We report that a layered iron-based compound LaOFeAs undergoes superconducting transition under doping with F- ions at the O2- site. The transition temperature (T c) exhibits a trapezoid shape dependence on the F- content, with the highest T c of ∼26 K at ∼11 atom %.
Transparent electronic devices formed on flexible substrates are expected to meet emerging technological demands where silicon-based electronics cannot provide a solution. Examples of active flexible applications include paper displays and wearable computers. So far, mainly flexible devices based on hydrogenated amorphous silicon (a-Si:H) and organic semiconductors have been investigated. However, the performance of these devices has been insufficient for use as transistors in practical computers and current-driven organic light-emitting diode displays. Fabricating high-performance devices is challenging, owing to a trade-off between processing temperature and device performance. Here, we propose to solve this problem by using a novel semiconducting material--namely, a transparent amorphous oxide semiconductor from the In-Ga-Zn-O system (a-IGZO)--for the active channel in transparent thin-film transistors (TTFTs). The a-IGZO is deposited on polyethylene terephthalate at room temperature and exhibits Hall effect mobilities exceeding 10 cm2 V(-1) s(-1), which is an order of magnitude larger than for hydrogenated amorphous silicon. TTFTs fabricated on polyethylene terephthalate sheets exhibit saturation mobilities of 6-9 cm2 V(-1) s(-1), and device characteristics are stable during repetitive bending of the TTFT sheet.
Nature © Macmillan Publishers Ltd 1997the same direction. A zero value of H j indicates ferromagnetically coupled films. H j is known 7,14 to oscillate as a function of t because of the RKKY interaction. We can clearly distinguish two situations. In Fig. 4b (Cu spacer grown at room temperature) only a few oscillations take place, the oscillation with the short wavelength l being marginal. This is in contrast to the theoretical expectations 7 , which require l to dominate over Λ for geometrically perfect samples. On the other hand, when the Cu spacer is grown at low temperatures, more oscillations appear (Fig. 4c), and l dominates over Λ. We note that cooling a room-temperature-deposited wedge structure does not change the results given in Fig. 4b. Thus, lowtemperature deposition is essential to minimize thickness fluctuations. We also note that, in for example Fe/Cr multilayers, just the opposite occurs: the shortest-wavelength oscillation is favoured by high-temperature growth 15 .The smallest oscillations detected in this experiment correspond to an energy change of ϳ10 −8 eV per atom. This value represents a challenge both to first-principles calculations and to spectroscopies aimed at unveiling the electronic structure of solids. Moreover, although exceedingly small, this energy scale participates in deter-mining a macroscopic observable (in this case the threshold magnetic field H s ) and thus might play an important role in the design of metallic nanostructures for device application. Ⅺ
The present status and recent research results on amorphous oxide semiconductors (AOSs) and their thin-film transistors (TFTs) are reviewed. AOSs represented by amorphous In-Ga-Zn-O (a-IGZO) are expected to be the channel material of TFTs in next-generation flat-panel displays because a-IGZO TFTs satisfy almost all the requirements for organic light-emitting-diode displays, large and fast liquid crystal and three-dimensional (3D) displays, which cannot be satisfied using conventional silicon and organic TFTs. The major insights of this review are summarized as follows. (i) Most device issues, such as uniformity, long-term stability against bias stress and TFT performance, are solved for a-IGZO TFTs. (ii) A sixth-generation (6G) process is demonstrated for 32″ and 37″ displays. (iii) An 8G sputtering apparatus and a sputtering target have been developed. (iv) The important effect of deep subgap states on illumination instability is revealed. (v) Illumination instability under negative bias has been intensively studied, and some mechanisms are proposed. (vi) Degradation mechanisms are classified into back-channel effects, the creation of traps at an interface and in the gate insulator, and the creation of donor states in annealed a-IGZO TFTs by the Joule heating; the creation of bulk defects should also be considered in the case of unannealed a-IGZO TFTs. (vii) Dense passivation layers improve the stability and photoresponse and are necessary for practical applications. (viii) Sufficient knowledge of electronic structures and electron transport in a-IGZO has been accumulated to construct device simulation models.
We report superconductivity in an iron-based layered oxy-pnictide LaOFeP. LaOFeP is composed of an alternate stack of lanthanum oxide (La3+O2-) and iron pnictide (Fe2+P3-) layers. Magnetic and electrical resistivity measurements verify the occurrence of the superconducting transition at approximately 4 K.
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