ZnO thin film with nanorod arrays applied to fluid sensor

A ZnO guiding layer with nanorod arrays grown on a 90°-rotated ST-cut (42°45) quartz substrate was used to fabricate a Love wave fluid sensor. ZnO nanorod arrays synthesized on the guiding layer enhance the sensitivity of the flow rate. ZnO thin films were deposited by radio frequency magnetron sputtering and ZnO nanorod arrays were then synthesized on the thin films via the hydrothermal method. The crystalline structure and surface morphology of ZnO thin films and nanorod arrays were examined by X-ray diffraction and scanning electron microscopy. The effects of the thickness of ZnO thin film and the surface morphology of ZnO nanorod arrays on the sensitivity of flow rate were investigated. A linear response between flow rate and the return loss of the sensor with one-port resonator type can be obtained by adjusting the thickness of ZnO thin film and the length of nanorod arrays.     

Effect of nanofluids on thin film evaporation in microchannels

A thin film evaporation model based on the augmented Young–Laplace equation and kinetic theories was developed to describe the nanofluid effects on the extended evaporating meniscus in a microchannel. The nanofluid effects include the structural disjoining pressure, a thin porous coating layer at the surface formed by the nanoparticle deposition and the thermophysical property variations compared with the base fluid. The results show that the nanofluid thermal conductivity enhancement mainly due to the Brownian motion tends to greatly increase the liquid film thickness and the thin film heat transfer. The structural disjoining pressure effect tends to enhance the nanofluid spreading capability and the thin film evaporation. The nanoparticle-deposited porous coating layer improves the surface wettability while significantly reducing the thin film evaporation with increasing layer thickness due to the thermal resistance across this layer. The nanofluid thermal conductivity enhancement together with the structural disjoining pressure effect can not counteract the thermal resistance effects of the porous coating layer when the coating layer thickness is sufficiently large.     

Magnetic phase diagram in a quasi-two-dimensional electron gas

Using spin density functional theory within the framework of the local spin density approximation with Perdew-Zunger type exchange-correlation energy, ferromagnetism in a quasi-two-dimensional electron gas (Q-2DEG) is studied. The electronic and magnetic structures of a thin film are calculated as a function of film thickness and electron density. Ferromagnetism in the Q-2DEG is found to appear at a higher electron density than in the three-dimensional electron gas. Unless a film is very thin, with decreasing electron density, a magnetic phase transition occurs from a spin-unpolarized fluid to a Wigner film with surface magnetism, in which the spin polarization localizes only in the neighborhood of surfaces. Further decreasing density induces another transition to a fully spin-polarized ferromagnetic Wigner film.     

Study on the damage of SiO2 thin films on LiNbO3 crystal in optical parametric oscillator by XRD spectrometry

In an attempt to elucidate the damage in high transmission thin films on LiNbO3 crystal in optical parametric oscillator, the authors employed XRD spectrometry to investigate the spectrum of laser-induced damage in thin film as well as the morphology of the damage. The authors observed that the damage of thin film was characterized by the depressions/craters in the surface of the films, which were surrounded by a deposition layer with the deceasing thickness from the center of the craters. The XRD measurements indicate that the film was crystallized. The authors analyzed the causes of morphologies and the mechanism of crystallization with the aid of the model for impurity-induced damage in thin solid films. The crystallization was due to the solidification of liquid and gaseous mixtures that result from the strong absorbing to the incident laser. The crater was generated because the mixtures were ejected under the extensive pressure of the laser plasma shock wave. During the process that the mixtures deposit around the craters, the density of the mixtures will decrease and crystallization takes place. As a result, the color of the deposition layer becomes lighter from inside to outside, and the crystallization of the thin film materials was observed by XRD spectrometry.     

Linear wave interaction at the charged fluid-fluid interface under tangential discontinuity of the velocity field

Capillary wave flow in a two-layer fluid with the upper layer moving parallel to the charged interface at a constant velocity is treated within a linear mathematical model. Interaction between waves excited on the free surface of the upper layer and at the interface results not only in classical Kelvin-Helmholtz instability (at low velocities of the upper layer) but also in oscillatory instability of the interface. The instability increment depends on the fluid density ratio, translational velocity, and charge density at the interface.     

Experimental and Theoretical Study of Sprays Produced by Ultrasonic Atomisers

The atomisation of liquids by means of low-frequency ultrasonic atomisers results from unstable surface waves generated on the free surface of a thin liquid film. These unstable waves are obtained from the tuning of the amplitude and the frequency of an imposed oscillation. The thin liquid film develops as the liquid spreads over the atomising surface of the atomiser. This paper focuses on a systematic experimental analysis of the sprays produced by low-frequency ultrasonic atomisers. The thickness of the liquid film was measured and its effects on the drop diameter were studied together with the effects of both the liquid's physical properties and the ultrasonic atomiser's characteristics. The relationship between the mean drop diameter and the surface wave wavelength was accurately determined and introduced into a mathematical approach based on the maximum entropy formalism to predict the drop size distribution of the spray. Within the range of working conditions tested, the application of this formalism is successful and provides a procedure for the prediction of spray drop size distributions from calculations only.     

Thermal conductivity of e-beam coatings

We present the results of the study on the thermal conductivity of different thin film materials produced by conventional thermal evaporation. The main features of the thermal pulse method employed for the measurement of the thermal conductivity are described. Thermal conductivity can be measured by determining the traveling time of a thermal wave propagating trough the film. A pump laser beam is directed onto a sample consisting of a thin transparent test layer and a totally absorbing substrate for the laser wavelength. As a consequence of the laser pulse, a temperature profile builds up at the substrate-film interface. A thermal pulse starts to diffuse from the substrate-film interface to the surface of the layer. Therefore, the temperature rise at the surface of the test layer starts with a time delay with respect to the laser pulse. The time delay depends on the propagation time of the thermal wave through the layer and is related to the thermal conductivity and the thickness of the layer. Measurements are evaluated by calculations based on the finite difference method. The results show that the analyzed thin films have lower thermal conductivity than the corresponding materials in bulk form.     

Stability of the viscous fluid film flow on a uniformly heated substrate

The linear stability is investigated of a viscous fluid film on a uniformly heated substrate under an arbitrary angle of inclination against the horizon. At the substrate, the heat flux is set; at the film surface, the fluid-gas heat transfer coefficient is specified. The waves are considered in the film propagating in an arbitrary direction. Within the frame of the integral model, the dispersion ratios are obtained for the wave increment and phase velocity. The analysis is performed of the dispersion ratios, and the flow instability range is determined. At the Marangoni numbers above a certain threshold, standing wave or traveling wave type disturbances take place; the waves increase in the horizontal direction. For the traveling waves, the Marangoni number threshold value is significantly lower than the same for the standing waves.     

声表面波生物传感器质量灵敏度的理论与实验验证

针对声表面波传感器在生物检测中的性能评价与优化,提出一种快捷验证适用于生物传感器的声表面波器件质量负载灵敏度的实时检测方法。首先基于二维近似假设和周期性边界条件,建立了以石英为压电基底材料、SiO₂为波导层的Love波传感器的三维有限元分析模型,从理论上验证了波导层对Love波传感器灵敏度的影响。在实验上,通过MEMS工艺制备以ST-90°X石英为基底的声表面波传感器,通过磁控溅射镀膜技术在其表面生长不同厚度的SiO₂波导层。利用热蒸镀技术在器件延迟线区域生长铝薄膜作为质量负载效应,利用Tetramethylammonium Hydroxide (TMAH)溶液对铝的缓慢腐蚀效果,模拟质量负载从有到无的逆过程,从而实现对声表面波传感器的灵敏度验证与评价,并从实验上探究不同厚度波导层对Love波传感器灵敏度的影响及其最佳波导层厚度。     

氮化铝薄膜中的二次谐波产生

利用X射线衍射技术对用直流反应磁控溅射技术沉积在蓝宝石基底(100)晶面上的氮化铝(AIN)薄膜进行了晶体结构分析,对X射线衍射图样的分析结果表明：用该法沉积在蓝宝石基底(100)晶面上的AIN薄膜为单晶膜;利用脉宽为10ns、重复频率10Hz、最大平均功率为20W、单脉冲的最大能量为2J的Nd：YAG脉冲激光器对其进行了二次谐波产生的实验研究,对实验结果进行分析表明：沉积在蓝宝石基底(100)晶面上的AIN薄膜能在一个很宽的入射角度范围存在有效二次谐波的输出;且输出的二次谐波功率相对于AIN薄膜的表面法线成对称分布,这表明该AIN薄膜的表面法线方向即为AIN的光轴方向。     

基底上覆分层薄膜超声Scholte波特性与薄膜定征

分层薄膜--基底结构广泛应用于微电子器件等诸多领域,但薄膜材料参数超声测量尤其是横波速度的定征是一个困难的问题。本文对液固界面Scholte界面波的频散特性和脉冲激励的声压响应进行了理论分析。结果表明,液固界面Scholte波频散与分层膜--基底结构的速度分布密切相关。薄膜材料各层的厚度和横波速度对界面波频散特性有显著影响。基于Scholte界面波的频散特性,提出了一种多层膜的多参数反演定征方法。首先针对理论信号进行薄膜参数反演,验证了该方法的可行性。后续对不同类型的多层膜材料样品进行了液固界面波激发与采集实验,实验信号的薄膜参数反演结果进一步验证了该方法的可行性和有效性。     

Effect of heterogeneity on the axisymmetric vibrations of cylindrical shells

The influence of large heterogeneity on the axisymmetric vibration characteristics of thin, composite cylindrical shells is studied, both analytically and numerically. In the neighborhood of the axisymmetric breathing mode, frequency spectra for shells of infinite and finite length are shown to be influenced qualitatively as well as quantitatively by large deviations from material and geometric symmetry in layer arrangement. A study of mode coupling in a semi-infinite shell is made for both end modes and modes with stationary frequency with real finite wave number, the latter being uniquely generated by a special class of heterogeneity. In each case, analytical estimates are given for frequencies, wave numbers, and modal amplitudes as functions of material and geometric properties of the shell.     

Mechanism and characteristics of steam laser patterning

Steam laser patterning of thin films and/or solid surfaces has been studied by jetting a beam of steam, such as water vapor, onto a sample surface to form a thin liquid film on it and patterning the sample by laser etching along predetermined path. In steam laser patterning, bubbles are formed in a thin liquid film on a sample surface irradiated by a pulsed laser. When the collapsed shock wave generated at the moment of bubble collapse and the high-speed liquid jet formed during bubble collapse are strong enough, cavitation erosion of the sample surface takes place. Compared to dry laser patterning, the etching rate can be greatly enhanced and no shoulder-like structure is formed at the rim of the laser-irradiated spot in steam laser patterning due to this cavitation erosion effect. PACS 81.65.cf; 52.38.Mf; 79.20.Ds; 42.62.-b; 62.50.+p     

Numerical simulation of ultrafast expansion as the driving mechanism for confined laser ablation with ultra-short laser pulses

Recently, a so-called “directly induced” laser ablation effect has been reported, where an ultra-short laser pulse (660 fs and 1053 nm) irradiates a thin Mo film through a glass substrate, resulting in a “lift-off” of the irradiated layer in form of a thin, solid, cylindrical fragment. This effect provides a new and very energy-efficient selective structuring process for the Mo back electrode in thin-film solar cell production. To understand the underlying physical mechanisms, a 3D axisymmetric finite element model was created and numerically solved. The model is verified by a direct comparison of experimental and numerical results. It includes volume absorption of the laser pulse, heat diffusion in the electron gas and the lattice, thermal expansion of the solid phase and further volume expansion from phase transition to fluid and gas, and finally the mechanical motion of the layer caused by the resulting stress wave and the interaction with the substrate. The simulation revealed that irradiation of the molybdenum layer with an ultra-short pulse causes a rapid acceleration in the direction of the surface normal within a time frame of a hundred picoseconds to a peak velocity of about 100 m/s. The molybdenum layer continues to move as an oscillating membrane, and finally forms a dome after about 100 ns. The calculated strain at the edges of the dome exceeds the tensile stress limit at fluences that initiate the “lift-off” in experimental investigations. In addition, the simulation reveals that the driving mechanism of the “lift-off” is the ultrafast expansion of the interface layer and not the generated gas pressure.     

Regular surface patterns on Rayleigh-Taylor unstable evaporating films heated from below

We study a thin liquid film with a free surface on the underside of a cooled horizontal substrate. We show that if the fluid is initially in equilibrium with its own vapor in the gas phase below, regular surface patterns in the form of long-wave hexagons having a well-defined lateral length scale are observed. This is in sharp contrast to the case without evaporation where rupture or coarsening to larger and larger patterns is seen in the long time limit. In this way, evaporation could be used for regular structuring of the film surface. Finally, we estimate the finite wave length for the simplified case of an extended Cahn-Hilliard equation.     

Capillary disintegration of a ferrofluid cylindrical film magnetized to saturation by an axial magnetic field

The subject of consideration is a film of a magnetic fluid applied on the surface of a thin magnetically soft cylinder. Quantities figuring in equations and boundary conditions describing the axisymmetric flow due to capillary and magnetic forces at capillary disintegration of the film are estimated in order of magnitude. The effect of magnetization on the capillary disintegration of the film is studied using simplified equations of ferrohydrodynamics. It is shown that magnetization shifts the range of Rayleigh capillary instability toward longer wave modes. As a result, drops arising at the final stage are larger than in the case of the nonmagnetic liquid.     

Modulation instability of electromagnetic excitations in nonlocal Josephson electrodynamics of thin films of nonmagnetic and magnetic (two-and three-dimensional) superconductors

Modulation instability of nonlinear electromagnetic excitations (oscillating with the Josephson frequency) of finite amplitude is investigated in a Josephson junction in a film of a nonmagnetic, as well as of a magnetic (two-or three-dimensional), superconductor. The instability is accompanied by a nonlinear shift in frequency. Dispersion relations are derived for the time increment of small perturbations of the amplitude. It is shown that, for this type of excitations in a Josephson junction in a thin film of nonmagnetic superconductor, modulation instability develops only in a certain finite range of wave vectors, whereas in a thin film of a two-or three-dimensional magnetic superconductor it develops for any wave vector.     

Plasmon‐enhanced polarized Raman spectroscopy for sensitive surface characterization

Local‐mode and localized surface plasmons generated on the silver thin film can selectively enhance the Raman signal from the surface. Further improvement of surface signal can be obtained by using the polarized Raman technique that results in a dramatic enhancement of the surface sensitivity by up to 25.4 times as compared to that without a silver coating. This technique will be very useful for Raman study on samples that suffer overlapping background signal. In this article, we show that it can be used to significantly improve the signal of thin strained‐Si layer on top of SiGe buffer layer. Copyright © 2008 John Wiley & Sons, Ltd.     

铁电双层膜的反转动力学行为

基于Landau-Khalatnikov运动方程,本文研究了含有表面过渡层和铁电界面耦合的反转动力学行为(包括平均极化、反转时间、反转电流和矫顽场).研究结果表明:在铁电双层膜系统中存在一个竞争的机理,即表面过渡层与界面耦合的竞争作用.我们发现在双层膜反转过程中出现了反常行为,这些反常行为归因于表面过渡层与界面耦合之间的竞争.表面过渡层与界面耦合的共同行为对铁电双层膜的动力学特性起到了决定性的作用.