High Bipolar Conductivity and Robust In‐Plane Spontaneous Electric Polarization in Selenene

Abstract

perovskite films. Fortunately, more and more atomic thickness spontaneous electric polarization has been discovered in ionic compound monolayer with the puckered lattice structure. For example, atomic thickness ferroelectricity has been found in monolayer chalcogenides: M (1) X, M (2) X 2 , and M 2 (3) X 3 (M (1) = Ge, Sn; M (2) = Mo, W; M (3) = Al, Ga, In; X = S, Se, Te). [4][5][6][7] Fascinatingly more, ferroelectricity was also discovered in the 2D elemental materials, such as phosphorene nanoribbons, [8] group-V (As, Sb, Bi) monolayer [9] and tellurium multilayers, [10] which was previously thought impossible because of the stabilized high symmetry in elemental bulk structures and the equal distribution of charge per atom. In other words, bulk element cannot satisfy the two main mechanisms of ferroelectric polarization: ion-displacement and electronic polarization. Therefore, the study of elemental ferroelectricity involved in structural reconstruction is a fundamental question and will undoubtedly expand the application of ferroelectrics in device miniaturization.In the last decade, intensive efforts have been devoted to discover the potential 2D materials for the application of micro-nano electronic devices. [11][12][13][14][15] Common 2D materials have a layered 3D structure with covalently bonded, atomically thin layers held together by weak van der Waals forces. Through high-throughput computations, however, more than a thousand 2D materials with various functions have been verified or predicted, even including elemental 2D metals. [16,17] Among elemental 2D materials, group-VI elements have been predicted and successfully fabricated at last year. [18][19][20][21] In the new study, Jia and co-workers point out the underlying formation mechanism of tellurene is inherently rooted in the multi valency nature of Te, and further predict the importance of multivalency in the layering behavior of Se. [18] Motivated by this discovery, we have performed a systematic densityfunctional study on various dimension elemental tellurium, and found that the atomic structure and electronic properties of 2D monolayers and bilayers of tellurene close related to the multivalency of Te. [22] In this paper, we found that the charge transfer from the central to the outer atoms amounts to 0.18 and 0.04 e in aand β-Se, respectively. Se has the multivalent nature with both metal and nonmetal characteristics as the previously reported. In addition, we have demonstrated that monolayer a-Se possesses a rather high carrier mobility, Selenene has been predicted as a new member of an atomically thin 2D crystalline material family as of last year. With first principle calculations, two different stable phases of selenene, one with the 1T-MoS 2 -like structure (α-Se) and the other with alternating arrangement structure of deformed four-membered and six-membered rings (b-Se) are identified. Further research indicates that monolayer α-Se exhibits excellent bipolar conductivity, possessing rather high hole mobility close to that of graphene,...

Emerging Group‐VI Elemental 2D Materials: Preparations, Properties, and Device Applications

“…[44] The Se FET with Ni/Au contacts exhibits typical p-type transport property with high ON/OFF ratio over 10 6 but low hole mobility of 0.26 cm 2 V −1 s −1 (Figure 5a). The ONstate current is relatively low with the maximum value of about 20 mA mm −1 at a drain voltage of 3 V. The field-effect mobility is much lower than the theoretical value (571 cm 2 V −1 s −1 ), [86] which possibly results from poor quality of nanosheet samples. The surface contaminations formed during device fabrication process can also lead to the poor performance, which deserves further improvement.…”

“…[43,83,[86][87][88] Wang et al conducted first principle calculations on the electrical properties of monolayer Se with 1T-MoS 2 -like structure (denoted as t-Se in this Review) and tiled helical-chain structure (denoted as c-Se). [86] As shown in Figure 4a, the calculated bandgap of t-Se and c-Se are 0.70 and 1.76 eV, which may be underestimated due to the calculation methods. The monolayer t-Se is predicted to possess high hole and electron mobilities, which are 9.48 × 10 3 cm 2 V −1 s −1 for hole and 6.97 × 10 3 cm 2 V −1 s −1 for electron.…”

“…Reproduced with permission. [86] Copyright 2018, WILEY-VCH Verlag GmbH & Co. KGaA. c) The positions of VBM and CBM in 2D Te related with Te thickness.…”

Advances in photonics of recently developed Xenes

“…the δ and ε phases [157]. Here, the nomenclature of allotropes is the same with tellurene from the aspect of structural feature, which should be noticed when reading references such as references [157,161,162]. Similar to α-Te, the α-selenene (α-Se) is composed of parallel-aligned independent one-dimensional helical chains, which has been synthesized experimentally [163,164].…”

“…Similar to α-Te, the α-selenene (α-Se) is composed of parallel-aligned independent one-dimensional helical chains, which has been synthesized experimentally [163,164]. In terms of β phase, there is a disagreement on the existence of monolayer β-selenene in references [157,161,162] from theoretical prediction. It is reported in reference [162] that the β-Se is thermodynamically metastable and dynamically stable with the lattice constants of a = 4.20 Å and b = 4.99 Å, but its existence is negative in the other two references.…”