荷能重离子辐照引起石墨烯电学性质变化研究

Graphene is currently the thinnest materials in the world, which has many excellent properties, such as half integer quantum hall effect, anomalous quantum tunneling effect, ferromagnetism, superconductivity and giant magneto resistance effect, etc. The pretty low resistivity and high electron speed of graphene makes it the probable material for developing a new generation of electronic components or transistors, which is thinner and has better conductivity. The special single atomic layer structure of graphene also introduces instability factors for the application of graphene devices. The research results show that the energetic ion irradiation will introduced defects into graphene. Under the same irradiation condition, monolayer graphene deposited on SiO2 /Si substrate is easier to damage than thin layer graphite films. In practice, different irradiation environment introduce structure defects into graphene, which will produce a great deal of restrictions to the application of graphene devices. Much more seriously, the graphene devices even cannot run normally in those practical application environment. Thus the influence of these defects to the graphene electronic properties is an important research topic which need to be figure out clearly. In this work, swift heavy ions and highly charged ions will be used to irradiate graphene nanoribbons. The electrical properties of graphene under various irradiation conditions, such as different ion beams, ion energies, ion charges and fluences would be investigated. Through the comparative study, we could figure out the influence of different irradiation parameters to graphene electrical properties. The experimental data offers a necessary reference for the applications of graphene devices.

石墨烯是目前世上最薄的纳米材料，具有诸多优良性能。如半整数量子霍尔效应、奇异量子遂穿效应、铁磁性、超导性和巨磁阻效应等。石墨烯的电阻率极低，电子迁移的速度极快，因此被期待可用来发展出更薄、导电速度更快的新一代电子元件或晶体管。石墨烯特殊的单原子层结构也为石墨烯的应用引入了不稳定的因素。现有研究表明荷能重离子辐照将在石墨烯中引入缺陷，并且，在相同的辐照条件下，沉积在SiO2/Si衬底上的单层石墨烯比薄层石墨更容易产生辐照损伤。在实际应用中，不同的离子辐照环境可能在石墨烯中引入缺陷，这对石墨烯器件的应用会产生极大的限制，甚至导致石墨烯器件不能正常运行。因此，辐照引入的缺陷对石墨烯电学性质的影响是石墨烯应用必须解决的问题。本工作将采用快重离子及高电荷态离子辐照不同长宽比的石墨烯纳米带，对比不同离子种类、离子能量、电荷态以及不同辐照注量条件下石墨烯的电学性质改变，为石墨烯器件应用环境提供参考。

石墨烯是目前为止最薄也是最坚硬的纳米材料，其电阻率极低，电子迁移率极高，有望利用石墨烯发展出更薄，迁移速度更快的新一代电子元器件和晶体管。此外石墨烯在探测器，光电器件，高性能晶体管等方面有很大应用前景。然而在应用于辐照环境时，石墨烯很容易受到辐照环境的影响，产生缺陷，从而改变石墨烯基器件的电学性能，甚至会导致石墨烯器件不能正常运行，这对石墨烯器件的应用产生极大的限制。本项目采用化学和物理方法制备石墨烯，并基于石墨烯制备出石墨烯场效应晶体管(GFET)。采用荷能重离子对GFET进行辐照实验，研究辐照前后石墨烯电学性能的改变。实验结果表明，辐照后石墨烯的电阻、载流子迁移率和狄拉克点具有明显变化。快重离子对石墨烯电学性能有调制作用，即在低注量(~10^9 ions/cm^2 )条件下，快重离子辐照可能会提升GFET的性能。在较高注量（~10^11 ions/cm^2）条件下GFET性能明显退化。进一步采用360个不同长宽的石墨烯带进行实验，探索出GFET性能优化的最佳条件：注量范围(1×10^9 ions/cm^2-4×10^10 ions/cm^2)条件下，石墨烯带长宽比小于5 的GFET更容易获得优化的性能。推测性能优化主要原因可能是快重离子辐照引起的石墨烯局部退火。在最高注量5.4×10^11 ions/cm^2 条件下GFET仍然能运行，表明石墨烯场效应晶体管比MOS2晶体管更抗辐照。拉曼光谱和透射电镜测试分析表明，快重离子辐照在石墨烯和衬底中引入的缺陷是导致GFET性能退化的主要原因。本项目为GFET的性能优化提供重要的实验数据，为石墨烯在航天电子器件中的应用提供重要的参考。