Search

The study of homonuclear diatomic molecules under high pressure and high temperature is a fundamental problem of condensed matter physics. In this research work, a cryogenic target (CT) was built to liquefy the gas and execute shock compression. The characteristics of the CT and the diagnostic system are explained in detail. We performed a shock compression of liquid nitrogen by using a two-stage light-gas gun at pressures up to 93 GPa (0.93 Mbar). Impactor velocities were measured with the magnetic velocimetry system, with a precision of 0.2%. The optical waveforms were recorded with the Doppler pin system, then further fast Fourier transform obtained velocity profiles in the sample. The measured velocity profiles were used to identify optical reflectance and obtain first-shock velocities, independent of the sample thickness above dissociative pressure (>30 GPa). The measured shock velocities had an uncertainty of less than 1%. First particle velocities were calculated by impedance matching, and the second velocities were directly calculated from the velocity profiles in an LiF anvil. The experimental shock Hugoniot results were observed to be consistent with those of the previous work. However, the principal Hugoniot softened above 27 GPa, and the uncertainties in the first and second-shock volumes were less than 0.7% and 3%, respectively. [ABSTRACT FROM AUTHOR]

The growing interest in hybrid devices that combine two-dimensional materials with a superconductor presents new challenges in material deposition. In this study, we demonstrate that achieving excellent superconducting properties by RF (radio frequency) sputtering does not require access to a high-end system but rather depends on the precise control of sputtering parameters and the selection of an appropriate lithographic process. We highlight the challenges and present practical solutions to deposit high-quality niobium thin films for the lithographic production of superconducting hybrid nanostructures. The influence of various deposition parameters, such as power, argon pressure, and film thickness, on the resultant superconducting characteristics can already be deduced at liquid nitrogen temperatures. Furthermore, niobium films tend to degrade when a PMMA [poly(methylmethacrylate)] resist is employed in the fabrication of superconducting nanostructures. We propose alternative and simple strategies to address this issue, which ultimately result in the restoration of the thin-film quality. [ABSTRACT FROM AUTHOR]

Microscopic jets of cryogenic substances such as liquid nitrogen are important regenerative high-density targets for high-repetition rate, high-brightness laser-plasma soft x-ray sources. When operated in vacuum such liquid jets exhibit several non-classical instabilities that negatively influence the x-ray source's spatial and temporal stability, yield, and brightness, parameters that all are important for applications such as water-window microscopy. In the present paper, we investigate liquid-nitrogen jets with a flash-illumination imaging system that allows for a quantitative stability analysis with high spatial and temporal resolution. Direct and indirect consequences of evaporation are identified as the key reasons for the observed instabilities. Operating the jets in an approximately 100 mbar ambient atmosphere counteracts the effects of evaporation and produces highly stable liquid nitrogen jets. For operation in vacuum, which is necessary for the laser plasmas, we improve the stability by introducing an external radiative heating element. The method significantly extends the distance from the nozzle that can be used for liquid-jet laser plasmas, which is of importance for high-average-power applications. Finally, we show that laser-plasma operation with the heating-element-stabilized jet shows improved short-term and long-term temporal stability in its water-window x-ray emission. [ABSTRACT FROM AUTHOR]

Studies the damage formed by 1.25 MeV, self-ions in silicon at liquid nitrogen temperature. Experimental procedure; Results of the study; Conclusion.

The generation of hydrogen clusters in gas jet is tested using the Rayleigh scattering method under liquid nitrogen temperature of 79 K. The self limiting effect of hydrogen cluster is studied and it is found that the cluster formation is greatly affected by the number of expanded molecules. The well designed liquid nitrogen cold trap ensured that the hydrogen cluster would keep maximum size for maximum 15 ms during one gas jet. The scattered light intensity exhibits a power scaling on the backing pressure ranging from 5 to 48 bar with the power value of 4.1. [ABSTRACT FROM AUTHOR]

Highly sensitive uncooled mid-wave infrared (MWIR) photodetectors have a very wide range of applications ranging from the sensor and image to communications. Traditional MWIR detection semiconductors require liquid nitrogen cooling to depress dark current, which impeded the wide applications of devices. Here, we report a metal electrode-enhanced double parallel BP/InSe/BP van der Waals heterostructure uncooled MWIR photodetector. The device exhibits ultrahigh light on/off ratio of 108 and a very low dark current of 0.16 pA. The competitive performance includes high photoresponsivity (R) of 27.8 A W−1, excellent specific detectivity (D*) of 3.8 × 1012 cm Hz1/2 W−1, very low noise equivalent power (NEP) of 3.7 × 10−16 W Hz−1/2, and fast response speed of τr = 3.5 μs and τd = 2.4 μs in the visible range. Notably, in the MWIR range, the light on/off ratio of ∼104, NEP of 3.0 × 10−13 W Hz−1/2, and D* of 4.8 × 109 cm Hz1/2 W−1 was realized. The work sheds light on developing a high-performance uncooled MWIR photodetector by designed band alignment. [ABSTRACT FROM AUTHOR]

We have investigated the formation and the morphology of carbon deposit on the cathode, after arc discharge between two graphite electrodes immersed in liquid nitrogen. We show that the deposit is mainly composed of disordered carbon structures at the bottom and at the external part of the deposit, forming like a bowl, whereas randomly oriented carbon nanotubes (CNTs) aggregated as pillars are found at the center of the deposit. The spatial distribution of the two kinds of structures in the deposit, the size and the sharpness of the CNT pillars are found to depend both on the applied voltage and the current values used for the arc discharge. A correlation between the plasma temperature field and the morphology of the deposit is reported. [ABSTRACT FROM AUTHOR]

The present article describes the energy evaluation of bubble generation and shock wave emission by laser focusing in liquid nitrogen at 78 K. By adjusting the ambient pressures to 164.9 kPa which corresponds to an overpressure, Δp, of 58.8 kPa, the threshold energy for bubble generation can be investigated. When the energy level of a laser beam at the focus exceeds an irradiance threshold, optical breakdown occurs, followed by a series of high-speed phenomena such as plasma formation, shock wave emission, and vapor bubble generation. It is found that at a threshold laser energy there is some probability of a cavitation bubble being generated whose extent tends to decrease with increasing Δp. For an incident laser energy larger than the energy capable of forming cavities with 100% probability, a cavitation bubble is inevitably generated and its maximum size tends to increase with the incident laser energy. The cavitation bubble energy E[sub B] reaches about 26% of the consumed laser energy, which is the energy substantially dissipated at the focus, fluctuating between 20% and 30% and independent of the overpressure. The shock wave energy E[sub s], is estimated by solving a nonlinear wave equation and calculated as about 35% of the consumed laser energy. Consequently, for liquid nitrogen, the conversion rate of absorbed laser energy to mechanical energy, E[sub B] + E[sub s], is calculated as 55%-65%. [ABSTRACT FROM AUTHOR]

The frequency f and amplitude B0 of applied magnetic field dependence of the loss behavior in the liquid nitrogen region is studied in high temperature superconducting slabs. The magnetothermal diffusion equations based on the power-law model are presented in this paper to estimate the effect of f and B0 on the loss. Numerical results obtained show that, generally, the loss is proportional to B03 in the nonpenetration field and to B0 in the penetration field, and the loss power is proportional to f whether the magnetic field penetrates it or not. [ABSTRACT FROM AUTHOR]

Arc discharge between two graphite rods in liquid nitrogen has been investigated in order to identify the main factors ruling the formation of carbon nanotubes (CNTs) and linear C chains. The influence of the experimental parameters on the structural properties of the produced materials was evaluated and interpreted, taking into account the existing models. We found that the electrode size and discharge current values greatly influence the structural quality of the nanotubes (e.g., presence of carbonaceous impurities, innermost tube diameter) and a proper combination of these parameters allows one to control the synthesis of CNTs and/or CNT-linear C chain hybrid systems. [ABSTRACT FROM AUTHOR]

In the present study, we compared the structure of ice formation in cryobiologically relevant solutions immersed in liquid nitrogen with solutions that were laser heated prior to immersion in a liquid-nitrogen bath. The results suggest that there is a distinct and observable difference in the type of ice formed. Furthermore, we also present data that suggest pulsed laser heating prior to immersion in liquid nitrogen enhances post-thaw survival of cells in suspension. The laser used in our experimental approach was a Q-switched Quanta-Ray DCR-3 laser (Nd:yttrium aluminum garnet laser) operating in the second harmonic at 532 nm. The laser irradiance consisted of pulses with a pulse width of 5–7 ns and a pulse energy stability of 3%. The pulse energy at a pulse repetition rate of 1 Hz was about 360 mJ and the peak power delivered was about 60 MW. The samples were held in a copper- (sheet thickness of 0.5 mm) molded rectangular box of 5 mm thick, 25 mm wide, and 15 mm long. Preliminary experiments were carried out using adipose-tissue-derived adult stem cells. The pre- and postfreeze/thaw viability of ADAS cells was assessed using membrane-excluded fluorescent dyes. ADAS cells enclosed in a copper box, laser irradiated, and exposed to liquid nitrogen had a viability of 69%±5%. Similarly, when the cells were exposed directly to liquid nitrogen (note that as before the cell suspension was enclosed and sealed in the copper box), the viability reduced significantly to 9%±10%. These results are very encouraging and demonstrate the feasibility of using lasers and liquid nitrogen to cryopreserve cells in suspension. [ABSTRACT FROM AUTHOR]

Provides information on a technique based on thermoelectric effect of semiconductors for screening the conductivity type of narrow band-gap HgCdTe materials at liquid nitrogen temperature. Temperature of the warm probe; Details on the calculation for the Seebeck coefficient; Effect of the technique.

We investigated the nature, optical properties, and decay kinetics of point defects causing large transient attenuation increase observed in silica-based optical fibers exposed to short duration and high-dose rate x-ray pulses. The transient radiation-induced attenuation (RIA) spectra of pure-silica-core (PSC), Ge-doped, F-doped, and Ge + F-doped optical fibers (OFs) were acquired after the ionizing pulse in the spectral range of [∼0.8–∼3.2] eV (∼1500–∼380 nm), from a few ms to several minutes after the pulse, at both room temperature (RT) and liquid nitrogen temperature (LNT). Comparing the fiber behavior at both temperatures better highlights the thermally unstable point defects contribution to the RIA. The transient RIA origin and decay kinetics are discussed on the basis of already-known defects absorbing in the investigated spectral range. These measurements reveal the importance of intrinsic metastable defects such as self-trapped holes (STHs), not only for PSC and F-doped fibers but also for germanosilicate optical fibers as clearly evidenced by our LNT measurements. Furthermore, our results show that fluorine co-doping seems to decrease the RIA related to the strain-assisted STHs absorption bands in both types of optical fibers. Regarding Ge-doped glasses, besides a description of the defects responsible of the RIA, highlighting the STHs' role in their transient response, we provide a clear correlation between the GeX and GeY centers' kinetics. In conclusion, the presented results improve our understanding of the transient RIA origin in the ultraviolet and visible domains. The lack of knowledge about the defects causing the RIA in the near-infrared domain will require future studies. [ABSTRACT FROM AUTHOR]

Chromium nitride nanoparticles with mean diameter distribution between 0.8 nm and 30 nm were produced by laser irradiation of a chromium target immersed in liquid nitrogen. Cr was directly converted to chromium nitride nanoparticles according to selected-area electron diffraction analyses using the transmission electron microscopy technique. Crystalline nanoparticles mostly consist of Cr 2 N , which is commonly reported together with the conversion of Cr 2 N to CrN and the mixture of chromium oxides. In addition, there is no evidence of oxidation by storage or photodegradation of the nanoparticles in isopropyl alcohol suspensions. The intensity profile of small-angle X-ray scattering indicates that the geometrical shape of the nanoparticles is not spherical but cylindrical with aspect ratio (height-to-radius) of 0.35 – 0.05. UV-Vis absorption spectroscopy reveals the presence of surface plasmon absorption at the ultraviolet region at wavelengths of 350, 372, and 397 nm. First-principles calculations of density of states, dielectric function, and optical conductivity performed within the theoretical framework of density functional theory for Cr 2 N with a hexagonal structure corroborate the formation of surface plasmons. [ABSTRACT FROM AUTHOR]

The frequency f and amplitude [B.sub.0] of applied magnetic field dependence of the loss behavior in the liquid nitrogen region is analyzed in high temperature superconducting slabs. The results have shown that the loss is proportional to [B.sub.0.sup.3] in the nonpenetration field and to [B.sub.0] in the penetration field and the loss power is proportional to f whether the magnetic field penetrates it or not.

The performance characteristics of Bi-Sr-Ca-Cu-O thick film radio frequency superconducting quantum interference devices (SQUID) in liquid nitrogen were evaluated. The results showed that the SQUID exhibited periodic oscillations up to 97 K in radio frequency. The device was successfully operated in the flux-locked-loop mode at 77K. Operation in this mode significantly improved stability and noise performance in the device.

Presents a study that examined the defects induced by boron[sup+] implantation at liquid-nitrogen temperature using transmission electron microscopy (TEM), secondary-ion-mass spectroscopy and electrical characterization of p[sup+n] diodes. Relation between implant temperature and thermal wave signal; TEM analysis for low-temperature implantation samples; Details on residual defect distribution and point defect diffusion at ion implantation.

Research describing the behavior and motion of a bubble in liquid nitrogen is presented. In particular the pressure and thermodynamic effects of cavitation are examined with respect to competition between thermal and liquid inertia parameters.

Ion implantation at -60 degrees centigrade confines defects induced by B+ implantation (35 kiloelectron volts) to shallow layers by cooling, which reduces the leakage current. Implantation at -60 degrees centigrade, due to low leakage current, is ideal for design of high-current implanters.

Epitaxially grown superconductor/dielectric/superconductor trilayers have the potential to form high-performance superconducting quantum devices and may even allow scalable superconducting quantum computing with low-surface-area qubits such as the merged-element transmon. In this work, we measure the power-independent loss and two-level-state (TLS) loss of epitaxial, wafer-bonded, and substrate-removed Al/GaAs/Al trilayers by measuring lumped element superconducting microwave resonators at millikelvin temperatures and down to single-photon powers. The power-independent loss of the device is (4.8 ± 0.1) × 10 − 5 , and the resonator-induced intrinsic TLS loss is (6.4 ± 0.2) × 10 − 5 . Dielectric loss extraction is used to determine a lower bound of the intrinsic TLS loss of the trilayer of 7.2 × 10 − 5 . The unusually high power-independent loss is attributed to GaAs's intrinsic piezoelectricity. [ABSTRACT FROM AUTHOR]

The structural stability of AlPO4-5 zeolite (AFI) has been studied as a function of pressure up to 34.4 GPa in a diamond anvil cell by using synchrotron x-ray diffraction. It is found that the AFI structural stability can be enhanced significantly when a mixture of silicone oil and liquid nitrogen is used as pressure transmission medium (PTM). In this case, the crystalline-to-amorphous transition pressure for AFI increased to be 15.9 GPa, much higher than that of 8.5 GPa observed in the experiment by using silicone oil as PTM. We found that the average distance of the interplanar crystal spacing along to most planes was expanded obviously when liquid nitrogen is used as one component in the PTM. The presence of liquid nitrogen in the PTM also affects the structural evolution of the AFI channel under pressure. The results demonstrated that nitrogen molecules can be inserted into the channels of porous zeolite AFI single crystals, exerting a supporting effect against the structure collapse of AFI and thus improving their structural stability. [ABSTRACT FROM AUTHOR]

Variable range hopping (VRH) conduction of Mott type for a constant and non-vanishing density of states at the Fermi level is observed over a wide range of temperature between 45 and 210K in the ordered defect compound CuIn3Te5 (CIT135). For this type of electrical conduction at a very high temperature, not reported before in elemental, II-VI, and I-III-VI2 compound semiconductors, we employed three different methods to analyze the data and to confirm this behavior. The occurrence of VRH at very high temperatures is explained as due to the presence of the electrically inactive (InCu+2 + VCu-1)) donor-acceptor defect pairs in CIT135. This defect-pair partially annihilates the shallow acceptor defect state Cu vacancy, which is responsible for the activated electrical conductivity observed in p-type ternary I-III-VI2 chalcopyrite compounds in the temperature range of liquid nitrogen. In such conditions, the only acceptor level available for electrical conduction in CIT135 is a deep acceptor state whose activation energy is about 200meV and cannot be activated below about 200K. Hence, the VRH conduction mechanism dominates the electrical properties of this material up to about 200K. The study of the temperature and magnetic field dependence of the magnetoresistance (MR) up to 27 T is made by taking into consideration different theoretical models. To explain the negative MR at lower fields, the theory based on quantum interference is used. At higher magnetic fields, the MR becomes positive and is explained with the model based on the shrinkage of the wave function. [ABSTRACT FROM AUTHOR]

The present investigation reports the first experimental evidence of ferromagnetism in the cryomilled pure α-Mn nano-rods. Cryomilling of Mn powder at liquid nitrogen temperature leads to the formation of long nanorods of a-Mn. The detailed electron microscopy reveals that the nanorods grow along [112] directions with surfaces bounded by {110} planes of FCC α-Mn. The magnetic measurements indicate ferromagnetic hysteresis loops, suggesting typical ferromagnetic order. The ab-initio density functional theory calculations indicate that the ferromagnetic response originates from the under coordinated surface atoms. [ABSTRACT FROM AUTHOR]

Examines the glow characteristics associated with stressed insulator-bridged vacuum gaps and their relation to prebreakdown currents. Use of a rotary-pump-backed oil diffusion pump with a liquid-nitrogen trap; Light-emission characteristics of various insulating materials bridging the vacuum gap; Correlation between luminescence of many crystals and the presence of a small concentration of impurities in the crystal.

Investigates the results of several analyses conducted on optical spectra to establish a Stark splitting scheme for lower-energy multiplets of Tb3+ ions. Calculation of an induced emission cross section of ions at liquid-nitrogen temperature (LNT) for TbAlO3; Methodology used to conduct the experiments; Information on the Stark splitting scheme; Findings of the experiments.

Presents information on a study which analyzed the improvement of operating temperature of a surface step-edge microbridge Josephson junction millimeter-wave detector up to near the liquid nitrogen temperature. Current-voltage characteristics; Block diagram used in the millimeter-wave video detection; Harmonic mixing detection.

Transport measurements revealed flux pinning properties and vortex phases in SmBa2Cu3O7-δ (Sm123) superconducting films with BaHfO3 nano-rods on LaAlO3 substrates. The films have large matching fields BΦ up to 9.9 T, nano-rod diameters of ∼6 nm, and a slight Tc degradation with Tc∼91.8K by using the low temperature growth technique. According to the transport results, a small critical exponent ∼4 indicates the presence of a Bose-glass phase in the films. Double peaks of the flux pinning force density are unexpectedly observed at high temperatures over 80 K, which is accompanied by steep drops of the crossover magnetic fields between the single vortex pinning and the collective pinning states. The drops are explained by the delocalization of the vortex where the vortex is pinned by many nano-rods in the single vortex pinning state. From the viewpoint of the vortex delocalization, we conclude that BΦ should be less than 11 T for applications at liquid nitrogen temperature. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the aging and field effect of discontinuous copper films deposited on glass substrates. Problem of instability in the physical properties of discontinuous films; Details of the study; Description of the mobility of islands on the substrate surface.

Presents a study that investigated interface state density of silicon metal-oxide-semiconductor transistors. Analysis of the subthreshold slope of the transistor; Measurement of the dynamic transconductance; Determination of the static transfer characteristics of the transistor.

Hard magnetic Sm2Fe17Nx nanoflakes were prepared by surfactant assisted ball milling (SABM) at low temperature using liquid nitrogen cooling (surfactant assisted cryomilling). 2-methyl pentane was used as a milling medium and oleylamine as a surfactant. The morphology, structure, and magnetic properties of Sm2Fe17Nx were investigated using scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometer, respectively. By comparing Sm2Fe17Nx nanoflakes produced by SABM at low temperature and at room temperature, we found that the former has many interesting features: more homogeneous morphology, smaller size, especially markedly increased remanent magnetization (Mr), saturation magnetization (Ms), and remanent magnetization ratio (Mr/Ms). These Sm2Fe17Nx nanoflakes have great potential to be used for preparing high performance bonded permanent magnets. [ABSTRACT FROM AUTHOR]

Nickel microspheres were produced by the spark erosion technique under both liquid nitrogen and water conditions. Density measurements and Scanning electron microscope analysis revealed that a significant portion of the Ni particles produced under the liquid nitrogen conditions are hollow spheres with a density of 6.67(4)g/cm3 while the particles produced in water are primarily solid spheres with a density of 8.40(1)g/cm3, close to the bulk nickel value of 8.90 g/cm3. Nickel/polymer composites incorporating the hollow and solid nickel microspheres were manufactured with volume fractions of 25% and 36%, respectively. The hollow and solid nickel composites exhibited saturation magnetostrictions of -24 and -28 ppm, respectively. In addition, small quantities of Terfenol-D (Tb0.3Dy0.7Fe2) were spark eroded under liquid argon conditions with ∼10% by volume of the spark eroded particles being solid microspheres. Calculations indicate that aligned composites that incorporate these Terfenol-D microspheres could reach a strain value of 2000 ppm. [ABSTRACT FROM AUTHOR]

Comprehensive study of the bulk generation-recombination mechanisms and the carrier lifetime in long wavelength and mid wavelength infrared indium-doped as well as arsenic- and mercury vacancies-doped HgCdTe ternary alloys at liquid nitrogen temperature has been done. The excess minority carrier lifetime in HgCdTe materials has been calculated by solving the set of non-linear transport equations under conditions of small deviation from equilibrium. The results of numerical calculations of the carrier lifetime determined by the Auger 1, Auger 7, and Shockley-Read-Hall mechanisms related to mercury vacancies have been compared with experimental data available in the literature. We re-examine the carrier lifetime, including the impact of the electrical screening on Coulomb interaction of carriers in the Auger process to explain certain inconsistency between theoretical prediction and experimental data especially in highly doped p-type HgCdTe material. Moreover, the marginal significance of the interband radiative recombination has been indicated. [ABSTRACT FROM AUTHOR]

We have used a photothermal technique, in which chopped light heats the front surface of a small (∼1mm2) sample and the chopping frequency dependence of thermal radiation from the back surface is measured with a liquid-nitrogen-cooled infrared detector. In our system, the sample is placed directly in front of the detector within its dewar. Because the detector is also sensitive to some of the incident light, which leaks around or through the sample, measurements are made for the detector signal that is in quadrature with the chopped light. Results are presented for layered crystals of semiconducting 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pn) and for papers of cellulose nanofibrils coated with semiconducting poly(3,4-ethylene-dioxythiophene):poly (styrene-sulfonate) (NFC-PEDOT). For NFC-PEDOT, we have found that the transverse diffusivity, smaller than the in-plane value, varies inversely with thickness, suggesting that texturing of the papers varies with thickness. For TIPS-pn, we have found that the interlayer diffusivity is an order of magnitude larger than the in-plane value, consistent with previous estimates, suggesting that low-frequency optical phonons, presumably associated with librations in the TIPS side groups, carry most of the heat. [ABSTRACT FROM AUTHOR]

The growth of Co precipitates in dilute AgCo alloys under 1.8 MeV Kr ion irradiation was investigated by a combination of x-ray diffraction and magnetic measurements. For alloys with Co compositions ranging from 8 to 20 at. % precipitates grow in volume approximately linearly with dose, with no indication of saturation. The variation of temperature from liquid nitrogen temperature to 300 °C had little effect on the growth behavior. Precipitation kinetics in these alloys is very different from that in dilute CuCo alloys, which showed steady state precipitate sizes at temperatures below 350 °C. We attribute the different behavior to the low solubility of Co in liquid Ag (in contrast to its complete solubility in liquid Cu). The quantitative results suggest that the growth of Co precipitates is derived from particle aggregation rather than Ostwald ripening. [ABSTRACT FROM AUTHOR]

We have presented herein the results of microstructure, surface magnetic domains (SMDs), and giant magneto-impedance (GMI) effect of melt-extracted Co68.15Fe4.35Si12.25B11.25Nb2Cu2 amorphous wires for the first time employed by using a cryogenic Joule annealing (CJA) technique with large DC current amplitude. Compared with the conventional JA method, experimental results indicate that the maximum GMI ratio [ΔZ/Z0]max achieves up to 425% at 8.1MHz with monotonic increase of the axial magnetic field Hex up to 6.5 Oe for 300mA (equal to around 1.06×106A/dm–2) CJA-ed wire, which is about 75% larger than the [ΔZ/Z0]max for the 100mA (nearly 3.53×105A/dm–2) JA-ed microwires. The remarkable features of large and linearly sensitive response field (2.5~6.5 Oe) and the sensitivity of 99.4%/Oe with higher GMI ratio simultaneously make the CJA tailored melt-extracted microwires promising candidate materials for miniaturized GMI sensors. Another interesting result of GMI profiles of 200mA (appropriately equal to 7.07×105A/dm–2) CJA-ed wire show a linear response to Hex (ranging from 10 to 80 Oe or more), this behavior of GMI curves can be explored to fabricate bi-sensor. Large response field proves to originate from the intensive coupling between the radial stress field and the circumferential magnetic field during CJA process. The effect of outer-shell microstructure and complex SMD for 300mA CJA-ed microwire is attributed to the fact that liquid nitrogen hinders the evolution of circumferential domain structure to some extent and protects the amorphous structure in the shell region. [ABSTRACT FROM AUTHOR]

The photoluminescence (PL) of ZnO is shown to be dependent on the excitation intensity (EI) of the laser, and the substantial shift observed in the band to band transition is attributed to the heating effect. In order to understand this phenomenon in detail, we investigate the EI dependent PL of various ZnO samples systematically from liquid nitrogen (LN) to room temperature by varying the laser power. Some of the samples exhibit substantial red shift in the band to band transition with increasing EI even in LN environment, negligible effect is observed for others. Hence, our results strongly suggest that the EI dependent PL is not a characteristic of all ZnO samples. This indicates that laser-induced heating effect is not the dominant factor that governs the shifts in the PL spectra. Rather, the defect level excitation accounts for such observation. [ABSTRACT FROM AUTHOR]

Powders of Ni-Mn-Ga ferromagnetic shape memory alloy (FSMA) were produced by spark erosion. Powders quenched in liquid nitrogen are primarily hollow spherical particles, whereas those quenched in liquid argon are mostly solid spheres. Electron microscopy observations of powders as-sparked in nitrogen show highly disordered nanocrystalline grains with an average size of less than 100 nm whereas those sparked in liquid argon display extensive crystallinity. Magnetic measurements indicate that the powders do not become fully ferromagnetic until after annealing at 973 K for 5 h. Investigations of annealed powders using differential scanning calorimetry reveal thermoelastic martensitic transition behavior. The annealed powders have a microtwinned martensite with many large grains showing a five-layer period modulation. These Ni-Mn-Ga powders should be suitable for the development of magnetic-field-driven FSMA powder/polymer microcomposites. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]