61 research outputs found
Reentrant phase transition in charged colloidal suspensions
We report the observation of a novel phase transition in dilute aqueous suspensions of polystyrene particles as a function of ionic impurity concentration C. The suspension phase separates into dense and rare phases only for a restricted range of C which depends on particle concentration n. The dense phase has liquidlike or crystalline order depending on n and C. Free energies of the homogeneous and the phase-separated states are calculated with an effective interparticle potential. The calculated phase diagram is in qualitative agreement with the present experimental results
Magnetism in C<SUB>60</SUB> films induced by proton irradiation
It is shown that polycrystalline fullerene thin films on hydrogen-passivated Si(111) substrates irradiated by 2 MeV protons display ferromagneticlike behavior at 5 K. At 300 K, both the pristine and the irradiated film show diamagnetic behavior. Magnetization data in the temperature range of 2-300 K in 1 T applied field, for the irradiated film show much stronger temperature dependence compared to the pristine film. Possible origins of ferromagneticlike signals in the irradiated films are discussed
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
Influence of Annealing on the Optical and Scintillation Properties of CaWO Single Crystals
We investigate the influence of oxygen annealing on the room temperature
optical and scintillation properties of CaWO single crystals that are being
produced for direct Dark Matter search experiments. The applied annealing
procedure reduces the absorption coefficient at the peak position of the
scintillation spectrum ( nm) by a factor of and leads to an
even larger reduction of the scattering coefficient. Furthermore, the annealing
has no significant influence on the \emph{intrinsic} light yield. An additional
absorption occurring at nm suggests the formation of O hole
centers. Light-yield measurements at room temperature where one crystal surface
was mechanically roughened showed an increase of the \emph{measured} light
yield by and an improvement of the energy resolution at 59.5 keV by
for the annealed crystal. We ascribe this result to the reduction of
the absorption coefficient while the surface roughening is needed to compensate
for the also observed reduction of the scattering coefficient after annealing
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
Nitrogen ion beam synthesis of InN in InP (100) at elevated temperature
InN phase is grown in crystalline InP(100) substrates by 50 keV N+
implantation at an elevated temperature of 400 deg C followed by annealing at
525 deg C in N2 ambient. Crystallographic structural and Raman scattering
studies are performed for the characterization of grown phases. Temperature-
and power-dependent photoluminescence studies show direct band-to-band
transition peak ~1.06 eV at temperatures <=150K. Implantations at an elevated
temperature with a low ion beam current and subsequent low temperature
annealing step are found responsible for the growth of high-quality InN phase.Comment: 11 pages, 4 figures, Journa
Ferromagnetism in cobalt doped n-GaN
Ferromagnetic ordering is reported in the post-annealed samples of Co doped
n-GaN formed by Co+ implantation. A maximum Curie temperature ~ 250K is
recorded for the sample with 8 atomic percent Co. Particle induced x-ray
emission-channeling study confirmed the substitutional Co in Ga lattice site.
Local atomic arrangement around magnetic impurities is also analyzed using
Raman study. A disordered model with carrier mediated coupling of localized
magnetic moments is made responsible for the observed ferromagnetic ordering.Comment: 11 pages, 3 figures, Journa
Optical characterization of GaN by N+ implantation into GaAs at elevated temperature
Both hexagonal wurtzite and cubic zinc blend GaN phases were synthesized in
GaAs by 50 keV N+ implantation at 400 deg C and subsequent annealing at 900 deg
C for 15 min in N2 ambient. Crystallographic structural and Raman scattering
studies revealed that GaN phases were grown for fluence above 2x1017 cm-2.
Temperature-dependent photoluminescence study showed sharp direct band-to-band
transition peak ~3.32 eV at temperature <= 200K. The intermediate bandgap
value, with respect to ~3.4 eV for hexagonal and ~3.27 eV for cubic phases of
GaN is an indicative for the formation of mixed hexagonal and cubic phases.Comment: 9 pages, 4 figuresn Journa
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