Search

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.

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.

Cu/MgO/La0.9Sr0.1MnO3 pillars are fabricated on SrTiO3 (001) substrates by the micro-fabrication patterning processes. Their electric transport properties have been measured in the temperature range from the temperature smaller than the Curie one to 300K. At 125K there emerges abrupt breaks of output voltage in voltage-current (V-I) curves, corresponding to switching in resistance to metastable states, and finally two closed loops are formed with double threshold biases. Around room temperature the V-I characteristics are non-ohmic and show some gradual hysteresis when sweeping the current in a round-trip scan. A large current-induced resistive change Delta R/R-o, similar to -63.2%, is obtained under a current density of 1.0 x 10(4) Acm(-2). Especially, Delta R/R-0 depends linearly on the applied current and is independent of the applied magnetic field. The current-induced resistive effect should be of interest for various applications such as switching and field effect devices.

Ten thousands of unit-cell multilayer heterosturctures, [SrNb0.05Ti0.95O3/La0.9Sr0.1MnO3]3 (SNTO/LSMO), have been epitaxial grown on SrTiO3 (001) substrates by laser molecular beam epitaxy. The monitor of in-situ reflection high-energy electron diffraction demonstrates that the heterosturctures are layer-by-layer epitaxial growth. Atomic force microscope observation indicates that the surface of the heterosturcture is atomically smooth. The measurements of cross-sectional low magnification and high-resolution transmission electron microscopy as well as the corresponding selected area electron diffraction reveal that the interfaces are of perfect orientation, and the epitaxial crystalline structure shows the orientation relation of SNTO(001)//LSMO(001), and SNTO[100]//LSMO[100].

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.

In this letter, we present the observation of phase conjugation at 9.27 μm in a GaAs/AlGaAs multiple step quantum well structure. The response is caused by the nearly resonant intersubband transition. The magnitude of χ(3) determined by this phase conjugation method is about 8 × 10-5 esu and the phase conjugate reflectivity η is about 6 × 10-3 uncorrected for Fresnel reflections.

The n-type conductive BaNb0.3Ti0.7O3 thin films were grown on SrTiO3(001) substrates by computer-controlled laser molecular beam epitaxy. The BaNb0.3Ti0.7O3 films with (001) orientation are epitaxially grown on SrTiO3 substrates, as confirmed by x-ray diffraction techniques. The root-mean-square surface roughness of the deposited thin films is measured to be 0.24 nm by atomic force microscopy. The resistivity, carrier concentration and mobility of the BaNb0.3Ti0.7O3 thin film are 5.9×10-4 Ω cm, 1.8×1021cm-3 and 10.7 cm2V-1s-1 at room temperature, respectively, which are the best values in Nb-doped BaTiO3 thin films reported so far to our knowledge.

The properties of intersubband transition of GaAs/AlxGa1-xAs multiple quantum wells with various well widths and doped-well concentrations have been studied. Both theoretical and experimental results are in good agreement. For the appropriate well width and higher doping concentration, we directly observed two intersubband absorption peaks from E1 → E2 and E2 → E3 transitions in well. The experimental results and theoretical analysis are given.

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.

Nanosecond photoelectric effect is observed in a ZrO2 single crystal at ambient temperature for the first time. The rise time is 20 ns and the full width at half maximum is about 30 ns for the photovoltaic pulse when the wafer surface of the ZrO2 single crystal is irradiated by 248 nm KrF laser pulses. The experimental results show that ZrO2 single crystals may be a potential candidate in UV photodetectors.

Oblique-incidence reflectivity difference (OI-RD) analysis is applied to detect the immunoglobulin-G and cytochrome biomolecules on standard glass substrates without fluorescence labelling. The OI-RD intensities not only depend on the protein structure, but also vary with the protein concentration. The results indicate that this method should have potential applications in detection of biochemical processes.

Ultrafast photoelectric effects have been observed in p-n heterojunctions of La0.7Sr0.3MnO3(LSMO)/Si and LSMO/SrTiO3_/Si for the first time. The rise time was about Ins and the full width at half maximum was about 2ns for the photovoltaic pulse when the heterojunction was irradiated by a laser of similar to25ps pulse duration and 1064 nm wavelength. The photovoltaic sensitivity was as large as 435 mV/mJ for a 1064 nm laser pulse. No such pulse was observed with irradiation from a pulsed 10.6mum CO2 laser.

Superconducting MgB2/Ta tapes with a critical temperature of 38 K have been prepared successfully by a two-step method. Boron/Ta tapes were fabricated by electrophoresis followed by a post-annealing process in magnesium vapour. The critical current density is 1.7×104 A/cm2 in zero field at 5K. Scanning electron microscopy and x-ray diffraction analysis reveal a dense flat surface with (101) orientated growth of the MgB2 phase in our MgB2/Ta tapes.

The maximum refrigeration power dependence on the doping density in the p-BaTiO3/BaTiO3/SrTiO3/BaTiO3/n-BaTiO3 system and in the p-AlGaAs/AlGaAs/GaAs/AlGaAs/n-AlGaAs system is obtained respectively based on the opto-thermionic refrigeration model. The results show that the maximum refrigeration power in the p-BaTiO3/BaTiO3/SrTiO3/BaTiO3/n-BaTiO3 system increases dramatically with the increase of doping density from 1.0 × 1018 cm−3 to 5.0 × 1019 cm−3 while that in the p-AlGaAs/AlGaAs/GaAs/AlGaAs/n-AlGaAs system is nearly a constant. It is found that the different Auger coefficients and the competition between radiative power and dissipation power lead to the different behavior of the maximum refrigeration power dependence on the doping density of the two systems.

Photovoltaic response in the heterojunction of La1−xSrxMnO3/SrNbyTi1−yO3 (LSMO/SNTO) is analyzed theoretically based on the drift-diffusion model. It is found that the decrease of acceptor concentration in the La1−xSrxMnO3 layer of heterojunction can increase the peak value of photovoltaic signal and the speed of photovoltaic response, whereas the changing of donor concentration in the SrNbyTi1−yO3 layer has no such evident effect. Furthermore, the result also indicates that the modulation of Sr doping in La1−xSrxMnO3 is an effective method to accommodate the sensitivity and the speed of photovoltaic response for LSMO/SNTO photoelectric devices.

Effect of oxygen vacancy on transport property of perovskite microstructures is studied theoretically. Compared with calculated and measured I–V curves, it is revealed that electron conduction plays an important role in the oxygen nonstoichiometry perovskite heterostructures even with hole-doped or un-doped material due to the oxygen vacancies. In addition, a detailed understanding of the influence of oxygen vacancy concentration and temperature on the conduction characteristics of oxide heterojunction with both forward and reverse biases is obtained by calculation.