arXiv subjects

S. Dash

Publications and source records attributed to S. Dash.

At least 19 recordsLinked to original sources

arXiv2025

Pion-Kaon femtoscopy as a probe of the space-time emission anisotropies due to interactions at the hadronic stage of matter evolution in relativistic heavy-ion collisions

Emission asymmetries between pions and kaons reflect the role of the hadronic phase in the cooling of a droplet of deconfined strongly-interacting matter. This study compares results from two models at the same collision energy of $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV to investigate how interactions in the hadronic phase affect particle emission. The first model, iHKM, provides a complete description of all stages of the evolution; from the initial scattering and thermalization to the final hadronic state, while the second model, LQTH (LHYQUID+THERMINATOR2), assumes a sudden conversion into hadrons, neglecting further interactions. To increase the sensitivity to hadronic interactions, the analysis was performed as a function of the pair transverse velocity for pairs with nearly equal velocity vectors. The obtained predictions are compared with previously measured ALICE data at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV as a function of the cube root of the average particle multiplicity density at midrapidity, showing that both radii and emission asymmetries scale with particle multiplicity, regardless of the collision energy. The iHKM model reproduces the measured trends both qualitatively and quantitatively, whereas the LQTH model requires additional parameters-in particular, a time delay in the emission of kaons-to achieve quantitative agreement. The comparative analysis also indicates a possible non-monotonic behavior of the asymmetry as a function of transverse velocity, and a constant scaling of the ratio between the emission asymmetry and femtoscopic radii with particle multiplicity. These results highlight the importance of including interactions in the hadronic stage for a complete description of the emission function.

hep-ph↗

arXiv2023

Artificial Intelligence for the Electron Ion Collider (AI4EIC)

The Electron-Ion Collider (EIC), a state-of-the-art facility for studying the strong force, is expected to begin commissioning its first experiments in 2028. This is an opportune time for artificial intelligence (AI) to be included from the start at this facility and in all phases that lead up to the experiments. The second annual workshop organized by the AI4EIC working group, which recently took place, centered on exploring all current and prospective application areas of AI for the EIC. This workshop is not only beneficial for the EIC, but also provides valuable insights for the newly established ePIC collaboration at EIC. This paper summarizes the different activities and R&D projects covered across the sessions of the workshop and provides an overview of the goals, approaches and strategies regarding AI/ML in the EIC community, as well as cutting-edge techniques currently studied in other experiments.

physics.acc-ph↗

arXiv2022

ATHENA Detector Proposal -- A Totally Hermetic Electron Nucleus Apparatus proposed for IP6 at the Electron-Ion Collider

ATHENA has been designed as a general purpose detector capable of delivering the full scientific scope of the Electron-Ion Collider. Careful technology choices provide fine tracking and momentum resolution, high performance electromagnetic and hadronic calorimetry, hadron identification over a wide kinematic range, and near-complete hermeticity. This article describes the detector design and its expected performance in the most relevant physics channels. It includes an evaluation of detector technology choices, the technical challenges to realizing the detector and the R&D required to meet those challenges.

physics.ins-det↗

arXiv2019

A next-generation LHC heavy-ion experiment

The present document discusses plans for a compact, next-generation multi-purpose detector at the LHC as a follow-up to the present ALICE experiment. The aim is to build a nearly massless barrel detector consisting of truly cylindrical layers based on curved wafer-scale ultra-thin silicon sensors with MAPS technology, featuring an unprecedented low material budget of 0.05% X$_0$ per layer, with the innermost layers possibly positioned inside the beam pipe. In addition to superior tracking and vertexing capabilities over a wide momentum range down to a few tens of MeV/$c$, the detector will provide particle identification via time-of-flight determination with about 20~ps resolution. In addition, electron and photon identification will be performed in a separate shower detector. The proposed detector is conceived for studies of pp, pA and AA collisions at luminosities a factor of 20 to 50 times higher than possible with the upgraded ALICE detector, enabling a rich physics program ranging from measurements with electromagnetic probes at ultra-low transverse momenta to precision physics in the charm and beauty sector.

physics.ins-det↗

arXiv2018

Particle identification studies with a full-size 4-GEM prototype for the ALICE TPC upgrade

A large Time Projection Chamber is the main device for tracking and charged-particle identification in the ALICE experiment at the CERN LHC. After the second long shutdown in 2019/20, the LHC will deliver Pb beams colliding at an interaction rate of about 50 kHz, which is about a factor of 50 above the present readout rate of the TPC. This will result in a significant improvement on the sensitivity to rare probes that are considered key observables to characterize the QCD matter created in such collisions. In order to make full use of this luminosity, the currently used gated Multi-Wire Proportional Chambers will be replaced. The upgrade relies on continuously operated readout detectors employing Gas Electron Multiplier technology to retain the performance in terms of particle identification via the measurement of the specific energy loss by ionization d$E$/d$x$. A full-size readout chamber prototype was assembled in 2014 featuring a stack of four GEM foils as an amplification stage. The performance of the prototype was evaluated in a test beam campaign at the CERN PS. The d$E$/d$x$ resolution complies with both the performance of the currently operated MWPC-based readout chambers and the challenging requirements of the ALICE TPC upgrade program. Detailed simulations of the readout system are able to reproduce the data.

physics.ins-det↗

arXiv2017

In-situ formation of SiGe alloy by electron beam evaporation and the effect of post deposition annealing on the energy band gap

We report the synthesis of polycrystalline (poly)-SiGe alloy thin films through solid state reaction of Si/Ge multilayer thin films on Si and glass substrates at low temperature of 500 {\deg}C. The pristine thin film was deposited using electron beam evaporation with optimized in-situ substrate heating. Our results show the co-existence of amorphous Si (a-Si) phase along with the poly-SiGe phase in the pristine thin film. The a-Si phase was found to subsume into the SiGe phase upon post deposition annealing in the temperature range from 600 to 800 {\deg}C. Additionally, dual energy band gaps could be observed in the optical properties of the annealed poly-SiGe thin films. The stoichiometric evolution of the pristine thin film and its subsequent effect on the band gap upon annealing are discussed on the basis of diffusion characteristics of Si in poly-SiGe.

cond-mat.mtrl-sci↗

arXiv2016

Carrier mediated reduction of stiffness in nanoindented crystalline Si(100)

We report the observation of carrier mediated decrease in the stiffness of crystalline (c)-Si(100) under nanoindentation. The apparent elastic modulii of heavily dopes (1E21 cm-3) p- and n-type c-Si are observed to be lower by 5.-7.5 percent that the estimated value for intrinsic (1E14 cm-3) c-Si. The deviation observed with respect to elastic modulus remarkably matches with the estimated value while considering the electronic elastic strain effect on carrier concentration as an influence of negative pressure coefficient of band gap for Si. The value is predominantly higher than the reported value of a decrease of 1-3 percent in stiffness as an effect of impurity in c-Si.

cond-mat.mtrl-sci↗

arXiv2015

XPS studies on AlN thin films grown by ion beam sputtering in reactive assistance of N+/N2+ ions: Substrate temperature induced compositional variations

We report on an XPS study of AlN thin films grown on Si(100) substrates by ion beam sputter deposition (IBSD) in reactive assistance of N+/N2+ ions to unravel the compositional variation of their surface when deposited at different substrate temperatures. The temperature of the substrate was varied as room temperature (RT), 100oC and 500oC. The binding energy of Al-2p, N-1s and O-1s core electrons indicate the formation of 2H polytypoid of AlN. The increase in concentration of AlN with substrate temperature during deposition is elucidated through detailed analysis with calculated elemental atomic concentrations (at. %) of all possible phases at the film surface. Our results show that predominate formation of AlN as high as 74 at. % is achievable using substrate temperature as the only process parameter. This high fraction of AlN in thin film surface composition is remarkable when compared to other growth techniques. Also, the formation of other phases is established based on their elemental concentrations.

cond-mat.mtrl-sci↗

arXiv2015

Novel single phase vanadium dioxide nanostructured films for methane sensing near room temperature

Methane (CH_4) gas sensing properties of novel vanadium dioxide (VO_2) nanostructured films is reported for the first time. The single phase nanostructures are synthesized by pulsed dc-magnetron sputtering of V target followed by oxidation in O_2 atmosphere at 550 ^oC. The partial pressure of O_2 is controlled to obtain stoichiometric VO_2 with the samples showing rutile monoclinic crystalline symmetry and regions of rod shaped nano-architectures. These nanostructured films exhibit a reversible semiconductor to metal transition in the temperature range of 60-70 ^oC. Gas sensing experiments are carried out in the temperature span from 25 ^oC to 200 ^oC in presence of CH_4. These experiments reveal that the films respond very well at temperatures as low as 50 ^oC, in the semiconducting state.

cond-mat.mtrl-sci↗

arXiv2015

Reduction of residual stress in AlN thin Films synthesized by magnetron sputtering technique

We report the reduction in residual stress of AlN thin films and also the crystal structure, surface morphology and nanomechanical properties of magnetron sputtered as a function of substrate temperature (Ts, 35 - 600 ?C). The residual stress of these films was calculated by sin2 technique and found that they are varying from tensile to compression with temperature (Ts). Evolution of crystalline growth of AlN films was studied by GIXRD and transmission electron microscopy (TEM) and a preferred a-axis orientation was observed at 400 ?C. The cross-sectional TEM micrograph and selected area electron difraction (SAED) of this film exhibited a high degree of orientation as well as a columnar structure. Hardness (H) measured by Nanoindentation technique on these films ranged between 12.8 - 19 GPa.

cond-mat.mtrl-sci↗

arXiv2015

Optical band gap and associated band-tails in nanocrystalline AlN thin films grown by reactive IBSD at different substrate temperatures

AlN thin films have been grown on Si (100) substrates by reactive ion beam sputter deposition (IBSD) at different substrate temperatures varying from room temperature (RT) to 500oC. Substrate temperature induced microstructural transition from amorphous at RT, nanocrystalline at 300oC to microcrystalline at 400oC has been observed by Transmission Electron Microscopy (TEM). Average surface roughness (Ra) and morphology has been explored by using Atomic Force Microscopy (AFM). UV-VIS spectrophotometry has been employed to probe the substrate temperature induced changes in optical band-gap (Eg) of grown thin films in reflectance mode. It was found that Eg was increased from 5.08 to 5.21 eV as substrate temperature was increased from RT to 500oC. Urbach energy tail (Eu) along with weak absorption tail (WAT) energy (Et) have been estimated to account for the optical disorder which was found to decrease with associated increase in Eg.

cond-mat.mtrl-sci↗

arXiv2014

Preferentially orientated E-beam TiN thin films using focused jet of nitrogen gas

A modified electron beam evaporator has been used judiciously to synthesize TiN thin films with (111) preferred orientation. This new design involved in creating local plasma by accelerating the secondary electrons emitted from the evaporating ingot by a positively biased semi-cylindrical anode plate kept in the vicinity and a jet of N2 gas has been focused towards the substrate as a reactive gas. We have observed a preferred orientation (111) with 25 degree angle to the surface normal and this was confirmed by pole figure analysis. The phenomenon of preferred orientation (111) has been explained based on the rate of evaporation. The residual stress by the classical sin2psi technique did not yield any tangible result due to the preferred orientation. The hardness and modulus measured by nanoindentation technique was around 19.5 GPa and 214 GPa. The continuous multicycle indentation test on these films exhibited a stress relaxation.

cond-mat.mtrl-sci↗

arXiv2014

Mass spectral analysis and quantification of Secondary Ion Mass Spectrometry data

This work highlights the possibility of improving the quantification aspect of Cs-complex ions in SIMS (Secondary Ion Mass Spectrometry), by combining the intensities of all possible Cs-complexes. Identification of all possible Cs-complexes requires quantitative analysis of mass spectrum from the material of interest. The important steps of this mass spectral analysis include constructing fingerprint mass spectra of the constituent species from the table of isotopic abundances of elements, constructing the system(s) of linear equations to get the intensities of those species, solving them, evaluating the solutions and employing a regularization process when required. These steps are comprehensively described and the results of their application on a SIMS mass spectrum obtained from D9 steel are presented. It is demonstrated that results from the summation procedure, which covers entire range of sputtered clusters, is superior to results from single Cs-complex per element. The result of employing a regularization process in solving a mass spectrum from an SS316LN steel specimen is provided to demonstrate the necessity of regularization.

cond-mat.mtrl-sci↗

arXiv2014

Growth Kinetics of Ion Beam Sputtered Al-thin films by Dynamic Scaling Theory

This paper reports the study of growth kinetics of ion beam sputtered aluminum thin films. Dynamic scaling theory was used to derive the kinetics from AFM measurements. AFM imaging revealed that surface incorporates distinctly different morphologies. Variation in deposition times resulted in such distinctiveness. The growth governing static (alpha) as well as dynamic (beta) scaling exponents have been determined. The exponent (alpha) decreased as the deposition time increased from 3 to 15 minutes. Consequently, the interfacial width (xi) also decreased with critical length (Lc), accompanied with an increase in surface roughness. Surface diffusion becomes a major surface roughening phenomenon that occurs during deposition carried out over a short period of 3 minutes. Extension of deposition time to 15 minutes brought in bulk diffusion process to dominate which eventually led to smoothening of a continuous film.

cond-mat.mtrl-sci↗

arXiv2014

Growth Kinetic studies of ion beam sputtered AlN-thin films: Effect of reactive assistance of nitrogen plasma

Reactive dual ion beam sputter deposition of AlN thin films was carried out for the analysis of surface growth characteristics by Atomic Force Microscopy. The variation of roughness as a function of deposition time was analysed by Dynamic Scaling Theory (DST). Two distinct exponents, static and dynamic were used to unravel the film growth characteristics. As the deposition time increased, static scaling exponent decreased gradually and substrate surface coverage was increased which is indicated by a decrease in critical length Lc. The rms roughness of the film was increased from 1.99 to 3.42 nm as the deposition time was increased from 3 minutes to 15 minutes. Dynamic scaling exponent was found to be 0.36. During the growth, surface diffusion (n = 4) becomes the major roughening phenomenon while Bulk diffusion (n = 3) turns into the dominating smoothening phenomenon.

cond-mat.mtrl-sci↗

arXiv2013

Temperature dependence of dielectric constants in Titanium Nitride

The temperature dependence of optical constants of titanium nitride thin film is investigated using spectroscopic ellipsometry between 1.4 to 5 eV in the temperature range 300 K to 650 K in steps of 50 K. The real and imaginary parts of the dielectric functions "1(E) and "2(E) increase marginally with increase in temperature. A Drude Lorentz dielectric analysis based on free electron and oscillator model are carried out to describe the temperature behavior. The parameters of the Lorentz oscillator model also showed that the relaxation time decreased with temperature while the oscillator energies increased. This study shows that owing to marginal change in the refractive index with temperature, titanium nitride can be employed for surface plasmon sensor applications even in environments where rise in temperature is imminent.

cond-mat.mtrl-sci↗

arXiv2013

Cation diffusion and hybridization effects at the Mn-GaSe(0001) interface probed by soft X-ray electron spectroscopies

The electronic properties of the Mn:GaSe interface, produced by evaporating Mn at room temperature on an epsilon-GaSe(0001) single crystal surface, have been studied by soft X-ray spectroscopies. Substitutional effects of Mn replacing Ga cations and Mn-Se hybridization effects are found both in core level and valence band photoemission spectra. The Mn cation valence state is probed by XAS measurements at the Mn L-edge, which indicate that Mn diffuses into the lattice as a Mn2+ cation with negligible crystal field effects. The Mn spectral weight in the valence band is probed by resonant photoemission spectroscopy at the Mn L-edge, which also allowed an estimation of the charge transfer and Mott-Hubbard energies on the basis of impurity-cluster configuration-interaction model of the photoemission process. The charge transfer energy is found to scale with the energy gap of the system. Competing effects of Mn segregation on the surface have been identified, and the transition from the Mn diffusion through the surface to the segregation of metallic layers on the surface has been tracked by core-level photoemission.

cond-mat.mtrl-sci↗

arXiv2012

Optical properties and hardness of highly a-axis oriented AlN films

This paper reports optical and nanomechanical properties of seldom studied highly a-axis oriented AlN thin films for the first time. These films were deposited by reactive DC magnetron sputtering technique at an optimal target to substrate distance of 180 mm. Bragg-Brentano geometry X-ray and rocking curve (FWHM = 52 arcsec) studies confirmed the preferred orientation. Spectroscopic ellipsometry revealed that these films exhibit a refractive index of 1.93 at a wavelength of 546 nm. The hardness and elastic modulus of these films were 17 GPa and 190 GPa, respectively. The mechanical properties obtained here are much higher than the earlier reported and therefore can be useful as protective coating in thermo printing devices, piezoelectric films in bulk acoustic wave resonators.

cond-mat.mtrl-sci↗