金基底引导制备二维黑磷及其生长机理

Growth of two-dimensional material black phosphorus guided by gold substrates and its growth mechanism

二维材料是近年来材料科学和凝聚态物理学的前沿研究方向.在众多的二维材料中,黑磷(black phosphorus,BP)因其独特的带隙、优异的光学和电学性质、各向异性等特性而受到研究人员的广泛关注.如何可控制备二维薄层BP是该领域的难题之一.本工作系统研究了基底对BP生长的影响,结果表明金基底对BP的生长具有重要促进作用.在此基础上,使用镀有金薄膜的硅基底为生长衬底,通过设计限域生长空间和调控温度梯度,在全新的生长体系中实现了BP纳米片的直接生长,并探讨了其生长机理.本研究所报道的结果为实现二维薄层BP的制备提供了一条新思路.

Two-dimensional(2D)materials are the frontier research direction of material sciences and condensed matter physics in recent years.Among different kinds of 2D materials,black phosphorus(BP)has received extensive attention due to its unique band gap and excellent optical and electrical anisotropy properties.Compared with graphene and transition metal dichalchogenides(TMDCs),BP stands out for its unique properties with widely tunable direct bandgaps ranging from 0.3-1.7 eV,covering the wavelength from~600 to 4000 nm,which fill in the gap between graphene(0 eV)and TMDCs(~1.0-2.5 eV)and is considered the ideal material for optoelectronic applications,such as light detection and light modulation.For example,photodetectors are basic devices for optoelectronics,as they transform the information stored in light into electric signals.BP based photodetectors not only stand out for their wide detection range reaching far infrared(IR)region,but also for their high responsivity and high gain,demonstrating their excellent performance for mid-IR detection.In order to achieve above-mentioned applications,few or even monolayer BP flakes or continuous BP films are required.However,how to control the preparation of thin layer of BP is one of the biggest challenges in this field.In this paper,we carried out a systematic study on the growth of BP on different substrates and found that Au can guide and promote the growth of BP,thereby controlling its growth.Based on the above findings,the growth of BP nanosheets on the Au-Si substrate is achieved by using a Si substrate deposited with Au thin film on top,and by designing a strategy with gradient temperature and in confined space.We observed that the BP nanosheets grown by this system exhibited different shapes such as ribbons and flakes,and their thicknesses can be reduced to be about 51 nm with a lateral size of around 10μm.In addition,by systematically tuning the growth parameters in the system,we found that the growth temperatures and the amount of red phosphorous loading are the key parameters for the growth of BP.With certain temperatures and precursor loadings,we achieve the growth of BP nanosheets,while by-products would be obtained on the substrate with other parameters.In our previous work,we found that the temperature gradients play a crucial role in the yield,purity,and crystal quality of bulk BP growth.Therefore,further optimization of temperature distribution is of great importance for the growth of BP nanosheets.In addition,we observed in this paper that Au would guide the nucleation and growth of BP.Therefore,it is important to regulate Au-P compounds during growth of BP,as on the one hand,it can control the by-products during the reaction and on the other hand,it can also improve the controllability of BP nucleation.Based on this,we believe that optimization of the temperature distribution and the growth regulation of Au-P compounds are important research directions,as to precisely control and reduce the thickness of BP nanosheets to grow few layer BP.The growth system proposed in this paper improves the chemical vapor transport(CVT)growth of traditional bulk BP from three aspects:Substrate design,confined space design,and temperature gradient control,which have paved the way for the future controllability growth of BP nanosheets and have deepened the understanding of BP growth mechanism.