• Y K Vijay

Articles written in Bulletin of Materials Science

• Irradiation of large area Mylar membrane and characterization of nuclear track filter

Ion irradiation of Si8+ ion beam of 100 MeV was scattered by a gold foil on a Mylar membrane of 25 𝜇m thickness in the form of film roll (width, 12.5 cm and length, 400 cm) at the Nuclear Science Centre, New Delhi. The characterization of etched nuclear tracks was carried out by gas permeation measurements. The samples cut from the film roll of required size for permeability measurements were etched in a controlled manner in a constant temperature bath of 6N NaOH solution. The opening of the conical etched tracks was characterized by hydrogen gas permeation.

• Effect of temperature and 𝛼-irradiation on gas permeability for polymeric membrane

In the present study the polyethersulphone (PES) membranes of thickness (35 ± 2) 𝜇m were prepared by solution cast method. The permeability of these membranes was calculated by varying the temperature and by irradiation of 𝛼 ions. For the variation of temperature, the gas permeation cell was dipped in a constant temperature water bath in the temperature range from 303–373 K, which is well below the glass transition temperature (498 K). The permeability of H2 and CO2 increased with increasing temperature. The PES membrane was exposed by 𝛼-source (${}_{95}$Am$^{241}$) of strength (1 𝜇 Ci) in vacuum of the order of 10-6 torr, with fluence 2.7 × 107 ions/cm2. The permeability of H2 and CO2 has been observed for irradiated membrane with increasing etching time. The permeability increases with increasing etching time for both gases. There was a sudden change in permeability for both the gases when observed at 18 min etching. At this stage the tracks are visible with optical instrument, which confirms that the pores are generated. Most of pores seen in the micrograph are circular cross-section ones.

• Optical, electrical and thermoelectric power studies of Al–Sb thin film bilayer structure

The III–V semiconductors are of great importance due to their applications in various electro-optic devices. The Al–Sb thin film was deposited on glass substrate by thermal evaporation method at a pressure of 10-5 torr. The samples were annealed for 3 h at different constant temperatures in a vacuum chamber at a pressure of 10-5 torr. The electrical resistance vs temperature studies show phase transformation from metallic to semiconducting. The observed positive thermoelectric power indicates that Al–Sb thin films are 𝑝-type in nature. The Rutherford back scattering analysis and optical band gap measurements also indicate that the interdiffusion concentration varies with temperature.

• Dielectric measurements on PWB materials at microwave frequencies

In quest of finding new substrate for printed wiring board (PWB) having low dielectric constant, we have made PSF/PMMA blends and evaluated the dielectric parameters at 8.92 GHz frequency and at 35°C temperature. Incorporating PMMA in PSF matrix results in reduced dielectric constant than that of pure PSF. The dielectric parameters of pure PMMA and PSF films of different thicknesses have also been obtained at microwave frequencies. We have used dielectric data at microwave frequencies as a tool to evaluate optical constants, absorption index 𝐾’ and refractive index 𝑛’. The blends of PSF/PMMA may be used as base materials for PWBs.

• Transport through track etched polymeric blend membrane

Polymer blends of polycarbonate (PC) and polysulphone (PSF) having thickness, 27 𝜇m, are prepared by solution cast method. The transport properties of pores in a blend membrane are examined. The pores were produced in this membrane by a track etching technique. For this purpose, a thin polymer membrane was penetrated by a single heavy ion of Ni7+ of 100 MeV, followed by preferential chemical etching of the ion track. Ion permeation measurements show that pores in polymeric membrane are charged or neutralized, which depends upon the variation in concentration of the solvent. The 𝑉–𝐼 curve at concentration, N/10, shows that the pores are negatively charged, whereas at concentration, N/20, the linear nature of 𝑉–𝐼 curve indicates that the pores approach towards neutralized state and on further concentration, N/40, the pores become fully neutralized, consequently the rectifier behaviour of pores has been omitted.

The gas permeability of hydrogen and carbon dioxide of this membrane was measured with increasing etching time. The permeability was measured from both the sides. Permeability at the front was larger than the permeability at the back which shows asymmetric behaviour of membranes.

• Dielectric parameters and a.c. conductivity of pure and doped poly (methyl methacrylate) films at microwave frequencies

Dielectric properties of pure and doped poly (methyl methacrylate) (PMMA) films at microwave frequency, 8.92 GHz, have been studied at 35°C. Iodine, benzoic acid and FeCl3 have been used as dopants. The losses in doped films are found to be larger than in pure PMMA films. The increased losses account for increased a.c. conductivity in doped films. The increase in conductivity is accounted due to creation of additional hopping sites for the charge carriers in doped samples. The dielectric data has also been used to evaluate optical constants, absorption index (𝐾) and refractive index (𝑛) of the films.

• Preparation of Al–Sb semiconductor by swift heavy ion irradiation

Al–Sb bilayer thin films having various thicknesses were deposited by thermal evaporation on ITO-coated conducting glass substrates at a pressure of 10-5 torr. These films were irradiated by Ag12+ heavy ions of energy, 160 MeV, with a fluence of 2.2 × 1013 ions/cm2, to get aluminum antimonide semiconductor. Rutherford back scattering and optical band gap data confirmed mixing of bilayer to form the semi-conducting system.

• Study of annealing effects in Al–Sb bilayer thin films

In this paper, we present preparation and characterization of Al–Sb bilayer thin films. Thin films of thicknesses, 3000/1000 Å and 3000/1500 Å, were obtained by the thermal evaporation (resistive heating) method. Vacuum annealing and rapid thermal annealing methods were used to mix bilayer thin film structure. Results obtained from optical band gap data and Rutherford back scattering spectrometry showed mixing of Al–Sb bilayer system.

• Study of annealing effects in In–Sb bilayer thin films

The thin films of In–Sb having different thicknesses of antimony keeping constant thickness of indium was deposited by thermal evaporation method on ITO coated conducting glass substrates at room temperature and a pressure of 10-5 torr. The samples were annealed for 1 h at 433 K at a pressure of 10-5 torr. The optical transmission spectra of as deposited and annealed films have been carried out at room temperature. The variation in optical band gap with thickness was also observed. Rutherford back scattering and X-ray diffraction analysis confirms mixing of bilayer system. The transverse 𝐼–𝑉 characteristic shows mixing effect after annealing at 433 K for 1 h. This study confirms mixing of bilayer structure of semiconductor thin films.

• Swift heavy ion irradiation effect on Cu-doped CdS nanocrystals embedded in PMMA

Semiconductor nanocrystals (NCs) have received much interest for their optical and electronic properties. When these NCs dispersed in polymer matrix, brightness of the light emission is enhanced due to their quantum dot size. The CdCuS NCs have been synthesized by chemical route method and then dispersed in PMMA matrix. These nanocomposite polymer films were irradiated by swift heavy ion (SHI) (100 MeV, Si+7 ions beam) at different fluences of 1 × 1010 and 1 × 1012 ions/cm2 and then compared their structural and optical properties by XRD, atomic force microscopy, photoluminescence, and UV-Vis spectroscopy before and after irradiation. The XRD spectra showed a broad hump around 2𝜃 ≈ 11.83° due to amorphous PMMA and other peaks corresponding to hexagonal structure of CdS nanocrystals in PMMA matrix. The photoluminescence spectra shows a broad peak at 530 nm corresponding to green emission due to Cu impurities in CdS. The UV-Vis measurement showed red shift in optical absorption and bandgap changed from 4.38–3.60 eV as the irradiation fluency increased with respect to pristine CdCuS nanocomposite polymer film.

• Optical properties of d.c. magneto sputtered tantalum and titanium nanostructure thin film metal hydrides

Nanostructured thin films of tantalum and titanium were deposited on glass substrate using d.c. magnetron sputtering technique under the argon gas environment at a pressure of 0.1 mbar. Optical transmission and absorption studies were carried out for these samples with pressure of hydrogen. Large changes in both transmission and absorption on loading these films with hydrogen are accompanied by significant phase changes and electronic transformation. Optical photograph shows the colour variation after hydrogenation in case of tantalum film which may be used as decorative mirrors and hydrogen sensors. The hydrogen storage capability of thin films was confirmed by variation in optical properties.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 6
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019