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 silverexchanged soda glass samples caused by the thermal effects of annealing in a high vacuumatmosphere. 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.

A spectral energy density based formalism is implemented to probe the temperature dependent frequency shift, linewidth, structural stability and coupling of normal modes of vibrations of freestanding graphene using a combination of lattice dynamics and molecular dynamics (MD). The inplane lattice parameter shows a thermal contraction upto 1300 K and it expands thereafter. Frequency of the bending mode (ZA) becomes imaginary in the quasi-harmonic dispersion at higher temperatures, suggestive of a structural instability. However, the frequency of the ZA mode becomes real in the dispersion obtained from MD. Dynamical stability to the structure is restored by strong anharmonic coupling of phonon modes which is automatically incorporated in the MD simulations, whereas it is ignored in the quasi-harmonic dispersion. The mode resolved phonon spectra at Γ point show a blue-shift of degenerate longitudinal and transverse (LO/TO) optic modes. The blue-shift observed in canonical (NVT) and isobaric-isothermal (NPT) ensembles are more prominent than the shift predicted by quasi-harmonic approximation (QHA) due to the additional contribution from phonon-phonon coupling. The out-of-plane optic (ZO) mode frequencies are red-shifted in the QHA due to membrane-effect, whereas MD simulations show that the strong phonon-phonon coupling dominates the membrane effect leading to a blue-shift. The linewidth of LO/TO and ZO modes increases non-monotonically with temperature. The anharmonic coupling of normal modes at high symmetry points in the Brillouin zone is also discussed.

a b s t r a c tThree model ODS alloys (Fe-0.3Y 2 O 3 , Fe-0.2Ti-0.3Y 2 O 3 and Fe-14Cr-0.2Ti-0.3Y 2 O 3 ) were prepared by ball milling and then hot extrusion to study the effect of Ti and Cr on the size, distribution, crystal structure and composition of the nano-oxide particles. All alloys were characterized by high resolution transmission electron microscopy (HRTEM), atom probe tomography (APT) and synchrotron-X-ray diffraction (S-XRD) to determine the distribution, structure and composition of the oxide nanoparticles samples. The median particle sizes were 9.6 nm, 7.7 nm and 3.7 nm for the Fe-Y 2 O 3 , Fe-Ti-Y 2 O 3 and Fe-Cr-Ti-Y 2 O 3 alloys, respectively, so the presence of Ti resulted in a significant reduction in oxide particle diameter and the addition of Cr gave a further reduction in size. In the Fe-0.3Y 2 O 3 alloy, the particles are found to be bcc Y 2 O 3 , whereas in the other two alloys (Fe-Ti-0.3Y 2 O 3 and Fe-Cr-Ti-Y 2 O 3 ), the oxide particles were found to be structurally consistent with both orthorhombic Y 2 TiO 5 and fcc Y 2 Ti 2 O 7 . Detailed APT studies showed Cr shells around oxide particles of all sizes in the Fe-Cr-Ti-Y 2 O 3 alloy, that a range of cluster compositions are present and that the particle chemistry varies with cluster size. We show that the addition of Cr has a strong effect on both the size and stoichiometry of the particles.

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

Electrophoresis deposition (EPD) of nanodiamond was found to be a very efficient process in forming the nucleation sites for the growth of ultrananocrystalline diamond (UNCD) films. Transmission electron microscopic investigations showed that the EPD-derived UNCD films grown on planar Si substrates contain uniform granular structure with sharp, smooth, and conductive UNCD-to-Si interface layer, which helps in better electron field emission (EFE) properties of the UNCD films. Moreover, contrary to ultrasonication process for nucleating the diamond, the EPD process is a gentle one that induced no damage to the silicon nanowire arrays (SiNWs), facilitating the formation of nuclei for growing UNCD films on SiNWs. Such a gentle process significantly enhanced the EFE properties of UNCD/SiNWs. The EPD-derived UNCD/SiNW emitters show superior EFE performances to the planar UNCD films, that is, a turn-on field of 7.19 V/μm and a large EFE current density of 2.21 mA/cm2 at 15.0 V/μm. Furthermore, a parallel plate plasma device fabricated using the EPD-derived UNCD/SiNW nanostructures as cathode shows a high Ar plasma current value of 3.5 mA/cm2 at a low applied field of 0.35 V/μm. These results demonstrate that these EPD-derived UNCD/SiNW nanostructures have great potential for the applications in flat panel displays due to their superior EFE properties and plasma illumination performances.