Atomic-scale morphology and electronic structure of manganese atomic layers underneath epitaxial graphene on SiC(0001).

We report the fabrication of a novel epitaxial graphene(EG)/Mn/SiC(0001) sandwiched structure through the intercalation of as-deposited Mn atoms on graphene surfaces, with the aid of scanning tunneling microscope, low energy electron diffraction, and X-ray photoelectron spectroscopy. We found that Mn can intercalate below both sp(3)-hybridized carbon-rich interface layer and monolayer graphene, along with the formation of various embedded Mn islands showing different surface morphologies. The unique trait of the sandwiched system is that the strong interaction between the carbon-rich interface layer and SiC(0001) can be decoupled to some degrees, and contemporaneous, an n-doping effect is observed by mapping the energy band of the system using angle-resolved photoemission spectroscopy. Moreover, what deserves our special attention is that the intercalated islands can only evolve below monolayer graphene when a bilayer coexists, accounting for an intriguing graphene thickness-dependent intercalation effect. In the long run, we believe that the construction of graphene/Mn/SiC(0001) systems offers ideal candidates for exploring some intriguing physical properties such as the magnetic property of two-dimensional transition metal systems.

Growth and atomic-scale characterizations of graphene on multifaceted textured Pt foils prepared by chemical vapor deposition.

The synthesis of centimeter-scale uniform graphene on Pt foils was accomplished via a traditional ambient pressure chemical vapor deposition (CVD) method. Using scanning electron microscopy (SEM) and Raman spectroscopy, we reveal the macroscopic continuity, the thickness, as well as the defect state of as-grown graphene. Of particular importance is that the Pt foils after CVD growth have multifaceted texture, which allows us to explore the substrate crystallography effect on the growth rate and the continuity of graphene. By virtue of atomically resolved scanning tunneling microscopy (STM), we conclude that graphene grows mainly in registry with the symmetries of Pt(111), Pt(110), and Pt(100) facets, leading to hexagonal lattices and striped superstructures. Nevertheless, the carbon lattices on interweaving facets with different identities are connected seamlessly, which ensure the graphene growth from nanometer to micrometer levels. With these results, another prototype for clarifying the preliminary growth mechanism of the CVD process is demonstrated as an analogue of graphene on Cu foils.

Defect-like structures of graphene on copper foils for strain relief investigated by high-resolution scanning tunneling microscopy.

Understanding of the continuity and the microscopic structure of as-grown graphene on Cu foils through the chemical vapor deposition (CVD) method is of fundamental significance for optimizing the growth parameters toward high-quality graphene. Because of the corrugated nature of the Cu foil surface, few experimental efforts on this issue have been made so far. We present here a high-resolution scanning tunneling microscopy (STM) study of CVD graphene directly on Cu foils. Our work indicates that graphene can be grown with a perfect continuity extending over both crystalline and noncrystalline regions, highly suggestive of weak graphene-substrate interactions. Due to thermal expansion mismatch, defect-like wrinkles and ripples tend to evolve either along the boundaries of crystalline terraces or on noncrystalline areas for strain relief. Furthermore, the strain effect arising from the conforming of perfect two-dimensional graphene to the highly corrugated surface of Cu foils is found to induce local bonding configuration change of carbon from sp(2) to sp(3), evidenced by the formation of "three-for-six" lattices.

Measurement of the rate of water translocation through carbon nanotubes.

We present an approach for measuring the water flow rate through individual ultralong carbon nanotubes (CNTs) using field effect transistors array defined on individual tubes. Our work exhibits a rate enhancement of 882-51 and a slip length of 53-8 nm for CNTs with diameters of 0.81-1.59 nm. We also found that the enhancement factor does not increase monotonically with shrinking tube diameter and there exists a discontinuous region around 0.98-1.10 nm. We believe that these single-tube level results would help understand the intrinsic nanofluidics of water in CNTs.

Investigation of the interactions between silver nanoparticles and Hela cells by scanning electrochemical microscopy.

The interactions between Hela cells and silver nanoparticles (AgNPs) have been studied by scanning electrochemical microscopy (SECM) with both IrCl(6)(2-/3-) and Fe(CN)(6)(3-/4-) as the dual mediators. IrCl(6)(2-), which can be produced in situ and react with AgNPs, is used as the mediator between the AgNPs on the cells and the SECM tip. Another redox couple, Fe(CN)(6)(3-/4-), which has a similar hydrophilicity to IrCl(6)(2-/3-), but cannot react with AgNPs, is also employed for the contrast experiments. The cell array is cultured successfully onto a Petri dish by microcontact printing (muCP) technique, which can provide a basic platform for studying of single cells. The approach curve and line scan are the two methods of SECM employed here to study the Hela cells. The former can provide the information about the interaction between Hela cells and AgNPs whereas the later gives the cell imaging. The permeability of cell membranes and morphology are two main factors which have effects on the feedback mode signals when K(3)Fe(CN)(6) is used as the mediator. The permeability of the cell membranes can be ignored after interaction with high concentration of AgNP solution and the height of the Hela cells is slightly decreased in this process. The kinetic rate constants (k(0)) between IrCl(6)(2-) and Ag on the Hela cell can be evaluated using K(3)IrCl(6) as the mediator, and they are increased with the higher concentrations of the AgNP solutions. The k(0) is changed about 10 times from 0.43 +/- 0.04 x 10(-4) to 1.25 +/- 0.07 x 10(-4) and to 3.93 +/- 1.9 x 10(-4) cm s(-1) corresponding to 0, 1 and 5 mM of AgNO(3) solution. The experimental results demonstrate that the AgNPs can be adsorbed on the cell surface and detected by SECM. Thus, the amount of AgNPs adsorbed on cell membranes and the permeability or morphology changes can be investigated simultaneously using this approach. The dual mediator system and cell array fabricated by muCP technique can provide better reproducibility because they can simplify experiments, and provide a platform for further single cell detection.

Electrochemical DNAzyme sensor for lead based on amplification of DNA-Au bio-bar codes.

An electrochemical DNAzyme sensor for sensitive and selective detection of lead ion (Pb(2+)) has been developed, taking advantage of catalytic reactions of a DNAzyme upon its binding to Pb(2+) and the use of DNA-Au bio-bar codes to achieve signal enhancement. A specific DNAzyme for Pb(2+) is immobilized onto an Au electrode surface via a thiol-Au interaction. The DNAzyme hybridizes to a specially designed complementary substrate strand that has an overhang, which in turn hybridizes to the DNA-Au bio-bar code (short oligonucleotides attached to 13 nm gold nanoparticles). A redox mediator, Ru(NH3)6(3+), which can bind to the anionic phosphate of DNA through electrostatic interactions, serves as the electrochemical signal transducer. Upon binding of Pb(2+) to the DNAzyme, the DNAzyme catalyzes the hydrolytic cleavage of the substrate, resulting in the removal of the substrate strand along with the DNA bio-bar code and the bound Ru(NH3)6(3+) from the Au electrode surface. The release of Ru(NH3)6(3+) results in lower electrochemical signal of Ru(NH3)6(3+) confined on the electrode surface. Differential pulse voltammetry (DPV) signals of Ru(NH3)6(3+) provides quantitative measures of the concentrations of Pb(2+), with a linear calibration ranging from 5 nM to 0.1 microM. Because each nanoparticle carries a large number of DNA strands that bind to the signal transducer molecule Ru(NH3)6(3+), the use of DNA-Au bio-bar codes enhances the detection sensitivity by five times, enabling the detection of Pb(2+) at a very low level (1 nM). The DPV signal response of the DNAzyme sensor is negligible for other divalent metal ions, indicating that the sensor is highly selective for Pb(2+). Although this DNAzyme sensor is demonstrated for the detection of Pb(2+), it has the potential to serve as a general platform for design sensors for other small molecules and heavy metal ions.

A chronocoulometric aptamer sensor for adenosine monophosphate.

The selective recognition of adenosine monophosphate by a half-duplex aptamer-modified electrode leads to a simple chronocoulometric aptasensor based on the changes in surface charges.

Fabrication and characterization of submicrometer- and nanometer-sized double-barrel pipets.

Submicro- and nanometer-sized glass double-barrel pipets have been fabricated by a laser puller with new pulling programs and have been used to support submicro- and nanometer dual liquid/liquid interfaces. The smallest pipet that can be made by this approach is approximately 20 nm in radius. These pipets have been characterized by cyclic voltammetry and scanning electron microscopy. Generation/collection mode of charge-transfer reaction is demonstrated at the submicro- and nanometer dual-liquid/liquid interfaces. The dependence of collection efficiency upon geometric parameters of the pipets has been discussed. Among the micro-, submicro-, and nanopipets, we have found that the submicro-double-barrel pipets have higher collection efficiencies than that of others and are also very close to the values predicted by the theory. Therefore, in terms of G/C mode applications, the optimal size of double-barrel pipets should be in submicrometer scale. As one of the examples of special application, we have also demonstrated that in the case of no supporting electrolyte, only the nanometer double-barrel pipets can provide reasonably good G/C results.