Monolayer GeSe Research Articles

Thermoelectric properties of XX- and XY-stacked GeS/GeSe van der Waals heterostructures from DFT and BTP calculations.

This study utilizes density functional theory (DFT) and the Boltzmann transport equation (BTE) to investigate the structural, electronic, and thermoelectric properties of germanium sulfide (GeS) and germanium selenide (GeSe) monolayers, along with their van der Waals (vdW) heterostructures. We analyzed XX-stacked and XY-stacked configurations, where the XX configuration features direct atomic stacking, while the XY configuration exhibits staggered stacking. Our first-principles calculations indicate that the formation of GeS/GeSe heterostructures results in a reduction of bandgaps compared to their bulk and monolayer counterparts, yielding bandgap values of 0.91 eV for the XX configuration and 0.84 eV for the XY configuration. Stability assessments reveal that the XY configuration is more stable, demonstrating a lattice thermal conductivity of 15.21 W/mK compared to 17.95 W/mK for the XX configuration T 300 K. The thermoelectric properties were systematically evaluated across a temperature range of 300-800 K, revealing high Seebeck coefficients of 1.51 mV/K for the XX heterostructure and 1.39 mV/K for the XY heterostructure. reflecting their excellent charge transport capabilities. Notably, the figure of merit (ZT) at 800 K was calculated to be 0.90 for the XX configuration and 1.01 for the XY configuration, underscoring the superior thermoelectric performance of the XY heterostructure. These findings contribute to a comprehensive understanding of 2D GeS/GeSe heterostructures for thermoelectric applications and provide a solid foundation for future research and technological advancements in this domain.

Impact of van der Waals corrected functionals on monolayer GeSe polymorphs: An in-depth exploration

A comprehensive ab initio calculations were conducted to analyze the structural, electronic, elastic, and phonon characteristics of monolayer GeSe polymorphs, utilizing various van der Waals corrections. The physical properties of layered GeSe polymorphs were investigated using the Perdew-Burke-Ernzerhof exchange–correlation functional, implemented within a generalized gradient approximation. The study presents findings on the effects of the DFT-D3 and DFT-D3(BJ) functionals with Grimme correction on the ground state properties, with a focus on weak van der Waals interactions. The mechanical and dynamic stability of monolayer GeSe polymorphs is indicated by the analysis of the elastic constants and phonon dispersion curves. Monolayer GeSe polymorphs are found to have an indirect band gap semiconductor structure using HSE06 for the considered phases. The band gaps of these polymorphs are predicted to range from approximately 0.95 to 2.47 eV, which falls within a highly useful energy range for practical applications. Additionally, this study is the first to investigate the anisotropic mechanical properties of these materials.

Achieving Giant Linear Optical Response Tunability in Monolayer GeSe for Advanced Strain Sensor Applications

Achieving Giant Linear Optical Response Tunability in Monolayer GeSe for Advanced Strain Sensor Applications

Adsorption and sensing performances of greenhouse gases (CO2，CH4，SF6, N2O) on Ni modified GeSe surface

The greenhouse effect has drawn significant recent attention due to its serious impact on Earth's climate and ecosystems. Therefore, this study investigates the adsorption and sensing properties of four greenhouse gases (CH4, CO2, SF6, and N2O) on the Ni-GeSe monolayer using first principles of DFT. The doping behavior of Ni on intrinsic GeSe monolayer is initially studied and the most stable doping structure is selected. Then the adsorption energies, adsorption distances, charge transfers, energy band structures, molecular frontier orbitals and recovery times of the selected Ni-GeSe structure with the four greenhouse gases are analyzed and compared. The results show that Ni modification can improve the surface activity of the intrinsic GeSe monolayers, thereby improving their adsorption and sensing properties. Ni-GeSe has weak adsorption of CH4 and CO2, while strong chemisorption of SF6 and N2O, making it suitable as an adsorbent for these two gases. Analysis of the recycling performance of Ni-GeSe monolayers shows that Ni-GeSe has a good recovery time for N2O at a temperature of 398 K, suggesting its potential as an efficient low-power resistive N2O gas sensor. And gas sensors based on GeSe and its modified materials can be theoretically guided by these calculations.

Tailoring Dispersion Property and Anisotropy of Second-Harmonic Generation by Strain Engineering in Monolayer GeSe

Tailoring Dispersion Property and Anisotropy of Second-Harmonic Generation by Strain Engineering in Monolayer GeSe

Theoretical study of the adsorption properties of transition metal atom-doped monolayer GeSe materials for SF6 decomposition components

The insulating gas SF6 will decompose and generate a series of by-products under fault conditions, affecting the power equipment's stable operation. In this paper, the adsorption characteristics of the two-dimensional material GeSe and doped with transition metal(TM) on SF6 decomposition gases HF, CS2, and SO2F2, including adsorption energy, charge transfer, density of states, and differential charge density, are investigated based on the First-principles, and their potentials to be used as a gas-sensitive material for monitoring SF6 decomposition are analyzed based on theoretical response heights and recovery times. The results show that the doping of TM atoms enhances the adsorption capacity of GeSe materials for SF6 decomposition components, in which Co-GeSe materials can be used to monitor the production of CS2 gas molecules. In contrast, Mn-GeSe materials have a promising prospect as adsorbents for SO2F2.

First-principles study on the adsorption properties of NH3 and NO2 on different layers of GeSe

By means of density functional theory (DFT), the most stable structures of NH3 and NO2 molecules adsorbed by different layers of GeSe were studied. The adsorption properties of the adsorption system were studied from the aspects of adsorption energy, band gap, state density, differential charge density and recovery time. Significant adsorption energy (−1.060 eV, −1279 eV, −1.390 eV), charge transfer (−0.370e, −0.382e, −0.379e) and electron localization function (ELF) indicated that NO2 was chemisorbed on the surface of GeSe. The recovery time indicates that the mono-layer GeSe adsorption NO2 system can complete the desorption between 298 K and 398 K, and the bi-layer GeSe adsorption NO2 system can complete the desorption in a shorter time with the recovery time of 8.66S at the temperature of 498 K. Therefore, the theoretical research in this paper provides a theoretical basis for the development of GeSe gas sensors for the detection of harmful gases NH3 and NO2.

The Negative Differential Resistance Effect of Substitutional Doped Monolayer GeS and Its Application in Gas Sensor

The Negative Differential Resistance Effect of Substitutional Doped Monolayer GeS and Its Application in Gas Sensor

First-principles calculations of electronic, optical and thermoelectric properties of the Ge2SeS/GeSe van der Waals heterostructure

In this research, we systematically investigate the electronic structure, optical and thermoelectric properties of the Ge2SeS/GeSe van der Waals (vdW) heterostructure in comparison to the Ge2SeS and GeSe monolayers by using density functional theory (DFT) implemented in Quantum ESPRESSO. We have constructed two configurations of the Ge2SeS/GeSe heterostructure by stacking the Ge2SeS monolayer on top of the GeSe monolayer (Stacking A1 and A2). According to our calculations, the calculated indirect electronic band gaps of both Stacking A1 and Stacking A2 are Eg = 0.80 eV and 0.88 eV, respectively. The transfer of charges from the Ge2SeS to the GeSe monolayer for both configurations has been predicted. By Bader charge analysis, the charge transfers for Stacking A1 and A2 are approximately 0.013 e and 0.020 e, respectively. The coefficient of absorption for the Ge2SeS/GeSe heterostructure is higher than that for Ge2SeS and GeSe monolayers in both regions of the spectrum (visible, and UV). Moreover, the Ge2SeS/GeSe heterostructure has a very good absorbing capability of light in the visible region up to 85 × 104 cm−1. Our calculations yielded a high thermoelectrical electronic figure of merit (ZTe) of 12.64 and 2.27 for Stacking A1 and A2, respectively. As a result, our findings show that the Ge2SeS/GeSe heterostructure is a promising material for thermoelectric and optoelectronic applications.

Thermoelectric properties of undoped and Bi-doped GeS monolayers: A first-principles study

Different from the extensive experimental investigations into the thermoelectric (TE) properties of the bulk IV–VI compounds, less attention has been paid to the TE properties of the monolayer IV–VI compounds. Here, we consider the TE transport properties including the Seebeck coefficient, electronic conductance, thermal conductance, power factor, and figure of merit ZT of the undoped and Bi-doped GeS monolayers. Our results show that for both the undoped and Bi-doped monolayers the anisotropy is widely observed in all their TE properties, and the maximum ZT at a certain temperature along the armchair direction is much greater than that along the zigzag direction. Moreover, Bi doping can lead to an increase of the maximum ZT, and there are more ZT peaks appearing near the zero chemical potential. This indicates that the Bi-doped GeS monolayer can work as a TE material at a lower bias voltage, and especially along the armchair direction it can work at zero bias voltage, which obviously strengthens the reliability of the TE devices. As the temperature increases, the maximum ZT will be uniformally increased along the armchair and zigzag directions for both the undoped and Bi-doped GeS monolayers. In the temperature scope from 300 to 800 K, the maximum ZT along the armchair direction of the Bi-doped GeS monolayer will increase from 3.39 to 4.85, which indicates that this Bi-doped GeS monolayer is a promising TE material in a wide-temperature zone. As an application, we have designed the GeS-based TE couples and found that their efficiencies can be greater than 27% at large temperature differences. This research should be an important guidance for designing a low-voltage, wide-temperature-scope, and high-stability TE device.

Adsorption behavior of CuO doped GeS monolayer on the thermal runaway gas evolution in lithium battery energy storage systems

Considering that the thermal runaway failure of lithium battery energy storage system will cause serious safety accidents, and lithium battery thermal runaway will precipitate various detectable gases through the safety gas valve. Effective monitoring of the precipitated gas can ensure the safe operation of the energy storage system. In this study, the adsorption behavior of CuO-GeS towards the main precipitated gases CO, CO2, CH4, and C2H4 in Lithium battery before thermal runaway is systematically studied based on DFT. The adsorption structure, DOS, DCD, and ELF are analyzed to explore the interactions between CuO-GeS monolayer and the gases. The results show that CuO-GeS monolayer achieves strong adsorption of CO and C2H4 and highly sensitive monitoring of CO2 and CH4. Furthermore, the relative molecular mass ratios of CxHy and CxHy-1F (x = 1, 2 y=2, 4, 6) gases to doped CuO can satisfy Smoothing Spline with adsorption energy and charge transfer, which can be used to estimate the adsorption properties of the homologous gases. The potential application of CuO-GeS monolayer in lithium battery energy storage systems lays a theoretical research foundation for the adsorption and detection of thermal runaway gas in lithium battery energy storage systems.

Realization of the Tunable Multivalley System in a GeSe Monolayer by Atomic Substitution

Realization of the Tunable Multivalley System in a GeSe Monolayer by Atomic Substitution

Quantifying the photocurrent fluctuation in quantum materials by shot noise

The DC photocurrent can detect the topology and geometry of quantum materials without inversion symmetry. Herein, we propose that the DC shot noise (DSN), as the fluctuation of photocurrent operator, can also be a diagnostic of quantum materials. Particularly, we develop the quantum theory for DSNs in gapped systems and identify the shift and injection DSNs by dividing the second-order photocurrent operator into off-diagonal and diagonal contributions, respectively. Remarkably, we find that the DSNs can not be forbidden by inversion symmetry, while the constraint from time-reversal symmetry depends on the polarization of light. Furthermore, we show that the DSNs also encode the geometrical information of Bloch electrons, such as the Berry curvature and the quantum metric. Finally, guided by symmetry, we apply our theory to evaluate the DSNs in monolayer GeS and bilayer MoS2 with and without inversion symmetry and find that the DSNs can be larger in centrosymmetric phase.

Adsorption Behavior of Dissolved Gas Molecules in Transformer Oil on Rh Modified GeSe Monolayer.

Dissolved gas analysis in transformer oil is useful for detecting early transformer failures. The research on gas sensors for monitoring dissolved gas in transformer oil has attracted wide attention from academia and industry. In this study, Rh-doped GeSe monolayers were used as gas sensing materials based on the density functional theory (DFT). The potential of the Rh-GeSe monolayer as a gas sensor was evaluated by calculating the geometric structure, adsorption distance (dsub/gas), binding energy (Eb), adsorption energy (Eads), transfer charge (ΔQ), the density of states (DOS), band structure, electron localization function (ELF), charge difference density (CDD), and sensitivity (S) of Rh-GeSe monolayer with eight gas molecules (SO2, C2H2, NO2, H2, CH4, CO2, H2S, and CO). The results show that the Rh-GeSe monolayer has a prominent response to SO2, C2H2, and NO2 gas molecules and has great potential to become an excellent gas sensor. This study provides a theoretical basis for the application of Rh-GeSe monolayer in the field of gas sensing and provides a new way for the development of other gas sensors.

Atomic and electronic structure of monolayer ferroelectric GeS on Cu(111)

Two-dimensional (2D) ferroelectric materials are important materials for both fundamental properties and potential applications. Especially, group Ⅳ monochalcogenide possesses highest thermoelectric performance and intrinsic ferroelectric polarization properties and can sever as a model to explore ferroelectric polarization properties. However, due to the relatively large exfoliation energy, the creation of high-quality and large-size monolayer group Ⅳ monochalcogenide is not so easy, which seriously hinders the integration of these materials into the fast-developing field of 2D materials and their heterostructures. Herein, monolayer GeS is successfully fabricated on Cu(111) substrate by molecular beam epitaxy method, and the lattice structure and the electronic band structure of monolayer GeS are systematically characterized by high-resolution scanning tunneling microscopy, low-energy electron diffraction, <i>in-situ</i> X-ray photoelectron spectroscopy, Raman spectra, and angle-resolved photoelectron spectroscopy, and density functional theory calculations. All atomically resolved STM images reveal that the obtained monolayer GeS has an orthogonal lattice structure, which consists with theoretical prediction. Meanwhile, the distinct moiré pattern formed between monolayer GeS and Cu(111) substrate also confirms the orthogonal lattice structure. In order to examine the chemical composition and valence state of as-prepared monolayer GeS, <i>in-situ</i> XPS is utilized without being exposed to air. The measured spectra of XPS core levels suggest that the valence states of Ge and S elements are identified to be +2 and –2, respectively and the atomic ratio of Ge/S is 1∶1.5, which is extremely close to the stoichiometric ratio of 1∶1 for GeS. To further corroborate the quality and lattice structure of the monolayer GeS film, <i>ex-situ</i> Raman measurements are also performed for monolayer GeS on highly oriented pyrolytic graphene (HOPG) and multilayer graphene substrate. Three well-defined typical characteristic Raman peaks of GeS are observed. Finally, <i>in-situ</i> ARPES measurement are conducted to determine the electronic band structure of monolayer GeS on Cu(111). The results demonstrate that the monolayer GeS has a nearly flat band electronic band structure, consistent with our density functional theory calculation. The realization and investigation of the monolayer GeS extend the scope of 2D ferroelectric materials and make it possible to prepare high quality and large size monolayer group Ⅳ monochalcogenides, which is beneficial to the application of this main group material to the rapidly developing 2D ferroelectric materials and heterojunction research.

First principles study of high-performance sub-5-nm monolayer SnS field-effect transistors

<sec>Currently, Si-based field-effect transistors (FET) are approaching their physical limit and challenging Moore's law due to their short-channel effect, and further reducing their gate length to the sub-10 nm is extremely difficult. Two-dimensional (2D) layered semiconductors with atom-scale uniform thickness and no dangling bonds on the interface are considered potential channel materials to support further miniaturization and integrated electronics. Wu et al. [Wu F, et al. 2022 <i>Nature</i> <b>603</b> 259] successfully fabricated an FET with gate length less than 1 nm by using atomically thin molybdenum disulfide with excellent device performance. This breakthrough has greatly encouraged further theoretical predictions regarding the performance of 2D devices. Additionally, 2D SnS has high carrier mobility, anisotropic electronic properties, and is stable under ambient condition, which is conducive to advanced applications in 2D semiconductor technology. Herein, we explore the quantum transport properties of sub-5 nm monolayer (ML) SnS FET by using first-principles quantum transport simulation. Considering the anisotropic electronic SnS, the double-gated-two-probe device model is constructed along the armchair direction and the zigzag direction of ML SnS. After testing five kinds of doping concentrations, a doping concentration of 5×10<sup>13</sup> cm<sup>−2</sup> is the best one for SnS FET. We also use the underlaps (ULs) with lengths of 0, 2, and 4 nm to improve the device performance. On-state current (<i>I</i><sub>on</sub>) is an important parameter for evaluating the transition speed of a logic device. A higher <i>I</i><sub>on</sub> of a device can help to increase the switching speed of high-performance (HP) servers. The main conclusions are drawn as follows.</sec><sec>1) <i>I</i><sub>on</sub> values of the <i>n</i>-type 2 nm (UL = 4 armchair), 3 nm (UL = 2), 4 nm (UL = 3), 5 nm (UL = 0) and the <i>p</i>-type 1 nm (UL = 2 zigzag), 2 nm (UL = 2 zigzag), 3 nm (UL = 2,4 zigzag), 4 nm (UL = 2,4 zigzag), and 5 nm (UL = 0, armchair/zigzag) gate-length devices can meet the standards for HP applications in the next decade in the International Technology Roadmap for semiconductors (ITRS, 2013 version).</sec><sec>2) <i>I</i><sub>on</sub> values of the n-type device along the armchair direction (31-2369μA/μm) are larger thanthose in the zigzag direction (4.04-1943μA/μm), while <i>I</i><sub>on</sub> values of the <i>p</i>-type along the zigzag direction (545-4119μA/μm) are larger than those in the armchair direction (0.7-924μA/μm). Therefore, the <i>p</i>-type ML GeSe MOSFETs have a predominantly anisotropic current.</sec><sec>3) <i>I</i><sub>on</sub> value of the <i>p</i>-type 3 nm gate-length (UL = 0) device along the zigzag direction has the highest value 4119 μA/μm, which is 2.93 times larger than that in the same gate-length UL = 2 (1407μA/μm). Hence, an overlong UL will weaken the performance of the device because the gate of the device cannot well control the UL region. Thus, a suitable length of UL for FET is very important.</sec><sec>4) Remarkably, <i>I</i><sub>on</sub> values of the <i>p</i>-type devices (zigzag), even with a gate-length of 1 nm, can meet the requirements of HP applications in the ITRS for the next decade, with a value as high as 1934 μA/μm. To our knowledge, this is the best-performing device material reported at a gate length of 1 nm.</sec><sec>5) Subthreshold swing (SS) evaluates the control ability of the gate in the subthreshold region. The better the gate control, the smaller the SS of the device is. The limit of SS for traditional FETs is 60 mV/dec (at room temperature). Values of SS for ML SnS FET alone zigzag direction are less than those along the armchair direction because the leakage current is influenced by the effective mass.</sec>

Promising transport properties of multifunctional monolayer GeSe nanodevices

In this study, we conducted a thorough investigation of the transport characteristics of thermoelectric devices, p–n junction diodes, and p–i–n homojunction phototransistors based on monolayer (ML) GeSe.

Gas Sensing Properties of Pd-Decorated GeSe Monolayer toward Formaldehyde and Benzene Molecules: A First-Principles Study.

In this study, the gas sensing properties of formaldehyde (HCHO) and benzene (C6H6) adsorbed on two-dimensional (2D) pristine GeSe and Pd-decorated GeSe (Pd-GeSe) monolayers are studied by using first-principles calculations. The adsorption energies, electronic properties, optical properties, sensitivity, and recovery time of the gas adsorption systems have been thoroughly investigated. It is found that the adsorption of C6H6 on two substrate surfaces and the adsorption of HCHO on pristine GeSe are examples of physical adsorption. However, after HCHO adsorption on the Pd-GeSe monolayer, the adsorption system exhibits an increased adsorption energy of -1.21 eV, which is more favorable compared with the other adsorption systems studied. Moreover, the electron localization function and charge transfer from Pd-GeSe to HCHO are significantly enhanced, indicating distinct chemical adsorption behavior. Furthermore, it demonstrates a larger band gap change rate of 18.8% and a significant enhancement of optical absorption upon the adsorption of HCHO on the Pd-GeSe monolayer. Additionally, the appropriate sensitivity and moderate recovery time for the adsorption of HCHO on the Pd-GeSe surface indicate that the Pd-GeSe monolayer possesses an outstanding sensing capability for HCHO gas.

Modulation of magnetic and optical properties for GeS monolayer

The layered structure of GeS exhibits commendable thermal stability and holds significant promise in the realms of optoelectronics and ion batteries. But its application is limited as dilute magnetic semiconductor. Therefore, this study delves into the impact of 3d transition metal (TM = V, Cr, and Mn) doping on the magnetic and optical characteristics of two-dimensional GeS monolayer through a first-principles calculation method grounded in density functional theory. The findings elucidate that all doping systems lead to a reduction in the band gap, with the V-doped system exhibiting the most significant diminishment. After doping process, magnetic coupling emerges between the electrons in the TM-3d state and those in the S-3p state, resulting in the manifestation of magnetic semiconductor characterized by magnetic moments of 3 μB, 4 μB, and 5 μB, respectively. Comparative analysis with the pristine GeS monolayer, it reveals enhancements in optical absorptivity and refractive index within both the infrared and visible spectra of the doped systems. Notably, the V-doped system showcases superior optical properties due to its narrower band gap, facilitating more efficient electron transitions to the conduction band. Consequently, TM (TM = V, Cr, and Mn)-doped GeS monolayer hold promising potential in the realms of spintronics and optoelectronics.

Blue phosphorus phase GeSe monolayer for nitrogenous toxic gas sensing: A DFT study

Continuing industrialization, a variety of toxic gases are emitted into the air, yet gas concentrations at low levels are extremely hard to detect. So the development of high-performance toxic gas sensors is imminent. Two-dimensional materials with advantages such as large specific surface area and unique electronic properties open new paths for gas sensors. In this study, a monolayer of blue phosphorus phase germanium selenide (GeSe) was used as the substrate material. The absorption performance of ambient nitrogenous toxic gases (NO, NO2, NH3, N2O) on the surface of GeSe monolayers was explored by the density-functional theory (DFT) calculations. The results show that the interaction between GeSe and the four gases exhibits physisorption. Based on four optimal adsorption structures, Bader charge, work function, band structure, density of states, and recovery time were calculated. Charge transfer is promoted due to the presence of GeSe intrinsic dipoles and only NH3 was found to be the charge donor. The significant changes in work function and electronic properties of GeSe monolayer adsorption of NO indicate significant changes in electrical signals during gas detection. This work reveals that GeSe monolayer has higher sensitivity and selectivity for NO hazardous gas.