GaSe monolayer suffers in electronic and photocatalytic applications due to its large bandgap (3.50 eV). In this study, we employed the hybrid density functional, the Heyd-Scuseria-Ernzerhof hybrid (HSE), to explore the effect of substitutional metal single doping (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, As, In, Sn, Sb) at the Gasite on the structural stability, electronic, magnetic, optical, and photocatalytic properties. Our findings indicate that the bond lengths M-Ga/Se increase as the atomic radius of the dopant increases. Most of the doped structures are found to be thermodynamically stable. The introduction of metal and non-metal dopants significantly alters the magnetic properties of GaSe nanosheets, with dopings of Ti, V, Cr, Mn, Fe, Ni, and Co, as well as Zn, resulting in diluted magnetic semiconductors. In contrast, dopings with Sc, Cu, As, In, and Sb maintained semiconductor characteristics. The As-and Sb-doping resulted in the narrowest bandgap of 2.1 eV, while Ge-and Sn-doped GaSe monolayers revealed promise for two-dimensional spintronic applications. Although most dopants enhanced visible-light absorption, many proved unsuitable for photocatalysis due to the created mid-gap states and unfavorable valence band edges. The study showed that V-doped GaSe monolayer is a promising two-dimensional material for photocatalytic water-splitting and CO2 reduction under visible light, making it a potential material for clean fuel production.

After the synthesis of two-dimensional (2D) structures, Mo(W)Si2N4 (Hong et al., 2020; Science 369 670), proclaimed the dawn of a new family of 2D materials, including CrSi2N4 (CrSiN) semiconductor, which has a band gap of 0.49 eV and boasts remarkable properties. In this regard, we conducted density functional theory to investigate the structural, magnetic, and electronic properties of mono cation doped CrSiN (TM-CrSiN) with substitutional 3d/4d transition metal (TM) (at the Cr site). The bond lengths of TM-N increase as the atomic size of TM increases, and the formation/binding energy can be explained by the atomic size and electronegativity of TM as compared to the corresponding value of Cr. The doped structures with Ti/Zr, V/Nb, Mo, and Mn/Tc are nonmagnetic monolayers. In contrast, the other doped monolayers are magnetic. The doped monolayers with Ti/Zr and Mo are semiconductors with a band gap of 0.20/0.25 eV and 0.52 eV, respectively. It is noteworthy that the structures with Sc/Y, Fe, Co/Rh, Ni/Pd, and Zn/Cd dopants are half-metallic, which makes them suitable monolayers for spintronic applications. We find Cu- and Ag-CrSiN sheets behave as metallic structures and could be utilized in spin-filter devices.

Graphene nanomeshes (GNMs) are porous structures that have attracted theoretical and experimental interest over the past decade. Pores of pristine graphene nanomeshes must be passivated by some species (X) to give chemically stable structures (X-GNM). Here, we consider semiconducting GNMs passivated with H, N, and O. We study substitutional implantation of X-GNM with transition metal elements M (M=Sc, Ti, V, Mn, Co, Ni, Cu, Zn), taking into account various doping locations from the center of the pore (P1, P2, P3, P4 and P5 located at 11.47 & Aring;, 10.03 & Aring;, 7.34 & Aring;, 5.57 & Aring;, and 5.98 & Aring;, respectively). We seek to understand how altering the position of the dopant can influence the electronic and magnetic properties of GNM using density functional theory. The pore induces new symmetries compared to the parent graphene structure, requiring the consideration of various doping positions in the X-GNM unit cell. The doped H-GNM structures remain planar, whereas the M atoms in the (N, O)-GNM structures protrude from the plane. The M-(N, O)-GNM systems generally demonstrated stability greater than that of the M-H-GNM, with Co-H-, Ti-(N, O)-GNMs being the most stable structures. We find that the electronic properties and magnetization of the M-X-GNM are M- and X-dependent. Structures can be semiconductors, diluted magnetic semiconductors (DMSC), and metals. Notably, we find that the Ti-X-, the Ni-(N, O)-, and the Zn-N-GNMs are semiconductors, irrespective of the doping location. The (Mn, Co)-(N, O)-, V-(H, O)-, and Cu-N-GNMs are DMSCs, while the (Sc, Co, Cu)-H- and Cu-O-GNMs are metals. The V-N-GNM at position P2 and Co-O-GNM at position P4 are half-metallic systems, and can thus be used in spintronic applications. Our results can be valuable for designing graphene-based semiconductor and spintronic devices.

Gallium sulfide (GaS) sheet encounters obstacles in electronic and photocatalytic applications due to its large bandgap of 3.6 eV. To boost up the applicability of GaS sheets, the effects of substitutional mono metal and nonmetal dopants (3d transition metals, Ge, As, Se, In, Sn, Sb) at the Ga‐site on their chemical stability, photocatalytic behavior, and physical properties such as electronic, magnetic, and optical characteristics are investigated, using hybrid density functional theory. Results reveal that the majority of the doped GaS (MD‐GaS) exhibit thermodynamic stability. The magnetic properties of MD‐GaS nanosheets change with doping for MD = Ti, V, Cr, Mn, Fe, Ni, Co, Zn, and Se, transforming the sheets into diluted magnetic semiconductors. In contrast, doping with Sc, Cu, As, In, and Sb retains the semiconductor properties of the pristine sheet. Ge‐ and Sn‐doped GaS nanosheets show potential for 2D spintronic applications. While many dopants enhance visible light absorption, they introduce mid‐gap states or unfavorable valence band edges, making them less suitable for photocatalysis. However, As‐ and Sb‐doped GaS are promising sheets for photocatalytic Co 2 reduction and water splitting under visible light making it a potential material for clean fuel production.

Two-dimensional (2D) hexagonal boron carbon nitride (h-BxCyNz) has garnered a lot of interest in the last two decades because of its remarkable physical and chemical characteristics. Because of the carbon atoms, it has a smaller gap than its cousin, boron nitride, and is hence more appropriate for a wider range of applications. In the frame of density functional theory, we discuss the structural, electronic, and magnetic properties of mono Ti-doped and Co-doped BC6N (Ti/Co-BC6N) at different sites of substitutional doping (Ti/Co) in the BC6N monolayer. The mono substitutional doping at the B (TiB/CoB), N (TiN/CoN), and two different C (C1 (TiC1/CoC1), C2 (TiC2/CoC2)) sites, are investigated. The position of the Ti/Co dopant is an important parameter that changes the electronic state, magnetic moment, and adsorption activity of the pristine BC6N nanosheet. We find that the adsorption of the gases NO, NO2, CO2, NH3, N2, and O2 is significantly improved on the doped sheet at all doped positions compared to the adsorption on the pristine structure. The Ti/Co-BC6N can adsorb NO and NO2 better than CO2 and NH3. TiC1-BC6N and TiB-BC6N are the best doped sheets for adsorbing NO and NO2, respectively. The CO2 and the N2 molecules are moderately adsorbed at all doped positions as compared to the other adsorbed molecules. Ti-doped sheets can adsorb the CO2, NH3, and O2 better than the corresponding Co-doped sheets. We also study the adsorption of molecular hydrogen on our single-atom Ti/Co-doped systems, as well as on 4-atom Ti and Co clusters embedded in the BC6N sheets. We show that the cluster-embedded sheets can adsorb up to four H2 molecules. These novel findings are important for many applications of BC6N, including spintronics, gas filtration, molecular sensing, and hydrogen storage.

The experimental knowledge of the AlSb monolayer with a double-layer honeycomb structure is largely based on a recent publication [Le Qin et al., ACS Nano 2021, 15, 8184]. In the present work, we aim to explore the effect of phosphorus alloying on the structural, electronic, and optical properties of the AlSb monolayer (AlSbxP1-x). Phonon dispersion curves and cohesive energies, along with the Born criterion, demonstrate the stability of these structures. Our results show that with increasing P-concentration (from 0.375 to 1.0), the bandgaps increase to 1.25 eV, PBE (1.15 eV, PBE + SOC) for the alloyed AlSb structure with 0.875 P content, and an increase of 0.95 eV (PBE) and 0.56 eV (PBE + SOC) compared to that of the pristine AlSb bandgap. The largest bandgap is calculated to be 1.7 eV, PBE (1.65, PBE + SOC) for the AlP monolayer. Interestingly, for all P-concentrations, the bandgaps are direct, signifying potential applications of the material in photovoltaic applications. For P-contents from P = 0 to 0.375, the bandgap initially slightly decreases. The adsorption spectra are also found to depend on the concentration of P-dopant, where low concentration is found to be better than the high concentration for adsorption in the visible light range, while high concentration is better than low concentration for ultraviolet radiation. The variation of the bandgap with P-dopant concentration suggests the potential of these monolayer alloys for tunable bandgap engineering and application in future nano-optoelectronic devices.

Very recently, the two-dimensional (2D) structure of poly-benzimidazobenzophenanthroline (C5N) has been effectively synthesized [Javeed Mahmood et al., Adv. Mater. 2021, 33, 2,004,707]. Inspired by interesting experimental findings on 2D layered C5N structures, we employ DFT study to examine the electronic, structural, and optical features of C5N in bulk, bilayer, and monolayer honeycomb crystal configurations. The obtained results demonstrate that all configurations of the C5N structures have a strong bond network with cohesive energies comparable to graphene. In the ground state, the C5N bulk, bilayer and monolayer honeycomb crystal structures are a semiconductor. It is found that the bandgap of the C5N structures slightly increases with the decrease in the number of layers. The optical properties indicate the bulk structure possesses a greater capacity to absorb a broad range of visible light compared to the monolayer and bilayer.

Recent exciting developments in synthesis and properties study of the germanane (GeH) mono-layer have inspired us to investigate the structural and electronic properties of the van der Waals heterostructures (HTS) of GeH/InSe and GeH/In2Se3 through a first-principles methodology. In this study, structural and electronic properties of the HTS are examined thoroughly. GeH/InSe and GeH/In2Se3 are determined as n-type Schottky with a Schottky barrier height (SBH) of 0.40 eV and n-type ohmic, respectively. GeH/InSe turns out as a semiconductor with a direct bandgap of 0.62 eV, while GeH/In2Se3 is seen to be a metal. The results show that changing of the bandgap and SBH in very small values. For GeH/In2Se3 the effects are even less substantial, as the metallic or n-type nature of the material does not change. The biaxial strain and electric field have more tangible effects on the characteristics of the HTS. A mixture of compressive and tensile strain is seen to have the capability of changing GeH/InSe into a metal and at the same time transform it to an n-type/p-type ohmic or p-type Schottky contact. The results given here can guide future research in the field of HTS and especially GeH-based devices.

Two-dimensional (2D) materials can be effectively functionalized by chemically modified using doping. Very recently, a flat AgSe monolayer was successfully prepared through direct selenization of the Ag(111) surface. Besides, the results indicate that the AgSe monolayer like CuSe, has a honeycomb lattice. Motivated by the experimental outcomes, in this work, employing first-principles calculations, we systematically investigate the electronic and optical properties of AgSe and CuSe monolayers, as well as the impact of alkali metals (Li, Na and K). Without functionalization, both the CuSe and AgSe monolayers exhibit metallic characteristics. The Li (Na)-CuSe and Na (K)-AgSe systems are dynamically stable while, the K- and Li-CuSe and Li-AgSe are dynamically unstable. Interestingly, the functionalized CuSe system with Li and Na atom as well as AgSe with K and Na atom, can open the band gaps, leading to the actualization of metal to semiconductor transitions. Our results show that, the electronic characteristics of the Na-CuSe/AgSe system can be modulated by adjusting the adsorption heights, which gives rise to the change in the electronic properties and the band gap may be controlled. Furthermore, from the optical properties we can find that the K-AgSe system is the best candidate monolayer to absorb infrared radiation and visible light. Consequently, our findings shed light on the functionalization of 2D materials based CuSe and AgSe monolayers and can potentially enhance and motivate studies in producing these monolayers for current nanodevices and future applications.

The experimental knowledge of two-dimensional penta-like PdPSe monolayer is largely based on a recent publication (Liet al2021Adv. Mater. 2102541). Therefore, the aim of our research is consequently to explore the effect of vacancy defects and substitutional doping on the electronic properties of the novel penta-PdPSe monolayer by using first-principles calculations. Penta-like PdPSe is a semiconductor with an indirect bandgap of 1.40 eV. We show that Pd and Se vacancy defected structures are semiconductors with band gaps of 1.10 eV and 0.95 eV respectively. While P single vacancy and double vacancy defected structures are metals. The doping with Ag (at Pd site) and Si (at P site) convert the PdPSe to nonmagnetic metallic monolayer while the doping with Rh (at Pd site), Se (at P site) and As (at site Se) convert it to diluted magnetic semiconductors with the magnetic moment of 1µB. The doping with Pt (at the Pd site), As (at the P site), S and Te (at Se site) are indirect semiconductors with a bandgap of ∼1.2 eV. We undertook this theoretical study to inspire many experimentalists to focus on penta-like PdPSe monolayer growth incorporating different impurities and by defect engineering to tune the novel two dimensional materials (PdPSe) properties for the advanced nanoelectronic application.

In this work, employing first-principles calculations, we systematically investigate the atomic structure and electronic and optical properties of the AgTe monolayer, as well as the impact of alkali metal (Li, Na, K) and alkaline earth metal (Be, Mg, Ca) atoms decoration. The AgTe monolayer exhibits metallic characteristics. When Li, Na, K, and Mg atoms are decorated on the AgTe monolayer, the decorated AgTe monolayers are dynamically stable. In contrast, with Be and Ca atoms, the decorated structures are found to be dynamically unstable. Interestingly, the decoration of Li, Na, and K atoms into the AgTe monolayer can open the band gaps in the decorated Li-, Na- and K-AgTe monolayers around the Fermi level, leading to the actualization of metal-to-semiconductor transitions. In contrast, the decorated Mg-AgTe monolayer maintains its metallic characteristic. The highest electron and hole mobilities are achieved in the Na-AgTe monolayer among the decorated structures, suggesting the applicability of this structure in photovoltaic applications. The optical study shows that Li-, Na- and K-decorated AgTe monolayers have improved light absorption in the visible light region. Consequently, our findings shed light on the decoration of these 2D material monolayers and can potentially enhance and motivate studies in producing these monolayers for current nanodevices and future applications.

Due to the fascinating properties of the BAs monolayer and its promising applications, we study the structural, electronic, magnetic, and optical properties of the 3 d transition metal mono-doped BAs nanosheets using first-principle calculations. Two substitutional doping configurations are considered at sites B (dopant B ) and As (dopant As ). The doped structure at site As is more stable than at site B for the same dopant because the difference in atomic size between the dopant and As atoms is smaller than the corresponding dopant and B atoms. We explain the magnetic moments of the doped monolayer in terms of the number of valence electrons, the oxidation number, and the coupling between the electrons in the outer shell of the dopant. The Mn B , Cu, and Zn B dopings convert the semiconducting behavior of the pristine BAs monolayer into metallic behavior. The BAs monolayer becomes a dilute magnetic semiconductor under the influence of V B , Cr, Fe B , Co B , and Ni dopings. Due to their half-metallic behavior, the Ti-, Mn-, Fe-, and Zn-doped BAs at the site As can be used in spintronic applications. The Ti As and Mn As doped BAs nanosheets can enhance light absorption in the infrared and small range of the visible light regions as compared to pristine and the other doped nanosheets. The results indicate that doped BAs monolayers can be used in various optoelectronic and spintronic applications.

In the last two decades, significant efforts have been particularly invested in two-dimensional (2D) hexagonal boron carbon nitride h-BxCyNz because of its unique physical and chemical characteristics. The presence of the carbon atoms lowers the large gap of its cousin structure, boron nitride (BN), making it more suitable for various applications. Here, we use density functional theory to study the structural, electronic, and magnetic properties of Pt-doped BC6N (Pt-BC6N, as well as its adsorption potential of small molecular gases (NO, NO2, CO2, NH3). We consider all distinct locations of the Pt atom in the supercell (B, N, and two C sites). Different adsorption locations are also considered for the pristine and Pt-doped systems. The formation energies of all Pt-doped structures are close to those of the pristine system, reflecting their stability. The pristine BC6N is semiconducting, so doping with Pt at the B and N sites gives a diluted magnetic semiconductor while doping at the C1 and C2 sites results in a smaller gap semiconductor. We find that all doped structures exhibit direct band gaps. The studied molecules are very weakly physisorbed on the pristine structure. Pt doping leads to much stronger interactions, where NO, NO2, and NH3 chemisorb on the doped systems, and CO2 physiorb, illustrating the doped systems’ potential for gas purification applications. We also find that the adsorption changes the electronic and magnetic properties of the doped systems, inviting their consideration for spintronics and gas sensing.

The synthesizing WSi2N4 (WSiN) monolayer opens an exciting avenue toward developing novel two-dimensional material device technology due to its physical and chemical properties. The structural, magnetic, electronic, and optical properties of substitutional doped WSiN (D-WSiN) are investigated using first-principles calculations. The mono-doped monolayers contain transition metal dopant (D) (D = 3d and 4d metals) at the W site. The bond lengths between D and the nearby N atoms, stabilities, and work functions of D-WSiN monolayers can be explained in terms of the ionic sizes and electronegativities of the metal dopant atoms. The Sc-, Y-, and Nb-WSiN are p-type conducting, while Tc-WSiN is an n-type conducting. The Co-, Ni-, Cu-, and Ag-WSiN monolayers are half-metal, which could benefit for spintronic applications. Moreover, Zn- and Cd-WSiN monolayers can be utilized in spin-filter devices. The V-, Cr-, Mn-, Fe-, Ru-, and Rh-WSiN are dilute magnetic semiconductors (DMSC). The Ti-, Zr-, Mo-, and Pd-WSiN sheets are semiconductor (SC) with small bandgaps compared to the bandgap of pristine WSiN sheet. The Mo-WSiN sheet is the best candidate to absorb a wide range of visible and ultraviolet light, and Ti-WSiN is the best sheet for absorbing infrared light better than the pristine WSiN. The DMSC and SC doped nanosheets can be used in nanoelectronic and optoelectronic appliances.

We respond to the recent criticism of our paper [ Phys. Chem. Chem. Phys. , 2022, 24 , 9990–9997] and provide further discussion on the analysis of the PdPSe monolayer.

Recent advances in experimental techniques allow for the fabrication of hybrid structures. Here, we study the electronic and molecular adsorption properties of the graphene (G)/hexagonal boron nitride (h-BN)-MXenes (Mo2C) hybrid nanosheets. We use first-principles calculations to explore the structure and electronic properties of the hybrid structures of G-2H-Mo2C and h-BN-2H-Mo2C with two different oxygen terminations of the Mo2C surface. The embedding of G or h-BN patches creates structural defects at the patch-Mo2C border and adds new states in the vicinity of the Fermi energy. Since this can be utilized for molecular adsorption and/or sensing, we investigate the ability of the G-M-O1 and BN-M-O1 hybrid structures to adsorb twelve molecules. Generally, the adsorption on the hybrid systems is significantly higher than on the pristine systems, except for N2 and H2, which are weakly adsorbed on all systems. We find that OH, NO, NO2, and SO2 are chemisorbed on the hybrid systems. COOH may be chemisorbed, or it may dissociate depending on its location at the edge between the G/h-BN and the MXene. NH3 is chemisorbed/physisorbed on the BN/G-M-O1 systems. CO, H2S, CO2, and CH4 are physisorbed on the hybrid systems. Our results indicate that the studied hybrid systems can be used for molecular filtration/sensing and catalysis.

Monolayer MoSi2N4 (MoSiN) was successfully synthesized last year [Hong et al., Science369, 670 (2020)]. The MoSiN monolayer exhibited semiconducting characteristics and exceptional ambient stability, calling for more studies of its properties. Here, we conduct first-principle calculations to examine the structural, magnetic, and electronic properties of substitutional doping of MoSiN monolayers with transition metals (TM) at the Mo site (TM-MoSiN). We find that the Sc-, Y-, Ti-, and Zr-MoSiN are metallic systems, while Mn-, Tc-, and Ru-MoSiN are n-type conducting. The Fe-MoSiN is a dilute magnetic semiconductor, and the Ni-MoSiN is a metal (or half-metal). The inclusion of spin-orbit coupling turns them into a half-metal and a semimetal, respectively. We also find that the work function of TM-MoSiN and the bond lengths between the TM and neighbor atoms increase as the atomic radius and electronegativity of the TM atom increase, respectively. The Fe-, Co-, and Ni-MoSiN may be used in spintronic devices, while Mn-, Rh- and Pd-MoSiN could be utilized for spin filter applications.

Motivated by the successful synthesis of the porous graphitic carbon nitride (C6N7) monolayer very recently, we investigate the structural and electronic properties of C6N7 with doped and embedded with various atoms by means of spin-polarized density functional theory calculations. C6N7 monolayers doped with B, N, C, and O atoms have been revealed as stable and predicted to be feasible for experimental fabrication as free-standing monolayers based on the energy and thermal stability. Our computations demonstrate that while the C6N7 is a semiconductor, the doped C6N7 monolayers can be metal, dilute-magnetic semiconductor or half-metal. Further, a non magnetic moment is discovered in three of the doped C6N7 models and their electronic properties are disclosed to depend strongly on the spin configurations. The electronic properties of C6N7 depend on the doping atoms and doping sites. Furthermore, the effect of embedding of common nonmetal atoms such as B, C, N, S, O, Al, Si and P as well as transition metal including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn atoms on the electronic and magnetic behavior of the C6N7 are studied. The charge transfer analysis shows that all embedded atoms act as electron donors, expect N, O and S atoms which act as electron acceptors when interacting with C6N7. The modification of the electronic band structure of C6N7 as the underlying mechanism for the changes in its electronic properties has been investigated. The intention is to demonstrate how entering the above mentioned impurities changes the nature of C6N7 into a metal, ferromagnetic-metal or dilute-magnetic semiconductor. These findings give not only an insight into the physical properties of doped and embedded C6N7 monolayer by different atoms, but also can serve as a guide to discover future possible applications of this novel material.

Very recently, two-dimensional (2D) iodinene, a novel layered and buckled structure has been successfully fabricated (Qian et al 2020 Adv. Mater. 32 2004835). Motivated by this latest experimental accomplishment, for the first time we conduct density functional theory, first-principles calculations to explore the structural, electronic, and optical properties of monolayer, few-layer and bulk iodinene. Unlike the majority of monoelemental 2D lattices, iodinene is predicted to be an intrinsic semiconductor. On the basis of calculations using the generalized gradient approximation of Perdew–Burke–Ernzerhof for the exchange-correlation functional and the Heyd-Scuseria-Ernzerhof (HSE06) functional, it is shown that the electronic bandgap of iodinene decreases with increasing the number of atomic layers. Our HSE06 results reveal that the bandgap of iodinene decreases from 2.08 to 1.28 eV as the number of atomic layers change from one to five, highlighting the finely tunable bandgap. The optical study shows the monolayer has the ability to absorb a wide range of ultraviolet light, more than multilayers and bulk iodinene. As the number of layers increases, the absorption spectra exhibits a blue shift relative to monolayer iodinene. This study confirms the remarkable prospect for the application of iodinene in nanoelectronics and optoelectronics owing to its intrinsic semiconducting nature.

In this work, novel two-dimensional BC2X (X = N, P, As) monolayers with X atoms out of the B-C plane, are predicted by means of the density functional theory. The structural, electronic, optical, photocatalytic and thermoelectric properties of the BC2X monolayers have been investigated. Stability evaluation of the BC2X single-layers is carried out by phonon dispersion, ab-initio molecular dynamics (AIMD) simulation, elastic stability, and cohesive energies study. The mechanical properties reveal all monolayers considered are stable and have brittle nature. The band structure calculations using the HSE06 functional reveal that the BC2N, BC2P and BC2As are semiconducting monolayers with indirect bandgaps of 2.68 eV, 1.77 eV and 1.21 eV, respectively. The absorption spectra demonstrate large absorption coefficients of the BC2X monolayers in the ultraviolet range of electromagnetic spectrum. Furthermore, we disclose the BC2N and BC2P monolayers are potentially good candidates for photocatalytic water splitting. The electrical conductivity of BC2X is very small and slightly increases by raising the temperature. Electron doping may yield greater electric productivity of the studied monolayers than hole doping, as indicated by the larger power factor in the n-doped region compared to the p-type region. These results suggest that BC2X (X = N, P, As) monolayers represent a new promising class of 2DMs for electronic, optical and energy conversion systems.