Photoluminescence in amorphous (PbLa)TiO3 thin films deposited on different substrates

Pb_1−XLa_XTiO₃ thin films, (X=0.0; 13 and 0.27 mol%) were prepared by the polymeric precursor method. Thin films were deposited on Pt/Ti/SiO₂/Si (1 1 1), Si (1 0 0) and glass substrates by spin coating, and annealed in the 200-300°C range in an O₂ atmosphere. X-ray diffraction, scanning electron microscopy and atomic force microscopy were used for the microstructural characterization of the thin films. Photoluminescence (PL) at room temperature has been observed in thin films of (PbLa)TiO₃. The films deposited on Pt/Ti/SiO₂/Si substrates present PL intensity greater than those deposited on glass and silicon substrates. The intensity of PL in these thin films was found to be dependent on the thermal treatment and lanthanum molar concentration.     

Effect of growth time on the structure, Raman shift and photoluminescence of Al and Sb codoped ZnO nanorod ordered array thin films

Al and Sb codoped ZnO nanorod ordered array thin films have been deposited on glass substrate with a ZnO seed layer by hydrothermal method at different growth time. The effect of growth time on structure, Raman shift, and photoluminescence (PL) was studied. The thin films at growth time of 5 h consist of nanorods growth vertically oriented with ZnO seed layer, and the nanorods with an average diameter of 27.8 nm and a length of 1.02 μm consist of single crystalline wurtzite ZnO crystal and grow along [0 0 1] direction. Raman scattering analysis demonstrates that the thin films at the growth time of 5 h have great Raman shift of 15 cm⁻¹ to lower wavenumber and have low asymmetrical factor Г_a/Г_b of 1.17. Room temperature photoluminescence reveals that there is more donor-related PL in films with growth time of 5 h.     

Study of structural and optical properties of ZnO films grown by pulsed laser deposition

Wurtzite zinc oxides films (ZnO) were deposited on silicon (0 0 1) and corning glass substrates using the pulsed laser deposition technique. The laser fluence, target-substrate distance, substrate temperature of 300 °C were fixed while varying oxygen pressures from 2 to 500 Pa were used. It is observed that the structural properties of ZnO films depend strongly on the oxygen pressure and the substrate nature. The film crystallinity improves with decreasing oxygen pressure. At high oxygen pressure, the films are randomly oriented, whereas, at low oxygen pressures they are well oriented along [0 0 1] axis for Si substrates and along [1 0 3] axis for glass substrates. A honeycomb structure is obtained at low oxygen pressures, whereas microcrystalline structures were obtained at high oxygen pressures. The effect of oxygen pressure on film transparency, band gap E_g and Urbach energies was investigated.     

Influences of the iron ion (Fe)-doping on structural and optical properties of nanocrystalline TiO2 thin films prepared by sol-gel spin coating

Titanium dioxide (TiO₂) thin films doping of various iron ion (Fe³⁺) concentrations were deposited on silicon (Si) (100) and quartz substrates by sol-gel Spin Coating technique followed by a thermal treatment at 600 °C. The structure, surface morphology and optical properties, as a function of the doping, have been studied by X-ray diffractometer (XRD), Raman, ultraviolet-visible (UV-vis) and Spectroscopic Ellipsometry (SE). XRD and Raman analyzes of our thin films show that the crystalline phase of TiO₂ thin films comprised only the anatase TiO₂, but the crystallinity decreased when the Fe³⁺ content increased from 0% to 20%. During the Fe³⁺ addition to 20%, the phase of TiO₂ thin film still maintained the amorphous state. The grain size calculated from XRD patterns varies from 29.3 to 22.6 nm. The complex index and the optical band gap (E_g) of the films were determined by the spectroscopic ellipsometry analysis. We have found that the optical band gap decreased with an increasing Fe³⁺ content.     

Anatase TiO2 films based CO gas sensor: Film thickness, substrate and temperature effects

Electrical response of anatase TiO₂ films is discussed for different concentrations of CO gas (20-100 ppm) in a nitrogen gas ambient. We investigated temperature (100-300 °C) and film thickness (100-1000 nm) effects for films deposited on glass, sapphire (0 0 0 1) and, Si(1 0 0) substrates. In general, there is a drop in resistance of the device when exposed to CO gas. Films deposited on sapphire showed a larger decrease in the resistance at 300 °C compared to those deposited on glass and silicon substrates. However, films grown on glass and silicon substrates showed a larger decrease in the resistance values for temperature around 200 °C when CO (ppm) values are greater than 40. The change in resistance of the films varies as square root of the CO gas concentration at 200 °C for films deposited on all the three substrates. In general, the decrease in resistance for thicker films is large compared to thinner ones, indicating participation of the bulk in the detection of CO gas. In the presence of O₂, film loses its sensitivity to CO gas when the concentration level of O₂ approaches 1800 ppm.     

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.     

Crystal structure and magnetic properties of SmCo-based films deposited on hot Si (1 0 0) substrates

SmCo-based films were deposited on Si (1 0 0) substrates by the rf magnetron sputtering process. The growth conditions are improved for the films deposited on hot Si substrates without the annealing process. The dependence of crystal structure and intrinsic coercivity on substrate temperature is chiefly investigated. It is suggested that TbCu₇ type structural films can be obtained with enhanced in-plane magnetic properties with proper substrate temperature.     

Properties of K0.5Bi0.5TiO3 thin films deposited on different substrates

K_0.5Bi_0.5TiO₃ thin films were deposited on fused quartz, n-type Si(100) and Pt/TiO₂/SiO₂/Si substrates by repeated coating/dying cycles. X-ray diffraction analysis shows that the films annealed at 700 °C for 10 min present perovskite phase. Atomic force microscopy reveals that the surface morphology is smooth, the grain sizes of the films on Si(100) are quite larger than on fused quartz. The capacitance-voltage hysteresis loops at various sweeping speed are collected as are polarization types. The films in the ON and OFF states are relatively stable. The films also exhibit a hysteresis loop at an applied voltage of 4 V, with a remanent polarization of 9.3 μC/cm² and a coercive voltage of 2 V. The insulating property of negative bias voltage is better than that of positive bias voltage. The transmittance of the films is between 74 and 82% in the wavelength range of 200-2000 nm.     

Pulsed laser deposited Er,Yb:YVO4 waveguiding films on MgO/Si substrates

Erbium, and erbium and ytterbium co-doped YVO₄ waveguiding films were deposited on MgO/Si substrates by PLD. The samples were post-annealed at two different temperatures in air atmosphere. The influence on the crystalline structure and waveguiding properties of the films at these annealing temperatures for two dopant concentrations was investigated. Layers annealed up to 900 °C are polycrystalline. The dominant fraction of YVO₄ crystallites exhibited preferred orientation of the (0 0 1) zone axes parallel to the substrate surface. The polycrystalline samples show difference in the refractive indexes Δn (Δn = n_TE − n_TM) for TE and TM polarizations.     

Crystallization and surface morphology evolution of erbium fluoride films on different substrates

Erbium fluoride (ErF₃) films were thermally deposited on Ge(1 1 1), Si(0 0 1) and copper mesh grid with different substrate temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the structure and morphology of the films. The structure of ErF₃ films deposited on germanium and silicon changed from amorphous to crystalline with increasing the substrate temperature, while the crystallization temperature of the films on silicon is higher than that of on germanium. The infrared optical properties of the films change greatly with the evolution of crystal structure. It is also found that the morphology of ErF₃ film on Ge(1 1 1) at 200 °C is modulated by the stress between the substrate and film. The SEM and TEM results confirmed that the ErF₃ films on copper mesh grid were crystalline even at 100 °C. Interestingly, the ErF₃ films show flower-like surface morphology when deposited on copper mesh at 200 °C. The crystallization temperature (T_c) of ErF₃ films on the three substrates has the relation which is which is induced by the wetting angle of ErF₃ films on different substrates.     

Fabrication and characterization of La-doped HfO2 gate dielectrics by metal-organic chemical vapor deposition

La-doped HfO₂ gate dielectric thin films have been deposited on Si substrates using La(acac)₃ and Hf(acac)₄ (acac = 2,4-pentanedionate) mixing sources by low-pressure metal-organic chemical vapor deposition (MOCVD). The structure, thermal stability, and electrical properties of La-doped HfO₂ films have been investigated. Inductive coupled plasma analyses confirm that the La content ranging from 1 to 5 mol% is involved in the films. The films show smaller roughness of ∼0.5 nm and improved thermal stability up to 750 °C. The La-doped HfO₂ films on Pt-coated Si and fused quartz substrates have an intrinsic dielectric constant of ∼28 at 1 MHz and a band gap of 5.6 eV, respectively. X-ray photoelectron spectroscopy analyses reveal that the interfacial layer is Hf-based silicate. The reliable value of equivalent oxide thickness (EOT) around 1.2 nm has been obtained, but with a large leakage current density of 3 A/cm² at V_g = 1V + V_fb. MOCVD-derived La-doped HfO₂ is demonstrated to be a potential high-k gate dielectric film for next generation metal oxide semiconductor field effect transistor applications.     

Improvement in micro-structural and mechanical properties of zinc film by surface treatment with low temperature argon plasma

Nanocrystalline zinc films were deposited on gold coated borosilicate glass substrates by thermal evaporation method using zinc powders as the source material and then treated with argon plasma at various temperatures. From X-ray diffraction study, the as-deposited films are found to be metallic Zn and polycrystalline in nature. The crystalline nature improves with the increase of temperature up to 200 °C and decreases with the further increase of temperature to 300 °C. The binding energy observed for Zn 2p_3/2, and the binding energy separation between Zn 2p_3/2 and Zn 2p_1/2 in the X-ray photoelectron spectrum indicate that the films are metallic zinc films. Transmission electron microscopic study shows hexagonal shaped grains having size ∼58 nm upon treatment with Ar plasma. It is clearly shown the grain growth and distinct grain boundary with the increase in temperature. The average Young's modulus (E) and hardness (H) are measured to be 84 GPa and 4.0 GPa for as-deposited film, whereas 98 GPa and 5.8 GPa for plasma treated film at 200 °C. The enhancement in mechanical properties is attributed to improvement in crystalline nature of the film and better interlinking between grains and boundaries.     

Chemical bath deposition of hausmannite Mn3O4 thin films

A low-temperature chemical bath deposition (CBD) technique has been used for the preparation of Mn₃O₄ thin films onto glass substrates. The kinetic behavior and the formation mechanism of the solid thin films from the aqueous solution have been investigated. Structure (X-ray diffraction and Raman), morphological (atom force microscope), and optical (UV-vis-NIR) characterizations of the deposited films are presented. The results indicated that the deposited Mn₃O₄ thin films of smooth surface with nanosized grains were well crystalline and the optical bandgap of the film was estimated to be 2.54 eV.     

Pulsed-laser deposition of smooth thin films of Er, Pr and Nd doped glasses

Thin films of complex oxides have been obtained by pulsed-laser deposition (PLD) from glass targets belonging to the system Li₂O-Al₂O₃-P₂O₅-(RE)₂O₃, with RE = Nd, Pr, Er. The films were deposited on quartz, silicon and ITO/glass substrates using a F₂ laser (λ = 157 nm, ι ≈ 20 ns) for ablation in vacuum. The structural, morphological and optical properties of the oxide films were investigated through IR and UV-VIS spectroscopy, Atomic Force Microscopy (AFM), Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Spectroscopic Ellipsometry. The laser wavelength was found to be the key parameter to obtain thin films with very smooth surface. In this way new possibilities are opened to grow multilayer structures for photonic applications.     

Structure and properties of transparent conductive doped ZnO films by pulsed laser deposition

High quality transparent conductive ZnO thin films were deposited on quartz glass substrates using pulsed laser deposition (PLD). We varied the growth conditions such as the substrate temperature and oxygen pressure. X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), and atomic force microscopy (AFM) measurements were done on the samples. All films show n-type conduction, the best transparent conductive oxide (TCO) performance (Al-doped ZnO = 1.33 × 10⁻⁴ Ω cm, Ga-doped ZnO = 8.12 × 10⁻⁵ Ω cm) was obtained on the ZnO film prepared at pO₂ = 5 mTorr and T_s = 300 °C.     

Effects of crystalline quality on the ultraviolet emission and electrical properties of the ZnO films deposited by magnetron sputtering

The ZnO films were deposited on c-plane sapphire, Si (0 0 1) and MgAl₂O₄ (1 1 1) substrates in pure Ar ambient at different substrate temperatures ranging from 400 to 750 °C by radio frequency magnetron sputtering. X-ray diffraction, photoluminescence and Hall measurements were used to evaluate the growth temperature and the substrate effects on the properties of ZnO films. The results show that the crystalline quality of the ZnO films improves with increasing the temperature up to 600 °C, the crystallinity of the films is degraded as the growth temperature increasing further, and the ZnO film with the best crystalline quality is obtained on sapphire at 600 °C. The intensity of the photoluminescence and the electrical properties strongly depend on the crystalline quality of the ZnO films. The ZnO films with the better crystallinity have the stronger ultraviolet emission, the higher mobility and the lower residual carrier concentration. The effects of crystallinity on light emission and electrical properties, and the possible origin of the n-type conductivity of the undoped ZnO films are also discussed.     

Optical and electrical properties of thermally evaporated In49Se48Sn3 films

Nearly stoichiometric thin films of In₄₉Se₄₈Sn₃ were deposited at room temperature, by conventional thermal evaporation of the presynthesized materials, onto precleaned glass substrates. The microstructural studies on the as-deposited and annealed films, using transmission electron microscopy and diffraction (TEMD), revealed that the as-deposited films are amorphous in nature, while those annealed at 498 K are crystalline. The optical properties of the investigated films were determined from the transmittance and reflectance data, in the spectral range 650-2500 nm. An analysis of the optical absorption spectra revealed a non-direct energy gap characterizing the amorphous films, while both allowed and forbidden direct energy gaps characterized the crystalline films. The electrical resistance of the deposited films was carried out during heating and cooling cycles in the temperature range 300-600 K. The results show an irreproducible behavior, while after crystallization the results become reproducible. The analysis of the temperature dependence of the resistance (ln(R) vs. 1000/T) for crystalline films shows two straight lines corresponding to both extrinsic and intrinsic conduction. The room temperature I-V characteristics of the as-deposited films sandwiched between similar Ag metal electrodes shows an ohmic behavior, while non-ohmic behavior attributed to space charge limited conduction has been observed when the films are sandwiched between dissimilar Ag/Al metal electrodes.     

Influence of Si substrate preparation on surface chemistry and morphology of L-CVD SnO2 thin films studied by XPS and AFM

Results of experimental studies of the influence of substrate preparation on the surface chemistry and surface morphology of the laser-assisted chemical vapour deposition (L-CVD) SnO₂ thin films are presented in this paper. The native Si(1 0 0) substrate cleaned by UHV thermal annealing (TA) as well as thermally oxidized Si(1 0 0) substrate cleaned by ion bombardment (IBA) have been used as the substrates. X-ray photoemission spectroscopy (XPS) has been used for the control of surface chemistry of the substrates as well as of deposited films. Atomic force microscopy (AFM) has been used to control the surface morphology of the L-CVD SnO₂ thin films deposited on differently prepared substrates. Our XPS shows that the L-CVD SnO₂ thin films deposited on thermally oxidized Si(1 0 0) substrate after cleaning with ion bombardment exhibit the same stoichiometry, i.e. ratio [O]/[Sn] = 1.30 as that of the layers deposited on Si(1 0 0) substrate previously cleaned by UHV prolonged heating. AFM shows that L-CVD SnO₂ thin films deposited on thermally oxidized Si(1 0 0) substrate after cleaning with ion bombardment exhibit evidently increasing rough surface topography with respect to roughness, grain size range and maximum grain height as the L-CVD SnO₂ thin films deposited on atomically clean Si substrate at the same surface chemistry (nonstoichiometry) reflect the higher substrate roughness after cleaning with ion bombardment.     

Structural, optical and morphological studies on laser ablated nanostructured WO3 thin films

Thin films of tungsten trioxide (WO₃) are prepared by reactive pulsed laser deposition (PLD) technique on glass substrates at three different substrate temperatures (T_s). The structural, morphological and optical properties of the deposited films are systematically studied using X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD), micro-Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-VIS spectrophotometry techniques. X-ray diffraction analysis reveals that crystalline WO₃ films can grow effectively even at 300 K at an oxygen pressure of 0.12 mbar. All the films deposited at various T_s exhibit mixed oxide phase consisting of orthorhombic and triclinic phase of tungsten oxide with a preferred orientation along (0 0 1) lattice plane reflection. Micro-Raman results are consistent with X-ray diffraction findings. The SEM analysis shows that deposited films are porous and crystalline grains are of nano-metric dimension. The effect of T_s on mean surface roughness studied by AFM analysis reveals that mean surface roughness decreases with increase in T_s. The optical response of WO₃ layers measured using UV-VIS spectrophotometry is used to extract the optical constants such as refractive index (n), extinction coefficient (k) and optical band gap (E_g), following the method of Swanepoel.     

Influence of MgO and ZrO2 buffer layers on dielectric properties of Ba(Zr0.20Ti0.80)O3 thin films prepared by sol-gel processing

Ba(Zr_0.20Ti_0.80)O₃ (BZT) thin films are deposited on Pt(1 1 1)/Ti/SiO₂/Si, MgO and ZrO₂ buffered Pt(1 1 1)/Ti/SiO₂/Si substrates by a sol-gel process. The BZT thin films directly grown on Pt(1 1 1)/Ti/SiO₂/Si substrates exhibit highly (1 1 1) preferred orientation, while the films deposited on Pt(1 1 1)/Ti/SiO₂/Si substrates with MgO and ZrO₂ buffer layers show highly (1 1 0) preferred orientation. At 100 kHz, dielectric constants are 417, 311 and 321 for the BZT thin films grown on Pt(1 1 1)/Ti/SiO₂/Si, MgO and ZrO₂ buffered Pt(1 1 1)/Ti/SiO₂/Si substrates, respectively. The difference in dielectric properties of three BZT films can be attributed to the series capacitance effect, interface conditions and their orientations.