N.G. Deshpande

Engineering of nanocrystalline cadmium sulfide thin films by using swift heavy ions

Swift heavy ion (SHI) irradiation experiments have been performed on as-deposited nanocrystalline cadmium sulfide (CdS) thin films by using 100 MeV Au8+ ions with 5 × 1012 ions cm−2. In addition, the as-deposited films were annealed at 300 °C in air for 1 h. Structural, optical and electrical properties of pristine (as-deposited), annealed and irradiated thin films were carried out by using x-ray diffraction (XRD), energy dispersive spectra, scanning electron microscopy, atomic force microscopy, UV-VIS spectroscopy and Arrhenius plots for resistivity and thermoemf, respectively. XRD shows the intrinsic peak of (0 0 2) for the hexagonal phase of CdS. After annealing and SHI irradiation this peak was enhanced drastically and dramatically, showing the dominant orientation in this plane. The grain growth observed in these two post-deposition processes was different. This resulted in a decrease in resistivity of the annealed and the irradiated samples by one and two orders from the pristine sample, respectively.

Room-temperature gas sensing studies of polyaniline thin films deposited on different substrates

Polyaniline thin films, doped with an inorganic acid (HCl), on glass and Si substrates were directly synthesized by an in situ polymerization technique. Studies on the surface morphology as well as topography proved that the film surface is evolved differently on different substrates. The formation of PANI on glass and Si substrates was confirmed by optical and infrared spectroscopy, respectively. Different surface characteristics for different substrates showed a strong effect on the gas sensing properties of these films. The porous fibril morphology on the Si substrate leads to significantly faster and more responsive sensing phenomena.

Gigantic irradiation effect of 100 MeV Au8+ swift heavy ions on the copper sulfide thin films with different chemical compositions

Gigantic deformations were found for the copper sulfide (Cu1.4S and Cu2S) thin films irradiated with 100 MeV Au8+ swift heavy ions (SHI) for 1011 and 1012 ions cm−2 fluencies. It was observed that the deformation due to SHI is dependent on the chemical composition of the film. The optical band gap (E g) of the Cu1.4S was blue shifted, whereas that of Cu2S was red shifted. The surface modifications were also different for these two compositions. These effects were studied by using the atomic force microscopy and scanning electron microscopy. The results are explained in the light of thermal spike model.

Studies on high electronic energy deposition in transparent conducting indium tin oxide thin films

We have examined the effect of swift heavy ions using 100 MeV Au8+ ions on the electrical properties of transparent, conducting indium tin oxide polycrystalline films with resistivity of 0.58 × 10−4 Ω cm and optical transmission greater than 78% (pristine). We report on the modifications occurring after high electronic energy deposition. With the increase in fluency, x-ray line intensity of the peaks corresponding to the planes (1 1 0), (4 0 0), (4 4 1) increased, while (3 3 1) remained constant. Surface morphological studies showed a pomegranate structure of pristine samples, which was highly disturbed with a high dose of irradiation. For the high dose, there was a formation of small spherical domes uniformly distributed over the entire surface. The transmittance was seen to be decreasing with the increase in ion fluency. At higher doses, the resistivity and photoluminescence intensity was seen to be decreased. In addition, the carrier concentration was seen to be increased, which was in accordance with the decrease in resistivity. The observed modifications after high electronic energy deposition in these films may lead to fruitful device applications.

Electrical characterization of 100 MeV heavy ion irradiated Au/p-Cu1.4S Schottky barrier diodes

Interface states play a vital role in Fermi-level pinning in Schottky barrier diodes. Here, we have modified the surface of copper sulfide by using 100 MeV Au8+ swift heavy ions. On this modified surface, a Schottky diode was fabricated using gold metal. This leads to an interface with different ‘interface states’, affecting the charge transport and diode properties. I–V measurements showed that the current decreases with increase in ion fluence from 1011 to 1013 ions cm−2, and barrier height increases while ideality factor decreases. These results are explained by taking into account the presence of free copper at the surface and grain boundaries of copper sulfide thin films and its diffusion into the matrix.