The enhancement of Raman scattering by optical phonon modes in quantum dots was achieved in resonant and surface-enhanced Raman scattering experiments by approaching the laser energy to the energy of ...either the interband transitions or the localized surface plasmons in silver nanoclusters deposited onto the nanostructures. Resonant Raman scattering by TO, LO, and SO phonons as well as their overtones was observed for PbS, ZnS, and ZnO quantum dots while enhancement for LO and SO modes in CdS quantum dots with a factor of about 700 was measured in surface enhanced Raman scattering experiments. Multiple phonon Raman scattering observed up to 5th and 7th order for CdS and ZnO, respectively, confirms the high crystalline quality of the grown QDs.
Uniaxial strain on wafer-level was realised by mechanically bending and direct wafer bonding of Si wafers in the bent state followed by thinning one of the Si wafers by the smart-cut process. This ...approach is flexible and allows to obtain different strain values at wafer-level in both tension and compression. UV micro-Raman spectroscopy was used to determine the strain in the thin transferred Si layers. Numerical modelling by 3D finite elements of the strain provided a good description of the experimental results.
Four-inch InP wafers were implanted with 100
keV helium ions with a dose of 5×10
16
cm
−2 and subsequently annealed in air in the temperature range of 225–400°C in order to determine the blistering ...kinetics of these wafers. An Arrhenius plot of the blistering time as a function of reciprocal temperature revealed two different activation energies for the formation of surface blisters in InP. The activation energy was found to be 0.30
eV in the higher temperature regime of 300–400
°C and 0.74
eV in the lower temperature regime of 225–300
°C. The implantation induced damage was analyzed by cross-sectional transmission electron microscopy, which revealed a band of defects extending from 400–700
nm from the surface of InP. The damage band was found to be decorated with a large number of nanovoids having diameters between 2 and 5
nm. These nanovoids served as precursors for the formation of microcracks inside InP upon annealing, which led to the formation of surface blisters.
Tensile strained Si (sSi) layers were epitaxially deposited onto fully relaxed Si
0.78Ge
0.22 (SiGe) epitaxial layers (4
μm) on silicon substrates. Periodic arrays of 150
nm
×
150
nm and 150
nm
×
750
...nm pillars with a height of 100
nm were fabricated into the sSi and SiGe layers by electron-beam lithography and subsequent reactive ion etching. The strain in the patterned and unpatterned samples was analyzed using high-resolution UV micro-Raman spectroscopy. The 325
nm excitation line used probes strain in Si close to the surface (penetration depth of ∼9
nm). The Raman measurements revealed that the nano-patterning yields a relaxation of strain of ∼33% in the large pillars and ∼53% in the small pillars of the ∼0.95% initial strain in the unpatterned sSi layer.
Modelling absorption and photoluminescence of TPD Vragović, Igor; Calzado, Eva M.; Díaz García, María A. ...
Journal of luminescence,
05/2008, Volume:
128, Issue:
5
Journal Article, Conference Proceeding
Peer reviewed
We analyse the optical spectra of
N
,
N
′
-diphenyl-
N
,
N
′
-bis(3-methyl-phenyl)-(
1
,
1
′
-biphenyl)-
4
,
4
′
-diamine (TPD) doped polystyrene films. The aim of the present paper is to give a ...microscopic interpretation of the significant Stokes shift between absorption and photoluminescence, which makes this material suitable for stimulated emission. The optimized geometric structures and energies of a neutral TPD monomer in ground and excited states are obtained by
ab initio calculations using Hartree–Fock and density functional theory. The results indicate that the second distinct peak observed in absorption may arise either from a group of higher electronic transitions of the monomer or from the lowest optical transitions of a TPD dimer.
Resonant Raman scattering by optical phonon modes as well as their overtones was investigated in ZnS and ZnO quantum dots grown by the Langmuir–Blodgett technique. The in situ formation of ZnS/ZnO ...core/shell quantum dots was monitored by Raman spectroscopy during laser illumination.
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