Composition depth profiles of Bi3.15Nd0.85Ti3O12 thin films studied by X-ray photoelectron spectroscopy

In the present work, X-ray photoelectron spectroscopy (XPS) was used to investigate the composition depth profiles of Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) ferroelectric thin film, which was prepared on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by chemical solution deposition (CSD). It is shown that there are three distinct regions formed in BNT film, which are surface layer, bulk film and interface layer. The surface of film is found to consist of one outermost Bi-rich region. High resolution spectra of the O 1s peak in the surface can be decomposed into two components of metallic oxide oxygen and surface adsorbed oxygen. The distribution of component elements is nearly uniform within the bulk film. In the bulk film, high resolution XPS spectra of O 1s, Bi 4f, Nd 3d, Ti 2p are in agreement with the element chemical states of the BNT system. The interfacial layer is formed through the interdiffusion between the BNT film and Pt electrode. In addition, the Ar⁺-ion sputtering changes lots of Bi³⁺ ions into Bi⁰ due to weak Bi-O bond and high etching energy.     

Effect of indium incorporation in Zn1−xCoxO thin films

In the present paper, the preliminary investigations of a series of ZnO thin films co-doped with indium and cobalt with an objective to elucidate the correlation, if any, between the carrier concentration and the induced room temperature ferromagnetism (RTFM), are presented. The single-phasic (Zn_99.5In_0.5)_1−xCo_xO thin films are deposited by spray pyrolysis. The substitution of Zn²⁺ by Co²⁺ has been established by optical transmission analysis of these films. The films are ferromagnetic at room temperature; and the magnetization has higher value for indium and cobalt co-doped thin film as compared with Zn0₉₀Co_0.1O thin film (having no indium).     

Structural and electrical transport properties of ZnxFe3−xO4 thin film deposited on Si (1 1 1) by pulsed-laser deposition

Polycrystalline thin films of Fe_3−xZn_xO₄ (x = 0.0, 0.01 and 0.02) were prepared by pulsed-laser deposition technique on Si (1 1 1) substrate. X-ray diffraction studies of parent as well as Zn doped magnetite show the spinel cubic structure of film with (1 1 1) orientation. The order–disorder transition temperature for Fe₃O₄ thin film with thickness of 150 nm are at 123 K (Si). Zn doping leads to enhancement of resistivity by Zn²⁺ substitution originates from a decrease of the carrier concentration, which do not show the Verwey transition. The Raman spectra for parent Fe₃O₄ on Si (1 1 1) substrate shows all Raman active modes for thin films at energies of T_2g¹, T_2g³, T_2g², and A_1g at 193, 304, 531 and 668 cm⁻¹. It is noticed that the frequency positions of the strongest A_1g mode are at 668.3 cm⁻¹, for all parent Fe₃O₄ thin film shifted at lower wave number as 663.7 for Fe_2.98Zn_0.02O₄ thin film on Si (1 1 1) substrate. The integral intensity at 668 cm⁻¹ increased significantly with decreasing doping concentration and highest for the parent sample, which is due to residual stress stored in the surface.     

Crystallinity and morphology dependent luminescence of Li-doped Y2−xGdxO3:Eu thin film phosphors

The influence of lithium doping on the crystallization, the surface morphology, and the luminescent properties of pulsed laser deposited Y_2−xGd_xO₃:Eu³⁺ thin film phosphors was investigated. The crystallinity, the surface morphology, and the photoluminescence (PL) of films depended highly on the Li-doping and the Gd content. The relationship between the crystalline and morphological structures and the luminescent properties was studied, and Li⁺ doping was found to effectively enhance not only the crystallinity but also the luminescent brightness of Y_2−xGd_xO₃:Eu³⁺ thin films. In particular, the incorporation of Li and Gd into the Y₂O₃ lattice could induce remarkable increase in the PL. The highest emission intensity was observed Li-doped Y_1.35Gd_0.6O₃:Eu³⁺ thin films whose brightness was increased by a factor of 4.6 in comparison with that of Li-doped Y₂O₃:Eu³⁺ thin films.     

Influence of pH on microstructural and optical properties of electrosynthesized CdSe thin films

Cadmium selenide (CdSe) thin films were electrosynthesized onto well cleaned stainless steel and fluorine-doped tin oxide (FTO) coated glass (10-15 Ω/cm²) substrates at different pH of the electrolytic solution. X-ray diffraction study reveals a cubic structure with preferential orientation along the (1 1 1) direction. The structural parameters such as grain size (D), lattice constant (a), strain (ε), dislocation density (δ), average internal stress (S) and degree of preferred orientation (I₁₁₀/I₂₂₀) in the film are calculated and they are found to be dependent on the pH of the depositing bath. EDAX analysis confirms nearly stoichiometric composition of the film deposited at pH 2.70. AFM analysis shows uniform deposition of the film over the entire substrate surface. In optical studies, the transition of the deposited film is found to be a direct allowed transition. The optical energy gaps are found to be in the range from 1.87 to 2.04 eV depending on the pH of the depositing bath. Photoluminescence (PL) spectrum shows blue shift in PL peak position and reduction in luminescence intensity for the film deposited at pH other than 2.70.     

A comparative study of the physical properties of Sb2S3 thin films treated with N2 AC plasma and thermal annealing in N2

As-deposited antimony sulfide thin films prepared by chemical bath deposition were treated with nitrogen AC plasma and thermal annealing in nitrogen atmosphere. The as-deposited, plasma treated, and thermally annealed antimony sulfide thin films have been characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy, scanning electron microscopy, atomic force microscopy, UV-vis spectroscopy, and electrical measurements. The results have shown that post-deposition treatments modify the crystalline structure, the morphology, and the optoelectronic properties of Sb₂S₃ thin films. X-ray diffraction studies showed that the crystallinity of the films was improved in both cases. Atomic force microscopy studies showed that the change in the film morphology depends on the post-deposition treatment used. Optical emission spectroscopy (OES) analysis revealed the plasma etching on the surface of the film, this fact was corroborated by the energy dispersive X-ray spectroscopy analysis. The optical band gap of the films (E_g) decreased after post-deposition treatments (from 2.36 to 1.75 eV) due to the improvement in the grain sizes. The electrical resistivity of the Sb₂S₃ thin films decreased from 10⁸ to 10⁶ Ω-cm after plasma treatments.     

Field electron emission from HfNxOy thin films deposited by direct current sputtering

HfN_xO_y thin films were deposited on Si substrates by direct current sputtering at room temperature. The samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). SEM indicates that the film is composed of nanoparticles. AFM indicates that there are no sharp protrusions on the surface of the film. XRD pattern shows that the films are amorphous. The field electron emission properties of the film were also characterized. The turn-on electric field is about 14 V/μm at the current density of 10 μA/cm², and at the electric field of 24 V/μm, the current density is up to 1 mA/cm². The field electron emission mechanism of the HfN_xO_y thin film is also discussed.     

Femtosecond laser patterning of Ta0.1W0.9Ox/ITO thin film stack

Selective laser patterning of thin films in a multilayered structure is an emerging technology for process development and fabrication of optoelectronics and microelectronics devices. In this work, femtosecond laser patterning of electrochromic Ta_0.1W_0.9O_x film coated on ITO glass has been studied to understand the selective removal mechanism and to determine the optimal parameters for patterning process. A 775 nm Ti:sapphire laser with a pulse duration of 150 fs operating at 1 kHz was used to irradiate the thin film stacks with variations in process parameters such as laser fluence, feedrate and numerical aperture of objective lens. The surface morphologies of the laser irradiated regions have been examined using a scanning electron microscopy and an optical surface profiler. Morphological analysis indicates that the mechanism responsible for the removal of Ta_0.1W_0.9O_x thin films from the ITO glass is a combination of blistering and explosive fracture induced by abrupt thermal expansion. Although the pattern quality is divided into partial removal, complete removal, and ITO film damage, the ITO film surface is slightly melted even at the complete removal condition. Optimal process window, which results in complete removal of Ta_0.1W_0.9O_x thin film without ablation damage in the ITO layer, have been established. From this study, it is found that focusing lens with longer focal length is preferable for damage-free pattern generation and shorter machining time.     

Averaged local field intensities in composite films

The photophysical properties of molecules adsorbed in composite films (e.g. surface island films) depend on the local electromagnetic field within the film. The ratio between the average field intensity 〈|E|²〉 in the film and the intensity |E_I|² associated with the incident field is a measure of the electromagnetic contribution to the surface influence on molecular photophysical phenomena. This ratio depends on the film composition and morphology, on the dielectric properties of the pure components making the film and on the frequency, direction and polarization of the incident radiation. Calculations of this ratio as a function of these parameters for several models of composite films are presented. Image interactions and retardation effects as well as radiative damping and finite size contributions to the dielectric response of the films are taken into account. In addition, an estimate of the field inhomogeneity within the film is obtained by calculating also the ratio 〈|E|²〉_shell/|E_I|² associated with the field in thin shells surrounding the dielectric particles which constitute the film.     

Local structure analysis of smoky and colorless topaz using single crystal Al NMR

The angular dependence of the ²⁷Al NMR spectrum was measured for single crystals of smoky and colorless topaz, Al₂SiO₄(F,OH)₂. Smoky topaz was obtained by irradiating high energy neutrons to colorless topaz. The quadrupole coupling constant e²Qq/h and the asymmetry parameter η were obtained from the analysis of the angular dependences of quadrupole splitting of the ²⁷Al NMR spectrum. The local structures around the aluminum atoms in smoky and colorless topaz were discussed from the magnitude and the direction of the electric field gradient. The directions of principal axes of the EFG tensor of ²⁷Al were close to the directions of Al-O and Al-F bonds. The difference in the bond lengths between Al(1)-F(1) and Al(1)-F(2) was found to affect the x and y components of the EFG tensor.     

Microstructure and magnetooptics of silicon oxide with implanted nickel nanoparticles

Metallic nickel nanoparticles of various sizes are formed in a thin near-surface layer in an amorphous SiO₂ matrix during 40-keV Ni⁺ ion implantation at a dose of (0.25−1.0) × 10¹⁷ ions/cm². The micro-structure of the irradiated layer and the crystal structure, morphology, and sizes of nickel particles formed at various irradiation doses are studied by transmission electron microscopy and electron diffraction. The magnetooptical Faraday effect and the magnetic circular dichroism in an ensemble of nickel nanoparticles are studied in the optical range. The permittivity [^(e)]\hat \varepsilon tensor components are calculated for the implanted samples using an effective medium model with allowance for the results of magnetooptical measurements. The spectral dependences of the tensor [^(e)]\hat \varepsilon components are found to be strongly different from those of a continuous metallic nickel film. These differences are related to a disperse structure of the magnetic nickel phase and to a surface plasma resonance in the metal nanoparticles.     

Surface characterization and microstructure of ITO thin films at different annealing temperatures

In this study, the electron beam evaporation method is used to generate an indium tin oxide (ITO) thin film on a glass substrate at room temperature. The surface characteristics of this ITO thin film are then investigated by means of an AFM (atomic force microscopy) method. The influence of postgrowth thermal annealing on the microstructure and surface morphology of ITO thin films are also examined. The results demonstrate that the film annealed at higher annealing temperature (300 °C) has higher surface roughness, which is due to the aggregation of the native grains into larger clusters upon annealing. The fractal analysis reveals that the value of fractal dimension D_f falls within the range 2.16-2.20 depending upon the annealing temperatures and is calculated by the height-height correlation function.     

Effect of modifying a methyl siloxane-based dielectric by a polymer thin film for pentacene thin-film transistors

We report on the fabrication of pentacene thin-film transistors (TFTs) utilizing a spun methyl siloxane-based spin-on-glass (SOG) dielectric and show that these devices can give a similar electrical performance as achieved by using pentacene TFTs with a silicon dioxide (SiO₂) dielectric. To improve the electrical performance of pentacene TFTs with the SOG dielectric, we employed a hybrid dielectric of an SOG/cross-linked poly-4-vinylphenol (PVP) polymer. The PVP film was deposited onto the spun SOG dielectric prior to pentacene evaporation, resulting in an improvement of the saturation field effect mobility (μ_sat) from 0.01 cm²/(V s) to 0.76 cm²/(V s). The good surface morphology and the matching surface energy of the SOG dielectric that was modified with the polymer thin film allow the optimized growth of crystalline pentacene domains whose nuclei are embedded in an amorphous phase.     

Synthesis of Cadmium Selenide thin films at low-temperature by simple Chemical route and their Characterization

Crystalline CdSe thin film has been deposited using appropriate precursor solution containing cadmium sulfate octahydrate, tartaric acid, potassium hydroxide, ammonia and sodium selenosulfate. The effect of parameters such as bath composition, deposition temperature, pH of the solution, speed of the rotation and the specificity of complexing agent on growth process is studied. The ‘as-deposited’ CdSe thin film was found to be red in color, specularly reflective and well adherent to the glass substrate. The crystalline phase of the deposited sample was hexagonal wurtzite-type. The analysis of optical absorption data shows energy band gap energy (E_g) 2.01 eV. The morphological study and compositional analysis of film sample have been discussed. The electrical resistivity of CdSe thin film was found to the order of 10⁶ Ω cm.     

Selective MOCVD of titanium oxide and zirconium oxide thin films using single molecular precursors on Si(1 0 0) substrates

Titanium oxide (TiO₂) and zirconium oxide (ZrO₂) thin films have been deposited on modified Si(1 0 0) substrates selectively by metal-organic chemical vapor deposition (MOCVD) method using new single molecular precursor of [M(OⁱPr)₂(tbaoac)₂] (M=Ti, Zr; tbaoac=tertiarybutyl-acetoacetate). For changing the characteristic of the Si(1 0 0) surface, micro-contact printing (μCP) method was adapted to make self-assembled monolayers (SAMs) using an octadecyltrichlorosilane (OTS) organic molecule which has -CH₃ terminal group. The single molecular precursors were prepared using metal (Ti, Zr) isopropoxide and tert-butylacetoacetate (tbaoacH) by modifying standard synthetic procedures. Selective depositions of TiO₂ and ZrO₂ were achieved in a home-built horizontal MOCVD reactor in the temperature range of 300-500 °C and deposition pressure of 1×10⁻³-3×10⁻² Torr. N₂ gas (5 sccm) was used as a carrier gas during film depositions. TiO₂ and ZrO₂ thin films were able to deposit on the hydrophilic area selectively. The difference in surface characteristics (hydrophobic/hydrophilic) between the OTS SAMs area and the SiO₂ or Si-OH layer on the Si(1 0 0) substrate led to the site-selectivity of oxide thin film growth.     

Enhanced flux pinning in pulsed laser deposited Y Ba2Cu3O7−δ : BaTiO3 nanocomposite thin films

The effect of incorporation of BaTiO₃(BTO) nanoparticles on the flux pinning properties of pulsed laser deposited YBCO:BTO thin films was studied. Substantial increase in the critical current density (J_C) and the pinning force density (F_p) of the nanocomposite thin films was observed. At 77 K, and zero applied magnetic field, the value of J_C for YBCO and YBCO:BTO (2%) thin films were 2.93 MA/cm² and 6.43 MA/cm², respectively. At the same temperature and an applied magnetic field of 4 T, the value of J_C increases from 3.6×10⁴ A/cm² for YBCO thin film to 2.7×10⁵ A/cm² for YBCO:BTO (2%) nanocomposite thin film. The study of temperature and field dependence of of YBCO and YBCO:BTO thin films indicates similar type of pinning. The lattice mismatch between YBCO and BTO seems to introduce more defects resulting in the improvement of flux pinning properties.     

Composition of the sputter deposited W-Ti thin films

Tungsten-titanium (W-Ti) thin film was deposited by dc Ar⁺ sputtering of W(70 at.%)-Ti(30 at.%) target. The thin film composition, determined by X-ray photoelectron spectroscopy (XPS) depth profiling, is W_(0.77±0.07)Ti_(0.08±0.03)O_(0.15±0.03). The presence of oxygen in the deposit is due to the rather poor vacuum conditions during the deposition, while significant deficiency of Ti, as compared to the sputtering target composition cannot be explained straightforwardly. Monte Carlo simulations of both, transport of sputtered particles from target to the substrate through the background gas (SRIM 2003 program) and thin film sputtering during the XPS depth profiling (program TRIDYN_FZR) are presented. The simulations show that the particle transport through the background gas is mainly responsible for the Ti depletion: the estimated composition of the thin film is W_0.61Ti_0.16O_0.23. Additional apparent Ti depletion occurs due to the preferential sputtering during the thin film composition analysis. The simulation of the sputtering process show that the surface concentration measured by XPS should be about W_0.74Ti_0.11O_0.15. The discrepancy between the estimated surface composition and the actual experimental result is in the range of the experimental error.     

Critical behaviour of magnetic thin film with Heisenberg spin-S model

The magnetic properties of a ferromagnetic thin film of face centered cubic (FCC) lattice with Heisenberg spin-S are examined using the high-temperature series expansions technique extrapolated with Padé approximations method. The critical reduced temperature of the system τ_c is studied as function of thickness of the film and the exchange interactions in the bulk, and within the surfaces J_b, J_s and J_⊥ respectively. A critical value of surface exchange interaction above which surface magnetism appears is obtained. The dependence of the reduced critical temperature on the film thickness L has been investigated.     

Effect of process parameters on surface morphology and characterization of PE-ALD SnO2 thin films for gas sensing

Tin dioxide (SnO₂) thin films were deposited by plasma enhanced-atomic layer deposition (PE-ALD) on Si(1 0 0) substrate using dibutyl tin diacetate (DBTA) ((CH₃CO₂)₂Sn[(CH₂)₃-CH₃]₂) as precursor. The process parameters were optimized as a function of substrate temperature, source temperature and purging time. It is observed that the surface phenomenon of the thin films was changed with film thickness. Atomic force microscopy (AFM) images and X-ray diffraction (XRD) pattern were used to observe the texture and crystallanity of the films. The films deposited for 100, 200 and 400 cycles were characterized by XPS to determine the chemical bonding properties. XPS results reveal that the surface dominant oxygen species for 100, 200 and 400 cycles deposited films are O₂⁻, O⁻ and O²⁻, respectively. The 200 cycles film has exhibited highest concentration of oxygen (O⁻) species before and after annealing. Conductivity studies revel that this film has best adsorption strength to the oxygen ions forming on the surface. The sensor with 200 cycles SnO₂ thin film has shown highest sensitivity to CO gas than other films. A correlation between the characteristics of Sn3d_5/2 and O1s XPS spectra before and after annealing and the electrical behavior of the SnO₂ thin films is established.