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Start Over Author "Kumar, S" Journal applied physics letters
150 results on '"Kumar, S"'

2. Oxygen migration during resistance switching and failure of hafnium oxide memristors

Author

Kumar, S, Wang, Z, Huang, X, Kumari, N, Davila, N, Strachan, JP, Vine, D, Kilcoyne, ALD, Nishi, Y, and Williams, RS

Subjects
cond-mat.mtrl-sci, Applied Physics, Engineering, Physical Sciences, Technology
Abstract

While the recent establishment of the role of thermophoresis/diffusion-driven oxygen migration during resistance switching in metal oxide memristors provided critical insights required for memristor modeling, extended investigations of the role of oxygen migration during ageing and failure remain to be detailed. Such detailing will enable failure-tolerant design, which can lead to enhanced performance of memristor-based next-generation storage-class memory. Here, we directly observed lateral oxygen migration using in-situ synchrotron x-ray absorption spectromicroscopy of HfOx memristors during initial resistance switching, wear over millions of switching cycles, and eventual failure, through which we determined potential physical causes of failure. Using this information, we reengineered devices to mitigate three failure mechanisms and demonstrated an improvement in endurance of about three orders of magnitude.

Published
2017

3. The phase transition in VO2 probed using x-ray, visible and infrared radiations

Author

Kumar, S, Strachan, JP, Kilcoyne, ALD, Tyliszczak, T, Pickett, MD, Santori, C, Gibson, G, and Williams, RS

Subjects
Applied Physics, Engineering, Physical Sciences, Technology
Abstract

Vanadium dioxide (VO2) is a model system that has been used to understand closely occurring multiband electronic (Mott) and structural (Peierls) transitions for over half a century due to continued scientific and technological interests. Among the many techniques used to study VO2, the most frequently used involve electromagnetic radiation as a probe. Understanding of the distinct physical information provided by different probing radiations is incomplete, mostly owing to the complicated nature of the phase transitions. Here, we use transmission of spatially averaged infrared (λ = 1.5 μm) and visible (λ = 500 nm) radiations followed by spectroscopy and nanoscale imaging using x-rays (λ = 2.25-2.38 nm) to probe the same VO2 sample while controlling the ambient temperature across its hysteretic phase transitions and monitoring its electrical resistance. We directly observed nanoscale puddles of distinct electronic and structural compositions during the transition. The two main results are that, during both heating and cooling, the transition of infrared and visible transmission occurs at significantly lower temperatures than the Mott transition, and the electronic (Mott) transition occurs before the structural (Peierls) transition in temperature. We use our data to provide insights into possible microphysical origins of the different transition characteristics. We highlight that it is important to understand these effects because small changes in the nature of the probe can yield quantitatively, and even qualitatively, different results when applied to a non-trivial multiband phase transition. Our results guide more judicious use of probe type and interpretation of the resulting data.

Published
2016

29. Terahertz heterodyne spectrometer using a quantum cascade laser

Author

Ren, Y., primary, Hovenier, J. N., additional, Higgins, R., additional, Gao, J. R., additional, Klapwijk, T. M., additional, Shi, S. C., additional, Bell, A., additional, Klein, B., additional, Williams, B. S., additional, Kumar, S., additional, Hu, Q., additional, and Reno, J. L., additional

Published
2010
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49. High magnetoresistance at room temperature in p-i-n graphene nanoribbons due to band-to-band tunneling effects.

Author

Gengchiau Liang, Bala Kumar, S., Jalil, M. B. A., and Tan, S. G.

Subjects
*MAGNETORESISTANCE, *HIGH temperatures, *QUANTUM tunneling, *GRAPHENE, *NANOSTRUCTURES
Abstract

A large magnetoresistance effect is obtained at room-temperature by using p-i-n armchair-graphene-nanoribbon (GNR) heterostructures. The key advantage is the virtual elimination of thermal currents due to the presence of band gaps in the contacts. The current at B = 0 T is greatly decreased while the current at B > 0 T is relatively large due to the band-to-band tunneling effects, resulting in a high magnetoresistance ratio, even at room-temperature. Moreover, we explore the effects of edge-roughness, length, and width of GNR channels on device performance. An increase in edge-roughness and channel length enhances the magnetoresistance ratio while increased channel width can reduce the operating bias. [ABSTRACT FROM AUTHOR]

Published
2011
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50. We present the structural, dielectric and magnetization study of single phase polycrystalline BixCo2-xMnO4 (0≤x≤0.3), synthesized by a conventional solid state route. All the samples have the cubic spinel str

Author

Rajeevan, N. E., Pradyumnan, P. P., Kumar, Ravi, Shukla, D. K., Kumar, S., Singh, A. K., Patnaik, S., Arora, S. K., and Shvets, I. V.

Subjects
FERROMAGNETISM, MATHEMATICAL crystallography, FICTION writing techniques, GALVANOMAGNETIC effects, PHYSICAL & theoretical chemistry
Abstract

We present the structural, dielectric and magnetization study of single phase polycrystalline BixCo2-xMnO4 (0≤x≤0.3), synthesized by a conventional solid state route. All the samples have the cubic spinel structure with Fd3m space group. Bi-substitution in Co2MnO4 stabilizes the ferroelectric transition at a temperature of ∼350 K and enhances the dielectric constant with a relaxor behavior. The capacitance-voltage (C-V) measurements confirm the ferroelectric nature at room temperature. Ferrimagnetic nature of the Co2MnO4 is preserved in the Bi-substituted samples. Magnetocapacitive coupling proves candidature of these materials from an application point of view [ABSTRACT FROM AUTHOR]

Published
2008
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