Gold nanoparticles (GNPs) are often used as island electrodes of single-electron (SE) devices. One of technical challenges in fabrication of SE devices with GNPs is the placement of GNPs in a nanogap between two lead electrodes. Utilization of dielectrophoresis (DEP) phenomena is one of possible solutions for this challenge, whereas the fabrication process with DEP includes stochastic aspects. In this brief paper, we present our experimental results on electric resistance of GNP arrays assembled by DEP. More than 300 pairs of electrodes were investigated under various DEP conditions by trial and error approach. We evaluated the relationship between the DEP conditions and the electric resistance of assembled GNP arrays, which would indicate possible DEP conditions for fabrication of SE devices.

Nano crystalline zinc oxide (ZnO) is deposited by room temperature atomic layer deposition (RT-ALD) using dimethylzinc and a plasma excited humidified Ar without thermal treatments. The TEM observation indicated that the deposited ZnO films were crystallized with grain sizes of ∼20 nm on Si in the course of the RT-ALD process. The crystalline ZnO exhibited semiconducting characteristics in a thin film transistor, where the field-effect mobility was recorded at 1.29×10-3cm2/V·s. It is confirmed that the RT deposited ZnO film has an anticorrosion to hot water. The water vapor transmission rate of 8.4×10-3g·m-2·day-1 was measured from a 20 nm thick ZnO capped 40 nm thick Al2O3 on a polyethylene naphthalate film. In this paper, we discuss the crystallization of ZnO in the RT ALD process and its applicability to flexible electronics.

Gallium oxide is expected as a channel material for thin film transistors. In the conventional technologies, gallium oxide has been tried to be fabricated by atomic layer deposition (ALD) at high temperatures from 100--450$^{circ}$C, although the room-temperature (RT) growth has not been developed. In this work, we developed the RT ALD of gallium oxide by using a remote plasma technique. We studied trimethylgallium (TMG) adsorption and its oxidization on gallium oxide surfaces at RT by infrared absorption spectroscopy (IRAS). Based on the adsorption and oxidization characteristics, we designed the room temperature ALD of Ga$_{2}$O$_{3}$. The IRAS indicated that TMG adsorbs on the gallium oxide surface by consuming the adsorption sites of surface hydroxyl groups even at RT and the remote plasma-excited water and oxygen vapor is effective in oxidizing the TMG adsorbed surface and regeneration of the adsorption sites for TMG. We successfully prepared Ga$_{2}$O$_{3}$ films on Si substrates at RT with a growth per cycle of 0.055,nm/cycle.

We investigated solid-phase growth reactions for the fabrication of β-FeSi2 films from Fe and FeSi sources by reflection high-energy electron diffraction (RHEED). To enhance the interdiffusion of Fe and Si for the growth of β-FeSi2, the use of FeSi instead of pure Fe as the source for the initial deposition was examined. The RHEED observation during the solid phase reaction indicated that the growth temperature was markedly decreased to 390 K using the FeSi source. We discuss the reaction mechanism of the solid phase growth of β-FeSi2 from Fe and FeSi sources in this paper.

Low-temperature deposition of Y2O3 at 80°C is studied using an yttrium precursor of tris(butylcyclopentadienyl)yttrium (Y(BuCp)3) and plasma exited humidified argon oxidizer. The deposition is demonstrated using an atomic-layer-deposition sequence; the Y(BuCp)3 and the oxidizing gases are time separately introduced to the reaction chamber and these injections are repeated. To determine the gas introduction conditions, surface reactions of Y(BuCp)3 adsorption and its oxidization are observed by an in-situ IR absorption spectroscopy. The deposited film is confirmed as fully oxidized Y2O3 by X-ray photoelectron spectroscopy. The present deposition is applicable for the deposition of Y2O3 film on flexible polyethylene terephthalate films.

The low temperature deposition of AlN at 160 °C is examined by using trimethyl aluminum (TMA) and NH radicals from plasma excited Ar diluted ammonia. For the deposition, a plasma tube separated from the reaction chamber is used to introduce the neutral NH radicals on the growing surface without the direct impacts of high-speed species and UV photons, which might be effective in suppressing the plasma damage to the sample surfaces. To maximize the NH radical generation, the NH3 and Ar mixing ratio is optimized by plasma optical emission spectroscopy. To determine the saturated condition of TMA and NH radical irradiations, an in-situ surface observation of IR absorption spectroscopy (IRAS) with a multiple internal reflection geometry is utilized. The low temperature AlN deposition is performed with the TMA and NH radical exposures whose conditions are determined by the IRAS experiment. The spectroscopic ellipsometry indicates the all-round surface deposition in which the growth per cycles measured from front and backside surfaces of the Si sample are of the same range from 0.39∼0.41nm/cycle. It is confirmed that the deposited film contains impurities of C, O, N although we discuss the method to decrease them. X-ray diffraction suggests the AlN polycrystal deposition with crystal phases of AlN (100), (002) and (101). From the saturation curves of TMA adsorption and its nitridation, their chemical reactions are discussed in this paper. In the present paper, we discuss the possibility of the low temperature AlN deposition.

Nitrogen adsorption on thermally cleaned Si(100) surfaces by pure and plasma excited NH$_{3}$ is investigated by extit{in situ} IR absorption spectroscopy and ex-situ X-ray photoelectron spectroscopy with various temperatures from RT (25$^{circ}$C) to 800$^{circ}$C and with a treatment time of 5,min. The nitrogen coverage after the treatment varies according to the treatment temperature for both pure and plasma excited NH$_{3}$. In case of the pure NH$_{3}$, the nitrogen coverage is saturated as low as 0.13--0.25 mono layer (ML) while the growth of the nitride film commenced at 550$^{circ}$C. For the plasma excited NH$_{3}$, the saturation coverage was measured at 0.54,ML at RT and it remained unincreased from RT to 550$^{circ}$C. This indicates that the plasma excited NH$_{3}$ enhances the nitrogen adsorption near at RT. It is found that main species of N is Si$_{2}=$ NH in case of the plasma excited NH$_{3}$ at RT while the pure NH$_{3}$ treatment gives rise to the Si--NH$_{2}$ passivation with Si--H at RT. We discuss the mechanism of the nitrogen adsorption on Si(100) surfaces with the plasma excited NH$_{3}$ in comparison with the study on the pure NH$_{3}$ treatment.

We present an optimization algorithm for the design of multilayer antireflection (AR) coatings for organic photovoltaic (OPV) cells. When a set of available materials for the AR films is given, the proposed method allows for searching the globally optimized AR structure that maximizes the short-circuit current density (JSC) under simulated solar light illumination (AM 1.5). By applying this method to an OPV solar cell with a configuration of Al/P3HT:PCBM/MoO3/ITO, we demonstrated that JSC can increase by 7.5% with a 6-layer AR coating, consisting of MgF2, ZnS, and Al2O3. A notable feature of this method is that it can find not only the optimal solution, which maximizes JSC , but also the quasi-optimal solutions, which increase JSC to nearly maximum levels. We showed that the quasi-optimal solution may have higher robustness against deviations in film thicknesses, from their designated values. This method indicates the importance of practically useful, non-optimal solutions for designing AR coatings. The present method allows for extending the user's choices and facilitates the realization of a practical design for an AR coating.

We numerically simulated electrical properties, i.e., the resistance and Coulomb blockade threshold, of randomly-placed conductive nanoparticles. In simulation, tunnel junctions were assumed to be formed between neighboring particle-particle and particle-electrode connections. On a plane of triangle 100×100 grids, three electrodes, the drain, source, and gate, were defined. After random placements of conductive particles, the connection between the drain and source electrodes were evaluated with keeping the gate electrode disconnected. The resistance was obtained by use of a SPICE-like simulator, whereas the Coulomb blockade threshold was determined from the current-voltage characteristics simulated using a Monte-Carlo simulator. Strong linear correlation between the resistance and threshold voltage was confirmed, which agreed with results for uniform one-dimensional arrays.

Current density-voltage (J-V) and capacitance-voltage (C-V) characteristics of P3HT/n--silicon heterojunction diodes were investigated to clarify the carrier conduction mechanism at the organic/inorganic heterojunction. The J-V characteristics of the P3HT/n--Si junctions can be explained by a Schottky diode model with an interfacial layer. Diode parameters such as Schottky barrier height and ideality factor were estimated to be 0.78 eV and 3.2, respectively. The C-V analysis suggests that the depletion layer appears in the n--Si layer with a thickness of 1.2 µm from the junction with zero bias and the diffusion potential was estimated at 0.40 eV at the open-circuit condition. The present heterojunction allows a photovoltaic operation with power conversion efficiencies up to 0.38% with a simulated solar light exposure of 100 mW/cm2. The forward bias current was enhanced by coating the Si surface with a SiC layer, where the ideality factor was improved to be the level of 1.451.50.

We report room-temperature atomic layer deposition (ALD) of SnO2 using tetramethyltin (TMT) as a precursor and plasma-excited humidified argon as an oxidizing gas and investigate the saturation behaviors of these gases on SnO2-covered Si prisms by IR absorption spectroscopy to determine optimal precursor/oxidizer injection conditions. TMT is demonstrated to adsorb on the SnO2 surface by reacting with surface OH groups, which are regenerated by oxidizing the TMT-saturated surface by plasma-excited humidified argon. We provide a detailed discussion of the growth mechanism. We also report the RT ALD application to the RT TFT fabrication.

We have developed an easy fabrication method of Si field effect transistors (FETs) with poly (methyl methacrylate) (PMMA) gate films for science education. In this process, we can easily fabricate the silicon FETs only by means of metal deposition and thermal diffusion without any lithography processes. The organic isolation films of PMMA can be deposited by casting or painting at room temperature in air. The metal-organic-semiconductor FETs with PMMA exhibited almost the same drain current -- gate voltage characteristics as those of conventional Si metal-oxide-semiconductor FETs, which are suitable for the education material of semiconductor engineering. The organic gate Si FETs can be used not only for education but also as thin film transistors for active matrix displays.

Electrical characteristics of P3HT/Aluminum organic/ inorganic heterojunction diodes were investigated V-I and capacitance-voltage (C-V) measurements. The V-I measurement exhibited current rectification inherent in the Schottky diode, suggesting their availabilities as rectification diodes in organic flexible circuits. C-V analysis indicated the fact that the depletion layer was generated in the P3HT film in the reversed bias condition. The flat band voltage analysis suggested that the interfacial charge affected the built-in potential of the diodes. Al/P3HT heterojunction is possible to be used as not only the rectification diodes but also gate junctions for junction type field effect or static induction transistors.