain increase with increasing with the film thickness. The fundamental optical parameters like absorption coefficient and optical band gap are calculated in the strong absorption region of transmittance and reflectance spectrum. The refractive indices have been evaluated in terms of the envelope method, which has been suggested by Swanepoel in the transparent region. The refractive index can be extrapolated by the Cauchy dispersion relationship over the whole spectra range, which extended from 400 to 2500 nm. The refractive index, n, increases on increasing the film thickness up to 733 nm and the variation of n with higher thickness lies within the experimental errors.     

Microstructural parameters and optical constants of ZnTe thin films with various thicknesses

Different thickness of polycrystalline ZnTe films have been deposited onto glass substrates at room temperature by vacuum evaporation technique. The structural characteristics studied by X-ray diffraction (XRD) showed that the films are polycrystalline and have a zinc blende (cubic) structure. The calculated microstructure parameters revealed that the crystallite size increases and microstrain decreases with increasing film thickness. The transmittance and reflectance have been measured at normal and near normal incidence, respectively, in the spectral range 400-2500 nm. For ZnTe films of different thicknesses, the dependence of absorption coefficient, α on the photon energy showed the occurrence of a direct transition with band gap energy (For ZnTe films of different thicknesses) confirming the independency of deduced energy gap on film thickness. The refractive indices have been evaluated in terms of envelope method, which has been suggested by Swanepoul in the transparent region. The refractive index could be extrapolated by Cauchy dispersion relationship over the whole spectra range, which extended from 400 to 2500 nm. It was observed that the refractive index, n increased upon increasing the film thickness up to 508 nm, lying within the experimental error for further increases in film thickness.     

Enhanced dielectric constant resolution of thin insulating films by electrostatic force microscopy

Electrostatic force microscopy has been shown to be a useful tool to determine the dielectric constant of insulating films of nanometer thicknesses that play a key role in many electrical, optical and biological phenomena. Previous approaches have made use of simple analytical formulas to analyze the experimental data for thin insulating films deposited directly on a metallic substrate. Here we show that the sensitivity of the EFM signal to changes in the dielectric constant of the thin film can be enhanced by using dielectric substrates with low dielectric constants. We present detailed numerical calculations of the tip-sample electrostatic interaction in the following setup: an insulating thin film, a dielectric substrate (or spacing layer) of known low dielectric constant and a metallic electrode. The EFM sensitivity to the dielectric constant increases with the thickness of the spacing layer and saturates for thicknesses above 100-300 nm, when it is close to that of an infinite medium.     

Ablation of transparent solids during self-limited deposition of diamond-like films from liquid hydrocarbons

A novel effect is studied of self-limitation of the diamond-like film thickness during laser irradiation of the interface of transparent substrates with liquid aromatic hydrocarbons. The interface is exposed through the transparent substrate to radiation of a copper vapor laser (wavelength of 510.6 nm, pulse duration of 20 ns). The thickness of diamond-like film increases linearly to 80-100 nm with the number of laser pulses and then saturates, while the substrate is ablated with nearly constant rate. This ablation rate depends on the thermal expansion coefficient of the substrate (glass, fused silica, sapphire, or CaF₂). The absorption of extinction coefficient of deposited films measured by ellipsometry is of order of 10⁴ cm^-1 and is sufficient to cause the significant heating of the interface. The ablation of the transparent substrates is due to their unequal thermal expansion compared to the diamond-like film having different thermal expansion coefficient. The measured ablation rates scale from 0.2 Å/pulse for glass to 4.5 Å/pulse for CaF₂. A 7m spatial resolution of the ablation process has been demonstrated for fused silica.     

调QNd∶YAG环形腔外腔倍频技术研究

用磷酸氧钛钾 (KTP)作为倍频晶体 ,对Nd∶YAG声光调Q激光的环形腔外腔倍频技术进行了实验和理论的研究 ,利用最大平均功率 5 0W、声光调Q、输出频率 10 0 5Hz、灯抽运Nd∶YAG激光器做为基频光光源 ,在基频输入功率 35W时 ,获得了大约为 31.4 %的光光转换效率的绿光输出。从实验结果分析了环形腔倍频的特性 ,指出了该方法的优缺点。从光束质量和聚焦光斑直径方面 ,对基频光和二次谐波进行了比较 ,提供了利用CCD测得光斑的部分图片 ,分析了环形腔倍频的工作原理 ,解决了困扰倍频技术的转换效率问题和光束质量问题     

Direct current magnetron sputter-deposited ZnO thin films

Zinc oxide (ZnO) is a very promising electronic material for emerging transparent large-area electronic applications including thin-film sensors, transistors and solar cells. We fabricated ZnO thin films by employing direct current (DC) magnetron sputtering deposition technique. ZnO films with different thicknesses ranging from 150 nm to 750 nm were deposited on glass substrates. The deposition pressure and the substrate temperature were varied from 12 mTorr to 25 mTorr, and from room temperature to 450 °C, respectively. The influence of the film thickness, deposition pressure and the substrate temperature on structural and optical properties of the ZnO films was investigated using atomic force microscopy (AFM) and ultraviolet-visible (UV-Vis) spectrometer. The experimental results reveal that the film thickness, deposition pressure and the substrate temperature play significant role in the structural formation and the optical properties of the deposited ZnO thin films.     

Laser decoration of precious metals

A technique for the laser coloration of precious metals is described that is based on the oxidation of a titanium film deposited on the surface of a metal. When laser radiation acts on the film, it is heated and oxidizes. Depending on the radiation parameters, the resulting oxide films have different thicknesses and, due to light interference, they acquire different colors. The visible color of the surface depends on the angle of viewing after imaging. The aim of this work is to identify the color palette of a gold plate’s surface with a thin film of titanium deposited on it. The titanium film is oxidized via fiber laser irradiation with a wavelength of 1.064 μm. Samples of color palettes are examined spectrophotometrically, and the chemical and mechanical stability of the resulting oxide coatings are tested.     

人眼安全激光测距与红外成像滤光膜的研制

从人眼安全的角度,设计并制备了对1 064 nm激光抑制并可用于1 550 nm激光测距以及3 m～5 m波段红外成像的滤光膜。选用ZnS、YbF3作为膜料组合、多光谱ZnS作为基底,利用薄膜设计软件对薄膜进行了优化设计。膜系设计通过合理的厚度控制和膜层安排,来增强薄膜的机械强度。滤光膜的制备采用了电子束沉积技术,通过离子辅助沉积和真空退火处理技术,进一步提高滤光膜的牢固性。光谱测试表明:在1 064 nm处的透射率仅为0.5%,1 550 nm处的透过率为99.3%,3 m～5 m波段的平均透过率大于96%,经分析YbF3的折射率在薄膜沉积过程中有所提高,但是对光谱曲线影响不大;可靠性测试表明:滤光膜能够耐受恶劣的环境考验,满足使用要求。     

基于PET基底透明屏蔽膜的制备研究

为满足光学器件透红外屏蔽电磁波的要求,在PET柔性基底上制作了金属网栅透明屏蔽膜.分析网栅参数对其屏蔽效率及透过率的影响,选取结构参数.针对PET基底的柔性特点及其热稳定性,经试验研究优化光刻工艺中的提拉速度、烘烤时间及温度等参数,从而得到高质量的图形结构.采用磁控溅射法制备透明屏蔽膜,通过优化溅射功率、溅射气压等参数使膜/基结合更牢固.最后得到线宽为3μm、周期为250μm的金属网栅透明屏蔽膜.采用分光光度计测得其在300~2 200nm波段的平均透过率为77%;采用屏蔽室法测得其在2~18GHz频段的电磁屏蔽效率为12dB以上.     

Study on metal microparticle content of the material transferred with Absorbing Film Assisted Laser Induced Forward Transfer when using silver absorbing layer

Absorbing Film Assisted Laser Induced Forward Transfer (AFA-LIFT) is a modified LIFT method where a high absorption coefficient thin film coating of a transparent substrate is used to transform the laser energy into kinetic in order to transfer the “target” material spread on it. This method can be used for the transfer of biomaterials and living cells, which could be damaged by direct irradiation of the laser beam. In previous experiments, ∼50-100 nm thick metal films have been used as absorbing layer. The transferred material can also contain metal microparticles originating from the absorbing thin film and acting as non-desired impurities in some cases. The aim of our work was to study how the properties (number, size and covered area) of metal particles transferred during the AFA-LIFT process depend on film thickness and the applied fluence. Silver thin films with different thickness (50-400 nm) were used as absorbing layers and real experimental conditions were modeled by a 100 μm thick water layer. The particles transferred without the use of water layer were also studied. The threshold laser fluence for the complete removal of the absorber from the irradiated area was found to strongly increase with increasing film thickness. The deposited micrometer and submicrometer particles were observed with optical microscope and atomic force microscope. Their size ranged from 100 nm to 20 μm and depended on the laser fluence. The increase in fluence resulted in an increasing number of particles of smaller average size.     

Laser direct imaging of transparent indium tin oxide electrodes using high speed stitching techniques

To accomplish an electrode patterning in large area, we present a high speed stitching technique used in an ultraviolet laser processing system and investigate the interaction between laser beams and indium tin oxide (ITO) thin films deposited on glass substrates. After optimizing the process parameters of the laser direct imaging (LDI) for the large-area electrode patterning, the ablated lines looked like regularly fish-scale marks of about a 40 μm diameter and a 120 nm depth around the processing path. The parameters includes the laser power of 1W, the scanning speed of galvanometers of 800 mm/s, and the laser pulse repetition frequency of 50 kHz. Moreover, the resistance value of the ablated ITO thin film is larger than 200MΩ that is electrically insulated from the other regions of electrode structure. LDI technology with UV laser beam has great potential applications in patterning on wafer or sapphire substrates and patterning a conductive layer deposited on the touch panels for semiconductor and optoelectric industries, respectively.     

Effects of Ag layer and ZnO top layer thicknesses on the physical properties of ZnO/Ag/Zno multilayer system

Two groups of transparent conductive ZnO/Ag/ZnO, ZAZ, multilayer coatings were successively deposited by direct current (DC) magnetron sputtering. Sputtering was carried out from zinc (Zn) and silver (Ag) metallic targets. The effects of Ag layer thickness and ZnO top layer thickness on the properties of the ZAZ multilayer system were examined using different analytical methods. The influences of the Ag layer thickness and ZnO top layer thickness on structural properties were studied using X-ray diffraction. The thicknesses of ZAZ multilayer system were determined using X-ray reflectometry. A sheet resistance of 2.3 Ω/sq at an Ag layer thickness of 17.7 nm was obtained. The sheet resistance changes slightly with ZnO top layer thickness. The optical properties of the films were analyzed. Both Ag layer thickness and ZnO top layer thickness affect transmittance. The optical constants of the ZAZ multilayer system were calculated from transmittance and reflectance measurements. The figure of merit was applied on the ZAZ coatings and the most suitable films for the application as transparent conductive electrodes were determined.     

Resonance characteristics of localized plasmonic structures with periodic ZnO nano-patterns

Localized plasmonic structures with the periodic ZnO nano-patterns are demonstrated to increase the sensing characteristics of plasmonic sensor. The ZnO nano-patterns with 30 and 50 nm thicknesses are formed on the Au thin film of 50 nm, which have the periodic nano-patterns of 300 nm. Localized plasmonic structures are optimized using the three-dimensional finite-difference time-domain method as a function of incident angle for the width and thickness of the ZnO nano-structures. Localized plasmonic structures with the periodic ZnO nano-holes are fabricated using the double exposure technique by laser interference lithography. The measured resonance angles of 47.5° and 54° are obtained in the localized plasmonic structures with the periodic ZnO nano-patterns of 30 and 50 nm thicknesses, respectively.     

All-fiber wavelength-swept laser near 2 μm

We report, for the first time to our knowledge, an all-fiber wavelength-swept Tm-doped laser based on a fiber Fabry-Perot tunable filter in the 2 μm spectral region. The laser wavelength can be continuously tuned over 200 nm from 1840 to 2040 nm in a short period of time. The demonstrated tuning speed was 12.5 μm/s with a tuning efficiency of 17.5 nm/V. The spectral linewidth of the laser was measured to be approximately 300 MHz or 0.01 cm(-1). This kind of laser can find potential applications in both high-resolution laser spectroscopy and tunable mid-IR generation via nonlinear frequency conversion.