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Register a new userFirst principles design of divacancy defected graphene nanoribbon based rectifying and negative differential resistance device
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Added by
Soubhik Chakrabarty
Publication date
2015
fields
Physics
and research's language is
English
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We have elaborately studied the electronic structure of 555-777 divacancy (DV) defected armchair edged graphene nanoribbon (AGNR) and transport properties of AGNR based two-terminal device constructed with one defected electrode and one N doped electrode, by using density functional theory and non-equilibrium Greens function based approach. The introduction of 555-777 DV defect into AGNRs, results in a shifting of the {pi} and {pi}* bands towards the higher energy value which indicates a shifting of the Fermi level towards the lower energy. Formation of a potential barrier, very similar to that of conventional p-n junction, has been observed across the junction of defected and N doped AGNR. The prominent asymmetric feature of the current in the positive and negative bias indicates the diode like property of the device with high rectifying efficiency within wide range of bias voltages. The device also shows robust negative differential resistance (NDR) with very high peak-to-valley ratio. The analysis of the shifting of the energy states of the electrodes and the modification of the transmission function with applied bias provides an insight into the nonlinearity and asymmetry observed in the I-V characteristics. Variation of the transport properties on the width of the ribbon has also been discussed.
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The electronic property of NiFe$_2$O$_4$ nanowire device is investigated through nonequilibrium Greens functions (NEGF) in combination with density functional theory (DFT). The electronic transport properties of NiFe$_2$O$_4$ nanowire are studied in terms of density of states, transmission spectrum and $I{-}V$ characteristics. The density of states gets modified with the applied bias voltage across NiFe$_2$O$_4$ nanowire device, the density of charge is observed both in the valence band and in the conduction band on increasing the bias voltage. The transmission spectrum of NiFe$_2$O$_4$ nanowire device gives the insights on the transition of electrons at different energy intervals. The findings of the present work suggest that NiFe$_2$O$_4$ nanowire device can be used as negative differential resistance (NDR) device and its NDR property can be tuned with the bias voltage, which may be used in microwave device, memory devices and in fast switching devices.
We investigate the transport properties of pristine zigzag-edged borophene nanoribbons (ZBNRs) of different widths, using the fist-principles calculations. We choose ZBNRs with widths of 5 and 6 as odd and even widths. The differences of the quantum transport properties are found, where even-N BNRs and odd-N BNRs have different current-voltage relationships. Moreover, the negative differential resistance (NDR) can be observed within certain bias range in 5-ZBNR, while 6-ZBNR behaves as metal whose current rises with the increase of the voltage. The spin filter effect of 36% can be revealed when the two electrodes have opposite magnetization direction. Furthermore, the magnetoresistance effect appears to be in even-N ZBNRs, and the maximum value can reach 70%.
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We report on the first model of a thermal transistor to control heat flow. Like its electronic counterpart, our thermal transistor is a three-terminal device with the important feature that the current through the two terminals can be controlled by small changes in the temperature or in the current through the third terminal. This control feature allows us to switch the device between off (insulating) and on (conducting) states or to amplify a small current. The thermal transistor model is possible because of the negative differential thermal resistance.
This work is the first step towards understanding thermionic transport properties of graphene/phosphorene/graphene van der Waals heterostructures in contact with gold electrodes by using density functional theory based first principles calculations combined with real space Greens function formalism. We show that for monolayer phosphorene in the heterostructure, quantum tunneling dominates the transport. By adding more phosphorene layers, one can switch from tunneling dominated transport to thermionic dominated transport, resulting in transporting more heat per charge carrier, thus, enhancing the cooling coefficient of performance. The thermionic coefficient of performance for the proposed device is 18.5 at 600 K corresponding to an equivalent ZT of 0.13, which is significant for nanoscale devices.
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