D. Sarkar

Effect of Zn source concentration on structural, optical and electrical properties of zinc sulphide–polyaniline (ZnS–PANI) nanocomposite thin films

Zinc sulphide–polyaniline (ZnS–PANI) nanocomposites are prepared by preparing ZnS nanoparticles in the same reaction bath for synthesis of PANI. Three different composites have been prepared by varying the concentration of zinc source. The films obtained from the colloidal dispersion are characterized by Scanning electron microscopy, energy dispersive analysis of X-rays, transmission electron microscopy, X-ray diffraction studies, Fourier transform infrared spectroscopy, UV–visible optical absorption, photoluminescence and current–voltage studies. Broadening of X-ray diffraction peaks suggest change in crystallite size and this is in agreement with the results from transmission electron microscopy. Fourier transform infrared spectra indicate crosslinking in the composite film. UV–visible absorption spectra of the film exhibit enhancement of doping level which is assigned to the existence of greater number of charges on the polymer backbone. Optical properties of the films are studied by measuring photoluminescence spectra. This shows decrease in intensity and blue shift with the increase in zinc source concentration. The blue shift indicates strong quantum confinement. Current–voltage characteristics exhibit excellent light response indicating tunneling type of conduction.

Effect of Cd Source Concentration on CdS-Polyaniline (CdS-PANI) Nanocomposite Thin Films

CdS-PANI composites are prepared through in situ synthesis of CdS during PANI preparation. The effect of Cd source concentration in the composite is studied. Elemental analysis is done through energy-dispersive X-ray analysis. UV-visible absorption spectra showed λ (abs) at about 460 nm. The band above ∼800 nm is due to conducting phase of polyaniline. The morphological properties are studied through SEM and TEM. Structural analysis is done through X-ray diffraction, which shows increase in crystallinity. UV-vis absorption and photoluminescence spectra show combined effect of parent materials. This is in conformation with I-V characteristics showing nonlinear diode like behavior and in one it shows tunnel diode type nonlinear nature.

Negative photoconductivity in silver nanocubes prepared by simple photochemical method

Silver nanocubes embedded in polyvinyl alcohol matrix have been synthesised by photoirradiation technique. The composite films are characterised by FESEM, XRD, UV-Visible absorption and photoluminescence. These show characteristics of silver nanoparticles with FESEM showing the cubic shape. The photoconductivity study of these films shows decrease in photocurrent with light irradiation. Such negative photoconductivity behaviour may be attributed to dominant scattering of electrons by excited surface plasmon polaritons in nanoscale.

Morphological and optical properties of n-type porous silicon: effect of etching current density

Morphological and optical properties of porous silicon (PS) layer fabricated on n-type silicon wafer have been reported in the present article. Method of PS fabrication is by photo-assisted electrochemical etching with different etching current densities (J). Porosity and PS layer thickness, obtained by the gravimetric method, increase with increasing J. Pore morphology observed by FESEM shows the presence of randomly distributed pores with mostly spherical shape. Calculated pore size is also seen to increase with increasing value of J. XRD gives the characteristic amorphous peak of PS along with some peaks corresponding to crystalline silicon (c-Si). Calculated crystallite size shows decreasing trend with increasing J value. The optical properties of these samples have been investigated by UV–visible reflectance, Raman spectroscopy and photoluminescence (PL) spectra. Reflectance measurement shows blue-shift of the spectrum with increased reflectivity for increasing J. Raman spectra show remarkable blue-shift with respect to the c-Si peak. PL spectra give the luminescence energy in the orange–red region of the visible spectrum and little change with variation of J.

High temperature ferromagnetism in Ni doped ZnO nanoparticles: Milling time dependence

We report on the room temperature ferromagnetism (RT FM) in the Zn1−xNixO (x = 0, 0.03, and 0.05) nanoparticles (NPs) synthesized by a ball milling technique. X-ray diffraction analysis confirms the single crystalline ZnO wurtzite structure with presence of small intensity secondary phase related peak which disappear with increasing milling time for Ni doped samples. HRTEM lattice images show that the doped NPs are single crystalline with a dspacing of 2.44 A. Energy-dispersive X-ray spectroscopy analysis confirms the presence of Ni ions in the ZnO matrix. Magnetic measurement (RT) exhibits the hysteresis loop with saturation magnetization (Ms) of 1.6–2.56 (emu/g) and coercive field (Hc) of 296–322 Oe. M-T measurement shows a Curie temperature of the order of 325°C for 3% Ni doped sample. Micro -Raman studies show doping/disorder induced additional modes at ∼510, 547, 572 cm−1 in addition to 437 cm−1 peak of pure ZnO. UV-Vis absorption spectra illustrate band gap shift due to doping. Alteration of Ms valu...