Fabrication and Physical Mechanics Study on Devices of Graphene-like Low-dimensional Materials

Author:Fei Zuo Zuo

Supervisor:guo wan lin


Degree Year:2019





With layered atomic strucutres and unique physico-mechanical properties,two-dimensional materials represented by graphene have triggered intense research effort,and become the fronties of fundamental sicientific research.Focused on fabrication and property study of graphene-based novel devices,we start from controllable synthesis of graphene by chemical vapor deposition,and then systematically investigate graphene-based thermoacoustic speaker,water-enrgy-harvester and ionic current rectifictifier,with both experimental and theoretical methods.Further study on electrical transport property of TMDCs heterostrucutres will also be included.Our main findings are as follows:(1)Graphene domains:Controllable synthesis and effect on copper oxidiation.Graphene growth by chemical vapor depositon is systematically studied.The nucleation densities and shapes of graphene domains are investigated to rely on the gas source ratio and local growth environmens.By controlling these parameters,graphene domains with high crystalline quality,large size and controlled shapes are obtained.The effect of graphene on copper oxidization process is also studied.Under the cover of graphene domains,copper is protected by graphene at high temperature for short time.However,as exposed to atmosphere enviroment for several months,the copper underneath graphene domains suffer from severe corrosions.These results provide important guidelines for graphene as a corrosion-protective layer.(2)Three-dimensional graphene thermoacoustic speaker with low driving voltage.Here we for the first time propose to employ three-dimensional graphene with interconnected graphene networks as a thermoacoustic speaker.The three-dimensional graphene is obtained by growing graphene on nickle foam template,followd by PMMA transfer and freeze drying.Acoustic performance study shows close relations with input electrical power,measuring distance,and sound frequency.Compared to graphene with plane structures,three-dimensional graphene exhibits less heat leakage to substrates and better acoustic performances.Moreover,the interconnected graphene networks facilate three-dimensional graphene with lower sheet resistances,which makes the driving voltage lower.It can generate sound pressure level of 60.7 dB at 1.5 V input voltage, showing potential application in portable sound sources.(3)Energy Harvesting from Dynamic Electrical Double Layer at Graphene-Solution Interface.Developing new-principle-based technology is very critical to harvest huge energy which water contains.Here,in a graphene-solution-graphene system,electricity is generated by mechanically modulating electrical double layers at graphene-solution interface.We employ molecular dynamics simulations together with a capacitance-circuit model to reveal the underlying mechanism.Our results suggest that the generated voltage is due to ions migration at graphene-solution interface,which induces potential difference from bulk solutions.Comprehensive experiments are further conducted to study possible influencing factors on electricity generation,such as graphene separation distance,moving speed,ion concentration and ion species.An open voltage of 1 V is finally obtained,showing graphene a great possibility for water energy harvesting.(4)Heterogeneous graphene oxide membrane for ionic current rectification.In analogous to electrons in solid materials,ions serve as charge carriers in biologic membranes for information transmission and processing.Here we demonstrate a heterogeneously-charged graphene oxide(GO) membrane with high ability of ionic current rectirication.The membrane is made of a negatively-charged GO layer and a positively-charged PEI-grafted-GO layer.Experimental results show that rectification factor of the membrane is related to its surface charge densities and the electrolyte concentration.Under certain conditions,a rectification factor of 108 is achieved.The underlying mechanism for ion current rectification is futher studied by molecular dynamics simulations,which is due to ions accumulation and depletion in junction region of the heterogeneous membrane.Our work should provide a potential paradigm for GO membranes in ion transport control and the use as ionic rectifiers.(5)Electrical transport property of TiSe2/NbSe2 heterostructure.We are motivated by the question of how interplay of charge density wave(CDW)and superconductivity can be studied by the proximity effect.By fabricating TiSe2/NbSe2 heterostucture devices,we investigate the electrical transport property in detail.After NbSe2 becomes superconducting,the resistance of junction increases with decreasing temperature.This result indicates that the change of superconductivity order in NbSe2 has an influence on electrical transport across junction.From differentcial conductance measurements,we infer that superconductivity order is introduced in the junction region of TiSe2,and embedded in its CDW state.