Discrete β-Ta2O5 crystallite formation in reactively sputtered amorphous thin films

The crystallization of thin amorphous TaOx films formed by d.c. reactive sputtering was investigated at temperatures from 500–700 °C. The films remained amorphous for times up to 100 h at 500 °C. The formation of discrete, single crystallites of the orthorhombic -Ta2O5 phase was observed after annealing at 600 °C for times from 8–108 h. The crystallites were 0.35 m×0.35 m after 8 h and grew to approximately 2.5 m×2.0 m after 108 h. A (2 0 0) fibre texture with a 6° spread was observed. More rapid in-plane growth in the [0 1 0] direction resulted in a near-rectangular shape and is attributed to a ledge growth mechanism. Higher temperature anneals at 650 and 700 °C produced less-textured polycrystalline films with remnant amorphous regions. © 1998 Kluwer Academic Publishers     

MOCVD growth of HfSixOy films from hafnium β-diketonato silylamides and siloxides

New hafnium β-diketonato-silylamide and siloxides namely Hf(thd)₂[N(SiMe₃)₂]₂ (1), Hf(thd)₂(OSiMe₃)₂ (2) and Hf(thd)₂(OSi^tBuMe₂)₂ (3) (thd=2,2,6,6-tetramethyl-3,5-heptanedionate) were investigated as single-source precursors for low-pressure pulsed liquid injection MOCVD of HfSi_xO_y thin films on Si(1 0 0) and R-plane sapphire. Films were characterized by XRD, XPS and AFM. The growth rate increased in order 1>2>3 in agreement with the decreasing precursor thermal stability. The activation energy was ∼80-100 kJ/mol. The as-deposited at 550-800 °C films were essentially amorphous; hafnia reflections appeared after 1 h annealing at 900 °C probably due to phase separation into amorphous Si-rich silicate and crystallized HfO₂. The surface of the films showed similar amounts of Hf and Si (∼1:1) and was overstoichiometric in oxygen (ratio O/(Hf+Si) >2). The bulk of the films was Hf-rich (70-85% of Hf/ Hf+Si) and slightly oxygen-deficient. The new complexes are attractive single-source precursors for the deposition of pure and very smooth (R_a∼0.7 nm, <1% relative to thickness) HfSi_xO_y films. Dielectric constant 11.3 and leakage current density 8×10⁻⁴ A/cm² (at −1 V) were measured for a 22 nm thick film.     

On the νSiO infrared absorption of polysiloxane films

The infrared absorption of polysiloxanes involves a strong band at around 1050 cm^− 1, attributed to the antisymmetric vibration of siloxane bridges. The splitting of this band into two components is generally attributed to coupling between next-neighbor siloxane groups along the polysiloxane chain. From a quantitative analysis of the spectra of these materials, we find that this splitting is larger when the material is in thin-film form, and that the relative intensity of the two components is polarization dependent. We show that these effects are fully understandable in the theoretical framework of infrared absorption by thin films, and are related to long-range dipolar interactions responsible for the longitudinal-transverse splitting effect in crystalline materials. As a consequence, the polarization dependence of the infrared absorption observed for thin films does not appear to be associated with an orientational ordering in the film.     

Power and gas pressure effects on properties of amorphous In–Ga–ZnO films by magnetron sputtering

Amorphous In–Ga–ZnO thin films were deposited on quartz glass substrate at room temperature utilizing radio frequency magnetron sputtering technique. Sputtering power and oxygen flow rate effects on the physical properties of the In–Ga–ZnO films were systematically investigated. It is shown the film deposition rate and the conductivity of the In–Ga–ZnO films increased with the sputtering power. The as-grown In–Ga–ZnO films deposited at 500 W exhibited the Hall mobility of 17.7 cm²/Vs. Average optical transmittance of the In–Ga–ZnO films is greater than 80% in the visible wavelength. The extracted optical band gap of the In–Ga–ZnO films increased from 3.06 to 3.46 eV with increasing the sputtering power. The electrical properties of the In–Ga–ZnO films are greatly dependent on the O₂/Ar gas flow ratio and post-growth annealing process. Increasing oxygen flow rate converted the In–Ga–ZnO films from semiconducting to semi-insulating, but the resistivity of the films was significantly reduced after being annealed in vacuum. Both the as-grown and annealed In–Ga–ZnO films show n-type electrical conductivity.     

The photoluminescence of SiCN thin films prepared by C implantation into α-SiNx:H

SiCN thin films were prepared by high-dosage (2 × 10¹⁷ cm^− 2) C⁺ ion implantation into α-SiN_x:H films. The prepared films were then processed by thermal annealing for 2 h at 800 °C, 1000 °C and 1200 °C respectively. The composition and bond structure of SiCN were analyzed by X-ray photoemission spectroscopy, Auger electron spectroscopy, Raman spectroscopy and X-ray diffraction, and photoluminescence. Ternary structure with N bridging C and Si of the film annealed at 800 °C was found. The luminescent properties of SiCN have also been studied by synchrotron radiation at 20 K. Four emission bands were observed, corresponding to 2.95, 2.58, 2.29 and 2.12 eV at 20 K, respectively. In this paper, we report the experimental results and try to explain them.     

Microstructure and tribological performance of CNx–TiNx composite films prepared by pulsed laser deposition

CN_x–TiN_x composite films were prepared on high-speed steel (HSS) substrate by pulsed KrF excimer laser co-deposition process with graphite/Ti combined targets and a substrate temperature of 200 °C. The composition, morphology and microstructure of the films were characterized by energy dispersive X-ray spectrum (EDS), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). The adhesion and tribological performance of the films were investigated using a conventional scratch tester and a ball-on-disk tribometer, respectively. In the graphite/Ti range of 0.5–2.0 of the target, TiN_x, a-CN_x and metallic Ti phase were found in the composite films. The TiN_x disappeared in the films at a high graphite/Ti ratio of the target. With increasing the graphite/Ti ratio of the target, the adhesion to substrate of the composite films deteriorated from 46 N to 26 N, and the friction coefficient decreased from 0.23 to 0.17. The composite film deposited at the graphite/Ti ratio of 1.0 showed a low friction coefficient, good adhesion and wear rate of 3.2 × 10⁻⁷ mm³/Nm in humid air.     

Prediction of hot compression flow curves of Ti–6Al–4V alloy in α + β phase region

Prediction of material flow behavior is essential for designing the forming process of any material. In this research, experimental flow curves of Ti–6Al–4 V alloy were obtained using the isothermal hot compression test done at 750–950 °C with 50 °C intervals and constant strain rates of 0.001, 0.005 and 0.01 s⁻¹. For prediction of hot deformation flow curves two methods of modeling were applied. In the first method, an entire flow curve was modeled using Sellars equation. In the second one, modeling of a flow curve up to the peak point was carried out with Cingara model, and modeling beyond that was performed with a model developed based on the Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory. The accuracy of each model was examined through a statistical method. Results showed that flow curve modeling using Cingara model and JMAK theory leads to results that are more consistent with the experimental data.     

Determination of Young's modulus and Poisson's ratio of thin films by combining sinψ X-ray diffraction and laser curvature methods

In this study, we have proposed a nondestructive method to simultaneously determine the Young's modulus (E) and Poisson's ratio (ν) of polycrystalline thin film materials. The method involved independent stress measurement by laser curvature technique and strain components determination by sin²ψ X-ray diffraction (XRD) method, and afterward, elasticity theory was employed to calculate E and ν. The proposed method was applied on two model specimens, TiN and ZrN thin films, using synchrotron X-ray and laboratory X-ray sources, respectively. The cos²αsin²ψ XRD method which measured the strain for diffraction planes at different location was performed on the same film, and the previously determined E and ν were used to calculate the stress. The residual stresses derived from cos²αsin²ψ method were close to the stresses from laser curvature measurements, which validated the measured values of E and ν. The depth profile of residual stress of the TiN thin film was assessed using cos²αsin²ψ method by appropriately adjusting the X-ray incident angle. In addition, the E value determined from nanoindentation (NIP) may depend on the indentation depth. Therefore, one should be cautious when employing the NIP-determined E in sin²ψ or cos²αsin²ψ methods to calculate the residual stress because the modulus may not always give correct stress value.     

Characteristics of organic-inorganic hybrid plasma polymer thin films for low-κ ILD applications

This study investigated the effects of plasma power and tetraethylorthosilane (TEOS) to cyclohexene ratios on low-κ organic-inorganic hybrid plasma polymer thin films deposited on silicon (100) substrates. These films were deposited using a plasma enhanced chemical vapor deposition (PECVD) method, in addition to the electrical and mechanical properties of the resulting composites. Cyclohexene and TEOS were used as organic and inorganic precursors, respectively, with hydrogen and argon as precursor bubbler gases. Furthermore, additional argon was used as a carrier gas. The as-grown polymerized thin films were analyzed using ellipsometry, Fourier-transform infrared (FT-IR) spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The ellipsometry results showed the thickness of the hybrid thin film, and the FT-IR spectra showed that the hybrid polymer thin films were completely fragmented and polymerized between cyclohexene and TEOS. AFM results showed that polymer films with a smooth surface could be grown under various deposition conditions, while TEM and XRD showed that the hybrid thin film was an amorphous plasma polymer thin film without porosity. In addition, current-voltage (C-V) curves were prepared to calculate the dielectric constants. Post-annealing was applied to investigate the thermal stability of hybrid plasma polymer thin films in the hardness, Young's modulus, thermal shrinkage, and the dielectric constant at 400 °C.     

Bandgap modifications by lattice deformations in β-FeSi2 epitaxial films

The modifications of direct transition energies by lattice deformations were investigated in β-FeSi₂ epitaxial films, polycrystal films and single crystal, systematically. The lattice deformations depending on thermal annealing temperature (T_a) were observed in β-FeSi₂ epitaxial films. In photoreflectance (PR) measurements, the direct transition energies of the epitaxial films shifted to lower energies as the T_a increased. The polycrystal films did not show the lattice deformation and the shift of direct transition energies. These results show that the direct bandgap is modified by the lattice deformation originating from the lattice mismatch at the hetero-interface of β-FeSi₂/Si.     

Fabrication and frequency response of solidly mounted resonators with 1/4λ mode configuration

A solidly mounted resonator (SMR) consists of a multilayered structure and requires material interfaces that confine waves to resonate as standing waves in order to avoid wave energy loss. The selection of high or low acoustic impedance for the first layer beneath piezoelectric layer results in 1/4λ mode and 1/2λ mode resonance configurations.In this study, Mo/SiO₂ is chosen to construct the Bragg reflector as the high/low acoustic impedance materials, respectively, and aluminum nitride (AlN) is used as the piezoelectric layer. For application at frequency of 2.5 GHz, the specific thicknesses of Mo, SiO₂, and AlN are considered individually in the deposition processes. AlN of 1/4λ thickness is deposited on a seven-layer Bragg reflector. The 1/4λ mode SMR shows the distinct resonant characteristics at 1.3 GHz (shear mode) and 2.4 GHz (longitudinal mode). The coupling coefficient K_eff² of 6.9% is in agreement with the theoretical analysis.     

Novel upconversion phenomenon of Nd sensitized by Yb in Nd-Yb-co-doped β-Na(Y1.5Na0.5)F6

Hexagonal phase Na(Y_1.5Na_0.5)F₆ co-doped with Yb³⁺ and Nd³⁺ was synthesized and its structure was studied by XRD and Raman methods. The Raman scattering spectrum illustrates it is a host with low phonon energy. Emissions in green (⁴G_7/2 → ⁴I_9/2), yellow (⁴G_7/2 → ⁴I_11/2), red (⁴G_7/2 → ⁴I_13/2), and infrared (⁴F_5/2 → ⁴I_9/2, ⁴F_3/2 → ⁴I_9/2) were observed and were the direct result of emissions of the Nd³⁺ ion. The luminescence intensity ratio (I₈₆₃/I₈₀₄) gradually decreased with the increase of excitation power. The long lifetime of 863 nm infrared emission was proved. The upconversion mechanism was deduced to be energy transfer from the Yb³⁺ to Nd³⁺ under 980 nm excitation, by analyzing the energy level structures of Nd³⁺ and Yb³⁺ ions and measuring the power dependence of upconverted emission intensities.     

Gas pressure dependence of composition in Ta–Ti–N films prepared by pulsed high energy density plasma

Tantalum titanium nitride (Ta–Ti–N) films were deposited on silicon wafer substrates by pulsed high energy density plasma (PHEDP), under different intake gas pressures, ranging from 0.1 to 0.4 MPa. The films were investigated by X-ray photoelectron spectroscopy. Results were analyzed in detail, which reveals that the contents of the metallic elements (Ta and Ti) tend to decrease with pressure, while that of nitrogen increases as expected. With increasing pressure, the films can be denoted as TaTi_3.9N_2.8, TaTi_4.7N_6.0, TaTi_2.2N_8.4 and TaTi_3.1N1_3.5, respectively. The bonding state of tantalum, titanium, as well as nitrogen was fitted and discussed. Our results demonstrate that almost all the titanium bonded with nitrogen. The Ta–N and Ti–N bonds have equal shares under low gas intake pressure, while the Ti–N bonds prevail under high pressure. The preferential sputtering between the coaxial electrodes should be responsible for this phenomenon. Under low nitrogen pressure, the preferential sputtering is quite significant; while it could be neglected under high pressure.     

Growth of CZTS thin films by sulfurization of sputtered single-layered Cu–Zn–Sn metallic precursors from an alloy target

Cu₂ZnSnS₄ (CZTS) thin films were prepared by sulfurizing single-layered metallic Cu–Zn–Sn precursors which were deposited by DC magnetron sputtering using a Cu–Zn–Sn ternary alloy target. The composition, microstructure and properties of the CZTS thin films prepared under different sputtering pressure and DC power were investigated. The results showed that the sputtering rate of Cu atom increases as the sputtering pressure and DC power increased. The microstructure of CZTS thin films can be optimized by sputtering pressure and DC power. The CZTS thin film prepared under 1 Pa and 30 W showed a pure Kesterite phase and a dense micro-structure. The direct optical band gap of this CZTS thin film was calculated as 1.49 eV with a high optical absorption coefficient over 10⁴ cm^?1. The Hall measurement showed the film is a p-type semiconductor with a resistivity of 1.06 Ω cm, a carrier concentration of 7.904 × 10¹⁷ cm^?3 and a mobility of 7.47 cm² Vs^?1.     

Crossover of magnetoresistance from positive to negative in La0.5Sr0.5CoO3 − σ/Si heterostructure

The magnetoresistance (MR) properties of a heterostructure fabricated by depositing a La_0.5Sr_0.5CoO_3 − σ film on an n-type Si substrate have been studied. The heterostructure exhibits a good rectifying behavior. A negative MR at T = 210 K and a positive MR at T = 300 K are observed for all bias currents whereas; for temperatures ranging from 240 to 280 K the MR changes from being positive to negative with the increase of the bias current. The observed behavior of the MR effect is discussed in terms of current-induced ferromagnetic spin order.     

Microstructure, magnetic and electronic transport properties of polycrystalline γ′-Fe4N films

The single-phase γ′-Fe₄N films were fabricated using reactive sputtering. The x-ray diffraction peaks from γ′-Fe₄N(111), (200) and (311) indicate that the films are γ′-Fe₄N. The grain size increases with the increase of film thickness (t), and the grains grow with a columnar structure. All of the films are soft ferromagnetic at room temperature. The saturation magnetization decreases with the increasing temperature, and satisfies the modified Bloch's spin wave theory. The electrical transport properties show a metallic conductance mechanism, and the room-temperature resistivity decreases with the increasing t, revealing that the electron scattering increases with the decrease of t. The magnetoresistance (MR) evolves from positive to negative with the increase of temperature, and the transition temperature decreases with the increase of t. The positive MR at 5 K increases with the increasing t. The complex MR should be dominated by Lorentz force effect, the suppression of the electron scattering, and the shift of minority and majority spin bands under a magnetic field.     

Effect of stacking fault probability and ε martensite on damping capacity of Fe–16%Mn alloy

The damping capacity of a Fe–16%Mn–1%Mg–2%Si (wt.%) alloy has been studied with respect to factors like stacking fault probability, ε martensite, and cold rolling. It was found that the damping capacity of 8% cold rolled specimen is much higher than 0% cold rolled specimen. In the 0% rolled specimen, the stacking faults are responsible for the damping capacity characterized by the large amplitude dependence. The improvement in damping capacity by cold rolling is attributed to the formation of ε martensite. As the temperature increases, the damping capacity improves, reaching its maximum around 1000 °C. A further increase in the temperature, however, degrades the damping capacity. The area of the γ/ε boundaries is the major factor for damping capacity. Heat treatment at 1100 °C reduces the number of ε martensite plates, leading to area reduction of γ/ε boundaries despite an increase in amount of ε martensite.     

AC plasma induced modifications in β-In2S3 thin films prepared by spray pyrolysis

β-In₂S₃ thin films, deposited by spray pyrolysis, were treated in N₂ and air plasmas at 240 and 400 Pa. X-ray diffraction, SEM, and EDS analysis, and optical and electrical studies have been used to characterize the as-prepared and plasma treated thin films. The post-deposition plasma treatments affect the morphology and the optoelectronic properties of the In₂S₃ thin films. The In₂S₃ thin films treated with N₂ plasma at 240 Pa showed an optical band gap, E_g, of 2.16 eV and an electrical conductivity of 2 × 10^− 2 (Ω cm)^− 1.     

Hydrothermal synthesis of β-cobalt hydroxide with various morphologies in water/ethanol solutions

Various morphologies of cobalt hydroxides have been successfully prepared from cobalt nitrate with the assistance of dimethylglyoxime in water/ethanol solutions by hydrothermal processing at 220 °C. The crystalline products are hexagonal phase of β-cobalt hydroxide, and the crystallinity increases as the volume ratio of water to ethanol rises. Hexagonal plate-like, broom-like or straw bundle-like, and grass-like cobalt hydroxides are obtained with water to ethanol ratios of 1:0, 2:1 and 1:2, respectively. The novel bundle-like assemblies are further constructed from lots of nanobelts, which mainly grow along [100] direction and evolve from less-crystalline disc-like structures and semi-crystalline flower-like assemblies as the hydrothermal time extended.     

Study of YBaCo4O7 + δ thin films grown by sputtering technique on (1012)-oriented sapphire substrates

We report the growth of thin films of the cobaltite YBaCo₄O_7 + δ by means of the dc magnetron sputtering technique at high oxygen pressure onto r (1012) sapphire substrates. The films were characterized according to their structural, morphological, electrical, magnetic, and optical properties. An analysis of the X-ray diffraction pattern indicates that the films grown on r-sapphire substrates are single phase polycrystalline. Despite the high growth temperature (850 °C), no indication of interface reaction (formation of BaAlO₄ or Y₂O₃) is detected. Measurements of resistivity as a function of temperature reveal a semiconductor-like character of the grown films. No indication of possible transitions is observed in the temperature range 50-300 K. The electronic transport mechanism seems to be dominated by Mott variable range hopping (VRH) conduction. Fitting the VRH model to the experimental data allows one to estimate the density of states of the material at the Fermi level N(E_F). The resistivity measured in magnetic fields as strong as 5 T increases notably, and positive magnetoresistance values as high as ~ 60% at 100 K are obtained. Magnetization measurements show well defined hysteresis loops at 300 K and 5 K. Nevertheless, calculated values of the magnetization have ended up being too small for the ferro- or ferrimagnetic states. Raman spectra, in turn, allow one to identify bands associated with vibrating modes of CoO₄ and YO₆ in tetrahedral and octahedral configurations, respectively. Additional bands which seem to stem from Co ions in octahedral configuration are also clearly identified. Measurements of transmittance and reflectance show two well defined energy gaps at 3.7 and 2.2 eV.