Analysis of weakly bonded oxygen in HfO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>/Si stacks by using HRBS and ARXPS

We have used transmission electron microscopy, high-resolution Rutherford backscattering spectrometry (HRBS), and angle-resolved X-ray photoelectron spectroscopy (ARXPS) to investigate the interfacial oxidized states of hafnium oxide/silicon oxide/Si gate oxide stacks. The atomic concentrations and profiles of HRBS analysis are similar before and after annealing; however, ARXPS shows a clear difference in bond status. These results imply that weakly bonded oxygen atoms existed in the stacks alongside the suboxides. In the as-deposited layers, dioxides are found at the interfaces and suboxides in the layers whereas after annealing suboxides are found at the interfaces and dioxides are found in the layers because of redistribution of bonds during annealing. The combination of HRBS and ARXPS analyses indicated that the main oxidized states transformed from the suboxides to the dioxides with no obvious quantitative difference in the content of oxygen atoms, suggesting that reactions of the weakly bonded oxygen atoms occurred with the suboxides within the layers.     

Analysis of Linewidth Tunable Terahertz Wave Generation in Periodically Poled Lithium Niobate

A new scheme of optical rectification of femtosecond laser pulses in a periodically poled lithium niobate crystal, which generates high energy and linewidth tunable multicycle terahertz (THz) pulses, is analyzed. The developed simple theoretical model allows investigating the generated THz spectrum and its dependence on spot size of the pump beam. It is shown that the transformation of THz radiation from narrowband to broadband is possible by simply reducing the pump beam size. The temporal waveform and energy of the multicycle THz pulses were calculated as well. It is shown that THz energy is inversely proportional to the pump beam size r _y , whereas energy spectral density is independent of r _y . The efficiency of optical-to-THz energy conversion for pump pulse energy of 1?mJ is estimated to be 0.8?×?10^?4. The possibility of tuning the generation frequency by changing the direction of the pump beam propagation is analyzed.     

On Homogeneous Nucleation of Dislocation Loops in Nanocrystalline Materials

In this article, we readdress the question of homogeneous nucleation of dislocation loops in the context of nanocrystalline materials. In this case, the commonly adopted assumption of an infinite medium is no longer valid, and image forces on dislocations must be accounted for in the analysis. An additional energy term associated with the presence of finite boundaries may act to promote homogeneous nucleation and growth of dislocation loops. Based on a simplified consideration of a circular dislocation loop in a spherical nanoparticle or nanosized grain in a polycrystal, energy calculations are carried out to estimate the activation energy for homogeneous nucleation of a dislocation loop in such a system. Two different cases are considered: (1) a single nanoparticle and (2) a grain in a polycrystalline nanomaterial. Based on simulations for aluminum, it is shown that this mechanism may be plausible in both cases, albeit only for small particles and grains in the nanometer range.     

Phase transformations during tempering of the Fe-15Cr-1Mo martensites containing nitrogen or carbon

Hardness measurements, dilatometry, internal friction measurements, Mössbauer spectroscopy and transmission electron microscopy are utilized in order to study the effect of tempering on the microstructure of a stainless martensitic steel containing 15% Cr, 1% Mo and 0.6% N. A similar carbon steel containing 15% Cr, 1% Mo and 0.6% C is used for comparison. Tempering of alloy Fe-15Cr-1Mo-0.6N in the low temperature range of 353-473 K leads to formation of hexagonal ?-nitride (Fe,Cr)₂N, which is followed by precipitation of the orthorombic ?-nitride (Fe,Cr)₂N at temperatures of 573-773 K. The hexagonal nitride Cr₂N is precipitated at 923 K and preferably formed at grain boundaries. The alloy Fe-15Cr-1Mo-0.6C shows the expected tempering behaviour. ?-carbide (Fe,Cr)₂C and cementite (Fe,Cr)₃C are precipitated during low temperature ageing, followed by the formation of Cr₇C₃ carbides after the temperature has risen to 873 K. With a similar interstitial content the amount of retained austenite in the nitrogen martensite is nearly twice as high as in the carbon one. Furthermore, the thermal stability of the retained austenite of the nitrogen alloy is substantially higher than that of the carbon steel.     

Long-term caregiving: What happens when it ends?

Data from a longitudinal study were used to examine what happens to caregivers in the years after their cognitively impaired spouse dies. Comparisons of 42 current caregivers, 49 former caregivers, and 52 noncaregivers over a 4-year period showed that former caregivers did not improve on several measures of psychological well-being. Although former caregivers experienced decreases in stress and negative affect, their scores on depression, loneliness, and positive affect did not rebound to levels comparable to noncaregivers and, in fact, remained similar to those of current caregivers up to 3 years after caregiving had ceased. The most consistent predictors of postcaregiving outcomes were social support and intrusive–avoidant thinking about caregiving. The data suggest that some consequences of long-term caregiving may be long-term as well. The needs of former spousal caregivers warrant greater attention both in research and in practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanical Properties and Bake Hardening Behaviour of two Cold Rolled Multiphase Sheet Steels subjected to CGL Heat Treatment Simulation

In recent years, multiphase steels have become a material of choice for use in the car manufacturing industry owing to their excellent mechanical properties. It is anticipated that in the years to come these steels will show the highest increase in usage. A particular aspect of their potential is that multiphase steels often show good bake hardening (BH) properties. The main factors that govern the microstructures and the properties of these steels are the chemical composition and the production process parameters. In this work two commercial cold rolled sheet steels with different carbon content were investigated. In order to produce dual phase (DP) steels with a ferrite‐martensite microstructure, the as‐received material was subjected to heat treatment simulating continuous galvanising line (CGL) cycles with an overageing zone before the zinc pot. After a first CGL cycle predominantly ferritic microstructures with small amounts of martensite, pearlite and retained austenite were obtained, which resulted in deviations from typical DP properties, e.g. in the occurrence of discontinuous yielding. A higher line speed led to improved mechanical properties. BH prestrain was varied between 0 and 10%. While only very little bake hardening was observed without prestrain, with increasing prestrain the amount of BH was evolving quickly towards larger values of more than 60 MPa. Generally, the BH values were somewhat larger for higher carbon content. Finally, an optimised CGL cycle was simulated at laboratory scale with changes in the process parameters. Thus, characteristic DP microstructures resulting in desired mechanical properties were obtained. For these optimised conditions, BH₂ values in excess of 60 MPa were achieved for both steels investigated.     

On a Crack in Viscoelastic Isotropic Media Opened by a Rigid Growing Wedge

Wedging of an isotropic linear viscoelastic space with crack by a rigid semi-infinite indentor is studied. The wedge is assumed to have growing with time thickness. An analysis is done in the framework of generalised Dugdale model and COD criterion using Volterra's principle. The results for safe wedge growth law as well as for the crack growth are obtained.     

Study of molecular packing density in boundary layers of some polymers

Packing density of macromolecules of some amorphous polymers, poly(methyl methacrylate), polystyrene and polydimethylsiloxane, in boundary layers formed at the solid-polymer interface, was studied by a ‘molecular probe’ technique. It was shown that the boundary layers of the above polymers have a complex structure composed of regions with different densities of molecular packing: a surface region of thickness 2 to 4 μm, and a transient and loosely-packed region of thickness of the order of 30 to 60 μm. It was established that both the structure and the thickness of boundary layers for each of the polymers depends both on polymer chain flexibility, and on cohesion energy density of a polymer.     

Generating vegetation leaf area index earth system data record from multiple sensors. Part 1: Theory

The generation of multi-decade long Earth System Data Records (ESDRs) of Leaf Area Index (LAI) and Fraction of Photosynthetically Active Radiation absorbed by vegetation (FPAR) from remote sensing measurements of multiple sensors is key to monitoring long-term changes in vegetation due to natural and anthropogenic influences. Challenges in developing such ESDRs include problems in remote sensing science (modeling of variability in global vegetation, scaling, atmospheric correction) and sensor hardware (differences in spatial resolution, spectral bands, calibration, and information content). In this paper, we develop a physically based approach for deriving LAI and FPAR products from the Advanced Very High Resolution Radiometer (AVHRR) data that are of comparable quality to the Moderate resolution Imaging Spectroradiometer (MODIS) LAI and FPAR products, thus realizing the objective of producing a long (multi-decadal) time series of these products. The approach is based on the radiative transfer theory of canopy spectral invariants which facilitates parameterization of the canopy spectral bidirectional reflectance factor (BRF). The methodology permits decoupling of the structural and radiometric components and obeys the energy conservation law. The approach is applicable to any optical sensor, however, it requires selection of sensor-specific values of configurable parameters, namely, the single scattering albedo and data uncertainty. According to the theory of spectral invariants, the single scattering albedo is a function of the spatial scale, and thus, accounts for the variation in BRF with sensor spatial resolution. Likewise, the single scattering albedo accounts for the variation in spectral BRF with sensor bandwidths. The second adjustable parameter is data uncertainty, which accounts for varying information content of the remote sensing measurements, i.e., Normalized Difference Vegetation Index (NDVI, low information content), vs. spectral BRF (higher information content). Implementation of this approach indicates good consistency in LAI values retrieved from NDVI (AVHRR-mode) and spectral BRF (MODIS-mode). Specific details of the implementation and evaluation of the derived products are detailed in the second part of this two-paper series.