107 research outputs found
Dynamic and Static Transmission Electron Microscopy Studies on Structural Evaluation of Au nano islands on Si (100) Surface
Transmission electron microscopy (TEM) study on morphological changes in gold
nanostructures deposited on Si (100) upon annealing under different vacuum
conditions has been reported. Au thin films of thickness ~2.0 nm were deposited
under high vacuum condition (with the native oxide at the interface of Au and
Si) using thermal evaporation. In-situ, high temperature (from room temperature
(RT) to 850\degreeC) real time TEM measurements showed the evaluation of gold
nanoparticles into rectangular/square shaped gold silicide structures. This has
been attributed to selective thermal decomposition of native oxide layer.
Ex-situ annealing in low vacuum (10-2 mbar) at 850\degreeC showed no growth of
nano-gold silicide structures. Under low vacuum annealing conditions, the
creation of oxide could be dominating compared to the decomposition of oxide
layers resulting in the formation of barrier layer between Au and Si.Comment: 15 pages, 4 figure
Growth of Oriented Au Nanostructures: Role of Oxide at the Interface
We report on the formation of oriented gold nano structures on Si(100)
substrate by annealing procedures in low vacuum (\approx10-2 mbar) and at high
temperature (\approx 975^{\circ} C). Various thicknesses of gold films have
been deposited with SiOx (using high vacuum thermal evaporation) and without
SiOx (using molecular beam epitaxy) at the interface on Si(100). Electron
microscopy measurements were performed to determine the morphology, orientation
of the structures and the nature of oxide layer. Interfacial oxide layer, low
vacuum and high temperature annealing conditions are found to be necessary to
grow oriented gold structures. These gold structures can be transferred by
simple scratching method.Comment: 13 pages, 3 figures, Accepted in J. Appl. Phy
Nanodot to Nanowire: A strain-driven shape transition in self-organized endotaxial CoSi2 on Si (100)
We report a phenomenon of strain-driven shape transition in the growth of
nanoscale self-organized endotaxial CoSi2 islands on Si (100) substrates. Small
square shaped islands as small as 15\times15 nm2 have been observed. Islands
grow in the square shape following the four fold symmetry of the Si (100)
substrate, up to a critical size of 67 \times 67 nm2. A shape transition takes
place at this critical size. Larger islands adopt a rectangular shape with ever
increasing length and the width decreasing to an asymptotic value of ~25 nm.
This produces long wires of nearly constant width.We have observed nanowire
islands with aspect ratios as large as ~ 20:1. The long nanowire
heterostructures grow partly above (~ 3 nm) the surface, but mostly into (~17
nm) the Si substrate. These self-organized nanostructures behave as nanoscale
Schottky diodes. They may be useful in Si-nanofabrication and find potential
application in constructing nano devices.Comment: 9 pages, 7 figure
Nano scale phase separation in Au-Ge system on ultra clean Si(100) surfaces
We report on the formation of lobe-lobe (bi-lobed) Au-Ge nanostructures under
ultra high vacuum (UHV) conditions (\approx 3\times 10^{-10} mbar) on clean
Si(100) surfaces. For this study, \approx 2.0 nm thick Au samples were grown on
the substrate surface by molecular beam epitaxy (MBE). Thermal annealing was
carried out inside the UHV chamber at temperature \apprx 500{\deg}C and
following this, nearly square shaped Au_{x}Si_{1-x} nano structures of average
length \approx 48 nm were formed. A \approx 2 nm Ge film was further deposited
on the above surface while the substrate was kept at a temperature of \approx
500{\deg}C. Well ordered Au-Ge nanostructures where Au and Ge residing side by
side (lobe-lobe structures) were formed. In our systematic studies, we show
that, gold-silicide nanoalloy formation at the substrate (Si) surface is
necessary for forming phase separated Au-Ge bilobed nanostructures. Electron
microscopy (TEM, STEM-EDS, SEM) studies were carried out to determine the
structure of Au - Ge nano systems. Rutherford backscattering Spectrometry
measurements show gold inter-diffusion into substrate while it is absent for
Ge.Comment: 23 pages, 6 Figures, 1 Tabl
Metal Cluster's Effect on the Optical Properties of Cesium Bromide Thin Films
Cesium Bromide films grown of glass substrates by thermal evaporation showed
interesting optical properties. The UV-visible absorption spectra showed peaks
which showed red shift with time. Structural and morphological studies
suggested decrease in grain size with time which was unusual. Theoretical
simulation shows the optical behaviour to be due to surface plasmon resonance
resulting from Cesium clyindrical rods embedded in the films.Comment: 22 pages and 10 figure
Origin of Shifts in the Surface Plasmon Resonance Frequencies for Au and Ag Nanoparticles
Origin of shifts in the surface plasmon resonance (SPR) frequency for noble
metal (Au, Ag) nanoclusters are discussed in this book chapter. Spill out of
electron from the Fermi surface is considered as the origin of red shift. On
the other hand, both screening of electrons of the noble metal in porous media
and quantum effect of screen surface electron are considered for the observed
blue shift in the SPR peak position.Comment: 37 pages, 14 Figures in the submitted book chapter of The Annual
Reviews in Plasmonics, edited by Professor Chris D. Geddes. Springer Scinec
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