Difference In Thermal Expansion Coefficients Research Articles

The Band-Structure Parameters of Bi1 –xSbx (0 ≤ x ≤ 0.15) Thin Films on Substrates with Different Thermal-Expansion Coefficients

The results of calculation of the charge-carrier concentration in bismuth–antimony films on substrates with different coefficients of thermal expansion are reported. The antimony content in the films is in the range 0–15 at %. Calculation is performed on the basis of experimental studies of the galvanomagnetic properties of the films. It is shown that the concentration is considerably higher in the case of substrates with a large coefficient of thermal expansion. The results of calculation of the position of the valence and conduction bands at 77 K in relation to the coefficient of thermal expansion of the substrate are reported. It is shown that, as the thin films experience in-plane strains defined by a difference between the coefficients of thermal expansion of the film and substrate materials, the position of the valence and conduction bands in the films changes relative to the position of the bands in the single crystal with the corresponding composition.

A hybrid silicon-sapphire cryogenic Fabry–Perot cavity using hydroxide catalysis bonding

The third-generation gravitational wave detectors under development will be operating at cryogenic temperature to reduce the thermal noise. Silicon and sapphire are promising candidate materials for the test masses and suspension elements due to their remarkable mechanical and thermal properties at cryogenic temperature. Here we present the performances of the cryogenic thermal cycling and strength testing on hydroxide catalysis bonding between sapphire and silicon. Our results suggest that although these two materials have very different coefficients of thermal expansion, if the flatness and the thermally grown SiO2 oxidation layer on the silicon surface are controlled well, the bonded samples can still survive thermal cycling from room temperature to 5.5 K. A breaking strength of MPa is measured for the bonds between sapphire and silicon with a 190 nm silicon oxidation thickness after cooling cycle. We construct a hybrid sapphire-silicon Fabry–Perot cavity with our bonding technique. The measurement results reveal that the cavity can survive repeated thermal cycling while maintaining a finesse of .

Glide of threading dislocations in (In)AlGaAs on Si induced by carrier recombination: Characteristics, mitigation, and filtering

III-V optoelectronics grown epitaxially on Si substrates have large networks of dislocations due to a lattice constant mismatch between the device layers and the substrate. Recombination-enhanced dislocation glide (REDG) allows these dislocations to move and increase in length during device operation, which degrades performance. In this paper, we study REDG dynamics of threading dislocations in situ in (In)AlGaAs double heterostructures grown on Si substrates using scanning electron microscopy cathodoluminescence. The driving force for REDG arises due to the coefficient of thermal expansion differences between Si and the III-V layers leading to large residual strains in the films. Tracking of threading dislocations as moving dark spot defects reveals glide characteristics that vary based on the nature of the dislocation. Remarkably, the alloying of a few atom percent of indium using metamorphic structures arrests threading dislocation glide by more than two orders of magnitude. Finally, we present REDG-based filtering as a pathway to reducing the threading dislocation density in select areas, removing a large fraction of the mobile dislocations. Together, these techniques will enable the understanding of dislocation–dislocation and carrier–dislocation interactions that have so far remained elusive during device operation, leading to reliable III-V integrated optoelectronics on silicon.

Copper-silicon carbide composite plating for inhibiting the extrusion of through silicon via (TSV)

For 3D packaging using TSV technology, it is required various techniques such as forming via holes on a wafer, filling conductive materials and interpretation of TSV reliability etc. Among them, solving the issue of reliability are standing out as a big problem for reaching commercialization in the future. When the conductive material filled in the TSV is expanded by the high-temperature process during the packaging process, it breaks the insulating layer and the metal interconnection which exist on via hole by extruding from the surface of the Si wafer. In this study, in order to suppress the Cu extrusion, electroplating was attempted by adding silicon carbide powder having almost no difference in thermal expansion coefficient with the Si chip in the Cu electroplating solution. As a result, the extrusion height of Cu-SiC was about 164 nm that is a height corresponding to 14.6% of the extrusion height of Cu. This is considered to be the result of extremely effectively suppressing the extrusion phenomenon after annealing by adding SiC powder with a low coefficient of thermal expansion into the conventional Cu plating solution.

Structure and Oxidation Resistance of Flamesprayed Fe–Ni–Al Coating

Two types of Fe-Ni-Al coatings as Fe75Ni15Al10 and Fe56Ni14Al30 were successfully deposited on the surface of low carbon steel using the flamespray technique. Coated samples were then annealed in avacuum furnace at 800°C for two hours and evaluated for high temperature oxidation resistance at 800°C for up to 8 cycles. The phases and structure of Fe-Ni-Al coatings before and after the oxidation test were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDX).According to the oxidation kinetic curve, both of the coating compositions had lower mass gains compared to the low carbon steel. After 8 cycles of exposure, however, the coatings tend to spall off due to the difference in thermal expansion coefficient between the substrate and coating.

Temperature-dependent photoluminescence characterization of compressively strained AlGaInAs quantum wells

A series of compressively strained AlGaInAs quantum well (QW) structures with different annealing treatment durations at 170 °C were investigated by temperature-dependent photoluminescence (PL). An abnormal S-shaped behavior in emission energy and a non-monotone evolution in spectral band width were observed at low temperature. A significant negative linear correlation between full width at half maximum (FWHM) and emission energy at different test temperature was exhibited in samples with different heat treatment durations. The highly linear relation demonstrated that the dependencies and relationships between PL peak energy and FWHM vs temperature are consistent. The anomalous blue shift and concomitant narrowing of FWHM in AlGaInAs QW were affected by lattice strain fluctuations due to the difference of thermal expansion coefficients between adjacent layers and strong carriers’ localization at low temperature.

Active Thermomechanical Stress Cancellation of Solder Joints in Surface-Mount Technology Integrated Circuits

One of the main difficulties that prevent the use of integrated circuits (ICs) with ball grid array packages in space is the early fatigue of their solder joints. Early solder fatigue originates in the thermomechanical stress cycles produced by the different coefficients of thermal expansion (CTEs) of the printed circuit board and the IC package and the temperature fluctuations that they suffer during a space mission. In this paper, we propose an active cancellation mechanism to extend the lifetime of the solder joints with minimum energy consumption and show the simulation results from its modeling.

Duplex and functionally graded Al@NiCr/8YSZ thermal barrier coatings on aluminum substrates

It is difficult to prepare non-ablative thermal barrier coatings (TBCs) on aluminum alloy owing to the sensitivity to oxygen and low melting temperature of the substrate and great difference of thermal expansion coefficient between the substrate and the coatings. In this work, the cladding-structured Al@NiCr was deposited as interlayer between the aluminum alloy substrate and the 8YSZ topcoat to enhance the bonding strength of TBCs. To avoid the oxidation of the bond coat and the substrate, different cooling systems were attempted. Al@NiCr/8YSZ functionally graded (FG) coatings were also designed and prepared on the aluminum alloy substrate. Microstructure, bonding strength and thermal cycling behavior were investigated and compared with the duplex TBCs. The results showed that selective oxidation of aluminum and chromium occurred for plasma-sprayed Al@NiCr interlayer, similar to traditional NiCrAlY bond coat. The aluminum oxides still wrap around NiCr splats in the coatings. With the application of dry-ice blasting, Al@NiCr interlayer presents more significant decrease in the porosity and the oxides than traditional NiCrAlY as well as more improvement in the bonding strength. Al@NiCr/8YSZ FG coatings have incremental density from ceramic to metal side and uniform layer density. The bonding strength of FG coatings was about twice as higher as that of the duplex ones. Al@NiCr/8YSZ TBCs on the aluminum alloy substrates exhibit an excellent thermal cycling lifetime.

Proposal of an effective mechanical reinforcement structure for a REBaCuO disk bulk pair by full metal encapsulation to achieve a higher trapped field over 20 T

In this paper, we propose an effective mechanical reinforcement of a REBaCuO superconducting disk bulk pair to avoid mechanical fracture due to a large hoop stress during field-cooled magnetization (FCM), and confirm the reinforcement effect using numerical simulation. In this reinforcement, the disk bulk is fully encapsulated by an outer metal ring with upper and lower plates made by stainless steel (SUS316). The trapped field, Bz, in the bulk pair with various critical current densities, Jc, was numerically simulated during FCM from Bapp = 22 T, and the hoop stress, σθ, was also estimated during FCM after cooling from 300 to 20 K. As a result, the trapped field of over 20 T can be achieved in the gap center of the bulk pair. A large compressive hoop stress, due to the difference of thermal expansion coefficients between the bulk and stainless steel, was effectively applied to the whole bulk during the cooling process, compared to that for the conventional reinforcement using only a SUS316 outer ring. The electromagnetic hoop stress, σθFCM, during FCM was also reduced, and the maximum of the total hoop stress, (= σθFCM + ), can be reduced below the fracture strength of the REBaCuO bulk. The possibility to achieve a higher trapped field over 20 T is suggested in the gap of the REBaCuO bulk pair without mechanical fracture.

Effect of glass-removal on the magnetostriction and magnetic switching properties in amorphous FeSiB microwires

Abstract Results on the influence of glass-removal on the magnetostriction, magnetic switching properties and domain wall propagation in amorphous Fe77.5Si17.5B15 microwires are reported. Glass removal releases high thermoelastic stresses originated by the difference in thermal expansion coefficients of glass and metal, which reduces the coercivity, increases the domain wall mobility and decreases the local nucleation fields and their distributions. Evening the distribution of nucleation fields and eliminating the local surface defects due to glass removal increase the field range of single domain wall propagation regime. It was also found that the saturation magnetostriction coefficient significantly decreases after glass removal, which strengthens the impact of the reduced magnetoelastic anisotropy. The effect of glass removal on magnetostriction was previously observed only in Co-rich microwires with small negative magnetostriction. Understanding the factors that control the magnetic switching and domain wall dynamics is of interest for practical applications in sensing, storage and logic devices.

Effects of SiC content on phase evolution and corrosion behavior of SiC-reinforced 316L stainless steel matrix composites by laser melting deposition

SiC dispersed (4, 8, 12 and 16 wt%) 316L stainless steel metal matrix composites (MMCs) have been prepared by laser melting deposition (LMD). The constituent phases, microstructure, microhardness and electrochemical properties of the MMCs were investigated as a function of SiC content. Experimental results showed that constituent phases of the MMCs evolved from single γ-(FeCrNi) phase with fcc structure for 4 wt% SiC dispersed MMC to γ-(FeCrNi) + α-(FeCrNi) + SiC phases for the 8, 12 and 16 wt% SiC dispersed MMCs. The presence of α-(FeCrNi) phase was due to the tensile stress resulting from the different coefficient of thermal expansion between SiC ceramic reinforcement and the γ-(FeCrNi) matrix in the MMCs. In addition, iron silicides (Fe3Si and FeSi) appeared in 16 wt% SiC dispersed MMC. The microstructure was dense, uniform and the addition of SiC obviously refined the solidification microstructure of the MMCs. In the 16 wt% SiC dispersed MMCs, a micro-crack can be clearly observed. The microhardness of MMCs increased obviously from 362 HV to 974 HV with the addition of SiC. Accompanying the increase in hardness, the corrosion current density increased and the charge transfer resistance decreased, and the corrosion resistance of 4 and 8 wt% SiC dispersed MMCs was superior compared to 12 and 16 wt% SiC dispersed MMCs in 3.5 wt% NaCl solution.

Relief Formation on the Free Surface of Metallic Polycrystals upon Recrystallization Annealing

The mechanism of the formation of a complicated relief first found on the recrystallized tungsten surface in studies performed by A.I. Belayeva and coauthors is described in this work. Its essence is the deformation of boundaries and near-boundary volumes of crystallites (grains) in the near-surface polycrystalline-metal layer upon cooling after high-temperature holding that is caused by the difference in the ultimate strength and thermal expansion coefficients of boundaries and bodies of grains. In the near-surface layer upon cooling of the metal, due to the difference in the size reduction of grain boundaries and grain bodies, cracks (grooves) arise at boundaries on whose banks identical ridges are formed. The bending of the boundary makes the profile of grooves asymmetric and creates rather shallow creases in front of ridges. The surface relief impairs the service properties of metals but its formation can be prevented, if articles become single-crystalline owing to recrystallization.

Development of sputtered Nb3Sn films on copper substrates for superconducting radiofrequency applications

Superconducting radiofrequency (SRF) cavities that could provide a higher quality factor as well as a higher operational accelerating gradient at an affordable cost are in high demand for the future generation of particle accelerators. This study aims to demonstrate the potential of Nb3Sn as material of choice for such SRF applications. Due to its brittle nature, the only way to produce an Nb3Sn SFR cavity is to synthesise a thin layer inside a cavity made of niobium or copper. In this work, direct current magnetron sputtering using a stoichiometric target of Nb3Sn was employed to produce films on copper samples. Assessment of the morphology, microstructure and superconducting properties were performed in order to ensure that this approach is suitable for SRF applications. The potential of the method is proven by obtaining films, which exhibit a crack-free surface, dense morphology and critical temperatures (Tc) up to 16 K. The essential properties of the films have also been investigated with respect to the deposition and annealing conditions. The use of krypton as working gas during deposition increases the atomic percent of Sn in the film compared to argon. However, in contrast to argon, higher krypton pressures reduce the atomic percent of Sn. It was also found that long-lasting high-temperature annealing leads to higher superconducting critical temperatures due to an increased crystallographic order. Particular attention was given to the influence of the copper substrate on the film growth as well as the microstructural and superconducting characteristics. We discuss the main constraints introduced by the copper substrate, such as copper interdiffusion during annealing, lattice mismatch and difference in thermal expansion coefficients and methods to overcome them.

Wet vs dry CFRP drilling: Comparison of cutting fluid delivery methods

This work studied the impact of flood and through-tool cutting fluid delivery methods during the drilling of carbon fibre reinforced polymer (CFRP) composite panels against a dry baseline condition. The cutting fluid considered was a water-based, composite-specific fluid, and the cutting tool was a Ø6.35 mm diamond-coated drill bit. After an initial design of experiments (DOE) approach enabled the establishment of appropriate cutting parameters to minimise delamination, both delivery methods and dry baseline drilling were compared in terms of tool wear and hole quality. The increased heat removal efficiency of through-tool delivery method is theorized to have prevented the localised softening of the resin and consequently maintained high abrasiveness of the composite workpiece, ultimately developing the highest tool wear for the given parameters. After drilling 600 holes, dry drilling exhibited the best results and lowest variation of hole quality metrics, i.e. the most stable process. However, after drilling 300 holes, flood delivery produced a better performance for cylindricity and perpendicularity and similar exit delamination factor (Fd) than dry drilling. Interestingly, through-tool delivery exhibited a slightly better performance than dry drilling when the analysis and comparison is conducted after the first 100 holes drilled only. These results indicate that hole diameter is highly dependent on tool wear and demonstrates that heat evacuation helps to produce holes with better cylindricity and perpendicularity, since hole distortion is highly affected by heat up and cool down cycles and the different coefficient of thermal expansion (CTE) across the laminate.

Thermal stress analysis around a cavity on a bimetal

The plates made of two materials joined to each other having the different coefficient of thermal expansions are frequently encountered in the industrial applications. The stress analysis of these members under the effect of high-temperature variation has great importance in design. In this study, the stress analysis of the experimental model developed for the problem considered here was performed by the method of photothermoelasticity. The thermal strains were formed by the mechanical way and these were fixed by the strain freezing method. For the stress measurements, the method of slicing is applied which provides three-dimensional stress analysis. The analytical solution in the literature was compared with the related stress distribution obtained from the model. Moreover, the axisymmetric finite element model developed for the problem was solved by ABAQUS and the results obtained here compared with those of the experimental model and the analytical solution. As a result of this study, this experimental method and numerical model can be used for these type of thermal stress problems which have not been comprehensively analyzed yet.

Shear-Assisted Laser Transfer of Metal Nanoparticle Ink to an Elastomer Substrate.

Selective laser sintering of metal nanoparticle ink is an attractive technology for the creation of metal layers at the microscale without any vacuum deposition process, yet its application to elastomer substrates has remained a highly challenging task. To address this issue, we introduced the shear-assisted laser transfer of metal nanoparticle ink by utilizing the difference in thermal expansion coefficients between the elastomer and the target metal electrode. The laser was focused and scanned across the absorbing metal nanoparticle ink layer that was in conformal contact with the elastomer with a high thermal expansion coefficient. The resultant shear stress at the interface assists the selective transfer of the sintered metal nanoparticle layer. We expect that the proposed method can be a competent fabrication route for a transparent conductor on elastomer substrates.

Research on Interfacial Reaction and Growth Behavior of Intermetallic Compound of Dip-Soldered Sn/Ni System

Interfacial reaction and the growth behavior of intermetallic compound (IMC) between Sn solder and Ni substrate by dip soldering under different aging conditions (120 °C, 170 °C and 200 °C) by using scanning electron microscope were investigated. Experimental results showed that the only scallop-shaped Ni3Sn4 IMC layer formed at the interface after aging process and the thickness of IMC layer increased with prolonged aging time. Moreover, the cracks formed in the interface between IMC and solder could be resulted from the residual stress caused by the difference in thermal expansion coefficients. In addition, the spalling behavior of IMC from substrate was caused by cyclic shear stresses and strains induced and the morphological changes in IMC formation. During the aging process, it was found that the thickness of IMC always had a linear relationship with the square root of aging time under different aging temperatures (120 °C, 170 °C and 200 °C). The growth rate constants of IMC layers aged at 120 °C, 170 °C and 200 °C were obtained by using fitting method from the experimental data, which were 4.65 × 10−18 m2 s−1, 9.94 × 10−18 m2 s−1 and 1.76 × 10−16 m2 s−1, respectively. Based on these data, the activation energy of IMC layer was determined to be 63.23 kJ/mol. Likewise, the mean diameter of IMC grains increased with the increase in aging time. It is suggested that the mean diameter of IMC grains was always plotted against the aging time on a double logarithmic scale under different aging temperatures. The time rate constants of IMC grains aged at 120 °C, 170 °C and 200 °C were obtained by using same method, which were 0.10, 0.27 and 0.26, respectively.

Effects and distribution of TiC on the nanoparticle strengthening A-TIG welded AZ31 magnesium alloy joints

AZ31 magnesium alloy sheets were A-TIG welded using mixed activating flux, which contained different ratio of TiC nanoparticles (TiCp) and TiO2 powder, as surface coating. From mechanical test, the values of ultimate tensile strength and microhardness increased from 120.2 MPa to 181.7 MPa, 46.4 HV to 84.2 HV, respectively, which mainly resulted from the grain boundary strengthening of α-Mg and the dispersion strengthening of TiCp. The theoretical calculation suggested that the improvement of the yield strength was mainly the combination of the Hall-Petch and Orowan strengthening mechanisms, and the mismatch strain caused by different coefficient of thermal expansion between the matrix and the particles. Numerical simulation showed that the TiCp had a centralized tendency toward middle and bottom part of welding pool and was confirmed by the micro-zone microhardness test results in the fusion zoon.

Tensilely Strained Ge Films on Si Substrates Created by Physical Vapor Deposition of Solid Sources

The development of Si-compatible active photonic devices is a high priority in computer and modern electronics industry. Ge is compatible with Si and is a promising light emission material. Nearly all Ge-on-Si materials reported so far were grown using toxic precursor gases. Here we demonstrate the creation of Ge films on Si substrates through physical vapor deposition of toxin-free solid Ge sources. Structural characterization indicates that a high tensile strain is introduced in the Ge film during the deposition process. We attribute the presence of such a tensile strain to the difference in thermal expansion coefficient between Si and Ge. A Ge peak, centered at ~2100 nm, is evident in the photoluminescence spectra of these materials, which might result from direct band gap photoluminescence alone, or from superposition of direct band gap and indirect band gap photoluminescence. These Ge-on-Si materials are therefore promising in light emission applications.

Effects of Residual Stress Distribution on Interfacial Adhesion of Magnetron Sputtered AlN and AlN/Al Nanostructured Coatings on a (100) Silicon Substrate.

The present study investigated the influence of nanoscale residual stress depth gradients on the nano-mechanical behavior and adhesion energy of aluminium nitride (AlN) and Al/AlN sputtered thin films on a (100) silicon substrate. By using a focused ion beam (FIB) incremental ring-core method, the residual stress depth gradient was assessed in the films in comparison with standard curvature residual stress measurements. The adhesion energy was then quantified by using a nanoindentation-based model. Results showed that the addition of an aluminum layer gave rise to additional tensile stress at the coating/substrate interface, which can be explained in terms of the differences of thermal expansion coefficients with the silicon substrate. Therefore, the coatings without the Al layer showed better adhesion because of a more homogeneous compressive residual stress in comparison with the coating having the Al layer, even though both groups of coatings were produced under the same bias voltage. Results are discussed, and some general suggestions are made on the correlation between coating/substrate property combinations and the adhesion energy of multilayer stacks. The results suggested that the Al bond layer and inhomogeneous residual stresses negatively affected the adhesion of AlN to a substrate such as silicon.