Penta-Pt2N4: an ideal two-dimensional material for nanoelectronics

First-Principles Study of Penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) Monolayer with Highly Anisotropic Electronic and Optical Properties

Two-dimensional (2D) semiconducting materials with anisotropic physical properties have induced lively interest due to their application in the field of polarizing devices. Herein, we have designed a family of penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers and predicted the electronic and optical properties based on the first-principles calculation. The results suggest that the penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers are indirect-gap semiconductors with a medium bandgap of 2.29-2.66 eV. The penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers own a remarkable mechanical anisotropy with a high Young's modulus anisotropic ratio (3.0). In addition, the penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers exhibit a high anisotropy ratio of hole/electron mobility in the x and y directions (1.16-3.54). The results calculated by the G0W0+BSE method indicate that the single-layers also bear a salient optical anisotropy ratio (1.56-2.11). The integration of the anisotropic electronic, optical, and mechanical properties entitles penta-PtXY (X = Se, Te; Y = S, Te; X ≠ Y) monolayers as potential candidates in multifunctional polarized nanodevices.

A first-principles prediction of novel Janus ZrGeZ3H (Z = N, P, and As) monolayers: Raman active modes, piezoelectric responses, electronic properties, and carrier mobility

In this article, an attempt is made to explore new materials for applications in piezoelectric and electronic devices. Based on density functional theory calculation, we construct three Janus ZrGeZ3H (Z = N, P, and As) monolayers and study their stability, piezoelectricity, Raman response, and carrier mobility. The results from phonon dispersion spectra, ab initio molecular dynamics simulation, and elastic coefficients confirm the structural, thermal, and mechanical stability of these proposed structures. The ZrGeZ3H monolayers are indirect band gap semiconductors with favourable band gap energy of 1.15 and 1.00 eV for the ZrGeP3H and ZrGeAs3H, respectively, from Heyd-Scuseria-Ernzerhof functional method. It is found that the Janus ZrGeZ3H monolayers possess both in-plane and out-of-plane piezoelectric coefficients, revealing that they are potential piezoelectric candidates. In addition, the carrier mobilities of electrons and holes along transport directions are anisotropic. Notably, the ZrGeP3H and ZrGeAs3H monolayers have high electron mobility of 3639.20 and 3408.37 cm2 V-1 s-1, respectively. Our findings suggest the potential application of the Janus ZrGeZ3H monolayers in the piezoelectric and electronic fields.

Tunable electronic and optical properties of BAs/WTe2heterostructure for theoretical photoelectric device design

The geometric structure of the BAs/WTe2heterojunction was scrutinized by employingab initiocalculations grounded on density functional theory. Multiple configurations are constructed to determine the equilibrium state of the heterojunction with optimal stability. The results show that the H1-type heterojunction with interlayer distance of 3.92 Å exhibits exceptional stability and showcases a conventional Type-II band alignment, accompanied by a direct band gap measuring 0.33 eV. By applying external electric field and introducing strain, one can efficaciously modulate both the band gap and the quantity of charge transfer in the heterojunction, accompanied by the transition of band alignment from Type-II to Type-I, which makes it expected to achieve broader applications in light-emitting diodes, laser detectors and other fields. Ultimately, the heterojunction undergoes a transformation from a semiconducting to a metallic state. Furthermore, the outstanding optical characteristics inherent to each of the two monolayers are preserved, the BAs/WTe2heterojunction also serves to enhance the absorption coefficient and spectral range of the material, particularly within the ultraviolet spectrum. It merits emphasis that the optical properties of the BAs/WTe2heterojunction are capable of modification through the imposition of external electric fields and mechanical strains, which will expand its applicability and potential for future progression within the domains of nanodevices and optoelectronic apparatus.

Rational Design of Stimuli-Responsive Inorganic 2D Materials via Molecular Engineering: Toward Molecule-Programmable Nanoelectronics

The ability of electronic devices to act as switches makes digital information processing possible. Succeeding graphene, emerging inorganic 2D materials (i2DMs) have been identified as alternative 2D materials to harbor a variety of active molecular components to move the current silicon-based semiconductor technology forward to a post-Moore era focused on molecule-based information processing components. In this regard, i2DMs benefits are not only for their prominent physiochemical properties (e.g., the existence of bandgap), but also for their high surface-to-volume ratio rich in reactive sites. Nonetheless, since this field is still in an early stage, having knowledge of both i) the different strategies for molecularly functionalizing the current library of i2DMs, and ii) the different types of active molecular components is a sine qua non condition for a rational design of stimuli-responsive i2DMs capable of performing logical operations at the molecular level. Consequently, this Review provides a comprehensive tutorial for covalently anchoring ad hoc molecular components-as active units triggered by different external inputs-onto pivotal i2DMs to assess their role in the expanding field of molecule-programmable nanoelectronics for electrically monitoring bistable molecular switches. Limitations, challenges, and future perspectives of this emerging field which crosses materials chemistry with computation are critically discussed.

Crystal lattice and electronic and transport properties of Janus ZrSiSZ2 (Z = N, P, As) monolayers by first-principles investigations

From the extending requirements for using innovative materials in advanced technologies, it is necessary to explore new materials for relevant applications. In this work, we design new two-dimensional (2D) Janus ZrSiSZ2 (Z = N, P, As) monolayers and investigate their crystal lattice and dynamic stability by using density functional theory investigations. The two stable structures of ZrSiSP2 and ZrSiSAs2 are then systematically examined for thermal, energetic, and mechanical stability, and electronic and transport properties. The calculation results demonstrate that both the ZrSiSP2 and ZrSiSAs2 monolayers have good thermal stability at room temperature and high energetic/mechanical stabilities for experimental synthesis. The studied structures are found to be in-direct semiconductors. Specifically, with moderate band-gap energies of 1.04 to 1.29 eV for visible light absorption, ZrSiSP2 and ZrSiSAs2 can be considered potential candidates for photovoltaic applications. The applied biaxial strains and external electric fields slightly change the band-gap energies of the monolayers. We also calculate the carrier mobilities for the transport properties based on the deformation potential method. Due to the lower effective masses, the carrier mobilities in the x direction are higher than those in the y direction. The carrier mobilities of the ZrSiSP2 and ZrSiSAs2 monolayers are anisotropic not only in transport directions but also for the electrons and holes. We believe that the results of our work may stimulate further studies to explore more new 2D Janus monolayers with novel properties of the MA2Z4 family materials.

Prediction of novel semi-conducting two-dimensional MX2 phosphides and chalcogenides (M = Zn, Cd; X = P, S, Se) with 5-membered rings

The discovery of novel two-dimensional (2D) materials is a significant obstacle for contemporary materials science. Research in the field of 2D materials has mainly focused on materials possessing 6-membered rings, high symmetry, and isotropic features. The examination of 2D materials presenting 5-membered rings, low symmetry and anisotropic characteristics properties has received scarce attention. In this study, we employed evolutionary algorithms and heuristic approaches combined with first-principles calculations to predict penta-MX2 structures (M = Zn, Cd; X = P, S, Se). All selected 2D penta-MX2 phases are dynamically, thermodynamically, mechanically, and thermally stable. Further discussion focuses on their structural, bonding, electronic and optoelectronic features. Our HSE06 calculations reveal that the penta-MP2, ZnPS, and MSSe structures are semiconductors with a band gap of 0.80-3.08 eV. Conversely, the 2D penta-MPSe (M = Zn, Cd) and CdPS phases are metallic. We additionally note that penta β-ZnP2 and CdP2 display direct band gaps (1.39 eV and 1.18 eV, respectively), while the penta α-ZnP2, ZnPS, ZnSSe, α-CdSSe and β-CdSSe possess indirect band gaps. Remarkably, 2D pentagonal MP2 (M = Zn, Cd), MSSe (M = Zn, Cd) and ZnPS 2D monolayers exhibit substantial optical absorption (>105 cm-1) throughout a broad range of the visible light spectra. Our results for crystal structure prediction expand the 2D penta-family of phosphides and chalcogenides, and demonstrate the potential of 2D penta-MX2 materials for optoelectronic applications.

Moderate direct band-gap energies and high carrier mobilities of Janus XWSiP2 (X = S, Se, Te) monolayers via first-principles investigation

Two-dimensional (2D) Janus materials with extraordinary properties are promising candidates for utilization in advanced technologies. In this study, new 2D Janus XWSiP2 (X = S, Se, Te) monolayers were constructed and their properties were systematically analyzed by using first-principles calculations. All three structures of SWSiP2, SeWSiP2, and TeWSiP2 exhibit high energetic stability for the experimental fabrication with negative and high Ecoh values, the elastic constants obey the criteria of Born-Huang, and no imaginary frequency exists in the phonon dispersion spectra. The calculated results from the PBE and HSE06 approaches reveal that the XWSiP2 are semiconductors with moderate direct band-gaps varying from 1.01 eV to 1.06 eV using the PBE method, and 1.39 eV to 1.44 eV using the HSE06 method. In addition, the electronic band structures of the three monolayers are significantly affected by the applied strains. Interestingly, the transitions from a direct to indirect semiconductor are observed for different biaxial strains εb. The transport parameters including the carrier mobility values along the x direction μx and y direction μy were also calculated to study the transport properties of the XWSiP2. The results indicate that the XWSiP2 monolayers not only have high carrier mobilities but also anisotropy in the transport directions for both holes and electrons. Together with the moderate and tunable energy gaps, the XWSiP2 materials are found to be potential candidates for application in the photonic, photovoltaic, optoelectronic, and electronic fields.

Two-Dimensional Planar Penta-NiPN with Ultrahigh Carrier Mobility and Its Potential Application in NO and NO2 Gas Sensing

Two-dimensional (2D) materials with novel structures and electronic properties are promising candidates for the next generation of micro- and nano-electronic devices. Herein, inspired by the recent experimental synthesis of penta-NiN₂ (ACS Nano, 2021, 15, 13539-13546), we propose for the first time a novel ternary penta-NiPN monolayer with high stability by partial element substitution. Our predicted penta-NiPN monolayer is a quasi-direct bandgap (1.237 eV) semiconductor with ultrahigh carrier mobilities (10³-10⁵ cm²V^-1s^-1). Furthermore, we systematically studied the adsorption properties of common gas molecules (CO, CO₂, CH₄, H₂, H₂O, H₂S, N₂, NO, NO₂, NH₃, and SO₂) on the penta-NiPN monolayer and its effects on electronic properties. According to the energetic, geometric, and electronic analyses, the penta-NiPN monolayer is predicted to be a promising candidate for NO and NO₂ molecules. The excellent electronic properties of and the unique selectivity of the penta-NiPN monolayer for NO and NO₂ adsorption suggest that it has high potential in advanced electronics and gas sensing applications.

Two-dimensional Janus MGeSiP4 (M = Ti, Zr, and Hf) with an indirect band gap and high carrier mobilities: first-principles calculations

Novel Janus materials have attracted broad interest due to the outstanding properties created by their out-of-plane asymmetry, with increasing theoretical exploration and more reports of successful fabrication in recent years. Here, we construct and explore the crystal structures, stabilities, electronic band structures, and transport properties - including carrier mobilities - of two-dimensional Janus MGeSiP₄ (M = Ti, Zr, or Hf) monolayers based on density functional theory calculations. From the cohesive energies, elastic constants, and phonon dispersion calculations, the monolayers are confirmed to exhibit structural stability with high feasibility for experimental synthesis. All the structures are indirect band-gap semiconductors with calculated band-gap energies in the range of 0.77 eV to 1.01 eV at the HSE06 (Heyd-Scuseria-Ernzerhof) level. Interestingly, by applying external biaxial strain, a semiconductor to metal phase transition is observed for the three Janus structures. This suggests potential for promising applications in optoelectronic and electromechanical devices. Notably, the MGeSiP₄ monolayers show directionally anisotropic carrier mobility with a high electron mobility of up to 2.72 × 10³ cm² V^-1 s^-1 for the ZrGeSiP₄ monolayer, indicating advantages for applications in electronic devices. Hence, the presented results reveal the novel properties of the 2D Janus MGeSiP₄ monolayers and demonstrate their great potential applications in nanoelectronic and/or optoelectronic devices. This investigation could stimulate further theoretical and experimental studies on these excellent materials and motivate further explorations of new members of this 2D Janus family.

Theoretical analysis of the thermoelectric properties of penta-PdX2 (X = Se, Te) monolayer

Based on the successful fabrication of PdSe2 monolayers, the electronic and thermoelectric properties of pentagonal PdX2 (X = Se, Te) monolayers were investigated via first-principles calculations and the Boltzmann transport theory. The results showed that the PdX2 monolayer exhibits an indirect bandgap at the Perdew–Burke–Ernzerhof level, as well as electronic and thermoelectric anisotropy in the transmission directions. In the PdTe2 monolayer, P-doping owing to weak electron–phonon coupling is the main reason for the excellent electronic properties of the material. The low phonon velocity and short phonon lifetime decreased the thermal conductivity (κl) of penta-PdTe2. In particular, the thermal conductivity of PdTe2 along the x and y transmission directions was 0.41 and 0.83 Wm−1K−1, respectively. Owing to the anisotropy of κl and electronic structures along the transmission direction of PdX2, an anisotropic thermoelectric quality factor ZT appeared in PdX2. The excellent electronic properties and low lattice thermal conductivity (κl) achieved a high ZT of the penta-PdTe2 monolayer, whereas the maximum ZT of the p- and n-type PdTe2 reached 6.6 and 4.4, respectively. Thus, the results indicate PdTe2 as a promising thermoelectric candidate.

Adsorption Behavior of Environmental Gas Molecules on Pristine and Defective MoSi2N4: Possible Application as Highly Sensitive and Reusable Gas Sensors

Inspired by the recent practical application of two-dimensional (2D) nanomaterials as gas sensors, catalysts, and materials for waste gas disposal, herein, the adsorption behaviors of environmental gas molecules, including NO, CO, O2, CO2, NO2, H2O, H2S, and NH3, on the 2D pristine and defective MoSi2N4 (MSN) monolayers were systematically investigated using spin-polarized density functional theory (DFT) calculations. Our results reveal that all the gas molecules are physically adsorbed on the MSN surface with small charge transfer, but the electronic structures of NO, NO2, and O2 are obviously modified due to the in-gap states. The introduction of N vacancy on the MSN surface enhances the interaction between gas molecules and the substrate, especially for NO2 and O2. Interestingly, the adsorption type of NO and CO evolves from physisorption to chemisorption, which may be utilized in NO and CO catalytic reaction. Furthermore, the moderate adsorption strength and obvious changes in electronic properties of H2O and H2S on the defective MSN make them have promising prospects in highly sensitive and reusable gas sensors. This work offers several promising gas sensors based on the MSN monolayer and also provides a theoretical reference of other related 2D materials in the field of gas sensors, catalysts, and toxic gas disposal.

Realization of an Ideal Cairo Tessellation in Nickel Diazenide NiN2: High-Pressure Route to Pentagonal 2D Materials

Most of the studied two-dimensional (2D) materials are based on highly symmetric hexagonal structural motifs. In contrast, lower-symmetry structures may have exciting anisotropic properties leading to various applications in nanoelectronics. In this work we report the synthesis of nickel diazenide NiN₂ which possesses atomic-thick layers comprised of Ni₂N₃ pentagons forming Cairo-type tessellation. The layers of NiN₂ are weakly bonded with the calculated exfoliation energy of 0.72 J/m², which is just slightly larger than that of graphene. The compound crystallizes in the space group of the ideal Cairo tiling (P4/mbm) and possesses significant anisotropy of elastic properties. The single-layer NiN₂ is a direct-band-gap semiconductor, while the bulk material is metallic. This indicates the promise of NiN₂ to be a precursor of a pentagonal 2D material with a tunable direct band gap.

Hydrogen-induced tunable electronic and optical properties of a two-dimensional penta-Pt2N4 monolayer

Most known two-dimensional materials lack a suitable wide-bandgap, and hydrogenation can be effectively utilized to tune the bandgap of some 2D materials. By employing density functional theory calculations, we investigate the effect of hydrogenation on the electronic and optical properties of a recently reported anisotropic penta-Pt2N4 monolayer. The results show that penta-Pt2N4 is thermally and mechanically stable after hydrogenation and also possesses anisotropic Young's modulus and Poisson's ratio. The electronic property analysis using the hybrid functional reveals that penta-Pt2N4 exhibits a bandgap of 1.10 eV, and the hydrogenation significantly enhances the bandgap to 2.70 eV. Furthermore, the hydrogenated Pt2N4 displays a strong optical absorption of up to 6.45 × 105 cm-1 in the ultraviolet region, and low absorption and low reflectivity in the visible region. Our results strongly suggest that the hydrogenated Pt2N4 has tunable electronic and optical properties for applications as a hole-transport material layer in solar cells in the visible region, and as an ultraviolet detector in the ultraviolet region of the electromagnetic spectrum.

The tesseract in two dimensional materials, a DFT approach

A series of novel two-dimensional materials inspired from a 4D polytope, tesseract, have been proposed by density functional theory (DFT) based computations. Both C24X12 and C16X16 (X = O, S and Se) are found to have great thermodynamic and dynamic stabilities, and C24X12 exhibited excellent thermal stability up to 1000 K. All these 2D crystals are semiconductors with 2.17 eV to 3.35 eV band gaps at the HSE06 theoretical level, except for C24S12 (4.14 eV energy gap). Moreover, the intrinsic pore sizes of C24Se12 are suitable to sieve He from the He/CH4 mixture, with over 80% separation ratio and nearly 100% selectivity. Our findings not only enlarged the boundary of the 2D family, but also offered another potential method to recover helium from natural gas at ambient conditions.

Symmetry-protected metallic and topological phases in penta-materials

We analyze the symmetry and topological features of a family of materials closely related to penta-graphene, derived from it by adsorption or substitution of different atoms. Our description is based on a novel approach, called topological quantum chemistry, that allows to characterize the topology of the electronic bands, based on the mapping between real and reciprocal space. In particular, by adsorption of alkaline (Li or Na) atoms we obtain a nodal line metal at room temperature, with a continuum of Dirac points around the perimeter of the Brillouin zone. This behavior is also observed in some substitutional derivatives of penta-graphene, such as penta-PC₂. Breaking of time-reversal symmetry can be achieved by the use of magnetic atoms; we study penta-MnC₂, which also presents spin-orbit coupling and reveals a Chern insulator phase. We find that for this family of materials, symmetry is the source of protection for metallic and nontrivial topological phases that can be associated to the presence of fractional band filling, spin-orbit coupling and time-reversal symmetry breaking.