Monolayer GeSe Research Articles

Thermal transport properties of monolayer GeS and SnS: A comparative study based on machine learning and SW interatomic potential models

Phonon transport properties of two-dimensional materials can play a crucial role in the thermal management of low-dimensional electronic devices and thermoelectric applications. In this study, both the empirical Stillinger–Weber (SW) and machine learning interatomic potentials are employed to investigate the lattice thermal conductivity of monolayer GeS and SnS through solving the phonon Boltzmann transport equation. The accuracy of the two types of interatomic potentials and their performance for the evaluation of thermal conductivity are verified by analyzing phonon harmonic and anharmonic properties. Our results indicate that the thermal conductivity can be predicted more accurately with a machine learning approach, while the SW potential gives rise to an overestimated value for both monolayers. In addition, the in-plane anisotropy of thermal transport properties existing in these monolayers can be confirmed by both potential models. Moreover, the origins of the deviation existing in calculated thermal conductivities, including both the effects of interatomic potential models and monolayer compositions, are elucidated through uncovering the underlying phonon transport mechanisms. This study highlights that in contrast to the machine learning approach, more careful verification is required for the simulation of thermal transport properties when empirical interatomic potential models are employed.

Gas adsorption effects of monolayer GeSe in terms of anisotropic transport properties

Two-dimensional layered semiconducting material germanium selenide (GeSe) has attracted significant attention due to its environmental friendship, anisotropic electronic structures, and strong air-stability. To evaluate the candidacy of monolayer GeSe as a potential gas sensing material, the adsorption characteristics of various small gas molecules on monolayer GeSe are comprehensively studied combining density functional theory calculations and non-equilibrium Green’s function formalism. The charge transfer reaction between gas molecules and monolayer GeSe leads to the marked change of the carrier density, which further affects the anisotropic transport characteristics of monolayer GeSe. The calculated band structures and I–V curves reveal distinctive responses of monolayer GeSe to the different gas molecules, and higher sensitivity of the monolayer GeSe in presence of SO2, NH3, NO2 gas molecules along the zigzag direction is obtained. These results suggest that monolayer GeSe along the zigzag direction has promising application in gas detector.

Tuneable Poisson’s ratio of monolayer GeS and Ge2SSe

A tuneable Poisson’s ratio is desirable to extend the applications of 2D materials. We demonstrate that Poisson’s ratio of monolayer GeS depends approximately linear on the applied strain and electric field strength. In contrast, monolayer Ge2SSe is subject to abrupt switching between positive and negative values (sign reversal) at particular critical values of the strain and electric field strength. The tuneability of Poisson’s ratio is attributed to the interplay of different bending stiffnesses. A structural transition is identified as origin of the sign reversal in the case of monolayer Ge2SSe.

Theoretical Exploration of C4F7N Decompositions on GeSe Monolayers for Gas Sensing Based on DFT Method

On account of its superior insulating performance and low global warming potential (GWP), C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N has been the focus of replacing SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> . Based on density functional theory, the adsorption mechanism and electrical characteristics of GeSe monolayer towards C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> N decomposition species (COF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> CN and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> CN) are explored to investigate the feasibility of GeSe gas sensors. Compared with other decomposition products, GeSe monolayers are more capable of capturing for C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> CN, as evidenced by the smallest band gap (0.781 eV) and the highest adsorption energy (−0.427 eV). The adsorption behaviors lead to a larger GeSe band gap and thus a decrease in the conductivity of the adsorption system. The adsorption types of GeSe for four gases are all physical adsorption and can have good desorption properties at room temperature (298 K) with the adsorption capabilities: C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> CN>CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> CN>COF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> >CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> . Theoretically, GeSe monolayers can be used to create a novel gas sensor for and industrial application, which can be utilized to monitor and diagnose high-voltage insulated equipment in real time.

Novel Gas-Sensitive Material for Monitoring the Status of SF6 Gas-Insulated Switches: Gese Monolayer

Detecting the decomposition components of SF6 insulating gas is recognized as an effective means to monitor the operating status of the SF6 insulating switch. In this paper, the adsorption characteristics of a new two-dimensional material GeSe for five SF6 decomposition gases (SO2, SOF2, SO2F2, H2S and HF) are reported by first-principles simulation. Through the analysis of the change of energy band structure, density of states distribution, and gas desorption time, it is found that GeSe has the potential as a gas-sensitive material for the selective detection of SO2F2, and the computational work in this paper provides theoretical guidance for the development of new gas-sensitive sensors applied in monitoring SF6 insulated switches.

The electronic properties and adsorption mechanism of Agn, Aun (n = 1–4) modified GeSe monolayer towards hazardous gases (H2S, NH3, NO2 and SOF2): A first-principles study

In this study, the first-principles were adopted to investigate adsorption behaviour and electrical properties of Agn, Aun (n = 1–4) modified GeSe monolayer towards hazardous gases (H2S, NH3, NO2, SOF2). The contributions of transition metal nanoparticles to the surface modification and gas adsorption behaviour of the two-dimensional material GeSe were analysed. We have studied the adsorption and sensing properties between the target gas molecules and GeSe substrate through the analysis of the adsorption energy, charge transfer, differential charge density, and density of states. In order to better simulate the mixture under the pragmatic doping situation, the number of gold and silver nanoparticles doped in this study ranged from 1 to 4, meanwhile the most stable computational structures were selected based on the binding energy. The results show that Agn, Aun cluster modifications can improve the electrical conductivity of GeSe monolayer, and the vibrant sites provided by the dopants significantly enhance the gas-sensitive response of the pristine GeSe to these hazardous gases. The adsorption type changes from initial non-spontaneous reactions to physico chemical adsorption, and the ideal adsorption energy make the doped system possess good adsorption and desorption properties. In addition, compared with peaceable interreaction of SOF2 adsorption system, Agn, Aun-GeSe has strong capturing ability for NO2. The results provide a theoretical basis for further manufacture of industrial toxic gas sensors and online monitoring of SF6 insulated equipment.

The quantum confinement effects on the electronic properties of monolayer GeS nanoribbon with tube-edged reconstruction

Monolayer α-phase GeS is promising for many novel applications due to its high carrier mobility and suitable band gap. Recently, the metal and nonmetal zigzag edges of monolayer α-phase GeS have been predicted to undergo universal ZZ(Ge-Tube)/ZZ(S-R) edge reconstruction. Therefore, studies on GeSNR should be reconsidered. In this paper, we study the quantum confinement effects on the electronic properties of edge reconstructed monolayer GeS nanoribbon (GeSNR) by using first-principles calculations. As width of the nanoribbon increases from 10 to 41 Å, the band gap keeps indirect and linearly decreases from 1.57 to 0.87 eV. Robust spatial separation of valence band maximum and conduction band minimum exist in reconstructed GeSNR with width larger than 19 Å. Moreover, high carrier mobility is expected in the reconstructed GeSNR. Our results suggest that reconstructed GeS nanoribbon is an important candidate for optoelectronics and photocatalytic.

Gas-Sensing Properties of Dissolved Gases in Insulating Material Adsorbed on SnO2–GeSe Monolayer

In a transformer, the insulation materials will produce different dissolved gases due to various faults in the operation of the transformer, in which C2H2, CH4, and H2 are the main dissolved gases. In this study, the adsorption characteristics of the above three gases on the SnO2–GeSe monolayer surface were discussed and analyzed based on the density functional theory. The adsorption energy, transfer charge, geometric structure parameters, electronic density of states, electronic local function, charge difference density, and recovery time were calculated and compared to characterize the gas-sensing adsorption mechanism. The results showed that the SnO2–GeSe monolayer exhibited good adsorption capacity, selectivity, and repeatability for the three characteristic dissolved gases. After adsorbing CH4 gas molecules, the conductivity of the SnO2–GeSe monolayer decreased. After adsorbing C2H2 and H2 gas molecules, the conductivity of the SnO2–GeSe monolayer increased. Therefore, the SnO2–GeSe monolayer has great application potential in the real-time monitoring of dissolved gases in insulating materials, which may become a new type of resistive gas sensor.

Monitoring Gases Content in Modern Agriculture: A Density Functional Theory Study of the Adsorption Behavior and Sensing Properties of CO2 on MoS2 Doped GeSe Monolayer.

The reasonable allocation and control of CO2 concentration in a greenhouse are very important for the optimal growth of crops. In this study, based on density functional theory (DFT), an MoS2–GeSe monolayer was proposed to unravel the issues of the lower selectivity, poorer sensitivity and non-recyclability of traditional nanomaterial gas sensors. The incorporation of MoS2 units greatly enhanced the sensitivity of the pure GeSe monolayer to CO2 and the high binding energy also demonstrated the thermal stability of the doped structures. The ideal adsorption energy, charge transfer and recovery time ensured that the MoS2–GeSe monolayer had a good adsorption and desorption ability. This paper aimed to solve the matter of recycling sensors within agriculture. This research could provide the theoretical basis for the establishment of a potentially new generation of gas sensors for the monitoring of crop growth.

Adsorption behavior of metal oxides (CuO, NiO, Ag2O) modified GeSe monolayer towards dissolved gases (CO, CH4, C2H2, C2H4) in transformer oil

In this study, the adsorption behavior of CuO-GeSe, NiO-GeSe, and Ag2O-GeSe towards the main dissolved gases CO, CH4, C2H2, and C2H4 in transformer oil was systematically studied based on DFT. The adsorption structure, band structure, density of states, deformation charge density, and molecular orbit were analyzed to explore the interaction between the modified monolayers and gases. The results show that the adsorption of the four target gases on pristine GeSe belongs to weak physical adsorption. Metal oxides modification improves the conductivity of GeSe, and the formation of numerous triangular structures makes the modified substrates hard to deform during gas adsorption. Due to the poor gas sensitivity and extremely short recovery time of CH4 on CuO-GeSe, NiO-GeSe, and Ag2O-GeSe, these three modified structures are not suitable to be used as a material for detecting CH4. The conductivity of MO-GeSe changes in different degrees after adsorbing CO, C2H2, and C2H4. The gases can be detected according to the different change rule of conductivity upon adsorption. In addition, gas desorption from the substrate can be achieved by controlling the temperature. This study provides a theoretical basis for the application of gas sensors used in DGA.

Flexoelectric effect induced p–n homojunction in monolayer GeSe

Recently, two-dimensional in-plane ferroelectric materials group-IV monochalcogenides MX (M = Ge, Sn; X = S, Se) have attracted much attention due to their rich physical properties. Here, we study the flexoelectric effect on the electronic, optical and transport properties in the monolayer germanium selenide (GeSe). We found that bending along the armchair (polarization) direction can separate the highest occupied molecular orbital and the lowest unoccupied molecular orbital in the real space and form the type-II band alignment, which can be used to fabricate p–n homojunctions. This outstanding property hints the potential applications of the bending monolayer GeSe for the exciton transport and solar cell, and provides new routines for advanced two-dimensional semiconductor devices.

Device simulation of GeSe homojunction and vdW GeSe/GeTe heterojunction TFETs for high-performance application

Compared with a two-dimensional (2D) homogeneous channel, the introduction of a 2D/2D homojunction or heterojunction is a promising method to improve the performance of a tunnel field-effect transistor (TFET), mainly by controlling the tunneling barrier. We simulate 10-nm-Lg double-gated GeSe homojunction TFETs and van der Waals (vdW) GeSe/GeTe heterojunction TFETs based on a ballistic quasi-static ab initio quantum transport simulation. Two device configurations are considered for both the homojunction and heterojunction TFETs by placing the bilayer (BL) GeSe or vdW GeSe/GeTe heterojunction as the source or drain, while the channel and the remaining drain or source use monolayer (ML) GeSe. The on-state current (Ion) values of the optimal n-type BL GeSe source homojunction TFET and the optimal p-type vdW GeSe/GeTe drain heterojunction TFET are 2320 and 2387 μA μm−1, respectively, which are 50% and 64% larger than Ion of the ML GeSe homogeneous TFET. Notably, the device performance (Ion, intrinsic delay time τ, and power dissipation PDP) of both the optimal n-type GeSe homojunction and p-type vdW GeSe/GeTe heterojunction TFETs meets the requirements of the International Roadmap for Devices and Systems for high-performance devices for the year 2034 (2020 version).

Batch active learning for accelerating the development of interatomic potentials

Classical molecular dynamics (MD) has been widely used to study atomistic mechanisms and emergent behavior in materials at length and time scales beyond the capabilities of first-principles approaches. The success of classical MD simulations relies on the ability of classical interatomic potentials to accurately map complex many-body interacting systems of electrons and nuclei into effective few-body interacting systems of atoms. In practice, the development of interatomic potentials is a nontrivial process and requires considerable amount of effort. Recently, machine learning has become a promising approach to accelerate interatomic potential development. However, these machine learning approaches are often computation and data intense, as they require a large amount of training data from first-principles calculations, such as total energies, atomic forces, and stress tensors of many atomistic structures. Here we propose an active learning approach combined with first-principles theory calculations to expedite the development of machine learning interatomic potentials. In particular, we develop a batch active learning method which combines both energy uncertainty and structure similarity metrics to efficiently sample the highly uncertain structures that are difficult to predict. This active sampling approach maximizes the utility of the dataset in each batch and generates interatomic potential with highly accurate and robust model coefficients which are difficult to achieve with conventional sampling approaches. To demonstrate this batch active learning method, we develop an active learning potential for monolayer GeSe, a two-dimensional ferroelectric-ferroelastic material, and compare the quality and robustness of the active learning potential with the potential obtained from random sampling. Batch active learning method opens up avenues for accelerating the development of robust and accurate machine learning potential using a small set of atomistic structures which will be valuable for computational materials, physics, and chemistry community.

Theoretical Study of Small Molecules Adsorption on Pristine and Transition Metal Doped GeSe Monolayer for Gas Sensing Application.

By using first-principles calculations, the sensing properties of pristine and transition metal (TM) atoms (Ti, V, and Co) embedded germanium selenide (GeSe) monolayer toward small gas molecules (H2, NH3, CO, O2, SO2, NO, and NO2) were investigated. The adsorption energies, electronic structure, optical properties, and recovery time of the adsorption systems were calculated and analyzed in detail. The results indicate that TM doped GeSe has stronger interaction with gas molecules compared with the pristine GeSe monolayer. Especially for Ti- and V-GeSe monolayer, the absolute value of adsorption energies are up to 2 eV for O2, NO, and NO2. The doping with TM atoms also changes the charge transfer and electronic structures of adsorption systems. Combined with the result of the calculated optical properties and recovery time, it can be concluded that Ti-GeSe monolayer has great potential for NH3 detection, while Co-GeSe monolayer can be very promising SO2 gas sensors.

Manipulating the Electronic Properties of Gas-Adsorbed Monolayer GeSe by External Electric Field

Manipulating the Electronic Properties of Gas-Adsorbed Monolayer GeSe by External Electric Field

Near-field thermal radiation of germanium selenide single layer

Recently, the two-dimensional (2D) material germanium selenide (GeSe) was shown to possess extraordinary physicochemical properties as well as great potential for electrical and optical applications, whereas its thermal radiative properties remain elusive. Here, we present a comprehensive study of the near-field thermal radiation (NFTR) of monolayer GeSe by means of fluctuational electrodynamics theory. It is shown that, at a small vacuum gap, such a 2D semiconductor not only supports a giant heat flux that surpasses the black-body limit by four orders of magnitude but is also far ahead of graphene with the same electron density. This extraordinary thermal radiation is attributed to the strong quasi-elliptic surface plasmon polaritons supported by the monolayer GeSe at near- and midinfrared frequency regions. In addition, we show how electron density affects the NFTR of monolayer GeSe, where the effect can be switched from suppression to enhancement by elevating the vacuum gap. Furthermore, we investigate the possibility of using mechanical rotation to modulate the NFTR. We find that, at a lower electron density, the NFTR of the monolayer GeSe could be more effectively modulated through mechanical rotation. Finally, we investigate the interference effect of the dielectric substrate on the NFTR, pointing out the nonmonotonic dependency between its thermal radiation and the dielectric constant of substrate. All in all, in this paper, we provide a fundamental understanding of the NFTR in GeSe single layer and offer guidance for further research and modulation in emerging energy conversion and thermal management.

Metal Oxide Nanoparticles (XO, X = Cu, Zn, Ni) Doped GeSe Monolayer: Theoretical Exploration of a Novel H2S Gas Sensor for Health and Industrial Monitoring

Real-time and accurate detection of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S has been an urgent problem in industry and human health. In view of practical problems of the existing nano sensors such as poor selectivity, low sensitivity, strong or weak adsorption capacity, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S sensors based on metal oxide nanoparticles (XO, X = Cu, Zn, Ni) doped GeSe monolayer are proposed. Compared with pure system, the improvement of the adsorption distance of doped systems proves the obvious interaction between the activated atoms and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S. The excellent sensitivity ensures the detection effect of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S at low concentration. The ideal adsorption energy makes doped systems have attractive adsorption and desorption properties. In addition, the excellent water resistance, high thermal stability and fascinating selectivity to H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S of doped systems verify the feasibility in practical application. This study lays a theoretical foundation for the development of new generation of wearable gas sensor for health and industrial monitoring.

Effect of Point Defects on Electronic Structure of Monolayer GeS.

Using density functional theory calculations, atomic and electronic structure of defects in monolayer GeS were investigated by focusing on the effects of vacancies and substitutional atoms. We chose group IV or chalcogen elements as substitutional ones, which substitute for Ge or S in GeS. It was found that the bandgap of GeS with substitutional atoms is close to that of pristine GeS, while the bandgap of GeS with Ge or S vacancies was smaller than that of pristine GeS. In terms of formation energy, monolayer GeS with Ge vacancies is more stable than that with S vacancies, and notably GeS with Ge substituted with Sn is most favorable within the range of chemical potential considered. Defects affect the piezoelectric properties depending on vacancies or substitutional atoms. Especially, GeS with substitutional atoms has almost the same piezoelectric stress coefficients as pristine GeS while having lower piezoelectric strain coefficients but still much higher than other 2D materials. It is therefore concluded that Sn can effectively heal Ge vacancy in GeS, keeping high piezoelectric strain coefficients.

Surface doping of nonmetal atoms enhances photocatalytic performance of monolayer GeSe for degradation of organic pollution

In this work, using first principles study, we report the structure, formation energy, electronic, optical and photocatalytic properties of a series of nonmetal atoms doped monolayer GeSe. O doped GeSe have the lowest formation energy (-1.73 eV). H, F, Cl, Br and I doped GeSe can absorb almost all sunlight. H and F doping reduced the photogenerated charge carrier recombination rate of GeSe by 1.28 and 1.84 times, respectively. H, F, Cl, Br and I doping enhances the oxidizability of photogenerated holes by more than 1.14 eV. This work provides an important guidance to design more efficient GeSe-based photocatalyst.

Optoelectronic and photocatalytic properties of GaN, GeS and SiS monolayers and their vdW heterostructures

Using first principles calculations the optoelectronic and photocatalytic properties of GaN, GeS, SiS monolayers, and GaN-GeS/SiS, GeS-SiS van der Waals (vdW) heterostructures are studied for the first time. Initially, it is confirmed that all monolayers and their vdW heterostructures are stable in energy and phonon vibrations, respectively. GaN, GeS, and SiS monolayers are found an indirect energy gap semiconductor with energy gap values are 2.17, 2.25, 2.17 eV, respectively. Type-II band alignment has been observed in GaN-GeS/SiS and GeS-SiS vdW heterostructures which represent application into photovoltaic and energy harvesting devices. Furthermore, charge transfer at the interface of GaN-GeS/SiS and GeS-SiS vdW heterostructures generates an inbuilt electric field which in turn pushing electrons and holes in opposite direction, this can avoid recombination of photogenerated electron-hole pairs. Charge carrier separation inside the materials is the prime criteria for optoelectronic and photocatalytic applications. Upgraded optical features of vdW heterostructures reveal their remarkable absorption of visible light which hold promise for future high-performance photocatalysts and optical devices. Moreover, the suitable band edge positions of GaN, GeS, SiS monolayers, and GaN-GeS/SiS, GeS-SiS van der Waals (vdW) heterostructures relative to the standard electrode potentials at PH = 0, indicates that these materials can be used as a photocatalyst.