[en] The optical research of single InGaN quantum dots is difficult due to the fact that their emission lines are significantly broadened. The emission energies of wurtzite InGaN QDs are strongly influenced by fluctuating electric fields, resulting in line-width broadening. We present spatially- and time-resolved photoluminescence measurements of single InGaN/GaN quantum dots. Therefore, a new microphotoluminescence setup was built. In order to investigate the behavior of different excitonic complexes and their recombination dynamics, power, polarization and time-dependent measurements were performed. Some lines saturate at high-power excitation, giving an indication for exciton-like behavior. Others have a super-linear intensity increase. Those lines might be biexcitionic. Most emission lines showed a strong linear polarization but with different polarization angles. That fact helps to assign the lines to different quantum dots. The presented time-resolved PL measurements might give additional informations about the origin of the observed emission lines. For some lines, the decay time is increased by a factor of 2 in respect to other lines, indicating biexcitionic behavior.

[en] We present a time- and temperature-resolved photoluminescence study of different carrier-phonon interactions in self-organized InAs/GaAs quantum dots (QD) under resonant excitation of the QD system. Resonant excitation leads to an enhancement of cross-sections of processes attributed to phonon interactions, like Raman scattering or hot-electron luminescence. Resonant PL techniques enable us to retrieve the energies of localized phonon modes. Time-resolved PL measurements allow us to differentiate between coherent and incoherent phonon-coupled processes. For the QD LO-phonon mode (34.6 meV), a very short radiative lifetime of under 30 ps is found, giving proof of the coherent character of the Raman scattering. In addition, temperature-dependent measurements are performed. Our results are compared with theoretical calculations.

[en] Small fluctuations in size, shape and composition of self-organized quantum dots (QDs) strongly effect the decay times of localized excitonic transitions. Here, we present time and spatially resolved photoluminesence measurements of single InGaN/GaN QDs. The sample is excited with the second harmonic of a modelocked and tuneable Ti:Sapphire laser through a metallic shadow mask, which improves the lateral resolution and allowing spectroscopy of single QDs. Using eight-band k.p modelling, we show that the built-in piezo- and pyroelectric fields within the QDs cause a sensitive dependence of the radiative lifetimes of the exact QD geometry and composition. Moreover, the radiative lifetimes also depend strongly on the composition of the direct surrounding of the QDs.

[en] A general trend and one of the important strategies in the automotive industry is reducing the lead time of a new car development. In order to obtain this goal the efficient use of simulation software is needed to effectively design a hydroformed part. The stages of the design chain are integrated in one simulation tool. The outcome of this feasibility analysis is a virtual prototype saying that it is possible to produce the part. In fact one process point has been defined whereas when going into production a process window must be know to guarantee a stable production process. In order to achieve this latter we are suggesting a process performance analysis. Based on multiple simulations the influence and sensitivity various process parameters on the forming process can be identified. Besides combining the analysis with statistical process control evaluation the process capability (Cpk-values) can be defined. This design chain analysis will be applied on a hydroformed part. The process performance analysis is the identification of the process window and process capability in advance, so before any tool has been milled. This will be demonstrated on a second hydroformed part

[en] In recent years, carrier-phonon interactions in semiconductor quantum dots have attracted considerable attention. They are important to understand the electronic properties of such systems, like carrier relaxation processes. Some are convinced that carriers confined in quantum dots are strongly coupled to the longitudinal optical (LO) vibrations of the semiconductor lattice. We report on exciton-phonon interactions in InGaAs/GaAs quantum dots. Photoluminescence and time-resolved experiments were performed on different MOCVD-grown InGaAs/GaAs samples to observe and investigate varying phonon interactions. In our measurements we observed photoluminescence peaks constantly shifting with varied excitation energy. The energy gap between the laser-peak and the observed two-peak structure remained unchanged. The ΔE-values of 33.8 meV and 36.9 meV precisely fit to the QD LO-Phonon mode and to the interface mode, respectively. The very short radiative lifetime also points to inelastically scattered phonons, i.e. Raman scattering

[en] Disseminated tumor cells (DTCs) can be detected using ultrasensitive immunocytochemical assays and their presence in the bone marrow can predict the subsequent occurrence of overt metastasis formation and metastatic relapse. Using expression profiling on early stage primary breast tumors, low IRX2 expression was previously shown to be associated with the presence of DTCs in the bone marrow, suggesting a possible role of IRX2 in the early steps of metastasis formation. The purpose of this study is to gain insights into the significance of IRX2 protein function in the progression of breast cancer. To assess the physiological relevance of IRX2 in breast cancer, we evaluated IRX2 expression in a large breast cancer cohort (n = 1992). Additionally, constitutive IRX2 over expression was established in BT-549 and Hs578T breast cancer cell lines. Subsequently we analyzed whether IRX2 overexpression effects chemokine secretion and cellular motility of these cells. Low IRX2 mRNA expression was found to correlate with high tumor grade, positive lymph node status, negative hormone receptor status, and basal type of primary breast tumors. Also in cell lines low IRX2 expression was associated with mainly basal breast cancer cell lines. The functional studies show that overexpression of the IRX2 transcription factor in basal cell lines suppressed secretion of the pro-metastatic chemokines and inhibited cellular motility but did not influence cell proliferation. Our results imply that the IRX2 transcription factor might represent a novel metastasis associated protein that acts as a negative regulator of cellular motility and as a repressor of chemokine expression. Loss of IRX2 expression could therefore contribute to early hematogenous dissemination of breast cancer by sustaining chemokine secretion and enabling mobilization of tumor cells. The online version of this article (doi:10.1186/s12885-015-1907-4) contains supplementary material, which is available to authorized users