Qualification: 
Ph.D, MPhil, MSc
Email: 
a_umamaheswari@cb.amrita.edu

Dr. Umamaheswari A. currently serves as Assistant Professor in Physics, Department of Sciences, School of Engineering, Coimbatore Campus. Her areas of research include Theoretical Physics.

Publications

Publication Type: Journal Article

Year of Publication Publication Type Title

2016

Journal Article

Dr. Umamaheswari A., Sivakumar, M., Indhumathi, N., and Mohan, S. R., “Corrosion Resistance of 304L SS Spray Coated with Zirconia Nanoparticles”, IOP Conference Series: Materials Science and Engineering, vol. 149, p. 012068, 2016.[Abstract]


Influence of substrate temperature on corrosion (in 3.5% NaCl) and wear resistance of nanostructured zirconia thin film coated 304L SS substrates are studied by electrochemical and nano-indentation methods. This analysis shows 304L SS substrate spray coated with nanostructured zirconia at substrate temperature closer to the boiling point of the spray solvent ethanol exhibited good corrosion and wear resistance behaviour. This is because of the compressive stress developed during film fabrication at lower substrate temperature (∼50 °C) and hence constrains the indentation plasticity, which leads to higher indentation load than the bare 304L SS. More »»

2016

Journal Article

V. P. Muhamed Shajudheen, Viswanathan, K., K Rani, A., Dr. Umamaheswari A., and S Kumar, S., “A Simple Chemical Precipitation Method of Titanium Dioxide Nanoparticles Using Polyvinyl Pyrrolidone as a Capping Agent and Their Characterization”, World Academy of Science, Engineering and Technology, International Journal of Chemical, Molecular, Nuclear, Materials and Metallurgical Engineering, vol. 10, pp. 552–555, 2016.

2015

Journal Article

Dr. Umamaheswari A., Mohan, S. R., Sivakumar, M., and S Kumar, S., “Tweaking Electrical and Dielectric Properties of Nickel Oxide Nanocrystals by Varying the Surfactant”, Journal of nanoscience and nanotechnology, vol. 15, pp. 9423–9430, 2015.[Abstract]


The influence of cationic cetyltrimethylammonium bromide (CTAB) and neutral polymeric polyvinylpyrrolidone (PVP) surfactants on electrical and dielectric properties of NiO nanocrystals is investigated. It is demonstrated that, compressive strain of nanocrystals is higher with PVP than that of CTAB. Consequently surfactant type has significant influence on intrinsic defects of nanocrystals. This is attributed to the difference in stabilization of metallic ions against agglomeration that leads to variation in rate of hydrolysis. Particularly, in the case of PVP assisted synthesis, higher stabilization leads to slow nucleation rate with lower defect density. As a result the hopping time of charge carriers decreases which in turn enhances the conductivity of nanocrystals as evidenced from the shifting of dielectric loss peak to higher frequency. More »»

2014

Journal Article

Dr. Umamaheswari A., Mohan, S. R., S. Kumar, S., and Sivakumar, M., “Phase tuning of zirconia nanocrystals by varying the surfactant and alkaline mineralizer”, Ceramics International, vol. 40, pp. 6561 - 6568, 2014.[Abstract]


The influence of cationic (CTAB)/neutral polymeric (PVP) surfactants and strong (NaOH)/weak (NH4OH) alkaline mineralizers on phase stabilization of zirconia nanocrystals synthesized by chemical precipitation is investigated. X-ray diffraction and micro-Raman analysis of the as-prepared samples show that tetragonal zirconia is predominant as compared to monoclinic using \{PVP\} with NH4OH. The phases are also evident from lattice fringes of \{TEM\} images and the corresponding \{SAED\} pattern. Photoluminescence spectra of samples reveal oxygen vacancies present in the zirconia nanocrystals. The group H Raman vibration modes identified are attributed to surface defects and quantum size effects of nanocrystals. The phase stabilization of zirconia nanocrystals is explained using the polymerization rate of tetramers during synthesis. The rate can be varied by proper selection of the surfactant and the mineralizer. A slow polymerization rate with \{PVP\} and \{NH4OH\} favors the formation of tetragonal zirconia. Thus, a simple method for phase stabilization of zirconia nanocrystals at room temperature using chemical precipitation by varying the surfactant and the mineralizer is demonstrated. More »»

2013

Journal Article

Dr. Umamaheswari A., S Kumar, S., and Sivakumar, M., “Influence of alkaline mineralizer on structural and optical properties of ZrO2 nanoparticles”, Journal of nanoscience and nanotechnology, vol. 13, pp. 4409–4414, 2013.[Abstract]


In this work, the influence of different alkaline mineralizers on structural and optical properties of zirconia nanoparticles synthesized by chemical co-precipitation technique using zirconium oxychloride octahydrate (ZrOCl2·8H2O) as precursor is studied. The mineralizers used for the synthesis of nanoparticles are NaOH and NH4OH. X-ray diffraction, Fourier Transform Infrared (FTIR) spectroscopy, UV-visible absorption spectroscopy and Photoluminescence (PL) spectroscopy were used for characterizing the nanoparticles. Structural analysis of the sample synthesized using NaOH shows monoclinic phase as predominant one, however when NH4OH is used the major phases are cubic and tetragonal. The difference is attributed to the number of hydroxyl ions produced and their rate of release during the reaction process. The presence of these phases in both samples is further confirmed by vibrational bands of FT-IR spectra. Also, the low energy bands due to the presence of defects in nanoparticles are also explicitly observed in the photoluminescence spectra. Further the defects lead to a red shift in the band gap of ZrO2 which is observed when the samples are subjected to UV-absorption spectroscopy analysis. It has been demonstrated that zirconia nanoparticles with desired structural properties can be synthesized by changing the type of mineralizer without the necessity of doping. More »»

2012

Journal Article

N. Sa Roshima, Kumar, S. Sb, Dr. Umamaheswari A., and Sivakumar, Mc, “Study on vacancy related defects of CdS nanoparticles by heat treatment”, Journal of Nano Research, vol. 18-19, pp. 53-61, 2012.[Abstract]


In this work a method of incorporating anion or cation vacancy during synthesis stage of CdS nanoparticles to induce defect level emission is presented. Further the influence of temperature on this vacancy related defects is also studied. The as-prepared samples with co-precipitation technique were heat treated with different time intervals at a constant temperature of 200 °C. From UV-Visible absorption spectra, the band gap of both the as-prepared and heat treated samples are calculated to be 3.51 eV indicating that there are no significant changes in the size of nanoparticles. The photoluminescence spectra of both samples showed emission bands corresponding to band edge and defect levels. Further from the spectra, it was observed that the intensity of band edge luminescence decreases with increase of heat treatment duration. This is due to the fact that induced defects have reached the surface of nanoparticles. © (2012) Trans Tech Publications, Switzerland.

More »»

2011

Journal Article

Dr. Umamaheswari A., “Study of resonances and absorption in one dimensional quantal scattering”, 2011.[Abstract]


Ever since the formulation of quantum laws governing the microworld, the study of quantum scattering in one dimension (1D) and three dimension (3D) has been indispensable in understanding the physics and interactions governing the world of molecules, atoms, nuclei and sub-atomic particles. Recently there is a renewed interest in the study of 1D quantum transmission and tunneling across heterostructures like barrier, well and its combination. This is because these structures are quite important for the fabrication of short-wavelength light-emitting diodes and diode lasers, and for other optoelectronic applications based on resonant tunneling. High quality heterostructures is possible by growth techniques like molecular beam epitaxy and metalorganic chemical vapor deposition. They posses predesigned potential profiles and impurity dis- tributions with dimensional control close to interatomic spacing. If the energy of the incident particle coincides with the resonance states generated by the heterostructure then the transmission gets enhanced and hence they play quite important role in the transport of charges in electronic devices. In view of this a systemic study of 1D scattering which is of pedagogical and academic interest is undertaken in this thesis. Analytical S matrix theory of 3D potential scattering provides a unified framework for the identification of bound and resonance states generated by the potential. Both these types of states are represented by the poles of S -matrix in complex energy or momentum planes. Bound states generated by the scattering potential are normalizable negative energy states with zero width. On the other hand resonance states are complex eigenstates, the real part corresponds to the resonance energy Er and imaginary part corresponds to its width Γr. If the resonance is very sharp, it corresponds to long lived quasibound (QB) state and within the interaction domain the QB state wave function behaves like a bound state wave function. More »»

2010

Journal Article

Dr. Umamaheswari A., Prema, P., and Shastry, C. S., “Resonant states and transmission coefficient oscillations for potential wells and barriers”, American Journal of Physics, vol. 78, pp. 412–417, 2010.[Abstract]


The oscillatory behavior of the transmission coefficient TT as a function of energy is examined for an attractive square well and a rectangular barrier. We calculate TT using resonant state boundary conditions and demonstrate that the maxima in TT are correlated with the broad resonances generated by these potentials. For barrier potentials the maxima signify resonances occurring at energies above the barrier height. It is shown that the resonance position and width can also be generated from the complex poles of the amplitude of the transmitted plane wave. We also explain the relation between the positions of the resonances generated by the square well and the rectangular barrier to the energy eigenvalues of the corresponding rigid box with the same range. We show for a potential with an attractive well and a repulsive barrier that TT exhibits oscillations when the particle energy is below the barrier, implying that in many cases the simple WKB type barrier penetration expression for TT is not adequate. These features of TT are likely to hold for most attractive potentials and flat repulsive barriers. We also discuss the attractive modified Poschl–Teller type potential for which TT does not show oscillations as a function of energy. More »»

2009

Journal Article

Dr. Umamaheswari A., Prema, P., Dr. Mahadevan S., and Shastry, C. S., “Quasi-bound states, resonance tunnelling, and tunnelling times generated by twin symmetric barriers”, Pramana, vol. 73, p. 969, 2009.[Abstract]


In analogy with the definition of resonant or quasi-bound states used in three-dimensional quantal scattering, we define the quasi-bound states that occur in one-dimensional transmission generated by twin symmetric potential barriers and evaluate their energies and widths using two typical examples: (i) twin rectangular barrier and (ii) twin Gaussian-type barrier. The energies at which reflectionless transmission occurs correspond to these states and the widths of the transmission peaks are also the same as those of quasi-bound states. We compare the behaviour of the magnitude of wave functions of quasi-bound states with those for bound states and with the above-barrier state wave function. We deduce a Breit-Wigner-type resonance formula which neatly describes the variation of transmission coefficient as a function of energy at below-barrier energies. Similar formula with additional empirical term explains approximately the peaks of transmission coefficients at above-barrier energies as well. Further, we study the variation of tunnelling time as a function of energy and compare the same with transmission, reflection time and Breit-Wigner delay time around a quasi-bound state energy. We also find that tunnelling time is of the same order of magnitude as lifetime of the quasi-bound state, but somewhat larger. More »»

2007

Journal Article

Dr. Umamaheswari A., Dr. Mahadevan S., Prema, Pa, Shastry, C. Sa, and Agarwalla, S. Kb, “Transmission and scattering by an absorptive potential”, American Journal of Physics, vol. 75, pp. 245-253, 2007.[Abstract]


Transmission and scattering problems involving complex potentials are important in physics, in particular in describing nuclear collisions. We describe many pedagogical features of transmission in one dimension and scattering and absorption cross sections in three dimensions for a rectangular absorptive potential and compare the results with scattering from real barriers and a hard sphere. For a given energy in one dimension we show that the absorption reaches a maximum for a critical value of the absorption strength and then monotonically decreases with an increase in the absorption strength. An infinitely absorptive well becomes almost fully reflective and thus is similar to an infinitely high barrier. Similar results are found in three dimensions. We show that the absorption cross section in three dimensions diverges at a threshold energy, which is of critical importance for exothermic reactions. © 2007 American Association of Physics Teachers. More »»

2006

Journal Article

Dr. Mahadevan S., Dr. Umamaheswari A., Prema, P., Shastry, C. S., and , “Quantum mechanical transmission with absorption”, Phys. Educ, vol. 23, pp. 13–21, 2006.[Abstract]


Transmission and reflection across a rectangular barrier at energies below and above barrier is the most commonly studied topic in nonrelativistic quantum mechanics. However the subtle inter-relationship between the barrier problem and the corresponding well problem is not widely known, in particular when absorption is present. In this article we show that when a particle traverses an absorptive medium, at any given energy the absorption peaks for a particular value of absorption potential strength W0. Similarly we study the corresponding cases when incident energy E is increased keeping W0 constant. Further, we show that for a given E when W0. is made very large absorption gradually decreases and reflection overtakes it and tends towards unity. We also study the case of transmission across a potential barrier and well and interpret physically the behavior of absorption, transmission and reflection. More »»

Publication Type: Conference Proceedings

Year of Publication Publication Type Title

2013

Conference Proceedings

Dr. Umamaheswari A., Mohan, S. R., and S. Kumar, S., “Effect of strong base on the crystalline phase of zirconia nanoparticles synthesized by arrested chemical precipitation method”, National Conference on Recent Advances in Surface Science(RASS 2013). Gandhigram Rural Institute - Deemed University, Gandhigram - 624 302, Dindigul, 2013.

Faculty Research Interest: 
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