R. J. Singh

Effect of hydrogen on ground state properties of silicon clusters (SinHm; n = 11–15, m = 0–4): a density functional based tight binding study

The effect of hydrogen addition to silicon clusters Sin (n = 11–15) is examined in terms of the change in their ground state geometry, bonding characteristics (bond lengths, bond angles and Si coordination numbers), structural stability, vibrational spectra and electronic structure. We found that addition of hydrogen caused a drastic change in the structural geometry of silicon clusters. Upon hydrogenation, some clusters become highly symmetric, while some others are completely distorted. Hydrogenation caused a structural transition in silicon clusters; from spherical to elongated in Si11 and Si12, from one side capped elongated to both side capped elongated in Si13 and Si14 and from both side capped elongated to one side capped elongated in Si15. Hydrogen preferred to bond with either under-coordinated or over-coordinated Si atoms. Each H atom is bonded to only one Si atom and localized outside the silicon cluster skeleton. Hydrogenation caused a significant change in the vibrational spectra and electronic structures of bare Sin silicon clusters. There exists a band gap near the Fermi level in EDOS in all the bare and hydrogenated silicon clusters. The band gap of a silicon cluster depends on its size and amount of hydrogenation.

Alpha Particle Induced Reactions on 27Al at 55.2 and 58.2 MeV

The alpha particle induced reactions on 2 Al have been studied using gamma ray spectrometry. The cross sections for the formation of 7 Be, 2 Na, 2 Na, 2 Mg, 2 Mg, A1 and A1 in the alpha particle induced reaction on A1 with alpha particles of energy 55.2 MeV and 58.2 MeV have been determined. The results are discussed in terms of increasing projectile energy and multi nucleon as well as cluster emission from the excited nucleus. o(-BEAM 25 4jjm Al

MAGNETIC COUPLING IN PSEUDOMORPHIC 2ML OVERLAYERS AND SANDWICH SUPERLATTICE STRUCTURES OF Cr, Mn, Fe, Co AND Ni ON FCC Cu(001)

The magnetic coupling in pseudomorphic overlayer and sandwich structures of 2ML magnetic ultrathin films on Cu(001) substrate is investigated by using spin-polarized density functional theory. The 2ML magnetic overlayers have significant magnetic moment except CrNi overlayer for which magnetic moment is very small (0.004 μB/atom). The overlayers having one layer of Cr turn out to be antiferromagnetically coupled except CrNi/Cu overlayer which has ferromagnetic coupling. All other overlayers have ferromagnetic coupling. In contrast to ferromagnetic MnMn/Cu overlayer, the Cu/MnMn/Cu sandwich has antiferromagnetic coupling. Similar to CrFe/Cu overlayer, the Cu/CrFe/Cu sandwich has antiferromagnetic coupling, while all other sandwiches have ferromagnetic coupling. The sandwiched structures have reduced magnetic moment as compared to their overlayer counterparts. The MnMn, MnFe, and MnCo sandwiches have highly reduced magnetic moment as compared to their overlayer counterparts.

Excitation Functions for Multi-Nucleon Emission in Helium Ion Reactions with 197Au

Excitation functions for the production of heavy residues through He reactions on Au targets have been measured in the incident energy range of 35 — 50 MeV which probes and extends the lower limits of the excitation functions for cluster and multi-nucleon emission. The older cross-section values that partially cover this energy region have been re-evaluated using more recent decay scheme data and compared with the present measurements. Interference from secondary neutrons in the cross-sections of interest were investigated.