Gold Nanoparticle Array-Assisted Fabrication Of Graphene Nanostructure

Graphene,a two-dimensional planar material that is one atom thick with a honeycomb lattice of carbon atoms,has brought a hot research field due to its unique properties:high charge carrier mobility,high mechanical strength,high flexibility,high optical transmittance and a relatively low manufacturing cost.It has many potential applications in electronics,which include biomedical applications,electrodes for transparent electronics,optical modulator device,electrocatalysis,sensors,energy harvesters and optical waveguides device.But several factors impose limitations in electronic application: 1.The absence of a bandgap in graphene.2.Graphene films are generally wrinkled or rippled,which could change its band-gap,wettability,transmittance,chemical potential,energy storage,and conductivity.So far using nanostructures to modify graphene's properties is the most common method.Herein,we have demonstrated that gold nanoparticle array-assisted modification of graphenes' properties,including photoelectric properties and wettability.In the first part of our work,we developed a new method to regulate gold NPs' morphology.Through horizontal lifting,gold NP monolayers were transferred from water/hexane interfaces to glass slides.Then a layer of polymer was spin-coated on the gold NP monolayer,after which thermal treatment was carried out.Polymethylmethacrylate(PMMA)and polyphenylene sulfone resins(PPSU)were chosen to control gold NPs' morphology in an auxiliary manner,these two kinds polymers have non chemical interaction with gold.Thus we can explore the influence of glass transition temperature(Tg)on gold NPs' morphology without the interferences from any other factors.In this work,when the temperature didn't reach the Tg of these two polymers(below 100 ?),the rigid polymer chain inhibited the fusion of gold NPs compared with reference sample.When the temperature arranged between 100? and 225 ?(beyond PMMA' Tg),the movement of PMMA' polymer chains promote the fusion of gold NPs.But the Tg of PPSU was higher than 225 ?,so PPSU still performed inhibition affect.Therefore,the temperature of thermal treat and Tg of polymer play critical roles in the process of gold NPs merging.Moreover,combining with colloidal lithography technique,three kinds of gold NP arrays were also fabricated.In the second part of our work,we transferred this gold nanoparticle monolayer to single-layer graphene surface,followed by O2 plasma treatment to obtain GQDs arrays.Firstly,gold nanoparticle monolayers with diameter of ~12 nm were used as etching mask to fabricate GQDs ~9 nm.The complete removal of the gold NPs is conformed by the disappearance of the Au(4f)peaks in X-ray photoelectron spectroscopy(XPS),which is one of the advantages compared with polymer mask.Accompanied with the etching process,the diameters of the GQDs decreased slightly and the O/C ratio is increasing,and the corresponding performance in the femtosecond broadband transient absorption(TA)spectroscopy is that the excited excitedstate absorption(ESA)signals become stronger and blue-shift obviously.Moreover,the blue-shift of the ESA signals could demonstrate the gradual opening of the bandgap.Then thermal reduction was performed on GQDs(~9 nm,etched for 15 s),it can be observed that the ESA signals become much weaker without a shift of signal positions.To sum up,the tunability of the bandgap could be achieved by changing the diameter of GQDs,and the signal intensity depends on the component ratio of oxygen in GQDs.In addition,GQDs with larger sizes(~19 nm)are fabricated for comparison.Althoug the variation trend of signals intensity is similar to GQDs(~9 nm),The ESA signals have almost no peak shift,as GQDs >10 nm in diameter can't exhibit quantum confinement effects.In summary,we report a feasible etching method to tune bandgap of graphene quantum dots(GQDs),which packed closely with large area.In the third part of our work,the etching template is fabricated from the self-assembled gold NP monolayer motioned above,and we demonstrate that the controllable formation of small wrinkles on single-layer graphene(SLG)could be realized by silicon nanopillar(SNP)arrays.High density SNP arrays with small diameter were fabricated by gold nanoparticles(NPs)as etching mask and the size parameters of SNP arrays could be controlled by adjusting etching duration.After transferring SLG onto SNP with heights of 69 nm(SNP69),small wrinkles are distributed all over this sample at high density,which lead the RMS roughness of SNP69/SLG increases obsviously.Therefore,the hydrophobicity of this sample increases heavily,which could prolong devices' lifetime.In addition,thermal treatment was carried out on these samples to make SLG wrap around the SNP arrays.SLG wraps around SNP23 after annealing.Simultaneously,many wrinkles emerge with a much higher density,and the hydrophobicity of this sample increase heavily.However,apart from the wrinkles increasing,SLG on SNP69 is tore into pieces after being heated because of the biaxial strain from the suspended graphene,so this samples' hydrophobicity reduces on the contrary.Considering that high conductivity is the fundamental requirement for graphene-related devices,electrical conductivity is measured for SNP/SLG,the test results demonstrate that these samples maintain excellent conductivity similar to the flat graphene.Moreover,transmittance of these SNP/SLG samples is tested,and all these hybrid structures maintain a transmittance >92%,which could be applied in industrial application.