Top Of Valence Band Research Articles

Fe−N Co‐Doped BiVO4 Photoanode with Record Photocurrent for Water Oxidation

AbstractBismuth vanadate (BVO) ranks among the most promising photoanodes for photoelectrochemical (PEC) water splitting. Nonetheless, slow charge separation and transport, besides the sluggish water oxidation kinetics, are key barriers to its photoefficiency. Here, we present a co‐doping strategy that significantly improves the charge separation performance of BVO photoanodes. We found that, under standard one sun illumination, the Fe−N co‐doped BVO photoanode (Fe−N−BVO) by N‐coordinated Fe precursor reaches a record photocurrent density of 7.01 mA cm−2 at 1.23 V vs RHE after modified a surface co‐catalyst (FeNiOOH), and exhibits an outstanding stability. By contrast, much lower photocurrent density is obtained for the N‐doped, Fe‐doped and Fe/N‐doped BVO photoanode with separated N and Fe precursors. The detailed experimental characterizations show that the high activity of the Fe−N co‐doped BVO photoanode is attributed to the enhanced photo‐induced bulk charge separation, as well as the accelerated surface water oxidation kinetics. XPS, EXAFS and DFT calculations clearly show that, instead of formation of deep trapping state in the individually doped BVO, the co‐doping of Fe−N into BVO generates Fe‐based electronic states just below the bottom of conduction band and N‐derived states just above the top of valence band. Such modulations in electronic structure enable the efficient trap of the electrons and holes to enhance the separation of photo‐induced carriers, but hinder the charge recombination originated from the deep trapping sites.

Depth profiles of hole traps in the tail region of Al ion implantation into p-type 4H-SiC

Abstract Hole traps generated in the tail region of Al ion implantation in p-type 4H-SiC were characterized by deep level transient spectroscopy measurements. Hole traps energetically located at Ev + 0.51 eV, Ev + 0.72 eV, Ev + 0.77 eV, and Ev + 1.40 eV (Ev : energy of the valence band top) were detected. The hole trap densities were roughly 7–40 times smaller than the implanted Al atom density in the tail region, and the densities of the observed traps exponentially decreased with the decay lengths of 84–150 nm.

Three Metal Complex‐Decorated Halobismuthates: Syntheses, Structures, Semiconducting Behaviors and Theoretical Investigations

AbstractEmploying metal complex cations as the structural modifiers, three new numbers of hybrid halobismuthates family, namely [NH4][Co(phen)3]BiI6 (phen=1,10‐phenanthroline; 1), [Zn(phen)2Br][Bi(phen)Br4] ⋅ H2O (2) and [Cu(2,2′‐bipy)2Br][Cu(2,2′‐bipy)2Bi2Br9] ⋅ H2O (2,2′‐bipy=2,2′‐bipyridine; 3) have been solvothermally constructed and structurally characterized. X‐ray crystallography analyses show that all compounds characteristic of abundant weak interactions feature the discrete anionic motifs. The obtained hybrid materials possess the semiconducting nature, with the visible light responding optical band gaps of 2.13–2.71 eV. Under the alternating light irradiation, they exhibit excellent photoelectric switching properties, whose photocurrent densities (0.85, 0.24, and 0.43 μA/cm2 for compounds 1–3, respectively) compare well with some high‐performance halobismuthate competitors. Further theoretical calculations of compound 1 reveal that the photosensitive [Co(phen)3]2+ cations contribute greatly to the bottom of conduction bands (CBs) and the top of valence bands (VBs), which may be the important reason for its excellent photoelectric behavior. The analyses of Hirshfeld surface, thermal stability, and X‐ray photoelectron spectroscopy were also discussed detailedly in this paper.

Nitrogen doping of cuprous oxide films: A surface science perspective

Nitrogen doping of Cu2O films grown on Au(111) and Pt(111) supports was explored by a variety of surface-science techniques, including electron-diffraction, X-ray photoelectron-spectroscopy (XPS), scanning tunneling microscopy and photoluminescence spectroscopy (PL). The films were prepared by Cu vapor deposition and high-pressure oxidation at 50 mbar O2. Nitrogen was inserted by adding N2 to the reactive gas or via sputter doping. Only the latter resulted in a clear N1s signal in XPS, compatible with the insertion of N-atoms at O substitutional sites. The N-doping caused an overall degradation of the oxide lattice and suppressed the formation of the (√3×√3)R30° surface reconstruction observed on pristine Cu2O(111). Moreover, the oxide Fermi level shifted from the valence-band top into the band gap, indicative for a reduced p-type conductivity of the sample upon doping. The N-dopants featured low thermal stability and largely desorbed at around 500 K, leaving behind a pronounced 850 nm PL peak due to O vacancy emission. Our findings indicate that the N-atoms initially occupy O substitutional sites but get removed easily at moderate temperature, casting doubts whether N-doping is a suitable pathway to improve the conductance and luminescence behavior of Cu2O.

Fe-N Co-Doped BiVO4 Photoanode with Record Photocurrent for Water Oxidation.

Bismuth vanadate ranks among the most promising photoanodes for photoelectrochemical water splitting. Nonetheless, slow charge separation and transportare key barriers to its photoefficiency. Here, we present a co-doping strategy that significantly improves the charge separation performance of BVO. Under standard one sun illumination, the Fe-N co-doped BVO photoanode (Fe-N-BVO) by N-coordinated Fe precursor reaches a record photocurrent density of 7.01 mA cm-2 at 1.23 V vs RHE after modified a surface co-catalyst. By contrast, much lower photocurrent density is obtained for the N-doped and Fe-doped BVO with separated N and Fe precursors. The detailed characterizations show that the high activity of the Fe-N-BVO is attributed to the enhanced photo-induced bulk charge separation and the accelerated surface water oxidation kinetics. XPS, EXAFS and DFT calculations clearly show that, instead of formation of deep trapping state in the individually doped BVO, the co-doping of Fe-N into BVO generates Fe-based electronic states just below the bottom of conduction band and N-derived states just above the top of valence band. Such modulations in electronic structure enable the efficient trap of the electrons and holes to enhance the separation of photo-induced carriers, but hinder the charge recombination originated from the deep trapping sites.

Understanding the atomistic behavior of small molecules (O2 and N2) on monometallic M13 nanoparticles

Both experimental data and density functional theory (DFT) calculations clearly indicate that the reactivity of metal clusters for NO is determined by the energy and orbital type (4d or 5s) of the valence band top. Here, we explore this correlation for the reactivity of M13 nanoclusters, being M = Ag, Au, Co, Cu, Fe, Ir, Ni, Os, Pd, Pt, Rh and Ru and adsorbed diatomic molecules, O2 or N2. The possible adsorption configurations, interatomic distances, and adsorption energies for O2 and N2 on M13 clusters have been analyzed in detail.

Characterization of ferromagnetic semiconductors and valley polarization in janus VBXS2(X = N, P) monolayers

The manipulation of the valley degree of freedom has attracted increasing attention in both fundamental scientific research and emerging applications. Here, we employ first-principles calculations to investigate the structural stability and electronic properties of Janus monolayers of VBXS2 (X=N, P). These materials exhibit characteristics of ferromagnetic semiconductors, with their valence band maximum located at the K/K′ point. Due to the combined effects of inversion symmetry breaking and time reversal symmetry breaking, VBNS2 and VBPS2 exhibit exotic spontaneous valley polarization in their top valence bands, measured at magnitudes of 48.6 meV and 47.6 meV, respectively. Consequently, this phenomenon potentially enables the observation of the anomalous valley Hall effect (AVHE). The unique electronic and valleytronic properties exhibited by Janus VBXS2 suggest a feasible experimental avenue for exploring ferrovalley (FV) and valley-related Hall effects within a two dimensional lattice.

Local bandgap narrowing in the forming state of threshold switching materials

Threshold switching (TS) materials, such as amorphous chalcogenide, have received significant attention for their application in storage class memory and in-memory computing. These materials contribute to efficient data processing and reduced power consumption in data centers. The initial switching process after fabricating a TS device, known as “forming,” has a profound impact on its subsequent TS behavior. However, it remains unclear how TS materials undergo changes in their atomic and electronic structures during the forming process. Consequently, the key factors that govern TS behavior remain obscure, necessitating a deeper understanding of the underlying physics behind TS phenomena. In this Letter, we investigated the forming state of the TS material AlTeN by combining scanning internal photoemission microscopy (SIPM) and ab initio calculations. Thanks to nondestructive evaluation by SIPM measurements, we observed local bandgap narrowing of AlTeN after its forming process. This is an experimental demonstration showing the presence of nuclei of the conductive filament formed in its ON state. Moreover, we conducted an ab initio calculation to reveal the origin of bandgap narrowing. We applied strong electrothermal stresses to the AlTeN model by ab initio molecular dynamics simulation with high electronic and lattice temperatures. By quenching from the electrothermal stress conditions, we reproduced an experimentally observed forming state with a narrowed bandgap. Analysis of the electronic structures of the forming state revealed that the origin of bandgap narrowing is the generation of the valence band top and conduction band bottom stemming from the increased homopolar bonds.

Structural, elastic, mechanical, and electronic properties of chalcogenide perovskite SnZrS3 under pressure

In this paper, we have presented the structural, elastic, mechanical, and electronic properties of the transition metal chalcogenide perovskite SnZrS3 under different pressures by using first-principles method. Our calculated lattice parameters at ambient pressure are in good agreement with the experimental and previous theoretical results. The elastic constants were evaluated numerically for orthorhombic SnZrS3 using the strain-stress approach. Orthorhombic SnZrS3 shows a strong anisotropic behavior of the elastic and structural properties. According to the calculations of the electronic properties, we find the states near the valence band top are derived from S 3p, Zr 4d, Sn 5p, and Sn 5s orbitals, and the lowest conduction band is composed of Zr 4d, S 3p, and Sn 5p orbitals. As the pressure increases, the conduction and valence band shift to lower and higher energies, respectively. These results indicated that lattice constants and band gap decrease with the increase of pressure.

Electronic and optical properties of pyrochlore Re2Ti2O7 (Re = Sm and Eu) from first-principles

Rare-earth titanate oxides are believed to be prospective functional materials for photocatalytic and photoluminescent applications because of their excellent optical properties and thermal stability of their physical properties. However, the relationships between optical properties and photoelectron trapping mechanisms are unclear. Herein, the structure, electronic, and optical properties of pyrochlore-structure Re2Ti2O7 (Re = Sm and Eu) were investigated using the first-principles approach with the Hubbard parameter U (GGA + U). The calculated bandgap is 2.5 eV for Sm2Ti2O7 and 2.4 eV for Eu2Ti2O7, which is in good agreement with the experimental observation. The results indicate that the strongly localized f states at the top of valence band are charge-trapping sites for photoexcitation of Re2Ti2O7, where electrons can absorb photon energy and transfer from the valence band to the conduction band, resulting in the photocatalytic and/or fluorescent effects in the visible and early UV regions. The important optical parameters, dielectric function ε(ω), refractive index n(ω), extinction coefficient k(ω), reflectivity R(ω), absorption coefficient I(ω), optical conductivity σ(ω), and electron energy-loss L(ω) were studied in detail, indicating that these optical parameters of Sm2Ti2O7 and Eu2Ti2O7 are insensitive to the ultra-violet (UV) radiation, but both Sm2Ti2O7 and Eu2Ti2O7 exhibit excellent optical properties in the visible and early UV regions. This work provides a clear understanding on the photoelectron trapping mechanism of pyrochlore-structure Re2Ti2O7, which will help to improve the photocatalytic and photoluminescent performance of Re2Ti2O7 and broaden their applications.

Structural, Elastic, Mechanical, Electronic, and Optical Properties of a Novel Quaternary Chalcogenide Semiconductor Ba3GeTeS4

The structural, elastic, mechanical, electronic and optical properties of Ba3GeTeS4 have been studied by pseudopotential density functional theory static calculations. The results indicated that both the lattice constant and cell volume decrease with the increase of pressure, which match well with available previous values. The pressure has a more significant influence on the b direction than the a and c direction. The obtained elastic constants reveal that Ba3GeTeS4 is mechanically stable between 0 GPa and 20 GPa. The bulk modulus, shear modulus, and Young’s modulus are evaluated by Voigt-Reuss-Hill approximations. All these elastic moduli exhibit a monotonic feature as a function of pressure. The Poisson’s ratio, and Pugh’s criterion indicate that the ductility of this quaternary Ba3GeTeS4 compound is more and more prominent with increasing applied pressure. Meanwhile, the analysis of the electronic structures reveals that the states near the valence band top are derived from Te 5p, S 3p, and Ba 6 s orbitals, and the lowest conduction band is composed of Ge 4 s and S 3p orbitals. We expect that the findings predicted the physical properties of this compound will promote future experimental studies on Ba3GeTeS4.

Effect of temperature on lanthanide charge transition levels and vacuum referred binding energies

Location of lanthanide levels in the bandgap, vacuum referred binding energy (VRBE) in the lanthanide ground state and energy of lanthanide charge transition levels (CTLs) are just three different namings for the same concept. A concept of importance for the performance of lanthanide activated compounds. Energy differences of CTLs with the conduction band bottom and valence band top are important when it concerns e.g. lanthanide luminescence, charge carrier trapping, and valence stability. Effect of temperature on CTL energy or VRBE has so far never been addressed despite that luminescence application and thermoluminescence studies may span a temperature range from 10 K to 1000 K. In this work information on the bandgap (or energy of host exciton creation) around 10 K and at RT in compounds is gathered to demonstrate that bandgap decreases by 0.1 eV to 0.3 eV when temperature increases to RT. A similar decrease will be demonstrated for the energy of electron transfer from the VB to a trivalent lanthanide. The findings have consequences for VRBE-diagram construction, i.e. the experimental parameters for such construction should all apply to the same temperature. They also have consequences on how to relate luminescence thermal quenching energy barriers and TL derived electron and hole trap depths with a VRBE diagram. By proper evaluating the effects of temperature, accuracy of VRBE diagrams and consistency with luminescence and thermoluminescence data can be improved.

Regulation of magnetic moment and magnetic anisotropy of magnetite by doping transition metal elements

Magnetic Fe<sub>3</sub>O<sub>4</sub> nanoparticles show promising applications in nanomedicine. The saturation magnetization (<i>M</i><sub>S</sub>) and magnetic anisotropy are critical for the applications of Fe<sub>3</sub>O<sub>4</sub> nanoparticles in drug delivery and magnetic hyperthermia. Here, by density functional computation, the doping effects of 3d and 4d transition metal elements (including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag and Cd) on the magnetic properties of Fe<sub>3</sub>O<sub>4</sub> are investigated in-depth. A conventional cell of Fe<sub>3</sub>O<sub>4</sub>, containing 24 Fe atoms and 32 O atoms, has been used to investigate the doping of group III elements. One 3d or 4d atom is doped in one conventional cell of Fe<sub>3</sub>O<sub>4</sub>, resulting in the formation of X<sub>0.125</sub>Fe<sub>2.875</sub>O<sub>4</sub> where X represents the dopant. The results show that the doping of most 3d and 4d transition metal elements will reduce the total magnetic moment, while the doping of Ag, Zn and Cd in Fe<sub>3</sub>O<sub>4</sub> will increase the total magnetic moment by 19%–22%. However, it is hard to dope Ag into Fe<sub>3</sub>O<sub>4</sub> according to the positive formation energy. Therefore, Zn and Cd are good candidates to improve the <i>M</i><sub>S</sub> of Fe<sub>3</sub>O<sub>4</sub>. The doping of Zn and Cd has also an influence on the magnetic anisotropy of Fe<sub>3</sub>O<sub>4</sub>. For Zn<sub>0.125</sub>Fe<sub>2.875</sub>O<sub>4</sub>, the magnetic anisotropy energy is about 0.25 meV per cell, which is slightly larger than that of intrinsic Fe<sub>3</sub>O<sub>4</sub> (0.2 meV per cell). Interestingly, the doping of Cd (Cd<sub>0.125</sub>Fe<sub>2.875</sub>O<sub>4</sub>) will greatly increase the magnetic anisotropy energy to 0.8 meV per cell, which is significant for the specific absorption rate in the magnetic hyperthermia application. In addition, the doping of Zn and Cd will not induce any defect states in the band gap according to the density of states. Zn<sub>0.125</sub>Fe<sub>2.875</sub>O<sub>4</sub> and Cd<sub>0.125</sub>Fe<sub>2.875</sub>O<sub>4</sub> are both semiconducting and both the top of valence band and the bottom of conduction band originate from octahedral Fe. This is because the impurity states are very deep in energy. Our research results show that doping Cd is a feasible way to improve the performance of Fe<sub>3</sub>O<sub>4</sub> as a material for drug delivery and magnetic hyperthermia.

First-Principle Prediction of a Ground State Crystal Properties of a One-dimensional Nanotube-like Structure on Bismuth

First-principle calculations and density functional theory (DFT) have been combined to comparatively investigate the band structure, phonon spectrum, and optical and elastic properties of one-dimensional nanotube-like Bi. Our calculation reveals that Bi exhibits metallic properties, based on the valence band top (VBT) that lies above the conduction band bottom (CBB), and this is known as a negative bandgap. The optical bandgap is found to be very small, with a value of 257[Formula: see text]meV. The absorption coefficient is observed to be very high, up to [Formula: see text][Formula: see text]cm[Formula: see text]. This quantity falls within the vacuum ultraviolet (VUV) region. According to our reflectivity data, up to 82% of light has been reflected, which could be suitable for optical coating. Our elastic calculations further suggest the Bi-material should be brittle and covalent. Our data provide a deep understanding of various properties of Bismuth and could be useful to other theoretical and experimentalists.

Effect of interfacial electronic structure on conductivity and space charge characteristics of core-shell quantum dots/polyethylene nanocomposite insulation

To investigate the effect of the interface electronic structure of core-shell quantum dots on the conductivity and space charge characteristics of polyethylene insulation, nanocomposite insulations, namely CdSe@ZnS/LDPE and ZnSe@ZnS/LDPE, are synthesized. The study focuses on elucidating the evolution patterns of DC conductivity and space charge in the nanocomposite insulation, and analyzing the effect of the interfacial electronic structure of core-shell quantum dots on the distribution of charge traps. Comparative analysis reveals that in contrast to LDPE insulation, ZnSe@ZnS/LDPE nanocomposite insulation demonstrates a substantial reduction in DC conductivity by 47.2% and a decrease in space charge accumulation by 40.3% under the conditions of elevated temperature and strong electric field. The increase of trap energy level means an enhanced trap effect on charger carriers. According to density functional theory, the band structure characteristics of core-shell quantum dots integrated with polyethylene are computationally assessed. The findings underscore that the band misalignment at the core-shell interface and the shell-insulation interface induces shifts in the conduction band bottom and at the valence band top, respectively. These shifts impose a confinement effect on electrons and holes, with the extent of this effect escalating with the augment of the difference in band gap between the core layer and the shell layer. Consequently, this phenomenon curtails carrier migration, thereby inhibiting space charge accumulation under the conditions of elevated temperature and strong electric fields.

Electronic Structure and Optical Property of 2D MgPX3 (X = S and Se) Monolayer by Density Functional Theory

2D metal phosphorus trichalcogenides (MgPX3) have attracted tremendous research interests in spintronic, electrocatalytic, and photoelectronic applications due to their unique magnetic and optical properties. Herein, a systematical investigation on the electronic structures and optical properties of 2D MgPX3 (X = S and Se) monolayers is performed by density functional theory. Owing to small cleavage energy, 2D MgPX3 monolayers can be obtained by mechanical exfoliation with an excellent structure stability of 2D MgPX3 monolayers demonstrated by elastic tensor, phonon dispersion, and molecular dynamics, respectively. 2D MgPX3 behaves as a direct bandgap semiconductor with a strong optical absorption in UV range whereas a weak adsorption near the band edge, demonstrated by both single‐ and quasiparticle approximations. Upon analyses on transition dipole moment along with the wave function symmetry, the weak optical absorption is attributed to the parity‐forbidden effect where the wave functions almost show the same parity between top valence band and bottom conduction band. The findings indicate that 2D MgPX3 monolayers hold promise as candidate materials for flexible UV photoelectronics devices and provide a theoretical insight into the optical properties of 2D semiconductors.

Experimental and Theoretical Investigation of Gadolinium Oxyhydride (GdHO) Thin Films: Optical, Photocatalytic, and Electronic Properties.

Oxyhydrides of rare-earth metals (REMOHs) exhibit notable photochromic behaviors. Among these, yttrium oxyhydride (YHO) stands out for its impressive transparency and swift UV-responsive color change, positioning it as an optimal material for self-cleaning window applications. Although semiconductor photocatalysis holds potential solutions for critical environmental issues, optimizing the photocatalytic efficacy of photochromic substances has not been adequately addressed. This research advances the study of REMOHs, focusing on the properties of gadolinium oxyhydride (GdHO) both theoretically and experimentally. The electronic and structural characteristics of GdHO, vital for ceramic technology, are thoroughly examined. Explicitly determined work functions for GdH2, GdHO, and Gd2O3 stand at 3.4 eV, 3.0 eV, and 4.3 eV, respectively. Bader charge analysis showcases GdHO's intricate bonding attributes, whereas its electron localization function majorly presents an ionic nature. The charge neutrality level is situated about 0.33 eV below the top valence band, highlighting these materials' inclination for acceptor-dominant electrical conductivity. Remarkably, this research unveils GdHO films' photocatalytic capabilities for the first time. Even with their restricted surface due to thinness, these films follow the Langmuir-Hinshelwood degradation kinetics, ensuring total degradation of methylene blue in a day. It was observed that GdHO's work function diminishes with reduced deposition pressure, and UV exposure further decreases it by 0.2 eV-a change that reverts post-UV exposure. The persistent stability of GdHO films, hinting at feasible recyclability, enhances their potential efficiency, underlining their viability in practical applications. Overall, this study accentuates GdHO's pivotal role in electronics and photocatalysis, representing a landmark advancement in the domain.

First-principles study on the electronic properties of atom passivating CsPbI2Br surface

The electronic properties of the bulk CsPbI2Br and the passivation of CsPbI2Br (110) surface states are calculated by using first-principles calculations. It is found that the band gap of CsPbI2Br is 1.42[Formula: see text]eV by using the generalized gradient approximation of the Perdew–Burke–Ernzerhof function. The band gap is about 1.96[Formula: see text]eV by using the more complex Heyd–Scuseria–Ernzerhof mixed functional, which is closer to the experimental value of 1.92[Formula: see text]eV. The valence band top of CsPbI2Br bulk is mainly contributed by I-5p orbital and Br-4p orbital, and the conduction band bottom is mainly contributed by Pb-6p orbital. Through the calculation of CsPbI2Br (110) surface states passivated by Cl, F and H atoms, it is found that H atom has the best passivation effect. Its adsorption energy value fluctuates less, it is less sensitive to the adsorption position, and the adsorption is stable. Followed by F atom, its passivation effect is worse than that of H atom, but better than that of Cl atom. Although the passivation position has a certain influence on it, it has little effect. The Cl atom is most affected by the passivation position. The different positions of passivated atoms have a significant impact on adsorption energy. The adsorption stability is poor, and the passivation effect is also poor. Through analyzing the charge density difference and Bader charges, it is found that the H atom gets more electrons from the I atom, which is beneficial to passivate surface states. The electron-acquiring ability of the F atom is inferior to that of the H atom and is superior to that of the Cl atom. The electron-acquiring ability and passivation ability of Cl atom are the weakest among the three elements.

Band splitting under strain: A route to broad-spectrum absorption

A strategy to split bright exciton bands is proposed to achieve broad-spectrum absorption in two-dimensional semiconductors. Based on ab initio many-body perturbation theory and Bethe-Salpeter equation calculations, we predict that post-transition-metal chalcogenides monolayers can realize broadband absorption under biaxial tensile strains. We find that top valence bands responsible for the strongly absorbing excitons exhibit disparate bonding characteristics and symmetries, thus responding to the strain differently. A moderate strain on the monolayers could yield large energy splitting of the exciton bands and a redshift of the band gap, broadening the absorption across the solar spectrum. The bright excitons have mixed inter- and intra-layer features, rendering them with relatively long lifetimes and strong absorption amplitudes. This work provides a new perspective to engineer two-dimensional materials with superior optoelectronic properties.

Large‐Gap Quantum Spin Hall State in Double‐Transition‐Metal Homologous Compounds of WSi2N4: A First‐Principles Study

Recently, the MoSi2N4(MoN)4n homologous compounds have been synthesized, extending the MA2Z4 family materials to the superthick MA2Z4(MZ)n form. Herein, a first‐principles study on the double‐transition‐metal W2TiSi2N6 and related group VI–IV M2M′Si2N6 nanosheets is performed. Robust structural stability is affirmed in this W2TiSi2N6 nanosheet from the energetic, mechanical, dynamical, and thermal perspectives. Unlike the WSi2N4 and WSi2N4(WN)n systems, the W2TiSi2N6 nanosheet exhibits a semimetal behavior with the top valence and bottom conduction bands touching each other at the Fermi level. With the inclusion of spin–orbit coupling, a nontrivial band gap is opened in the W2TiSi2N6 nanosheet, which has a sizeable bulk gap of 0.11 eV. The Z2 invariant is 1 and a pair of topologically protected edge states emerges in the gap region, confirming that W2TiSi2N6 nanosheet is a quantum spin Hall (QSH) insulator. Through in‐plane strain engineering, the bulk gap can be further increased to 0.23 eV, which is sufficiently large for the room‐temperature QSH effect. Such a large‐gap QSH state is also present in other group VI–IV M2M′Si2N6 systems with the combinations of MM′ = WZr, MoZr, and MoHf. This study demonstrates that the double‐metal M2M′Si2N6 nanosheets are promising candidates to realize fascinating topological quantum states.