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oe1(光电查) - 科学论文

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  • Ethiopian natural zeolites for photocatalysis

    摘要： The combination of zeolites and photochemistry has recently shown excellent results due to the special structure of the zeolites that helps a better use of the solar energy improving the selectivity of the chemical reactions carried out. There are several reports on the preparation of TiO2 confined nanoparticles in synthetic zeolites. However, very few reports are found on the use of natural zeolites. Zeolites are a vast natural resource in Ethiopia that remains unexploited. Their microporous structure can accommodate a wide variety of cations such as sodium, potassium and magnesium among others. The main objective of our work was to test the potential use of the naturally occurring zeolites, with high content in titanium, as photocatalysts. The samples have been characterized by X-ray diffraction (XRD), chemical analysis (ICP-OES), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (UV-Vis) and photocatalytic activities of the samples were tested in photocatalytic degradation of methyl orange (MO).

    关键词： Natural zeolite,Photocatalysis,Methyl orange,Band gap energy,TiO2 loading

    更新于2025-09-04 15:30:14

  • Light energy accumulation by cholesteric liquid crystal layer at oblique incidence

    摘要： Oblique propagation of light through a planar layer of a cholesteric liquid crystal (CLC) is solved by Ambartsumian’s modified layer addition method. Two cases are considered, namely, the case when dielectric boundaries have a minimum influence on light transmission and the case when the CLC layer is in a vacuum. It is shown that in the first case a total internal reflection can happen for the fast eigen-mode at large incidence angles. New important features of light reflection (transmission) spectra, photonic density of states and accumulated energy density in the CLC layer are studied. The light localisation peculiarities in the CLC layer at oblique incidence is investigated too. It is shown that the light localisation for both the long-wavelength edge mode and the short-wavelength edge mode changes differently when the incidence angle changes. The obtained results can be used in the design of low-threshold lasers, in solar cell systems, in chiral photonics, in systems strongly absorbing light at certain wavelengths and when designing systems with absorption suppression created on the base of absorbing media, etc.

    关键词： total internal reflection,Cholesteric liquid crystals,photonic band gap,light localisation

    更新于2025-09-04 15:30:14

  • Opening a band gap in graphene by C-C bond alternation: A tight binding approach

    摘要： In the present work, we consider the electronic properties of graphene with Kekule structure formed from two different C–C bonds in its hexagonal lattice. When the C–C bond alternation was introduced, a small band gap has been opened in the band structure of graphene and it increases linearly by a difference in the bond lengths δ. While the applied strain along the zigzag or armchair direction causes band gap to decrease rapidly to zero, the strain in the other directions can increase the band gap. Interestingly, when the graphene with Kekule structure is strained, its band gap is inversely proportional to the bond length difference δ. Opening a band gap in graphene due to bond alternation and strain can open up new applications in nanoelectronic devices.

    关键词： band gap,Kekule structure,strain,tight binding,graphene

    更新于2025-09-04 15:30:14

  • Optical characterization of nanostructured Ge1???xSnxSe2.5 (x?=?0, 0.3, 0.5) films

    摘要： The paper reports the optical properties of thin films of nanostructured Ge1 ? xSnxSe2.5 (x = 0, 0.3, 0.5) glassy alloys. The glassy alloys of Ge1 ? xSnxSe2.5 (x = 0, 0.3, 0.5) were prepared using melt quenching method. Thin films of nanostructured Ge1 ? xSnxSe2.5 (x = 0, 0.3, 0.5) glassy alloys were prepared using physical vapor deposition method. The films were characterized using XRD, EDX and TEM, which confirmed the amorphous nature, composition and formation of nanorods in the samples. Absorption and transmission spectra of thin films were recorded in the spectral range 400–2500 nm to obtain energy band gap, refractive index, extinction coefficient, dielectric constant etc. Results show that refractive index increases while band gap decreases on increase of Sn content in the Ge–Se system. This is due to the increase in density of defect states within band gap. The values of Urbach energy support the obtained results.

    关键词： Thin films,Nanostructured glasses,Optical properties,Band gap

    更新于2025-09-04 15:30:14

  • Influence of complexing agent on the growth of chemically deposited Ni3Pb2S2 thin films

    摘要： Ni3Pb2S2 thin films were prepared by chemical bath deposition method. Here, the objective of this research is to investigate the influence of complexing agent on the properties of films.These films were characterized using atomic force microscopy, UV-Visible spectrophotometery and X-ray diffraction. It was found that the increase in the concentration of tartaric acid, film thickness increased, but, the band gap reduced. For the films prepared using 0.1M of tartaric acid, were found uniform and completely covered with the substrates.

    关键词： chemical bath deposition,band gap,thin films,thickness

    更新于2025-09-04 15:30:14

  • Bandgap Renormalization, Carrier Multiplication and Stark Broadening in Photoexcited Black Phosphorous

    摘要： We investigate black phosphorous by time and angle resolved photoelectron spectroscopy. The electrons excited by 1.57 eV photons, relax down to conduction band minimum within 1 ps. Despite the low bandgap value, no relevant amount of carrier multiplication could be detected at excitation density 3 ? 6 × 1019 cm?3. In the thermalized state, the bandgap renormalization is negligible up to a photoexcitation density that fills the conduction band by 150 meV. Astonishingly, a Stark broadening of the valence band takes place at an early delay time. We argue that electrons and holes with high excess energy lead to inhomogeneous screening of near surface fields. As a consequence the chemical potential is no longer pinned in a narrow impurity band.

    关键词： Stark,ARPES,Ultrafast,Black Phosphorous,Band-Gap-Renormalization

    更新于2025-09-04 15:30:14

  • Influence of Post-deposition Heat Treatments on the Optical Properties of Chemically Deposited Nanocrystalline TiO2 Thin Films

    摘要： The aim of this study is to investigate the potentials of TiO2 thin films for device applications. Nanocrystalline single phase of rutile TiO2 thin films have been prepared by Chemical Bath Deposition (CBD) technique at bath temperature range from 75-80°C, keeping other deposition variables constant. The films were then subjected to post-deposition heat treatments with annealing temperatures in the range 373 to 673 K. The optical characterisation was done using the Elmer Lambda-2 spectrometer to investigate the transmittance and absorbance versus wavelength measurements. The data obtained from the transmittance and absorbance measurements were used to deduce the important optical constants. The results show that the energy bandgap was direct, with values in the range ≤1.8 eV for the as-deposited layers and ≥2.2 eV for the annealed layers. At lower temperatures, the band gaps of the annealed samples did not differ significantly from the energy gap (1.8 eV) of the as-deposited film. At higher thermal treatment, the energy gaps increased with the increase in annealing temperatures and a maximum of 2.2 eV for the energy gap was determined for TiO2 film annealed at 673 K. The values of the energy bandgap obtained in study, are within the range suitable for application in photovoltaic solar cell devices and in related photonic applications.

    关键词： thermal annealing,Energy band gap,solar cells,TiO2

    更新于2025-09-04 15:30:14

  • DESIGNING PLANE WAVE MODULATORS USING 1DPC NANOSTRUCTURE WITH R-GRIN DEFECT LAYER

    摘要： In this paper, we introduce plane wave modulators that are designed using one-dimensional photonic crystals (1DPC) containing radial gradient refractive index (r-GRIN) defect layers. Three kinds of r-GRIN materials with di?erent refractive index distribution functions are applied in numerical analysis. The properties of the phase and intensity of the transmitted plane wave beam through proposed structures are studied using the transfer matrix method. Radially-dependent defect modes, modulated phase and intensity are obtained according to the refractive index distribution functions. The results are predictable by regarding the Bragg condition and destructive interference, which are the origins of the photonic band gap (PBG). Due to the radial-dependency of the defect layer’s refractive index, the rays passing through di?erent transverse positions experience di?erent optical pathways. Therefore, the defect modes and transmitted spectrum (phase and amplitude) vary transversely. This study demonstrates another ability of the arti?cial PC structures to design plane wave modulators and manipulate its phase and intensity.

    关键词： radial gradient refractive index,transfer matrix method,one-dimensional photonic crystals,plane wave modulators,photonic band gap

    更新于2025-09-04 15:30:14

  • NUMERICAL INVESTIGATION ON THE SPECTRAL PROPERTIES OF ONE-DIMENSIONAL TRIADIC-CANTOR QUASI-PERIODIC STRUCTURE

    摘要： We numerically investigate the optical spectra of a photonic band gap material realized by one-dimensional Triadic-Cantor quasi-periodic structure. The studied system is composed of two elementary layers H and L with refractive indices nL = 1.45 (SiO2) and nH = 2.3 (T iO2), respectively. Analytical calculations using a trace and antitrace maps approach have been used to ?nd the re?ection and transmission theoretical expressions in visible range under quarter wavelength condition. In our results we present the e?ect of iteration order of Triadic-Cantor sequence on the optical properties of these multilayer systems, namely the photonic band gap behavior and the optical windows presence, which makes this type of structures good candidates for interesting applications in the ?eld of the nano-optical Engineering.

    关键词： trace and antitrace maps,Triadic-Cantor,optical properties,quasi-periodic structure,photonic band gap

    更新于2025-09-04 15:30:14

  • [Smart Innovation, Systems and Technologies] Information and Communication Technology for Intelligent Systems Volume 107 (Proceedings of ICTIS 2018, Volume 2) || Performance Booster Electrical Drain SiGe Nanowire TFET (EDD-SiGe-NW-TFET) with DC Analysis and Optimization

    摘要： In this paper, new concept for TFET nanowire is proposed to eliminate the issues aroused in MOSFET due to continuous scaling the device dimensions. Proposed device uses the concept of electrically doping as well as physically doping. Other than that low band gap material, silicon germanium (SiGe), is used at source region and high k dielectric is used at source–channel interface to improve the performance of the proposed structure. Simulation is done using 3D TCAD ATLAS simulator, and result validates that the proposed device is suitable for low power application. Furthermore, simulation is done for the different diameters and channel lengths for optimization.

    关键词： Electrical drain,Nanowire TFET,Low band gap,Hetero dielectric

    更新于2025-09-04 15:30:14