Nanometer-Scale Synthesis and Atomic-Scale Modification with the Scanning Tunneling Microscope

The structure or composition of a surface may be locally altered in either of two fundamental ways using the scanning tunneling microscope (STM). A modification of the surface may be induced resulting in the rearrangement and/or removal of surface atoms, or in the transfer of atoms from the tip to the sample surface. In many recent experiments, the modification of surfaces has involved a single atom or an ensemble of a few atoms. Alternatively, the localized synthesis of a new material from reactants external to the STM tip and sample can be induced using at least three experimental strategies. A typical distance scale involved in such experiments is 10 nm (i.e., the smallest lateral dimension of the material synthesized). Progress in the areas of localized modification and localized syntheses with the STM (with greater emphasis on the latter) is summarized in this review

AC impedance analysis of polypyrrole thin films

The AC impedance spectra of thin polypyrrole films were obtained at open circuit potentials from -0.4 to 0.4 V vs SCE. Two limiting cases are discussed for which simplified equivalent circuits are applicable. At very positive potentials, the predominantly nonfaradaic AC impedance of polypyrrole is very similar to that observed previously for finite porous metallic films. Modeling of the data with the appropriate equivalent circuit permits effective pore diameter and pore number densities of the oxidized film to be estimated. At potentials from -0.4 to -0.3 V, the polypyrrole film is essentially nonelectronically conductive and diffusion of polymer oxidized sites with their associated counterions can be assumed to be linear from the film/substrate electrode interface. The equivalent circuit for the polypyrrole film at these potentials is that previously described for metal oxide, lithium intercalation thin films. Using this model, counterion diffusion coefficients are determined for both semi-infinite and finite diffusion domains. In addition, the limiting low frequency resistance and capacitance of the polypyrrole thin fims was determined and compared to that obtained previously for thicker films of the polymer. The origin of the observed potential dependence of these low frequency circuit components is discussed

Determination of diffusion coefficients in polypyrrole thin films using a current pulse relaxation method

The current pulse E sub oc relaxation method and its application to the determination of diffusion coefficients in electrochemically synthesized polypyrrole thin films is described. Diffusion coefficients for such films in Et4NBF4 and MeCN are determined for a series of submicron film thicknesses. Measurement of the double-layer capacitance, C sub dl, and the resistance, R sub u, of polypyrrole thin films as a function of potential obtained with the galvanostatic pulse method is reported. Measurements of the electrolyte concentration in reduced polypyrrole films are also presented to aid in the interpretation of the data

Mechanistic investigations of nanometer-scale lithography at liquid-covered graphite surfaces

Pulse-induced nanometer-scale lithography has been performed on graphite surfaces that were in contact with pure water or other organic liquids. Very reproducible control over the pit diameter was observed in aqueous solutions, and a well-defined voltage threshold (4.0±0.2 V) was also apparent. Near the threshold voltage, 7 Å diameter×2 Å high protrusions were formed, while larger initial pulse voltages resulted in pits of diameter>~20 Å

Atomic resolution imaging of electrode surfaces in solutions containing reversible redox species

Procedures are described for insulating metal scanning tunneling microscope (STM) tips with either glass or polymer coatings. In solutions containing 0.10 M of a reversible redox couple, Fe(CN) - 3/-46 , the faradaic limiting current to polymer coated tips was 200–500 pA and that for glass coated tips was <10 pA. For polymer insulated tips, steady-state currents of 10–100 pA were observed at tip-sample displacements less than 0.3 µm. The suppression of faradaic current achieved by these coating procedures enabled the collection of the first atomic resolution STM images of highly ordered pyrolytic graphite electrodes in contact with redox-active electrolytes. Preliminary data for the in situ electrochemical characterization of these tips are also discussed

Understanding preventive behaviors among mid-Western African-American men: a pilot qualitative study of prostate screening

http://dx.doi.org/10.1016/j.jomh.2011.03.00

Diverse Applications of Nanomedicine

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic. \ua9 2017 American Chemical Society