Pulse laser acoustics for the characterization of inhomogeneities at interfaces of microstructures

Interfaces between neighbouring materials are often subjected to diffusion processes which cause layers having gradually varying mechanical properties--like densities, Young's moduli or shear moduli--perpendicular to the surface or interface. In this investigation particular interest is drawn on the question how the propagation characteristics of bulk acoustic waves are affected by diffusion layers. The reflection and transmission behavior of bulk acoustic waves encountering a continuum having a spatially dependent sound velocity is discussed based on numerical simulations as well as on experimental verifications. The simulated results are part of an on-going project in which material properties of MEMS devices are investigated by short pulse laser acoustic methods. Mechanical waves are excited and detected thermoelastically using laser pulses of 70 fs duration. For metals this leads to wavelengths of 10-20 nm and the corresponding frequencies amount to 0.3-0.6 THz. In contrast to previous work done in this field in which diffusion effects are generally considered as undesirable phenomena, the deliberate realization of microstructures having well defined gradually varying material properties in one or more dimensions represents a goal of this investigation. For metallic thin film multilayers thermally induced diffusion processes have shown to be an easy and reliable technique for the realization of layered structures having continuously varying mechanical properties within several 10 nm. Among the experimental methods suitable for the in-depth profiling of submicron metallic thin films providing resolutions of several nanometers, are short pulse laser acoustic methods, Rutherford backscattering spectroscopy (RBS), and glow discharge optical emission spectroscopy (GDOES). Short pulse laser acoustic methods and RBS have the advantage to be nondestructive. The short pulse laser acoustic method is described in detail and RBS measurements are presented for verification purposes. Finally potential engineering applications like micro-machined spectrum analyzers, acoustic isolation layers, and band pass filters, operating at very high frequencies are presented.     

Ferromagnetism and metal-insulator transition in the disordered Hubbard model

A detailed study of the paramagnetic to ferromagnetic phase transition in the one-band Hubbard model in the presence of binary-alloy disorder is presented. The influence of the disorder (with concentrations x and 1-x of the two alloy ions) on the Curie temperature T(c) is found to depend strongly on electron density n. While at high densities, n>x, the disorder always reduces T(c); at low densities, n相似文献   

The 'apparent' hydrolysis of alkyl esters during electrospray ionization

Electrospray ionization (ESI) mass spectrometry was employed to obtain both molecular weight confirmation and structural information for a series of novel alkenyldiarylmethane (ADAM) analogs. The mass spectral data were intended for use during the structure elucidation of ester hydrolysis products formed during an in vitro metabolism study of a series of novel ADAM analogs. The data on the precursor molecules show the presence of the molecular ion peak, [M+H](+), as well as a peak consistent with the hydrolysis product of the original ester ([MH-ROH+H(2)O](+)). However, chemical ionization mass spectrometry, elemental analysis and (1)H NMR data indicated the presence of only the intact diester compounds, suggesting that the formation of the hydrolysis product was an instrumental artifact, i.e., in-beam hydrolysis during ESI or a result of longer ion residence times of the ion trap mass analyzer.     

N-(17-Acyloxy-acyl)-glutamines: novel surfactants from oral secretions of lepidopteran larvae

N-(17-Acyloxy-acyl)-glutamine conjugates such as N-(17-linolenoyloxy-linolenoyl)-glutamine (6), N-(17-linolenoyloxy-linoleoyl)-glutamine (7), N-(17-linoleoyloxy-linolenoyl)-glutamine (8), and N-(17-linoleoyloxy-linoleoyl)-glutamine (9) were identified as novel surfactants in the oral secretion of several lepidopteran larvae (S. exigua, S. littoralis, S. frugiperda, and H. virescens) by LC-MS/MS and chemical degradation. Authentic reference compounds were synthesized via a dissymmetric bis-Wittig approach and confirmed the assigned structures.     

Morphology of Electropolymerized Poly(N-Methylaniline) Films

The influence of polymerization conditions on the morphology of thin films of poly-(N-methylaniline) (PNMA) was studied. The films were prepared by electropolymerization on gold and platinum electrodes and studied by optical and electron microscopy. It was demonstrated that the film morphology does not depend on the polymerization rate or on the electrode metal. However, it is sensitive to the kind of counter ion of PNMA. The polymers containing acetate or chloride do not form stable films. Polymer films containing phosphate or sulfate display inhomogeneous structures. A formation of sprouts and nanotubes was observed for PNMA sulfate. The films formed by PNMA perchlorate are smooth and transparent (glass-like structure). A sublayer of 4-aminothiophenol increases the adhesion of polymers to the gold surface.     

Modular diphosphine ligands based on bisphenol A backbones

A straightforward two-step synthesis is used to obtain new phosphorus-containing ligands based on readily available bisphenol A type backbones. Five diphosphine ligands have been prepared in good yields. An X-ray crystallographic study is presented for ligand 5. Preliminary results on rhodium-catalyzed hydroformylation exemplify the use of these ligands for homogeneous catalysis.