Fabrication of stable Pd nanowire assisted by hydrogen in solution

We have mechanically fabricated a Pd nanowire in solution under electrochemical potential control. A clear feature appeared in the conductance histogram when the electrochemical potential of the Pd wire was kept at the hydrogen evolution potential. Conductance traces showed the Pd wire was stretched 0.4 nm in length just before breaking, suggesting that at least two Pd atoms might contribute to the formation of the Pd wire. The results indicate that a certain atomic configuration of the Pd nanowire is stabilized by hydrogen. We discuss the stabilization mechanism due to changes in bond strengths caused by hydrogen adsorption or incorporation.Comment: 4 pages, 3 figures, Appl. Phys. Lett., in pres

Accumulation and depletion layer thicknesses in organic field effect transistors

We present a simple but powerful method to determine the thicknesses of the accumulation and depletion layers and the distribution curve of injected carriers in organic field effect transistors. The conductivity of organic semiconductors in thin film transistors was measured in-situ and continuously with a bottom contact configuration, as a function of film thickness at various gate voltages. Using this method, the thicknesses of the accumulation and depletion layers of pentacene were determined to be 0.9 nm (VG=-15 V) and 5 nm (VG=15 V).Comment: 3 pages, 4 figures, Jap. J. Appl. Phys. in pres

Atomic Motion in Single H2_{2} and D2_{2} Molecule Junction Induced by Phonon Excitation

We have investigated Au atomic contacts in H$_{2}$ and D$_{2}$ environment by conductance measurement and $dI/dV$ spectroscopy. A single H$_{2}$ or D$_{2}$ molecule was found to bridge Au electrodes. In the case of the Au/H$_{2}$/Au junction, symmetric peaks were observed in $dI/dV$ spectra, while they were not observed for the Au/D$_{2}$/Au junction. The shape of the peaks in $dI/dV$ spectra originated from the structural change of the single molecule junction induced by the phonon excitation. The structural change could occur only for the Au/H$_{2}$/Au junction. The difference in the two single molecule junctions could be explained by larger zero point energy of Au-H$_{2}$ vibration mode than that in the Au/H$_{2}$/Au junction.Comment: 5 pages, 4 figures, to be appear in Phys. Rev.

Electric Conductance of Rh Atomic Contacts under Electrochemical Potential Control

The electric conductance of Rh atomic contacts was investigated under the electrochemical potential control. The conductance histogram of Rh atomic contacts varied with the electrochemical potential. When the electrochemical potential of the contact was kept at $\Phi_{0}$= 0.1 V vs. Ag/AgCl (Rh potential), the conductance histogram did not show any features. At $\Phi_{0}$= -0.1 V (under potential deposited hydrogen potential), the conductance histogram showed a feature around 2.3 $G_{0}$ ($G_{0}$ =2$e^{2}/h$), which agreed with the conductance value of a clean Rh atomic contact, which was observed in ultrahigh vacuum at low temperature. At $\Phi_{0}$= -0.25 V (over potential deposited hydrogen potential), the conductance histogram showed features around 0.3 and 1.0 $G_{0}$. The conductance behavior of the Rh atomic contact was discussed by comparing previously reported results of other metals, Au, Ag, Cu, Pt, Pd, Ni, Co, and Fe. The conductance behavior of the metal atomic contacts related with the strength of the interaction between hydrogen and metal surface.Comment: 5 pages, 4 figures, Phys. Rev. B, in press

One-dimensional ordered structure of a-sexithienyl on Cu(110)

We have studied atomic structures of a-sexithienyl (6T) films grown on Cu(110) by near-edge x-ray absorption fine structure (NEXAFS). A one-dimensional (1D) ordered structure of 6T with its molecular long axis parallel to the Cu[001] direction could be fabricated by deposition at 300 K and subsequent annealing at 360 K. Polarization and azimuth-dependent NEXAFS revealed the formation process of the 1D structure and showed the molecular orientation in the in-plane direction directly. We propose here a method to obtain the orientation distribution function of molecules using NEXAFS.Comment: 4 figures, to be published in Appl. Phys. Let

Hydrogen-assisted stabilization of Ni nanowires in solution

We have studied conductance characteristics of mechanically fabricated Ni nanoconstrictions under controlling electrochemical potential and pH of the electrolyte. Conductance histogram showed clear feature peaked at 1-1.5 $G_{0}$ (=$2e^{2}/h$) when the potential of the constriction was kept at more negative potential than -900 mV vs. Ag/AgCl in pH=3.7. Comparable feature also appeared at more positive potential when lower pH solution was used. We have revealed that Ni mono atomic contact or mono atomic wire can be stabilized in solution at room temperature under the hydrogen evolution.Comment: 4 pages, 3 figures; to appear in Appl. Phys. Let

Electronic properties of metal-induced gap states formed at alkali-halide/metal interfaces

The spatial distribution and site- distribution of metal induced gap states (MIGS) are studied by thickness dependent near edge x-ray absorption fine structure (NEXAFS) and comparing the cation and anion edge NEXAFS. The thickness dependent NEXAFS shows that the decay length of MIGS depends on rather an alkali halide than a metal, and it is larger for alkali halides with smaller band gap energy. By comparing the Cl edge and K edge NEXAFS for KCl/Cu(001), MIGS are found to be states localizing at anion sites.Comment: 4 pages, to be published in Phys. Rev.

Electric field induced charge injection or exhaustion in organic thin film transistor

The conductivity of organic semiconductors is measured {\it in-situ} and continuously with a bottom contact configuration, as a function of film thickness at various gate voltages. The depletion layer thickness can be directly determined as a shift of the threshold thickness at which electric current began to flow. The {\it in-situ} and continuous measurement can also determine qualitatively the accumulation layer thickness together with the distribution function of injected carriers. The accumulation layer thickness is a few mono layers, and it does not depend on gate voltages, rather depends on the chemical species.Comment: 4 figures, to be published in Phys. Rev.