富锌条件下生长氮掺杂氧化锌薄膜的光学和电学性质

报道了采用等离子体辅助分子束外延方法(P-MBE),利用NO作为N源和O源,在c-面蓝宝石(c-Al₂O₃)衬底上外延生长了N掺杂ZnO薄膜。X射线衍射谱(XRD)和吸收谱中都出现了不同于未掺杂样品的特性,X射线光电子谱(XPS)中也发现了N的受主信号。但是在霍尔效应(Hall-effect)测量中,发现该样品并没有出现预期的p型导电特性,而是出现载流子浓度很高(2.15×10²⁰cm^-3)的n型导电特性。结合XPS结果和理论分析,认为在富Zn条件下生长会导致过量的填隙Zn原子,补偿了全部的受主后,又促使其出现了从半导体-金属的Mott转变。     

Effects of annealing conditions on the electrical properties of Bi4-xNdxTi3O12 (x = 0.46) thin films processed at low temperature

Neodymium-substituted Bi₄Ti₃O₁₂ (BNdT) thin films were prepared by a chemical solution deposition technique on platinum- coated silicon substrates. All of the samples were annealed at the relatively low temperature of 600 °C by a rapid thermal annealing process in different atmospheres, such as O₂, air, and nitrogen, and vacuum. Irrespective of different annealing atmospheres, all of the BNdT thin films exhibit good ferroelectric properties, such as a saturated hysteresis loop, good fatigue endurance, and low leakage current density. A large remanent polarization (P_r) of ∼48 μC/cm² with an electric field of 240 kV/cm was observed from the BNdT thin film annealed in O₂ atmosphere. The BNdT thin films annealed in nitrogen and vacuum, at reduced oxygen partial pressures, exhibit smaller P_r than that annealed in oxygen. The difference of P_r of the BNdT thin films annealed in different atmospheres may originate from differences in the grain sizes and the number of oxygen vacancies. PACS 77.55.+f; 77.80.-e; 77.80.Fm; 81.15.-z     

Solid-phase epitaxy of CaSi2 on Si(1 1 1) and the Schottky-barrier height of CaSi2/Si(1 1 1)

Thin Ca films were evaporated on Si(1 1 1) under UHV conditions and subsequently annealed in the temperature range 200–650 °C. The interdiffusion of Ca and Si was examined by ex situ Auger depth profiling. In situ monitoring of the Si 2p core-level shift by X-ray photoemission spectroscopy (XPS) was employed to study the silicide formation process. The formation temperature of CaSi₂ films on Si(1 1 1) was found to be about 350 °C. Epitaxial growth takes place at T≥400 °C. The morphology of the films, measured by atomic force microscopy (AFM), was correlated with their crystallinity as analyzed by X-ray diffraction (XRD). According to measurements of temperature-dependent I–V characteristics and internal photoemission the Schottky-barrier height of CaSi₂ on Si(1 1 1) amounts to qΦ_Bn=0.25 eV on n-type and to qΦ_Bp=0.82 eV on p-type silicon.     

Compact integration operators for Fréchet-space-valued measures

Many operators in Banach spaces occur as the integration operator of a suitable vector measure; their compactness is completely described in [19]. However, many important spaces X in analysis (and integration operators in such spaces) do not fall into this scheme because X is not normable. Characterizing the compactness of integration operators in this setting is the aim of this note. The methods and techniques employed are quite different to the Banach space arguments used in [19].     

Rigidity and finiteness under Ricci curvature and volume controls

Consider the class of closed Riemannian manifolds M of dimension dim(M) \geqq 3 \dim(M) \geqq 3 , Ricci curvature Ric(M) \geqq -(n - 1) \textrm{Ric}(M) \geqq -(n - 1) , diameter diam(M) < D and almost maximal volume. We show that the isomorphism types of fundamental groups characterize the diffeomorphism types of manifolds in such a class. In particular, it can be viewed as a generalization of the well-known Mostow‘s rigidity theorem and a finiteness theorem.     

Applications of coupled LC-GC: A review

Although coupled liquid chromatographygas chromatography (LC-GC) was first demonstrated ten years ago, only in the last few years has there been a sudden surge of interest in the technique. Approximately 70% of the total number of LC-GC applications have been published in the last two years (1987–88) alone. This review categorizes LC-GC publications into four main application areas: fossil fuels, foods, environmental samples, biologiical/pharmaceutical samples, and miscellaneous samples. Multidimensional separations carried out using other coupled-column chromatographic techniques (such as supercritical fluid chromatography (SFC) with GC, and on-line trace enrichment-GC) have also been included in this review.     

Development and investigation of perovskite (ABO3)-type oxides for power generation

Critical problems of the present approach of electrolytes for Solid Oxide Fuel Cells (SOFCs) for commercialization are discussed. Major progress is expected from the development of materials based on the “SEA (Single Element Arrangement)” concept. The galvanic cell consists in this case basically of a single chemically homogeneous compound, which functions as electrodes at high and low activity and as electrolyte at intermediate activities of the electroactive component. In view of the large structural flexibility of the chemical nature of the constitutents, we explored perovskite (ABO₃)-type compounds to be used as SEAs for SOFCs. Results of studies on Pr-substituted LSGM and Fe-substituted SrSnO₃ perovskite-type oxides are presented. For instance, SrSn_1-xFe_xO_3-δ with x=0.1 exhibits p and n-type electronic conduction at the cathode and anode sides of the SOFC, respectively, while oxide ion conduction prevails at intermediate oxygen partial pressures. The SEA concept is also applicable for other devices in the field of Ionics.     

Charge transport in a polypeptide chain

Charge transport is one important example of signal transduction in a protein which is responsible for action at a distance, and is a fundamental process in biochemical action. A model is presented in which electronic effects interact with motional processes to combine into a bifunctional model. This model is investigated with new detailed molecular dynamics calculations and successfully explains such action at a distance. Received 1st February 2002 / Received in final form 26 May 2002 Published online 13 September 2002     

The electrical resistivity of some uranium tellurides

Electrical resistivity of U₃Tein4, U₂Te₃ (cubic) and UTe₃ has been measured over temperature range 4.2–300 K. The two former compounds appear to be semimetallic conductors while the last one has semiconducting character. The results are discussed in the terms of available magnetic data.     

Invertible point transformations,Painlevé test,and the second Painlevé transcendent

The techniques of invertible point transformations and the Painlevé analysis can be used to construct integrable ordinary differential equations. We compare both techniques for the second Painlevé transcendent.