K. F. Wang

Magnetocapacitance of polycrystalline Bi5Ti3FeO15 prepared by sol-gel method

Bi5Ti3FeO15 bulk ceramic and thin film samples are prepared using the sol-gel method. The dielectric, ferroelectric, and magnetic behaviors of these samples are measured in order to investigate the possible multiferroic effect. The superparamagnetic behavior with dominant antiferromagnetic (AFM) interaction background for the as-prepared Bi5Ti3FeO15 samples is revealed. The clearly identified magnetocapacitance effect at low temperature is argued to originate from the suppression of the AFM interaction by external magnetic field.

Characterization of oxygen vacancies and their migration in Ba-doped Pb(Zr0.52Ti0.48)O3 ferroelectrics

We investigate in detail the migration kinetics of oxygen vacancies (OVs) in Ba-doped Pb(Zr(0.52)Ti(0.48))O(3) (PZT) ferroelectrics by complex impedance spectroscopy. The temperature dependent dc-electrical conductivity sigma(dc) suggests that Ba doping into PZT can lower significantly the density of OVs, leading to the distinctly decreased sigma(dc) and slightly enhanced activation energy U for the migration of OVs, thus benefiting the polarization fatigue resistance. Furthermore, the polarization fluctuation induced by the relaxation of OVs is reduced by the Ba doping. The Cole-Cole fitting to the dielectric loss manifests strong correlation among OVs, and the migration of OVs appears to be a collective behavior.

Enhanced ferromagnetism and ferroelectricity in multiferroic CuCr1-xNixO2

Polycrystalline CuCr1−xNixO2 is synthesized and its multiferrocity is characterized in order to enhance the ferromagnetism and ferroelectricity of CuCrO2-based multiferroics. At the optimized doping level x=0.05, we observe not only an enhancement of one order of magnitude in magnetization but also a remarkable increasing of polarization up to ∼50 μC/m2 from ∼35 μC/m2 of polycrystalline CuCrO2. It is argued that the Ni-doping may modulate the antiferromagnetic interactions between Cr3+ ions and probably induce the conical-like spin component responsible for the enhanced ferromagnetism.

Unipolar resistive switching effect in YMn1−δO3 thin films

Steady unipolar resistive switching of Pt/YMn(1-delta)O(3)/Pt MIM structure is investigated. High resistance ratio (>10(4)) of high resistance state (HRS) over low resistance state (LRS) and long retention (>10(5) s) are achieved. It is suggested that the Joule heating and Poole-Frenkel effect dominate respectively the conduction of the LRS and HRS in high electric field region. The resistive switching is explained by the rupture and formation of conductive filaments in association with the local Joule-heat-induced redox inside YMn(1-delta)O(3).

Specific heat anomalies and possible Griffiths-like phase in La0.4Ca0.6MnO3 nanoparticles

The specific heat of La(0.4)Ca(0.6)MnO(3) in bulk and nanoparticle (similar to 60 nm in grain size) forms was investigated. It is found that the charge-ordered state highly stabilized in the bulk samples can be significantly suppressed in the nanoparticle. The low temperature specific heat data reveal a Schottky-like anomaly at similar to 5 K for the bulk sample, while a large electronic linear term (gamma=17.8 mJ/mole K(2)) was identified for the nanoparticle samples. The magnetic measurements unveil the small magnetic entropy as low as similar to 0.255 J/kg K and the possible existence of a Griffiths-like phase in the nanoparticle samples. We argue that the physics underlying the size effect is associated with the dimension-dependent interactions based on which the ferromagnetic/charge-ordering transition occurs. (c) 2008 American Institute of Physics.

Polarization fatigue of ferroelectric Pb(Zr0.1Ti0.9)O3 thin films: Temperature dependence

The polarization switching fatigue behaviors of tetragonal Pb(Zr0.1Ti0.9)O3(PZT0.1) thin films deposited on Pt-coated silicon wafers by the sol-gel method are investigated by testing the fatigue endurance at different temperatures and by measuring the small-signal dielectric loss associated with the fatigued samples. It is observed that the fatigue endurance can be significantly improved at low temperature, while the low-temperature fatigue becomes more serious with increasing magnitude of the electrical pulses for fatigue testing. The fatigued thin films exhibit much bigger dielectric loss than the fresh films over the whole temperature range, due to the domain pinning by the aggregated defects (oxygen vacancies). In addition, the temperature dependence of the fatigue resistance performance of the thin films can be well described by the exponential law. The long-range diffusion and aggregation of the defects and the consequent domain pinning as one of main origins for switching fatigue in the PZT0.1 thin...

Proteomic analysis of protein methylation in the yeast Saccharomyces cerevisiae

UNLABELLED Protein methylation catalyzed by SAM-dependent methyltransferase represents a major PTM involved in many important biological processes. Because methylation can occur on nitrogen, oxygen and sulfur centers and multiple methylation states exist on the nitrogen centers, methylproteome remains poorly documented. Here we present the methylation by isotope labeled SAM (MILS) strategy for a highly-confident analysis of the methylproteome of the yeast Saccharomyces cerevisiae based on the online multidimensional μHPLC/MS/MS technology. We identified 43 methylated proteins, containing 68 methylation events associated with 64 methylation sites. More than 90% of these methylation events were previously unannotated in Uniprot database. Our results indicated, 1) over 2.6% of identified S. cerevisiae proteins are methylated, 2) the amino acid residue preference of protein methylation follows the order Lys≫Arg>Asp>Asn≈Gln≈His>Glu>Cys, and 3) the methylation state on nitrogen center is largely exclusive. As our dataset covers various types of methylation centers, it provides rich information about yeast methylproteome and should significantly contribute to the field of protein methylation. BIOLOGICAL SIGNIFICANCE In this paper, we presented the methylation by isotope labeled SAM (MILS) strategy for a highly-confident analysis of the methylproteome of the yeast S. cerevisiae and collected a comprehensive list of proteins methylated on a set of distinct residues (K, R, N, E, D, Q, H, C). Our study provided useful information about the amino acid residue preference and methylation state distributions on nitrogen centers of protein methylation in S. cerevisiae.

InP-based InAs/InGaAs quantum wells with type-I emission beyond 3 μm

This work reports on InAs/In0.53Ga0.47As strain compensated quantum well structures on InP-based metamorphic buffer to generate the type-I emission of beyond 3 μm. The metamorphic buffer is composed of InxAl1−xAs graded layer and In0.8Ga0.2As virtual substrate layer. Atomic force microscope, transmission electron microscope and x-ray diffraction measurements show the moderate surface and structural properties. A photoluminescence signal up to 3.05 μm has been achieved at 300 K, which is one of the longest wavelengths from the interband emission of InP-based antimony-free structure. It is promising to employ this quantum well structure on metamorphic buffer for the laser demonstration with emission around 3 μm.

Kinetics controlled aging effect of ferroelectricity in Al-doped and Ga-doped BaTiO3

Our experiments on ferroelectric aging of Al3+- and Ga3+-doped BaTiO3 ceramics reveal the crucial role of migration kinetics of point defects (oxygen vacancies) besides the thermodynamic driving force based on the symmetry conforming short-range ordering scenario. The doping with Ga3+ or tiny Al3+ ions shows the clear aging effect, while the high-level Al3+-doping suppresses the aging effect. The suppression is mainly attributed to the kinetically limited migration of oxygen vacancies due to the lattice shrinkage, while the other mechanisms may also make sense.

Reversible resistance switching in La0.225Pr0.4Ca0.375MnO3: The Joule-heat-assisted phase transition

The reversible resistance switching (RS) controlled by current pulse pairs, accompanied with an overshooting relaxation, is observed in bulk La(0.225)Pr(0.4)Ca(0.375)MnO(3). We demonstrate that the reversible RS effect is not the result of current-induced intrinsic transition of charge-ordered insulator (COI) into ferromagnetic metal (FMM) phase, but the outcome of Joule-heat-assisted transition between the FMM and COI phases. A local thermal-cycle assisted rearrangement of the FMM phase in the COI matrix is controllable by a current pulse, opening a possibility for multistate memory applications