Thermoluminescence of Al2O3:Cr3+ films synthesized by the nonaqueous sol–gel method

The thermoluminescence (TL) properties of Al₂O₃:Cr³⁺ thin films prepared by the nonaqueous sol–gel method were evaluated. The obtained thin films were characterized by scanning electron microscope and energy dispersive spectrometry. They were irradiated with ⁶⁰Co gamma rays of the different doses. TL glow curves exhibited two peaks centered at 197°C and 322°C.The heights of peaks were found to be sensitive to exposures of ionizing irradiation and the integral area of the TL signals had a linear response in the dose range of 5–60 Gy.This remarkable result suggests that Al₂O₃:Cr³⁺ films might potentially be used for radiation dosimetry.     

Electrical transport properties of thermally evaporated phthalocyanine (H2Pc) thin films

Thin films of H₂Pc of various thicknesses have been deposited onto glass substrates using thermal evaporation technique at room temperature. The dark electrical resistivity measurements were carried out at different temperatures in the range 298-473 K. An estimation of mean free path (l_o) of charge carriers in H₂Pc thin films was attempted. Measurements of thermoelectric power confirm that H₂Pc thin films behave as a p-type semiconductor. The current density-voltage characteristics of Au/H₂Pc/Au at room temperature showed ohmic conduction mechanism at low voltages. At higher voltages the space-charge-limited conduction (SCLC) accompanied by an exponential trap distribution was dominant. The temperature dependence of current density allows the determination of some essential parameters such as the hole mobility (μ_h), the total trap concentration (N_t), the characteristic temperature (T_t) and the trap density P(E).     

Structural and electrical properties of the α-form of metal-free phthalocyanine (α-H2Pc) semiconducting thin films

An X-ray structural study of thermally evaporated metal-free phthalocyanine thin films with various film thicknesses was performed. All samples studied had polycrystalline structure and the unit cell was found to be of the α-form. Variation of the deposition rate from 0.5 to 1 nm s⁻¹ had little effect on the structure. The films exhibit preferential orientation at low thickness; however, at higher thickness they become less orientated as additional peaks appear in the spectrum. The increase in the intensity of the first significant low angle peak with increasing thickness is attributed to the increased volume of the crystal probed during the X-ray exposure.The current density–voltage (J–V) characteristics of α-H₂Pc films sandwiched between two aluminum electrodes showed ohmic behavior at low voltages and space–charge-limited conduction (SCLC) at higher voltages. For comparison, similar measurements of the current density as a function of voltage were performed on zinc phthalocyanine, ZnPc, thin films using aluminum electrodes. The J–V characteristics showed ohmic behavior at low voltages followed by SCLC dominated by an exponential trap distribution at higher voltages. Consequently, in both H₂Pc and ZnPc films, aluminum electrodes act as if they are ohmic contacts. The implied provision of ohmic contacts using aluminum in this case is attributed to the formation of a thin Al₂O₃ layer during the deposition process.     

Gamma-induced modifications of polycarbonate polymer

Gamma-induced modifications in polycarbonate polymer have been studied in the dose range of 10¹–10⁶ Gy. Thin films of polycarbonate have been irradiated with different gamma doses from a Co⁶⁰ source. To monitor the modifications caused by gamma radiation, FT-IR, differential scanning calorimetry and X-ray diffraction studies have been performed. The studies have indicated that at the dose of 10⁶ Gy, phenolic group forms through scissioning of ester linkage. Though the effect of radiation is most significant at the highest dose, the process of modifications starts at 10³ Gy. Scissioning of the polymeric chain initiates a different morphological zone within the polymer matrix, and the polymer becomes more crystalline with increasing dose. Owing to chain scissioning, the mobility of the polymer increases, which in turn reduces the glass transition temperature of the polymer.     

Gamma irradiation effects on structural and optical properties of amorphous and crystalline Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films

The structural and optical properties of RF sputtered Nb₂O₅ thin films are studied before and after gamma irradiation. The films are subjected to structural and surface morphological analyses by using X-ray (XRD) and field emission scanning electron microscope techniques. In the wavelength range of 300–2000 nm, the optical parameters for amorphous and crystalline Nb₂O₅ thin films are estimated at differently exposed γ-irradiation doses (0, 50, 100 and 200 kGy). The optical constants, such as optical energy band gap, absorption coefficient, refractive index and oscillators parameters of amorphous and crystalline Nb₂O₅ thin films are calculated. The optical band gaps of γ-irradiated amorphous and crystalline Nb₂O₅ thin films are determined. In the non-absorbing region, the real part of the refractive index of amorphous and crystalline Nb₂O₅ thin films slightly increases with the increase in the exposed γ-irradiation dose.     

Optical,photo-acoustic and electrical switching studies of amorphous GeS2 thin films

This paper reports optical, photo-acoustic and electrical switching investigations of GeS₂ amorphous thin films of different thicknesses, deposited on glass substrates in vacuum. The Tauc parameter (B ^1/2) and Urbach energy (E _U) have been determined from the transmittance spectra, to understand the changes in structural disorder; it is found that B ^1/2 increases whereas E _U decreases as the thickness of the films increases. Based on the results, it is suggested that bond re-arrangement, i.e. transformation from homopolar bonds to heteropolar bonds, takes place with increase in thickness. The thermal diffusivity values of GeS₂ thin films also show the presence of a chemically ordered network in the GeS₂ thin films. Further, it is found that these films exhibit memory-type electrical switching. The observed variation in the switching voltages has been understood on the basis of increase in chemical order.     

关于热生长SiO2薄膜厚度的测量

在半导体硅器件的研究工作中,需要准确地测量和控制SiO₂薄膜的厚度。由于干涉原理,SiO₂薄膜在白光照射下呈现颜色。但薄膜厚度与颜色相应的单色光的波长并不成简单的函数关系。本文叙述了用干涉显微镜测量热生长SiO₂薄膜厚度的方法。由测量结果得到SiO₂薄膜的折射率以及SiO₂和硅界面及空气和硅界面反射相移之差。并且测量了一组标准样品的薄膜厚度,列出了薄膜厚度与干涉颜色的对应关系。所得结果与从Rollet数据所推算的结果大致符合。样品厚度还包括了Rollet数据中所未包括的范围(3300—4200?)。     

Tuning the properties of tin oxide thin films for device fabrications

Tin oxide thin films were deposited on well cleaned glass substrates by thermal evaporation in vacuum and were annealed at 500?^°C in the open atmosphere inside a furnace for 90 min for promoting the sensitivity of the films. The X-ray diffraction studies revealed that the as-deposited films were amorphous in nature and the annealed films showed appreciable crystalline behavior. The annealed thin films were then irradiated using ⁶⁰Co gamma source. The radiation induced changes were then studied by X-ray diffraction, scanning electron microscopy, UV–vis spectroscopy and I–V characterization. The remarkable increase in the average grain size, the decrement in the energy band gap and resistivity due to the gamma irradiations up to a certain dose and the reversal of these properties at higher doses are the important observations. The large changes in the conductivity and energy band gap of the annealed thin films due to gamma irradiation make these films quite important device material for the fabrication of gamma sensors and dosimeters.     

Synthesis,electrical properties and transport mechanisms of thermally vacuum evaporated CdTe nanocrystalline thin films

A stoichiometry CdTe nano-structured powder was synthesized by chemical process. Thin films of different thicknesses (40, 60, and 100 nm) of CdTe were prepared by thermal evaporation method onto silicon substrates. Current–voltage (I–V) and capacitance–voltage (C–V) characteristics of CdTe nanocrystalline thin films deposited on p-Si as heterojunction have been investigated. At low voltages, current in the forward direction was found to obey the diode equation and the conduction was controlled by thermionic emission mechanism. Also, various electrical parameters were determined from the I–V and C–V analysis. The thickness dependence of the obtained capacitance–voltage (C–V) characteristics was also considered.     

Structure-related infrared optical properties of BaTiO3 thin films grown on Pt/Ti/SiO2/Si substrates

BaTiO₃ thin films with different thickness have been grown on Pt/Ti/SiO₂/Si substrates by a modified sol-gel method. X-ray diffraction analyses show that the BaTiO₃ thin films are polycrystalline. The crystalline quality of the films is improved with increasing thickness. The infrared optical properties of the BaTiO₃ thin films have been investigated using an infrared spectroscopic ellipsometry in the wave number range of 800-4000 cm⁻¹ (2.5-12.5 μm). By fitting the measured pseudodielectric functions with a three-phase model (Air/BaTiO₃/Pt), and a derived classical dispersion relation for the thin films, the optical constants and thicknesses of the thin films have been simultaneously obtained. The refractive index of the BaTiO₃ thin films increases and on the other hand, the extinction coefficient does not change with increasing thickness in the entirely measured wave number range. The dependence of the refractive index on the film thickness has been discussed in detail and was mainly due to both the crystalline quality of the films and packing density. Finally, the absorption coefficient was calculated in the infrared region for applications in the pyroelectric IR detectors.     

Gamma-photon induced modifications in Polyvinylchloride (PVC) film

Gamma photon induced modifications in Polyvinylchloride (PVC) polymer have been studied in the dose range of 10¹-10⁶Gy at room temperature. Polyvinylchloride films have been irradiated with different doses of gamma radiation from a ⁶⁰Co source. To monitor the chemical and structural changes caused by gamma radiation IR and UV-Vis spectroscopy of pristine and irradiated PVC have been performed and using the spectral data some changes in the properties have been investigated. The spectral studies have indicated that at a dose of 10⁶Gy scissioning of the C-a bonds takes place. This scissioning of the chain initiates decomposition at a lower temperature. Thermal stability of the polymer reduces due to irradiation but the decomposition patterns remain the same. The optical band-gap is found to decrease due to irradiation at doses bigher than 10³Gy.     

Feasibility study of thin film Al/SnOx/n-Si gate stack for gamma radiation dosimetry

MOS (Al/SnO_x/n-Si) structure is fabricated by thin film deposition technique for gamma radiation dosimetry. A cumulative gamma dose of 480 Gy was given to the devices in steps of 120 Gy each at the dose-rate of 2 Gy/min. Forward bias I–V characteristics and C–V characteristics of the gamma irradiated devices have shown the changes in the current and capacitance values, respectively with gamma irradiation dose. This structure in future will be useful for personal and accidental radiation dosimetry.     

Raman scattering studies of monolayer-thickness oxide and tellurium films on PbSnTe

Raman backscattering spectra from fractured and etched surfaces of PbTeSnTe alloys have been studied and compared with X-ray photoelectron spectroscopy (XPS) analysis of the surfaces. For samples freshly broken in air or suitably etched electrolytically, the spectra are identified with very thin (?monolayer) films of oxide, chemically as TeO₂. For samples etched in HNO₃ and HCl and for as-grown epi-films the spectra are identified with thin films of elemental tellurium. On n-type material, the surface oxide spectrum is found to change with time after fracture going from an initial rapidly formed TeO₂ spectrum, similar to that of p-type material, to a spectrum identified with a mixture of Pb and Te oxides.     

Gamma induced changes in the structural and optical properties of Makrofol LS 1–1 polycarbonate

ABSTRACT

Samples from sheets of the polymeric material Makrofol LS 1–1 have been exposed to gamma radiation in the dose range 10–250?kGy. The modifications induced in Makrofol samples due to gamma irradiation have been studied through different characterization techniques such as intrinsic viscosity as a measure of the average molecular mass, Fourier Transform Infrared spectroscopy FTIR, refractive index and color difference studies. The results indicate that the crosslinking dominates at the dose range 50–250?kGy. The crosslinking reported by viscosity measurements is supported by the trend of the function groups present in the sample with the gamma dose. Also, the increase in intrinsic viscosity indicating an increase in the average molecular mass was associated with an increase in the refractive index. Additionally, the non-irradiated Makrofol samples showed significant color sensitivity towards gamma irradiation. The color intensity ΔE, which is the color difference between the non-irradiated sample and those irradiated with different gamma doses, increased (0–5.56) with increasing the dose up to 250?kGy, convoyed by an increase in the red and yellow color components.     

Specific features of the formation of arrays of silver clusters from a thin film on a SiO2 surface

The decomposition of thin silver films into clusters on a SiO₂ surface during thermal heating in vacuum has been studied. The experimental histograms of distribution of clusters formed from films of different thicknesses over their diameters have been constructed. It has been found that the decomposition of the films with thickness to 10 nm leads to the formation of monoclusters having one predominant diameter in the range from 15 to 20 nm. After a longer term annealing, the array of clusters almost does not change with time, and the predominant diameter is retained. From films with thicknesses ranging from 10 to 130 nm, an array of clusters with two predominant diameters containing monoclusters (40–80 nm) and globular clusters (400 nm) is formed. It is noted that, with increasing annealing time, the array is enlarged due to the coalescence process and is gradually evaporated; in this case, the predominant cluster diameters remain the same.     

Spectroscopic and thermal studies of gamma irradiated polypropylene polymer

Thin films of polypropylene have been irradiated with different doses of gamma radiation from a ⁶⁰Co source. IR, UV-VIS spectra of this polymer before and after irradiation have been recorded and from the spectral data some modifications in the properties have been investigated. The spectra indicated that polypropylene film was oxidised at the dose of 10⁶ Gy. Due to the removal of additives, total destruction of the polymer takes place at this dose. Isotactic arrangement of the polymer is no longer present after irradiation. Growth of carbon cluster takes place above a gamma dose of 10² Gy. Thermal stability of the polymer changes due to irradiation and the polymer seems to decompose in four different steps at the highest dose of 10⁶ Gy.     

Structure and dielectric behavior of TlSbS2

A comparison of structure and dielectric properties of TlSbS₂ thin films, deposited in different thicknesses (400–4100 Å) by thermal evaporation of TlSbS₂ crystals that were grown by the Stockbarger–Bridgman technique and the bulk material properties of TlSbS₂ are presented. Dielectric constant ε ₁ and dielectric loss ε ₂ have been calculated by measuring capacitance and dielectric loss factor in the frequency range 20 Hz–10 KHz and in the temperature range 273–433 K. It is observed that at 1 kHz frequency and 293 K temperature the dielectric constant of TlSbS₂ thin films is ε ₁=1.8–6 and the dielectric loss of TlSbS₂ thin films is ε ₂=0.5–3 depending on film thickness. In the given intervals, both of dielectric constant and dielectric loss decrease with frequency, but increase with temperature. The maximum barrier height W _m is calculated from the dielectric measurements. The values of W _m for TlSbS₂ films and bulk are obtained as 0.56 eV and 0.62 eV at room temperature, respectively. The obtained values agree with those proposed by the theory of hopping over the potential barrier. The temperature variation of ac conductivity can be reasonably interpreted in terms of the correlated barrier hopping model since it obeys the ω ^s law with a temperature dependent s (s<1) and going down as the temperature is increased. The temperature coefficient of capacitance (TCC) and permittivity (TCP) are evaluated for both thin films and bulk material of TlSbS₂.     

Effect of thickness on the structural,optical and electrical properties of thermally evaporated PbI2 thin films

This work describes the physical properties of lead iodide (PbI₂) thin films with different thicknesses that were deposited on ultrasonically cleaned glass substrates using a thermal evaporation technique at 5×10^-6 torr. The initial material was purified by the zone refining technique under an atmosphere of argon gas. XRD analysis of the material demonstrates that the thin films were preferably oriented along the (001) direction. The size of the crystallites was calculated from the Scherer relation and found to be in the range of ～5–10 nm, with higher values being observed for increasing film thicknesses. The optical energy band gaps were evaluated and determined to belong to direct transitions. Because the band gap increased with decreasing film thickness, a systematic blue shift was observed. The surface morphologies of PbI₂ films exhibited a clear increase in grain size with increasing film thickness. The photoluminescence and dc conductivity of the thin films are also discussed.     

Morphological and optical characterization of thermally evaporated copper sulphide thin films

Thin films of Cu₂S on opaque gold layers and quartz substrates at the temperature of 393 K were deposited by a thermal evaporation technique. The surface morphology of the Cu₂S thin films at different thicknesses is investigated by AFM. It is seen that all the films are composed of highly coordinated spherical nano-sized particles well adhered to the substrate. The transmittance and reflectance spectra of Cu₂S thin films on the quartz substrate were recorded by a UV–visible spectrophotometer. The results show that the thermally evaporated Cu₂S thin films have the characteristic transmittance and reflectance suitable for optoelectronic applications. The stoichiometry and surface morphology of a grown Cu₂S thin film were confirmed by energy-dispersive X-ray spectroscopy (EDAX) and scanning electron microscopy (SEM), respectively. The dependence of the refractive index and the extinction coefficient on the photon energy for both the surface film and the opaque gold layer have been determined by ellipsometry. From the spectral behaviour of the absorption coefficient at two distinct absorption regions, a dual-band scheme of optical absorption for a Cu₂S thin film is described. The indirect and direct edges of Cu₂S are found to be about at 0.91 eV and 2.68 eV, respectively.     

MgB2 thin film fabrication with excess Mg by sequential e-beam evaporation and transport properties under magnetic fields

Superconducting MgB₂ thin films with different thicknesses were fabricated by excess Mg using sequential electron beam evaporation technique. The flux rate of Mg and B were chosen as 3 nm/sn and 0.5 nm/sn respectively. The thickness of Mg/B layer was determined as 3/1 which causes an excess Mg for MgB₂ formation. After two-step preparation process, the superconducting transition temperatures were found in the range of 32–37 K with a sharp transition to zero resistance state. The irreversibility fields, upper critical fields and activation energies were derived from magneto resistivity curves. The transport critical current densities of films were determined from I–V characteristics under different applied fields and the data was extrapolated for determination of value of the 0 K.