Direct Transition Energy Research Articles

Optical properties and antimicrobial of ionic chitosan-MgO-SiO2@ aminolsilane nanocomposites

This investigation involved synthesizing a nanocomposite heterostructure, Chitosan-MgO-SiO2@aminosilane, using the physical blending of chitosan-MgO-silica with aminosilane using the sol–gel technique. The prepared nanocomposites were characterized using x-ray diffraction (XRD), Scanning/Transmission Electron Microscope (SEM-EDX/TEM), Fourier Transform Infrared Spectroscopy (FTIR), and optical analysis to investigate the microstructural and spectroscopic properties. XRD results confirmed the formation of orthorhombic Mg2SiO4 within the fabricated system. FTIR analysis verified interactions among chitosan, MgO-silica, and aminosilane, leading to the development of diverse functional groups, including M-O bonds, silanol-hydroxyl ions, and heteropolymeric-O-M within the chitosan-MgO-SiO2@aminosilane nanocomposite. Optical studies demonstrated that aminosilane-incorporated samples have two distinct absorption bands around 215 nm and 419 nm, corresponding to the electronic transitions π–π* (k-band) and n–π* (R-band), respectively. The absorption band at 400 nm is ascribed to localized surface plasmon resonance (SPR). The incorporation of aminosilane resulted in a decrease in the direct transition energy gap from 2.677 to 2.399 eV. The nanocomposites displayed significant antimicrobial activity against pathogenic microorganisms such as Gram-positive Staphylococcus aureus, Gram-negative Pseudomonas aeruginosa, and pathogenic fungi Candida albicans and Aspergillus niger. The positive antimicrobial response of the fabricated nanocomposites candidates them for various applications, including wound dressings and food packaging.

Compositional dependence of direct transition energies in SixGe1−x−ySny alloys lattice-matched to Ge/GaAs

SixGe1−x−ySny ternary alloys are a candidate material system for use in solar cells and other optoelectronic devices. We report on the direct transition energies and structural properties of Ge-rich SixGe1−x−ySny alloys with six different compositions (up to 10% Si and 3% Sn), lattice-matched to Ge or GaAs substrates. The direct interband transitions occurring at energies between 0.9 and 5.0 eV were investigated using spectroscopic ellipsometry, and the resulting data were used to obtain the dielectric functions of the SixGe1−x−ySny layer by fitting a multilayer model. Values for the E0, E1, Δ1, E0′, and E2 transition energies were then found by identifying critical points in the dielectric functions. Structurally, the composition of the samples was measured using energy-dispersive x-ray measurements. The lattice constants predicted from these compositions are in good agreement with reciprocal space maps obtained through x-ray diffraction. The results confirm that a 1 eV absorption edge due to direct interband transitions can be achieved using relatively low Si and Sn fractions (<10% and <3%, respectively), although the bandgap remains indirect and at lower energies. The higher-energy critical points show smaller shifts relative to Ge and match results previously observed or predicted in the literature.

Structural and Spectroscopic Effects of Li+ Substitution for Na+ in LixNa1−xCaLa0.5Er0.05Yb0.45(MoO4)3 Upconversion Scheelite-Type Phosphors

New triple molybdates LixNa1−xCaLa0.5(MoO4)3:Er3+0.05/Yb3+0.45 (x = 0, 0.05, 0.1, 0.2, 0.3) were manufactured successfully using the microwave-assisted sol-gel-based technique (MAS). Their room-temperature crystal structures were determined in space group I41/a by Rietveld analysis. The compounds were found to have a scheelite-type structure. In Li-substituted samples, the sites of big cations were occupied by a mixture of (Li, Na, La, Er, Yb) ions, which provided a linear cell volume decrease with the Li content increase. The increased upconversion (UC) efficiency and Raman spectroscopic properties of the phosphors were discussed in detail. The mechanism of optimization of upconversion luminescence upon Li content variation was shown to be due to the control of excitation/energy transfer channel, while the control of luminescence channels played a minor role. The UC luminescence maximized at lithium content x = 0.05. The mechanism of UC optimization was shown to be due to the control of excitation/energy transfer channel, while the control of luminescence channels played a minor role. Over the whole spectral range, the Raman spectra of LixNa1−xCaLa0.5(MoO4)3 doped with Er3+ and Yb3+ ions were totally superimposed with the luminescence signal of Er3+ ions, and increasing the Li+ content resulted in the difference of Er3+ multiple intensity. The density functional theory calculations with the account for the structural disorder in the system of Li, Na, Ca, La, Er and Yb ions revealed the bandgap variation from 3.99 to 4.137 eV due to the changing of Li content. It was found that the direct electronic transition energy was close to the indirect one for all compounds. The determined chromaticity points (ICP) of the LiNaCaLa(MoO4)3:Er3+,Yb3+ phosphors were in good relation to the equal-energy point in the standard CIE (Commission Internationale de L’Eclairage) coordinates.

Stress-Tuned Optical Transitions in Layered 1T-MX2 (M=Hf, Zr, Sn; X=S, Se) Crystals.

Optical measurements under externally applied stresses allow us to study the materials’ electronic structure by comparing the pressure evolution of optical peaks obtained from experiments and theoretical calculations. We examine the stress-induced changes in electronic structure for the thermodynamically stable 1T polytype of selected MX compounds (M=Hf, Zr, Sn; X=S, Se), using the density functional theory. We demonstrate that considered 1T-MX materials are semiconducting with indirect character of the band gap, irrespective to the employed pressure as predicted using modified Becke–Johnson potential. We determine energies of direct interband transitions between bands extrema and in band-nesting regions close to Fermi level. Generally, the studied transitions are optically active, exhibiting in-plane polarization of light. Finally, we quantify their energy trends under external hydrostatic, uniaxial, and biaxial stresses by determining the linear pressure coefficients. Generally, negative pressure coefficients are obtained implying the narrowing of the band gap. The semiconducting-to-metal transition are predicted under hydrostatic pressure. We discuss these trends in terms of orbital composition of involved electronic bands. In addition, we demonstrate that the measured pressure coefficients of HfS and HfSe absorption edges are in perfect agreement with our predictions. Comprehensive and easy-to-interpret tables containing the optical features are provided to form the basis for assignation of optical peaks in future measurements.

Structure, optical properties and antimicrobial activities of MgO–Bi2−xCrxO3 nanocomposites prepared via solvent-deficient method

MgO–Bi2−xCrxO3 nanocomposites for x = 0 and 0.07 were fabricated using the solvent-deficient route. X-ray diffraction method, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA) and UV–Vis spectroscopy were employed to study the properties. The samples were also evaluated for the antibacterial activity. The x = 0 sample showed a dominant monoclinic crystalline structure of alphatext{-}{text{Bi}}_{2}{text{O}}_{3} phase. No peaks attributed to MgO were observed. Cr-doped text{MgO}{-}{text{Bi}}_{2}{text{O}}_{3} in which Bi was substituted showed that {text{the tetragonal BiCrO}}_{3} phase was also present in the text{MgO}{-}{text{Bi}}_{2}{text{O}}_{3} composite. The Scherrer formula was employed to determine the crystallite size of the samples. The Cr-doped sample showed a decrease in the crystallite size. The microstructures of the non-doped MgO–Bi2O3 and MgO–Bi1.93Cr0.07O3 composites consisted of micrometer sized grains and were uniformly distributed. Direct transition energy gap, {E}_{text{g}} decreased from 3.14 to 2.77 eV with Cr-doping as determined from UV–Vis spectroscopy. The Cr-doped text{MgO}{-}{text{Bi}}_{2}{text{O}}_{3} nanocomposites exhibited two energy gaps at 2.36 and 2.76 eV. The antibacterial activity was determined against gram-negative bacteria (Salmonella typhimurium and Pseudomonas aeruginosa) and gram-positive bacteria (Staphylococcus aureus) by disc diffusion method. Cr-doping led to a decrease in inhibitory activity of MgO–Bi2−xCrxO3 nanocomposite against the various types of bacteria.

Shift-current response as a probe of quantum geometry and electron-electron interactions in twisted bilayer graphene

Moir\'e materials, and in particular twisted bilayer graphene (TBG), exhibit a range of fascinating phenomena that emerge from the interplay of band topology and interactions. We show that the nonlinear second-order photoresponse is an appealing probe of this rich interplay. A dominant part of the photoresponse is the shift current, which is determined by the geometry of the electronic wave functions and carrier properties and thus becomes strongly modified by electron-electron interactions. We analyze its dependence on the twist angle and doping and investigate the role of interactions. In the absence of interactions, the response of the system is dictated by two energy scales: (i) the mean energy of direct transitions between the hole and electron flat bands and (ii) the gap between flat and dispersive bands. Including electron-electron interactions both enhances the response at the noninteracting characteristic frequencies and produces new resonances. We attribute these changes to the filling-dependent band renormalization in TBG. Our results highlight the connection between nontrivial geometric properties of TBG and its optical response, as well as demonstrate how optical probes can access the role of interactions in moir\'e materials.

Electronic and optical properties of SixGe1−x−ySny alloys lattice-matched to Ge

We present a combined experimental and theoretical analysis of the evolution of the near-band gap electronic and optical properties of Si$_{x}$Ge$_{1-x-y}$Sn$_{y}$ alloys lattice-matched to Ge and GaAs substrates. We perform photoreflectance (PR) and photoluminescence (PL) measurements on Si$_{x}$Ge$_{1-x-y}$Sn$_{y}$ epitaxial layers grown via chemical vapour deposition, for Si (Sn) compositions up to $x =$ 9.6% ($y =$ 2.5%). Our measurements indicate the presence of an indirect fundamental band gap, with PL observed $\approx$ 200-250 meV lower in energy than the direct $E_0$ transition identified by PR measurements. The measured PL is Ge-like, suggesting that the alloy conduction band (CB) edge is primarily derived from the Ge L-point CB minimum. Interpretation of the PR and PL measurements is supported by atomistic electronic structure calculations. Effective alloy band structures calculated via density functional theory confirm the presence of an indirect fundamental band gap, and reveal the origin of the observed inhomogeneous broadening of the measured optical spectra as being alloy-induced band hybridisation occurring close in energy to the CB edge. To analyze the evolution of the band gap, semi-empirical tight-binding (TB) calculations are employed to enable calculations for large supercell sizes. TB calculations reveal that the alloy CB edge is hybridized in nature, consisting at low Si and Sn compositions of an admixture of Ge L-, $\Gamma$- and X-point CB edge states, and confirm that the alloy CB edge retains primarily Ge L-point CB edge character. Our experimental measurements and theoretical calculations confirm a direct transition energy close to 1 eV in magnitude for Si and Sn compositions $x =$ 6.8 - 9.6% and $y =$ 1.6 - 2.2%.

Structural and optical characteristics of charge transfer complex of plasma deposited 2-(diethylamino)ethyl methacrylate thin films and iodine

The effect of iodine doping on the optical and structural characteristics of plasma polymerized 2-(diethylamino)ethyl methacrylate (PPDEAEMA) thin films are described in this paper. Scanning electron micrographs show that both as-deposited and iodine doped PPDEAEMA thin films are homogeneous. Thermogravimetric analysis demonstrates the stability temperature as 560 K for iodine doped PPDEAEMA. The degradation temperature of iodine doped PPDEAEMA is slightly greater than that of as deposited PPDEAEMA. Fourier transform infrared spectroscopy shows shifts in absorption bands due to the incorporation of iodine in PPDEAEMA. The absorption coefficient and allowed direct and indirect transition energy gaps were calculated from the ultraviolet–visible absorbance spectra. The energy band gap value decreases due to iodine doping. Urbach energy, steepness parameter and extinction coefficient were calculated as well for the PPDEAEMA thin films of thicknesses 100, 200 and 300 nm which were iodine doped for 45, 360 and 720 min.

Phase Pure Silver Pyrovanadate (Ag4V2O7) Thin Films: Synthesis via a Hybrid Cathodic/Anodic Approach and Characterization

Combining two or more binary compounds to generate a multinary compound is a strategy for enhancing the photoelectrochemical (PEC) performance and properties of the parent binary compounds. In this vein, multinary compound semiconductors have recently come under the spotlight in a variety of device applications. In particular, the low energy band gap of the Ag-V-O ternary family (Ag3VO4, Ag4V2O7, AgVO3, Ag2V4O11, and AgV7O18) has recently sparked interest in using these visible light active semiconductor for photovoltaic solar cells, solar water splitting, CO2 photoreduction, and environmental remediation applications. In particular, Ag4V2O7, a visible light active semiconductor with a low band gap (2.49 eV) has been synthesized in powder form using solid state, hydrothermal, and precipitation methods.1,2 However, for device applications, deposition techniques that facilitate direct synthesis of semiconductor in film form, are attractive.In this vein, electrochemical deposition is a fast, low temperature, and scalable method to prepare large active area films of a given semiconductor. Therefore, this paper presents a hybrid cathodic and anodic route for the electrodeposition of Ag4V2O7 thin films and its subsequent physical and optoelectronic characterizations. Ag4V2O7 thin film on fluorine-doped tin oxide (FTO) substrate was synthesized using a hybrid cathodic and anodic route previously developed in our laboratory.3 In the cathodic step, a metallic silver thin film was electrosynthesized from silver ions in a nonaqueous medium on fluorine-doped tin oxide (FTO) support. In the anodic step, the generated silver ion (Ag+) from anodic stripping of the silver thin film in a pyrovanadate ion (V2O7 4-)containing-solution resulted in an in situ precipitation reaction with V2O7 4- to form Ag4V2O7 thin film on FTO. Electrochemical quartz crystal nanogravimetry (EQCN) confirmed one and four electron stoichiometry for the cathodic and anodic steps respectively.Energy-dispersive X-ray analysis (EDX) of as-prepared sample gave the Ag/V ratio: 1.95 ± 0.02, close to the expected stoichiometric Ag/V ratio for Ag4V2O7. X-ray diffraction analyses of the as-synthesized sample significantly confirmed that room temperature electrodeposited sample was crystalline and phase-pure. To measure the direct and indirect energy band gaps, Tauc plots were constructed from diffuse reflectance spectroscopy (DRS) data. The estimated direct and indirect optical transition energies of Ag4V2O7 thin films were 2.58 ± 0.04 and 2.52 ± 0.02 eV respectively. A valence band energy position as -4.88 ± 0.03 eV (on the vacuum energy scale) was estimated for Ag4V2O7 using atmospheric photoemission spectroscopy (APS) results. By combining the DRS and APS results, the calculated conduction band edge position of Ag4V2O7 was determined to be -2.36 eV on the vacuum energy scale. Kelvin-probe measurement located the Fermi level of silver pyrovanadate thin films at -4.82 ± 0.02 eV on the vacuum energy scale. The corresponding EF for Ag4V2O7 was only 0.06 eV above the valence band position consistent with a moderately-doped p-type semiconductor. These new results will be discussed in the framework of the application of silver pyrovanadate for PEC reduction processes such as hydrogen evolution or CO2 reduction.

Integrated use of nickel cobalt aluminoferrite/Ni2+ nano-crystallites supported with SiO2 for optomagnetic and biomedical applications

Among the most dangerous concerns for public health is a nosocomial bacterial infection of burn wounds. Nanocomposites with strong antibacterial activity have developed as a feasible candidate for these potential infects. Nix/SiO2co-doped NiAl(1-x)CoFe2O4nanocrystallites (sampled S0-S3) were prepared through the sol–gel method and calcined at 650 °C.Direct and/or indirect transition can be experienced in the prepared nanocrystallites with increased probability of direct type. Both the direct and indirect transition energy increase with Ni content increase.Further, the antibacterial activity against four nosocomial pathogens was evaluated through analysis of zone of inhibition, minimum inhibitory concentration (MIC), and some physiological changes. The S3 nanocomposites revealed excellent antibacterial activity against all studied nosocomial strains. Besides, it prevents bacterial growth and releases massive amounts of bacterial proteins compared to the others. Results demonstrated that it can fight nosocomial pathogens, especially those that infect the wounds and delay wound healing.

Effect of combination of etching modes on the design, structural and optical properties of the compliant substrates based on porous silicon

This study examines the effect of etching modes and their combination on the design, microstructure and optical properties of compliant substrates based on porous silicon. Data obtained from microstructural and spectroscopic methods of analysis showed that, under invariable parameters of the crystal lattice, the value of residual stresses, size of the crystallites, volume of crystalline fraction, and the reflectivity and energy of direct transitions in the porous layer of silicon all depend on the combination of the etching modes. However, they do not always correlate with the value of the layer porosity calculated from an analysis of SEM images. Competent selection of these parameters can provide additional advantages in case of monolithic integration of A III B V layers and the obtained compliant silicon substrate. Proper selection also ensures an efficient solution to problems concerning the control of deformation and residual stresses in the epitaxial layer. As an outcome, this will open up new methods of design and development for effective devices related to silicon-based electronics. • The effect of etching modes and their combination on the design, microstructure and optical properties of compliant substrate. • The residual stresses, size of the crystallites, volume of crystalline fraction depend on the etching modes combination. • The idea will open up new methods for the design of effective devices on the basis of silicon electronics.

Electronically Weak Coupled Bilayer MoS2 at Various Twist Angles via Folding

Constructing a bilayer system with defined twist angles is an effective way to engineer the physical properties of two-dimensional (2D) materials, opening up a new research area of twistronics. How to achieve high-quality bilayer 2D materials in a controlled and mass production way is of primary importance to this emerging area. In this work, we present a strategy for the large-scale fabrication of twisted bilayer molybdenum disulfide (MoS2) through photolithography patterning and folding of single-crystal monolayer MoS2. Atomic resolution transmission electron spectroscopy directly confirms that the as-achieved folded bilayer MoS2 is of high quality with targeted twist angles. Various twist angles result in tuning Raman mode frequencies and direct optical transition energies. Due to the weak interlayer coupling between the twisted layers, folded bilayers exhibit an extremely high photoluminescence with doubled intensity as compared to the unfolded monolayer, indicating a possible application in optoelectronic devices. Our work provides a new strategy to tailor the properties of MoS2, which will be beneficial to twistable electronics.

Spectroscopic ellipsometry and morphological studies of nanocrystalline NiO and NiO/ITO thin films deposited by e-beams technique

The current article reported a new data on the structural, surface morphology and optical properties of multi-thickness nanocrystalline NiO/glass substrate and NiO/ITO/glass substrate semiconductor thin films prepared by electron beam deposition technique. Structural investigation shows that the as-deposited multi-thickness NiO films deposited on a glass substrate crystallize in the form of cubic NaCl type structure. However, ITO thin film has a cubic type structure. Besides, the increase in the crystallite size was observed with increasing the thickness of NiO film, this behavior was confirmed by AFM micrographs. In the spectral range 280 nm–1800 nm, the optical properties of the NiO/glass substrate and NiO/ITO/glass substrate thin films have been investigated using spectroscopic ellipsometry (SE) technique. For NiO/glass substrate sample, the SE results providing direct energy E g d i r ≈ 3.954 eV, indirect energy E g i n d i r ≈ 2.855eV and phonon energy of order 200 meV. In addition, the analysis of the refractive index dispersion gives the atomic number density to be N f i j = 2.213 x 10 22 c m − 3 . On the other hand, for the NiO (410 nm)/ITO (99 nm)/glass substrate thin film sample, a reduction in the direct transition energy to E g d i r ≈ 3.24eV and also in the factor N f i j to 1.6 x 10 22 c m − 3 was observed. Additionally, the values of the oscillator parameters were calculated for NiO/glass substrate and NiO/ITO/glass substrate thin films using the Wemple-DiDomenico single oscillator model (WDD). Finally, it was found that the values of Urbach energy for NiO/glass substrate and NiO (410 nm)/ITO (99 nm)/glass substrate are very small relative to the energy gap values which indicates that the region of localized sates is very narrow compared to the width of the energy gap. • The D/nm of NiO film increase from 16.86 to 22.75nm and for NiO/ITO from 15 to 26nm with increasing thickness from 75 to 410nm. • Good correlation between the increase in D/nm and reduction of dislocation density (δ) is found. • SE provides E g d i r ≈ 3.954 eV, E g i n d i r ≈ 2.855eV and E phon 200meV. For NiO/glass film a reduction in E g d i r to 3.24eV for the NiO(410nm)/ITO (99 nm)/glass. • The refractive index of NiO film is independent of the film thickness and atomic number density is found to be N f i j = 2.213 x 10 22 c m − 3 • The values of E o = 6.828eV, E d = 19.3eV for NiO film and E o = 4.56eV, E d = 15.1eV for (410 nm)/ITO (99nm)/glass substrate film are found.

Sn-rich CZTS films spin-coated from methanol-based sol-gel solution: annealing effect on microstructure and optoelectronic properties

Photovoltaic light absorber Cu2ZnSnS4 (CZTS) with Sn-rich composition is the least studied compound compared with its stoichiometry and Zn-rich/Cu-poor compositions. Sn-rich CZTS films were prepared by spin coating from a nontoxic methanol-based solution. A brief (10 min) annealing in nitrogen was performed in the temperature range of 350–550 °C. The effect of annealing temperature on the film composition, morphology, crystallite size, microstrain, dislocation density, optoelectronic, and transport properties was investigated. For this study, scanning electron microscopy, x-ray diffraction, energy dispersive x-ray analysis, Raman spectroscopy, x-ray photoelectron spectroscopy, photocurrent spectroscopy, and Hall-effect techniques were employed. The annealed films were compact, uniform, and photosensitive. A systematic increase in the crystallites size and decrease in the microstrain and dislocation density was observed as the annealing temperature was increased. The films had a direct band gap energy of 1.47–1.50 eV. The presence of two sub-band gap direct transition energies of 1.04–1.08 eV and 1.16–1.21 eV were detected and their origins were discussed. Films were highly p-type in which the hole concentration increased systematically from 1.8 × 1018 to 1.5 × 1019 cm−3, and the hole mobility decreased steadily from 7.7 cm2/V-s to 0.94 cm2/V-s with the increase of annealing temperature. This behavior revealed that the ionized-impurity scattering is the dominant mechanism for the transport of holes in Sn-rich CZTS films. These highly p-type Sn-rich films have favorable properties suitable for device applications.

Electronic Structure and Optical Absorption Spectrum of Icosahedral Golden Fullerene Au32

Abstract—The electronic structure of golden fullerene Au32 has been studied using quantum field theory methods in the framework of the Hubbard model. Expressions for the Fourier transforms of a Green’s function, the poles of which determine the energy spectrum of the nanosystem under consideration, have been derived. The energy spectrum of Au32, studied in comparison with the spectrum of icosahedral carbon fullerene C60, indicates the semiconductor state of golden fullerene Au32. The peaks of the density of states correspond to Van Hove singularities. The optical absorption spectra of the neutral and negatively charged fullerene Au32 are presented. The energy of the first direct optical transition of the negatively charged ion of golden fullerene $${\text{Au}}_{{32}}^{ - }$$ is 1.26 eV.

Type of Optical Transitions at the Fundamental Absorption Edge in TlGaSe2 and TlInS2 Crystals Subjected to γ-Radiation

The effect of γ-radiation on the optical properties of layered TlGaSe2 and TlInS2 crystals has been studied within a wavelength range of 400–1100 nm at 300 K. By means of analysis of optical absorption spectra, the energies of direct and indirect optical interbend transitions before and after γ-irradiation have been determined. It has been shown that the energies of direct and indirect nonforbidden optical transitions grow with accumulation of γ-radiation dose within 0–25 Мrad in TlGaSe2 and TlInS2 single crystals from Egd = 2.06 eV and Egi = 1.90 eV at D = 0 Мrad to Egd = 2.11 eV and Egi = 1.98 eV at D = 25 Мrad for TlGaSe2 crystals and from Egd = 2.32 eV and Egi = 2.27 eV at D = 0 Мrad to Egd = 2.35 eV and Egi = 2.32 eV at D = 25 Мrad for TlInS2 crystals. A decrease in the transmission coefficient at doses from 0 to 5 Mrad with a further increase in the transmission coefficient at a radiation dose of D = 25 Мrad is observed.

Effect of iodine doping on the characteristics of polythiophene thin films prepared by aerosol assisted plasma jet polymerization at atmospheric pressure

Iodine-doped polythiophene thin films are prepared by aerosol assisted plasma jet polymerization at atmospheric pressure and room temperature. The doping of iodine was carried out in situ by employing iodine crystals in thiophene monomer by weight mixing ratios of 1%, 3%, 5% and 7%. The chemical composition analyses of pure and iodine-doped and heat-treated polythiophene thin films are carried out by FTIR spectroscopy studies. The optical band gaps of the films are evaluated from absorption spectrum studies. Direct transition energy gaps are determined from Tauc plots. The structural changes of polythiophene upon doping and the reduction of optical band gap are explained on the basis of the results obtained from FTIR spectroscopy, UV–VIS absorption studies, X-ray diffraction and atomic force microscope (AFM) analysis. The energy band gap will be different according to the concentration of polythiophene iodine. It can be concluded that iodine-doped polythiophene thin films can be prepare by aerosol assisted plasma jet polymerization and control the optical energy band gap regulars by controlling the thiophene -iodine weight mixing ratios.

Investigation of GeSn/Ge quantum dots’ optical transitions for integrated optics on Si substrate

The effects of self-organized GeSn/Ge quantum dot’s size and shape on the direct band gap interband emission energy, oscillator strength and radiative lifetime are evaluated. The electron’s and the hole’s confined energies and their corresponding wave function are driven by solving the 3D Schrodinger equation in Cartesian coordinates using the finite elements method. Dome and pyramidal shaped quantum dots are considered within practically exploitable size and aspect ratio that allows direct band gap transition energies. It is found that bigger quantum dots with higher aspect ratio are likely to have higher oscillator strength and longer radiative lifetime. For smaller aspect ratio, the emission energy, oscillator strength and radiative lifetime are found to be very sensitive to the quantum dot’s size and shape. These results demonstrate that this quantum dot QD system could be very interesting for CMOS compatible light emitters and detectors operating in the mid-IR range.

Coupling of coherent misfit strain and composition distributions in core–shell Ge/Ge1-xSnx nanowire light emitters

Core–shell Ge/Ge1-xSnx nanowires exhibit strong room temperature light emission under optical pumping in photoluminescence compared with Ge as a consequence of the elastic strain distribution across the coherent core–shell interface. We examine the interplay between strain and Sn composition distributions to gain insight into how these affect optical properties. There is a two-fold synergistic effect on the optical properties produced by the core–shell nanowire geometry. First, the Ge core acts as an elastically compliant substrate for growth of an axially lattice-matched epitaxial Ge1-xSnx shell, which facilitates growth of high-quality single-crystal Ge1-xSnx having intense photoluminescence. At the same time, tensile misfit strain in the Ge core serves to decrease the direct gap transition energy with respect to the indirect gap transition energy, thus enhancing its optical emission. Although characterization of strain in core–shell nanowire cross sections is complicated, choice of thinning orientation allows accurate, spatially localized strain analysis in the electron microscope. Phase field simulations provide an estimate of the expected strain, which matches well with experimental results, and they explain the stability of six Sn-poor spokes that form approximately 60° apart during growth of the Ge1-xSnx shell by considering the elastic strain energy. The evolution of the strain distribution during shell growth is also simulated using the phase field model. The coupling of core–shell strain arising from Sn incorporation in the shell and the resulting enhancement of optical properties makes this core–shell nanowire architecture promising for group IV semiconductor nanophotonics.

Тип оптических переходов на краю фундаментального поглощения кристаллов TlGaSe-=SUB=-2-=/SUB=- и TInS-=SUB=-2-=/SUB=-, подвергнутых γ-облучению

The effect of gamma irradiation on the optical properties of layered TlGaSe2 and TlInS2 crystals in the wavelength range of 400–1,100 nm at 300 K is studied. From the analysis of optical absorption spectra, the energies of direct and indirect optical interband transitions before and after gamma irradiation are determined. It is shown that as the gamma-irradiation dose is accumulated in the range of 0–25 Mrad by TlGaSe2 and TlInS2 single crystals, the energies of direct and indirect allowed optical transitions increase from Egd = 2.06 eV and Egi = 1.90 eV at D = 0 Mrad to Egd = 2.11 eV and Egi = 1.98 eV at D = 25 Mrad for TlGaSe2 and Egd = 2.32 eV crystals and Egi = 2.27 eV at D = 0 Mrad to Egd = 2.35 and Egi = 2.32 eV at D = 25 Mrad for TlInS2 crystals. A decrease in the transmittance at doses from 0 to 5 Mrad and a further increase in the transmittance at the radiation dose D = 25 Mrad are observed.