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Among the three primary colors, blue emission in organic light-emitting diodes (OLEDs) are highly important but very difficult to develop. OLEDs have already been commercialized; however, blue OLEDs have the problem of requiring a high applied voltage due to the high-energy of blue emission. Herein, an ultralow voltage turn-on at 1.47 V for blue emission with a peak wavelength at 462 nm (2.68 eV) is demonstrated in an OLED device. This OLED reaches 100 cd/m2, which is equivalent to the luminance of a typical commercial display, at 1.97 V. Blue emission from the OLED is achieved by the selective excitation of the low-energy triplet states at a low applied voltage by using the charge transfer (CT) state as a precursor and the triplet-triplet annihilation, which forms one emissive singlet from two triplet excitons. We found that the essential component for efficient blue emission is a smaller energy difference between the CT state and triplet exciton, accelerating the energy transfer between the two states and achieving the optimal performance by avoiding direct decay from the CT state to the ground state. Our study demonstrates that the developed OLED allows for a much longer operation lifetime than that from a typical blue phosphorescent OLED because the blue emission originates from a stable low-energy triplet exciton that avoids degrading the constituent materials.

Nanostructure-induced L10-ordering of twinned single-crystals in CoPt ferromagnetic nanowires on Si/SiO2 substrates is demonstrated, where nanostructure-induced L10-ordering is driven by ultrasmall 10 nm-scale curvature radii of the nanowires.

L10-ordered CoPt with a large coercivity (H c) of 13 kOe was demonstrated on Si/SiO2 substrates by hydrogen annealing. Equiatomic 11.2 nm thick (Co/Pt)4 multilayer thin films were fabricated by electron-beam evaporation and were annealed at 500 °C–900 °C for 10–90 min under an Ar/H2 mixed gas atmosphere. The annealing temperature and time dependences of the crystal structures, magnetic properties, and surface morphologies of the films were systematically analyzed based on the experimental results obtained from grazing incidence X-ray diffraction (GI-XRD), vibrating sample magnetometer, and scanning electron microscope, respectively. Hydrogen annealing effectively promoted the out-of-plane c-axis orientation of L10-ordered CoPt compared to the vacuum annealing according to the GI-XRD patterns. A maximum H c of 13.3 kOe was obtained in L10-ordered CoPt with angular-outlined isolated grains by hydrogen annealing at 800 °C for 60 min, where the c-axis of L10-ordered CoPt was randomly distributed.

Single-electron transistors (SETs) are sub-10-nm scale electronic devices based on conductive Coulomb islands sandwiched between double-barrier tunneling barriers. Chemically assembled SETs with alkanethiol-protected Au nanoparticles show highly stable Coulomb diamonds and two-input logic operations. The combination of bottom-up and top-down processes used to form the passivation layer is vital for realizing multi-gate chemically assembled SET circuits, as this combination enables us to connect conventional complementary metal oxide semiconductor (CMOS) technologies via planar processes. Here, three-input gate exclusive-OR (XOR) logic operations are demonstrated in passivated chemically assembled SETs. The passivation layer is a hybrid bilayer of self-assembled monolayers (SAMs) and pulsed laser deposited (PLD) aluminum oxide (AlO[Formula: see text]), and top-gate electrodes were prepared on the hybrid passivation layers. Top and two-side-gated SETs showed clear Coulomb oscillation and diamonds for each of the three available gates, and three-input gate XOR logic operation was clearly demonstrated. These results show the potential of chemically assembled SETs to work as logic devices with multi-gate inputs using organic and inorganic hybrid passivation layers.

Single-electron transistors (SETs) represent a new generation of electronic devices with high charge sensitivity, high switching speed, and low power consumption. Here a simple and controlled fabrication of graphene quantum dot (GQD)-based SETs for photon detectors has been demonstrated. The plasma-synthesized GQDs exhibit stable photoluminescence and are successfully used as the Coulomb islands between heteroepitaxial spherical-gold/platinum (HS-Au/Pt) nanogap electrodes. The as-fabricated GQD-SETs enable photon detection with 410 nm excitation owing to the ability of GQDs to generate photoluminescence emission.

Organic semiconductor-based thin-film transistors’ (TFTs) charge-carrier mobility has been enhanced up to 25 cm2/V s through the improvement of fabrication methods and greater understanding of the microstructure charge-transport mechanism. To expand the practical feasibility of organic semiconductor-based TFTs, their electrical properties should be easily accessed from the fully printed devices through a scalable printing method, such as a roll-to-roll (R2R) gravure. In this study, four commercially available organic semiconductors were separately formulated into gravure inks. They were then employed in the R2R gravure system (silver ink for printing gate and drain–source electrodes and BaTiO3 ink for printing dielectric layers) for printing 20 × 20 TFT-active matrix with the resolution of 10 pixels per inch on poly(ethylene terephthalate) (PET) foils to attain electrical properties of organic semiconductors a practical printing method. Electrical characteristics (mobility, on–off current ratio, threshold voltage, and transconductance) of the R2R gravure-printed 20 × 20 TFT-active matrices fabricated with organic semiconducting ink were analyzed statistically, and the results showed more than 98% device yield and 50 % electrical variations in the R2R gravure TFT-active matrices along the PET web.

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.

Rhombic Coulomb diamonds are clearly observed in a chemically anchored Au nanoparticle single-electron transistor. The stability diagrams show stable Coulomb blockade phenomena and agree with the theoretical curve calculated using the orthodox model. The resistances and capacitances of the double-barrier tunneling junctions between the source electrode and the Au core (R1 and C1, respectively), and those between the Au core and the drain electrode (R2 and C2, respectively), are evaluated as 4.5 MΩ, 1.4 aF, 4.8 MΩ, and 1.3 aF, respectively. This is determined by fitting the theoretical curve against the experimental Coulomb staircases. Two-methylene-group short octanedithiols (C8S2) in a C8S2/hexanethiol (C6S) mixed self-assembled monolayer is concluded to chemically anchor the core of the Au nanoparticle at both ends between the electroless-Au-plated nanogap electrodes even when the Au nanoparticle is protected by decanethiol (C10S). This is because the R1 value is identical to that of R2 and corresponds to the tunneling resistances of the octanedithiol chemically bonded with the Au core and the Au electrodes. The dependence of the Coulomb diamond shapes on the tunneling resistance ratio (R1/R2) is also discussed, especially in the case of the rhombic Coulomb diamonds. Rhombic Coulomb diamonds result from chemical anchoring of the core of the Au nanoparticle at both ends between the electroless-Au-plated nanogap electrodes.

L12-ordered CoPt3 and L10-ordered CoPt are formed in electron-beam-deposited (Co/Pt)4 multilayer thin films with and without a Ti underlayer, respectively, on Si/SiO2 substrates by rapid thermal annealing. The crystal structures, magnetic properties, and surface morphologies of the films are investigated by grazing incidence X-ray diffraction (GI-XRD), vibrating sample magnetometer (VSM), and scanning electron microscope (SEM), respectively. In the film without a Ti underlayer, L10-ordered CoPt with an isolated round grain structure is confirmed, showing an in-plane coercivity of 2.7 kOe. In contrast, in the film with a Ti underlayer, L12-ordered CoPt3 is confirmed together with Co-rich A1-disordered CoPt, showing an in-plane coercivity of 500 Oe, which exhibits an angular-outlined continuous film structure. The three sets of experimental results from GI-XRD, VSM, and SEM coincide well with each other.

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.

Electroless Au plating (ELGP) on Pd thin films is performed. The ELGP time dependence on the surface morphology is investigated by a scanning electron microscope. Continuous nucleation and growth of hemispherical Au islands are observed as the plating time increases. Heteroepitaxial growth of the electroless plated Au on the Pd surface is confirmed by cross-sectional scanning transmission electron microscope images. Cross-sectional energy-dispersive X-ray spectroscopy reveals interdiffusion between the Pd atoms and the plated Au atoms at room temperature, which allows the formation of Au–Pd alloys. The heteroepitaxial Au growth on Pd is significant for reducing contact resistance of Au/Pd structures.

We investigated reversible switching behaviors of a molecular floating-gate single-electron transistor (MFG-SET). The device consists of a gold nanoparticle-based SET and a few tetra-tert-butyl copper phthalocyanine (ttbCuPc) molecules; each nanoparticle (NP) functions as a Coulomb island. The ttbCuPc molecules function as photoreactive floating gates, which reversibly change the potential of the Coulomb island depending on the charge states induced in the ttbCuPc molecules by light irradiation or by externally applied voltages. We found that single-electron charging of ttbCuPc leads to a potential shift in the Coulomb island by more than half of its charging energy. The first induced device state was sufficiently stable; the retention time was more than a few hours without application of an external voltage. Moreover, the device exhibited an additional state when irradiated with 700 nm light, corresponding to doubly charged ttbCuPc. The life time of this additional state was several seconds, which is much shorter than that of the first induced state. These results clearly demonstrate an alternative method utilizing the unique functionality of the single molecule in nanoelectronics devices, and the potential application of MFG-SETs for investigating molecular charging phenomena.

In this review, we describe recent progress made in the study of nanoparticles characterized by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Basic principles of STM measurements and single-electron tunneling phenomena through a single NP are summarized. We highlight the results of electrical and photonic properties on NPs studied by STM and STS. Because nanoparticles are single-digit nanometre in diameter, a single-electron transport on individual nanoparticles such as Coulomb blockade and resonant tunneling through discrete energy levels are investigated. Photon-emission from NPs is also introduced based on STM measurements. Novel single-nanoparticle functions such as stochastic blinking and one-write erasing behaviours are presented. This review provides an overview of nanoparticle characterization methods based on STM and STS that include the detailed understanding of the electrical and photonics properties of nanoparticles.

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.

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.

To demonstrate that roll-to-roll (R2R) gravure printing is a suitable advanced manufacturing method for flexible thin film transistor (TFT)-based electronic circuits, three different nanomaterial-based inks (silver nanoparticles, BaTiO3 nanoparticles and single-walled carbon nanotubes (SWNTs)) were selected and optimized to enable the realization of fully printed SWNT-based TFTs (SWNT-TFTs) on 150-m-long rolls of 0.25-m-wide poly(ethylene terephthalate) (PET). SWNT-TFTs with 5 different channel lengths, namely, 30, 80, 130, 180 and 230 μm, were fabricated using a printing speed of 8 m/min. These SWNT-TFTs were characterized and the obtained electrical parameters were related to major mechanical factors such as web tension, registration accuracy, impression roll pressure and printing speed to determine whether these mechanical factors were the sources of the observed device-to-device variations. By utilizing the electrical parameters from the SWNT-TFTs, a Monte Carlo simulation for a 1-bit adder circuit, as a reference, was conducted to demonstrate that functional circuits with reasonable complexity can indeed be manufactured using R2R gravure printing. The simulation results suggest that circuits with complexity, similar to the full adder circuit, can be printed with a 76% circuit yield if threshold voltage (Vth) variations of less than 30% can be maintained.

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.

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.

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.

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.

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.

In this study, we have developed secondary resonance magnetic force microscopy (SR-MFM) for imaging alternating magnetic fields from a sample surface at the secondary resonant frequency of the magnetic cantilever at the same time as the topographic image. SR-MFM images of alternating magnetic fields diverging from the main pole in a driving perpendicular magnetic recording head are presented, and the divergence and convergence of the fields are discussed. The spatial resolution of SR-MFM is estimated to be 18 nm; this is 2.5 times smaller than that of conventional MFM.

En este trabajo se estudia la morfología y cristalización de la superficie de películas delgadas de Cu (expuestos al medio ambiente) sobre sustratos de SiO2/Si. Las muestras fueron sometidas a tratamientos térmicos mediante el uso de un horno tubular, en un rango de temperaturas comprendidas entre 250ºC y 1000ºC durante 3 horas para luego ser enfriadas a razón de 1.4ºC/min. La cristalización de las muestras luego de los tratamientos térmicos fueron caracterizadas mediante difracción de Rayos X (DRX), mientras que la morfología de la superficie se analizo usando Microscopia Electrónica de Barrido (MEB). Los resultados obtenidos fueron analizados y encontramos que la temperatura de recocido mas optima que mejor la dirección (111) en la pelicula de cobre y que permite conocer la dinámica de los átomos de la superficie del sistema Cu/SiO2 con respecto a la temperatura, está comprendida en el rango de 400 y 500ºC. Durante todo el proceso de recocido las superficies de las muestras se oxidan y notamos la presencia de siliciuros de cobre

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.

有機分子膜を流れる電流には, 大きく分けると変位電流とトンネル電流がある。変位電流の検出には短絡回路が用いられるが, 電極と分子膜との接触は必ずしも必要ではない。その上, 種々の外部刺激 (圧力,熱光など) を加えたときの分子の動的な挙動にともなって流れる電流が単分子膜においても計測されるので, 分子膜の極限の機能を引き出すことが可能となる。この方法による電流検出は原理的に分子レベルのオーダーで実現可能であるので, 分子エレクトロニクスの基盤技術の一つとして重要になると思われる。一方, トンネル電流の検出では, 電極と膜との接触が必要であるので, 膜質の良い分子膜を作製することが重要となる。ポリイミドLB膜では膜質が極めて良いので, トンネル接合素子への応用が期待できる。