Indications of field-directing and self-templating effects on the formation of organic lines on silicon

It has previously been shown that multimolecular organic nanostructures form on H-Si(100)-2×1 via a radical mediated growth process. In this mechanism, growth begins through the addition of a molecule to a silicon surface dangling bond, followed by the abstraction of a neighboring H atom and generation of a new dangling bond on the neighboring site. Nanostructures formed by this mechanism grow along one edge of a dimer row. Here, we explored the possibility of using lithographically prepared, biased metal contacts on the silicon surface to generate an electric field that orients molecules during the growth process to achieve growth in the perpendicular-to-row direction. The formation of some nanostructures in a direction that was nearly perpendicular to the dimer rows was achieved, whereas such features were not formed in the absence of the field. Analysis of the scanning tunneling microscopy images suggests that the formation of these nanostructures may involve self-templating effects in addition to dangling bond diffusion rather than a straightforward addition∕abstraction mechanism. These initial results offer some indication that a molecular pattern writer can be achieved.     

A simple and accurate approach for calculating the vibration spectra of molecules on surfaces: Comparisons to high resolution electron energy loss data for ethylene on silicon

Peak assignment is a complex but important task for analyzing the vibration spectra of surface-bound molecules. Here we describe a simple approach for calculating infrared and Raman spectra for surface-bound molecules using a cluster model approach with quantum capping potentials (QCPs). The utility of the approach is demonstrated by comparisons to the measured high resolution electron energy loss spectra for ethylene on clean silicon. By capping the silicon cluster with QCPs we computed spectra that agree very well with the HREEL spectrum, allowing us to easily assign the experimental peaks. QCPs are similar to effective core potentials, can be used with any ab initio technique and most computational chemistry packages, and their use requires no special expertise.     

Linear nanostructure formation of aldehydes by self-directed growth on hydrogen-terminated silicon(100)

The self-directed growth of organic molecules on silicon surfaces allows for the rapid, parallel production of hybrid organic-silicon nanostructures. In this work, the formation of benzaldehyde- and acetaldehyde-derived nanostructures on hydrogen-terminated H-Si(100)-2x1 surface is studied by scanning tunneling microscopy in ultrahigh vacuum and by quantum mechanical methods. The reaction is a radical-mediated process that binds the aldehydes, through a strong Si-O covalent bond, to the surface. The aldehyde nanostructures are generally composed of double lines of molecules. Two mechanisms that lead to double line growth are elucidated.     

Synthesis of N-Fmoc-O- (N'-Boc-N'-methyl)-aminohomoserine,an amino acid for the facile preparation of neoglycopeptides

The synthesis of N-Fmoc-O-(N'-Boc-N'-methyl)-aminohomoserine in 35% overall yield from l-homoserine is described. This amino acid can be efficiently incorporated into peptides using Fmoc-chemistry-based solid-phase peptide synthesis, and the resulting peptides can be chemoselectively glycosylated at the aminooxy side chains to generate neoglycopeptides. The synthesis of this derivative greatly expands the availability of a previously developed neoglycopeptide synthesis strategy.     

Regio- and diastereoselectivity of the cycloaddition of aldonitrones with benzylidenecyclopropane: An experimental and theoretical study

1,3-Dipolar cycloaddition of benzylidenecyclopropane with various aldonitrones proceeds regioselectively giving good yields of 4-spirocyclopropane isoxazolidines. In the case of aldonitrones, bearing carbamoyl- or aryl-groups on the carbon atom, only the cis-isomer is formed. The compounds synthesized were tested for their virus-inhibiting activity.     

New data on protonation and hydration of perovskite-type layered oxide KCa2Nb3O10

Journal of Thermal Analysis and Calorimetry - Protonation and hydration processes of layered perovskite-like oxide KCa2Nb3O10 during the reaction with nitric acid solutions with different...     

Theoretical and spectroscopic study of the reaction of diethylhydroxylamine on silicon(100)-2 x 1

Incorporating diversity into structures constructed from the organic modification of silicon surfaces requires the use of molecules that contain multiple substituents of different types. In this work we examine the possible dissociation pathways of diethylhydroxylamine (DEHA, (C(2)H(5))(2)NOH) on the surface of clean silicon(100)-2x1 using cluster and planewave computational methods and high resolution electron energy loss spectroscopy. Our computational results show that DEHA initially forms a strongly-bound complex with the surface via a dative N-Si bond. A low-barrier O-H bond scission then occurs yielding a surface silicon dimer capped by the (C(2)H(5))(2)NO and H fragments. Calculated and measured vibrational spectra support the computed reaction mechanism.