First-principles calculation on the transport properties of molecular wires between Au clusters under equilibrium

Based on the matrix Green's function method combined with hybrid tight-binding / density functional theory, we calculate the conductances of a series of gold-dithiol molecule-gold junctions including benzenedithiol (BDT), benzenedimethanethiol (BDMT), hexanedithiol (HDT), octanedithiol (ODT) and decanedithiol (DDT). An atomically-contacted extended molecule model is used in our calculation. As an important procedure, we determine the position of the Fermi level by the energy reference according to the results from ultraviolet photoelectron spectroscopy (UPS) experiments. After considering the experimental uncertainty in UPS measurement, the calculated results of molecular conductances near the Fermi level qualitatively agree with the experimental values measured by Tao et. al. [{\it Science} 301, 1221 (2003); {\it J. Am. Chem. Soc.} 125, 16164 (2003); {\it Nano. Lett.} 4, 267 (2004).]Comment: 12 pages,8 figure

Giant Thermoelectric Effect from Transmission Supernodes

We predict an enormous order-dependent quantum enhancement of thermoelectric effects in the vicinity of a higher-order `supernode' in the transmission spectrum of a nanoscale junction. Single-molecule junctions based on 3,3'-biphenyl and polyphenyl ether (PPE) are investigated in detail. The nonequilibrium thermodynamic efficiency and power output of a thermoelectric heat engine based on a 1,3-benzene junction are calculated using many-body theory, and compared to the predictions of the figure-of-merit ZT.Comment: 5 pages, 6 figure

Breakdown into nanoscale of graphene oxide: Confined hot spot atomic reduction and fragmentation

Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedical applications due to its small size, intrinsic optical properties, large specific surface area, and easy to functionalize. To fully exploit nano-GO properties, a reproducible method for its production is of utmost importance. Herein we report, the study of the sequential fracture of GO sheets onto nano-GO with controllable lateral width, by a simple, and reproducible method based on a mechanism that we describe as a confined hot spot atomic fragmentation/reduction of GO promoted by ultrasonication. The chemical and structural changes on GO structure during the breakage were monitored by XPS, FTIR, Raman and HRTEM. We found that GO sheets starts breaking from the defects region and in a second phase through the disruption of carbon bonds while still maintaining crystalline carbon domains. The breaking of GO is accompanied by its own reduction, essentially by the elimination of carboxylic and carbonyl functional groups. Photoluminescence and photothermal studies using this nano-GO are also presented highlighting the potential of this nanomaterial as a unique imaging/therapy platform

Directed electroless growth of metal nanostructures on patterned self-assembled monolayers

The directed placement of Cu nanostructures on surfaces has been studied using a combination of scanning probe lithography and electroless metal deposition onto nanopatterned SAMs of 16-mercaptohexadecanoic acid (16-MHA) on Au. In situ studies using nanoscale molecular gradients reveal how controlling the areal density of the 16-MHA molecules dictates the nucleation and growth of the metal nanostructures. The influence of controlling pattern line spacing and tip path on pattern feature fidelity is also discussed. © 2007 American Chemical Society

A New Route to Low Resistance Contacts for Performance-Enhanced Organic Electronic Devices

The barrier to charge carrier injection across the semiconductor/electrode interface is a key parameter in the performance of organic transistors and optoelectronic devices, and the work function of the electrode material plays an important role in determining the size of this barrier. We present a new, chemical route for making metal surfaces with low work functions, by functionalizing gold surfaces with self-assembled monolayers of n,n-dialkyl dithiocarbamates. Ultraviolet photoemission spectroscopy measurements show that work functions of 3.2 eV +/- 0.1 eV can be achieved using this surface modification. Electronic structure calculations reveal that this low work function is a result of the packing-density, polarization along the N-C bond, and charge rearrangement associated with chemisorption. We demonstrate that electrodes functionalized with these monolayers significantly improve the performance of organic thin-film transistors and can potentially be employed in charge selective contacts for organic photovoltaics

Structural and chemical characterization of monofluoro-substituted oligo(phenylene-ethynylene) thiolate self-assembled monolayers on gold

Monolayers of oligo(phenylene-ethynylene) (OPE) molecules have exhibited promise in molecular electronic test structures. This paper discusses films formed from a novel molecule within this class, 2-fluoro-4-phenylethynyl-1-[(4-acetylthio)phenylethynyl]benzene (F-OPE). The conditions of self-assembled monolayer (SAM) formation were systematically altered to fabricate reproducible high-quality molecular monolayers from the acetate-protected F-OPE molecule. Detailed characterization of the F-OPE monolayers was performed by using an array of surface probes, including reflection absorbance infrared spectroscopy (RAIRS), contact angle (CA) measurements, spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and atomic force microscopy (AFM). XPS and RAIRS established that the SAM formed without removal of the F substituent and without oxidation of the thiol. The monolayer thickness, determined from SE and AFM based nanolithography, was consistent with the formation of a densely packed monolayer. The valence electronic structure of the SAM was consistent with an aromatic structure shifted by the electron-withdrawing fluorine substituent and intermolecular coupling within an oriented array of molecules