Difference In Thermal Expansion Coefficients Research Articles

Temperature dependence of the biaxial tensile strain in suspended Ge cross-shaped microstructures

We fabricate suspended Ge cross-shaped microstructures to biaxially enhance the residual tensile strain induced by a difference of thermal expansion coefficients. The strain and optical properties are characterized by means of micro-Raman spectroscopy and micro-photoluminescence. A maximum biaxial strain of 1.05% is obtained by cooling the sample to a temperature of 100 K.

(Invited) The Effect of Heat-Treatment on Mechanical Property and Wetting Behavior of α-LiAlO2

α-LiAlO2 is widely used as membrane structural material to support electrolyte in molten carbonate fuel cell (MCFC) stacks. The α-LiAlO2 electrolyte matrix always experiences mechanical and thermal stress during the initial start-up and operation (550-650oC) due to (1) insufficient mechanical strength of non-sintered α-LiAlO2, (2) thermal expansion coefficient difference between the α-LiAlO2 matrix and carbonate electrolyte, and (3) high capillary force, which may cause cracking of the matrix. A non-sintered/heat-treated pure α-LiAlO2 matrix has low mechanical strength. In this study, heat-treatment was used to enhance the mechanical strength of the α-LiAlO2 matrix. It has been found that the mechanical strength of the α-LiAlO2 matrix was increased four folds (2.72MPa) after heat-treated at 800oC for 5h to that of pure α-LiAlO2 matrix (0.57MPa). The porosity of those matrices was not changed significantly after the heat-treatment. The XRD results showed that the crystal structure of α-LiAlO2 did not change during the heat-treatment at 800oC. The wetting behavior and carbonate electrolyte distribution of those pure α-LiAlO2 matrix and heat-treated α-LiAlO2 matrix was investigated. Non-heat-treated and heat-treated α-LiAlO2 matrices were all completely wetted by liquid carbonate electrolyte. Non-heat-treated α-LiAlO2 sample cracked during the melting and wetting process of carbonate electrolyte, however, the heat-treated α-LiAlO2 matrices did not crack due to enhanced mechanical strength.

Oxidation induced stress in SiO2/SiC structures

Physical stress in SiO2/SiC stacks formed by the thermal oxidation of SiC is studied experimentally through both room temperature ex-situ and variable temperature (25–1150 °C) in-situ investigations. Mechanisms giving rise to the stress are a thermal component, associated with differences in thermal expansion coefficients of the oxide and the substrate, and an intrinsic component associated with the different atomic densities and structure of the film and substrate. Ex-situ results show a ∼108 Pa compressive stress in the SiO2 film in a SiO2/SiC stack with a strong crystal face dependence (C face(000ī) and Si face (0001)) and processing (temperature, growth rate) dependence. Real-time stress determination demonstrates that at temperatures above ∼900 °C, the total intrinsic stress and a portion of the thermal stress may be relieved. On the basis of these findings, a viscous model is proposed to discuss the stress relaxation.

Non-Contact Technique for Determining the Mechanical Stress in thin Films on Wafers by Profiler

This paper presents an algorithm for analysis of relief for the purpose of calculating mechanical stresses in a selected direction on the plate in the form of software package Matlab. The method allows for the measurement sample in the local area. It provides a visual representation of the data and allows to get stress distribution on wafer surface. Automated analysis process reduces the likelihood of errors researcher. Achieved time saving during processing results. In carrying out several measurements possible drawing card plate to predict yield crystals. According to this technique done in measurement of mechanical stresses of thermal silicon oxide film on a silicon substrate. Analysis of the results showed objectivity and reliability calculations. This method can be used for selecting the optimal parameters of the material deposition conditions. In software of device–technological simulation TCAD defined process time, temperature and oxidation of the operation of the sample environment for receiving the set value of the dielectric film thickness. Calculated thermal stresses are in the system silicon–silicon oxide. There is a good correlation between numerical simulations and analytical calculation. It is shown that the nature of occurrence of mechanical stress is not limited to the difference of thermal expansion coefficients of materials.

Effects of varying the through silicon via liners thickness on their hoop stresses and deflections

Through silicon via (TSV) interconnect reliability is a problem in electronic packaging. The authors address the insertion losses, deflections which can result to separation of TSV layers and hoop stresses. These problems are due to different coefficient of thermal expansion between materials. The authors propose a robust methodology for (TSV) liners in this paper which in turn solves the reliability problem in (TSV). Silicon dioxide material is used in their paper as a TSV liner. First, they modelled the equivalent TSV circuit in advanced design systems (ADS). The authors then simulated it to obtain the TSV characterisation from which they obtained the S-parameter S21 which represents the insertion losses. Insertion losses have been described with changes in frequencies from 0 to 20 GHz with changes in TSV thickness from 7 to 8 µm. Later two different shapes of the TSV liner; the disc- and rod-shaped are modelled in analysis system 14 software. The two shapes with a radius of 5 µm each and a fixed pressure of 100 µPa developed changes in hoop stresses and deflections when the liners thicknesses are varied from 2 to 3 µm. The disc shape experienced least reliability problems so the authors propose its use in via structures.

고감도 그림자 무아레 기법을 이용한 모바일 전자부품의 변형 측정

모바일 기기 내부에 있는 전자부품들은 반도체 칩이나 그 밖의 여러 가지 재료로 구성되어 있다. 이러한 전자부품들은 매우 얇고, 구성된 재료들은 다양한 열팽창 계수를 가지고 있으므로 온도 변화나 외부 하중에 의해서 쉽게 굽힘이 일어난다. 그림자 무아레 방법은 비접촉으로 전체 영역에 걸친 면외변위를 측정하는 광학적 방법이지만 측정 감도를 <TEX>$50{\mu}m/fringe$</TEX> 이내로 하기 어려워서 반도체 패키지의 굽힘변형을 측정하기에는 적당하지 않은 면이 있었다. 본 논문에서는 그림자 무아레 기법의 여러 실험조건들을 최적화하여 <TEX>$25{\mu}m/fringe$</TEX>의 향상된 감도를 갖는 측정 방법을 구현하였다. 또한 이로부터 위상이동에 의해 기록되는 4장의 그림자 무늬를 영상 처리하여 감도가 4배 향상된 그림자 무늬를 얻어내고 이를 스마트폰의 소형 전자부품들에 적용하여 온도변화에 따라 발생하는 굽힘 변위를 <TEX>$5{\mu}m/fringe$</TEX>의 고감도로 측정하였다. The electronic components in mobile device are composed of electronic chips and various other materials. These components become extremely thin and the constituent materials have different coefficient of thermal expansion, so that considerable warpages occurs easily due to temperature change or external load. Shadow <TEX>$moir{\acute{e}}$</TEX> is non-contact, whole field technique for measuring out-of-plane displacement, but the measurement sensitivity is not less than <TEX>$50{\mu}m/fringe$</TEX>, which is not suitable for measuring the warpage of the electronic components. In this paper, we implemented a measurement method with enhanced sensitivity of <TEX>$25{\mu}m/fringe$</TEX> by investigating and optimizing various experimental conditions of the shadow <TEX>$moir{\acute{e}}$</TEX>. In addition, four <TEX>$moir{\acute{e}}$</TEX> fringe patterns recorded by the phase shift are processes to obtain a <TEX>$moir{\acute{e}}$</TEX> fringe patterns with a sensitivity four times higher. The measurement technique is applied to small electronic components of a smart phone for measuring warpage with a high sensitivity of <TEX>$5{\mu}m/fringe$</TEX> at room temperature and at the temperature of <TEX>$100^{\circ}C$</TEX>.

Influence of the Slurry Thickness and Heat Treatment Parameters on the Formation of Aluminium Diffusion Coating

Formation of the FeAl3 or Fe2Al5 phase during the aluminization of iron-based alloys causes detrimental behaviour of the material due to the brittleness of these phases and the different coefficient of thermal expansion between the base material and the resulting diffusion coating. In order to control the microstructure of the produced diffusion zone and its evolution, two different slurry thicknesses (30–50 and 100–150 µm) using high-purity aluminium spherical particles and three different heat treatments times (5, 10 and 20 h) were tested over ferritic–martensitic P92 steel. After the heat treatment, iron–aluminide phases rich in aluminium content were formed. After 1350 hours of exposure in air at 650 °C, it was found that for the coatings in the range of 30–50 µm neither FeAl3 nor Fe2Al5 phase remained in the diffusion coating, while Fe2Al5 did remain in those coatings in the range of 100–150 µm.

Hydrogen generation from hydrolysis of activated Al-Bi, Al-Sn powders prepared by gas atomization method

Highly activated Al-based composite powders with compositions of Al-20Bi and Al-20Sn (wt.%) were prepared by gas atomization method for hydrogen generation. The Al-20Bi powders formed incomplete core–shell structure with Bi aggregating on the powder surface, while the Al-20Sn powders presented eutectic structure with Sn distributed homogeneously on the grain boundaries of Al. The hydrolysis characteristics of these powders were investigated in distilled water. The results showed that the Al-20Bi and Al-20Sn powders exhibited high hydrolysis performance and violently reacted with distilled water at 30 °C. Elevated temperature could significantly shorten the incubation time, as well as improve hydrogen generation rate and conversion yield of the powders. The hydrolysis mechanism and oxidation resistance property of the powders were carefully investigated too. The miscibility gap and the large difference of linear thermal expansion coefficient between Al and Bi are responsible for the activation and high oxidation resistance of the Al-20Bi powders.

Enhanced NMR with Optical Pumping Yields 75As Signals Selectively from a Buried GaAs Interface.

We have measured the 75As signals arising from the interface region of single-crystal semi-insulating GaAs that has been coated and passivated with an aluminum oxide film deposited by atomic layer deposition (ALD) with optically pumped NMR (OPNMR). Using wavelength-selective optical pumping, the laser restricts the volume from which OPNMR signals are collected. Here, OPNMR signals were obtained from the interface region and distinguished from signals arising from the bulk. The interface region is highlighted by interactions that disrupt the cubic symmetry of the GaAs lattice, resulting in quadrupolar satellites for nuclear [Formula: see text] isotopes, whereas NMR of the "bulk" lattice is nominally unsplit. Quadrupolar splitting at the interface arises from strain based on lattice mismatch between the GaAs and ALD-deposited aluminum oxide due to their different coefficients of thermal expansion. Such spectroscopic evidence of strain can be useful for measuring lattice distortions at heterojunction boundaries and interfaces.

Fabrication of oriented wrinkles on polydopamine/polystyrene bilayer films.

Wrinkles exist widely in nature and our life. In this paper, wrinkles on polydopamine (PDA)/polystyrene (PS) bilayer films were formed by thermal annealing due to the different thermal coefficients of expansion of each layer. The factors that influenced the dimensions of wrinkles were studied. We found that oriented wrinkles could be formed if the bilayer films were patterned with micro-grooves, and the degree of the orientation depended on the thickness of the PDA and the dimensions of the grooves. Combined with the strong adhesion, biocompatibility and reactivity of PDA, the oriented wrinkles on PDA/PS patterned bilayers may find potential application in diffraction gratings, optical sensors and microfluidic devices.

Separation of III–N/SiC epitaxial heterostructure from a Si substrate and their transfer to other substrate types

A chemical-etching based method for separating GaN/AlN and AlN epitaxial heterostructures grown on silicon with a silicon-carbide buffer layer and transferring them to substrates of any type is developed. GaN/AlN/SiC and AlN/SiC heterostructures 2.5 μm and 18 μm thick, respectively, are separated and transferred to a glass substrate. It is shown that a silicon-carbide buffer layer on silicon, grown by the substitution method, has a developed subsurface structure which allows easy separation of the film from the substrate and promotes the relaxation of elastic energy caused by a difference in thermal-expansion coefficients of the film and substrate. It is shown that mechanical stresses in the film after its separation from the silicon substrate almost completely relaxed.

Features of bicrystal growth during the directional crystallization of metal melts

The factors responsible for the formation of different configurations of boundaries between adjacent crystallites during their growth from melt by Bridgman and Czochralski methods have been considered by an of example Fe–20 wt % Ga alloy and Ni bicrystals. It is found that the configuration of intercrystallite boundary is related to the features of crystallite growth, caused by the strained state of intercrystallite and interphase (crystal–melt) boundaries, the difference in the linear thermal expansion coefficients of the crystallite boundaries and bulk, and the shape (geometry) of the bicrystal cross section. It is suggested that the strained state of boundaries and the formation of substructure in crystallites during directional crystallization from metal melt are significantly affected by their deformation under the melt weight.

Effect of metallization on the strength and fracture behaviour of functional co-fired multilayer ceramics

Functional components are commonly fabricated combining a ceramic substrate with external and/or internal metallization. Different layers are printed and fired onto the ceramic part to provide the component with a functionality. As a result of the combination of materials with different coefficients of thermal expansion, internal stresses during the fabrication steps may lead to cracks and/or reduce the strength. In this work, several architectures combining metal and glass layers on the surface of ZnO substrates were analyzed to identify critical fabrication steps in functional co-fired multilayer ceramics. Three-point bending tests were performed on samples taken after different process steps. Experimental results showed a strong effect of the layered architecture on the strength distributions: details of geometrical designs can have a dramatic impact on the strength. Fractographic analyses and ex-situ Focused Ion Beam experiments in pre-loaded samples were the key to assess the location of failure and predict critical configurations.

Strain analysis of plasma CVD graphene for roll-to-roll production by scanning transmission electron microscopy and Raman spectroscopy

The establishment of the roll-to-roll CVD is one of the key factors for realizing the commercial application of graphene. The strain in graphene synthesized by high-throughput plasma CVD using two different conditions related to growth rate and tension to the substrate is analyzed by scanning transmission electron microscopy (STEM) and Raman spectroscopy. The compressive strain generated during the growth by the tension to the substrate and the difference in thermal expansion coefficient between the graphene and the copper substrate is observed, which affects electrical conductivity. It was confirmed by STEM observation that no particularly large strain was accumulated at grain boundaries and their surroundings.

Enhancement in CMOS-MEMS Resonator for High Sensitive Temperature Sensing

This paper presents the enhancement in frequency shift per Celsius for high-temperature sensitive applications of microresonators. Using materials with different coefficients of thermal expansion in a substrate and beam, larger axial load on fixed ends are demonstrated. This results in a larger frequency shift with the increase in the ambient temperature. An analytical model is presented that closely matches simulation and measurement results. The 120- $\mu \text{m}$ CMOS-MEMS fixed–fixed beam resonators, consisting of multiple metal, dielectric layers, and polysilicon layer, were designed and measured with a center frequency around 640 kHz. A sensitivity up to −2983 Hz/°C is achieved without sacrificing stiffness constant.

Theoretical Study of the Interfacial Force-Field, Thermodynamic Property, and Heat Stress for Plastic Bonded Explosives

The force-fields across the TATB/(paraffin, fluoropolymer), RDX/TATB, RDX/graphite and fluoropolymer/graphite interfaces are obtained by first-principles calculations and parameter optimization. Based on them, the composite materials are simulated in atomistic scale, and a set of thermodynamic properties are calculated, including the heat capacity, thermal expansion coefficient, Gruneisen coefficient, isothermal curve, Hugoniot curve, pressure field, and tension field. We find that the thermal expansion coefficient difference across the explosive/additive interface induces interfacial tension in warming process, the interfacial tension induces positive pressure on the explosive particle, and the positive pressure restrains the thermal expansion of the composite material. A physical picture to describe the influence mechanism of the interface effect on the composite property is obtained.

Laser welding of fused silica glass with sapphire using a non- stoichiometric, fresnoitic Ba2TiSi2O8·3 SiO2 thin film as an absorber

Laser welding of dissimilar materials is challenging, due to their difference in coefficients of thermal expansion (CTE). In this work, fused silica-to-sapphire joints were achieved by employment of a ns laser focused in the intermediate Si-enriched fresnoitic glass thin film sealant. The microstructure of the bonded interphase was analyzed down to the nanometer scale and related to the laser parameters used. The crystallization of fresnoite in the glass sealant upon laser process leads to an intense blue emission intensity under UV excitation. This crystallization is favored in the interphase with the silica glass substrate, rather than in the border with the sapphire. The formation of SiO2 particles was confirmed, as well. The bond quality was evaluated by scanning acoustic microscopy (SAM). The substrates remain bonded even after heat treatment at 100°C for 30min, despite the large CTE difference between both substrates.

Effect of an increased thermal contact resistance in a salt PCM-graphite foam composite TES system

Thermal Energy Storage systems using inorganic salts as Phase Change Materials (PCM) are ideal solutions for solar thermal direct steam generation power plants. However, the main limitation of these PCM is their low thermal conductivity. Though a composite PCM solution including graphite foam will increase the effective thermal conductivity of the storage material, the system performance is limited by the thermal contact resistance at the heat exchanger surface.An infiltrated PCM (sodium nitrate, NaNO3) in different commercial graphite foam structures, with variable porosity and apparent density is analyzed experimentally and numerically. The thermal properties of the PCM and the graphite matrix are experimentally determined to calculate effective properties of the composite. The performance of the composite PCM-graphite foam in a heat exchanger with embedded metallic tubes is analyzed for each foam type. During system operation, the difference in thermal expansion coefficients between the composite PCM and metallic tubes creates a void at the interface, which is gradually filled by the liquid salt. The effect on the discharge process of this low thermal conductivity layer forming around the steel tube is evaluated numerically, analyzing the deviation from the expected thermal performance of the ideal system.

Cantilever beam temperature sensors for biological applications

This review presents two types of cantilever beams employed as highly sensitive temperature sensors. One type is fabricated from composite materials and is operated in the deflection mode. The second type, used as a temperature sensor and presented in this review, is a resonant cantilever beam. The materials used for the fabrication of the bimaterial cantilever beam are silicon or silicon nitride and thin metallic films such as gold or aluminum. When the temperature changes, the different coefficients of thermal expansion of the metal and silicon cause the sensor to deflect. Considering the models of temperature measurement for biological cells, the heat should be applied locally at the tip of the cantilever beam. Formulas for the calculation of the deflection as a function of incident power applied at the free end of the cantilever beam operated in a liquid are presented in this review. The natural convective heat transfer coefficient was estimated by using the mathematical model and experimental values. For biological applications, the cantilever beam temperature sensor was operated in a liquid, and the heat transfer coefficients were between 381 and 642 W/m2K when the temperature applied to the cantilever's free end varied from 28 to 71.8 °C. The resonant cantilever beam was also demonstrated as a sensitive temperature sensor for biological applications. As a thermogenic sample, brown fat cells (BFCs), which are related to metabolic heat production, are employed. The working principle of the resonator cantilever beam temperature sensor is based on the shift in resonant frequency in response to temperature changes. The resonant frequency and the temperature coefficient were 960 kHz and 22.0 ppm/K, respectively. The measurements were performed by stimulating the activity of BFCs by flowing a norepinephrine (NE) solution (1 µM).

Interfacial microstructure of diffusion-bonded SiC and Re with Ti interlayer

SiC plates were diffusion bonded to Re metal using a Ti interlayer by hot-pressing. For the joining, a uniaxial pressure of 25 MPa was applied from 1400 to 1600 °C for 2 h in an argon atmosphere. The interfacial microstructure and elemental composition of the SiC/Ti/Re joints were investigated. The Ti interlayer diffused into the SiC substrate to form carbide intermediate phases that enhance the bonding strength and also that of the layer brazed with Re metal. Multi-component phases (Ti3SiC2, Ti5Si3Cx, and TiC) were formed in the Ti interlayer with different atomic ratios. Each phase had a different coefficient of thermal expansion, causing micro-cracks and pulverization at high temperature. At 1600 °C, the phase ratio and thickness of the detrimental phase Ti5Si3Cx were much lower than those at other joining temperatures. For the Re/Ti interfaces, the diffusion of Ti and Si into Re gradually induced the formation of bcc-Ti precipitates, ReTi, and Re-Si alloys depending on the joining temperature. The micro-hardness was measured for the joined SiC/Ti/Re along all the interfaces.