Aggregate States and Energetic Disorder in Highly Ordered Nanostructures of para‐Sexiphenyl Grown by Hot Wall Epitaxy

We report on photoluminescence (PL) and thermally stimulated luminescence (TSL) in highly ordered nanostructures of para‐sexiphenyl (PSP) grown by hot wall epitaxy (HWE). A low‐energy broad band is observed in the PL spectra that can be attributed to the emission from molecular aggregates. While the intrinsic exciton emission in steady‐state PL dominates at low temperatures, the emission from aggregates increases with elevating temperature and its magnitude depends sensitively on film preparation conditions. Time‐resolved PL measurements showed that the aggregate emission decays with a life‐time of ≈ 4 ns, which is approximately an order of magnitude larger than the lifetime of singlet excitons. TSL data suggests the presence of an energetically disordered distribution of localized states for charge carriers in PSP films, which results from an intrinsic disorder in this material. A low‐temperature TSL peak with the maximum at around 30 K evidences for a weak energy disorder in PSP films, and has been interpreted in terms of a hopping model of TSL in disordered organic materials.     

Operational transfer path analysis

One of the tools used to study the NVH behaviour of a system is the transfer path analysis. It aims to identify the operational forces and the propagation paths of the vibrations and is especially interesting in the case when the system is composed of different subsystems. The classical techniques identify the transfer paths when the system is disassembled. This way one eliminates flanking transfer paths. Yet it is very time-consuming and the boundary conditions are not correct anymore. The presented method makes it possible to identify the transfer paths without disassembling the system. The advantages are that the overall testing time is reduced and that the real boundary conditions are present. In this article the theory will be reviewed and it will be validated using data generated by finite element simulations.     

Feasibility of MRI in the diagnosis of acute diverticulitis: initial results

Purpose: The purpose of this study was to evaluate MRI as a diagnostic tool in patients with suspected acute sigmoid diverticulitis. Furthermore, we sought to develop an optimal imaging protocol in these patients.Patients and methods: Eleven patients with suspected acute diverticulitis were included in the study. All patients were imaged in a 1.0 T clinical scanner using a body-array coil. Imaging sequences were single-shot TSE, HASTE-, STIR- and TrueFisp-sequence. All were obtained in the frontal plane. The diagnosis was verified by a single experienced investigator, using ultrasound, and overall clinicopathological outcome.Results: MRI enabled visualization of signs of an acute diverticulitis in all patients. However, the diagnosis of acute diverticulitis was obtained in 10 patients only. The mean imaging time was 17.5 ± 5.5 min. STIR- and TrueFisp-sequences alone displayed all findings, e.g pericolonic exsudation, edema and segmental narrowing, whereas SSTSE and HASTE-sequences showed no additional information. Therefore, it appeared that the imaging protocol could be restricted to STIR- and TrueFisp-sequences.Conclusion: MRI is feasible as a fast, accurate and investigator-independent diagnostic tool in patients with suspected acute diverticulitis. To prove its value in comparison to computed tomography or ultrasound, further studies are needed.     

Search for a wetting layer in thin film growth of para-hexaphenyl on KCl(001)

The non-existence of a strongly bound wetting layer for the system para-hexaphenyl (6P)-KCl(001) was verified by thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS). The 6P films were grown by physical vapour deposition under ultrahigh vacuum conditions at 400 K. TDS showed just a single desorption peak even down to a coverage of 0.1 nm mean film thickness. The heat of evaporation for 6P was determined to 2.3 eV. From the change of the XPS K2p substrate signal as a function of the mean film thickness one can conclude that a strong de-wetting exists at the very beginning of the 6P layer growth at 400 K. Additional investigations with atomic force microscopy reveal that at this initial stage the film grows in a form of needle like islands with a high aspect ratio and subsequently terraced mounds of 6P are formed. No dissociation of 6P on KCl was observed.     

Zerstörungsfreie Messung dünner Schichten mit polarisationsoptischen Methoden

Two methods, Spectroscopic Ellipsometry and Reflectance Difference Spectroscopy, are presented, which give essential and basic information on surface processes of semiconductors, currently investigated by scientific research. Industrial applications of these methods are presented for the characterization of thin films. These methods are not restricted to semiconductors but are also successfully applied to polymer thin films and hardcoatings of metals, like titanium-nitride.     

Effects of hemodialysis on circulating adrenomedullin concentrations in patients with end-stage renal disease

PURPOSE: A homogeneous dose distribution according to the demands of the ICRU-publication 50 often can only be achieved by the use of compensators. Because of the expense those are seldom applied. The purpose of this work is to find practical methods for the production and verification. MATERIAL AND METHODS: Two procedures for the production of compensators using 3 different materials and suitable dose verification methods were investigated. The first procedure uses a laser system to get the patient contour, from which the compensator can be calculated. In a second method a 3D planning system calculates the dose modulators on the basis of CT-slices. The production is done by the use of a computer driven milling machine either via a founding form or direct milling. Mixtures of a polymer and lead powder, a mixture of tin granules and wax and the commercially available alloy MCP-96 were used. Dose verification was done using film-, TL- and the three-dimensional MR Fricke gel dosimetry as well as a diode array scanner. RESULTS: Though both methods can be used, the CT-based procedure proved to be more appropriate. Among the materials the direct milled MCP-96 compensator is favorable with respect to the handling, mechanical properties and inhomogeneous radiation attenuation. The dose verification has been done in an Alderson phantom for mantlefield and head-and-neck irradiation techniques. Here the dose modulation yielded an improvement of the homogeneity. The dose maxima normalized to the dose reference point could be reduced from 127% to 103% respectively 122% to 104%. Verifications of compensators for patient treatments confirmed the good results from the phantom measurements. CONCLUSION: The demonstrated investigations show a practicable way for the clinical application of compensators. The necessity for the use of them can be derived from the verified decrease of the dose maxima.     

An electrooptic and optoelectric bistable interconnect at 514 nm:the photothermal CdS self-electrooptic effect devices

Illumination of CdS at room temperature with the green (514 nm) line of an Ar⁺ laser may lead to intrinsic photothermal-induced absorption optical bistability. If the samples are covered with two metal contacts resulting in a small slit, the additional feedback introduced through the photocurrent by Joule's heat may lead to a reduction of the necessary optical input power. In particular, CdS single-crystal platelets, CdS epitaxial layers, or CdS evaporated layers contacted with either Au or In are used. The experimental characteristics are compared with detailed model calculations, which explain deviations from ideal behavior. Special emphasis is laid upon the modulator characteristics (i.e. controlling photonics by electronics) and the possibility of controlling electronics by photonics     

Modification of para-sexiphenyl layer growth by UV induced polarity changes of polymeric substrates

We report on the deposition of para-sexiphenyl (PSP) on poly(diphenyl bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate) (PPNB) by hot wall epitaxy (HWE). The surface polarity of the substrate, PPNB, can be increased by UV-illumination via a photo-Fries rearrangement. The influence of the changed surface polarity on the surface morphology and the structure of the PSP layers were studied by atomic force microscopy (AFM), X-ray diffraction (XRD) and grazing incidence X-ray diffraction (GIXD). The observation of growth spirals and islands, providing mono-layer step heights of standing PSP molecules, underline a high crystallographic order of the films which is confirmed by XRD analysis. GIXD experiments show a strong preferential (0 0 1) orientation of the PSP layers with better alignment on substrates with smaller surface polarity. The γ- and Baker-crystal structures are present in the films grown at low substrate temperatures, but only Baker structure was found in the films deposited at high substrate temperatures. However the main influence on the growth of PSP, is caused by the polarity change induced by pre-treating the PPNB substrate by UV-illumination.     

Coherent imaging with two-dimensional focal-plane arrays: design and applications

Scanned, single-channel optical heterodyne detection has been used in a variety of lidar applications from ranging and velocity measurements to differential absorption spectroscopy. We describe the design of a coherent camera system that is based on a two-dimensional staring array of heterodyne receivers for coherent imaging applications. Experimental results with a single HgCdTe detector translated in the image plane to form a synthetic two-dimensional array demonstrate the ability to obtain passive heterodyne images of chemical vapor plumes that are invisible to normal video infrared cameras. We describe active heterodyne imaging experiments with use of focal-plane arrays that yield hard-body Doppler lidar images and also demonstrate spatial averaging to reduce speckle effects in static coherent images.