Qiu Xiang-Gang

Nanosecond-time-resolved infrared spectroscopic study of fast relaxation kinetics of protein folding by means of laser-induced temperature-jump

Elucidating the initial kinetics of folding pathways is critical to the understanding of the protein folding mechanism. Transient infrared spectroscopy has proved a powerful tool to probe the folding kinetics. Herein we report the construction of a nanosecond laser-induced temperature-jump (T-jump) technique coupled to a nanosecond time-resolved transient mid-infrared (mid-IR) spectrometer system capable of investigating the protein folding kinetics with a temporal resolution of 50 ns after deconvolution of the instrumental response function. The mid-IR source is a liquid N2 cooled CO laser covering a spectral range of 5.0?m (2000 cm?1)~ 6.5?m (1540 cm?1). The heating pulse was generated by a high pressure H2 Raman shifter at wavelength of 1.9?m. The maximum temperature-jump could reach as high as 26?1?C. The fast folding/unfolding dynamics of cytochrome C was investigated by the constructed system, providing an example.

Infrared active phonon modes and ionicity of single crystal MgAl2O4

Near-normal incident infrared reflectivity spectra of (100) MgAl2O4 spinel single crystal have been measured at different temperatures in the frequency region between 50 and 6000 cm(-1). Eight infrared-active phonon modes are identified, which are fitted with the factorized form of the dielectric function. The dielectric property and optical conductivity of the MgAl2O4 crystal are analysed. From TO/LO splitting, the effective Szigeti charges and Born effective charges at different temperatures are calculated for studying the ionicity and the effect of polarization. Based on the relationship between the (LO-TO)(1) splitting, which represents the transverse and longitudinal frequencies splitting of the highest energy phonon band in the reflectivity spectrum, and the ionic-covalent parameter, the four main phonon modes are assigned. MgAl2O4 can be considered as a pure ionic crystal and its optical characters do not change with decreasing temperature, so it may be used as a suitable substrate for high-T-c superconducting thin films.

Spin-glass-like behaviour and positive magnetoresistance in oxygen deficient La2/3Ca1/3MnO3?? thin films

The magnetism and magnetoresistance (MR) in a series of oxygen-deficient La2/3Ca1/3MnO3−δ (LCMO) thin films have been investigated. Compared with the films with stoichiometric oxygen concentration, the oxygen-deficient LCMO thin films show a spin-glass-like behaviour at low temperatures and a positive MR effect above the metal–insulator transition temperature. The mechanism of such unusual phenomena is discussed.

Structural and Electrical Characteristics of Pb(Zr 0.53 ,Ti 0.47 )O 3 Thin Films Deposited on Si (100) Substrates

Pb(Zr0.53, Ti0.47)O3 (PZT) films were directly deposited on Si substrates without a buffer layer by pulsed laser deposition. Only (110)-oriented PZT peaks (other than Si substrate peaks) were observed from the XRD data. The electrical properties of the PZT/Si capacitor were characterized in terms of both the capacitance versus voltage (C–V) and current versus voltage (I–V) measurements. The clockwise trace of the C–V curve shows ferroelectric polarization switching, as is expected. From the I–V curves, the Schottky emission and space-charge-limited-current behaviour are found to be the mainly leakage current mechanism in a certain electric field range in the negative and positive bias, respectively.

Interstitial vortex in superconducting film with periodic hole arrays

The response of superconducting Nb films with a diluted triangular and square array of holes to a perpendicular magnetic field are investigated. Due to small edge-to-edge separation of the holes, the patterned films are similar to multi-connected superconducting islands. Two regions in the magnetoresistance R(H) curves can be identified according to the field intervals of the resistance minima. Moreover, in between these two regions, variation of the minima spacing was observed. Our results provide strong evidence of the coexistence of interstitial vortices in the islands and fluxoids in the holes.

Matching effect in superconducting NbN thin film with a square lattice of holes

A square hole array is fabricated over a micro-bridge of NbN thin film by electron beam lithography and reactive ion milling. Magneto-resistance is measured across the micro-bridge filled with a hole array near the superconducting transition temperature. It is found that magneto-resistance minima occur when the number of vortices is an integer multiple or a fractional multiple of the number of holes. The temperature and the current dependences of the matching effect are studied.

Temperature dependent phonon modes and ionicity of LiGaO2 single crystal

This paper reports that polarized far-infrared reflectivity measurements have been done on LiGaCO2 single crystal along two crystalline axes at different temperatures. The temperature dependent frequencies of the longitudinal and transverse optical phonon have been obtained from the real part of optical conductivity and the loss function respectively. A small Drude component is observed at frequency below 300 cm-1 which could arise from Li ions or oxygen deficiencies. The ionicity of LiGaCO2 has been studied from the analysis of the Born effective charge of different ions.

Structural and Electrical Properties of Barium Strontium Titanate Thin Film on Conductive La1−xSrxMnO3 Bottom Layer

Ferroelectrics and colossal magnetoresistance heterostructure Ba1−xSrxTiO3(BST)/La1−xSrxMnO3 (LSMO) have been fabricated on a LaAlO3 substrate by the pulse laser deposition method. The dielectric measurements show that at room temperature and 100 kHz, the dielectric constant and loss tangent are about 990 and 0.012, respectively; the highest tunability is about 45% near 200 K under the applied electric field of 200 kV/cm. Further study indicates that the leakage current for the BST/LSMO heterostructure obeys the Schottky emission mechanism in the electric field region higher than 100 kV/cm at room temperature.

A New Bipolar Type Transistor Created Based on Interface Effects of Integrated All Perovskite Oxides

Oxide transistor is the basic device to construct the oxide electronic circuit that is the backing to develop integrated oxide electronics with high efficiency and low power consumption. By growing the perovskite oxide integrated layers and tailoring them to lead semiconducting functions at their interfaces, the development of oxide transistors may be able to perform. We realize a kind of p-i-n type integrated layers consisting of an n-type cuprate superconductor, p-type colossal magnetoresistance manganite, and a ferroelectric barrier (i). From this, bipolar transistors were fabricated at the back-to-back p-i-n junctions, for which the Schottky emission and p-n junction barriers, as well as the ferroelectric polarization, were integrated into the interfaces to control the transport properties; a preliminary but distinct current gain greater than 1.6 at input current of microampers order was observed. These results present a real possibility to date for developing bipolar all perovskite oxide transistors.

Temperature-dependent far-infrared properties of Bi12GeO20 single crystal

Far-infrared reflectivity spectra of bismuth germanium oxide (Bi12GeO20) single crystals are measured from room temperature down to 10 K. All the reflectivity spectra are fitted to a complex dielectric function (ω) in the factorised form. Phonon modes at low frequency are found to develop upon decreasing temperature and gain considerable spectrum weight below 150 K. The temperature-dependent static dielectric constants are obtained from the Lyddane–Sachs–Teller relation based on the obtained oscillator parameters. The dielectric constants are found to increase upon decreasing temperature, which is attributed to the charge transfer among the ions in the unit cell with the temperature varying.