Microstructure and electrical properties of Ti-Si-C-Ag nanocomposite thin films

Ti-Si-C-Ag nanocomposite coatings consisting of nanocrystalline TiC in an amorphous Si matrix with segregated Ag were deposited by dual magnetron sputtering from Ti₃SiC₂ and Ag targets. As evidenced by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, for Ag contents below 10 at.%, the Ag forms ∼ 10 nm large crystallites that are homogeneously distributed in the films. For higher Ag contents, coalescence during growth results in the formation of > ∼ 100 nm Ag islands on the film surface. The electrical resistivity of the coatings was measured in a four-point-probe setup, and ranged from 340 μΩcm (for Ti-Si-C coatings without Ag) to 40 μΩcm (for high Ag content).     

Photoluminescence in laser ablated nanostructured indium oxide thin films

Nanocrystalline indium oxide films have been deposited using pulsed laser ablation technique at different substrate temperatures and the films are post-annealed at different temperatures. The structural, optical and electrical properties of the films are investigated by XRD, SEM, AFM, UV–vis spectra, photoluminescence spectra and electrical conductivity measurements. X-ray diffractograms of the as-deposited and post-annealed films A–C show that films are amorphous at lower substrate temperatures and transform to mixture of amorphous and crystalline phases. The grain size determination based on Debye Scherrer's formula shows that the average grain size of the crystallites in the films ranges from 6 to 32 nm. Dislocation density, biaxial strain, lattice strain and lattice stress of the films are also calculated. SEM micrographs show that all the films are densely packed with the crystallites in the nanodimensions. SEM images show porous nanocrystalline nature for the films of samples B and C which make them suitable for gas sensing. The as-deposited samples show decrease in resistivity with increase in substrate temperature and the lowest resistivity obtained is 6.6 × 10^?5 Ω m for the as-deposited films at substrate temperature 773 K. Efficient photoluminescence emission is observed in all the films and this can be attributed to higher values of rms surface roughness exhibited by these films. In₂O₃ films exhibit a PL emission property in the UV region at room temperature which suggests possible applications in nanoscale optoelectronic devices in the future.     

Microstructure and nanomechanical properties of Mn-rich Ni–Mn–Ga thin films

We report the effect of post-annealing on the crystalline phase, grain growth, magnetic and mechanical properties of Ni–Mn–Ga thin films deposited at room temperature followed by post-annealing at different temperatures. The phase and microstructural analysis reveal that amorphous to crystalline transformation occurs in as-deposited films after post-annealing above 873 K. The transformation of disordered phase into nanocrystalline phase by the influence of annealing has been confirmed by transmission electron microscopy. The crystalline films exhibit soft magnetic behavior with the Curie temperature of 314 K, while the amorphous films exhibit the Pauli-paramagnetic behavior even down to 4 K. The mechanical properties like hardness and elastic modulus of the films also show a strong dependence on the annealing temperature with crystalline film exhibiting maximum values of 6 GPa and 103 GPa, respectively. The Ni–Mn–Ga film annealed at 873 K exhibits enhanced nanomechanical properties and room temperature ferromagnetism which make this a potential candidate for use in MEMS devices.     

Crystallization of amorphous ceria solid solutions

Next-generation micro-solid oxide fuel cells for portable devices require nanocrystalline thin film electrolytes in order to allow fuel cell fabrication on chips at low operating temperatures and with high fuel cell power outputs. In this study amorphous gadolinia-doped ceria (Ce_0.8Gd_0.2O_1.9−x) thin film electrolytes were fabricated by spray pyrolysis and their crystallization to nanocrystalline microstructures was investigated by means of X-ray diffraction and transmission electron microscopy. At temperatures higher than 500 °C the amorphous films crystallize to a biphasic ceramic that is amorphous and nanocrystalline. The driving force for the crystallization is the reduction of the free enthalpy resulting from the transformation of amorphous into crystalline material. Self-limited grain growth kinetics prevail for the nanocrystalline grains where stable microstructures are established after short dwell times. A transition to classical curvature-driven grain growth kinetics occurs when the fully crystalline state is reached for average grain sizes larger than 140 nm and annealing temperatures higher than 1100 °C.     

Pitting and alkaline dissolution of an amorphous-nanocrystalline alloy with solute-lean nanocrystals

The corrosion resistance of partially devitrified metallic glasses is a critical concern for the viability of the glasses in many technological applications. Although partial devitrification is detrimental to the corrosion resistance of some metallic glasses, both the pitting and alkaline corrosion behavior of partially nanocrystalline Al₉₀Fe₅Gd₅ is similar to that of its amorphous precursor. This is in spite of the fact that the microstructure of the amorphous-nanocrystalline alloy is effectively a composite consisting of f.c.c. Al crystals embedded in an amorphous matrix. Here the pitting corrosion and alkaline dissolution of the amorphous-nanocrystalline alloy is compared to that of its fully amorphous precursor, pure polycrystalline Al, and to a micrometer scale composite consisting of electrically connected pure Al wires and amorphous ribbons.     

磁控溅射偏压对Zr-Si-N扩散阻挡层组织结构的影响

用反应磁控溅射法在不同偏压下沉积了Zr-Si-N扩散阻挡层.结果表明:Zr-Si-N膜的成分、电阻率和结构均随偏压的改变而不同;随着溅射偏压的增加,Zr-Si-N膜的表面粗糙度值增大;Zr/Si比值也随着偏压的增加而增大;电阻率随偏压的增加显著降低;Zr-Si-N膜的结构为类似Si3N4的氮硅化物非晶相与ZrN组成的复合结构,随着偏压的升高ZrN由非晶转变为纳米晶,而且ZrN晶体相增加.     

Strengthening gold thin films with zirconia nanoparticles for MEMS electrical contacts

Thin gold films can be strengthened by the incorporation, during reactive sputtering, of nanosized dispersions of monoclinic zirconia. Micron-thick films containing ∼2 vol.% zirconia particles having a particle size of 1–3 nm are found to have an indentation hardness of 3.8 GPa after annealing for 60 h at 500 °C in air. Sputtered gold films of the same thickness and annealed under the same conditions had a hardness of 2.3 GPa. The nanoparticles of zirconia resist coarsening with no change in diameter between deposition and after 60 h at 500 °C. They also suppress grain growth of the gold grains. The electrical resistivity of the strengthened gold films was 4.5 μΩ cm, about 55% higher than gold films. The temperature coefficient of resistivity was unaffected.     

非晶对置换反应中Ag纳米晶生长的影响

研究在Zn、Cu置换AgNO3溶液反应中非晶膜的形成对纳米Ag晶体生长的影响.HRTEM的观察表明,置换反应中形成的纳米Ag晶体的生长前沿沉积有一层5～10 nm宽的非晶膜,纳米Ag晶体的长大取决于该非晶膜的自发晶化.非晶膜的自发晶化主要是在非晶层内原位成核、长大,也可在晶体和非晶的界面成核长大,还可观察到非晶层内的Ag原子直接排列到原晶体的界面上而不需要成核的过程.在纳米Ag晶体生长前沿沉积的非晶的稳定性取决于AgNO3溶液的浓度.在80 mmol·L-1或更低的AgNO3溶液中生成的Ag纳米晶的生长前沿沉积有较稳定的非晶膜,而在400 mmol·L-1的高浓度AgNO3溶液中Zn置换还原形成的纳米Ag晶体的生长前沿无非晶存在.     

The influence of the transformation of electronic structure and micro-structure on improving the thermoelectric properties of zinc antimonide thin films

Measurements of electronic structure, microstructure and thermoelectric properties of zinc antimonide thin films prepared by direct current magnetron co-sputtering were carried out. The as-deposited zinc antimonide thin film had a very high resistivity similar to insulating ceramics, which was due to a low binding energy of both zinc and antimony, with the electron scattering increases and impedes the current transport. With the increase in annealing temperature, the films became more crystalline and the thermoelectric properties were also improved. The resistivity of the film decreased rapidly with its crystallinity when the annealing temperature was above 350 °C. The Seebeck coefficients of the thin films were positive, indicating that the films were P-type. The Seebeck coefficient of those samples increased with increasing annealing temperature. The thin film annealed at 400 °C has an optimal power factor of 1.87 × 10⁻³ Wm⁻¹ K⁻² with a Seebeck coefficient of 300 μVK⁻¹ and a resistivity of 4.82 × 10⁻⁵ Ωm at 573 K.     

Microstructure evolution of Ti–Si–C–Ag nanocomposite coatings deposited by DC magnetron sputtering

Nanocomposite coatings consisting of Ag and TiC_x (x < 1) crystallites in a matrix of amorphous SiC were deposited by high-rate magnetron sputtering from Ti–Si–C–Ag compound targets. Different target compositions were used to achieve coatings with a Si content of ～13 at.%, while varying the C/Ti ratio and Ag content. Electron microscopy, helium ion microscopy, X-ray photoelectron spectroscopy and X-ray diffraction were employed to trace Ag segregation during deposition and possible decomposition of amorphous SiC. Eutectic interaction between Ag and Si is observed, and the Ag forms threading grains which coarsen with increased coating thickness. The coatings can be tailored for conductivity horizontally or vertically by controlling the shape and distribution of the Ag precipitates. Coatings were fabricated with hardness in the range 10–18 GPa and resistivity in the range 77–142 μΩ cm.     

Friction and wear mechanisms in MoS2/Sb2O3/Au nanocomposite coatings

Fundamental phenomena governing the tribological mechanisms in sputter deposited amorphous MoS₂/Sb₂O₃/Au nanocomposite coatings are reported. In dry environments the nanocomposite has the same low friction coefficient as pure MoS₂ (～0.007). However, unlike pure MoS₂ coatings, which wear through in air (50% relative humidity), the composite coatings showed minimal wear, with wear factors of ～1.2–1.4 × 10^?7 mm³ Nm^?1 in both dry nitrogen and air. The coatings exhibited non-Amontonian friction behavior, with the friction coefficient decreasing with increasing Hertzian contact stress. Cross-sectional transmission electron microscopy of wear surfaces revealed that frictional contact resulted in an amorphous to crystalline transformation in MoS₂ with 2H-basal (0 0 0 2) planes aligned parallel to the direction of sliding. In air the wear surface and subsurface regions exhibited islands of Au. The mating transfer films were also comprised of (0 0 0 2)-oriented basal planes of MoS₂, resulting in predominantly self-mated “basal on basal” interfacial sliding and, thus, low friction and wear.     

Grain growth inhibition in thin nanocrystalline Au films by grain boundary diffusion and oxidation of Ti

We studied grain growth in thin nanocrystalline Au films deposited on a sapphire substrate with and without an ultrathin Ti underlayer (adhesion promoter). The samples were annealed at 200 °C for 2 h in air. The reference thin Au film without a Ti underlayer exhibited significant grain growth during annealing, whereas no changes in microstructure of the Au layer were observed in the Au/Ti bilayers. This stabilization of the microstructure of the Au layer was attributed to thermal grain boundary grooves on the Au surface filled with Ti oxide. The grooves exhibited an elongated morphology characterized by a low apparent dihedral angle value, atypical for thermal grain boundary grooves in pure metals. We demonstrated that grooves with this morphology are very efficient in pinning grain boundary motion. We also developed a quantitative model of grain boundary grooving coupled with grain boundary interdiffusion in thin bilayer films. The model predicted the formation of long, narrow grooves at the grain boundaries, which are very efficient in suppressing grain growth in nanocrystalline thin films.     

Microstructure and electrical properties of thin films of ReSi1.75 produced by co-sputtering

Microstructural evolution and changes in electrical resistivity of ReSi_1.75 thin films produced by co-sputtering has been investigated as a function of annealing temperature. Crystallization of amorphous ReSi_1.75 thin films occurs at 600 °C without forming any metastable phases. The crystallization temperature for ReSi_1.75 is considerably higher than those observed for other transition-metal disilicides. The crystal structure as well as the domain (twinned) structure observed for crystallites in ReSi_1.75 thin films annealed above 600 °C are essentially the same as those observed in bulk crystals of ReSi_1.75. Although the grain size of crystallites increases with the increase in annealing temperature, thin films annealed below 650 °C exhibit a nano-crystalline structure. Thin films of amorphous and crystalline ReSi_1.75 and bulk polycrystalline ReSi_1.75 all exhibit electrical resistivity values decreasing with the increase in temperature, indicating the semiconducting nature. Values of electrical resistivity for crystallized thin films are systematically higher than those for amorphous ReSi_1.75 thin films and bulk polycrystalline ReSi_1.75 and increase with the decrease in annealing temperature, exhibiting a peak at just above the crystallization temperature. The high values of electrical resistivity around the crystallization temperature are discussed in terms of the formation of the nano-crystalline structure in thin films, for which the effective medium approximation is not valid.     

Comparison in mechanical and tribological properties of Cr-W-N and Cr-Mo-N multilayer films deposited by DC reactive magnetron sputtering

Cr-W-N and Cr-Mo-N films were deposited on high speed steel substrate by unbalanced DC reactive magnetron sputtering. Cross-sectional scanning electron microscopy (SEM) morphologies of the films confirmed that the bilayer thickness of multilayer became thinner, and then structural transformation occurred from multilayer to composite with increasing the rotation velocity of substrate holder. X-ray diffraction (XRD) patterns indicated that the Cr-W-N films were composed of CrN and W₂N crystalline phases, and the Cr-Mo-N films consisted of crystalline CrN and amorphous/nanocrystalline Mo₂N. Mechanical and tribological properties were investigated by using a nanoindentor and a ball-on-disk tribometer, respectively. The Cr-W-N films exhibited excellent mechanical properties and wear resistance, while Cr-Mo-N films showed lower friction coefficient. Optimal mechanical and tribological properties were obtained in the Cr-W-N multilayer film with a bilayer period of 12 nm.     

Microstructure of pulsed laser deposited FePd thin films on amorphous and crystalline substrates

Equiatomic FePd thin films have been deposited at room temperature by pulsed laser deposition (PLD) on amorphous, Si₃N₄ and SiO₂, and crystalline, (100)-NaCl, substrates. The resulting FePd film microstructures have been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). We observed a complex orientation relationship between grains in nanocrystalline thin films of FCC FePd and the single crystal NaCl substrates. FePd films obtained under identical deposition conditions using the amorphous substrates also exhibited nanocrystalline morphology but with a fiber texture and consisted of a phase mixture of FCC FePd and the tetragonal ordered L1₀-FePd phase.     

Nanocrystalline Al–Fe intermetallics – light weight alloys with high hardness

Nanocrystalline Al–Fe alloys containing 60–85 at.% Al were produced by consolidation of mechanically alloyed nanocrystalline or amorphous (Al85Fe15 composition) powders at 1000 °C under a pressure of 7.7 GPa. The hardness of the alloys varied between 5.8 and 9.5 GPa, depending on the Al content. The specific strength, calculated using an approximation of the yield strength according to the Tabor relation, was between 544 and 714 kNm/kg. Based on the results obtained, we infer that application of high pressure affected crystallisation of amorphous Al₈₅Fe₁₅ alloy, influencing the phase composition of the crystallisation product, and phase changes in nanocrystalline Al₈₀Fe₂₀ alloy, inhibiting them.     

On the role of Fe in the growth of single crystalline heteroepitaxial Au thin films on sapphire

Thin Au–Fe bilayers were deposited on c-plane sapphire (α-Al₂O₃) substrates at room temperature employing the electron beam deposition method. The layers were found to be single crystalline (i.e. the grain size was much larger than the film thickness), with a [1 1 1] and [1 1 0] texture for Au and Fe, respectively, and strong heteroepitaxy to the substrate. Au films deposited on sapphire and Au–Fe bilayers deposited on amorphous SiO₂ were polycrystalline and exhibited random in-plane orientation of the grains. The effects of Fe and the Fe–sapphire interface on the microstructure of the Au film were investigated and discussed in terms of the orientation relationships, in-plane strain, interface energy and adhesion. The microstructures of annealed and as-deposited films were very similar, indicating that as-deposited films are close to thermodynamic equilibrium in terms of the orientation relationship with the substrate. This is uncommon for non-equilibrium thin film deposition processes, which usually result in a high density of defects in the as-deposited films.     

Thermal stability of Ta-Si-N nanocomposite thin films at different nitrogen flow ratios

Ta-Si-N thin films were applied as diffusion barriers for Cu interconnections or hard coatings in mechanical application. The resistivity, hardness and thermal stability were the important issues in the interconnections and hard coatings, respectively. In this paper, we investigated the relationship between the microstructures, resistivity, nanohardness and thermal stability of the Ta-Si-N thin films at different nitrogen flow ratios of 0-30% (N₂% = N₂ / (Ar + N₂) × 100%) by magnetron reactive co-sputtering. The Ta-Si-N films were annealed at 600, 750 and 900 °C at about 6 × 10⁻³ Pa for 1 h, respectively, to examine their thermal stability. The microstructures of Ta-Si-N films at low N₂% of 2-10% still retained the amorphous-like phase with nanocrystalline grains in an amorphous matrix at annealing of 600-900 °C. The nanohardness of amorphous-like Ta-Si-N film at N₂% of 3% was measured to be 15.2 GPa much higher than that of polycrystalline film of 10.1 GPa at N₂% of 20%. The average nanohardness of both films is stable up to 900 °C and varied in the range of 0.43-0.83 GPa. The resistivity of the as-deposited Ta-Si-N films increase with increasing N₂ flow rate. It is small around 220-540 μΩ cm for low N₂% of 2-10% while it increases abruptly to about 7700-43,000 μΩ cm at high N₂% of 20-30%. The best thermal stability of resistivity of Ta-Si-N film occurs at the N₂% of 2% in the range of 220 to 250 μΩ cm from RT to 900 °C.     

Structure and magnetic properties of SmxCo72−xFe16Zr7B4Cu1 (x = 8, 12, 15) alloys

Sm_xCo_72−xFe₁₆Zr₇B₄Cu₁ (x = 8, 12, 15) alloys with low level of Sm and mixed addition of several elements (Fe, Zr, B, Cu) were prepared via arc melting and rapid quenching technique. The influences of Sm content and cooling rate on the microstructure and magnetic properties of alloys were investigated. The ribbons melt-spun at 40 m/s present a novel composite microstructure with nanocrystalline phases embedded in amorphous matrix. Such a unique structure endows the x = 12 ribbons a coercivity as high as ∼20,000 Oe. Ferromagnetism of the amorphous matrix, the pinning effect of amorphous phase during the movement of domain-walls and exchange interactions among adjacent grains may contribute to the high coercivity performance.     

Ni- and Cu-free Ti-based metallic glasses with potential biomedical application

In the present work Ti–Fe–Si and Ti–Fe–Si–X (X = Zr, Pd, Ge) glassy alloys are discussed as potential biomedical materials. Depending on composition and experimental conditions these alloys possess glassy, quasicrystalline or crystalline structure. The glassy state and crystallization behavior of the melt spun ribbons were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and the Hank's solution was used as simulated body fluid for corrosion tests. Ternary Ti–Fe–Si alloys near the Ti₆₅Fe₃₀Si₅ eutectic point were prone to form quasicrystals if the cooling rate was not high enough to retain amorphous structure. The compositions on the steeper side of the eutectic point could be vitrified. The results indicate that small additions of Zr can have a positive effect on glass formation, while additions of Ge, Pd may have a detrimental effect by promoting crystallization. Ti–Fe–Si and Ti–Fe–Si–Zr alloys exhibited high corrosion properties, superior to that of pure Ti and most of Ti-based glassy alloys reported in the literature. Being free of Ni and Cu this group of alloys may be considered for possible biomedical application.