Dynamic roughening of tetrahedral amorphous carbon

The roughness of tetrahedral amorphous carbon (ta-C) films grown at room temperature is measured as a function of film thickness by atomic force microscopy, to extract roughness and growth exponents of alpha approximately 0.39 and beta approximately 0-0.1, respectively. This extremely small growth exponent shows that some form of surface diffusion and relaxation operates at a homologous temperature of 0.07, much lower than in any other material. This is accounted for by a Monte Carlo simulation, which assumes a smoothening during a thermal spike, following energetic ion deposition. The low roughness allows ta-C to be used as an ultrathin protective coating on magnetic disk storage systems with approximately 1 Tbit/in.(2) storage density.     

Scalable silicon nanowire photodetectors

This paper presents photodetectors having vertically stacked electrodes with sub-micron (300 nm) separation based on silicon nanowire (SiNW) nanocomposites. The thin-film-like devices are made using standard photolithography instead of electron beam lithography and thus are amenable to scalable low-cost manufacturing. The processing technique is not limited to SiNWs and can be extended to different nanowires (NWs) (e.g., ZnO, CdSe) and substrates. The current–voltage characteristics show Schottky behaviour that is dependent on the properties of the contact metal and that of the pristine SiNWs. This makes these devices suitable for examination of electronic transport in SiNWs. Preliminary results for light sensitivity show promising photoresponse that is a function of effective NW density.     

Grain boundary impurity segregation and neutron irradiation effects in ferritic alloys

Segregation of alloying and impurity elements to grain boundaries in ferritic steels and alloys is known to modify the mechanical properties. This paper considers segregation of such elements, in particular phosphorus and carbon, that occur in ferritic nuclear pressure vessel steels subject to neutron irradiation and temperature typical of that encountered in service. Models are presented that allow the prediction of equilibrium and non-equilibrium segregation of phosphorus to grain boundaries and also take into account synergistic interaction with carbon under various combinations of neutron-irradiation temperature. These are related to a wide range of experimental observations compiled from data in the literature for mainly phosphorus and carbon measured at grain boundaries in neutron-irradiated ferritic vessel steels and alloys. The predictions from the segregation models are compared with these experimental data. The discussion provides a rationalization for the apparent variability in the measured grain boundary phosphorus compositions and thereby fracture susceptibility for various nuclear pressure vessel ferritic steels.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

Interfacial immobilization of monoclonal antibody and detection of human prostate-specific antigen

Antibody orientation and its antigen binding efficiency at interface are of particular interest in many immunoassays and biosensor applications. In this paper, spectroscopic ellipsometry (SE), neutron reflection (NR), and dual polarization interferometry (DPI) have been used to investigate interfacial assembly of the antibody [mouse monoclonal anti-human prostate-specific antigen (anti-hPSA)] at the silicon oxide/water interface and subsequent antigen binding. It was found that the mass density of antibody adsorbed at the interface increased with solution concentration and adsorption time while the antigen binding efficiency showed a steady decline with increasing antibody amount at the interface over the concentration range studied. The amount of antigen bound to the interfacial immobilized antibody reached a maximum when the surface-adsorbed amount of antibody was around 1.5 mg/m(2). This phenomenon is well interpreted by the interfacial structural packing or crowding. NR revealed that the Y-shaped antibody laid flat on the interface at low surface mass density with a thickness around 40 ?, equivalent to the short axial length of the antibody molecule. The loose packing of the antibody within this range resulted in better antigen binding efficiency, while the subsequent increase of surface-adsorbed amount led to the crowding or overlapping of antibody fragments, hence reducing the antigen binding due to the steric hindrance. In situ studies of antigen binding by both NR and DPI demonstrated that the antigen inserted into the antibody layer rather than forming an additional layer on the top. Stability assaying revealed that the antibody immobilized at the silica surface remained stable and active over the monitoring period of 4 months. These results are useful in forming a general understanding of antibody interfacial behavior and particularly relevant to the control of their activity and stability in biosensor development.