CENSR (Computational &
Experimental Nano Science Research)
Jagadish Chandra Mahato, Assistant Professor
Department of Physics
Visva-Bharati (A Central University)
Santiniketan, Bolpur-731235, West Bengal
Research work in brief
RP | 01
Project | 01 Nanodot to nanowire shape transition
We report a phenomenon of strain-driven shape transition in the growth of nanoscale self-organized endotaxial CoSi2 islands on Si(100) substrates. Nanodots of CoSi2 grow in the square shape following the four fold symmetry of the Si(100) substrate, up to a critical size of 67x67 nm2, where a shape transition takes place. Larger islands grow as nanowires with ever increasing length and the width decreasing to an asymptotic value of ~25 nm. This
produces long nanowires of nearly constant width. The endotaxial nanostructures grow into the Si substrate with a small extension above the surface.
RP | 02
Project | 02 Control of surface defects and its influence on growth of epitaxial islands
How does the surface defect influence the epitaxial nano-islands growth on the Si(111)7x7 surfaces?
The morphology and the size distribution of self-organized cobalt silicide nanostructures, grown on Si(111) substrates with controlled defects, have been investigated. An initial defect structure on the Si(111) surface is produced by quenching the substrate from just below the 7×7⇌‘1×1’ (disordered) phase transition temperature. This has produced predominantly the Si(111)-(7×7) reconstructed structure along with some disordered regions and defect lines on the substrate surface. The disordered regions contain randomly placed Si adatom ring clusters or a lattice gas of ring clusters and small patches of √7×√7R19° structure. These substrates have been preannealed for different durations before 0.5 monolayer Co deposition on them for forming CoSi2 by reactive deposition epitaxy.
With increasing duration of substrate annealing and consequent reduction of defect density and surface roughness, a change of island morphology, a transition from bimodal to monomodal size distribution and an increase of average island size have been observed. Reduction of surface defects via substrate preannealing appears to lead to the growth of homogeneous nanostructures.
RP | 03
Project | 03 Adsorption induced surface structural transformations
The quest for the growth behavior of Ge in the sub-monolayer to a monolayer regime on the √3Ag-terminated Si/Ge(111)-5 × 5 surface by in-situ STM and STS. Also, if there is any preferential growth of deposited germanium on three different regions of √3 ‘island’, √3 ‘hole’ and 5x5 structure has been explored.
The growth of Ge on Si(111)/Ge-(√3 ×√3)Ag substrates was investigated for Ge coverages up to 1 mono-layer (ML). The√3Ag substrate was obtained by depositing 0.2 ML Ag on Si(111)/Ge(111)-5×5 surfaces. Because of the low Ag coverage, three types of regions– √3Ag ‘island’, √3Ag ‘hole’ and exposed Ge(111)-5×5– are produced. This has allowed investigation of Ge growth simultaneously on these three types of surface features by scanning tunneling microscopy.