arXiv subjects

Giridhar U. Kulkarni

Publications and source records attributed to Giridhar U. Kulkarni.

2 recordsLinked to original sources

arXiv2026

High-Resolution X-ray Spectro-Microscopy of Au Microcrystallites

Understanding the functionalities of heterogeneous catalysts requires high-resolution nanoscale chemical imaging tools. X-ray spectro-ptychography offers this capability by enabling X-ray absorption near edge structure (XANES) based amplitude and phase contrasts imaging with high spatial resolution. However, such demonstrations at energies above 10 keV, such as the Au L-edges, remain limited due to weak X-ray absorption cross-sections and correspondingly, low signal levels. Here, multimodal spectro-microscopy has been performed on Au microcrystallites that host both conventional face-centered cubic (fcc) and unconventional non-cubic lattices, particularly important for catalysis. Amplitude and phase contrasts across the $\mathrm{L}_3$ edge are resolved on thin Au crystallites (150 nm to 1.71 $μ\mathrm{m}$) with 45 nm spatial resolution. The resulting XANES spectra exhibit excellent agreement with standard transmission and fluorescence contrasts, while providing complementary chemical insights with improved spatial resolution. Quantitative retrieval of anomalous phase variations ~12 keV further demonstrates the suitability of this method for high-resolution chemical imaging across a wide range of functional materials.

cond-mat.mtrl-sci↗

arXiv2011

Ultrafast Large Area Micropattern Generation in Non-absorbing Polymer Thin-Films by Pulsed Laser Diffraction

We report an ultrafast, parallel and beyond-the-master micro-patterning technique for ultrathin (30 nm-400 nm) non-absorbing polymer films by diffraction of a laser light through a two dimensional periodic aperture. The redistribution of laser energy absorbed by the substrate causes self-organization of polymer thin-film in the form of wrinkle like surface relief structures caused by localized melting and freezing of the thin-film. Unlike the conventional laser ablation and laser writing processes, low laser fluence is employed to only passively swell the polymer as a pre-ablative process without the loss of material, and without absorption/reaction with the incident radiation. Self-organization in the thin polymer film aided by the diffraction pattern produces micro-structures made up of thin raised lines. These regular microstructures have far more complex morphologies than the mask geometry and very narrow line widths that can be an order of magnitude smaller than the openings in the mask. The microstructure morphology is easily modulated by changing the film thickness, aperture size and geometry and by changing the diffraction pattern, e.g., by changing the aperture-substrate distance.

cond-mat.soft↗