Effect of oxidation on thickness dependencies of thermoelectric properties in PbTe/mica thin films

The dependencies of the Hall coefficient R_H and Seebeck coefficient S at room temperature on the thickness (d=10-550 nm) of thin PbTe films prepared by the thermal evaporation in vacuum of n-type PbTe crystals with various charge carrier concentrations (10¹⁷-10¹⁹ cm⁻³) and their deposition on mica substrates were obtained. It was established that, with decreasing thickness of PbTe films, a transition from an electron to a hole conductivity occurs, and the inversion point shifts to smaller d values as the electron concentration in the target material increases. The experimental R_H(d) and S(d) dependencies are interpreted in terms of the acceptor states created by oxygen on the film surface. These dependencies were also calculated theoretically, taking into account the existence of two types of charge carriers (electrons and holes). The theoretical curves are found to be in good agreement with the experimental data.     

Synthesis of PbTe nanocubes, worm-like structures and nanoparticles by simple thermal evaporation method

Nanocrystalline PbTe thin films are prepared by thermal evaporation on glass substrates. The investigations of X-ray diffractograms have shown that the structure of film is found to possess stable face centred cubic (fcc) phase in which the grains predominantly grow in the direction of (200) plane. The grain size of the films is within the range of 27–43 nm. Morphologies like assembly of nanoparticles, worm-like structures and nanocubes were prepared by tuning the film thickness. Electrical resistivity is measured using four-probe technique and its thickness dependence has been analysed on the basis of ‘effective mean free path model’. A change in conductivity from n-type to p-type is observed due to the increase of migration of tellurium vacancies in the films with temperature. Bandgap energy of the PbTe nanocrystalline thin films suffered a large blue shift of about 1 $\cdot$ 299 eV due to quantum confinement of charge carriers. The nanocrystalline PbTe thin films of different morphologies such as nanoparticles, worm-like and nanocubes have the optical bandgap energies of 1·61, 1·23 and 1·01 eV, respectively. Photoconductivity measurement shows that the prepared nanocrystalline PbTe thin films of different morphology exhibits good response. This structure induced change in optical properties may have potential applications in optoelectronics devices.     

Preparation and study of thickness dependent electrical characteristics of zinc sulfide thin films

Zinc sulfide thin films have been deposited onto glass substrates by chemical bath deposition. The various deposition parameters such as volume of sulfide ion source, pH of bath, deposition time, temperature etc are optimized. Thin films of ZnS with different thicknesses of 76–332 nm were prepared by changing the deposition time from 6–20 h at 30° C temperature. The effect of film thickness on structural and electrical properties was studied. The electrical resistivity was decreased from 1.83 × 10⁵ Ω-cm to 0.363 × 10⁵ Ω-cm as film thickness decreased from 332 nm to 76 nm. The structural and activation energy studies support this decrease in the resistivity due to improvement in crystallinity of the films which would increase the charge carrier mobility and decrease in defect levels with increase in the thickness.     

Structural and optical properties of Ag2SeTe nano thin films prepared by thermal evaporation

Semiconducting Ag₂SeTe thin films were prepared with different thicknesses onto glass substrates at room temperature using thermal evaporation technique. The structural properties were determined as a function of thickness by XRD exhibiting no preferential orientation along any plane, however the films are found to have peaks corresponding to mixed phase. The XRD studies were used to calculate the crystallite size and microstrain of the Ag₂SeTe films. The calculated microstructure parameters reveal that the crystallite size increases and micro strain decreases with increasing film thickness. The refractive index, dielectric constants and thereby the optical bandgap of the films were calculated from transmittance spectral data recorded in the range 400?C1200 nm by UV?CVIS-Spectrometer. The direct optical bandgap of the Ag₂SeTe thin films deposited on glass substrates with different thicknesses 50?C230 nm were found to be in the range 1.48?C1.59 eV. The carrier density value is estimated to be around 9.8 × 10²¹ cm^?1 for the film thickness of 150 nm. The compositions estimated from the optical band gap studies reveal a value of 0.75 for Tellurium concentration. These structural and optical parameters are found to be very sensitive to the thin film thickness.     

Analysis of the lattice thermal conductivity of thin films by means of a modified Mayadas-Shatzkes model: The case of bismuth films

The lattice thermal conductivity λ_øx(d, T) of bismuth films in a direction of the film plane (x direction) with the thicknesses d ranging from 20 to 400 nm was determined in the temperature range 80 K ⩽ T ⩽ 400 K from the measured total thermal conductivity λ_x(d, T) and the calculated charge carrier contribution λ_ex(d, T). A modified Mayadas-Shatzkes model of phonon scattering on polycrystalline films is presented. Following this model the thickness and temperature dependence of λ_øx(d, T) can be interpreted.     

Impact of thickness on vacuum deposited PbSe thin films

Lead Selenide thin films were prepared by vacuum evaporation technique with different thickness ranges from 50 to 200 nm on glass substrates. The structural studies revealed that the prepared films are strongly oriented on (2 0 0) plane with rock-salt crystal structure. The various structural parameters such as grain size (D), lattice constant (a), micro strain (ε) and dislocation density (δ) were calculated. The surface morphology of the films was also analyzed. The optical absorption of the films starts with visible region and obtained energy gap of the films lies between 1.5 and 1.9 eV. The room temperature Photoluminescence spectrum shows the emission peak at visible region (380-405 nm) and the blue shift was observed with decreasing the film thickness. The electrical mobility, resistivity, carrier concentration and mean free path (L) of the free carriers of the films were studied for all the samples and compared.     

The effect of LaNiO3 buffer layer thickness on the electric properties of Pb(Zr0.53Ti0.47)O3 thin films deposited on titanium foils

Sol-gel derived Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on LaNiO₃ (LNO) buffered titanium foils. The effect of LNO buffer layer thickness on the electric properties of PZT thin films was investigated. The room temperature dielectric constant of PZT thin films increased with increasing LNO thickness. The remnant polarization of PZT thin films on 150 and 250 nm LNO was about 20 uC/cm². Curie temperatures of PZT thin films were 310, 330 and 340 °C for LNO of 250, 150 and 50 nm respectively. The current-voltage characteristics of PZT thin films were examined for different LNO buffer layer thicknesses, and the space charge limited conduction model was followed in PZT thin films on 50 nm LNO.     

Microstructure and electrical properties of ultrathin gold films prepared by DC sputtering

Ultrathin gold films with different thicknesses were prepared by direct current magnetron sputtering technique and analyzed by X-ray diffraction, atomic force microscopy, transmission electron microscopy and temperature-varying four-wire technique. For thicknesses d < 24.1 nm, both D_{avg {111}} and D_{avg {220}} increase rapidly with the thickness. For 24.1 ≤ d ≤ 97.8 nm, D_{avg {220}} increases at a slower rate than before but D_{avg {111}} remains the same. Surface morphology analysis shows that, as the thickness increases, the average particle size changes from 22.1 to 54.3 nm; at the same time, rms roughness decreases to a minimum and then increases. The electrical properties of the thin films from 80 to 300 K were measured. The results show that the temperature coefficient of resistance of the thin films is positive, and increases from 2.2 × 10⁻⁴ to 8.5 × 10⁻⁴ K⁻¹ with increasing film thickness.     

Room temperature magneto-optics of nanostructured ZnO:Mn thin film grown by spray pyrolysis

Undoped ZnO and ZnO:Mn thin films with different amounts of Mn concentration (5, 10 and 15 mol%) were grown on glass substrates by spray pyrolysis technique. X-ray diffraction patterns showed that the undoped ZnO thin film exhibited wurtzite structure preferably oriented in c-axis direction and the doped samples were polycrystalline. The surface morphology and topography of the films were investigated by SEM and STM micrographs. Magneto-optical characterizations of the samples were carried out by using Kerr and Faraday effects spectroscopy. Kerr effect studies showed that all Mn doped thin films exhibited the room temperature ferromagnetism. The magnetic ordering observed in the film with 5 mol% Mn concentration was stronger comparing to the other doped samples. The carrier densities of the samples were calculated by using a method based on the Faraday rotation. A clear relation between sp-d coupling and strength of magnetic ordering with carrier density was observed.     

Changes in electrical and structural properties of indium oxide thin films through post-deposition annealing

The annealing effects on the electrical properties and microstructures of indium oxide (In₂O₃) thin films were investigated. The In₂O₃ thin films with the thickness of about 150 nm were annealed at various temperatures ranging from 100 to 600 °C in air after the sputtering deposition. It was found that the carrier density of the In₂O₃ thin films decreased with increasing in the annealing temperature and then started to increase at a certain temperature. This indicated that the reduction of the In₂O₃ thin films was promoted at high annealing temperature. The Hall mobility of the In₂O₃ thin films increased through the reduction; furthermore, the d-spacing of the In₂O₃ crystal lattice plane tended toward ideal value. It can be believed from these results that one of the principal electron scattering in the In₂O₃ thin films is attributed to excess oxygen atoms that expand the d-spacing.     

Optical properties of Sb2Se3 thin films

The optical constants (the refractive index n and the absorption index k) of Sb₂Se₃ thin films deposited at room temperature on quartz have been calculated in the wavelength range (5000–2000 nm) using a transmission spectrum. Both n and k were found to be practically independent on either time, up to 6 months, or the film thickness in the range of 102–760 nm. Beyond the absorption edge, the absorption is due to allowed indirect and direct transitions with energy gaps of 1.225 and 1.91 eV, respectively. The value of the optical gap depends on the annealing temperature. X-ray analysis showed that the prepared films at room temperature had amorphous structure while the films annealed at 200°C for 1 h were verified to be crystalline.     

Control of the deposition temperature by the use of a magnetic field in r.f. sputtering

The effect of a magnetic field on the deposition temperature T_d of a thin film prepared by r.f. sputtering is reported. The variation in T_d with the configuration of the magnetic field is illustrated. For the sputtering parameters used, T_d rises to 200°C when no field is applied, but it remains close to room temperature when a d.c. magnetic field is applied at the level of the substrate, parallel to the substrate surface, perpendicular to the motion of the sputtered particles and essentially localized outside the plasma. The results are explained by considering the various contributions to the heating. The application of the present experimental process to the preparation of amorphous thin films is pointed out.     

Influence of target to substrate distance on the sputtered CuCl film properties

CuCl is a potential candidate for UV optoelectronic devices due to its superior optical properties and lattice matching with Si. Stoichiometric CuCl thin films of polycrystalline nature were grown by RF magnetron sputtering technique. The effect of varying the target to substrate distance on the compositional, structural and optoelectronic properties of the sputtered films was analysed. A critical target to substrate distance (d_ts) was observed and the film properties were clearly different above and below this distance. Based on the film properties, the optimum spacing of d_ts = 6 cm was found to yield stoichiometric and high optical quality films. The existence of more than one chemical bonding state was identified in nonstoichiometric, chlorine rich, films by analysing the Cu 2p_3/2 core level XPS spectra. Chlorine rich samples were found to show a noticeable emission from deep levels at ∼ 515 nm in cathodoluminescence (CL) spectroscopy. An exciton mediated sharp UV luminescence (385 nm) emission was realized at room temperature in the stoichiometric CuCl thin films.     

Structural and plasmonic characteristics of sputtered SnO<Subscript>2</Subscript>:Sb and ZnO:Al thin films as a function of their thickness

Heavily doped metal oxide semiconductors are being developed as thin film transparent electrodes for many applications and their deposition at low substrate temperature can extend the use on heat sensitive devices. The structural and electro-optical characteristics of such metal oxide coatings are tightly related and depend on the specific deposition parameters apart from the material composition. In this work, SnO₂:Sb (ATO) and ZnO:Al (AZO) thin films have been prepared by sputtering at room temperature on glass substrates, changing the deposition time to obtain various layer thicknesses from 0.2 to 0.9 μm; and they have been analyzed by X-ray diffraction, spectrophotometry, and Hall-effect measurements. ATO samples crystallize in the tetragonal structure with mean crystallite size increasing from 8 to 20 nm when the film thickness grows. The comparison of Hall mobility and optical mobility values indicates a significant contribution of grain boundary scattering for these ATO layers. Otherwise, AZO films show larger crystallites (21–27 nm) and a strong preferential orientation for analogous thickness increment, resulting in a lower contribution of the grain boundary scattering to the overall Hall mobility. The in-grain mobility for each sample is also related to the respective crystallite size and carrier concentration values.     

Ellipsometric determination of optical properties of carbazole-containing poly(l-glutamate) thin films prepared from different solvents

In this study, the refractive indices (n) and thicknesses of carbazole-containing hole-transport materials such as poly(γ-carbazolylethyl l-glutamate) (PCELG) and poly(N-vinyl carbazole) (PVCz) films were determined by carrying out ellipsometric measurements. The thicknesses of PCELG and PVCz films determined by ellipsometric analysis were in good agreement with those determined by surface profilometry. The dependence of the refractive indices of the PCELG films on film thickness was classified into two types on the basis of the solvent from which the films were prepared: the refractive indices either increased with increasing film thickness, as in the case of PCELG films prepared from 1,2-dichloroethane (DCE) and monochlorobenzene (?-Cl), or were independent of the film thickness, as in the case of films prepared from 1,1,2,2-tetrachloroethane (TCE). A comparison of these results with the structures of the polymers, as determined by ¹H NMR, reveals that the two types of dependences of the refractive indices of the PCELG thin film on the film thickness can be attributed to the two types of aggregation structures and/or orientational characteristics corresponding to the helical conformation of the polymer. In contrast, the refractive indices of PVCz films are governed mainly by the film thickness. Finally, we would like to emphasize that the combination of ellipsometry and other techniques such as NMR and surface profilometry provide information not only on the film thickness and refractive index but also on the aggregation structure in thin films with thicknesses on the order of 50 nm.     

Optical and photoconductivity properties of ZnO thin films grown by pulsed filtered cathodic vacuum arc deposition

High quality transparent conductive ZnO thin films with various thicknesses were prepared by pulsed filtered cathodic vacuum arc deposition (PFCVAD) system on glass substrates at room temperature.The high quality of the ZnO thin films was verified by X-ray diffraction and optical measurements. XRD analysis revealed that all films had a strong ZnO (200) peak, indicating c-axis orientation. The ZnO thin films are very transparent (92%) in the near vis regions. For the ZnO thin films deposited at a pressure of 0.086 Pa (6.5 × 10⁻⁴ Torr) optical energy band gap decreased from 3.21 eV to 3.19 eV with increasing the thickness. Urbach tail energy also decreased as the film thickness increased.Spectral dependence of the photoconductivity was obtained from measurements of the samples deposited at various thicknesses. Photoconductivities were observed at energies lower than energy gap which indicates the existence of energy states in the forbidden gap. Photoconductivities of ZnO thin films increase with energy of the light and reach its maximum value at around 2.32 eV. Above this value surface recombination becomes dominant process and reduces the photocurrent. The photoconductivity increases with decreasing the film thickness.     

Electrical properties of AgGaSe2 films

Single phase polycrystalline films of AgGaSe₂ with different thicknesses are prepared on glass substrates by flash evaporation technique, at a substrate temperature of 523 K. The electrical properties of these films such as resistivity. Hall mobility, carrier concentration and activation energy are determined with different thicknesses of the films. The optical absorption in these films is studied in the energy range 1.3-1.9 eV and found to possess a direct band gap with an energy gap of 1.61 eV for a AgGaSe₂ film having thickness 250 nm. The implications are discussed.     

Surface modification and enhanced multiferroic behavior of BiFe<Subscript>0.25</Subscript>Cr<Subscript>0.75</Subscript>O<Subscript>3</Subscript> films with different thickness over Pt(111)/Ti/SiO<Subscript>2</Subscript>/Si substrate

Polycrystalline BiFe_0.25Cr_0.75O₃ thin films have been fabricated via a chemical deposition technique at various thicknesses (60-, 130-, 190-, 240 nm). The effect of Cr substitution on BiFeO₃ structures have been briefly discussed by performing X-ray diffraction and SAED pattern. The nature of the films surface at different thicknesses were briefly discussed using scanning electron microscope and transmission electron microscope. Roughness and other amplitude parameters of the film at different thickness are studied through atomic force microscopy. The result indicates that, when changing the thickness of the film, the average bond length gets changed causing difference in electrical and magnetic properties. Electrical and dielectric study reveals thickness dependent property and is deeply understood from space charge, oxygen vacancies and super-exchange interaction. Film at 60 nm shows higher magnetization with 8.5042 emu/cm³ and with a retentivity of 3.852 emu/cm³ than the thick film. Further, the spin-cooling behavior and magnetization below room temperature from 2 to 300 K were analyzed briefly for spintronics applications.     

Thickness dependence of electrical resistivity and activation energy in AgSbTe2 thin films

Thin films of AgSbTe₂ with different thicknesses were prepared by thermal evaporation on glass substrates held at room temperature. The films were all found to be semiconducting in nature. The film resistivity was found to be a function of inverse thickness and was discussed on the basis of the effective mean free path model. The activation energy was found to be a linear function of the inverse square of film thickness. It was attributed to the quantization of the momentum component of charge carriers normal to the film plane.     

Thermal properties of TiO2 films grown by atomic layer deposition

We study the thermal properties of amorphous TiO₂ thin films of various thicknesses t, grown by atomic layer deposition. The thermo-optic coefficient dn/dT and the temperature coefficient dρ/dT of film density ρ are determined from ellipsometric data in wavelength range 380 < λ < 1800 nm with the Cauchy model and the Lorentz-Lorenz relation. It is found that dn/dT exhibits negative values for films with t < 150 nm and positive values for thicker films, while no significant changes in the two coefficients take place if t < 200 nm. A qualitative physical explanation based on porosity of the thin films is suggested. Films with t = 60 nm are illustrated in detail at λ = 640 nm: the room-temperature values of the coefficients are found to be dn/dT = − 3.1 × 10^− 5 °C^− 1 and dρ/dT = − 4.8 × 10^− 5g cm^− 3° C^− 1.