Electronic, Magnetic And Transport Properties Of The New Low-dimensional Materials Studied By Numerical Simulations

Recently, two new low-dimensional materials, namely, phosphorene (two dimensional black phosphorus) and rhenium disulfide (ReS2) have been successfully fabricated. Owing to their unique optoelectronic properties that can not be found in bulk systems and high surface-volume ratio, they have attracted a lot of interests as a potential candicate material for application in some nano-electronic devices such as high-performance field-effect transistor (FET), Lithium ion battery, spintronic device. Phosphorene exhibits a good room-temperature carrier mobility (～1000 cm2/Vs) and high on-off ratio (105), however, the carrier mobility of bare phosphorene nanoribbon is very low. Therefore, the investigation on tunning the carrier mobility of phosphorene nanoribbon has important theoretical significance. In addition, ReS2 is a semiconductor, the direct band gap of which is indenpendent on the thickness of layers. However, it is intrinsically not magnetic. An important indicator of modern electronic devices is simultaneous using of both the charge and spin degree, therefore, it is a very important scientific hotspot to achieve the magnetic behavior in ReS2. In this work, through the first principles calculation based on the density functional theory (DFT) and deformation potential theory, we systemically investigated edge engineering and tensile strain modulated the carrier transport behavior in phosphorene nanoribbons, and then studied the effects of nonmetal atom adsorption, strain, and defects on the electronic and magnetic properties of ReS2 monolayer. The main conclusions list below:1. Investigations of modulating the carrier mobilities of phosphorene nanoribbon through edge passivation and tensile strain. Using first-principles calculations and deformation potential theory, we have studied the effects of different edge passivation groups on the carrier mobility of the phosphorene nanoribbons (PNRs) and strain effect on the transport property in H-PNRs. The numerical results show that the carrier mobility of passivated PNRs is not very sensitive to the different passivation groups, such as hydrogen (H), fluorine (F) and chlorine (C1), but strongly associated with the orientation of nanoribbon. Passivated armchair-PNR (APNR) has much larger carrier mobility than passivated zigzag-PNR (ZPNR) at the similar ribbon width. With increasing ribbon width, the electron mobility of passivated APNRs can be further enhanced. We also find that the anisotropy of carrier mobility in passivated PNRs can be reversed by applying tensile strain resulting from order switching of the conduction bands around Fermi level. The investigations provide a theoretical basis for application in FETs based on phosphorene nanoribbon.2. Modulation of the electronic and magnetic properties of ReS2 monolayer via nonmetal atom adsorption. Surface adsorption is a promising and effective strategy to tune the electronic and magnetic properties of 2D materials, due to their large surface-volume ratio. Through first-principle calculation, we have systemically investigated the stable configurations, electronic and magnetic properties of nonmetal atoms (H, N, P, O, S, F, and Cl) adsorbed ReS2 monolayers. It is found that the ReS2 sheet exhibits good adsorption capability to nonmetal atoms. Most adatoms prefer to occupy S-p site on ReS2 monolayer except for N and P. The reconstruction of the surface is pronounced in N-and P-adsorbed ReS2 monolayers. The electronic structure of ReS2 monolayer can be widely tuned by adsorbed atoms. The same magnetic moment of 1μB is found in the N-, P-, F-and Cl-adsorbed ReS2 monolayers, and the contributions of N (P) to the total magnetism are much smaller than those of F (C1) due to the surface reconstruction of N (P)-adsorbed cases. Our results show that nonmetal atom adsorption can effectively modulate the electronic and magnetic properties of ReS2 monolayer, which provides a new way for low dimensional materials application in spintronic devices.3. The modulation of electronic and magnetic properties of ReS2 monolayer with S-containing defects by strain. We have systemically explored the strain-induced magnetism in ReS2 monolayer with Vs and V2S point vacancies. It is found that when the tensile strain of 8% is applied, Vs-doped ReS2 monolayer result in magnetic half-metal feature, in which Re atoms around vacancy anti-ferromagnetically coupled each other. For V2s-doped ReS2 monolayer, system has a phase transition from magnetic semiconductor under strain of 6% to magnetic metal under strain of 7%, therefore, the partial extension of spin density in ReS2 monolayer is increasing with increasing strain. Our results show that strain engineering can provide an effective approach to tune magnetism in defect doped ReS2 monolayer, provide a new way for ReS2 application in low-dimensional spintronic devices.In a word, our investigations in this paper are rich in the understanding of two new nanomaterials, phosphorene and ReS2, and provide a theory basis for their applications on nanodevices such as FET, spintronic device.