Fabrication And Transport Properties Of Ion Transport Devices Based On Graphene

Graphene,a single layer of carbon atoms arranged in hexagonal honeycomb,has attracted much attention in the biomolecule detection,ion selection and seawater desalination applications due to its ultrathin thickness,superhigh mechanical properties and excellent thermal transport properties.Recently,graphene-based ion transport devices are constantly studied and reported.However,when the feature size of graphene-based ion transport devices reaches the sub-nanoscale,classical fluid theroies may not work.We focus on the fabrication and manipulation of graphene-based ion transport devices in this work.Combining micro Raman spectroscopy and ultra-sensitive current detection technology,the basic properties of graphene,the fabrication of graphene nanopores and graphene channels and their ion transport properties have been studied comprehensively.The main studies are as follows:1.A suspended flexible graphene device was prepared by combining electron beam lithography and transfer technology.Based on Raman spectroscopy,the thermal conductivity of single-layer and double-layer graphene under different strains was measured.Taking advantage of atomic force microscope(AFM)and Kelvin probe force microscope(KPM),the elastic modulus and surface potential of graphene in sodium chloride solution with different pH values were studied.2.A simple fabrication technology of graphene-based ion transport devices with a high yield was developed.Based on the plasma bombardment technology,graphene nanopores with a diameter of less than 1nm were fabricated.The volt-current characteristics of graphene nanopores in different electrolyte solutions were measured.Based on the first principle calculation,the ion transport characteristics of graphene under different processes were analyzed,and the numerical results showed the energy barrier of oxygen-modified graphene for ion transport was much lower than that of graphene only with vacancies.Based on the experimental measurement and numerical calculation results,an ion transport model was established,and the rheological behavior of different electrolyte solutions in nanopores was studied,which provided a theoretical model for the active control of proton,sodium and chloride transport.3.Using a combination of different plasma techniques,graphene nanopores with adjustable sizes and surface charge densities were fabricated,and the rheological behavior of different electrolyte solutions in the nanopores was studied.The manipulation on the ion transport in the nanopores were also investigated.It was demonstrated that graphene nanopores could not only select different inter-cations,but also could sieve cations/anions.4.A novel fabrication method of nanochannels was proposed,which was different from the traditional RIE etching on silicon substrates.For this new fabrication method,both the high cleanliness and low roughness of the nanochannel surface were achieved.At the same time,the transport characteristics of hydrated ions in graphene nanochannels and Si₃N₄ nanochannels were also studied.Under the applied electric field and with the same feature size,it was found that the ionic current in the graphene nanochannels was larger than that in the Si₃N₄nanochannels.It was theoretically supposed that the ion mobility affected by the interface properties and structured water was the main cause.