Anelastic properties of aluminium thin films on silicon cantilevers

Thin films (thickness 40 to 250 nm) of Al on microstructurized Si substrates have been investigated by the vibrating-reed technique (typical frequencies 100 Hz to 10 kHz) with strain amplitudes in the range of 10⁻⁷ to 10⁻⁴ and for temperatures up to 850 K. The combined evaluation of flexural and torsional vibrations permits to separate the complex shear modulus and biaxial modulus of the thin layer, which helps to identify the damping mechanisms. For Al thin films with thickness <200 nm, in addition to the well-known damping peak due to grain boundary sliding (peak temperature about 370 K), a further maximum of damping has been observed around 600 K, the nature of which is discussed.     

Surface roughness and dispersion parameters of indium doped amorphous As2Se3 thin films

Both a binary amorphous system of composition As₂Se₃ and a ternary amorphous system of composition amorphous (As₂Se₃)_0.99In_0.01 with thickness in the range 150–250 nm have been prepared by thermal evaporation technique. Indium doping and thickness effects on the features of As₂Se₃ thin films have investigated. The optical transmission spectra of these films have been measured in the range 200–1200 nm where the absorption coefficient and the optical energy gap Eg are evaluated. The refractive index and surface roughness of the prepared films are found to be highly dependent on film thickness and indium doping, using Swanepoel method.The single oscillator energy (E_o) and the energy dispersion parameter (E_d) have been calculated and discussed in terms of the Wemple and DiDomenico model. The results reveal that, they are thickness dependent—both E_o and E_d being higher for the undoped samples than that for the doped films.     

Effects of processing parameters on the properties of tantalum nitride thin films deposited by reactive sputtering

The effects of processing parameters on the properties of tantalum nitride thin films deposited by radio frequency reactive sputtering have been investigated. The influence of the N₂ partial and (Ar + N₂) total gas pressures as well as the sputtering power on the microstructure and electrical properties is reported. Rising the N₂ partial pressure, from 2 to 10.7%, induces a change in the composition of the δ-TaN phase, from TaN to TaN_1.13. This composition change is associated with a drastic increase of the electrical resistivity over a 7.3% N₂ partial pressure. The total gas pressure is revealed to strongly affect the film microstructure since a variation in both composition and grain size is observed when the gas pressure rises from 6.8 to 24.6 Pa. When the sputtering power varied between 50 and 110 W, an increase of the grain size related to a decrease of the electrical resistivity is observed.     

Substrates effect on Zn1−xMnxO thin films grown by RF magnetron sputtering

In this paper, we have presented the surface effect of the substrates on Mn doped ZnO (Zn_1−xMn_xO) thin films grown on Si(1 0 0) and sapphire [i.e. Al₂O₃(0 0 0 1)] by RF magnetron sputtering. These grown films have been characterized by X-ray diffraction (XRD), photoluminescence (PL) and vibrating sample magnetometer (VSM) to know its structural, optical and magnetic properties. All these properties have been found to be strongly influenced by the substrate surface on which the films have been deposited. The XRD results show that the Mn doped ZnO films deposited on Si(1 0 0) exhibit a polycrystalline nature whereas the films on sapphire substrate have only (0 0 2) preferential orientations indicating that the films are single crystalline. The studies of room temperature PL spectra reveal that the Zn_1−xMn_xO/Si(1 0 0) system is under severe compressive strain while the strain is almost relaxed in Zn_1−xMn_xO/Al₂O₃(0 0 0 1) system. It has been observed from VSM studies that Zn_1−xMn_xO/Al₂O₃(0 0 0 1) system shows ferromagnetic nature while the paramagnetic behaviour observed in Zn_1−xMn_xO/Si(1 0 0) system.     

High quality TbMnO3 films deposited on YAlO3

High quality thin films of TbMnO₃ were grown by pulsed laser deposition on orthorhombicYAlO₃ (1 0 0). The interface and surface roughness of a 55 nm thick film were probed by X-ray reflectometry and atomic force microscopy, yielding a roughness of 1 nm. X-ray diffraction revealed untwinned films and a small mosaic spread of 0.04° and 0.2° for out-of-plane and in-plane reflections, respectively. This high degree of epitaxy was also confirmed by Rutherford backscattering spectrometry. Using polarized neutron diffraction we could identify a magnetic structure with the propagation vector (0 0.27 0), identical to the bulk magnetic structure of TbMnO₃.     

Properties of exchange biased Co/Co3O4 bilayer films

Co/Co₃O₄ bilayer films were fabricated by RF sputtering with Co and Co₃O₄ targets. Exchange bias effect in the bilayer films was observed at 80 K by vibrating sample magnetometer. The bias effect disappeared about 240 K slightly lower than the Néel point of CoO and much higher than the Néel temperature of Co₃O₄ about 40 K. To clarify the origin of the exchange bias effect, Auger and X-ray photoelectron spectroscopy were employed and CoO was found at a transition region from Co₃O₄ layer to Co layer due to oxygen diffusion during sputtering. The angular dependence of exchange bias field H_E was obtained to obey function of H_E(θ)=18.06 (kA/m)[−cos θ+0.22 cos 3θ+0.03 cos 5θ−0.01 cos 7θ+].     

Mechanical behavior of 30–50 nm thick aluminum films under uniaxial tension

We present uniaxial tensile test results for 30–50 nm thick freestanding aluminum films. Young’s modulus and ductility were found to decrease monotonically with grain size. Reverse Hall–Petch behavior was observed with no appreciable room temperature creep. Non-linear elasticity with small irreversible deformation was observed for 50 nm thick specimens.     

Synthesis and characterization of hardness-enhanced multilayer oxide films for high-temperature applications

Multilayer oxide coatings consisting of amorphous Al₂O₃ and crystalline TiO₂ nanolayers have been deposited using reactive pulsed d.c. magnetron sputtering at different partial pressures of oxygen. Hardness enhancement has been observed in oxide multilayer coatings with amorphous Al₂O₃ as the majority component. These coatings had greater hardness-to-modulus ratios and showed greater resistance to wear over monolithic Al₂O₃ and TiO₂ majority phase multilayers. Multilayer films retain their high hardness up to ~ 800 °C in air; some hardness enhancement in the Al₂O₃ majority phase multilayer coating remains even after 1 h of air annealing at 1000 °C. The hardness decrease at elevated temperatures is due to the roughening of interfaces between nanolayers, which can be attributed to the annealing-driven change of crystallographic texture of TiO₂ layers.     

Thickness effects of Bi0.89Ti0.11FeO3 thin films deposited on PbZr0.2Ti0.79Nb0.01O3 buffer layers

Bi_0.89Ti_0.11FeO₃ thin films with the thicknesses of 200-440 nm were fabricated on the 40-nm-thick PbZr_0.2Ti_0.79Nb_0.01O₃ (PZTN)-buffered Pt(1 1 1)/Ti/SiO₂/Si substrates using a metal organic decomposition process. As a result of the good insulating property and high breakdown characteristic of the PZTN buffer layer, the leakage currents in the Bi_0.89Tb_0.11FeO₃ films are significantly reduced. All the films show well-saturated and rectangular P-E hysteresis loops without any evident leaky behavior. The remnant polarization P_r and coercive field E_c for all Bi_0.89Ti_0.11FeO₃ films are around 45-50 μC/cm² and 200 kV/cm, respectively, and show weak dependent on the film thickness. The 200-nm-thick Bi_0.89Ti_0.11FeO₃ film exhibits better fatigue-free characteristic and charge-retaining ability, and the domain backswitching is significantly restrained due to the strong anti-aging ability of the PZTN buffer layer.     

Mechanical spectroscopy and structural evolution of CuMo thin films

CuMo thin films with a typical thickness of 200 nm have been prepared by Ion Beam Sputtering (IBS) on oxidised silicon (100) substrates. Two samples with symmetric (atomic) composition Cu30Mo70 and Cu70Mo30 where studied. ‘Direct’ observations of the microstructure were performed by X-ray diffraction. The samples have been characterised in their as-sputtered state, then after annealing at increasing temperature. On the other hand, a vibrating reed device specially adapted for thin adherent films has been used to determine the mechanical properties over a temperature range between 20°C and 500°C. In this paper, it is shown that the structural evolution in temperature highly depends on the sample composition. Particularly, in the Mo-rich specimen, two independent stages have been shown. Indeed, the segregation process is preceded by a structural relaxation phenomenon. We have also shown that internal friction experiments are quite useful in the study of these structural modifications occurring in thin films.     

Structure and mechanical properties of Cr–B–N films deposited by reactive magnetron sputtering

Cr–B–N films with various B contents were deposited by reactive magnetron sputtering from the co-deposition of Cr and B targets in the presence of the reactive gas mixture. Comparative studies on microstructure and mechanical properties between CrN and Cr–B–N films with various B contents were conducted. The addition of B to CrN films caused a decrease of the crystallization of the films, while the B existed mainly as amorphous phase of BN compound in the CrBN films. The mechanical properties were also improved. And the Cr–B–N films with 6.1 at.% B content showed highest hardness and lowest wear rate.     

Preparation of delafossite-type CuCrO2 films by sol-gel method

High-quality c-axis oriented delafossite-type CuCrO₂ films were successfully prepared by a simple sol-gel method. The microstructure, optical properties as well as room temperature resistivity were studied. It was found that the grain sizes of CuCrO₂ films pretreated with different temperatures are different; the films were smooth and consisted of fine particles. The maximal transmittance of CuCrO₂ films can reach 70% in the visible region. Optical transmission data of CuCrO₂ films indicate a direct band gap and an indirect-gap of about 3.15 eV and 2.66 eV, respectively. The carrier mobility of the films pretreated at 300 °C is smaller than that of the films pretreated at a higher temperature, because of the stronger carrier scattering.     

Physical properties of tin oxide thin films improved by vapour chopping

The vapour chopping technique has been successfully used to lower the ambient air ageing effect on the tin oxide thin films. The films were prepared by thermal oxidation (in air) of vacuum evaporated vapour chopped and nonchopped tin thin films. The films showed SnO and SnO₂ phases with tetragonal and orthorhombic structure. All the films showed increase in optical transmittance with increase in oxidation temperature and duration. The vapour chopped films showed higher refractive index and band gap than those of nonchopped films. The refractive index was found to increase with the thickness. Due to air ageing, the refractive index of both the films was found to increase. The ageing effect was found lower on the vapour chopped (0.008) than those on nonchopped (0.02) tin oxide thin films. These films can have potential use in optical waveguides.     

Electric and dielectric behavior of CaCu3Ti4O12-based thin films obtained by soft chemical method

CaCu₃Ti₄O₁₂ (stoichiometric) and Ca_1.1Cu_2.9Ti₄O₁₂ (non-stoichiometric) thin films have been prepared by the soft chemical method on Pt/Ti/SiO₂/Si substrates, and their electrical and dielectric properties have been compared as a function of the annealing temperature. The crystalline structure and the surface morphology of the films were markedly affected by the annealing temperature and excess calcium. The films show frequency-independent dielectric properties at room temperature which is similar to those properties obtained in single-crystal or epitaxial thin films. The room temperature dielectric constant of the 570-nm-thick CCTO thin films annealed at 600 °C at 10 kHz was found to be 124. The best non-ohmic behavior (α = 12.6) presented by the film with excess calcium annealed at 500 °C. Resistive hysteresis on the I-V curves was observed which indicates these films can be used in resistance random access memory (ReRAM).     

Fabrication of hexagonal gallium nitride films on silicon (111) substrates

Hexagonal gallium nitride films were successfully fabricated through ammoniating Ga2O3 films deposited on silicon (111) substrates by electrophoresis. The structure, composition, and surface morphology of the formed films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The measurement results reveal that the polycrystalline GaN films with hexagonal wurtzite structure were successfully grown on the silicon (111) substrates. Preliminary results suggest that varying the ammoniating temperature has obvious effect on the quality of the GaN films formed with this method.     

Effect of annealing temperature on the structure and optical properties of sputtered TiO2 films

TiO₂ thin films were deposited by DC reactive magnetron sputtering. Some TiO₂ thin films samples were annealed for 5 min at different temperatures from 300 to 900 °C. The structure and optical properties of the films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM) and ultraviolet-visible (UV-vis) spectrophotometry, respectively. The influence of the annealing temperature on the structure and optical properties of the films was investigated. The results show that the as-deposited TiO₂ thin films are mixtures of anatase and rutile phases, and possess the column-like crystallite texture. With the annealing temperature increasing, the refractive index and extinction coefficient increase. When the annealing temperature is lower than 900 °C, the anatase phase is the dominant crystalline phase; the weight fraction of the rutile phase does not increase significantly during annealing process. As the annealing temperature rises to 900 °C, the rutile phase with the large extinction coefficient becomes the dominant crystalline phase, and the columnar structure disappears. The films annealed at 300 °C have the best optical properties for the antireflection coatings, whose refractive index and extinction coefficient are 2.42 and 8 × 10⁻⁴ (at 550 nm), respectively.     

Preferential grain growth and improved fatigue endurance in Sr substituted PZT thin films on Pt(1 1 1)/TiOx/SiO2/Si substrates

Pb(Zr_0.5Ti_0.5)O₃ and (Pb_0.9Sr_0.1)(Zr_0.5Ti_0.5)O₃ thin films were grown on Pt/TiO_x/SiO₂/Si substrates by chemical solution deposition. 10% Sr substituted PZT film showed high degree of (0 0 1) type preferential grain growth. Surface morphology revealed a clear correlation between preferred grain orientation and grain size. Room temperature dielectric constant was 1200 and 700 for the PZT and PSZT films, respectively. Dielectric loss reduced with Sr substitution. PZT film showed severe fatigue, and hence the polarization reduced to 20% of the initial value (24 μC/cm²) after 10⁸ cycles where as PSZT showed less fatigue, 75% of the initial polarization (12 μC/cm²) was retained after 10⁸ switching cycles.     

Origin of significant visible-light absorption properties of Mn-doped TiO2 thin films

It is highly desirable to induce significant red-shift in the optical absorption edges of TiO₂ phases so that this class of low-cost and environmentally friendly materials can be used as effective optical absorbing materials in novel photovoltaic cells with long-term sustainability or smart photo-catalysts beyond the ultraviolet range. This work focuses on studying the mechanisms of Mn-induced red-shift by combining theoretical modeling with advanced structural and spectroscopic characterization of doped thin films, aiming to provide fundamental guidance for effective doping through enhanced understanding of doping chemistry resulting from the interplay between doping atoms and defects. It is shown that Mn atoms doped into the Ti lattice sites are associated with oxidation valency higher than +3, resulting in maximized effectiveness in modifying the band structure to achieve remarkable optical red-shifting. The presence of oxygen vacancies reduces the Mn valency and its red-shifting effect, but their detrimental effect in bringing about localized defect levels is reduced owing to their association with Mn atoms, making Mn doping highly promising in activating various visible light functionalities of TiO₂.