Magnetically Doped Molybdenum Disulfide Layers for Enhanced Carbon Dioxide Capture

Carbon capture and storage (CCS) technologies have the potential for reducing greenhouse gas emissions and creating clean energy solutions. One of the major aspects of the CCS technology is designing energy-efficient adsorbent materials for carbon dioxide capture. In this research, using a combination of first-principles theory, synthesis, and property measurements, we explore the CO₂ gas adsorption capacity of MoS₂ sheets via doping with iron, cobalt, and nickel. We show that substitutional dopants act as active sites for CO₂ adsorption. The adsorption performance is determined to be dependent on the type of dopant species as well as its concentration. Nickel-doped MoS₂ is found to be the best adsorbent for carbon capture with a relatively high gas adsorption capacity compared to pure MoS₂ and iron- and cobalt-doped MoS₂. Specifically, Brunauer-Emmett-Teller (BET) measurements show that 8 atom % Ni-MoS₂ has the highest surface area (51 m²/g), indicating the highest CO₂ uptake relative to the other concentrations and other dopants. Furthermore, we report that doping could lead to different magnetic solutions with changing electronic structures where narrow band gaps and the semimetallic tendency of the substrate are observed and can have an influence on the CO₂ adsorption ability of MoS₂. Our results provide a key strategy to the characteristic tendencies for designing highly active and optimized MoS₂-based adsorbent materials utilizing the least volume of catalysts for CO₂ capture and conversion.

An Ab Initio Study of Lithization of Two-Dimensional Silicon-Carbon Anode Material for Lithium-Ion Batteries

This work is devoted to a first-principles study of changes in the structural, energetic, and electronic properties of silicene anodes during their lithium filling. Anodes were presented by silicene on carbon substrate and free-standing silicene. The ratio of the amount of lithium to silicon varied in the range from 0.06 to 1.125 for silicene on bilayer graphene and from 0.06 to 2.375 for free-standing silicene. It is shown that the carbon substrate reduces the stability of the silicene sheet. Silicene begins to degrade when the ratio of lithium to silicon (N_Li/N_Si) exceeds ~0.87, and at N_Li/N_Si = 0.938, lithium penetrates into the space between the silicene sheet and the carbon substrate. At certain values of the Li/Si ratio in the silicene sheet, five- and seven-membered rings of Si atoms can be formed on the carbon substrate. The presence of two-layer graphene imparts conductive properties to the anode. These properties can periodically disappear during the adsorption of lithium in the absence of a carbon substrate. Free-standing silicene adsorbed by lithium loses its stability at N_Li/N_Si = 1.375.

Silicene/ZnI2van der Waals heterostructure: tunable structural and electronic properties

By utilizingab initiodensity functional theory, the structural and electronic properties of novel silicene/ZnI₂heterobilayers (HBLs) were investigated. Constructing HBLs with ZnI₂in different stacking configurations leads to direct bandgap opening of silicene at K point, which ranges from 138.2 to 201.2 meV. By analyzing the projected density of states and charge density distribution, we found that the predicted HBLs conserve the electronic properties of silicene and ZnI₂can serve as a decent substrate. The tunability of electronic properties can be achieved by enforcing biaxial strain and by varying interlayer distance where bandgap can get as low as zero to as high as 318.8 meV and 290.7 meV, respectively depending on the stacking patterns. Maintenance of the remarkable features of silicene, high mobility of charge carriers, and fine-tuning of bandgap pave the way to construct new nanoelectronic devices using these novel silicene/ZnI₂HBLs.

Structures, Mobilities, and Electronic Properties of Functionalized Silicene: Superhalogen BO2 Adsorption

The narrow band gap of silicene severely hinders its application in nanoelectronic devices. Therefore, it is significant to open the band gap of silicene and maintain its high carrier mobility. And for that, the adsorption of different coverage superhalogens BO₂ on the silicene surface have been investigated based on density functional theory and the CALYPSO method. The results show that BO₂ unit prefers to adsorb on silicene with adjacent mode irrespective of the size of substrate. The electronic structure analysis indicates that the density of states near the Fermi level are mainly contributed by Si-p and BO₂-p orbitals. (BO₂)_n-silicene exhibits metallic character with the exception of (BO₂)₂ adsorbed on 4 × 4 supercell. As for (BO₂)₂-silicene, silicene transforms from a gapless direct semiconductor to an indirect semiconductor. Furthermore, the effective electron mass of two BO₂ superhalogens on 4 × 4 silicene is estimated and found to be smaller than that of graphene. It is expected to result in higher electron mobility.

SiGe/AsSb bilayer heterostructures: structural characteristics and tunable electronic properties

Tunable band gap along with high carrier mobility are attractive characteristics for high speed nano electronic device applications. In this work we studied the structural and electronic properties of atomically thin silicon germanide (SiGe) and antimony arsenide (AsSb) heterobilayers using first principle calculations within density functional theory. Monolayer SiGe is a semimetal with a Dirac cone at the K point of the Brillouin zone (BZ) which combines superior properties of germanene and synthesis advantages of silicene. The study shows that a considerable band gap (90-459 meV) is introduced in SiGe when modulated by monolayer AsSb without degrading the carrier mobility. Moreover AsSb introduces negligible lattice mismatch in optimized heterobilayers which is favorable for synthesis purposes. We studied the density of states and space charge distribution to investigate the mechanism of the band gap opening and interlayer binding. Finally we modulated the band gap at K the point of the BZ efficiently by applying biaxial strain and also by changing the interlayer spacing. The calculated electron effective mass as a function of strain reveals that linear energy dispersion relation is preserved and the effective mass remains significantly small within the strained structure. The results predict that SiGe/AsSb heterobilayers can be an excellent choice in Si and Ge-based nano electronics and spintronic applications.

Bidirectional heterostructures consisting of graphene and lateral MoS2/WS2 composites: a first-principles study

First-principles calculations have been performed to explore the structural and electronic properties of bidirectional heterostructures composed of graphene and (MoS₂) _X /(WS₂)_4-X (X = 1, 2, 3) lateral composites and compare them with those of heterobilayers formed by graphene and pristine MS₂ (M = Mo, W). The band gaps of the lateral heterostructures lie between those of pristine MoS₂ and WS₂. The weak coupling between the two layers can induce a tiny band-gap opening of graphene and formation of an n-type Schottky contact at the G-(MoS₂) _X /(WS₂)_4-X interface. Moreover, the combination ratio of MoS₂/WS₂ can control the electronic properties of G-(MoS₂) _X /(WS₂)_4-X . By applying external electric fields, the band gaps of (MoS₂) _X /(WS₂)_4-X (X = 0, 1, 2, 3, 4) monolayers undergo a direct-indirect transition, and semiconductor-metal transitions can be found in WS₂. External electric fields can also be used effectively to tune the binding energies, charge transfers, and band structures (the types of Schottky and Ohmic contacts) of G-(MoS₂) _X /(WS₂)_4-X heterostructures. These findings suggest that G-(MoS₂) _X /(WS₂)_4-X heterostructures can serve as high-performance nano-electronic devices.

Boosting Performance of Na-S Batteries Using Sulfur-Doped Ti3C2Tx MXene Nanosheets with a Strong Affinity to Sodium Polysulfides

Sodium-sulfur batteries using abundant elements offer an attractive alternative to currently used batteries, but they need better sulfur host materials to compete with lithium-ion batteries in capacity and cyclability. We report an in situ sulfur-doping strategy to functionalize MXene nanosheets by introducing heteroatomic sulfur into the MXene structure form the MAX phase precursor. By employing the vacuum freeze-drying method, a three-dimensional (3D) wrinkled MXene nanoarchitecture with the high specific surface area was prepared. The tailor-made wrinkled sulfur-doped MXene (S-Ti₃C₂T_x) nanosheets were applied as an electrode host material in room temperature sodium-sulfur batteries. The S-Ti₃C₂T_x matrix shows high polarity with sodium polysulfides, restricting the diffusion of sodium polysulfides. The MXene/sulfur electrode can achieve high areal sulfur loading up to 4.5 mg cm^-2 as well as good electrochemical performance (reversible capacity of 577 mAh g^-1 at 2 C after 500 cycles).

Tunable electronic and optical properties of the WS2/IGZO heterostructure via an external electric field and strain: a theoretical study

In this study, the structural, electronic and optical properties of a tungsten disulfide (WS2) hybrid with indium-gallium-zinc-oxide (IGZO) heterostructures were investigated based on density functional theory (DFT) calculations. According to the results of binding energy, charge density difference and electron localization function of heterostructures, we found that the WS2 and IGZO monolayers were bound to each other via non-covalent interactions with large binding energy. The calculated results illustrate that the AAii stacking pattern has an indirect band gap of 1.643 eV, while AAi and AB stacking patterns have maximum direct-gaps of 1.102 eV and 1.234 eV, respectively. Under an external E-field and mechanical strain, the response of the energy gap of the WS2/IGZO heterostructure monotonically decreased over a wide range, even with a semiconductor-metal transition. In addition, we investigated the optical properties of the heterostructure and found that it exhibits a much broad spectral responsivity (from visible light to deep UV light) and a more pronounced optical absorption than WS2 and IGZO monolayers. Moreover, the tensile strain could weaken the photoresponse of the heterostructure to the UV light and enhance the response for the visible light; under compressive strain, the heterostructure showed a strong absorption peak in the UV light. Meanwhile, a red-shift was observed under an external strain. All these unique and tunable properties indicate that the WS2/IGZO heterostructure is a good candidate for nanoelectronic and photoelectronic devices, such as field-effect transistors, flexible sensors, photodetectors and photonic devices.

Electroic and optical properties of germanene/MoS2 heterobilayers: first principles study

First principles calculations have been performed to investigate the structural, electronic, and optical properties of germanene/MoS₂ heterostructures. The results show that a weak van der Waals coupling between germanene and MoS₂ layers can lead to a considerable band-gap opening (53 meV) as well as the preserved Dirac cone with a linear band dispersion of germanene. The applied external electric filed can not only enhance the interaction strength between two layers, but also linearly control the charge transfer between germanene and MoS₂ layers, and consequently lead to a tunable band gap. Furthermore, the reduction in the optical absorption intensity of the heterostructures with respect to the separated monolayers has been predicted. These findings suggest that the Ge/MoS₂ hybrid can be designed as the device where both finite band gap and high carrier mobility are required.

Transport and Photoelectric Properties of 2D Silicene/MX2 (M = Mo, W; X = S, Se) Heterostructures

The transport and photoelectric properties of four two-dimensional (2D) silicene/MX₂ (M = Mo, W; X = S, Se) heterostructures have been investigated by employing density functional theory, nonequilibrium Green's function, and Keldysh nonequilibrium Green's function methods. The stabilities of silicene (SiE) are obviously improved after being placed on the MX₂ (M = Mo, W; X = S, Se) substrates. In particular, the conductivities of SiE/MX₂ are enhanced compared with free-standing SiE and MX₂. Moreover, the conductivities are increased with the group number of X, i.e., in the order of SiE < SiE/MS₂ < SiE/MSe₂. An evident current oscillation phenomenon is observed in the SiE/WX₂ heterostructures. When a linear light illumination is applied, SiE/MSe₂ shows a stronger photoresponse than SiE/MS₂. The maximum photoresponse with a value of 9.0a ₀ ²/photon was obtained for SiE/WSe₂. More importantly, SiE/MS₂ (M = Mo, W) heterostructures are good candidates for application in designing solar cells owing to the well spatial separation of the charge carriers. This work provides some clues for further exploring 2D SiE/MX₂ heterostructures involving tailored photoelectric properties.

Substrate-induced magnetism and topological phase transition in silicene

Silicene has shown great potential for applications as a versatile material in nanoelectronics and is particularly promising as a building block for spintronic applications. Unfortunately, despite its intriguing properties, such as a relatively large spin-orbit interaction, one of the greatest obstacles to the use of silicene as a host material in spintronics is its lack of magnetism or a topological phase transition owing to the silicene-substrate interaction, which influences its fundamental properties and has yet to be fully investigated. Here, we show that when silicene is grown on a CeO2 substrate, an appreciable robust magnetic moment appears in silicene covalently bonded to CeO2 (111), while a topological phase transition from a topological insulator to a band insulator occurs regardless of van der Waals (vdW) interactions or covalent bonding interactions at the interface. The induced magnetism of silicene is due to the breaking of Si-Si π-bonds, which also results in a trivial topological phase. The silicene-substrate interaction, and even weak vdW forces (equivalent to an electric field), can destroy the quantum spin Hall effect (QSHE) in silicene. We propose a viable strategy-the construction of an inverse symmetrical sandwich structure (protective layer/silicene/substrate)-to preserve the quantum spin Hall (QSH) state of silicene in a system with weak vdW interactions. This work takes a critical step towards the fundamental physics and realistic applications of silicene-based spintronic devices.

Functionalization of group-14 two-dimensional materials

The great success of graphene has boosted intensive search for other single-layer thick materials, mainly composed of group-14 atoms arranged in a honeycomb lattice. This new class of two-dimensional (2D) crystals, known as 2D-Xenes, has become an emerging field of intensive research due to their remarkable electronic properties and the promise for a future generation of nanoelectronics. In contrast to graphene, Xenes are not completely planar, and feature a low buckled geometry with two sublattices displaced vertically as a result of the interplay between sp² and sp³ orbital hybridization. In spite of the buckling, the outstanding electronic properties of graphene governed by Dirac physics are preserved in Xenes too. The buckled structure also has several advantages over graphene. Together with the spin-orbit (SO) interaction it may lead to the emergence of various experimentally accessible topological phases, like the quantum spin Hall effect. This in turn would lead to designing and building new electronic and spintronic devices, like topological field effect transistors. In this regard an important issue concerns the electron energy gap, which for Xenes naturally exists owing to the buckling and SO interaction. The electronic properties, including the magnitude of the energy gap, can further be tuned and controlled by external means. Xenes can easily be functionalized by substrate, chemical adsorption, defects, charge doping, external electric field, periodic potential, in-plane uniaxial and biaxial stress, and out-of-plane long-range structural deformation, to name a few. This topical review explores structural, electronic and magnetic properties of Xenes and addresses the question of their functionalization in various ways, including external factors acting simultaneously. It also points to future directions to be explored in functionalization of Xenes. The results of experimental and theoretical studies obtained so far have many promising features making the 2D-Xene materials important players in the field of future nanoelectronics and spintronics.

Germanene on single-layer ZnSe substrate: novel electronic and optical properties

In this work, the structural, electronic and optical properties of germanene and ZnSe substrate nanocomposites have been investigated using first-principles calculations. We found that the large direct-gap ZnSe semiconductors and zero-gap germanene form a typical orbital hybridization heterostructure with a strong binding energy, which shows a moderate direct band gap of 0.503 eV in the most stable pattern. Furthermore, the heterostructure undergoes semiconductor-to-metal band gap transition when subjected to external out-of-plane electric field. We also found that applying external strain and compressing the interlayer distance are two simple ways of tuning the electronic structure. An unexpected indirect-direct band gap transition is also observed in the AAII pattern via adjusting the interlayer distance. Quite interestingly, the calculated results exhibit that the germanene/ZnSe heterobilayer structure has perfect optical absorption in the solar spectrum as well as the infrared and UV light zones, which is superior to that of the individual ZnSe substrate and germanene. The staggered interfacial gap and tunability of the energy band structure via interlayer distance and external electric field and strain thus make the germanene/ZnSe heterostructure a promising candidate for field effect transistors (FETs) and nanoelectronic applications.

Non-Dirac Chern insulators with large band gaps and spin-polarized edge states

Based on first-principles calculations and k·p models, we demonstrate that PbC/MnSe heterostructures are a non-Dirac type of Chern insulator with very large band gaps (244 meV) and exotically half-metallic edge states, providing the possibilities of realizing very robust, completely spin polarized, and dissipationless spintronic devices from the heterostructures. The achieved extraordinarily large nontrivial band gap can be ascribed to the contribution of the non-Dirac type electrons (composed of px and py) and the very strong atomic spin-orbit coupling (SOC) interaction of the heavy Pb element in the system. Surprisingly, the band structures are found to be sensitive to the different exchange and correlation functionals adopted in the first-principles calculations. Chern insulators with various mechanisms are acquired from them. These discoveries show that the predicted nontrivial topology in PbC/MnSe heterostructures is robust and can be observed in experiments at high temperatures. The system has great potential to have attractive applications in future spintronics.

Silicene on Monolayer PtSe2: From Strong to Weak Binding via NH3 Intercalation

We study the properties of silicene on monolayer PtSe₂ by first-principles calculations and demonstrate a much stronger interlayer interaction than previously reported for silicene on other semiconducting substrates. This fact opens the possibility of a direct growth. A band gap of 165 meV results from inversion symmetry breaking and large spin-splittings in the valence and conduction bands from proximity to monolayer PtSe₂ and its strong spin-orbit coupling. It is also shown that the interlayer interaction can be effectively reduced by intercalating NH₃ molecules between silicene and monolayer PtSe₂ without inducing charge transfer or defect states near the Fermi energy. A small NH₃ diffusion barrier makes intercalation a viable experimental approach to control the interlayer interaction.

Study of the layer-dependent properties of MoS2 nanosheets with different crystal structures by DFT calculations

The main features of the electronic structure of MoS₂ nanosheets are contributed by the intra-layer interaction, and the inter-layer interaction only induces slight perturbation. But the latter has an important influence on the electronic structure of MoS₂ ultrathin nanosheets, especially the monolayer.

Intercalation of Si between MoS2 layers

We report a combined experimental and theoretical study of the growth of sub-monolayer amounts of silicon (Si) on molybdenum disulfide (MoS₂). At room temperature and low deposition rates we have found compelling evidence that the deposited Si atoms intercalate between the MoS₂ layers. Our evidence relies on several experimental observations: (1) Upon the deposition of Si on pristine MoS₂ the morphology of the surface transforms from a smooth surface to a hill-and-valley surface. The lattice constant of the hill-and-valley structure amounts to 3.16 Å, which is exactly the lattice constant of pristine MoS₂. (2) The transitions from hills to valleys are not abrupt, as one would expect for epitaxial islands growing on-top of a substrate, but very gradual. (3) I(V) scanning tunneling spectroscopy spectra recorded at the hills and valleys reveal no noteworthy differences. (4) Spatial maps of dI/dz reveal that the surface exhibits a uniform work function and a lattice constant of 3.16 Å. (5) X-ray photo-electron spectroscopy measurements reveal that sputtering of the MoS₂/Si substrate does not lead to a decrease, but an increase of the relative Si signal. Based on these experimental observations we have to conclude that deposited Si atoms do not reside on the MoS₂ surface, but rather intercalate between the MoS₂ layers. Our conclusion that Si intercalates upon the deposition on MoS₂ is at variance with the interpretation by Chiappe et al. (Adv. Mater.2014, 26, 2096-2101) that silicon forms a highly strained epitaxial layer on MoS₂. Finally, density functional theory calculations indicate that silicene clusters encapsulated by MoS₂ are stable.

Metal-free spin and spin-gapless semiconducting heterobilayers: monolayer boron carbonitrides on hexagonal boron nitride

The interfaces between monolayer boron carbonitrides and hexagonal boron nitride (h-BN) play an important role in their practical applications. Herein, we respectively investigate the structural and electronic properties of two metal-free heterobilayers constructed by vertically stacking two-dimensional (2D) spintronic materials (B₄CN₃ and B₃CN₄) on a h-BN monolayer from the viewpoints of lattice match and lattice mismatch models using density functional calculations. It is found that both B₄CN₃ and B₃CN₄ monolayers can be stably adsorbed on the h-BN monolayer due to the van der Waals interactions. Intriguingly, we demonstrate that the bipolar magnetic semiconductor (BMS) behavior of the B₄CN₃ layer and the spin gapless semiconductor (SGS) property of the B₃CN₄ layer can be well preserved in the B₄CN₃/BN and B₃CN₄/BN heterobilayers, respectively. The magnetic moments and spintronic properties of the two systems originate mainly from the 2p_z electrons of the carbon atoms in the B₄CN₃ and B₃CN₄ layers. Furthermore, the BMS behavior of the B₄CN₃/BN bilayer is very robust while the electronic property of the B₃CN₄/BN bilayer is sensitive to interlayer couplings. These theoretical results are helpful both in understanding the interlayer coupling between B₄CN₃ or B₃CN₄ and h-BN monolayers and in providing a possibility of fabricating 2D composite B₄CN₃/BN and B₃CN₄/BN metal-free spintronic materials theoretically.

Band engineering of the MoS2/stanene heterostructure: strain and electrostatic gating

In a fast developing field, it has been found that van der Waals heterostructures can overcome the weakness of single two-dimensional layered materials and extend their electronic and optoelectronic applications. Through first-principles methods, the studied MoS₂/stanene heterostructure preserves high-speed carrier characteristics and opens the direct band gap. Simultaneously, the band alignment shows that the electrons transfer from stanene to MoS₂, which forms an internal electric field. As an effective strategy, the out-of-plane strain remarkably changes the band gaps of the heterostructure and enhances its carrier concentration. In addition, the combined effects of the internal and external electric fields can further open the band gaps and induce a direct-to-indirect gap transition in the heterostructure. More interestingly, when the external electric field is equal to the reverse internal one, the heterostructure regains a Dirac cone. Our results show that the MoS₂/stanene heterostructure has potential applications in high-speed optoelectronic devices.

Novel electronic and optical properties of ultrathin silicene/arsenene heterostructures and electric field effects

The variable band-gap of the Si/As heterostructure (left) and optical absorption spectra for AA-stacking under a vertical electric field (right).

Modulation of silicene properties by AsSb with van der Waals interaction

Our present work provides a new promising material AsSb monlayer as the substrate for silicene with a negligible mismatch, sizable band gap and high carrier mobility.

A theoretical review on electronic, magnetic and optical properties of silicene

Inspired by the success of graphene, various two dimensional (2D) structures in free standing (FS) (hypothetical) form and on different substrates have been proposed recently. Silicene, a silicon counterpart of graphene, is predicted to possess massless Dirac fermions and to exhibit an experimentally accessible quantum spin Hall effect. Since the effective spin-orbit interaction is quite significant compared to graphene, buckling in silicene opens a gap of 1.55 meV at the Dirac point. This band gap can be further tailored by applying in plane stress, an external electric field, chemical functionalization and defects. In this topical theoretical review, we would like to explore the electronic, magnetic and optical properties, including Raman spectroscopy of various important derivatives of monolayer and bilayer silicene (BLS) with different adatoms (doping). The magnetic properties can be tailored by chemical functionalization, such as hydrogenation and introducing vacancy into the pristine planar silicene. Apart from some universal features of optical absorption present in all these 2D materials, the study on reflectivity modulation with doping (Al and P) concentration in silicene has indicated the emergence of some strong peaks having the robust characteristic of a doped reflective surface for both polarizations of the electromagnetic (EM) field. Besides this, attempts will be made to understand the electronic properties of silicene from some simple tight-binding Hamiltonian. We also point out the importance of shape dependence and optical anisotropy properties in silicene nanodisks and establish that a zigzag trigonal possesses the maximum magnetic moment. We also suggest future directions to be explored to make the synthesis of silicene and its various derivatives viable for verification of theoretical predictions. Although this is a fairly new route, the results obtained so far from experimental and theoretical studies in understanding silicene have shown enough significant promising features to open a new direction in the silicon industry, silicon based nano-structures in spintronics and in opto-electronic devices.

Controllable electronic and magnetic properties in a two-dimensional germanene heterostructure

Based on first-principles calculation, we predict a new kind of ferromagnetic half-metal (HM) with a Curie temperature of 244 K in a two dimensional (2D) germanene vdW heterostructure.

In-plane interfacing effects of two-dimensional transition-metal dichalcogenide heterostructures

Two-dimensional TMD in-plane heterostructures demonstrate true type-II band alignment and the built-in electric field makes the defect states consecutive.

Electric-field and strain-tunable electronic properties of MoS2/h-BN/graphene vertical heterostructures

The structural and electronic properties of vertical heterostructures (MoS₂/BN/graphene) are sensitive to applied vertical electric fields and strain.

First Principles Study on the Electronic Structure and Interface Stability of Hybrid Silicene/Fluorosilicene Nanoribbons

The interface stability of hybrid silicene/fluorosilicene nanoribbons (SFNRs) has been investigated by using density functional theory calculations, where fluorosilicene is the fully fluorinated silicene. It is found that the diffusion of F atoms at the zigzag and armchair interfaces of SFNRs is endothermic, and the corresponding minimum energy barriers are respectively 1.66 and 1.56 eV, which are remarkably higher than the minimum diffusion energy barrier of one F atom and two F atoms on pristine silicene 1.00 and 1.29 eV, respectively. Therefore, the thermal stability of SFNRs can be significantly enhanced by increasing the F diffusion barriers through silicene/fluorosilicene interface engineering. In addition, the electronic and magnetic properties of SFNRs are also investigated. It is found that the armchair SFNRs are nonmagnetic semiconductors, and the band gap of armchair SFNRs presents oscillatory behavior when the width of silicene part changing. For the zigzag SFNRs, the antiferromagnetic semiconducting state is the most stable one. This work provides fundamental insights for the applications of SFNRs in electronic devices.

Vertical and Bidirectional Heterostructures from Graphyne and MSe2 (M = Mo, W)

Vertical and lateral heterostructures with atomically clean and sharp interfaces have opened up new realms in materials science, device physics and engineering. Herein, inspired by recent experiments, the unprecedented bidirectional heterostructures (BDHs) of γ-graphyne@MoSe2/WSe2 as well as γ-graphyne@MoSe2 and γ-graphyne@WSe2 are proposed and examined on the basis of first-principles calculations. Our results reveal that a novel wrinkled γ-graphyne with narrowed energy gap and strong binding strength is achieved on the planar and smooth substrate in γ-graphyne@MoSe2/WSe2. The direct-indirect band gap crossover is also found in terms of interlayer coupling. Furthermore, we demonstrate that electron-hole pairs can be spatially separated, and the carrier mobility would be benefited from the absorbed γ-graphyne in the BDHs. These results provide not only new insights into the physical and chemical properties of the vertical and bidirectional heterostructures, but also a new strategy for fabricating unprecedented 2D nanomaterials with exciting properties.

Silicene: a review of recent experimental and theoretical investigations

Silicene is the silicon counterpart of graphene, i.e. it consists in a single layer of Si atoms with a hexagonal arrangement. We present a review of recent theoretical and experimental works on this novel two dimensional material. We discuss first the structural, electronic and vibrational properties of free-standing silicene, as predicted from first-principles calculations. We next review theoretical studies on the interaction of silicene with different substrates. The growth and experimental characterization of silicene on Ag(1 1 1) is next discussed, providing insights into the different phases or atomic arrangements of silicene observed on this metallic surface, as well as on its electronic structure. Recent experimental findings about the likely formation of hexagonal Si nanosheets on MoS2 are also highlighted.

Stacked functionalized silicene: a powerful system to adjust the electronic structure of silicene

Herein, we employed first principle density functional periodic calculations to characterize the silicon counterpart of graphene:silicene. We found that silicene is far more reactive than graphene, very stable and strong Si-X bonds can be formed, where X = H, CH3, OH and F. The Si-F bond is the strongest one, with a binding energy of 114.9 kcal mol(-1). When radicals are agglomerated, the binding energy per functional grows up to 17 kcal mol(-1). The functionalization with OH radicals produces the largest alterations of the structure of silicene, due to the presence of intralayer hydrogen bonds. The covalent addition of H, CH3, OH and F to silicene enables the adjustment of its electronic structure. In effect, functionalized silicene can be a semiconductor or even exhibit metallic properties when the type and concentration of radicals are varied. The most interesting results were obtained when two layers of functionalized silicene were stacked, given that the band gaps experienced a significant reduction with respect to those computed for symmetrically and asymmetrically (Janus) functionalized monolayer silicenes. In the case of fluorine, the largest changes in the electronic structure of bilayer silicene were appreciated when at least one side of silicene was completely fluorinated. In general, the fluorinated side induces metallic properties in a large number of functionalized silicenes. In some cases which presented band gaps as large as 3.2 eV when isolated, the deposition over fluorinated silicene was able to close that gap and induce a metallic character. In addition to this, in four cases small gaps in the range of 0.1-0.6 eV were obtained for bilayer silicenes. Therefore, functionalization of silicene is a powerful method to produce stable two-dimensional silicon based nanomaterials with tunable optical band gaps.

Tuning the electronic and magnetic properties of graphene-like AlN nanosheets by surface functionalization and thickness

Semiconductor → half-metal → metal transition with nonmagnetic → magnetic transfer can be achieved for AlN nanosheets by surface hydrogenation and increasing nanosheet thickness.

The effects of thermal and electric fields on the electronic structures of silicene

We have investigated the effects of thermal and electric fields on the electronic properties of silicene.

Tunable electronic and magnetic properties of monolayer MoS2 on decorated AlN nanosheets: a van der Waals density functional study

The structural, electronic, and magnetic properties of monolayer MoS₂ on decorated AlN nanosheets have been systematically investigated using density functional theory with van der Waals corrections.

Geometric and electronic properties of graphene modified by “external” N-containing groups

Due to electron transfer fromortho-carbon to nitrogen, theortho-carbon is the most stable binding site between pyridine derivatives and graphene or the catalytic site for a lot of reactions.