Narrow Results

Based on density functional theory, we have calculated and analyzed the electrical characteristics of silicon (100) - 2×1 surfaces. The calculation results show that the sulfur atom establishes a Schottky-like contact when it is used to tethering the surface and the molecule. In contrast to the Si – S linkage, a direct Si – C linkage does not build up a barrier between the molecule and the surface of silicon. This type of contact is a Ohmic-like contact. The origin of the characteristics of the contacts is analyzed. A basic rule for designing the electrical characteristics of the molecule - surface of silicon is presented.

There is considerable interest in electrical sensing of biomolecular binding since it has the potential to be label free, to work easily in aqueous environments native to the biomolecules, and to be integrated with small, fast, and inexpensive microelectronoics as detection instrumentation. Although electrochemical methods have been used successfully in detections of DNA molecules with Ag labels at very high sensitivity (~ p ml), detection of DNA molecules in terms of label free techniques has a lower sensitivity (~ μ ml). Here, the surface attachment chemistry is critical towards the detection of ultra-low concentration of biomolecules. In this article, based on density functional theory, we have calculated and analyzed the electrical characteristics of the contact between aromatic molecules and silicon (100) − 2×1 surfaces. Design principles for silicon based electrodes of electrochemically biomolecular sensing instruments for label-free sensing of single or a few biomolecular molecules have also been discussed.

In order to investigate surface structure change due to phase transition, surface melting, surface segregation and thin film growth, we have developed a new system for reflection high-energy electron diffraction (RHEED) with two pairs of magnetic coils to measure rocking curves in short time. This system is the most suitable tool to determine the structure change with temperature in a wide range, and we studied the dynamical structure change during film growth of Si on Si(111) and the phase transitions of Si(111) and Si(100) surfaces at high temperature.

In this review paper, we address the important research topic of adsorption on the silicon surface. The deposition of single Si ad-species (adatom and ad-dimer) on the p(2×2) reconstructed Si(100) surface has been simulated by the empirical tight-binding method. Using the clean and defective Si surfaces as the deposition substrates, the deposition energies are mapped out around the clean surface, dimer vacancies, steps and kink structures. The binding sites, saddle points and several possible diffusion paths are obtained from the calculated energy. With further analysis of the deposition and diffusion behaviors, the influences of the surface defects can be found. Then, by adopting the first-principle calculations, the adsorptions of the II-VI group elements on the clean and As-passivated Si(211) substrates have been calculated as the example of adsorption on the high-miller-index Si surface.

Amphiphilic comb-shaped 2-hydroxyethyl methacrylate-graft-poly(styrene)-block-poly(poly (ethylene glycol) monomethacrylate) (P(HEMA)–g–PS–b–P(PEGMA)) copolymer brushes, covalently tethered on Si(100) substrate, have been successfully prepared by (i) UV-induced hydrosilylation of 4-vinylbenzyl chloride (VBC) with the hydrogen-terminated Si(100) (Si–VBC surface), (ii) surface-initiated atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate (HEMA) to give the Si–VBC–g–P(HEMA) surface, (iii) coupling of 2-bromoisobutyryl bromide with the HEMA units via esterification to provide the comb-shaped macroinitiators (Si–VBC–g–P(HEMA)–R₃Br) for the subsequent ATRP, (iv) surface-initiated ATRP of styrene (St) to produce the Si–VBC–g–P(HEMA)–g–PS surface, and (v) the persisting of an active PS chain end can be used as the initiator for the subsequent ATRP of poly(ethylene glycol) monomethacrylate (PEGMA) to give the amphiphilic Si–VBC–g–P(HEMA)–g–PS–b–P(PEGMA) brush surface. The chemical composition and functionality of the silicon surface were tailored by the well-defined comb-shaped PS and P (PEGMA) brushes.

The adsorption of polydimethylsiloxane (PDMS) single chain with different chain lengths on a silicon (111) surface were studied by molecular dynamics simulations. The relative dielectric constant was selected to be 1 and 78.0 to mimic in vacuum and in solution environment, respectively. The chains were all present as two-dimensional (2D) adsorption conformation on the surface but different conformations and dynamic properties were found in the two absolutely different environments. The relationship between the adsorption energy of the different chain lengths and the degree of polymerization follows a linear function and the average adsorption energy per segment is -0.42 kcal/mol. In addition, the diffusion coefficient (D) of such chains scales with the degree of polymerization (N) as N^-3/2.

Oligo- and polythiophenes on surfaces play a fundamental role in building molecular circuits and organic-based electronics and may be assembled via interaction of the monomer units with the surface. In this framework, the nature of interaction of 2-vinyl thiophene (2VTP), a conjugated heteroaromatic monomer unit, with the Si(100) surface was studied by means of density functional theory (DFT). In particular, structural optimizations were performed comparing the effects of the inclusion of van der Waals (VdW) forces. It came out that the adsorption through the double bond is energetically favored, if VdW forces are included, whereas the adsorption through both aromatic ring and double bond simultaneously is more stable, if they are excluded. Physisorbed states were singled out and the barriers between two of them and the corresponding chemisorbed states were calculated along with the imaginary frequencies of the transition states. Also the transition energies have different values if the VdW forces are included.

Based on density functional theory, we have calculated and analyzed the electrical characteristics of silicon (100) – 2×1 surfaces. The calculation results show that the sulfur atom establishes a Schottky-like contact when it is used to tethering the surface and the molecule. In contrast to the Si – S linkage, a direct Si – C linkage does not build up a barrier between the molecule and the surface of silicon. This type of contact is a Ohmic-like contact. The origin of the characteristics of the contacts is analyzed. A basic rule for designing the electrical characteristics of the molecule – surface of silicon is presented.

There is considerable interest in electrical sensing of biomolecular binding since it has the potential to be label free, to work easily in aqueous environments native to the biomolecules, and to be integrated with small, fast, and inexpensive microelectronoics as detection instrumentation. Although electrochemical methods have been used successfully in detections of DNA molecules with Ag labels at very high sensitivity (∼ p ml), detection of DNA molecules in terms of label free techniques has a lower sensitivity (∼ µ ml). Here, the surface attachment chemistry is critical towards the detection of ultra-low concentration of biomolecules. In this article, based on density functional theory, we have calculated and analyzed the electrical characteristics of the contact between aromatic molecules and silicon (100) – 2×1 surfaces. Design principles for silicon based electrodes of electrochemically biomolecular sensing instruments for label-free sensing of single or a few biomolecular molecules have also been discussed.