S. K. Deshpande

Effect of nitrogen ion implantation on the optical and structural characteristics of CR-39 polymer

The effect of nitrogen ion implantation has been examined in transparent surfaces of CR-39 polymer. Samples were implanted with 100keV N+ ions to various doses ranging from 1014to1017cm−2. The chemical and structural changes in the implanted specimens were performed using Raman spectroscopy and glancing angle x-ray diffraction. Ultraviolet-visible absorption analysis indicates a drastic decline in optical band gap from 3.50eV in virgin sample to 0.80eV at an implantation dose of 1017ionscm−2.The effect of nitrogen ion implantation has been examined in transparent surfaces of CR-39 polymer. Samples were implanted with 100keV N+ ions to various doses ranging from 1014to1017cm−2. The chemical and structural changes in the implanted specimens were performed using Raman spectroscopy and glancing angle x-ray diffraction. Ultraviolet-visible absorption analysis indicates a drastic decline in optical band gap from 3.50eV in virgin sample to 0.80eV at an implantation dose of 1017ionscm−2.

Surface disordering and its correlations with properties in argon implanted CR-39 polymer

The influence of Ar+ implantation induced disordering in the surface layers of the CR-39 polymer on its optical properties and surface hardness has been studied. The specimens were implanted at 130 keV to the doses of 5 × 1014, 1 × 1015, 1 × 1016 Ar+ cm−2. The structural behavior of the pre- and postimplanted specimens was investigated using UV-Visible, Raman, and x-ray diffraction techniques. Formation of disordered graphitelike structures in the implanted layers of polycarbonate has been observed using Raman and UV-Visible spectroscopy. A significant increase in the value of disorder content (Urbach energy) from 0.77 eV to 1.48 eV and a continuous decline in optical bandgap (from 3.43 eV to 2.32 eV) with increasing implantation dose have been observed. This decrease in optical bandgap has been found to have linear dependence on the increase in the Urbach energy, which points toward the formation of disordered structures in the implanted layers of CR-39 polymer. Further, Knoop microhardness is found to b...

Changes in Structural and Optical Properties of Polycarbonate Induced by Ag+ Ion Implantation

Transparent polycarbonate samples were implanted with 1 MeV Ag+ ions to various doses ranging from 5 × 1014 to 3 × 1016 ions cm−2 with a beam current density of 900 nA cm−2. Modification in the structure of polycarbonate as a function of the implantation fluence was investigated using micro-Raman spectroscopy, glancing angle X-ray diffraction, and UV-Vis spectroscopy. Raman spectroscopy pointed toward the formation of graphite structures/clusters due to the ion implantation. UV-Vis absorption analysis suggests the formation of a carbonaceous layer and a drastic decrease in optical band gap from 4.12 eV to 0.50 eV at an implanted dose of 3 × 1016 ions cm−2. The correlation between the decrease in band gap and the structural changes is discussed.

Dielectric spectroscopy of silver nanoparticle embedded soda glass

Silver-soda glass nanocomposites have been synthesized by using ion exchange technique followed by thermal annealing. Ultraviolet-visible absorption spectroscopy and transmission electron microscopy of the ion exchanged and annealed samples confirmed the presence of silver nanoparticles embedded inside the glass matrix. The size of silver nanoparticles has been found to increase with annealing temperature. The frequency response of the dielectric constant (e′) and dielectric loss (tan δ) has been studied in both the soda glass and the silver nanoparticle embedded soda glass samples. The dielectric constant increases from 0.9 to 1.89 in the frequency range from 900 kHz to 70 MHz with increasing silver nanoparticle size, which in turn is enhanced as a result of increasing annealing temperature. Possible Coulomb blockade effects have been discussed to explain this novel dielectric behavior.

Analysis of vertical alignment and bending of crystalline α-Fe2O3 nanowires using normal and grazing incidence x-ray diffraction intensities

Owing to the increasing importance of orderly placed nanostructures, the following study was conducted on oriented and disoriented nanowires. Use of grazing incidence x-ray diffraction (GIXRD) and normal x-ray diffraction (XRD) as possible tools to assess their alignment is discussed. The property of crystalline nanowires to grow in a preferred direction over a substrate is made use of, in which deviation in diffraction intensities is measured on a group of oriented and disoriented nanowires. We find that the difference is sufficiently large to predict the spread in orientations away from a reference direction. The observed intensity variation is explained using a modeled view of diffraction geometry with different nanowire orientations. An alignment index Anw has been calculated using (110) and (300) peak intensities in XRD and GIXRD measurements. The values were found to be related to the extent of vertical alignment as observed using scanning electron microscopy (SEM). The difference in diffraction geo...

The dielectric response of La0.5Ca0.5−xSrxMnO3(0.1≤x≤0.4) manganites with different magnetic ground states

The dielectric behavior of half doped manganites La0.5Ca0.5−xSrxMnO3 (0.1≤x≤0.4) with varying magnetic ground states has been studied. The real part of relative permittivity as a function of temperature e′(T), exhibits a maximum around the ferromagnetic (TC) and charge ordering transition (TCO) temperatures accompanied with high dielectric losses. The activation energies obtained for x=0.1 and 0.3 samples below TCO are the same ∼0.12 eV, whereas the relaxation time constant varies in the range 2.8×10−9 s–6.03×10−11 s. In contrast to samples having x≤0.3, for x=0.4 doping, the dielectric permittivity exhibits a strong temperature dependence in the vicinity of magnetic phase transitions. This behavior may be correlated with the presence of competing magnetic interactions (magnetic polarons) close to the magnetic transitions.

Dielectric behavior of Ar+ implanted CR-39 polymer

The frequency dependent dielectric response of Ar+ implanted CR-39 specimens has been studied. Samples were implanted with 130 keV Ar+ ions to various doses ranging from 5×1014 to 1×1016 cm−2. The frequency response of dielectric constant (e) and dielectric loss has been studied both in the pristine and argon ion implanted samples of CR-39 polymer in the frequency range 104 to 108 Hz. Structural changes produced in CR-39 specimens due to implantation have been studied using Attenuated total reflectance (ATR) Fourier transform infrared spectroscopic technique. Results of dielectric analysis indicate the lowering in dielectric constant (e′) and similar behavior of dielectric loss with increase in ion fluence. An attempt has been made to correlate these changes produced in the dielectric properties of implanted specimens with the structural changes produced due to implantation.

Structural and Optical Behaviour of Ar+ Implanted Polycarbonate

Effects of 130 keV Ar+ ion implantation on the structural and optical properties of polycarbonate specimens have been studied using Raman, UV‐Visible spectroscopy and glancing angle X‐ray diffraction techniques. Formation of disordered carbonaceous network in the implanted layers has been observed using Raman and UV‐Visible spectroscopy. A sharp decline in band gap values (4.1 eV to 0.63 eV) with increase in implantation dose has been observed. This decrease in optical band gap has been correlated with the formation of disordered structures in the implanted layers of polycarbonate.

Dielectric Behavior In Half Doped Manganites La0.5Ca0.5‐xSrxMnO3 (0.1≤x≤0.4)

The dielectric behavior of half doped manganites La0.5Ca0.5‐xSrxMnO3 (0.1≤x≤0.4) with varying antiferromagnetic ground states has been studied. The relative permittivity e′(T) exhibits a maximum accompanied with high dielectric losses around the ferromagnetic (TC) and charge ordering transition (TCO) temperatures. The activation energies obtained below TCO are the same ∼0.12 eV whereas the relaxation time constant varies in the range 2.8×10−9 s–6.03×10−11 s.