A.H. Bhuiyan

UV-Vis absorption spectroscopic studies of plasma-polymerized m-xylene thin films

Abstract Plasma-polymerized m-xylene (PPm-X) thin films have been prepared using a dry and flawless process. Films were smooth and of light-tea colour. UV-Vis spectroscopic investigations have been carried out on unannealed, annealed and aged PPm-X thin films to ascertain the effect of annealing temperature and aging on the optical properties of PPm-X. The bandgap, allowed direct transition energy gap and indirect transition energy gap have been determined. The results are discussed in the light of possible structural modification in PPm-X thin film on annealing and aging.

Dielectric properties of plasma-polymerized diphenyl thin films

Abstract Thin polymeric films of diphenyl were prepared by a plasma polymerization technique using a capacitively-coupled reactor. The dielectric relaxation spectroscopy was employed to investigate the behaviour of the as-deposited and heat-treated plasma-polymerized diphenyl (PPDP) thin films in a aluminium/PPDP/aluminium configuration over the frequency range from 10 −1 to 10 6 Hz and temperature range from 223 to 423 K. The ac conductivity is more dependent on temperature in the low frequency region than in the high frequency region. In these materials the conduction may be dominated by hopping of carriers between the localized states at low temperatures and thermally excited carriers from energy levels within the band gap in the vicinity of high temperature. Dielectric constant is dependent on frequency above 303 and 343 K in the as-deposited and heat-treated PPDP, respectively. The as-deposited PPDP shows superposed α and β relaxation processes. For different relaxation processes, the activation energies are estimated to be about 0.45 and 0.67 eV for the as-deposited and 1.35 eV for heat-treated PPDP. The dielectric data analyses show the existence of distribution of relaxation time in these materials.

An investigation of the optical properties of plasma-polymerized diphenyl thin films

Abstract Highly adhering plasma-polymerized diphenyl (PPDP) thin films were grown by a dry and flawless process in glow discharge. The structural analyses of as-deposited and heat treated PPDP samples (unaged and aged) were performed by infrared (IR) spectroscopy. The PPDP thin films were transparent and light yellow in colour. Optical properties were evaluated from ultraviolet–visible (UV–Vis) spectroscopic measurements of as-deposited, heat treated and aged (as-deposited and heat treated) PPDP thin films. From the optical absorption data band gaps, allowed direct and indirect transition energy gaps were determined. The results are discussed in the light of possible structural modification in PPDP thin films on heat treatment and aging.

Electrical, optical and ESR study of thin films of plasma polymerized acrylonitrile

Thin films of plasma-polymerized acrylonitrile (PPAN) were deposited by glow discharge polymerization and were made semiconducting by the process of pyrolysis. Electrical and optical measurements along with electron spin resonance (ESR) measurements were used to study the extent of conjugation in the pyrolysed system. The onset and building up of conjugation due to the structural remodifications was investigated by differential thermal analysis (DTA), thermogravimetric analysis (TGA) and infrared (IR) spectroscopy. A major structural transition was observed at around 550 K which is responsible for the drastic reduction in the electrical resistivity and optical band gap. ESR studies revealed that pyrolysis causes conjugation and generation of free radicals in PPAN, thereby enhancing the electrical conductivity The mechanism of conduction was observed to be dominated by the variable-range hopping.

A few electronic properties of thin films of plasma-polymerized acrylonitrile

Abstract The ionization potential and work function of plasma-polymerized zcrylonitrile thin films have been measured using a low energy electron gun in an ultrahigh vacuum system. The optical absorption and electrical resistivity were also measured as a function of pyrolization temperature and doping. A change in ionization potential, work function, electron affinity and band gap was observed. This is discussed in the light of the structural modification owing to pyrolization and doping. The work function of indium tin oxide was also measured and its use in photovoltaic devices is illustrated.

Effect of Cerium doping on microstructure and dielectric properties of BaTiO3 Ceramics

A solid state reaction method was used to synthesize barium titanate (BT) and barium cerium titanate (BCT) ceramics at sintering temperature of 1473 K for 4 h. The effect of cerium (Ce) on the structure, microstructure and dielectric properties of BCT was investigated. The scanning electron microscopy (SEM) investigations revealed that the grain size increases with increasing Ce content. The X-ray diffraction (XRD) patterns showed mostly the BT phase, where the lattice parameter decreased with the addition of Ce. The temperature dependence of dielectric constant showed decrease in the phase transition temperature with higher Ce content. The dielectric constant decreased slightly with increasing frequency. The direct current (dc) density-voltage characteristics of the ceramics showed ohmic behavior for both the BT and BCT. As the temperature increased, the dc resistivity of the ceramics decreased. The activation energy increased with increasing Ce content.

Electrical and optical properties of plasma-polymerized N, N,3,5-tetramethylaniline thin films

Plasma polymerization is a versatile and important technique for depositing uniform, pinhole-free and flawless thin films of organic materials. So plasma-polymerized N,N,3,5-tetramethylaniline (PPTMA) thin films were deposited onto glass substrates at room temperature by a capacitively coupled plasma polymerization system using TMA as a precursor. Infrared spectroscopy, elemental analysis and UV?visible (UV?vis) spectroscopy reveal that there are conjugations in the matrix of the PPTMA thin films. From UV?vis spectroscopy it is found that indirect energy gap varies from 1.49 to 1.86?eV with film thickness. Current density?voltage characteristics indicate that the conduction mechanism in PPTMA thin films is space charge-limited conduction (SCLC). The activation energies in the SCLC region are 0.21???0.05 and 0.93???0.08?eV at lower and higher temperature regions respectively. Electrical and optical measurements suggest that the top of valance band and the bottom of the conduction band may have gap states and the middle of the energy gap may be equal to the high-temperature activation energy.

On the conduction mechanism in plasma polymerized m-xylene thin films

Abstract Plasma polymerized m-xylene (PPm-X) thin films were deposited using a capacitively coupled glow discharge reactor. The structural analysis was done by infrared (IR) spectroscopy. The current-voltage ( I-V ) characteristics of the PPm-X thin films were investigated at different temperatures and different thicknesses. The IR analysis reveals that the structure of the PPm-X thin films is different from that of the monomer liquid m-xylene. The nonlinear I-V characteristics were analyzed following three different mechanisms of carrier conduction. It is seen that Poole-Frenkel conduction mechanism is most probable in PPm-X thin films.

Evidence of the formation of a charge-transfer complex between iodine and plasma-polymerized acrylonitrile

Abstract Thin films of plasma-polymerized acrylonitrile (PPAN) were deposited by plasma polymerization and modified by post pyrolysis and by doping with iodine. X-ray photoelectron spectroscopy (XPS), electrical and optical investigations were used to reveal structural changes during the modifications. It was found from XPS studies that iodine forms a weak charge-tranfer complex between iodine and PPAN. These results agree well with the electrical and optical results.

Photovoltaic properties of thin films of plasma-polymerized acrylonitrile

Abstract The evaluation of thin films of plasma-polymerized acrylonitrile (PAN) for photovoltaic devices is presented in this paper. An increase in the electrical conductivity has been achieved by pyrolysis of as-deposited insulating films. A decrease in the optical band gap ( E g ≈4.3 eV for the as-deposited film) by 1–2 eV was observed when the films were pyrolysed at temperatures ranging from 473 to 773 K. The contact properties of PAN with different electrodes have been studied. Hall and IR measurements were used to obtain the information about carrier type and structural changes respectively. Photovoltaic properties ( V oc , I sc , ff etc.) for the indium tin oxide/PAN/Al structure are reported. A typical value of about 10 -5 % for the conversion efficiency is obtained for air mass 1 incident radiation.