Investigation of Micromechanical Structures by Photoacoustic Elastic Bending Method

Photoacoustic (PA) and photothermal (PT) science and technology extensively developed new methods for the investigation of micro (nano)-mechanical structures. PA and PT effects can be important also as driven mechanisms for optically excited micromechanical structures. The photoacoustic elastic bending method (PA-EBM) is based on the optical excitation of the micromechanical structure and detection of the acoustic response (PA signal) with a very sensitive PA detection system. The experimental PA elastic bending signals of the whole micromechanical structure were measured by using a special constructed PA cell (the gas-microphone detection technique with transmission configuration). The PA amplitude and phase spectra were measured, as a function of the modulation frequency in a frequency range from 20?Hz to 20?000?Hz, for different samples (Si chip with square membrane). The electronic and thermal elastic PA effects (electronic deformation and thermoelastic mechanisms of elastic wave generation) in a Si simply supported rectangular plate (3D geometry), photogenerated by a uniform and intensity-modulated optical beam, were studied. The theoretical model for the PA elastic bending frequency distribution by using the Green function method was given. The amplitude and phase PA signals were calculated and analyzed, including the thermalization and surface and volume recombination heat sources. The theoretical results were compared with experimental data.     

Bending of Semiconducting Cantilevers Under Photothermal Excitation

In this study, the elastic vibrations of semiconducting cantilevers, which were excited with a frequency-modulated uniform laser beam, were studied theoretically and experimentally. The three-dimensional distributions for the carrier density and temperature were obtained analytically using the Green function method. The elastic bending of a cantilever was given by the theory of a thin rectangular plate. Using an optical interferometric setup, the experimental photothermal signals were investigated near the first resonant frequency and the results showed that the theoretical calculation results were in good agreement with that of the experimental measurement.     

Recovery of the Elastic Constants from Wavespeed Measurements in Viscoelastic Composites by Photoacoustic Technique

Mixtures of black rubber (natural rubber) vulcanizates containing various concentrations of sand particles, as hard fillers, were prepared to determine their elastic constants at low and high frequency using the photoacoustic technique. These parameters are related with the degree of sand filler dispersion which determines the changes in stiffness, as well as its potential as reinforcement material for treads in tires. The constants are recovered through measurements of the longitudinal wave and complemented with the predictions from the Kerner model to obtain the Poisson’s ratio. Some results are corroborated with tension and compression tests. The acoustic waves are acquired by two piezoelectric transducers, one centered at 3 kHz and the other at 240 kHz. The results show a slight increase in Young’s modulus at low frequencies; meanwhile at high frequencies, it increases by two orders of magnitude. In addition, we found that on adding small amounts of prepared sand, the stiffness increases and this is particularly convenient to reduce the energy losses by the rolling resistance in automotive vehicles.     

电偶腐蚀法制备多孔硅的研究EI

用电偶腐蚀法制备多孔硅,主要研究了铂电极的优化制备工艺以及腐蚀条件对多孔硅厚度的影响,并且结合SEM,AFM等测试手段对所制备的多孔硅的表面形貌进行了分析。实验发现,在相同的腐蚀条件下,多孔硅的厚度随铂电极的厚度以及铂电极与腐蚀硅片的面积比的增大而增大。     

Influence of Plasma Waves on the Photoacoustic Signal of Silicon Samples

This article presents the results of theoretical and experimental studies of the influence of plasma waves on the photoacoustic signals of Si samples. The aim of these investigations was to find and examine the sensitive measurement configurations and the configurations of the sample in the photoacoustic cell for detection and measurement of the lifetime of excess carriers. Two measurement configurations were examined: transmission and phase lag and two configurations of the sample in the photoacoustic cell. This article demonstrates that both configurations for samples with differently prepared surfaces are effective for observation and detection of plasma waves with the photoacoustic method.     

用光声法测量陶瓷材料的热参量

以固体光声效应的RG理论为依据,用光声法测量了压电陶瓷材料PZT的热参量。实验结果表明:用此方法只需要测出一个量就能同时确定PZT的α、k和C的值,并且实验设备简单,速度快,是一种很有前途的测热参量方法。     

Enhanced Performance of a Molecular Photoacoustic Imaging Agent by Encapsulation in Mesoporous Silicon Nanoparticles

Photoacoustic (PA) imaging allows visualization of the physiology and pathology of tissues with good spatial resolution and relatively deep tissue penetration. The method converts near‐infrared (NIR) laser excitation into thermal expansion, generating pressure transients that are detected with an acoustic transducer. Here, we find that the response of the PA contrast agent indocyanine green (ICG) can be enhanced 17‐fold when it is sealed within a rigid nanoparticle. ICG encapsulated in particles composed of porous silicon (pSiNP), porous silica, or calcium silicate all show greater PA contrast relative to equivalent quantities of free ICG, with the pSiNPs showing the strongest enhancement. A liposomal formulation of ICG performs similar to free ICG, suggesting that a rigid host nanostructure is necessary to enhance ICG performance. The improved response of the nanoparticle formulations is attributed to the low thermal conductivity of the porous inorganic hosts and their ability to protect the ICG payload from photolytic and/or thermal degradation. The translational potential of ICG‐loaded pSiNPs as photoacoustic probes is demonstrated via imaging of a whole mouse brain.     

Bending of Circular Sandwich Plate on Elastic Foundation

Bending of elastic circular sandwich plate with light filler, which is on an elastic foundation, is considered. To describe the kinematics of plate bending that is nonsymmetric in sandwich thickness, broken normal hypotheses are accepted. The foundation reaction is described by the Winkler model. The load is local symmetrical. A set of equilibrium equations and their exact solution in displacements have been obtained. Numerical results for a metal-polymeric sandwich plate are given. __________ Translated from Problemy Prochnosti, No. 6, pp. 68 – 78, November – December, 2005.     

纳米Si薄膜光学性质和弹性常数的研究

采用基于密度泛函理论的第一性原理的方法,对厚度为0.54～3.30nm纳米Si薄膜的电子结构、光学性质及弹性常数进行了计算。结果表明,纳米Si薄膜是直接带隙半导体材料;随着纳米Si薄膜厚度的减小,带隙逐渐增大;薄膜的光学吸收边发生蓝移,吸收带出现宽化现象;弹性常数、杨氏模量和泊松比呈现尺寸效应。     

Study of the Solidification Dynamic of a Photocurable Resin by Photoacoustic

This paper reports on the photoacoustic (PA) study of a photopolymer (resin) that changes its physical properties when being irradiated with ultraviolet light from a xenon lamp. The wavelength range necessary for the curing of the resin, characterized by the PA technique, was found to be between 300 nm and 400 nm. PA measurements show a sigmoidal change of heat transport properties as a function of time during the curing process. By describing the PA signal evolution by a parametrized model, a characteristic curing time was introduced. The PA measurements were complemented with UV–Vis Spectroscopy, which was used to characterize the polymer in order to study the optical absorption. The proposed method can support the optimization of the settings of curing parameters in applications of stereolithography and 3D printing.     

后天抑制剂取向硅钢析出物的研究

采用"后天抑制剂法"制备取向硅钢,通过TEM研究热轧、常化、脱C和渗N阶段析出物的类型和分布。结果表明,热轧、常化和脱C板中的析出物主要是AlN颗粒,AlN颗粒在热轧、常化和脱C板中分布密度低;渗N后钢中形成非晶态Si3N4颗粒,非晶态Si3N4颗粒有多边形大块状和规则小四方形2种形貌,多边形大块状Si3N4颗粒分布在晶界,规则小四方形Si3N4颗粒主要分布在晶内。     

单晶硅纳米梁杨氏模量的弯曲测试

为研究纳米梁的力学特性,采用SOI晶圆制备了硅双端固支梁纳米梁,利用典型的原子力显微镜（AFM）弯曲测试方法测试了硅纳米梁〈100〉晶向的杨氏模量.AFM悬臂探针定位在纳米梁的中点处向下移动,纳米梁受到挤压发生弹性形变,形变过程存在一个最大形变点,在该点后,纳米梁被挤压在SOI硅片底层硅上.最大形变前的测试数据用于计算力-位移曲线斜率,最大形变后的测试数据用于计算探针的灵敏度,其实验值分别为0.792N/m和81.83nm/V.最终得到的杨氏模量为104GPa,该值小于体硅的杨氏模量,表面应力和缺陷可能是导致实验值偏小的原因.     

Alternative Method to Characterize Corn Grain by Means of Photoacoustic Spectroscopy

The application of photothermal (PT) techniques to obtain the optical and thermal properties of different materials has been widely reported in the literature. Among the PT techniques, photoacoustic spectroscopy stands out because this technique has been used to characterize different types of materials in solid, liquid, and gaseous phases, as well as homogeneous and inhomogeneous samples as biological materials which present great complexity in their structure. In particular, the seeds and corn kernels comprise different structural components such as endosperm, pericarp, embryo, and pedicel. The color attribute is very important in the grains because it gives information about the chemical composition and nutritional quality attributes which are important in consumer acceptance. In this investigation optical absorption spectra of corn grains were obtained by using photoacoustic spectroscopy in a wavelength range from 325 nm to 800 nm. Two varieties of corn grains were studied, establishing a complete block design at random for the measurements. From the obtained optical absorption spectra, the optical absorption coefficient ( $\beta $ ) was calculated as a function of the wavelength for each sample. A complementary study of the percentage of reflectance for these samples was carried out by using ultraviolet/visible spectrometry with an integrating sphere. The data were subjected to an analysis of the variance using software of the statistical analysis system. The results revealed significant differences ( $P\le 0.05$ ) between corn varieties in the range of 325 nm to 670 nm. The application of the photoacoustic spectroscopy technique as an alternative to conventional methods for the characterization of maize grain through an analysis of $\beta $ could be important for characterizing non-homogeneous materials like grains of corn, whose characterization is relevant in the food industry.     

Measurement of the Thermal Diffusivity of Metallic Foils and Films by the Photoacoustic Method1

The thermal diffusivities of four kinds of metallic foils from 20 to 200m in thickness were measured by a photoacoustic method on the basis of the Rosencwaig and Gersho theory. The measured data for continuous foils of uniform microscopic structure almost agreed with the literature values. Measurements were also carried out on two kinds of metallic thin films with of 10m thickness produced by sputtering. The difference in thermal diffusivity between the foils and the sputtered films depended on the uniformity of the microscopic structure.     

Study on the Phase Transition of Lanthanide-Doped Titania Nanoparticles by Photoacoustic Spectroscopy

In this study, fairly uniform anatase TiO₂ spheres doped with neodymium (III) have been prepared. It is found that the impregnation of neodymium (III) can remarkably inhibit the anatase?Crutile transition. In order to analyze the correlation of the dopant effect with the local environment of neodymium (III) ions, photoacoustic spectra of the f?Cf transitions of neodymium (III) have been studied. The variation of the nephelauxetic parameters can be attributed to the substitutional neodymium (III) ions at low doping level (???1?mol%), and to both the substitutional and interstitial neodymium (III) ions at high doping level (1?mol% to 8?mol%). The phase transformation mechanism of the samples has been interpreted based on the X-ray diffraction and transmission electron microscopy results. The nephelauxetic parameters are the same for all the samples calcined at 1150?°C. This is due to the segregation of neodymium (III) ions in the samples as a separated phase.