Wu Menghao, Professor of Huazhong University of science and technology research group: solution method, light and functional, endowing two-dimensional carbon nitride ferroelectric / multiferroic, Valley electronics and photovoltaic properties

Since the advent of graphene, a variety of two-dimensional materials have been proposed and studied Electronic devices based on two-dimensional materials are regarded as the hope to continue "Moore's law" Among them, graphene like layered carbonitrides (C3N4, C2n, CN) are also widely concerned, and their research focuses on catalysis and energy conversion This kind of material has wide band gap, which leads to its poor absorption of visible light band, thus limiting its photocatalytic and light energy conversion efficiency; in addition, the wide band gap also hinders its application in Nano Electronics Recently, Professor Wu Menghao's research group of Huazhong University of science and technology proposed that metal chloride solution can be used to infiltrate two-dimensional carbonitride to functionalize it through first principle calculation Compared with the usual strategies of high temperature ion source diffusion or ion implantation by accelerator, the new method has higher efficiency and lower cost, and can adjust the density of material functionalization by changing the concentration of solution In addition, a variety of functional groups that can be selected also bring new properties of ferroelectric / multiferroic, Valley electronics and photovoltaic to the original 2D carbonitride Relevant research results were published in adv funct Mater (DOI: 10.1002/adfm.201905752) Prof Wu Menghao's research group is mainly concerned with the ferroelectric, ferroelastic and ferromagnetic properties of low dimensional materials The research methods include first principles calculation, molecular dynamics simulation and Monte Carlo simulation The research group has published many articles in famous international journals such as J am Chem SOC., nano lett., ACS Nano, adv SCI., etc., and many predictions about two-dimensional ferroelectricity have been confirmed by experiments At present, there are 5 doctors and 1 master About Professor Wu Menghao, male, born in 1987, graduated from the science strengthening Department of Nanjing University in 2007 to obtain a bachelor's degree, graduated from the University of Nebraska Lincoln to obtain a doctor's degree in 2011, engaged in post doctoral research at the Federal University of Virginia from 2012 to 2013, and engaged in post doctoral research at the Massachusetts Institute of technology from 2013 to 2014 In 2014, he became a professor in the school of physics, Huazhong University of science and technology Cutting edge scientific research achievements: the solution method is light and functional, which endows two-dimensional carbon nitrides with ferroelectric / multiferroic, valley electronic and photovoltaic properties The wide energy gap of two-dimensional carbon nitrides has seriously hindered its application in photocatalysis, energy conversion and nano electronic devices In the past, many studies have tried to improve the catalytic performance and electronic structure by docking a metal atom in each pore using the periodic distribution of nanopores (radius 2 ~ 3 Å) However, metals generally have a large binding energy, so it is a great challenge to make the metal atoms uniformly distributed and prevent their agglomeration on the surface In addition, the introduction of metal atoms will make the bonding between layers, making it difficult to separate the single layer Based on the first principle calculation, it is found that the metal chloride solution can be used to infiltrate the two-dimensional carbonitride to realize the efficient and controllable functionalization, to adjust the band gap to improve its optical performance, and to introduce the ferroelectric / multiferroic, valley electronic and other functional properties Fig 1 original C 3N 4, C 2n and CN and their geometry modified by metal chloride (MCL x, x = 1,2,3) (source: adv funct Mater.) table 1 energy difference Δ e = e (MCL x (C2n) 6) - E (C2n) 6) - E (bulk MCL x), negative value means MCL x is more likely to combine with C2n; e g means energy gap; m means magnetic moment; Δ e m = e (FM) - E (AFM), which means energy difference between ferromagnetic and antiferromagnetic configuration; MAE A positive value indicates that the magnetizable axis is perpendicular to out of plane; P indicates ferroelectric polarization (source: adv funct Mater.) based on the first principle, the author calculated the energy difference between the functionalized 2D carbonitride and the original carbonitride and bulk metal chloride crystal (i.e energy difference Δ E in Table 1) It was found that the 2D carbonitride can achieve spontaneous functionalization in a variety of metal chloride solutions The geometric structure of the functionalized two-dimensional carbonitride is shown in Figure 1 Fig 2 ferroelectric polarization and flip barrier of NiCl2 (C2n) 6; relationship between polarization and strain of MgCl2 (C2n) 6 and ZnCl2 (C2n) 6 (source: adv funct Mater.) the introduction of metal dichloride breaks the inversion symmetry of monolayer C2n Mcl2 (c2n6) (M = mg, Ni, Cu, Zn) is a ferroelectric material with in-plane spontaneous polarization The polarization of NiCl2 (C2n) 6 shown in Fig 2 has six equivalent directions NiCl2 monomer can migrate along the edge of nanopore under the electric field, making the polarization switch from one direction to another At the same time, 3D metal atoms also bring magnetism to the material MnCl2 (c2n6) and VCl3 (c2n6) are two-dimensional ferromagnetic materials Two dimensional NiCl2 (C2n) 6 with both antiferromagnetic and ferroelectric order is a multiferrous material Fig 3 energy band diagram of MgCl2 (C2n) 6 and ZnCl2 (C2n) 6 (source: adv funct Mater.) due to the introduction of MgCl2, the symmetry of the original 2D C2n is reduced, and the degeneracy of the high symmetry point m 3 and M 1 / M 2 in the Brillouin zone of MgCl2 (C2n) 6 is removed As shown in Figure 3, when the iron electrode is in the direction of γ - K 1, m 3 is the valence band top (VBM), which is 6 MeV higher than M 1 / M 2 When the ferroelectric polarization direction changes to γ - K 2, VBM moves to M 1 at the same time It is shown that ferroelectric polarization can be controlled to shift the energy valley This kind of energy valley manipulation is non-volatile, which is obviously different from the spin Valley locking mechanism that is usually studied depending on the strong spin orbit coupling Fig 4 band structure of C2n, ZnCl2 (C2n) 6, MgCl2 (C2n) 6, mgi2 (C2n) 6 and (C2n) 6 / ZnCl2 (C2n) 6 heterojunction (source: adv funct Mater.) the energy band structure of functionalized two-dimensional carbonitrides was further studied It was found that the heterojunction of zncl2n 6 and original C2n was beneficial to separate photogenerated electrons and holes and improve photovoltaic efficiency More importantly, the gap width of 2D carbonitride can be adjusted by the concentration of functional metal chloride As shown in Fig 4C, the gap of (mgi2) xc2n can be adjusted in the range of 1.0-2.5ev under different concentrations of mgi2 The controllable gap enhances the potential application of 2D carbonitrides in nanoelectronics in the future Fig 5 based on various applications of functionalized 2D carbonitrides (source: adv funct Mater.) in the experiment, if the concentration gradient of functionalization can be controlled, the formation is as shown in Fig 5D The structure shown in this paper, the concentration gradient along the longitudinal direction will lead to the gradient change of the band gap of each layer of material, thus greatly broadening the optical absorption spectrum of the material At the same time, the alignment of energy bands formed by vertical stacking is also conducive to the separation of photogenerated electrons and holes, which greatly improves the energy conversion efficiency of materials in photovoltaic applications P-type doping region, n-type doping region, ferromagnetic region and ferroelectric region can be obtained on the same layer of two-dimensional C2n by different kinds of solution infiltration, which is comparable to the convenience of silicon wafer integration and has great application potential in the future Nano Electronics The research results were recently published in adv funct Mater (DOI: 10.1002/adfm.201905752) The first author of this paper is Li Lei, a doctoral student of the research group The corresponding author is Professor Wu Menghao of Huazhong University of science and technology and Professor Zeng Xiaocheng of University of Nebraska Lincoln The research was supported by NSFC (No 21573084), Shanghai Supercomputing Center and unl Holland computing center Nowadays, people and scientific research have been paid more and more attention in the economic life China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism CBG information website, chembeangoapp, chembeango official micro blog, CBG information wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the representative research groups in China, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit.