High c-axis preferred orientation ZnO thin films prepared by oxidation of metallic zinc

Thin films of zinc oxide were grown on glass substrates by thermal oxidation. The metallic zinc films were thermally oxidized at different temperatures ranging from 300 to 600 °C to yield ZnO thin films. The structural property of the thin films was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The X-ray diffraction measurements showed that the films oxidized at 300 °C were not oxidized entirely, and the films deposited at 600 °C had better crystalline quality than the rest. When the oxidation temperature increased above 400 °C, the films exhibited preferred orientation along (002) and high transmittance ranging from 85% to 98% in vis–near-infrared band. Meanwhile, the films showed a UV emission at about 377 nm and green emission. With the increasing of oxidation temperature, the intensity of green emission peak was enhanced, and then decreased, disappearing at 600 °C, and the case of UV emission increased. Furthermore, a strong green emission was observed in the film sintered in pure oxygen atmosphere.     

Field electron emission from amorphous carbon thin films grown by RF magnetron sputtering

Using a RF magnetron sputtering, amorphous carbon (a-C) and N-doped a-C (a-C:N) thin films were fabricated as field electron emitter. These thin films were deposited on Si(0 0 1) substrate at several temperatures. The field emission property was improved for a-C thin films grown at higher substrate temperatures. Furthermore, a-C:N film exhibits field emission property better than that of undoped a-C film. These results are explained in terms of the change in surface morphology and structural properties of a-C film.     

Preparation of cadmium stannate films by spray pyrolysis technique

Cadmium stannate thin films were prepared by spray pyrolysis technique using cadmium acetate and tin(II) chloride precursors at substrate temperatures 450 °C and 500 °C. XRD pattern confirms the formation of orthorhombic (1 1 1) cadmium stannate phase for the film prepared at substrate temperature of 500 °C, whereas, films prepared at 450 °C are amorphous. Film formation does not occur at substrate temperature from 300 to 375 °C. SEM images reveal that the surface of the prepared Cd₂SnO₄ film is smooth. The average optical transmittance of ∼86% is obtained for the film prepared at substrate temperature of 500 °C with the film thickness of 400 nm. The optical band gap value of the films varies from 2.7 to 2.94 eV. The film prepared at 500 °C shows a minimum resistivity of 35.6 × 10⁻⁴ Ω cm.     

Photoluminescence of chemical solution-derived amorphous ZnO layers prepared by low-temperature process

Growth characteristic and optical properties of the amorphous ZnO thin films prepared on soda-lime–silica glass substrates by chemical solution process at 100 and 200 °C were investigated by using X-ray diffraction analysis, scanning probe microscope, ultraviolet spectrophotometer, and photoluminescence. The films exhibited an amorphous pattern even when finally heat treated at 100–200 °C for 60 min. The photoluminescence spectrum of amorphous ZnO films shows a strong near-band-edge emission, while the visible emission is nearly quenched.     

Diffusion and chemical composition of TiNxOy thin films studied by Rutherford Backscattering Spectroscopy

Thickness and chemical composition of the TiN_xO_y thin films deposited by reactive magnetron sputtering from Ti target at controllable oxygen flow rate were determined by Rutherford Backscattering Spectroscopy (RBS) using 2 MeV He⁺ ions. The films were deposited on carbon foils and amorphous silica (a-SiO₂) substrates at 25 °C and 250 °C. The estimated film thickness is of 75-100 nm. The O/Ti atomic ratio in the films increases up to 1.5 with increasing oxygen flow rate, while that of N/Ti decreases from about 1.1 for TiN to 0.4 at the highest oxygen flow rate. Substantial out-diffusion of carbon from the substrate is observed which is independent of the substrate temperature. Films grown onto a-SiO₂ substrates can be treated as homogeneous single layers without interdiffusion. It is more difficult to determine the nitrogen and oxygen content due to superposition of RBS signals arising from film and substrate. RBS analysis of the depth profile indicates that for the investigated films the carbon diffusion and oxidation not only at the topmost surface layers but over the bulk of the films were found. Comparison with XPS results indicates substantial oxygen adsorption at the surface of TiN_x thin films obtained at zero oxygen flow rate.     

Influence of heat treatment on field emission characteristics of boron nitride thin films

Boron nitride (BN) nanometer thin films are synthesized on Si (1 0 0) substrates by RF reactive magnetron sputtering. Then the film surfaces are treated in the case of the base pressure below 5 × 10⁻⁴ Pa and the temperature of 800 and 1000 °C, respectively. And the films are studied by Fourier transform infrared spectra (FTIR), atomic force microscopic (AFM) and field emission characteristics at different annealing temperature. The results show that the surface heat treatment makes no apparent influence on the surface morphology of the BN films. The transformations of the sample emission characteristics have to do with the surface negative electron affinity (NEA) of the films possibly. The threshold electric fields are lower for BN samples without heat-treating than the treated films, which possibly ascribed to the surface negative electron affinity effect. A threshold field of 8 V/μm and the emission current of 80 μA are obtained. The surface NEA is still presence at the heat treatment temperature of 800 °C and disappeared at temperature of 1000 °C.     

Influence of substrate temperature on physical properties of sprayed Zn0.85Mn0.15O films

Zn_1−xMn_xO thin films have been synthesized by chemical spray pyrolysis at different substrate temperatures in the range, 250–450 °C for a manganese composition, x = 15%, on corning 7059 glass substrates. The as-grown layers were characterized to evaluate their chemical and physical behaviour with substrate temperature. The change of dopant level in ZnO films with substrate temperature was analysed using X-ray photoelectron spectroscope measurements. The X-ray diffraction studies revealed that all the films were strongly oriented along the (0 0 2) orientation that correspond to the hexagonal wurtzite structure. The crystalline quality of the layers increased with the increase of substrate temperature up to 400 °C and decreased thereafter. The crystallite size of the films varied in the range, 14–24 nm. The surface morphological studies were carried out using atomic force microscope and the layers showed a lower surface roughness of 4.1 nm. The optical band gap of the films was ∼3.35 eV and the electrical resistivity was found to be high, ∼10⁴ Ω cm. The films deposited at higher temperatures (>350 °C) showed ferromagnetic behaviour at 10 K.     

Growth and characterization of CoSi2 films on Si (1 0 0) substrates

In the present work, a special solid phase epitaxy method has been adapted for the preparation of CoSi₂ film. This method includes an epitaxial growth of Co films on Si (1 0 0) substrate, and in situ annealing of the Co/Si films in vacuum. It has been found that at the substrate temperature of 360°C, fcc cobalt film grows epitaxially on the Si (1 0 0) surface. The crystallographic orientation relations between fcc Co film and Si substrate determined from the electron diffraction result are: (0 0 1) Co//(0 0 1) Si, [1 0 0] Co//[1 1 0]Si. Upon annealing at temperatures range from 500 to 600°C, Co film reacts with Si substrate and transforms into CoSi₂. The CoSi₂ films prepared by this way are characterized by XTEM, XPS and AFM.     

Characterization on electron beam evaporated α-MoO3 thin films by the influence of substrate temperature

Electrochromic molybdenum oxide (MoO₃) thin films were prepared by electron beam evaporation technique using the dry MoO₃ pellets. The films were deposited on glass and fluorine doped tin oxide (SnO₂:F or FTO) coated glass substrates at different substrate temperatures like room temperature (RT, 30 °C), 100 °C and 200 °C. The influence of substrate temperature on the structural, surface morphological and optical properties of the films has been studied. The X-ray diffraction analysis showed that the films are having orthorhombic phase MoO₃ (α-MoO₃) with 〈1 1 0〉 preferred orientation. The laser Raman scattering spectrum shows the polycrystalline nature of MoO₃ films deposited at 200 °C. The Raman-active band at 993 cm⁻¹ is corresponding to Mo–O stretching mode that is associated with the unique character of the layered structure of orthorhombic MoO₃. Needle—like morphology was observed from the SEM analysis. The energy band gap of MoO₃ films was evaluated which lies between 2.8 and 2.3 eV depending on the substrate temperature and substrates. The decrease in band gap value with increasing substrate temperature is owing to the oxygen-ion vacancies. The absorption edge shift shows the coloration effect on the films.     

Characterization and organic electric-double-layer-capacitor application of KOH activated coal-tar-pitch-based carbons: Effect of carbonization temperature

The present study reports the influence of pre-carbonization on the properties of KOH-activated coal tar pitch (CTP). The change of crystallinity and pore structure of pre-carbonized CTPs as well as their activated carbons (ACs) as function of pre-carbonization temperature are investigated. The crystallinity of pre-carbonized CTPs increases with increasing the carbonization temperature up to 600 °C, but a disorder occurs during the carbonization around 700 °C and an order happens gradually with increasing the carbonization temperatures in range of 800–1000 °C. The CTPs pre-carbonized at high temperatures are more difficult to be activated with KOH than those pre-carbonized at low temperatures due to the increase of micro-crystalline size and the decrease of surface functional groups. The micro-pores and meso-pores are well developed at around 1.0 nm and 2.4 nm, respectively, as the ACs are pre-carbonized at temperatures of 500–600 °C, exhibiting high specific capacitances as electrode materials for electric double layer capacitor (EDLC). Although the specific surface area (SSA) and pore volume of ACs pre-carbonized at temperatures of 900–1000 °C are extraordinary low (non-porous) as compared to those of AC pre-carbonized at 600 °C, their specific capacitances are comparable to each other. The large specific capacitances with low SSA ACs can be attributed to the structural change resulting from the electrochemical activation during the 1st charge above 2.0 V.     

Properties of Bi2O3 thin films prepared via a modified Pechini route

Thin bismuth oxide films have been prepared by a modified Pechini route on glass substrate and annealed at temperatures ranging between 400 °C and 700 °C using bismuth nitrate as raw material. The thin films were then characterized for structural, surface morphological, optical and electrical properties by means of X-ray diffraction (XRD), Atomic force microscopy (AFM), scanning electron microscopy (SEM), optical absorption and d.c. two-probe, respectively. Structural investigations indicated that as-prepared bismuth oxide films were polycrystalline and multiphase, and annealing temperatures played a key role in the composition and optical properties of these films. AFM and SEM images revealed well defined particles which are highly influenced by annealing temperatures. The optical studies showed a direct band gap which varied with annealing temperatures between 3.63 eV and 3.74 eV. The electrical measurement showed that the electrical resistivity increased with annealing temperatures and the films were typical semiconductors. As catalyst, bismuth oxide films annealed at 550 °C had the best photocatalytic performance for photodegradation of methyl orange.     

Application of indium tin oxide (ITO) thin film as a low emissivity film on Ni-based alloy at high temperature

Indium tin oxide (ITO) films as the low emissivity coatings of Ni-based alloy at high temperature were studies. ITO films were deposited on the polished surface of alloy K424 by direct current magnetron sputtering. These ITO-coated samples were heat-treated in air at 600–900 °C for 150 h to explore the effect of high temperature environment on the emissivity. The samples were analyzed by X-ray diffraction (XRD), SEM and EDS. The results show that the surface of sample is integrity after heat processing at 700 °C and below it. A small amount of fine crack is observed on the surface of sample heated at 800 °C and Ti oxide appears. There are lots of fine cracks on the sample annealed at 900 °C and a large number of various oxides are detected. The average infrared emissivities at 3–5 μm and 8–14 μm wavebands were tested by an infrared emissivity measurement instrument. The results show the emissivity of the sample after annealed at 600 and 700 °C is still kept at a low value as the sample before annealed. The ITO film can be used as a low emissivity coating of super alloy K424 up to 700 °C.     

Structural and magnetic properties of thin epitaxial Fe films on (1 1 0) GaAs prepared by metalorganic chemical vapor deposition

Iron films have been grown on (1 1 0) GaAs substrates by atmospheric pressure metalorganic chemical vapor deposition at substrate temperatures (T_s) between 135°C and 400°C. X-ray diffraction (XRD) analysis showed that the Fe films grown at T_s between 200°C and 330°C were single crystals. Amorphous films were observed at T_s below 200°C and it was not possible to deposit films at T_s above 330°C. The full-width at half-maximum of the rocking curves showed that crystalline qualities were improved at T_s above 270°C. Single crystalline Fe films grown at different substrate temperature showed different structural behaviors in XRD measurements. Iron films grown at T_s between 200°C and 300°C showed bulk α-Fe like behavior regardless of film thickness (100–6400 Å). Meanwhile, Fe films grown at 330°C (144 and 300 Å) showed a biaxially compressed strain between substrate and epilayer, resulting in an expanded inter-planar spacing along the growth direction. Magnetization measurements showed that Fe films (>200 Å) grown at 280°C and 330°C were ferromagnetic with the in-plane easy axis along the [1 1 0] direction. For the thinner Fe films (⩽200 Å) regardless of growth temperature, square loops along the [1 0 0] easy axis were very weak and broad.     

The preparation and characterization of nanoparticle TiO2/Ti films and their photocatalytic activity

Nanoparticle TiO₂/Ti films were prepared by a sol–gel process using Ti(OBu)₄ as raw material, the as-prepared film samples were also characterized by TG-DTA, XRD, TEM, SEM, XPS, DRS, PL, SPS and EFISPS testing techniques. TiO₂ nanoparticles experienced two processes of phase transition, i.e. amorphous to anatase and anatase to rutile at the calcining temperature range from 450 to 700 °C. TiO₂ nanoparticles calcined at 600 °C had similar composition, structure, morphology and particle size with the internationally commercial P-25 TiO₂ particles. Thus, the conclusion that 600 °C might be the most appropriate calcining temperature during the preparation process of nanoparticle TiO₂/Ti film photocatalysts could be made by considering the main factors such as the properties of TiO₂ nanoparticles, the adhesion of nanoparticle TiO₂ film to Ti substrate, the effects of calcining temperature on Ti substrate and the surface characteristics and morphology of nanoparticle TiO₂/Ti film for the practice view. The Ti element mainly existed on the nanoparticle TiO₂/Ti(3) film calcined at 600 °C as the chemical state of Ti⁴⁺, while O element mainly existed as three kinds of chemical states, i.e. crystal lattice oxygen, hydroxyl oxygen and adsorbed oxygen with increasing band energy. Its photoluminescence (PL) spectra with a peak at about 380 nm could be observed using 260 nm excitation, possibly resulting from the electron transition from the bottom of conduction band to the top of valence band. The PL peak position was nearly the same as the onset of its diffuse reflection spectra (DRS) and surface photovoltage spectroscopy (SPS), demonstrating that the effects of the quantum size on optical property were greater than that of the Coulomb and surface polarization. The PL spectra with two peaks related to the anatase and rutile, respectively, could be observed using the excited wavelength of 310 nm. Weak PL spectra could be observed using the excited wavelength of 450 nm, resulting from surface states. In addition, during the experimental process of the photocatalytic degradation phenol, the photocatalytic activity of nanoparticle TiO₂/Ti film with three layers calcined at 600 °C was the highest.     

Structure and magnetic properties of 300-nm-thick FePt films with Hf underlayer

Structure, microstructure, magnetic properties of 300-nm-thick FePt films with 10-nm-thick Hf underlayer have been studied. The experimental results showed that the very thin Hf underlayer could promote the ordering at reduced temperatures by facilitating the nucleation of the order phase, leading to refined grain size and magnetic domain size. Therefore, the permanent magnetic properties of FePt films were enhanced. (BH)_max and H_c of FePt films were greatly enhanced from 5.0–21.0 MGOe and 1.4–11.0 kOe for single layer to 10.2–23.6 MGOe and 4.5–13.2 kOe for Hf-underlayered films annealed in T_a region of 400–600 °C, respectively. Nevertheless, the severe interdiffusion between the Hf and FePt layers at T_a=800 °C resulted in the decreased S, coarsened surface morphology, grain and magnetic domain sizes, and therefore the slightly decreased (BH)_max to 18.0 MGOe.     

Preparation of carbon nanoparticles from electrolysis of molten carbonates and use as anode materials in lithium-ion batteries

The electrochemical reduction of molten Li–Na–K carbonates at 450 °C provides “quasi-spherical” carbon nanoparticles with size comprised between 40 and 80 nm (deduced from AFM measurements). XRD analyses performed after washing and heat-treatment at various temperatures have revealed the presence of graphitised and amorphous phases. The d₀₀₂ values were close to the ideal one obtained for pure graphite. Raman spectroscopy has pointed out surface disordering which increases with increasing temperature of the heat-treatment. The presence of Na and Li on the surface of the carbon powder has been evidenced by SIMS. The maximum Na and Li contents were observed for carbon samples heat-treated at 400 °C. Their electrochemical performances vs. the insertion/deinsertion of lithium cations were studied in 1 M LiPF₆–EC : DEC : DMC (2 : 1 : 2). The first charge–discharge cycle is characterised by a high irreversible capacity as in the case of hard-disordered carbon materials. However, the potential profile in galvanostatic mode is intermediate between that usually observed for graphite and amorphous carbon: rather continuous charge–discharge curves sloping between 1.5 and 0.3 V vs. Li / Li⁺, and successive phase transformations between 0.3 and 0.02 V vs. Li / Li⁺. The best electrochemical performances were obtained with carbon powders heat-treated at 400 °C which exhibits a reversible capacity value of 1080 mAh g^− 1 (composition of Li_2.9C₆). This sample has also both the lowest surface disordering (deduced from Raman spectroscopy), and the highest Na and Li surface contents (deduced from SIMS).     

Growth-induced perpendicular magnetic anisotropy and clustering in NixPt1−x alloys

Polycrystalline and epitaxial (1 0 0), (1 1 0), and (1 1 1)-oriented Ni₃Pt, NiPt, and NiPt₃ films were deposited over a range of growth temperatures from 80°C to 700°C. Films grown at moderate temperatures (200–400°C) exhibit growth-induced properties similar to Co–Pt alloys: enhanced and broadened Curie temperature, perpendicular magnetic anisotropy and large coercivity. As in Co–Pt, the magnetic properties suggest a clustering of Ni into platelets on the growth surface, as the films are being grown. Unlike Co–Pt, however, NiPt films exhibit a strong orientational dependence of anisotropy and enhanced Curie temperature, possibly resulting from different types of surface reconstructions which affect the growth surface.     

Effect of annealing temperature on the characteristics of ZnO thin films

Effect of annealing temperature on characteristics of sol–gel driven ZnO thin film spin-coated on Si substrate was studied. The UV–visible transmittance of the sol decreased with the increase of the aging time and drastically reduced after 20 days aging time. Granular shape of ZnO crystallites was observed on the surface of the films annealed at 550, 650, and 750 °C, and the crystallite size increased with the increase of the annealing temperature. Consequently nodular shape of crystallites was formed upon increasing the annealing temperature to 850 °C and above. The current–voltage characteristics of the Schottky diodes fabricated with ZnO thin films with various annealing temperatures were measured and analyzed. It is found that, ZnO films showed the Schottky characteristics up to 750 °C annealing temperature. The Schottky diode characteristics were diminished upon increasing the annealing temperature above 850 °C. XPS analysis suggested that the absence of oxygen atoms in its oxidized state in stoichiometric surrounding, might be responsible for the diminished forward current of the Schottky diode when annealed above 850 °C.     

Nanocrystalline diamond thin films deposited by 35 kHz Ar-rich plasmas

We give evidence of nanometric size (5–15 nm) crystalline diamonds in carbon thin films obtained at low substrate temperature (15 °C) under the action of low pressure (0.1–0.3 Torr) 35 kHz excited CH₄/Ar (80–95%) plasmas. The decrease in Ar concentration was found to lead to higher film hardness while crystalline nanodiamonds are observed in a wide interval (1–3.5 h) of deposition times but only for very high Ar concentration (95%). The polycrystalline nanodiamond grains are found over 10–20% within an amorphous carbon matrix. It is suggested that the distribution of nanodiamond grains might be connected to the nonuniform ion energy distribution in the Ar-rich plasma generated at 35 kHz. Morphological and structural features of the deposited films were also investigated.     

Growth and characterization of indium oxide films

In₂O₃ films have been deposited using chemical spray pyrolysis technique at different substrate temperatures that varied in the range, 250–450 °C. The structural and morphological properties of the as-deposited films were studied using X-ray diffractometer and scanning electron microscope as well as atomic force microscope, respectively. The films formed at a temperature of 400 °C showed body-centered cubic structure with a strong (2 2 2) orientation. The structural parameters such as the crystallite size, lattice strain and texture coefficient of the films were also calculated. The films deposited at a temperature of 400 °C showed an optical transmittance of >85% in the visible region. The change of resistivity, mobility, carrier concentration and activation energies with the deposition temperature was studied. The highest figure of merit for the layers grown at 400 °C was 1.09 × 10⁻³ Ω⁻¹.