Qualification: 
Ph.D, M.Tech, B-Tech
r_abhilash@blr.amrita.edu

Dr. Abhilash Ravikumar currently serves as Assistant Professor (Sr.Gr.) at the department of Electronics and Communication Engineering, School of Engineering, Amrita Vishwa Vidyapeetham, Bengaluru Campus.

Dr. Abhilash Ravikumar primary research focus has been the study of electronic, magnetic, morphological and spectroscopic properties of condensed matter systems with closed synergy to experiments. This includes molecular dynamics and ab-initio investigation of 2-D heterostructures, interfacial interactions of crystals, organic molecular adsorbates and other realistic nanostructures and quantum transport calculation using non-equilibrium Greens function approach to design novel electronic devices. He also contributed in development of theoretical methods and computational tools to better describe and visualize the electronic structure of materials.

Education

  • 2017: Ph. D. in Materials Science and Nanotechnology
    University of Milano-Bicocca
  • 2014: M.Tech. in Materials Science
    National Institute of Technology-Surathkal
  • 2011: B.Tech. in Electronics and Communication Engineering
    School of Engineering, Amrita Vishwa Vidyapeetham, Bengaluru

Professional Appointments

Year Affiliation
2017 Post-Doctoral Fellow at the University of Milano-Bicocca
2012 Research Associate at Centre for Nano science and Excellence (CeNSE), Indian Institute of Science, Bangalore

Membership in Professional Bodies

  • IEEE Electronic devices

Certificates, Awards & Recognitions

  • Marie Curie Doctoral Fellow (2012)
  • Early Career Research Award (Start-up Research grant) (2019)

Publications

Publication Type: Journal Article

Year of Publication Title

2021

S. Chakraborty and Abhilash Ravikumar, “Substrate induced electronic phase transitions of CrI[Formula: see text] based van der Waals heterostructures.”, Sci Rep, vol. 11, no. 1, p. 198, 2021.[Abstract]


<p>We perform first principle density functional theory calculations to predict the substrate induced electronic phase transitions of CrI[Formula: see text] based 2-D heterostructures. We adsorb graphene and MoS[Formula: see text] on novel 2-D ferromagnetic semiconductor-CrI[Formula: see text] and investigate the electronic and magnetic properties of these heterostructures with and without spin orbit coupling (SOC). We find that when strained MoS[Formula: see text] is adsorbed on CrI[Formula: see text], the spin dependent band gap which is a characteristic of CrI[Formula: see text], ceases to remain. The bandgap of the heterostructure reduces drastically ([Formula: see text] 70%) and the heterostructure shows an indirect, spin-independent bandgap of [Formula: see text] 0.5 eV. The heterostructure remains magnetic (with and without SOC) with the magnetic moment localized primarily on CrI[Formula: see text]. Adsorption of graphene on CrI[Formula: see text] induces an electronic phase transition of the subsequent heterostructure to a ferromagnetic metal in both the spin configurations with magnetic moment localized on CrI[Formula: see text]. The SOC induced interaction opens a bandgap of [Formula: see text] 30 meV in the Dirac cone of graphene, which allows us to visualize Chern insulating states without reducing van der Waals gap.</p>

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2018

Abhilash Ravikumar, Kladnik, G., Müller, M., Cossaro, A., Bavdek, G., Patera, L. L., Sánchez-Portal, D., Venkataraman, L., Morgante, A., Brivio, G. Paolo, Cvetko, D., and Fratesi, G., “Tuning Ultrafast Electron Injection Dynamics at Organic-Graphene/Metal Interfaces”, Nanoscale, vol. 10, pp. 8014-8022, 2018.[Abstract]


We compare the ultrafast charge transfer dynamics of molecules on epitaxial graphene and bilayer graphene grown on Ni(111) interfaces through first principles calculations and X-ray resonant photoemission spectroscopy. We use 4,4′-bipyridine as a prototypical molecule for these explorations as the energy level alignment of core-excited molecular orbitals allows ultrafast injection of electrons from a substrate to a molecule on a femtosecond timescale. We show that the ultrafast injection of electrons from the substrate to the molecule is ∼4 times slower on weakly coupled bilayer graphene than on epitaxial graphene. Through our experiments and calculations, we can attribute this to a difference in the density of states close to the Fermi level between graphene and bilayer graphene. We therefore show how graphene coupling with the substrate influences charge transfer dynamics between organic molecules and graphene interfaces.

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2018

Abhilash Ravikumar, Brivio, G. Paolo, and Fratesi, G., “Core Level Spectra of Organic Molecules Adsorbed on Graphene”, Materials , vol. 11, no. 4, p. 518, 2018.[Abstract]


We perform first principle calculations based on density functional theory to investigate the effect of the adsorption of core-excited organic molecules on graphene. We simulate Near Edge X-ray absorption Fine Structure (NEXAFS) and X-ray Photoemission Spectroscopy (XPS) at the N and C edges for two moieties: pyridine and the pyridine radical on graphene, which exemplify two different adsorption characters. The modifications of molecular and graphene energy levels due to their interplay with the core-level excitation are discussed. We find that upon physisorption of pyridine, the binding energies of graphene close to the adsorption site reduce mildly, and the NEXAFS spectra of the molecule and graphene resemble those of gas phase pyridine and pristine graphene, respectively. However, the chemisorption of the pyridine radical is found to significantly alter these core excited spectra. The C 1s binding energy of the C atom of graphene participating in chemisorption increases by ∼1 eV, and the C atoms of graphene alternate to the adsorption site show a reduction in the binding energy. Analogously, these C atoms also show strong modifications in the NEXAFS spectra. The NEXAFS spectrum of the chemisorbed molecule is also modified as a result of hybridization with and screening by graphene. We eventually explore the electronic properties and magnetism of the system as a core-level excitation is adiabatically switched on.

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2018

G. Fratesi, Achilli, S., Manini, N., Onida, G., Baby, A., Abhilash Ravikumar, Ugolotti, A., Brivio, G., Milani, A., and Casari, C., “Fingerprints of sp1 Hybridized C in the Near-Edge X-ray Absorption Spectra of Surface-Grown Materials”, Materials , 2018.[Abstract]


Carbon structures comprising sp1 chains (e.g., polyynes or cumulenes) can be synthesized by exploiting on-surface chemistry and molecular self-assembly of organic precursors, opening to the use of the full experimental and theoretical surface-science toolbox for their characterization. In particular, polarized near-edge X-ray absorption fine structure (NEXAFS) can be used to determine molecular adsorption angles and is here also suggested as a probe to discriminate sp1/sp2 character in the structures. We present an ab initio study of the polarized NEXAFS spectrum of model and real sp1/sp2 materials. Calculations are performed within density functional theory with plane waves and pseudopotentials, and spectra are computed by core-excited C potentials. We evaluate the dichroism in the spectrum for ideal carbynes and highlight the main differences relative to typical sp2 systems. We then consider a mixed polymer alternating sp1 C4 units with sp2 biphenyl groups, recently synthesized on Au(111), as well as other linear structures and two-dimensional networks, pointing out a spectral line shape specifically due to the the presence of linear C chains. Our study suggests that the measurements of polarized NEXAFS spectra could be used to distinctly fingerprint the presence of sp1 hybridization in surface-grown C structures.

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2018

A. Baby, Lin, H., Abhilash Ravikumar, Bittencourt, C., Wegner, H. A., Floreano, L., Goldoni, A., and Fratesi, G., “Lattice Mismatch Drives Spatial Modulation of Corannulene Tilt on Ag (111)”, The Journal of Physical Chemistry C , vol. 122 , no. 19, pp. 10365–10376, 2018.[Abstract]


We investigated the adsorption of corannulene (C20H10) on the Ag(111) surface by experimental and simulated scanning tunneling microscopy (STM), X-ray photoemission (XPS), and near-edge X-ray absorption fine structure (NEXAFS). Structural optimizations of the adsorbed molecules were performed by density functional theory (DFT) and the core excited spectra evaluated within the transition-potential approach. Corannulene is physisorbed in a bowl-up orientation displaying a very high mobility (diffusing) and dynamics (tilting and spinning) at room temperature. At the monolayer saturation coverage, molecules order into a close-compact phase with an average intermolecular spacing of ∼10.5 ± 0.3 Å. The lattice mismatch drives a long wavelength structural modulation of the molecular rows, which, however, could not be identified with a specific superlattice periodicity. DFT calculations indicate that the structural and spectroscopic properties are intermediate between those predicted for the limiting cases of an on-hexagon geometry (with a 3-fold, ∼8.6 Å unit mesh) and an on-pentagon geometry (with a 4-fold, ∼11.5 Å unit mesh). We suggest that molecules smoothly change their equilibrium configuration along the observed long wavelength modulation of the molecular rows by varying their tilt and azimuth in between the geometric constraints calculated for molecules in the 3-fold and 4-fold phases.

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2017

B. Javvaji, Shenoy, B. Maithry, D Mahapatra, R., Abhilash Ravikumar, Hegde, G. M., and Rizwan, M. R., “Stable configurations of graphene on silicon”, Applied Surface Science , vol. 414, 31 , pp. 25-33, 2017.[Abstract]


Integration of graphene on silicon-based nanostructures is crucial in advancing graphene based nanoelectronic device technologies. The present paper provides a new insight on the combined effect of graphene structure and silicon (001) substrate on their two-dimensional anisotropic interface. Molecular dynamics simulations involving the sub-nanoscale interface reveal a most favourable set of temperature independent orientations of the monolayer graphene sheet with an angle of ∽15° between its armchair direction and [010] axis of the silicon substrate. While computing the favorable stable orientations, both the translation and the rotational vibrations of graphene are included. The possible interactions between the graphene atoms and the silicon atoms are identified from their coordination. Graphene sheet shows maximum bonding density with bond length 0.195 nm and minimum bond energy when interfaced with silicon substrate at 15° orientation. Local deformation analysis reveals probability distribution with maximum strain levels of 0.134, 0.047 and 0.029 for 900 K, 300 K and 100 K, respectively in silicon surface for 15° oriented graphene whereas the maximum probable strain in graphene is about 0.041 irrespective of temperature. Silicon–silicon dimer formation is changed due to silicon–carbon bonding. These results may help further in band structure engineering of silicon–graphene lattice.

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2016

Abhilash Ravikumar, Baby, A., Lin, H., Brivio, G. Paolo, and Fratesi, G., “Femtomagnetism in Graphene Induced by Core Level Excitation of Organic Adsorbates and the Role of Electron Transfer”, Nanophotonics: principles and applications, 2016.

2016

Abhilash Ravikumar, Baby, A., Lin, H., Brivio, G. Paolo, and Fratesi, G., “Femtomagnetism in Graphene Induced by Core Level Excitation of Organic Adsorbates”, Scientific reports, vol. 6, p. 24603, 2016.[Abstract]


We predict the induction or suppression of magnetism in the valence shell of physisorbed and chemisorbed organic molecules on graphene occurring on the femtosecond time scale as a result of core level excitations. For physisorbed molecules, where the interaction with graphene is dominated by van der Waals forces and the system is non-magnetic in the ground state, numerical simulations based on density functional theory show that the valence electrons relax towards a spin polarized configuration upon excitation of a core-level electron. The magnetism depends on efficient electron transfer from graphene on the femtosecond time scale. On the other hand, when graphene is covalently functionalized, the system is magnetic in the ground state showing two spin dependent mid gap states localized around the adsorption site. At variance with the physisorbed case upon core-level excitation, the LUMO of the molecule and the mid gap states of graphene hybridize and the relaxed valence shell is not magnetic anymore.

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Publication Type: Conference Paper

Year of Publication Title

2020

D. Ramadas, Chakravarthy, M. Bhaskar, Rajeev, N., and Abhilash Ravikumar, “An ab initio Method to Predict Phase Transitions in crystalline CO2”, in 2020 IEEE International Conference for Innovation in Technology (INOCON), Bangluru, India, 2020.[Abstract]


A crystal can exist in different phases and can change from one crystal symmetry to another when varying ranges of temperatures and pressures are applied. Solid Carbon dioxide (CO2) has been widely researched over decades mainly due its structural simplicity and importance in terrestrial chemistry, planetary chemistry, its abundance and its rich polymorphism. Various Density Functional Theory (DFT) methods have been devised and yet there exists challenges in computationally evaluating the interactions that exist in crystals using DFT. Here we consider an ab initio method which involves the calculation of Gibbs free energies and hence predicting the phase transition diagrams of solid CO2 and its phases I,II and III using Density Functional Perturbation theory (DFPT). The DFPT method is able to model accurately the crystal structure, at any given temperature and pressure which is based on the electronic interactions and forces acting on the lattice structures. We predict that for low values of temperatures, as pressure increases CO2 changes its crystalline phase from I to III and for higher values of temperature and pressure we observe a transition from phase III to I. The results obtained are in excellent agreement with the experimental results.

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2019

M. Sreelakshmi, Chakraborty, S., Abhilash Ravikumar, and Bhowmick, K., “Modified structural arrangement of InAs-based quantum dots and nanostructures for high efficiency multi-junction solar cells”, in AIP Conference Proceedings, 2019.[Abstract]


We present a new strategy to theoretically design InAs-based quantum dots (QD) and nanostructures (NS) by modifying the morphology of a multi-junction solar cell (MJSC). This InAs-based structural arrangement comprising of 24 QD each of radius 100 nm radius embedded in 6 NS layers result in cell efficiency of 47.03%, which is an enhancement of 13% over the previously reported structure with a configuration of 12 InP spacing layers and 169 QD each of radius 25 nm. The open circuit voltage obtained is 2.25 V and filling factor attained is 85.05%. The modified MJSC structure exhibits absorption response for a part of the NIR spectrum (900 - 1200) nm, which makes it an ideal prospect for cloudy conditions.

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2016

Abhilash Ravikumar, Baby, A., Lin, H., Brivio, G., and Fratesi, G., “Transient Magnetism in Graphene Induced by Core Level Excitation of Organic Adsorbates”, in APS March Meeting, 2016.[Abstract]


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2016

Abhilash Ravikumar, Baby, A., Lin, H., Brivio, G. Paolo, and Fratesi, G., “Transient Magnetization of Core Excited Organic Molecules Adsorbed on Graphene”, in APS Meeting Abstracts, 2016.[Abstract]


This work presents a density functional theory based computational investigation of electronic and magnetic properties of physisorbed and chemisorbed organic molecules on graphene in the ground state and core excited one at low molecular coverage. For physisorbed molecules, where the interaction with graphene is dominated by van der Waals forces and the system is non-magnetic in the ground state, it is found that the valence electrons relax towards a spin polarized configuration upon excitation of a core-level electron. The magnetism depends on efficient electron transfer from graphene on the femtosecond time scale. On the contrary, when graphene is covalently functionalized, the system is magnetic in the ground state presenting two spin dependent mid gap states localized around the adsorption site. At variance with the physisorbed case upon core-level excitation, the LUMO of the molecule and the mid gap states of graphene hybridize and the relaxed valence shell is not magnetic anymore.

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2016

G. Fratesi, Baby, A., Lin, H., Abhilash Ravikumar, Muller, M., Sànchez-Portal, D., Selloni, A., and Brivio, G., “Electron Transfer with Core-Level Excitations at Hybrid Interfaces”, in Workshop on Surfaces, Interfaces and Functionalization Processes in Organic Compounds and Applications (SINFO), 2016.

2015

Abhilash Ravikumar, Lin, H., Baby, A., Fratesi, G., and Brivio, G., “Adsorption of Organic Molecules on Graphene”, in School on Organic Electronics, 2015.

2015

G. Paolo Brivio, Fratesi, G., Lin, H., Abhilash Ravikumar, Adak, O., Venkataraman, L., Kladnik, G., Cvetko, D., and Morgante, A., “Lifetimes for Fast Charge Transfer of Core Excited Molecules on Gold and Graphene”, in APS Meeting Abstracts, 2015.[Abstract]


The charge transfer time from an excited organic molecule both adsorbed on gold and graphene is studied in terms of the resonant linewidth of the molecular orbital energy levels interacting with the valence band of the substrate. The calculations are performed by density functional theory including the van der Waals contribution. Experiments are carried out by the core level resonant spectroscopies with fs resolution. The core valence exciton is described by a static perturbation of the atomic potential. The calculated widths are consistent with the experimental transfer times. They display a dependence on the molecular adsorption angle both in theory and experiments, and this effect is predicted to be function of the excited orbital.

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2014

Abhilash Ravikumar, Lin, H., Fratesi, G., and Brivio, G., “Adsorption of Pyridine on Graphene”, in XIX ETSF Workshop on Electronic Excitations, 2014.

2014

B. Javvaji, Abhilash Ravikumar, Shenoy, B. M., D Mahapatra, R., Rahman, M. R., and Hegde, G. M., “Electronic Band Structure and Photoemission Spectra of Graphene on Silicon Substrate”, in Physics and Simulation of Optoelectronic Devices XXII, SPIE OPTO, 2014, San Francisco, California, United States, 2014.[Abstract]


Synergizing graphene on silicon based nanostructures is pivotal in advancing nano-electronic device technology. A combination of molecular dynamics and density functional theory has been used to predict the electronic energy band structure and photo-emission spectrum for graphene-Si system with silicon as a substrate for graphene. The equilibrium geometry of the system after energy minimization is obtained from molecular dynamics simulations. For the stable geometry obtained, density functional theory calculations are employed to determine the energy band structure and dielectric constant of the system. Further the work function of the system which is a direct consequence of photoemission spectrum is calculated from the energy band structure using random phase approximations.

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Publication Type: Book Chapter

Year of Publication Title

2019

G. Fratesi, Abhilash Ravikumar, and Brivio, G. Paolo, “Graphene Properties by Functionalization with Organic Molecules”, in World Scientific Reference of Hybrid Materials, 2019, pp. 41-60.[Abstract]


We review first the unique band structure of graphene and explain how the linear dispersion near the Fermi level determines the so called Dirac cones and relativistic effects. Then we will deal with simple organic moieties on graphene and discuss the modification of the electronic structure of the pristine graphene by donor and acceptor chemisorbed radicals and physisorbed molecules. The peculiar magnetism induced by functionalization with chemisorbed molecules is accounted for. For excited organic molecules we will outline the charge transfer process to graphene. Electron core-level excitations to the valence shell will be considered as in the measurements of transfer times by resonant spectroscopies. The lifetimes for charge transfer are considered and possible applications outlined. Femtomagnetism in graphene with core-excited adsorbates is presented together with its implications for magnetic ordering. The electric conduction in single molecular switches with graphene electrodes is analyzed. Finally, the properties of functionalized graphene as sensor are summarized.

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Publication Type: Thesis

Year of Publication Title

2017

Abhilash Ravikumar, “Electronic, Spin Dependent Conductive Properties of Modified Graphene”, 2017.[Abstract]


Understanding the adsorption mechanisms of organic molecules on graphene and their subsequent influence on the electronic and magnetic properties of this interface is essential in designing graphene based devices. In this thesis we perform first principles calculations based on density functional theory (DFT) in an effort to understand these phenomena. Most organic electronic devices are composed of interfaces formed by the organic overlayer and a metallic electrode. Understanding the charge transfer dynamics at the interface would help engineer efficient organic devices. With this in mind, the first part of research we present is the adsorption of core-excited organic molecules on graphene. We predict the induction or suppression of magnetism in the valence shell of physisorbed and chemisorbed organic molecules on graphene occurring on the femtosecond time scale as a result of core level excitations. We consider three organic molecules: Pyridine - whose interaction with graphene is mainly facilitated by van der Waals forces, Picoline radical - an intermediate case where there is a strong van der Waals interaction of the pyridine π ring with graphene but a covalent bonding of the molecule and pyridine radical - where the interaction is mainly through covalent bonding, and study the ground state and N 1s core excited state electronic properties for these systems. 

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Research Grants Received

Year Funding Agency Title of the Project Investigators Status
2019 SERB-SRG Design novel 2-D magnetic storage devices using CrI3 based van der Waals heterostructures Abhilash Ravikumar Ongoing
2020 VGST-K-FIST-L1 Implementation of Dynamic light scattering (DLS) technique using Ocular fluorometer: a noninvasive method to quantify intraocular inflammation Abhilash Ravikumar, Surekha Paneerselvam Ongoing

Keynote Addresses/Invited Talks/Panel Memberships

  • "Charge transfer dynamics with core-level excitations in 2- heterostructures", FDP workshop, MS Ramaiah Institute of Technology, Bangalore. (February 2019)
  • "Electronics of 2-D van der Waals heterostructures" National Webinar, Arka Jain University, Jamshedpur, Jharkhand. (July 2020)

Courses Taught

  • Solid State Physics (3 credit course), Bachelors in Electronics and Communication Engineering
  • Electrical and electronic measurements (4 credit course), Bachelors in Electronics and Instrumentation Engineering.
  • Physics of MOS Devices (3 credit course), Masters in VLSI.
  • Applied Electromagnetics (4 credit course), Bachelors in Electronics and Communication Engineering.

Student Guidance

Undergraduate Students

Sl. No. Name of the Student(s) Topic Status – Ongoing/Completed Year of Completion
1 Adiraju Lakshmi Sowmya, Akshara Pudhota, Sumanth Reddy Predecting the phase transition diagram of CdS and ZnS under adiabatic conditions. Ongoing 2021
2 K Dinesh Krishna, Rahul Nair, Shilpa Shree Design of a quantum transistor using 2-D van der Waals heterostructures Onging 2021
3 Aditya Varma, Anuli Jadhav, Praveen S Design of 2-D memory using van der Waals heterostructures Completed 2020
4 Dhanya Ramadas, Medha Bhaskar Chakravarthy, Neha Rajeev, An Ab Initio method to predict phase transitions in Crystalline CO₂ Completed 2020

Postgraduate Students

Sl. No. Name of the Student(s) Topic Status – Ongoing/Completed Year of Completion
1 Mayur Mestry Electronic transport in 2-D van der Waals heterostructures Ongoing 2021

Research Scholars

Sl. No. Name of the Student(s) Topic Status – Ongoing/Completed Year of Completion
1 Shamik Chakraborty Electronic spin dependent transport in 2-D van der Waals heterostructures Ongoing -
2 Sirisha Tadapelli Implementation of Dynamic light scattering (DLS) technique using Ocular fluorometer: Ongoing -
3 Krishnadas Bhagawat Echocardiography wprk flow automation using deep learning Ongoing -