Study On The Energy Band Modulation And Mechanism Of Triboelectric Microplasma On Graphene Monolayers

Graphene has many excellent properties,which has been used in many fields of life.However,the valence band of graphene is connected with the conduction band,which hinders its application in electronicsfield,so opening the band gap of graphene has become a top priority in graphene research direction.Depending on whether the structure of graphene is destroyed directly,the methods to open graphene can be divided into two categories.One is to directly destroy the structure of graphene and open the band gap,such as doping,absorbing atoms and introducing periodic defects.The other is to open the band gap without directly destroying the structure of graphene,such as applying electric field,external stress and substrate effect.These methods can either destroy the structure of graphene and affect the original properties of graphene,or the experimental conditions are harsh and not suitable for large-scale production and application.Therefore,new ways of opening graphene band gaps need to be found.The triboelectric nanogenerator（TENG）has the characteristics of high output voltage,which can easily ionize air molecules.The chemical adsorption of O₂^-ions produced by triboelectric microplasma on the surface of materials will change the structure and photoelectric properties of materials.At present,the triboelectric microplasma technology has been used to modulate the electron transport and photodetection characteristics of one-dimensional Zn O and two-dimensional Mo S2.Therefore,in this paper,we apply the triboelectric microplasma technology to the modulation of single-layer graphene,so as to expand the application of this technology in the field of two-dimensional materials.The chemical adsorption of O₂^-ions generated by triboelectric microplasma on the surface of single graphene will distort the structure of single graphene,which provides a new research method and technical means for opening the band gap of graphene.As the state of O₂^-ions on the surface of monolayer graphene is not stable,partial O₂^-ions desorption can be obtained by heating and applying high voltage,so as to realize reversible modulation of the energy band structure and electrical characteristics of monolayer graphene.In this paper,the graphene film was transferred to the fork finger electrode by wet transfer method,and the transferred graphene was characterized by Raman spectroscopy.The results showed that the monolayer graphene devices with relatively complete structure were prepared by this method.The triboelectric microplasma in the independent layer mode was studied.Different discharge types can be obtained by adjusting the distance d between the tip and the plate.When d ≤ 0.38 mm,the arc discharge with larger discharge current is generated.when d ≥ 0.50 mm,the corona discharge with smaller discharge current is generated.Monolayer graphene is regulated by triboelectric microplasma in pure oxygen atmosphere.When the distance between the tip and monolayer graphene was 0.50 mm,the current of monolayer graphene decreased gradually with the increase of the regulation times of the triboelectric microplasma,and the switching ratio was up to 107.When effectively regulates monolayer graphene by triboelectric microplasma,the current received by the monolayer graphene is about 5.5 μA,which is consistent with the current produced by the short distance negative corona discharge.The surface structure of monolayer graphene was studied by Raman spectroscopy.With the increase of triboelectric microplasma regulation times,the defect peak（D peak）in the Raman characteristic peak of monolayer graphene increased gradually,and the degree of structure disorder of monolayer graphene increases.The type of contact between monolayer graphene and metal electrode changed to Schottky contact after triboelectric microplasma regulation.The variable temperature current curve of monolayer graphene was tested after triboelectric microplasma regulation.The regulated monolayer graphene opened the band gap and showed semiconductor properties.The monolayer graphene was subjected to rise temperature or high voltage recovery after triboelectric microplasma regulation,and the current of monolayer graphene increased after recovery.The structure of monolayer graphene before and after restoration was studied by Raman spectroscopy.The defect peak（D peak）in the characteristic peak of monolayer graphene Raman decreases and the structure of monolayer graphene becomes orderly after temperature rise or voltage increase.The contact type between monolayer graphene and metal electrode was studied before and after restoration.The type of contact between monolayer graphene and metal electrode is converted back to ohmic contact after temperature rise or high voltage resumption.The regulation device is optimized and the electrons generated by triboelectric microplasma are filtered out by copper network,avoiding the influence of electrons in the regulate process.Only O₂^-ions can still play a regulatory role when acting on the surface of monolayer graphene,and the structure and performance of monolayer graphene cannot be completely recovered after temperature rise.X-ray photoelectron spectroscopy（XPS）was used to study the chemical composition and elemental valence on the surface of monolayer graphene before and after regulation and temperature recovery.After the regulation of triboelectric microplasma,the oxygen content of monolayer graphene surface increased from 9.16 % before the regulation to 24.54 % after the regulation.The C content of sp2 hybrid and sp3 hybrid changed from 67.65 % and 22.19 % before the regulation to 42.64 % and 32.95 % after the regulation.After recovery of temperature rise,the oxygen content of monolayer graphene decreased from 24.54% after regulation to 16.93% after heating recovery.The C content of sp2 hybrid and sp3 hybrid changed from 42.64% and 32.95% after regulation to 61.78% and 24.94% after heating recovery.The mechanism of triboelectric microplasma regulation was studied through theoretical calculation.The O₂^-ions generated by triboelectric microplasma changed the original adsorption path,and then realized the chemical adsorption on the surface of monolayer graphene.At the same time,theoretical calculations show that monolayer graphene opens the 0.23eV band gap under the regulation of triboelectric microplasma.