Tunnel current in self-assembled monolayers of 3-mercaptopropyltrimethoxysilane

The current density-voltage (J-V) characteristics of self assembled monolayers of 3-mercaptopropyltrimethoxysilane (MPTMS) chemisorbed on the native oxide surface of p+-doped Si demonstrate the excellent tunnel dielectric behavior of organic monolayers down to 3 carbon atoms. The J-V characteristics of MPTMS SAMs on Si are found to be asymmetric, and the direction of rectification has been found to depend upon the applied voltage range. At voltages < 2.45V, the reverse bias current was found to be higher than forward bias current; while at higher voltages this trend was reversed. This result is in agreement with Simmons theory. The tunnel barrier heights for this short chain (2.56 and 2.14 eV respectively at Au and Si interfaces) are in good agreement with the ones for longer chains (>10 carbon atoms) if the chain is chemisorbed at the electrodes. These results extend all previous experiments on such molecular tunnel dielectrics down to 3 carbon atoms. This suggests that these molecular monolayers, having good tunnel behavior (up to 2.5 eV) over a large bias range, can be used as gate dielectric well below the limits of Si-based dielectrics.Comment: Small, in pres

Structural disorder in alkaline earth metal doped Ba_xMn[Fe(CN)₆]₂(x+1)/3&#183;zH₂O molecular magnets: a reverse Monte Carlo study

We report a detailed structural disorder study of the BaxMn[Fe(CN)6]2(x+1)/3&#183;zH2O (x = 0 and 0.3) molecular magnets by carrying out Reverse Monte Carlo (RMC) simulations of neutron diffraction data. Both samples have also been investigated using X-ray diffraction, infrared spectroscopy and dc magnetization techniques. Rietveld refinement of X-ray and neutron diffraction patterns confirmed the single phase formation for both compounds in a face-centered cubic structure. IR spectral study establishes the presence of cyanide flipping in both compounds, thereby revealing inherent structural disorder in the compounds. A ferrimagnetic coupling of Mn2+ (S = 5/2) spins and the Fe3+ (S = 1/2) spins is found for both compounds. Results of RMC simulations of neutron diffraction data for both compounds show that: (i) around the coordinated oxygen atoms (located at the 24e crystallographic sites with [Fe(CN)6] vacancies), there are formations of small clusters of non-coordinated oxygen atoms; and (ii) Ba substitution leads to a reduction in this structural disorder. The role of reduced water content as well as vacancies of [Fe(CN)6] towards the observed reduction in the structural disorder is discussed

SOM assembly of hydroxynaphthoquinone and its oxime: Polymorphic X-ray structures and EPR studies

22-12 FIELD Section Title:Physical Organic Chemistry 6, 26, 41, 52, 75 Department of Chemistry,University of Pune,Pune,India. FIELD URL: written in English.Study on solvent-induced polymorphism in x-ray structures of 2-hydroxy-1,4-naphthoquinone (Lawsone) 1, is carried out. In protic methanol, 1 crystallizes in monoclinic space group P21/c (1a) comprising of 2-dimensional hydrogen bonded network via cyclic dimers. In aprotic solvent such as acetone however, 1 exhibits orthorhombic space group Pna21 (1b) and emerges with 1-dimensional catemeric chain. Solvent-induced topol. isomerism of cyclic dimers and helical catemeric chains arising from (i) bifurcated intra- and inter mol. hydrogen bondings viz. O-H...O-C interactions between C(2) hydroxyl and C(1), C(4) carbonyls, (ii) C-H...O interactions viz., C(3)-H...O(1)C(1) were discussed. A signal for radical in 1 at g = 2.0058 is signatured by EPR spectrum and it's oxime deriv. viz. 2-hydroxy-4-naphthoquinone-1-oxime 2, in solid state shows biradical and monoradical formation with aggregation of dimer and monomer due to noncovalent hydrogen bonds. Zero field split parameters for 2 are D = 215 G, Ex = 13 G, Ey = 47 G at 298 K A half field signal at 77 K indicates triplet ground state. Frozen glass EPR of 2 resolves as regioregular dimeric-monomeric species showing hyperfine interactions with 1-oximino nitrogen in dimer .hivin.A(14N) = 15.5 G. [on SciFinder (R)