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.     

Boron-doped nanocrystalline silicon germanium thin films for uncooled infrared bolometer applications

In this paper, boron-doped nanocrystalline Si_0.78Ge_0.22:H thin film is assessed for use as resistive sensing layer in uncooled infrared bolometer applications. The silicon germanium thin films were deposited by PECVD (plasma enhanced chemical vapor deposition) through decomposition of silane, germane and diborane diluted with argon at substrate temperature of 230 °C. Under optimum deposition parameters, the sensing films with modulate electrical resistivity (<10⁴ Ω cm) and high temperature coefficient of resistance (TCR) (>−3%/K) were obtained at room temperature. 1/f noise character in the form of the normalized Hooge parameter was measured in the frequency range of 1–64 Hz, resulting in a lower 1/f noise compared to other materials currently used for device application.     

Growth kinetics and photoelectrochemical (PEC) performance of cadmium selenide thin films: pH and substrate effect

Cadmium selenide (CdSe) thin films have been electrochemically deposited on the stainless steel (SS) and fluorine-doped tin oxide (FTO) coated glass substrates at room temperature (27 °C). The growth kinetics of CdSe thin films was studied by using cyclic voltammetry and chronoamperometry with variation in the pH of the electrolytic bath. In addition, the influence of the substrate on the microstructural properties of CdSe is plausibly explained. The photoelectrochemical (PEC) characterization of the film has been carried out to optimize the preparative parameters. X-ray diffraction data reveal growth of the cubic phase with preferential orientation along (1 1 1) direction. Compositional analysis of the film shows nearly stoichiometric film formation at pH 2.7. Uniform film formation with nano-sized grains was seen from SEM images. Optical absorption studies reveal that the pH of the electrolytic solution has a significant effect on the band gap of the film. PEC study revealed that CdSe film deposited at pH 2.7 on SS substrate showed better photosensitivity as compared to the film deposited on FTO coated glass.     

Comparative study on structural and optical properties of ZnO thin films prepared by PLD using ZnO powder target and ceramic target

Zinc oxide thin films have been obtained in O₂ ambient at a pressure of 1.3 Pa by pulsed laser deposition (PLD) using ZnO powder target and ceramic target. The effect of temperature on structural and optical properties of ZnO thin films was investigated systematically by XRD, SEM, FTIR and PL spectra. The results show that the best structural and optical properties can be achieved for ZnO thin film fabricated at 700 °C using powder target and at 400 °C using ceramic target, respectively. The PL spectrum reveals that the efficiency of UV emission of ZnO thin film fabricated by using powder target is low, and the defect emission of ZnO thin film derived from Zn_i and O_i is high.     

Characteristics of nitrogen-incorporated silicon oxycarbide films and plasmas for plasma enhanced chemical vapor deposition with TMOS/N2/NH3

Plasma enhanced chemical vapor deposition of nitrogen-incorporated silicon oxycarbide thin films obtained from the gas mixture of TMOS (tetramethoxysilane), N₂, and NH₃ is studied. The effects of the TMOS to N₂ pressure ratio on the properties of the film and the plasma are investigated. The deposited films are analyzed by in situ ellipsometry, ex situ Fourier transform infrared spectroscopy (FTIR), and by X-ray photoelectron spectroscopy (XPS). The plasma is characterized by using optical emission spectroscopy (OES). The mass spectra of the constituents in the plasma are obtained by quadrupole mass spectroscopy. The correlation between the film properties and the plasma characteristics is explained wherever possible. As the partial pressure of N₂ is decreased, the refractive index begins to decrease, reaches a minimum, and then saturates. The FTIR absorption bands are observed from about 850 to 1000 cm⁻¹ and from 1000 to 1250 cm⁻¹, and can be attributed to the formation of a nitrogen-incorporated silicon oxycarbide thin film. The variation of the refractive index is discussed in relationship with the deposition rate, the OES spectra, the mass spectra of the plasma, the film composition obtained by XPS, and FTIR spectra.     

Effect of Al-doping on optical and electrical properties of spray pyrolytic nano-crystalline CdO thin films

CdO and Al-doped CdO nano-crystalline thin films have been prepared on glass at 300 °C substrate temperature by spray pyrolysis. The films are highly crystalline with grain size (18–32 nm) and found to be cubic structure with lattice constant averaged to 0.46877 nm. Al-doping increased the optical transmission of the film substantially. Direct band gap energy of CdO is 2.49 eV which decreased with increasing Al-doping. The refractive index and dielectric constant varies with photon energy and concentration of Al as well. The conductivity of un-doped CdO film shows metallic behavior at lower temperature region. This behavior dies out completely with doping of Al and exhibits semiconducting behavior for whole measured temperature range. Un-doped and Al-doped CdO is an n-type semiconductor having carrier concentration is of the order of ∼10²¹ cm⁻³, confirmed by Hall voltage and thermo-power measurements.     

Hydrogen permeation of tungsten phosphate glass thin films

Thin films of tungsten phosphate glasses were deposited on a Pd substrate by a pulsed laser deposition method and the flux of hydrogen passed thorough the glass film was measured with a conventional gas permeation technique in the temperature range 300–500 °C. The glass film deposited at low oxygen pressure was inappropriate for hydrogen permeation because of reduction of W ions due to oxygen deficiency. The membrane used in the hydrogen permeation experiment was a 3-layered membrane and consisted of Pd film (~ 20 nm), the glass film (≤ 300 nm) and the Pd substrate (250 µm). When the pressure difference of hydrogen and thickness of the glass layer were respectively 0.2 MPa and ~ 100 nm, the permeation rate through the membrane was 2.0 × 10^? 6 mol cm^? 2 s^? 1 at 500 °C. It was confirmed that the protonic and electronic mixed conducting glass thin film show high hydrogen permeation rate.     

Epitaxial ZnO thin films grown by pulsed electron beam deposition

In this work, the pulsed electron beam deposition method (PED) is evaluated by studying the properties of ZnO thin films grown on c-cut sapphire substrates. The film composition, structure and surface morphology were investigated by means of Rutherford backscattering spectrometry, X-ray diffraction and atomic force microscopy. Optical absorption, resistivity and Hall effect measurements were performed in order to obtain the optical and electronic properties of the ZnO films. By a fine tuning of the deposition conditions, smooth, dense, stoichiometric and textured hexagonal ZnO films were epitaxially grown on (0001) sapphire at 700 °C with a 30° rotation of the ZnO basal plane with respect to the sapphire substrate. The average transmittance of the films reaches 90% in the visible range with an optical band gap of 3.28 eV. Electrical characterization reveals a high density of charge carrier of 3.4 × 10¹⁹ cm^?3 along with a mobility of 11.53 cm²/Vs. The electrical and optical properties are discussed and compared to ZnO thin films prepared by the similar and most well-known pulsed laser deposition method.     

Investigation of reduced graphene oxide effects on ultra-violet detection of ZnO thin film

The reduced graphene oxide (rGO) incorporated ZnO thin films were fabricated by dip-coating method. The Raman and FT-IR spectra of 0.075 wt% incorporated composite film showed reduction of GO in composite film. The transmittanceProd. Type: FTP spectra have shown that rGO incorporation increase the visible light absorption of ZnO thin film while the calculated band gaps of samples were decreased from 3.28 to 3.25 eV by increasing the rGO content. The linear trend of I–V curve suggests an ohmic contact between ZnO and rGO. Besides, it was found that by increasing the rGO content, the electrical resistivity was decreased from 4.32×10² Ω cm for pure ZnO film to 2.4×10¹ Ω cm for 0.225 wt% rGO incorporated composite film. The composite photodetectors not only possessed a desirable UV photosensitivity, but also the response time of optimum sample containing 0.075 wt% rGO was reduced to about one-half of pure ZnO thin film. Also, the calculated signal to noise (SNR) showed that highly conductive rGO in composite thin films facilitate the carrier transportation by removing the trapping centers. The mechanism of photoresponsivity improvement of composite thin films was proposed by carrier transportation process.     

Synthesis of oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)] and anomalous proton conductivities of the thin films

New proton-conductive polyamide oligomers, oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)], were synthesized to investigate the proton transport properties of bulk and thin films. The obtained oligomers were characterized by the X-ray diffraction, FT-IR spectra, ¹H NMR, Matrix Assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) mass spectrum, and electrical conductivity measurements. The bulk proton conductivity is 3.0 × 10^? 4 S cm^? 1 at the relative humidity (RH) of 80%. The proton conductivity of thin film is relatively higher than that of bulk sample. Thickness dependence of the proton conductivity was observed in these thin films. The maximum proton conductivity of the thin film is 4.0 × 10^? 3 S cm^? 1 at the relative humidity (RH) of 80%, which is higher one order magnitude than that of the bulk sample. The activation energies of bulk and 200 nm thick film are 1.0 and 0.69 eV at the RH of 60%, respectively.     

Photo-curable epoxy functionalized cyclotetrasiloxane as a gate dielectric for organic thin film transistors

We synthesized a new photo-curable organic/inorganic hybrid material, cyclotetrasiloxane (CTS) derivative containing cyclohexene-1,2-epoxide functional groups (CTS-EPOXY), and its characteristics are compared with a prototypical organic gate insulator of poly(4-vinylphenol) (PVP) in the organic thin film transistors (OTFTs) using pentacene as an active p-type organic semiconductor. Compared with PVP, CTS-EPOXY shows better insulating characteristics and surface smoothness. A metal/insulator/metal (MIM) device with the 300-nm-thick CTS-EPOXY film shows more than two orders of magnitude lower current (less than 40 nA/cm² over the voltage range up to 60 V) compared with PVP. In addition, the pentacene TFT with CTS-EPOXY as a gate dielectric layer shows slightly higher field-effect mobility of μ_FET = 0.20 cm²/V s compared to that with PVP.     

Effective utilization of spray pyrolyzed CeO2 as optically passive counter electrode for enhancing optical modulation of WO3

Nanocrystalline cerium oxide (CeO₂) thin films were deposited onto the fluorine doped tin oxide coated glass substrates using methanolic solution of cerium nitrate hexahydrate precursor by a simple spray pyrolysis technique. Thermal analysis of the precursor salt showed the onset of crystallization of CeO₂ at 300 °C. Therefore, cerium dioxide thin films were prepared at different deposition temperatures from 300 to 450 °C. Films were transparent (T ~ 80%), polycrystalline with cubic fluorite crystal structure and having band gap energy (Eg) in the range of 3.04–3.6 eV. The different morphological features of the film obtained at various deposition temperatures had pronounced effect on the ion storage capacity (ISC) and electrochemical stability. The larger film thickness coupled with adequate degree of porosity of CeO₂ films prepared at 400 °C showed higher ion storage capacity of 20.6 mC cm^? 2 in 0.5 M LiClO₄ + PC electrolyte. Such films were also electrochemically more stable than the other studied samples. The Ce⁴⁺/Ce³⁺ intervalancy charge transfer mechanism during the bleaching–lithiation of CeO₂ film was directly evidenced from X-ray photoelectron spectroscopy. The optically passive behavior of the CeO₂ film (prepared at 400 °C) is affirmed by its negligible transmission modulation upon Li⁺ ion insertion/extraction, irrespective of the extent of Li⁺ ion intercalation. The coloration efficiency of spray deposited tungsten oxide (WO₃) thin film is found to enhance from 47 to 53 cm² C^? 1 when CeO₂ is coupled with WO₃ as a counter electrode in electrochromic device. Hence, CeO₂ can be a good candidate for optically passive counter electrode as an ion storage layer.     

Surface engineering of biomedical metallic materials by plasma-based low-energy ion implantation

Plasma-based low-energy ion implantation, including plasma source ion nitriding/carburizing and plasma source low-energy ion enhanced deposition of thin films, for surface engineering of metallic materials was emerged as low-temperature, low-pressure surface modification technique. Plasma source ion nitriding onto AISI 316L austenitic stainless steel produced a high nitrogen face-centered-cubic phase (γ_N) layer about 10 μm thick at the temperature of 380 °C during 4 h with the high microhardness of HK_0.1 N 22.0 GPa. The microhardness of the nitrided surface from the titanium nitride phase [(Ti, Al, V)N] layer on Ti6Al4V alloy at 750 °C during 4 h achieved up to about HK_0.1 N 15.5 GPa. No pitting corrosion in the Ringer’s solution at 37 °C was detected by electrochemical polarization measurement for the nitrided AISI 316L stainless steel and Ti6Al4V alloy, respectively. Plasma source ion nitriding of the metallic materials provided the engineering surfaces with combined improvement in hardness and corrosion resistance.     

Effect of GZO thickness and annealing temperature on the structural,electrical and optical properties of GZO/Ag/GZO sandwich films

The GZO/Ag/GZO sandwich films were deposited on glass substrates by RF magnetron sputtering of Ga-doped ZnO (GZO) and ion-beam sputtering of Ag at room temperature. The effect of GZO thickness and annealing temperature on the structural, electrical and optical properties of these sandwich films was investigated. The microstructures of the films were studied by X-ray diffraction (XRD). X-ray diffraction measurements indicate that the GZO layers in the sandwich films are polycrystalline with the ZnO hexagonal structure and have a preferred orientation with the c-axis perpendicular to the substrates. For the sandwich film with upper and under GZO thickness of 40 and 30 nm, respectively, it owns the maximum figure of merit of 5.3 × 10⁻² Ω⁻¹ with a resistivity of 5.6 × 10⁻⁵ Ω cm and an average transmittance of 90.7%. The electrical property of the sandwich films is improved by post annealing in vacuum. Comparing with the as-deposited sandwich film, the film annealed in vacuum has a remarkable 42.8% decrease in resistivity. The sandwich film annealed at the temperature of 350 °C in vacuum shows a sheet resistance of 5 Ω/sq and a transmittance of 92.7%, and the figure of merit achieved is 9.3 × 10⁻² Ω⁻¹.     

Investigation of enhancement mode HfO2 insulated N-polarity GaN/InN/GaN/In0.9Al0.1N heterostructure MISHEMT for high-frequency applications

In this paper, we examined normally-OFF N-polar InN-channel Metal insulated semiconductor high-electron mobility transistors (MISHEMTs) device with a relaxed In_0.9Al_0.1N buffer layer. In addition, the enhancement-mode operation of the N-polar structure was investigated. The effect of scaling in N-polar MISHEMT, such as the dielectric and the channel thickness, alter the electrical behavior of the device. We have achieved a maximum drain current of 1.17 A/mm, threshold voltage (V_T) =0.728 V, transconductance (g_m) of 2.9 S mm⁻¹, high I_ON/I_OFF current ratio of 3.23×10³, lowest ON-state resistance (R_ON) of 0.41 Ω mm and an intrinsic delay time (τ) of 1.456 Fs along with high-frequency performance with f_t/ f_max of 90 GHz/109 GHz and 180 GHz/260 GHz for T_CH =0.5 nm at V_ds =0.5 V and 1.0 V. The numerically simulated results of highly confined GaN/InN/GaN/In_0.9Al_0.1N heterostructure MISHEMT exhibits outstanding potential as one of the possibility to replace presently used N-polar MISHEMTs for delivering high power density and frequency at RF/power amplifier applications.     

SILAR deposited Bi2S3 thin film towards electrochemical supercapacitor

Bi₂S₃ thin film electrode has been synthesized by simple and low cost successive ionic layer adsorption and reaction (SILAR) method on stainless steel (SS) substrate at room temperature. The formation of interconnected nanoparticles with nanoporous surface morphology has been achieved and which is favourable to the supercapacitor applications. Electrochemical supercapacitive performance of Bi₂S₃ thin film electrode has been performed through cyclic voltammetry, charge-discharge and stability studies in aqueous Na₂SO₄ electrolyte. The Bi₂S₃ thin film electrode exhibits the specific capacitance of 289 Fg⁻¹ at 5 mVs⁻¹ scan rate in 1 M Na₂SO₄ electrolyte.     

Tetraalkoxylated-PPV derivative: An efficient and pure green electroluminescent polymer with good solution processability

A new solution-processable tetraalkoxy-substituted poly(1,4-phenylenevinylene) derivative, poly{[2-(3′,7′-dimethyloctyloxy)-3,5,6-trimethoxy]-1,4-phenylenevinylene} (TALK-PPV), was synthesized through a dehydrohalogenation polymerization route, and its light-emitting properties were investigated. The TALK-PPV showed highly blue-shifted UV–visible absorption and PL emission spectra compared to the dialkoxy-substituted PPV derivatives. This is because of the disturbance to the π-conjugation caused by a steric hindered structure. The TALK-PPV thin film exhibited an absorption peak at 446 nm, with an onset at 515 nm. Its PL emission maximum was at 554 nm. Cyclic voltammetric analysis showed the HOMO and LUMO energy levels of the TALK-PPV to be 5.77 and 3.36 eV, respectively. Light-emitting devices were fabricated with an ITO (indium-tin oxide)/PEDOT/polymer/Ca/Al configuration. The TALK-PPV component leads to pure green light emission with a CIE 1931 chromaticity of (0.20, 0.74) at 100 cd/m² brightness, which is very close to the standard green (0.21, 0.71) demanded by the NTSC (National Television System Committee). The maximum brightness of this device was 24,900 cd/m² with an efficiency of 1.45 cd/A.     

Raman gain in modified tellurite glasses and thin films

We report the tailoring of Raman spectra of the tellurite glass by varying molar concentrations of phosphates, fluorides in phosphate modified tellurite glasses to analyze the Raman gain. From the measured Raman spectrum, the Raman gain and gain bandwidth in these glasses were calculated and compared. The structural features that give rise to the observed spectra and its dependence on glass composition are identified and reported. Raman gain as high as 170 × 10^? 13 m/W is obtained for glass modified by zinc oxide. Glass thin films prepared by pulsed laser deposition show a Raman gain of 5.0 × 10^? 13 m/W suggesting their importance in short waveguide Raman amplifier fabrication.     

Influence of argon ambience on the structural,morphological and optical properties of pulsed laser ablated zinc sulfide thin films

Nanostructured zinc suplhide thin films are successfully deposited on quartz substrates using pulsed laser deposition (PLD) under different argon pressures (0, 5, 10, 15 and 20 Pa). The influence of argon ambience on the microstructural, optical and luminescence properties of zinc sulfide (ZnS) thin films is systematically investigated. The GIXRD data suggests rhombohedral structure for ZnS films prepared under different argon ambience. Self-assembly of grains into well-defined patterns along the y direction is observed in the AFM image of the film deposited under argon pressure 20 Pa. All the films show a blue shift in optical band gap. This can be due to the quantum confinement effect and less widening of conduction and valence band for the films with less thickness and smaller grain size. The PL spectra of the different films are recorded at excitation wavelengths 250 nm and 325 nm and the spectra are interpreted. The PL spectra of the films recorded at excitation wavelength 325 nm show intense yellow emission. The film deposited under an argon pressure of 15 Pa shows the highest PL intensity for excitation wavelength 325 nm. For the PL spectra (excitation at 250 nm), the highest PL intensity is observed for the film prepared under argon free ambience. In our study, 15 Pa is the optimum argon pressure for better crystallinity and intense yellow emission when excited at 325 nm.     

Oxidation of ultra-thin Ti films on Mo(100): Soft X-ray photoelectron spectroscopy study

Titanium oxide films grown on Mo(100) have been investigated by low-energy electron diffraction (LEED) and soft X-ray photoelectron spectroscopy (PES). The film was grown by Ti deposition on Mo(100) and subsequent oxidation of the film by 12 L of O₂ exposure at room temperature. As the film was annealed at 700–1000 °C, the film in which the Ti atoms were in a Ti³⁺ oxidation state was formed. As the film was annealed at 1100–1500 °C, the oxidation state of Ti in the film was converted to Ti²⁺. The valence electronic structure of the film was measured under the condition that the emission from the Mo substrate was minimized due to a Cooper minimum of the Mo 4 d photoionization cross sections (hν = 100 eV). It was found that the Ti 3 d band in normal-emission spectra was increased in intensity when the film was annealed at 1100–1500 °C. As the film was annealed at 1300 °C for 10 s and 20 s, the film-covered Mo(100) gave (2 × 2) and (4 × 1) LEED patterns, respectively. The two-dimensional band structure of the (2 × 2) system was investigated by angle-resolved PES, and it was found that the film with a (1 × 1) periodicity with respect to the Mo(100) substrate existed in the (2 × 2) system.