Introduction Of Point Defects Research Articles

Study on the mechanism of enhancing photocurrent in TiS2 photodetector by vacancy- and substitution-doping

In materials lacking spatial inversion symmetry, the photovoltaic generation effect (PGE) manifests under polarized irradiation without the necessity of a p-n junction and demonstrates high polarization sensitivity across a broad spectrum. This characteristic presents significant potential for applications in low-power two-dimensional optoelectronic devices. In this study, we investigate the electronic structure, optical properties, and PGE in 2H-TiS2 by first-principles simulations, incorporating various types of point defects. We propose a mechanism to enhance photoconductivity in 2H-TiS2 by substitution doping and vacancy defects. When the photodetector is aligned along the armchair direction, the photocurrent exhibits a cosine dependency on the linear polarization angle. We achieved a remarkable enhancement in photocurrent, with a maximum value of 1.33 a20/photon, in contrast to only 0.11 a20/photon for the pure membrane. This improvement can be attributed to the introduction of point defects, which diminish the symmetry of the device and increase its asymmetry, thereby enhancing the photocurrent. Furthermore, we attained high polarization sensitivity, evidenced by a maximum extinction ratio of 262.4. Our findings not only propose an effective mechanism for enhancing PGE by substitution doping but also underscore the promising applications of the two-dimensional 2H-TiS2 monolayer in optoelectronics, particularly in photoelectric detection.

Growth Behavior of Ni on Hydrogen-Etched WS2 Surface.

Transition metal dichalcogenides (TMDs) are 2D materials in which the layers are stacked together by van der Waals forces. Although TMDs are expected to be promising for electronic applications, forming a uniform electrode on them is challenging because of the low adhesion forces between metals and TMDs. This study focuses on improving the quality of metal electrodes by introducing atomic H to create surface defects, using Ni on WS2 as an example. The detailed effects of H etching and subsequent Ni growth were investigated using scanning tunneling microscopy (STM) and synchrotron-based X-ray photoemission (XPS) techniques. Our studies reveal that introducing point defects of ∼3.05 × 1011 cm-2 on the WS2 surface, results in a significant shift in Ni growth from the Volmer-Weber to a near Frank-van der Merwe mode. The origin of the change is the bond formation between the Ni and W atoms, which is expected to realize ohmic contact. The optimization of metal-TMD interfaces offers valuable insights for advanced applications.

Defect-Induced Sensitivity Improvement in HfNBr Monolayers for Ammonia Detection.

Two-dimensional materials, owing to their unique physical properties and high surface area, play a crucial role in intelligent sensing, particularly in the domain of atmospheric pollutant monitoring. In this work, we have extensively investigated the gas-sensing capabilities of the HfNBr monolayer for ammonia detection by introducing point defects, utilizing density functional theory and nonequilibrium Green's function calculations. Upon the introduction of point defects, the adsorption energy of HfNBr monolayers for ammonia significantly increased (from -0.162 to -1.257 eV), indicating a markedly strengthened affinity. To further elucidate the sensing mechanism, we conducted an in-depth investigation into the charge transfer dynamics, the density of states, and the charge density difference between the adsorbent and the adsorbate. Besides, we employed the NEGF method to evaluate the changes in the current-voltage characteristics of the HfNBr monolayer before and after adsorption, which revealed a remarkable change in the apparent resistance, thereby demonstrating excellent sensitivity. The exceptional performance of the HfNBr monolayer toward NH3 demonstrates its significant value in practical applications for ammonia detection.

Engineering the electronic and magnetic properties of monolayer TiS[formula omitted] through systematic transition-metal doping

Despite substantial interest, most of the two-dimensional (2D) materials are not magnetic in their pristine form. Several standard approaches, such as adsorption of atoms, introduction of point defects, and edge engineering, have been developed to induce magnetism in two-dimensional materials. In this way, we investigate the electronic and magnetic properties of monolayer TiS2 doped with 3d transition metals (TMs) atoms in both octahedral 1T and trigonal prismatic 1H structures using first-principles calculations. In its pristine form, TiS2 is a non-magnetic semiconductor. The bands near the Fermi energy primarily exhibit d orbital characters, and due to the presence of ideal octahedral and trigonal arrangements, they are well separated from other bands with p character. Upon substituting 3d-TM atoms in both structures, a variety of electronic and magnetic phases emerge, including magnetic semiconductor, magnetic half-metal, and magnetic metal. Chromium exhibits the largest magnetic moment in both the 1T and 1H structures. The 1T structure shows a slightly higher magnetic moment of 3.4 μB compared to the 1H structure 3.1 μB, attributed to the distorted octahedral structure of the 1T structure. Unlike pristine TiS2, the deficiency in saturation of neighboring S atoms in the presence of impurities leads to the proximity of energy levels of d and p states, resulting in unexpectedly sizeable magnetic moments. Another interesting case is Cobalt, which leads to a magnetic moment of approximately 0.8 μB in the 1H structure, while the Co exhibits a non-magnetic state in the 1H structure. These materials demonstrate a high degree of tunability and can be optimized for various magnetic applications.

Influence of Xe+ and Ga+ milling species on the cathodoluminescence of wurtzite and zincblende GaN

III-nitride materials, such as GaN and its alloys, are essential for modern microelectronics and optoelectronics due to their unique properties. Focused ion beam (FIB) techniques play a crucial role in their prototyping and characterization at the micro- and nanoscale. However, conventional FIB milling with Ga ions presents challenges, including surface amorphization and point defect introduction, prompting the exploration of alternative ion sources. Xenon-based inductively coupled plasma or plasma FIB has emerged as a promising alternative, offering reduced damage and better sample property preservation. Despite extensive research on FIB-induced damage in GaN, systematic comparisons between Ga and Xe ion milling on the luminescence characteristics of GaN remain limited. This study aims to fill this gap by evaluating and comparing the extent of FIB-induced damage caused by Ga and Xe ions in wurtzite and zincblende GaN through cathodoluminescence measurements. Our findings indicate that Xe ion milling yields higher integrated intensities compared to Ga ion milling, attributed to shallower implantation depths and reduced lattice disorder. We also observe a decrease in integrated intensity with increasing ion beam acceleration voltage for both wurtzite and zincblende GaN layers. This study provides valuable insights into optimizing FIB-based sample preparation techniques for III-nitride materials, with implications for enhancing device performance and reliability.

Defects and oxygen impurities in ferroelectric wurtzite Al1−xScxN alloys

III-nitrides and related alloys are widely used for optoelectronics and as acoustic resonators. Ferroelectric wurtzite nitrides are of particular interest because of their potential for direct integration with Si and wide bandgap semiconductors and unique polarization switching characteristics; such interest has taken off since the first report of ferroelectric Al1−xScxN alloys. However, the coercive fields needed to switch polarization are on the order of MV/cm, which are 1–2 orders of magnitude larger than oxide perovskite ferroelectrics. Atomic-scale point defects are known to impact the dielectric properties, including breakdown fields and leakage currents, as well as ferroelectric switching. However, very little is known about the native defects and impurities in Al1−xScxN and their effect on the dielectric and ferroelectric properties. In this study, we use first-principles calculations to determine the formation energetics of native defects and unintentional oxygen incorporation and their effects on the polarization switching barriers in Al1−xScxN alloys. We find that nitrogen vacancies are the dominant native defects, and unintentional oxygen incorporation on the nitrogen site is present in high concentrations. They introduce multiple mid-gap states that can lead to premature dielectric breakdown and increased temperature-activated leakage currents in ferroelectrics. We also find that nitrogen vacancy and substitutional oxygen reduce the switching barrier in Al1−xScxN at low Sc compositions. The effect is minimal or even negative (increases barrier) at higher Sc compositions. Unintentional defects are generally considered to adversely affect ferroelectric properties, but our findings reveal that controlled introduction of point defects by tuning synthesis conditions can instead benefit polarization switching in ferroelectric Al1−xScxN at certain compositions.

Rapid Defect Engineering in FeCoNi/FeAl2O4 Hybrid for Enhanced Oxygen Evolution Catalysis: A Pathway to High-Performance Electrocatalysts.

Rational modulation of surface reconstruction in the oxygen evolution reaction (OER) utilizing defect engineering to form efficient catalytic activity centers is a topical interest in the field of catalysis. The introduction of point defects has been demonstrated to be an effective strategy to regulate the electronic configuration of electrocatalysts, but the influence of more complex planar defects (e.g., twins and stacking faults), on their intrinsic activity is still not fully understood. This study harnesses ultrasonic cavitation for rapid and controlled introduction of different types of defects in the FeCoNi/FeAl2O4 hybrid coating, optimizing OER catalytic activity. Theoretical calculations and experiments demonstrate that the different defects optimize the coordination environment and facilitate the activation of surface reconstruction into true catalytic activity centers at lower potentials. Moreover, it demonstrates exceptional durability, maintaining stable oxygen production at a high current density of 300 mA cm-2 for over 120 hours. This work not only presents a novel pathway for designing advanced electrocatalysts but also deepens our understanding of defect-engineered catalytic mechanisms, showcasing the potential for rapid and efficient enhancement of electrocatalytic performance.

Rapid Defect Engineering in FeCoNi/FeAl2O4 Hybrid for Enhanced Oxygen Evolution Catalysis: A Pathway to High‐Performance Electrocatalysts

AbstractRational modulation of surface reconstruction in the oxygen evolution reaction (OER) utilizing defect engineering to form efficient catalytic activity centers is a topical interest in the field of catalysis. The introduction of point defects has been demonstrated to be an effective strategy to regulate the electronic configuration of electrocatalysts, but the influence of more complex planar defects (e.g., twins and stacking faults), on their intrinsic activity is still not fully understood. This study harnesses ultrasonic cavitation for rapid and controlled introduction of different types of defects in the FeCoNi/FeAl2O4 hybrid coating, optimizing OER catalytic activity. Theoretical calculations and experiments demonstrate that the different defects optimize the coordination environment and facilitate the activation of surface reconstruction into true catalytic activity centers at lower potentials. Moreover, it demonstrates exceptional durability, maintaining stable oxygen production at a high current density of 300 mA cm−2 for over 120 hours. This work not only presents a novel pathway for designing advanced electrocatalysts but also deepens our understanding of defect‐engineered catalytic mechanisms, showcasing the potential for rapid and efficient enhancement of electrocatalytic performance.

Enhanced photoelectrochemical water splitting via hydrogenated TiO2 nanotubes modified with Cu/CuO species

This study explores the collective influence of hydrogenation thermal treatment and the decoration of Cu/CuO onto TiO2 nanotubes (TiO2-NTs) concerning photoelectrochemical water splitting. To introduce point defects such as oxygen vacancies and Ti3+, electrochemically anodized Ti foils underwent hydrogenation in a 90 % Ar-10 % H2 atmosphere at 500 °C. Subsequently, Cu/CuO species were deposited on the hydrogenated TiO2-NTs through chemical decoration for varying stirring durations of 15, 30, 45, and 60 min. EPR analysis of the hydrogenated sample unveiled resonances at g-values distinct from the typical 1.997 signal associated with oxygen vacancies in TiO2-NTs, signifying the presence of Ti3+ and VO defects. Analysis via XPS identified Cu and CuO as the primary compositions of the decorated species on the hydrogenated TiO2-NTs. Additionally, SEM/EDS results showcased that longer stirring times, specifically 60 min., caused localized agglomeration of Cu/CuO species and TiO2-NTs breakage. The Cu/CuO-decorated hydrogenated TiO2-NTs exhibited enhanced absorption of visible light, leading to a band gap reduction to 2.09 eV after 45 min of Cu/CuO decoration. Notably, this particular sample demonstrated the highest photocurrent of 3.6 mA/cm2 and a photo-conversion efficiency of 2.48 % at 1.23 V vs. RHE. Overall, the presence of Cu/CuO species prolonged the lifetime of charge carriers, as evidenced by Nyquist plots and Mott-Schottky analysis. A schematic model is suggested based on the modified band gap of hydrogenated TiO2-NTs subsequent to Cu/CuO loading.

Defect-Induced Low-Energy Majorana Excitations in the Kitaev Magnet α−RuCl3

The excitations in the Kitaev spin liquid (KSL) can be described by Majorana fermions, which have characteristic field dependence of bulk gap and topological edge modes. In the high-field state of layered honeycomb magnet α−RuCl3, experimental results supporting these Majorana features have been reported recently. However, there are challenges due to sample dependence, and the impact of inevitable disorder on the KSL is poorly understood. Here, we study how low-energy excitations are modified by introducing point defects in α−RuCl3 using electron irradiation, which induces site vacancies and exchange randomness. High-resolution measurements of the temperature dependence of specific heat C(T) under in-plane fields H reveal that, while the field-dependent Majorana gap is almost intact, additional low-energy states with C/T=A(H)T are induced by introduced defects. At low temperatures, we obtain the data collapse of C/T∼H−γ(T/H) expected for a disordered quantum spin system but with an anomalously large exponent γ. This leads us to find a power-law relationship between the coefficient A(H) and the field-sensitive Majorana gap. These results are consistent with the picture that the disorder induces low-energy linear Majorana excitations, which may be considered as a weak localization effect of Majorana fermions in the KSL. Published by the American Physical Society 2024

Band gap engineering through calcium addition in (Mg, Co, Ni, Cu, Zn)O high entropy oxide for efficient photocatalysis

Multicomponent metal oxides have shown the potential to be excellent catalysts mainly because of synergistic interactions between the active sites. We report (Co, Mg, Ni, Cu, Zn)1-xCaxO (x = 0.05, 0.1) high entropy oxide (HEO) photocatalyst with single phase rocksalt structure (space group Fm3¯m) synthesized by solution combustion synthesis (SCS) technique. HEOs contain elements with varying electronegativities and crystal field splitting and thus exhibit a relatively lower band gap when compared to the individual constituent oxides. Adding Ca2+ results in increased covalency due to the greater exchange interaction between O 2p and transition metal (TM) 3d orbital, engendering further reduction in band gap and consequently improving photocatalytic activity in the visible region. In addition, the introduction of point defects, mainly metal/oxygen vacancy, to accommodate the larger size Ca2+ cation also contributed to the catalytic activity. The photocatalytic activity enhancement is demonstrated by visible light-assisted photodegradation of methylene blue (MB). The MB dye degradation rate constant for (Co, Ni, Cu, Zn, Mg)0.9Ca0.1O catalyst was found to be ∼0.0445 min−1, which was about six times faster than that of the pristine (Co, Mg, Ni, Cu, Zn)O.

Study on the Effect of Sn, In, and Se Co-Doping on the Thermoelectric Properties of GeTe.

GeTe and Ge0.99-xIn0.01SnxTe0.94Se0.06 (x = 0, 0.01, 0.03, and 0.06) samples were prepared by vacuum synthesis combined with spark plasma sintering (SPS). The thermoelectric properties of GeTe were coordinated by multiple doping of Sn, In, and Se. In this work, a maximum zT(zT = S2σT/κ) of 0.9 and a power factor (PF = S2σ) of 3.87 μWmm-1 K-2 were obtained in a sample of Ge0.99In0.01Te0.94Se0.06 at 723K. The XRD results at room temperature show that all samples are rhombohedral phase structures. There is a peak (~27°) of the Ge element in GeTe and the sample (x = 0), but it disappears after Sn doping, indicating that Sn doping can promote the dissolution of Ge. The scattering mechanism of the doped samples was calculated by the conductivity ratio method. The results show that phonon scattering Is dominant in all samples, and alloy scattering is enhanced with the increase in the Sn doping amount. In doping can introduce resonance energy levels and increase the Seebeck coefficient, and Se doping can introduce point defects to suppress phonon transmission and reduce lattice thermal conductivity. Therefore, the thermoelectric properties of samples with x = 0 improved. Although Sn doping will promote the dissolution of Ge precipitation, the phase transition of the samples near 580 K deteriorates the thermoelectric properties. The thermoelectric properties of Sn-doped samples improved only at room temperature to ~580 K compared with pure GeTe. The synergistic effect of multi-element doping is a comprehensive reflection of the interaction between elements rather than the sum of all the effects of single-element doping.

The effect of iron ion irradiation on the ionic conductivity of lithium lanthanum zirconium oxide garnet thin films

The ionic conductivity of most lithium lanthanum zirconium oxide (LLZO, Li7La3Zr2O12) solid electrolytes requires improvement. In this study, LLZO thin films were fabricated through sputtering, and various doses of iron ion irradiation (Fe11+) were employed. As the irradiation dose increased from 1014 ions cm−2 to 1016 ions cm−2, the half-height width of the X-ray diffraction peak gradually broadened. Concurrently, the ionic conductivity increased from 2.3 × 10−9 S cm−1 to 2.4 × 10−5 S cm−1, while the activation energy decreased from 0.37 eV to 0.18 eV. The improved ionic conductivity can be attributed to the introduction of point defects in the microstructure of the LLZO thin film upon irradiation. Overall, the findings demonstrate the effective enhancement of the ionic conductivity of LLZO solid electrolytes through iron ion irradiation.

Advances in Mg3Sb2 thermoelectric materials and devices.

Thermoelectric technology offers a green-viable and carbon-neutral solution for energy problems by directly converting waste heat to electricity. For years, Bi2Te3-based compounds have been the main choice materials for commercial thermoelectric devices. However, Bi2Te3 comprises scarce and toxic tellurium (Te) elements, which might limit its large-scale application. Recently, Mg3Sb2 compounds have drawn increasing attention as an alternative to Bi2Te3 thermoelectrics due to their excellent thermoelectric performance. Enabled by effective strategies such as optimizing carrier concentration, introducing point defects, and manipulating carrier scattering mechanisms, Mg3Sb2 compounds have realized an improved thermoelectric performance. In this review, optimizing strategies for both Mg3Sb2-based thermoelectric materials and devices are discussed. Moreover, the flexibility and plasticity of Bi-alloyed Mg3Sb2 mainly stemming from the dense dislocations are outlined. The above strategies summarized here for enhancing Mg3Sb2 thermoelectrics are believed to be applicable to many other thermoelectrics.

Mechanical properties of defective kaolinite in tension and compression: A molecular dynamics study

Influenced by the external environment, clays often contain a large number of lattice defects inside, and the defects have an essential influence on the physical and mechanical properties of clays. In order to reveal the mechanical properties and deformation failure mechanism of defective kaolinite, kaolinite containing Si vacancy defects was constructed, and the mechanical properties of two types of perfect/defective kaolinite were investigated under uniaxial tensile and compressive conditions, respectively, by using molecular dynamics methods. The anisotropy of the micromechanical behavior of kaolinite and the formation mechanism was revealed. Based on the radial distribution function between atoms, the cutoff distance of individual bonds inside the crystal was determined, and the evolution rules of individual bonds inside the crystal during the deformation and destruction were elucidated. Results showed that the introduction of point defects caused different degrees of reduction in the peak strength and elastic modulus of kaolinite, and the decrease was related to the loading direction, and the decline was more significant for parallel clay layers (x- and y-) than for perpendicular clay layers (z-), with pronounced anisotropy. When the defected kaolinite was extended along the x- and y-directions, the silicon‑oxygen tetrahedral and aluminum‑oxygen octahedral sheets were fractured, and the broken sites were concentrated at the defected locations; when extended along the z-direction, the failure was dominated by the fracture of interlayer hydrogen bonds. When the defective kaolinite was compressed along the x- and y-directions, the failure was mainly caused by the gradual accumulation of the bending of the clay layer, which was distinctly different from the direct fracture under the tensile condition, and when compressed along the z-direction, the clay layer collapsed until it was failure. The tendency of the broken bonds within kaolinite corresponded well with the stress-strain curve, the number of broken bonds increased with the increase of strain, and the number of broken bonds of various bonds stabilized when the crystal structure was destroyed. The bond-break types and the number of bonds broken under different simulation conditions were somewhat different, affected by the layered structure of kaolinite and the loading patterns.

Investigation of the Impact of Point Defects in InGaN/GaN Quantum Wells with High Dislocation Densities.

In this work, we report on the efficiency of single InGaN/GaN quantum wells (QWs) grown on thin (<1 µm) GaN buffer layers on silicon (111) substrates exhibiting very high threading dislocation (TD) densities. Despite this high defect density, we show that QW emission efficiency significantly increases upon the insertion of an In-containing underlayer, whose role is to prevent the introduction of point defects during the growth of InGaN QWs. Hence, we demonstrate that point defects play a key role in limiting InGaN QW efficiency, even in samples where their density (2-3 × 109 cm-2) is much lower than that of TD (2-3 × 1010 cm-2). Time-resolved photoluminescence and cathodoluminescence studies confirm the prevalence of point defects over TDs in QW efficiency. Interestingly, TD terminations lead to the formation of independent domains for carriers, thanks to V-pits and step bunching phenomena.

Effect of sub-micron grains and defect-dipole interactions on dielectric properties of iron, cobalt, and copper doped barium titanate ceramics.

Introduction: Dilutely doped ferroelectric materials are of interest, as engineering these materials by introducing point defects via doping often leads to unique behavior not otherwise achievable in the undoped material. For example, B-site doping with transition metals in barium titanate (BaTiO3, or BTO) creates defect dipoles via oxygen vacancies leading enhanced polarization, strain, and the ability to tune dielectric properties. Though defect dipoles should lead to dielectric property enhancements, the effect of grain size in polycrystalline ferroelectrics such as BTO plays a significant role in those properties as well. Methods: Herein, doped BTO with 1.0% copper (Cu), iron (Fe), or cobalt (Co) was synthesized using traditional solid-state processing to observe the contribution of both defect-dipole formation and grain size on the ferroelectric and dielectric properties. Results and discussion: 1.0% Cu doped BTO showed the highest polarization and strain (9.3μC/cm2 and 0.1%, respectively) of the three doped BTO samples. While some results, such as the aforementioned electrical properties of the 1.0% Cu doped BTO can be explained by the strong chemical driving force of the Cu atoms to form defect dipoles with oxygen vacancies and copper's consistent +2 valency leading to stable defect-dipole formation (versus the readily mixed valency states of Fe and Co at +2/+3), other properties cannot. For instance, all three Tc values should fall below that of undoped BTO (typically 120°C-135°C), but the Tc of 1.0% Cu BTO actually exceeds that range (139.4°C). Data presented on the average grain size and distribution of grain sizes provides insight allowing us to decouple the effect of defect dipoles and the effect of grain size on properties such as Tc, where the 1.0% Cu BTO was shown to possess the largest overall grains, leading to its increase in Tc. Conclusion/future work: Overall, the 1% Cu BTO possessed the highest polarization, strain, and Tc and is a promising dopant for engineering the performance of the material. This work emphasizes the challenge of extricating one effect (such as defect-dipole formation) from another (grain size modification) inherent to doping polycrystalline BTO.

Rejuvenation of giant electrostrain in doped barium titanate single crystals

Engineering materials through the introduction of point defects has resulted in significant advances in semiconductor processing and, more recently, the observation of novel phenomena such as large reconfigurable strains in ferroelectrics as a result of defect dipole complexes. Up to 0.8% strain has been demonstrated in BaTiO3 crystals dilutely doped with iron. However, the defect dipole pinning sites and the corresponding achievable strains are found to degrade as the crystal is electrically cycled as part of the measurement process. The strain degradation rate is dependent on the applied field values but shows an exponential change in materials properties regardless of the electric field. This behavior, plus a change in impedance with number of times cycled, suggests these changes are due to electric field induced oxygen migration—similar to the cause of the resistance degradation effect. Despite this, effective piezoelectric coefficients of over 4700 pm/V were recorded with 1.5 kV/cm fields, one of the largest values for a lead-free piezoelectric material thus far. In addition, the defect dipole-aligned state and the high strains can be repeatably recovered by a subsequent heat treatment step after cycling. Potential paths to exploiting the defect dipole induced effects and large piezoelectric coefficient in these dilutely doped systems are proposed.

Defect-Engineering of 2D Dichalcogenide VSe2 to Enhance Ammonia Sensing: Acumens from DFT Calculations

Opportune sensing of ammonia (NH3) gas is industrially important for avoiding hazards. With the advent of nanostructured 2D materials, it is felt vital to miniaturize the detector architecture so as to attain more and more efficacy with simultaneous cost reduction. Adaptation of layered transition metal dichalcogenide as the host may be a potential answer to such challenges. The current study presents a theoretical in-depth analysis regarding improvement in efficient detection of NH3 using layered vanadium di-selenide (VSe2) with the introduction of point defects. The poor affinity between VSe2 and NH3 forbids the use of the former in the nano-sensing device's fabrications. The adsorption and electronic properties of VSe2 nanomaterials can be tuned with defect induction, which would modulate the sensing properties. The introduction of Se vacancy to pristine VSe2 was found to cause about an eight-fold increase (from -012 eV to -0.97 eV) in adsorption energy. A charge transfer from the N 2p orbital of NH3 to the V 3d orbital of VSe2 has been observed to cause appreciable NH3 detection by VSe2. In addition to that, the stability of the best-defected system has been confirmed through molecular dynamics simulation, and the possibility of repeated usability has been analyzed for calculating recovery time. Our theoretical results clearly indicate that Se-vacant layered VSe2 can be an efficient NH3 sensor if practically produced in the future. The presented results will thus potentially be useful for experimentalists in designing and developing VSe2-based NH3 sensors.

Approaches to Estimate the Magnitude of Phonon Scattering via Point Defects in Mo(Se1-xTex)2 Thermoelectric Alloys

One of the most popular routes used to improve the thermoelectric performance of materials is to suppress their lattice thermal conductivities. Thermoelectric performance is characterized by a figure-of-merit &lt;i&gt;zT&lt;/i&gt;, which is defined as &lt;i&gt;σS&lt;sup&gt;2&lt;/sup&gt;T&lt;/i&gt;/(&lt;i&gt;κe&lt;/i&gt; + &lt;i&gt;κl&lt;/i&gt;), where the &lt;i&gt;σ&lt;/i&gt;, &lt;i&gt;S&lt;/i&gt;, &lt;i&gt;T&lt;/i&gt;, &lt;i&gt;κe&lt;/i&gt;, and &lt;i&gt;κl&lt;/i&gt; are the electrical conductivity, Seebeck coefficient, temperature (in Kelvin), electronic thermal conductivity, and the lattice thermal conductivity, respectively. Among the variables in &lt;i&gt;zT&lt;/i&gt;, the &lt;i&gt;κl&lt;/i&gt; is the only variable that is independent of all other variables. In other words, reduction in &lt;i&gt;κl&lt;/i&gt; guarantees &lt;i&gt;zT&lt;/i&gt; improvement. Therefore, several different strategies to decrease &lt;i&gt;κl&lt;/i&gt; have been introduced and implemented. Among the many &lt;i&gt;κl&lt;/i&gt; reduction strategies, introducing point defects in the material by forming an alloy is particularly effective. Here, phonon scattering due to point defects in Mo(Se1-xTex)2 (&lt;i&gt;x&lt;/i&gt; = 0.0, 0.25, 0.50, 0.75, 1.0) was studied using both the Debye-Callaway (DC) model and Callaway-von Baeyer (CvB) model. The advantages and disadvantages of using DC or CvB models are thoroughly discussed. When analyzing the effect of phonon scattering due to point defects, the CvB model is simpler and gives more information about the details of phonon scattering.