Functional Devices Based On Ultrathin Two-dimensional Materials:Design,Construction And Properties Research

As is well-known,when bulk materials are shrunk to nanoscale,its properties unique change(such as electrical/mechanical/optical and thermal magnetism)would occur,thus the application of low-dimensional materials has been a hot topic in the research of materials science.Since the discovery of graphene proved that two-dimensional materials can stably exist,the two-dimensional materials get rapid development especially in the area of electron transport;At the same time,with the deepening of the research,new chemosynthetic thin-layer materials(such as organic semiconductor film,metal organic framework,etc)are also gradually applied to the field of electronic devices.This opens up a new path for the development of functional devices.Therefore,the purpose of this paper is to design and build functional devices based on the excellent properties of two-dimensional materials,and systematic exploration of its potential application prospects.The main research contents are as follows:1.Nondestructive transfer and device fabrication of single crystal graphene grown by chemical vapor depositionSingle crystal graphene grown on copper foil by chemical vapor deposition(CVD)was transferred to boron nitride substrate by dry transfer method to form heterogeneous structures using a two-dimensional transfer platform device.We explored a series of influence factors such as transfer media,transfer temperature and transfer time to achieve non-destructive transfer of single crystal graphene.Raman mapping characterization can clearly prove that the whole single crystal graphene is transferred with high-quality and non-destructive.Then a series of experiments including electron beam exposure,ion beam etching and thermal evaporation were carried out to fabricate the electronic device.The carrier mobility was measured at low temperature(2K)and its value can reach 250000 cm2 V-1 s-1,which can be compared with mechanical exfoliation of intrinsic graphene.Compared to traditional methods,it further explains that the advantage of dry transfer can realize the atomically clean surface,which is helpful for research on device properties.Based on the above research,we successfully constructed heterojunction devices and obtained high electrical performance,which laid a solid foundation for the further development of functional devices.2.Study on the controllable preparation and photoelectrical properties of twodimensional(2D)organic thin films with light response characteristicsIn this paper,a novel two-dimensional thin film material was prepared using chemical synthesis,and we constructed field-effect transistors(FET)to study its photoelectric properties in depth.The specific methods are as follows:the two-dimensional organic film was formed with organic molecular monomers triphenylene-2,3,6,7,10,11-hexaamine(HATP)via oxidative coupling polymerization in Langmuir Blodget(LB)device.A series of characterizations show that the material is a kind of large area two-dimensional material with regular porous structure.To investigate the charge transport property of 2D HATP polymeric films,we constructed FET to measure its electronic transport behavior.With the gate voltage decreasing at a given drain voltage,the drain current gradually increased,which confirms that the device is a typical p-type transistor,indicating that 2D HATP film is a semiconductor with holes as the majority carrier,and the mobility is calculated to be 3.2 cm2 V-1 s-1.Besides,under illumination with a 980 nm laser,photocurrent was generated,and the the responsivity was calculated to be up to 160 mA cm-2.With the increase of power density,the photocurrent gradually increases to saturation,and the corresponding functional relationship was obtained.This demonstrates that the photocurrent comes from pumping electron to traps of the surface and leaving hole carriers in the valence band for conduction.Under high power illumination,saturation of the trap states and increased recombination rate of photoexcited carriers limit the photocurrent.In this part of work,the functional devices with photoelectric response are constructed using the new two-dimensional materials synthesized by the chemical method,which provides a new idea for the construction of various functional devices in the future.3.Seawater desalination based on reduced graphene oxide(RGO)membrane corrosion resistant deviceOn the basis of the work in the first two parts,we further explore the application of anti-corrosion devices based on functionally-modified carbon materials in the field of seawater desalination.Graphene oxide(GO)has the abilities of chemical stability,strong resistance to corrosion and wide band absorption.These natural characteristics make it has very broad application prospects in water desalination.In this section,we prepared high-quality graphene oxide and synthesized reduced graphene oxide hydrogel by hydrothermal reduction.Then we freezed RGO hydrogel and modified to form reduced graphene oxide-Polypyrrole(RGO-PPy)aerogel.By means of local heating,the steam can be condensed through the internal pore channel of the material and the desalination effect can be achieved.Under the irradiation of sunlight,the surface of RGO-PPy aerogel,similar to the black body,has the highest absorbability of light under the same condition,thus,it can reach higher temperature per unit time.Therefore,it exhibited higher evaporation efficiency and the evaporation rate in the same sunlight,and the highest evaporation efficiency can reach 86.4%.At the same time,its desalination rates are as high as 99.3%and circulation dozens of desalting rate has no attenuation.In the case of applied electric field,impressed voltage causes the material to produce joule heat which locally heats seawater,the results indicate that the evaporation rate and efficiency enhanced with the increase of voltage.