| 1. |
- Shiri, Daryoush, 1975, et al.
(författare)
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An Electrically Controlled Heat Rectifier using Graphene Nanoribbons
- 2019
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Ingår i: 2019 IEEE 14th Nanotechnology Materials and Devices Conference, NMDC 2019. - 2378-377X. - 9781728126371 ; October 2019, s. 1-4
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Konferensbidrag (refereegranskat)abstract
- Using Molecular Dynamics (MD) simulations we propose that splitting a graphene nanoribbon into two unequal strained sections using external force leads to large asymmetry in the forward and reverse heat fluxes. We find that the corresponding rectification ratio (RR) is enhanced to 60% compared to previous proposals. More importantly, the polarity of the proposed heat diode is controllable on-the-fly i.e. by changing the position where force is applied. This technique obviates the complex nano-patterning and lithography required to pattern graphene every time a new rectification value or sign is sought for and opens a route to simpler fabrication of phononic devices in 2D materials.
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| 2. |
- Shiri, Daryoush, 1975, et al.
(författare)
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Heat-to-mechanical energy conversion in graphene: Manifestation of Umklapp enhancement with strain
- 2019
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 125:12
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Tidskriftsartikel (refereegranskat)abstract
- Conversion of heat-flux from a steady state temperature difference to mechanical vibration is demonstrated in graphene nanoribbons using direct non-equilibrium molecular dynamics. We observe that this effect is independent of the method of imposing the temperature gradient, heat flux, as well as imposed boundary conditions. We propose that simply dividing the nanoribbon in long and short sections using a partially immobilized area will lead to excitation of long-wavelength vibrations into the long section of the nanoribbon. This results in simpler architectures for heat-to-vibration converter devices based on graphene. Furthermore, we observe that applying tensile axial strain to nanoribbons facilitates vibrational instability by reducing the required threshold heat flux or the temperature gradient. Finally, we discuss the role played by Umklapp scattering for physical mechanisms behind these observations.
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| 3. |
- Islam, Shadli, et al.
(författare)
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Ab-initio Calculation of Nonlinear Optical Susceptibilities in Germanium Quantum Dots
- 2019
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Ingår i: 2018 IEEE 13TH NANOTECHNOLOGY MATERIALS AND DEVICES CONFERENCE (NMDC). - 2378-377X. - 9781538610169 ; , s. 113-116
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Konferensbidrag (refereegranskat)abstract
- Using Time Independent Density Functional Theory (TIDFT) implemented in SIESTA (R) we calculated the 2nd order and 3rd order nonlinear optical susceptibilities of small Germanium Quantum Dots (GeQD). We observe that the symmetry breaking due to surface termination enhances chi((2)) up to 299.1 pm/V which promises a strong Second Harmonic Generation (SHG) in GeQDs. Diagonal components for chi((2)) tensor are 52.5, 11.2, 299.1 pm/V, for xxx, yyy and zzz, respectively. The 3rd order susceptibility, chi((3)), is within the range of (0.2-0.4) x 10(-18) m(2)/V-2 which is close to the reported experimental values of bulk Germanium. This study suggests possibilities of enhancing SHG in GeQDs through symmetry breaking via strain and surface termination/reconstruction as well as suitability of this fast and less-computationally intensive Density Functional Theory (DFT)-based method in predicting nonlinear optical susceptibilities of nano structures.
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