Synchrotron X-ray Diffraction Studies of Surface Phase Transitions PDF Download
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Author: Kenneth W. Evans-Lutterodt
Publisher:
ISBN:
Category :
Languages : en
Pages : 264
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Author: Kenneth W. Evans-Lutterodt
Publisher:
ISBN:
Category :
Languages : en
Pages : 264
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Author: Ola Synnergren
Publisher:
ISBN:
Category : Phase transformations (Statistical physics)
Languages : en
Pages : 146
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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The behavior of nanocrystals under extreme pressure was investigated using synchrotron x-ray diffraction. A major part of this investigation was the testing of a prototype synchrotron endstation on a bend magnet beamline at the Advanced Light Source for high pressure work using a diamond anvil cell. The experiments conducted and documented here helped to determine issues of efficiency and accuracy that had to be resolved before the construction of a dedicated ''super-bend'' beamline and endstation. The major conclusions were the need for a cryo-cooled monochromator and a fully remote-controllable pressurization system which would decrease the time to change pressure and greatly reduce the error created by the re-placement of the diamond anvil cell after each pressure change. Two very different types of nanocrystal systems were studied, colloidal iron oxide (Fe[sub 2]O[sub 3]) and thin film TiN/BN. Iron oxide nanocrystals were found to have a transition from the[gamma] to the[alpha] structure at a pressure strongly dependent on the size of the nanocrystals, ranging from 26 GPa for 7.2 nm nanocrystals to 37 GPa for 3.6 nm nanocrystals. All nanocrystals were found to remain in the[alpha] structure even after release of pressure. The transition pressure was also found, for a constant size (5.7 nm) to be strongly dependent on the degree of aggregation of the nanocrystals, increasing from 30 GPa for completely dissolved nanocrystals to 45 GPa for strongly aggregated nanocrystals. Furthermore, the x-ray diffraction pattern of the pressure induced[alpha] phase demonstrated a decrease in intensity for certain select peaks. Together, these observations were used to make a complete picture of the phase transition in nanocrystalline systems. The size dependence of the transition was interpreted as resulting from the extremely high surface energy of the[alpha] phase which would increase the thermodynamic offset and thereby increase the kinetic barrier to transition that must be overridden with pressure. The anomalous intensities in the x-ray diffraction patterns were interpreted as being the result of stacking faults, indicating that the mechanism of transition proceeds by the sliding of[gamma](111) planes to form[alpha](001) planes. The increasing transition pressure for more aggregated samples may be due to a positive activation volume, retarding the transition for nanocrystals with less excess (organic) volume available to them. The lack of a reverse transition upon decompression makes this interpretation more difficult because of the lack of an observable hysteresis, and it is therefore difficult to ascertain kinetic effects for certain. In the case TiN/BN nanocomposite systems, it was found that the bulk modulus (B[sub 0]) of the TiN nanoparticles was not correlated to the observed hardness or Young's modulus of the macroscopic thin film. This indicates that the origin of the observed super-hard nature of these materials is not due to any change in the Ti-N interatomic potential. Rather, the enhanced hardness must be due to nano-structural effects. It was also found that during pressurization the TiN nanoparticles developed a great deal of strain. This strain can be related to defects induced in individual nanoparticles which generates strain in adjacent particles due to the highly coupled nature of the system.
Author: Stephen Gerald Prilliman
Publisher:
ISBN:
Category :
Languages : en
Pages : 342
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Author: J. Bohr
Publisher:
ISBN:
Category :
Languages : en
Pages : 135
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Author: Jakob Bohr
Publisher:
ISBN: 9788755010147
Category : Gases, Rare
Languages : en
Pages : 135
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Author: Hartmut Zabel
Publisher: Springer Science & Business Media
ISBN: 3642771440
Category : Science
Languages : en
Pages : 237
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Book Description
Owing to the increased availability of synchrotron sources, surface X-ray scattering is a rapidly expanding technique with important applications to surface structures and surface phase transitions, roughening of surfaces and interfaces, and the structure of liquid surfaces, including polymers, liquid crystals, and organic films. Surface studies with neutrons, on the other hand provide important information on liquid andmagnetic films. The contributions to this volume, written by active researchers in the field, provide an up-to-date overview of the highly sophisticated techniques and their applications.
Author: Jae Pill Chang
Publisher:
ISBN:
Category :
Languages : en
Pages : 334
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Author: H. Taub
Publisher: Springer Science & Business Media
ISBN: 1468459708
Category : Science
Languages : en
Pages : 505
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The Advanced Study Institute (AS I) entitled "Phase Transitions in Surface Films" was held at the Ettore Majorana Centre for Scientific Culture in Erice, Sicily from June 19 to June 29, 1990. It reviewed the present understanding (experimental and theoretical) of phase transitions of surfaces, interfaces, and thin ftlms as well as the related structural and dynamical properties of these systems. From its inception, this ASI was envisioned as a sequel to one of the same title organized eleven years earlier by J. G. Dash and J. Ruvalds which was also held at the Ettore Majorana Centre. The previous ASI reflected the progress which had been made in understanding quasi two-dimensional (2D) states of matter, particularly adsorbed monolayers, and the phase transitions which occur in them. At that time, the field was barely ten years old. The modern field to which we are referring here can be traced to the landmark experiments of A. Thorny and X. Duval. Beginning in 1967, they published a series of papers presenting evidence from vapor pressure measurements of 2D phases of krypton and other gases adsorbed on polycrystalline (exfoliated) graphite. Their work led to a large number of thermodynamic and scattering experiments on physisorbed ftlms. This in turn motivated a great deal of theoretical interest in 2D systems and their phase transitions.
Author: J.G. Dash
Publisher: Springer Science & Business Media
ISBN: 1461330572
Category : Science
Languages : en
Pages : 369
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Book Description
The Advanced Study Institute on Phase Transitions in Surface Films was held at the Ettore Majorana Centre for Scientific Cul ture in Erice, Sicily, during June 11 to June 25, 1979. This Institute was the second course of the International School of Low Temperature Physics which was established at the Centre in 1977, with the guidance and inspiration of T. Regge and A. Zichichi. The 1979 course selected a topic on one of the most rapidly advancing fields of condensed matter physics in the late 70's. The program of topics and speakers was developed with the advice of the Organizing Committee, composed of J. Friedel, N. D. Mermin, R. E. Peierls, T. Regge and J. Wheatley. These two weeks were memorable for the range and depth of the lectures and seminars, and the sustained high interest of the students and faculty through a damanding schedule of over 5 hours a day of formal sessions. A large fraction of the leading researchers in the field were there. It would have been impossible to gather such a large group five years earlier, for the field itself is hardly 10 years old. Although the foundations of the thermodynamics of surface films were laid down by Gibbs about 100 years ago, and experiments on oil/water monolayers were carried out by Pockels and Rayleigh at about the same time, the beginnings of the modern field were much more recent.
