Tohru Den

High-mobility thin-film transistor with amorphous InGaZnO4 channel fabricated by room temperature rf-magnetron sputtering

Thin-film transistors (TFTs) were fabricated using amorphous indium gallium zinc oxide (a-IGZO) channels by rf-magnetron sputtering at room temperature. The conductivity of the a-IGZO films was controlled from ∼10−3to10−6Scm−1 by varying the mixing ratio of sputtering gases, O2∕(O2+Ar), from ∼3.1% to 3.7%. The top-gate-type TFTs operated in n-type enhancement mode with a field-effect mobility of 12cm2V−1s−1, an on-off current ratio of ∼108, and a subthreshold gate voltage swing of 0.2Vdecade−1. It is demonstrated that a-IGZO is an appropriate semiconductor material to produce high-mobility TFTs at low temperatures applicable to flexible substrates by a production-compatible means.

Combinatorial approach to thin-film transistors using multicomponent semiconductor channels: An application to amorphous oxide semiconductors in In–Ga–Zn–O system

A combinatorial approach was applied to thin-film transistors (TFTs) using amorphous In–Ga–Zn–O semiconductor channels. A large number of TFTs, having n-type channels with different chemical compositions, were fabricated simultaneously on a substrate. A systematic relation was clarified among the compositional ratio of In:Ga:Zn, oxygen partial pressure in film deposition atmosphere, and TFT characteristics. The results provide an experimental basis to understand the roles of each metallic element in the In–Ga–Zn–O system. This information leads to a guideline to tune the metallic compositions for required TFT specifications.

Multiwalled carbon nanotubes growth in anodic alumina nanoholes

Carbon nanotubes (CNTs), standing perpendicularly to a substrate with an electrode, were fabricated by thermal catalytic decomposition of ethylene from Co particles electrochemically embedded at the bottom of anodic alumina nanoholes. The thermal durability of the alumina nanoholes for the CNTs growth process was achieved by using Nb as an underlying electrode. The CNTs were electrically connected to the electrode through the conductive paths, which were formed at the bottom of alumina nanoholes by Nb ion migration from the underlying electrode during anodization.

Preparation and properties of YSr2Cu3−xMxOy (M = Li, Al, Ti, V, Cr, Fe, Co, Ga, Ge, Mo, WandRe)

Abstract We have investigated the composition YSr2Cu3-xMxOy and obtained the 123-structure for M= Li, Al, Ti, V, Cr, Fe, Co, Ga, Ge, Mo, W and Re. Superconductivity is observed for the compounds with M=Ti, V, Fe, Co, Ga, Ge, Mo, W and Re at low levels of substitution context x. The highest Tzeroc is 73 K for the compound YSr2Cu2.85Re0.15O7.12. Tcs are enhanced by decreasing x or increasing y, which draw the rise of hole concentration pave (Cu2+p). Except for the compounds with M=V and Cr, the structures are tetragonal, while those of the compounds YSr2Cu3-xCrxOy are orthorhombic, and YSr2Cu3-x VxOy shows the structural transition from tetragonal to orthorhombic by HIP treatment with the simultaneous transition from superconductivity to metallic transport property. This Sr-based 123-structure is stabilized by doping elements with ionic radii=0.35-0.49 A or 0.525-0.62 A supposing 4- or 6-coordination, respectively, except for M=Li.

Phase-separated Al–Si thin films

Phase-separated Al–Si films composed of Al nanocylinders embedded in an amorphous-Si matrix have been prepared by a sputtering method. By controlling the deposition rate, substrate temperature, and film composition, the average diameter of the Al cylinders can be varied systematically from less than 5to13nm with a cylinder density ranging from 1015 to in excess of 1016cylindersm−2. A three-dimensional simulation of phase separation in binary thin films was performed using a modified Cahn-Hilliard [J. Chem. Phys. 28, 258 (1958)] equation to understand the growth mechanism. The simulation studies indicate that the surface diffusion length and film composition are important factors which determine film morphology. Experimental and simulation studies are compared and discussed.

The Superconductivity in the Bi-Sr-Ln-Cu-O System (Ln=Pr, Nd and La)

The superconductivity in samples nominally described as Bi2(Sr1-xLnx)2Cu1+nOy (Ln: lanthanide elements and yttrium: n=0 and 1) was investigated. The effect of an increasing TC compared with that of Bi2Sr2CuOy was observed for Ln=La, Pr and Nd. The highest end-point of the transition temperature of Bi2(Sr1-xNdx)2CuOy was 20.4 K with x=0.25. Compounds described as Bi2(Sr0.95Ln0.05)2CuOy (Ln=Pr and Nd) had an onset TC of about 60 K, and small but definite Meissner effects were also observed.

Development of Phase‐Separated Scintillators with Light‐Guiding Properties

Alkali halide systems that function as phase-separated scintillators (PSSs) with light-guiding properties are sucessfully created. Furthermore, it is the matrix phases of the PSSs which display the light-guiding properties. CsI-NaCl:Tl is a practical material pair because of its high pixel light output and good spatial resolution.

Superconductivity in the Bi2Sr3-xLnxCu2Oy System and the Excess of Hole Concentration in Bi2Sr2CanCu1+nOy (n=0 and 1)

A new family of high-Tc superconductors of Bi2Sr3-xLnxCu2Oy(Ln=Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Y) has been found by means of resistivity and magnetization measurements. The highest superconducting transition temperature was obtained when the substitution concentration x was about 0.3. The X-ray powder diffraction measurement showed that Bi2Sr2-xLnxCuOy (221 phase) is stable for x<0.3 and Bi2Sr3-xLnxCu2Oy (232 phase) becomes major when x exceeds 0.3. The 232 phase has the same structure as Bi2Sr2CaCu2Oy. It is also demonstrated that the hole number p of [Cu-O]+p in Bi2Sr2CuOy and Bi2Sr2CaCu2Oy is excessive compared with the proper value giving the highest Tc.

Superconductor with Tc up to 8 K in the compound (Ln,Ca)(Sr,Ba)2(C,Cu)Cu2O7-δ

Abstract We have synthesized a new family of oxycarbonate compounds (Ln,Ca) (Sr,Ba) 2 (C,Cu)Cu 2 O 7-δ (Ln: rare-earth metals) with a so-called “CO 3 -1212” structure. Two kinds of single phase in the general formula Er 0.5 Ca 0.5 Sr 2- x Ba x Cu 3- y C y O 7-δ with ( x , y )=(0.6, 0.5) and (1.3, 0.4) were prepared at different CO 2 partial pressures. The former compound shows a superconducting transition at about 45 K, and the latter has T c up to 80 K. This rise in T c may come from the increase of carrier density because of the decrease of carbon content. We have also studied the Ln-dependence, and it is revealed that most of the compounds Ln 0.5 Ca 0.5 Sr 0.7 Ba 1.3 Cu 2.6 C 0.4 O 7−δ show the same results, except for Ln = Ce and Tb, which did not construct the structure, and also Ln = Pr , which shows suppressed superconductivity with T c of 30 K.

Crystallite Size Dependence of Plasmon Energies in Polycrystalline Graphite Observed by Reflected Electron Energy Loss Spectroscopy

Both the energy losses of π electron plasmon and valence electron plasmon in polycrystalline graphite have been measured by reflected electron energy loss spectroscopy (REELS). It was found that when crystallites are smaller than 10 nm, the π plasmon energy is lower than the value estimated from the valence plasmon energy which directly reflects the density. Moreover, there is a correlation between the π plasmon energy and the relative intensity of the π plasmon peak to the elastic peak. Thus, the decrease of the π plasmon energy was explained by a crystallite size effect such as a decrease in π electron density. This REELS technique was applied to estimate the chemical state in carbon films obtained by thermal chemical vapor deposition (CVD). The two-dimensional distribution of the graphitic carbon was successfully measured at a spatial resolution of less than 1 µm.