Studies On Optoelectronic Properties Of Low-dimensional All-carbon Hybrid Materials

Low-dimensional carbon nanomaterials such as OD fullerenes,1D carbon nanotubes and 2D graphene,have attracted intense attention due to its excellent electrical and photoelectric properties.Especially after the discovery of graphene in 2004,the research for carbon nanomaterials has been revived.For the practical applications,the individual material is often limited to its "cask effect".For example,graphene has ultra-high mobility,but its zero band gap limits its application in logic circuits.Recently,the low-dimensional van der Waals heterojunction can effectively combine the advantages of the two materials to study the interfacial physical properties and build the devices with novel functions.In this paper,we constructed the low-dimensional all-carbon hybrid film or heterostructure based on the low-dimensional carbon materials,and systematically studied the ground-and excited-state interfacial carrier dynamics.We demonstrated the high-performance photodetectors based on all-carbon materials,and analyzed its physical mechanism.There are two main aspects in this thesis.The first part mainly focuses on the photodetectors based on 0D C60 FET and 0D-2D C60/graphene all-carbon films.The absorption spectrum of graphene,extending from ultraviolet to the far-infrared range,allows the fabrication of ultra-broadband photodetectors.In particular,the pronounced photon absorption near the saddle-point singularity makes graphene well suited for ultraviolet(UV)detector.However,for graphene photodetectors without a gain mechanism,too small an external quantum efficiency(EQE)and responsivity hampers its practical exploitation.Fullerene(C60),a zero-dimensional(OD)carbon allotrope,presents numerous exciting chemical and physical properties.The strong and tunable absorption of UV light by C60 molecules opens up the potential for forming synergetic composite with graphene for UV photodetectors.Here,using graphene as a template for C60 assembly,we synthesized a large-scale all-carbon hybrid film with inherently strong and tunable UV aborption.Efficient exciton dissociation at the heterointerface and enhanced optical absorption enables extremely high photoconductive gain,resulting in a UV photoresponsivity exceeding I07 A/W.In addition,the full carbon film can be applied to flexible photodetectors,showing excellent flexibility and robustness,demonstrating the great potential of all-carbon film in the field of flexible optoelectronics.Finally,we explore the photoelectric properties of C60 using graphene as the electrodes,and achived the high photoresponsivity of>5000A/W with the response bandwidth of 6 kHz,indicating that C60 has good potential in the ultraviolet range.The second part is about the synaptic bionics based on 1D carbon nanotubes and 2D graphene all-carbon materials.Inspired by biological neural systems,neuromorphic chips are rapidly developed as a viable technological avenue in artificial intelligence.Currently,most state-of-the-art synaptic devices with pure electronic components,based on either transistor or memristor,which are faced with a number of limitations.First,in conventional artificial synapses,neuromorphic computing is isolated from the data acquisition sensors(ocular,olfactory or auditory stimuli).Furthermore,real neuronal system always involves multiple steps of plasticity mechanism that convey considerable flexibility in the modulation of the connectivity strength.However,the coupling coefficient of conventional artificial synapses is typically fixed,which is inadequate to emulate the complex activities of real organisms,so the in-situ adjustment of the artificial bionic device is also a challenge.We constructed all-carbon films based on 2D graphene and 1D carbon nanotube and investigated the interfacial carrier dynamics.The synaptic plasticity including short-term plasticity(STP)and long-term plasticity(LTP)were achieved by photo-and electric-stimulation.The STP can be flexibly modulated by the gate voltage,which results in a dynamic synapse with in-situ adjustable weight,and the effects of action time,frequency and number of pulses were also discussed.Furthermore,by exciting the device with multiple light beams,we demonstrate the capability of advanced optical spike processing,i.e.optical logic operation,pointing to the potential of more sophisticated computing.In summary,the photoelectric performance and carrier kinetics of low-dimensional carbon nanomaterials and their heterojunction film systems,have been experimental investigated.The results obtained in my dissertation provide a important reference for designing the high-performance optoelectronic devices.