Laptop photothermal reflectance measurement instrument assembled with optical fiber components

In this article, we propose a laptop photothermal reflectance measurement instrument assembled with optical fiber components. The primary feature of this instrument is that all of the optical routes for the pumping and probing beams, as well as the beam sources using a laser diode, are composed of optical fiber and optical fiber components. With this configuration, the problems related to the technical shortcomings of the conventional instrument can be solved completely. Our proposed instrument is also appropriate for in situ measurement of the thermoproperties of thin film. The dimensions of our instrument's case are 400 mm wide, 250 mm deep, and 60 mm tall, and its weight is approximately 1 kg, containing the power supply for driving the laser diode of the pumping beam and electronics for the detection of photothermal reflectance. These are at least 120 and 150 smaller than the volume and weight of the conventional commercial instrument, respectively. Nevertheless, it is only necessary to prepare a synchronous detection instrument for signal recovery (e.g., lock-in amplifier) with our instrument. To evaluate our instrument's thermoproperty measurement capability, we measured the thermal diffusivity and thermal conductivity of Au thin film. The thermal diffusivity of 1.5-microm-thick Au film measured by our instrument matched previously reported values within a margin of error of a few percent.     

High-throughput analysis of thin-film stresses using arrays of micromachined cantilever beams

We report on a technique for making high-throughput residual stress measurements on thin films by means of micromachined cantilever beams and an array of parallel laser beams. In this technique, the film of interest is deposited onto a silicon substrate with micromachined cantilever beams. The residual stress in the film causes the beams to bend. The curvature of the beams, which is proportional to the residual stress in the film, is measured by scanning an array of parallel laser beams generated with a diffraction grating along the length of the beams. The reflections of the laser beams are captured using a digital camera. A heating stage enables measurement of the residual stress as a function of temperature. As the curvature of each beam is determined by the local stress in the film, the film stress can be mapped across the substrate. This feature makes the technique a useful tool for the combinatorial analysis of phase transformations in thin films, especially when combined with the use of films with lateral composition gradients. As an illustration, we apply the technique to evaluate the thermomechanical behavior of Fe-Pd binary alloys as a function of composition.     

A travelling photothermal technique employing pyroelectric detection to measure thermal diffusivity of films and coatings

A travelling thermal wave technique employing optical excitation and pyroelectric detection of thermal waves propagating along a material film/coating on a substrate is described. The method enables direct measurement of thermal diffusivity. The technique involves measurement of the phase lag undergone by an optically excited thermal wave as it propagates along the coating. The set up has been automated for convenient and fast data acquisition and analysis. The technique has been adapted to measurement of thermal diffusivity of a commercial paint sample coated on glass and copper substrates. It is found that thermal diffusivity of the coating is independent of the thermal conductivity of the substrate. Dependence of thermal diffusivity on coating thickness shows exponential increase, with value reaching a constant at a characteristic high thickness. Measurements have been carried out on a few other samples with wide variations in thermal diffusivity, and the results compared with available reports or results obtained following other techniques. Analyses of the results show that the technique allows measurement of thermal diffusivity of coatings and films with uncertainties better than ±2.5%.     

Thermal stability of Ti and Pt nanowires manufactured by Ga+ focused ion beam

Ti and Pt nanowires have been produced by ultra high‐vacuum molecular beam epitaxy deposition of Ti thin films and focused ion beam (FIB) deposition of Pt thin films, followed by cross‐sectional FIB sputtering to form electron‐transparent nanowires. The thermal stability of the nanowires has been investigated by in situ thermal cycling in a transmission electron microscope. Epitaxial single crystal Ti nanowires on (0001)Al₂O₃ substrates are microstructurally stable up to 550–600 °C, above which limited dislocation motion is activated shortly before the Ti‐wires oxidize. The amorphous FIB‐deposited Pt wires are stable up to 580–650 °C where partial crystallization is observed in vacuum. Faceted nanoparticles grow on the wire surface, growing into free space by surface diffusion and minimizing contact area with the underlying wire. The particles are face‐centred cubic (fcc) Pt with some dissolved Ga. Continued heating results in particle spheroidization, coalescence and growth, retaining the fcc structure.     

Electric charging of thin films measured using the contrast transfer function

The phase shift of electron waves due to charging of thin films is investigated using the contrast transfer properties of the microscope. We take two photos, one with film at the back focal plane and the other one without film. The phase difference between the contrast transfer functions of the two photos is evaluated using our theoretical predictions. The theoretical model is based on an analytical solution of the Laplace equation with appropriate boundary conditions. From the resulting electrostatic potential function the phase shift of electron waves is derived in a weak lens approximation. With this method, information about the radius of the electron beam and the magnitude of the electrostatic potential at the thin film is obtained. The excellent agreement between the theoretical model and experimental results is observed.     

基于离子束溅射Ta2O5薄膜的紫外吸收膜技术

为获得高性能紫外激光薄膜元件,急需研制紫外高反射吸收薄膜,实现吸收损耗的精确测量。本文采用离子束溅射技术,通过调控氧气流量实现了具有不同吸收的Ta_2O_5薄膜的制备。以Ta_2O_5薄膜作为高折射率材料,设计了355nm的紫外高反射吸收薄膜。采用离子束溅射沉积技术,在熔融石英基底上制备了355nm的吸收薄膜,对于A=5%的紫外吸收光谱,在355nm的透射率、反射率和吸收率分别为0.1%,95.0%和4.9%;对于A=12%的紫外吸收光谱,在355nm的透射率、反射率和吸收率分别为0.1%,87.4%和12.5%。实验结果表明,采用离子束溅射沉积技术,可以实现不同吸收率的355nm高反射吸收薄膜的制备,对于基于光热偏转测量技术的紫外光学薄膜弱吸收测量仪的定标具有重要的意义。     

Application of a transmission crystal x-ray spectrometer to moderate-intensity laser driven sources

In the pursuit of novel, laser-produced x-ray sources for medical imaging applications, appropriate instrumental diagnostics need to be developed concurrently. A type of transmission crystal spectroscopy has previously been demonstrated as a survey tool for sources produced by high-power and high-energy lasers. The present work demonstrates the extension of this method into the study of medium-intensity laser driven hard x-ray sources with a design that preserves resolving power while maintaining high sensitivity. Specifically, spectroscopic measurements of characteristic Kα and Kβ emissions were studied from Mo targets irradiated by a 100 fs, 200 mJ, Ti: sapphire laser with intensity of 10(17) W/cm(2) to 10(18) W∕cm(2) per shot. Using a transmission curved crystal spectrometer and off-Rowland circle imaging, resolving powers (E/ΔE) of around 300 for Mo Kα(2) at 17.37 keV were obtained with an end-to-end spectrometer efficiency of (1.13 ± 0.10) × 10(-5). This sensitivity is sufficient for registering x-ray lines with high signal to background from targets following irradiation by a single laser pulse, demonstrating the utility of this method in the study of the development of medium-intensity laser driven x-ray sources.     

表面加工多晶硅薄膜热扩散系数在线测试结构

基于目前已有的真空桥式薄膜热扩散系数测试结构和测试方法，综合考虑辐射、对流以及向衬底的传热等因素的影响，从而使得本文设计的测试结构和提取方法更具有实际价值。文中通过分析两个长度不同，但宽度与厚度相同的梁在相同加热电流下的瞬态电阻变化特性，来提取多晶硅薄膜的热扩散系数。同时利用有限元分析软件ANSYS进行了模拟分析，分析表明模拟提取值与理论值较好地吻合，从而验证了模型建立的正确性，说明该方法能够实现对多晶硅薄膜热扩散系数的在线提取，且具有较高的测试精确度。     

Deassociate the initial temporal phase deviation provided by photoelastic modulator for stroboscopic illumination polarization modulated ellipsometry

In addition to operating the imaging ellipsometric measurements by four-specific temporal phases in the photoelastic modulated ellipsometry, we added the fifth one to solve the initial phase of the photoelastic modulator. This methodology has been developed to conquer the slow imaging processing of charge-coupled device camera for the stroboscopic illumination in the polarization modulated imaging ellipsometry. Without any calibration in its initial phase, we can perform the ellipsometric measurement by the measurements of intensity at five-specific temporal phases. The intensities of a full cycle for a point on SiO(2)∕Si thin film were measured and analyzed for verifying this algorithm. The five stroboscopic illuminations were performed to measure the two-dimensional distribution of the same SiO(2)∕Si thin film.     

Laser surface hardening of 42CrMo cast steel for obtaining a wide and uniform hardened layer by shaped beams

For laser surface hardening (LSH) of large-sized workpieces, a wide and uniform hardened layer of a single track is pursued. In this study, two kinds of shaped laser beams were used in LSH of 42CrMo cast steel to obtain the required hardened layer. One is a stripy spot with uniform-intensity array spots and the other a stripy spot with intensity blowup in the edge of the whole array spots. As a comparison, a Gaussian laser beam was also adopted. A three-dimensional finite element model was used to simulate the thermal history of specific points by the latter shaped beam and the Gaussian laser beam. The surface morphology, microstructure, microhardness, and uniformity of hardened layers were studied. The results showed that a wider and more uniform hardened layer could be obtained using the latter shaped beam at relative higher scanning velocities and laser power. The thermal history of a material has an important effect on the microstructure and microhardness finally formed. Due to the high peak temperature and heating rate caused by the latter shaped beam, a higher value of microhardness in the transformation hardened zone was found.     

Laser assisted atom probe analysis of thin film on insulating substrate

We demonstrate that the atom probe analyses of metallic thin films on insulating substrates are possible using laser assisted field evaporation. The tips with metallic thin film and insulating substrate (0.6-3 μm in thickness) were prepared by the lift-out and annular ion beam milling techniques on tungsten supports. In spite of the existence of thick insulating layer between the metallic film and the tungsten support, atom probe tomography with practical mass resolution, signal-to-noise ratio and spatial resolution was found to be possible using laser assisted field evaporation.     

Nonlinear effects in transient electrothermal characterization of anatase TiO2 nanowires

As an effective transient thermal characterization technique, the transient electrothermal (TET) technique features a capability of measuring micro∕nanoscale samples of diverse electrical conducting natures. In this work, single anatase titanium dioxide (TiO(2)) nanowires fabricated using the electrospinning method are characterized using the TET technique. Time-dependent nonlinear effect is observed for both rise and fall stages in the voltage-time (U-t) response profile. The coated iridium film and soldered platinum pads possibly compromise the linear Ohmic effect and introduce undesired effects into the whole system. Two quantitative methods: generalized function analysis and direct capacitance derivation, are developed to suppress the nonlinear effect based on U-t profiles. Data processing is performed to determine the thermal diffusivity using global fitting under non-constant electrical heating. The effective thermal diffusivities from modified analysis processes stay in the range from 2 to 6 × 10(-6) m(2)/s. The results from both methods agree well with each other. The general function analysis method is also applicable for samples of short time thermal transport or for an experimental instrument that has relatively long rise time.     

The Change in Surface Properties of Magnetic Recording Media Under Pulsed Laser Application

The effects of laser heating on surface properties of magnetic recording media were systematically investigated through novel experiments and analytical simulations. When controlled laser pulses were applied onto the surface of a perpendicular magnetic recording (PMR) media, the measured values of surface roughness, surface free energy, and surface adhesive force were significantly increased with the number of the applied laser pulses. The heat transfer modeling and simulation was performed to evaluate the change in surface temperature of PMR media by the pulsed laser. The resulting temperature was not high enough to affect the carbon film and the underlying magnetic materials, but it could change the properties of the molecularly thin lubricant film on the media surface. Based on the thermal stability of the perfluoropolyether lubricant, it was found that the change of surface properties in experiments could be attributed to the thermal degradation of the lubricant through desorption process.     

ZnO薄膜非线性光学特性的实验研究

利用金属有机化学气相沉积(MOCVD)技术在蓝宝石衬底上生长一层高质量的ZnO薄膜。为了考察沉积温度对样品的非线性特性的影响,在200~500 ℃生长了一系列ZnO薄膜。用X射线衍射谱(XRD)及扫描电镜(SEM)对样品结构进行了评价。以Nd:YAG激光器输出的1.06 μm的激光为基频光,对ZnO薄膜样品的二阶及三阶非线性光学特性进行了实验研究。实验发现,对于250 ℃沉积温度的样品有较强的非线性效应,实验测得的二阶非线性极化张量 χ ⁽²⁾_ZZZ=9.2 pm/V, 三阶有效非线性系数χ⁽³⁾=5.28×10^－20 m²/V²。     

On the challenges of greyscale-based quantifications using X-ray computed microtomography

Label-free superresolution effect of nonlinear reverse saturation absorption (NRSA) thin films was investigated through difference method, where a subdiffraction-limit spot signal was constructed by intensity subtraction of two spots obtained under different laser intensities. By using annealed InSb films as the NRSA thin films, we experimentally obtained the subdiffraction-limit spot signal, and the optimal reduction ratio was approximately 52.5% of the original spot. Experimental results agreed well with theoretical simulations. The simulation results of a 9-point array sample showed the capability to achieve nonfluorescence superresolution imaging using the NRSA effect.     

薄膜疲劳失效预测方法与损伤机制的研究进展

薄膜材料的尺寸范围、结构以及其服役环境的特殊性,制约了薄膜失效行为、寿命预测及可靠性评估技术研究的开展。对薄膜疲劳寿命的预测方法进行综述,分析常用的单向循环加载法和悬臂梁弯曲法。详细介绍纳米级动态载荷法,包括连续刚度法和纳米冲击试验法,此法能够对实际服役环境更好地模拟,可以实现分相测试以及多种功能模块的原位定点检测,以及定量分析薄膜的疲劳性能。对薄膜疲劳损伤失效机制与寿命预测模型的研究进行探讨与展望,发现薄膜材料失效过程的研究与定量分析是今后研究的重点。     

Influence of substrate orientation on the morphologyand orientation of LaNiO3 thin films

LaNiO₃ thin films were successfully prepared by a chemical method from citrate precursors. The LNO precursor solution was spin‐coated onto Si (100) and Si (111) substrates. To obtain epitaxial or highly oriented films, the deposited layers were slowly heated in a gradient thermal field, with a heating rate of 1° min^?1, and annealed at 700°C. The influence of different substrate orientations on the thin film morphology was investigated using atomic force microscopy and X‐ray diffraction analysis. Well‐crystallized films with grains aligned along a certain direction were obtained on both substrates. Films deposited on both substrates were very smooth, but with a different grain size and shape depending on the crystal orientation. Films deposited on Si (100) grew in the (110) direction and had elongated grains, whereas those on Si (111) grew in the (211) direction and had a quasi‐square grain shape.     

Reconstruction of the electric charge density in thin films from the contrast transfer function measurements

The radial distribution of the beam-induced charge in thin films is investigated using the contrast transfer properties of the transmission electron microscope. The phase shift due to charging is measured as the phase difference between the contrast transfer functions of two photos taken with and without film at the back focal plane. Solving the inverse Laplace problem with this input data recovers the charge density of the measured film. The electric potential function in the whole area is reconstructed using the boundary integral method and the analytical solution of the Laplace equation for the electric potential is induced from unit step-wise surface charge. The phase shift of electron waves is derived in a weak lens approximation. In this way, the radial dependence of the charge density and the magnitude of the electrostatic potential at the thin film are obtained. The surface charge density reaches quasi-equilibrium state after the first 30 min of the electron beam pre-irradiation. The hydrocarbon contamination layer on the surface of the film is considered to be the main source of charging. An explanation of the qualitative behavior of the charge density, based on the contamination diffusion theory, is proposed.     

几种红外薄膜材料的光学特性

采用电阻蒸发和电子束蒸发方法,制备了9种红外薄膜材料的单层膜,包括氟化物、硫化物和硒化物。通过测量在可见近红外波段的透射率,采用包络线法计算出这些薄膜从可见到红外的折射率,高温退火能改善薄膜的光学性能。     

Design and implementation of a versatile and variable-frequency piezoelectric coefficient measurement system

We present a simple but versatile piezoelectric coefficient measurement system, which can measure the longitudinal and transverse piezoelectric coefficients in the pressing and bending modes, respectively, at different applied forces and a wide range of frequencies. The functionality of this measurement system has been demonstrated on three samples, including a PbZr(0.52)Ti(0.48)O(3) (PZT) piezoelectric ceramic bulk, a ZnO thin film, and a laminated piezoelectric film sensor. The static longitudinal piezoelectric coefficients of the PZT bulk and the ZnO film are estimated to be around 210 and 8.1 pC∕N, respectively. The static transverse piezoelectric coefficients of the ZnO film and the piezoelectric film sensor are determined to be, respectively, -0.284 and -0.031 C∕m(2).