arXiv subjects

K. S. Subrahmanyam

Publications and source records attributed to K. S. Subrahmanyam.

4 recordsLinked to original sources

arXiv2010

Graphene produced by radiation-induced reduction of graphene oxide

Effect of irradiation on graphene oxide by sunlight, UV light and KrF excimer laser has been investigated in detail. Both sunlight and ultraviolet light reduce graphene oxide well after prolonged irradiation, but laser irradiation produces graphene with negligible oxygen functionalities within a short time. Laser irradiation is also useful for one-step synthesis of metal particle decorated graphene. Laser irradiation of graphene oxide appears to be an efficient procedure for large-scale synthesis of graphene.

cond-mat.mes-hall↗

arXiv2010

Femtosecond carrier dynamics and saturable absorption in graphene suspensions

Nonlinear optical properties and carrier relaxation dynamics in graphene, suspended in three different solvents, are investigated using femtosecond (80 fs pulses) Z-scan and degenerate pumpprobe spectroscopy at 790 nm. The results demonstrate saturable absorption property of graphene with a nonlinear absorption coefficient, $beta$, of ~2 to 9x10^-8 cm/W. Two distinct time scales associated with the relaxation of photoexcited carriers, a fast one in the range of 130-330 fs (related to carrier-carrier scattering) followed by a slower one in 3.5-4.9 ps range (associated with carrier-phonon scattering) are observed.

cond-mat.mtrl-sci↗

arXiv2009

Novel magnetic properties of graphene: Presence of both ferromagnetic and antiferromagnetic features and other aspects

Investigations of the magnetic properties of graphenes prepared by different methods reveal that dominant ferromagnetic interactions coexist along with antiferromagnetic interactions in all the samples. Thus, all the graphene samples exhibit room-temperature magnetic hysteresis. The magnetic properties depend on the number of layers and the sample area, small values of both favoring larger magnetization. Molecular charge-transfer affects the magnetic properties of graphene, interaction with a donor molecule such as tetrathiafulvalene having greater effect than an electron-withdrawing molecule such as tetracyanoethylene

physics.chem-ph↗

arXiv2009

Synthesis, Structure and Properties of Boron and Nitrogen Doped Graphene

Two-dimensional graphene exhibits many fascinating properties such as ballistic electronic conduction and quantum Hall effect at room temperature.1-4 Graphene doped electrochemically or through charge-transfer with electron-donor and -acceptor molecules,5-7 shows marked changes in electronic structure, with characteristic signatures in the Raman spectra.5-10 Substitutional doping, universally used in tuning properties of semiconductors, could be a powerful tool to control the electronic properties of graphene. Here, we present the structure and properties of boron and nitrogen doped graphenes, obtained by more than one method involving arc discharge in appropriate gaseous atmosphere, by using modified graphite electrode or by the transformation of nano-diamond. Using a combination of experiment and firstprinciples theory, we demonstrate systematic changes in the carrier-concentration and electronic structure of graphenes with B/N-doping, accompanied by stiffening of the Gband and intensification of the defect related D-band in the Raman spectra. Such n/p - type graphenes obtained without external fields or chemical agents should find device applications.

cond-mat.mtrl-sci↗