arXiv subjects

Santanu Ghosh

Publications and source records attributed to Santanu Ghosh.

15 recordsLinked to original sources

arXiv2025

Enhancing the Plasmonic Hotspot Density via Structural Engineering of Multi-layered MoO3-Ag-Au Systems Under Extreme Electronic Excitation Conditions for Ultra-Sensitive SERS Applications

We illustrate ion-beam engineering of MoO3 Ag Au multilayer plasmonic substrates to improve SERS performance, We illustrate ion-beam engineering of MoO3-Ag-Au multilayer plasmonic substrates to improve SERS performance. Orthorhombic {\alpha}-MoO3 microflakes were produced via chemical vapour deposition (CVD) on Si-SiO2 substrates. Thin films of Ag (5 nm) and Au (5 nm) were thermally evaporated onto the MoO3 flakes, and the samples were subjected to 100 MeV Ag8+ swift heavy ion irradiation at fluences of 3e11 and 3e12 ions cm-2. Irradiation causes dewetting of metal films, prompting structural and morphological changes that result in the formation of dispersed Ag-Au nanoparticles, enhanced surface roughness, and defect generation within the MoO3 lattice. X-ray diffraction (XRD) verifies the {\alpha}-MoO3 phase; field emission scanning electron microscopy (FESEM) elucidates nanoparticle formation and surface reorganisation; Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) disclose vibrational alterations and binding-energy shifts in Mo 3d, indicative of oxygen vacancies (V_O) and partial reduction of Mo. SERS measurements of molecular probes demonstrate significantly increased Raman intensities following ion irradiation.

cond-mat.mtrl-sci↗

arXiv2025

Grain Size and Temperature-Dependent Response of 5-mol% Gd-Doped Ceria to Swift Heavy Ion Irradiation with 80 MeV Ag and 120 MeV Au Ions

The response of 5-mol% Gd-doped ceria to swift heavy ion beam irradiation has been studied to observe the effects of changes in ion energies and environmental temperature. The study involved irradiating two different grain sizes (nano and bulk) with two different ion energies: 80 MeV Ag and 120 MeV Au. Additionally, a comprehensive analysis of Gd-doped ceria's response to ion beam irradiation at high temperatures (1000 K) was conducted, taking into account the effect of grain size dependency. Based on GIXRD and Raman spectroscopy, it is evident that electronic excitation from 80 MeV Ag and 120 MeV Au ions at a fluence $1 \times 10^{14}$ ions/cm$^2$ caused damage to Gd-doped ceria samples. However, bulk grain size shows significant stability against SHI in all cases. These findings align with thermal spike simulations and indicate the formation of ion tracks due to electronic excitation by Swift Heavy Ion beam irradiation.

cond-mat.mtrl-sci↗

arXiv2025

Highly Enhanced robust room temperature ferromagnetism in CVD-grown nano-dimensional MoS2 flakes by modifying edges and defect engineering

The alterations in the magnetic properties and electronic structure of chemical vapor deposition (CVD) grown nano-dimensional molybdenum disulfide (MoS2) after low energy ion irradiation are thoroughly investigated. The formation of pure hexagonal 2-H phase has been identified by Raman spectroscopy and X-ray diffraction (XRD). The pristine samples are irradiated by Argon (Ar) ions with low energy at different fluences. A comprehensive analysis of Raman spectroscopy data manifests the formation of lattice defects like S-vacancies across the samples after irradiation. Triangular-flake formation in the pristine sample is confirmed by field emission scanning electron microscopy (FESEM) images. After increasing irradiation fluences the big flakes commenced to fragment into smaller ones enhancing the number of edge-terminated structures. The electron probe microanalyzer (EPMA) analysis verifies the absence of any magnetic impurity. Rutherford backscattering spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS) study confirm the formation of S-vacancies after irradiation. The pristine sample exhibits diamagnetic behavior at room temperature. The saturation magnetization value increases with increasing the ion irradiation fluences, and the sample irradiated with 1e15 ions/cm2 demonstrates the highest magnetization value of 4.18 emu/g. The impact of edge-terminated structure and point defects like S-vacancies to induce room-temperature ferromagnetism (RTFM) is thoroughly examined.

cond-mat.mtrl-sci↗

arXiv2024

Enhanced room temperature ferromagnetism in nanostructured MoS2 flakes by hydrogen post-treatment: Combined experimental and first-principles-based studies

We meticulously study the individual effects of hydrogen irradiation and annealing on the electronic structure and magnetic properties of nanostructured MoS2 thin films grown through Chemical Vapor Deposition (CVD). The role of edge-terminated structure and point defects to induce room-temperature ferromagnetism (RTFM) is thoroughly investigated. The nanostructured pristine MoS2 thin films show the formation of a pure 2-H MoS2 phase, confirmed by X-ray diffraction (XRD) and Raman spectroscopy. Pristine MoS2 thin films are independently annealed in a reducing hydrogen environment and irradiated with low-energy hydrogen ions to study the significance of point defects like sulfur vacancies. RTFM with saturation magnetization value (Ms: 1.66 emu/g) has been observed in the pristine film. Magnetization increases after irradiation and annealing processes. However, hydrogen annealing at a temperature of 200oC exhibits a maximum Ms value of 2.7 emu/g at room temperature. The increase in ferromagnetism is attributed to an increment in sulfur vacancies, hydrogen adsorption with sulfur, and modification in edges, which is confirmed by the analysis of Electron probe micro-analyzer (EPMA), X-ray photoelectron spectroscopy (XPS), and Field emission scanning electron microscopy (FESEM) measurements. The Density Functional Theory (DFT) calculations have demonstrated that the edge-oriented structure of MoS2 exhibits a magnetization value of 3.2 {\mu}B. Additionally, introducing an S-vacancy and H-adsorption in a parallel position to the sulfur further enhances the magnetization value to 3.85 {\mu}B and 3.43 {\mu}B respectively. These findings align broadly with our experimental results.

cond-mat.mtrl-sci↗

arXiv2024

In Situ Growth of Copper Channels within CuCl and PVDF Composite for Durable WORM Device Formation

This study details the creation of a Write Once-Read Many (WORM) memory device utilizing cuprous chloride (CuCl) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymers. Employing an in-plane configuration, a deliberate 1:10 ratio of CuCl to PVDF-HFP has been selected. This ratio aims to establish an in-situ copper channel within the device. The electrical response exhibits consistent memory retention over an extended duration. The WORM characteristics are attributed to the development of multiple conducting filaments or a highly conductive percolative path created by Cu ions within the polymer matrix. The UV-Vis study also reinforces the obtained results. Additionally, the memristor undergoes specific poling and cooling conditions. The fabrication approach employed in this research yields a distinctive type of Resistive Switching Device (RSD). Once the device is activated, it maintains its state even after the applied field is reduced. This specialized device holds potential applications in Compact Disc-Recordable (CD-R), Digital Versatile Disc-Recordable (DVD-R), Blu-ray Disc Recordable (BD-R), and Write Once USB Drives.

cond-mat.mes-hall↗

arXiv2024

Highly Sensitive Label-free Biomolecular Detection Using Au-WS2 Nanohybrid Based SERS Substrates

Recent advancements in nanotechnology have led to the development of surface-enhanced Raman spectroscopy (SERS) based rapid and low-cost technologies for ultra-sensitive label-free detection and identification of molecular analytes. Herein, we utilized the synergistic plasmonic and chemical enhancement effects of Au-WS2 nanohybrids to attain the high-intensity Raman signals of targeted analytes. To develop these nanohybrids, a series of monodispersed Au nanoparticles (NPs) of varying diameters from 20 to 80 nm was chemically synthesized and successively blended with liquid-phase exfoliated WS2 nano-flakes of average lateral size 90 nm. They provided a maximum enhancement factor (EF) of ~1.80 109 corresponding to the characteristic peaks at 1364 cm-1 and 1512 cm-1 for R6G analyte molecules. Theoretical studies based on the finite-difference time-domain simulations on Au-WS2 nanohybrid systems revealed a huge field-intensity enhancement with an EF of more than 1000 at the plasmonic hotspots, which was induced by the strong coupling of individual plasmon oscillations of the adjacent Au NPs upon light interactions. These electromagnetic effects along with the chemical enhancement effects of WS2 nanoflakes were found to be mainly responsible for such huge enhancement in Raman signals. Furthermore, these hybrids were successfully employed for achieving highly sensitive detection of the E. coli ATCC 35218 bacterial strain with a concentration of 104 CFU/mL in phosphate-buffered saline media, indicating their real capabilities for practical scenarios. The findings of the present study will indeed provide vital information in the development of innovative nanomaterial-based biosensors, that will offer new possibilities for addressing critical public health concerns.

physics.app-ph↗

arXiv2024

Synergetic effect of edge states and point defects to tune ferromagnetism in CVD-grown vertical nanostructured MoS2: A correlation between electronic structure and theoretical study

Room-temperature ferromagnetism (RTFM) exhibited by nanostructured two-dimensional semiconductors for spintronics applications is a fascinating area of research. The present work reports on the correlation between the electronic structure and magnetic properties of defect-engineered nano-structured MoS2 thin films. Low-energy light and heavy-mass ion irradiation have been performed to create defects and tune magnetic properties. Vertical nanosheets with edge state termination in the pristine sample have been examined by field emission scanning electron microscopy (FESEM). Deterioration of vertical nanosheets is observed in low-energy Ar+ and Xe+ irradiated samples. An appreciably high magnetization value of 1.7 emu/g was observed for edge-oriented nanostructured pristine MoS2 thin films, which decreased after ion irradiation. From X-ray photoelectron spectroscopy (XPS) data, it is evident that, due to oxygen incorporation in the sulfur vacancy sites, Mo5+ and 6+ states increase after ion irradiation. The density functional theory (DFT) calculations suggest that the edge-oriented spins of the prismatic edges of the vertical nanosheets are primarily responsible for the high magnetic moment in the pristine film, and the edge degradation and reduction in sulfur vacancies by the incorporation of oxygen upon irradiation result in a decrease in the magnetic moment.

cond-mat.mtrl-sci↗

arXiv2023

Probing defect induced room temperature ferromagnetism in CVD grown MoO3 flakes: A correlation with electronic structure and first principle-based calculations

In this paper, we report the growth of pure {\alpha}-MoO3 micro-flakes by CVD technique and their structural, electronic, optical, and magnetic properties. Samples are annealed at various temperatures in an H2 atmosphere to induce ferromagnetism. All the samples exhibit ferromagnetism at room temperature, and 250oC annealed sample shows the highest magnetic moment of 0.087 emu/g. It is evident from PL data that pristine as well as annealed samples contain different types of defects like oxygen vacancies, surface defects, interstitial oxygen, etc. It is deduced from the analysis of Mo3d and O1s core-level XPS spectra that oxygen vacancies increase up to an annealing temperature of 250oC that correlates with the magnetic moment. Significant changes in the total density of states and also in the magnetic moment for two and three oxygen vacancies are noticed through first-principle-based calculations. It is concluded that the magnetic moment is produced by oxygen vacancies or vacancy clusters, which is consistent with our experimental findings.

cond-mat.mtrl-sci↗

arXiv2023

Performance analysis of InAlN/GaN HEMT and optimization for high frequency applications

An InAlN/GaN HEMT device was studied using extensive temperature dependent DC IV measurements and CV measurements. Barrier traps in the InAlN layer were characterized using transient analysis. Forward gate current was modelled using analytical equations. RF performance of the device was also studied and device parameters were extracted following small signal equivalent circuit model. Extensive simulations in Silvaco TCAD were also carried out by varying stem height, gate length and incorporating back barrier to optimize the suitability of this device in Ku-band by reducing the detrimental Short Channel Effects (SCEs). In this paper a novel structure i.e., a short length T gate with recess, on thin GaN buffer to achieve high cut-off frequency (f$_T$) and high maximum oscillating frequency (f$_{max}$) apt for Ku-band applications is also proposed.

physics.app-ph↗

arXiv2023

Investigation of RF performance of Ku-band GaN HEMT device and an in-depth analysis of short channel effects

In this paper, we have characterized an AlGaN/GaN High Electron Mobility Transistor (HEMT) with a short gate length (Lg $\approx$ 0.15$\mu$m). We have studied the effect of short gate length on the small signal parameters, linearity parameters and gm-gd ratio in GaN HEMT devices. To understand how scaling results in the variation of the above-mentioned parameters a comparative study with higher gate length devices on similar heterostructure is also presented here. We have scaled down the gate length but the barrier thickness(t$_{bar}$) remained same which affects the aspect ratio (L$_{g}$/t$_{bar}$) of the device and its inseparable consequences are the prominent short channel effects (SCEs) barring the optimum output performance of the device. These interesting phenomena were studied in detail and explored over a temperature range of -40$^\circ$C to 80$^\circ$C. To the best of our knowledge this paper explores temperature dependence of SCEs of GaN HEMT for the first time. With an approach to reduce the impact of SCEs a simulation study in Silvaco TCAD was carried out and it is observed that a recessed gate structure on conventional heterostructure successfully reduces SCEs and improves RF performance of the device. This work gives an overall view of gate length scaling on conventional AlGaN/GaN HEMTs.

physics.app-ph↗

arXiv2019

Radiation tolerance: Nano triumphs bulk

Materials are subjected to energetic particles in a number of radiation environments,and are hence prone to undesirable (radiation) damage.We report here the superiority of the nanocrystalline phase over bulk for radiation tolerance under simultaneous irradiation with high energy (electronic energy loss (Se) dominant) and low energy (nuclear energy loss (Sn) dominant) particles.Nano-crystalline yttria stabilized zirconia is found to exhibit lesser radiation damage (viz.degradation in crystallinity),when compared to its bulklike counterpart,against simultaneous irradiation with high energy 27 MeV Fe and low energy 900 keV I ions.This is interpreted within the framework of the thermal spike model after considering (i) the fact that there is essentially no spatial and time overlap between the damage events of the two simultaneous ion beams,and (ii) the influence of grain size on the radiation damage against separate Sn and Se.The present work besides being of keen interest for fundamental understanding of ion material interactions,also paves the way for the potential application of nanocrystalline materials in the nuclear industry where such simultaneous irradiations are encountered.

cond-mat.mtrl-sci↗

arXiv2019

Oxygen vacancy mediated cubic phase stabilization at room temperature in pure nano-crystalline Zirconia films: A combined experimental and first-principles based investigation

We report the formation of cubic phase, under ambient conditions, in thin films of Zirconia synthesized by electron beam evaporation technique. The stabilization of the cubic phase was achieved without the use of chemical stabilizers and/or concurrent ion beam bombardment. Films of two different thickness (660 nm, 140 nm) were deposited. The 660 nm and 140 nm films were found to be stoichiometric (ZrO2) and off-stoichiometric (ZrO1.7) respectively by Resonant Rutherford back-scattering spectroscopy. While the 660 nm as-deposited films were in the cubic phase, as indicated by X-ray diffraction and Raman spectroscopy measurements, the 140 nm as-deposited films were amorphous and the transformation to cubic phase was obtained after thermal annealing. Extended X-ray absorption fine structure measurements revealed the existence of Oxygen vacancies in the local structure surrounding Zirconium for all films. However, the amount of these Oxygen vacancies was found to be significantly higher for the amorphous films as compared to the films in the cubic phase (both 660 nm as-deposited and 140 nm annealed films). The cubic phase stabilization is explained on the basis of suppression of the soft X2- mode of vibration of the Oxygen sub-lattice due to the presence of the Oxygen vacancies. Our first-principles modeling under the framework of density functional theory shows that the cubic structure with Oxygen vacancies is indeed more stable at ambient conditions than its pristine (without vacancies) counterpart. The requirement of a critical amount of these vacancies for the stabilization of the cubic phase is also discussed.

cond-mat.mtrl-sci↗

arXiv2018

Sign Reversal and Tunability of Exchange Bias in Nanoscale AuFe Alloy Film: A New Material for Spintronic Application

We report here sign reversal and tunability of exchange bias in AuFe cosputtered films of thickness about 63 nm. As deposited film exhibits exchange bias effect at room temperature without external triggering field and its magnitude increases gradually with decrease in temperature down to 5 K. Upon irradiation with 100 MeV Au9+ ions at a fluence of 5*1013 ions/cm2, hysteresis loop shifts completely from origin towards positive field side at room temperature and reverses sign when temperature is reduced to 5 K as studied by SQUID magnetometry. A well defined uniaxial magnetic anisotropy has been seen by magneto optical Kerr effect (MOKE) in as deposited film as well as in irradiated one. The results are explained on the basis of stress induced magnetic anisotropy in thin films.

cond-mat.mtrl-sci↗

arXiv2018

Enhanced radiation tolerance of YSZ at high temperature against swift heavy ions: key role of interplay between material microstructure and irradiation temperature

Yttria stabilized Zirconia (YSZ) pellets with different crystallite sizes were irradiated with 80 MeV Ag$^{6+}$ ions at room temperature and 1000 K to understand the role of crystallite size/material microstructure and irradiation temperature on the radiation tolerance against high electronic energy loss (S$_e$). X-ray diffraction and Raman spectroscopy measurements reveal that, irrespective of the irradiation temperature, the nano-crystalline samples suffered more damage as compared to the bulk-like sample. A reduction in the irradiation damage i.e. improvement in the radiation tolerance, was observed for all the samples irradiated at 1000 K. The reduction in the damage, however, was remarkably higher for the two nano-crystalline samples compared to the bulk-like sample, and hence the difference in the damage between the bulk-like and nano-crystalline samples was also significantly lower at 1000 K than that at room temperature. The irradiation damage, against S$_e$, was thus found to be critically dependent on the interplay between the irradiation temperature and crystallite size. These results are explained with the help of detailed theoretical calculations/simulations based on the 'in-elastic thermal spike' model by taking into consideration the combined effect of crystallite size and environmental (irradiation) temperature on the electron-phonon coupling factor and lattice thermal conductivity (and hence on the resulting thermal spike). Our results are crucial from the fundamental perspective of comprehending the size and temperature dependent radiation damage against S$_e$ ; and also for a number of applications, in various radiation environments, where nano-materials are being envisioned for use.

cond-mat.mtrl-sci↗

arXiv2015

Design & Implementation Approach for Error Free Clinical Data Repository for the Medical Practitioners

The modern treatment of any disease is heavily dependent on the medical diagnosis. Clinical data obtained through the diagnostics tests need to be collected and entered into the computer database in order to make a clinical data repository. In most of the cases, manual entry is an absolute necessity. However, manual entry can cause errors also, leading to wrong diagnosis. This paper explains how data could be entered free of error to reduce the chances of wrong diagnosis by designing and implementation of a simple database driven application.

cs.DB↗