Biomedical subjects

J N Crain

Publications and source records attributed to J N Crain.

4 recordsLinked to original sources

PubMed2006

Electronic effects in the length distribution of atom chains.

Gold deposited on Si(553) leads to self-assembly of atomic chains, which are broken into finite segments by defects. Scanning tunneling microscopy is used to investigate the distribution of chain lengths and the correlation between defects separating the chains. The length distribution reveals oscillations that indicate changes in the cohesive energy as a function of chain length. We present a possible interpretation in terms of the electronic scattering vectors at the Fermi surface of the surface states. The pairwise correlation function between defects shows long-range correlations that extend beyond nearest-neighbor defects, indicating coupling between chains.

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PubMed2005

End states in one-dimensional atom chains.

End states--the zero-dimensional analogs of the two-dimensional states that occur at a crystal surface--were observed at the ends of one-dimensional atom chains that were self-assembled by depositing gold on the vicinal Si(553) surface. Scanning tunneling spectroscopy measurements of the differential conductance along the chains revealed quantized states in isolated segments with differentiated states forming over end atoms. A comparison to a tight-binding model demonstrated how the formation of electronic end states transforms the density of states and the energy levels within the chains.

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PubMed2004

Dipole-induced structure in aromatic-terminated self-assembled monolayers: a study by near edge x-ray absorption fine structure spectroscopy.

The structure of self-assembled monolayers presenting aromatic rings at a surface is studied by near edge x-ray absorption fine structure spectroscopy (NEXAFS). Fluorine substitution at asymmetric positions in the aromatic rings is used to generate a layer of dipoles at the surface of the monolayer. We find that fluorine substituted aromatic rings are more ordered than unsubstituted aromatic rings by a factor of two based on the polarization dependence of the lowest C 1s to pi* transition, which is associated with transitions from phenyl carbons attached to hydrogens. This result is consistent with the influence of dipole-dipole interactions and quadrupolar interactions between the aromatic groups due to the substitution of fluorine atoms. The work also serves to illustrate how subtle variations in the orientation of an end group of a self-assembled monolayer can be determined by using NEXAFS.

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PubMed2003

Fractional band filling in an atomic chain structure.

A new chain structure of Au is found on stepped Si(111) which exhibits a 1/4-filled band and a pair of > or =1/2-filled bands with a combined filling of 4/3. Band dispersions and Fermi surfaces for Si(553)-Au are obtained by photoemission and compared to that of Si(557)-Au. The dimensionality of both systems is determined using a tight binding fit. The fractional band filling makes it possible to preserve metallicity in the presence of strong correlations.

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