EVANESCENT X-RAYS PROBING SURFACE-DOMINATED PHASE TRANSITIONS

1992 ◽  
Vol 06 (17) ◽  
pp. 2773-2808 ◽  
Author(s):  
H. DOSCH
Keyword(s):  
Free Surface ◽  
Phase Transitions ◽  
Surface Segregation ◽  
Theoretical Models ◽  
X Rays ◽  
Near Surface ◽  
Disorder Transition ◽  
Angle Scattering ◽  
Strong Surface ◽  
Experimental Findings

This article reviews the scattering of evanescent x-ray waves as they occur inside a solid in the regime of total external reflection. The theoretical and experimental details of glancing angle scattering and the use of synchrotron radiation are discussed. It is shown how strong surface disorder and surface roughness affect the Bragg scattering of these exponentially damped waves and how these scattering signals can be interpreted in a straightforward way within the distorted wave Born approximation (DWBA). The application of this novel surface technique to bulk phase transitions allows the observation of surface-dominated behaviour. This is illustrated via two examples:. 1. The discontinuous order-disorder transition in Cu 3 Au has been studied near the (001) and (111) surface by evanescent x-rays. It turns out that the order parameter close to the free surface of the alloy decays in a very pronounced way upon approaching the transition temperature. The quantitative analysis of the evanescent superlattice intensity is compatible with a wetting phenomenon. 2. The critical phenomena associated with the continuous order-disorder transition in Fe 3 Al become distinctly modified due to the presence of a free surface. By applying the evanescent wave method three new universal surface exponents β1, γ11 and η‖ could be determined. This allows for the first time a critical exprimental test of surface scaling relations which turn out to be in good agreement with the experimental findings. At the surface of binary alloys surface segregation phenomena occur which complicate the experimental observation of near-surface ordering and disordering phenomena as well as the theoretical models which have to account for these effects. Some implications of these surface effects is briefly presented.

COMPARATIVE STUDY ON THEORETICAL MODELS AND DESIGN CODES FOR THE SHEAR CONTRIBUTION OF NSM FRP BARS IN RC BEAMS

2016 ◽  
Vol 78 (5) ◽  
Author(s):  
Abdul Aziz Abdul Samad ◽  
Noridah Mohamad ◽  
Josef Hadipramana ◽  
Mohamad Razi Ashaari Amiruddin
Keyword(s):  
Comparative Study ◽  
Theoretical Models ◽  
Design Codes ◽  
Rc Beams ◽  
Near Surface ◽  
Reinforced Polymer ◽  
Close Observation ◽  
Fibre Reinforced Polymer ◽  
Near Surface Mounted ◽  
Experimental Findings

This paper presents a comparative study on various theoretical models and design codes for the shear contribution of Near-Surface Mounted (NSM) using Fibre Reinforced Polymer bars to reinforced concrete (RC) beams. Theoretical models from De Lorenzis and A. Nanni, Anwarul Islam and Diaz and Barros, and ACI440.1R-06 and CSA-S806 design codes were selected. All the equations were compared by integrating experimental parameters from Rizzo and De Lorenzis, and Cisneros D. et al. From analysis, it was observed that the theoretical models shows substantial differences by underestimating the experimental findings of Rizzo and De Lorenzis from -68% to -38%. Similarly with Cisneros experimental work, the three theoretical models also produces large differences ranging from -73% to +41%. The analysis from the two design codes from ACI440.1R-06 and CSA-S806 also resulted with both design codes having significant differences ranging from -60% to +48%. However, from close observation, Dias and Barros theoretical model showed more accuracy by having a difference of just -4% with ACI440.1R-06 design code giving a much higher but acceptable difference of +26% compared to CSA-S806 at -60%. 

scholarly journals Small-Angle Scattering from Fractals: Differentiating between Various Types of Structures

Symmetry ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 65 ◽  
Author(s):  
Eugen Mircea Anitas
Keyword(s):  
Small Angle ◽  
Scattering Problem ◽  
Inverse Scattering Problem ◽  
Theoretical Models ◽  
Small Angle Scattering ◽  
X Rays ◽  
Fractal Structures ◽  
Practical Applications ◽  
Additional Information ◽  
Angle Scattering

Small-angle scattering (SAS; X-rays, neutrons, light) is being increasingly used to better understand the structure of fractal-based materials and to describe their interaction at nano- and micro-scales. To this aim, several minimalist yet specific theoretical models which exploit the fractal symmetry have been developed to extract additional information from SAS data. Although this problem can be solved exactly for many particular fractal structures, due to the intrinsic limitations of the SAS method, the inverse scattering problem, i.e., determination of the fractal structure from the intensity curve, is ill-posed. However, fractals can be divided into various classes, not necessarily disjointed, with the most common being random, deterministic, mass, surface, pore, fat and multifractals. Each class has its own imprint on the scattering intensity, and although one cannot uniquely identify the structure of a fractal based solely on SAS data, one can differentiate between various classes to which they belong. This has important practical applications in correlating their structural properties with physical ones. The article reviews SAS from several fractal models with an emphasis on describing which information can be extracted from each class, and how this can be performed experimentally. To illustrate this procedure and to validate the theoretical models, numerical simulations based on Monte Carlo methods are performed.

Phase Transitions Near Surfaces Studied By Grazing Incidence Diffraction of X-Rays

1990 ◽  
Vol 208 ◽  
Author(s):  
L. Mailander ◽  
H. Dosch ◽  
J. Peisl ◽  
R. L. Johnson
Keyword(s):  
Phase Transitions ◽  
Transition Temperature ◽  
Single Crystal ◽  
Critical Behavior ◽  
Scaling Laws ◽  
Grazing Incidence ◽  
Critical Surface ◽  
X Rays ◽  
Near Surface ◽  
Grazing Incidence Diffraction

ABSTRACTWe review two different experiments in order to demonstrate the power of grazing incidence diffraction of x-rays in studying phase transitions near surfaces and to show that it is well suited to get information on structural details even from subsurface layers: We have measured the near surface critical scattering at the continuous order disorder transition of an Fe3Al single crystal which provides information on modifications of critical behavior of a bulk transition near a surface. These modifications are detectable to a considerable depth due to the diverging range of correlations. We determined three different critical surface exponents which allow, for the first time, to confirm scaling laws for near surface critical behavior.- The experiment at a (100) surface of a discontinuous ordering Cu3Au single crystal shows that the surface is wetted by a disordered layer below the transition temperature. By means of the adjustable depth sensitivity of grazing incidence scattering we were able to demonstrate that the thickness of this layer increases logarithmically when approaching the transition temperature.

Near-Surface Aggregation of Sn In Heavily Sn-Doped GaAs Films Grown By Molecular Beam Epitaxy

1985 ◽  
Vol 43 ◽  
pp. 368-369
Author(s):  
S. H. Chen
Keyword(s):  
Molecular Beam Epitaxy ◽  
Cross Section ◽  
Electron Spectroscopy ◽  
Molecular Beam ◽  
Surface Segregation ◽  
Secondary Ion Mass Spectrometry ◽  
Specimen Preparation ◽  
Near Surface ◽  
Gaas Films ◽  
Secondary Ion

Sn has been used extensively as an n-type dopant in GaAs grown by molecular-beam epitaxy (MBE). The surface accumulation of Sn during the growth of Sn-doped GaAs has been observed by several investigators. It is still not clear whether the accumulation of Sn is a kinetically hindered process, as proposed first by Wood and Joyce, or surface segregation due to thermodynamic factors. The proposed donor-incorporation mechanisms were based on experimental results from such techniques as secondary ion mass spectrometry, Auger electron spectroscopy, and C-V measurements. In the present study, electron microscopy was used in combination with cross-section specimen preparation. The information on the morphology and microstructure of the surface accumulation can be obtained in a fine scale and may confirm several suggestions from indirect experimental evidence in the previous studies.

scholarly journals Thermal properties of metal-halide perovskites

2020 ◽  
Vol 8 (41) ◽  
pp. 14289-14311
Author(s):  
Tobias Haeger ◽  
Ralf Heiderhoff ◽  
Thomas Riedl
Keyword(s):  
Thermal Properties ◽  
Phase Transitions ◽  
Metal Halide ◽  
Halide Perovskites ◽  
Experimental Findings

The thermal properties of metal-halide perovskites are reviewed with respect to experimental findings, theoretical insights, dimensionalities, and phase transitions.

Mesoscopic structure of SiC fibers by neutron and x-ray scattering

1996 ◽  
Vol 11 (5) ◽  
pp. 1169-1178 ◽  
Author(s):  
Kentaro Suzuya ◽  
Michihiro Furusaka ◽  
Noboru Watanabe ◽  
Makoto Osawa ◽  
Kiyohito Okamura ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Volume Fraction ◽  
X Rays ◽  
X Ray ◽  
Sic Fibers ◽  
X Ray Scattering ◽  
Mesoscopic Structure ◽  
Angle Scattering ◽  
Momentum Transfer Range ◽  
First Time

Mesoscopic structures of SiC fibers produced from polycarbosilane by different methods were studied by diffraction and small-angle scattering of neutrons and x-rays. Microvoids of a size of 4–10 Å in diameter have been observed for the first time by neutron scattering in a medium momentum transfer range (Q = 0.1–1.0 Å−1). The size and the volume fraction of β–SiC particles were determined for fibers prepared at different heat-treatment temperatures. The results show that wide-angle neutron scattering measurements are especially useful for the study of the mesoscopic structure of multicomponent materials.

scholarly journals Experiments on generation of surface waves by an underwater moving bottom

2015 ◽  
Vol 471 (2178) ◽  
pp. 20150069 ◽  
Author(s):  
Timothée Jamin ◽  
Leonardo Gordillo ◽  
Gerardo Ruiz-Chavarría ◽  
Michael Berhanu ◽  
Eric Falcon
Keyword(s):  
Free Surface ◽  
Surface Waves ◽  
Surface Deformation ◽  
Fluid Layer ◽  
Fluid Velocity ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Low Pass ◽  
Spatio Temporal ◽  
Experimental Findings

We report laboratory experiments on surface waves generated in a uniform fluid layer whose bottom undergoes an upward motion. Simultaneous measurements of the free-surface deformation and the fluid velocity field are focused on the role of the bottom kinematics (i.e. its spatio-temporal features) in wave generation. We observe that the fluid layer transfers bottom motion to the free surface as a temporal high-pass filter coupled with a spatial low-pass filter. Both filter effects are often neglected in tsunami warning systems, particularly in real-time forecast. Our results display good agreement with a prevailing linear theory without any parameter fitting. Based on our experimental findings, we provide a simple theoretical approach for modelling the rapid kinematics limit that is applicable even for initially non-flat bottoms: this may be a key step for more realistic varying bathymetry in tsunami scenarios.

Calculation of the low angle scattering of X-rays for different models of oriented polymer structures

1976 ◽  
Vol 18 (6) ◽  
pp. 1509-1516 ◽  
Author(s):  
B.A. Asherov ◽  
B.M. Ginzburg ◽  
S.Ya. Frenkel'
Keyword(s):  
X Rays ◽  
Oriented Polymer ◽  
Angle Scattering
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