Graphene Nanoribbon Morphology Engineering And Stretchable Devices Preparation By Nanowire Lithography

Graphene nanoribbons(GNR)as an atomic-thick layered crystal with ultra-high electron mobility and optical transparency,are considered to be ideal materials for transparent electrodes in flexible electronic devices.However,patterning narrow GNRs below 100nm wide usually requires inefficient micro/nano fabrication process,which is hard to implement for large area or flexible electronic and sensory applications.Here we develop a precise and scalable nanowire lithography(NWL)technology that enables a reliable batch-manufacturing of ultra-long GNR arrays with programmable geometry and narrow width between 50nm to 150nm.The ultra-long silicon nanowires(SiNWs)produced via an in-plane solid-liquid-solid guided growth was used as masks to pattern graphene sheet into ordered GNRs in stiff or flexible substrates by using oxygen/argon plasma etching.More importantly,the geometry of the GNRs can be pre-designed and engineered into elastic two-dimensional(2D)springs to achieve an outstanding stretchability above 30%,while carrying stable and repeatable electronic transport.We suggest that this convenient NWL technology has a great potential to establish a rather general and efficient strategy to batch-pattern or integrate various 2D materials as active channels and interconnections for the emerging flexible electronic applications.Specifically,the main research contents and innovations of this paper are summarized as follows:1?Using programmable SiNWs as a mask to prepare GNR array of a specific shape in large area.Based on IPSLS nanowire growth technology and NWL etching technology,it is proposed to use programmable planar self-assembled SiNWs array as an etching mask to prepare ultra-long GNR arrays with specific geometry in batches.This method keep the advantages of low-cost,large-area,nano-scale precision definition of traditional NWL etching technology,and achieve the precise shape definition and preparation of GNR on arbitrary rigid or flexible substrates by regulating the growth morphology of SiNWs.It provides an effective approach for the large-area topography design of graphene.2?The etching parameters was optimized to prepare narrow GNR for logic applications of GNR-FET.In order to endow the device excellent performance,a standard mechanical exfoliation method was employed to isolate few-layer graphene fakes and transferred them onto a highly doped Si wafer capped by a 285-nm-thick SiO2 layer.Thickness of the exfoliated graphene fakes was measured by means of optical contrast and Raman spectra.O2 plasma etching of graphene sheets with different thicknesses was carried out by reactive ion etching(RIE)equipment to etch 1-3 layers of graphene by the following parameters:gas flow rate 10 sccm,gas pressure 3 Pa,upper electrode power 30W,etching time 10s.the gap between SiNWs mask and graphene sheet,caused by the electrode height,was firstly filled by a layer of poly-methyl-methacrylate(PMMA),and then both the PMMA and graphene were etched together by increasing the etching time to 30 s.The GNR-FET is characterized by Raman and electrical properties.Interestingly,we found that the GNR width was obviously smaller than the SiNWs mask diameter under the etching time to 60 s because of an inscribed etching effect.This found help us to prepare sub-60nm width GNR-FET with a switching ratio of 270 at room temperature,which provides a feasible idea for the preparation of GNR logic switching devices.3?Programmable morphology engineering of SiWNs and GNR,including elastic design and process improvement for flexible devices preparation.Obviously elastic structure endue additional stretchability to rigid materials which are somewhat flexible but not stretchable.Since graphene is optically transparent which cannot be observed under an optical microscope(OM),SiNWs was first used for reliable preparation methods exploration.It was found that the flexible device prepared by"pitting"self-configured poly-dimethylsiloxane(PDMS)on the surface of SiNWs was easy to break while stretching,and SiNWs which in industrial PDMS film(which A:B=35:1,thickness of 0.15mm and have a smooth surface)has good tensile properties.Therefore,the industrial PDMS film was used as the substrate to prepare the 2D GNR spring,and tensile test results showed it maintain good electrical properties at 30%stretch,far exceeding the fracture limit of graphene(1-3%).The internal strain of the 2D GNR spring was analyzed by finite element method,A commercial software COMSOL was used for that.It was found that under a stretch of 35%,the maximum strain applied to 100 nm GNR was only 0.35%,while the maximum strain in 1?m GNR was much greater to be 3%at the same tensile degree.Therefore,achieving a high geometric factor of g=Rbend/DGNR>50,as demonstrated in this work,has been the key to fabricate highly stretchable GNR spring channels.