Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics
Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics
High mobility graphene devices Paritosh Karnatak, T Phanindra Sai, Srijit Goswami, Subhamoy Ghatak, Arindam Ghosh Department of Physics, Indian Institute of Science, Bangalore-560012 Graphene being a single atomic layer is significantly affected by the substrate, as the intrinsic properties of graphene are often masked in the presence of disorder. It is well known that the presence of substrate trap charges, polar phonons, roughness and ripples collectively hinder studies on ultrahigh quality graphene. It was also predicted that if the effect of such external disorder could be eliminated, graphene would show extremely high mobility. Here we report the methods followed in making high mobility graphene devices. One of the ways to achieve high mobility is by etching out the substrate underneath the graphene. In such suspended graphene devices we have achieved mobilities of ~150,000 cm 2 /V-s. Such devices are potential candidates to explore new physics and may find viable applications as sensor devices. Another approach to produce high mobility graphene is to transfer graphene on to thin flakes of hexagonal boron nitride, which has a similar arrangement of atoms as graphite. Boron nitride flakes are found to be atomically flat, do not contain dangling bonds or traps. The result is that graphene on boron nitride has significantly higher mobilities ~50,000 cm 2 /V-s, which is significantly higher than the common graphene/SiO 2 /Si system. In addition, these systems are mechanically more stable than suspended graphene structures, and open up the possibilities of designing more intricate device structures.
Measurement of Proton-Carbon Dipolar Couplings using an improved DAPT pulse sequence R.V. Sudheer Kumar $, # and K.V. Ramanathan # Department of Physics $ , NMR research centre # Indian Institute of Science, Bangalore, India Dipolar couplings provide valuable information on order and dynamics of liquid crystals. Experiments to measure heteronuclear dipolar couplings are very powerful and widely important in solid state NMR, since it provides site specific dipolar couplings in aligned samples. Interpretation of these heteronuclear dipolar couplings are hampered by the chemical shift anisotropy (CSA) and dipolar interactions among abundant spins ( 1 H- 1 H couplings). Additionally, multiple 13 C- 1 H dipolar couplings found in complicated systems make the spectra more difficult to use. For static samples the complications are resolved partially by separated local field (SLF) spectroscopy where the local field due to heteronuclear dipolar coupling and chemical shift interactions are separated into two frequency domains in a 2D experiment. A method of separated local field experiment is presented for measuring heteronuclear dipolar couplings in oriented systems. This method is based on Dipolar assisted polarization transfer (DAPT). Compared to rotating frame techniques based on Hartmann-Hahn match, this approach is easy to implement and is independent of any matching condition. DAPT can be utilized either as a proton encoded local field (PELF) technique or as a separated local field (SLF) technique, which mean s that the heteronuclear dipolar coupling can be obtained by following either evolution of the abundant spin like proton (PELF) or that of the rare that of carbon (SLF).The DAPT pulse sequence has been improved for efficient homonuclear decoupling by the interpretation of BLEW-48 pulse sequence. The implementations of the modified DAPT experiment both as a PELF and as SLF on oriented liquid crystalline samples have been carried out. The performance of this experiment is compared with PISEMA.
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High mobility graphene devices<br />
Paritosh Karnatak, T Phanindra Sai, Srijit Goswami, Subhamoy Ghatak, Arindam Ghosh<br />
Department <strong>of</strong> <strong>Physics</strong>, Indian Institute <strong>of</strong> Science, Bangalore-560012<br />
Graphene being a single atomic layer is significantly affected by the substrate, as the<br />
intrinsic properties <strong>of</strong> graphene are <strong>of</strong>ten masked in the presence <strong>of</strong> disorder. It is well known<br />
that the presence <strong>of</strong> substrate trap charges, polar phonons, roughness and ripples collectively<br />
hinder studies on ultrahigh quality graphene. It was also predicted that if the effect <strong>of</strong> such<br />
external disorder could be eliminated, graphene would show extremely high mobility.<br />
Here we report the methods followed in making high mobility graphene devices. One <strong>of</strong><br />
the ways to achieve high mobility is by etching out the substrate underneath the graphene. In<br />
such suspended graphene devices we have achieved mobilities <strong>of</strong> ~150,000 cm 2 /V-s. Such<br />
devices are potential candidates to explore new physics and may find viable applications as<br />
sensor devices. Another approach to produce high mobility graphene is to transfer graphene on<br />
to thin flakes <strong>of</strong> hexagonal boron nitride, which has a similar arrangement <strong>of</strong> atoms as graphite.<br />
Boron nitride flakes are found to be atomically flat, do not contain dangling bonds or traps. The<br />
result is that graphene on boron nitride has significantly higher mobilities ~50,000 cm 2 /V-s,<br />
which is significantly higher than the common graphene/SiO 2 /Si system. In addition, these<br />
systems are mechanically more stable than suspended graphene structures, and open up the<br />
possibilities <strong>of</strong> designing more intricate device structures.
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