Structural and electrical properties of evaporated ZnTe thin films

Zinc telluride thin films of various thicknesses are deposited by vacuum evaporation onto glass substrates at room temperature. The X-ray diffraction technique is used to determine the crystalline structure and grain size of the films, respectively. The structure was found to be cubic with preferential orientation along a (1 1 1) plane and crystallite size of about 50-80 nm. The degree of preferred orientation and crystallite size are increased as the film thickness increases. The current density-voltage (J-V) characteristics showed ohmic conduction in the lower voltage range and space-charge-limited conductivity in the higher voltage range. Capacitance measurements indicated that the films have a relative permittivity, ε_r, of approximately 8.19. Further evidence for this conduction process was provided by linear dependence of V_t on d². Analysis of the results yielded hole concentration , which is correlated with the structural properties.     

Effect of the substrate on the properties of ZnO-MgO thin films grown by atmospheric pressure metal-organic chemical vapor deposition

The ZnO-MgO alloys possess attractive properties for possible applications in optoelectronic and display devices; however, the optical properties are strongly dependent on the deposition parameters. In this work, the effect of the glassy and metallic substrates on the structural, morphological and optical properties of ZnO-MgO thin films using atmospheric pressure metal-organic chemical vapor deposition was investigated at relatively low deposition temperature, 500 °C. Magnesium and zinc acetylacetonates were used as the metal-organic source. X-ray diffraction experiments provided evidence that the kind of substrates cause a deviation of c-axis lattice constant due to the constitution of a oxide mixture (ZnO and MgO) in combination with different intermetallic compounds(Mg₂Zn₁₁ and Mg₄Zn₇) in the growth films. The substitutional and interstitial sites of Mg²⁺ instead of Zn²⁺ ions in the lattice are the most probable mechanism to form intermetallic compounds. The optical parameters as well as thickness of the films were calculated by Spectroscopic Ellipsometry using the classical dispersion model based on the sum of the single and double Lorentz and Drude oscillators in combination with Kato-Adachi equations, as well as X-ray reflectivity.     

Thickness dependent electronic structure of ultra-thin tetrahedral amorphous carbon (ta-C) films

Microstructural properties of ultrathin (1-10 nm) tetrahedral amorphous carbon (ta-C) films are investigated by Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, X-ray Photoelectron Spectroscopy, Raman spectroscopy and Atomic Force Microscopy (AFM). The CK-edge NEXAFS spectra of 1 nm ta-C films provided evidence of surface defects (C―H bonds) which rapidly diminish with increasing film thickness. A critical thickness for stabilization of largely sp³ matrix structure distorted by sp² sites is observed via the change of π*C═C peak behavior. Meanwhile, an increase in the film thickness promotes an enhancement in sp³ content, the film roughness remains nearly constant as probed by spectroscopic techniques and AFM, respectively. The effect of thickness on local bonding states of ultrathin ta-C films proves to be the limiting factor for their potential use in magnetic and optical storage devices.     

Irradiation induced effects on Ni3N/Si bilayer system

The irradiation effect in Ni₃N/Si bilayers induced by 100 MeV Au ions at fluence 1.5 × 10¹⁴ ions/cm² was investigated at room temperature. Grazing incidence X-ray diffraction determined the formation of Ni₂Si and Si₃N₄ phases at the interface. The roughness of the thin film was measured by atomic force microscopy. X-ray reflectivity was used to measure the thickness of thin films. X-ray photoelectron spectroscopy has provided the elemental binding energy of Ni₃N thin films. It was observed that after irradiation (Ni 2p_3/2) peak shifted towards a lower binding energy. Optical properties of nickel nitride films, which were deposited onto Si (100) by ion beam sputtering at vacuum 1.2 × 10⁻⁴ torr, were examined using Au ions. In-situ I–V measurements on Ni₃N/Si samples were also undertaken at room temperature which showed that there is an increase in current after irradiation.     

Deposition and characterization of BN/Si(0 0 1) using tris(dimethylamino)borane

Boron nitride thin films could be deposited on Si(0 0 1) by chemical vapor deposition (CVD) at atmospheric pressure using a single source precursor. IR absorption spectra of films deposited between 750 and 1000°C using B[N(CH₃)₂]₃ (tris(dimethylamino)borane, TDMAB) as the boron and nitrogen source showed a peak absorption at ∼1360 cm⁻¹ characteristic of the in-plane vibrational mode seen in h-BN. It was noted that the mode at 800 cm⁻¹ is very weak. The observed growth rate varied exponentially with temperature in the range 850-900°C. Ellipsometry measurements were used to investigate the thickness and optical constant of the films. The refractive index, slightly lower than the bulk material, is close to 1.65-1.7 depending on the surface morphology of the films. The surface morphology of thin layers has been observed by atomic force microscopy with an increase of the surface roughness from 0.3 to 3.5 nm as the growth temperature increases from 800 to 950°C.     

Characterization of CuInGeSe<Subscript>4</Subscript> thin films and Al/n–Si/p–CuInGeSe<Subscript>4</Subscript>/Au heterojunction device

CuInGeSe₄ thin films of various thicknesses were prepared on a glass substrate by thermal evaporation followed by selenization at 700 K. Energy dispersive X-ray analysis shows that the CuInGeSe₄ thin films are near stoichiometric. The X-ray diffraction patterns indicate that the as-deposited CuInGeSe₄ thin films are amorphous, while the CuInGeSe₄ thin films annealed at 700 K are polycrystalline with the chalcopyrite phase. The structure of the films was further investigated by transmission electron microscopy and diffraction, with the results verifying the X-ray diffraction data. High-resolution scanning electron microscopy images show well-defined grains that are nearly similar in size. The surface roughness increases with film thickness, as confirmed by atomic force microscopy. The optical transmission and reflection spectra of the CuInGeSe₄ thin films were recorded over the wavelength range of 400–2500 nm. The variation of the optical parameters of the CuInGeSe₄ thin films, such as the refractive index n and the optical band gap E_g, as a function of the film thickness was determined. The value of E_g decreases with increasing film thickness. For the studied films, n were estimated from the Swanoepl’s method and were found to increase with increasing film thickness as well as follow the two-term Cauchy dispersion relation. A heterojunction with the configuration Al/n–Si/p–CuInGeSe₄/Au was fabricated. The built-in voltage and the carrier concentration of the heterojunction was determined from the capacitance–voltage measurements at 1 MHz and were found to be 0.61 V and 3.72?×?10¹⁷ cm^?3, respectively. Under 1000 W/m² solar simulator illumination, the heterojunction achieved a conversion efficiency of 2.83%.     

Impact of various irradiation photon energies and gamma doses on the optical properties of ZnSe nanostructure thin film

ZnSe thin films were prepared by thermal evaporation technique under high vacuum (10⁻⁶ Torr) at 300 K and different film thickness. The structure of thin films was measured using grazing incident in-plane X-ray diffraction (GIIXD) and shows single phase zinc blende structure. The particle sizes of the deposited films were estimated for low film thickness by TEM and high film thickness by GIIXD. The particle size of ZnSe films was decreased from ~8.53 to 3.93 nm as film thickness lowered from 200 to 20 nm which ensures the nanocrystalline structure. The optical transmission (T) and reflection (R) in the wavelength range 190–2,500 nm for irradiated and unirradiated ZnSe thin films under investigation were measured. The effect of irradiation of different energies in range (0.1–1.25 MeV) from X-ray, ¹³⁷Cs and ⁶⁰Co irradiation sources were studied for ZnSe thin films of 100 and 200 nm thicknesses. The dependence of the absorption spectra and refractive index were investigated for different energies irradiation sources. The ZnSe films show direct allowed interband transition. The effect of particle size of nanocrystalline ZnSe thin films for unirradiated and irradiated by gamma (γ) doses from ¹³⁷Cs on the optical properties was studied. Both the optical energy bandwidth and absorption coefficient (α) were found to be (γ) dose dependent.     

Thickness dependence of (001) texture evolution in FePt thin films on an amorphous substrate

Thickness dependency of (001) texture evolution in Fe₅₄Pt₄₆ thin films on an amorphous substrate was investigated using in-house X-ray diffraction or a synchrotron source. The (001) texture was well developed in Fe₅₄Pt₄₆ thin films, especially when its thickness was equivalent to the grain height. The findings show that strain relaxation anisotropy along the film axis, which leads to a (001) crystal (a crystal with a (001) plane parallel to the film plane) that is more stable than others, was large for a low thickness film. In addition, abnormal grain growth was used to explain the abrupt development of a (001) texture. The advantage of multilayered as-deposited structure is also discussed.     

Development of free-standing submicron formvar films with multiple thickness steps for XUV-soft X-ray applications

Preparation of free-standing submicron Formvar films with multiple thickness steps is reported. This is done by using a dipping and pulling technique in which film thickness is controlled by varying the pulling speed. Dependence of film thickness on the pulling speed is presented. Planar unsupported films of a single thickness or with multiple thickness steps in the range of 0.25μm to ∼ 5μm and of area up to ≈ 800 mm² are made in this manner. Such films should be useful in XUV-soft X-ray spectral measurements and as targets for plasma ablation studies.     

A simple electrophoretic deposition method to prepare TiO2-B nanoribbon thin films for dye-sensitized solar cells

This paper describes a simple method utilizing electrophoretic deposition (EPD) to quickly synthesize hydrogen titanate nanoribbon films. The subsequent heating of the hydrogen titanate nanoribbon films causes the dehydration of interlayered OH groups, thereby leading to TiO₂-B nanoribbon films. Thick, uniform TiO₂-B nanoribbon films were obtained from prepared alkali suspensions. The crystal structure of the hydrogen titanate and TiO₂-B nanoribbon films obtained from EPD underwent analysis by X-ray diffraction and high-resolution transmission electron microscope. EPD controlled the thickness of TiO₂-B nanoribbons films. TiO₂-B-coated fluorine-doped tin oxide films were dye-sensitized with N3 and used as a photoanode in an electrochemical solar cell. The solar cell yielded conversion efficiencies of 0.87% for an incident solar energy of 100 mW/cm².     

Effect of complexing agents: investigations on structural,morphological, topographical and optical analysis of copper iron sulphide thin films deposited by chemical bath deposition method

Copper iron sulphide (FeCuS₂) thin films deposited by chemical bath deposition method using ferrous sulphate and copper sulphate as cationic sources and sodium sulphide as anionic source with complexing agents, EDTA and Leishman stain were reported. The structural, optical and morphological studies were carried out using X-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV–Visible spectroscopy techniques. The X-ray spectrum reveals that the films are polycrystalline nature and also showed the deposition of cubic phases at room temperature. The SEM images for prepared films have clear morphology influenced by the complexing agents used in deposition process. The result of AFM studies shown that the particles in the film have grain size around ~?60–70 nm and also have almost similar thickness. Based on the optical absorbance spectra the FeCuS₂ film exhibited a high absorbance in the visible region. The absorption edge shifted toward lower wavelength with varying complexing agents. The band gap value obtained was found to be 3.57–3.85 eV. From these results, it is indicated that the prepared films are suitable candidate for solar cell applications.     

X-ray diffraction investigations on evaporated iron films

The structure of thin iron films of thickness about 1500 Å was studied by means of X-ray diffraction analysis. Evaporation and X-ray examination were carried out in the 10^?10 Torr range without exposing the films to the atmosphere using a recently developed ultrahigh vacuum diffraction chamber. The films were deposited onto glass substrates at a rate of 10 Å min^?1 at room temperature and were subsequently annealed at 320°C. They show a (110) fibre texture with a mean crystallite size of the (110)-oriented crystals that was distincly smaller than the film thickness. The lattice parameter was found to be always less than the corresponding value for a bulk iron standard, which can be ascribed to the formation of thermally induced strains.     

Structural and optical properties of nanocrystalline CdS thin films prepared using microwave-assisted chemical bath deposition

Cadmium sulfide (CdS) nanocrystalline thin films were prepared using the microwave-assisted chemical bath deposition method onto glass substrates at 80 °C. Aqueous solutions of either cadmium chloride or cadmium acetate and thiourea were used as sources of Cd²⁺ and S²⁻ ions, respectively. Two sets of samples with different concentrations were prepared. A microwave oven was used as a heating source to synthesize the nanocrystalline CdS thin films. The prepared thin films had a good adhesion with no pinholes. These films were examined for their structural and surface morphologies by X-ray diffraction (XRD), scanning electron microscopy, and atomic force microscopy. The optical properties were investigated using UV-vis spectrophotometer, photoluminescence, and Raman spectroscopy. Particle size values obtained from XRD were compared with these calculated using effective mass models. The values of optical band gaps according to optical transmission measurements decreased as the ion source molar concentration increased.     

Study of electrical polarization hysteresis in ferroelectric polyvinylidene fluoride films

Electric properties of polyvinylidene (PVDF) films fabricated using the Langmuir-Schaefer method have been studied. Films of different thickness were deposited on silicon substrates and analyzed using several techniques. X-ray diffraction (XRD) data showed that PVDF films crystallize at an annealing temperature above 130 °C. Polarization versus electric field (PE) ferroelectric measurements was done for samples prepared with electrodes. PE measurements show that the coercivity of the films increases as the maximum applied electric field increases. The coercivity dependence on the frequency of the applied electric field can be fitted as f^0.6. The results also show that the coercivity decreases with increasing the thickness of PVDF film due to the pinning effect.     

Phenomenology of the “explosive” crystallization of sputtered non-crystalline germanium films

Certain non-crystalline germanium films (> 10 μm in thickness) prepared by rf-sputtering crystallize “explosively” at room temperature when initiated by pricking the surface with a sharp point (or certain other methods). The propagation velocity of the crystallization at room temperature was found to be as fast a 1200 mm sec^?1 depending somewhat on the conditions of film preparation, thickness, etc. The density of several such crystallizable films was determined as 5.05 g cm^?3±1%. The crystallite size in the crystallized films, measured by X-ray broadening, was typically larger than 500 Å. A model for the crystallization process invokes a cascade energy transfer process, basically thermal in nature.     

Synthesis and optical properties of CeO<Subscript>2</Subscript> nanocrystalline films grown by pulsed electron beam deposition

The nanocrystalline cerium dioxide (CeO₂) thin films were deposited on soda lime (SLG) and Corning glass by pulsed e-beam deposition (PED) method at room temperature. The structure of the produced CeO₂ thin films was investigated by X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and micro Raman spectroscopy. The surface topography of the films was examined by atomic force microscopy (AFM). Film thickness and growth morphologies were determined with FEG-SEM from the fracture cross sections. XPS studies gave a film composition composed of +4 and +3 valent cerium typical to nanocrystalline ceria structures deficient in oxygen. The ceria films were polycrystalline in nature with a lattice parameter (a) of 0.542 nm. The Raman characteristics of the source material and the films deposited were very similar in character. Raman lines for thin film and bulk CeO₂ was observed at 465 cm⁻¹. The optical properties of the CeO₂ films were deduced from reflectance and transmittance measurements at room temperature. From the optical model, the refractive index was determined as 1.8–2.7 in the photon energy interval from 3.5 to 1.25 eV. The optical indirect band gap (E _g) of CeO₂ nanocrystalline films was calculated as 2.58 eV.     

Structural properties of low-temperature grown ZnO thin films determined by X-ray diffraction and X-ray absorption spectroscopy

The epitaxial growth of ZnO thin films on Al₂O₃ (0001) substrates have been achieved at a low-substrate temperature of 150 °C using a dc reactive sputtering technique. The structures and crystallographic orientations of ZnO films varying thicknesses on sapphire (0001) were investigated using X-ray diffraction (XRD). We used angle-dependent X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to examine the variation of local structure. The XRD data showed that the crystallinity of the film is improved as the film thickness increases and the strain is fully released as the film thickness reached about 800 Å. The Zn K-edge XANES spectra of the ZnO films have a strong angle-dependent spectral feature resulting from the preferred c-axis orientation. The wurtzite structure of the ZnO films was explicitly shown by the XRD and EXAFS analysis. The carrier concentration, Hall mobility and resistivity of the 800 Å-thick ZnO film were 1.84 × 10¹⁹ cm^− 3, 24.62 cm²V^− 1s^− 1, and 1.38 × 10^− 2 Ω cm, respectively.     

Microstructure and optical characterization of nanometric silicon films prepared by pulsed laser ablation

The effect of laser energy density, during pulsed laser ablation, on the microstructure and optical properties of silicon films has been investigated using techniques such as atomic force microscopy, scanning electron microscopy, X-ray diffraction, and UV–visible absorption/transmission spectroscopy. The thickness of prepared films increases with increase in laser energy density. The crystallite size and hence the crystallinity of prepared films have been estimated by X-ray diffraction and found to be dependent on laser energy density. The transmittance of films changes with laser energy density. The absorption coefficient of films has been found to be?>10⁴?cm^?1 in wavelength region 450–1100?nm. The band gap of silicon films has been determined as 2.27, 2.11, and 1.90?eV corresponding to laser energy density of 1.5, 2.5, and 3.5?J?cm^?2, respectively.     

Study of annealing effects in In-Sb bilayer thin films

The thin films of In-Sb having different thicknesses of antimony keeping constant thickness of indium was deposited by thermal evaporation method on ITO coated conducting glass substrates at room temperature and a pressure of 10⁻⁵ torr. The samples were annealed for 1 h at 433 K at a pressure of 10⁻⁵ torr. The optical transmission spectra of as deposited and annealed films have been carried out at room temperature. The variation in optical band gap with thickness was also observed. Rutherford back scattering and X-ray diffraction analysis confirms mixing of bilayer system. The transverse I-V characteristic shows mixing effect after annealing at 433 K for 1 h. This study confirms mixing of bilayer structure of semiconductor thin films.     

Thin film growth of boron nitride on α-Al2O3 (0 0 1) substrates by reactive sputtering

Boron nitride thin films were grown on α-Al₂O₃ (0 0 1) substrates by reactive magnetron sputtering. Infrared attenuated total reflection (ATR) spectra of the films gave an intense signal associated with in-plane B-N stretching TO mode of short range ordered structure of BN hexagonal sheets. X-ray diffraction for the film prepared at a low working pressure (ca. 1 × 10⁻³ Torr) gave a diffraction peak at slightly lower angle than that corresponding to crystal plane h-BN (0 0 2). It is notable that crystal thickness calculated from X-ray peak linewidth (45 nm) was close to film thickness (53 nm), revealing well developed sheet stacking along the direction perpendicular to the substrate surface. When the substrates of MgO (0 0 1) and Si (0 0 1) were used, the short-range ordered structure of h-BN sheet was formed but the films gave no X-ray diffraction. The film showed optical band gap of 5.9 eV, being close to that for bulk crystalline h-BN.