Preparation and characterization of transparent NiO thin films deposited by spray pyrolysis technique

Nickel oxide thin films were successfully fabricated with various deposition time (t_d = 5, 10, and 15 min) on glass substrates using spray pyrolysis technique. The deposited films undergo thermal treatment at 350 °C for various annealing time (t_a = 0, 15, 30 and 60 min). In this study, the effect of t_d and t_a on film thickness was observed and their influence on structural, morphological and optical properties were investigated. The films deposited with t_d = 5 min showed amorphous structure while the films grown at higher deposition time became partially crystallized with preferred growth along (1 1 1) direction. Heat treatment carried out in air allowed us to tune the polycrystalline structure and the diffraction intensity at preferred peak increases with the increase in t_a which is a consequence of better crystallinity. This was reflected in the AFM micrographs of the films which suggested that the thermal annealing (or increasing t_a) facilitates the process of grain-growth, and improves the crystalline microstructure. The optical transmission of the films was found to vary with t_d and t_a and thus film thickness. The thinner films show higher transparency in the UV–vis spectral region. The optical band gap was blue-shifted from 3.35 eV to 3.51 eV depending on t_a. The effect of t_a on the various optical constants of the NiO films has also been discussed.     

An investigation of structural phase transformation and electrical resistivity in Ta films

In this work, we report the effect of substrate, film thickness and sputter pressure on the phase transformation and electrical resistivity in tantalum (Ta) films. The films were grown on Si(1 0 0) substrates with native oxides in place and glass substrates by varying the film thickness (t) and pressure of the working gas (p_Ar). X-ray diffraction (XRD) analysis showed that the formation of α and β phases in Ta films strongly depend on the choice of substrate, film thickness t and sputter pressure p_Ar. A stable α-phase was observed on Si(1 0 0) substrates for t ≤ 200 nm. Both α and β phases were found to grow on glass substrates at all thicknesses except t = 100 nm. All the films grown on Si(1 0 0) substrates for p_Ar ≤ 6.5 mTorr had α-phase with strong (1 1 0) texture normal to the film plane. The glass substrates promoted the formation of β-phase in all p_Ar except p_Ar = 5.5 mTorr. The resistivity ρ was observed to decrease with t, whereas ρ was increased with p_Ar on Si(1 0 0) substrates. In all films, the measured resistivity ρ was greater than the bulk resistivity. The resistivity ρ was influenced by the effects of surface roughness and grain size.     

Electrical performance of Ti/Pt thin films on glass-ceramic substrates after high temperature loading

In this study, the influence of post-deposition annealings (PDA) up to temperatures of T _PDA=700°C on the room-temperature resistivity of e-beam evaporated titanium/platinum (Ti/Pt) bi-layers on low temperature co-fired (LTCC) substrates covered with a glass encapsulate is investigated. The thickness of the platinum top layer is varied between 24 and 95 nm (titanium film thickness: 5 nm) and between 23 and 90 nm (titanium film thickness: 15 nm), respectively. In the “as-deposited” state and up to post-deposition annealing temperatures of T _PDA=450°C, the film resistivity is linearly correlated with the reciprocal value of the platinum film thickness according to the size effect. When applying, however, solely the Fuchs-Sondheimer model for evaluation, the effective mean free path for electrons is substantially above the value reported for crystalline platinum at room temperature. Compared to similar investigations on smooth Si/SiO₂ substrates yielding interpretable results within this theoretical approach, this is due to the increase of the thickness-dependent fraction in film resistivity which is strongly affected by the enhanced LTCC/glass surface roughness. At T _PDA>600°C, diffusion of titanium into the platinum top layer and the roughening of the LTCC/glass substrate dominate the electrical behavior, both causing an increase in film resistivity above average. In contrast to Si/SiO₂ substrates, thermal induced grooving effects in the Pt top layer play a minor role as the temperature coefficients of expansion of metallization and glass-ceramic substrate match better and the effective temperature difference for stress generation is lower due a glass softening temperature of about 450°C.     

Synthesis and surface modified hard magnetic properties in Co0.5Pt0.5 nanocrystallites from a rheological liquid precursor

Small crystallites of a metastable phase Co_0.5Pt_0.5 are precipitated by heating a rheological liquid precursor of cobalt–hydrazine complex and platinum chloride H₂PtCl₆·xH₂O in polymer molecules of poly(vinylpyrrolidone) (PVP) in ethylene glycol. The hydrazine co-reduces nascent atoms from the Co²⁺ and Pt⁴⁺ that recombine and grow as Co_0.5Pt_0.5. The PVP molecules cap a growing Co_0.5Pt_0.5 as it achieves a critical size so that it stops growing further in given conditions. X-ray diffraction pattern of a recovered powder reveals a crystalline Co_0.5Pt_0.5 phase (average crystallite size D∼8 nm) of a well-known Fm3m-fcc crystal structure with the lattice parameter a=0.3916 nm (density ρ=14.09 g/cm³). A more ordered L1₀ phase (ρ=15.91 g/cm³) transforms (D≥25 nm) upon annealing the powder at temperature lesser than 700 °C (in vacuum). At room temperature, the virgin crystallites bear only a small saturation magnetization M_s=5.54 emu/g (D=8 nm) of a soft magnet and it hardly grows on bigger sizes (D≤31 nm) in a canted ferromagnetic structure. A rectangular hysteresis loop is markedly expanded on an optimally annealed L1₀ phase at 800 °C for 60 min, showing a surface modified coercivity H_c=7.781 kOe with remnant ratio M_r/M_s=0.5564, and M_s=39.75 emu/g. Crystallites self-assembled in an acicular shape tailor large H_c from ideal single domains and high magnetocrystalline anisotropy of a hard magnet L1₀ phase.     

Effect of substrate temperature and annealing temperature on the structural, electrical and microstructural properties of thin Pt films by rf magnetron sputtering

Influence of both substrate temperature, T_s, and annealing temperature, T_a, on the structural, electrical and microstructural properties of sputtered deposited Pt thin films have been investigated. X-ray diffraction results show that as deposited Pt films (T_s = 300, 400 °C) are preferentially oriented along (1 1 1) direction. A little growth both along (2 0 0) and (3 1 1) directions are also noticed in the as deposited Pt films. After annealing in air (T_a = 500-700 °C), films become strongly oriented along (1 1 1) plane. With annealing temperature, average crystallite size, D, of the Pt films increases and micro-strain, e, and lattice constant, a₀, decreases. Residual strain observed in the as deposited Pt films is found to be compressive in nature while that in the annealed films is tensile. This change in the strain from compressive to tensile upon annealing is explained in the light of mismatch between the thermal expansion coefficients of the film material and substrate. Room temperature resistivity of Pt films is dependant on both the T_s and T_a of the films. Observed decrease in the film resistivity with T_a is discussed in terms of annihilation of film defects and grain-boundary. Scanning electron microscopic study reveals that as the annealing temperature increases film densification improves. But at an annealing temperature of ∼600 °C, pinholes appear on the film surface and the size of pinhole increases with further increase in the annealing temperature. From X-ray photoelectron spectroscopic analysis, existence of a thin layer of chemisorbed atomic oxygen is detected on the surfaces of the as deposited Pt films. Upon annealing, coverage of this surface oxygen increases.     

Fabrication and characterization of sputtered titanium dioxide films

TiO₂ thin films were prepared under various conditions by using a reactive RF sputtering technique. The structural, optical and electrical characteristics of the films have been investigated. All as-deposited films were amorphous. After annealing at T > 673 K, the crystallinity of the observed tetragonal anatase phase appeared improved. The optical band gap, determined by using Tauc plot, has been found to amount to 3.38 ± 0.03 and 3.21 ± 0.03 eV for the direct and indirect transition, respectively. Also the complex optical constants for the wavelength range 300-2500 nm are reported. Using the two-point probe technique, the dark resistivity has been measured as a function of the film thickness, d. The resistivity, ρ, of the samples has been found to decrease markedly with increasing thickness, but only for d < 100 nm. The behaviour of ρd versus d was found to fit properly with the Fuchs and Sondheimer relation with parameters ρ_o = 4.95 × 10⁶ Ω cm and mean free path, l = 310 ± 2 nm. The log ρ versus 1/T curves show three distinct regions with values for the activation energy of 0.03 ± 0.01, 0.17 ± 0.01 and 0.50 ± 0.02 eV, respectively.     

Influence of Pt thickness on magnetization reversal processes in (Pt/Co)3 multilayers with perpendicular anisotropy

We present a detailed study of the magnetization reversal in perpendicularly magnetized (Pt/Co)₃ multilayers with different values of the platinum interlayer thickness t_Pt. To study the magnetization reversal in our samples we combined measurements of relaxation curves with the direct visualization of domain structures. Magnetization reversal was dominated by domain wall propagation for t_Pt=1 nm and by domain nucleation for t_Pt=0.2 nm, while a mixed process was observed for t_Pt=0.8 nm. We interpret our results within the framework of a model of thermally activated reversal where a distribution of activation energy barriers is taken into account. The reversal process was correlated with the energy barrier distribution.     

Theoretical investigation of the intrinsic piezoelectric properties for tetragonal BaTiO3 epitaxial films

The orientation dependences of the converse longitudinal piezoelectric constant d_33,f, and the in-plane converse piezoelectric constant e_31,f, are calculated for tetragonal barium titanate epitaxial films. The calculations demonstrate that both e_31,f and d_33,f have their maximum values along an axis close to the (1 1 1) direction of the pseudo-cubic system, which are similar to the orientation dependence results for a tetragonal BaTiO₃ single crystal. The calculated piezoelectric constants for a (1 1 1) oriented BaTiO₃ epitaxial film (e_31,f = −23 C/m², d_33,f = 124 pm/V) suggest that it is a good candidate material for lead-free MEMS applications.     

Comparison of annealing effects on Zn-doped GaMnAs and undoped GaMnAs epilayers

To compare the annealing effects on GaMnAs-doped with Zn (GaMnAs:Zn) and undoped GaMnAs (u-GaMnAs) epilayers, we grew GaMnAs thin films at 200 °C by molecular beam epitaxy (MBE) on GaAs substrates, and they were annealed at temperatures ranging from 220 °C to 380 °C for 100 min in air. These epilayers were characterized by high-resolution X-ray diffraction (XRD), electrical, and magnetic measurements. A maximum resistivity at temperatures T_m close to the Curie temperatures T_c was observed from the measurement of the temperature-dependent resistivity ρ(T) for both the GaMnAs:Zn and the u-GaMnAs samples. We found, however, that the maximum temperature T_m observed for GaMnAs:Zn epilayers increased with increasing annealing temperature, which was different from the result with the u-GaMnAs epilayers. The formation of GaAs:Zn and MnAs or Mn-Zn-As complexes with increasing annealing temperature is most likely responsible for the differences in appearance.     

Influence of atomic hydrogen annealing on the optical properties of vacuum-deposited a-Si:H films

The influence of atomic hydrogen annealing on the optical parameters of a-Si:H films was studied using spectrophotometric measurements of the film transmittance and reflectance in the wavelength range 200-3000 nm. In this annealing, the deposition of a thin layer and treatment with atomic hydrogen were repeated alternately, where the thickness of the thin cyclic layer, d_cyc, and the treatment time of each cycle, t_ca, were kept fixed for each sample. A series of different samples with average thickness of 0.5 μm and different d_cyc and t_ca were prepared. It was found that the refractive index, n, and the optical energy gap, E_g, increase as the treatment time, t_ca, increases from 0 to 60 s, while at t_ca=120 s both n and E_g decrease. Also, both the refractive index and the optical energy gap decrease with increasing the relative diffusion length of hydrogen, √t_ca/d_cyc from 0.39 to 0.77. The widening of E_g is due to the structural relaxation resulting from impingement of atomic hydrogen on the growing surface. Thus, a good-quality a-Si:H with Urbach parameter 65 mev and optical energy gap of 1.78 eV was successfully prepared.     

Crystallization and electrical properties of V2O5 thin films prepared by RF sputtering

V₂O₅ thin films were prepared under various conditions by using reactive RF sputtering technique. The microstructure and electrical properties of the films are have been investigated. X-ray diffraction data revealed the films deposited at low O₂/Ar ratio are amorphous. The orthorhombic structure of film improved after post annealing at 873 K. The microstructure parameters (crystallite/domain size and macrostrain) have been evaluated by using a single order Voigt profile method. Using the two-point probe technique, the dark conductivity as a function of the condition parameters such as film thickness, oxygen content and temperature are discussed. It was also found that, the behaviour of ρd versus d was found to fit properly with the Fuchs-Sondheimer relation with the parameters: ρ_o = 2.14 × 10⁷ Ω cm and ?_o = 112 ± 2 nm. At high temperature, the electrical conductivity is dominated by grain boundaries, the values of activation energy and potential barrier height were 0.90 ± 0.02 eV and 0.92 ± 0.02 V, respectively.     

Magnetic,structural and electrical properties of ordered and disordered Co50Fe50 films

Co₅₀Fe₅₀ films with thickness varying from 100 to 500 Å were deposited on a glass substrate by sputtering process, respectively. Two kinds of CoFe films were studied: one was the as-deposited film, and the other the annealed film. The annealing procedure was to keep the films at 400 °C for 5 h in a vacuum of 5×10⁻⁶ mbar. From the X-ray study, we find that the as-deposited film prefers the CoFe(1 1 0) orientation. Moreover, the body-centered cubic (bcc) CoFe(1 1 0) line is split into two peaks: one corresponding to the ordered body-centered tetragonal (bct) phase, and the other, the disordered bcc phase. After annealing, the peak intensity of the ordered bct phase becomes much stronger, while that of the disordered bcc phase disappears. The annealing has also caused the ordered CoFe(2 0 0) line to appear. When the amount of the ordered bct phase in Co₅₀Fe₅₀ is increased, the saturation magnetization (M_s) and coercivity (H_c) become larger, but the electrical resistivity (ρ) decreases. From the temperature coefficient of resistance (TCR) measurement, we learn that the bct grains in the CoFe film start to grow at temperature 82 °C.     

Characterization of chemically deposited ZnSe/SnO2/glass films: Influence of annealing in Ar atmosphere on physical properties

The Zinc Selenide (ZnSe) thin films have been deposited on SnO₂/glass substrates by a simple and inexpensive chemical bath deposition (CBD). The structural, optical and electrical properties of ZnSe films have been characterized by X-ray diffraction (XRD), Energy Dispersive X-ray Analysis (EDAX), optical absorption spectroscopy, and four point probe techniques, respectively. The films have been subjected to different annealing temperature in Argon (Ar) atmosphere. An increase in annealing temperature does not cause a complete phase transformation whereas it affects the crystallite size, dislocation density and strain. The optical band gap (E_g) of the as-deposited film is estimated to be 3.08 eV and decreases with increasing annealing temperature down to 2.43 eV at 773 K. The as-deposited and annealed films show typical semiconducting behaviour, dρ/dT > 0. Interestingly, the films annealed at 373 K, 473 K, and 573 K show two distinct temperature dependent regions of electrical resistivity; exponential region at high temperature, linear region at low temperature. The temperature at which the transition takes place from exponential to linear region strongly depends on the annealing temperature.     

Effects of rapid thermal annealing on structural, magnetic and optical properties of Ni-doped ZnO thin films

XPS depth profiles were used to investigate the effects of rapid thermal annealing under varying conditions on the structural, magnetic and optical properties of Ni-doped ZnO thin films. Oxidization of metallic Ni from its metallic state to two-valence oxidation state occurred in the film annealed in air at 600 °C, while reduction of Ni²⁺ from its two-valence oxidation state to metallic state occurred in the film annealed in Ar at 600 and 800 °C. In addition, there appeared to be significant diffusion of Ni from the bottom to the top surface of the film during annealing in Ar at 800 °C. Both as-deposited and annealed thin films displayed obvious room temperature ferromagnetism (RTFM) which was from metallic Ni, Ni²⁺ or both with two distinct mechanisms. Furthermore, a significant improvement in saturation magnetization (M_s) in the films was observed after annealing in air (M_s = 0.036 μ_B/Ni) or Ar (M_s = 0.033 μ_B/Ni) at 600 °C compared to that in as-deposited film (M_s = 0.017 μ_B/Ni). An even higher M_s value was observed in the film annealed in Ar at 800 °C (M_s = 0.055 μ_B/Ni) compared to that at 600 °C mainly due to the diffusion of Ni. The ultraviolet emission of the Ni-doped ZnO thin film was restored during annealing in Ar at 800 °C, which was also attributed to the diffusion of Ni.     

Surface characterization and luminescent properties of SrAl2O4:Eu,Dy nano thin films

SrAl₂O₄:Eu²⁺, Dy³⁺ thin films were grown on Si (1 0 0) substrates in different atmospheres using the pulsed laser deposition (PLD) technique. The effects of vacuum, oxygen (O₂) and argon (Ar) deposition atmospheres on the structural, morphological and photoluminescence (PL) properties of the films were investigated. The films were ablated using a 248 nm KrF excimer laser. Improved PL intensities were obtained from the unannealed films prepared in Ar and O₂ atmospheres compared to those prepared in vacuum. A stable green emission peak at 520 nm, attributed to 4f⁶5d¹→4f⁷ Eu²⁺ transitions was obtained. After annealing the films prepared in vacuum at 800 °C for 2 h, the intensity of the green emission (520 nm) of the thin film increased considerably. The amorphous thin film was crystalline after the annealing process. The diffusion of adventitious C into the nanostructured layers deposited in the Ar and O₂ atmospheres was most probably responsible for the quenching of the PL intensity after annealing.     

Effects of cap layer on ohmic Ti/Al contacts to Si implanted GaN

A low resistivity ohmic contact to Si-implanted GaN was achieved using a metal combination of Ti/Al. The effect of a protection cap during post-implantation annealing is investigated, and how it affects the specific contact resistivity (ρ_c). Relevant differences between the protected (PR) sample with SiO₂ and unprotected (UP) sample during the post-implantation annealing were observed after metal alloying at 700 °C. The lower values of ρ_c have been obtained for UP sample, but with very low reproducibility. In contrast, SiO₂ cap layer has demonstrated its relevance in yielding a much more uniformity of a relatively low ρ_c around 10⁻⁵ Ω cm². Related mechanism for the uniformity in ρ_c was discussed based on the results obtained from electrical measurements, XRD (X-ray diffraction) analysis, AFM (atomic force microscopy) and SEM (scanning electron microscopy) observations.     

Preparation of superhydrophobic films on titanium as effective corrosion barriers

Stable superhydrophobic films were prepared on the electrochemical oxidized titania/titanium substrate by a simple immersion technique into a methanol solution of hydrolyzed 1H,1H,2H,2H-perfluorooctyltriethoxysilane [CF₃(CF₂)₅(CH₂)₂Si(OCH₂CH₃)₃, PTES] for 1 h at room temperature followed by a short annealing at 140 °C in air for 1 h. The surface morphologies and chemical composition of the film were characterized by means of water contact angle (CA), field emission scanning electron microscopy (FESEM), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). The water contact angle on the surface of this film was measured to be as high as 160°. SEM images showed that the resulting surfaces exhibited special hierarchical structure. The special hierarchical structure along with the low surface energy leads to the high surface superhydrophobicity. The corrosion resistance ability and durance property of the superhydrophobic film in 3.5 wt.% NaCl solution was evaluated by the electrochemical impedance spectroscopy (EIS). The anticorrosion properties of the superhydrophobic film are compared to those of unmodified pure titanium and titania/titanium substrates. The results showed that the superhydrophobic film provides an effective corrosion resistant coating for the titanium metal even with immersion periods up to 90 d in the 3.5 wt.% NaCl solution, pointing to promising future applications.     

Investigation of hard magnetic properties in the Fe-Pt system by combinatorial deposition of thin film multilayer libraries

The magnetic properties of annealed Fe-Pt multilayer thin films with a broad composition range were investigated in order to identify the effects of composition and annealing temperature on the achievable coercive field, and to identify its maximum at low processing temperatures. Two types of multilayer systems were deposited as materials libraries to vary the composition from Fe₂₀Pt₈₀ to Fe₇₅Pt₂₅. The first type of multilayer was comprised of alternating opposing wedges, whereas the second type consisted of repeated uniform Fe and Pt layers interspersed periodically with Fe wedge layers. It was found that coercive fields μ₀H_C > 0.7 T can be achieved at an annealing temperature of about 300 °C (60 min) for both types of multilayers as long as the composition is close to 50:50. Higher annealing temperatures are needed for films, which deviate from this composition. Increasing the annealing temperature up to 700 °C leads to increased coercivity values. Multilayers with additional Fe layers showed increased remanence but reduced coercive fields.     

Nanostructuring of Fe films by oblique incidence deposition on a FeSi2 template onto Si(1 1 1): Growth, morphology, structure and faceting

The growth of thin Fe films deposited at oblique incidence on an iron silicide template onto Si(1 1 1) single crystal has been investigated as a function of Fe thickness (0 < t_Fe ? 180 monolayers (MLs)) and incidence angle (0 ? θ ? 80°). The growth mode is determined in situ by means of scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED). Stripes oriented perpendicularly to the incident atomic flux are formed for θ ? 30°. Self-correlation functions are used to extract characteristic lengths from STM images. The correlation lengths in the direction of the incident flux (ξ_x) and perpendicular to the atomic flux (ξ_y) grow with different powers versus time (ξ_x∝t^σ and ξ_y∝t^ρ, with σ = 0.34 ± 0.03 and ρ = 0.67 ± 0.03) following the exact solution of the (1 + 1) dimensional Kardar-Parisi-Zhang (KPZ) equation. The root mean square roughness follows also a scaling law for t_Fe < 120 ML leading to a growth exponent β = 0.73 ± 0.02. Shadowing and steering effects are discussed on the basis of our STM data.