Lu Hui-Bin

Colossal Magnetoresistive p-n Junctions of Te-Doped LaMnO3/Nb-doped SrTiO3

We have fabricated colossal magnetoresistive (CMR) p-n junctions made of Te-doped LaMnO3 and Nb-doped SrTiO3 with laser molecular beam epitaxy. The I-V characteristics of the La0.9Te0.1MnO3/SrNb0.01Ti0.99O3 p-n junctions as a function of applied magnetic field (0-5xa0T) were experimentally studied in the temperature range 77-300xa0K. The results indicate that the p-n junction exhibited the CMR behaviour. The magnetoresistance (MR) is positive at 220xa0K and 300xa0K, while it displays a negative MR at 77xa0K. For a positive bias, the MR ratios (ΔR/R0, ΔR = RH-R0) are 7.5% at 0.1xa0T and 18% at 5xa0T for 300xa0K, 5% at 0.1xa0T and 33% at 5xa0T for 220xa0K, -14% at 0.1xa0T and -71% at 5xa0T for 77xa0K. For a negative bias, the MR ratios are 6.3% at 0.1xa0T and 10.8% at 3xa0T for 300xa0K, 5.1% at 0.1xa0T and 15% at 3xa0T for 220xa0K, -19% at 0.1xa0T and -72% at 5xa0T for 77xa0K. The CMR behaviour of the p-n junction is different from those of the LaMnO3 compound family.

Label-Free and High-Throughput Detection of Protein Microarrays by Oblique-Incidence Reflectivity Difference Method

We label-free detected the biological process of preparing a microarray that includes 400 spots of mouse immunoglobulin G (IgG) as well as the specific hybridization between mouse IgG and goat anti-mouse IgG by an oblique-incidence reflectivity difference (OI-RD) method. The detection results after each process including printing, washing, blocking, and hybridization, demonstrate that the OI-RD method can trace the preparation process of a microarray and detect the specific hybridization between antigens and antibodies. OI-RD is a promising method for label-free and high-throughput detection of biological microarrays.

Superconducting MgB2 Thin Films with Tc≈39 K Grown by Pulsed Laser Deposition

Superconducting MgB2 thin films were fabricated on Al2O3(0001) substrates under ex situ processing conditions. Boron thin films were deposited by pulsed laser deposition followed by a post-annealing process. Resistance measurements of the deposited MgB2 films show Tc of ~39 K, while scanning electron microscopy and x-ray diffraction analysis indicate that the films consist of well-crystallized grains with a highly c-axis-oriented structure.Superconducting MgB2 thin films were fabricated on Al2O3(0001) substrates under an ex-situ processing conditions. Boron thin films were deposited by pulsed laser deposition followed by a post-annealing process. Resistance measurements of the deposited MgB2 films show Tc of about 39K, while scanning electron microscopy and x-ray diffraction analysis indicate that the films consist of well-crystallized grains with a highly c-axis-oriented structure.

Dielectric and ferroelectric properties of La-doped SrBi2Nb2O9 ceramics

Sr1−xLa2x/3Bi2Nb2O9 (0≤x≤0.2) ceramic samples are prepared by the solid-state reaction method. Their structure, dielectric and ferroelectric properties are investigated. The incorporation of La3+ improves the densification and decreases the grain size of the ceramics without changing the crystal structure. The remanent polarization 2Pr increases with increasing La content and reaches a maximum value of 22.8 μC/cm2 at x = 0.125, which is approximately 60% larger than that of pure SrBi2Nb2O9. The Curie temperature keeps almost unchanged at a value of about 440°C. The relationship between doping and the ferroelectric and dielectric properties are discussed.

Simulation of Anisotropic Resistivity for Mixed-Phase Manganite La2/3Ca1/3MnO3 Thin Films

We utilize the random network model based on phase separation scenario to simulate the conductive behaviour and anisotropic characteristics of resistivity for La2/3Ca1/3MnO3 (LCMO) thin films. The simulated results agree well with our experimental data, showing a metal-to-insulator transition from a high-T paramagnetic (PM) insulating phase to a low-T ferromagnetic (FM) metallic phase in both the untilted film deposited on a (001) SrTiO3 (STO) substrate and the tilted film grown on a vicinal cut STO substrate. It is found that the resistivity of the tilted sample is higher than that of the untilted one, displaying prominent anisotropic characteristics. The studies reveal that the tilting not only decreases the conduction of the FM domains, but also increases the activation energy of the PM regions, inducing the enhancement of resistivity. All those results suggest that the intrinsic inhomogeneity in the phase separation system plays a significant role in the electrical conductivity and the resistive anisotropy is related to the structure of the crystal lattice.

N-Doped LaAlO3/Si(100) Films with High-k, Low-Leakage Current and Good Thermal Stability

High quality amorphous N-doped LaAlO3 (LaAlON) films have been deposited on Si (100) in nitrogen gas by laser molecular beam epitaxy. The chemical nature and physical distribution of N in LaAlON films has been performed by x-ray photoemission spectroscopy. Compared with LaAlO3, a significant improvement in the interfacial quality and leakage current density was obtained by nitrogen additive. At gate voltage +1 V, the leakage current density of the LaAlON film with an equivalent oxide thickness as thin as 2 nm is obtained to be 2.9×10−6 A/cm2, which decreases almost two orders of magnitude from that of LaAlO3 film with the same thickness. Moreover, high-resolution transmission electron microscope analysis show that the LaAlON sample is still amorphous with a very sharp interface between the LaAlON layer and the Si substrate after annealed at 900 degrees C for 60 s.

Monolayer Oscillation Observed by an Oblique-Incidence Reflectance Difference Technique for the Epitaxial Growth of Oxides

We report the optical oscillations with monolayer periodicity observed by an oblique-incidence reflectance difference (OIRD) technique on the epitaxial growth of Nb-doped SrTiO3 on SrTiO3 substrate. The periodicity was verified by the simultaneously measured reflection high-energy electron diffraction intensity oscillations. The OIRD oscillation damps during deposition, but can recover after the growth is interrupted for some time. We interpret the optical oscillations as a result of the periodic changes of the surface morphologies due to the two-dimensional layer-by-layer growth of thin films.

Field-Effect Transistor Based on Si with LaAlO3−δ as the Source and Drain

N-type LaAlO3−δ thin films are epitaxially grown on p-type Si substrates. An enhancement mode field-effect transistor is constructed with oxygen deficient LaAlO3−δ as the source and drain, p-type Si as the semiconducting channel, and SiO2 as the gate insulator, respectively. The typical current-voltage behavior with field-effect transistor characteristic is observed. The ON/OFF ratio reaches 14 at a gate voltage of 10V, the field-effect mobility is 10 cm 2/V s at a gate voltage of 2 V, and the transconductance is 5 × 10−6 A/V at a drain-source voltage of 0.8 V at room temperature. The present field-effect transistor device demonstrates the possibility of realizing the integration of multifunctional perovskite oxides and the conventional Si semiconductor.

Current-voltage characteristics with several threshold currents in insulating low-doped La1−xSrxMnO3 (x=0.10) thin films

The current-induced resistive switching behavior in the micron-scale pillars of low-doped La0.9Sr0.1MnO3 thin films using laser molecular-beam epitaxy was reported. It was demonstrated that the current-voltage curves at 120 K showed hysteresis with several threshold currents corresponding to the switching in resistance to metastable low resistance states, and finally, four closed loops were formed. A mode was proposed, which was based on the low-temperature canted antiferromagnetism ordering for a lightly doped insulating regime.

Oxygen pressure dependence of properties of epitaxial LaAlO3 films grown on Si(100)

Heteroepitaxial LaAlO3 films were grown on a SrTiO3/Si (100) substrate by laser molecular beam epitaxy under different oxygen pressures, and their properties such as crystallinity and electrical characteristics were experimentally investigated using the various measurement methods. The results show that most properties depend mainly on the deposition oxygen pressure. The crystallinity and the C–V and I–V characteristics can be greatly improved with the increasing oxygen deposition pressure. Moreover, after annealed at 1050 degrees C in N2 ambient, the C–V and I–V characteristics of LAO films deposited at the lower oxygen pressure are also improved due to the decrease of oxygen vacancies in LAO films.