Influences of film composition and annealing on the mechanical and electrical properties of W–Mo thin films

In this article, the mechanical and electrical characteristics of co-sputtered W–Mo thin films investigated for the application to microelectromechanical systems are described. W–Mo thin films with various compositions were deposited by co-sputtering onto a cover glass and silicon oxide (SiO _x ) film-coated Si wafer. The internal stress measured by Newton-ring method depended on film composition and Ar pressure, but were independent on annealing at 623 K. The hardness gradually decreased with an increase in Ar pressure, whereas the effective Young’s modulus stayed constant throughout Ar pressures ranging from 0.2 to 0.4 Pa. Both the mechanical properties showed no dependences of film composition and annealing. The resistivity was proportional to Ar pressure, but was not related to film composition. Annealing slightly affected the resistivity. Auger spectroscopy clarified that, by annealing, an oxide layer of approximately 10 nm thick was produced on the top surface, but film composition did not change. From the experimental results obtained, annealing at 623 K did not affect the mechanical and electrical properties of W–Mo films. This indicates that the co-sputtered film is very stable at temperatures ranging from RT to 623 K. By controlling Ar pressure, stress-free W–Mo films with superior mechanical characteristics and low resistivity can be produced regardless of film composition.     

Enhanced dielectric and electrical properties of three-component PMMA–NaNbO3–starch percolative composite films

Journal of Materials Science: Materials in Electronics - Three-component PMMA–NaNbO3–starch percolative composites with starch and sodium niobate (NaNbO3; NN) particles embedded into...     

Phase composition,structure, and mechanical properties of arc PVD Mo–Si–Al and Mo–Si–Al–N coatings

Using an arc physical vapor deposition process, we have produced nanostructured Mo–Si–Al coatings with a uniform distribution of equiaxed grains 8–12 nm in size and Mo–Si–Al–N coatings with a multilayer structure and a modulation period from 22 to 25 nm. The former coatings consist of MoSi₂ and Mo and the latter consist of Mo2N and amorphous Si₃N₄ and AlN. The hardness of the Mo–Si–Al–N and Mo–Si–Al coatings is 41 and 18 GPa, respectively; they are similar in resistance to elastic deformation; and the Mo–Si–Al–N coating has a considerably higher resistance to plastic deformation. The coatings have roughly identical coefficients of friction (~0.67–0.69 at 20°C and ~0.52–0.56 at 550°C), but the wear resistance of the Mo–Si–Al–N coating is higher by three and two orders of magnitude at 20 and 550°C, respectively. The coatings of the two systems exhibit good adhesion to the substrate and cohesive fracture. Partial wear of the Mo–Si–Al and Mo–Si–Al–N coatings in the course of scratch testing occurs at indentation loads of 80 and 63 N, respectively.     

Microstructure and mechanical properties of Si3N4–TiC nanocomposites

Abstract

Si₃N₄–TiC nanocomposites are fabricated by hot press sintering from silicon nitride nanopowders and ultrafine TiC powders. The microstructure and mechanical properties are analysed and discussed. Scanning electron microscopy images show that the microstructure consists of equiaxed grains and grain boundary phase. The TiC added as a dispersed phase reacts with the nitrogen from Si₃N₄ during the liquid phase sintering, with the formation of TiC_0.7 N_0.3 , trace of SiC and N₂. The adding of a proper amount of TiC powders increases the flexural strength and has little influence on fracture toughness. The hardness increases with increasing TiC content.     

Anomalies in electrical and dielectric properties of nanocrystalline Ni–Co spinel ferrite

Nanocrystalline Ni-substituted cobalt ferrite sample is prepared by chemical co-precipitation method. X-ray diffraction and scanning electron microscopy techniques are used to obtain structural and morphological characterizations. Nanocrystalline nature is clearly seen in SEM picture. Variation of electrical resistivity as a function of temperature in the range 300–900 K is investigated. ln ρ versus 1/T plot shows four break resulting into five regions in 300–900 K temperature range of measurements. The magnetic transition temperature of the sample is determined from resistivity behavior with temperature. The activation energy in different regions is calculated and discussed. Variation of dielectric constant (?′) with increasing temperature show more than one peak; one at around 773 K and other around 833 K, which is unusual behavior of ferrites. The observed peaks in ?′ variation with temperature show frequency dependence. Electrical and dielectric properties of Ni_0.4Co_0.6Fe₂O₄ sample show unusual behavior in the temperature range 723–833 K. To our knowledge, nobody has discussed anomalous behavior in the temperature range 723–833 K for Ni_0.4Co_0.6Fe₂O₄. The possible mechanism responsible for the unusual electrical and dielectric behavior of the sample is discussed.     

Al–O–N and Al–O–B–N thin films applied on Si–O–C fibers

Protective coatings (Al–O–N and Al–O–B–N) on Si–O–C fibers (Tyranno ZMI) were applied in order to enhance oxidation resistance under severe thermo-mechanical conditions in the 400–600 °C temperature range. The coating process consisted in three steps: (i) the transformation of the Si–O–C fiber surface into microporous carbon; (ii) the impregnation of these carbon microporous layers by an aluminium trichloride (AlCl₃) solution and then, (iii) a final heat treatment under ammonia. Processing parameters were studied in order to select the best conditions. Using these conditions, obtained results have shown that coatings were present around each fiber, with a controlled thickness, and that the mechanical properties of the fibers were preserved. Although, these coatings did not entirely stop the oxygen ingress, it has been shown that they strongly reduced the oxidation of the fiber.     

Effect of the POSS–Polyimide nanostructure on its mechanical and electrical properties

Nanocomposite films consisted of Polyhedral Oligomeric Silsesquioxane (POSS) filler in a Polyimide (PI) matrix were prepared. The effect of the nanocomposites’ structure on its mechanical and electrical properties was evaluated with respect to survival in the low Earth orbit (LEO) environment. The POSS–PI structure consists of POSS nano-aggregates formed in the bulk and on the surface. The aggregates’ size and distribution are POSS content-dependant. The fracture mechanism during hypervelocity impact at extreme temperature conditions was studied. The hypervelocity impacts of the POSS–PI films result in a brittle fracture, compared to ductile fracture in the case of PI, and in formation of radial cracks. A model based on formation and coalescence of voids around the aggregates, when load is applied, is suggested to explain the effect of the POSS content on the POSS–PI fracture mechanism. The size and density of the POSS aggregates also affect the nanocomposite’s volume electrical resistivity. An inverse dependence exists between the POSS aggregates’ surface density and the nanocomposites’ volume electrical resistivity.     

Annealing effect on the structural,electrical and 1/f noise properties of Mn–Co–Ni–O thin films

Thin films of Mn_1.4Co_1.0Ni_0.6O₄ (MCN) spinel oxide are grown by radio frequency (RF) magnetron sputtering method on amorphous Al₂O₃ substrate. We investigate the annealing effect on the micro structural and electrical properties of RF sputtered MCN films. It is found that the crystallinity of MCN film is improved with increasing annealing time at 750 °C, and the annealed films present excellent cubic spinel (220) preferred orientation in X-ray diffraction patterns. Comparing to as-sputtered thin film, the annealed films show a decrease of 60 to 70 % in resistivity at 300 K. The annealed samples with post annealing time longer than 18 min acquire a negative temperature coefficient of resistance of about ?3.73 %K^?1 and resistivity of about 210–220 Ω cm at 300 K. 1/f noise of MCN films are also studied and the Hooge’s parameters (γ/n) are calculated. After annealing for 18 to 90 min, the γ/n values of the films are on the order of 10^?21 cm³, which ranks about two orders lower than that of amorphous silicon.     

Microstructure and mechanical properties of in situ Al–Mg2Si composites

Abstract

In situ metal matrix composites (MMCs) with Mg₂Si particulate reinforcement have been developed recently as ultralight materials. In this paper, a brief overview of the physical and mechanical properties of Mg₂Si and the current status of research on Mg₂Si reinforced MMCs is presented, followed by more detailed information on recent progress in the research group of the present authors. The effects of element additions and processing parameters on the microstructure of the composites obtained by gravity casting are discussed, together with some mechanical property data.     

Synthesis, structural, electrical and dielectric properties of Zn–Zr doped strontium hexaferrite nanoparticles

Zinc-Zirconium doped Strontium hexaferrite SrZn_xZr_xFe_12?2xO₁₉ (where x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) have been successfully synthesized via sol–gel auto combustion technique. The as-synthesized samples were characterized by thermo gravimetric analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The X-ray powder diffraction results showed that the sample was single phase with the space group of P6₃/mmc. The lattice constant ‘a’ almost remains constant while ‘c’ increases as Zn–Zr concentration ‘x’ increases. The crystallite size obtained from XRD data is in the range of 36–47 nm. The average grain size as determined by SEM was found in the range of 40–90 nm. EDS analysis showed that the composition obtained is near stoichiometric. D.C. electrical resistivity measurements were carried out within the temperature range of 300–923 K. It is observed that the resistivity decreases whereas the drift mobility increases as Zn–Zr content ‘x’ increases. The activation energy is found to decrease with the concentration ‘x’. Dielectric measurements were carried out within the frequency range of 50 Hz–5 MHz. It is found that dielectric constant (ε′) and dielectric loss tangent (tan δ) both increases as the Zn–Zr concentration ‘x’ increases. Moreover, the structural, morphological, electrical and dielectric properties of Sr–M ferrite powders were strongly depend upon the synthesis condition.     

Copper effects in mechanical,thermal and electrical properties of rapidly solidified eutectic Sn–Ag alloy

The Sn–3.5 wt%Ag alloy considered as a good alternative to Pb–Sn alloys. This study aims to investigate the effects of Cu or Sb additions by 3 or 5 wt% to melt-spun Sn–3.5%Ag alloy. Ternary melt-spun Sn–Ag–Cu and Sn–Ag–Sb alloys investigated using X-ray diffractions (XRD), Scanning electron microscope (SEM), Dynamic resonance technique (DRT), Instron machine, Vickers hardness tester and Differential scanning calorimetry (DSC). The results revealed that the microstructures of the β-Sn phase, Ag₃Sn and Cu₃Sn intermetallic compounds (IMCs) in the solder matrices were refined due to the effect of Cu additions and melt-spun process. Moreover, increasing Cu content promotes Ag₃Sn intermetallic compound (IMC) formation. Consequently, the addition of “3 wt%” of Cu reduced the creep rate ? from (3.79?×?10^?3) to (1.65?×?10^?3) and delayed the fracture point. The tensile results showed an improvement in Young’s modulus by 47% (30.3 GPa), ultimate tensile strength (UST) by 11.6% (23.9 MPa), and in toughness by 20.5% (952.32 J/m³) compared to the eutectic Sn–Ag alloy. Vickers hardness has improved by 3.3% (136.71 MPa) and thermal activation energy by 54% (90.40 KJ/mol) when compared with that of eutectic Sn–Ag alloy. Those improvements are related to the lack of lattice strain from 7.56?×?10^?4 without “3 wt%” of Cu to 5.26?×?10^?4 with “3 wt%” of Cu. Its melting temperature (T_m) increased by 3 °C due to Ag₃Sn IMC increased and Cu₃Sn formation, but the pasty rang (mushy zone) decreased by 4 °C with “3 wt%” of Cu. The small lattice strains resulted with “3 wt%” of Cu made the electrical resistivity of this alloy more stable at elevated temperatures. The mechanical, thermal and electrical improvements of Sn_93.5–Ag_3.5–Cu₃ alloy provide good physical performance for soldering process and electronic assembly.     

Low indium content In–Zn–O system towards transparent conductive films: structure,properties and comparison with AZO and GZO

In this work, low content indium doped zinc oxide (IZO) thin films were deposited on glass substrates by RF magnetron sputtering using IZO ceramic targets with the In₂O₃ doping content of 2, 6, and 10 wt%, respectively. The influences of In₂O₃ doping content and substrate temperature on the structure and morphology, electrical and optical properties, and environmental stability of IZO thin films were investigated. It was found that the 6 wt% doped IZO thin film deposited at 150?°C exhibited the best crystal quality and the lowest resistivity of 9.87?×?10^?4 Ω cm. The corresponding Hall mobility and carrier densities were 9.20 cm² V^?1 s^?1 and 6.90?×?10²⁰ cm^?3, respectively. Compared with 2 wt% Al₂O₃ doped ZnO and 5 wt% Ga₂O₃ doped ZnO thin films, IZO thin film with the In₂O₃ doping content of 6 wt% featured the lowest surface roughness of 1.3 nm. It also showed the smallest degradation with the sheet resistance increased only about 4.4% at a temperature of 121?°C, a relative humidity of 97% for 30 h. IZO thin film with 6 wt% In₂O₃ doping also showed the smallest deterioration with the sheet resistance increased only about 2.8 times after heating at 500?°C for 30 min in air. The results suggested that low indium content doped ZnO thin films might meet practical requirement in environmental stability needed optoelectronic devices.     

The relationship between the electrical and mechanical properties of polymer–nanotube nanocomposites and their microstructure

A range of polymer–nanotube nanocomposites were produced using different processing routes. Both polymer-grafted and as-grown nanotubes were used and latex and polystyrene matrices investigated. The microstructures of the nanocomposites were studied, mainly by electron microscopy, in terms of the dispersion state of the nanotubes and the polymer–nanotube interface. The mechanical and electrical properties of the composites were also measured. The relationship between the microstructures observed and the resulting physical properties are discussed. It is found that composites with apparently similar microstructures can exhibit similar mechanical properties but very different electrical behaviours. Moreover, the nanocomposites produced using polymer-grafted nanotubes exhibit a clear improvement of the stress at large deformation. Thus, from our results, it appears that the mechanical and electrical properties do not necessarily depend on the same microstructural parameters. However it is still a challenge to simultaneously improve both physical properties.     

Investigation on the mechanical properties and frictional performance of Ni–Cu–Si alloy

The microstructure evolution, mechanical properties and dry sliding behaviour of Ni–30Cu–xSi alloy have been investigated systematically. As the volume fraction of microscale second-phase particles and nanoscale precipitates increases, the hardness, yield strength and ultimate tensile strength of alloy are improved significantly but elongation is reduced. Through confocal laser scanning microscope and atomic force microscope, it is suggested that the wear mode changes from the mixture of abrasive and adhesive wear to single abrasive wear. Owing to the existence of netlike microscale second-phase particles which are more likely to split the matrix, the Ni–30Cu–5.5Si alloy exhibits an abnormal higher wear rate even with the highest hardness. The netlike structure which deteriorates the friction performance should be avoided in wear-resistant materials.     

Optical and electrical properties of ink-jet printed indium–tin-oxide nanoparticle films

In this work, spherical indium tin oxide (ITO) nanoparticles (~ 15 nm) synthesized by co-precipitation method were successfully applied for direct ink-jet printing of transparent conducting patterns on polyethylene terephthalate substrates. The printed ITO nanoparticle patterns with various thicknesses were investigated for understanding fundamental properties and potentials for soft electronics. It has been found that the optical transmittance in the visible region as well as the band-gap absorption edge of the printed ITO films significantly varies with thickness, which is related to the huge nanoparticle scattering effect as evidenced. The electrical resistivity can be effectively improved by increasing the pattern thickness, indicating that the present printed ITO films are of great potential for optoelectronic applications.     

Effects of Pb–B–Si–O glass on the microstructures and electrical properties of silver electrode for LTCC application

The co-firing compatibility between green tape and the Ag electrode is a crucial characteristic in low-temperature co-fired ceramic (LTCC) technology and plays a vital role in improving the performance and application status of LTCC device modules. In this work, we studied the effects of lead content on the glass viscosity, the microstructure, and co-firing compatibility of silver electrode film. It was found that the softening point and viscosity of the glass were decreased, and the wettability between the glass and silver was improved with the increase of the lead content, which promoted the co-firing densification and interfacial bonding between the silver electrode film and the ceramic layer. The film presented the best electrical properties co-firing at 875 °C for 15 min, with the resistivity of 1.21 mΩ/sq. And the film was densified. The sintering interface was clear and well bonded. The results showed that an appropriate lead content in glass could effectively improve the interfacial bonding and the electrical properties during co-fired process, providing a new control methodology for realizing co-fired matching of the silver electrode film with low-temperature co-fired ceramics.

     

Evaluating the microstructure and mechanical properties of friction stir processed Al–Si alloy

In this study, mechanical behaviour and microstructural evolution in friction stir processing (FSP) of casting hypereutectic A390 aluminium alloy have been investigated. The mechanical behaviour of FSP samples was investigated by measuring the strain rate sensitivity using shear punch testing. The room-temperature shear punch tests were conducted at shear strain rates in the range of 10^?4–10^?1?s^?1. The results indicate that the strain rate sensitivity index increases from about 0.015 to 0.120 for as-cast A390 after third FSP pass and then experiences a further growth in FSP passes. The increase in the grain size and CuAl₂ intermetallic particle size result in a reduction in strain sensitivity index as well as shear strength after third FSP pass.