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The Dzyaloshinskii–Moriya interaction (DMI), which only exists in noncentrosymmetric systems, plays an important role in the formation of exotic chiral magnetic states.

The combination of ML-CGT and Sc2CO2 provides a way for the design of new non-volatile FE memory devices.

Based on first-principles calculations, we study the hydrogen evolution reaction (HER) on novel 2D monolayers namely OsN2 and ReN2, and indicate their excellent catalytic performance.

Two-dimensional (2D) Weyl semi-half-metals (WSHMs) have attracted tremendous interest for their fascinating properties combining half-metallic ferromagnetism and Weyl fermions. In this work, we present a NiCS3 monolayer as a new 2D WSHM material using systematic first-principles calculations. It has 12 fully spin-polarized Weyl nodal points in one spin channel with a Fermi velocity of 3.18 × 105 m s−1 and a fully gapped band structure in the other spin channel. It exhibits good mechanical and thermodynamic stabilities and the Curie temperature is estimated to be 403 K. The Weyl points are protected by vertical mirror plane symmetry along Γ-K, and each of them remains gapless even under spin–orbit coupling when the direction of spin is perpendicular to the Γ-K line including the Weyl point, which makes it possible to control the opening and closing of Weyl points by applying and rotating external magnetic fields. Our work not only provides a promising 2D WSHM material to explore the fundamental physics of symmetry protected ferromagnetic Weyl fermions, but also reveals a potential mechanism of band engineering of 2D WSHM materials in spintronics.

Ferroelasticity and band topology are two intriguing yet distinct quantum states of condensed matter materials. Their coexistence in a single two-dimensional (2D) lattice, however, has never been observed. Here, we found that the 2D tetragonal HfC monolayer allowed simultaneous presence of ferroelastic and topological orders. By using first-principles calculations, we found that it could allow a low switching barrier with reversible strain of 17.4%, indicating that the anisotropic properties are achievable experimentally for a 2D tetragonal lattice. More interestingly, the tuning of topological behaviors with strain led to spin-separated and gapless edge states, that is, the quantum spin Hall effect. These findings from the coupling of two quantum orders offer insights into ferroelastic control over topological edge states for achieving multifunctional properties in next-generation 2D nanodevices.

The quantum spin Hall effect, the valley Hall effect and ferroelectricity are all extensively studied yet distinct properties of insulators and it would be very interesting to see if they could coexist in certain two-dimensional (2D) materials. We present a family of fluorinated methyl-functionalized bismuthene (Bi2C2H6−xFx) films to achieve the 2D ferroelectric valley topological insulator (FEVTI) state, due to strong spin–orbit coupling (SOC) and non-centrosymmetric layer structures. Bi2C2H6−xFx films have topological non-trivial band gaps up to 1.08 eV, which are robust against the coverage and distribution of fluorine atoms, and the strongest out-of-plane ferroelectric polarization is up to 0.25 × 10−10 C m−1. Moreover, some Bi2C2H6−xFx configurations exhibit an extra valley degree of freedom by the valley splitting at the K and K′ points in the Brillouin zone due to the symmetry breaking, resulting in the coexistence of quantum spin and valley Hall states. These phenomena could also be found in other similarly decorated 2D materials, therefore offering unique quantum material platforms for discovering novel physics and exploring innovative applications.

Using ab initio calculations, we present a two-dimensional (2D) α-2D-germanene dioxide material with an ideal sp3 bonding network which possesses a large band gap up to 2.50 eV. The phonon dispersion curves and molecular dynamics (MD) simulation under the chosen parameters suggest that the novel 2D structure is stable. The dielectric function and absorption spectrum also show the consistent band gap within the electronic structure diagram, suggesting possible application as an ultraviolet light optical detector. The calculated carrier mobility of 4.09 × 103 cm2 V−1 s−1 can be observed along the x direction, which is much higher than that of MoS2 (∼3.0 cm2 V−1 s−1). Finally, we found that α-2D-germanene dioxide could potentially act as an ideal monolayer insulator in so-called van der Waals (vdW) heterostructure devices. These findings expand the potential applications of the emerging field of 2D α-2D-germanene dioxide materials in nanoelectronics.

Recent experimental success in the realization of two-dimensional (2D) magnetism has invigorated the search for new 2D magnetic materials with a large magnetocrystalline anisotropy, high Curie temperature, and high carrier mobility. Using first-principles calculations, here we predict a novel class of single-spin Dirac fermion states in a 2D Ta2S3 monolayer, characterized by a band structure with a large gap in one spin channel and a Dirac cone in the other with carrier mobility comparable to that of graphene. Ta2S3 is dynamically and thermodynamically stable under ambient conditions, and possesses a large out-of-plane magnetic anisotropy energy and a high Curie temperature (TC = 445 K) predicted from the spin-wave theory. When the spin and orbital degrees of freedom are allowed to couple, the Ta2S3 monolayer becomes a Chern insulator with a fully spin-polarized half-metallic edge state. An effective four-band tight-binding model is constructed to clarify the origin of a semi-Dirac cone in a spin-up channel and nontrivial band topology, which can be well maintained on a semiconducting substrate. The combination of these unique single-spin Dirac fermion and quantum anomalous Hall states renders the 2D Ta2S3 lattice a promising platform for applications in topologically high fidelity data storage and energy-efficient spintronic devices.

A quantum spin Hall (QSH) insulator with high stability, large bulk band gap and tunable topological properties is crucial for both fundamental research and practical application due to the presence of dissipationless edge conducting channels. Recently, chemical functionalization has been proposed as an effective route to realize the QSH effect. Based on first-principles calculations, we predict that a two-dimensional TlP monolayer would convert into a topological insulator with the effect of bromination, accompanied by a large bulk band gap of 76.5 meV, which meets the requirement for room-temperature application. The topological nature is verified by the calculation of Z2 topological invariant and helical edge states. Meanwhile, an appreciable Rashba spin splitting of 77.2 meV can be observed. The bulk band gap can be effectively tuned with external strain and electric field, while the Rashba spin splitting shows a parabolic variation trend under an external electric field. We find that the topological property is available for the TlP film when the coverage rate is more than 0.75. BN and SiC are demonstrated as promising substrates to support the topological nature of TlPBr2 film. Our findings suggest that a TlPBr2 monolayer is an appropriate candidate for hosting the nontrivial topological state and controllable Rashba spin splitting, and shows great potential applications in spintronics.

The prospect of a Dirac half-metal (DHM) and the realization of the quantum anomalous Hall effect (QAHE) on a honeycomb lattice without external fields are a great challenge in experiments due to the structural complexities of two-dimensional (2D) crystals. Here, based on density-functional theory calculations, we propose an ideal candidate material for realizing these exotic quantum states in a 2D honeycomb metal–halogen lattice, single-layer PdCl3. We find that the ground state of PdCl3 is a 100% spin-polarized DHM with a ferromagnetic Curie temperature TC = 528 K predicted from Monte Carlo simulations. Upon including spin–orbit coupling (SOC), PdCl3 reveals the QAHE due to the splitting of the manifold of Pd |dxz〉 and |dyz〉 bands near the Fermi level, which is characterized by the nontrivial Chern number (C = −1) and chiral edge states. In particular, the origin of the topological properties of the PdCl3 honeycomb lattice is explained by the tight-binding model. The sensitivity of nontrivial topology to the cooperative effect of the electron correlation of Pd-4d electrons and SOC is demonstrated: when increasing the on-site Coulomb repulsion U, a sizable nontrivial band gap Eg = 68.6 meV is obtained. Additionally, we explore the mechanical and dynamical stability, as well as strain response of PdCl3 for possible epitaxial growth conditions in experiments. The coexistence of a high temperature DHM and the QAHE in PdCl3 presents a promising platform for the emerging area of spintronics devices with dissipationless edge states.

A Dirac half-metal material, which has a gapped band structure in one spin channel but Dirac cones in the other, combines two intriguing properties of 100% spin polarization and massless Dirac fermions and has recently started to attract increasing attention. In this work, using first-principles calculations we predict that the disodium carbide (Na2C) monolayer is an intrinsic 2p Dirac half-metal material with 12 fully spin-polarized and symmetry-protected Dirac cones, and a slightly gapped (53 meV) spin-polarized nodal line coexisting in one spin channel, leaving the other spin channel insulated with a gap of 1.9 eV. There are two kinds of Dirac cones in Na2C, protected by different crystalline symmetries, both of which are robust against biaxial strains (±5%) and spin–orbit coupling effects, with Fermi velocities of up to 5.2 × 105 m s−1. Ferromagnetism is mainly contributed to by the unpaired 2p electrons in the carbon, with a Curie temperature estimated to be 382 K, and the origin of the 2p magnetism could be explained by the superexchange mechanism between C2− anions with the Na+ cation as a bridge. Our results not only indicate a promising candidate for high-speed spintronic devices, but also reveal the hidden mechanism of the origin of symmetric protection and ferromagnetic exchange interactions in a Dirac semi-metal, which would provide a feasible strategy for the design of Dirac materials.

Nodal-ring materials with a spin-polarized feature have attracted intensive interest recently due to their exotic properties and potential applications in spintronics. However, such a type of two-dimensional (2D) lattice is rather rare and difficult to realize experimentally. Here, we identify the first 2D Honeycomb-Kagome (HK) lattice, Mn-Cyanogen, as a new single-spin nodal-ring material by using first-principles calculations. Mn-Cyanogen shows gapless and semiconducting properties in spin-up and spin-down orientations, respectively, indicating a spin-gapless semiconductor nature. Remarkably, a spin-polarized nodal ring induced by px,y/pz band inversion is captured from the 3D band structure, which is irrelevant to spin-orbit coupling. The origin of the single-spin nodal-ring can be further clarified by the effective tight-binding (TB) model. These results open a new avenue to achieving spin-polarized nodal-ring materials with promising applications in spintronic devices.

Exploring experimentally feasible two-dimensional (2D) films with high carrier mobility and tunable band structure is one key to developing next-generation nanodevices. Motivated by successful synthesis of the layered GaGeTe in previous experiments, we performed first-principles calculations to explore the geometric and electronic properties of GaGeTe few-layers, with a focus on the monolayer. The interlayer interaction in layered GaGeTe was found to be rather weak, with a cleavage energy of 0.53 J m−2, suggesting that the exfoliation of bulk crystal is a viable means for the preparation of GaGeTe few-layers. When thinned from bulk to few-layers, a transition from semimetal to semiconductor occurs with a band gap in the range of 0–0.74 eV, which is promising for the photovoltaic emitting devices. Moreover, the indirect band gap of the GaGeTe monolayer can be effectively tuned by applying mechanical strain and decreases with increasing tensile strain, while it increases and turns into a direct band gap under a compressive strain of 2.0%. Anisotropic carrier mobility can be observed along zigzag and armchair directions of the GaGeTe monolayer, and particularly for the former, a maximum of 7.83 × 104 cm2 V−1 s−1 was observed. Considering that the GaGeTe monolayer is both dynamically and thermodynamically stable at a temperature of 600 K, these findings expand the potential applications of the emerging field of 2D germanene-based crystals in nanoelectronics.

The quantum spin Hall (QSH) effect may promote revolutionary device development due to dissipationless propagation of spin currents. The bottleneck preventing applications from the QSH effect, however, is a lack of large nontrivial bulk gap and highly stable two-dimensional (2D) films. In this work, we design a novel 2D honeycomb lattice, namely a SnCH3 monolayer, using comprehensive density-functional theory (DFT) computations. The structural stability is confirmed using a phonon spectrum and molecular dynamics simulations. Interestingly, its nontrivial bulk gap can reach up to 0.34 eV, which is further tunable via external strain. The nontrivial topology stems mainly from band inversion between the s–px,y orbitals, demonstrated by the nonzero topological invariant Z2 and a single pair of gapless helical edge states located in the bulk gap. The effects of a growth substrate on the QSH effect are also checked by hydrogen bonding on a single side in stanene, showing the robustness of the observed QSH phase. Considering its compatibility with the current electronics industry, these findings present an efficient platform to enrich topological phenomena and expand potential applications of 2D stanene at high temperature.

Bismuth (Bi) and antimony (Sb) have similar electronic structures but distinct topological properties in their two-dimensional (2D) films, due to their different spin–orbit coupling strengths. An Sb/Bi hetero-junction is a good candidate for the formation of normal band insulator (NI)–topological insulator (TI) boundary states where dissipationless spin currents exist. However, the topological properties of 2D Bi/Sb alloy films, forming at the boundaries of their hetero-junctions, have not been well studied yet. Here, first-principles calculations are performed to study the geometric and band structures of buckled and puckered SbBi alloy 2D films. The transition point between the TI and NI phases is at x = 5 in buckled BixSb8−x and at x = 3 in puckered BixSb4−x. The topological transition of buckled SbBi can be explained using the well-known band inversion mechanism between p orbits, caused by the variation of either components or lattice parameters. According to the analysis on the SOC strength, we propose an experiential ratio rule for the topological phase transition point of SbBi, by simply comparing the number of Bi and Sb atoms, which will be useful in the designing of topological materials and devices for experiment.

Rashba spin–orbit coupling (SOC) in topological insulators (TIs) has recently attracted significant interest due to its potential applications in spintronics. However, to date, the coexistence of a giant Rashba SOC and band topology has rarely been investigated in two-dimensional (2D) films. Herein, we applied first-principles calculations to design a family of large-gap 2D topological insulators composed of hexagonal Bi and PbX (X = F, Cl, Br, and I) dimers. The nontrivial topology, induced via a pxy–pz band inversion, was confirmed by the Z2 index and helical edge states. Note that the Rashba splitting energy in these films reaches 81 meV, which is further tunable over a wide range of strains (−2–14%). Considering the robustness of the band topology on a h-BN substrate, this study provides a route for designing topological spintronic devices based on 2D films consisting of group IV–V–VI elements.

The exploration of Dirac materials is a great challenge in condensed matter physics and material chemistry. In this paper we present a novel 2D magnetic graphene-like Dirac material with a Honeycomb–Kagome (HK) lattice, named as C3Ca2. The ground state of C3Ca2 is a half-metal with a 100% spin polarized Dirac cone locating exactly at the Fermi level in the metallic spin channel, and has a large band gap in the insulating spin channel. In particular, C3Ca2 has 2p magnetism with the Dirac cones mainly contributed by pxy orbitals of C atoms, instead of 3d magnetism or pz dominated Dirac cones in other HK or Kagome materials, and it is robust against spin–orbit coupling and biaxial strains. The mechanism of magnetism could be understood by double exchange between carbon anions, using Ca2+ cations as bridges. These outstanding properties of C3Ca2 indicate it to be a promising 2D material for applications in spintronics.

The effect of a MoS2 substrate on the structural and electronic properties of stanene were systematically investigated by first-principles calculations. The Brillouin zone of isolated stanene has a Dirac cone at the K point. MoS2 helps to open an energy gap at the K point, whereas contributes no additional transport channels near the Fermi level. Our results suggest that the carrier mobility remains large, which makes the stanene/MoS2 heterostructure a competitive material for electronic applications. Subsequently, strain engineering study by changing the interlayer spacing between stanene and MoS2 layer and changing lattice constants indicates that the energy gap at K point can be effectively tuned to meet the demands of experiments and device design in nanoelectronics. Moreover, a large enough strain leads to a metal–semiconductor phase transition to make the intrinsic semiconductor turn into self-doping phase. Our study indicates that MoS2 is a good substrate to promote the development of Sn-based nanoelectronics.

Searching for two-dimensional (2D) group IV films with high structural stability and large-gaps is crucial for the realization of a dissipationless transport edge state using the quantum spin Hall effect (QSHE). Based on first-principles calculations, we predict that 2D germanene decorated with ethynyl-derivatives (GeC2X; X = H, F, Cl, Br, I) can be a topological insulator (TI) with a large band-gap for room-temperature applications. Both GeC2I and GeC2Br films are intrinsic TIs with a gap reaching up to 180 meV over a wide range, while GeC2H, GeC2F, and GeC2Cl transform from trivial to nontrivial phases under tensile strain. This topological characteristic can be confirmed by s–pxy band inversion, topological invariant Z2, and time-reversal symmetry protected helical edge states. Notably, the characteristic properties of edge states, such as the Fermi velocity and edge shape, can be tuned by edge modifications. Furthermore, we demonstrate that the h-BN sheet is an ideal substrate for the experimental realization of GeC2X, maintaining their nontrivial topology. Considering their higher thermo-stability, these GeC2X films may be good QSHE platforms for topological electronic device design and fabrication in spintronics.

The control of spin without a magnetic field is one of the challenges in developing spintronic devices. Here, based on first-principles calculations, we predict a new kind of ferromagnetic half-metal (HM) with a Curie temperature of 244 K in a two-dimensional (2D) germanene van der Waals heterostructure (HTS). Its electronic band structures and magnetic properties can be tuned with respect to external strain and electric field. More interestingly, a transition from HM to bipolar-magnetic-semiconductor (BMS) to spin-gapless-semiconductor (SGS) in a HTS can be realized by adjusting the interlayer spacing. These findings provide a promising platform for 2D germanene materials, which hold great potential for application in nanoelectronic and spintronic devices.

Band topology and Rashba spin splitting (RSS) are two extensively explored exotic properties in condensed matter physics. However, the coexistence has rarely been reported in simplest stoichiometric films so far. Here, by using first-principles calculations, we demonstrate that a series of inversion-asymmetric group-IV XYH2 monolayers (X, Y = Si, Ge, Sn, Pb) allow for the simultaneous presence of topological order and large RSS that derives from their peculiarly atomic structure. The topological bulk gaps and RSS energies of PbSnH2, PbGeH2, and PbSiH2 are tunable over a wide range of strains (−8 to 8%), even the maximum value can be enhanced to 0.68 eV and 0.24 eV under achievable strain, but another three configurations transform from trivial to nontrivial phases under tensile strain. Furthermore, we find that the Te(111)-terminated BaTe surface is an ideal substrate for the growth of these monolayers, without destroying their intrinsic band topology. Our findings provide a possible route to future applications of inversion-asymmetric topological insulators in spintronic devices.

Band topology and Rashba spin splitting (RSS) are two extensively explored yet exotic properties in condensed matter physics. Nonetheless, their coexistence has rarely been achieved in simple stoichiometric two-dimensional (2D) ultrathin films. Here we use first-principles calculations to predict a new inversion-asymmetric BiPbH monolayer, which allows for the simultaneous presence of nontrivially topological order and large RSS. Interestingly, the coexistence of the topological band gaps and RSS in this system are robust and stable over a wide range of strain (−6 to 6%), with the maximum bulk gap being enhanced to 0.40 eV and Rashba energy as large as 53.1 meV under achievable strains, respectively, which makes them viable for practical realization of the QSH state at room temperature. The nontrivial quantum state originated from pxy–pz band inversion is confirmed by Z2 index and helical edge states. Additionally, the h-BN semiconductor is an ideal substrate for experimental realization of BiPbH, without destroying its nontrivial topology. Our works open a new route for designing topological spintronics devices based on 2D inversion-asymmetric films.

The quantum spin Hall (QSH) effect is promising for achieving dissipationless transport devices due to the robust gapless states inside the insulating bulk gap. However, QSH insulators currently suffer from requiring extremely high vacuums or low temperatures. Here, using first-principles calculations, we predict cyanogen-decorated plumbene (PbCN) to be a new QSH phase, with a large gap of 0.92 eV, that is robust and tunable under external strain. The band topology mainly stems from s–pxy band inversion related to the lattice symmetry, while the strong spin–orbit coupling (SOC) of the Pb atoms only opens a large gap. When halogen atoms are incorporated into PbCN, the resulting inversion-asymmetric PbFx(CN)1−x can host the QSH effect, accompanied by the presence of a sizable Rashba spin splitting at the top of the valence band. Furthermore, the Te(111)-terminated BaTe surface is proposed to be an ideal substrate for experimental realization of these monolayers, without destroying their nontrivial topology. These findings provide an ideal platform to enrich topological quantum phenomena and expand the potential applications in high-temperature spintronics.

On the basis of first principles calculations, we predict that the PbPo monolayer is a new 2D topological crystalline insulator (TCI) with crystalline-protected Dirac states at the edges. This topologically nontrivial phase stems from the strong crystal field effect in the monolayer, which lifts the degeneracy between Po-px,y and Pb-pz orbitals, thus giving rise to a px,y–pz band inversion. As compared to the narrow band gap in bulk PbPo, the quantum confinement of the 2D structure leads to a larger band gap of 364.77 meV, making it viable for the practical realization of the TCI phase at room temperature. Additionally, its band topology is preserved in quantum well formed by sandwiching the PbPo monolayer between NaI layers. This new 2D TCI with a large bulk gap is a potential candidate in future spintronic devices with ultralow dissipation.

The new quantum materials known as inversion-asymmetry topological insulators (IATIs) have recently drawn intense attention because these structures possess distinct properties from those of inversion-symmetry insulators. However, the reported IATIs are rare in monolayer structures thus far. On the basis of first-principles calculations, we predict that the two-dimensional I-decorated HgSe monolayer (HgSeI2) is a new IATI with a large gap of 59.1 meV, as well as large Rashba spin splitting (RSS) of 37.2 meV, which derives from the polarity of atoms. The topological characteristic is confirmed by the s–pxy band inversion, topological invariant Z2, and time-reversal symmetry-protected helical edge states. The topologically nontrivial band gap and RSS of HgSeI2 can be effectively modulated with a wide range of strain (−12 to 6%) and external electric field (−10 to 10 V nm−1), and the maximum band gap can be improved to 156 meV under compressive strain, while other F-, Cl-, and Br-decorated cases can transform from trivial to nontrivial TIs with respect to appropriate strain. These novel IATIs with controlled band gap and RSS provide excellent platforms to realize topological spintronic devices based on inversion-asymmetry films.

Based on first-principles calculations, we study the electronic structure, magnetic properties and optical properties of transition metal (TM) doped SnO2NSs. Computational results indicate that pristine SnO2NSs is a direct gap semiconductor with nonmagnetic states. Cr, Mn, Fe atom doping can induce 2μB, −3μB and 2μB magnetic moment, respectively, while Ni atom doped SnO2NSs keeps the nonmagnetic states. More interestingly, Fe doped SnO2NSs becomes an indirect gap semiconductor, and the Cr, Mn and Ni atom doping maintain the character of direct gap semiconductor. For optical properties, the optical absorption edge shows red shift phenomenon for a TM atom (Cr, Mn, Fe or Ni) doped SnO2NSs. In addition, the tensity of absorption, reflection and refraction coefficient are enhanced significantly in the visible light region, which may be very useful for the design of solar cells, photoelectronic devices and photocatalysts.

It is challenging to epitaxially grow germanene on conventional semiconductor substrates. Based on first-principles calculations, we investigate the structural and electronic properties of germanene/germanane heterostructures (HTSs). The results indicate that the Dirac cone with nearly linear band dispersion of germanene is maintained in the band gap of the substrate. Remarkably, the band gaps opened in these HTSs can be effectively modulated by the external electric field and strain, and they also feature very low effective masses and high carrier mobilities. These results provide a route to design high-performance FETs operating at room temperature in nanodevices.

The electronic structures and optical properties of pristine and transition-metal (TM) atom doped ZnSe nanosheets (ZnSeNSs) have been studied based on first-principles calculations. The results indicate that the pristine ZnSeNSs are nonmagnetic direct gap semiconductors, while Mn, Fe or Co doped ZnSeNSs are all spin-polarized, and the Cr doped one is half-metallic with 100% spin-polarized currents. Cr or Co doped ZnSeNSs can improve the absorption properties and broaden the absorption range, compared to pristine, Fe or Mn doped ZnSeNSs. Moreover, red-shift phenomena are observed. These results can provide an important reference for designing and fabricating infrared and visible photoelectric nanodevices.

Very recently, graphene/SnO2 heterostructures (G/SnO2 HTSs) were successfully synthesized experimentally. Motivated by this work, the adhesion and electronic properties of G/SnO2 HTSs have been studied by using first-principles calculations. It is found that the graphene interacts overall with the SnO2 monolayer with a binding energy of −67–−70 meV per carbon atom, suggesting a weak van der Waals interaction between graphene and the SnO2 substrate. Although the global band gap is zero, a sizable band gap of 10.2–12.6 meV at the Dirac point is obtained in all G/SnO2 HTSs, mainly determined by the distortion of isolated graphene peeled from the SnO2 monolayer, independent of the SnO2 substrate. When the bilayer graphene is deposited on the SnO2 substrate, however, a global gap of 100 meV is formed at the Fermi level, which is large enough for the gap opening at room temperature. Interestingly, the characteristics of the Dirac cone with a nearly linear band dispersion relation of graphene can be preserved, accompanied by a small electron effective mass, and thus higher carrier mobility is expected. These finds provide a better understanding of the interfacial properties of G/SnO2 HTSs and will help to design high-performance FETs in nanoelectronics.

We performed extensive density functional theory (DFT) calculations of palladium (Pd) and gold (Au) alloy clusters adsorbed on a graphene monolayer in order to clarify the geometries and charge transfer of Pd–Au bimetal alloy clusters on graphene. It is found that the Pd–Au cluster prefers to bind with graphene through Pd atoms, with strong p-d hybridization between graphene and Pd atoms. Although the gold atom has an unpaired electron, the magnetic moments are mainly contributed by palladium. Compared with Pd–Au bimetal, the bonds between Au atoms are stronger; therefore, the gold atoms form a gold cap covering the Pd cluster. Furthermore, Bader charge analysis demonstrates that Pd in alloy clusters tends to lose electrons, and the number of charge transfers increases with the introduction of the graphene monolayer. Gold atoms and graphene synergistically improve electron loss on the Pd atom, thus weakening the adsorption of anions, which is expected to prevent poisoning of Pd nanocatalysts and enhance the catalytic reactivity of alloy clusters. However, the Au–Au coupling could weaken their ability to gain electrons from Pd significantly. So, an important task for experimental research is to find a way to disperse gold atoms as far apart as possible to improve the catalytic properties of the Pd–Au alloy cluster.

We perform first-principles calculations to study the geometric, energetics and electronic properties of graphene supported on BC3 monolayer. The results show that overall graphene interacts weakly with BC3 monolayer via van der Waals interaction. The energy gap of graphene can be up to ∼0.162 eV in graphene/BC3 heterobilayers (G/BC3 HBLs), which is large enough for the gap opening at room temperature. We also find that the interlayer spacing and in-plane strain can tune the band gap of G/BC3 HBLs effectively. Interestingly, the characteristics of a Dirac cone with a nearly linear band dispersion relationship of graphene can be preserved, accompanied by a small electron effective mass, and thus the higher carrier mobility is still expected. These findings provide a possible way to design effective FETs out of graphene on a BC3 substrate.

Structural, electronic and optical properties have been calculated for Tin dioxide nanoribbons (SnO2 NRs) with both zigzag and armchair shaped edges by first principle spin polarized total energy calculation. We find that both zigzag and armchair SnO2NR have indirect band gaps. The band gap oscillates between the maximum of 3.38 eV and the minimum of 1.69 eV and eventually levels off to a value of 2.09 eV for armchair nanoribbons, while for zigzag nanoribbons, the band gap oscillates between the maximum of 2.25 eV and the minimum of 2.04 eV and eventually levels off to 2.18 eV. Our investigation further reveals that the optical absorption capacity enhanced with increasing ribbon width for both Z-SnO2NRs and A-SnO2NRs. More interestingly, when introducing Ag impurities, the optical absorption edge shifts to the low energy region. These findings can be a useful tool for the design of a new generation of materials with improved solar radiation absorption.

Correction for ‘Prediction of topological property in TlPBr2 monolayer with appreciable Rashba effect’ by Min Yuan et al., Phys. Chem. Chem. Phys., 2018, 20, 4308–4316.