Search

Al-doped ZnO (AZO) films with various Ga contents were prepared by magnetron co-sputtering in order to investigate the effect of Ga additions on the structural and optoelectronic characteristics of AZO films. The appropriate Ga doping level improved the crystallinity of the AZO films, investigated by X-ray diffraction analysis. The resistivity of AZO films decreased from 3.5 ×10-3 to 8.1 ×10-4 Ω cm by Ga doping at 2.1 at. %. The Hall mobility was improved by enhancing the polycrystalline growth of the films. The carrier concentration was increased by Ga doping, which was activated as an extrinsic donor. At a further increase in the Ga content of more than 2.1 at. %, the crystallinity and resistivity of the Ga-doped AZO films deteriorated. The optical band gap was increased, and the transmittance in the visible region was increased from 86.7 to 91.0% using the same level of Ga doping at 2.1 at. %.

not Available.

We report the electrical stability of bottom-gate nanocrystalline silicon (nc-Si) thin film transistors (TFTs) with various channel lengths under drain bias stress for the first time. As the bias stress at the drain terminal increases at a fixed gate bias, the threshold voltage (V TH) shift of the nc-Si TFTs decreases significantly. Under the drain bias stress, the V TH shift decreases with channel length. The smaller V TH shift was analyzed on the basis of the concentration of the channel charge. A high drain bias reduces the carrier concentration near the drain terminal. Also, the ratio of the depleted charges to total charges increases with decreasing channel length due to the drain bias. Thus, a short-channel TFT has a smaller normalized channel charge than a long-channel TFT. A low carrier concentration induces a small number of defect states; thus the V TH shift of a short-channel TFT is smaller than that of a long-channel TFT.

We have investigated the electrical characteristics of short-channel p-type excimer laser annealed (ELA) polycrystalline silicon (poly-Si) thin-film transistors (TFTs) under high gate and drain bias stress. We found that the threshold voltage of short-channel TFTs was significantly shifted in the negative direction owing to high gate and drain bias stress (ΔV TH = -2.08 V), whereas that of long-channel TFTs was rarely shifted in the negative direction (ΔV TH = -0.10 V). This negative shift of threshold voltage in the short-channel TFT may be attributed to interface state generation near the source junction and deep trap state creation near the drain junction between the poly-Si film and the gate insulator layer. It was also found that the gate-to-drain capacitance (C GD) characteristic of the stressed TFT severely stretched for the gate voltage below the flat band voltage V FB. The effects of high gate and drain bias stress are related to hot-hole-induced donor like interface state generation. The transfer characteristics of the forward and reverse modes after the high gate and drain bias stress also indicate that the interface state generation at the gate insulator/channel interface occurred near the source junction region.

The stability of oxide-based TFT under bias stress was considerably improved by employing in-Situ thermal pretreatment, which suppresses hydrogen content in the oxide active layer. By suppressing the inflow of hydrogen, easily movable, back interface trapping was reduced and the VTH shift of the oxide TFT was suppressed successfully.

We have fabricated p-channel metal oxide semiconductor (PMOS) solid-phase crystallization silicon (SPC-Si) thin-film transistors (TFTs) employing an alternating magnetic field on a glass substrate, which exhibit better current uniformity than excimer-laser annealed low-temperature polycrystalline silicon (ELA LTPS) TFTs, and superior stability to hydrogenated amorphous silicon (a-Si:H) TFTs. The leakage current of the SPC-Si TFT was larger than that of an a-Si:H TFT and an ELA poly-Si TFT owing to its many grain boundaries. The leakage current of the SPC-Si TFT was successfully suppressed through off-state-bias annealing. Off-state-bias annealing forced electron carriers to be trapped in the gate insulator, thus reducing the gate–drain field and suppressing the leakage current of the SPC-Si TFT. Our experimental result showed that the trapped electron charges in the gate insulator did not escape under thermal annealing or AC-bias stress. The off-state-bias annealed PMOS SPC-Si TFT could be a suitable pixel element for high-quality display applications employing an alternating magnetic field.

Titanate nanotubes containing 2.5 wt% Ni were synthesized from TiO2 sol using alkali hydrothermal treatment followed by a simple ion-exchange process. The changes in phase, shape and morphology, surface area, and photocatalytic activity of these nanotubes have been explored as a function of calcination temperature. The samples were characterized using standard techniques, including x-ray diffraction, transmission electron microscopy, scanning electron microscopy, inductively coupled plasma spectrometry, energy dispersive x-ray spectroscopy, and Brauner-Emmett-Teller surface area analysis. The study revealed that the titanate phase containing Ni ions can be converted to the anatase phase after certain heat treatments but, at the same time, the tubular morphology was partially lost. Investigation of photocatalytic properties demonstrated that the as-prepared Ni-titanate nanotubes were photocatalytically inactive, but when heated at temperatures below 500 degrees C their activity was significantly enhanced with the change in phase. The calcined nanotube samples carrying nickel ion showed better photocatalytic activity than calcined nanotube samples containing protons. The hydrogen adsorption capacity of these titanates has also been measured, and it was found that Ni-titanate nanotubes can adsorb more hydrogen than its counterpart Na-titanate.

We fabricated nanocrystalline silicon (nc-Si) thin-film transistors (TFTs) without any substrate heating. High quality nc-Si and silicon dioxide films were deposited at room temperature employing an inductively coupled plasma chemical vapor deposition (ICP-CVD) system. For the nc-Si film, a crystalline phase was grown as a columnar structure and the crystalline volume fraction was 27%. On the silicon dioxide film, hydrogen plasma post-treatment was performed, and the electrical characteristics of silicon dioxide film improved owing to charge reduction and the annealing effect. The nc-Si and silicon dioxide films were used for the fabrication of nc-Si TFTs without substrate heating. Although there was no external heating, a mobility of 6.42 cm2V-1s-1 was achieved. This result indicates that nc-Si TFTs fabricated without substrate heating may be a suitable devices for a flexible display.

not Available.

We studied excimer laser annealing effects on silicon-rich silicon nitride films containing silicon quantum dots to develop silicon based flexible Light emitting diodes. The silicon-rich silicon nitride films were deposited by catalytic chemical vapor deposition system using a mixture of SiH4, NH3 and H2 gas. The substrate temperatures in all deposition process were less than 200 ° to use polyethersulphone substrate. The changing crystallity and density of silicon quantum dots were analyzed by photoluminescence spectra. The change in the luminescence behavior with nucleation of silicon quantum dots was observed after excimer laser annealing.

We fabricated bottom gate nanocrystalline silicon (nc-Si) thin film transistor (TFT). We report the instability phenomena of the nc-Si TFT under light illumination under gate bias stress for the first time. The comparison with hydrogenated amorphous silicon (a-Si:H) TFT was carried out. Under only light illumination was induced, the transfer characteristic of nc-Si TFT was almost unchanged. Also, positive gate bias stress hardly changed the VTH of nc-Si TFT, while that of a-Si:H TFT was shifted considerably. However, under negative bias stress, a-Si:H TFT showed rather high stability. Instability mechanism under light illumination under gate bias stress was different in nc-Si TFT and a-Si:H TFT. The VTH shift of both TFT was opposite direction.

Bottom-gate nanocrystalline silicon (nc-Si) thin film transistors (TFTs) were fabricated and evaluated their characteristics and electrical stability under various stress condition. nc-Si with high crystallinity was deposited employing Inductively coupled plasma chemical vapor deposition(ICP-CVD) system. We employed helium gas diluted deposition and all the process temperature was kept under 350oC. We fabricated conventional inverted-staggered nc-Si TFTs. Fabricated nc-Si TFTs showed fine electrical characteristics, such as electrical mobility of 0.64~0.77 cm2/V⋅sec. We investigated its stability through constant-voltage stress and constant-current stress. The threshold voltage shift after 30,000 seconds gate bias (10V) stress was only 0.098V, which is considerably less compared to a-Si:H TFT. Under the static current stress condition, the threshold voltage of the nc-Si TFT was shifted less than that of a-Si:H TFT. It demonstrates that nc-Si TFT exhibit better stability than conventional a-Si:H TFT.

We have fabricated nc-Si film and SiO2 film without substrate heating using ICP-CVD. nc-Si film has amorphous incubation layer of 12nm and crystalline volume fraction of 27%. Hydrogen plasma post-treatment was performed SiO2 film and electrical characteristic of SiO2 film was improved due to reduction of charges and annealing effect. And we have fabricated nc-Si TFT without substrate heating using ICP-CVD. Although there was no external heating, mobility of 6.42cm2/V⋅s was obtained. This result indicates that nc-Si TFT fabricated without any substrate heating may be suitable device for a flexible display.

In this study, titanium metal acts as the titanium source to prepare oriented titanate nanotube thin film. The effects of preparation parameters, such as reaction temperature, duration and post-treatment conditions, on the film morphology and stability have been examined. A general formation mechanism for oriented titanate nanotube thin film is proposed on the basis of detailed observations of the products using two-dimensional surface SEM studies and TEM images. The overall formation of titanate nanotubes can be summarized as a sequence of four steps: (a) titanium dissolution and alkali titanate hydrogel formation; (b) alkali titanate hydrogel dissolution, increased TiO32−, TiO2(OH)22− or TinO2n+m2m− concentration and layered Na2Ti3O7 formation; (c) layered Na2Ti3O7 growth; (d) nanotube formation via Na2Ti3O7 splitting and the multilayer scrolling process. The Na2Ti3O7 lamellar structures split between the (010) planes into nanosheets.

not Available.

Preparation of nanostructured TiO2 powders for efficient photocatalyst was investigated through a direct crystallization from aqueous TiOCl2 solutions containing various metal–chlorides. The TiO2 powders without any additives and those added with Ni2+, Fe3+ and Nb5+ions, respectively, which has a similar cationic radius to Ti4+, were mainly crystallized to rutile phase, whereas those added with Al3+ and Zr4+ ions, which have a quite different positive ionic radius, were mainly crystallized to anatase phase. On the other hand, the secondary particles in the TiO2 powder consisted of acicular and spherical primary particles corresponding to rutile and anatase phases, respectively. From these results, it seems that the cationic radius of the additives could affect phase formation as well as morphology of TiO2 precipitates. Among the TiO2 powders prepared, Ni2+ doped powder, showing mainly rutile phase, had excellent photocatalytic ability in decomposition of 4-chlorophenol.

The photocatalytic performance of thin films coated on porous alumina balls using various aqueous solutions as starting precursors, to which 1.0 transition metal () chlorides had been already added, has been investigated, together with characterizations for sols synthesized simultaneously in the same autoclave through hydrothermal method. The synthesized sols were all formed with an anatase phase, and their particle size was between several nm and 30 nm showing of mV, being maintained stable for over 6 months. However, the sol added with Cr had a much lower value of -potential and larger particle sizes. The coated thin films had almost the same shape and size as those of the sol. The pure sol showed the highest optical absorption in the ultraviolet light region, and other sols containing showed higher optical absorption than pure sol in the visible light region. According to the experiments for removal of a gas-phase benzene, the pure film showed the highest photo dissociation rate in the ultraviolet light region, but in artificial sunlight the photo dissociation rate of coated films containing was measured higher together with the increase of optical absorption by doping.

【For mass product of nanocrystalline ZnO ultrafine powders, self-sustaining combustion process(SCP) and ultrasonic spray combustion method(USCM) were applied at the same time. Ultrasonic spray gun was attached on top of the vertical type furnace. The droplet was sprayed into reaction zone of the furnace to form SCP which produces spherical shape with soft agglomerate crystalline ZnO particles. To characterize formed particles, fuel and oxidizing agent for SCP were used glycine and zinc nitrate or zinc hydroxide. Respectively, with changing combustion temperature and mixture ratio of oxidizing agent and fuel, the best ultrasonic spray conditions were obtained. To observe ultrasonic spray effect, two types of powder synthesis processes were compared. One was directly sprayed into furnace from the precursor solution (Type A), the other directly was heated on the hot plate without using spray gun (Type B). Powder obtained by type A was porous sponge shape with heavy agglomeration, but powder obtained using type B was finer primary particle size, spherical shape with weak agglomeration and bigger value of specific surface area. 9/ This can be due to much lower reaction temperature of type B at ignition time than type A. Synthesized nanocrystalline ZnO powders at the best ultrasonic spray conditions have primary particle size in range 20~30nm and specific surface area is about 20m $^2$ /g.】

The redox properties of a homogeneously-precipitated rutile powder with a BET surface area of ~/g, consisting of an acicular primary particle, were characterized using photocatalytic reaction in aqueous 4-chlorophenol, Cu-EDTA and Pb-EDTA solutions under ultraviolet irradiation, compared to those of commercial P-25 X powder with a spherical primary particle as well as home-made anatase powder with ~/g BET surface area. Here, the anatase powder also includes mainly the primary particles very similar to the acicular shapes of the rutile powder. The rutile powder showed the fastest decomposition rate and the largest amount in the photoredor, compared with the anatase or P-25 powder, while the anatase powder unexpectedly showed the slowest rate and the smallest amount in the same experiments regardless of almost the same surface area. From results, the excellent photoredox abilities of this rutile powder appears to be due to specific powder preparation method, like a homogeneous precipitation leading to direct crystallization from the solution, regardless of their crystalline structures even when having the similar particle shape and surface area.

Ultrafine crystalline TiO2 powder was prepared by homogeneous precipitation by heating aqueous TiOCl2 solution below 70°C. The TiO2 powder was formed even at room temperature. By spontaneous hydrolysis of the aqueous TiOCl2 solution, all the precipitates were completely crystallized in the rutile phase. These, however, were transformed into the anatase phase by adding more TiOSO4 solution to the aqueous TiOCl2 solution. The formed secondary particles consisted of needle-shaped, spherical and mixed primary particles corresponding to the rutile, anatase and mixed phases, respectively. It seems that the formation and phase determination of crystalline TiO2 powder during the precipitation may be affected by capillary pressure. This pressure probably depends on the shape of the primary particles.

Ultrafine crystalline TiO2 powders were prepared by just heating and stirring aqueous TiOCl2 solution with a Ti+4 concentration of 0.5 mol/l at room temperature to 100°C under one atmosphere. The crystallinity, the phase transformation and the particle shape of ultrafine TiO2 powders obtained by this simple precipitation method were analyzed using an X-ray diffractometer (XRD), transmission electron microscopy (TEM), differential thermal analyzer (DTA), and scanning electron microscopy (SEM). TiO2 crystalline precipitates with a pure rutile phase were formed below 65°C, then TiO2 crystalline precipitates with an anatase phase started forming at temperatures higher than 65°C, which ends with the pure anatase phase at 100°C. The direct formation of TiO2 crystalline precipitates from an aqueous TiOCl2 solution is due to the existence of the OH- ions in distilled water which cause the crystallization of TiOCl2 to TiO2 without hydrolyzation to Ti(OH)4. Conventionally, rutile-phase TiO2 is obtained at much higher temperatures. However, in this study a stable rutile-phase TiO2 was obtained by a simple method at close to room temperature.

Doped CeO2–(CeO2)0.9(Gd2O3)0.1 pellets were prepared using the glycine-nitrate process with various sintering times and sintering temperatures. Compositional and structural characterizations were carried out using X-ray diffraction (XRD) with CuKα radiation, a scanning electron microscope (SEM) and a Transmission electron microscope (TEM). Sintering and electrical characteristics were investigated using dilatometer measurement and the AC impedance analyser. Powder characteristics were also investigated by the BET method. Polycrystalline (CeO2)0.9(Gd2O3)0.1 powders with specific surface areas of 19–23 m2/ g were obtained. Green bodies from the synthesized powders after milling shrunk up to about 1470° C, above which they expanded with heating temperature, whereas those before milling shrank continuously up to a temperature of 1600° C. This difference might be attributed to the change of the packing density of the synthesized powders upon milling: from 25% without milling to about 40% after milling. Therefore the sintered (CeO2)0.9(Gd2O3)0.1 bodies having a theoretical density of 7.25 g/cm3 were considered to be obtained from the as-milled powders by controlling the sintering time at a sintering temperature higher than 1470° C in air. In the AC impedance measurements, the electrical resistivity of the (CeO2)0.9–(Gd2O3)0.1 bodies, produced from as-milled powders, and sintered at 1500° C with increasing sintering time, showed the minimum total value at the sintering time of 10 h. The minimum total resistivity of the (CeO2)0.9(Gd2O3)0.1 bodies sintered at 1500° C for 10 h seems to be obtained when the sum of the activation energy for the resistivities in the grain and at the grain boundary.

Background Belt or wire shaped TiO2(B) particles were synthesized for lithium ion battery application by a hydrothermal and heat treatment process. In order to facilitate TiO2(B)/C composites fabrication, the synthesized TiO2(B) particles were crushed into smaller sizes by ball milling. Results Ball mill treated TiO2(B) particles of less than 1.0 μm with a fraction of anatase phase, compared to as-synthesized TiO2(B) particles with about 24 μm in average particle size, showed a significant improvement in the electrochemical properties. They showed a much improved stability in the charge–discharge cycles and irreversibility. They maintained about 98% of the initial capacity during 50 cycles while as-synthesized sample before ball mill treatment showed a gradual decrease in the capacity with the cycles. The irreversibility of 12.4% of as-synthesized sample was also greatly improved to 7% after ball milling treatment. Conclusions Our results indicate ball mill treatment can be an economical way to improve electrochemical properties of TiO2(B) anode materials for lithium ion battery application.