58 research outputs found
Growth of silver nanoclusters embedded in soda glass matrix
Temperature-controlled-growth of silver nanoclusters in soda glass matrix is
investigated by low-frequency Raman scattering spectroscopy. Growth of the
nanoclusters is ascribed to the diffusion-controlled precipitation of silver
atoms due to annealing the silver-exchanged soda glass samples. For the first
time, Rutherford backscattering measurements performed in this system to find
out activation energy for the diffusion of silver ions in the glass matrix.
Activation energy for the diffusion of silver ions in the glass matrix
estimated from different experimental results is found to be consistent.Comment: 16 pages, 5 figures, pdf fil
Optical absorption and photoluminescence spectroscopy of the growth of silver nanoparticles
Results obtained from the optical absorption and photoluminescence (PL)
spectroscopy experiments have shown the formation of excitons in the
silver-exchanged glass samples. These findings are reported here for the first
time. Further, we investigate the dramatic changes in the photoemission
properties of the silver-exchanged glass samples as a function of postannealing
temperature. Observed changes are thought to be due to the structural
rearrangements of silver and oxygen bonding during the heat treatments of the
glass matrix. In fact, photoelectron spectroscopy does reveal these chemical
transformations of silver-exchanged soda glass samples caused by the thermal
effects of annealing in a high vacuum atmosphere. An important correlation
between temperature-induced changes of the PL intensity and thermal growth of
the silver nanoparticles has been established in this Letter through precise
spectroscopic studies.Comment: 15 pages,4 figures,PDF fil
'Spillout' effect in gold nanoclusters embedded in c-Al2O3(0001) matrix
Gold nanoclusters are grown by 1.8 MeV Au^\sup{2+} implantation on
c-Al\sub{2}O\sub{3}(0001)substrate and subsequent air annealing at temperatures
1273K. Post-annealed samples show plasmon resonance in the optical (561-579 nm)
region for average cluster sizes ~1.72-2.4 nm. A redshift of the plasmon peak
with decreasing cluster size in the post-annealed samples is assigned to the
'spillout' effect (reduction of electron density) for clusters with ~157-427
number of Au atoms fully embedded in crystalline dielectric matrix with
increased polarizability in the embedded system.Comment: 14 Pages (figures included); Accepted in Chem. Phys. Lett (In Press
Blue luminescence of Au nanoclusters embedded in silica matrix
Photoluminescence study using the 325 nm He-Cd excitation is reported for the
Au nanoclusters embedded in SiO2 matrix. Au clusters are grown by ion beam
mixing with 100 KeV Ar+ irradiation on Au [40 nm]/SiO2 at various fluences and
subsequent annealing at high temperature. The blue bands above ~3 eV match
closely with reported values for colloidal Au nanoclusters and supported Au
nanoislands. Radiative recombination of sp electrons above Fermi level to
occupied d-band holes are assigned for observed luminescence peaks. Peaks at
3.1 eV and 3.4 eV are correlated to energy gaps at the X- and L-symmetry
points, respectively, with possible involvement of relaxation mechanism. The
blue shift of peak positions at 3.4 eV with decreasing cluster size is reported
to be due to the compressive strain in small clusters. A first principle
calculation based on density functional theory using the full potential linear
augmented plane wave plus local orbitals (FP-LAPW+LO) formalism with
generalized gradient approximation (GGA) for the exchange correlation energy is
used to estimate the band gaps at the X- and L-symmetry points by calculating
the band structures and joint density of states (JDOS) for different strain
values in order to explain the blueshift of ~0.1 eV with decreasing cluster
size around L-symmetry point.Comment: 13 pages, 7 Figures Only in PDF format; To be published in J. of
Chem. Phys. (Tentative issue of publication 8th December 2004
- …