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Presents a study that grew high-purity galliumarsenic (GaAs) on A[sub1] and B orientations by molecular-beam epitaxy. Type of growth in undoped GaAs; Liquid-nitrogen electron mobility of B orientation; Results of the low-temperature photoluminescence.

We investigate the limit of weak infrared photodetection based on a systematic analysis of three main noise mechanisms, and point out the principles to achieve the ultimate performance. Two key issues should be addressed to realize ultra-sensitive infrared photodetection: suppression of background radiation, selection and optimization of photodetectors. We quantitatively studied the dependence of ultimate performance on the background temperature and emissivity. It is revealed that the background limited infrared performance detectivity for mid-infrared photodetection can be increased from the range of 1010 to 1011 cmHz1/2/W to 1015 cmHz1/2/W or even higher values, when the background radiation temperature decreases from the ambient to liquid nitrogen temperature. Furthermore, we investigate the feasibility of photoconductive infrared photodetectors for ultra-sensitive photodetection. Our simulations shows that ideal quantum well infrared photodetectors (QWIPs) can reach background limited infrared performance at feasible operation temperatures facing even very weak background radiation. For specific and quantitative analyses, QWIPs are used as the examples. However, the conclusions apply to a broader range of cases. [ABSTRACT FROM AUTHOR]

The complex permittivity of conducting polyaniline and zeolite-polyaniline blends was measured in the frequency range of 10-2–2×106 Hz from room temperature to liquid nitrogen temperature. A loss peak is detected for 25, 35, and 50 wt % zeolite blends. Its position in the frequency domain, activation energy, and intensity is a function of composition. The experimental results are interpreted through the competing multiple role of zeolite: as being less conducting than polyaniline, it impedes the electric charge flow by dividing large conducting polyaniline regions into smaller pieces, subsequently provides short-range pathways, and, moreover, enriches the blend in interfaces separating zeolite from polyaniline. [ABSTRACT FROM AUTHOR]

Emerging interest in utilizing the transverse coherence properties of thermal energy atomic and molecular beams motivates the development of ionization detectors with near unit detection efficiency and adequate spatial resolution to resolve interference fringes of submicron dimension. We demonstrate that a field ionization tip coupled to a charged particle detector meets these requirements. We have systematically studied the current-voltage relationship for field ionization of helium using tungsten tips in diffuse gas and in a supersonic helium beam. For all 16 tips used in this study, the dependence of ion current on voltage for tips of fixed radius was found to differ from that for tips held at constant surface electric field. A scaling analysis is presented to explain this difference. Ion current increased on average to the 2.8 power of voltage for a tip at fixed field and approximately fifth power of voltage for fixed radius for a liquid nitrogen cooled tip in room temperature helium gas. For the helium beam, ion current increased as 2.2 power of voltage with constant surface field. The capture region of the tips was found to be up to 0.1 μm2 for diffuse gas and 0.02 μm2 in the beam. Velocity dependence and orientation of tip to beam were also studied. [ABSTRACT FROM AUTHOR]

The structural dependence of the magnetic, transport, optical, and magneto-optical (MO) properties of Cu2MnAl Heusler alloy (HA) thin-film samples was investigated. Disordered thin films of Cu2MnAl HA fabricated by vapor-quenching deposition onto substrates cooled by liquid nitrogen behave as highly resistive Pauli paramagnets down to 5 K, while an annealing of the disordered films at 580 K for 1 h restores the L21-type ordered structure, as well as the ferromagnetic order and other physical properties typical for the ordered Cu2MnAl HA film. The film deposition onto substrates held at T>=690 K leads to the formation of a multiphase crystalline structure. A significant influence of the structural disorder on the optical and MO properties of Cu2MnAl was experimentally observed and discussed in terms of the electronic structure of the alloy. [ABSTRACT FROM AUTHOR]

The dielectric properties of polypyrrole-zeolite composites up to 50% w/w zeolite are studied in the frequency range from 10-2 to 2×106 Hz from room temperature to liquid nitrogen temperature. The complex permittivity formalism reveals a temperature dependent relaxation in all samples except for the 25% w/w zeolite composite. The frequency fmax where a maximum of a loss peak is located varies with temperature by the Williams-Lander-Ferry law. The values of the activation energy of the relaxation process (which are of the order of polaronic dc conductivity) have the tendency to reach a minimum in the 25% w/w composition, which is a loss-free composite. The 50% w/w zeolite behaves as a dielectric where ionic relaxation dominates. The temperature variation of the strength of the dielectric mechanism follows a Curie law, apart from 50% w/w zeolite where the dielectric strength is practically constant. The frequencies, where loss peaks are maximum, as well as dc conductivity follow qualitatively the same temperature law, but the parameters are quite different. Moreover, the locations of the relaxation peaks diverge from the predictions of Barton-Nakajima-Namikawa model. Long-range electric charge transport (dc conductivity) and the relaxation that corresponds to short-range localized motion probably involve different processes. [ABSTRACT FROM AUTHOR]

A remanent polarization of 130 ± 3 mC/m², large among the values reported for organic materials, and rectangular D-E hysteresis curves were realized in synthesized vinylidene fluoride (VDF) oligomer [CF[sub 3](CH[sub 2]CF[sub 2])[sub 17]I] film evaporated onto a platinum surface around liquid nitrogen temperature. The results suggested that the VDF oligomer film has an extremely high crystallinity, and the electric dipoles arrange almost perfectly perpendicular to the film surface, and that a Lorentz local field factor of ferroelectric VDF oligomer crystals is nearly zero. Moreover, the obtained value of the coercive field, which was larger than those of ferroelectric polymers, might be attributed to the steric hindrance arising from the existence of iodine atoms at the VDF oligomer chains. [ABSTRACT FROM AUTHOR]

The normal operation of various superconducting magnets is greatly influenced by the thermal stress of the insulating system, commonly made of epoxy resins with vacuum pressure impregnation (VPI) technology, throughout the curing and cooling processes. In this work, we developed a Fiber Bragg Grating (FBG) strain measurement method to monitor the real-time strain responses of an epoxy resin IR-3 and its glass fiber-reinforced composite during both curing and cooling processes. Then, we also monitored the same process of a Nb–Ti superconducting magnet coil prepared by VPI technology. With the help of FBG strain sensors, the residual strains of the coil at various positions and directions were investigated. The results show that the large residual strain occurred near the end of the coil in the axial direction. In addition, the interlaminar shear stress properties were measured at both room temperature and liquid nitrogen temperature. The strain characteristics of the epoxy resin IR-3 and the insulating system can provide useful guidance for the design and construction of high-field Nb–Ti superconducting magnets. [ABSTRACT FROM AUTHOR]

Nanowires of polypyrrole have exhibited switching transition that reduces the resistance of the wires by several orders of magnitude under certain bias around and below 30 K temperature. Here, we have shown that by incorporating gold in these polypyrrole nanotubes using a cost effective template based single-step chemical synthesis technique, this novel resistance switching transition could be extended beyond liquid nitrogen temperature (>90 K) to make this phenomena technologically relevant. The single step synthesis technique, reported here, provides us uniform mixing of gold and polypyrrole during the formation of composite-nanotubes; with appropriate choice of materials, this synthesis technique can be extended to form nanotubes of other metal-polymer composites. [ABSTRACT FROM AUTHOR]

Improved fabrication and conditioning techniques for gated p-Si field emitter arrays (FEAs) (1×1 mm2 in size with 50×50 emitters) greatly reduces the bulk damage and surface states. Consequently, only 0.9 μA of the anode dark field-emission current was measured for 50 V applied gate potential with a very low gate leakage current. At these low gate leakage currents, the transition between the tunneling-limited field-emission regime and the supply-limited saturation regime is clearly revealed in current-voltage plots. This transition is accompanied by a reduction in the anode current fluctuation. The standard deviation of the noise current drops from a few percent in the tunneling-limited regime to <1% in the supply limited regime at 50 V. A photocurrent of 0.41 mA was obtained for photoexcitation at 840 nm wavelength. This corresponded to 40 dB contrast ratio between the photocurrent and the dark current at room temperature. Additionally, our findings showed that surface states were fully depleted at low applied fields, the concentration of bulk defects was low and the area contributing to the dark current was confined to the emitter regions. In contrast, previously reported ungated Si field emitters had high concentrations of surface states and bulk defects. Furthermore, the contributing area to the dark current corresponded to the whole area of the device as opposed to only the emitter areas for a gated FEA. Photofield emission and dark current measurements from our gated p-Si FEA correlate well to theoretical models without requiring cooling to liquid-nitrogen temperatures. [ABSTRACT FROM AUTHOR]

An induction magnetometer consisting of a search coil and an inverting operational amplifier is simple in structure and in signal transferring mechanism from the magnetic field input to the voltage output. Because this magnetometer is based on Faraday's law of induction, it has a lower cutoff frequency r/(2πL), where r is the resistance of the coil and L is its inductance. An attempt has been made to lower the cutoff frequency of the induction magnetometer by using a high-Tc superconductor coil. With a pancake coil (inner diameter ≈18 cm and outer diameter ≈23 cm, 92 turns, 3.23 mH) made of a Bismuth strontium calcium copper oxide (BSCCO) superconductor tape of 5 mm in width and 0.23 mm in thickness, the cutoff frequency achieved was 1.7 Hz which is much lower than that obtained with a bulky copper search coil which is typically in the range of 10-20 Hz. In the experiment, an inverting amplifier was made with a complementary metal-oxide semiconductor operational amplifier and was immersed in liquid nitrogen together with a BSCCO high-Tc superconducting coil. Discussion is made on the resolution of the induction magnetometer using a high-Tc superconductor search coil. [ABSTRACT FROM AUTHOR]

Measures the thermally stimulated current (TSC) of nominally undoped bismuth silicon oxide crystals after ultraviolet excitation at liquid nitrogen temperature. Information on TSC without bias voltage; Effect of field strength; Determination of energy level.

Reports on the measurement of the properties of amorphous germanium barriers deposited on liquid nitrogen cooled substrates. Information on the calculated tunnel current; Temperature dependence; Discussion on electron spin polarization.

In this study we present a technique to obtain ordered fct FePt particles embedded in a C matrix. FePt nanoparticles are formed inside a high-pressure sputtering cell, called a particle gun (PG), and subsequently deposited on the substrate through a small orifice. These particles have a uniform size distribution with an average particle size that can be controlled in the range of 3-10 nm by adjusting the sputtering cell pressure, power, distance between the magnetron and the orifice, and by using a liquid nitrogen cooling jacket. The particles are converted to the L1[SUB0] phase as they pass through a)specially designed heating stage, attached to the top of the PG, heated by halogen lamps, thus avoiding alloying and oxidation effects. A strong dependence of coercivity on both the particle size and temperature was observed. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the noise and flux sensing area of a field cooled direct current superconducting quantum interference device magnetometer. Application of magnetometer; Use of liquid nitrogen in measuring the noise of the magnetometer.

Superconducting nanowire single photon detector (SNSPD) is a leading candidate for applications requiring the fundamental limit of light detection at high detection rates. While SNSPD technology employing nanowires from conventional low temperature superconducting detectors is mature with several commercial solutions, other material options with higher transition temperature approaching liquid nitrogen with faster signal responses are actively being explored. In this context, we develop a comprehensive model that predicts the final potential response from an SNSPD incorporating several physical and material aspects. A phase diagram of photon detection is developed that describes the latching phases and the photon sensitivity as a function of biasing current and temperature for both low temperature and high temperature superconductors. On the one hand, while low temperature superconductors are observed to be more sensitive than high temperature superconductors (HTSs) under any given biasing condition, a biasing window for a single photon detection with HTS nanowires is identified. On the other hand, HTS nanowires demonstrate three orders of magnitude faster response times than the low temperature superconductor nanowire at the same biasing condition, making it uniquely suited for several practical applications. [ABSTRACT FROM AUTHOR]

Presents a study that used excimer laser irradiation to induce rapid formation of nitride and oxide layers on beryllium (Be) samples immersed in liquid nitrogen (N) and water. Elemental composition of the irradiated surfaces; Use of Rutherford backscattering spectrometry; Compound formation of Be[sub3]N[sub2].

Conductivity noise in dc current biased La0.82Ca0.18MnO3 single crystals has been investigated in different metastable resistivity states enforced by applying voltage pulses to the sample at low temperatures. Noise measured in all investigated resistivity states is of 1/f-type and its intensity at high temperatures and low dc bias scales as a square of the bias. At liquid nitrogen temperatures for under bias exceeding a threshold value, the behavior of the noise deviates from above quasi-equilibrium modulation noise and depends in a non monotonic way on applied bias. The bias range of nonequilibrium 1/f noise coincides with the range at which the conductance increases linearly with bias voltage. This feature is attributed to a broad continuity of states enabling indirect inelastic tunneling across intrinsic tunnel junctions. The nonequilibrium noise has been ascribed to indirect intrinsic tunneling mechanism while resistivity changes in metastable states to variations in the energy landscape for charge carriers introduced by microcracks created by the pulse procedures employed. [ABSTRACT FROM AUTHOR]

We report an unexplored type-II multiferroic order in NiMn 2 O 4 , exhibiting strong linear magnetoelectric coupling above liquid-nitrogen (LN) temperature. The compound becomes ferroelectric at ∼ 100 K, coinciding with ferrimagnetic ordering, with a polarization value of ∼ 535 μ C/m 2 for a poling field of 5 kV/cm. At LN temperature, the polarization value increases linearly (∼ 21 %) with a magnetic field up to 30 kOe. Rietveld refinement of neutron diffraction patterns reveals a ferrimagnetic model with antiparallel moments at tetrahedral and octahedral sites, as well as a canting of octahedral moment persisting up to ∼ 100 K. Low-temperature synchrotron diffraction confirms a step-like oxygen displacement during multiferroic ordering, suggesting that the Dzyaloshinskii–Moriya interaction polarizes the intervening oxygen atoms through magnetostriction, providing a microscopic mechanism for spontaneous electric polarization in this linear magnetoelectric multiferroic compound. [ABSTRACT FROM AUTHOR]

We report microsecond timescale switching between the superconducting and normal states of commercially manufactured high-T c superconducting wires using optical radiation to heat the conductor above T c. The achieved voltages and switching times have significant implications for a new class of thermal switches. The report contains experimental data for photo-induced microsecond scale voltage transients as well as numerical analysis of heat propagation through the material in response to optical radiation. The microbridges are etched into commercially manufactured coated conductors and submerged in liquid nitrogen. By varying the magnitude of the transport current, two different optical responses are identified. At low transport currents, short-lived voltage transients occur, transitioning to persistent latching once the current is increased above a threshold value. The microbridge, therefore, behaves as a fast opening and closing switch when carrying low currents or an optically latched thyristor at high currents. This is understood to occur due to critical current suppression as a result of heating from the optical pulse. Optically induced heating reduces the superconducting volume fraction, and Joule heating due to the transport current interaction with the high temperature superconducting occurs, which either causes short-lived or stable self-heating normal regions dependent on the magnitude of the transport current. This study is concluded with an estimate of the energy necessary to drive the microbridge into the resistive state. The observed behavior can potentially be utilized as a switching element in superconducting transformer rectifiers where high frequency switch operation is required. [ABSTRACT FROM AUTHOR]

Niobium (Nb) and its hydrides have been the focus of many studies due to applications as a hydrogen storage material, as a dielectric coating in semiconductor devices and in superconducting radio-frequency cavities. In this paper, we will present the atomic-scale characterization of Nb hydrides using scanning transmission electron microscopy and electron energy loss spectroscopy (EELS) at room and liquid nitrogen temperatures. Although such cavities are formed from ultrahigh purity Nb, using electron beam diffraction, we found that at LN2 temperature, the grains near the surface of cold-worked Nb sheets contain regions exhibiting three different superlattice features, which are identified as β, [variant_greek_epsilon], and ζ-NbHx phases. Z-contrast imaging and EELS at LN2 temperature are utilized to qualify their atomic and electronic structures. [ABSTRACT FROM AUTHOR]

The interaction of helium atoms with the radiation damage transferred to silicon single crystal by He+ implantation at a dose of 5x10(sup 15) cm-2 and energy of 20 keV, and liquid-nitrogen temperature is analyzed using a variety of complementary methods during and after treatments. To determine the dissociation kinetics of helium from the defects and to plan appropriate heat treatments for the other approaches, thermal programmed desorption was employed. The results are discussed.

Magnetic, transport, and optical properties of thin film and bulk Fe 2 CrGa alloy samples with different types of atomic order were experimentally investigated. The obtained data were discussed in terms of first-principle calculation results made for the stoichiometric Fe 2 CrGa alloy with different types of atomic order and disorder. An ultimate atomic disorder in Fe 2 CrGa alloy films was obtained by employing vapor quenching deposition onto substrates cooled by liquid nitrogen. Annealing of as-quenched Fe 2 CrGa alloy films causes their crystallization at T a n n = 750 K with the formation of the disordered A2-type structure, which is accompanied by the rapid growth of alloy resistivity in a narrow temperature range, formation of multi-phase magnetic structure and changes in the optical properties. Crystalline bulk and film Fe 2 CrGa alloy samples show the dome-like temperature dependence of the resistivity with maximums near their Curie temperatures and explained in terms of competition between negative with temperature contribution from highly resistive media and positive from the electron–magnon scattering. The big resemblance between calculated for Hg 2 CuTi type of atomic order and experimental optical conductivity spectra for annealed Fe 2 CrGa alloy films proves that Hg 2 CuTi type of atomic order is more probable for this alloy. [ABSTRACT FROM AUTHOR]

As one of the most widely used infrared (IR) detectors, a mercury cadmium telluride (MCT) detector usually requires liquid nitrogen refrigeration to suppress thermally activated noise mechanisms that are inherent to its narrow bandgap, which limits its practical applications. Therefore, it is essential to develop strategies to suppress dark current with reduced cooling demand. In this work, a surface plasmon resonance (SPR) enhanced MCT microcavity was proposed to intensify optical absorption across a broadband while diminishing the thickness of the MCT layer to reduce intrinsic dark current proportional to the volume of the absorber. The microcavity is formed by sandwiching the MCT layer between a top well-designed hybrid golden-cross antenna array and a bottom golden reflector. The microcavity is employed to trap the incident light to amplify the absorption, and the golden-cross antenna array is introduced to not only significantly enhance the incident light field through the SPR effect but also to broaden the microcavity resonant mode. Numerical calculation indicated that an absorptance exceeding 95.3% can be attained at 3.4 μm with the full width at half maxima (FWHM) extending beyond 1.38 μm, which almost covers the absorption band of MCT in mid-wavelength IR (MWIR), all while the MCT layer is only 530 nm. Moreover, the prototype device unit was fabricated and tested. Measured peak absorption reached 98.7% @ 3.6 μm and FWHM was as broad as 1.12 μm. These results demonstrate that the high and wideband absorption in an ultrathin MCT layer is achieved based on the synergistic effects of SPR and microcavity resonance. [ABSTRACT FROM AUTHOR]

Hole mobility degradation is analyzed in high-dose boron-implanted ultrashallow junctions containing high concentrations of boron-interstitial clusters (BICs) by combining an empirical method based on the self-consistent interpretation of secondary-ion-mass spectrometry (SIMS) and all measurements and liquid-nitrogen (L[N.sub.2]) to room temperature (RT) hole mobility measurements. BICs dissolution through multiple f lash anneals at high temperature has reduced the mobility degradation.

We report measurements of the critical current of two commercial coated conductors at low temperatures when in-plane magnetic fields up to 15 T are applied. The comparison between the two samples suggests that the presence of a magnetic substrate may have a detrimental effect, at least at low and medium fields. Nevertheless, the critical current density at 30 K and 15 T is in the range of that measured in self field at 77 K. We ascribe its reduction in presence of the field to inter-vortex forces. [ABSTRACT FROM AUTHOR]

Ar with liquid nitrogen cooling and Xe with water cooling are two methods of ion etching that avoid damage to the characteristics of YBaCuO thin films. This method of ion etching can be applied down to the narrow lines without using complicated lithographic process. Conventional Ar ion etching damages the features of YBaCuO superconducting thin films due to heating and ion damage.

We report an unexplored type-II multiferroic order in NiMn 2 O 4 , exhibiting strong linear magnetoelectric coupling above liquid-nitrogen (LN) temperature. The compound becomes ferroelectric at ∼ 100 K, coinciding with ferrimagnetic ordering, with a polarization value of ∼ 535 μ C/m 2 for a poling field of 5 kV/cm. At LN temperature, the polarization value increases linearly (∼ 21 %) with a magnetic field up to 30 kOe. Rietveld refinement of neutron diffraction patterns reveals a ferrimagnetic model with antiparallel moments at tetrahedral and octahedral sites, as well as a canting of octahedral moment persisting up to ∼ 100 K. Low-temperature synchrotron diffraction confirms a step-like oxygen displacement during multiferroic ordering, suggesting that the Dzyaloshinskii–Moriya interaction polarizes the intervening oxygen atoms through magnetostriction, providing a microscopic mechanism for spontaneous electric polarization in this linear magnetoelectric multiferroic compound. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) spectra of bound excitons are measured in uniaxially strained GaP by performing shock-wave experiments at liquid nitrogen temperatures. GaP samples doped with sulfur or nitrogen are shock compressed up to 3 GPa when subjected to uniaxial strains along the [100] crystallographic orientation.

The strong coupling between 3d and 4f based magnetic sublattices in double perovskite (DP) compounds results in various exotic complex magnetic interactions, and the ground state contains multiple fascinating and remarkable magnetic states. In this article, we have performed a detailed investigation of the crystal structure, magnetic, and magnetocaloric properties of the ordered monoclinic polycrystalline double perovskite Ho 2 CoMnO 6 (HCMO) compound. A study of the magnetization dynamics employing temperature and magnetic field shows a powerful correlation between Ho and Co/Mn sublattices. Due to the presence of the ferromagnetic superexchange interaction in between Co 2 + − O − Mn 4 + networks, the system undergoes an ordered state at the transition temperature, T C ≈ 77 K. Below T C , a clear compensation point continued by negative magnetization is noticed in the virgin state of the compound. The reduction of the saturation magnetization ( M S) in the hysteresis curves (M-H) can be explained by the existence of local anti-site defects or disorders and anti-phase boundaries in the system. Temperature dependence of magnetic entropy change (− Δ S) curves shows a maximum value of 13.4 J/kg K for Δ H = 70 kOe at a low temperature along with a noticeable inverse magnetocaloric effect. Moreover, the material holds reasonable values of magnetocaloric parameters. The absence of thermal hysteresis along with a large value of | Δ S | makes the system a potential candidate for low temperature as well as liquid nitrogen temperature-based magnetic refrigeration. Additionally, our experimental findings should encourage further detailed studies on the complex 3d–4f exchange interaction in the double perovskite system. [ABSTRACT FROM AUTHOR]