Influence of external temperature gradient on acoustoelectric current in graphene (original) (raw)

Thermoelectric effects in graphene nanostructures

Journal of physics. Condensed matter : an Institute of Physics journal, 2015

The thermoelectric properties of graphene and graphene nanostructures have recently attracted significant attention from the physics and engineering communities. In fundamental physics, the analysis of Seebeck and Nernst effects is very useful in elucidating some details of the electronic band structure of graphene that cannot be probed by conductance measurements alone, due in particular to the ambipolar nature of this gapless material. For applications in thermoelectric energy conversion, graphene has two major disadvantages. It is gapless, which leads to a small Seebeck coefficient due to the opposite contributions of electrons and holes, and it is an excellent thermal conductor. The thermoelectric figure of merit ZT of a two-dimensional (2D) graphene sheet is thus very limited. However, many works have demonstrated recently that appropriate nanostructuring and bandgap engineering of graphene can concomitantly strongly reduce the lattice thermal conductance and enhance the Seebec...

Thermoelectric properties of a single graphene sheet and its derivatives

Journal of Materials Chemistry C, 2014

The thermoelectric properties of pristine graphene and H 2 S adsorbed onto bridge, hollow and top sites of a graphene sheet are investigated using the semi-classical Boltzmann transport theory. The average values of electrical conductivity, thermal conductivity, Seebeck coefficient, figure of merit (ZT) and the average value of the power factor (P av ) are reported and discussed in detail. While pristine graphene is a zero band gap semiconductor, adsorption of H 2 S onto the bridge site opens up a direct energy gap of about 0.04 eV, adsorption of a H 2 S molecule onto the top site opens up a gap of 0.3 eV, and adsorption of H 2 S onto the hollow site makes it metallic. The investigation of ZT and power factor values suggests that a top-site configuration could be a potential candidate for thermoelectric applications in the range 300-600 K.

Design and Simulation of a Graphene Based Thermoelectric Device

2017

The thermoelectric effect refers to phenomena by which either a temperature difference creates an electric potential or an electric potential creates a temperature difference and any device which utilizes this effect is known as thermoelectric device. So thermoelectric devices are used as generators and coolers to convert thermal energy into electrical energy or vice versa. A highly efficient thermoelectric material is desired in either case. Graphene, a 2D allotrope of carbon, has a very high electrical conductivity but its application in thermoelectric devices is limited by the high thermal conductivity and low Seebeck coefficient. However, various modification methods has been suggested to enhance the Seebeck coefficient and to reduce the thermal conductivity which will make it an amazing thermoelectric material. In this paper, we propose to design a thermoelectric device utilizing graphene and create a simulation to explore the prospects of graphene in thermoelectric devices.

Thermoelectric properties of bilayer graphene: Effect of screening

NATIONAL CONFERENCE ON PHYSICS AND CHEMISTRY OF MATERIALS: NCPCM2020

The acoustic-phonon-limited thermoelectric properties (TEPs), namely, mobility (μ), electronic thermal conductivity (κe) and diffusion thermopower (Sd) in bilayer graphene (BLG) are investigated over a temperature range 2<T<100K. We consider two physically distinct temperature ranges with respect to phonon scattering-the Bloch-Gruneisen (BG), and equipartition (EP) regimes taking into account the temperature dependent effects arising from screening of electronphonon interaction within random phase approximation. The numerical calculations of Sd shows a signature of BG regime. The mobility and electronic thermal conductivity are found to increase rapidly with decrease in temperature, while Sd follows a non-linear behavior at low temperatures. At higher temperatures TEPs are found to merge with values calculated using EP approximation. The importance of screening function in BLG is discussed. The study helps a better understanding of electronphonon interaction in bilayer graphene.

Phonon thermal conductivity of graphene

Superlattices and Microstructures, 2015

The study of graphene thermal conductivity is of great importance, as its anomalous thermal and electrical conductivities (the largest among the all known materials so far) provide very good perspectives for graphene-based nanoelectronics devices. Thermal conductivity of graphene is phonon-based, since its electronic-based thermal conductivity represents less than 1% of the total thermal conductivity at room temperature. For the consideration of the thermal conductivity of graphene the Boltzmann equation in the approximation of relaxation time is used. The relaxation time is determined, with three mechanisms of phonon scattering accounted simultaneously: at defects, at borders, and on phonons. Temperature dependence of thermal conductivity is determined numerically in the range from 15 K to 400 K. The results obtained are in accordance with some other available results found in literature, obtained either experimentally or by numerical calculations.

Experimental validation of bulk-graphene as a thermoelectric generator

2021

Quest for alternate energy sources is the core of most of the research activities these days. No matter how small or large amount of energy can be produced by utilizing the non-conventional techniques and sources, every bit of innovation can reshape the future of energy. In this work, experimental analysis of the thermoelectric (TE) properties of bulk-graphene in the temperature range of (303 to 363) K is presented. Graphene powder was pressed to form a pellet which was used to fabricate the TE device. The effects of temperature on the Seebeck coefficient, electrical and thermal conductivities, and the dimensionless figure of merit (FOM) were measured. The increasing value of the Seebeck coefficient (thermopower) with temperature is indicant of the metallic behavior. Additionally, the observed thermopower (TEP) is positive, which shows that the majority charge carriers are holes and peaked to a value of 56 μV K−1 at 363 K. The thermopower of the pellet is four times larger than the ...

Large thermoelectric figure of merit in graphene layered devices at low temperature

2D Materials, 2018

Nanostructured materials have emerged as an alternative to enhance the figure of merit (ZT) of thermoelectric (TE) devices. Graphene exhibits a high electrical conductivity (in-plane) that is necessary for a high ZT; however, this effect is countered by its impressive thermal conductivity. In this work TE layered devices composed of electrochemically exfoliated graphene (EEG) and a phonon blocking material such as poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), polyaniline (PANI) and gold nanoparticles (AuNPs) at the interface were prepared. The figure of merit, ZT, of each device was measured in the cross-plane direction using the Transient Harman Method (THM) and complemented with AFM-based measurements. The results show remarkable high ZT values (0.81 < ZT < 2.45) that are directly related with the topography, surface potential, capacitance gradient and resistance of the devices at the nanoscale.

Thermoelectric effect in high mobility single layer epitaxial graphene

Applied Physics Letters, 2011

The thermoelectric response of high mobility single layer epitaxial graphene on silicon carbide substrates as a function of temperature and magnetic field have been investigated. For the temperature dependence of the thermopower, a strong deviation from the Mott relation has been observed even when the carrier density is high, which reflects the importance of the screening effect. In the quantum Hall regime, the amplitude of the thermopower peaks is lower than a quantum value predicted by theories, despite the high mobility of the sample. A systematic reduction of the amplitude with decreasing temperature suggests that the suppression of the thermopower is intrinsic to Dirac electrons in graphene. PACS numbers: 73.63.Bd, 72.15.Jf, 73.43.Fj Graphene, a single layer of graphite, has a unique band structure, in which electrons are described by the relativistic Dirac equation. Extensive electrical transport studies have been performed to understand Dirac electrons in the material. Compared with electrical transport, the thermoelectric properties provide complementary information to the electronic structure and the detail of electron scattering, but investigations have been started only recently . The newly discovered topological insulators, whose electrons in surface states are also Dirac electrons, are extraordinary thermoelectric materials. The possibility of further improving the performance in its nanostructures by exploiting the Dirac nature of electrons also calls for studies on the thermoelectric response of Dirac electrons . The thermoelectric effect of Dirac electrons has been experimentally investigated in exfoliated graphene on SiO 2 [6-8]. It was found that the Mott relation, which is used to describe the thermoelectric effect in conventional 2-dimensional electron gases, is basically obeyed, but not in the vicinity of the charge neutrality point. In the quantum Hall regime, though theories predict a quantized value for the thermopower , experiments saw a smaller value . In those studies, the mobilities of the samples are low, in the order of a few thousand cm 2 /V·s. Thus, questions have been raised about whether the quantization of the thermopower is intrinsic to graphene and can be realized in high mobility samples . Generally, high mobility is crucial for studying the intrinsic properties of Dirac electrons. Therefore, achieving high mobility in graphene samples has been a main effort in many experiments. A few milestone experiments are indeed consequences of improved or new techniques for obtaining high mobilities, e.g. recent success in greatly improving the mobility of graphene by suspending and in situ annealing it directly led to observation of the fractional quantum Hall effect .