Unconventional bismuthate glasses containing lithium oxide have been prepared by a conventional meltquench technique. X-ray diffraction, scanning electron microscopy, and differential thermal analysis show that stable binary glasses of composition xLi 2 O-(100-x)Bi 2 O 3 can be achieved for xϭ20-35 mol %. Systematic variation of the glass-transition temperature, density, and molar volume observed in these glasses indicates no significant structural change with composition. Differential thermal analysis and optical studies show that the strength of the glass network decreases with the increase of Li 2 O content in the glass matrix with a small deviation for the extra stable 30Li 2 O-70Bi 2 O 3 glass composition. Studies of Raman spectra and molar volume ensure that all glasses are built up of ͓BiO 6 ͔ octahedral units, while the influence of Li ϩ ions in the glass matrix is also confirmed from optical, Raman, and electrical studies. Wide transmitting window in the optical region having sharp cutoffs in both ultraviolet-visible and infrared regimes may make these glasses useful in spectral devices. High dielectric values in these glasses compared to glasses formed with conventional glass former can be attributed to the influence of the high polarizability of the unconventional network forming cations, Bi 3ϩ. ͓S0163-1829͑97͒08937-6͔

A Langmuir monolayer of stearic acid on pure water and in the presence of certain divalent metal ions such as Cd and Pb at pH approximately 6.5 of the subphase water collapses at constant area, while for other divalent ions such as Mg, Co, Zn, and Mn at the same subphase pH the monolayer collapses nearly at constant pressure. Films of stearic acid with Cd, Pb, Mn, and Co in the subphase (at pH approximately 6.5) have been transferred onto hydrophilic Si(001) using a horizontal deposition technique, just after and long after collapse. Electron density profiles obtained from X-ray reflectivity analysis show that a three-molecular-layer structure starts to form just after constant area collapse, where in the lowest molecular layer, in contact with the substrate, molecules are in asymmetric configuration, i.e., both hydrocarbon tails are on the same side of the metal-bearing headgroup that touches the substrate, while the molecules above the first layer are in symmetric conformation of the tails with respect to the headgroups. Further along collapse, when the surface pressure starts to rise again with a decrease in area, more layers with molecules in the symmetric configuration are added, but the coverage is poor. On the other hand, only bimolecular layers form after constant pressure collapse, with the lower and upper layers having molecules in asymmetric and symmetric configurations, respectively, and the upper molecular layer density increases with compression of the monolayer after collapse. A "Ries mechanism" for constant area collapse and a "folding and sliding mechanism" for constant pressure collapse have been proposed.

Deviation from a perfect 2D-hexagonal (p6m) structure, for CTAB-silica mesostructured films prepared by adding different amounts of excess ethanol to a solution of CTAB and TEOS just before spin coating on OH-and H-terminated Si substrates, is observed from combined X-ray reflectivity and grazing incidence small angle X-ray scattering measurements. Such a deviation can be well understood in terms of the shape and ordering of the micelles, with or without the silica coating layer's contribution, inside the film. For example, cylindrical shaped micelles, which are initially circular on a hydrophilic OH-terminated Si substrate in order to form a perfect 2D-hexagonal structure, become elliptical (extended along the in-plane) on a hydrophobic H-terminated Si substrate to form a slightly compressed 2D-hexagonal structure due to a different attachment of the film to the substrate. With time, due to the drying of the silica materials and its restricted movement along the in-plane direction, the films on both the substrates are compressed along the out-of-plane direction only, to form observed centered rectangular (c2mm) structures. Also, due to the asymmetric shrinkage, stress is developed, which deteriorates the ordering in the film. The final shape of the micelles, including the silica coating layer's contribution, shows maximum and minimum deviations from the circular shape inside the thick film on a OH-Si substrate and the thin film on a H-Si substrate, respectively. The deviation in the shape of the micelles itself, which is of actual importance, seems to be maximum and minimum inside the thick film on a H-Si substrate and the thin film on a OH-Si substrate, respectively, and is essentially determined by the substrate nature and initial silica wall thickness.

Growth of Langmuir-Blodgett ͑LB͒ films of nickel arachidate ͑NiA͒ on differently terminated ͑OH-, H-, or Br-terminated͒ Si͑001͒ substrates and their structural evolution with time have been investigated by x-ray reflectivity technique and complemented by atomic force microscopy. Stable and strongly attached asymmetric monolayer ͑AML͒ of NiA is found to grow on freshly prepared oxide-covered Si substrate while unstable and weakly attached symmetric monolayer ͑SML͒ of NiA grows on H-terminated Si substrate, corresponding to stable hydrophilic and unstable hydrophobic natures of the substrates, respectively. The structure of LB film on Br-terminated Si substrate, however, shows intermediate behavior, namely, both AML and SML are present on the substrate, indicative of coexisting ͑hydrophilic and hydrophobic͒ nature of this terminated surface. Such coexisting nature of the substrate shows unusual growth behavior of LB films: ͑i͒ hydrophilic and hydrophobic attachments of NiA molecules in single up stroke of deposition and ͑ii͒ growth of few ring-shaped largeheights islands in subsequent deposition. These probably occur due to the presence of substrate-induced perturbation in the Langmuir monolayer and release of initially accumulated strain in the film structures near hydrophilic/hydrophobic interface, respectively, and provide the possibility to grow desired structures ͑AML or SML͒ of LB films by passivation-selective surface engineering.

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In solution-aged thin films, edge-on oriented ordering of nanofibers, along the z-direction, extends by thermal annealing, while near the film–substrate interface, it improves by combined solvent vapor and thermal annealing