Zhi-Yong Yang

Optimizing label-free DNA electrical detection on graphene platform.

The anodized epitaxial graphene (EG) electrode demonstrates a high level of performance for electrochemical impedance as well as differential pulse voltammetry detection of immobilized DNA and free DNA, respectively, at solid-liquid interfaces. On the anodized EG surface, because of the presence of oxygen functionalities as well as π conjugated domains, the anchoring of the DNA probe can be achieved by either covalent grafting or noncovalent π-π stacking readily. The effect of different binding modes on the sensitivity of the impedimetric sensing was investigated. Equivalent circuit modeling shows that the sensitivity of EG to DNA hybridization is controlled by changes in the resistance of the molecular layer as well as the space charge layer. The linear dynamic detection range of EG for DNA oligonucleotides is in the range of 5.0 × 10(-14) to 1 × 10(-6) M. In addition, with the use of differential pulse voltammetry, single stranded DNA, fully complimentary DNA, as well as single nucleotide polymorphisms can be differentiated on anodized EG by monitoring the oxidation signals of individual nucleotide bases.

Scanning tunneling microscopy of the formation, transformation, and property of oligothiophene self-organizations on graphite and gold surfaces.

Two alkyl-substituted dual oligothiophenes, quarterthiophene (4T)-trimethylene (tm)-octithiophene (8T) and 4T-tm-4T, were used to fabricate molecular structures on highly oriented pyrolytic graphite and Au(111) surfaces. The resulted structures were investigated by scanning tunneling microscopy. The 4T-tm-8T and 4T-tm-4T molecules self-organize into long-range ordered structures with linear and/or quasi-hexagonal patterns on highly oriented pyrolytic graphite at ambient temperature. Thermal annealing induced a phase transformation from quasi-hexagonal to linear in 4T-tm-8T adlayer. The molecules adsorbed on Au(111) surface in randomly folded and linear conformation. Based on scanning tunneling microscopy results, the structural models for different self-organizations were proposed. Scanning tunneling spectroscopy measurement showed the electronic property of individual molecules in the patterns. These results are significant in understanding the chemistry of molecular structure, including its formation, transformation, and electronic properties. They also help to fabricate oligothiophene assemblies with desired structures for future molecular devices.

Using the graphene Moiré pattern for the trapping of C60 and homoepitaxy of graphene.

The graphene Moiré superstructure offers a complex landscape of humps and valleys to molecules adsorbing and diffusing on it. Using C(60) molecules as the classic hard sphere analogue, we examine its assembly and layered growth on this corrugated landscape. At the monolayer level, the cohesive interactions of C(60) molecules adsorbing on the Moiré lattice freeze the molecular rotation of C(60) trapped in the valley sites, resulting in molecular alignment of all similarly trapped C(60) molecules at room temperature. The hierarchy of adsorption potential well on the Moiré lattice causes diffusion-limited dendritic growth of C(60) films, as opposed to isotropic growth observed on a smooth surface like graphite. Due to the strong binding energy of the C(60) film, part of the dentritic C(60) films polymerize at 850 K and act as solid carbon sources for graphene homoepitaxy. Our findings point to the possibility of using periodically corrugated graphene in molecular spintronics due to its ability to trap and align organic molecules at room temperature.

Submicron patterning of Co colloid catalyst for growth of vertically aligned carbon nanotubes

Applications of carbon nanotubes such as field emission or microelectrode sensor arrays require a patterning of vertically aligned carbon nanotubes over large areas. A highly purified and concentrated monodisperse cobalt colloid was produced for use as a catalyst for growth of carbon nanotubes. Nanocontact printing was employed to deposit the cobalt nanoparticles in regular patterns with feature sizes at the 100?nm scale onto silicon wafers at low cost over large areas. Vertically aligned carbon nanotubes were grown by direct current plasma enhanced chemical vapour deposition at temperatures ranging from 300 to 640??C.

Effect of the bridge alkylene chain on adlayer structure and property of functional oligothiophenes studied with scanning tunneling microscopy and spectroscopy.

Five dual-quinquethiophene self-assemblies are prepared on a highly oriented pyrolytic graphite (HOPG) surface. The dual-quinquethiophenes are quinquethiophenes (5T)-di to hexamethylene (n, 2-6)-quinquethiophenes (5T), abbreviated as 5T-n-5T (n = 2-6). The effect of the bridge alkylene chains on the structure and property of the five assemblies are investigated by scanning tunneling microscopy (STM). It is found that all 5T-n-5T molecules form ordered adlayers on a HOPG surface with stripe feature. The alkylene bridge part in a molecule appears in a dark contrast in an STM image. Intriguingly, the thiophene backbones of individual molecules in the adlayer always keep an angle with the direction of molecular stripes. With alkylene bridge length increasing, different structures are found in 5T-5-5T and 5T-6-5T assemblies. To understand the effect of bridge chains on single molecular property, scanning tunneling spectroscopy is used to probe the electronic property of the different adlayers. The results will be important in surface engineering by self-assembly and molecular device fabrication with oligothiophenes.

Synergistically Improving the Activity, Antipoisonous Ability, and Long-Term Stability of Pt to Methanol Oxidation through Developing Favorable Graphene-Based Supports

An interconnected framework of reduced graphene oxide/phenyl formaldehyde polymer composites was synthesized by a one-pot hydrothermal reaction followed by carbonizing under different conditions. Then, the obtained porous materials with varied surface properties were used to disperse ultrasmall Pt nanoparticles. The catalyst with the optimized support demonstrates superior achievements to methanol oxidation reaction (MOR): distinctive improved mass activity (MA) and specific activity at both forward peak position and at the potential range near the operation of fuel cells, best antipoisonous ability revealed by 17 times MA and 7 times the retaining rate of commercial Pt/C in chronoamperometric evaluations, and outstanding long-term stability verified by 3-4 times MA and the retaining rate of Pt/C in the accelerated duration tests. By analyzing the performances of all studied catalysts, we proposed that fruitful oxygen groups and defects on the surface of supporting materials play a key role in boosting the MOR fulfillments through strengthening the Pt-substrate interaction or facilitating the removal of CO from the Pt surface. Elimination of surface oxygen groups and defects may promote the conductivity and mechanical strength of the catalysts but could result in a serious deterioration of antipoisonous ability, which means that only if the deliberate balance is achieved in the preparation of supporting materials can the MOR performances of Pt be improved synergistically.

Altering the ordering and disordering of a triangular nanographene at room temperature.

Molecular self-organization has the potential to serve as an efficient and versatile tool for the spontaneous creation of low-dimensional nanostructures on surfaces. We demonstrate how the subtle balance between intermolecular interactions and molecule-surface interactions can be altered by modifying the environment or through manipulation by means of the tip in a scanning tunnelling microscope (STM) at room temperature. We show how this leads to the distinctive ordering and disordering of a triangular nanographene molecule, the trizigzag-hexa-peri-hexabenzocoronenes-phenyl-6 (trizigzagHBC-Ph6), on two different surfaces: graphite and Au(111). The assembly of submonolayer films on graphite reveals a sixfold packing symmetry under UHV conditions, whereas at the graphite-phenyloctane interface, they reorganize into a fourfold packing symmetry, mediated by the solvent molecules. On Au(111) under UHV conditions in the multilayer films we investigated, although disorder prevails with the molecules being randomly distributed, their packing behaviour can be altered by the scanning motion of the tip. The asymmetric diode-like current-voltage characteristics of the molecules are retained when deposited on both substrates. This paper highlights the importance of the surrounding medium and any external stimulus in influencing the molecular organization process, and offers a unique approach for controlling the assembly of molecules at a desired location on a substrate.

Tracking the Evolution of Polymer Interface Films during the Process of Thermal Annealing at the Domain and Single Molecular Levels using Scanning Tunneling Microscopy

Structural evolution of polymer (NTZ12) interface films during the process of annealing is revealed at the domain and single molecular levels using the statistical data measured from scanning tunneling microscopy images and through theoretical calculations. First, common features of the interface films are examined. Then, mean values of surface-occupied ratio, size and density of the domain are used to reveal the intrinsic derivation of the respective stages. Formation of new domains is triggered at 70 °C, but domain ripening is not activated. At 110 °C, the speed of formation of new domains is almost balanced by the consumption due to the ripening process. However, formation of new domains is reduced heavily at 150 °C but restarted at 190 °C. At the single molecular level, the ratio of the average length of linear to curved backbones is increased during annealing, whereas the ratios of the total length and the total number of linear to curved skeletons reaches a peak value at 150 °C. The two major conformations of curved backbones for all samples are 120° and 180° bending, but the ripening at 150 °C reduces 180° folding dramatically. Molecular dynamic simulations disclose the fast relaxing process of curved skeletons at high temperature.