[en] A new calixarene hydroxamic acid, 25,26,27,28-tetra-hydroxy 5,11,17,23-tetrakis(N-p-chlorophenyl)calix [4]-arene hydroxamic acid (CPCHA) is used for the extraction and spectrophotometric determination of thorium(IV). The molar absorptivity of the thorium(IV)-CPCHA-SCN complex is 2.2 x 10⁴ m² mol^-1 at 450 nm. The system obeys Beer's law over the range 1.3-13.2 ppm of thorium. The thorium-calixarene hydroxamate ethyl acetate extract was directly subjected to ICP-AES measurements which increases the sensitivity by fifteen-fold. Thorium can be estimated at the 0.1 ppm level. The method is applied for the trace determination of thorium(IV) in geological samples at the low ppb level even after a 1: 100 dilution (dissolution). (author)

[en] The diffusion process on Si (0 0 1) in the presence of a 5 keV Ar⁺ ion beam has been investigated by monitoring initiation of ripple-pattern formation. The morphology of the surface obtained by scanning tunnelling microscopy measurements in ultrahigh vacuum were characterized using the height-difference correlation function. These measurements clearly show formation of nanostructured ripple patterns having wavelength ∼60 nm and height ∼0.32 nm at 200 ⁰C. The results demonstrate that ion beam induced and thermal diffusions cannot be treated as additive processes and the observed enhancement of surface diffusion requires lowering of activation energy that arises due to creation of ion-beam induced vacant regions

[en] Si/Ge multilayers are of great technological importance as is evident from the research studies of the past two decades. Here, we have presented a method for the morphological and structural characterization of such MBE grown epitaxial Si/Ge superlattice structures using simultaneous analysis of x-ray reflectivity and x-ray diffraction data, respectively. The consistent analysis of the data collected in the Indian Beamline at Photon Factory Synchrotron have allowed for the determination of electron density and strain profile as a function of depth.

[en] The three-tailed amphiphile ferric stearate molecule, which forms a bimolecular layer on water surface with molecules in the lower and upper layers in different conformations, has been studied to understand transfer and growth of bimolecular films on the surface of hydrophilic silicon substrates. This bimolecular film forms a two-dimensional lattice on water with a slightly distorted hexagonal lattice where both the in-plane and out-of-plane domain sizes are small. The film also showed larger microscopic rigidity compared to its macroscopic mechanical response. This asymmetric bimolecular layer was found to be preserved when the film is transferred on the substrates at different values of surface pressures ranging from 1 mN/m to near-collapse (55 mN/m). Both the upper and lower layers become denser and interfaces between these layers become sharper with increase in deposition pressure but the growths have different natures. The lower layer of transferred film is dense from 1 mN/m and, except for a steplike increase between 20 and 30 mN/m, changes slowly in density. The density of the upper molecular layer grows continuously with surface pressure

[en] Using grazing-incidence x-ray scattering technique the authors have investigated the evolution of the damage profile of the transition layer between the ion-induced ripplelike pattern on top surface and the ripples at buried crystalline interface in silicon created after irradiation with 60 keV Ar⁺ ions under 60 deg. . The transition layer consists of a defect-rich crystalline part and a complete amorphous part. The crystalline regions are highly strained but relaxed for low dose and high dose irradiations, respectively. The appearance of texture in both cases shows that the damage of the initial crystalline structure by the ion bombardment takes place along particular crystallographic directions

[en] Nanometer sized Au clusters deposited on a silicon substrate forming Au-SiO₂-Si structure are important for the development of contacts in nanotechnology. Systematic x-ray reflectivity, scanning probe microscopy, and scanning tunneling spectroscopy measurements were done to understand the relationship between morphology and electrical transport properties of this nanostructural metal-insulator-semiconductor system. The presence of an interfacial layer at the metal-insulator interface dictates the tunneling current through this structure and exhibits a gap leading to a suppression of current. Local density of states and electron density/thickness of the interfacial layer have been extracted from the measurements to understand the evolution of metallicity of this Au-SiO₂-Si structure