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Current fabrication of nanomaterials is facing the following two challenges: high selectivity toward specific chemical compositions or morphologies and their scalable production. This usually requires new extreme fabrication conditions beyond the conventional approaches. Thermal plasma jets are flows of partially ionized gases where gas and electron temperatures reach their equilibrium state around 10 000 K, and thus provide high fluxes of energy and chemically active species including electrons and ions with their strong spatial gradients. Such extreme environments can trigger reactions that are not thermodynamically favorable or require high activation barriers, leading to the production of materials with exotic chemical compositions or structures. Since their first operation in 1960, thermal plasma jets were soon recognized as a unique and effective medium for material transformation such as melting, vaporization, and pyrolysis and recently have also found their important applications in nanomaterial fabrication. In this Perspective, we briefly review the latest progress in the thermal plasma jet-assisted fabrication of nanomaterials from nanoparticles to low-dimensional nanostructures. A special focus is made on the advantages of the thermal plasma jet technology in nanostructure fabrication, discussing plasma properties responsible for the nanomaterial growth with high throughput, high purity, anisotropy, desired compositions, or narrow size distributions. This Perspective closes with an outlook of challenges and opportunities for further advancement in this emerging field. [ABSTRACT FROM AUTHOR]

The output power of InGaN multiple-quantum-well laser diodes (LDs) emitting at 405 nm wavelength is compared for several Al composition in the AlGaN n-cladding layer. The Al composition has been varied from 2% to 6% to study the effect of n-cladding refractive index on threshold current and slope efficiency of the LDs. As the Al composition in the AlGaN n-cladding layer increases, both threshold current and slope efficiency decrease. This behavior can be explained by the change in optical field distribution with refractive index of the AlGaN n-cladding layer. It is found that the Al composition of ¿4% would be advantageous for achieving more than 100 mW output power and high level of catastrophic optical damage. [ABSTRACT FROM AUTHOR]

The effects of InGaAs/GaNAs barrier combinations were investigated in the metal organic vapor phase epitaxy grown GaInNAs quantum wells (QWs). Significant improvement was made in the optical performance of the 1.3 μm range with the proposed structures. Structural investigation linked with the optical properties reveals that a thin InGaAs layer, placed between GaInNAs QWs and GaNAs layers, plays a role in redistributing the nitrogen within the QWs while maintaining a sharp interface. The amount of diffused nitrogen is proportional to the strain residing in the InGaAs layer, which explains the tendency of blueshift with the increase in GaNAs thickness. [ABSTRACT FROM AUTHOR]

A magnetization switching method for magnetic random access memory (MRAM), recently proposed by Savtchenko et al. [U.S. Patent No. 6,545,906 (2003)], is known to have an important advantage of a wide window for bit writing over the conventional method based on the asteroid curve, but it has a serious problem of high switching fields. In an effort to solve this problem, the effects of the thickness asymmetry and antiferromagnetic exchange coupling of the synthetic antiferromagnetic free-layer structure on the switching field have been investigated by micromagnetic computer simulation. At conditions relevant to high-density MRAM, magnetization switching in the direct write mode occurs at reasonably low values of word- and bit-line fields (below 100 Oe), combined with a substantially wide window for bit writing. A much wider window is observed in the toggle mode, but the required switching fields are too high, being over 150 Oe. [ABSTRACT FROM AUTHOR]

Oxidation of an AlOx insulating barrier in a magnetic tunneling junction (MTJ) was carried out by a tilted-plasma oxidation method. It was found that the tilted-plasma oxidation induced a gradual change in the extent of oxidation of an insulating layer, which consequently led to a gradual change in the tunneling magnetoresistance (TMR) and specific junction resistance (RA) of the MTJ. We found a linear relation in the TMR versus RA curve with positive and negative slopes for less- and overoxidized junctions, respectively, and a parabolic relation for optimally oxidized junctions. The crossover in the TMR versus RA curves provides an effective and useful way to optimize (and monitor) the oxidation condition of a tunneling barrier in MTJs especially of a tunneling barrier less than 10 Å thick. The tunneling junctions were also investigated after thermal annealing at various temperatures. The observations after thermal annealing were found to be consistent with transmission electrons microscopy images and a scenario of the partial formation of an additional ultrathin tunneling barrier at the top surface of the bottom magnetic layer. [ABSTRACT FROM AUTHOR]

The voltage dependence of magnetoresistance (MR) and the low-frequency voltage fluctuation were studied in magnetic tunnel junctions with an AlN or an Al[sub 2]O[sub 3] barrier formed by plasma nitridation or oxidation. The junctions consist of free and pinned NiFe layers by a FeMn antiferromagnetic layer. For the Al[sub 2]O[sub 3] junction, the variation of half-reduction voltage of MR is about 50 mV from 401.3 mV in maximum to 351.4 mV in minimum depending upon the oxidation time. For the AlN junction, the less nitrided junction with a nitridation time of 120 s shows the higher-half-reduction voltage by about 100 mV than for optimally nitrided or oxidized ones. From the low-frequency voltage noise data, the less nitrided AlN junction shows larger 1/f noise magnitude compared with other junctions with an optimal condition, implying more defect states in the barrier due to unnitrided Al metals. In order to investigate the influence of nitrogen on ferromagnetic layer, another junction with an Al[sub 2]O[sub 3] barrier was made after the pinned NiFe layer was exposed to N[sub 2] plasma for 10 s. This junction reveals a lower MR and worse bias voltage dependence than any junctions studied here. The voltage dependence of MR, therefore, is likely influenced by the interface state rather than the defects in the barrier, although the two factors play an important role in determining MR. [ABSTRACT FROM AUTHOR]

Small arrays of microcavity plasma devices have a two stage structure comprising multilayer stacks of nanostructure Al2O3 grown on Al foil with cylindrical microcavities produce intense ultraviolet and visible emission when operated in Ar/3% N2 gas mixtures or Ne and excited by sinusoidal voltage wave form. Two or more coaxial cavities of differing diameters provide a convenient means for confining a microplasma to progressively smaller volumes as the power disposition is increased.

Biomolecule ferritin is a subject for the study of the magnetism at nanoscale level and in biological systems. This study is aimed at the investigation on the effect of biomineralization process in ferritin protein cage on the magnetic properties, mainly on the uncompensated spins of ferritin core.

Small arrays (3×3→10×10) of microcavity plasma devices, having a two-stage structure comprising multilayer stacks of nanostructured Al2O3 grown on Al foil with cylindrical microcavities 100–300 μm in diameter, produce intense ultraviolet (UV) and visible emission when operated in Ar/3% N2 gas mixtures or Ne and excited by a sinusoidal ac voltage wave form. Near-UV (300–400 nm) intensities emitted into a solid angle of ∼10-2 sr above 30 mW per cm2 of radiating area are measured for Ar/N2 gas mixture pressures of 400–800 Torr, an excitation frequency of 15 kHz, and an average current >=20 mA (rms). Two or more conjoined cylindrical microcavities of differing diameters allow for the confinement of the plasma to progressively smaller volumes as the power deposited is increased (thereby decreasing the Debye length and the spatial extent of the cathode fall region) and provides a convenient tool with which the luminosity of an array can be modulated. The transition of a microplasma from confinement in a 200-μm-diam cavity into an adjacent 100-μm-diam microcavity is accompanied by an order-of-magnitude increase in the luminance of Ne plasmas in a 3×3 array as the rms current is increased by ∼1 mA. [ABSTRACT FROM AUTHOR]

The magnetization behaviors have been measured for amorphous Fe90-xMnxZr10 (x=8 and 10) alloys. The Curie temperature is decreased from 210 K to 185 K with increasing Mn concentration (x=8 to x=10). The magnetization measurements were conducted at temperatures above the Curie temperature in the paramagnetic region. In both samples, the magnetic properties showed superparamagnetic behavior above Tc where the mean magnetic moment of the superparamagnetic spin clusters decreased with increasing temperature. A large magnetic entropy change ΔSM, which is calculated from H vs M curves associated with the ferromagnetic-paramagnetic transitions in amorphous, has been observed. The maximum ΔSM of Fe82Mn8Zr10 is 2.87 J /kg K at 210 K for an applied field of 5 T. The peak of magnetic entropy change was observed at the Curie temperature. The ΔSM decreases with increasing Mn concentration to 2.33 J /kg K. [ABSTRACT FROM AUTHOR]

Human ferritin homopolymers with H or L subunits (rHF and rLF) were genetically engineered in E coli. Apoferritins were then reconstituted with 2000 Fe atoms. A big difference was observed in the rates of iron uptake, whereas the mean core size was similar in rHF and rLF. Magnetization of the recombinant human ferritins were measured as functions of temperature and field. The blocking temperature TB(H) at low fields is considerably higher in rLF than in rHF. From the fit of M(H) data to a modified Langevin function: M(H)=M0L(μpH/kBT)+χaH, the effective magnetic moment μp is found to be much larger in rLF than in rHF. Experimental data demonstrate that the magnetic properties, in particular, the uncompensated spins of ferritin core are related to the biomineralization process in ferritins. [ABSTRACT FROM AUTHOR]

The measurements of voltage fluctuations at room temperature are performed for magnetic tunnel junction, patterned by photolithography to have 20 × 10 µm² in junction area. The observed noise power follows 1/f behavior for the whole applied magnetic field (H) range (-30 Oe≤H ≤30 Oe) and shows strong field dependence. The sharp increase in noise power spectral density is observed near a transition region from antiparallel to parallel magnetic state in two electrodes during field ramping down. In addition, the reduction of noise power density is accompanied by the reduction of magnetoresistance ratio after thermal annealing at 300°C for 700 s in the same junction. It is conjectured that the observed reduction of the noise level in our junction is due mainly to magnetic origin, such as thermally activated domain wall motion, rather than electrical origin. [ABSTRACT FROM AUTHOR]

Provides information on a study which investigated the effect of cooling rate, followed immediately after the isothermal annealing, on the magnetic properties of a melt-spun iron compound alloy. Methods; Results; Discussion.

Presents a study that obtained a rapid quenched (RQ) palladium-based borocarbides with large fractions of the superconducting phase. Description of RQ technique; Composition regimes for superconductivity in the Y-Pd-B-C system; Thermal stability of the metastable phase in rapid quenched YPd[sub2]B[sub2]C.