scholarly journals Formation of Irregular Al Islands by Room-Temperature Deposition on NiAl(110)

2011 ◽  
Vol 1318 ◽  
Author(s):  
Dapeng Jing ◽  
Yong Han ◽  
Bariş Ünal ◽  
J. W. Evans ◽  
P. A. Thiel
Keyword(s):  
Room Temperature ◽  
Lattice Gas ◽  
Island Growth ◽  
Site Lattice ◽  
Adsorption Sites ◽  
Temperature Deposition ◽  
Diffusion Paths ◽  
Kinetics Of ◽  
And Diffusion ◽  
Multiple Adsorption

ABSTRACTSTM studies reveal that irregular non-equilibrium two-dimensional Al islands form during deposition of Al on NiAl(110) at 300 K. These structures reflect the multiple adsorption sites and diffusion paths available for Al adatoms on the binary alloy surface, as well as the details of inhibited edge diffusion and detachment-attachment kinetics of Al adatoms for numerous distinct step edge configurations. We attempt to capture these features by multi-site lattice-gas modeling incorporating DFT energetics for adatoms both at adsorption sites and transition states. This formulation enables description and elucidation of the observed island growth shapes.

Integrating multiple adsorption sites and tortuous diffusion paths into a metal–organic framework for C3H4/C3H6 separation

2019 ◽  
Vol 7 (44) ◽  
pp. 25254-25257 ◽  
Author(s):  
Xue-Qian Wu ◽  
Yabo Xie ◽  
Jing-Hao Liu ◽  
Tao He ◽  
Yong-Zheng Zhang ◽  
...  
Keyword(s):  
Metal Organic Framework ◽  
High Adsorption ◽  
Adsorption Sites ◽  
Open Metal Sites ◽  
Metal Organic ◽  
Diffusion Paths ◽  
High Adsorption Capacity ◽  
Multiple Adsorption ◽  
Excellent Selectivity ◽  
Organic Framework

By integrating open metal sites, Lewis basic sites, and tortuous diffusion paths, a new metal–organic framework has been designed and synthesized, which exhibits high adsorption capacity and excellent selectivity for separating a C3H4/C3H6 mixture.

scholarly journals Identification of stable adsorption sites and diffusion paths on nanocluster surfaces: an automated scanning algorithm

2019 ◽  
Vol 5 (1) ◽  
Author(s):  
Tibor Szilvási ◽  
Benjamin W. J. Chen ◽  
Manos Mavrikakis
Keyword(s):  
Potential Energy ◽  
Potential Energy Surfaces ◽  
Rational Design ◽  
Computational Cost ◽  
Three Dimensional ◽  
Adsorption Sites ◽  
Automated Method ◽  
Diffusion Paths ◽  
Energy Surfaces ◽  
And Diffusion

Abstract The diverse coordination environments on the surfaces of discrete, three-dimensional (3D) nanoclusters contribute significantly to their unique catalytic properties. Identifying the numerous adsorption sites and diffusion paths on these clusters is however tedious and time-consuming, especially for large, asymmetric nanoclusters. Here, we present a simple, automated method for constructing approximate 2D potential energy surfaces for the adsorption of atomic species on the surfaces of 3D nanoclusters with minimal human intervention. These potential energy surfaces fully characterize the important adsorption sites and diffusion paths on the nanocluster surfaces with accuracies similar to current approaches and at comparable computational cost. Our method can treat complex nanoclusters, such as alloy nanoclusters, and accounts for cluster relaxation and adsorbate-induced reconstruction, important for obtaining accurate energetics. Moreover, its highly parallelizable nature is ideal for modern supercomputer architectures. We showcase our method using two clusters: Au18 and Pt55. For Au18, diffusion of atomic hydrogen between the most stable sites occurs via non-intuitive paths, underlining the necessity of exploring the complete potential energy surface. By enabling the rapid and unbiased assessment of adsorption and diffusion on large, complex nanoclusters, which are particularly difficult to handle manually, our method will help advance materials discovery and the rational design of catalysts.

scholarly journals The Adsorption and Diffusion Manners of Hydrogen Atoms on Pt (100), Pt (110), and Pt (111) Surfaces

2018 ◽  
Vol 2018 ◽  
pp. 1-10
Author(s):  
Can Doğan Vurdu
Keyword(s):  
Binding Energy ◽  
Potential Energy ◽  
Potential Energy Surfaces ◽  
Surface Scattering ◽  
Hydrogen Atoms ◽  
Adsorption Sites ◽  
Diffusion Paths ◽  
Energy Surfaces ◽  
And Diffusion ◽  
Theoretical Results

In this study, the interactions between H atoms and the (100), (110), and (111) surfaces of platinum have been investigated by using the London-Eyring-Polanyi-Sato (LEPS) potential function. The adsorption zones (sites) and LEPS energy values of these sites have been determined theoretically. In addition, the potential-energy surfaces for each Pt surface have been obtained in detail. Further, the adsorption sites on the surface, scattering from the surface, diffusion paths on the surface, and transition regions to the subsurface, have been determined and the differences have been examined in detail among the surfaces. From these results, it is found that an H atom has the lowest binding energy at the hollow sites on the Pt (100) and Pt (111) surfaces and that it has the lowest binding energy at the long-bridge sites on the Pt (110) surface. It has also been determined that the hollow sites on the three surfaces are the regions through which H atoms can penetrate into the subsurface. In addition, it has also been found that, for each of the three Pt surfaces, the diffusion of an H atom across the surface may follow a bridge-hollow-bridge pathway. These results are in agreement with previous experimental and theoretical results. Besides, the adsorption and diffusion manners of hydrogen atoms on each of the Pt surfaces have been analyzed deeply.

Low Energy Ion Bombardment and Microstructural Evolution in Thin Films

1989 ◽  
Vol 157 ◽  
Author(s):  
Chih M. Yang ◽  
Harry A. Atwater
Keyword(s):  
Thin Films ◽  
Ion Bombardment ◽  
Island Growth ◽  
New Approach ◽  
Enhanced Diffusion ◽  
Rate Laws ◽  
Island Evolution ◽  
Diffusion Limited ◽  
Kinetics Of ◽  
And Diffusion

ABSTRACTA new approach to modeling the evolution of islands in thin films by growth and coarsening during ion bombardment is described. Solution of a continuity equation and matter conservation relation, coupled with interface-limited and diffusion-limited rate laws for island growth and coarsening allows the kinetics of island evolution to be modeled. Results from the model indicate distinct kinetic paths for island evolution during ion bombardment as a result of growth, enhanced diffusion, island dissociation and monomer sputtering.

Atomistic Aspects of Silicide Reactions Studied with STM

1993 ◽  
Vol 320 ◽  
Author(s):  
P. A. Bennett ◽  
S. A. Parikh ◽  
M. Y. Lee ◽  
David G. Cahill ◽  
M. Copel ◽  
...  
Keyword(s):  
Room Temperature ◽  
Lattice Gas ◽  
Bond Breaking ◽  
Prototype System ◽  
Near Surface ◽  
Metal Atoms ◽  
Temperature Deposition ◽  
Low Coverage ◽  
Stm Images ◽  
Very High

ABSTRACTWe discuss atomistic aspects of the silicide contact reaction inferred primarily from STM observations of the prototype system Co/Si(1 11). For room temperature deposition and low coverage (0.01M1) we find that metal atoms exist as near-surface interstitials within the 7×7 reconstruction. Bond breaking associated with silicide formation occurs only at higher coverages. Deposition at 320C results in flat-topped triangular islands of epitaxial CoSi2 with a metastable 7-fold (111) interface, stabilized by the lateral silicon-silicide interface along the island edges. Some islands are covered with a 2×2 array of silicon adatoms. Very high temperature annealing (1200C) results in an “impurity stabilized 1×1” surface which is in fact a lattice gas of ring-clusters that appear like tiny donuts or bagels in empty states STM images. These structures phase-separate from the clean 7×7 structure upon cooling below 850C.

A Comparative Study of Thin-Film and Bulk Reaction Kinetics and Diffusion Path: the Ir/GaAs System

1988 ◽  
Vol 144 ◽  
Author(s):  
Kevin J. Schulz ◽  
Y. Austin Chang
Keyword(s):  
Thin Film ◽  
Reaction Kinetics ◽  
Equilibrium Phase ◽  
Bulk Diffusion ◽  
Diffusion Path ◽  
Phase Sequence ◽  
Bulk Reaction ◽  
Diffusion Paths ◽  
Kinetics Of ◽  
And Diffusion

ABSTRACTControl of the structure and chemistry at the interfaces of compound semiconductors is essential for the commercial use of these materials in electronic and optical technologies. This can only be achieved when the governing thermodynamics and kinetics of interfacial reactions are understood. Based primarily on the experience of metal/Si interactions, however, a prevailing belief was born that thin-film reactions follow a separate set of thermodynamic and kinetic “rules” which are different from bulk reactions. The intent of our work has been to not only characterize metal/GaAs contact reactions but also to rationalize these reactions with equilibrium phase diagrams and bulk metal/GaAs diffusion couple experiments. Through this approach, a better understanding of thin-film and bulk differences has been obtained.The Ir/GaAs system is used as an example. Phase formation and reaction kinetics were studied for 30 nm Ir films on (100) GaAs using TEM, XTEM, and AEM. Bulk diffusion between 0.25 mm thick Ir foil and (100) GaAs wafers was studied with SEM and electron probe microanalysis (EPMA). The diffusion paths and kinetics were the same for thin-film and bulk. The phase sequence Ir/IrGa/IrAs2/GaAs formed for all diffusion couples. Reaction kinetics were parabolic with an activation energy of 3.0 eV for both thin-film and bulk, and the data was colinear in an Arrhenius plot. Reacted layer morphology in both cases was layered. The effects of grain size, crystallographic texturing, and the relative diffusivities of the components on the reaction mechanisms in bulk versus thin-film reactions are considered.

Investigation of irradiation-induced nucleation processes in silicon and germanium

1995 ◽  
Vol 53 ◽  
pp. 224-225
Author(s):  
Harry A. Atwater ◽  
C.M. Yang ◽  
K.V. Shcheglov
Keyword(s):  
Room Temperature ◽  
Crystal Size ◽  
Initial Distribution ◽  
Engineering Control ◽  
Size Evolution ◽  
Silicon And Germanium ◽  
Ge Quantum Dot ◽  
And Control ◽  
Germanium Quantum Dots ◽  
Kinetics Of

Studies of the initial stages of nucleation of silicon and germanium have yielded insights that point the way to achievement of engineering control over crystal size evolution at the nanometer scale. In addition to their importance in understanding fundamental issues in nucleation, these studies are relevant to efforts to (i) control the size distributions of silicon and germanium “quantum dots𠇍, which will in turn enable control of the optical properties of these materials, (ii) and control the kinetics of crystallization of amorphous silicon and germanium films on amorphous insulating substrates so as to, e.g., produce crystalline grains of essentially arbitrary size.Ge quantum dot nanocrystals with average sizes between 2 nm and 9 nm were formed by room temperature ion implantation into SiO2, followed by precipitation during thermal anneals at temperatures between 30°C and 1200°C[1]. Surprisingly, it was found that Ge nanocrystal nucleation occurs at room temperature as shown in Fig. 1, and that subsequent microstructural evolution occurred via coarsening of the initial distribution.

Comparative Labelling and Biokinetic Studies of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn)

1977 ◽  
Vol 16 (01) ◽  
pp. 30-35 ◽  
Author(s):  
N. Agha ◽  
R. B. R. Persson
Keyword(s):  
Complex Formation ◽  
Significant Influence ◽  
Room Temperature ◽  
Ph Value ◽  
Maximum Activity ◽  
Reduction Step ◽  
Labelling Yield ◽  
Different Temperatures ◽  
Kinetics Of

SummaryGelchromatography column scanning has been used to study the fractions of 99mTc-pertechnetate, 99mTcchelate and reduced hydrolyzed 99mTc in preparations of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn). The labelling yield of 99mTc-EDTA(Sn) chelate was as high as 90—95% when 100 μmol EDTA · H4 and 0.5 (Amol SnCl2 was incubated with 10 ml 99mTceluate for 30—60 min at room temperature. The study of the influence of the pH-value on the fraction of 99mTc-EDTA shows that pH 2.8—2.9 gave the best labelling yield. In a comparative study of the labelling kinetics of 99mTc-EDTA(Sn) and 99mTc- DTPA(Sn) at different temperatures (7, 22 and 37°C), no significant influence on the reduction step was found. The rate constant for complex formation, however, increased more rapidly with increased temperature for 99mTc-DTPA(Sn). At room temperature only a few minutes was required to achieve a high labelling yield with 99mTc-DTPA(Sn) whereas about 60 min was required for 99mTc-EDTA(Sn). Comparative biokinetic studies in rabbits showed that the maximum activity in kidneys is achieved after 12 min with 99mTc-EDTA(Sn) but already after 6 min with 99mTc-DTPA(Sn). The long-term disappearance of 99mTc-DTPA(Sn) from the kidneys is about five times faster than that for 99mTc-EDTA(Sn).

Kinetics of the Thermal Disappearance of Radicals Formed During the Radiolysis of Aspartic Acid

2009 ◽  
Vol 59 (12) ◽  
Author(s):  
Mihai Contineanu ◽  
iulia Contineanu ◽  
Ana Neacsu ◽  
Stefan Perisanu
Keyword(s):  
Thermal Resistance ◽  
Aspartic Acid ◽  
Room Temperature ◽  
Esr Spectra ◽  
Complex Mechanism ◽  
Radical Species ◽  
Mechanisms Of Formation ◽  
Kinetics Of

The radiolysis of the isomers L-, D- and DL- of the aspartic acid, in solid polycrystalline state, was investigated at room temperature. The analysis of their ESR spectra indicated the formation of at least two radicalic entities. The radical, identified as R3, resulting from the deamination of the acid, exhibits the highest concentration and thermal resistance. Possible mechanisms of formation of three radical species are suggested, based also on literature data. The kinetics of the disappearance of radical R3 indicated a complex mechanism. Three possible variants were suggested for this mechanism.

The Reactivity of Different Active Forms of Sodium Carbonate with Respect to Sulfur Dioxide

1992 ◽  
Vol 57 (11) ◽  
pp. 2302-2308
Author(s):  
Karel Mocek ◽  
Erich Lippert ◽  
Emerich Erdös
Keyword(s):  
Thermal Decomposition ◽  
Liquid Phase ◽  
Sulfur Dioxide ◽  
Specific Surface ◽  
Surface Area ◽  
Sodium Carbonate ◽  
Room Temperature ◽  
Active Form ◽  
The Other ◽  
Kinetics Of

The kinetics of the reaction of solid sodium carbonate with sulfur dioxide depends on the microstructure of the solid, which in turn is affected by the way and conditions of its preparation. The active form, analogous to that obtained by thermal decomposition of NaHCO3, emerges from the dehydration of Na2CO3 . 10 H2O in a vacuum or its weathering in air at room temperature. The two active forms are porous and have approximately the same specific surface area. Partial hydration of the active Na2CO3 in air at room temperature followed by thermal dehydration does not bring about a significant decrease in reactivity. On the other hand, if the preparation of anhydrous Na2CO3 involves, partly or completely, the liquid phase, the reactivity of the product is substantially lower.

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