SERS of Rhodamine 6G on substrates with laterally ordered and random gold nanoislands

Preparation and study of laterally ordered and disordered arrays of Au nanoislands as SERS substrates are reported. Developed technology allows obtaining SERS substrates with long-term stability (up to six months), efficient (up to 10⁴) and laterally homogenous enhancement of the Raman signal from molecular analyte. The substrates developed are suitable for Raman bio-diagnostics, because their plasmon resonance can be tuned within the range 700-900 nm that falls into the transparency window of human tissues. The dependence of optical and enhancement properties of the substrates on their morphology has been studied. The morphology of the Au island film and their plasmon resonance spectrum depend noticeably on the nominal Au thickness and post-annealing temperature, while the duration of annealing is of minor importance. Formation of nanoholes in the case of Au substrates on holographically pre-patterned polymer film opens up the possibility of additional Raman enhancement via the "hot spot"-effect

Optical and acoustical phonon modes in superlattices with SiGe QDs

Multilayers with SiGe nanoislands grown in a broad temperature range (300-600 °C) are studied using Raman spectroscopy, HRXRD and AFM. It is shown that the islands are fully strained when obtained at 300 °C and gradually relax with the growth temperature increase. The main contribution to the Raman peaks caused by scattering on folded acoustic phonons in multilayers (n ≤ 10) with nanoislands is due to the islands themselves. The enhancement of the scattering intensity due to resonance of the exciting light with the electronic transitions inside the islands is shown to play a significant role

Surface Enhanced Raman Scattering of Light by ZnO Nanostructures

Raman scattering (including nonresonant, resonant, and surface enhanced scattering) of light by optical and surface phonons of ZnO nanocrystals and nanorods has been investigated. It has been found that the nonresonant and resonant Raman scattering spectra of the nanostructures exhibit typical vibrational modes, E-2(high) and A(1)(LO), respectively, which are allowed by the selection rules. The deposition of silver nanoclusters on the surface of nanostructures leads either to an abrupt increase in the intensity (by a factor of 10(3)) of Raman scattering of light by surface optical phonons or to the appearance of new surface modes, which indicates the observation of the phenomenon of surface enhanced Raman light scattering. It has been demonstrated that the frequencies of surface optical phonon modes of the studied nanostructures are in good agreement with the theoretical values obtained from calculations performed within the effective dielectric function model

Strange Meson Enhancement in PbPb Collisions

The NA44 Collaboration has measured yields and differential distributions of K+, K-, pi+, pi- in transverse kinetic energy and rapidity, around the center-of-mass rapidity in 158 A GeV/c Pb+Pb collisions at the CERN SPS. A considerable enhancement of K+ production per pi is observed, as compared to p+p collisions at this energy. To illustrate the importance of secondary hadron rescattering as an enhancement mechanism, we compare strangeness production at the SPS and AGS with predictions of the transport model RQMD.Comment: 11 pages, including 4 figures, LATE

Miniband-related 1.4–1.8 μm luminescence of Ge/Si quantum dot superlattices

The luminescence properties of highly strained, Sb-doped Ge/Si multi-layer heterostructures with incorporated Ge quantum dots (QDs) are studied. Calculations of the electronic band structure and luminescence measurements prove the existence of an electron miniband within the columns of the QDs. Miniband formation results in a conversion of the indirect to a quasi-direct excitons takes place. The optical transitions between electron states within the miniband and hole states within QDs are responsible for an intense luminescence in the 1.4–1.8 µm range, which is maintained up to room temperature. At 300 K, a light emitting diode based on such Ge/Si QD superlattices demonstrates an external quantum efficiency of 0.04% at a wavelength of 1.55 µm