Understanding of stress and its correlation with microstructure near the layer continuous limit in nano-scaled multilayers

The evolution of residual stress and its correlation with microstructure are investigated systematically in nano-scaled periodic W/B4C multilayers (MLs) as a function of individual layer thicknesses at the ultra-thin limit (∼0.4–3 nm). Details of the microstructure are accessed through hard X-ray reflectivity and X-ray diffuse scattering (rocking scan) measurements. To understand the contributions of stresses in the layers of each type of material to the total stress in ML films, both the total stress in MLs and the stress in nanocrystalline W layers are analyzed and correlated. It is observed that the physical properties of the materials as well as their interfacial morphology undergo significant modification as the layer thickness varies from the continuous to the quasi-discontinuous regime. A non-monotonic variation of compressive total residual stress in the MLs is observed as a function of thicknesses of W and B4C and explained using a model of the mechanism of film growth. The observed value of in-plane total compressive residual stress of W/B4C MLs is less than the residual stress in W layers in the MLs, which indicates that the net combined stress from B4C layers and interfaces is tensile in nature. The observed compressive stress and the increase of lattice spacing with respect to the stress-free structure in W layers provide evidence of a peening effect. The observed higher surface density of grains with smaller average size and phase formation also provide high compressive stress in W layers.

Soft X-ray Reflection Spectroscopy for Nano-Scaled Layered Structure Materials

We introduce a novel approach that addresses the probing of interfacial structural phenomena in layered nano-structured films. The approach combines resonant soft x-ray reflection spectroscopy at grazing incidence near the "critical angle" with angular dependent reflection at energies around the respective absorption edges. Dynamic scattering is considered to determine the effective electron density and hence chemically resolved atomic profile across the structure based on simultaneous data analysis. We demonstrate application of the developed technique on the layered model structure C (20 Å)/B (40 Å)/Si (300 Å)/W (10 Å)/substrate. We precisely quantify atomic migration across the interfaces, a few percent of chemical changes of materials and the presence of impurities from top to the buried interfaces. The results obtained reveal the sensitivity of the approach towards resolving the compositional differences up to a few atomic percent. The developed approach enables the reconstruction of a highly spatio-chemically resolved interfacial map of complex nano-scaled interfaces with technical relevance to many emerging applied research fields.

Efficacy of Mycophenolate Mofetil as a Remission Maintaining Agent in Idiopathic Childhood Nephrotic Syndrome

Of all cases of idiopathic steroid-sensitive nephrotic syndrome (NS) in children, 40%-75% cases need long-term continuous steroids and/or other immunosuppressants to maintain remission, the effects of which on growth and renal function remain an issue of concern. The study aimed at exploring the safety and efficacy of mycophenolate mofetil (MMF) as a remission-maintaining agent in children with a diagnosis of frequent relapsing or steroid-dependent NS (FRNS/SDNS) requiring continuous medication for at least 1 year. Thirty-two children thus included received MMF (1000-1200 mg/m²/day) for 7 months along with tapering doses of oral prednisolone if it was being given from before with an attempt at tapering at 0.25 mg/kg/month ultimately stopping it altogether. Individuals were followed up for at least 5 more months after stopping MMF. Out of 32 children, 26 had SDNS and 6 had FRNS with male:female ratio being 2.2:1. The mean standard deviation (± SD) age of onset of disease was 2.72 ± 1.3 years and that entry to the study was 7.17 ± 2.2 years. Significant fall in number of relapses was observed following the introduction of MMF (110 in pre-MMF12 month period vs. 52 in post-MMF 12 months [p = 0.002]). The mean relapse rate/year/patient also decreased from 3.43 ± 1.26 to 1.62 ± 1.14 after entry in the study. Significant reduction of the cumulative dose of steroid regarding mean ± SD of mg/kg/year was also found following the introduction of MMF (190.9 ± 47.81 vs. 119.09 ± 60.09 [p = 0.001]). MMF is an efficacious agent in maintaining remission and reducing steroid requirement in children with FRNS and SDNS.