Shammi Verma

Role of surface composition in morphological evolution of GaAs nano-dots with low-energy ion irradiation

The surface chemistry of GaAs (100) with 50-keV Ar+ ion beam irradiation at off-normal incidence has been investigated in order to elucidate the surface nano-structuring mechanism(s). Core level and valence band studies of the surface composition were carried out as a function of fluences, which varied from 1 × 1017 to 7 × 1017 ions/cm2. Core-level spectra of samples analyzed by X-ray photoelectron spectroscopy confirmed the Ga enrichment of the surface resulting in bigger sized nano-dots. Formation of such nano-dots is attributed to be due to the interplay between preferential sputtering and surface diffusion processes. Valence band measurement shows that the shift in the Fermi edge is higher for Ga- rich, bigger sized nano-dots due to the partial oxide formation of Ga. ‘One-dimensional power spectral density’ extracted from atomic force micrographs also confirms the significant role of surface diffusion in observed nano-structuring.

Fabrication of ordered ripple patterns on GaAs(100) surface using 60 keV Ar+ beam irradiation

Abstract Ion beam induced ripples have limitations to be used in widespread nanoscale device applications due to the presence of deformity in surface patterns. Defect free ripples can only be produced on binary materials if the ion species, energy and angle of incidence are appropriately chosen. Fabrication of highly ordered defect free ripples is observed on GaAs(100) surfaces after the irradiation of 60 keV Ar+ ion beam for different fluences. Atomic force microscopy study demonstrates that the ordering as well as coarsening of ripples are increased with increase in fluence. X-ray photoelectron spectroscopy was carried out to study the significant role of altered surface composition for the generation of defect free ripples. The evolution of high degrees of order is explained with the help of existing formalisms of coupling between surface topography and preferential sputtering.

Synthesis of cobalt nanoparticles on Si (100) by swift heavy ion irradiation.

We report the growth and characterization of uniform-sized nanoparticles of cobalt on n-type silicon (100) substrates by swift heavy ion (SHI) irradiation. The Co thin films of 25-nm thicknesses were grown by e-beam evaporation and irradiated with two different types of ions, 45-MeV Li3+ and 100-MeV O7+ ions with fluences ranging from 1 × 1011 to 1 × 1013 ions/cm2. SHI irradiation, with the beam rastered over the area of the film, resulted in the restructuring of the film into a dense array of Co nanostructures. Surface topography studied by atomic force microscopy revealed narrowed size distributions, with particle sizes ranging from 20 to 50 nm, formed through a self-organized process. Ion fluence-dependent changes in crystallinity of the Co nanostructures were determined by glancing angle X-ray diffraction. Rutherford backscattering spectroscopy analysis showed the absence of beam-induced mixing in this system. Surface restructuring and beam-induced crystallization are the dominant effects, with the nanoparticle size and density being dependent on the ion fluence. Results are analyzed in the context of molecular dynamics calculations of electron-lattice energy transfer.

Recovery of Electrical Characteristics of Au/n-Si Schottky Junction Under

The electrical transport characteristics of a Au/n-Si metal-semiconductor Schottky barrier junction under exposure to 60Co gamma rays have been reported in this paper. The role of energy loss mechanisms in the Schottky junction due to gamma irradiation is studied using the current-voltage (I-V ) and capacitance-voltage (C-V ) measurements. The electrical characteristics were measured at various doses of gamma by incrementally increasing the exposure from 0.85 Mrad (Si) to 340 Mrad (Si) to systematically study the dose effects on electrical transport across the Schottky interface. After irradiation, the ideality factor was found to decrease initially up to a dose of 17 Mrad (Si), and thereafter, it started increasing. At a dose of 340 Mrad (Si), the characteristics of the Schottky interface were found to recover toward the pristine characteristics. The recovery effect is attributed to annealing of interface defects due to the electronic energy loss Se of gamma ray photons.

{}^{60}\hbox{Co}

Nano structuring of silicon surface by low energy ion irradiation is reported. Semi insulating n‐Si (100) has been irradiated by 50 keV Ar+ ion beam at an angle of 50° with respect to surface normal. The irradiated sample’s surfaces were analyzed by Atomic Force Microscopy. Irradiation caused formation of nano‐sized elliptical dots aligned in rows perpendicular to ion beam direction at fluence of 1×1017 ions/cm2. At higher fluences of 3×1017 ions/cm2 and 7×1017 ions/cm2 self organized ripples were developed on the surface.