Indirect Band Gap Semiconductor Research Articles

Theoretical study of piezoelectric and light absorption properties, and carrier mobilities of Janus TiPX (X = F, Cl, and Br) monolayers.

Janus TiPX (X = F, Cl, and Br) monolayers were systematically investigated through first-principles calculations. The Janus TiPX monolayers exhibit mechanical and dynamic stability. Two monolayers are indirect bandgap semiconductors, except the TiPBr monolayer, which has the features of a quasi-direct bandgap semiconductor. Biaxial strain can modify the band gap of single layers. The Janus TiPX monolayers have remarkable flexibility and piezoelectric properties. In particular, the TiPF monolayer shows high horizontal (44.18 pm V-1) and vertical piezoelectric coefficients (-3.59 pm V-1). These values exceed those of conventional bulk materials, like GaN (3.1 pm V-1) and α-quartz (2.3 pm V-1). All of the monolayers have absorption coefficients of 105 cm-1 for visible and ultraviolet (UV) light, which are one order of magnitude greater than that of MoSSe. Furthermore, TiPX monolayers have high carrier mobility. Janus TiPX monolayers represent a class of two-dimensional (2D) materials with exceptional properties and multifunctionality, holding significant promise for various applications in piezoelectric sensors, solar cells, and nano-electronic devices.

Exploring the heteroanionic 2D materials RhSeCl and RhTeCl as promising semiconductor materials.

Heteroanionic materials show promising potential as 2D semiconductors due to their tunable band gaps, making them excellent candidates for photocatalytic water splitting applications. We conducted detailed theoretical and experimental analysis of two selected materials by synthesizing crystals through chemical vapor transport and investigating the impact of anion variation on crystal structure and properties. Using powder X-ray diffraction and convergent beam electron diffraction, we elucidated the non-centrosymmetric space groups of these compounds. Thermochemical studies revealed the influence of the crystal structure on the decomposition points of both compounds. Theoretical investigations predict that both materials are indirect bandgap semiconductors, which is confirmed by electron energy loss spectroscopy and photoluminescence studies.

First-principles calculations of carrier mobility in monolayer IrSCl and IrSI

Carrier mobility is a key parameter determining the response speed of charge carriers to electric fields in nanoelectronic devices. This study aims to investigate the charge carrier transport properties of monolayer IrSCl and IrSI. Using first-principles calculations based on density functional theory, we systematically investigate the electronic structure and transport properties of monolayer IrSCl and IrSI. The phonon dispersion calculations indicate that both IrSCl and IrSI exhibit no imaginary frequencies, confirming their structural stability. Furthermore, molecular dynamics simulations demonstrate that these materials maintain thermal stability at room temperature (300 K). The evaluation of the bandgap by using the Perdew-Burke-Ernzerhof (PBE) functional and the hybrid HSE06 functional shows that both IrSCl and IrSI are indirect bandgap semiconductors. The bandgap values for monolayer IrSCl are 0.37 eV and 1.58 eV under the PBE functional and the HSE06 functional, respectively, while those for monolayer IrSI are 0.23 eV and 1.36 eV under the PBE functional and the HSE06 functional, respectively. We further investigate the effects of biaxial tensile strain on the bandgap. The bandgap of IrSCl and IrSI decrease with the increase of strain, respectively reaching 0.05 eV and 0.01 eV under the PBE functional at a strain of 6%, indicating a strain-induced transition to metallic behavior. According to deformation potential theory and the Boltzmann transport equation, we calculate the carrier mobility for each of monolayer IrSCl and IrSI. The predicted maximum carrier mobility at room temperature is 407.77 cm<sup>2</sup>/(V·s) for monolayer IrSCl, and 202.64 cm<sup>2</sup>/(V·s)for monolayer IrSI. Additionally, the results from the Boltzmann transport equation show that the highest mobility is 299.15 cm<sup>2</sup>/(V·s) for IrSCl and 286.41 cm<sup>2</sup>/(V·s) for IrSI. These findings suggest that both IrSCl and IrSI possess favorable electronic and transport properties, thus they have become promising candidates for future applications in the field of two-dimensional nanoelectronic devices. Notably, the combination of a moderate bandgap and high carrier mobility at room temperature indicates their potential applications in the fields of transistors, sensors, and other electronic components. This study provides valuable insights into the material properties of IrSCl and IrSI, contributing to the design of novel two-dimensional materials for electronic applications.

Density functional theory study of the electronic and optical properties of pentagraphyne nanotubes.

Pentagraphyne (PG-yne), a recently predicted two-dimensional (2D) carbon allotrope with appealing properties, has opened up possibilities for a wide range of applications. In this study, we investigate the structural, electronic, optical, and electrical transport properties of a novel one-dimensional (1D) system called pentagraphyne nanotubes (PG-yneNTs), formed by rolling a PG-yne sheet, using density functional theory (DFT) calculations. We design PG-yneNTs with diameters ranging from 6.94 Å to 13.62 Å and employ state-of-the-art theoretical calculations to confirm their energetic, dynamic, and thermodynamic stability. Our electronic band structure calculations reveal that all these nanotubes are wide indirect band gap semiconductors. Remarkably, PG-yneNTs exhibit superior optical properties, including high absorption coefficients and absorption spectra covering the visible regime of the electromagnetic spectrum, making them potential candidates for visible-light-driven photocatalysis and solar cells. Interestingly, both the electronic and optical band gaps increase with the diameter of the nanotubes. Additionally, the observation of negative differential resistance (NDR) phenomena in (4, 0) PG-yneNT suggests their potential applications in NDR devices such as fast switches, frequency multipliers, and memory devices.

Electronic transitions and vibrational properties of bulk and monolayer g-C3N4, and a g-C3N4/MoS2 heterostructure from a DFT study.

Successful recognition of a dynamically stable carbonitride structure revealed that unlike other planar layered structures in the case of g-C3N4 the stable configurations are distorted [J. Wang et al., Chem. Mater., 2017, 29(7), 2694-2707, DOI: https://doi.org/10.1021/acs.chemmater.6b02969.]. This generates interest in a detailed study of the possibilities of controlling the structure and its properties both in its pristine and heterostructure forms. Here, we present the results of the investigation of dynamically stable bulk and monolayer g-C3N4, and a g-C3N4/MoS2 heterostructure. The bulk g-C3N4 was found to be an indirect band gap semiconductor exhibiting an indirect-to-direct band gap transition upon dimensionality reduction. In the case of the heterostructure, the analysis of partial density of states shows a charge transfer from nitrogen ions in g-C3N4 to the MoS2 layer. The Raman spectra of bulk g-C3N4 are discussed in detail, and the changes occurring in the spectra upon the transition to the monolayer form and in the g-C3N4/MoS2 heterostructure are demonstrated. It was found that the characteristic features of such an atomic transition can be seen in the region below 300 cm-1 and between 700 and 800 cm-1.

Two-dimensional Janus monolayers SPtAZ2 (A = Si and Ge; Z = N, P, and As): insight into their photocatalytic properties via first-principles calculations.

As a derivative of the two-dimensional material family, two-dimensional Janus materials have garnered widespread attention in recent years. Consequently, in this work, we systematically investigated the stability, electronic properties, photocatalytic properties, optical properties, and carrier mobility of SPtAZ2 (A = Si and Ge; Z = N, P, and As) monolayers using first-principles calculations. In the equilibrium state, we identified four stable structures that exhibited the properties of indirect band gap semiconductors using the HSE06 hybrid functional. Through the exploration of the photocatalytic and optical properties of these four stable structures, we observed that SPtSiN2, SPtSiP2, and SPtGeAs2 monolayers possess favorable band edge positions, high solar-to-hydrogen efficiency (up to 30.74%), and light absorption efficiency, thus endowing these three structures with commendable photocatalytic and light absorption performance. We additionally calculated the carrier mobility of these three structures and identified significant differences in electron and hole mobilities in the same direction, facilitating the effective separation of electrons and holes. Finally, we explored the effects of biaxial strain on the electronic properties, photocatalysis, and light absorption of stable SPtAZ2 monolayers. Our research results not only expand the 2D Janus material family, but also successfully predict a type of photocatalyst capable of utilizing visible light for overall water splitting.

First-principles study on the structural, electronic, elastic, optical and thermodynamic properties of double antiperovskites X6BiSbN2 (X = Mg, Ca, Sr)

The perovskite materials have been widely used because of their excellent properties. Based on density functional theory, the structural, electronic, elastic, optical and thermodynamic properties of double antiperovskites X6BiSbN2 (X = Mg, Ca, Sr) are calculated. The results show that X6BiSbN2 (X = Mg, Ca, Sr) have stable crystal structures, and their band gaps are 1.172eV, 1.303eV and 0.965eV, respectively. Mg6BiSbN2 is an indirect bandgap semiconductor, which may be more suitable for use as a photocatalyst. Ca6BiSbN2 and Sr6BiSbN2 are direct bandgap semiconductors with high polarization and absorption coefficients, low reflectivity in the visible light region and good mechanical durability, which may be suitable candidates for the absorption layer of perovskite solar cells. In addition, X6BiSbN2 (X = Mg, Ca, Sr) have broad absorption range and high absorption coefficient in the ultraviolet region, which indicates that they may be potential photodetector materials. Sr6BiSbN2 has no entanglement between acoustic and optical branches in the phonon spectrum and a low Debye temperature, which helps to improve the thermoelectric coefficient, so it may be suitable for thermoelectric devices. The calculation results in this paper show that X6BiSbN2 (X = Mg, Ca, Sr) are expected to be used in the absorption layer of solar cells and photodetector field, and Sr6BiSbN2 may also be suitable for thermoelectric devices.

Nanodevice simulations and electronic transport properties of a two-dimensional PbBr2 monolayer

Two-dimensional (2D) wide bandgap semiconductors are promising blocks for applications in photodetections, spintronics and high energy radiation detection. Here, we probe the mechanical, biaxial strain-relate, electronic transport, and optoelectronic properties of PbBr2 monolayer with wide bandgaps using first-principles calculations. The 2D Young's modulus of PbBr2 monolayer is determined to be 14.68 N m−1 and the shear modulus is calculated to be 5.83 N m−1 at 300 K, revealing that PbBr2 monolayer is mechanically more flexible than other 2D materials, such as hexagonal-BN and MoB2. Interestingly, a specific forbidden bandwidth can be obtained by implementing a suitable strain on PbBr2 monolayer, and such effect leads to indirect bandgap semiconductor properties. Furthermore, various PbBr2 monolayer nanodevices, including p-n junction diodes, p-i-n junction field-effect transistors (FETs), and phototransistors, are designed and explored to investigate their transport properties. A variety of excellent transport properties, including prominent unidirectional transport, remarkable electrical anisotropy, obvious field-effect property, strong photoelectric response, and prominent absorption characteristics in the ultraviolet region, have been observed in these nanodevices. Our results unveil the multifunctional nature and superior performance of PbBr2 monolayer and suggest a practical configuration for the experimental realization in next-generation semiconductor nanodevices.

High stability and tunable hydrogen evolution material with defect-enhanced photocatalytic properties:penta-BAs5 monolayer

In this work, on the basis of first principles calculations, we theoretically predict a pentagonal structure material called penta-BAs5 and discuss the photocatalytic properties under its intrinsic and defective modes. Formation energy and phonon dispersion curve all proved its high stability. Penta-BAs5 has a 2.38 eV bandgap and has indirect bandgap semiconductor performance. Surprisingly, by analyzing the band edge distribution, the Gibbs free energy changes (ΔG), and applying strain, it is found that penta-BAs5 can spontaneously proceed the hydrogen evolution reaction (HER) can under neutral and acidic conditions. Interestingly, after applying electric field in the range of 0–0.8 eV/Å, the band edge alignment can keep stable. Intriguingly, the hydrogen evolution capacity of penta-BAs5 was greatly improved when the defects were present. Our study predicted a new two-dimensional pentagonal binary compound, broadened the field of the pentagonal structure families, and identified its application prospects in photocatalysis.

Mechanical, electronic and dynamical properties of T2-Al2MgC2 under pressure

The presence of T2-Al2MgC2 compound has significant influence on the mechanical properties of magnesium alloys. The mechanical, electronic and dynamical properties of T2-Al2MgC2 under high pressure are investigated by plane wave pseudopotential method based on the first-principles calculation. The results show that T2-Al2MgC2 is mechanically stable under high pressure, the elastic constants except [Formula: see text] increase with the increase of pressure. This compound presents brittleness and the brittleness decreases with increasing pressure when [Formula: see text][Formula: see text]GPa, but it displays ductility when [Formula: see text][Formula: see text]GPa. T2-Al2MgC2 has strong anisotropy, and the anisotropy decreases with increasing pressure. T2-Al2MgC2 is an indirect bandgap semiconductor material. Our calculated bandgap is 1.893[Formula: see text]eV at ambient pressure, the bandgap first increases and then decreases with increasing pressure. The phonon band structure as well as the total and partial phonon density of the state under different pressures had been analyzed. The constant volume heat capacity [Formula: see text] and entropy S of T2-Al2MgC2 increase with increasing pressure.

Mechanical, magneto-electronic and thermoelectric properties of Ba2MgReO6 and Ba2YMoO6 based cubic double perovskites: an ab initio study

We report an analysis of the structural, electronic, mechanical, and thermoelectric properties of oxide double perovskite structures, specifically the compounds Ba2MgReO6 and Ba2YMoO6. Our study employs first-principles density functional theory (DFT) as the investigative methodology. The electronic attributes of the examined compounds are explained by investigating their energy bands, as well as the total and partial density of states. The computational evaluation of the electronic band structure reveals that both compounds exhibit an indirect band gap semiconductor behavior in the spin-down channel, while demonstrating metallic properties in the spin-up channel. The magnetic attributes indicate a ferromagnetic nature, thus categorizing some double perovskite compounds as materials displaying half-metallic ferromagnetism (HM-FM) in addition to some other properties such as metallic and semiconductor in paramagnetic or antiferromagnetic states. The outcomes derived from the analysis of elastic constants confirm the mechanical robustness of the studied double perovskite compounds. Notably, the computed data for bulk modulus (B), shear modulus (G), and Young’s modulus (E) for Ba2MgReO6 surpass those of Ba2YMoO6. The calculated ratio of Bulk to shear modulus (B/G) indicates that both compounds possess ductile characteristics, rendering them suitable for device fabrication. Furthermore, both compounds display outstanding electronic and elastic properties, positioning them as promising contenders for integration within mechanical and spintronic devices. Finally, we investigate into the thermoelectric potential by evaluating parameters such as the Seebeck coefficient, electrical conductivity, thermal conductivity, figure of merit, and power factor. This assessment is conducted using the semiclassical Boltzmann theory and the constant relaxation time approximation, implemented through the BoltzTraP code. The results indicate that the investigated double perovskite oxides hold promise for utilization in thermoelectric applications.

Thermoelectric performance of indium-rich thiospinels [formula omitted] ([formula omitted] ≈ 0.16, 0.22 and x ≈ 0.1, 0.2)

Powder x-ray diffraction and Raman spectroscopy studies showed In-rich thiospinels with the chemical formula In1−y□yIn2S4−xTex (y ≈ 0.16, 0.22 and x ≈ 0.1, 0.2) to be composed of the cubic α-modification [space group (SG) Fd3̅m] with a minor admixture of tetragonal β-phase (SG I41/amd). Tellurium incorporation in the crystal structures is confirmed by Rietveld refinements, energy dispersive x-ray- and Raman spectroscopies. All samples are found to be indirect band gap semiconductors with an Egopt≈ 2 eV, which decreases with increasing Te-content. The thiospinels with y ≈ 0.16, 0.22 and x ≈ 0.1 revealed by two orders of magnitude enhanced charge carrier concentration (i.e., n≈ 1018 cm−3) and ≈ 6–9 times larger charge carrier mobilities (μ) than corresponding binary specimens. A kink at 200 K in ρT is found to originate from a stepper increase of n. The Seebeck coefficient is negative for all samples indicating electrons to be the dominant charge carriers. The total thermal conductivity of the compounds is almost completely phonon (κph) mediated. The Debye-Callaway fits of κph reveal an enhanced point-defect scattering in the In2.78S4−xTex series compared to In2.84S4−xTex, in accordance with the higher vacancy concentration (i.e., smaller y). The Balkanski-Klemens analysis of the temperature dependent Raman shifts indicated domination of three-phonon scattering mechanism agreeing with the lowered κph values. The appearance of low-energy optical modes confirms the In1-atoms, randomly occupying [In1S4]-tetrahedra, to reveal a ‘rattling’ motion and thus, to be a probable source of enhanced anharmonic effects limiting κph. Te-doping of In-rich thiospinels (y ≈ 0.16, 0.22) results in the improvement of the electrical transport characteristics and simultaneously in an increase of their thermal conductivities due to smaller vacancy concentration. The possible reduction of κph and the improvement of the TE performance are discussed.

Unlocking structural and photoelectric properties of lead-free double perovskites at high temperature

The lead-free double perovskite, increasingly sought for optoelectronic pursuits, is distinguished by its notable stability, optical properties, and non-toxic characteristic. An extensive inquiry into the structural and photoelectric properties of Cs2NaBiCl6 at heightened temperatures was undertaken using experimental evaluations and theoretical computations. The compound Cs2NaBiCl6, synthesized using a hydrothermal technique, was confirmed via various analytical methods. Advanced techniques such as high-temperature X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, and selected area electron diffraction were employed for the investigation of its crystal structure. Further investigation of microstructure was undertaken using electron microscopes. High-temperature luminescence stability disclosed a high exciton binding energy of 326 meV. The Huang-Rhys factor (6.4) denotes a robust electron-phonon coupling effect and facile formation of self-trapped excitons (700 nm). Applied first principles render valuable insight into structural and photoelectric nuances, notably at escalated temperatures. Cs2NaBiCl6 as an indirect bandgap semiconductor and details the experimental and theoretical bandgap, which exhibits an increasing trend before subsequently declining at elevated temperatures. These results strongly support the material's high-temperature stability, emphasizing its applicability in applications such as rare-earth-doped phosphors. The dynamic stability of the material, evidenced by its mechanical performance, further underscores its potential for application in photoelectric devices.

Structural, electronic, optical and elastic properties of AgMO2 (M = K, Rb, Cs): ab initio investigation

Silver alkali oxides (AgMO2; M = K, Rb, Cs) properties are investigated in depth via pseudo-potential plane-wave (PP-PW) scheme within the density functional theory (DFT) framework. The reflectivity, loss function and all the elastic properties of AgKO2, AgRbO2, AgCsO2 compounds are newly studied here. As unveiled by the band structure the AgMO2 materials are indirect bandgap semiconductors. The density of states illustrates the covalent character of silver oxygen bonds (Ag–O). Moreover, the notable contribution of O-2p in the edge of the valence band provokes the delocalization of the holes, consequently improving the p-type conductivity in the studied compounds. Optically analyzed, our systems show birefringent behavior, with high positive Δn0, allowing them to be candidate in non-linear optical devices applications. The obtained elastic constants state that our materials are mechanically stable, with a pronounced anisotropic nature. Finally, from the thermal investigation, the three oxides AgKO2, AgRbO2 and AgCsO2 have lower thermal conductivity, synonymous of lower melting temperature.

Semiconductivity induced by spin–orbit coupling in Pb9Cu(PO4)6O

Recently, a possible room-temperature superconductor known as LK-99 (Pb10-xCux(PO4)6O (0.9 < x < 1.1)) has sparked a wave of research. However, many experimental works have proven that it is a semiconductor. At the same time, many theoretical works have reached the conclusion that it is a flat band metal. The inconsistency between theoretical and experimental works may be caused by neglecting the spin–orbit coupling effect in calculations. We performed calculations of electronic structure of Pb9Cu(PO4)6O with spin–orbit coupling, and the results show that it's indeed a semiconductor, not a metal. In the ferromagnetic state it is an indirect-bandgap semiconductor with a bandgap of 292 meV. While in the antiferromagnetic-A state, it is a direct-bandgap semiconductor with a bandgap of 300 meV. Our work provides a possible explanation for the contradictions of previous experiments and theories, and provides some theoretical basis for the potential application of Pb9Cu(PO4)6O as a semiconductor.

First-principle study of shear deformation effect on Mg adsorption by monolayer SnS2.

In this study, the effects of different shear deformations on the structural stability, electronic structure, and optical properties of a Mg atom adsorption system of S vacancy defect SnS2 are systematically investigated based on density functional theory. It is shown that the presence of an S-vacancy defect makes the band gap of the SnS2 system significantly smaller than that of the perfect SnS2 system, and the SnS2 system is changed from a direct band gap semiconductor to an indirect band gap semiconductor. The optimal adsorption position of a Mg atom on the S-vacancy SnS2 system is above the S atom where the adsorption energy is the largest and the system is the most stable. The density of states of the adsorption system is predominantly contributed by the S-3p and Sn-5s orbital electrons. The imposition of shear deformation leads to the introduction of certain impurity energy levels in the adsorption system, and the forbidden bandwidth near the Fermi energy level decreases. As compared to the intrinsic SnS2, the absorption and reflection peaks of adsorption systems under different shear deformation are red-shifted and appear in the ultraviolet region. This improves the utilization of the adsorption system for ultraviolet light to a great extent. The model calculations in this paper are performed using the CASTEP module of the Material Studio (MS) software based on the first principles of Density Functional Theory (DFT) (Wei et al. in Physica B 545:99-106, 2018) for plane wave artifacts. Geometrical optimization and computational procedures are used to calculate the exchange-correlation energy using the Perdew-Burke-Ernzerhof (PBE) generalized function (Perdew et al. in Phys Rev B Condens Matter 48:4978, 1993) of the generalized gradient approximation (GGA). The Monkhorst-Pack method (Monkhorst and Pack in Phys Rev B 13:5188-5192, 1976) was used to rationalize the sampling of the highly symmetric k-points in the Brillouin zone. The grid of k-points is set to be 6 × 6 × 1. The plane-wave truncation energy is set to be 400eV. The energy convergence criterion is 1.0 × 10-5eV. The residual stress of all atoms is 0.01eV/Å. A vacuum layer with a thickness of 15Å is set up in the z-direction, which ensures that the interactions of the system along the z-axis between the top and the bottom layers can be ignored during the whole simulation process. We construct a 3 × 3 × 1 SnS2 system containing 27 atoms as the computational model. The intrinsic SnS2 contains 9 Sn atoms and 18 S atoms.

First-principles study on the adsorption of divalent heavy metal ions by black phosphorus in water

With the rapid development of electronics, the application and research of two-dimensional materials have been at the forefront of the world’s scientific research. Black phosphorus (BP) has the advantages of large specific surface area, anisotropy, band tunability, high electrical conductivity and high theoretical specific capacity, which make it very promising for research in the fields of medicine, aerospace and electrochemistry. This paper calculates the electronic structure and adsorption properties of BP in water for different heavy metal ions of Pb[Formula: see text], Hg[Formula: see text] and Cd[Formula: see text], including adsorption energy, bandgap, electron density and Mulliken population analysis, based on the first-principles approach of density generalized theory. First principles are quantum mechanical calculations based on density functional theory (DFT), which is a dominant well-developed method in the field of materials simulations, with low errors and high efficiency, especially in systems containing metallic particles. The results showed that the Pb[Formula: see text] adsorption system in water was more stable than the Hg[Formula: see text] adsorption system and the Cd[Formula: see text] adsorption system. The bandgap values of 0.617, 0.785 and 0.715[Formula: see text]eV of BP after adsorption of Pb[Formula: see text], Hg[Formula: see text] and Cd[Formula: see text] in water are smaller compared to 0.891[Formula: see text]eV of intrinsic BP, and its properties change from direct bandgap semiconductor to indirect bandgap semiconductor. The higher the stability of a system for the adsorption of different heavy metal ions by BP, the higher the internal electron activity of the adsorption system and the amount of electron transfer. Meanwhile, it is concluded that the electrons mainly transfer from P to heavy metal ions in all the adsorption systems. The electron transfer of the BP-Pb[Formula: see text], Hg[Formula: see text], and Cd[Formula: see text] adsorption system occurs mainly in the p, s, and s/p orbitals, respectively. The above content investigated the electronic structure changes and internal electron transfer of heavy metal ions adsorbed by black phosphorus in water, expecting to provide a new reference basis for the detection of heavy metal ions in industrial wastewater using black phosphorus.

First principle examination of two dimensional rare-earth metal germanide halides Y2GeX2 (X = Cl, Br, I) for thermoelectric applications

In the present work electronic, structural and thermoelectric properties of newly designed layered rare-earth metal germanide halides such as Y2GeX2 (X = Cl, Br, I) are investigated. These materials are indirect band gap semiconductors with narrow band gap 0.30 eV for Y2GeCl2,0.36 eV for Y2 GeBr2, and 0.41 eV for Y2GeI2 respectively. First principles method along with Boltzmann transport equations (BTE) is utilized together to analyse the thermoelectric properties. These materials are dynamically and mechanically stable. Thermoelectric coefficients such as electrical conductivity, seebeck coefficient and thermal conductivity are computed and put together to ultimately get the Figure of merit (ZT). Y2GeI2 has highest figure of merit (ZT) of 0.42 with Seebeck coefficient 532.12 VK−1, electrical conductivity 8.6 ×105Sm−1 and has lowest lattice thermal conductivity value of 5.55 Wm−1K−1 among three materials, which is necessary to achieve high figure of merit. The computed value of Figure of merit 0.07, 0.22 and 0.42 for Y2GeCl2, Y2GeBr2 and Y2GeI2 accordingly, shows that these materials can be considered as good candidates for energy harvesting in thermoelectric applications.

Synthesis of sol-gel TiO2 nanoparticles and assessment of their antifungal activity for the eventual conservation of historical documents

One of the main causes of deterioration of ancient documents is the presence of microorganisms, especially fungi. In this study, we report on the detection of microbiological contamination in ancient books from the Franciscan Library of San Pedro Cholula, in the state of Puebla, Mexico. The microscopic observation of different organic pigments and in vitro assays indicated the presence of Rhizopus sp., Mucor sp., and Alternaria sp. on the papers. The fungicidal activity of TiO2 nanoparticles (NPs), synthesized by the sol gel process, was then evaluated against these strains by two different methods: i) the agar well diffusion method using Petri dishes and ii) in pieces of old book pages, where the strains had been previously incubated. From TEM measurements, it was determined that the TiO2 NPs had a diameter of 70 nm. Anatase TiO2 NPs were synthesized as indicated by Raman spectroscopy and XRD. From UV–Vis spectroscopy and the Tauc´s method for an indirect band-gap semiconductor, a band-gap energy value of 2.9 eV was obtained. The surface chemistry of the TiO2 NPs/paper substrates was analyzed by XPS. In addition, a core-level XPS analysis of the O 1s and C 1s orbitals was used to identify signals related to cellulose. The antifungal activity of TiO2 NPs was demonstrated for the investigated fungi. A higher inhibition occurred for Rhizopus sp., followed by Mucor sp., and Alternaria sp. with inhibition halos of 26, 24, and 18 % in diameter, respectively. This work used highly sensitive techniques with the aim of proposing methodologies that contribute to the preservation of historical documents.

Modulation of electronic and optical properties of BlueP/MoSSe heterostructures via biaxial strain and vertical electric field

Constructing van der Waals heterostructures (vdWHs) is an efficient approach for enhancing the desirable properties of two-dimensional (2D) materials and greatly expanding the range of applications of the original monolayer materials. The structure, stability, electronic and optical properties of BlueP/MoSSe heterostructures are explored by density functional theory (DFT) calculations. The different configurations of BlueP/MoSSe vdWHs are all indirect bandgap semiconductors and have similar energy band structures, with the bandgap of about 1.0 eV under the PBE method. The bandgap of the A3 (B3) configuration calculated with HSE06 method is 1.608 (1.377) eV. The A3 configuration exhibits type-II band alignment while the B3 configuration shows type-I band alignment, both of which have high stability. The bandgap and band edge of A3 (B3) configuration can be modulated effectively by biaxial strain and vertical electric field (Efield). The BlueP/MoSSe vdWHs have broader absorption range and higher absorption intensity than their monolayers. The optical absorption intensity of heterostructures is gradually improved with increasing compressive strain, and the optical absorption spectrum is red-shifted under tensile strain. We hope that our findings will provide meaningful theoretical guidance for the preparation and potential application of BlueP/MoSSe vdWHs.