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In this paper, we investigate the electronic, optical, and thermoelectric properties of Ga2SSe monolayer by using density functional theory. Via analysis of the phonon spectrum and ab initio molecular dynamics simulations, Ga2SSe is confirmed to be stable at room temperature. Our calculations demonstrate that Ga2SSe exhibits indirect semiconductor characteristics and the spin–orbit coupling (SOC) effect has slightly reduced its band gap. Besides, the band gap of Ga2SSe depends tightly on the biaxial strain. When the SOC effect is included, small spin–orbit splitting energy of 90 meV has been found in the valence band. However, the spin–orbit splitting energy dramatically changes in the presence of biaxial strain. Ga2SSe exhibits high optical absorption intensity in the near-ultraviolet region, up to 8.444 × 104 cm−1, which is needed for applications in optoelectronic devices. By using the Boltzmann transport equations, the electronic transport coefficients of Ga2SSe are comprehensively investigated. Our calculations reveal that Ga2SSe exhibits a very low lattice thermal conductivity and high figure of merit ZT and we can enhance its ZT by temperature. Our findings provide further insight into the physical properties of Ga2SSe as well as point to prospects for its application in next-generation high-performance devices.

Van der Waals heterostructures, created by putting graphene on other two-dimensional semiconducting materials, have become an effective strategy to enhance the physical properties and extend the possible applications of two-dimensional (2D) materials. Motivated by the successful synthesis of a graphene/${\mathrm{PbI}}_{2}$ heterostructure in a recent experiment [Nat. Commun. 11, 823 (2020)], here we use first-principles calculations to construct and investigate the electronic properties and interface characteristics of graphene/${\mathrm{PbI}}_{2}$ heterostructure. We find that the weak forces occurring at the interface keep heterostructures stable and maintain the intrinsic properties of the constituent graphene and ${\mathrm{PbI}}_{2}$ monolayers. At the equilibrium interlayer distance of 3.48 \AA{}, the graphene/${\mathrm{PbI}}_{2}$ heterostructure forms an $n$-type Schottky contact. More interestingly, the Schottky barrier height and contact types in the graphene/${\mathrm{PbI}}_{2}$ heterostructure can be adjusted by electric field and interlayer coupling. The graphene/${\mathrm{PbI}}_{2}$ heterostructure can transform from a $n$-type Schottky contact to a $p$-type one or to Ohmic contact by applying electric field or by adjusting interlayer distance. The controllable electronic properties and contact types in graphene/${\mathrm{PbI}}_{2}$ heterostructure make it a promising candidate for designing and improving the performance of high-efficiency Schottky nanodevices.

In this work, we systematically investigate the electronic and optical properties of surface-functionalized GeC monolayer with F and Cl using density functional theory. Our calculations indicate that the surface functionalization of the GeC with F and C atoms leads to the disruption of the planar structure of the GeC monolayer and the surface-functionalized GeC monolayer has a low-bucking structure. At equilibrium, all four configurations of surface-functionalized GeC monolayer with F and Cl, i.e., F–GeC–F, F–GeC–Cl, Cl–GeC–F, and Cl–GeC–Cl, are direct semiconductors. Their band gaps vary from 2.839 eV to 3.175 eV which are calculated using Heyd–Scuseria–Ernzerhof (HSE) hybrid functional. Compared to the other configurations, the formation energy of F–GeC–F is the smallest, − 9 . 097 eV , which implies that this configuration is the most likely to occur. We also used the Mulliken population analysis to estimate the internal charge distribution and transferred charge in the systems. The functionalization of the surface leads to the shifting the first optical gap of the material. The fully chlorination of GeC causes its absorption coefficient to increase significantly, up to 14 . 912 × 1 0 4 cm−1 at the incident light energy of 13.173 eV. Besides, surface-functionalized GeC monolayer with F and Cl strongly absorbs light in the near ultraviolet region. Our calculation results provide detailed information on how to change the electronic and optical properties of monolayer GeC by surface functionalization, which has promising applications in opto-electronic devices.

In this paper, the potential of engineering and manipulating the electronic heat capacity and Pauli susceptibility of pristine and perturbed hydrogenated AA-stacked graphene, SiC (silicon carbide), and h-BN (hexagonal boron nitride) bilayers is studied using a designed transverse Zeeman magnetic field and the dilute charged impurity. The tight-binding Hamiltonian model, the Born approximation and the Green’s function method describe the carrier dynamics up to a certain degree. The unperturbed results show that the heat capacity and susceptibility of all bilayers increase with different hydrogenation doping configurations. We also found that the maximum heat capacity and susceptibility relates to the chair-like and table-like configurations. Also, the graphene possesses the highest activity compared to SiC and h-BN lattices due to its zero on-site energies. For the Zeeman magnetic field-induced Schottky anomaly and the Neel temperature corresponding to the maximum electronic heat capacity, EHCMax., and Pauli spin paramagnetic susceptibility, PSPSMax., respectively, the pristine EHCMax. (PSPSMax.) decreases (increases) with the Zeeman field. On the other hand, the corresponding results for reduced table-like and reduced chair-like lattices illustrate that both EHCMax. and PSPSMax. decrease with the Zeeman field, on average. However, under the influence of the dilute charged impurity, the pristine EHCMax. of graphene (SiC and h-BN) decreases (increases) with impurity concentration for all configurations while the corresponding PSPSMax. fluctuates (decreases) for the pristine (reduced table-like and reduced chair-like) case. These findings introduce hydrogenated AA-stacked bilayers as versatile candidates for real applications.

In this work, the influence of biaxial strain on electronic, optical, and effective masses characteristics of Janus MSSe (M = Mo, W) have been investigated through first-principles calculations as implemented in WIEN2k package. From the obtained results, we remark that MoSSe and WSSe monolayers exhibit, respectively, a direct and indirect bandgap transition at equilibrium. Our achieved results demonstrate that the biaxial strain fundamentally alters the electronic states of Janus MSSe monolayers, and mainly, a semiconductor-metal transition phase has been determined to occur at a biaxial strain ratio of 12%. Moreover, it has been revealed that both electrons and holes effective masses of MSSe monolayers can be tuned by biaxial strain. For the optical properties of Janus monolayers, the polarization direction of the incident light plays a vital role in defining the light absorption domain. The MSSe Janus monolayers are shown to have a wide range of absorption spectrum , including the visible light domain with perpendicular polarized light . Furthermore, our computations of the dielectric function indicate that the optical responses of Janus monolayers MoSSe and WSSe strongly depend on the applied strain ratio; particularly, for the high photon energy domain. Overall, the findings revealed that both Janus MoSSe and WSSe monolayers could be potential materials for applications in optoelectronics.

We comprehensively study the electronic and optical properties of InTe monolayer in the presence of biaxial strain and electric field using density functional theory. Via analysis phonon spectrum, InTe monolayer is confirmed to be dynamically stable. InTe monolayer has an indirect semiconducting characteristic with a band gap of 1.25 eV at equilibrium and can be controlled by strain or electric field. The semiconductor–metal phase transition has been found in InTe monolayer at a large electric field of E = 5 V/nm. The optical attributes of InTe monolayer depend strongly on the polarization direction of the incident light. The optical absorption coefficient is activated in the infrared region and increases rapidly in the visible light region. While optical properties are independent of the electric field, strain engineering alters not only the intensity of optical peaks but also their position.

In present work, the strain effect on the electronic, optical and thermoelectric properties of the Boron phosphide (BP) monolayer have been systematically investigated using first-principles calculations. Simulations show that the single layer at hand is a direct semiconductor possessing a K − K band gap of 0.910 eV. This parameter increases when switching the strain nature from compressive to tensile. Results indicate that the optical absorption in the visible and near ultraviolet regimes may be enhanced by the lattice compression. Finally, the thermoelectric properties are considered by determining the Seebeck coefficient, electrical conductivity, electronic thermal conductivity and dimensionless figure of merit. Compressive strains lead to the improvement of the thermoelectric performance with the figure of merit up to 0.665 at room temperature. However, chemical potential variations may favor the figure of merit increasing up to values close to unity. The findings may provide important information to estimate the prospective applicability of the BP monolayer in the optoelectronic and thermoelectric technologies.

SnO2 nanocrystals with an average partiaxsxddccle size around 50 nm were prepared by using hydrothermal method. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) data show that the doping of Eu3+ with concentrations ranging from 0 to 2 mol% resulted in a slight decrease of size from 50 to 35 nm. The High Resolution Transmittance Electron Microscopy (HRTEM) results of 1 mol% doping sample provide that the crystals size is around 38 nm and the interplanar spacing is 0.34 nm characterized for (110) planes of SnO2. Moreover, the peak shape and relative intensity of Eu3+ emission upon a direct and indirect excitation indicate the presence of two sites around Eu3+ ions, that are in the D2h sites of SnO2 and on the surface of nanocrystals. The Eu3+ ions located in different sites are selectivity excited. An optimizing of synthesis parameters can promote the incorporation of Eu3+ ions in SnO2 crystal lattice. Specially, the doping leads to the growth of crystallites along (101) preferred plane. The competition between red and orange emission as a function of Eu3+ contents was also considered. Under indirect excitation, the asymmetric ratio between 5D0-7F2 and 5D0-7F1 transitions of Eu3+ ions is unaltered at 0.3 in the range of Eu concentrations from 0.5 to 2 mol% achieved for the first time. PL spectra and decay measurements give evidence about the strong energy transfer between SnO2 and Eu3+ ions.

Two-dimensional (2D) materials design for nanoscience and nanotechnology has attracted continuously the researchers' attention because of the important role in the next generation of optoelectronics. In this paper, we report results concerning the prediction of a new 2D material, Lithium Chloride LiCl, using first-principles calculations. This material is proposed for the detection and absorption of ultraviolet (UV) radiation. Our calculations assert that the pristine LiCl monolayer, which crystallizes in the D3h symmetry (space group P 6 ‾ 2 m) is dynamically stable. The monolayer at hand is an indirect gap insulator with a band gap of 6.048(7.212) eV predicted by WC(HSE06) functional. The external strains effect on the electronic structure of LiCl monolayer is also investigated. Optical absorption calculations show a wide absorption band in the UV region and high absorption coefficients. Results suggest that the LiCl monolayer may be a promising candidate for optoelectronic applications in the UV-detection and absorption. We believe that results presented in this work should pave a solid way for the applications of alkaline halides monolayers with a wide electronic band gap in optoelectronic devices.

An analysis of the strain-induced group velocity(GV) and effective mass(EM) of massless topological Dirac fermions on the SnTe(001) surface, protected by crystalline symmetry, is presented. Using the traditional semi-classical k → ⋅ p → approach by associating fermions with wave-packets, we find that the expression for the energy dispersion surface as well as both GV and EM are anisotropic in the absence and presence of strain. The band structure calculations indicate that the massive Dirac fermions emerge for strained SnTe(001) surface. However, under strong strains, GVs and EMs of all branches of conduction and valence bands are the same quantitatively, but still anisotropic along different directions. On the other hand, depending on the special critical compressive and/or tensile strains, the direction of the fermionic waves is reversed. Further, the behavior of heavy and light masses are characterized qualitatively with strain modulus and direction. Our results are favorable for the thermoelectric properties of SnTe semiconductor since electronic features are coupled to the heat transports.

Rashba effect has become important in the realization of exotic topological features. Herein, we theoretically investigate the Rashba spin–orbit coupling(RSOC) effects on the dispersion energy, group velocity(GV) and effective mass(EM) of Dirac fermions in the topological crystalline insulator SnTe(001) surface. We found that different classes of RSOCs do not change the qualitative behavior of the band structure; its main effect is to break the symmetry of the gapless bands down to a group of discrete rotations and to slightly shift the phase boundaries. Moreover, the inherent anisotropic surface features hold with RSOC. The modulation mechanism of RSOC effects is further analyzed from the orientation-dependent GV and EM at different RSOC values. It is found that the GV and EM of fermions are band-dependent and symmetric concerning the RSOC sign, which plays a decisive role in modifying the optical properties. Our study provides new insight into the designing nanodevices for electric-field-controllable topological electronics.

Combining different two-dimensional materials into layered van der Waals heterostructures are recently considered as an effective route to enhance the electronic properties of the constituent materials and to extend the application range in next-generation nanodevices. Here, the GeC/GaSe heterostructure and its electronic properties controlled by electric field have been constructed and systematically investigated using first-principles calculations. Five different stacking patterns of the GeC/GaSe heterostructure are constructed to consider the stacking effects on the electronic properties. We find that the GeC/GaSe heterostructure is mainly characterized by the weak van der Waals forces, dominating between GeC and GaSe layers, preserving their intrinsic properties in GeC/GaSe heterostructure. The GeC/GaSe heterostructure exhibits the type-II band alignment, where the electron–hole pairs are separated, making it suitable for fabricating next-generation optoelectronic nanodevices. Moreover, the stacking configurations have little affect the structural and electronic properties of the GeC/GaSe heterostructures. The pattern-I stacking configuration has the lowest binding energy and shortest interlayer distance as compared with other stacking patterns of the GeC/GaSe heterostructure. Furthermore, our results demonstrate that the electric field is considered as an effective route to modulate the electronic properties of GeC/GaSe heterostructure from semiconductor to metal. This finding makes the GeC/GaSe heterostructure promising material for optoelectronic nanodevices.

In this work, the electronic and optical properties of monolayer GaTe under biaxial strain and external electric field were investigated by density functional theory. Our calculated results indicate that the monolayer GaTe is an indirect-semiconductor with an energy gap of 1.41eV at equilibrium. Electronic properties of monolayer GaTe, especially the energy gap, depend greatly on the biaxial strain and external electric field. While the compressive strain slightly increases the energy gap, the tensile strain reduces quite rapidly the energy gap of the monolayer GaTe. In particular, semiconductor–metal phase transition can be observed when the external electric field was introduced. The GaTe monolayer strongly absorbs light in the ultraviolet region and the biaxial strain greatly changes its optical characteristics, especially the compression strain significantly increasing the absorption coefficient of the monolayer. Our results can provide more useful information for the prospect of application of the GaTe monolayer in next-generation optoelectronic devices.

In this work, we study the electronic, optical, and photocatalytic properties of fully hydrogenated GeC monolayer under strain engineering and external electric field using first-principles investigations. Our calculations demonstrate that at the equilibrium state, fully hydrogenated GeC monolayer is a indirect semiconductor with band gap of 3.493 eV and it possesses photocatalytic characteristics for water splitting and in particular, photocatalytic activities can be enhanced by a negative electric field under ultraviolet light.We can control the band gap of fully hydrogenated GeC monolayer by biaxial strain or external electric field and semiconductor-metal phase transition happens at certain elongation of biaxial strain. Compared to pure monolayer GeC, the fully hydrogenation causes optical absorption peaks of GeC shifting to a higher energyregion. While the optical spectra of the fully hydrogenated GeC monolayer are strongly dependent on the strain, the effect of the electric field on them is negligible. Our findings can provide useful information for the applicability of fully hydrogenated GeC monolayer in nanoelectronic devices and photocatalytic water splitting. Refereed/Peer-reviewed

We have used trivalent terbium to investigate the mechanism behind fluorescence enhancement by Al 3+ co-doping. Our results indicate that rare-earth (RE) ions cluster together in aluminum-rich regions of the glass, and behave as if they were dispersed uniformly throughout these regions when the ratio of Al to RE is ∼10 or greater. We also studied the effects of adding chemical drying agents to the precursor solution for the synthesis of sol–gel-derived silicate glasses. Such glasses can be treated at significantly higher annealing temperatures without degradation of optical quality, and have the density of melt glass. Fluorescence yield from doped RE ions improves markedly with the addition of the drying agents, and the denser glasses are not subject to rehydration.