First-Principle Investigation Of Electronic Structure And Transport Properties Of Carbyne Chains And Cyclo [18] Carbon

With the rapid development of science and technology,the silicon-based semiconductor devices and integrated circuits can no longer meet the demands due to the higher requirement on the reliability and integration for electronic devices.In order to improve the integration and operating speed,functional electronic devices are gradually developing towards miniaturization.Therefore,the field of molecular electronics has become an inevitable trend in the development of device miniaturization.In recent years,carbon allotropes,including graphene,carbon nanotubes and fullerenes,have shown the huge application potential in many fields such as new electronic materials,energy materials,and composite materials owning to their excellent mechanical,thermal,and electrical transport properties.Simultaneously,carbon allotropes have attracted intensive attention in the field of molecular electronics.The successful synthesis of carbyne chain and its derivative cyclo[18]carbon(C₁₈)provide new opportunities for the design of carbon-based nanodevices.However,there are several key problems need to be resolved for the research on the carbyne chain and C₁₈.For example,the electronic and thermal properties of carbyne chain can be effectively controlled under axial strain,but the underlying mechanisms on the variation of its chemical bond properties and heat capacity are unclear.Additionally,it is still in infancy for the investigation of C₁₈-based molecular device under different external magnetic fields or other ambient conditions.In order to explore the strain effect on the chemical bond properties and related properties,we study the band structure,heat capacity,and electrical transport properties of carbyne chain and C₁₈-based electronic circuit under the condition of external perturbations based on the first-principles calculations within the framework of density functional theory.The achievements are shown as follows:1.We address the regulation effects of thermal and mechanical properties in the carbyne chain under different strains,and explore the evolution of bond length with tensile.It was found that the electronic structure and heat capacity of carbyne chain show obvious variation under the approach of strain owing to changes of their chemical bond properties and spatial symmetry.Particularly,carbyne chain changes from an alternate bond length structure(semiconductor)to a repetitive bond structure(metal)attributed to the transfer of charge density near single/triple bond at-16%axial strain.Furthermore,the heat capacity of carbyne chain can also be enhanced significantly due to the variation of the vibration frequency under tensile strain.2.We explore the spin transport properties of a new kind of multifunctional integrated molecular device made of a single C₁₈ molecular bridged by ferromagnetic ZGNR electrodes,and reveal the modulation mechanism of the coupling strength between C₁₈ and zigzag graphene electrodes.Meanwhile,we found that relative magnetic orientations of two electrodes can dramatically affect transport state of spin electrons,which results in almost 100%spin-polarized current in the device.Also,the device can display negative differential resistance effect,spin filtering effect and rectifier effect simultaneously.3.We investigate the switching effect of the molecular device,formed by the C₁₈between two metal carbon chains,bridged by nonmagnetic ZGNR electrodes,and establish the connection between the transport properties of device and twist angle.Interestingly,the strong switching effect of chain-ring combination molecular device can be achieved on account of the quantum tunneling effect between the molecular energy level and the Fermi level of the electrodes.Furthermore,the switch ratio can be up to 2737,and the value is much larger than single benzene molecular device.