Effects of mechanical pressure on charge transport in ferrocene in the presence of adsorbed vapours

The change in the adsorption-induced electrical conductivity of ferrocene as a function of temperature has been studied under moderate pressure. At constant temperature, the logarithm of conductivity has been observed to be proportional to the applied pressure. A drastic change in the electrical conductivity behaviour of ferrocene, at the adsorbed state, as a function of temperature under mechanical pressure has been observed. The results are discussed in the light of different existing theories. Our results suggest that ferrocene in the vapour-adsorbed state undergoes phase transition which is modified by both temperature and pressure, and the effect of such phase transition is reflected in the unusual variation of conductivity with temperature under different pressures.     

Electrochemical properties of ferrocene adsorbed on multi-walled carbon nanotubes electrode

The adsorbed process of ferrocene on a glassy carbon (GC) electrode modified by multi-walled carbon nanotubes (MWNTs) and electrochemical properties of the adsorbed layers are investigated. It is found that the redox process of ferrocene in solution is controlled by diffusion and surface electrochemical steps on the MWNT/GC electrode in contrast to the diffusion-controlled process of ferrocene on the GC electrode. The adsorbed ferrocene exhibits a pair of well-defined redox waves in the potential range from − 0.2 V to 0.6 V. Interestingly, two pairs of obvious redox waves for the adsorbed ferrocene are observed at the switching potential over 0.8 V and the peak current values of redox waves in more positive potential increase with the enlarging switching potential. The electrochemical reaction model of ferrocene adsorbed on the MWNT/GC electrode is proposed.     

Concentration dependence of the charge of atoms adsorbed on single-sheet graphene

Simple schemes for calculating the dependences of the charge Z _a of adatoms on their coverage of a single graphene sheet are developed with allowance for the dipole-dipole repulsion. The proposed schemes are applied to the adsorption of alkali metals and atomic hydrogen. It is established that an increase in the adsorption coverage leads to a decrease in the adatom charge, which concerns both the band and local contributions to this value.     

Field evaporation of tungsten in the presence of adsorbed water

The field evaporation of tungsten at T=300 and 600 K in the presence of water vapor in the residual atmosphere was studied using a static mass spectrometer with a moderate resolution (M/ΔM=200). The room-temperature mass spectrum of field-evaporated particles displayed only the peaks of triply charged ions; an increase in the temperature to 600 K added the peaks of doubly charged ions of approximately the same intensity. The presence of adsorbed water reduced the evaporating field strength by a factor of 2-2.5. At 300 K, an increase in the water content in the residual atmosphere markedly enhanced the field etching. No singly or quadruply charged tungsten ions were observed. The results are indicative of the activation mechanism of field evaporation at the temperatures studied and show evidence of a substantial decrease in the magnitude of evaporating field caused by the presence of water.     

Ultraviolet-induced surface modification of polyurethane films in the presence of oxygen or acrylic acid vapours

An efficient surface functionalization of polyurethane (PU) films has been obtained by ultraviolet (UV)-assisted modification in the presence of oxygen or acrylic acid (AA) vapours. Film analyses were carried out by water contact angle measurements, X-ray photoelectron spectroscopy (XPS) and Near-edge X-ray absorption fine structure (NEXAFS). Film hydrophilicity increased with photolysis time in the presence of oxygen or AA vapours. Incorporation of COO and CO functional groups at the polymer surface after the UV-assisted treatments was observed. In addition, High resolution XPS and NEXAFS results showed that a thin film of poly (acrylic acid) (PAA) is formed over the PU films during the UV irradiation with AA vapours. The obtained results are compared with previous published oxygen and AA low-power plasma treatments. Similarity between both treatment methodologies is shown. UV surface functionalization and polymerization of PAA can be used instead of a traditional plasma treatment with the advantage of set-up simplicity and lower costs.     

The charge transport properties of a-Si:H thin films under hydrostatic pressure

Time resolved thermoelectric effects (TTE) were used to simultaneously determine trap levels and trap state density differences in amorphous (a-Si:H) samples. In particular, the trap state density differences are obtained from the decay of the ambipolar charge distribution, i.e. stage 2 of the TTE transients. The trap state difference density is measured under hydrostatic pressures, up to 2.2 kbar. The trap state density difference changes from a negative peak to a positive peak with increasing hydrostatic pressure, suggesting a significant pressure induced shift of the electron and hole trap levels.     

Surfactant-associated electrochemical properties of ferrocene adsorbed on a glassy carbon electrode modified with multi-walled carbon nanotubes

The electrochemical properties of ferrocene (Fc) on a glassy carbon (GC) electrode modified by multi-walled carbon nanotubes (MWNTs) in the presence and absence of surfactants have been investigated by progressively voltammetric sweeping. Dihexadecyl phosphate (DHP) and hexadecyl trismethyl ammonium chloride (HTAC) are found to impact the redox reactions of Fc adsorbed on MWNT surfaces. An excess amount of DHP dispatches Fc from MWNTs surfaces, leading to weakly adsorbed configuration of Fc. The formal potential of the adsorbed Fc in the presence of DHP shifts to a lower potential. Cationic surfactant HTAC on MWNT surfaces depresses the redox reactions corresponding to the weakly adsorbed configuration of Fc. It becomes evident that the configuration and hence redox reactions of Fc depend strongly on the presence and concentrations of surfactants on the electrode surfaces and in the buffer solutions.     

High-voltage thermionic polaron emission in the presence of adsorbed nonmetal nanofilm on a cathode

The equation of thermionic emission has been derived, which takes into account the presence of thin films of adsorbed gas-environment molecules on a cathode under conditions of high-voltage gas discharge. It is shown that the consideration of electron polaron tunneling mechanism leads to a significant (by more than an order of magnitude) decrease in the emission-current density. A comparison with the classical Richardson–Schottky equation is performed. The role of the polaron effect is shown to strongly increase with an increase in the applied electric field strength and a decrease in temperature, which is due to an increase in the electron work function because of polaron nature.     

Effects of crystal structures and intermolecular interactions on charge transport properties of organic semiconductors

In this study, the effects of the packing configuration and intermolecular interaction on the transport properties are investigated based on density functional theory. Molecular design from the standpoint of a quantum-chemical view is helpful to engender favorable molecular packing motifs. The transfer integral along the orientation with π–π overlap is much larger than other directions without π–π overlap, and the mobility along this orientation is higher than that along other directions. The intermolecular interaction analyses demonstrate that hydrogen bonds play a crucial role with strong electrostatic interactions in charge transfer. There will be a synergistic relationship when the π–π stacking and intermolecular interaction coexist in the same direction. It turns out that intermolecular interactions are responsible for charge transport, while π–π stacking interactions dominate donor–acceptor transport. Incorporating the understanding of the molecular packing motifs and intermolecular interactions into the design of organic semiconductors can assist in the development of novel materials.     

Electrical and spectrophotometric properties of charge transfer complexes of picric acid and some aniline derivatives

The charge transfer complexes produced by the reaction between picric acid and some aniline derivatives were prepared. The prepared charge transfer complexes (CTC) were investigated using infrared and nuclear magnetic resonance spectroscopy aiming to throw more light on their molecular structure. It was proved that a proton transfer interaction takes place between PiOH and x-Ph.NH₂ leading to the formation of PiO^} and x-Ph.NH₃ ⁺ ions. The normal -¹ electronic interaction takes place by transferring an electron from the aniline ring to the picric acid. The semiconducting properties of the CTC were investigated. All the prepared complexes were proved to have a semiconducting character within the temperature range investigated.     

Vapor pressure measurements of para-hydrogen adsorbed on exfoliated graphite

Monolayer isotherms were measured for 15, 18, and 20 K for para-hydrogen adsorbed on exfoliated graphite foam, and for the second, third, and fourth layers in the temperature interval of 8 to 20 K, using the standard volumetric method. From the data, the isosteric heat of adsorption, molar entropies and internal energies were obtained as a function of coverage. The values for coverages above the third layer were compared to those at the p-H₂ bulk triple point, showing that, within our experimental uncertainty, the results are closer to the values of bulk solid para-hydrogen. Critical temperatures for the second and third layers and the triple point temperature for the second layer, were determined, yielding values of T_c2 = (10.0±0.1) K, T_c3 = (11.0±0.5) K and T_t2 = (6.5±0.1) K respectively. Features occurring along the monolayer coverages are compared to transitions which occur in the para-hydrogen phase diagrams adsorbed on graphite, obtained from heat capacity measurements by other authors. From the isotherms, compressibilities were calculated as a function of coverage for several temperatures. Whenever possible the obtained results were compared to existing data in the literature.     

Non-Gaussian fluctuation in the charge transport of Si nanochains

The stability of the tunneling charge transport of a tangle of Si nanochains is investigated at high bias voltages using a micromanipulator in a scanning electron microscope. We confirm that the influence of electron injection due to the electron beam of a scanning electron microscope on the charge transport properties of nanochains is negligible when the electrode gap is small and the bias voltage is large. Under such conditions, current-time curves show large fluctuations. We find that the fluctuation is not a simple Brownian motion, but its distribution function can be fitted well by a Lévy distribution. Its origin is discussed in terms of percolation theory.     

Features of the charge transfer in nanoporous silicon nd silicon oxide with adsorbed water

The experimental plots of electric conductivity versus temperature for a porous silicon and a silicon oxide with adsorbed water exhibit features at temperatures significantly below 0°C, which are related to an ice-water phase transition in nanopores of the solid matrix.     

Universal scaling of the charge transport in large-area molecular junctions

Charge transport through alkanes and para-phenylene oligomers is investigated in large-area molecular junctions. The molecules are self-assembled in a monolayer and contacted with a top electrode consisting of poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonic acid) (PEDOT:PSS). The complete set of J(V,T) characteristics of both saturated and π-conjugated molecules can be described quantitatively by a single equation with only two fit parameters. The derived parameters, in combination with a variation of the bulk conductivity of PEDOT:PSS, demonstrate that the absolute junction resistance is factorized with that of PEDOT:PSS.     

Effects of deionized water pressure and purified nitrogen gas on the chemical mechanical polishing process

The chemical mechanical polishing (CMP) process is widely used for the global planarization of inter-layer dielectric (ILD) for deep sub-micrometer technology. But hot-spots due to partial over-polishing generated in the edges of wafers, have become a major concern. Thus, it is very important to understand the correlation between the ILD-CMP process and various facility factors of the CMP equipment system. With a facility shortage of de-ionized water (DIW) pressure, we introduced an additional purified nitrogen (PN₂) gas in the polishing-head-cleaning station to increase the cleaning effect. Our experimental results show that DIW pressure and PN₂ gas factors were not related to the removal rate, but edge hot-spots on the patterned wafer had a strong relation with them. We estimated two factors (DIW pressure and PN₂ gas) for the improvement of the CMP process. In particular, we obtained a uniform planarity in the patterned wafer and prevented more than 90% of wafer edge over-polishing. Finally, we suggest that the facility factors for an equipment system play an important role in the ILD-CMP process.     

Observation of quantum interference in molecular charge transport

As the dimensions of a conductor approach the nanoscale, quantum effects begin to dominate, and it becomes possible to control the conductance through direct manipulation of the electron wavefunction. Such control has been demonstrated in various mesoscopic devices at cryogenic temperatures, but it has proved to be difficult to exert control over the wavefunction at higher temperatures. Molecules have typical energy level spacings (～eV) that are much larger than the thermal energy at 300?K (～25?meV), and are therefore natural candidates for such experiments. Previously, phenomena such as giant magnetoresistance, Kondo effects and conductance switching have been observed in single molecules, and theorists have predicted that it should also be possible to observe quantum interference in molecular conductors, but until now all the evidence for such behaviour has been indirect. Here, we report the observation of destructive quantum interference in charge transport through two-terminal molecular junctions at room temperature. We studied five different rigid π-conjugated molecular wires, all of which form self-assembled monolayers on a gold surface, and find that the degree of interference can be controlled by simple chemical modifications of the molecular wire.