Thermoelectric and Magnetothermoelectric Transport Measurements of Graphene

The conductance and thermoelectric power (TEP) of graphene is simultaneously measured using microfabricated heater and thermometer electrodes. The sign of the TEP changes across the charge neutrality point as the majority carrier density switches from electron to hole. The gate dependent conductance and TEP exhibit a quantitative agreement with the semiclassical Mott relation. In the quantum Hall regime at high magnetic field, quantized thermopower and Nernst signals are observed and are also in agreement with the generalized Mott relation, except for strong deviations near the charge neutrality point

Nernst-Ettingshausen effect in two-component electronic liquids

A simple model describing the Nernst-Ettingshausen effect (NEE) in two-component electronic liquids is formulated. The examples considered include graphite, where the normal and Dirac fermions coexist, superconductor in fluctuating regime, with coexisting Cooper pairs and normal electrons, and the inter-stellar plasma of electrons and protons. We give a general expression for the Nernst constant and show that the origin of a giant NEE is in the strong dependence of the chemical potential on temperature in all cases

Thermoelectric power measurements of wide band gap semiconducting nanowires

We investigated the temperature-dependent thermoelectric power (TEP) of individual wide band gap ZnO and GaN semiconducting nanowires by fabricating the devices with good Ohmic contacts. In the temperature range of 10-300 K, the measured TEP of both nanowires was linearly dependent on temperature, indicating the degenerate doping nature of these nanowires. The room temperature TEP value of ZnO nanowires was as high as -400 mu V/K while an order of magnitude smaller TEP value was observed in GaN. The negative sign of TEP values shows that electrons are the majority carriers in these wide band gap nanowires. More importantly, in comparison with gate-dependent transport measurements of the nanowire field effect transistors, analysis of temperature-dependent TEP measurements provides a reliable way of estimating the majority carrier concentration of nanowires, where conventional Hall effect measurements cannot be used.

Multilayer graphene films grown by Molecular Beam Deposition

Few-layer graphene films are grown using a Molecular Beam Deposition (MBD) technique in ultra-high vacuum by evaporation of atomic carbon and subsequent annealing of the samples at 800–900 °C. The graded thickness layers are grown on strip-shaped oxidized silicon substrates which are covered with 300 nm thick nickel films deposited by e-beam evaporation. The thickness of the deposited carbon layers changes continuously from 70 Å to less than 4 Å. The relatively narrow optical phonon bands in Raman spectroscopy reveal that good quality multilayer graphene films form on the Ni surface.This work is supported by ONR (N000140610138 and Graphene Muri), NSF (CHE-0117752 and CHE-0641523),NYSTAR, Spanish CAM (Q&C Light, S2009ESP-1503), Spanish MICINN (NANINPHO-QD, TEC2008-06756-C03- 01, CONSOLIDER QOIT and Salvador de Madariaga Grant no. PR2007-0036).Peer reviewe