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The surface structure of C 2 H 4 on Si(001) has been investigated by coaxial impact collision ion scattering spectroscopy (CAICISS). To determine the adsorption structure of the C 2 H 4 molecules definitely, the computer simulation with the two-dimensional trajectory count method has been applied to the recently proposed most possible two single molecular adsorption configurations (di-σ on-top and di-σ end-bridge). The CAICISS spectra and simulation results show that the di-σ on-top structure is better fitted with the experimental results rather than the di-σ end-bridge.

ZnO nanowires (NWs) were fabricated on Au coated sapphire (0001) substrates by using a pulsed laser deposition (PLD) system in vacuum furnace with a Q-switched Nd:YAG laser. ZnO NWs have various size and shape with a substrate position inside a furnace, and their morphologic construction is reproducible. Scanning electron microscopy (SEM) images indicate that the diameters of ZnO NWs ranged from 100 to 150 nm and the average length was greater than 3 μm. Room-temperature photoluminescence spectra of the NWs show the near band-edge emissions and the deep-level green light emissions. The formation mechanism of the NWs is discussed.

Shubnikov–de Haas (SdH), Van der Pauw Hall‐effect, and cyclotron resonance measurements on InxGa1−xAs/In0.52Al0.48As asymmetric step quantum wells were carried out to investigate the electrical properties of a free electron gas and to determine the effective mass of the electron gas, the subband energies, and the wave functions in the InxGa1−xAs quantum wells. The SdH measurements at 1.5 K demonstrated clearly the existence of a quasi‐two‐dimensional electron gas in the InxGa1−xAs quantum wells, and the fast Fourier transformation results for the SdH data indicated clearly the occupation by that gas of two subbands in the quantum wells. The electronic effective masses determined from the slopes of the main peak absorption energies as a function of the magnetic field were 0.0477 and 0.053 me for the first excited and the ground subbands, respectively. The electronic subband energies and the wave functions in the InxGa1−xAs/In0.52Al0.48As step quantum wells were calculated by a self‐consistent method taking...

Publisher Summary This chapter discusses the electrical conductance of directly linked porphyrin arrays. The regularly arranged porphyrin arrays with ample electronic interactions can be promising in the applications, such as molecular wires, sensors, and optical nonlinear materials. For the application of molecular photonic and electronic wires, the overall length of the porphyrin arrays should be long enough for linkage of a nanoelectrode as a molecular electronic wire. To explore the electrical transport properties of individual porphyrin molecules for the application as molecular-scale devices, the electrical transport measurements of two extreme types of porphyrin arrays are performed. Directly linked linear orthogonal (Zn) and fused (Tn) porphyrin arrays for the possible applications as molecular photonic and electric wire are prepared. All electrical transport measurements are performed in vacuum to eliminate the effect of water on the conductance. Zn is promising as a photonic wire because of the exceptionally strong excitonic interactions between the neighboring porphyrin moieties arising from a close proximity with a reasonably long length. On the other hand, Tn has proven to be a good optical nonlinear material induced by extensive π-electron delocalization throughout the entire Tn arrays.

Shubnikov–de Haas (SdH) and van der Pauw Hall effect measurements on In0.52Al0.48As/InxGa1−xAs coupled double quantum wells grown by metalorganic chemical vapor deposition have been carried out to investigate the magnetotransport properties of an electron gas and to determine the subband energies and wave functions in the coupled quantum wells. Transmission electron microscopy measurements showed that In0.8Ga0.2As and In0.53Ga0.47As quantum wells were separated by an In0.25Ga0.75As potential barrier in an active region. The SdH measurements at 1.5 K demonstrated clearly the existence of a quasi‐two‐dimensional electron gas in the quantum wells. The fast Fourier transformation results for the SdH data clearly indicate the occupation of three subbands in the In0.52Al0.48As/InxGa1−xAs coupled quantum wells. Electron subband energies and wave functions in the quantum wells were calculated by a self‐consistent method taking into account exchange‐correlation effects. The first and second excited subband wave fu...

We report the observation of the resonant transport in multiwall carbon nanotubes in a crossed geometry. The resonant transport is manifested by an asymmetric peak in the differential conductance curve. The observed asymmetric conductance peak is well explained by Fano resonance originating from the scattering at the contact region of the two nanotubes. The conductance peak depends sensitively on the external magnetic field and exhibits Aharonov-Bohm-type oscillation., 4 pages, 3 figure, to appear in Phys. Rev. Lett

We have fabricated very small Al/AlO/sub x//Al junctions connected in series using electron-beam lithography and double-angle evaporation techniques. The average junction area is obtained to be 150/spl times/150 nm/sup 2/.

The abnormal drift rate of Thomas type 1 ohm resistors according to temporary temperature change is described and they are compared with NML 1 ohm resistors with almost the same drift rate. It is thought that the major origin of difference between the two types is the coil-mounting structure suffering from stress.

We investigated scaling behaviors for NiO nanowire array devices with different nanowire diameters. Plots of the reset current and the third harmonic generation signal as a function of the on-state resistance (R0) show scaling behaviors for all devices, such as NiO film devices. However, the scaling exponents of NiO nanowire devices were different from those of NiO film devices, and hence the fractal dimension estimated from the scaling exponent was smaller for the NiO nanowire devices than for the NiO film devices. This decrease in the fractal dimension was attributed to the confinement of the conducting filaments within each nanowire.

Non-local electric transport phenomena were observed for a multi-wall carbon nanotube. The magnetic field dependence of non-local resistance was out of phase with respect to the conventional four-probe resistance, which could be explained in terms of the Landauer-Buttiker formula. Our observations indicate that the phase coherence length of multi-wall carbon nanotube exceeds the whole sample length of 3.8 µm up to the measured temperature 18 K.

As obesity and its associated metabolic diseases become a worldwide epidemic, the demand for novel anti-obesity agents is increasing. We report a label-free and real-time monitoring method that uses a capacitance sensor array to screen anti-obesity agents. The results for the real-time capacitance of 3T3-L1 cells treated with 12 different chemicals extracted from natural products were consistent with the biochemical indicators of adipogenesis such as the expression of perilipin, the major protein coating the surface of lipid droplets in adipocytes. The data demonstrate that a capacitance change during adipocyte differentiation is closely associated with lipid accumulation in the cells, suggesting that adipocyte differentiation can be monitored in real time. This capacitance sensor might be used for label-free and real-time monitoring of adipocyte differentiation, and may facilitate the development of high throughput screening methods for anti-obesity drugs.

Fabrication of one dimensional metal nanomaterials offers many beneficial aspects due to their unique size- and shape-dependent characteristics. However, facile fabrication of a robust one dimensional nanostructure has still remained a great challenge. Here, we developed a new synthetic route of one-step electrochemical deposition of silver nanograss without the assistance of a template. By applying an overpotential of −2.0 V (vs. Ag/AgCl) under aqueous alkaline conditions, silver nanograss with a slight tilt in a randomly oriented direction was spontaneously formed on the working electrode surface. Two applications that utilize advantageous features of this silver nanograss were demonstrated: (i) an efficient surface-enhanced Raman scattering substrate for a chemical sensor and (ii) an enzyme-less hydrogen peroxide sensor. Compared to silver nanowire arrays fabricated using anodized aluminum oxide (AAO) templates, the silver nanograss exhibited comparable hydrogen sensing due to its catalytic hydrogen peroxide reduction activity and produced a much stronger surface-enhanced Raman spectroscopy (SERS) signal due to its innate structure.

New mercury-based. superconductors, Hgl−xTlxBa2(Ca0.86Sr 0.14)2Cu3O 8+δ (x=0.25, 0.50, 0.75; denoted as Hg,Tl-1223), were prepared by solid state reactions of HgO, Tl2O3, Ba2CuO3+x, and Ca0.86Sr 0.14CuO2. X-ray powder diffraction data and EPMA results revealed that the Hg, Tl-1223 compounds form complete solid solution. All the diffraction lines are well indexed on the tetragonal ‘1223’ (space group: P4/mmm) structure. The superconducting transition temperatures for the as-synthesized samples are about 128 K. After annealing the samples in an argon atmosphere at 400 °C for 10 h, the superconducting transition temperatures have been found to increase to 132 K. In contrast to other mercury-based superconductors, the Hg, Tl-1223 compounds are quite stable even at 500 °C. The critical current densities of the Hg, Tl-1223 largely enhance as the thallium concentration increases.

We report the a-axis resistivity ρa(T) and Hall coefficient RH(T) measurements on Bi2Sr2CaCu2−xNixO8+δ (x=0.0, 0.02, 0.04) single crystals. The superconducting transition temperature decreases with increasing x. RH in the normal state is dependent on 1/T and in the mixed state the sign reversal of RH is observed for all samples. The impurity effects on the sign reversal of RH in the mixed state are discussed.

We have studied the effect of local gates on the electrical transport properties of single-walled carbon nanotubes (SWNT). The local gate have been incorporated into individual SWNT by depositing Al top gate in between Au/Ti electrodes. Noticeable increase of resistance was observed after the deposition of the Al top gates, implying that the Al top gate acted as a barrier for electrical conduction.

We fabricated the organic photovoltaic (OPV) cells on the transparent and low resistive multilayer electrode of a few nm Ag layer embedded Al doped zinc oxide film (AZO/Ag/AZO) on a glass. AZO and Ag consisting of the continuous multilayer were fabricated using rf magnetron at room temperature successively. AZO (45 nm)/Ag (11 nm)/AZO (45 nm) electrode shows an electrical resistivity of 6.56×10-5 Ω cm, optical transmittance of 89.3% at 550 nm and figure of merit (FOM) value of 4.94×10-2 Ω-1. An inverted structure OPV was fabricated on AZO/Ag/AZO transparent electrode in which TiO x and PEDOT:PSS were used as an electron transport and hole transport layer respectively. The OPVs showed power conversion efficiency and fill factor as high as 2.07%, 0.51 respectively.

The polyaniline–carbon nanotube composite thin film bolometric near-infrared sensor exhibited more than a two orders of magnitude sensitivity enhancement over both the polyaniline thin film and carbon nanotube network NIR sensor. We also investigated the mechanism of the effectively enhanced sensitivity of the composite material and demonstrated that it is a synergistic effect due to the higher heat generation of carbon nanotubes and higher temperature coefficient of resistance of polyaniline.

We have investigated the effect of oxygen content on the c-axis transport in normal and mixed states on a Bi2Sr2CaCu2O8+x single crystal. The temperature dependence of normal state resistivity along the c axis is changed to be from semiconducting to metallic by annealing independently of the annealing atmosphere. In the mixed state, ρc(T, H) is found to be explained by the flux motion model. The fitting of ρc(T, H) with the form ρ = ρoexp[-Uo(T, H)/kBT] yields different magnetic field dependence of Uo for different oxygen content x. Some implications of these results are discussed.

We describe a rapid, sensitive, and low-cost method to detect bisphenol A (BPA) using an anodized aluminum oxide-based capacitive sensor. BPA is detected by measuring the change in capacitance caused by the biospecific binding of BPA with a BPA aptamer that is immobilized on the electrode surface. For a solution containing 100 pM BPA, the capacitance decreased by approximately 3%. In addition, we fabricated a capacitive sensor array and demonstrated that BPA in environmental samples can be measured using our capacitive sensor.

We report a simple and scalable method for the separation of semiconducting single-walled carbon nanotubes (SWNTs) from metallic SWNTs using magnetic nanoparticles (MNPs) functionalized with polycationic tri-aminated polysorbate 80 (TP80). MNPs-TP80 are selectively adsorbed on acid-treated semiconducting SWNTs, which makes the semiconducting SWNTs be highly concentrated to over 95% under a magnetic field. Almost all the field effect transistor network devices, which were fabricated using separated semiconducting SWNTs, exhibited a p-type semiconducting behavior with an on/off ratio of higher than 10(4).

In this paper, the feasibility of utilization of a single element double split-ring resonator as a biosensing device has been demonstrated. The compact resonator has been excited by time-varying magnetic fields generated from the 50 Ω microstrip transmission line. In this work, DNA hybridization is recognized with shift in S21 resonant frequency. When thiol-linked single stranded-DNA is immobilized onto a gold (Au) surface and is then coupled with complementary-DNA, the frequency changes by Δfss-DNA=20 MHz and Δfhybridization=60 MHz, respectively. Thus, it is clear that the resonator can be utilized as a DNA sensing element in the microwave regime.

We have synthesized mesoporous TiO2 nanofibers loaded with Au nanoparticles (MTNF-Au) and fabricated single nanofiber-based devices. MTNF-Au devices exhibited surface plasmon enhanced photoconductance under visible light, whereas MTNF devices without Au nanoparticles did not. Moreover, Coulomb oscillations were observed at 4.2 K in MTNF-Au devices, indicating that Au nanoparticles embedded in MTNF-Au played a role of Coulomb islands. These results suggested that the enhanced photoconductance was ascribed to electron tunneling of hot electrons generated by the surface plasmon resonance.

The electric and the magnetic transport properties of the loop-type Al/Al 2 O 3 /Al single-electron tunneling device were studied. Even for the sample with charging energy about one order of magnitude greater than the Josephson coupling energy, the magnetoresistance showed h /2 e -oscillation at low bias voltage, attributed to the phase-coherent pair tunneling. The behavior of the magnetoresistance depends on the gate voltage, showing large and noiseless oscillations with the even number of excess charges but small and noisy oscillations with the odd number of excess charges in the metal islands.

Two di!erent kinds of mesoscopic N}S}N junctions were fabricated by sandwiching Al or Pb "lm between two closely separated Au wires. d

The electric transport properties of an Al/Al2O3/Ni/Al2O3/Al single-electron transistor were studied. Compared to the all-normal-metal single-electron transistors, our sample showed enhanced tunnel current inside the Coulomb gap both in the superconducting and the normal state of the Al. The tunnel current showed sharp increase for the magnetic field H≈±1.57 T , which also was evidenced by the change of current–voltage (I–V) characteristics with the magnetic field.

Magnetotransport in GaAs/Ga 1− x Al x As heterostructures with a square array of antidots has been investigated. Quantum lifetimes τ q are estimated from the amplitudes of Shubnikov–de Haas oscillations and two values of τ q are found at low and high magnetic fields. The critical field at which τ q changes corresponds to the magnetic field where the cyclotron diameter 2 R c is almost equal to the effective constriction length L c between two antidots. This suggests that the influence of scattering from antidots on τ q is different in the regions where 2 R c > L c and where 2 R c L c .

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A functional protein of bacteriorhodopsin has been employed for an approach to develop molecular single-electron transistors. A purple-membrane nanofragment shows a characteristic, cyclic, and reproducible I-V curve having negative differential resistance and an on-off peak-to-valley ratio of 660. The conductance increases exponentially with temperature increase with an activation energy of 47 meV, comparable to the charging energy of a bacteriorhodopsin molecule. This with observed I-V scaling relationship indicates that the Coulomb blockade is the primary conductance-limiting feature and that charges are carried by arrayed Coulomb islands of bacteriorhodopsin.

We have investigated resistive switching phenomena in NiO nanowires fabricated using anodized aluminum oxide membranes. We show that NiO nanowires exhibit reversible and bistable resistive switching behaviors like those in NiO thin films. However, compared to NiO thin films, electroforming in NiO nanowires takes place at much lower electric fields. Thus, a 1-μm-long NiO nanowire device operates under 2.5V and even a 25-μm-long NiO nanowire array operates under 20V. These results suggest the possibility of developing nanowire-based resistance memory devices.

We investigated the electrical properties of a GaN nanorod p-n junction diode patterned on a SiO2 substrate using e-beam lithography. The electron transport mechanisms were characterized by temperature-dependence and current-voltage measurements. At a low temperature, the current-voltage curves showed that the current slowly increased with a given voltage for the forward bias and hardly changed for the reverse bias, indicating the tunneling current dominates through the deep trap barrier. At a high temperature, however, the current-voltage curves exhibited strong temperature dependence suggesting that thermionic emission with an activation energy of 19.1meV over a barrier dominated.

We report electrically refreshable carbon-nanotube (CNT)-based gas sensors with a field effect transistor (FET) structure. The sensors can be refreshed by applying a negative gate voltage pulse in NO2 and a positive gate voltage pulse in NH3. Furthermore, the temporal response of the conductance to the gate voltage pulse is observed to be dependent on the gas species, but independent of gas concentration. These results show the possibility of distinguishing gas species using CNT-FET sensors.

This paper describes the fabrication of pentacene-based thin film transistors (TFTs) with ultrathin (4.5nm) SiO2 and SiON gate dielectric layers for low-voltage operations. The device with the SiON gate dielectric layer operated at gate voltages lower than −3.0V, showing a threshold voltage of −0.45V, which was lower than the threshold voltage of the SiO2 device (−2.5V). The electronic structures of the interface between the pentacene and dielectric layers were investigated by in situ ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS) to determine the reason for the lower operating voltage. The UPS and XPS results demonstrated that the interface dipole modified the potential of the dielectric layer, explaining the lower operating voltage. The electronic structure allowed for band bending at the interface, resulting in complete energy level diagrams for pentacene on SiO2 and SiON. The shifts in the threshold and turn-on voltages were explained by the energy level diagrams.

The interfacial electronic structures of N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB)/copper phthalocyanine (CuPc)∕Au, NPB∕C60∕Au, and NPB∕CuPc:C60 composite/Au were investigated by in situ ultraviolet photoelectron spectroscopy to understand the highly efficient hole injection in organic light-emitting diode. The hole-injection barrier of CuPc:C60∕Au was 0.52eV, while those of CuPc∕Au and C60∕Au were 0.96 and 1.62eV, respectively. The lowered injection barrier is attributed to the smaller interface dipole of CuPc:C60 compared to that of pristine CuPc. This small interface dipole pulled up the highest occupied molecular orbital of CuPc in composite, which results in the decreased hole-injection barrier.

The authors report two organic photovoltaic devices using a Ga-doped ZnO (GZO) film as a transparent conducting electrode. In the first structure, the conventional In2O3:Sn hole-collecting anode was replaced by GZO and an efficiency of 0.35% was obtained. The second has the inverse structure where GZO was used as the electron-collecting cathode and gave a nonoptimized device efficiency of about 1.4%. Furthermore, this inverse structure of GZO devices provides a passivation layer to protect the active layer from the atmosphere.

The structural and electrical properties of organic thin-film transistors with rubrene/pentacene and pentacene/rubrene bilayered structures were investigated using x-ray diffraction, atomic force microscopy, and x-ray emission spectroscopy. High-quality rubrene thin films with orthorhombic structure were obtained in the rubrene/pentacene bilayer while the pentacene/rubrene bilayer only had an amorphous rubrene phase present. The rubrene/pentacene thin-film transistor shows more desirable current-voltage characteristics compared to the pentacene/rubrene transistor. The overall results suggest that the presence of a chemically active organic buffer layer and its associated crystal structure are crucial in enhancing the structural and electrical properties of rubrene-based transistors.

We have studied the electrical properties of a GaN nanorod p-n junction diode by deep level transient spectroscopy measurements. The p-n junction nanorods were patterned on a SiO2 substrate by using e-beam lithography. In order to confirm the formation of p-n junction, cathodoluminescence and current-voltage measurements, as a function of temperature, were made. The current-voltage curve exhibits strong temperature dependence, suggesting that thermionic emission over a barrier dominates. This barrier most likely corresponds to emission from a deep level in the band. The deep level appears to be an electron trap at Ec-0.40eV below the conduction band with a capture cross section of 2.22×10cm2 near the depletion region of the p-n junction.

The origin of the lowered electron injection barrier height of C60∕Cu was investigated by in situ ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy (XPS). The onset of the highest occupied molecular orbital level was shifted by 0.2eV toward high binding energy upon the heat treatment, resulting in the improved injection characteristics of the device. Moreover, an unexpected gap state has been observed at 1.2eV below the Fermi level. The XPS core-level spectra revealed that the chemical reaction between C60 and Cu at the interface induced the gap state after heat treatment. The gap state pinned the Fermi level close to the lowest unoccupied molecular orbital of C60. We obtained the complete energy level diagram of C60∕Cu before and after the heat treatment.

We fabricated ambipolar organic thin-film transistors (OTFTs) using C60 and pentacene. The electronic structure of the interface was investigated by using ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy. The magnitude of the interface dipole and the band bendings at the interface was determined, and the complete energy level diagram for C60 on pentacene (C60/pentacene) was obtained. The lowered band offsets, due to the enhanced charge redistribution in C60/pentacene relative to pentacene on C60, are favorable for the ambipolar OTFTs. The measured field-effect mobilities were 0.017cm2∕Vs and 0.007cm2∕Vs for the p-channel and the n-channel operations, respectively. The threshold voltages were −2V for the p channel and 15.6V for the n channel, comparable to those of unipolar OTFTs using C60 or pentacene.

We fabricated perylene-based organic thin-film transistor (OTFT) with an octadecyltrichlorosilane (OTS) monolayer in an ultrahigh vacuum condition. By current–voltage characteristics, the saturation current and the field effect mobility of OTS–OTFT (gold∕perylene∕OTS∕SiO2∕p+-Si) increased over ∼100 times in comparison with normal-OTFT (gold∕perylene∕SiO2∕p+-Si), and on/off ratio increased over ∼100 times. The saturation current, field effect mobility, and on/off ratio were >1μA, 0.042cm2∕Vs, and >106, respectively. The uniformity of the OTS layer was confirmed by x-ray reflectivity. Perylene thin films on SiO2 and OTS∕SiO2 were compared by atomic force microscopy, scanning electron microscopy, x-ray diffraction, and x-ray photoscopy.

We have observed a memory effect in an aluminum single-electron memory cell with a floating node. Electrons were injected to or emitted from the floating node by field emission, which was evidenced by the sudden change in the Coulomb oscillation of a single-electron transistor. With the compensating voltage applied to the back gate, the Coulomb oscillation could be completely suppressed if the gate voltage sweep direction was reversed. We found that the Coulomb-oscillation period changed with the ratio of control-gate to back-gate voltage, being fitted well to the expected formula.

Hereditary hemochromatosis (HFE), which affects 1 in 400 and has an estimated carrier frequency of 1 in 10 individuals in Western population, results in multiple organ damage caused by iron deposition, and is treatable if detected early. C282Y mutation in HFE gene has been known to be responsible for the most hereditary hemochromatosis cases and 5-10% of white subjects are heterozygous for this mutation. However, the prevalence of hemochromatosis in the Asian population was reported to be very low and ethnic heterogeneity has been suspected. The aim of our study was to determine the prevalence of heterozygosity and homozygosity for the C282Y HFE gene mutations in 502 unrelated Koreans. Results revealed that none of them had the mutant gene, suggesting a significant ethnic difference when compared with Caucasians. Our study excluded underlying possibility of hereditary hemochromatosis in Korean which could mimic the findings of alcoholic liver disease with iron overload or liver cirrhosis with chronic hepatitis C.