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Two-dimensional (2D) materials with high carrier mobility and tunable magnetism are in high demand for nanoelectronics and spintronic applications. Herein, we predict a novel two-dimensional monolayer KTlO that possesses an indirect band gap of 2.25 eV (based on HSE06) and high carrier mobility (1.86×10 3 cm 2 V -1 s -1 for electron and 2.54 ×10 3 cm 2 V -1 s -1 for hole) by means of ab initio calculations. KTlO monolayer has a calculated cleavage energy of 0.56 J m -2 , which suggests exfoliation of bulk material as viable means for the preparation of mono-and few-layer materials. Remarkably, the KTlO monolayer suggests tunable magnetism and half-metallicity with hole doping, which are attributed to the novel Mexican-hat-like bands and van Hove singularities in its electron structure. Furthermore, monolayer KTlO exhibits moderate optical 2 absorption over visible light and ultraviolet region. The band gap value and band characteristics of monolayer KTlO can be strongly manipulated by biaxial and uniaxial strains to meet the requirements of various applications. All these novel properties render monolayer KTlO a promising functional material for future nanoelectronics and spintronic applications.

Two-dimensional materials with a proper band gap and high carrier mobility are urgently desired in the field of nanoelectronics. We propose a novel twodimensional crystal monolayer TlP5, which is dynamically and thermodynamically stable and possesses a direct band gap of 2.02 eV with high carrier mobilities (13960 cm 2 V -1 s -1 for electrons and 7560 cm 2 V -1 s -1 for holes), comparable to that of phosphorene. The band gap value and band characteristics of monolayer TlP5 can be adjusted by biaxial and uniaxial strains, and excellent optical absorption over the visible-light range is predicted. These properties, especially for the balanced high mobilities for not only the electrons but also the holes, render monolayer TlP5 an exciting functional material for future nanoelectronics and optoelectronic applications. 2 Since the successful mechanical exfoliation of graphene in 2004, 1,2 twodimensional (2D) materials such as silicene, 3 borophene, 4,5 phosphorene, 6,7 and transitional metal dichalcogenides (TMDCs) 8-11 have attracted intensive interests because of their extraordinary electrical, mechanical and thermal properties that enable extensive application potential in various fields. 9,12-18 For example, phosphorene, with a direct 2.0 eV band gap as well as a high carrier mobility of about 1.14×10 3 cm 2 V -1 s -1 -2.60×10 4 cm 2 V -1 s -1 , has been considered to be a candidate for high performance field effect transistors. 6 Yet, its chemical instability under ambient conditions and the low electron mobility still hinder its practical application. MoS2 possesses a suitable direct band gap (1.8 eV) for microelectronic and optoelectronic applications, but it suffers from the low carrier mobility (~200 cm 2 V -1 s -1 ). Nowadays, 2D materials with a proper band gap and high carrier mobilities for both electrons and holes are still urgently desired for logic and optoelectronic devices.Very recently, a series of 2D phosphides, such as InP3, 19 GeP3, 20 SnP3, 21 and CaP3, 22 have been theoretically proposed as novel 2D semiconductors with high carrier mobilities (~10 3 cm 2 V -1 s -1 -10 4 cm 2 V -1 s -1 ) that are comparable to those of phosphorene. In addition, their theoretical cleavage energy is relatively low (0.57~1.32 J m -2 ), indicating that they can be obtained through mechanical exfoliation from bulk.On the other hand, a layered material composed of P and Tl with the TlP5 stoichiometry

Highly-efficient water splitting based on solar energy is one of the most attractive research focuses in the energy field. Searching for more candidate photocatalysts that can work under visible-light irradiation are highly demanded. Herein, using first principle calculations based on density functional theory (DFT), we predict that the two dimensional silicon chalcogenides, i.e. SiX (X=S, Se, Te) monolayers, as semiconductors with 2.43 eV~3.00 eV band gaps, exhibit favorable band edge positions for photocatalytic water splitting. The optical adsorption spectra demonstrate that the SiX monolayers have pronounced optical absorption in the visible light region. Moreover, the band gaps and band 2 edge positions of silicon chalcogenides monolayers can be tuned by applying biaxial strain or increasing the number of layers, in order to better fit the redox potentials of water. The combined novel electronic, high carrier mobility, and optical properties render the two dimensional SiX a promising photocatalyst for water splitting.Recently, a variety of two dimensional (2D) materials have been extensively studied as the photocatalysts for water splitting, due to their large specific surface areas as well as the short charge migration distances, which could enhance the catalytic performance by hindering the electronhole recombination. 10-15 A typical example is monolayer SnS 2 , which 3 yielded a photocurrent density of 2.75 mA cm -2 at 1.0 V, nearly 72 times larger than that of bulk SnS 2 , proven in theory and experiment. 9 Other 2D materials such as transition metal dichalcogenides, 16 MXenes, 17 group-III monochalcogenides, 18 ternary zinc nitrides, 19,20 and MPSe 3 21 etc. have also been predicated theoretically for photocatalyst application.Moreover, the booming research advancements of the stabilities and electronic properties of group IV-VI monolayers, which are isoelectronic counterparts of group V such as phosphorene, have been reported in the last few years. [22][23][24][25][26][27][28][29][30][31][32] The group IV mono-chalcogenides MX (M= Si, Ge, Sn and X = S or Se), whose buckled honeycomb lattice is similar to that of black phosphorene, are also candidate materials for photocatalytic water splitting. Nevertheless, their calculated overpotentials for OER are quite large, or a specific basic or acidic condition is required to obtain good photocatalytic activity. 33 The monolayer germanium monochalcogenides, like blue phosphorene, was predicted as UV-light-driven photocatalyst, owing to the large band gap. 34 Therefore, it is highly worthwhile to further investigate the electronic and optical properties of other group IV-VI monolayers, for the sake of finding new candidate materials with improved properties for optoelectronic devices. Motivated by this conception, we have conducted a comprehensive investigation of the stability and electronic properties of silicon chalcogenides, i.e. SiX (X=S, Se and Te) monolayers, based on density 4 functional theory. It is found that the SiX monolayers are of high dynamic, m...

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Searching for materials with single atom-thin as well as planar structure, like graphene and borophene, is one of the most attractive themes in two dimensional materials.Herein, using density functional theory calculations, we have proposed a series of single layer planar penta-transition metal phosphide and arsenide, i.e. TM2X4 (TM= Ni, Pd and Pt; X=P, As). According to the calculated phonon dispersion relation and elastic constants, as well as ab initio molecular dynamics simulation results, monolayers of planar penta-TM2X4 are dynamically, mechanically, and thermally stable. In addition, the band structures calculated with the screened HSE06 hybrid functional including spin-orbit coupling show that these monolayers are direct-gap semiconductors with sizeable band gaps ranging from 0.14 eV to 0.69 eV. Besides, the optical properties in 2 these monolayers are further investigated, where strong in-plane optical absorption with wide spectral range has been revealed. Our results indicate that planar penta-TM2X4 monolayers are interesting narrow gap semiconductors with excellent optical properties, and may find potential applications in photoelectronics.

The exact composition and structure of conductive filaments in hafnia-based memristors are still not fully understood, but recent theoretical investigations reveal that hexagonal HfOx phases close to the h.c.p. Hf structure are probable filament candidates. In this work we list h.c.p. Hf, Hf6O, Hf3O and Hf2O as possible phases for the filament in hafnia memristors. Their differences in lattice parameters, electronic structures and O charge states are studied in details. Migration of O ions for both in-plane and out-of-plane directions in these phases is investigated using first-principles calculations. Both single-phase supercells and filament-in-dielectric models are used for migration barrier calculations, while the latter is proven to be more accurate for the c-direction. The migration of O ions is fastest in metal Hf, while slowest in Hf2O. The existence of O interstitials in Hf tends to hinder the transport of O.

Searching for novel two-dimensional (2D) materials is highly desired in the field of nanoelectronics. We here propose a new 2D crystal barium tri-arsenide (BaAs3) with a series of encouraging functionalities. Being kinetically and thermally stable, the monolayer and bilayer forms of BaAs3 possess narrow indirect band gaps of 0.87 eV and 0.40 eV, respectively, with high hole mobilities on the order of ~10 3 cm 2 V -1 s -1 . The electronic properties of 2D BaAs3 can be manipulated by controlling the layer thickness. The favorable cleavage energy reveals that layered BaAs3 can be produced as a freestanding 2D material. Furthermore, by introducing vacancy defects monolayer BaAs3 can be transformed from a semiconductor to a metal. 2D BaAs3 may find promising applications in nanoelectronic devices.