Laser-induced chemical etching of silicon in NF3 atmosphere

Chemical etching of single-crystal Si in an NF₃ atmosphere is performed by continuous irradiation with an Ar⁺ laser at 514.5 nm. The etching process proves to be a thermally stimulated chemical reaction between solid Si and NF₃ gas. The experimental results show how the depth and width of the etched grooves depend on laser power, scan speed, and gas pressure. The etch rates observed may exceed 25 m/s.     

A combinatorial algorithm for calculating ligand binding

We consider the problem of predicting the mode of binding of a small molecule to a receptor site on a protein. One plausible approach, given a rigid molecule and its geometry, is to search directly for the orientation in space that maximizes the degree of contact. The computation time required for such a naive procedure is proportional to n³m³, where n is the number of points in the site where binding can occur, and m is the number of atoms in the ligand. We give an alternative, combinatorial approach, in which only “contact–no-contact” criteria are considered. We relate this problem to the well-known combinatorial problem of finding cliques in a graph and show that we can use a solution to the clique problem not only to solve our original problem, but also the problem of avoiding energetically unfavorable matches. Our experience with this method indicates that the computation time required is proportional to nm^2.8, with a lower constant of proportionality than that of the naive procedure.     

Neue ternäre Käfigverbindungen aus den Systemen Barium–Indium/Zink/Cadmium–Germanium: Zintl-Verbindungen mit Phasenbreite?

New Ternary Clathrate Compounds in the Systems Barium–Indium/Zinc/Cadmium–Germanium: Zintl Compounds with Phase Width? By systematic investigations in the systems barium–indium/zinc/cadmium–germanium we found a couple of new electrovalent ternary compounds with A₈X₄₆ clathrate (I) type structures. They crystallize cubically in space-group Pm3n. For Ba₈In₁₆Ge₃₀ (a = 1 075.8 pm), Ba₈Zn₈Ge₃₈ (a = 1 082.0 pm) and Ba₈Cd₈Ge₃₈ (a = 1 096.0 pm) the structures were verified by X-ray single crystal diffraction data. According to valence and bounding distances the new clathrates should be Zintl compounds. Measurements of the temperature dependence of the electrical resistivity proved, that they are indeed semiconductors. A part of the 2B/3B metal atoms can be substituted by germanium. Charge balance will be retained by creation of vacancies in the A₈X₄₆ type structures. By phase analysis the limits of the composition range were determined as Ba₈In₄Ge₉[]₃Ge₃₀ (a = 1 084.9 pm), Ba₈Zn₄Ge₁₀[]₂Ge₃₀ (a = 1 073.6 pm) and Ba₈Cd₄Ge₁₀[]₂Ge₃₀ (a = 1 082.0 pm).     

Thickness and refractive index of DPPC and DPPE monolayers by multiple-beam interferometry

The thickness and refractive index of 1,2-dipalmitoyl-sn-glycero-3-phosphatidyl choline (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) monolayers Langmuir--Blodgett (LB) deposited on mica were measured in dry air and bulk water using multiple-beam interferometry (MBI). Measurements of thickness using atomic force microscopy (AFM) of identical monolayers, and X-ray reflectivity (XRR) of the monolayers on quartz were taken for comparison. The measurement of the properties of solid-supported monolayers in dry air allows lipid optical properties to be determined free from solvent effects. The thickness and refractive index measured by MBI were 25.5?±?0.6 Å and 1.485?±?0.007 for DPPE monolayers, and 23.9?±?0.5 Å and 1.478?±?0.006 for DPPC monolayers in dry air. These thicknesses are consistent with the other techniques used in this work as well as other measurements in the literature. The refractive indices of solid-supported lipid monolayers have not been previously measured. The values are higher than previous measurements on black lipid films done by reflectometry, which is attributed to increased lipid packing density and the absence of hydrocarbon solvents. Applying water to the monolayers had no measurable effect on their properties, indicating that any change in hydration was below detection.

Technological properties of CSK-1 crystallizer for material research in space

The crystallizer CSK-1 is based on a tubular furnace with five heating elements. The crystallizer operates in an automatic mode, i.e., the setting up of the temperature fields, setting of the sample position in the tube and of the rate and direction of their movement are controlled by a microprocessor running according to a program stored on a magnetic tape. The crystallizer is placed on the Soviet Orbital Laboratory “MIR”. Basic technological properties of the crystallizer were studied by means of an standard probe connected with a computer and of the special ARP device, respectively. The topic of the study was especially the creation of various types of axial temperature fields and of various temperature gradients, the rate of heating and spontaneous cooling of the furnace, the temperature stability, and so on.