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In order to extend the application of single-stage dual active bridge type isolated AC-DC converter and improve its current characteristics, in this paper, a novel topology with a three-level half-bridge matrix converter and a resonant tank is proposed. The operation principle and steady-state characteristics are analyzed in detail based on the PWM plus phase-shift modulation. Furthermore, the relationship of the equivalent three phase shifts to realize a minimum rms value of resonant current is introduced to enhance the operation efficiency. The proposed converter reduces the voltage stress of the power switches of the AC side matrix converter to half the AC voltage and it is helpful to reduce the power loss and cost. Especially, it is valuable to realize the excellent high-frequency power conversion in the medium voltage applications. Furthermore, the current stress of the power switches is decreased by using the resonant tank as the temporary energy storage loop. The detailed experimental results verify the correctness and feasibility of the proposed topology and theoretical analysis.

In this article, a hybrid three-level current-fed series-resonant isolated bidirectional dc–dc converter is proposed, containing an interleaved parallel bidirectional buck/boost converter at the low-voltage side and a half-bridge three-level converter at the high-voltage side. The operation principles and characteristics of the proposed converter are thoroughly analyzed with the duty-cycle plus dual phase-shift control. The relationship between the general case of three independent control variables and the transfer power is derived. Then, a modulation strategy optimization algorithm by taking the minimum root mean square (rms) value of the resonant current as the objective function is presented. Under the optimal operation point, the converter operates efficiently with the minimum rms value of the resonant current and accordingly increases the efficiency. The detailed experimental results verify the correctness and feasibility of the proposed converter and modulation strategy.

The bidirectional buck–boost current-fed isolated dc–dc converter is an emerging topology and has the advantages of low current stress, high efficiency, and wide power/voltage conversion range. However, it suffers from the inductor current mutation and transient voltage spike when the converter is directly switched between the buck and boost modes in the actual operation. By analyzing in detail the process of directly switching the two operation modes, it reals the reason of causing these transient problems is the duty ratio, and shoot-through duty ratio is not correctly set when the operation mode is switched. In order to solve this problem, a smooth switching scheme between the buck/boost operation modes is proposed by setting a special relationship between the closed-loop controller output of the inductor current and the two control variables based on the system model. The detailed simulation and experimental results verify the theoretical analysis and the proposed solutions.

The semi-dual-bridge resonant isolated dc–dc converter (SDBRC), as a class of emerging topologies, is suitable for the application situation that requires only the unidirectional power transfer while a wide buck–boost voltage conversion range. In this article, a three-level SDBRC is proposed. Its operation principle is analyzed, and the transfer power and voltage conversion ratio as the functions of the two phase shifts are derived. Furthermore, a coordinated control rule of the two phase shifts is proposed, which ensures the monotonicity between the phase shifts and the average output power over the entire power/voltage range. The voltage stress of the power devices of the proposed topology is reduced to half of the power supply voltage; therefore, the cost and ON-state loss of the power switches are effectively reduced. The detailed simulation and experimental results validate the correctness and feasibility of the proposed topology and its modulation strategy.

As the key part of the electric vehicle charger with the V2G functions, the isolated dual-active-bridge (DAB) dc–dc converter should possess good current characteristics. The cooperative triple-phase shift (CTPS) modulation for the DAB converter realizes the best inductor current performance. However, the dead band and transient actions deteriorate the actual performance of the CTPS. In this article, the effect is analyzed for the first time, and the analysis results indicate that both the dead band and transient actions cause the dc-bias inductor current and the dc-side flow back currents. The corresponding solutions to eliminate these effects are proposed accordingly. First, a phase shift compensation related to the dead time is added to the ideal phase shifts from CTPS to eliminate the effect of the dead band. Second, the relationship between the three phase shifts is recalculated considering the old values of the phase shifts to eliminate the transient dc-bias currents and flow back currents. The proposed solutions are validated in detail in an experimental way.

The bidirectional buck-boost current-fed isolated dc–dc converter (B3CFIdc) has the advantages of low current stress, high efficiency, and wide power/voltage conversion range. The linear models of buck mode and boost mode of B3CFIdc are originally derived using state-space averaging method. The dual-closed-loop control configuration with the inductor current and output voltage is designed. In order to ensure the stability of both operation modes at the same time, the parameters of the controllers are designed using the method of Hurwitz criterion plus frequency response. The asymptotic stability of the operating conditions with periodic switching between the two modes caused by the periodic fluctuation of input voltage is verified using the linear switching theory. The detailed experimental results verify the correctness of the built small-signal models and the feasibility of the designed closed-loop control configuration and the design rule of the controller parameters.

In this paper, a modified single-carrier and multimodulation sine pulse width modulation (MSCMM-SPWM) is proposed to simplify the implementation of the single-phase asymmetrical neutral-point clamped grid-connected inverter (ANPC-GCI) for the PV generation system application. Furthermore, the expressions of the total switching loss and grid current total harmonic distortion (THD) of ANPC-GCI controlled by the proposed MSCMM-SPWM are derived. Then taking the grid current THD meet the grid-connected standard in the entire operational range as the constraint, an efficiency enhancement scheme for ANPC-GCI based on online adjusting the carrier frequency and the obtained THD expression is proposed. The control configuration of ANPC-GCI, including the proposed MSCMM-SPWM and online efficiency enhancement scheme, is designed. The detailed experimental results verify the correctness and feasibility of the proposed MSCMM-SPWM and the efficiency enhancement scheme.

In this study, the essential reason for causing the dual-side flow back currents in the isolated dual active bridge (DAB) DC-DC converter is originally revealed first. It is because the polarities of the AC side output voltages of the two H-bridge converters in DAB converter are not able to be always kept the same as that of the inductor current in the conventional modulation strategies. An improved triple-phase-shift (ITPS) control is proposed according to the analysis results to ensure that the dual-side flow back currents are eliminated, and all of the power switches achieve soft switching in the entire power range. The detailed experimental results of the ITPS control validate its validity and feasibility.

We proposed a novel photosensitive hydrogel based holographic sensor for the detection of hydrogel swelling and hence the chemical concentrations, which formed by thermally polymerizing 2-hydroxyethyl methacrylate. Holographic volume grating recorded in the hydrogel as an optical sensing platform was employed in response to the hydrogel deformation induced by target molecules. Co-monomer methacrylic acid with carboxyl groups functionalized the polymer matrix for improving the selectivity. Peak wavelength shift of the diffraction spectrum was a significant parameter in sensing the pH value of the buffer. The extracted time constant of the wavelength shift curve evaluated the sensitivity of the novel holographic sensor. There were good exponential relations between peak wavelength and pH value with various thicknesses. The novel sensor could be considered as an effective platform for sensing the analytes concentration of solution. The reversible measurement experimentally demonstrated the repeatability of the holographic sensor. The novel photosensitive hydrogel and its sensor provided a probability for sensing the performance of solution and accelerating the development of water resistant holographic sensor based on polymer hydrogel.

We reveal the self-accelerating performance of an Airy beam under space-variable spectrum modulation, which corresponds to the extension of the field of view (FOV) and imaging depth in Airy-beam tomographic microscopy (ATM), resulting in the decline of fidelity and resolution of a reconstructed image with an increased FOV and depth of field (DOF). A strategy of spectrum modulation is proposed, and high-fidelity, high-resolution 3D imaging is realized in a 150 µm × 50 µm × 12 µm volume. This study offers a paradigm to improve the quality of reconstructed 3D images based on spectrum modulation for other light fields.

We reveal that polymerization degree is a significant factor that affects the holographic properties of glass-like photopolymer. By modulating polymerization degree, as well as changing the photosensitizer concentration, we fabricate multilayer PQ/PMMA photopolymer, exhibiting excellent performances in storage fidelity and reproduction resolution. A reflection geometry holographic disk system is established using the multilayer sample, in which a high storage density of 40.5GB/cm3 is realized. The reproduced images exhibit high quality with an average diffraction efficiency of 7.4 × 10−4 and average peak SNR of 27.4. This study provides a paradigm for the fabrication and holographic application of other photopolymers.

In the IGBT-based bidirectional isolated dual-active-bridge (DAB) dc–dc converter, it is not necessary that the IGBTs of the secondary-side H-bridge inverter (HB2) retain under on state because in this system, the function of synchronous rectification cannot be realized. This paper firstly analyzes the characteristics of the DAB converter with all of the IGBTs of HB2 keeping under OFF state. Its main drawback is that the flow back current in the primary dc side is caused and the current stress is increased. Furthermore, a hybrid modulation strategy is proposed and the control rule of the two inner phase shifts of the primary and secondary H-bridge inverters is determined to eliminate the flow back currents in the entire power range, enhance the maximum transfer power, and achieve a good inductor current characteristic. The experimental results verify the correctness of the theoretical analysis and the feasibility and practicability of the proposed hybrid modulation strategy.

Optical sensor based on pH-sensitive hydrogel has important practical applications in medical diagnosis and bio-sensor areas. This report details the experimental and theoretical results from a novel photosensitive polymer hydrogel holographic sensor, which formed by thermal polymerization of 2-hydroxyethyl methacrylate, for the detection of pH in buffer. Volume grating recorded in the polymer hydrogel was employed in response to the performance of solution. Methacrylic acid with carboxyl groups was selected as the primary co-monomer to functionalize the matrix. Peak diffraction spectrum of holographic grating determined as a primary sensing parameter was characterized to reflect the change in pH. The extracted linear relation between peak wavelength and pH value provided a probability for the practical application of holographic sensor. To explore the sensing mechanism deeply, a theoretical model was used to describe the relevant holographic processes, including grating formation, dark diffusional enhancement, and final fringe swelling. Numerical result further showed all of the dynamic processes and internal sensing physical mechanism. These experimental and numerical results provided a significant foundation for the development of novel holographic sensor based on polymer hydrogel and improvement of its practical applicability.

The LiNbO3 crystals doped with Fe2O3, CuO and various In2O3, respectively, have been grown by the Czochralski method in air atmosphere. The photorefractive properties at 532 nm wavelength were measured by using the typical two-wave coupling experiments. Meanwhile, the incident exposure energy flux threshold for the light-induced scattering was characterized to investigate the scattering properties of the crystals. The results show that the response time shortens, the recording sensitivity improves, and the light-induced scattering decreases with the increasing In3+ ions concentration. However, the doping of In3+ ions leads to the decrease of the diffraction efficiency and the gain coefficient. So, the appropriate In3+ ions concentration should be doping in In:Fe:Cu:LiNbO3 crystals to adapt our practical application in the green light region photorefractive holographic recording.

A volume grating based holographic sensor on a flexible substrate for real-time characterization of the bending deformation of polymer has been studied. Two kinds of deformations, i.e., unilateral and bilateral bending, are analyzed by using the diffraction spectrum of a transmission grating. The dependence of the peak wavelength on the angle displacement in unilateral bending presents a linear relationship. The relation between the peak wavelength and the curvature radius in bilateral bending is also a linear relationship. The maximum bending angle is 18 deg in unilateral bending, and the curvature radius reduces to 44 mm in bilateral bending. The diffraction spectrum coverage is up to 200 nm. In straightening a curved grating, the spatial width of the rainbow spectrum presents a linear relation to the curvature radius. The sensing feedback of bending deformation provides an effective method for characterizing the bending movement of polymer. It can even qualitatively present the deformation by observing the center color and its width with the naked eye. The optical measurement of bending deformation further validates the practical applicability of the holographic sensor.

A volume grating-based holographic sensor in highly stretchable PVA/AA polymer for sensing its micro-deformation and, hence, the displacement has been studied. One-dimensional micro-displacement induced by tensile stress is analyzed using a diffraction spectrum in two kinds of sensor construction methods, i.e., transmission and reflection. The dependence of the peak wavelength on the displacement presents a good linear relationship which provides a quantitative sensing strategy for hydrogel micro-deformation. The available sensitivity is better than 4 μm/0.5 nm (displacement/wavelength shift) using a commercial spectrometer with a resolution of 0.5 nm. Finally, the reversible deformation response further validates the practical applicability of a holographic sensor constructed by photosensitive hydrogel. The optical measurement of micro-displacement as a novel sensing strategy can accelerate the development of the holographic optical element.

The optical damage resistance ability of the co-doped M:Fe:LiNbO3 crystals with 0.03 wt% Fe2O3 and various concentration of M (M = Mn, Mg, or Zn,) were measured experimentally. The shift of the fundamental absorption edge as well as the absorption coefficient was obtained in order to investigate their defect structures. A method of confirming the polarization ability dimension of doped ions is brought forward. The indirect transition properties of the fundamental absorption edge below 3.8 eV were investigated experimentally. Possible models to explain the experiments results are discussed.

Congruent LiNbO3 crystal doped with Fe2O3, CuO and In2O3, respectively, were grown by Czochralski method. The blue photorefractive performance (the change refractive index Δn, response time τw and recording sensitivity S, at different recording angle) was investigated by using the typical two-wave coupling experimental setup. The results show that Δn reduces, τw first decreases then increase, S first increase then decreases with the recording angle increasing within our measurement range. It should be compromised between the change refractive index and the recording sensitivity when we using In:Fe:Cu:LiNbO3 crystal to holographic storage. The compromising recording angle is near 50° in air under our experimental conditions. The experimental results also indicates that In:Fe:Cu:LiNbO3 crystal becomes a promising candidate for blue photorefractive holographic recording materials.

A novel thermo-sensitive N-isopropylacrylamide photopolymer was developed for improving the temperature and humidity responses of holographic sensors. Diffraction spectra of holographic volume gratings recorded in the materials were characterized to explore the sensing response capacity. A dependence of peak wavelength on the temperature was observed and provided a quantitative strategy for holographic sensing applications. Expansion of the humidity range induced a strong extension of wavelength shift. Finally, the temperature response reversibility was demonstrated experimentally. Our sensing results were completely different from the reported typical acrylamide polymer system. Compared with the former, we obtained a more sensitive temperature response and an evident shift expansion (>200 nm) at a relative humidity of 70% or higher. These results can obviously improve the thermo-sensitivity of a holographic sensor and expand the practical application area of the holographic sensing strategy.

Holographic data storage is promised to be the next-generation optical storage technology for many years. The Zn:Fe:LiNbO 3 crystal is studied widely because of its promising holographic storage properties. The forced oscillator model is used to explain the self-erasing phenomenon in the reduced Zn:Fe:LiNbO 3 crystals. It is showed that the total spatial charge field is dominated by two kinds of carrier with different respond time, which are electron and hole, respectively. The cooperative action of two kinds carrier induces that the total charge field non-monotonically varies with the recording time. The same diffraction efficiency of hologram with equal exposure energy is realized by the self-erasing property. The precision of the optical correlation recognition based on holographic storage will be improved.

Zr:Fe:LiNbO3 crystals were grown in air by the Czochralski technique with various [Li]/[Nb] ratios of 0.85, 1.05, and 1.38 in melt. Based on the ICP-AES (inductively coupled plasma atomic emission spectrometry) analyzed results, the chemical formulas of Zr:Fe:LiNbO3 crystals were obtained. The sign of the dominate charge carriers as well as the two-wave coupling gain coefficient as a function of the [Li]/[Nb] ratios in crystal were investigated by using the typical two-wave coupling experimental setup. The results show that electrons are the dominate charge carriers and the gain coefficient is the largest when the recording angle 2θ=21° in the sample with [Li]/[Nb]=0.7111 in crystal. In addition, the dependence of the light-induced birefringence on the [Li]/[Nb] ratios was measured in Zr:Fe:LiNbO3 crystals, which shows that the optical damage resistance of Zr:Fe:LiNbO3 crystals increases with the increasing of [Li]/[Nb] ratios at 532 nm wavelength. The dependences of the green photorefraction on the defect structure of Zr:Fe:LiNbO3 crystals are discussed in detail based on the obtained chemical formulas.

The LiNbO 3 crystal co-doped with ZrO 4 and Fe 2 O 3 has been grown with [Li]/[Nb]=0.85 and 1.20, respectively, by the Czochralski method in air atmosphere. The incident exposure energy flux threshold for the light-induced scattering was characterized to investigate the scattering properties of the crystals. Applying the results of the incident exposure energy flux threshold effect, the photorefractive properties at different laser wavelengths (473 nm and 532 nm) were also measured by using the typical two-wave coupling experiments. The results show that Zr:Fe:LiNbO 3 crystal has a larger refractive index change, higher recording sensitivity and larger two-wave coupling gain coefficient at 473 nm wavelength than those obtained at 532 nm wavelength under the same experimental conditions. Moreover, the photorefractive properties decrease with the increasing [Li]/[Nb] ratios. The material of Zr:Fe:LiNbO 3 crystal is a promising candidate for blue photorefractive holographic recording.

The high sensitivity, fast response and the high quality reconstructions are observed in various [Li]/[Nb] ratios In:Fe:Cu:LiNbO 3 crystals at 488 nm wavelength based on the two-beam coupling experiment. The strong blue photorefraction is contributed by the two-center effect and the remarkable characteristic of being in phase between the two gratings recorded in shallow and deep trap centers. The blue photorefraction is enhanced significantly with the increasing of [Li]/[Nb] ratios under the same experimental conditions. The sensitivity S " is reduced to 0.46 J/cm, simultaneously the response time is as fast as 4.4 s and the erase phenomenon is not obvious in In:Fe:Cu:LiNbO 3 crystals which [Li]/[Nb] ratio is 0.986 in crystal. Increasing [Li]/[Nb] ratios improve the damage-resistant ability of the crystals, but lead to a more serious beam fanning. Experimental results definitely show that the near-stoichiometric In: Fe: Cu: LiNbO 3 crystal becomes a promising candidate for blue photorefractive holographic recording.

In:Fe:Cu:LiNbO3 crystals were grown in air by the Czochralski technique with various [Li]/[Nb] ratios of 0.946, 1.050, 1.200, and 1.380 in melt. Based on the ICP-AES (inductively coupled plasma atomic emission spectrometry) analyzed results, the chemical formula of the triple-doped In:Fe:Cu:LiNbO3 crystals were obtained. It can be seen that the near-stoichiometric ratio value is between 1.050 and 1.200 for our samples. The optical damage resistance of In:Fe:Cu:LiNbO3 crystals was characterized by changes in light-induced birefringence and it increases with the increasing of [Li]/[Nb] ratios. The dependence of the optical damage resistance on the defect structure of In:Fe:Cu:LiNbO3 crystals is discussed in detail based on the obtained chemical formulas. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A series of Hf:Fe:LiNbO3 crystals were grown by the Czochralski technique with various doping concentrations of HfO2. Their defect structures were analyzed by the UV–visible absorption spectra and infrared absorption spectra. The optical damage resistance of Hf:Fe:LiNbO3 crystals was measured by the photo-induced birefringence change and the transmitted light spot distortion method. The results show that the optical damage resistance ability of Hf:Fe:LiNbO3 crystals enhances remarkably with the HfO2 concentration increasing when the HfO2 concentration is lower than its threshold concentration (4 mol%). However, when the HfO2 concentration exceeds its threshold concentration, the optical damage resistance ability of the crystals returns to decrease. This unusual behavior is explained by using the photovoltaic field produced in the crystals.

This publisher's note amends the funding section in Appl. Opt.56, 9006 (2017)APOPAI0003-693510.1364/AO.56.009006.

The dark enhancements with various exposure energies are studied in thick PQ/PMMA photopolymer. Considered the weak molecules diffusion of PQ component and the grating detuning, a new mechanism of dark reaction is proposed to explain the dark enhancement. Moreover, the influences of dark reaction on Bragg angular selectivity and grating recording are analyzed. The results are beneficial to the practical holography application.

In:Fe:Cu:LiNbO3 crystals with reduced/oxidized treatments were prepared by the Czochralski method. The defect structure was analyzed by the UV-Visible absorption spectra. The blue photorefractive properties, such as the refractive index change, response time, recording sensitivity, dynamic range as well as two-wave coupling gain coefficient, were also investigated at 488 nm wavelength using the two-wave coupling experiment. Comparing the as-grown and oxidized In:Fe:Cu:LiNbO3 crystals, the reduced sample has the highest recording sensitivity and largest dynamic range. Meanwhile, the high diffraction efficiency is still maintained. Experimental results definitely show that reduction treatment is an effective method to improve the blue photorefractive performance of In:Fe:Cu:LiNbO3 crystals. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The shift of Bragg angular selectivity curve after exposure was studied by recording single hologram and multiplexed holograms, respectively. The evolution of shift with probe time after recording, as well as the saturated shift with exposure energy, was investigated in detail. The mechanism of Bragg mismatch was analyzed. By optimizing parameters of material synthesis and holographic recording, the shift of Bragg matched angle was alleviated in PQ/PMMA photopolymer after hologram recording.

The threshold effect of incident exposure energy flux is proposed to measure the light-induced scattering in doped LiNbO3 crystals. The dependences of the exposure energy flux threshold on the concentration of damage-resistant dopants as well as oxidation–reduction treatment are investigated experimentally in doped LiNbO3 crystals. The results show that doping with damage-resistant dopants and oxidation–reduction treatment are simple and effective methods to control and optimize the photorefractive properties of doped LiNbO3 crystals. The high signal-to-noise ratio reconstructions are also demonstrated experimentally according to the incident exposure energy flux threshold in triply-doped LiNbO3 crystals. Comparing with the known incident intensity threshold method, the exposure energy flux threshold method is more effective for estimating the light-induced scattering of photorefractive recording materials.

The near-stoichiometric LiNbO3 crystal co-doped with In2O3, Fe2O3, and CuO has been grown from a Li-rich melt (Li/Nb = 1.38, atomic ratio) by the Czochralski method in air atmosphere for the first time. The OH− absorption spectra were characterized to investigate the structure defects of the crystals. The appearance of the 3506 cm−1 absorption peak manifests that the composition of the grown crystal is close to the stoichiometric ratio. The photorefractive properties were also measured by the two-wave coupling experiments. The results show that the near-stoichiometric In:Fe:Cu:LiNbO3 crystal has a larger refractive index change, higher recording sensitivity and larger two-wave coupling gain coefficient than those obtained in the congruent In:Fe:Cu:LiNbO3 crystal under the same experimental conditions. The material of near-stoichiometric In:Fe:Cu:LiNbO3 crystal is a promising candidate for blue photorefractive holographic recording.

The threshold concentration for In3+ ions was found in In:Fe:Cu:LiNbO3 crystals by measurements of the infrared absorption spectra and the Curie temperature of the crystals. The optical damage resistance of In:Fe:Cu:LiNbO3 crystals was characterized by changes in light-induced birefringence as well as by distortion of the transmitted beam pattern. The resistance of In:Fe:Cu:LiNbO3 crystals to optical damage increases remarkably when the concentration of In3+ ions exceeds its threshold concentration. The resistance to optical damage of In(3.0 mol.%):Fe:Cu:LiNbO3 crystals is two orders of magnitude higher than that of Fe:Cu:LiNbO3 crystals. The change in light-induced birefringence also decreases with increasing concentration of In3+ ions. The dependence of the optical damage resistance on the defect structure of In:Fe:Cu:LiNbO3 crystals is discussed in detail.

The nonvolatile photorefractive characteristics of LiNbO3:Fe:Cu and In-doped LiNbO3:Fe:Cu crystals are investigated. The stronger nonvolatile blue photorefraction observed can be ascribed to its remarkable characteristic of being in phase between the two gratings recorded in shallow and deep trap centers, which is one or two orders of magnitude higher than those obtained in conventional two-color recordings under the same recording conditions. Furthermore, it is interesting that, compared with LiNbO3:Fe:Cu, the recording properties, such as the saturation refractive index change, nonvolatile sensitivity and response time at 488 nm wavelength are enhanced in LiNbO3:In:Fe:Cu crystals under the same recording conditions. The so-called damage-resistant dopants such as In3+ ions in red photorefraction are not damage resistant at 488 nm wavelength but they enhance the blue photorefraction.

Ultra-long rutile tin dioxide nanowires and nanobelts are synthesized by thermal oxidation of tin powder using gold film as the catalyst. Nanowire or nanobelts can be selectively produced by tuning the reaction temperature. The vapour-liquid-solid growth mechanism is proposed. The band gaps of the nanowires and nanobelts are 3.74 and 3.81 eV respectively, determined from UV/visible absorption spectral results. The SnO2 nanowires show stable photoluminescence with two emission peaks centred at around 470 and 560 nm. Their wavelengths stay almost fixed while their intensities depend sensitively on the temperatures within the examination ranges from 10 to 300 K. The SnO2 nanobelts show similar photoluminescence behaviours and the origin of the luminescence is discussed.

It is experimentally demonstrated that the self-erasing phenomenon, diffraction efficiency grows gradually to its maximum and then decays a great extent during the recording process, existed in reduced Zn:Fe:LiNbO 3 crystal. To analyze this phenomenon, the absorption spectra were measured by UV–Visible Spectrophotometer in the region of 200–700 nm, and the nonlinear dependence of photoconductivity on light intensity were studied. The cooperative action of the two kinds of carriers and their own shallow or deep traps was considered to explain the self-erasing phenomenon in reduced Zn:Fe:LiNbO 3 crystal.

Relaxed SiGe-on-Insulator (SGOI) is fabricated using a modified fabrication technique based on Ge condensation by oxidizing the SiGe layer on SOI. In this procedure, the Ge atoms are condensed into the remaining SiGe layer due to the rejection of Ge atoms from the oxide layer and the large diffusion coefficient of Ge in SiGe. Raman measurements reveal that the strain in the SiGe layer is fully relaxed at high oxidation temperature (� 11501C). Atomic force microscopy (AFM) and transmission electron microscopy (TEM) results indicate that no dislocation is introduced for strain relaxation during the oxidation process. The strain relaxation is explained by a relaxation model involving a compliant substrate, on which the SiGe layer expands laterally via an ultra-low viscosity slippage plane at the SiGe/ buried oxide (BOX) interface. r 2005 Elsevier B.V. All rights reserved.

A fully depleted SiGe-on-insulator (SGOI) substrate has been fabricated by a modified Ge condensation technique. The characteristics of the SiGe/ buried-oxide (BOX) interface and the influence on the electrical performance of the SGOI substrate are investigated. The long oxidation time during the fabrication of the fully depleted (FD) SGOI substrate leads to Ge atom pileup at the SiGe/BOX interface, and consequently a large number of interfacial trapped charges are produced. Furthermore, our results disclose that Ge diffusion into the BOX increases the interfacial trapped charges and the fixed oxide charges during oxidation. As a result, the electrical properties of the FD-SGOI substrate degrade due to the poor SiGe/BOX interface.

The effect of reduction treatment on the photorefractive properties of Zn:Fe:LiNbO3 crystal was studied experimentally. It was found that, after reduction treatment, the response time of the crystal is shortened, the ability of optical damage resistance is enhanced and the absorption edge is shifted towards the infrared band. Meanwhile, a self-erasing phenomenon was observed for the first time in reduced Zn:Fe:LiNbO3 crystal. The evolution of diffraction efficiency with time going on is non-monotonic, but grows gradually to its maximum and then decays a great extent during the recording process. The mechanism of the electron–hole competition was presented to explain this phenomenon.

Zr0.6Al0.4O1.8 dielectric films were deposited directly on strained SiGe substrates at room temperature by ultra-high vacuum electron-beam evaporation (UHV-EBE) and then annealed in N2 under various temperatures. X-ray diffraction (XRD) reveals that the onset crystallization temperature of the Zr0.6Al0.4O1.8 film is about 900 °C, 400 °C higher than that of pure ZrO2. The amorphous Zr0.6Al0.4O1.8 film with a physical thickness of ∼12 nm and an amorphous interfacial layer (IL) with a physical thickness of ∼3 nm have been observed by high-resolution transmission electron microscopy (HRTEM). In addition, it is demonstrated there is no undesirable amorphous phase separation during annealing at temperatures below and equal to 800 °C in the Zr0.6Al0.4O1.8 film. The chemical composition of the Zr0.6Al0.4O1.8 film has been studied using secondary ion mass spectroscopy (SIMS).

SnO2 nanowhiskers were synthesized by thermal oxidation with and without a gold film as a catalyst. The SEM images reveal wire-like and rod-shaped nanowhiskers about several hundred micrometers in length and 100 nm in diameter. The three observed Raman peaks at 474, 632, and 774 cm � 1 indicate the typical rutile phase which is in agreement with the X-ray diffraction results. The photoluminescence properties were measured at room temperature. The peaks at 342 nm corresponding to the excitation transitions from the conduction band to the valence band of the SnO2 nanowhiskers were not observed. However, a strong emission band at w600 nm was detected indicating the existence of oxygen vacancies in both samples. A new emission band at w398 nm was also observed in the sample with the gold film and it could be attributed to the near band-edge emission. 2005 Elsevier Ltd. All rights reserved.