ZnO:Co diluted magnetic semiconductor or hybrid nanostructure for spintronics?

We have studied the influence of intrinsic and extrinsic defects in the magnetic and electrical transport properties of Co-doped ZnO thin films. X-ray absorption measurements show that Co substitute Zn in the ZnO structure and it is in the 2+ oxidation state. Magnetization (M) measurements show that doped samples are mainly paramagnetic. From M vs. H loops measured at 5 K we found that the values of the orbital L and spin S numbers are between 1 and 1.3 for L and S = 3/2, in agreement with the representative values for isolated Co 2+. The obtained negative values of the Curie–Weiss temperatures indicate the existence of antiferromagnetic interactions between transition metal atoms.     

Nanostructure and magnetic properties of the MnZnO system, a room temperature magnetic semiconductor?

The magnetic properties of the system MnZnO prepared by conventional ceramic procedures using ZnO and MnO(2) starting powders are studied and related to the nanostructure. Thermal treatment at 500?°C produces a ferromagnetic phase, although this temperature is not high enough to promote proper sintering; thus the thermally treated compact shows brittle characteristics of unreacted and poorly densified ceramic samples. Scanning electron microscopy and x-ray analysis reveal the appearance of a new phase, most probably related to the diffusion of Zn into MnO(2) oxide nanocrystals. The magnetic properties deviate considerably from what would be expected of an unreacted mixture of ZnO (diamagnetic) and MnO(2) particles (paramagnetic above 100?K and anti-ferromagnetic below that temperature), exhibiting a ferromagnetic like behaviour from 5 to 300?K and beyond mixed with a paramagnetic component. The ferromagnetic phase seems to be originated by diffusion at the nanoscale of Zn into MnO(2) grains. The Curie temperature of the ferromagnetic phase, once the paramagnetic component has been subtracted from the hysteresis loops, is measured to be 450?K. EPR resonance experiments from 100 to 600?K confirm a ferromagnetic to paramagnetic like transition above room temperature for these materials.     

Synthesis,growth mechanism,photoluminescence and field emission properties of metal–semiconductor Zn–ZnO core–shell microcactuses

Metal–semiconductor Zn–ZnO core–shell microcactuses have been synthesized on Si substrate by simple thermal evaporation and condensation route using NH₃ as carrier gas at 600 °C under ambient pressure. Microcactuses with average size of 65–75 μm are composed of hollow microspheres with high density single crystalline ZnO rods. The structure, composition and morphology of the product were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). A vapor–liquid–solid (VLS) based growth mechanism was proposed for the formation of Zn–ZnO core–shell microcactuses. Room temperature photoluminescence (PL) investigations revealed a strong and broad blue emission band at 441 nm associated with a weak ultraviolet (UV) peak at 374 nm. This blue emission (BE) is different from usually reported green/yellow-green emission from Zn–ZnO or ZnO structures. The field emission (FE) measurements exhibited moderate values of turn-on and threshold fields compared with reported large field emissions for other materials. These studies indicate the promise of Zn–ZnO core–shell microcactuses for the applications in UV-blue light display and field emission microelectronic devices.     

A Ferromagnetic Shimming Method for NMR/MRI Magnets Adopting Two Consecutive Optimization Techniques: Linear?Programming and Evolution Strategy

Shimming is very important for nuclear magnetic resonance (NMR) magnets because image resolution is highly dependent on the homogeneity of the magnetic field. There are two types of shimming: active and passive. Active shimming is done using coils with adjustable current. Passive shimming involves pieces of steel with good magnetic qualities. The steel pieces are placed near a superconducting magnet. They are magnetized and produce their own magnetic field. Additional magnetic fields (produced by coils or steel) add to the original magnetic field of the superconducting magnet in such a way that the total field becomes more homogeneous. In this paper, we developed a passive shimming method adopting consecutive optimization techniques, i.e., linear programming (LP) and evolution strategy (ES). The LP is relatively fast and mostly guarantees a global minimum for a linear problem, whereas the ES is easy to formulate and can digitize design variables. So we suggested an optimization method combining both the LP and the ES consecutively for passive shimming of NMR magnets.     

Graphite → diamond transition under high pressure: A kinetics approach

The graphite diamond transition in the diamond stability field can be either direct or solvent-assisted. The direct transition may proceed by spreading a puckered basal plane of graphite in the direction perpendicular to it. The kinetics of such a transition may be approximated by the growth of a two-dimensional nucleus. The threshold temperature of the transition appears to depend on the degree of perfection of the original graphite. Hence, the more perfect the graphite is, the lower temperature it will transform into diamond. The solvent-assisted transition normally proceeds by rapid nucleation followed by growth of these nuclei. The kinetic model for continuous nucleation may be applied to the early stage of such transition. The activation energies for the transition can then be calculated. It is found that these activation energies seem to vary inversely with the solubility of carbon in these solvents at ambient pressure. Hence, the higher the amount of carbon a solvent dissolves at ambient pressure, the more effective it can be as a catalyst for the graphite diamond transition under high pressure.     

Measurements of the A ⇄ B transition in a magnetic field for superfluid3He near the polycritical point

Measurements of both AB and BA transitions have been made as a function of magnetic field up to 100 G at temperatures and pressures close to the polycritical point (PCP). Forms for the specific heat differenceC _A–C _B=C ₀ (P)–(P)(T _c –T)/T _c and for the magnetization differenceM _A–M _B=H(T _c –T)/T _c fit the data satisfactorily except very nearT _c , where some other mechanism, thought to be a free energy difference due to residual heat flows, tends to stabilize the A phase. The pressure of the PCP, taken to be that at whichC ₀ =0, is found to be 21.22±0.02 bar.Work supported by the U.S. Energy Research and Development Administration under contract number E(04-3)-34, P.A. 143.     

Cell death induced by metal ions: necrosis or apoptosis?

We have evaluated if the cytotoxic effects of metals released from implants are due to necrosis or apoptosis. Peripheral blood mononuclear cells were exposed to different concentrations of chromium, nickel and cobalt extracts and the characteristics of both apoptosis and necrosis were evaluated by flow-cytometry at different culture endpoints. In order to define the prevalence of apoptosis or necrosis, the ratio cell death/apoptosis was calculated. A ratio of 1 means the prevalence of apoptotic events; a ratio >1 indicates the acute toxicity of the tested substance (necrosis). The extracts of chromium, cobalt and nickel had a cytotoxic effect on the mononuclear cells; high concentrations of cobalt and nickel produced cell necrosis, whereas by lowering the extract concentration apoptotic phenomena were observed. High chromium concentrations can induce cell death by apoptosis. Our data suggest that when large amounts of nickel and cobalt are released from implanted metal devices, necrosis is produced and consequently a strong inflammatory tissue reaction is likely to occur. The release of either chromium or limited amounts of nickel and cobalt induces toxicity characterized by apoptotic phenomena, which allows an adaptation of the tissue to the implant.     

Cell response to magnetic glyconanoparticles: does the carbohydrate matter?

Magnetic nanoparticles have been used in therapeutic and diagnostic approaches in biomedicine for many years. For these applications, it is very important to investigate the nanoparticle-cell interactions. In this study we report a simple method for the preparation of gold-iron nanoparticles protected and functionalized with biologically relevant saccharides (maltose, lactose, and glucose). The nanoparticles were subsequently tested in vitro with a human fibroblast cell line to determine biocompatibility, and the cell-particle interactions, using fluorescence and scanning electron microscopies. Different cellular responses were obtained for each type of glyconanoparticle, demonstrating that the cells can recognize the saccharides on the nanoparticles.     

Synthesis and characterization of maghemite iron oxide (γ-Fe2O3) nanofibers: novel semiconductor with magnetic feature

Among the reported nanostructural shapes, nanofibers have special interest due to the long axial ratio which has a distinct impact on many chemical and physical properties. In this study, synthesis of the desirable maghemite iron oxide (γ-Fe₂O₃) nanofibers is introduced. Calcination of electrospun mats composed of ferrous acetate and poly(vinyl alcohol) in argon atmosphere resulted in producing maghemite nanofibers. Detailed characterization affirmed that the obtained γ-Fe₂O₃ nanofibers are free of other iron oxides. Due to the axial ratio impact, the synthesized nanofibers which have an average diameter of ~70 nm do have magnetic properties resemble γ-Fe₂O₃ nanoparticles having an average diameter of ~5 nm. Accordingly, the produced nanofibers are considerable candidate for biomagnetic separation of the biomaterials. The prepared γ-Fe₂O₃ nanofibers can be easily handled as they were obtained in the form of strong mats. Electrical properties study indicated that the introduced nanofibers behave as a semiconducting material. Moreover, the synthesized γ-Fe₂O₃ nanofibers have band gap energy of ~4.2 eV. Based on the simplicity, effectiveness, high-yield, and low-cost features of the utilized preparation process and the studied physiochemical properties of the obtained product, the synthesized γ-Fe₂O₃ nanofibers might have considerable application fields.     

A comparison of Ga:ZnO and Ga:ZnO/Ag/Ga:ZnO source/drain electrodes for In–Ga–Zn–O thin film transistors

We compared the characteristics of single Ga:ZnO (GZO) and GZO/Ag/GZO multilayer electrodes for source/drain (S/D) contacts in amorphous In–Ga–Zn–O (a-IGZO)-based thin film transistors (TFTs). Due to the existence of a Ag metallic layer between the GZO layers, the GZO/Ag/GZO multilayer electrode exhibited low sheet resistance (3.95 ohm/sq.) and resistivity (3.32 × 10^?5 ohm-cm). The saturation mobility (10.2 cm² V^?1 s^?1) of the a-IGZO TFT with GZO/Ag/GZO S/D electrodes is much higher than that attained for the a-IGZO TFT with single GZO S/D electrodes (0.7 cm² V^?1 s^?1) due to the lower resistivity of the GZO/Ag/GZO multilayer S/D electrode. Furthermore, it is expected that the high transparency of the GZO/Ag/GZO multilayer will allow for the possible realization of fully transparent a-IGZO TFTs.     

Ultraviolet Resistance and Antimicrobial Properties of ZnO in the Polypropylene Materials:A Review

ZnO is a multifunctional material with UV-blocking,antimicrobial,photo-catalytic activity and selfcleaning properties.The application of ZnO has become an interesting subject both in science and industries in the polymer materials.A great number of investigation indicated that introduction of ZnO can improve ultraviolet resistance and endow antimicrobial properties of polypropylene(PP) materials to broaden the application range and prolong the usage life of polypropylene materials.This mini-review contains examples of recent research advances on ultraviolet resistance and antimicrobial properties of ZnO in the filled polypropylene materials.It is found that ultraviolet resistance and antimicrobial properties of ZnO supported on the surface of other inorganic particles are higher than those of nanoand micro-ZnO particles,which may inspire further developments of filled PP and its copolymer materials with high ultraviolet resistance and antimicrobial properties.