To discuss the concentration dependence of coupled mode-frequencies in systems like solid solutions K(H1-xDx2PO4 we present a RPA theory for an extended Kobayashi model including anharmonic phonons. Using a consistent structure averaging we analyse particular the effect of phonon fluctuations.
A series of ZnSe/GaAs(001) samples grown with various epilayer thicknesses from 50 to 1800 nm is investigated to study the role of polar misfit dislocations in respect of their nucleation and propagation behavior in the process of layer strain relaxation. Photoluminescence spectroscopy and SEM cathodoluminescence, both applied at low temperatures, are exploited to investigate misfit dislocation configurations and related stress relief in the ZnSe epilayers. Expected effects concerning the asymmetry in the dislocation misfit arrangements and optical anisotropy could be proved and analyzed in the framework of a modified Dodson-Tsao-Model.
In order to obtain high reflectance of EUV and X-ray multilayer mirrors, highly polished substrate surfaces with rms roughness σrms = 0,1-0.2 nm are necessary. However, the simultaneous achievement of low micro-roughness and precise surface figure is very challenging and often not accomplished. Therefore deposition techniques capable to deposit layers with smoothing properties are very desirable. One potential method that enables the formation of such layers is the pulsed laser deposition (PLD). This technique generates particles with high kinetic energies of up to several 100 eV. We investigated the deposition of carbon based smoothing layers by PLD on numerous substrates with roughness between σrms = 0.15 and 0.75 nm using different laser power densities and film thicknesses. Besides pure carbon layers we also used metal/carbon (metal = Ni, W, Pt) multilayers with respect to their capabilities to smooth surface roughness. As a general trend it turns out that a better smoothing can be obtained with higher laser power densities, whereby diamond-like carbon films are created. Furthermore, the intrinsic stress of the smoothing layers has been investigated. Due to the high kinetic energy of the impinging particles during the film growth, the layers show compressive stress. The degree of the stress depends on the concrete metal that is combined with carbon in the multilayer stack. Up to now the lowest compressive stress is obtained with Ni/C multilayers.
Mass production in microelectronics and solar cell industry poses a problem of creating cheap and fast sensors being able to perform on-line quality testing of semiconductor wafers and bulk dielectric components in fab conditions. A challenging task is to determine areas of residual stress and associated high density of dislocation and microcracks in large format (up to 30 x 30 mm) but ultra-thin (less than 0.32 mm) polycrystalline Si wafers. In addition to microwave and ultrasound inspection methods, which only partially address the problem, the optical polarization heterodyne interferometry seems to be a promising solution. The method exploits the fact that the residual stress within silica wafer induces the anisotropy (birefringence) of the optical properties of the material due to the photo-elastic effect. The birefringence, in turn, can be evaluated by registering the phase difference between two orthogonally polarized waves passing through or reflecting off the wafer. Recently, the feasibility of polariscopy method was discussed for stress detection in Si, which exploits similar physical principles. These approaches determine depolarization analyzing the beam intensity for different polarization orientation. However, especially solar cell wafers have rough surfaces and hence a polarization dependent modification of the beam intensity will be observed. Hence the birefringence information will be masked by the surface effect. In this contribution we propose an alternative implementation of the polarization interferometry, where the birefringence phase shift of two beams with a polarization perpendicular to each other is measured directly independent on the intensity of both beams. The developed testing system provides a number of advantages over the polariscopy, in particular, the absence of mechanical movement of components, larger field of view, better accuracy for depolarizing non-polished wafers, and much higher operating rates. With the help of an industrial demonstrator it was able to analyse the mechanical stress state of a solar cell of 160x160 mm² in transmission as well as in reflection in less than 1 s with a resolution less than 80 µm.
State of the art X-ray imaging sensors comprise a trade-off between the achievable efficiency and the spatial resolution. To overcome such limitations, the use of structured and scintillator filled aluminum oxide (AlOx) matrices has been investigated. We used Monte-Carlo (MC) X-ray simulations to determine the X-ray imaging quality of these AlOx matrices. Important factors which influence the behavior of the matrices are: filling factor (surface ratio between channels and `closed` AlOx), channel diameter, aspect ratio, filling material etc. Therefore we modeled the porous AlOx matrix in several different ways with the MC X-ray simulation tool ROSI [1] and evaluated its properties to investigate the achievable performance at different X-ray spectra, with different filling materials (i.e. scintillators) and varying channel height and pixel readout. In this paper we focus on the quantum efficiency, the spatial resolution and image homogeneity.
Abstract Predictions of a mode-coupling approximation (MCA) are compared with molecular dynamics simulations of d=1,2 Φ-lattice systems with different next neighbour interaction strengths. In the long-time behaviour we find complete disagreement for weak coupling, whereas some predictions of MCA are qualitatively verified in the strong coupling case for d=1.
