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The main purpose of this study is to establish a guideline for controlling the device properties of organic antiambipolar transistors. Our key strategy is to use interface engineering to promote carrier injection at channel/electrode interfaces and carrier accumulation at a channel/dielectric interface. The effective use of carrier injection interlayers and an insulator layer with a high dielectric constant (high-k) enabled the fine tuning of device parameters and, in particular, the onset (Von) and offset (Voff) voltages. A well-matched combination of the interlayers and a high-k dielectric layer achieved a low peak voltage (0.25 V) and a narrow on-state bias range (2.2 V), indicating that organic antiambipolar transistors have high potential as negative differential resistance devices for multivalued logic circuits.

Organic multivalued logic circuits (OMVLs) have drawn tremendous attention due to their high data processability and simple fabrication techniques. However, OMVLs have so far been achieved only on rigid silicon substrates, and this limits their potential for broader applications. In this study, we develop an organic ternary inverter on plastic substrates. The inverters showed well-balanced ternary logic states with high voltage gain and low power consumption. Importantly, the devices exhibited stable operation even after 100 bending cycles, demonstrating high flexibility and reliability. This device has high potential to attain mechanical flexibility and data handling capability at the same time.

Quantum molecular devices have a potential for the construction of new data processing architectures that cannot be achieved using current complementary metal–oxide–semiconductor (CMOS) technology. The relevant basic quantum transport properties have been examined by specific methods such as scanning probe and break-junction techniques. However, these methodologies are not compatible with current CMOS applications, and the development of practical molecular devices remains a persistent challenge. Here, we demonstrate a new vertical resonant tunneling transistor for large-scale integration. The transistor channel is comprised of a MOS structure with C60 molecules as quantum dots, and the structure behaves like a double tunnel junction. Notably, the transistors enabled the observation of stepwise drain currents, which originated from resonant tunneling via the discrete molecular orbitals. Applying side-gate voltages produced depletion layers in Si substrates, to achieve effective modulation of the drain currents and obvious peak shifts in the differential conductance curves. Our device configuration thus provides a promising means of integrating molecular functions into future CMOS applications.

Highly oriented, multilayer molecular films of picene and dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) molecules with the long axis parallel to the substrate (parallel configuration, hereafter) were fabricated on their characteristic bulklike monolayer. These molecules form a dense monolayer with a bulklike molecular arrangement on metal surfaces such as Au(111), which allows further stacking of parallel molecules. Indeed, upon adsorption of picene and DNTT on these dense monolayers, growth of straight islands of multilayer without the dendritic layer was observed. Particularly, in the case of picene, one-dimensional islands with lengths over 100 μm were formed and aligned in 3-fold symmetric directions of the substrate, which was not observed in the case of DNTT. X-ray diffraction measurements revealed the presence of [201̅] and [211̅] planes and the absence of the [001] diffractions, indicating that the one-dimensional islands of picene indeed consist of parallel molecules. The formation of huge crystalline islands in the case of picene, in contrast to the case of DNTT, is likely induced by the stronger intermolecular force, as suggested from the calculation of the vibrational energy.

Graphene superlattices have recently been attracting growing interest as an emergent class of quantum metamaterials. In this paper, we report the observation of nonlocal transport in bilayer graphene (BLG) superlattices encapsulated between two hexagonal boron nitride (hBN) layers, which formed hBN/BLG/hBN moir\'e superlattices. We then employed these superlattices to detect a long-range charge-neutral valley current using an all-electrical method. The moir\'e superlattice with broken inversion symmetry leads to a hot spot with Berry curvature accumulating at the charge neutral point (CNP), and it harbors satellites of the CNP. We observed nonlocal resistance on the order of 1 $\text{k}\Omega$, which obeys a scaling relation. This nonlocal resistance evolves from the quantum Hall effect but without magnetic field/time-reversal symmetry breaking, which is associated with a hot-spot-induced topological valley current. This study should pave the way to developing a Berry-phase-sensitive probe to detect hot spots in gapped Dirac materials with inversion-symmetry breaking., Comment: 9 pages, 3 figures

International audience; The main purpose of this study is to clarify the factors for the stable operation of a poly(3-hexylthiophene) (P3HT)-based water gated organic field effect transistor (WG-OFET). To this end, the influence of the surface morphologies and electrode metals on the transistor properties were investigated. The experimental results indicated that a flat surface improved the on/off ratio and switching repeatability. Treating the surface with a lipid membrane was found to reduce hysteresis loops in the transfer curves probably due to the reduced number of carrier traps. The Au gate electrode effectively lowered the threshold voltage. Consequently, stable transistor operation with a low threshold voltage of 35 mV was achieved by employing a gold gate electrode and lipid membrane treatment. These results suggest that WG-OFETs with an ultra-thin lipid membrane have great potential for sensor applications, and in particular for sensing water-soluble analytes.

Multi-step chemical vapor deposition (CVD) is a synthesis method which is capable of producing a uniform, large area, and high-quality thin films. In this work, we report the effect of post-annealing on the structural and optical properties of few-layers (FL) MoS2 thin films synthesized by multi-step CVD. Based on atomic force microscopic image, the thickness of the MoS2 thin film is ∼3 nm, which is equivalent to five layers. After annealing at 900°C for 17 min, intensity of the A1g and [Formula: see text] Raman modes increased by ∼3 times while the full-width-at-half-maximum (FWHM)* reduced from ∼10 cm−1 to ∼7.5 cm−1 for A1g and from ∼13.6 cm−1 to ∼7.5 cm−1 for [Formula: see text]. Both of the as-grown and annealed samples showed X-ray (002) diffraction peak at 14.2° but the intensity was more prominent for the annealed sample. It was found that the annealed sample showed clear and distinct absorbance peaks at 666, 615, 448, 401, and 278 nm which correspond to the A, B, C, D, and E excitons, respectively. The results indicate that annealing significantly improved the optical and structural quality of the MoS2 film. Field-effect transistor based on annealed MoS2 thin film was fabricated and showed electron mobility of 0.21 cm2V−1s−1, on/off ratio of 1.3 × 102 and a threshold voltage of 0.72 V. Our work highlights the importance of high-temperature annealing in multi-step CVD to obtain a uniform and high-quality FL MoS2 thin films.

Optical switching organic field-effect transistors (OFETs) provide a new direction for optoelectronics based on photochromic molecules. However, the patterning of OFETs is difficult because conventional fabrication processes, including lithography and ion etching, inevitably cause severe damage to organic molecules. Here, we demonstrate laser patterning of one-dimensional (1D) channels on an OFET with a photochromic diarylethene (DAE) layer. The main findings are (i) a number of 1D channels can be repeatedly written and erased in the DAE layer by scanning focused ultraviolet and visible light laser beams alternately between the source and drain electrodes, (ii) the conductivity (or resistivity) of the 1D channel can be controlled by the illumination conditions, such as the laser power density and the scan speed, and (iii) it is possible to draw an analogue adder circuit by optically writing 1D channels so that a portion of the channels overlaps and to perform optical summing operations by local laser illumination of the respective channels. These findings will open new possibilities for realizing various optically reconfigurable, low-dimensional organic transistor circuits, which are not possible with conventional thin film OFETs.

Well-defined monolayers with single-crystalline-like molecular arrangements of dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]-thiophene (DNTT) and picene, which are a new class of organic semiconductors with enhanced intermolecular interactions, were fabricated and characterized. Although both molecules initially form a loosely packed monolayer with a flat-lying molecule, they undergo phase transition into a densely packed monolayer with single-crystalline-like molecular arrangements with increasing molecular density. Upon the phase transition of the monolayer, the highest occupied molecular orbital (HOMO) level of these molecules splits into two features, as suggested from both the ultraviolet photoelectron spectroscopy and density functional theory calculations. The splitting of the HOMO level was observed to be similar to that expected for the molecular arrangement in the single crystal. This splitting, which has not been observed in the polycrystalline film, suggests a substantial overlap of the HOMO in the we...

Future one-dimensional electronics require single-crystalline semiconductor free-standing nanorods grown with uniform electrical properties. However, this is currently unrealistic as each crystallographic plane of a nanorod grows at unique incorporation rates of environmental dopants, which forms axial and lateral growth sectors with different carrier concentrations. Here we propose a series of techniques that micro-sample a free-standing nanorod of interest, fabricate its arbitrary cross-sections by controlling focused ion beam incidence orientation, and visualize its internal carrier concentration map. ZnO nanorods are grown by selective area homoepitaxy in precursor aqueous solution, each of which has a (0001):+c top-plane and six {1–100}:m side-planes. Near-band-edge cathodoluminescence nanospectroscopy evaluates carrier concentration map within a nanorod at high spatial resolution (60 nm) and high sensitivity. It also visualizes +c and m growth sectors at arbitrary nanorod cross-section and history of local transient growth events within each growth sector. Our technique paves the way for well-defined bottom-up nanoelectronics., Semiconductor nanocrystals are potential nanoelectronic materials but often display nonuniform electric properties due to their anisotropic growths. Here, the authors report cross-sectional cathodoluminescence imaging of a single-crystalline ZnO nanowire to resolve its growth sectors with different carrier concentrations.

We investigate the humidity sensing performance and mechanism of few-layer-thick rhenium disulfide (ReS2) field-effect transistors (FETs) under gate bias operation. Consequently, a negative gate bias exhibits the sensor response, exceeding 90% mainly in the low relative humidity (RH) range. Meanwhile, the threshold voltage change was discovered to be a superior sensing parameter to achieve a broad monitoring of RH range with high response and sensitivity. The approach obtained a practical sensitivity of 0.4 V per 1% RH, which exceed a majority of previous studies with the pristine 2D materials. Besides, our devices display reversible adsorption–desorption and long-term stability operations even after a one-month period. This suggests the sensor capacity to function in real-time applications with a short response and recovery times. These outcomes offer support in the development of adaptable tunable humidity sensors based on ReS2 FETs.

A main purpose of this work is to develop a new ultra-highly sensitive sensor in particular for the detection of Cs+ ions in natural water. The radioactivity of Cs+ ions produced in nuclear power stations (NPSs) causes serious impact on the health condition of humans, as well as aquatic plants and animals. Therefore, it should be strictly controlled. However, a large amount of radioactive Cs+ had been distributed from Fukushima NPS due to the tragic accident after the great earthquake in Japan. Because of these reasons, the detection and monitoring of Cs+ ions in natural water are necessary. To tackle this issue, we developed an organic field-effect transistor (OFET)-based ion sensor. The sensor is composed of three main components: (1) organic semiconducting channel with high stability in working with natural water, (2) monolayer lipid membrane working as ultra-thin dielectric layer to allow low operating voltage and high sensitivity, and (3) novel calixarene-crown ether probe for high selectivity to Cs+ , which is grafted with lipid layer. Here, gate bias voltage is applied through electrolyte solution, in which the target ion and other competing ions are simultaneously contained. Once ion probes form metal-complex with Cs+, the electrical signal from the ion, the concentration of which is even on the ppb order, can be detected as a shift of threshold voltage. This is owing to the large electrical capacitance of monolayer lipid membrane. In comparison with other conventional methods like ICP-MS, our new sensor has many advantages: high sensitivity and selectivity, high-throughputs, integration and portability associated to real-time and on-site monitoring capabilities. In this presentation, we demonstrate a label-free sensor operation with the sensitivity of femtomolar (pg/l) concentrations of Cs+ ion with high selectivity.

Carbon-based superlattices represent a novel class of quantum metamaterials having promising prospects. Here, we show the first fabrication of folded bilayer-bilayer graphene (fBBLG)/hexagonal boron nitride (hBN) superlattices. In the transport properties at low temperatures, satellite peaks are observed due to the crystallographic angle alignment of fBBLG and hBN. The peculiar resistance peaks appear away from the charge neutrality point and the hBN-induced satellites, which may be signatures of possible competing orders. Our results suggest the emergence of a unique electronic band-structure in the fBBLG, providing a way for investigating the correlated electron phenomena by performing energy-band engineering with superlattice structures.

The electrical stability and reliability of molybdenum disulfide (MoS2) thin film transistors (TFTs) were investigated by associating thickness-dependent structural defects with degradation mechanism. Patterned MoS2 films with different thicknesses were fabricated for use as transistor channels via the modified multi-step chemical vapor deposition method. X-ray photoelectron spectroscopic (XPS) analyses revealed that highly layered and stoichiometric MoS2 films of up to ∼3 nm thickness were formed around the surface, whereas Mo metal bonds were dominant around the bottom of the films (9 nm). Variations in transistor properties of the thus prepared MoS2 films were examined by applying positive and negative bias stress (PBS and NBS, respectively). The experimental data indicated that MoS2 TFTs with 3-nm-thick films exhibited stable behavior under both PBS and NBS conditions, whereas those with 9-nm-thick films exhibited clear shifts in electrical performance ( △ V t h △ μ s a t s ). These results, together with XPS analyses, revealed that the instability of the MoS2 TFTs under PBS is dominated by sulfur interstitials, whereas their instability under NBS is caused by oxygen vacancies and metallic Mo defects. Additional details about the correlation between the atomic structural defects, which are generated due to insufficient sulfurization of thick films, and the electrical instability of the MoS2 TFTs were discussed.

Multivalued logic circuits, which can handle more information than conventional binary logic circuits, have attracted much attention as a promising way to improve the data-processing capabilities of integrated circuits. In this study, we developed a ternary inverter based on organic field-effect transistors (OFET) as a potential component of high-performance and flexible integrated circuits. Key elements are anti-ambipolar and n-type OFETs connected in series. First, we demonstrate an organic ternary inverter that exhibits three distinct logic states. Second, the operating voltage was greatly reduced by taking advantage of an Al2O3 gate dielectric. Finally, the operating voltage was finely tuned by the designing of the device geometry. These results are achievable owing to the flexible controllability of the device configuration, suggesting that the organic ternary inverter plays an important role with regard to high-performance organic integrated circuits.

The balance between good solubility and high crystallinity is an advantageous characteristic of 2,6-bis(4-pentylphenylethynyl)anthracene (1). Organic field-effect transistors featuring either a vacuum-deposited film or a simple drop-cast film of 1 both showed high hole mobilities of 0.94 and 0.63 cm2 V−1 s−1, respectively.

For most thin film structures, by changing the wavelength range to fit ellipsometric spectra, the values of the fitted parameters also change to a certain extent. The reason is that compared with the ellipsometric sensitivity many thin films are vertically non-uniform. In absorbing films with significant dispersion in the used wavelength range, the penetration depth of probing light can show large variations depending on the wavelength. Consequently, the value of a fitted parameter for a certain wavelength range is a weighted sum of structural information over different depth ranges corresponding to the different wavelengths. By changing the wavelength range, the range of penetration depths can be adjusted, and the fitted values can be plotted as a function of the probed depth range calculated directly from the determined or tabulated extinction coefficients. We demonstrate the results on deposited polycrystalline thin films. The advantage of this approach over the parameterization of structural properties as a function of depth is that the wavelength scan approach requires no parameterized depth distribution model for the vertical dependence of a layer property. The difference of the wavelength scan method and the vertical parameterization method is similar to the difference between the point-by-point and the parameterized dielectric function methods over the used wavelength range. The lateral structures strongly influence the ellipsometric response, as well. One of the most remarkable effects is when the lateral feature sizes approach the wavelength of the probing light. In this case the effective medium method is not valid any more, since scattering and depolarization occurs. By scanning the wavelength range, the limit wavelength of the onset of scattering can be found, and used for the determination of the corresponding critical lateral period length.

Thermally induced structural change in photoisomerization molecules is a serious obstacle to the development of optically controllable organic field-effect transistors (OFETs). This is because the thermal relaxation of molecular structures degrades photo-induced change in drain current and removes the memory function. To deal with this issue, a naphthopyran (NP) derivative, namely 3,13-dihydro-3-(4-triphenylaminyl)-3,13-diphenylbenzopyrano[5,6-a]carbazole (NP-TPAC) was tested that displays pseudo p-type photochromism at room temperature. The NP-TPAC-doped poly(triarylamine) (PTAA) film exhibited a reversible change in transistor properties; the drain current was reduced by ultraviolet (UV) and returned to its original value by visible (VIS) light irradiation. Importantly, no change in the drain current was observed at room temperature for more than 30 h under dark conditions. This was because the open-ring trans–trans (TT) isomer of NP-TPAC is thermally stable owing to the CH-π interaction and the steric force exerted by the phenyl ring of the carbazole unit onto the double bond responsible for the thermal back reaction. In other words, the thermal stability of photochromism-based optical devices can be greatly improved by adopting an appropriate molecular design.

We report a didactic and simple example of the subtleness in the balance of intermolecular and molecule-substrate interactions and its effect on molecular self-assembly. The study is performed on two closely related molecular blends of copper phthalocyanines and pentacene, in each of which one of the two molecules is fluorinated. Reversing the fluorination brings about changes in the intermolecular hydrogen bonds, as well as in the interactions with the substrate. As a result, on Au(100) substrates one blend assembles into a crystalline structure, whereas the other, displaying weaker intermolecular interactions and a larger corrugation in the molecule-substrate interaction potential, results in a disordered layer. However, the difference between the two blend's structures vanishes when substrates with less corrugated interaction potentials are used. © 2014 American Chemical Society., This work was supported by the Spanish Grant Nos. MAT2010-21156-C03- and PIB2010US-00652 and the Basque Government Grant No. IT-621-13. J.M.G.-L. acknowledges support from the Spanish Ministry of Economy and Competitiveness under projects FIS2012-30996 and FIS2010-21282-C02-01 and from the ReLiable project funded by the Danish Council for Strategic Research-Programme Commission on Sustainable Energy and Environment (project no. 11-116792).

We produced an optically controllable dual-gate organic field-effect transistor by a simple one-step spin-coating of a mixed solution of photochromic spiropyran (SP) and poly(3-hexylthiophene) (P3HT). Postannealing enhanced polymer chain ordering of P3HT to induce phase separation into an SP-rich lower layer and an SP-free upper layer. These layers worked independently as transistor channels with distinct optical responsivity. The top channel was optically inactive, but the bottom channel was optically active, because of the photoisomerization of SP. These results demonstrate the potential of our technique to produce a multifunctional photoactive organic transistor by a simple process.

We attained multilevel manipulation of resonant tunneling in a metal–insulator–semiconductor (MIS) structure, in which heterogeneous molecules of copper hexadecafluorophthalocyanine (F16CuPc) and copper phthalocyanine (CuPc) were embedded in an insulating layer to form a double-tunneling junction. Resonant tunneling was observed in samples with either molecule, revealing that the molecules worked as intermediate electrodes for the tunneling current. The carrier transport was ascribed to resonant tunneling through the energy levels of individual molecules. That is, the threshold voltage of resonant tunneling can be controlled according to the energy levels of the molecules. We achieved multilevel resonant tunneling operation with binary molecules of F16CuPc and CuPc, in which the carriers were injected into the respective molecules at corresponding threshold voltages. Our findings point to a new multilevel operation of resonant tunneling through organic molecules in a practical MIS device structure.

Recent progress on nanoscale molecular devices is reviewed. The advantages of organic molecules are highlighted in terms of their unique features such as quantum effects based on their nanometer size, optical properties originating from photochromism and chemical syntheses for various structural designs. This review covers three topics: a scanning probe microscope-based evaluation of individual molecules, nano-gap electrodes for electrical current through single-molecules and the incorporation of molecular functions into Si-based devices. In particular, the importance of the incorporation of organic molecules into Si-device architecture is emphasized with a view to realizing the large-scale integration of nanoscale molecular devices.

We demonstrate a technique for growing fine molecular films on a monolayer scale. We achieve layer-by-layer growth under thermally equilibrium condition by precisely controlling the conditions of an ultra-slow deposition technique. This technique is applicable to various kinds of p-type and n-type organic semiconductors and makes it possible to form a hetero-molecular interface (p-n junction) with molecular level flatness. The technique was used to produce a molecular superlattice, which enables the well-controlled design of energy level alignments in organic semiconductors.

We used hard X-ray photoelectron spectroscopy (HX-PES) to investigate the polarity effect of ZnO, which has Zn terminated (+ polar) and O terminated (− polar) surfaces, on poly(3-hexylthiophene-2,5-diyl) (P3HT)/ZnO photovoltaic structures. HX-PES, which has a longer inelastic mean free path than conventional X-ray photoelectron spectroscopy, revealed that the open circuit voltage (V OC ), estimated from the gap between the highest occupied molecular orbital of P3HT and the conduction band minimum of Zn-polar ZnO, was larger than that of the O-polar ZnO. Although polarity dependence was observed for the electrical structure at the P3HT/ZnO interface, the V OC of the photovoltaic property of Zn-polar ZnO was almost the same as that of O-polar ZnO (~ 0.4 V) due to electron–hole recombination, which degrades the photovoltaic properties at the interface. The HX-PES results also suggested that the recombination could be attributed to the short depletion length of the ZnO surface.

A technique is established for fabricating a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester (PEDOT:PSS/P3HT:PCBM) multi-layered structure in one step by transferring a continuous P3HT:PCBM solid film floating on PEDOT:PSS solution onto an indium tin oxide/glass substrate with a size of 2.5 × 1.5 cm 2 . This structure can be obtained under simple experimental conditions and can be fabricated over a large area. Preliminary testing shows that the prepared structure can yield a photovoltaic effect.

This study investigates quantized electron transport in high-mobility quantum point contact (QPC) devices in hBN/graphene/hBN in the quantum Hall regime. This study primarily focuses on the effect of the gap width of split gates on edge-channel manipulations, which defines the QPC structure and its electrostatic potential distribution. The quantized conductance is governed by the dynamics of edge channels passing through or backscattered at the QPC, which is controlled by both the top-gate and back-gate biases. The effects of the split-gate gap width and the filling in the QPC on the edge-channel manipulations are experimentally verified. The experimental results are consistent with the theoretical predictions of open/closed configurations of the edge channels around QPC with different gate gap widths.

We demonstrated optical manipulation of single-electron tunneling (SET) by photoisomerization of diarylethene molecules in a metal-insulator-semiconductor (MIS) structure. Stress is placed on the fact that device operation is realized in the practical device configuration of MIS structure and that it is not achieved in structures based on nanogap electrodes and scanning probe techniques. Namely, this is a basic memory device configuration that has the potential for large-scale integration. In our device, the threshold voltage of SET was clearly modulated as a reversible change in the molecular orbital induced by photoisomerization, indicating that diarylethene molecules worked as optically controllable quantum dots. These findings will allow the integration of photonic functionality into current Si-based memory devices, which is a unique feature of organic molecules that is unobtainable with inorganic materials. Our proposed device therefore has enormous potential for providing a breakthrough in Si technology.

We report on improved electrical conductivity in poly(3-hexylthiophene) (P3HT)/2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) composite nanowires grown using an anodized aluminum oxide (AAO) template. The electrical conductivity of individual nanowire measured by four-probe scanning tunneling microscopy shows that F4-TCNQ molecules are effectively doped into P3HT by capillary force. The resistivity is tuned in the 0.1-10 Ω cm range by changing the F4-TCNQ concentration from 10 to 0.1 wt % and is 2-4 orders of magnitude smaller than that of the corresponding P3HT/F4-TNCQ thin film composites. The AAO template-assisted synthesis approach thus appears to be effective for high chemical doping and for improving the electrical conductivity of the molecular wires.

Model donor-acceptor assemblies at metal-organic interfaces, namely, fluorinated copper-phthalocyanines (F 16CuPC) and pentacene (PEN) assemblies on the Au(111) surface, have been the focus of the present study. A full picture of the crystallographic and electronic structure of PEN and F 16CuPC monolayers as well as of their 1:1 binary mixture on the Au(111) surface has been explored by means of a variety of surface-sensitive techniques, providing important information on the intermolecular and molecule-substrate interactions governing the self-assembly process. A long-range ordered donor-acceptor network is observed for the mixture as a result of the greatly enhanced intermolecular interaction via C-F···H-C hydrogen bonds. Interestingly, the new supramolecular structure involves changes in the electronic structure of the molecular components. In particular, the strongest changes are observed at the C and F atoms of the F 16CuPc, as opposed to the F 16CuPc N, Cu, or PEN C atoms. With the aid of theoretical calculations, such effects are found to be at least partially related to an upward shift in energy of the F 16CuPc molecular orbitals, concomitant with a molecule-to-metal charge donation, not from the HOMO, but deeper lying orbitals. © 2012 American Chemical Society., This work was supported by the Spanish MICINN (MAT2010-21156-C03-01, C03-03, PIB2010US-00652) and the Basque Government (IT-257-07). The SRC is funded by the National Science Foundation (award no. DMR-0084402). B.P.D. thanks the ICTP (Trieste) for travel funding. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 226716. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007- 2013) through the Integrated Infrastructure Initiative “European Light Sources Activities − Synchrotrons and Free Electron Lasers” (grant agreement no. 226716).

We examined the transistor properties of an N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8)/quaterrylene (QT) heteromolecular layer, in which the highly ordered molecular layers were stacked on the monolayer level. Ambipolar behavior was clearly observed when behaving as a field effect transistor (FET). The field effect mobilities and threshold voltages were evaluated to gain an insight into the injection and transport of the carriers. The obtained carrier mobilities for holes and electrons were calculated to be 3.6 × 10−3 and 2.7 × 10−2 cm2 V−1 s−1, respectively. These values are comparable to those of the respective FET behaviors of QT (p-channel) and PTCDI-C8 layers (n-channel), indicating that a well-defined heteromolecular interface is an essential factor for improving carrier transport in ambipolar FETs. On the other hand, in the PTCDI-C8 layer, a marked shift from 5 to 61.6 V was observed in the threshold voltage for electron transport. We concluded this drastic change in threshold voltage to be due to the presence of hole carriers in the underlying QT layers. This finding demonstrates the potential to manipulate threshold voltage according to the electronic states of the underling layer without disturbing carrier transport.

The temperature dependences of the photoluminescence (PL) spectra of N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8)/Quaterrylene (QT) heteromolecular thin film and neat-PTCDI-C8 thin film were investigated to elucidate the effects of a heteromolecular interface on exciton relaxation and recombination processes. The PL spectra were deconvoluted into six components related to Frenkel, two charge-transfer (CT), and excimer exciton states. With the heteromolecular thin film, we found the behavior of the CT excitons to be intriguingly different in terms of luminous efficiency and temperature dependence from that of the Frenkel exciton. In this Letter, we provide detailed analyses of the exciton relaxation and recombination processes at a heteromolecular interface.

A sigle-electron tunneling (SET) in a metal-insulator-semiconductor (MIS) structure is demonstrated, in which C60 and copper phthalocyanine (CuPc) molecules are embedded as quantum dots in the insulator layer. The SET is found to originate from resonant tunneling via the energy levels of the embedded molecules, (e.g., the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)). These findings show that the threshold voltages for SET are tunable according to the energy levels of the molecules. Furthermore, SET is observable even near room temperature. The results suggest, together with the fact that these properties are demonstrated in a practical device configuration, that the integration of molecular dots into the Si-MIS structure has considerable potential for achieving novel SET devices. Moreover, the attempt allows large-scale integration of individual molecular functionalities.

The impact of various ZnO templates on the alignment and geometry of wet-chemically grown vertical ZnO nanowire (NW) arrays was investigated. The NWs were seeded at nucleation windows which were patterned in poly(methyl methacrylate)-coated ZnO surfaces using electron beam lithography. This growth approach was shown to have the potential for low-cost and low-temperature fabrication of regular, highly aligned, and transparent NW arrays with tunable conductivities on cheap substrates with precise engineering of the NW dimensions and positioning. The compared ZnO templates included a single crystal ZnO substrate, an epitaxial film on a c-sapphire substrate, and polycrystalline films on Si(111), Si(100), and Pt/c-sapphire. Scanning electron microscopy and X-ray diffraction revealed that the alignment, crystal structure, and geometry of the NW arrays were dictated by the crystal structure of the underlying ZnO, while the influence of the surface roughness was negligible. Thus, the choice of seed layer crystall...

We reveal the effect of UV–ozone treatment on the electrical properties of poly (styrenesulfonate) doped poly (3,4-ethylenedioxythiophene) (PEDOT:PSS) film by clarifying the respective roles of UV light irradiation and exposure to ozone gas. The UV–ozone treatment induced increases in both work function and resistivity. Furthermore, the film thickness was reduced at a rate of 0.13 nm/min. The ozone-exposed films also exhibited a marked increase in the work function. However, such variations were not observed in the resistivity and film etching. Angle resolved X-ray photoelectron spectroscopy revealed that the main role of the UV light was to decompose the chemical bonds in the PEDOT:PSS film, resulting in a resistivity increase and film etching. In contrast, the ozone and atomic oxygen were absorbed and oxidized the surface, which was responsible for the increase in the work function. Due to these different functions, UV–ozone treatment is capable of controlling the work function and resistivity of PEDOT:PSS film thus allowing them be adjusted to the device application.