Thin tantalum pentoxide films deposited by photo-induced chemical vapor deposition using an injection liquid source

We report the growth of thin tantalum pentoxide films on Si (100) by ultraviolet-assisted injection liquid source (UVILS) chemical vapor deposition (CVD) at low temperatures (200-350 °C). This new technique combines the intense radiation from an excimer lamp (5=222 nm) with a novel injection liquid source capable of delivering precisely controllable quantities of a liquid metalorganic precursor into the CVD chamber. The composition and optical properties of the oxides were determined using a variety of standard characterization methods. After optimization of the deposition parameters, the best layers were incorporated into simple MOS test structures to enable electrical characterization. Refractive index values of 2.09ǂ.07, fixed oxide charge content of <5᎒¹⁰ cm^-2, breakdown fields higher than 2 MV/cm and dielectric constant values of 18-24 were readily achievable in the as-deposited films. These properties compare favorably with those for layers prepared by conventional thermal-CVD at significantly higher temperatures of 500 °C.     

Covalent attachment of acetylene and methylacetylene functionality to Si(111) surfaces: scaffolds for organic surface functionalization while retaining Si-C passivation of Si(111) surface sites

Si(111) surfaces have been functionalized with Si-CC-R species, where R = H or -CH3, using a two-step reaction sequence involving chlorination of H-Si(111) followed by treatment with Na-CC-H or CH3-CC-Na reagents. The resulting surfaces showed no detectable oxidation as evidenced by X-ray photoelectron spectroscopic (XPS) data in the Si 2p region, electrochemical measurements of Si-H oxidation, or infrared spectroscopy. The Si-CC-R-terminated surfaces exhibited a characteristic CC stretch in the infrared at 2179 cm-1, which was strongly polarized perpendicular to the Si(111) surface plane. XPS measurements in the C 1s region showed a low binding energy peak indicative of Si-C bonding, with a coverage that was, within experimental error, identical to that of the CH3-terminated Si(111) surface, which has been shown to fully terminate the Si atop sites on an unreconstructed Si(111) surface. The Si-CC-H-terminated surfaces were further functionalized by exposure to n-C4H9Li followed by exposure to para Br-C6H5-CF3, allowing for introduction of para -C6H5CF3 groups while maintaining the desirable chemical and electrical properties that accompany complete Si-C termination of the atop sites on the Si(111) surface.     

Steroidal ureas as enantioselective receptors for an N-acetyl alpha-amino carboxylate

[reaction: see text] Cholic acid has been elaborated into three regioisomeric bis-carbamoylureas, which have been investigated as enantioselective receptors for N-acetyl phenylalanine. L/D selectivities, peaking at 5:1, have been determined by a sensitive and rapid MS-based extraction method that should be generalizable to related systems.     

Connected components of attractors and other stable sets

Summary We study the action of a continuous mapf on a locally connected metric space, with an emphasis on the action induced byf on the space of connected components of an attractorA or a stable setY off. The main result for attractors is that, ifA is an attractor in the sense of C. Conley, thenf permutes the components ofA and that the permutation is cyclic if and only if the attractor is indecomposable. This is related to similar results obtained recently by Buescu and Stewart. In the case of an indecomposable stable invariant setY we show that either the action off on the components ofY is as described above for the action on the attractor, or elseY has infinitely many components, the action off on them is a generalized adding machine, so that there are no periodic points inY. Results along these lines are due to Buescu and Stewart and to Melbourne, Dellnitz and Golubitsky.     

Resolution of matrix effects on analysis of total and methyl mercury in aqueous samples from the Florida Everglades

 Aqueous samples from the Florida Everglades present several problems for the analysis of total mercury (HgT) and methyl mercury (MeHg). Constituents such as dissolved organic carbon (DOC) and sulfide at selected sites present particular challenges due to interferences with standard analytical techniques. This is manifested by 1) the inability to discern when bromine monochloride (BrCl) addition is sufficient for sample oxidation for HgT analysis; and 2) incomplete spike recoveries using the distillation/ethylation technique for MeHg analysis. Here, we suggest ultra-violet (UV) oxidation prior to addition of BrCl to ensure total oxidation of DOC prior to HgT analysis and copper sulfate (CuSO₄) addition to aid in distillation in the presence of sulfide for MeHg analysis. Despite high chloride (Cl^-) levels, we observed no effects on MeHg distillation/ethylation analyses. Received: 24 September 1996/Revised: 12 February 1997/Accepted: 19 February 1997     

A geometrical framework for dyons in the presence of the dilaton and the axion in four dimensions

The action of the bosonic sector of the effective field theory induced by heterotic strings in four dimensions, which is relevant (for instance) to the study of dyons (Shapere et al. in Mod Phys Lett A6: 2677, 1991), is re-interpreted geometrically by using the new concept of ‘D-Differentiation’. This extends the authors’ geometrical unification of the Einstein–Maxwell theory.