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• The most stable and energetically metastable structures of V–Ti–O monolayer of various compositions on the rutile TiO 2 (011) substrate are predicted, and phase diagram of the V–Ti–O monolayer structures are obtained according to the calculated formation energies. • The predicted V–Ti–O structures can be considered as V-doped reconstruction of rutile TiO 2 (011) surface. Some new energetically stable reconstructions were predicted, which enrich the reconstruction models of rutile TiO 2 (011) surface. • The electronic structures of all the predicted structures and the oxidation states of V and Ti atoms in them are determined, which is important for understanding the mechanism of V doping to improve the photocatalytic properties of TiO 2. The formation of various structural V–Ti–O intermixed oxide monolayers on the rutile TiO 2 (011) substrates have been observed in experiments. The atomic structures and formation mechanism of them are still unclear. To this end, a global search of V–Ti–O ordered structures on rutile TiO 2 (011) surface is performed based on the evolutionary method. Nine energetically stable or metastable structures of different compositions are predicted, which can be considered as V-doping in different type of 2 × 1 reconstruction of rutile TiO 2 (011) surface. The calculated electronic structures indicate that the V atoms in most structures are not fully oxidized and introduce localized impurity states in the band gap. The oxidation states of the V atoms and surface Ti atoms are determined. The stabilization regions of them are determined based on the calculated surface energies. Our results are instructive for the experimental synthesis of different structural V–Ti–O monolayers, and significant for deep understanding of the photo- or electro-catalytic properties of them. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The successful demonstration of monolayer films as promising thermoelectric materials highlights alternative strategies to nanostructuring for achieving high thermoelectric efficiency. Due to this reason, the electronic structure and thermoelectric properties of the monolayer Sb2Te3 are studied by using the density functional theory and the semiclassical Boltzmann transport equation. The dynamical stability of the monolayer Sb2Te3 can be guaranteed by the absence of imaginary frequencies in the phonon band structure. The monolayer Sb2Te3 can reduce the lattice thermal conductivity. The Seebeck coefficient S of the p-type monolayer Sb2Te3 is almost three times as high as those of the n-type monolayer Sb2Te3. The power factor for p-type doping is significantly larger than that for the n-type doping. Our calculated ZT values for the monolayer Sb2Te3 are far higher than those of nanomaterials Sb2Te3, bulk Sb2Te3, and the eutectic PbTe-Sb2Te3 composites, indicating that the thermoelectric performance of low-dimensional structure is indeed superior. [ABSTRACT FROM AUTHOR]

• The energy bands of Fe and Mn co-adsorbed monolayers of SnSe 2 exhibit semi-metallicity. • As tensile strain increases, the adsorption system transitions from semi-metallic to metallic, accompanied. • The co-adsorption system's curie temperature is calculated to be 205.2 K. • The application of Fe and Mn double transition metal atoms to monolayer SnSe 2 may have potential. Pure 2D SnSe 2 is not magnetic, which limits its application in spintronics. However, magnetic properties can be induced in pure 2D SnSe 2 by introducing transition metal elements. In this study, we used first-principles calculations based on density-functional theory to predict the electronic structure and magnetic properties of monolayer SnSe 2 under adsorption of Fe and Mn double transition metal atoms. Our findings show that the energy bands of Fe and Mn co-adsorbed monolayers of SnSe 2 exhibit semi-metallicity. As tensile strain increases, the adsorption system transitions from semi-metallic to metallic, accompanied by an increase in total magnetic moment. Based on the Heisenberg model, the co-adsorption system's Curie temperature is calculated to be 205.2 K. Our studies suggest that the application of Fe and Mn double transition metal atoms to monolayer SnSe 2 may have potential in spintronics. [ABSTRACT FROM AUTHOR]

It can be seen from the figure that the magnetocrystalline anisotropy energy (MAE) of Ti, V, Cr, Mn, Fe and Co adsorption by two-dimensional SnSe 2. The scale on the left means positive and the scale on the right means negative. Positive values represent the in-plane magnetic anisotropy (IMA), in red on the graph, and negative values represent the perpendicular magnetic anisotropy (PMA), in blue on the graph. Case of V, Cr, Mn, Fe, Co showed different IMA of 0.00131, 0.00051, 0.00545, 0.00026, 0.00841 mJ/m2, respectively. That means they're more easily magnetized in the X axis. Ti-adsorbed case showed a larger PMA value of −0.06408mJ/m2, which means it is easier to be magnetized on the Y axis. [Display omitted] • It was found that Ti adsorbed 2D SnSe2 has perpendicular magnetic anisotropy. • V, Cr, Mn, Fe and Co adsorbed 2D SnSe2 has in-plane anisotropy. • TM adsorbed 2D SnSe2 have prospective applications in spintronic devices. • Two-dimensional materials have attracted widespread interest in the field of spintronics. Two-dimensional materials have attracted widespread interest in the field of spintronics due to their unique electronic structure and properties. Monolayer SnSe 2 has been widely used in thermoelectric and optoelectronic applications, but its application for spintronics is limited by its inherent lack of magnetic properties. Tuning the electronic structure and magnetic properties of two-dimensional materials (TDMs) by introducing transition metal elements (TM) to be applicable in the field of spintronic devices is a common means of accomplishing this. The electronic structure and magnetic characteristics of 3d TM adsorbed with two-dimensional SnSe 2 are predicted by first-principles calculations. The value of the magnetic moments from 0.16 to 4.07 μB in the adsorption systems, reaching a maximum in the case of Mn atom adsorption. The case of Ti atom adsorption has the maximum value of MAE in [0 0 1] direction. These results have shown that TM adsorbed 2D SnSe 2 have prospective applications in spintronic devices. [ABSTRACT FROM AUTHOR]

The figure of merit of n-type monolayer BiSbS 3 increases with the increase of temperature, and does not show a downward trend in the temperature range studied in this paper. The maximum figure of merit of p-type monolayer BiSbS 3 is 0.78025, which is obtained at a temperature of 1100 K and carrier concentration of 1 × 1020 cm−3. The optimal figure of merit, which is procured from n-type monolayer BiSbS 3 within the range of carrier concentration interval considered in this paper, is about 1.27742 at 1500 K and 5 × 1019 cm−3, which is larger than the maximum figure of merit of p-type monolayer BiSbS 3. The optimal figure of merit of monolayer BiSbS 3 studied in this paper is higher than that of Bi 2 O 2 Se (ZT = 0.53 at 800 K) [87] , Bi 2 O 2 Te (ZT = 0.62 at 800 K) [87] , SnS (ZT = 1.0 at 750 K) and PdTe 2 (ZT = 0.91 at 700 K). [Display omitted] The electronic structure and thermoelectric properties of bulk to monolayer BiSbS 3 are studied by density functional theory and semi-classical Boltzmann transport equation. Meanwhile, it is clear that bulk and monolayer BiSbS 3 are semiconductors with indirect band gaps by using the TB-mBJ scheme, respectively. Further, it can be known that the phonon spectrum of thin film BiSbS 3 has no negative frequency, and it can be inferred further that thin film BiSbS 3 is stable. Monolayer BiSbS 3 studied in this paper has extremely low lattice thermal conductivity at room temperature, which is lower than that of single quintuple layer Bi 2 Te 3 , bulk Sb 2 Te 3 , single-QL Bi 2 Se 3 and Bi 2 Te 3 S at room temperature. The maximum figure of merit of p-type monolayer BiSbS 3 is obtained at a temperature of 1100 K and carrier concentration of 1 × 1020 cm−3. The optimal figure of merit, which is procured from n-type monolayer BiSbS 3 within the range of carrier concentration interval considered in this paper, is obtained at 1500 K and 5 × 1019 cm−3. [ABSTRACT FROM AUTHOR]

The edge of phonon spectrum, that is, the highest optical frequency is only 170 cm−1, which will cause the large optical mode scattering. The strong coupling of acoustic and optical modes will enhance phonon scattering. Phonon optical modes contribute little to thermal conductivity. The lattice thermal conductivity of monolayer Sb 2 Te 2 Se is very low, only 0.46 W/mK at 300 K, it's less than 0.85W/mK of TlBiSe 2. The lattice thermal conductivity of monolayer Sb 2 Te 2 Se is less than 0.06 W/mK at 1000 K. The lattice thermal conductivity of monolayer Sb 2 Te 2 Se is much lower. The reasons for the low thermal conductivity of monolayer Sb 2 Te 2 Se are as follows. First of all, monolayer Bi 2 Te 2 Se contains heavy elements. Secondly, the small band gap between acoustic and optical branches causes the large phonon scattering rate is and the small average free path is, which will produce small K l. • The seebeck coefficient is the highest at 300 K. • The lattice thermal conductivity is much lower than other thermoelectric materials. • The heavy elements and small band gap cause the low thermal conductivity. • The strong coupling of acoustic and optical modes causes lower lattice thermal conductivity. • For the better n-type, Z e T reaches 1.5 at a temperature of 1000 K. The electronic structure and thermoelectric properties of monolayer Sb 2 Te 2 Se are studied by density functional theory and semi-classical Boltzmann transport equation. The Seebeck coefficient for monolayer Sb 2 Te 2 Se is very high, comparing with other thermoelectric materials. The strong coupling of acoustic and optical modes enhanced phonon scattering, which will cause lower lattice thermal conductivity. The heavy elements and small band gap cause the low thermal conductivity of monolayer Sb 2 Te 2 Se, so the lattice thermal conductivity of monolayer Sb 2 Te 2 Se is much lower than other thermoelectric materials. The optimal value Z e T of monolayer Sb 2 Te 2 Se is so high, mainly due to the very low lattice thermal conductivity. For the better n-type, Z e T reaches 1.5 at a temperature of 1000 K, which proves that monolayer Sb 2 Te 2 Se is a good choice for thermoelectric materials. [ABSTRACT FROM AUTHOR]

The electronic structure and thermoelectric properties of monolayer Bi 2 Te 2 Se were studied by density functional theory and semi-classical Boltzmann transport equation. The band gap with TB-mBJ can be improved for monolayer Bi 2 Te 2 Se. Monolayer Bi 2 Te 2 Se have ultra-low thermal conductivity comparing with other well-known two-dimensional materials. The monolayer Bi 2 Te 2 Se can improve electrical conductivities. ZT increases with increasing temperature for monolayer Bi 2 Te 2 Se. Comparing to GGA, TB-mBJ has larger ZT value in p-type doping. Monolayer Bi 2 Te 2 Se have larger ZT comparing with other well-known two-dimensional materials. Our calculated results show that our calculation greatly underestimates ZT value, therefore, monolayer Bi 2 Te 2 Se should have a higher ZT value. • Monolayer Bi 2 Te 2 Se have ultra-low thermal conductivity. • The monolayer Bi 2 Te 2 Se can improve electrical conductivities. • TB-mBJ can't reduce the electronic thermal conductivity. • Comparing to GGA, TB-mBJ has larger ZT value in p-type doping. • Monolayer Bi 2 Te 2 Se have larger ZT comparing with other well-known two-dimensional materials. [ABSTRACT FROM AUTHOR]