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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.

The localized growth of materials has been realized in a dielectric barrier discharge reactor in the mixture of acetylene and argon in previous work. In this paper, the morphology of the materials synthesized in the process is studied. The results indicate that the polymer's structure consists of three layers. The layer near the substrate is homogeneous with thickness of several micrometres; the middle layer is composed of dense bulges with height of about more than 10mum in average. The distance between two neighbouring bulges is about 230mum; the top layer is made up of a few large columns with the height up to 2mm, and with the average distance of about 3.5mm. The growth of the three layers corresponds to three types of discharge. The discharge mechanism is analysed through studying the morphology of the polymer. It can be deduced from the morphology that the first and second discharge phases should belong to the Townsend breakdown, and the last discharge phase should be explained on the basis of the streamer mechanism.

Nanometre-sized gold particles embedded in BaTiO3 composite thin films (Au/BaTiO3) were fabricated by the pulsed laser deposition technique. The films were grown on MgO (100) substrates at 700°C. The crystalline property of the films was studied with x-ray diffraction. X-ray photoelectron spectroscopy was used to check the Au composition and chemical nature for the deposited films. The absorption peak due to the surface plasmon resonance of Au particles was observed at the wavelength of about 570 nm, which increased as the metal particle size was increased. The nonlinear optical properties of the Au/BaTiO3 films were determined using the z-scan method at the wavelength of 532 nm, which was close to the resonant frequency. The real and imaginary parts of the third-order nonlinear susceptibility χ(3) at an Au concentration of about 6.7 at.% were determined to be 6.62×10-7 esu and -6.24×10-8 esu, respectively. The films showed a very large absorption, masking the nonlinear refraction effect at high metal concentrations.

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].

The laser molecular beam epitaxy system and its key technologies have been successfully developed in China. Atomically regulated unit-cell by unit-cell homoepitaxial SrTiO3 (STO) and heteroepitaxial BaTiO3 (BTO) films and STO/BTO superlattices were fabricated on STO (100) substrates by the laser molecular beam epitaxy. The fine streak patterns and more than 1000 cycles of undamping intensity oscillation were obtained by using in-situ reflection high-energy electron diffraction. The surfaces of films are atomically smooth.

MgB2 superconducting films have been successfully fabricated on single crystal MgO (111) and c-AL2O3 substrates by different methods. The film deposited by pulsed laser deposition is c-axis oriented with zero resistance transistion temperature of 38.4K, while the other two films fabricated by chemical vapor deposition and electrophoresis are c-axis textured with zero resistance transistion temperature of 38 K and 39 K, respectively. Magnetization hysteresis measurements yield critical current density J c of 107 A/ cm2 at 15K in zero field for the thin film and of 105 A/ cm2 for the thick film. For the thin film deposited by chemical vapor deposition, the microwave surface resistance at 10 K is found to be as low as 100µΩ, which is comparable with that of a high-quality high-temperature superconducting thin film of YBCO. * Supported by the Major State Basic Research Development Program of China (Grant No. 1999064604)

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.

A circular polarized microstrip antenna with a working frequency of 6.26 GHz was fabricated from YBCO HTS films. The transmission coefficient and circular polarization ratio of the antenna at different external magnetic field B were measured at 4.2 K. The experimental results showed that its transmission coefficient and circular polarization ratio hardly changed with B up to 1 T. It is concluded that the field-induced increase of surface resistance of YBCO films would not influence the microwave properties of this antenna at B ⩽ 1T and T = 4.2 K.

We have systematically investigated the structures, morphologies, microwave surface resistance, DC performances and the substrate qualities of three YBa2Cu3O7-x(YBCO) thin films 30 mm in diameter. The three samples deposited by the same process have been proved of different properties. It has been shown that the structure and superconducting properties of the thin film depend strongly on the quality of substrate.

The microstructure of the laser-ablated YBa2Cu3O7 (YBCO) thin film deposited on heated (100) SrTiO3 substrate was examined by transmission electron microscope. The particles on the film mainly consist of CuO and few CuYO2. Most of these non-superconducting particles nucleate on or near the surface of the film and protrude about 100-400 nm in height. A large amount of a-axis YBCO grains also exist in the film, which nucleate at the substrate surface and grow perpendicularly above the c-axis YBCO film. The YBCO thin film deposited under low oxygen pressure has very different microstructure compared with YBCO thin film deposited under high oxygen pressure.

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 experimental results showed that the microstructures of defects on the edges and walls of the single groove with their dimensions smaller than the wavelength of the incident light can produce effects not only on the diffraction of different polarization light but also on the symmetry of both positive and negative diffraction orders. It is possible to cause the narrow peaks with opposite directions appearing at corresponding positions on the two diffraction intensity curves when the polarization directions of the incident light are perpendicular to each other, and to cause the diffraction peaks to be asymmetric when the incident light for the two curves is of the same polarization direction.

Experimental results are presented for the diffractive properties of wavelength-sized single groove in Si-Si3N4 substrate. The experimental results show that the diffraction of wavelength-sized single grooves in a non-perfectly conducting material is more complex than that of perfectly conducting material. The diffraction intensities change with the change of polarization angle of the incident light. The diffraction intensities for TM polarization light are larger as the groove width is larger. The diffraction intensities of TM polarization light decrease gradually and that of TE polarization light increase gradually when the groove width is close to the wavelength of the incident light. The variations of diffraction intensities are quite different not only for various grooves with different widths but also for different diffraction angles for the same groove. Although the intensity variation of each diffraction order has a very regular sinusoidal dependence on the polarization angles of the incident light, the variation phase of each diffraction order is not all the same.

Highly c-axis oriented MgB2 thin films with T-c(onset) of 39.6K were fabricated by magnesium diffusing into pulsed-laser-deposited boron precursors. The estimation of critical current density J(c), using hysteresis loops and the Bean model, has given the value of 10(7) A/cm(2) (15K, 0T), which is one of the highest values ever reported. The x-ray photoemission study of the MgB2 thin films has revealed that the binding energies of Mg 2p and B 1s are at 49.4 eV and 186.9 eV, which are close to those of metallic Mg and transition-metal diborides, respectively.

We have gained a very comprehensive set of results for infrared diffraction (10.6 μm wavelength) from fabricated single grooves of reflection with widths in the range of 5μm to 65μm. The experimental results show that the diffraction can still occur when the groove width becomes comparable to or less than the wavelength of the probing light. Variations of the diffraction intensities have a very regular sinusoidal relationship with the polarization angle of the incident light; and the diffraction intensities are the maximal when the incident light is TM polarized. However, the diffraction intensities will be a minimum when the incident light is TE polarized; and the bigger the diffraction angle, the higher the rate of change of the diffractive intensity with increasing polarization angle of the incident light.

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.

We have investigated theoretically enhanced quantum well IR detector. The field enhancement expressions are given by means of the perturbation method. The quantum efficiency and enhancement ratio have been obtained for a doped GaAs/AlGaAs quantum well structure at λ = 10 μm for different grating periods. We explained why Goossen and Lyon only observed a small enhancement.

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.

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.

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.

TiN thin films have been successfully epitaxially grown on Si substrates by laser molecular-beam epitaxy using the two-step method. The thin film has a smooth surface with a root-mean-square roughness of 0.842 nm over a 10 mu m x 10 mu m area. Hall measurement shows that the resistivity of the TiN film is 3.6 x 10(-5) Omega center dot cm and the mobility is up to 583.0 cm(2)/V center dot S at room temperature, which implies that TiN thin film is an excellent electrode material. The X-ray diffraction (XRD) theta-2 theta scan result together with the very high mobility show that the TiN film has high quality. The result that SrTiO3 thin film can be subseguently epitaxially grown on TiN/Si substrate indicates that the TiN thin film on Si substrate not only has good thermal stability, but also can be used as buffers or bottom electrode for epitaxial growth of other thin films or multilayer films.

Thin films of iron were fabricated on MgO(100) substrates using pulsed laser dep osition technique. The crystalline property and surface roughness of the films w ere investigated by x-ray diffraction and atomic force microscopy, respectively . It is found that the Fe films deposited at 500 and 800℃ are of single phase, and no diffraction from randomly oriented grains or impurity phases can be obser ved. The nonlinear optical properties of continuous 9 nm-thick iron film were d etermined using the z-scan method. The results show that the ultra-thin ir on film exhibits large nonlinear refractive coefficient, n2= 709×1 0-5cm2/kW, and nonlinear absorption coefficient, β=-552×10 -3(cm/W), at the wavelength of 532 nm.

MgB2 thick films were grown on metal substrates Ta, Mo and W using th e electrophoresis technique. The scanning electron microscopy and x-ray diffraction show that the grains in the MgB2 thick films are in random orientation wi th their size below 1μm. The onset temperatures of superconducting transition of MgB2/Ta，MgB2/Mo，MgB2/W are observed at 36.5, 34.8 and 33.4K, with the transition widths of 0.3, 1.5 and 2.0K, respectively. The critical current density of th e MgB2/Mo thick film at 5 K and 1T is more than 105 A/cm2. This n ew method provides a great potential for MgB2 in practical applicatio ns.

The colossal magnetoresistance oxide compound La0.9Sb0.1Mn O3 has been prepared by solid-state reaction method.The electrical transport and magnetic properties have been measured by superconducting quantum interference device magnetometer.The valence state of Sb is confirmed to be +5 through x-ray photoelectron spectroscopy,so this compound is an electron-doped colossal magnetoresistance material.

The formulae of second harmonic generation at a nonlinear crystal-metal interface with a rectangular grating are presented. According to the nonlinear medium theory given by Bloembergen and Pershan, we have solved the Maxwell equations by means of the perturbation method in power of the surface roughness parameter. All formulae and calculation show that the surface-enhanced second harmonic generation arises from the resonant excitation of surface polaritons, which is true to the direct contribution of free waves. The signals of the surface-enhanced second harmonic generation have been measured at GaAs-Al interface with different grating periods and groove depths using a tunable TEA CO2 laser. The experimental results are in good agreement with the theoretical prediction.

By using a tunable TEA CO(2) laser and by grating coupling at the interface of GaAs-Al, we have obtained, for the first time to our knowledge, second-harmonic generation from a resonantly excited infrared surface polariton. The experimental results provided a dispersion relation that compares well with theoretical calculations. The deduced value of chi(2), 5.9 x 10(-7) esu, agrees well with other measurements.