Changes In Layer Structure Research Articles

Thermally-induced phase transitions in LB multilayers of lead stearate

Pb-stearate multilayers prepared by the Langmuir-Blodgett (LB) technique on silicon show a change of layer structure just below the melting point. At temperatures between 98 °C and 112 °C the samples have been investigated by energy dispersive X-ray scattering in specular and diffuse scattering geometry. The time constants of the transition at fixed temperature was determined. After the disappearance of the old structure, new Bragg peaks grow out of an amorphous intermediate phase corresponding to a 20% smaller layer distance compared with the initial LB structure. At fixed temperature the intensity of the respective Bragg peaks increases and, after reaching a maximum, it decreases again until the new peaks disappear. Maximum Bragg intensity was observed at a transition temperature of 106 °C. The new phase is instable in time. Our results are compared with related effects of Cd stearate, which have been interpreted as a transformation into a two-dimensional ordered hexagonal structure of long columns.

Neutron reflectivity of adsorbed β-casein and β-lactoglobulin at the air/water interface

Adsorption of the pure milk proteins, β-casein and β-lactoglobulin, at the air/water interface has been studied using the technique of specular neutron reflectance. By fitting appropriate models of the protein films to the reflectivity data the detailed structures of the interfaces have been determined. The effects of protein concentration, substrate pH, film ageing and the presence of calcium ions on the film structures have been investigated.At neutral pH both β-casein and β-lactoglobulin form a monolayer at the air/water boundary that can be divided into a protein-rich, hydrophobic, inner layer closest to the interface, and a more diffuse, hydrophilic, outer layer extending into the bulk aqueous phase. The adsorbed amount of protein follows the adsorption isotherms determined by other methods. Ageing has little effect on β-casein layers, but with β-lactoglobulin there is an increases in the adsorbed amount of protein with time and the two-layer model of the film configuration tends to become less distinct such that a one-layer model form is equally appropriate. The rate and extent of the changes occurring as a function of the age of the surface depend on the pH of the substrate solution. The adsorbed amount of both proteins increases as the pH is lowered towards their respective isoelectric points. Models are proposed to account for the changes in layer structure occurring during these processes. The presence of calcium ions modifies the structure of β-casein layers, reducing the hydrophilic layer thickness and the adsorbed amount of protein.

Thermal Stability of Cu / CoSi2 Contacted p+n Shallow Junction with and without TiW Diffusion Barrier

The thermal stability of contacted p+n shallow junction diodes with and without diffusion barrier was investigated with respect to metallurgical reaction and electrical characteristics. Without the diffusion barrier, the (with a junction depth of 0.2 μm measured from the silicide surface) were able to sustain a 30 s rapid thermal annealing (RTA) in ambient up to 450°C without losing the integrity of the devices characteristics. The phase was observed at the interface after 500°C annealing; the phase penetrated through the layer causing a catastrophic change in layer structure after 700°C annealing. With the addition of a 1200 Å thickness of diffusion barrier between Cu and , the junction diodes were able to sustain the RTA treatment up to 775°C without degrading the basic electrical characteristics, and no metallurgical reaction could be observed even after an 800°C annealing.

Epitaxial Insulating Fluoride Layers on Semiconductors

The epitaxial growth of the rare earth fluorides HoF3 and GdF3 on Ge, Si, and GaAs has been investigated. At the same time the detailed nature of the interfaces formed has been probed by X-ray photoelectron spectroscopy. Epitaxial layers can readily be grown and it is shown that layers with the high temperature tysonite-like phase may be prepared in such a way as to be stable at room temperature. A critical thickness exists where the layer structure changes to a multidomain orthorhombic form; this is dependent on the degree of mismatch of the lattices of overlayer and substrate. Whereas the GdF3-Ge interface is unreactive, strong reactions are seen for HoF3-Si, GdF3-GaAs, and LaF3-Si. Reactions at the latter interface may be attenuated by an intermediate ordered layer of arsenic just one monolayer thick.

Life and Death in Moving Fluids: Hydrodynamic Effects on Chemosensory‐Mediated Predation

Previous studies in taxonomically diverse marine animals have established the general existence, and importance, of the olfactory sense in a wide variety of behavioral processes. Evidence suggests that the sense of smell mediates predatory search in many marine animals. Past investigations have not, however, been designed to link either the degree of successful olfactory—mediated search or guidance mechanisms with the hydraulic environment in which predatory activities naturally take place. In an effort to examine the interaction between hydrodynamics and chemoreception, we investigated predatory success and search strategies of blue crabs foraging in controlled hydrodynamic environments generated in a flume. Hydrodynamics were characterized by quantifying boundary layer shear velocity (°) and roughness Reynolds number (Re°), two measures that describe the structure of boundary layer flows. Flow properties affected the ability of crabs to orient to odor plumes emanating from actively pumping infaunal bivalves (Mercenaria mercenaria). High flow speed or large sediment particle size increased boundary layer turbulence, thereby decreasing the success of crab chemo—orientation ability. In addition, high flow speed also lessened the probability that crabs contacted odor plumes. Thus, habitats with high flows can provide hydrodynamic refuges from olfactory—mediated predation. Because search ability is contingent on the magnitude of boundary layer turbulence, olfactory—mediated predation may also be ineffective in slow flows, if bottom roughness elements can generate sufficient turbulence. Further, search ability in blue crabs is extremely sensitive to small changes in benthic boundary layer structure. The presence of a thick viscous sublayer, dominated by quasilaminar flow, seems especially critical for successful location of an odor source by crabs. Benthic estuarine crustaceans inhabit an environment where flows are transitional between smooth—and rough—turbulence conditions. Accordingly, chemosensory systems appear geared primarily to extracting information from hydraulically smooth flows. These results indicate that mechanisms governing the physical transport of odor signals can have profound influences, not only on the development of sensory and behavioral mechanisms, but also on biotic interactions such as predation, which, in turn, can mediate community structure.

Layer structure deformation and electro-optic response in electroclinic effect

Abstract Switching in layer structure and molecular orientation due to the electroclinic effect was studied by means of X-ray and light transmittance measurements. The followings were confirmed; (1) A bookshelf layer structure in an unperturbed state deforms in part to bend or tilt. The layer tilt angle linearly increases with increasing field strength. (2) Normalized transmittance change between crossed polarizers is independent of an applied field strength, and is described by an exponential function composed of at least two decay times. The second component may be attributed to the layer structure change.

Thermal Stability of Compositionally Modulated Amorphous Nitride Alloy Films

Co-based amorphous alloy films composed of non-nitride and nitride layers were prepared by N 2 reactive sputtering. The layered films showed soft magnetic properties when the layer thickness was less than 300 A. The saturation magnetization (4?M s ) was increased by nitriding. The 4?M s of the non-nitride films in the present study was about 7400 G, and that of the layered films was about 8400 G. The layered structure changes into a compositionally modulated structure after annealing above 400°C, and the 4?M s of films is thereby increased up to 11,300 G. The resulting compositionally modulated films are thermally stable and were found to have a high crystallization temperature (T x ≫ 600°C).

組成変調窒化アモルファス合金膜の熱的安定性

Co-based amorphous alloy films composed of nonnitride and nitride layers are prepared by N2 reactive sputtering. The layered films show soft magnetic property when the layer thickness is less than 300A. The saturation magnetization (4πMs) is increased by nitriding. 4πMs of the non-nitride films of the present study is about 7400 G and that of the layered films is about 8400 G. The layered structure changes into compositionally modulated structure after annealing above 400°C and 4πMs of the films is increased up to 11300 G. The compositionally modulated films are thermally stable and are found to have high crystallization temperature (Tx>600°C).

Magnetic properties of compositionally modulated nitride amorphous alloy films

Superstructured Co-based amorphous alloy films comprising non-nitride and nitride layers are prepared by sputtering alternatingly in Ar and in N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> mixed Ar gas. The layered structure changes into compositionally modulated structure by high temperature annealing above 400°C. The films with modulation wave length λ < 600 Å show appreciable soft magnetic properties. The saturation magnetization, Curie temperature and crystallization temperature increase by nitriding. The obtained compositionally modulated films mainly composed of Co-Nb-N are found to have high saturation magnetization ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4\piM_{s} \approx 10,000</tex> G) as well as high permeability ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\mui \geq 1,000</tex> at 10 MHz) and show high thermal stability even up to 580°C, which was impossible to attain for conventional amorphous films.

Magnetic properties of multilayered Fe/Cu film deposited by facing targets sputtering (abstract)

Iron and copper both form solid solutions with only a few atomic percent in ultimate concentration. Thus, multilayered films of ferromagnetic Fe and diamagnetic Cu provide unique means for investing the magnetic interaction among Fe thin layers distinctly separated by Cu layers and the role of Fe/Cu interface. Facing targets sputtering (FTS) apparatus has been developed for preparing multilayered films composed of very thin continuous layers of different metals with high mobility adatoms and low energy bombarding particles. Multilayered Fe/Cu films have been prepared on glass slide substrates by depositing alternatively Fe and Cu layers with 99.99% in purity using FTS apparatus. The thickness of individual Fe and Cu layers is in the range of 5–70 Å. Small-angle x-ray diffractometry indicates that the multilayered structure is formed even for each layer as thin as 5 Å. Saturation magnetization 4πMs of the Fe layer as thin as about 7 Å is comparable to that of bulk Fe. However, 4πMs of the films with an Fe layer thinner than 7 Å is remarkably small than that of the films with the thicker Fe layer. Coercivity Hc monotonously decreases with decreasing thicknesses of Fe and Cu layers from 70 Å to about 10 Å. The hysteresis M-H loop of the multilayered films with Fe layers thinner than 10 Å shows rotatable anisotropy, impling perpendicular anisotropy. When the thickness of the Fe layer is fixed at 13 Å, perpendicular anisotropy increases with decreasing the thickness of the Cu layer in the range below 13 Å. Heat treatments of the multilayered films up to 300 °C resulted in a change of layer structure and also magnetic properties. Dependence in magnetic properties and multilayered structures on annealing temperature will be discussed in detail.

Hydrogen and helium ion interaction with fused silica

Thermal degassing, hydrogen ion capture and re-emission are investigated. Some data on ion backscattering and surface layer structure change due to the ion bombardment and annealing are given. The activation energy for captured deuterium re-emission is defined as much as Q = 40 kcal/mol. The charge, angle and energy distributions of scattered particles are measured.Ion bombardment at 600–1000°C results in the emission of a significant amount of structural oxygen with a rate of approximately one atom per incident ion.

Vertical Structure of the Tropical Boundary Layer

Abstract Obsemations presented show that the undisturbed subcloud layer near the ITCZ resembles that of the trades. Mixed and transition layers are also seen between cloud drafts during disturbed periods when shallow mixed layers (∼200 m) can persist for several hours. Modification of the lower atmosphere during disturbed periods is most marked in the lowest 1200 m. Mixed layers are observed during prolonged disturbed periods; disturbed mixed layers are shallower and cooler than undisturbed ones. Light and moderate rainfall events moisten the mixed layer, but mixed layers in the environment around strong rainfall are drier. It is hypothesized that that the effect of a number of downdrafts spreading laterally produces the mixed layer cooling and drying. Observed changes of mixed layer structure with stability, measured by the ratio of mixed layer height to the Monin-Obukhov length, are presented.

An Initial Application of Polarization Lidar for Orographic Cloud Seeding Operations

Abstract Ground-based polarization lidar measurements have been obtained in conjunction with a commercial cloud seeding program to evaluate the potential of pulsed laser remote sensing techniques for increasing the effectiveness of orographic cloud seeding operations. The lidar measurements, supplemented by microwave radar cloud top and rawinsonde data, are shown to aid in the determination of seeding criteria. Our real-time seed, no-seed decisions based on lidar polarization measurements of cloud ice-water balance compare favorably with the declarations issued locally by the project meteorologists. Moreover, the lidar has detected changes in cloud layer structure and ice-water balance brought about by aerial seeding operations which are quite distinct from the background conditions, indicating that lidar observations may also find application as part of a physical evaluation method of seeding effects. It is concluded that despite the range limitations of lidar, the application of the remote sensing techn...

Soft mode behavior and anharmonicity of some two-dimensional layer compounds

The far infrared reflection spectra of the layer structure compounds of the type (CnH2n+1NH3)2MCL4, n=1,2,..., (M=Cu,Cd) have been measured in the region 10–200 cm−1 as function of temperature between 20 and 300 K. The change of the number of modes in the spectra at ∼120 K is in agreement with a structural phase transition where the layer structure changes from not entirely square to square with increasing temperature. The presence of two-phonon transitions in the spectra is an indication for anharmonicity of the potential energy. The observed strong increase of the damping of several modes with increasing temperature is explained by interaction with a (infrared inactive) soft mode of the two-dimensional layer. The critical temperature of this soft mode has been determined as 180 K for (CH3NH3)2CuCl4 and 160 K for (CH3NH3)2CdCl4.

An eclipse in the equatorial F-region

A study of the observed changes in the F-layer during an annular eclipse of the Sun at an equatorial station is presented. Values of the effective electron loss coefficients α and β are found; and some properties of these parameters are deduced. Changes of layer structure during the formation of an F1 1 2 - layer are shown. A measurement of the total columnar electron content during the eclipse demonstrates a pronounced eclipse effect in the topside ionosphere.