arXiv subjects

Shankar Dutt

Publications and source records attributed to Shankar Dutt.

9 recordsLinked to original sources

arXiv2025

Strain induced stabilization of high symmetry phase in MAPbBr3 perovskite

Structural phase transitions in the organic inorganic metal halide perovskites are driven via rearrangement of methylammonium cation and distortion in the PbX6 octahedra. Compositional tuning is usually incorporated for suppression of the structural phase transition in these systems with cation or anion tuning. Along with the compositional tuning, behaviour of strain present in the system can also lead to stabilization of single phase in these systems. In the present investigation, two different samples of CH3NH3PbBr3 perovskite were studied and it is observed that structural phase transition is absent for one of the sample while it is present in the other sample. The non-observance of structural phase transition and stabilization of single phase has been attributed to the perceived tensile strain in the system contrary to the compressive strain observed in the system showing structural phase transitions. This observation is further supported by theoretical calculations. Extended X-ray absorption fine structure measurements revealed distorted octahedra with varying bond lengths along planar and axial directions in both samples, along with observed increase in bond lengths in one of the sample. This stabilization of the cubic phase can enhance device performance and increase overall environmental stability, making these systems more effective for practical applications.

cond-mat.mtrl-sci↗

arXiv2025

Characterization of ion track etched conical nanopores in thermal and PECVD SiO$_{2}$ using small angle X-ray scattering

Conical nanopores in amorphous SiO$_{2}$ thin films fabricated using the ion track etching technique show promising potential for filtration, sensing and nanofluidic applications. The characterization of the pore morphology and size distribution, along with its dependence on the material properties and fabrication parameters, is crucial to designing nanopore systems for specific applications. Here, we present a comprehensive study of track-etched nanopores in thermal and plasma-enhanced chemical vapor deposited (PECVD) SiO$_{2}$ using synchrotron-based small-angle X-ray scattering (SAXS). We present a new approach for analyzing the complex highly anisotropic 2-dimensional SAXS patterns of the pores by reducing the analysis to two orthogonal 1-dimensional slices of the data. The simultaneous fit of the data enables an accurate determination of the pore geometry and size distribution. The analysis reveals substantial differences between the nanopores in thermal and PECVD SiO$_{2}$. The track-to-bulk etching rate ratio is significantly different for the two materials, producing nanopores with cone angles that differ by almost a factor of 2. Furthermore, thermal SiO$_2$ exhibits an exceptionally narrow size distribution of only ~2-4%, while PECVD SiO$_2$ shows a higher variation ranging from ~8-18%. The impact of ion energy between 89 MeV and 1.6 GeV on the size of the nanopores was also investigated for pores in PECVD SiO$_{2}$ and shows only negligible influence. These findings provide crucial insights for the controlled fabrication of conical nanopores in different materials, which is essential for optimizing membrane performance in applications that require precise pore geometry.

physics.app-ph↗

arXiv2023

Annealing of swift heavy ion tracks in amorphous silicon dioxide

The annealing kinetics of the high energy ion damage in amorphous silicon dioxide (a-SiO2) are still not well understood, despite the material's widespread application in material science, physics, geology, and biology. This study investigates how annealing temperature, duration, and ambient environment affect the recovery of irradiation damage produced along the trajectory of swift heavy ions in a-SiO2. The track-annealing kinetics and the changing ion track morphology were investigated using synchrotron-based small-angle X-ray scattering (SAXS) and etching methods. We found that track annealing proceeds quicker near the sample surface demonstrated by a changing track etch rate as a function of depth. Measurements of ion tracks using SAXS show only small changes in the radial density distribution profile of the ion tracks. Activation energy of the annealing process at different sample depths was determined and the effect of the capping layer during the annealing process was also studied. Combination of oxygen diffusion and stress relaxation may contribute to the observed behaviour of preferential and anisotropic healing of the ion track. The results add to the fundamental understanding of ion track damage recovery and may have direct implications for materials for radioactive waste storage and solid state nanopores.

cond-mat.mtrl-sci↗

arXiv2023

The human factor: results of a small-angle scattering data analysis Round Robin

A Round Robin study has been carried out to estimate the impact of the human element in small-angle scattering data analysis. Four corrected datasets were provided to participants ready for analysis. All datasets were measured on samples containing spherical scatterers, with two datasets in dilute dispersions, and two from powders. Most of the 46 participants correctly identified the number of populations in the dilute dispersions, with half of the population mean entries within 1.5% and half of the population width entries within 40%, respectively. Due to the added complexity of the structure factor, much fewer people submitted answers on the powder datasets. For those that did, half of the entries for the means and widths were within 44% and 86% respectively. This Round Robin experiment highlights several causes for the discrepancies, for which solutions are proposed.

physics.data-an↗

arXiv2023

High Accuracy Protein Identification: Fusion of solid-state nanopore sensing and machine learning

Proteins are arguably the most important class of biomarkers for health diagnostic purposes. Label-free solid-state nanopore sensing is a versatile technique for sensing and analysing biomolecules such as proteins at single-molecule level. While molecular-level information on size, shape, and charge of proteins can be assessed by nanopores, the identification of proteins with comparable sizes remains a challenge. Here, we present methods that combine solid-state nanopore sensing with machine learning to address this challenge. We assess the translocations of four similarly sized proteins using amplifiers with bandwidths (BWs) of 100 kHz (sampling rate=200 ksps) and 10 MHz (sampling rate=40 Msps), the highest bandwidth reported for protein sensing, using nanopores fabricated in <10 nm thick silicon nitride membranes. F-values of up to 65.9% and 83.2% (without clustering of the protein signals) were achieved with 100 kHz and 10 MHz BW instruments, respectively, for identification of the four proteins. The accuracy of protein identification was significantly improved by grouping the signals into several clusters depending on the event features, resulting in F-value and specificity reaching as high as 88.7% and 96.4%, respectively, for combinations of four proteins. The combined improvement in sensor signals through the use of high bandwidth instruments, advanced clustering, machine learning, and other advanced data analysis methods allows identification of proteins with high accuracy.

physics.bio-ph↗

arXiv2023

Highly Rectifying Conical Nanopores in Amorphous SiO2 Membranes for Nanofluidic Osmotic Power Generation and Electroosmotic Pumps

Nanopore membranes are a versatile platform for a wide range of applications ranging from medical sensing to filtration and clean energy generation. To attain high-flux rectifying ionic flow, it is required to produce short channels exhibiting asymmetric surface charge distributions. This work reports on a system of track etched conical nanopores in amorphous SiO$_2$ membranes, fabricated using the scalable track etch technique. Pores are fabricated by irradiation of 1 $\mu$m thick SiO$_2$ windows with 2.2 GeV $^{197}$Au ions and subsequent chemical etching. Structural characterisation is performed using atomic force microscopy (AFM), scanning electron microscopy (SEM), small angle X-ray scattering (SAXS), ellipsometry, and surface profiling. Conductometric characterisation of the pore surface is performed using a membrane containing 16 pores, including an in-depth analysis of ionic transport characteristics. The pores have a tip radius of (5.7 $\pm$ 0.1) nm, a half-cone angle of (12.6 $\pm$ 0.1)$^{\circ}$, and a length of (710 $\pm$ 5) nm. The $pK_a$, $pK_b$, and $pI$ are determined to 7.6 $\pm$ 0.1, 1.5 $\pm$ 0.2, and 4.5 $\pm$ 0.1, respectively, enabling the fine-tuning of the surface charge density between +100 and -300 mC $m^{-2}$ and allowing to achieve an ionic current rectification ratio of up to 10. This highly versatile technology addresses challenges that contemporary nanopore systems face, and offers a platform to improve the performance of existing applications.

cond-mat.mes-hall↗

arXiv2022

Ultra-Thin, High-Lifetime Silicon Nitride Membranes for Nanopore Sensing

Thin membranes are highly sought-after for nanopore-based single-molecule sensing and fabrication of such membranes becomes challenging in the \lesssim10 nm thickness regime where a plethora of useful molecule information can be acquired by nanopore sensing. In this work, we present a scalable and controllable method to fabricate silicon nitride (SixNy) membranes with effective thickness down to ~1.5 nm using standard silicon processing and chemical etching using hydrofluoric acid (HF). Nanopores were fabricated using the controlled breakdown method with estimated pore diameters down to ~1.8 nm yielding events >500,000 and >1,800,000 from dsDNA and bovine serum albumin (BSA) protein, respectively, demonstrating the high-performance and extended lifetime of the pores fabricated through our membranes. We used two different compositions of SixNy for membrane fabrication (near stoichiometric and silicon-rich SixNy) and compared them against commercial membranes. The final thicknesses of the membranes were measured using ellipsometry and were in good agreement with the values calculated from the bulk etch rates and DNA translocation characteristics. The stoichiometry and the density of the membrane layers were characterized with Rutherford backscattering spectrometry while the nanopores were characterized using pH-conductance, conductivity-conductance and power spectral density (PSD) graphs.

cond-mat.mtrl-sci↗

arXiv2020

van der Waals coefficients of the multi-layered MoS$_2$ with alkali metals

The van der Waals coefficients and the separation dependent retardation functions of the interactions between the atomically thin films of the multi-layered transition metal molybdenum disulfide (MoS$_2$) dichalcogenides with the alkali atoms are investigated. First, we determine the frequency-dependent dielectric permittivity and intrinsic carrier density values for different layers of MoS$_2$ by adopting various fitting models to the recently measured optical data reported by Yu and co-workers [Sci. Rep. {\bf 5}, 16996 (2015)] using spectroscopy ellipsometry. Then, dynamic electric dipole polarizabilities of the alkali atoms are evaluated very accurately by employing the relativistic coupled-cluster theory. We also demonstrate the explicit change in the above coefficients for different number of layers. These studies are highly useful for the optoelectronics, sensing and storage applications using layered MoS$_2$.

cond-mat.mtrl-sci↗

arXiv2017

High-charge relativistic electron bunches from a kHz laser-plasma accelerator

We report on electron wakefield acceleration in the resonant bubble regime with few-millijoule near-single-cycle laser pulses at a kilohertz repetition rate. Using very tight focusing of the laser pulse in conjunction with microscale supersonic gas jets, we demonstrate a stable relativistic electron source with a high charge per pulse up to 24 pC/shot. The corresponding average current is 24 nA, making this kilohertz electron source useful for various applications.

physics.acc-ph↗