In this work, SnS1−xSex ternary nanobelts were synthesized by a facile hydrothermal method without the assistance of surfactants. The structure, morphology, microstructure, compositions, chemical valences, phonon modes, and optical band gaps of the SnS1−xSex nanobelts were characterized in detail. The results indicate that the SnS1−xSex nanobelts have uniform one-dimensional morphology and are single crystals with high crystallinity. Se is incorporated into the SnS lattice to substitute for S-forming ternary SnS1−xSex alloy. With the increase of Se doping concentration, the optical band gaps of the nanobelts gradually decrease from 1.15 to 1.01 eV, confirming the tunable optical property achieved here.

Zn1−xGax/2Fex/2O (x= 0, 0.0156, 0.0312) represents the polycrystalline hexagonal (wurtzite) phase with a space group P63mc synthesized using the sol–gel technique. A comparative study and investigation of structural, optical, and photo-sensing properties of these samples were performed. Structural and vibrational studies show enhancement in the crystallinity of the codoped samples. Optical band gap increases from ∼3.21 to 3.24 eV with substitution because of the improved crystallinity. The photoluminescence properties show modification from yellowish green for x= 0 to a more distinct green for x= 0.0156. The intensity of the luminescence decreases with doping, indicating an overall reduction of defects in the band gap helping the material to become more transparent to visible light. Photocurrent and photosensitivity are modified with the illumination wavelength (290, 450, 540 and 640 nm) with codoping. Sensitivity toward visible lights reduced with codoping. On the other hand, it is more sensitive to ultraviolet light. It indicates the material becomes more transparent for visible light and may be used as photostable device.

Antiperovskite materials are of high research interest because of their unusual physical properties and technological applications. Here, we report the structural stability and transport properties of Sr3AsN from first-principles study. The calculated equilibrium lattice parameters are in good agreement with the available data. We find that Sr3AsN is mechanically, energetically and dynamically stable at ambient conditions. Our calculated electronic structure indicates that it is a direct band gap semiconductor, with a band gap value ∼1.2 eV. Sr-4d and N-2p orbitals predominantly contribute to the formation of the direct band gap. The calculated Seebeck coefficient of Sr3AsN is high (298 μV/K at 300 K), while the lattice thermal conductivity is comparatively low (1.73 W/m K). The considerable mass difference between Sr, As, and N gives rise to an intense phonon scattering that results in such low lattice thermal conductivity. Our calculated maximum thermoelectric figure of merit (ZT) is 0.75 at 700 K, indicating that it is a potential material for thermoelectric device applications.

Manganese sulfides (MnS) with a diversity of well-defined morphologies and phases have been successfully synthesized by the solvothermal approach. The phase structure and morphology of MnS could readily be tuned by adjusting the sulfur sources and solvents. Hollow γ-MnS spheres were obtained by treating L-cysteine and manganese source in ethylene glycol (EG) at 200 °C for 2 h, whereas a replacement of the mixture solvent by EG and deionized water yields the hierarchical flower-like γ-MnS. γ-MnS tubes were also produced under the same condition by using diethylene glycol and deionized water as solvents. When thioacetamide used as the sulfur source and oleylamine used as the solvent, monodisperse α-MnS nanoparticles with the mean diameter of 17 nm could be synthesized successfully. The phase structures, sizes, and morphologies of samples were investigated in detail by powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The UV-vis absorption peak and the width of band gap with different morphologies of the as-prepared MnS were measured. The samples described in this paper are promising to be utilized in solar cells, biomedicine, short wavelength electronic devices, photocatalysis, and other fields.

In the investigation of MgO–Y2O3–B2O3 system, six three-phase regions, five binary compounds, and one ternary compound MgYB5O10 were confirmed in the subsolidus phase relations. Single-phase powder sample of MgYB5O10 was successfully prepared through solution synthesis method. By using the Rietveld method from the step-scanning X-ray powder diffraction data, the crystal structure of MgYB5O10 was determined. It crystallizes in the monoclinic system with the space group P121/c1 and lattice parameters a = 8.5113(2) Å, b = 7.5892(2) Å, c = 12.2460(3) Å, β = 130.200(1)°, and Z = 4. The infrared spectrum of MgYB5O10 at room temperature demonstrates the existence of BO3 and BO4 groups. The UV–visible spectrum shows a wide absorption band within the range of 190–400 nm, while the absorption in the visible region is negligible. According to the electronic structure derived by first-principles calculations, MgYB5O10 is an insulator with a wide indirect energy band gap of about 5.95 eV. Layered structural characteristics, existence of one-dimensional YnO8n+2 chains, and the large band gap should be the immanent reason why MgYB5O10-based materials have exhibited outstanding performances in the luminescence field.

In the present work, the dielectric response of III-nitride semiconductors is studied using density functional theory (DFT) band structure calculations. The aim of this study is to improve our understanding of the features in the low-loss electron energy-loss spectra of ternary alloys, but the results are also relevant to optical and UV spectroscopy results. In addition, the dependence of the most remarkable features with composition is tested, i.e. applying Vegard’s law to band gap and plasmon energy. For this purpose, three wurtzite ternary alloys, from the combination of binaries AlN, GaN, and InN, were simulated through a wide compositional range (i.e., AlxGa1−xN, InxAl1−xN, and InxGa1−xN, with x=[0,1]). For this DFT calculations, the standard tools found in Wien2k software were used. In order to improve the band structure description of these semiconductor compounds, the modified Becke–Johnson exchange–correlation potential was also used. Results from these calculations are presented, including band structure, density of states, and complex dielectric function for the whole compositional range. Larger, closer to experimental values, band gap energies are predicted using the novel potential, when compared with standard generalized gradient approximation. Moreover, a detailed analysis of the collective excitation features in the dielectric response reveals their compositional dependence, which sometimes departs from a linear behavior (bowing). Finally, an advantageous method for measuring the plasmon energy dependence from these calculations is explained.

This work presents a systematic study that evaluates the feasibility and reliability of local band gap measurements of Cu(In,Ga)Se2 thin films by valence electron energy-loss spectroscopy (VEELS). The compositional gradients across the Cu(In,Ga)Se2 layer cause variations in the band gap energy, which are experimentally determined using a monochromated scanning transmission electron microscope (STEM). The results reveal the expected band gap variation across the Cu(In,Ga)Se2 layer and therefore confirm the feasibility of local band gap measurements of Cu(In,Ga)Se2 by VEELS. The precision and accuracy of the results are discussed based on the analysis of individual error sources, which leads to the conclusion that the precision of our measurements is most limited by the acquisition reproducibility, if the signal-to-noise ratio of the spectrum is high enough. Furthermore, we simulate the impact of radiation losses on the measured band gap value and propose a thickness-dependent correction. In future work, localized band gap variations will be measured on a more localized length scale to investigate, e.g., the influence of chemical inhomogeneities and dopant accumulations at grain boundaries.

High-resolution monochromated electron energy loss spectroscopy (EELS) at subnanometric spatial resolution and <200 meV energy resolution has been used to assess the valence band properties of a distributed Bragg reflector multilayer heterostructure composed of InAlN lattice matched to GaN. This work thoroughly presents the collection of methods and computational tools put together for this task. Among these are zero-loss-peak subtraction and nonlinear fitting tools, and theoretical modeling of the electron scattering distribution. EELS analysis allows retrieval of a great amount of information: indium concentration in the InAlN layers is monitored through the local plasmon energy position and calculated using a bowing parameter version of Vegard Law. Also a dielectric characterization of the InAlN and GaN layers has been performed through Kramers-Kronig analysis of the Valence-EELS data, allowing band gap energy to be measured and an insight on the polytypism of the GaN layers.

In this paper, the band structures of Lamb waves in the two-dimensional phononic-crystal plates are calculated and analyzed based on the plane wave expansion method. The phononic-crystal plates are composed of an array of circular crystalline iron cylinders embedded in the epoxy matrix. Square lattice and triangular lattice are analyzed and discussed, respectively. For the square lattice, two complete band gaps exist, and a narrow pass band between the complete band gaps separates them apart. For the triangular lattice, a wide complete band gap existing with the ratio of gap width to midgap frequency Δω/ωm equal to 72% is found. Furthermore, the influence of the plate thickness is crucial for band structures of Lamb waves. Tuning plate thickness can shift the pass bands effectively, and band shifting causes the variation of the width of complete band gap and its opening and closure.

We report on the investigation of GaN(0001)−1×1 using synchrotron radiation x-ray excited photoelectron spectra from the core levels Ga 3p and N 1s, as well as from the contaminants O 1s and C 1s. Measurements were done after outgassing (a) and during three surface treatment methods performed in sequence; (b) ammonia (NH3) flux anneals, (c) Ga deposition with sample held at room temperature followed by vacuum anneal, and (d) Ga deposition on a heated sample followed by Ga desorption during NH3 flux anneal. We have found that the initial NH3 flux anneals increased the amount of present N on the surface and enabled the formation of a well-ordered surface structure, according to the low energy electron diffraction (LEED) pattern. After treatment (b) and (d) the core level spectra of Ga 3p are much improved showing clearly distinct features indicative of increased Ga-N bonding. The Ga to N concentration ratio decreases during the surface treatments from 4.0 to 1.1, hence towards stoichiometry. The amounts of C (and O) present on the surface after outgassing corresponded to 1.1 (0.9) monolayers (ML) but reduced to 0.1 (0.1) ML after the final treatment (d). The Fermi level position in the band gap shifts down by 0.55 eV during the surface treatments, indicating a change of states present in the band gap. We have also found strong support that this Ga-polar sample is initially Ga-terminated.

We have studied optical properties of GaN grown on sapphire by metalorganic chemical vapor deposition in the near band-edge energy range by cathodoluminescence. A large shift of the band-edge luminescence to lower energies is induced by increasing the beam energy. The free exciton position shifts about 20 meV when the beam energy is increased from 5 keV to 25 keV at room-temperature. The effect is explained by internal absorption caused by an exponential absorption tail at the band-edge. An Urbach parameter of about 30 to 40 meV for the exponential band-tail in our samples is estimated by comparing experimental with simulated spectra.

The virtual crystal approximation has been used to determine the temperature-composition dependence of the GaN-AlN, GaN-InN, and InN-AlN band gap energies. Also, the thermodynamic instability states in the mixed crystals were studied. The expression for the band gap of mixed A-B crystals has been derived: EgAB = (1−x)EgA + xEgB − bSxx, where EgA and EgB are the direct gaps for compounds A and B, respectively, and x is the alloy concentration. The term Sxx ~ T0/(∂2G/∂x2) where G is the thermodynamic potential of the mixed crystal, b is a bowing parameter, and T0 has the meaning of a growth temperature.