Improving carrier injection in colloidal CdSe nanocrystals by embedding them in a pseudomorphic ZnSe/ZnMgSe quantum well structure.

The incorporation of colloidal nanocrystals in a high crystalline quality semiconductor matrix, the efficient carrier injection into the embedded nanocrystals and the fast optical response are key features for the fabrication of novel optoelectronic nanodevices based on colloidal nanostructures as active optical material. Using a novel growth approach, colloidal bare CdSe and core-shell CdSe/ZnS nanocrystals were monolithically incorporated in pseudomorphic ZnSe/ZnMgSe quantum wells in order to control and enhance the carrier transfer into the nanocrystals. The photoluminescence for bare CdSe nanocrystals incorporated in ZnSe/ZnMgSe quantum well structures is substantially enhanced in comparison to nanocrystals sandwiched in ZnSe epilayers, which we attribute to increased carrier injection into the embedded nanocrystals via the quantum well, resembling the function of a wetting layer in Stranski-Krastanov-grown quantum dots. Core-shell CdSe/ZnS nanocrystals embedded in quantum well structures do not show considerable PL modifications because the ZnS shell prevents the efficient carrier migration between the nanocrystal and the matrix. Systematic investigations of structural and optical properties by high-resolution x-ray diffraction, temperature-dependent photoluminescence and time-resolved emission are presented.

Relevance of laser irradiance threshold in the induction of alkaline phosphatase in human osteoblast cultures.

Induction of matrix synthesis by low-level laser has been demonstrated extensively. However, the question of dose- or power intensity-dependency is under-investigated. To address this issue we chose human osteoblast cell cultures and measured their alkaline phosphatase (ALP) activity after laser irradiation. The cell cultures were irradiated periodically by 690 nm radiation via optical transmission fiber-based laser needles, reaching into the culture dishes. The osteoblasts showed no induction of ALP activity when we used a single laser needle stimulation with a laser irradiance of 51 mW/cm(2), an increase of approximately 43% at 102 mW/cm(2) irradiance (two needles per well) and a ninefold increase at 204 mW/cm(2) irradiance (four needles per well), leaving the temperature of the culture medium unaffected. We concluded that the osteoblastic response in ALP activity to a laser stimulus shows a logarithmic relationship, with a distinct threshold, rather than a linear dose-dependency. Secondly, the laser irradiance, rather than the dose, is relevant for the impact of the laser.

Hybrid epitaxial-colloidal semiconductor nanostructures.

We present a growth technique which combines wet-chemical growth and molecular beam epitaxy (MBE) to create complex semiconductor nanostructures with nanocrystals as active optical material. The obtained results show that wet-chemically prepared semiconductor nanocrystals can be incorporated in an epitaxally grown crystalline cap layer. As an exemplary system we chose CdSe nanorods and CdSe(ZnS) core-shell nanocrystals in ZnSe and discuss the two limits of thin (d approximately 2R) and thick (d>2R) ZnSe cap layers of thickness d for CdSe nanorods and nanodots of radii R between 2 and 4 nm. In contrast to the strain-induced CdSe/ZnSe Stranski-Krastanow growth of a quantum dot layer in a semiconductor heterostructure, the technique proposed here does not rely on strain and thus results in additional degrees of freedom for choosing composition, concentration, shape, and size of the nanocrystals. Transmission electron microscopy and X-ray diffractometry show that the ZnSe cap layer is of high crystalline quality and provides all parameters for a consecutive growth of Bragg structures, waveguides, or diode structures for electrical injection.

Acupuncture using laser needles modulates brain function: first evidence from functional transcranial Doppler sonography and functional magnetic resonance imaging.

Acupuncture using laser needles is a new totally painless stimulation method which has been described for the first time. This paper presents an experimental double-blind study in acupuncture research in healthy volunteers using a new optical stimulation method. We investigated 18 healthy volunteers (mean age +/- SD: 25.4 +/- 4.3 years; range: 21-30 years; 11 female, 7 male) in a randomized controlled cross-over trial using functional multidirectional transcranial ultrasound Doppler sonography (fTCD; n = 17) and performed functional magnetic resonance imaging (fMRI) in one volunteer. Stimulation of vision-related acupoints resulted in an increase of mean blood flow velocity in the posterior cerebral artery measured by fTCD [before stimulation (mean +/- SE): 42.2 +/- 2.5; during stimulation: 44.2 +/- 2.6; after stimulation: 42.3 +/- 2.4 cm/s, n.s.]. Mean blood flow velocity in the middle cerebral artery decreased insignificantly. Significant changes (p < 0.05) of brain activity were demonstrated in the occipital and frontal gyrus by fMRI. Optical stimulation using properly adjusted laser needles has the advantage that the stimulation cannot be felt by the patient (painless and no tactile stimulation) and the operator may also be unaware of whether the stimulation system is active. Therefore true double-blind studies in acupuncture research can be performed.

[Quantification of gender specific thermal sensory and pain threshold before and after laser needle stimulation]. / Quantitative Bestimmung geschlechtsspezifischer thermischer Empfindungs- und Schmerzschwellen vor und nach Lasernadelstimulation.

Quantitative thermal sensory and pain threshold testing (QST) was performed in 29 adult healthy volunteers (mean age 24.2 +/- 2.7 years; range: 18-29 years; 20 females, 9 males) using the Thermal Sensory Analyser TSA-II (Medoc Advanced Medical Systems, Ramat Yishai, Israel, and Minneapolis, Minnesota, USA) before and after laser needle acupuncture and placebo stimulation, respectively. Significant (p < or = 0,001; t-test) gender-specific differences were seen on cold pain threshold analysis. No significant changes in parameters of thermal sensory and pain thresholds were found before and after laser needle or placebo stimulation at acupuncture points for acute pain. However, a trend towards change in the median value of cold pain sensation after laser needle stimulation (p = 0.479; paired t-test; n.s.) was seen within the group of healthy females. The influence of stimulation of acupuncture points for chronic pain on the various parameters needs to be clarified in future studies.

[Histological investigation of the micromorphological effects of the application of a laser needle--results of an animal experiment]. / Histologische Untersuchungen zu mikromorphologischen Einflüssen von Lasernadelstrahlung--Ergebnisse einer tierexperimentellen Untersuchung.

In an experimental animal study (Sus scrofa domesticus) we investigated the effects of the new technique of laser needle stimulation (wavelength: 685 nm; energy density: 4.6 kJ/cm2 per point; application duration: 20 min). The results revealed changes in microcirculatory parameters of the skin resulting in an increase in blood flow. However, the quality and intensity of the laser light did not induce micromorphological alterations in the skin.

Cerebral vascular effects of non-invasive laserneedles measured by transorbital and transtemporal Doppler sonography.

Laserneedles represent a new non-invasive optical stimulation method which is described for the first time in this paper. We investigated 27 healthy volunteers (mean age+/-SD: 25.15+/-4.12 years; range: 21-38 years; 14 female, 13 male) in a randomised cross-over trial to study differences between laserneedle acupuncture and manual needle acupuncture in specific cerebral parameters. Mean blood flow velocity ( v(m)) showed specific and significant increases in the ophthalmic artery during laserneedle stimulation ( p=0.01) and during manual needle stimulation ( p<0.001) at vision-related acupoints. At the same time insignificant alterations in v(m) were found in the middle cerebral artery for both acupuncture methods. The eight laserneedles used in this study were arranged at the end of the optical fibres. Each fibre was connected to a semiconductor laser diode emitting at 685 nm with a primary output power of about 55 mW. Optical stimulation using properly adjusted laserneedles has the advantage that the stimulation can hardly be felt by the patient and the operator may also be unaware of whether the laserneedle system is active, and therefore true double blind studies in acupuncture research can be performed.

Evidence for phase-separated quantum dots in cubic InGaN layers from resonant raman scattering

The emission of light in the blue-green region from cubic InxGa1-xN alloys grown by molecular beam epitaxy is observed at room temperature and 30 K. By using selective resonant Raman spectroscopy (RRS) we demonstrate that the emission is due to quantum confinement effects taking place in phase-separated In-rich quantum dots formed in the layers. RRS data show that the In content of the dots fluctuates across the volume of the layers. We find that dot size and alloy fluctuation determine the emission wavelengths.