Selective reactions and adsorption geometries of a multifunctional molecule: cis-2-butene-1,4-diol on Si(100)-2 x 1.

The adsorption geometry of cis-2-butene-1,4-diol (BEDO, HOCH(2)CH=CHCH(2)OH) on Si(100)-2 x 1 was studied using scanning tunneling microscopy (STM), high resolution X-ray photoemission spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Bias-voltage-dependent STM images exhibited features characteristic of two distinct BEDO adsorption geometries. One feature was a bright protrusion located on the center of a single dimer, indicating an on-top configuration. The low bias-voltage STM image clearly showed dark features indicative of the formation of Si-H bonds on adjacent dimers in the same dimer row. The other feature was a bright protrusion bridged on end between two adjacent dimers in the same dimer row, indicating an end-bridge configuration. Accompanying this feature, two dark features attributed to Si-H bonds were observed on opposite positions to the bridged protrusion. From the XPS results, the Si 2p core level spectra revealed that the dimer atoms are involved in the formation of Si-O and Si-H bonds. On the other hand, carbon K-edge NEXAFS spectra showed that the C=C bond does not participate in the adsorption reaction and remains as an unreacted group. Collectively, the experimental results indicate that the adsorption of BEDO on Si(100)-2 x 1 occurs through the formation of two Si-O bonds via nucleophilic reaction between the two OH groups of BEDO and two Si-Si dimers. Importantly, the maintenance of the C=C bond means that the C=C functional group can be utilized as a new reaction site for further surface chemical reactions.

Pattern formation through selective chemical transformation of self-assembled benzaldimine monolayer by soft X-ray irradiation.

Benzaldimine monolayer was exposed to soft X-rays, and the involved chemical transformation was investigated using X-ray photoelectron spectra and near-edge X-ray absorption fine structure spectroscopy. The spectroscopy indicated that irradiation of soft X-ray (550 eV)-induced selective transformation of the imine group into a nonhydrolyzable one, i.e., the amine group. Utilizing the selective chemical transformation of the imine group with the soft X-ray irradiation, we were able to generate a micropattern. AFM images showed that the patterning with alternating surface topology was effective. The patterned monolayer was further modified with biotin and Cy3-tagged Streptavidin sequentially. Fluorescence images showed that the above molecules were selectively immobilized onto the amine-terminated region of the patterned surface. The current system is found to be more efficient than the predecessor, 4-nitrobenzaldimine monolayer.

Selective catalytic burning of graphene by SiOx layer depletion.

We report catalytic decomposition of few-layer graphene on an Au/SiOx/Si surface wherein oxygen is supplied by dissociation of the native SiOx layer at a relatively low temperature of 400 °C. The detailed chemical evolution of the graphene covered SiOx/Si surface with and without gold during the catalytic process is investigated using a spatially resolved photoelectron emission method. The oxygen atoms from the native SiOx layer activate the gold-mediated catalytic decomposition of the entire graphene layer, resulting in the formation of direct contact between the Au and the Si substrate. The notably low contact resistivity found in this system suggests that the catalytic depletion of a SiOx layer could realize a new way to micromanufacture high-quality electrical contact.