Lü Hui-Bin

Unit-Cell by Unit-Cell Epitaxial Growth of SrTiO3 and BaTiO3 Thin Films by Laser Molecular Beam Epitaxy

Atomically regulated unit-cell by unit-cell homoepitaxial SrTiO3 and heteroepitaxial BaTiO3 films were fabricated on SrTiO3(100) substrates by laser molecular beam epitaxy. The fine streak patterns and more than 1000 cycles undamping intensity oscillation were obtained by in situ reflection high-energy electron diffraction with precisely controlled intermittence between each unit-cell layer. The surface morphology of the films was examined by atomic force microscopy. The root-mean-square surface roughness of the films is about 0.1 nm.

Laser Molecular Beam Epitaxy Growth of BaTiO3 in Seven Thousands of Unit-Cell Layers

BaTiO3 thin films in seven thousands of unit-cell layers have been successfully fabricated on SrTiO3 (001) substrates by laser molecular beam epitaxy. The fine streak pattern and the undamping intensity oscillation of reflection high-energy electron diffraction indicate that the BaTiO3 film was layer-by-layer epitaxial growth. The measurements of scanning electron microscopy and atomic force microscopy show that surfaces of the BaTiO3 thin film are atomically smooth. The measurements of x-ray diffraction and transmission electron microscopy, as well as selected-area electron diffraction reveal that the BaTiO3 thin film is a c-oriented epitaxial crystalline structure.

Structure and electrical characteristics of Nb-doped SrTiO3 substrates

The studies on structure and electrical characteristic of Nb-doped SrTiO3 (SNTO) substrates by XRD, Hall measurements, R-T and SEM, show that the SNTO substrates with the same Nb-doping concentration have different electrical properties because of the nonuniformity of Nb-doping. The uniformly doped high-quality substrates are extremely important for fabricating multilayer structure and devices. In addition, the experimental results also provide us with SEM method to judge the uniformity of conducting material.

Structure, Electrical, and Optical Properties of Nb-doped BaTiO3 Thin Films Grown by Laser Molecular Beam Epitaxy

Structure, electrical, and optical properties of Nb-doped BaTiO3 (Nb:BTO) thin films on MgO substrates grown by laser molecular beam epitaxy with increasing Nb content were investigated. The Nb:BTO thin films with high crystallinity are epitaxially grown on MgO substrates. With more Nb-doped content, the impurity phases are found in Nb:BTO thin films. Hall measurement at room temperature confirms that the charge carriers of the Nb:BTO thin films are n-type. When the Nb-doped content increases, the carrier concentration and carrier mobility increase. Meanwhile the optical transmittance decreases with the increase of the Nb-doping, and the width of the forbidden band in each group is not affected by the presence of Nb in the samples. Raman spectra show that the structural phase transition may occur with the increase of the Nb-doping content, in the meantime more defects and impurities exist in the Nb:BTO thin films.

Photoelectric Characteristic of La0.9Sr0.1MnO3/SrNb0.01Ti0.99O3 p–n Heterojunctions

Good rectifying current–voltage characteristics and nanosecond photoelectric effects are observed in the p–n heterojunctions of La0.9Sr0.1MnO3/SrNb0.01Ti0.99O3 fabricated by laser molecular beam epitaxy. The rise time is about 26 ns and the full width at half maximum is about 125 ns for the open-circuit photovoltaic pulses when the La0.9Sr0.1MnO3 film in the heterojunction is irradiated by a laser operated at wavelength 308 nm with pulse duration of about 25 ns. A qualitative explanation is presented, based on an analysis of the photoelectric effect of p–n heterojunction.

Atomic Force Microscopy Studies of Barium Titanate Thin Films Prepared by Laser Molecular Beam Epitaxy

Laser molecular beam epitaxy (laser MBE) technique was utilized to grow the barium titanate (BaTiO3, BTO) thin films on SrTiO3(100) substrates. The surface morphology of the BaTiO3 thin films was studied by atomic force microscopy (AFM). Two- and three-dimensional AFM images were obtained. The root mean square surface roughness, the height profile, the histogram and the bearing ratio of the height distributions for the BaTiO3 thin films were analyzed in detail. The results indicate that the laser MBE thin films exhibit an atomically smooth surface.

Structure Stability of LaAlO3 Thin Films on Si Substrates

A series of amorphous and single-crystalline LaAlO3 (LAO) thin films are fabricated by laser molecular-beam epitaxy technique on Si substrates under various conditions of deposition. The structure stability of the LAO films annealed in high temperature and various ambients is studied by x-ray diffraction as well as high-resolution transmission electron microscopy. The results show that the epitaxial LAO films have very good stability, and the structures of amorphous LAO thin films depend strongly on the conditions of deposition and post-annealing. The results reveal that the formation of LAO composition during the deposition is very important for the structure stability of LAO thin films.

Growth of MgB2 Thin Films by Chemical Vapour Deposition Using B2H6 as a boron Source

Superconducting MgB2 thin films were grown on single crystal Al2O3 (0001) by chemical vapour deposition using B2H6 as a boron source. MgB2 film was then accomplished by annealing the boron precursor films in the presence of high-purity magnesium bulk at 890°C in vacuum. The as-grown MgB2 films are smooth and c-axis-oriented. The films exhibit a zero-resistance transition of about 38 K with a narrow transition width of 0.2 K. Magnetic hysteresis measurements yield the critical current density of 1.9×107 A/cm2 at 10 K in zero field.

Double-sided YBa2CU3O7-δ superconducting films prepared by laser ablation with a Si radiation heater

Double-sided superconducting YBa2Cu3O7−δ thin films have been prepared by pulsed laser ablation with a Si radiation heater. Measurements show that those samples are of good quality with zero resistance temperatures of ≥90 K, critical current densities of ≥3 x 106 A/cm2 at 77 K and zero field, and 10 GHz microwave surface resistances of 370μΩ (second side) and 1.7 mΩ (first side), respectively. The X-ray diffraction patterns indicate that each side of the samples isc-axis oriented epitaxial YBa2Cu3O7−δ film. Scanning electron microscopy (SEM) reveals that the surface of the films is rather smooth with no particle larger than 1 μm.

Growth model for pulsed-laser deposited perovskite oxide films

We present a multi-level growth model that yields some of the key features of perovskite oxide film growth as observed in the reflection high energy electron diffraction (RHEED) and ellipsometry studies. The model describes the effect of deposition, temperature, intra-layer transport, interlayer transport and Ostwald ripening on the morphology of a growth surface in terms of the distribution of terraces and step edges during and after deposition. The numerical results of the model coincide well with the experimental observation.