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Theoretical Study On Electrical Transport Characteristics Of Graphyne-based Novel Functional Molecular Devices

Posted on:2021-05-26Degree:MasterType:Thesis
Country:ChinaCandidate:H AnFull Text:PDF
GTID:2381330611957078Subject:Microelectronics and Solid State Electronics
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With the rapid development of technology,the development trend of electronic components is smaller size,higher integration,lower energy consumption,more stable operation and higher intelligence.However,the reduction of size leads to obvious quantum effects and heat dissipation problem.Molecular electronics devices have become a new direction in the development of electronic devices because they avoid the limitation of quantum effects.In this paper,a new type of graphyne-based molecule device is designed and constructed,in which graphyne nanoribbons are selected as electrodes,and one-dimensional carbon atom chains or graphyne chains are used as the central scattering region.Basing on density functional tight binding method with nonequilibrium Green’s Function formalism,the electrical transport characteristics of the constructed devices were investigated,which provided a useful theoretical guidance for the application of graphyne in molecular devices.In this paper,the main research work and the conclusions obtained are described as follows:(1)The electrical transport characteristics of carbon chains with graphyne electrodes under different connection modes were discussed.The results show that the length and number of carbon atom chains can well modulate the electronic transmission capability of the device.As the length of the chain increases,the conductance of the device exhibits odd-even effect,that is,the current of the odd-numbered carbon-chain device is greater than that of the even-numbered carbon-chain device under the same bias.Graphyne-based molecule devices connected by a single carbon atom chain exhibit good ohmic contact characteristics,negative differential resistance(NDR)effects,and bidirectional tunnel diodes effects.Graphyne-based molecule devices connected by two carbon atom chains possess remarkable steady current characteristics.In addition,by calculating the total density of states(DOS),the projected density of states(PDOS),the molecular projected self-consistent Hamiltonian(MPSH),and electrostatic potential distribution,the micro-mechanism of the device with rich physical effects is given fromthe perspective of electronic structure.(2)The electrical transport characteristics of graphyne chains with graphyne electrodes under different connection modes were investigated,and the effect of nitrogen substitution on the electrical transport properties of graphyne-chains molecular devices was discussed.The results show that the symmetry,length,number,and nitrogen atom substitution position of the graphyne chain play a key role in the electrical transport characteristics of the device.Without doping,the asymmetric graphyne-chain molecular devices have better electrical transport characteristics than the symmetric graphyne chains,and the shorter the graphyne chain,the better the conductivity of the device.The NDR phenomenon is modulated by the configuration of the graphyne-chain molecule,and the asymmetric single short garphyne-chain molecule has a more obvious NDR effect.After doping nitrogen atom,the replacement of carbon atoms on the six-membered ring by the nitrogen atom facilitates the electron transport between the two electrodes,and the longer the chain,the better the electron transport.The substitution of nitrogen atoms for carbon atoms at the electrode connection inhibits electron transport,and the shorter the chain,the greater the current.Remarkably,rotating the graphyne chain causes a switching effect.After the graphyne chain is rotated 90° in the direction perpendicular to the electron transport,the device assumes an "off" state,which indicates the potential application of molecular switches.In addition,the constructed molecular devices composed of single graphyne chain with graphyne electrodes exhibited good ohmic contact characteristics and bidirectional negative differential resistance effects,and the molecular devices composed of double graphyne chain with graphyne electrodes possesses significant steady current characteristics.The research results can provide a good reference for the design of next generation molecular devices.
Keywords/Search Tags:molecular device, graphyne nanoribbon, carbon atom chains, graphyne chains, electron transport properties
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