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A novel Z-scheme graphitic C3N4/reduced TiO2 microsphere (g-C3N4/r-TiO2) has been successfully synthesized by a solvothermal method. The as-prepared samples with different contents of g-C3N4 were characterized by X-ray diffraction, electron paramagnetic resonance, scanning electron microscope, UV–vis. diffuse reflectance and photoluminescence spectra. The r-TiO2 microspheres are aggregated on the surface of g-C3N4 sheets in the as-prepared g-C3N4/r-TiO2 composites. All g-C3N4/r-TiO2 catalysts show enhanced photocatalytic activity for the degradation of rhodamine B under visible light irradiation. It could be attributed to these influences of oxygen vacancy (changing the band gap of TiO2), the large specific surface area (providing much more active sites for photocatalytic reaction), and the synergetic effect between g-C3N4 and r-TiO2 (promoting the separation for photoinduced electron-hole pairs). Moreover, the Z-scheme carriers transfer mechanism in the photocatalytic process has been discussed through trapping experiments of active species. The work demonstrates the strategies of the construction of Z-scheme carriers transfer system, the introduction of oxygen vacancy and structure designing are beneficial to design materials toward solar energy conversion like contaminant degradation. Keywords: TiO2, C3N4, Oxygen vacancy, Z-scheme heterojunction, Photocatalytic performance

Computational simulation method was used in two models of calcium carbonate aqueous solution to explore the mechanism of anti-scaling under electrostatic field on the molecular level. The binding energy between the surface and ions indicated that the surface (104) was more favorable for the growth of the new crystal, while it was much easier to decompose under field strength 1300 V/m. The diffusion coefficients of Ca2+ and CO3 2- revealed that the chemical reaction of Ca2+ and CO3 2- ions in Model-II was much difficult to form calcium carbonate crystal under electrostatic field. The hydration degree of Ca2+ with O atoms from water molecules showed that the electric field could enhance the hydration degree of Ca2+ under certain field length, hence preventing the chemical reaction with CO3 2- to produce crystal. In short, the scale inhibition effect under electrostatic field in Model-II was much better.

Polycrystalline ZnO/La0.7Sr0.3MnO3 (LSMO) heterostructures were fabricated onto Si(100) substrates by magnetron sputtering. A rectifying behavior, as well as an enhanced magnetoresistance (MR) ratio (∼ 12%), was obtained in the heterostructure with respect to the LSMO single layer (a MR ratio ∼ 6%). The degradation of the rectifying behavior for the LSMO layer thinner than 20 nm is mainly due to the change in hole concentration. We suggest a possibility that the magneto-transport and the magneto-optical properties of manganites can be modified by the formation of this kind of heterostructure. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

To investigate the feasibility of a long-term left ventricular assist device (LVAD) placed in the aortic valve annulus, an implantable aortic valve pump (21 mm outer diameter, weighing 27 g) was developed. The device consists of a central rotor and a stator. The rotor assembly incorporates driven magnets and an impeller. The stator assembly has a motor coil with an iron core and outflow guide vanes. The device is to be implanted identically to an aortic valve replacement, occupying no additional anatomic space. The pump delivers the blood directly from left ventricle to the aortic root, like a natural ventricle, therefore causing less physiologic disturbance to the natural circulation. Neither connecting conduits nor 'bypass' circuits are necessary. The pump is designed to cycle between a peak flow and zero net flow to approximate systole and diastole. Bench testing indicates that the pump can produce a blood flow of 5 l min(-1) with 50 mmHg pressure increase at 17,500 rpm. At zero net flow rate, the pump can maintain a diastole aortic pressure against 80 mmHg at the same rotating speed.

In fabrication of free form optical surfaces, spot exposure is a typical mode in laser photolithography. Proper selection of spot exposure superposing ratio is the key to optimize etching quality and writing speed. In this paper, a new composite diffractive grating structure is modeled for the influence on diffraction efficiency of binary optical elements caused by spot exposure superposing ratio. Composite grating can be transformed into one simple rectangular grating and two triangular gratings. Angular spectrum theory is used to describe the mathematical expression of the composite diffractive grating. Through simulation analysis, the relationships between diffraction efficiency and the other three items as grating depth, spot radius, and blaze wavelength, has been shown. Simulation results indicate that shape error caused by spot exposure ratio impact the diffraction efficiency greatly in deep etching, and the transmittance will reach maximal point approximately while spot exposure ratio is over 60%. This conclusion can be taken as the theoretical foundation for exposure frequency selection in laser photolithography figure generation.

The problem of the extension of subinterface microcracks in an infinite metal/ceramic bimaterial solid is studied. For the microcrack growth, the values of the M-integral are calculated under the assumption of a self-similar growth. First, the role that the M-integral plays in a metal/ceramic bimaterial solid with growing subinterface cracks is analyzed. It is concluded that an inherent relation exists between the value of the M-integral and the decrease of the effective elastic moduli for a bimaterial solid with growing subinterface microcracks. Second, it is concluded that mutual amplification and shielding effects exist during the microcrack extension, while they are substantially dependent on the increment of the microcrack length as well as the geometry of the microcrack arrangement under given loads. This strong mutual shielding effect of interacting microcracks makes the microcrack extension become increasingly difficult, and may stop the growth of the microcracks even under constant loads. Also, it is concluded that for a certain microcrack growth, the value of the M-integral in metal/ceramic bimaterial solid is always larger than that in homogeneous brittle solid for the same crack configuration. This means that the same microcrack growth in the former case shows lower stability than that in the latter one, due to the existence of a ductile phase.

Schottky barrier diodes, on both Ga and N faces of a ∼300-μm-thick free-standing GaN layer, grown by hydride vapor phase epitaxy (HVPE) on Al2O3 followed by laser separation, were studied by capacitance–voltage and deep level transient spectroscopy (DLTS) measurements. From a 1/C2 vs V analysis, the barrier heights of Ni/Au Schottky contacts were determined to be different for the two polar faces: 1.27 eV for the Ga face, and 0.75 eV for the N face. In addition to the four common DLTS traps observed previously in other epitaxial GaN including HVPE-grown GaN a new trap B′ with activation energy ET = 0.53 eV was found in the Ga-face sample. Also, trap E1 (ET = 0.18 eV), believed to be related to the N vacancy, was found in the N-face sample, and trap C (ET = 0.35 eV) was in the Ga-face sample. Trap C may have arisen from reactive-ion-etching damage.

A ZnO film was deposited on a silicon wafer by magnetron sputtering, and the magnetic and the electronic properties have been studied The magnetic property measurements show that the ZnO film is ferromagnetic at room temperature. Through the magnetoresistance (MR) measurement, it is found that ZnO reveals a negative MR at 80, 50, 20, 10 and 6 K, which is induced by the weak‐localization effect. However, a positive MR as large as 19.8% was observed, when temperature was reduced to 2 K. As far as the mechanism of the huge positive MR is concerned, it is suggested to be due to the spin splitting induced by the s‐d‐like interaction. Through the discussion on the huge positive MR, we demonstrate that the observed ferromagnetism in ZnO is intrinsic, not from external impurities.

In the early 1990s, Yamazaki et al. developed a partly intra-ventricular pump, which was inserted into the left ventricle via the apex and then into the aorta through the aortic valve. The pump delivered blood flow directly from the left ventricle to the aorta, like a natural heart, and needed no inflow and outflow connecting tubes; it could be weaned off after the left ventricle had been recovered. The shortcomings were that the driving DC motor remained outside of the ventricle, causing an anatomic space problem, and the sealing and bearing were not appropriate for a durable device. Recently, a totally implantable trans-ventricular pump has been developed in the authors' laboratory. The device has a motor and a pump entirely contained within one cannula. The motor has a motor coil with iron core and a rotor with four-pole magnet; the pump has an impeller and an outflow guide vane. The motor part is 60 mm in length and 13 mm in diameter; the pump part is 55 mm in length and 11 mm in diameter. The total length of the device is therefore 115 mm. The total weight of the device is 53 g. The motor uses rolling bearing with eight needles on each side of the rotor magnets. A special purge system is devised for the infusion of saline mixed with heparin through bearing to the pump inlet (30 - 50 cc per hour). Thus neither mechanical wear nor thrombus formation along the bearing will occur. In haemodynamic testing, the pump can produce a flow of 4 l min-1 with 60 mmHg pressure increase, at a pump rotating speed of 12,500 rpm. At zero flow rate, corresponding to the diastolic period of the heart, the pump can maintain aortic blood pressure over 80 mmHg at the same rotating speed. This novel pump can be quickly inserted in an emergency and easily removed after recovery of natural heart. It will be useful for patients with acute left ventricular failure.

In this work, the stability of the insulating phase of the 1D chiral Kondo lattice model is studied at half-filling, within the framework of self-consistent variational theory. It is found that arbitrarily small interaction would drive the system from a conducting phase to an insulating phase, in spite of the chirality of the conducting band., 10 pages, IPT-EPFL preprint, submitted to PRB as a brief report for publication

Photoenhanced electrochemical (PEC) etching in an unstirred KOH solution under He–Cd laser illumination was used for delineating extended defects in GaN films. When a low-excitation intensity was employed, the process yielded threading vertical features at dislocation sites. Application of an external voltage or a higher-illumination intensity led to high-etch rates with smooth surfaces. Some highly resistive samples, for which no etching was obtained under normal etching conditions, could be etched with the application of a single-polarity external voltage. Finally, in a GaN sample with an AlN/GaN superstructure inside, high selectivity between AlN and GaN was achieved; in this case, the PEC process stopped at the thin AlN stop layer.

Zn0.96Mn0.04O∕ZnO coaxial nanocable and Zn0.96Mn0.04O film were prepared by two-step method and magnetron sputtering, respectively. The x-ray diffraction analysis reveals that Mn is incorporated well into the wurtzite ZnO without formation of Mn or Mn oxide. The high resolution transmission electron microscopy image and the selected-area electron diffraction pattern demonstrate that both ZnO and Zn0.96Mn0.04O layers are single crystalline and an epitaxial growth is achieved between Zn0.96Mn0.04O and ZnO in the coaxial nanocable. The magnetic property measurements show that both Zn0.96Mn0.04O∕ZnO nanocable and Zn0.96Mn0.04O film are ferromagnetic at room temperature. Moreover, the saturated magnetization and the coercive field of Zn0.96Mn0.04O∕ZnO coaxial nanocable are larger than those of Zn0.96Mn0.04O film.

This paper describes an experimental study of the anelastic strain relaxation (ASR) behaviour of a synthetic sandstone aimed at assessing the use of core-based techniques for stress measurement. The “sandstone” was compacted and “cemented” under stress, unloaded and placed in an ASR cell to monitor its strain response. The relationships between the axial and radial strains and applied stresses were studied for a number of stress fields including isotropic (7 to 28 MPa), anisotropic (7, 14 MPa) and complex (7, 14 MPa, reversed to 14, 7 MPa). The ASR response of the material was generally consistent with theory, showing greater relaxation in the direction of the larger stress, and isotropic relaxation after isotropic loading. The behaviour became more consistent at loads exceeding 10 MPa, applied for durations exceeding 12 hours. The ratio of relaxation strain to applied stress was remarkably consistent in the radial and axial directions for isotropic and anisotropic loading cases. However, the relaxation strain decreased with increasing stress, showing a non-linear “stress-strain” response. The preliminary results from the complex stress field experiments show a “memory” of both applied stress fields, which seems to be controlled by duration of loading. These findings promise to give us greater confidence in the use of the ASR stress measurement technique on sandstones.

Photoenhanced electro-chemical (PEC) wet etching has been shown to be suitable for dislocation-density estimation in n-GaN films as well as for GaN-based device fabrication. We report on PEC etching of n-GaN samples grown by MBE and HVPE methods in unstirred aqueous KOH solution under He-Cd laser illumination. Characterization of the etched samples was carried out using atomic force microscopy (AFM) in both cross-sectional and plan-view configurations and scanning electron microscopy (SEM). At moderate illumination densities, the SEM and AFM analyses reveal sub-100 nm scale threading vertical wires on the etched surfaces. The calculated density (∼1×10 9cm−2) is in agreement with dislocation density found by transmission electron microscopy. Using cross-sectional AFM, we find that these vertical wires are ∼1[.proportional]m high and are perpendicular to the sapphire surface. Applying a higher illumination density or an external voltage, we obtain a higher etch rate with a smooth free-feature etched surface. Some highly resistive samples that cannot be etched under normal conditions because the band bending is too small to confine the holes to the surface for them to participate in the PEC process, can be etched with the application of a voltage to the sample. In this case, the etch rate depends on both the polarity and the magnitude of the voltage applied. In an MBE-grown sample with an AlN/GaN superstructure inside, we report on high selectivity between AlN and GaN (AlN is an etch stop); the selectivity is due to the etching mechanism of the PEC process.

The structural quality of the buffer layer juxtaposed to the substrate is pivotal in attaining high quality GaN layers. In MBE deposition, low temperature, medium temperature and high temperature AlN buffer layers are at the disposal of the grower. There are quite a few reports, some discussing the benefits of high temperature buffer layers and others doing the same for low temperature buffer layers. The reports emanate from different laboratories; and due to stringent parameter control required, it is difficult to compare one type of buffer with another. To gain some insight, we undertook an investigation wherein these varieties of buffer layers were grown on nitridated sapphire substrate under similar conditions for a comparative analysis. In addition to the single buffer layers of both GaN and AlN varieties, some combinations of stacked buffer layers, including cases where these buffer layers were separated by GaN layers, were employed. Structural analysis by high resolution X-ray diffractometry and topological analysis by AFM were carried out to assess the quality of the epilayers grown on these buffers. Hall measurements at room temperature were carried out to characterize the electrical transport properties.