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Studies of the temperature dependence of the short range structure and local dynamics in silver borate glasses
No full textEXAFS temperature dependent measurements have been
carried out on the borate glass doped with silver iodide,
(AgI)0·55(Ag2O.4B2O3)0·45, at the K-edges of Ag and I,
in the range 39–500 K. Local negative thermal expansion
has been measured in the explored temperature range; in the same range, crystalline AgI shows a positive trend. This behaviour, already found for another silver borate glass containing a higher content of silver iodide, was interpreted in terms of a relaxing of the AgI amorphous network within the silver borate host matrix. In the light of the results obtained for the glass (AgI)0·55(Ag2O.4B2O3)0·45, having a much lower AgI concentration and showing an almost equal thermal expansion, a different interpretation is now necessary. The Ag–I first shell distance contraction is a specific characteristic of the AgI amorphous network within the silver borate host matrix: temperature increase favours shorter average distance of the mobile Ag+ cations from I ions. The host matrix influences, however, the local thermal disorder around Ag and I species
EXAFS and local thermal expansion: the case of silver oxide
No full textTemperature dependent extended X-ray absorption fine structure (EXAFS) measurements give original information
on local structure and dynamics of materials with framework structure, exhibiting negative thermal expansion. By
proper cumulant data analyses, the temperature dependence of the nearest neighbours distance can be directly measured
and the degree of rigidity of basic structural units monitored. Recent results obtained for Ag2O show that the
contraction of the lattice parameter is accompanied by the expansion of the 1st-shell Ag–O distance, and that the
deformation of the Ag4O tetrahedral units is not negligible
Dopant Redistribution Analysis in RiSi2/Si Systems by SIMS
No full textThe progressive shrinking of microelectronic devices has determined an increasing interest in silicides for contacts and interconnections manufactoring. In particular TiSi2 has shown the most interesting technological features, such as low resistivity, comparable with Al one, a good thermal stability, and the availability of self-aligning processes.
The analytical characterization of these materials plays a relevant role in developing and setting up the process necessary for the integration of the related technology in devices manufactoring. We develope an analytical pethodology in order to obtain accurate and reliable dopant depth profiles in TiSi2/Si systems by SIMS analysis.
We apply our methodology both to suitable standard samples and to some real device made in an industrial production proces
Local thermal expansion in a cuprite structure: the case of Ag2O
Full text linkThe local thermal behavior of the Ag2O framework structure has been studied by extended x-ray
absorption fine structure. The average Ag-O nearest-neighbor distance expands upon heating, while the
Ag-Ag next-nearest-neighbor distance contracts. An original implementation of the cumulant analysis
shows that the Ag-O expansion is a joint effect of potential anharmonicity and geometrical deformation
of the Ag4O basic tetrahedral units. Accordingly, the negative thermal expansion of the lattice parameter
in Ag2O cannot be explained uniquely in terms of rigid unit modes
Extended x-ray-absorption fine-structure measurements of copper: local dynamics, anharmonicity, and thermal expansion
Full text linkExtended x-ray-absorption fine-structure (EXAFS) of copper has been measured from 4 to 500 K and
analyzed by the cumulant method, to check the effectiveness of EXAFS as a probe of local dynamics and
thermal expansion. The comparison between parallel mean square relative displacements (MSRD) of the first
four coordination shells has allowed detecting a significant deviation from a pure Debye behavior. The firstshell
EXAFS thermal expansion is larger than the crystallographic one: the difference has allowed evaluating
the perpendicular MSRD, whose Debye temperature is slightly larger than the one of the parallel MSRD, due
to anisotropy effects. High-order first-shell cumulants are in good agreement with quantum perturbative models.
The anharmonic contribution to the first-shell parallel MSRD amounts to less than 1.5 percent. The third
cumulant cannot be neglected in the analysis, if accurate values of the first cumulant are sought; it cannot
however be used to directly estimate the thermal expansion. The shape of the effective pair potential is
independent of temperature; a rigid shift, partially due to the relative motion perpendicular to the bond
direction, is however observed
Local thermal expansion in copper: extended x-ray absorption fine-structure measurements and path-integral Monte Carlo calculations
Full text linkA combined approach has been used to study thermal effects on the extended x-ray absorption fine-structure
(EXAFS) of copper between 4 and 500 K. A phenomenological data analysis shows that the thermal expansions
measured from the first and third cumulants significantly differ between each other and from the crystallographic
thermal expansion. Path-integral Monte Carlo calculations of EXAFS cumulants have been performed,
using a many-body potential. The good reproduction of experimental values validates the
phenomenological analysis and opens more perspectives for applications to more complex systems. It is shown
that the reproduction of EXAFS parameters allows for a test of the interaction potentials with regard to
anharmonicity
Studies of the temperature dependence of the short range structure and local dynamics in silver borate glasses
No full textEXAFS temperature dependent measurements have been carried out on the borate glass doped with silver iodide, (AgI)(0.55)(Ag2O.4B(2)O(3))(0.45), at the K-edges of Ag and I, in the range 39-500 K Local negative thermal expansion has been measured in the explored temperature range; in the same range, crystalline AgI shows a positive trend. This behaviour, already found for another silver borate glass containing a higher content of silver iodide, was interpreted in terms of a relaxing of the AgI amorphous network within the silver borate host matrix. In the light of the results obtained for the glass (AgI)(0.55)(Ag2O.4B(2)O(3))(0.45), having a much lower AgI concentration and showing an almost equal thermal expansion, a different interpretation is now necessary. The Ag-I first shell distance contraction is a specific characteristic of the AgI amorphous network within the silver borate host matrix: temperature increase favours shorter average distance of the mobile Ag+ cations from I ions. The host matrix influences, however the local thermal disorder around Ag and I species
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