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A I Frenkel

Publications and source records attributed to A I Frenkel.

7 recordsLinked to original sources
PubMed2006

Strain-induced bond buckling and its role in insulating properties of Cr-doped V2O3.

Structural transformations around both V and Cr atoms in (V1-xCrx)2O3 across its metal-insulator transition (MIT) at x approximately 0.01 are studied by extended x-ray absorption fine-structure technique. Our new results for Cr made possible by the use of a novel x-ray analyzer that we developed reveal the substitutional mechanism of Cr doping. We find that this system has a buckled structure with short Cr-V and long V-V bonds. This system of bonds is disordered around the average trigonal lattice ascertained by x-ray diffraction. Such local distortions can result in a long range strain field that sets in around dilute Cr atoms in microscopic regions. We suggest that such locally strained regions should be insulating even at small x. The possibility of local insulating regions within a metallic phase, first suggested by Rice and Brinkman in 1972, remains unaccounted for in modern MIT theories.

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PubMed2005

Size-controlled synthesis and characterization of thiol-stabilized gold nanoparticles.

Size-controlled synthesis of nanoparticles of less than a few nanometers in size is a challenge due to the spatial resolution limit of most scattering and imaging techniques used for their structural characterization. We present the self-consistent analysis of the extended x-ray absorption fine-structure (EXAFS) spectroscopy data of ligand-stabilized metal nanoclusters. Our method employs the coordination number truncation and the surface-tension models in order to measure the average diameter and analyze the structure of the nanoparticles. EXAFS analysis was performed on the two series of dodecanethiol-stabilized gold nanoparticles prepared by one-phase and two-phase syntheses where the only control parameter was the gold/thiol ratio xi, varied between 6:1 and 1:6. The two-phase synthesis resulted in the smaller particles whose size decreased monotonically and stabilized at 16 A when xi was lowered below 1:1. This behavior is consistent with the theoretically predicted thermodynamic limit obtained previously in the framework of the spherical drop model of Au nanoparticles.

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PubMed2001

A study of the coordination environment in aqueous cadmium-thiol complexes by EXAFS spectroscopy: experimental vs. theoretical standards.

Using EXAFS, we investigated the changes in the local structure of Cd(II) complexes formed with a series of low-molecular-weight thiols at different thiol/cadmium stoichiometries. For dilute solutions, a comparison of theoretical and experimental standards proved the latter approach superior. The number of bound oxygen atoms decreased while the number of sulfur atoms increased as the thiol/cadmium ratios increased, indicating that up to four thiol compounds can bind to cadmium in aqueous solutions. The computer code FEFFIT was modified to employ experimental and theoretical standards with equal facility.

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