Search

We report the fabrication and characterization of copper microelectrodes obtained by a homemade lithography technique and after gold electroless deposition. For the fabrication, planes consisting of arrays of electrodes (black in color) with bow tie shape were designed and printed on a transparent paper (Canson ltd.). Using an embroidery frame with a silk fabric, a photographic emulsion was spread on the silk and simultaneously pressing the Canson paper on it. The system was introduced into a closed box and exposed with a UV light. The designed electrode templates prevented direct exposition of the UV light over copper films and indelible ink was spread over it. After the ink was dried, the copper film is immersed into ferric acid to attack the uncovered copper parts (where there is no ink). In this way, we obtained copper electrodes with initial gap separation of ~142μm and subsequently, they followed electroless deposition of gold to make the copper electrodes to contact. For the characterization, electrical measurements were performed. They present ohmic resistance values in the order of 106 Ω produced by surface scattering of the electrons within the gold microwire and enhanced by oxidation of the copper electrodes.

Author(s): Sun, J; Sapkota, A; Park, H; Wesley, P; Jung, Y; Maskey, BB; Kim, Y; Majima, Y; Ding, J; Ouyang, J; Guo, C; Lefebvre, J; Li, Z; Malenfant, PRL; Javey, A; Cho, G | Abstract: A limitless-length flexible active-matrix implies that virtually any surface can be rendered into an interactive medium when laminated with electrophoretic or organic light-emitting diode sheets. However, performance, cost, and size limitations of current fabrication technologies and semiconducting materials, typically utilized in thin film transistor (TFT) active matrices (TFT-AMs), have hindered progress, thus preventing the realization of fully printed TFT-AMs on a plastic roll. A new high-purity semiconducting single-walled carbon nanotube (s-SWCNT) ink is prepared by first isolating 99.9% pure s-SWCNTs via conjugated polymer extraction, and then utilizing a ligand-exchange method to formulate a novel hydrophilic gravure-compatible semiconducting ink. Based on the s-SWCNT ink, a fully additive manufacturing process using roll-to-roll (R2R) gravure printing enables the fabrication of a flexible TFT-AM, overcoming performance, cost, and size limitations. TFT-AMs with 10 to 40 PPI resolution where average mobility of 0.23 ± 0.12 cm2 V−1 s−1, average on–off ratio of 104.1, and threshold voltage variation of ±13% are attained. As a proof of concept, an inexpensive and flexible electrophoretic display is demonstrated by simply laminating an electrophoretic sheet onto the R2R gravure-printed s-SWCNT-based TFT-AM.

The phenylazomethine dendrimer exhibits “atom mimicry,” and its polymerization (and Lewis acid accumulation) is demonstrated., The phenylazomethine dendrimer (DPA) has a layer-by-layer electron density gradient that is an analog of the Bohr atom (atom mimicry). In combination with electron pair mimicry, the polymerization of this atom-mimicking dendrimer was achieved. The valency of the mimicked atom was controlled by changing the chemical structure of the dendrimer. By mimicking a divalent atom, a one-dimensional (1D) polymer was obtained, and by using a planar tetravalent atom mimic, a 2D polymer was obtained. These poly(dendrimer) polymers could store Lewis acids (SnCl2) in their unoccupied orbitals, thus indicating that these poly(dendrimer) polymers consist of a series of nanocontainers.

Tribenzosubporphyrins are boron(III)-chelated triangular bowl-shaped ring-contracted porphyrins that possess a 14π-aromatic circuit. Their flat molecular shapes and discrete molecular orbital diagrams make them ideal for observation by scanning tunneling microscopy (STM). Expanding their applications toward single molecule-based devices requires a fundamental knowledge of single molecular conductance between tribenzosubporphines and the STM metal tip. We utilized a tungsten (W) STM tip to investigate the electronic properties of B-(5-mercaptopentoxy)tribenzosubporphine 1 at the single molecular level. B-(5-mercaptopentoxy)-tribenzosubporphine 1 was anchored to the Au(111) surface via reaction with 1-heptanethiol linkers that were preorganized as a self-assembled monolayer (C7S SAM) on the Au(111) substrate. This arrangement ensured that 1 was electronically decoupled from the metal surface. Differential conductance (dI/dV - V) measurements with the bare W tip exhibited a broad gap region of low conductance and three distinct responses at 2.4,-1.3, and -2.1 V. Bias-voltage-dependent STM imaging of 1 at 65 K displayed a triangle shape at -2.1V-1.3 V and a circle shape at V-2.1 V, reflecting its HOMO and HOMO-1, respectively. In addition, different conductance behaviors were reproducibly observed, which has been ascribed to the adsorption of a tribenzosubporphine-cation on the W tip. When using a W tip doped with preadsorbed tribenzosubporphine-cation, negative differential resistance (NDR) phenomena were clearly observed in a reproducible manner with a peak-to-valley ratio of 2.6, a value confirmed by spatial mapping conductance measurements. Collectively, the observed NDR phenomena have been attributed to effective molecular resonant tunneling between a neutral tribenzosubporphine anchored to the metal surface and a tribenzosubporphine cation adsorbed on a W tip.

In this work, we report the mechanical reorientationof thiolated ferromagnetic microspheres bridging a pairof gold electrodes under an external magnetic field. Whenan external magnetic field (7 kG) is applied during themeasurement of the current–voltage characteristics of a carboxylferromagnetic microsphere (4 μm diameter) attachedto two gold electrodes by self-assembled monolayers(SAMs) of octane dithiol (C8H18S2), the current signal isdistorted. Rather than due to magnetoresistance, this effectis caused by a mechanical reorientation of the ferromagneticsphere, which alters the number of SAMs between thesphere and the electrodes and therefore affects conduction.To study the physical reorientation of the ferromagneticparticles, we measure their hysteresis loops while suspendedin a liquid solution.Keywords Magnetic microparticles

An n-type organic semiconductor 2:3,5:6-bis(1,1-dicyanoethylene-2,2-dithiolate)-quinone (BDQ) has been successfully synthesised and characterised. The single crystal structure of BDQ, determined by single-crystal X-ray crystallography, indicated that BDQ is a planar molecule with strong face-to-face π-π stacking (3.40 Å) and S···S interactions (3.66 Å) between neighbouring molecules, which might be in favour of the effective charge transport. The UV-vis spectrum shows that BDQ has shoulder absorption up to 550 nm (2.25 eV). The electrochemical property displays that the HOMO-LUMO gap of BDQ obtained from the half-wave redox potential is 1.92 eV. The displacement current measurement of BDQ-based devices is demonstrated and discussed.

LaCaBaCu3O7 is a high critical temperature superconductor (HTS) below the Tc = 80 K and its structure is similar to that of YBCO. In this work we study the effect in the irreversibility line and the Curie-Weiss temperature of this superconductor after borate (BO3) 3- doping (LaCaBaCu3-x(BO3)xO7-δ x=0.2 and 0.3). Interestingly, borate doping enhances the irreversibility line and this effect is probably caused from alteration the arrangement of the oxygen atoms in the crystalline structure. Moreover, the Curie-Weiss temperature (□p) in the normal state increases with doping concentration. Calculated □p for pure LaCaBaCu3O7 is around -98K, this value increases to -75 and 49 K for x=0.2 and 0.3 respectively and indicating transition from antiferromagnetic to ferromagnetic coupling between ions in the structure. This study provides additional data for the magnetic characteristics of doped like-123 crystalline structures with oxyanions.

For the better performance of organic thin-film transistors (TFTs), gate-insulator surface treatments are often applied. However, the origin of mobility increase has not been well understood because mobility-limiting factors have not been compared quantitatively. In this work, we clarify the influence of gate-insulator surface treatments in pentacene thin-film transistors on the limiting factors of mobility, i.e., size of crystal-growth domain, crystallite size, HOMO-band-edge fluctuation, and carrier transport barrier at domain boundary. We quantitatively investigated these factors for pentacene TFTs with bare, hexamethyldisilazane-treated, and polyimide-coated SiO2 layers as gate dielectrics. By applying these surface treatments, size of crystal-growth domain increases but both crystallite size and HOMO-band-edge fluctuation remain unchanged. Analyzing the experimental results, we also show that the barrier height at the boundary between crystal-growth domains is not sensitive to the treatments. The res...

The structures of nanomaterials determine their individual properties and the suprastructures they can form. Introducing anisotropic shapes and/or interaction sites to isotropic nanoparticles has been proposed to extend the functionality and possible suprastructure motifs. Because of symmetric anisotropy, Platonic solids with regular polygon faces are one of the most promising nanoscale structures. Introduction of Platonic solid anisotropy to isotropic nanomaterials would expand the functionality and range of possible suprastructure motifs. Here, we demonstrate a novel strategy to obtain nano-Platonic solids through the face coordination of square porphyrins on an inscribed Au sphere with adequate size. The face coordination of the multidentate porphyrin derivatives, with four acetylthio groups facing the same direction, on the Au cluster encased the Au cluster in a Platonic hexahedron with six porphyrin faces. Transmission electron microscopy, mass spectrometry, elemental analysis, and scanning tunnelling microscopy were used to confirm the formation of the nano-Platonic hexahedron.

In this work, we study the long-term aging effect caused by Fe atoms in the superconductor CaLaBa{Cu1 − xFex}3O7 − δ with 0 ≤ x ≤ 0.07. XRD confirms that this system has a YBCO-like structure. The critical temperature (Tc) is strongly affected by aging and depends on the amount of Fe in the structure. Room temperature Mossbauer spectroscopy reveals the presence of the typical species A, B–B ′, C and new species E ′ and F. Interestingly; A, which corresponds to the Fe3 + atom located in the Cu(1) of the chains with spin S z = 3/2, shows a drastic reduction which means migration to the species B, B ′ and C. Species B and B ′ correspond to the Fe3 + in the Cu(2) site forming planar quasi-octahedral and planar square pyramidal, while the C specie is a square pyramidal with O(5) respectively (spin Sz = 3/2 in all these cases). Aging causes loss of superconductivity in the samples with 5 and 7% of iron content.

In this work we report the preparation of magnetic hematite hollow sub-micron spheres (α-Fe2O3) by colloidal suspensions of ferric nitrate nine-hydrate (Fe(NO3)3·9H2O) particles in citric acid solution by following the sol–gel method. After the gel formation, the samples were annealed at different temperatures in an oxidizing atmosphere. Annealing at 180°C resulted in an amorphous phase, without iron oxide formation. Annealing at 250°C resulted in coexisting phases of hematite, maghemite and magnetite, whereas at 400°C, only hematite and maghemite were found. Pure hematite hollow sub-micron spheres with porous shells were formed after annealing at 600°C. The characterization was performed by X-ray diffraction (XRD), Mossbauer spectroscopy (MS) and scanning electron microscopy (SEM).

We identified the orientation of individual Lu@C82 molecules on alkanethiol self-assembled monolayers (SAMs) by scanning tunneling microscopy (STM) at a molecular resolution. STM images of Lu@C82 on alkanethiol SAMs at 65 K showed a striped structure corresponding to the molecular orbitals of the Lu@C82 molecule, suggesting that thermal rotation of Lu@C82 on alkanethiol SAMs is prevented at 65 K. By comparing these molecular-resolution STM images with Kohn−Sham molecular orbitals of Lu@C82 calculated by density functional theory (DFT), we identified the molecular orientation of Lu@C82. Spatial mapping of the differential conductance on individual Lu@C82 molecules revealed that the local conductivity within a molecule became large around the Lu atom at a negative sample bias voltage. From spatial mapping of the differential conductance measurements, we also evaluated the HOMO−LUMO gap of Lu@C82 to be 0.47 eV. From the results of the spatial mapping of the differential conductance and DFT calculations, the ...

The interface trap level in top-contact pentacene thin-film transistors (TFTs) is obtained by displacement current measurement (DCM) during device operation at temperatures ranging from 260 to 340 K. The carrier injection voltage at the source electrode (Vinj) was measured from the displacement current and found to be independent of temperature, suggesting an Ohmic contact at the Au source electrode/pentacene interface. On the contrary, the threshold voltage (Vth) depended on the temperature. The interface trap level at the pentacene/gate dielectric interface was estimated as 36 meV from the temperature dependence of the interface trap density. By using the DCM method, it becomes possible to demonstrate the carrier injection and transport properties of top-contact pentacene TFTs.

A crystallization and surface evolution study of Au thin film on SiO2 substrates following annealing at different temperatures above the eutectic point of the Au/Si system are reported. Samples were prepared by conventional evaporation of gold in a high vacuum (10−7 mbar) environment on substrates at room temperature. Thermal treatments were performed by both furnace and flame annealing techniques. Au thin films can be crystallized on SiO2 substrates by both furnace and flame annealing. Annealing arranges the Au crystallites in the (1 1 1) plane direction and changes the morphology of the surface. Both, slow and rapid annealing result in a good background in the XRD spectra and hence clean and complete crystallization which depends more on the temperature than on the time of annealing. The epitaxial temperature for the Au/SiO2 system decreases in the range of 350–400 °C. Furnace and flame annealing also form crystallized gold islands over the Au/SiO2 surface. Relaxation at high temperatures of the strained Au layer, obtained after deposition, should be responsible for the initial stages of clusters formation. Gold nucleation sites may be formed at disordered points on the surface and they become islands when the temperature and time of annealing are increased. The growth rate of crystallites is highest around 360 °C. Above this temperature, the layer melts and gold diffuses from the substrate to the nucleation sites to increase the distance between islands and modify their shapes. Well above the eutectic temperature, the relaxed islands have hexagonally shaped borders. The mean crystallite diameters grow up to a maximum mean size of around 90 nm. The free activation energy for grain boundary migration above 360 °C is 0.2 eV. Therefore the type of the silicon substrate changes the mechanism of diffusion and growth of crystallites during annealing of the Au/Si system. Epitaxial Au(1 1 1) layers without formation of islands can be prepared by furnace annealing in the range of 300–310 °C and by flame annealing of a few seconds and up to 0.5 min.

Drain-to-source current (IDS ¼ð IDISÞ=2) and displacement current (Idis ¼ IS þ ID) are evaluated using the simultaneous measurements of source (IS) and drain (ID) currents during the application of a constant drain voltage and a triangular-wave gate voltage (VGS) to top-contact pentacene thin-film transistors. The carrier mobility, threshold voltages and mean potential drops at the source/channel and channel/drain interface are simultaneously obtained from IDS-VGS and Idis-VGS relationships. Carrier injection properties, namely, the carrier injection voltage at the source electrode and the mean potential drop-VGS relathionship are discussed on the basis of results of the simultaneous measurements of IDS and Idis. (DOI: 10.1143/JJAP.46.390)

We present the analysis of chemically assembled double-dot single-electron transistors using orthodox model considering offset charges. First, we fabricate chemically assembled single-electron transistors (SETs) consisting of two Au nanoparticles between electroless Au-plated nanogap electrodes. Then, extraordinary stable Coulomb diamonds in the double-dot SETs are analyzed using the orthodox model, by considering offset charges on the respective quantum dots. We determine the equivalent circuit parameters from Coulomb diamonds and drain current vs. drain voltage curves of the SETs. The accuracies of the capacitances and offset charges on the quantum dots are within ±10%, and ±0.04e (where e is the elementary charge), respectively. The parameters can be explained by the geometrical structures of the SETs observed using scanning electron microscopy images. Using this approach, we are able to understand the spatial characteristics of the double quantum dots, such as the relative distance from the gate electrode and the conditions for adsorption between the nanogap electrodes.

The interaction control between endohedral metallofullerenes and a metal substrate has been demonstrated by introducing hexanethiol, octanethiol, and decanethiol self-assembled monolayers (SAMs) as the interlayer. We observe the electric properties of terbium endohedral metallofullerenes (Tb@C82) on alkanethiol SAMs with different chain lengths by scanning tunneling microscopy (STM) and spectroscopy (STS). Based on the comparison of the high-resolution STM images of a Tb@C82 molecule on hexanethiol and octanethiol SAMs, the interaction between Tb@C82 and a hexanethiol SAM is found to be larger than that between Tb@C82 and an octanethiol SAM; this is because at 68 K, the rotational states of Tb@C82 terminate only on the hexanethiol SAM. Furthermore, we find that the tunneling current-voltage characteristics of Tb@C82 on the hexanethiol SAM show the rectifying effects that are also caused by the molecular energy level shifts of Tb@C82 molecules due to the large interaction.

The single molecular orientation switching of the Tb@C82 endohedral metallofullerene has been studied by using low-temperature ultrahigh vacuum (UHV) scanning tunneling microscopy (STM). An octanethiol self-assembled monolayer (SAM) was introduced between Tb@C82 and the Au(111) substrate to control the thermal rotational states of Tb@C82. Scanning tunneling spectroscopy (STS) of Tb@C82 on an octanethiol SAM at 13 K demonstrated hysteresis including negative differential conductance (NDC). This observed hysteresis and NDC is interpreted in terms of a switching of the Tb@C82 molecular orientation caused by the interaction between its electric dipole moment and an external electric field.

Simultaneous measuring system of tunneling current and displacement current has been developed for direct detecting the single electron motion in nanomechanical single electron devices. Tunneling current and displacement current staircases have been observed simultaneously in current-voltage characteristics of the double barrier tunneling junctions (DBTJs) that consist of scanning vibrating probe/vacuum/colloidal Au nanoparticles/Au(111) substrate. Single electron motion on and through the colloidal Au nanoparticles has been analyzed by both the displacement current and tunneling current staircases. The negative differential conductance has also been observed in the current-voltage dependence of the same DBTJs. For realizing the nanomechanical single electron device with self-excitation, the utilization of alkanethiol molecules as the tunneling barrier has been discussed.

Simultaneous measurements of tunneling current and displacement current spectroscopy are demonstrated in nanomechanical double-barrier tunneling structures which consist of scanning vibrating probe/vacuum/colloidal Au dots/self-assembled monolayer (SAM)/Au substrate. The displacement current staircase due to Coulomb blockade is observed together with the tunneling current staircase in the nanomechanical double-barrier tunneling structures. In the case of tunneling current spectroscopy, negative differential resistances (NDRs) are also observed. NDRs are concerned with the change in the number of electrons on the Au dot and the tunneling resistance.

Surface potentials of Cu-tetra- tert -butyl-phthalocyanine (CuttbPc) Langmuir–Blodgett (LB) films on metal electrodes were measured under photoillumination in a vacuum vessel. The surface potential of CuttbPc LB films on Al and Cr electrodes, positively charged as deposited. Decreases very little but not zero by photoillumination, whereas the potential of films on Al and Cr electrodes increases. A linear relationship between the work function of metal electrodes and the saturated surface potential of CuttbPc LB films was obtained in dark and under photoillumination, indicating that electronic charges are exchanged at the interface between metal electrodes and film. The space charge distribution in CuttbPc LB films was determined on the order of nanometer film-thickness scale. It was concluded that about 1% of CuttbPc molecules make a contribution to the charge exchange and 9–27% of the contributed charges lose the charge exchange by photoillumination.

A single-electron transistor (SET) consists of source, drain, Coulomb island, and gate to modulate the number of electrons and control the current. For practical applications, it is important to operate a SET at room temperature. One proposal towards the ability to operate at room temperature is to decrease Coulomb island size down to a few nanometres. We investigate a SET using Sn-porphyrin (Sn-por) protected gold nanoparticles (AuNPs) with 1.4 nm in core diameter as a Coulomb island. The fabrication method of nanogap electrodes uses the combination of a top-down technique by electron beam lithography (EBL) and a bottom-up process through electroless gold plating (ELGP) as our group have described before. The electrical measurement was conducted at room temperature (300 K). From current–voltage (I d–V d) characteristics, we obtained clear Coulomb blockade phenomena together with a Coulomb staircase due to a Sn-por protected gold NP as a Coulomb island. Experimental results of I d–V d characteristics agree with a theoretical curve based on using the orthodox model. Clear dI d/dV d peaks are observed in the Coulomb staircase at 9 K which suggest the electron transports through excited energy levels of Au NPs. These results are a big step for obtaining SETs that can operate at room temperature.

An electrostatic space charge layer of nanometer thickness is formed at organic film/metal interfaces due to the displacement of electrons from the metal to the film. This space charge layer directly affects the current–voltage (I–V) characteristics of artificially layered rhoadamine–dendorimer thin films, which show a step structure similar to a Coulomb staircase. The capacitance between one rhodamine–dendorimer molecule and a metal electrode is calculated using a sphere-plane model, assuming that excess electronic charges are displaced from the plane metal electrode into the film. This capacitance is found to increase as the excess charge increases which leads to a change in the voltage steps in the I–V characteristics as observed in metal/polyimide/ rhodamine–dendorimer/polyimide/metal junctions. Such a voltage step is derived theoretically, and will explain the difference between Au/polyimide/rhodamine–dendorimer/ polyimide/Al and Al/polyimide/rhodamine–dendorimer/polyimide/Al junctions.

Using Maxwell displacement current (MDC) and second harmonic generation (SHG) measurements, the linear and nonlinear dielectric properties of organic monolayer films on a material surface can be examined. In this study, we have developed a novel experimental system which can detect MDC and SHG signals, and examined the molecular motion of 4-cyano-4′-n-alkyl-biphenyls (5CB) on the water surface by monolayer compression. The orientational order parameters expressed by using Legendre polynomials were successfully determined from both MDC and SHG signals, and the difference in the determined order parameters was discussed in association with the molecular motion of 5CB monolayers.

Surface potentials of Cu tetra-tert-butyl-phthalocyanine (CuttbPc) Langmuir-Blodgett (LB) films on metal electrodes were measured under photoillumination. The surface potential of CuttbPc LB films on Au electrode, positively charged as deposited, decreases by photoillumination, whereas the potential of films on Al and Cr electrodes, negatively charged as deposited, increases. A linear relationship was obtained between the work function of metal electrodes and the saturated surface potential of CuttbPc LB films in the dark, and a similar relationship was also suggested under photoillumination. These results indicate that electronic charges are exchanged at the interface between metal electrodes and the films until the surface Fermi level of films and the Fermi level of metals mutually coincide. The space charge distribution in CuttbPc LB films was determined on the order of nanometer film thickness, and the distribution of the electronic density of states was also determined assuming the presence of both electron donor and acceptor states at the film/metal interface. It was concluded that about 1% of CuttbPc molecules contribute the charge exchange and 9–27% of these contributed charges lose the charge exchange by photoillumination. Finally, the surface potential decay process was analyzed assuming thermodynamics quasi-equilibrium at the interface.

We develop a facile process to integrate colloidal silicon nanocrystals (Si NCs) with metal electrodes in a single-electron transistor by self-assembly. Gold (Au) surface is modified by an amine-terminated self-assembled monolayer to have a positive potential. All-inorganic boron (B) and phosphorus (P) codoped Si NCs, with a negative surface potential and size-controllability, are selectively adsorbed on an amine-terminated Au surface by electrostatic attraction. We demonstrate the fabrication of SETs consisting of electroless-plated Au nanogap electrodes and codoped Si NCs using this process and observation of clear Coulomb diamonds at 9 K.

In this work we report the thermal oxidation of amorphous germanium (a-Ge) thin films (140 nm thickness) in air. Following fabrication by conventional thermal evaporation on SiO2 substrates, the samples were annealed in air at different temperatures ranging from 300 to 1000 °C. By means of x-ray diffraction, x-ray reflectivity, synchrotron grazing-incidence wide-angle x-ray scattering and cross-sectional transmission electron microscopy analysis it is found that the a-Ge films abruptly crystallize at 475 °C, while simultaneously increasing the thickness of the oxide (GeO2) in a layer by layer fashion. X-ray photoemission spectroscopy reveals that the oxidation state of the Ge atoms in the GeO2 layer is 4+. However, a reaction at the GeO2/Ge interface occurs between 500 and 550 °C reducing the oxide layer to GeO x (x < 2) and containing Ge2+ and Ge+. The thickness of the oxide layer grows with the annealing temperature following an Arrhenius behavior with an activation energy of 0.82 ± 0.09 eV up to 500 °C. Remarkably, we observed simultaneous enhancement of the oxidation and crystallization of the a-Ge in the temperature interval 450 °C–500 °C, in which the oxidation rate reaches a maximum of around 0.8 nm °C−1 at around 500 °C.

A measuring system that separates the both waveforms of displacement and tunneling current using a scanning vibrating probe is described. In the measuring system, the displacement and tunneling current flow periodically in accordance with the perpendicular vibration of the probe. The external circuit current is measured by oscilloscope and is separated into both waveforms of the displacement and tunneling current by utilizing the phase difference of them. The waveform of the displacement current is also analyzed by assuming the presence of excessive surface charges above the sample. Consequently, we can determine the mean distance between the probe and sample, and the offset voltage which is built up by excessive surface charges and work function difference of the probe and sample.

The current-voltage (I-V) characteristic of Au/PI/(Rh-G2 + PI)/PI/Au (or Al) junctions was examined. An asymmetrical I-V characteristic with several steps was observed for Au/PI/PI:Rh-G2/PI/Al junctions, whereas a symmetric I-V characteristic with steps was obtained for Au/PI/PI:Rh-G2/PI/Au junctions. It was concluded that the presence of metal/organic interfacial states made a significant contribution to the I-V characteristics of these junctions.

We have developed a scanning displacement current microscope (SDM) which measures the electrical surface properties of samples by displacement current. SDM vibrates its probe perpendicularly to the sample with applying d.c. voltage to the probe. Both displacement current and tunneling current flow periodically in accordance with the vibration of the probe and are separated by using a two-phase lock-in amplifier. In this paper, we observe both displacement current image and the topographic image of a sample with grating profile simultaneously under constant tunneling current operation. We also analyze the resolution of the displacement current image.

Maxwell displacement current (MDC) measurement coupled with second harmonic generation (SHG) measurement was employed for the orientational order study of Langmuir films. 4-alkyl-4′-cyanobiphenyl ( n CB, n =5, 6, 7 and 8) Langmuir films were examined, and the orientational order parameters were determined. The difference in the generation between MDC and SHG was revealed, and was discussed based on the difference in the contribution of n CBs. It is shown that the measurement employed here is very helpful for the orientational study of Langmuir films.

The scanning probe microscope used for the simultaneous measurement of tunneling current and surface potential (TSM) is analyzed. Using an electric image method, the capacitance formed between the vibrating tip and plane sample is calculated, assuming that the vibrating tip is a sphere electrode with a radius r. The formula expressing the displacement current and the capacitance is obtained. The resolution of the TSM is discussed, and concluded that the lateral resolution of the displacement current mode is better than one fifth of the tip radius r, e.g., about 1 μm for r=5 μm. Finally, the distance between the tip and plane sample, and the tip radius were experimentally determined by comparing the theoretical relationship between the displacement current and the distance.

Using the Maxwell displacement current (MDC) measurement with alternating monolayer compression and expansion process, the dielectric property of monolayers has been investigated. The monolayer expansion and compression processes were analyzed on the basis of the Debye theory, and the relaxation time of dl-alpha-dilaurylphosphatidylcholine (DLPC) was determined using a whole curve of MDCs. It was suggested that the interaction among molecules makes a contribution to the dielectric relaxation phenomena, although the change in the orientational order of polar molecules is a main contribution of MDC. Copyright 1999 Academic Press.

Cantilever resonance is detected by a tunneling current between a scanning tunneling microscope probe and an Au–Ti-coated SiO2 cantilever on a Si substrate under the application of an RF signal from a Si back electrode under the SiO2 layer. The cantilever resonance frequency obtained by tunneling current measurements corresponds well with those obtained by displacement current measurements between a cantilever array and the Si back electrode. The tunneling current at the resonant condition depended on the power of the RF signal. The vibration amplitude of the cantilever was evaluated to be of the order of 1–3 A by the tunneling current.

Threshold voltage instabilities in SiO2/polyimide dual-gate dielectric pentacene thin-film transistors are investigated as a function of bias stress time for 1000 s at temperatures between 260 and 340 K in nitrogen atmosphere. Field-effect mobility maintains constant values at every measurement temperature during the application of constant bias stress voltage. The threshold voltage shift at all measurement temperatures is described by the stretched exponential stress time dependence of ΔVth(t) = ΔVth0{1-exp [-(t/τ)β]}. These experimental results suggest that our threshold voltage shift can be interpreted as carrier injection from the pentacene channel into traps located at the channel/gate dielectric interface.

The stochastic single-molecule conductance switchings of nitro-substituted oligo(phenylene–ethynylene) (OPE) molecules in three kinds of host matrices of octanethiol (C8), decanethiol (C10), and dodecanethiol (C12) self-assembled monolayers (SAMs) have been studied by scanning tunneling microscopy (STM). The stochastic single-molecule conductance switching of OPE molecules has been observed repeatedly in both the low-density striped phase of the C8 SAM and the high-density standing-up phases of the C10 and C12 SAMs by successive STM. The mean apparent height differences between the inserted OPE and the host matrices of the C8, C10, and C12 SAMs are approximately 11.9, 4.8, and 4.2 A, respectively.

The preparation and optical properties of the novel silicon-related material named oxygen-crosslinked polysilane were investigated. The oxygen-crosslinked polysilane was prepared by the thermal annealing of the precursor polysilane bearing alkoxyl groups. The photoluminescence consisting of a broad visible band at about 440 nm and a relatively sharp band at about 360 nm was observed at room temperature. The relative intensities of the visible emission were changed during the crosslinking. The visible emission was greatly affected by the steric hindrance of the alkoxyl groups of the precursor. The visible electroluminescene (EL) was also observed uniformly from the EL cell consisting of the oxygen-crosslinked polysilane film sandwiched between A1 electrode and indium-tin-oxide (ITO) electrode. The current densities of the EL cell increased with an increase in the oxygen-crosslinking. © 1997 John Wiley & Sons, Ltd.

We report the elaboration of SiN x -passivated chemically assembled single-electron transistors (SETs) by bottom-up processes involving electroless Au plating and the chemisorption of Au nanoparticles. With a Au top-gate electrode, the SiN x -passivated SETs showed a clear Coulomb diamond at 9 K and the top-gate capacitance was 17 times larger than the side-gate capacitance. Moreover, Coulomb oscillation and the Coulomb diamond were observed even at 160 K. Thus, planar technology is applicable to chemically assembled SETs.

Energy transfer distances from polysilanes bearing alkyl groups to those bearing aromatic groups are estimated by employing heteropolysilane Langmuir−Blodgett (LB) films. In the heteropolysilane films, AL1-LB film (10 layers, poly((hydroxyhexyl)hexylsilane))/I1-LB film (n layers, insulator polymer, (isobutyl methacrylate))/AR1-LB film (10 layers, poly((hydroxyphenyl)butylsilane)), AL1 is selectively excited with 310 nm light and the fluorescence from AR1-LB film is observed, as the number of insulator layers, n, is changed. The results imply that energy does not transfer from AL1-LB film to AR1-LB film when two insulator LB layers (22 A) are inserted between the two polysilane LB films. The electron transfer distances from polysilanes to (2,2‘-(2-(cholan-24-yl)-2,5-cyclohexadiene-1,4-diylidene)bis(propanedinitrile) (TCNQ1) are also estimated by employing a heteropolysilane LB film, AL1-LB film (10 layers)/I1-LB film (insulator, n layers)/TCNQ1-LB film (10 layers). The electron transfer distance from AL1-L...

Ideal discrete energy levels in synthesized Au nanoparticles (6.2 ± 0.8 nm) for a chemically assembled single-electron transistor (SET) are demonstrated at 300 mK. The spatial structure of the double-gate SET is determined by two gate and drain voltages dependence of the stability diagram, and electron transport to the Coulomb box of a single, nearby Coulomb island of Au nanoparticles is detected by the SET. The SET exhibits discrete energy levels, and the excited energy level spacing of the Coulomb island is evaluated as 0.73 meV, which well corresponds to the expected theoretical value. The discrete energy levels show magnetic field evolution with the Zeeman effect and dependence on the odd–even electron number of a single Au nanoparticle.

Polysilane polymers bearing hydroxyalkyl or alkoxyalkyl groups form monolayers (L films) at an air-water interface. It is possible to transfer all of the L films to hydrophobic substituents to provide Langmuir-Blodgett films. Among these polymers, polysilanes having more than three alkyl carbons have provided, oriented polysilane thin films in which the silicon main chains align with each other in the direction parallel to the dipping direction of the substrates. The orientations were evaluated by their polarized UV absorptions

Displacement current staircase due to Coulomb blockade is observed together with a tunneling current staircase in nanomechanical double barrier tunneling structures that consist of scanning vibrating probe/colloidal Au particles/vacuum/PtPd substrate. We discuss the motion of single electrons on and through the Au particles from both the tunneling and displacement current staircases, and demonstrate the electron shuttle phenomenon due to nanomechanical probe vibration.

We report that the high critical temperature superconductor (HTCS) LaCaBaCu3O7 in the form of nanograins can be linked to Au(111) surfaces through self assembled monolayers (SAMs) of HS–C8H16–HS [octane (di)thiol]. We show that La1113 particles (100 nm mean diameter) can be functionalized by octane (di)thiol without affecting their superconducting critical temperature (T C=80 K). X-ray photoemission spectroscopy (XPS) analysis reveals that the thiol functional heads link the superconducting grain surfaces creating sulfonates and we deduce that bonding between the S atoms and Cu(1) atoms of the La1113 structure would be formed. We suggest a design for a superconducting transistor fabricated by immobilized La1113 nanograins in between two gold electrodes which could be controlled by an external magnetic field gate.

We measured the surface potential of 1,10-decanedithiol (C10S2) molecules inserted into 1-octanethiol (C8S) self-assembled monolayers (SAMs) using Kelvin-probe force microscopy (KFM) with noncontact atomic force microscopy (NC-AFM) under ultrahigh-vacuum (UHV) conditions. C8S SAMs on Au(111) were used as host matrices for C10S2 molecular insertion. Molecular insertion was used to orient the inserted C10S2 molecules to form a Au(111) surface−thiol bond at one end, whereas the thiol termini at the other end protruded from the C8S SAMs. The histograms of the surface potential images of the mixed C10S2:C8S SAMs exhibited two Gaussian peaks; however, the histograms of the surface potential images of the C8S SAMs exhibited only one peak. The surface fractions of C10S2 molecules in the mixed C10S2:C8S SAMs were evaluated from the Gaussian peaks. The surface potential of the inserted C10S2 molecules was 11 mV higher than that of the host C8S SAMs. The dipole moment difference between C10S2 molecules and C8S molec...

The effect of TiO 2 mesoporous structures sensitized with poly(3-thiophene acetic acid) (PTAA) on the photovoltaic performance was investigated. In contrast to conventional Ru-complex dye-sensitized solar cells (DSCs), the cell efficiency (η) of PTAA-sensitized solar cells exhibited strong dependence on the Ti0 2 pore structures. Incorporation of up to 40 wt % large TiO 2 nanoparticles (L-Ti0 2 ) into small TiO 2 nanoparticles (S-TiO 2 ) increased η, in spite of a reduction in dye loading due to a decrease in surface area. The highest η of 2.36 ± 0.04% was obtained for a TiO 2 film comprised of S-TiO 2 (60 wt %) and L-TiO 2 (40 wt %). Electrochemical impedance measurements suggested that the 25% increase in η for the DSC comprised of 40 wt % L-Ti02 resulted not from rapid diffusion of the redox electrolyte through the larger pores, but instead was due to the higher electron density in the conduction band of TiO 2 . It was inferred, therefore, that the highest η obtained for the DSC comprised of 40 wt % L-TiO 2 was due to the high degree of anchoring of COOH groups. This inference was further confirmed by obtaining an η of 2.92 ± 0.06%, the highest η ever reported for a polymer-dye based DSC, using a low-molecular weight PTAA sensitizer.

The Maxwell displacement current was generated from 4‐octyl‐4’‐(5‐carboxylpentamethyleneoxy)‐azobenzene (denoted as 8A5H) monolayer Langmuir–Blodgett films prepared on SnO2‐coated glass substrates due to trans‐cis photoisomerization of 8A5H by application of alternate irradiation with UV light and visible light. The generation of the displacement current by the photoirradiation was examined in connection with the degree of H‐aggregate of 8A5H molecules. It was concluded that the high‐H‐aggregate molecule of the azobenzene group is not appropriate for the application of the molecular switching based on the displacement‐current measurement.