P. Magudapathy

Crystalline to amorphous transition and band structure evolution in ion-damaged silicon studied by spectroscopic ellipsometry

Crystalline to amorphous transition and subsequent microstructural evolution in silicon induced by Ar+-ion implantation over a wide range of ion fluences (6×1013–1×1017 cm−2) have been investigated by spectroscopic ellipsometry. In the evaluation of the optical and microstructural properties of the damaged layer, the contribution of the surface overlayer to the measured dielectric spectra was separated by fitting a multilayer model with an effective medium approximation. The best fit to the dielectric spectra for disordered silicon could be obtained by taking our highest-fluence implanted (fluence=1×1017 ions/cm2) amorphous silicon (a-Si) data as reference data instead of a-Si data available in the handbook. The derivative spectra as a function of fluence show a distinct and sharp transition from the crystalline to amorphous phase. The threshold fluence for this transition is derived from fitting. Evaluation of standard sum rules and optical moments for imaginary part of the pseudodielectric function reve...

Structural and electronic properties of nitrogen ion implanted ultra nanocrystalline diamond surfaces

Enhanced electron field emission (EFE) properties have been observed for nitrogen implanted ultra-nanocrystalline diamond (UNCD) films grown by microwave plasma enhanced CVD. X-ray photoelectron spectroscopy (XPS) measurements show that sp2 fraction and C-N bonding increase upon N-implantation and annealing. Significant difference in current-voltage (I-V) curves at the grain and grain boundary has been observed from scanning tunneling spectroscopic (STS) measurement. From the variation of normalized conductance (dI/dV)/(I/V) versus V, bandgap is measured to be 4.8 eV at the grain and 3.8 eV at the grain boundary for as prepared UNCD. Upon nitrogen implantation and annealing, the bandgap decreases for both grain and grain boundary and density of states are introduced in the bandgap. Current imaging tunneling spectroscopy (CITS) imaging shows that the grain boundaries have higher conductivity than the grains and are the prominent electron emitters. The enhancement in EFE properties upon nitrogen implantatio...

Effects of argon ion irradiation on nucleation and growth of silver nanoparticles in a soda-glass matrix

The present article explores an experimental study for nucleation and non-equilibrium growth of silver nanoparticles in a soda-glass matrix. Ion-irradiation induced recoiling of silver atoms with argon ions (at energy 100 keV) facilitates nucleation as well as growth of the silver nanoparticles in the soda-glass matrix. Small growth of the silver nanoparticles in the soda-glass matrix has been experimentally observed after the irradiation with higher fluences of the argon ions. Role of the argon ions for the evolution of the silver nanoparticles in the soda-glass matrix has been elucidated in the present report. With increase of the argon-ion fluences, while slight athermal growth of the silver nanoparticles has been estimated, drastic increase in the optical responses and Rutherford backscattering (RBS) yields of the silver nanoparticles have been observed in the sample with the maximum fluences. Possible correlations of increase of argon-ion fluences and the observed experimental results (optical and RB...

Low field magnetoconductance studies in aggregated Al nano-clusters

Abstract Nano-aggregates of Al have been formed by 70 keV He+ irradiation on spin cast films of aluminum acetyl acetonate. Three fold increase in conductivity was observed for a fluence range of 1×1016–5×1017 ions/cm2. Electrical transport of the charge carriers was observed to follow Mott’s variable range hopping (VRH) mechanism in 3D nano-aggregates of Al in the temperature regime of 110–300 K. Low field (≤1 T) magnetoresistance (MR) studies in these samples showed change in sign of MR from positive for a sample with low zero field resistance [R(H=0)] to negative for samples with high R(H=0) owing to quantum interference phenomena of hopping paths.

High efficient electron field emission from rGO conformally coated NiO nanoflakes architecture

In the study, we report the facile synthesis of reduced graphene oxide (rGO) conformally coated vertically aligned, densely packed NiO nanoflakes (NFs) architecture for high efficient electron field emission applications. The NiO NFs architecture was grown on the Si substrate by a simple hydrothermal method, followed by decoration with rGO by drop casting method. The grazing incidence X-ray diffraction measurements reveal the formation of cubic structured NiO. The grown NiO NFs architecture is in better stoichiometry as evidenced from the resonant Rutherford backscattering spectrometry measurements. The rGO conformally coated NiO NFs (GNiO NFs) shows higher mobility and lower sheet resistance in comparison with its counterparts. X-ray absorption near edge structure analyses at O K-edge reveals the increase in unoccupied density of states due to the charge transfer from NiO to rGO. The rGO conformally coated NiO NFs architecture exhibits low turn-on voltage and enhanced field emission (FE) current as compared to the NiO NFs architecture. The observed low turn-on voltage and enhanced FE current for the GNiO NFs architecture is ascribed to the synergistic effect of addition of rGO as the conductive channels, which results in better charge transport and the enhanced field emission current characteristics.

Morphological investigations on the growth of defect-rich Bi2Te3 nanorods and their thermoelectric properties

Bi2Te3 nanorods (NRs) have been successfully synthesized at different reaction temperatures via a surfactant-assisted hydrothermal method. The experimental observations revealed that the reaction temperature, SDBS surfactant (sodium dodecylbenzene sulphonate) and its concentration affect the morphology of Bi2Te3. It is identified that an imperfect oriented attachment mechanism is the dominant growth mechanism for the evolution of Bi2Te3 NRs. Moreover, a subsidiary growth mechanism namely the Oswald ripening process could also affect the Bi2Te3 NR growth process at higher reaction temperatures. Thermoelectric property measurements revealed that flake-decorated Bi2Te3 NRs achieved the maximum power factor value of ∼1.32 μW cm−1 K−2 at 410 K, which was higher than those of porous and smooth Bi2Te3 NRs. Such an enhancement in the power factor of flake-decorated Bi2Te3 NRs is primarily attributed to their outstanding electrical conductivity at 410 K.