Lateral and flexural thermal transport in stanene/2D-SiC van der Waals heterostructure

Phonon transport in vacancy induced defective stanene/hBN van der Waals heterostructure

In this study, Non-Equilibrium Molecular Dynamics (NEMD) simulation is employed to investigate the phonon thermal conductivity (PTC) of Sn/hBN van der Waals heterostructures with different vacancy-induced defects. We deliberately introduce three types of vacancies in Sn/hBN bilayer point vacancies, bivacancies, and edge vacancies at various concentrations ranging from 0.25% to 2%, to examine their effects on PTC across temperatures from 100 K to 600 K. The key findings of our work are (i) PTC declines monotonically with increasing vacancy concentration for all types of vacancies, with a maximum reduction of ∼62% observed at room temperature compared to its pristine form. (ii) The position of defects has an impact on PTC, with a larger decrease observed when defects are present in the hBN layer and a smaller decrease when defects are in the Sn layer. (iii) The type of vacancy also influences PTC, with point vacancies causing the most substantial reduction, followed by bivacancies, and edge vacancies having the least effect. A 2% defect concentration results in a ∼62% decrease in PTC for point vacancies, ∼51% for bivacancies, and ∼32% for edge vacancies. (iv) Finally, our results indicate that for a given defect concentration, PTC decreases as temperature increases. The impact of temperature on thermal conductivity is less pronounced compared to the effect of vacancies for the defective Sn/hBN bilayer. The presence of vacancies and elevated temperatures enhance phonon-defect and phonon-phonon scattering, leading to changes in the phonon density of states (PDOS) profile and the distribution of phonons across different frequencies of Sn/hBN bilayer, thus affecting its thermal conductivity. This work offers new insights into the thermal behavior of vacancy-filled Sn/hBN heterostructures, suggesting potential pathways for modulating thermal conductivity in bilayer van der Waals heterostructures for applications in thermoelectric, optoelectronics, and nanoelectronics in future.

Crucial role of interfacial interaction in 2D polar SiGe/GeC heterostructures

The planar charge transfer is a distinctive characteristic of the two-dimensional (2D) polar materials. When such 2D polar materials are involved in vertical heterostructures (VHs), in addition to the van der Waals (vdW) interlayer interaction, the interfacial interaction triggered by the in-plane charge transfer will play a crucial role. To deeply understand such mechanism, we conducted a comprehensive theoretical study focusing on the structural stability and electronic properties of 2D polar VHs built by commensurate SiGe/GeC bilayers with four species ordering patterns (classified as a C-group with patterns I and II and a Ge-group with patterns III and IV, respectively). It was found that the commensurate SiGe/GeC VHs are mainly stabilized by interfacial interactions (including the electrostatic interlayer bonding, the vdW force, as well as thesp2/sp3orbital hybridization), with the Ge-group being the most energetically favorable than the C-group. A net charge redistribution occurs between adjacent layers, which is significant (∼0.23-0.25 e cell-1) in patterns II and IV, but slightly small (∼0.05-0.09 e cell-1) in patterns I and III, respectively, forming spontaneousp-nheterojunctions. Such interlayer charge transfer could also lead to a polarization in the interfacial region, with the electron depletion (accumulation) close to the GeC layer and the electron accumulation (depletion) close to the SiGe layer in the C-group (the Ge-group). This type of interface dipoles could induce a built-in electric field and help to promote photogenerated electrons (holes) migration. Furthermore, a semi-metal nature with a tiny direct band gap at the SiGe layer and a semiconducting nature at the GeC layer indicate that the commensurate SiG/GeC VHs possess a type-I band alignment of heterojunction and have a wide spectrum of light absorption capabilities, indicating its promising applications for enhancing light-matter interaction and interfacial engineering.

Growth mechanisms of monolayer hexagonal boron nitride (h-BN) on metal surfaces: theoretical perspectives

Two-dimensional hexagonal boron nitride (h-BN) has appeared as a promising material in diverse areas of applications, including as an excellent substrate for graphene devices, deep-ultraviolet emitters, and tunneling barriers, thanks to its outstanding stability, flat surface, and wide-bandgap. However, for achieving such exciting applications, controllable mass synthesis of high-quality and large-scale h-BN is a precondition. The synthesis of h-BN on metal surfaces using chemical vapor deposition (CVD) has been extensively studied, aiming to obtain large-scale and high-quality materials. The atomic-scale growth process, which is a prerequisite for rationally optimizing growth circumstances, is a key topic in these investigations. Although theoretical investigations on h-BN growth mechanisms are expected to reveal numerous new insights and understandings, different growth methods have completely dissimilar mechanisms, making theoretical research extremely challenging. In this article, we have summarized the recent cutting-edge theoretical research on the growth mechanisms of h-BN on different metal substrates. On the frequently utilized Cu substrate, h-BN development was shown to be more challenging than a simple adsorption-dehydrogenation-growth scenario. Controlling the number of surface layers is also an important challenge. Growth on the Ni surface is controlled by precipitation. An unusual reaction-limited aggregation growth behavior has been seen on interfaces having a significant lattice mismatch to h-BN. With intensive theoretical investigations employing advanced simulation approaches, further progress in understanding h-BN growth processes is predicted, paving the way for guided growth protocol design.

Excellent photocatalytic properties in 2D ZnO/SiC van der Waals hetero-bilayers: water-splitting H2-fuel production

This research unravels the photocatalytic properties of a 2D ZnO/SiC van der Waals hetero-bilayer for potential water-splitting applications by first-principles calculations. Four unique stacking patterns are considered in studying the electronic and optical properties in the presence and absence of biaxial external strain. For pattern-I and II, large negative binding energy and positive phonon frequencies are observed, denoting chemical and mechanical stabilities. Under the HSE-06 pseudo potential, the calculated bandgap value for pattern-I and II reaches 2.86 eV and 2.74 eV, respectively. 2D ZnO/SiC shows a high absorption coefficient (∼10⁵ cm^-1). The absorption peak under biaxial strain could reach ∼3.5 times the peak observed under unstrained conditions. Under strain, a shift from compressive to tensile biaxial strain (-6% to 6%) results in a bandgap decrease from 3.18 eV to 2.52 eV and 3.09 eV to 2.43 eV, for pattern-I and II, respectively. The observed strain-driven kinetic overpotential for 2D ZnO/SiC pattern-I and II easily engenders photocatalytic redox reactions. The excellent mechanical durability and strain-driven large kinetic overpotential suggest 2D ZnO/SiC heterobilayers as a prospective material for water-splitting H₂-fuel production.

Two-dimensional SiC/AlN based type-II van der Waals heterobilayer as a promising photocatalyst for overall water disassociation

Two-dimensional (2D) van der Waals (vdW) heterostructures made by vertical assembling of two different layers have drawn immense attention in the photocatalytic water disassociation process. Herein, we suggest a novel 2D/2D vdW heterobilayer consisting of silicon carbide (SiC) and aluminum nitride (AlN) as an exciting photocatalyst for solar-to-hydrogen conversion reactions using first-principles calculations. Notably, the heterostructure presents an inherent type-II band orientation wherein the photogenic holes and electrons are spatially separated in the SiC layer and the AlN layer, respectively. Our results indicate that the SiC/AlN heterostructure occupies a suitable band-gap of 2.97 eV which straddles the kinetic overpotentials of the hydrogen production reaction and oxygen production reaction. Importantly, the built-in electric field at the interface created by substantial charge transfer prohibits carrier recombination and further improves the photocatalytic performance. The heterostructure has an ample absorption profile ranging from the ultraviolet to the near-infrared regime, while the intensity of the absorption reaches up to 2.16 × 10⁵ cm^-1. In addition, external strain modulates the optical absorption of the heterostructure effectively. This work provides an intriguing insight into the important features of the SiC/AlN heterostructure and renders useful information on the experimental design of a novel vdW heterostructure for solar energy-driven water disassociation with superior efficiency.

Molecular dynamics investigation of the thermal behaviors of magnesium oxide ceramics at different pressures and temperatures

Today, magnesia ceramics have attracted considerable attention due to their essential properties. Therefore, this paper investigates the impact of temperature (T) and pressure (P) on the thermal manner of magnesia ceramics using molecular dynamics simulations (MDS). As the T increases, the mobility of the structures increases. Therefore, the heat flux (HF) in the structures increments slightly due to the greater movement and the larger oscillation amplitude of the atomic samples. On the other hand, with increasing P, the oscillation amplitude and displacement of atomic samples are limited. Therefore, the thermal properties of the structure are expected to decrease. Studies show that increasing T from 250 to 350 K increases the average HF from 0.73 to 0.89 W/m². Also, the average thermal conductivity (TC) increases from 30.58 to 38.27 W/mK. So, increasing the T means a certain amount of energy is fluxed in a shorter time. On the other hand, increasing the P from 0 to 5 bar decreases the average HF from 0.82 to 0.65 W/m². Also, this issue leads to a decrease in the average TC from 33.49 to 30.96 W/mK.

Two-layer silicene on the SiC substrate: lithiation investigation in the molecular dynamics experiment

The functioning of the lithium ion battery anode composed of silicene/SiC composite is studied by the method of molecular dynamics. In this composite, silicene has vacancy defects of different sizes. Approximately the same degree of filling of such an anode with lithium is shown for both horizontal and vertical intercalations. However, during the horizontal intercalation as opposed to vertical one, lithium atoms not only fill the channel and deposit on its walls, but also penetrate into the substrate. In both cases, the self-diffusion coefficients of lithium atoms have similar values. However, the process of filling the system with lithium occurs with a smoother change in the total energy, when the intercalation is performed vertically. A detailed study of the lithium atoms packing via the construction of Voronoi polyhedra for each of the systems under consideration shows the better uniformity of the Li atoms distribution over the volume of the system during the vertical intercalation.

Interfacial thermal transport between graphene and diamane

Similar to graphene, diamane is a single layer of diamond that has been investigated in recent years due to its peculiar mechanical, thermal, and electronic properties. Motivated by earlier work that showed an exceptionally high intra-plane thermal conductivity in diamane, in this work, we investigate the interfacial thermal resistance (R) between graphene and diamane using non-equilibrium classical molecular dynamics simulations. The calculated R for a pristine graphene and AB-stacked diamane at room temperature is 1.89 × 10^-7 K m²/W, which is comparable to other common graphene/semi-conductor bilayers. These results are understood in terms of the overlap of the phonon density of states between the graphene and diamane layers. We further explore the impact of stacking pattern, system temperature, coupling strength, in-plane tensile strain, and hydrogenation ratio on R. Intriguingly, we find that unlike single layer diamane, where the intra-plane thermal conductively is reduced by ∼50% under 5% strain, the inter-plane thermal conductance of the graphene-diamane bilayer is enhanced by ∼50% under 8% strain. The difference is caused by the opposite behavior between the inter- and intra-layer conductances as phonon relaxation time is decreased. The high intra-plane thermal conductivity and low inter-plane thermal resistance shows the high potential of using graphene-diamane heterostructures in electronic applications.

Vacancy-Induced Thermal Transport and Tensile Mechanical Behavior of Monolayer Honeycomb BeO

Because of the rapid shrinking trend of integrated circuits, the performances of nanodevices and nanomechanical systems are greatly affected by the joule heating and mechanical failure dilemma. In addition, structural defects are inevitable during experimental synthesis of nanomaterials, which may alter their physical properties significantly. Investigation of the thermal transport and mechanical behavior of nanostructured materials with structural defects is thus a crucial requirement. In this study, the thermal conductivity (TC) and tensile mechanical behavior of monolayer honeycomb BeO are systematically explored using molecular dynamics simulations. An infinite length bulk TC of ∼277.77 ± 8.93 W/mK was found for the pristine monolayer BeO. However, the insertion of 1% single vacancy (SV) and double vacancy (DV) defects reduces the TC by ∼36.98 and ∼33.52%, respectively. On the other hand, the uniaxial tensile loading produces asymmetrical fracture stress, elastic modulus, and fracture strain behaviors in the armchair and zigzag directions. The elastic modulus was reduced by ∼4.7 and ∼6.6% for 1% SV defects along the armchair and zigzag directions, respectively, whereas the reduction was ∼2.7 and ∼ 5.1% for 1% DV defects. Moreover, because of the strong symmetry-breaking effect, both the TC and mechanical strength were significantly lower for the SV defects than those for the DV defects. The highly softening and decreasing trends of the phonon modes with increasing vacancy concentration and temperature, respectively, were noticed for both types of defects, resulting in a reduction of the TC of the defected structures. These findings will be helpful for the understanding of the heat transport and mechanical characteristics of monolayer BeO as well as provide guidance for the design and control of BeO-based nanoelectronic and nanoelectromechanical devices.

Insight into the stacking and the species-ordering dependences of interlayer bonding in SiC/GeC polar heterostructures

Two-dimensional (2D) polar materials experience an in-plane charge transfer between different elements due to their electron negativities. When they form vertical heterostructures, the electrostatic force triggered by such charge transfer plays an important role in the interlayer bonding beyond van der Waals (vdW) interaction. Our comprehensive first principle study on the structural stability of the 2D SiC/GeC hybrid bilayer heterostructure has found that the electrostatic interlayer interaction can induce theπ-πorbital hybridization between adjacent layers under different stacking and out-of-plane species ordering, with strong hybridization in the cases of Si-C and C-Ge species orderings but weak hybridization in the case of the C-C ordering. In particular, the attractive electrostatic interlayer interaction in the cases of Si-C and C-Ge species orderings mainly controls the equilibrium interlayer distance and the vdW interaction makes the system attain a lower binding energy. On the contrary, the vdW interaction mostly controls the equilibrium interlayer distance in the case of the C-C species ordering and the repulsive electrostatic interlayer force has less effect. Interesting finding is that the band structure of the SiC/GeC hybrid bilayer is sensitive to the layer-layer stacking and the out-of-plane species ordering. An indirect band gap of 2.76 eV (or 2.48 eV) was found under the AA stacking with Si-C ordering (or under the AB stacking with C-C ordering). While a direct band gap of 2.00-2.88 eV was found under other stacking and species orderings, demonstrating its band gap tunable feature. Furthermore, there is a charge redistribution in the interfacial region leading to a built-in electric field. Such field will separate the photo-generated charge carriers in different layers and is expected to reduce the probability of carrier recombination, and eventually give rise to the electron tunneling between layers.

Temperature and interlayer coupling induced thermal transport across graphene/2D-SiC van der Waals heterostructure

Graphene based two-dimensional (2D) van der Waals (vdW) materials have attracted enormous attention because of their extraordinary physical properties. In this study, we explore the temperature and interlayer coupling induced thermal transport across the graphene/2D-SiC vdW interface using non-equilibrium molecular dynamics and transient pump probe methods. We find that the in-plane thermal conductivity κ deviates slightly from the 1/T law at high temperatures. A tunable κ is found with the variation of the interlayer coupling strength χ. The interlayer thermal resistance R across graphene/2D-SiC interface reaches 2.71 [Formula: see text] 10-7 [Formula: see text] at room temperature and χ = 1, and it reduces steadily with the elevation of system temperature and χ, demonstrating around 41% and 56% reduction with increasing temperature to 700 K and a χ of 25, respectively. We also elucidate the heat transport mechanism by estimating the in-plane and out-of-plane phonon modes. Higher phonon propagation possibility and Umklapp scattering across the interface at high temperatures and increased χ lead to the significant reduction of R. This work unveils the mechanism of heat transfer and interface thermal conductance engineering across the graphene/2D-SiC vdW heterostructure.

Superior tunable photocatalytic properties for water splitting in two dimensional GeC/SiC van der Waals heterobilayers

The photocatalytic characteristics of two-dimensional (2D) GeC-based van der Waals heterobilayers (vdW-HBL) are systematically investigated to determine the amount of hydrogen (H2) fuel generated by water splitting. We propose several vdW-HBL structures consisting of 2D-GeC and 2D-SiC with exceptional and tunable optoelectronic properties. The structures exhibit a negative interlayer binding energy and non-negative phonon frequencies, showing that the structures are dynamically stable. The electronic properties of the HBLs depend on the stacking configuration, where the HBLs exhibit direct bandgap values of 1.978 eV, 2.278 eV, and 2.686 eV. The measured absorption coefficients for the HBLs are over ~ 105 cm-1, surpassing the prevalent conversion efficiency of optoelectronic materials. In the absence of external strain, the absorption coefficient for the HBLs reaches around 1 × 106 cm-1. With applied strain, absorption peaks are increased to ~ 3.5 times greater in value than the unstrained HBLs. Furthermore, the HBLs exhibit dynamically controllable bandgaps via the application of biaxial strain. A decrease in the bandgap occurs for both the HBLs when applied biaxial strain changes from the compressive to tensile strain. For + 4% tensile strain, the structure I become unsuitable for photocatalytic water splitting. However, in the biaxial strain range of - 6% to + 6%, both structure II and structure III have a sufficiently higher kinetic potential for demonstrating photocatalytic water-splitting activity in the region of UV to the visible in the light spectrum. These promising properties obtained for the GeC/SiC vdW heterobilayers suggest an application of the structures could boost H2 fuel production via water splitting.

Temperature- and Defect-Induced Uniaxial Tensile Mechanical Behaviors and the Fracture Mechanism of Two-Dimensional Silicon Germanide

Recently, monolayer silicon germanide (SiGe), a newly explored buckled honeycomb configuration of silicon and germanium, is predicted to be a promising nanomaterial for next-generation nanoelectromechanical systems (NEMS) due to its intriguing electronic, optical, and piezoelectric properties. In the NEMS applications, the structure is subjected to uniaxial tensile mechanical loading, and the investigation of the mechanical behaviors is of fundamental importance to ensure structural stability. Here, we systematically explored the uniaxial tensile mechanical properties of 2D-SiGe through molecular dynamics simulations. The effects of temperature ranges from 300 to 1000 K and vacancy defects, for instance, point and bi vacancy, for both armchair and zigzag orientations of 2D-SiGe were investigated. In addition, the influence of system areas and strain rates on the stress-strain performance of 2D-SiGe has also been studied. With the increase in temperature and vacancy concentration, the mechanical properties of 2D-SiGe show decreasing behavior for both orientations and the armchair chirality shows superior mechanical strength to the zigzag direction due to its bonding characteristics. A phase transformation-induced second linearly elastic region was observed at large deformation strain, leading to an anomalous stress-strain behavior in the zigzag direction. At 300 K temperature, we obtained a fracture stress of ∼94.83 GPa and an elastic modulus of ∼388.7 GPa along the armchair direction, which are about ∼3.17 and ∼2.83% higher than the zigzag-oriented fracture strength and elastic modulus. Moreover, because of the strong regularity interruption effect, the point vacancy shows the largest decrease in fracture strength, elastic modulus, and fracture strain compared to the bi vacancy defects for both armchair and zigzag orientations. Area and strain rate investigations reveal that 2D-SiGe is less susceptible to the system area and strain rate. These findings provide a deep insight into controlling the tensile mechanical behavior of 2D-SiGe for its applications in next-generation NEMS and nanodevices.

Thermal transport in monolayer zinc-sulfide: effects of length, temperature and vacancy defects

Of late, atomically thin two-dimensional zinc-sulfide (2D-ZnS) shows great potential for advanced nanodevices and as a substitute to graphene and transition metal di-chalcogenides owing to its exceptional optical and electronic properties. However, the functional performance of nanodevices significantly depends on the effective heat management of the system. In this paper, we explored the thermal transport properties of 2D-ZnS through molecular dynamics simulations. The impact of length, temperature, and vacancy defects on the thermal properties of 2D-ZnS are systematically investigated. We found that the thermal conductivity (TC) rises monotonically with increasing sheet length, and the bulk TC of ∼30.67 W mK^-1is explored for an infinite length ZnS. Beyond room temperature (300 K), the TC differs from the usual 1/Trule and displays an abnormal, slowly declining behavior. The point vacancy (PV) shows the largest decrease in TC compared to the bi vacancy (BV) defects. We calculated phonon modes for various lengths, temperatures, and vacancies to elucidate the TC variation. Conversely, quantum corrections are used to avoid phonon modes' icing effects on the TC at low temperatures. The obtained phonon density of states (PDOS) shows a softening and shrinking nature with increasing temperature, which is responsible for the anomaly in the TC at high temperatures. Owing to the increase of vacancy concentration, the PDOS peaks exhibit a decrease for both types of defects. Moreover, the variation of the specific heat capacity and entropy with BV and PV signify our findings of 2D-ZnS TC at diverse concentrations along with the different forms of vacancies. The results elucidated in this study will be a guide for efficient heat management of ZnS-based optoelectronic and nano-electronic devices.

Phonon thermal conductivity of the stanene/hBN van der Waals heterostructure

We use classical non-equilibrium molecular dynamics (NEMD) simulations to investigate the phonon thermal conductivity (PTC) of hexagonal boron nitride (hBN) supported stanene. At first, we examine the length dependent PTCs of bare stanene and hBN, and the stanene/hBN heterostructure and realize the dominance of the hBN layer to dictate the PTC in the heterostructure system. Afterward, we assess the length-independent bulk PTCs of these materials. The bulk PTCs at room temperature are found as ∼15.20 W m-1 K-1, ∼550 W m-1 K-1, and ∼232 W m-1 K-1 for bare stanene and hBN, and stanene/hBN, respectively. Moreover, our simulations reveal that bare stanene exhibits a substantially lower PTC compared to bare hBN, and the predicted PTC of stanene/hBN lies between those of stand-alone stanene and hBN. We also found that the PTC obtained for the stanene/hBN system from NEMD simulations nicely agrees with the theoretical formula developed to predict the PTC of heterostructures of two distinct materials. Temperature studies suggest that the PTC of the stanene/hBN heterostructure system follows a decreasing trend with increasing temperature. Additionally, corresponding phonon density of states (PDOS) and phonon dispersion data are provided to comprehensively understand the phonon properties of bare stanene and hBN, and stanene/hBN. Overall, this NEMD study would offer a deep understating towards the PTC of the stanene/hBN heterostructure and would widen the scope of its successful operations in future nanoelectronic, spintronic, and thermoelectric devices.

The Impact of Interlayer Rotation on Thermal Transport Across Graphene/Hexagonal Boron Nitride van der Waals Heterostructure

Graphene/hexagonal boron nitride (h-BN) van der Waals (vdW) heterostructure has aroused great interest because of the unique Moiré pattern. In this study, we use molecular dynamics simulation to investigate the influence of the interlayer rotation angle θ on the interfacial thermal transport across graphene/h-BN heterostructure. The interfacial thermal conductance G of graphene/h-BN interface reaches 509 MW/(m²K) at 500 K without rotation, and it decreases monotonically with the increase of the rotation angle, exhibiting around 50% reduction of G with θ = 26.33°. The phonon transmission function reveals that G is dominantly contributed by the low-frequency phonons below 10 THz. Upon rotation, the surface fluctuation in the interfacial graphene layer is enhanced, and the transmission function for the low-frequency phonon is reduced with increasing θ, leading to the rotation angle-dependent G. This work uncovers the physical mechanisms for controlling interfacial thermal transport across vdW heterostructure via interlayer rotation.

Characterization of the mechanical properties of van der Waals heterostructures of stanene adsorbed on graphene, hexagonal boron-nitride and silicon carbide

Stanene has revealed a new horizon in the field of quantum condensed matter and energy conversion devices but its significantly lower tensile strength limits its further applications and effective operation in these nanodevices. Van der Waals heterostructures have given substantial flexibility to integrate different two-dimensional (2D) layered materials over the past few years and have proven highly functional with exceptional features, appealing applications, and innovative physics. Considerable efforts have been made for the preparation, thorough understanding, and applications of van der Waals heterostructures in the fields of electronics and optoelectronics. In this paper, we have executed Molecular Dynamics (MD) simulations to predict the tensile strength of van der Waals heterostructures of stanene (Sn) adsorbed on graphene (Gr), hexagonal boron nitride (hBN), and silicon carbide (SiC) (Sn/Gr, Sn/hBN, and Sn/SiC, respectively) subjected to both armchair and zigzag directional loading at different strain rates for the first time, which has enticing applications in electronic, optoelectronic, energy storage and bio-engineered devices. Among all the van der Waals heterostructures, the Sn/SiC heterostructure exhibits the lowest tensile strength and tensile strain. Furthermore, it has been found that zigzag directional loading could endure more tensile strain before fracture. Besides, it has been disclosed that though the rule of mixtures may accurately reproduce the Young's modulus of these heterostructures, it has limitations to predict the tensile strength. Fracture analysis suggests that for the Sn/hBN heterostructure the fracture initiates from the stanene layer while for the Sn/Gr and Sn/SiC heterostructures the fracture initiates from the Gr and SiC layer, respectively, for both armchair and zigzag directional loading. Overall, this study would aid in the design and efficient operation of Sn/Gr, Sn/hBN, and Sn/SiC heterostructures when subjected to mechanical force.

Tunable electronic properties of BSe-MoS2/WS2 heterostructures for promoted light utilization

With applications in high performance electronics, photovoltaics, and catalysis, two-dimensional (2D) transition metal dichalcogenides (TMDCs) attract extensive attention due to their extraordinary physical properties. People have focused on TMDC-based materials for years, while the low mobility greatly hinders their further application. TMDC-based heterostructures with tunable band alignment have been experimentally confirmed to be feasible for photoelectronic devices or photocatalysts. Based on the density functional theory (DFT), there are four discoveries in this work: (1) we propose two new heterostructures based on BSe and MoS2/WS2 that have quite low mismatches and intrinsic type-II alignments. (2) Even though the VBM of BSe-MoS2 are completely contributed by BSe, the heterostructure is still endowed with a lower effective mass and a better transport characteristic in comparison with pristine structures. (3) A promoted absorption ability and a better transport characteristic oppose each other and the two characteristics cannot be obtained at the same time. (4) Tension strained structures can induce promoted light absorption in the solar spectrum and the predicted efficiency of the BSe-MoS2 bilayer can be as high as ∼19.3%, when the external electric field is applied. This theoretical survey proves that BSe-MoS2/WS2 with high flexibility and tunability are potential candidates for novel electronic devices and photocatalysts.

Exceptional in-plane and interfacial thermal transport in graphene/2D-SiC van der Waals heterostructures

Graphene based van der Waals heterostructures (vdWHs) have gained substantial interest recently due to their unique electrical and optical characteristics as well as unprecedented opportunities to explore new physics and revolutionary design of nanodevices. However, the heat conduction performance of these vdWHs holds a crucial role in deciding their functional efficiency. In-plane and out-of-plane thermal conduction phenomena in graphene/2D-SiC vdWHs were studied using reverse non-equilibrium molecular dynamics simulations and the transient pump-probe technique, respectively. At room temperature, we determined an in-plane thermal conductivity of ~ 1452 W/m-K for an infinite length graphene/2D-SiC vdWH, which is superior to any graphene based vdWHs reported yet. The out-of-plane thermal resistance of graphene → 2D-SiC and 2D-SiC → graphene was estimated to be 2.71 × 10⁻⁷ km²/W and 2.65 × 10⁻⁷ km²/W, respectively, implying the absence of the thermal rectification effect in the heterobilayer. The phonon-mediated both in-plane and out-of-plane heat transfer is clarified for this prospective heterobilayer. This study furthermore explored the impact of various interatomic potentials on the thermal conductivity of the heterobilayer. These findings are useful in explaining the heat conduction at the interfaces in graphene/2D-SiC vdWH and may provide a guideline for efficient design and regulation of their thermal characteristics.

Atomic-scale analysis of the physical strength and phonon transport mechanisms of monolayer β-bismuthene

Bismuthene has opened up a new avenue in the field of nanotechnology because of its spectacular electronic and thermoelectric features. The strong spin-orbit-coupling enables its operation as the largest nontrivial bandgap topological insulator and quantum spin hall material at room temperature, which is unlikely for any other 2D material. It is also known to be the most promising thermoelectric material due to its remarkable thermoelectric properties, including a substantially high power factor. However, an in-depth understanding of the mechanical and thermal transport properties of bismuthene is crucial for its practical implementation and efficient operation. Employing the Stillinger-Weber potential, we utilized molecular dynamics simulations to inspect the mechanical strength and thermal conductivity of the monolayer β-bismuthene for the first time. We analyzed the effect of temperature on the tensile mechanical properties along the armchair and zigzag directions of bismuthene nanosheets and found that increasing temperature causes a significant deterioration in these properties. The material shows superior fracture resistance with zigzag loading, whereas the armchair direction exhibits an improved elasticity. Next, we showed that increasing vacancy concentration and crack length notably reduce the fracture stress and strain of β-bismuthene. Under all these conditions, β-bismuthene showed a strong chirality effect under tensile loading. We also explored the fracture phenomena of a pre-cracked β-bismuthene, which reveal that the armchair-directed crack possesses a higher fracture resistance than the zigzag-directed crack. Interestingly, branching phenomena occurred during crack propagation for the armchair crack; meanwhile, the crack propagates perpendicular to loading for the zigzag crack. Afterward, we investigated the effect of loading rate on the fracture properties of bismuthene along the armchair and zigzag directions. Finally, we calculated the thermal conductivity of bismuthene under the influence of temperature and vacancy and recorded a substantial decrement in thermal conductivity with increasing temperature and vacancy. The obtained results are comprehensively discussed in the light of phonon density of states, phonon dispersion spectrum, and phonon group velocities. It is also disclosed that the thermal conductivity of β-bismuthene is considerably lower than that of other analogous honeycomb structures. This study can add a new dimension to the successful realization of bismuthene in future (opto)electronic, spintronic, and thermoelectric devices.