Pb1－xMnxSe薄膜的光学特性

采用分子束外延的方法在BaF₂(111)衬底上制备出了高质量的Pb_1-xMn_xSe(0≤x≤0.0681)薄膜.X射线衍射结果表明，Pb₁-xMn_xSe薄膜为立方相NaCl型结构，没有观察到MnSe相分离现象，薄膜的取向为平行于衬底(111)晶面.晶格常数随着Mn含量的增加逐渐减小，Mn含量由Vegard公式得到.通 关键词： 1-xMn_xSe外延薄膜')" href="#">Pb_1-xMn_xSe外延薄膜 透射光谱 带隙 折射率     

Superconductivity of Pb films studied with superconducting Pb tips

<正>Studying the superconductivity of materials using scanning tunneling microscopy (STM) remains a challenge to this day[1]. In this regard, the stability of the tunneling junction is a critical factor, together with the spectroscopy resolution.Using a superconducting tip is an effective way to increase the resolution of the obtained tunneling spectra [2-6]. For example, Pan et al.[2] showed that the use of super-     

Structural and ferroelectric properties of Pb1-xSrxTiO3 thin films

Strontium-modified lead titanate (PST) thin films with composition Pb_1-xSr_xTiO₃ (0.10<x0.60) were grown on Pt/Ti/SiO₂/Si substrates using a soft chemical process. The crystallization of the PST thin films was achieved by heat treatment at 600 °C. The structural and microstructural modifications in the films were studied using X-ray diffraction (XRD) and atomic force microscopy, respectively. The XRD study shows that the lattice parameters of polycrystalline PST thin films calculated from X-ray data indicate a decrease in lattice tetragonality with the increase in strontium content in these films. This indicates a gradual change from tetragonal to cubic structure. By atomic force microscopy analysis, the average grain size of the thin films was systematically reduced with the increase in Sr content. The dielectric property of the thin films was found to be strongly dependent on the Sr concentration. With 60 at.% Sr content, a ferroelectric to paraelectric phase transition was observed at room temperature. PACS 61.10.Nz; 68.37.Ps; 77.55.+f; 77.84.-s; 81.15.-z     

Negative photoconductance in thin indium antimonide films

Negative photoconductance or optical quenching has been observed in thin InSb films, fabricated by vacuum evaporation on glass substrates. An electronic flash was used as the light source. The time constant of the photocurrent measured on several samples ranges from 30 sec to 3 min. Whereas bulktraps localised in the narrow band gap of InSb (0.18 eV) can hardly be responsible for the high time constants, it is believed that slow surface traps or traps inside an In₂O₃ layer, covering the InSb film, are responsible for the optical quenching.     

Optical parameters and photoluminescence of cadmium-doped epitaxial Pb1−xSnxTe films

Barium fluoride (111) cleaved surfaces have been used with the hot-wall method to grow epitaxial Pb_1−xSn_xTe films from source materials either undoped or doped with 0.1, 0.5, or 1 at. % cadmium and having x=0.2. The absorption in the wavelength range 2–13 μm has been measured together with the spectral dependence of the photoluminescence. The cadmium affects the optical width of the forbidden band and the high-frequency dielectric constant, as well as the photoluminescence intensity. The optical absorption spectra of the doped epitaxial films contain additional absorption bands due to the impurity level in the forbidden band. The position of the impurity level has been determined and the shift in it relative to the bottom of the conduction band as the temperature is reduced. Materials Science Institute, National Academy of Sciences of Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 8–11, May, 1996.     

Negative differential resistance in nanotube devices

Carbon nanotube junctions are predicted to exhibit negative differential resistance, with very high peak-to-valley current ratios even at room temperature. We treat both nanotube p-n junctions and undoped metal-nanotube-metal junctions, calculating quantum transport through the self-consistent potential within a tight-binding approximation. The undoped junctions in particular may be suitable for device integration.     

Negative differential resistance in amorphous germanium

Results of a study of static current-voltage curves of amorphous germanium diodes with gap-type electrode construction are presented. It is shown that with increase in the interelectrode distance there occurs a transition from a switching regime with irreversible memory to a stable negative differential resistance regime. The diode current-voltage curves and data obtained by studying potential distribution over specimen length are explained with a model of space charge-limited currents.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 103–107, March, 1980.     

Superheating of confined Pb thin films

In this work we report, for the first time, an experimental observation of a superheating phenomenon in metal thin films. By means of cold rolling, Pb thin films of about 20 nm thick were sandwiched by Al layers, and between them semicoherent epitaxial Pb/Al interfaces were formed. In situ x-ray diffraction analysis indicated that the confined Pb thin films could be superheated for at least 6 degrees C. Thermodynamic analysis indicated that such a substantial superheating in the confined two-dimensional thin films may originate from suppression of growth of the molten droplets by the epitaxial Al/Pb/Al confinement, instead of suppression of melt nucleation for the confined particle superheating.     

Anomalous magnetization jumps in granular Pb superconducting films

In granular superconductors, the grain boundaries are closely related to the vortex dynamics and the macroscopic superconducting properties. In our research, Pb films with different grain sizes were prepared by tuning the substrate temperature. With the grain size decreasing, Pb films are prone to feature the anomalous magnetization jumps in the M − T curves, while in the M − H curves flux avalanche happens. Both phenomena appear in the same region of the H − T phase diagram and thus are considered to have the same origin. The further theoretical analysis shows that with grain size decreasing the pinning mechanism evolves from a mixed δT_c and δl pinning to the δl pinning mechanism. The results shed light on the study of pinning mechanism for granular superconductors and is beneficial to the potential application of manipulating vortex pinning by regulation of intrinsic defects.     

Electrical resistance and 1/f fluctuations in thin titanium films

The thickness of a metallic layer has been determined and the resistivity and spectral density of voltage fluctuations in thin titanium films with initial thicknesses of 5–100 nm, which were obtained by magnetron sputtering and intended for promising elements of the neutron optics, have been investigated. It has been found that a continuous metallic layer necessary for functioning is retained even in thinnest samples, and excess fluctuations of the layer resistance with the 1/f-type spectrum are observed. It has been shown that the method of measuring film resistivity can be used as effective express-method of determining the thickness of metallic nanolayers.     

Negative resistance effects in AgCl single crystals

Hysteresis effects in the current-voltage characteristic, negative resistance, and electroluminescence in the high-conductivity state have been found in AgCl single crystals.     

Charge-carrier transport properties of ultrathin Pb films

The charge-carrier transport properties of ultrathin metallic films are analysed with ab initio methods using the density functional theory (DFT) on free-standing single crystalline slabs in the thickness range between 1 and 8 monolayers and compared with experiments for Pb films on Si(111). A strong interplay between bandstructure, quantised in the direction normal to the ultrathin film, charge-carrier scattering mechanisms and magnetoconduction was found. Based on the bandstructure obtained from the DFT, we used standard Boltzmann transport theory in two dimensions to obtain results for the electronic transport properties of 2 to 8 monolayers thick Pb(111) slabs with and without magnetic field. Comparison of calculations and experiment for the thickness dependence of the dc conductivity shows that the dominant scattering mechanism of electrons is diffuse elastic interface scattering for which the assumption of identical scattering times for all subbands and directions, used in this paper, is a good approximation. Within this model we can explain the thickness dependences of the electric conductivity and of the Hall coefficient as well as the anomalous behaviour of the first Pb layer.Received: 19 September 2003, Published online: 8 December 2003PACS: 73.50.Jt Electronic transport phenomena in thin films: Galvanomagnetic and other magnetotransport effects - 73.61.At Electrical properties of specific thin films: Metals and metallic alloys - 73.20.At Electron states at surfaces and interfaces - 71.15.Mb Density functional theory     

Negative resistance and local charge-density-wave dynamics

Charge-density-wave (CDW) dynamics is studied on a submicron length scale in NbSe(3) and o-TaS(3). Regions of negative absolute resistance are observed in the CDW sliding regime at sufficiently low temperatures. The origin of the negative resistance is attributed to the different forces that the deformed CDW and quasiparticles feel: the force on the CDW is merely caused by a difference of the electric potentials, while the quasiparticle current is governed by a difference of the electrochemical potentials.     

Negative differential resistance in ZnO coated peptide nanotube

We investigate the room temperature electronic transport properties of a zinc oxide (ZnO) coated peptide nanotube contacted with Au electrodes. Current–voltage (I–V) characteristics show asymmetric negative differential resistance (NDR) behavior along with current rectification. The NDR phenomenon is observed in both negative and positive voltage sweep scans, and found to be dependent on the scan rate and humidity. Our results suggest that the NDR is due to protonic conduction arising from water molecule redox reaction on the surface of ZnO coated peptide nanotubes rather than the conventional resonant tunneling mechanism.     

Negative differential thermal resistance in coupled rotor lattices

Contributions of homogeneous and Goldstone modes of the spin precession were distinguished in FMR spectra of Cr_1/3NbS₂ chiral helimagnet. The resonance field of homogeneous mode is determined by uniaxial magnetic anisotropy. The resonance field of Goldstone mode is determined by six-fold anisotropy in basal plane. For the first time, it has been shown experimentally that effective excitation of Goldstone mode is realized only when microwave magnetic field vector h is perpendicular to wave vector of magnetic structure Q.