Search

Diverse efforts undertaken to mitigate the Debye screening effect of field-effect transistor (FET) biosensors have achieved higher sensitivity. However, the charge transfer or induction mechanism between the captured biomolecules and the sensing surface, resulting in shift of surface potential and, hence, the drain current magnitude, shows poor selectivity for real time detection of ultra-low biomolecule concentration in unamplified samples. Herein, enabling direct interaction of the target molecule with edge passivated thermally reduced graphene oxide, through the template of molecularly imprinted polymer (MIP), specific trap induced characteristic bulges in the noise spectrum has been observed only in the presence of target molecule. Such a phenomenon has not been observed either with antibodies or aptamers as receptors. Hence, the direct interface of MIP with a graphene FET (GFET) results in the generation of an additional electronic label in FET transduction. As a proof of concept, this principle has been validated for serotonin detection in serum in the presence of other neurotransmitters, resulting in detection limit of 0.05 fM in real time, which is more than two orders of magnitude lower than existing reports and, hence, is expected to pave the way for advancing GFET based sensors toward ultrasensitive point-of-care applications without requiring complex machine learning algorithms. [ABSTRACT FROM AUTHOR]

Detailed structural and magnetic investigations have been performed on two equally Fe-doped MnCoGe alloys of nominal compositions Mn 0.875 Fe 0.125 CoGe and MnCo 0.875 Fe 0.125 Ge. The presence of martensitic phase transition (MPT) in both alloys is clear from the temperature variation of structural and magnetic properties. The nature of MPT is found to be complete in the Mn site Fe-doped alloy. On the other hand, a partial nature of the MPT is observed for the Co site Fe-doped alloy. The application of external hydrostatic pressure hardly affects the magnetic and structural transition temperatures. Both alloys show a significant amount of the magnetocaloric effect in ambient as well as in high pressure situation around their magnetic and structural transition regions. [ABSTRACT FROM AUTHOR]

The magnetic behavior of three Ni-Mn-(Sn,In) based shape memory alloys are investigated under hydrostatic pressure. Among them, Ni 51.2 Mn 32.8 In 16 (NM-In 16) and Ni 51 Mn 35 Sn 14 (NM-Sn 14) have their martensitic transition close to room temperature and undergo several magnetic transitions at lower temperatures. They order ferromagnetically at T C A , which is just above room temperature. However, the ferromagnetism is destroyed by the martensitic transition at T M S (< T C A ). The ferromagnetic order is revoked further at a lower temperature T C M (< T M S ) in the martensite phase. The third alloy, namely, Ni 50 Mn 34 Sn 16 (NM-Sn 16), has a relatively stable ferromagnetic state (Curie point T C A = 347 K), and it survives below the martensitic transition temperature, T M S . Our magnetic study under hydrostatic pressure indicates that T M S and T C M (only for the first two alloys) increase systematically with pressure. However, the saturation magnetization at base temperature is found to be an increasing function of pressure for NM-Sn 14 only, and a decreasing trend is observed for the other two alloys. Most interestingly, NM-Sn 14 shows a large enhancement in magnetocaloric effect (MCE) with pressure, whereas the other two compositions show a drop in MCE with pressure. A subtle competition between the change in Ni-Mn hybridization strength and the Mn-Mn magnetic interaction with pressure can be responsible for the observed anomalous behavior. [ABSTRACT FROM AUTHOR]

We study the condition of the occurrence of the rim instability in the solvent-induced dewetting process. Our experimental results show that the film thickness not only greatly influences the occurrence of the rim instability, but also influences the wavelength λ as characterized by the undulation of the deformed contact line. The molecular weight of polymer does not almost influence the occurrence of the rim instability and the wavelength λ. The wavelength λ is proportional to the width of the rim in the rim instability region. The receding contact angle θ of polymer solutions on substrates in the dewetting process is an important factor to influence the rim instability in the solvent-induced dewetting. [ABSTRACT FROM AUTHOR]

In this paper we have investigated the effect of nanometric grain size modulation on the behavior of magnetoimpedance (MI), magnetoresistance, and magnetic properties of a series of single-phase nanocrystalline colossal magnetoresistance La0.7Sr0.3MnO3 (LSMO) manganites all synthesized through chemical route “pyrophoric reaction process.” MI measurements were carried out at room temperature (T=300 K) in the ac signal frequency (f) range of 40 kHz-110 MHz and in dc magnetic field (H) range of -2.5 kOe

The coexistence of the magnetic and the electrical properties in lanthanum (La)-modified bismuth ferrite (Bi1-xLaxFeO3, x=0.05, 0.1, 0.15, and 0.2) ceramics was studied and compared with those of bismuth ferrite (BiFeO3). The presence of a small secondary phase of BiFeO3 (arises due to excess Bi2O3) was removed on La substitution at the Bi site, as observed in x-ray diffraction (XRD). The effect of La substitution on dielectric constant, loss tangent, and remnant polarization of the samples was studied in a wide range of temperature (77–400 K) and frequency (1 kHz–1 MHz). The variation of magnetization, coercive field, and exchange bias with temperature (2–300 K) and La concentration were investigated. These changes in the magnetic parameters with La doping along with those of the electron magnetic resonance parameters measured at 300 K and 9.28 GHz are understood in terms of increase in the magnetic anisotropy and magnetization. These results also show that stabilization of crystal structure and nonuniformity in spin cycloid structure by La substitution enhances the multiferroic properties of BiFeO3. [ABSTRACT FROM AUTHOR]

In this work, we report the synthesis of sol-gel-derived lead iron niobate [Pb1.10(Fe0.5Nb0.5)O3] (PFN) powders and sintered ceramics. The PFN powders were calcined at (Ta), 973, 1073, 1173, 1273, and 1373 K for 3 h in air. As envisaged from x-ray-diffraction analyses, PFN powder calcined at 1173 K was crystallized into pure monoclinic perovskite phase whereas powders calcined at all other temperatures had varied amounts of retained pyrochlore (Pb3Nb4O13) phase coexisted with dominant monoclinic perovskite phase. The PFN pellet (prepared using the phase pure powder calcined at 1173 K) sintered at 1373 K for 4 h in air also had a minute quantity of retained pyrochlore phase coexisting with desired perovskite phase. From the temperature dependence of measured capacitance and loss tangent at different frequencies, the ferroelectric to paraelectric phase-transition temperature of PFN ceramics was observed at Tc≈370 K. The diffused nature of this transition and high dielectric constant of PFN is related to the cation disorder at the B site of A(BI+3BII+5)O3 lattice. For PFN powders, calcined at different temperatures, the temperature dependence of the magnetic susceptibility (χ) was measured in a temperature range of 2–360 K, whereas the magnetic hysteresis loops and electron magnetic resonance (EMR) spectra were measured at room temperature. Room-temperature ferromagnetism is observed in all the calcined powder samples and it was found that the magnetization increases with the increase in calcination temperature (Ta). The symmetric EMR line shape with g≈2.01 observed in all calcined samples was identified to be due to Fe3+ ions. It is suggested that the observed weak ferromagnetism, which increases with an increase in Ta, may be due to canting of the Fe3+ spins. These observations suggest PFN to be a very attractive single-phase ferroelectric/ferromagnetic material for room-temperature applications. [ABSTRACT FROM AUTHOR]

The below band-gap optical-absorption characteristics of GaxIn1-xSb alloy system have been reported. The different dependencies of the hole and electron absorption mechanisms on wavelength result in significant changes of the absorption characteristics with alloy composition. In the undoped Ga-rich alloy compositions that are p type in nature (due to residual holes resulting from native defects), the inter-valence-band absorption has been found to be the dominant absorption mechanism. With decreasing Ga (increasing indium) mole fraction, the hole to electron ratio decreases for undoped samples. For such samples, absorption due to electrons becomes significant. With n-type extrinsic doping, intervalley transitions are seen for certain Ga-rich compositions, which also alter the absorption characteristics. The dependencies of various absorption mechanisms as a function of wavelength have been analyzed and discussed in this paper. Based on the theoretical analysis presented in this paper, one can calculate the extrinsic doping level necessary for each alloy composition in order to obtain high optical transparency necessary for infrared optical applications. [ABSTRACT FROM AUTHOR]

A radio-frequency photoreflectance technique, which senses changes in sample conductivity as carriers recombine following excitation by a laser pulse, has been used to measure the recombination parameters in 0.55-eV InGaAsSb lattice matched to GaSb. Doubly capped lifetime structures with variable active layer thicknesses are used to extract the surface recombination velocity, while an analysis of the samples with different doping concentrations is used to obtain Auger (C) and radiative (B) recombination parameters. Parameter extraction for the samples evaluated gives C=(1±0.4)×10-28 cm6/s and B=(3±1.5)×10-11 cm3/s for 0.55-eV InGaAsSb lattice matched to GaSb. The Auger and radiative recombination coefficients obtained from high-level injection decay times in low doping concentration samples show very good agreement with the values obtained from low-level injection conditions. [ABSTRACT FROM AUTHOR]

The optical and electrical properties of tellurium- (Te) compensated Ga1-xInxSb bulk crystals with alloy compositions ranging from x=0.37 to x=0.98 have been investigated. It has been observed that the Burstein-Moss shift plays an important role in the optical properties of Ga1-xInxSb crystals for the alloy compositions greater than x=0.5 and net donor concentrations in the 2.9×1017 to 2.6×1018 cm-3 range at 300 K. A good agreement has been obtained between the theory and experimental observations. Furthermore, electrical characterizations at 300 and 77 K show that Te compensates the native defects in Ga1-xInxSb, irrespective of the alloy composition. [ABSTRACT FROM AUTHOR]

With the advancement of nano-technology and push toward flexible electronics, the opportunity to generate electricity using solid-state devices has ushered tremendous research interest in improving the thermoelectric (TE) properties of flexible semiconducting materials. The majority of research done so far was focused on finding suitable doping schemes for all-organic flexible substrates or mixing organic and inorganic components to obtain flexible substrates with an optimized thermoelectric performance. Unfortunately, their performance is limited by their low power factor (PF) values and often suffers from degradation issues due to the organic component that limits them to low temperature applications. Here, through coupled microstructural and thermoelectric analysis, we show how to overcome these limitations by introducing a new inorganic GaAs flexible substrate with enhanced TE performance. We show that these flexible thin films are single-crystal-like biaxially textured with low angle grain boundary misalignment; and charge transport is dominated by multi- valley electron conduction. This results in a PF ∼1300 µW/mK2, the highest value for non-toxic inorganic flexible thin films and an estimated 3-fold enhancement in the figure of merit compared with bulk GaAs. We present the temperature-dependent experimental PF, mobility, and carrier concentration data coupled with the theoretical models to elucidate the charge transport characteristics of this new class of films. Moreover, these unique charge transport characteristics are material growth dependent, and thus, such novel thermoelectric properties are expected in different material systems. [ABSTRACT FROM AUTHOR]

Focuses on an expression derived for the srtucture factor of a superlattice with rough interfaces. Interpretation of the random variables; Ratio of satellite intensities to peak intensity.

Recent advances in nonsilica fiber technology have prompted the development of suitable materials for devices operating beyond 1.55 μm. The III-V ternaries and quaternaries (AlGaIn)(AsSb) lattice matched to GaSb seem to be the obvious choice and have turned out to be promising candidates for high speed electronic and long wavelength photonic devices. Consequently, there has been tremendous upthrust in research activities of GaSb-based systems. As a matter of fact, this compound has proved to be an interesting material for both basic and applied research. At present, GaSb technology is in its infancy and considerable research has to be carried out before it can be employed for large scale device fabrication. This article presents an up to date comprehensive account of research carried out hitherto. It explores in detail the material aspects of GaSb starting from crystal growth in bulk and epitaxial form, post growth material processing to device feasibility. An overview of the lattice, electronic, transport, optical and device related properties is presented. Some of the current areas of research and development have been critically reviewed and their significance for both understanding the basic physics as well as for device applications are addressed. These include the role of defects and impurities on the structural, optical and electrical properties of the material, various techniques employed for surface and bulk defect passivation and their effect on the device characteristics, development of novel device structures, etc. Several avenues where further work is required in order to upgrade this III-V compound for optoelectronic devices are listed. It is concluded that the present day knowledge in this material system is sufficient to understand the basic properties and what should be more vigorously pursued is their implementation for device fabrication. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the hole transport properties of gallium antimonide with various degrees of tellurium compensation in the temperature range of 4.2-300 K. Details of the single-crystal substrates of undoped and Te-compensated p-GaSb used; Illustration of the plots of the temperature dependence of hall coefficient; Conclusions.

Presents a comprehensive treatment of the nature of luminescence centers in tellurium-diffused gallium-antimony. Experimental details; Results and discussion; Conclusions.

Deals with a study which discussed the photoluminescence and cathodluminescence properties of a-Si:H treated undoped and tellurium-compensated p-GaSb. Background to the study; Experimental details; Results and discussion.

We have used molecular dynamics to study a two-dimensional system of point particles with screened Coulomb interactions, in a ‘‘box’’ whose size is allowed to vary. In addition to determining the familiar energy–temperature relations at both constant area and constant pressure, we have obtained pressure–area isotherms, diffusion constants, and pair-correlation functions. The results of our simulation are expected to be relevant to such systems as polar monolayers on the surface of water (Langmuir films) and thin colloidal suspensions. By monitoring the energy–temperature relation and the diffusion constant, we have observed first order solid–liquid transitions with hysteresis under both constant area and constant pressure conditions. However, the discontinuities in the pressure–area isotherms at the transition are almost imperceptible. Other thermodynamic relations such as area vs temperature at constant pressure, and the derivative of pressure vs area, are presented to support the analysis. [ABSTRACT FROM AUTHOR]

X-ray diffraction data from water-supported monolayers of fatty acids with chain lengths from 19 to 22 is presented. The structures of the tilted mesophases L2’, L2, and Ov are characterized in detail. The contributions to the unit cell distortion from the tilt and the ordering of the backbone planes of the molecules are separated. It is shown that at the swiveling transition L2’–L2, not only the tilt azimuth but also the packing of the backbone planes change discontinuously. We demonstrate that the tilting transition LS–L2 is accompanied by the ordering of the backbone planes and may be discontinuous. Evidence is presented for a herringbone ordering transition within the L2 region. The distortions are related to symmetry of the phases and described by the order parameters responsible for tilt and herringbone ordering of the backbone planes of the molecules. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have studied Langmuir monolayers composed of mixtures of heneicosanoic acid and heneicosanol using π-A isotherms and x-ray diffraction. We find that the two materials are miscible in monolayer form. We have determined how the phase diagram of the acid evolves to that of the alcohol as the composition varies. X-ray diffraction data along isotherms and isobars show that the head–head interactions, like the tail–tail interactions, are anisotropic. The ‘‘swiveling transition’’ between phases with different tilt directions is accompanied by a rotation of the molecules about their long axes. [ABSTRACT FROM AUTHOR]

We have studied Langmuir monolayers of CH3(CH2)20OH (heneicosanol) using x-ray diffraction. Over the temperature range 7–55 °C, the monolayer isotherms show only one discontinuity, which may be either a ‘‘flat section’’ or a ‘‘kink;’’ we find that these are transitions between tilted and untilted phases. There are several untilted phases, with hexagonal and distorted-hexagonal structures, as in monolayers of the corresponding (heneicosanoic) acid. However, in contrast to the acid, when the pressure is lowered the molecules tilt only towards a next-nearest neighbor. The dependence of the lattice spacings on pressure and temperature indicate that the monolayer does not form a ‘‘tilted hexagonal’’ phase, even at temperatures where the untilted phase is hexagonal (rotator-II). [ABSTRACT FROM AUTHOR]

We have studied the effect of pressure and pH on Langmuir monolayers of heneicosanoic acid in the presence of calcium ions in the subphase. At very low pH the monolayer is unaffected by calcium ions; as the pH is increased, the head groups are pulled closer together and the chain tilt at zero pressure decreases. As a result, the phase transitions seen along the isotherms occur at lower pressures. When the isotherms become featureless, the chains are untilted at all pressures. At very high pH, a new untilted structure is observed. [ABSTRACT FROM AUTHOR]

Studies the kinetics of a structural phase transition in Langmuir monolayers of amphiphilic molecules. Microscopic relaxation mechanism in monolayers; Relationship between temperature and monolayer structure; rate of nucleation of a hexagonal phase from a metastable shear-induced structure.

We have studied the structure of a monolayer of C21H43OH on water, in the region near close packing, by grazing incidence in-plane x-ray diffraction. For all temperatures studied the isotherms in the πa plane show a kink, signaling a phase transition. Along an isotherm, and for pressures above the kink, we observe that the transverse structure factor has one peak which has constant position, width, and intensity; below the kink the diffraction peak shifts to smaller scattering vector (larger separation) and the amplitude decays as the surface pressure decreases, but the width of the peak remains constant. We rationalize these observations in terms of the influence on the transverse structure factor of gauche configurations in the amphiphile tails, with the kink representing the point at which the last of the gauche configurations is squeezed out of the chain. Along an isobar which is at higher pressure than the kink pressures of all isotherms crossed, the transverse structure factor has a single peak above a transition temperature and two peaks below that temperature; for π=30 dyn/cm the transition temperature is in the range 16.3

Deals with a study which examined in situ x-ray diffraction studies of the growth of thin films using a synchrotron light source. Information on an off-axis faced magnetron sputtering chamber; Methodology of the study; Results and discussion.

Reports on the use of specular x-ray reflectivity to probe the structures of self-assembled monolayers and multilayers deposited using a three-step siloxane self-assembly technique that is repeated to form periodic multilayers. Increase in the film thickness as a function of the number of trilayers; Bragg peaks corresponding to the inter-trilayer spacing.

Magnetic properties of oleic acid/oleylamine coated magnetite nanoparticles of average diameter D=4, 6, 8, 10, and 12 nm are reported. The samples were characterized by transmission electron microscopy and x-ray diffraction (XRD) with XRD showing increasing disorder with decreasing D. Magnetization M vs temperature T data show the blocking temperature TB decreasing with decreasing D from TB=38 K for 12 nm to TB=6.5 K for D=4 nm. The saturation magnetization Ms at 2 K also decreases from Ms=62 emu/g for 12 nm to Ms=17 emu/g for 4 nm but the coercivity at 2 K increases with a decrease in D. It is shown that Ms fits Ms=92(1-2d/D)3 with d=0.68 nm for D>4 nm and d=0.86 for D=4 nm. This equation is derived assuming a core-shell model with shell of thickness d consisting of disordered spins not contributing to Ms. [ABSTRACT FROM AUTHOR]

The nature of magnetism in 10% Cu-doped ZrO2, TiO2, MgO, SiO2, and Al2O3 is investigated using superconducting quantum interference device magnetometry and electron magnetic resonance (EMR). The doping was done by the incipient wetness impregnation technique. X-ray diffraction studies showed the presence of some CuO notably in TiO2, SiO2, and Al2O3. However, EMR yielded typical Cu2+ spectra in all the samples, resulting from some doping. Magnetic field (H) and temperature (T) dependences of the magnetization (M) show only paramagnetism in these oxides in contrast to ferromagnetism with Tc=380 K observed in Cu/ZnO. Concentrations x of Cu2+ doped into the oxides are determined from the M vs T and M vs H data, showing Cu/ZrO2 with the largest x and hence largest magnetization. [ABSTRACT FROM AUTHOR]

The effects of nanometric grain size ([lowercase_phi_synonym]=14–28 nm) modulation on the behavior of magnetoimpedance (MI), magnetoresistance, and magnetic properties of chemically synthesized a series of single-phase soft ferromagnetic nanocrystalline colossal magnetoresistance La0.7Sr0.3MnO3 (LSMO) manganites at room temperature have been reported. From the frequency and magnetic filed dependent MI measurement it is found that the MI percent increases with the increase in nanometric grain size ([lowercase_phi_synonym]) for this series of samples. This behavior has been explained in the light of classical electrodynamics, which relates this effect with the dependency of skin depth on external magnetic field and applied ac signal frequency. Room temperature low field magnetoresistance (LFMR) study of this series of LSMO nanoparticles has also been carried out for comparison. [ABSTRACT FROM AUTHOR]

Magnetic studies in bulk 57% CuxZn1-xO/43% CuO composite prepared chemically with x=0.10 (0.03) are reported. Temperature dependence of the magnetic susceptibility shows clear signature of the Néel temperature TN≃230 K for pure CuO. Hysteresis loop studies in the zero-field-cooled sample show room-temperature ferromagnetism with coercivity Hc≃50 Oe at 300 K with strong temperature dependence for T<300 K. A negative exchange bias He at 5 K is observed when the sample is cooled from RT in H=20 kOe, and its temperature dependence yields He→0 at TN=230 K of CuO. These results and the temperature dependence of remanence Mr provide strong evidence that the CuxZn1-xO phase with x≃0.10 is a ferromagnet with Tc≃400 K. An electron magnetic resonance signal due to Cu2+ substituting for Zn2+ in CuxZn1-xO is also observed. [ABSTRACT FROM AUTHOR]

In the present work we report multiferroic behavior in lead zirconate titanate (PZT)–cobalt iron oxide (CFO) composite thin films. It is found that upon annealing, the multilayered structures are intermixed at least partially, and CFO is phase separated into PZT matrix to form a composite film. The phase separation behavior has been characterized by x-ray photoelectron spectroscopy depth profiling of the constituent elements in conjunction with dielectric spectroscopy measurements. The composite films exhibited ferroelectric as well as ferromagnetic characteristics at room temperature. The coupling between the ferroelectric and the ferromagnetic order parameters has been demonstrated through the reduction of ferroelectric polarization when measured under an applied magnetic field. [ABSTRACT FROM AUTHOR]

Magnetic properties of sol-gel-prepared bulk samples of Co0.05Zn0.95O and Mn0.05Zn0.95O are reported before and after annealing in 5%H2/95%Ar at 573 K for 6 h. The as-prepared samples are paramagnetic with the magnetic susceptibility χ following the Curie-Weiss law: χ=χ0+C/(T-θ). The magnitudes of C are consistent with the magnetic moments expected for the Co2+ and Mn2+ states. After hydrogenation, the magnetism of Mn/ZnO is unchanged but Co/ZnO acquires room-temperature ferromagnetism (RTFM) with a magnetic moment of 0.35μB/Co site and hysteresis loop with coercivity Hc≃600 Oe, remanence Mr≃0.45 emu/g, and saturation magnetization Ms≃1.2 emu/g. Electron magnetic-resonance spectroscopy at 9.28 GHz gives signals corresponding to the Co2+ and Mn2+ states for the paramagnetic states and a broad FM signal for the hydrogenated Co/ZnO. This difference under hydrogenation between Co/ZnO and Mn/ZnO suggests that n-type doping leads to stabilizing of RTFM in Co/ZnO but not in Mn/ZnO, the latter perhaps requiring p-type doping. [ABSTRACT FROM AUTHOR]

Starting with 7 nm γFe2O3 nanoparticles, synthesis of DNA-γFe2O3 nanocomposite and its structural/magnetic properties vis-a-vis the parent γFe2O3 are reported. Analysis of the x-ray diffraction shows an increase in the particle strain and average particle size (to 9.7 nm) in DNA-γFe2O3 nanocomposite. Transmission electron microscopy also shows an increase in size and a considerably wider size distribution. Temperature (5–300 K) variation of the magnetization (M) shows a wider distribution of the blocking temperatures (TB), as expected from the wider size distribution. Above TB, the data of M vs H fit the modified Langevin function with magnetic moment/particle μp≈11 000μB, somewhat larger than μp≈8000μB for the parent γFe2O3. However, M/g(γFe2O3) is not significantly affected. In electron magnetic-resonance spectroscopy at 9.28 GHz, only a single line is observed in DNA-γFe2O3 nanocomposite compared to two lines in γFe2O3. These effects are discussed in terms of the above structural differences. [ABSTRACT FROM AUTHOR]

Magnetic properties of nanorods of NiO (diameter ≈5 nm and average aspect ratio ≈12), with and without oleic acid coating, are reported. Temperature variations (5 to 300 K) of the magnetization and electron magnetic resonance (EMR) spectra were measured to determine the respective blocking temperatures Tb(m) and Tb(EMR). The following differences are noted: (1) Tb(m) is reduced from 230 K suncoatedd to 85 K scoatedd for H=25 Oe (2.5 mT); (2d) Decrease of Tb(m) with H is weaker and the ratio Tb(EMR) /Tb(m) is smaller for the uncoated particles. These differences are due to stronger interparticle interaction present in the uncoated particles. [ABSTRACT FROM AUTHOR]

We report that Co0.1Ti0.9O2-δ prepared by the sol-gel technique is a paramagnet following the Curie-Weiss law: x =x0+C/(T+θ) with θ≃5 K. However, hydrogenation at 673 K in H2/Ar (5%/95%) gas converts a part of the paramagnetic (P) sample to room temperature ferromagnet (RTFM) and reheating the sample at 573 K in air converts it back to a paramagnet completely. This reversible P⇄RTFM transition has been observed for additional cycles by alternately heating in air and H2/Ar. It is argued that this RTFM is intrinsic and it is due to Co2+-Co2+ exchange interaction mediated by oxygen holes which are produced by hydrogenation but eliminated by oxidation. [ABSTRACT FROM AUTHOR]

Provides information on a study which observed improvements in the optical and electrical properties of gallium antimonide after ruthenium passivation. Effect of ruthenium passivation on gallium antimonide; Observation on the passivation and luminescence efficiency of ruthenium; Discussion of the boundary passivation of polycrystallines.

We demonstrate heteroepitaxial growth of single-crystalline-like n and p-type doped GaAs thin films on inexpensive, flexible, and light-weight metal foils by metal-organic chemical vapor deposition. Single-crystalline-like Ge thin film on biaxially textured templates made by ion beam assisted deposition on metal foil served as the epitaxy enabling substrate for GaAs growth. The GaAs films exhibited strong (004) preferred orientation, sharp in-plane texture, low grain misorientation, strong photoluminescence, and a defect density of ~107cm-2. Furthermore, the GaAs films exhibited hole and electron mobilities as high as 66 and 300 cm² /V-s, respectively. High mobility single-crystalline-like GaAs thin films on inexpensive metal substrates can pave the path for roll-to-roll manufacturing of flexible III-V solar cells for the mainstream photovoltaics market. [ABSTRACT FROM AUTHOR]

Describes the development of an apparatus to study the viscoelastic response and measure the complex shear moduli of Langmuir monolayers as functions of the frequency and amplitude of the applied sinusoidal shear strain. Measurement of the angle of rotation; Dynamic range for shear modulus measurement; Sensitivity of the apparatus.

We have constructed an apparatus that radially compresses monolayers on the surface of water. This mode of compression prevents the anisotropy that is sometimes observed in films that are compressed uniaxially. The area is changed using an elastic band stretched around 12 fingers which move synchronously. The ratio of maximum to minimum diameter of the elastic barrier is ∼7:1, so that the compression ratio is ∼50:1. The apparatus can accommodate dishes of various sizes up to 8 in. in diameter. The temperature is controlled by circulating water under the dish. Isotherms obtained using this apparatus illustrate the difference between uniaxial compression and radial compression for a fatty acid monolayer. [ABSTRACT FROM AUTHOR]

Generating capillary waves with an alternating electric field gradient is a noncontact way to study the mechanical properties of monolayers. By studying capillary waves the surface tension can be calculated. In addition, the surface elasticity can be deduced and film inhomogeneity can be determined. We have incorporated a fiber-optic detection system into a capillary wave apparatus. This makes the apparatus more compact, movable, versatile, and easier to use than detection systems currently in use. [ABSTRACT FROM AUTHOR]

We describe an instrument consisting of two adjacent Langmuir troughs and an apparatus capable of dipping substrates in either trough. Such a capability permits the fabrication of Langmuir–Blodgett multilayer films consisting of two alternating components. The troughs are housed in a hermetically sealed enclosure which may be evacuated to permit the establishment of a clean and/or modified (e.g., O2 free) atmosphere. The enclosure is double walled for circulation of thermostating fluid (e.g., ethylene glycol) in order to establish temperatures in the range -30 to 130 °C. The monolayer pressures, film size, and dipping sequence can be controlled manually or by a computer. The surface pressure in each trough is sensed by independent Cahn balances employing filter paper ‘‘Wilhelmy plates’’ in such a manner as to maintain the hermetic seal. [ABSTRACT FROM AUTHOR]

We have investigated the temperature dependence of the linear thermal expansion along the hexagonal c axis (ΔL), in-plane resistivity (ρ), and specific heat (Cp) of the topological insulator Sb2Te3 single crystal. ΔL exhibits a clear anomaly in the temperature region 204-236 K. The coefficient of linear thermal expansion α decreases rapidly above 204 K, passes through a deep minimum at around 225 K, and then increases abruptly in the region 225-236 K. α is negative in the interval 221-228 K. The temperature dependence of both α and Cp can be described well by the Debye model from 2 to 290 K, excluding the region around the anomaly in α. [ABSTRACT FROM AUTHOR]

The terahertz emission mechanisms from the surface of bulk InAsxP1-x crystals have been examined. The dominant terahertz emission mechanism from InAsxP1-x for low-fluence optical excitation is the photo-Dember effect for As compositions of 78% and greater while the surface field effect is dominant for As compositions of 50% and lower for the measured transport properties. The observed terahertz emission magnitude from the photo-Dember effect increased with As composition due to decreasing absorption depth. The observed terahertz emission magnitude from the surface field effect decreased with increasing As composition and was lower than modeled values due to the lower high-field mobility in the depletion region in those samples. [ABSTRACT FROM AUTHOR]

The terahertz emission mechanisms from the surface of bulk InAsxP1-x crystals have been examined. The dominant terahertz emission mechanism from InAsxP1-x for low-fluence optical excitation is the photo-Dember effect for As compositions of 78% and greater while the surface field effect is dominant for As compositions of 50% and lower for the measured transport properties. The observed terahertz emission magnitude from the photo-Dember effect increased with As composition due to decreasing absorption depth. The observed terahertz emission magnitude from the surface field effect decreased with increasing As composition and was lower than modeled values due to the lower high-field mobility in the depletion region in those samples. [ABSTRACT FROM AUTHOR]

In gold nanoparticles (Au NPs) capped with dodecanethiol (DT), the authors report the observation of superparamagnetic blocking temperature TB≃50 K in D≃5 nm NPs but only diamagnetism in 12 nm NPs. For T

Lattice mismatched layers of InxGa1-xAsySb1-y with band edge corresponding to a wavelength of 10.9 μm have been grown on GaAs substrates using a self-graded compositionally organized near-equilibrium growth process based on quaternary melt thermochemistry. A variable composition quaternary acts as a buffer layer between the GaAs substrate and the final layer of uniform composition. Layers of a constant composition with thicknesses as high as 100 μm have been achieved. The dislocation densities in the layers are as low as 8×105 cm-2 even for a lattice mismatch of 13.08%. van der Pauw measurements showed room temperature electron mobility as high as 1.4×104 cm2/V s and carrier concentration of 4.2×1016 cm-3. With further optimization in the growth conditions and improvements in the material quality, the grown layers are expected to be suitable for infrared optoelectronics, high speed electronic devices, and magnetoresistive sensors. [ABSTRACT FROM AUTHOR]

We report significant enhancement of magnetoresistance (MR) in melt-processed La[sub 0.67]Ca[sub 0.33]MnO[sub 3] (LCM) and in Ho-doped LCM samples. The LCM system exhibits surprising enhancement of metal-insulator transition (T[sub IM]) that coincides with the Curie transition temperature (T[sub c]), T[sub IM]approx. T[sub c], illustrating the enhanced percolative transport and spin-polarization through grain boundaries. Surprisingly, 1 mol % of addition of Ho enhances T[sub c] of ∼70 K with remarkable colossal MR. The nanoscale Ho distribution is consistent with the magnetic inhomogeneity-induced MR due to phase segregation in Ho-doped sample whereas charge-segregation picture is valid for undoped LCM. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Specular x-ray reflectivity has been used to probe the microstructures of siloxane-based self-assembled electro-optic superlattices composed of high-hyperpolarizable organic chromophore arrays intercalated with Ga and In oxide sheets. The film thickness increases linearly as a function of the number of layers, underscoring the high structural regularity and efficiency of the synthetic approach. Relatively dense metal oxide structures are detected in these systems. The x-ray reflectivity data also indicate that the dependence of the relative surface roughness on the number of layers is nearly identical for self-assembled organic and organic–inorganic hybrid film structures. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports on the representation of small rigid spherical particles advected in a time-periodic bounded flow by a dissipative dynamical system with simple or strange attractors. Difference between the behavior of such particles and the patterns in the fluid flow driving the system; Implications for transport, mixing and separation in multiphase flows.

Examines the effect of oxygen partial pressure on the growth of YBCO thin film on strontium titanate. Observation of nucleated c-axis orientation; Link between critical thickness and axis orientation; Nucleation of YBCO films.