Au Metal Electrodes Research Articles

Thermo-compressive transfer printing for facile alignment and robust device integration of nanowires

Controlled alignment and mechanically robust bonding between nanowires (NWs) and electrodes are essential requirements for reliable operation of functional NW-based electronic devices. In this work, we developed a novel process for the alignment and bonding between NWs and metal electrodes by using thermo-compressive transfer printing. In this process, bottom-up synthesized NWs were aligned in parallel by shear loading onto the intermediate substrate and then finally transferred onto the target substrate with low melting temperature metal electrodes. In particular, multi-layer (e.g. Cr/Au/In/Au and Cr/Cu/In/Au) metal electrodes are softened at low temperatures (below 100 °C) and facilitate submergence of aligned NWs into the surface of electrodes at a moderate pressure (∼5 bar). By using this thermo-compressive transfer printing process, robust electrical and mechanical contact between NWs and metal electrodes can be realized. This method is believed to be very useful for the large-area fabrication of NW-based electrical devices with improved mechanical robustness, electrical contact resistance, and reliability.

Highly Conducting π-Conjugated Molecular Junctions Covalently Bonded to Gold Electrodes

We measure electronic conductance through single conjugated molecules bonded to Au metal electrodes with direct Au-C covalent bonds using the scanning tunneling microscope based break-junction technique. We start with molecules terminated with trimethyltin end groups that cleave off in situ, resulting in formation of a direct covalent σ bond between the carbon backbone and the gold metal electrodes. The molecular carbon backbone used in this study consist of a conjugated π system that has one terminal methylene group on each end, which bonds to the electrodes, achieving large electronic coupling of the electrodes to the π system. The junctions formed with the prototypical example of 1,4-dimethylenebenzene show a conductance approaching one conductance quantum (G(0) = 2e(2)/h). Junctions formed with methylene-terminated oligophenyls with two to four phenyl units show a 100-fold increase in conductance compared with junctions formed with amine-linked oligophenyls. The conduction mechanism for these longer oligophenyls is tunneling, as they exhibit an exponential dependence of conductance on oligomer length. In addition, density functional theory based calculations for the Au-xylylene-Au junction show near-resonant transmission, with a crossover to tunneling for the longer oligomers.

Electrode metal dependence of the rectifying performance for molecular devices: A density functional study

Carrying out theoretical calculations using the nonequilibrium Green’s function method combined with the density functional theory, the transport properties of the terphenyl molecule connected to the two Y (Y=Li, Al, or Au) metal electrodes are investigated. The results show that the electrode metals have a distinct influence on rectifying performance of such devices. For the Au electrode system, we can observe a best rectifying performance, next for the Al electrode system, and the rectifying effect can be nearly neglected for the Li electrode system. Our findings suggest that the rectifying characteristics are intimately related to electrode materials.

ZnO 나노와이어를 이용한 FET 소자 제작 및 특성 평가

The zinc oxide(ZnO) nanowires were deposited on Si(001) substrates by thermal chemical vapour deposition without any catalysts. SEM data suggested that the grown nanostructures were the well-aligned ZnO single crystals with preferential orientation. Back-gate ZnO nanowire field effect transistors(FET) were successfully fabricated using a photolithography process. The fabricated nanowire FET exhibits good contact between the ZnO nonowire and Au metal electrodes. Based on I-V characteristics it was found out that the ZnO nanowire revealed a characteristic of n-type field effect transistor. The drain current increases with increasing drain voltage, and the slopes of the curves are dependent on the gate voltage.

Comparison of electrical properties of M- and λ-DNA attached on the Au metal electrodes with nanogap

We successfully prepared the modified M-DNA molecular wires by the insertion of the divalent zinc ions (Zn 2+) in every base pair of λ-DNA molecules. We found that the current–voltage ( I– V) characteristics of M-DNA are distinctively different from those measured using other types of DNA molecules including λ-DNA: one of the unique features of the modified M-DNA molecular wires was the metallic property observed in the I– V characteristics (i.e., a linear I– V relationship), suggesting that they might be used to build the metallic nanowire for the future nanodevices. Several parameters such as (1) humidity during the electrical measurement and (2) pH in preparation of M-solution are important factors to decide the I– V characteristics of M-DNA molecular wires. For instance, if the λ-DNA molecules were treated with the pH value of less than 8, they did not show the characteristics of metallic M-DNA molecular wires. In addition, the conductivity of M-DNA molecular wires decreases as the measurement pressure moves to the high vacuum range, although the unique feature (i.e., linear relationship) was maintained even at 10 − 5 Torr.

Comparison of nanometer-scale gold structures electrodeposited on Au and Pt seed electrode

We report a new method to fabricate nanometer-scale gaps between two Au metal electrodes electrodeposited on either Au or Pt seed layer. The techniques used in this work are conventional photolithography, where specifically designed photomask and lift-off methods and pulse/DC electroplating are used. In addition, the effects of pulse plating variables are investigated with respect to DC plating. The results obtained from the electroplated Au films on the Au seed layer are compared with those on the Pt one. The method is simple, inexpensive, faster, and robust, and gaps between metal electrodes could be easily controlled to nanometer-scale dimensions.

Formation of Electrical Interconnects by Self-Trapping of Deoxyribonucleic Acid Molecules

The formation of electrical interconnection is proposed and realized using thiol-modified 60 base pairs of poly-(dG) and poly-(dC) deoxyribonucleic acid (DNA) molecules by self-trapping method. DNA molecules are synthesized by annealing 60 base pairs of poly-(dG) and poly-(dC) single strands with thiol groups at both 5' and 3' ends in deionized water at 97°C. Thiol-modified DNA molecules are self-trapping with Au molecules and form a good electrical interconnection between the Au metal electrodes without any external physical force. Transport measurements of a particular sample show resistance values of interconnection of approximately 10 MΩ. The self-trapping method by thiol-modified DNA molecules could be a very promising technique for the interconnection of nanometer-scale devices.

Spectroscopic consideration of the surface potential built across phthalocyanine thin films on a metal electrode

The nonlinear optical properties of tert-butyl phthalocyanine copper Langmuir-Blodgett (CuttbPc LB) films and vacuum-evaporated phthalocyanine copper (CuPc) films deposited on a metal surface were investigated by second-harmonic generation (SHG) spectroscopy. At the organic/metal interface, a space charge field is formed due to the presence of excess charge injected from a metal electrode to the organic layer. Since the Pc molecule has D4h symmetry, an inversion center is present and the optical SH process is not allowed under the electric-dipole approximation. However, the space charge field at the interface directly influences the symmetric structure of the electrons in the Pc molecule. We investigated the contributions of the surface potential to the SHG using Pc LB and vacuum-evaporated films deposited on aluminum (Al) and gold (Au) metal electrodes, where a distinctive difference in the spectrum for the Pc films on the Al and Au surfaces was observed. The contribution of the surface potential was revealed based on the resonant conditions of the SH process, taking into account the electric-quadrupole transition and dc-field-induced electric-dipole transition.

Observation of electrostatically released DNA from gold electrodes with controlled threshold voltages.

DNA oligo-nucleotides, localized at Au metal electrodes in aqueous solution, are found to be released when applying a negative bias voltage to the electrode. The release was confirmed by monitoring the intensity of the fluorescence of cyanine dyes (Cy3) linked to the 5' end of the DNA. The threshold voltage of the release changes depending on the kind of linker added to the DNA 3'-terminal. The amount of released DNA depends on the duration of the voltage pulse. Using this technique, we can retain DNA at Au electrodes or Au needles, and release the desired amount of DNA at a precise location in a target. The results suggest that DNA injection into living cells is possible with this method.

Formation of nanometer-scale gaps between metallic electrodes using pulse/DC plating and photolithography

We report a new method to fabricate nanometer-scale gaps (less than 50 nm) between two Au metal electrodes. The techniques used in this work are conventional photolithography, where specifically designed photomask and lift-off methods were used, and pulse/DC electroplating. In addition, the effects of pulse plating variables were investigated with respect to DC plating. The method is simple, inexpensive, faster, and robust, and gaps between metal electrodes could be easily controlled to atomic scale dimensions.

Current–voltage characteristics of λ- and poly-DNA

We have studied the current–voltage characteristics of λ- and poly-DNA molecules attached on the gap formed between two Au metal electrodes. Under high humidity condition, all types of deoxyribonucleic acid (DNA) show a similar shape in I– V curves, as well as a comparable magnitude in current level at the given voltage. The conductivity of DNA molecules, however, was drastically changed after minimizing the humidity level in a vacuum chamber, causing a rectifying property in I– V characteristics. More important, the G–C content in DNA molecules decides the conductivity level at the given voltage, suggesting that the electrical conductions of DNA molecules are strongly dependent on both humidity in a measurement chamber and intrinsic properties of DNA itself.

Determination of the Electric Field Intensities in a Mid-Infrared Spectroelectrochemical Cell Using Attenuated Total Reflection Spectroscopy with the Otto Optical Configuration

The normalized mean-squared electric field intensities in a thin-layer spectroelectrochemical cell with the attenuated total reflection (ATR) optical configuration have been determined and are compared with those for the overlayer-ATR and normal ATR methods. The components of the system were ZnSe or Ge hemispherical internal reflection elements, a Au metal electrode, and water. The calculations were performed for two different values of the molar absorption coefficient for water, namely, k = 0.133 (at 1635 cm-1) and k = 0.010 (at 1885 cm-1). It was determined that the electric field enhancements in the overlayer-ATR cell can also be found in the thin-layer (TL) ATR cell. This is important in that the TL-ATR cell allows greater control over the surface properties of the chosen electrode material.

Electrical properties of polymer/Si heterojunctions

Metal/conjugated polymer film/silicon structures have been fabricated. Current-voltage measurements have been performed with both Al and Au metal electrodes on n- and p-type Si substrates. The conjugated polymer was regioregular poly (3-octylthiophene) (P3OT). Rectification ratios as high as ~10 6 have been observed, with turn on voltages of ~1.5 V. Evidence of Schottky barrier formation at the Al/polymer interface, and Fowler-Nordheim tunnelling at the P3OT/p-Si interface is shown. Capacitance-voltage characteristics were obtained in the frequency range 10 Hz to 1 MHz. Strong frequency dispersion is observed which is indicative of the presence of traps. A model is proposed to explain this dispersion which shows good agreement with the experimental results. Preliminary optical results indicate that these diodes may have applications as optical sensors.

Electrical breakdown in very thin Al2O3films

Electrical breakdown in very thin A12O3 films of thickness less than 100 A and sandwiched between Al and Au metal electrodes has been studied experimentally. Recovery of high resistance of the oxide insulator film has been observed (after breakdown) on the application of either a reverse voltage or a high current pulse or just by resting the junction for a few hours after the removal of the applied external voltage. An explanation for the effect is suggested. The breakdown field is found to depend on the insulator thickness, the temperature and the nature of the electrode metals. On the basis of experimental results the mechanisms for electrical break down at room temperatures and above, in very thin Al2O3 films, can be attributed to electronic modified thermal breakdown.

Effects of ionizing radiation on thin-oxide (20–1500 Å) MOS capacitors

Metal-oxide-semiconductor capacitors with SiO2 oxides ranging from 20 to 1500 Å thick were exposed to a 60Co γ radiation dose of 106 rad(Si). Both p- and n-type substrates and Al- and Au-metal electrodes were used. For devices with oxides less than 100 Å thick, little or no parallel shift, no increased distortion, and no increased dispersion as a result of irradiation were observed in the C-V characteristic, indicating negligible buildup of oxide charge and negligible change in the interface density upon irradiation. For oxides thicker than 100 Å, the oxide-charge buildup increased greatly with thickness in the p-type devices, whereas in the n-type devices the oxide-charge buildup was comparable to the thin-oxide value. Interpretation of the p-type Al-metal electrode devices for oxides thicker than 100 Å are consistent with 1018 cm−3 hole traps residing in the oxide. However, for oxides thinner than 100 Å, a larger value of oxide-charge buildup is predicted in these p-type Al-metal electrode devices than observed. Differences in oxide-charge buildup between p- and n-type Al-metal electrode thick-oxide devices can be understood qualitatively by metal-semiconductor work-function differences.