Daniel M Schaadt

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Surface plasmon resonances in metallic nanoparticles are of interest for a variety of applications due to the large electromagnetic field enhancement that occurs in the vicinity of the metal surface, and the dependence of the resonance wavelength on the nanoparticle's size, shape, and local dielectric environment. Here we report an engineered enhancement of(More)
Sub-wavelength photonic structures and nanoscale materials have the potential to greatly improve the efficiencies of solar cells by enabling maximum absorption of sunlight. Semiconductor heterostructures provide versatile opportunities for improving absorption of infrared radiation in photovoltaic devices, which accounts for half of the power in the solar(More)
Scanning force microscopy was used to study localized charge deposition and subsequent transport in Co nanoclusters embedded in SiO 2 deposited on an n-type Si substrate. Co nanoclusters were charged by applying a bias voltage pulse between tip and sample, and electrostatic force microscopy was used to image charged areas, to determine quantitatively the(More)
In this study, we investigated pre-structured (100) GaAs sample surfaces with respect to subsequent site-selective quantum dot growth. Defects occurring in the GaAs buffer layer grown after pre-structuring are attributed to insufficient cleaning of the samples prior to regrowth. Successive cleaning steps were analyzed and optimized. A UV-ozone cleaning is(More)
A portable synchrotron molecular beam epitaxy (MBE) system is designed and applied for in situ investigations. The growth chamber is equipped with all the standard MBE components such as effusion cells with shutters, main shutter, cooling shroud, manipulator, reflection high energy electron diffraction setup, and pressure gauges. The characteristic feature(More)
: The number of quantum dots which nucleate at a certain place has to be controllable for device integration. It was shown that the number of quantum dots per nucleation site depends on the size of the hole in the substrate, but other dimensions of the nucleation site are vague. We report on the influence of hole shape on site-selectively grown InAs quantum(More)
High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) images of electron-transparent samples show dominant atomic number (Z-) contrast with a high lateral resolution. HAADF STEM at low electron energies <30 keV is applied in this work for quantitative composition analyses of InGaAs quantum wells. To determine the local(More)
We have investigated the structure of non-polar GaN, both on the M - and A-plane, grown on LiGaO2 by plasma-assisted molecular beam epitaxy. The epitaxial relationship and the microstructure of the GaN films are investigated by transmission electron microscopy (TEM). The already reported epi-taxial relationship and for M -plane GaN is confirmed. The main(More)
We investigated segregation of indium in an InxGa1-xAs/GaAs heterostructure via high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), where contrast strongly depends on the nuclear charges of the scattering atoms (Z-contrast). Indium concentration maps have been deduced from HAADF-STEM images by comparing normalized measured(More)
A new measure to enhance the performance of InAs quantum dot solar cell is proposed and measured. One monolayer AlAs is deposited on top of InAs quantum dots (QDs) in multistack solar cells. The devices were fabricated by molecular beam epitaxy. In situ annealing was intended to tune the QD density. A set of four samples were compared: InAs QDs without in(More)
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