Department Of Physics

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Femtosecond laser-assisted surface texturing of compression piston rings is proposed and demonstrated. A femtosecond pulsed Ti3+:sapphire laser is used to generate dimples of the same size but with different area density on a moly-chrome ceramic deposited cast iron piston ring. The influence of the surface morphology and tribology operating conditions, such as reciprocating frequency and temperature of the lubricant, on friction and wear characteristics of textured piston rings and plateau honed liner samples is investigated. A decrease in the friction coefficient is observed with the texturing of rings. The dimple area density, which is defined as the ratio of the total textured area and the total area of the surface, of 16% and 27% offered a reduced coefficient of friction and minimize wear on the liner surface. © 2020 Royal Society of Chemistry. All rights reserved.

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Department of Engineering Design

Journal of Tribology

Femtosecond Pulsed Ti:Sapphire Laser-Assisted Surface Texturing on Piston Ring and Its Tribology Characterization

We report a detailed study of the structural and magnetic properties of Ni80Cr20 fine particles prepared by physical methods, such as mechanical alloying, wire explosion process (WEP), and chemical methods like sodium borohydride reduction, polyol method. From the analysis of structural and microstructural data, phase formation with the desired composition is confirmed in the particles prepared by the WEP. A comparative study of magnetization data of bulk and nanoparticles of Ni80Cr20 suggests that a weak magnetic moment develops in nanoparticles due to finite-size effects. Analysis of magnetization data suggests a superparamagnetic (SPM) behavior in the smallest sized (34 nm) particles prepared by WEP, while nanoparticles prepared by other methods show ferromagnetic ground state. Further, it is shown that the origin of weak magnetic moment and development of SPM state in the nanoparticles is due to uncompensated surface spins with a negligible interaction effect. © 2021 Elsevier Ltd

Department of Electrical Engineering

Materials Research Bulletin

Anomalous magnetic behavior in Ni80Cr20 nanoparticles prepared by physical and chemical methods

a-axis (100) oriented Aluminium Nitride (AlN) favours transverse acoustic wave applications. We have been able to realize preferential (100) oriented AlN films on Molybdenum (Mo) coated Si substrate using reactive RF magnetron sputtering. X-ray diffraction and Fourier-transform infrared spectroscopy studies reveal the crystallinity, preferred orientation and bond formation between Al and N2. Al 2p subpeak at 73.8 eV and N 1s subpeak at 396.6 eV from X-ray photoelectron spectroscopy studies confirm the Al-N and N-Al formation in wurtzite hexagonal phase. From the fabricated Mo-AlN-Mo capacitors, the measured dielectric constant and electrical resistivity were ( 18) and ( 7.5 × 106 Ω.m) respectively. The piezoelectric coefficient d33(eff) of AlN film was ( 4.5) pmV−1. These excellent properties of preferential (100) AlN/Mo films will be very useful for high frequency resonator and energy harvesting applications. © 2021 Elsevier B.V.

Applied Surface Science

Realization of preferential (100) oriented AlN thin films on Mo coated Si substrate using reactive RF magnetron sputtering

Recent literature has shown that the spectral characteristics of a harvester can be significantly improved by invoking internal resonance between the modes. Taking motivation from this premise, the present work analyzes the nonlinear dynamics and harvesting performance of a 1:3 internally resonant piezoelectric cantilever beam with a lumped mass under harmonic excitation. The governing modal equations are derived using Galerkin's approach and Hamilton's principle of least action. The method of multiple scales has been used to study the dynamics of the harvester in the proximity of primary resonances. The steady state periodic responses of the harvester are obtained using a pseudo-arc continuation technique and subsequently, their implications on the harvested power are discussed. The frequency responses of the harvested power are shown to boast significantly high magnitudes across a wide frequency band due to the energy transfer between the modes near the primary resonances. Results presented in the study show that the higher mode invoked through internal resonance plays a significant role in broadband power generation. The transfer of energy between the modes is found to occur only within a certain threshold of excitation level which in turn affects the magnitude of harvested power. Numerical simulations have also been carried out the results of which are compared against the analytical results. The outcomes of this first-hand analysis shall aid in the proposition of an efficient design for a broadband energy harvester.

Department of Applied Mechanics

Mechanical Systems and Signal Processing

Exploring 1:3 internal resonance for broadband piezoelectric energy harvesting

We show that electrically poled ferroelectric matrix considerably enhances the localized magnetostrictive deformations in a ferroelectric-ferrimagnetic composite. Magnetostrain measurements performed on Dy-free and Dy-modified BiFeO3-PbTiO3 (BF-PT) ferroelectric ceramics revealed no measurable macroscopic strain in poled and unpoled Dy-free nonferromagnetic specimens. Dy-modified BF-PT, on the other hand, exhibit ferrimagnetic dysprosium-iron garnet (DyIG) as precipitates and exhibit a macroscopic strain of -4 ppm in the poled state. Despite the small (6%) volume fraction of DyIG, the macroscopic strain in Dy-modified BF-PT is almost 50% of the strain of pure DyIG. Our results suggest that the amplification of the localized magnetostrictive deformation in the ferrimagnetic islands by the neighboring ferroelectric regions is caused by the magnetostrictive stress-induced motion of ferroelectric-ferroelastic domains of the poled ferroelectric matrix. © 2021 American Physical Society.

Department of Management Studies

Physical Review B

Strain transfer in ferroelectric-ferrimagnetic magnetoelectric composite

Cupric oxide (CuO) nanostructure arrays have been extensively investigated for solar energy harvesting, electrochemical energy storage, chemical sensing, field-effect transistors, etc. Although most of these applications depend on the collective behavior of an array of such structures, analysis of electrical transport in a single nanostructure, which are the building blocks, is essential for understanding both the fundamental aspects and device performance. Here we report the electrical conduction mechanism in thermally grown single CuO nanowire (NW), which reveals that the current density has an anomalous dependence on the diameter of the NWs - decreasing with an increase in diameter. An analysis of the electrical behavior at room temperature shows that the current density in CuO NWs has different slopes in different regions of the applied bias indicating distinct types of charge transport, which are characterized as near Ohmic (lower voltage), trap controlled, and space charge limited conduction (higher applied voltage). Further, the trap density and activation energy are calculated from the temperature-dependent current density data, which shows higher values (9.38 × 1015cm-3, 79.4 meV) in thicker NWs compared to that in the thinner ones (3.96 × 1015 cm-3, 63.9 meV). Investigation of the NWs with Raman and photoluminescence spectra establishes the presence of Cu2O phase in thicker NWs, which act as hole traps to hinder the charge transport in p-type CuO and resulting in lower conductivity at higher diameters. This study helps to design and fabricate prototype nanodevices with desired conductivity based on CuO NWs. © 2021 IOP Publishing Ltd.

Journal of Physics D: Applied Physics

Anomalous diameter dependent electrical transport in individual CuO nanowire

Desiccation cracks in colloidal deposits occur to release the excess strain energy arising from the competition between the drying induced shrinkage of the deposit and its adhesion to the substrate. Here we report remarkably different morphology of desiccation cracks in the dried patterns formed by the evaporation of sessile drops containing colloids on elastomer (soft) or glass (stiff) substrates. The change in the crack pattern, i.e., from radial cracks on stiff substrates to circular cracks on soft substrates, is shown to arise solely due to the variation in elasticity of the underlying substrates. Our experiments and calculations reveal an intricate correlation between the desiccation crack patterns and the substrate's elasticity. The mismatch in modulus of elasticity between the substrate and that of the particulate deposit significantly alters the energy release rate during the nucleation and propagation of cracks. The stark variation in crack morphology is attributed to the tensile or compressive nature of the drying-induced in-plane stresses. © 2021 American Physical Society.

Department Of Chemical Engineering

Physical Review E

Synergy between the crack pattern and substrate elasticity in colloidal deposits

A major loss mechanism in high intensity organic light-emitting devices is the quenching of excitons in the presence of polarons. In this work, the interaction of excitons in N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) with holes in pentacene is studied in a pentacene/NPB bilayer organic field-effect transistor. Gate-modulated steady-state photoluminescence quenching measurements are performed. The excitons are confined in NPB and the polarons in an ultrathin layer of pentacene at the pentacene/NPB organic heterojunction. It is shown that excitons are quenched by polarons, even if they are located on different materials, provided that the exciton and polaron are separated by a length within which efficient Förster resonance energy transfer can occur. The experimental findings are supported by a steady-state three-dimensional simulation of the gate voltage-dependent exciton-polaron quenching efficiency. The Förster resonant energy transfer radius for exciton-polaron interaction at the pentacene/NPB heterojunction is estimated to be in the range of 2.3-3.0 nm. © 2021 American Chemical Society.

ACS Photonics

Spatial Extent of Interaction between Excitons and Polarons in a Bilayer Organic Field-Effect Transistor

The rare decay η′→π+π-e+e- is studied using a sample of 1.3×109 J/ψ events collected with the BESIII detector at BEPCII in 2009 and 2012. The branching fraction is measured with improved precision to be (2.42±0.05stat±0.08syst)×10-3. Due to the inclusion of new data, this result supersedes the last BESIII result on this branching fraction. In addition, the CP-violating asymmetry in the angle between the decay planes of the π+π - pair and the e+e - pair is investigated. A measurable value would indicate physics beyond the standard model; the result is ACP=(2.9±3.7stat±1.1syst)%, which is consistent with the standard model expectation of no CP-violation. The precision is comparable to the asymmetry measurement in the KL0→π+π-e+e- decay where the observed (14±2)% effect is driven by a standard model mechanism. © 2021 authors. Published by the American Physical Society.

Fulltext

Physical Review D

Measurement of the branching fraction of and search for a CP -violating asymmetry in η′ →π+π-e+e- At BESIII

We measure the time-dependent CP violation parameters in B0→KS0KS0KS0 decays using 772×106BB¯ pairs collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. The obtained mixing-induced and direct CP asymmetries are -0.71±0.23 (stat)±0.05 (syst) and 0.12±0.16 (stat)±0.05 (syst), respectively. These values are consistent with the Standard Model predictions. The significance of CP violation differs from zero by 2.5 standard deviations. © 2021 authors. Published by the American Physical Society.