Optical properties of one-dimensional subwave plasmonic nanostructures

Nanogratings formed by parallel gold nanowires on a quartz substrate have been fabricated. Their transmission and reflection spectra have been studied experimentally. Numerical simulation of the transmission (reflection) spectra has been performed. The simulated spectra agree well with the experimental ones. A package has been proposed, which combines the experimental techniques of the structure fabrication and theoretical methods for calculating the parameters of optical spectra. This package is a promising tool for designing and fabricating optoelectronic devices such as filters, polarizers, and switches.     

Magnetic and electrical properties of several equiatomic ternary U-compounds

Magnetisation, specific heat, electrical resistivity, magnetoresistivity and Hall effect were measured for several equiatomic ternary (1-1-1) intermetallic compounds of formula RTX with R = U, Th, Hf and Ti, T a transition metal (Co, Ni, Ru, Rh, Pd, Ir, Pt and Au), and X = Al, Ga, Sn and Sb. These compounds crystallize in three different crystal structures: the cubic MgAgAs-type, and the hexagonal Fe₂P- and CaIn₂-types. All U-compounds, which we focus upon in this paper, exhibit magnetic moments of about 3μ_B/U at high temperature and encompass U-U distances from 3.51 to 4.68 Å. For the compounds which the largest U-U distances, Kondo-lattice behaviour was observed. The specific heat coefficient γ shows typical metallic values with some enhancement. Remarkably these compounds have an electrical resistivity up to three orders of magnitude larger than that expected and usually found for U-based intermetallic compounds. The Hf- and Th-based compounds serve as nonmagnetic reference materials, however, they also exhibit anomalously larger resistivities.     

内嵌圆饼空心方形银纳米结构的光学性质

采用离散偶极子近似方法计算了内嵌圆饼空心方形银纳米结构的消光光谱以及其近场的电场强度分布,并进一步与空心方形纳米结构的消光光谱和表面电场做比较.结果表明,在耦合作用下内嵌圆饼空心方形银纳米结构不仅产生了新的共振模式,而且新的共振模式在传统表面增强拉曼散射的激发波长范围内,进而可以弥补由于实验上运用纳米切片法所制备的空心方形纳米结构尺寸较大导致其共振吸收峰在远红外波长范围的不足.此外,可以通过改变内嵌圆饼空心方形银纳米结构的形貌参数调节其表面等离子体共振峰的共振波长,以满足在表面增强拉曼散射、生物分子或化学分子探测上的应用.     

Optical properties of nanostructures in layered metal tri-iodide crystals

The optical response of excitons confined in characteristic nanostructures in layered metal tri-iodide crystals introduced by some irregular stackings from the bulk structures is reviewed. In BiI₃ a specific stacking fault takes place during crystal growth constructing macroscopic planar defects. In this space conspicuous localized exciton transitions occur below the intrinsic absorption edge. Another stacking disorder introduced by applying external stress in this crystal brings about a new nanostructure domain of symmetry D_3d different from that of bulk symmetry C²_3i. The optical transitions due to new structures appear in the lower energy region as an absorption and luminescence line series. The similar nanostructures are induced in SbI₃ crystals under the hydrostatic pressure. In these nanostructures, the electronic structure is analyzed by a model based on the confined excitons in a nanoscale disk-like shape space. The magnetic field effect confirms the structure in the wave function-size scale. The nanoscale disk-like structure of BiI₃ in CdI₂ matrices is also obtained by a hot wall technique and mixed crystal annealing, which is realized by observing the size distribution with an electron microscope. In a BiI₃ disk in CdI₂ Stokes shifted photoluminescence bands appear. The Stokes shifts of the luminescence bands are understood by considering the size-dependent exciton-phonon interaction. In these nanostructures large optical nonlinearity under the intense laser field was obtained.     

Optical properties of ternary β electronphases based on NiAl

Optical constants of several ternary β Hume-Rothery phases have been investigated as a function of the valence electron concentration and defect structure. The composition of the alloys was based on the β phase NiAl, the absorption spectrum of which is dominated by two maxima at 2·5 and 4 eV. The intensity of the 2·5 eV-ε₂ peak is considerably increased with increasing valence-electron concentration, whereas that of the other peak is decreased. The valence electron concentration is varied by substituting Cu for Ni in Ni_1?yCu_yAl or Si for Al in NiAl_1?ySi_y. The 2·5 eV absorption peak disappears when Co is substituted for Ni in Ni_1?yCo_yAl. The absorption peaks are attributed to interband transitions of electrons and are discussed according to the rigid band model. The absorption in the infrared is explained by the scattering of electrons from lattice defects and phonons. The position of the d-band relative to the Fermi level is discussed in connection with s-d band scattering.     

Optical properties of the ternary compound Tl Sb S2

We present an investigation of the near band-gap optical properties of TlSbS₂ between 2 and 300 K. We use both transmission and reflectivity measurements. The resolution of the first exciton line permits to obtain an accurate determination of the temperature coefficients of both the direct band-gap E₀ and the second threshold E₁. The absorption curves have been fitted according to the Toyozawa's model. We find a strong interaction with a phonon mode of energy 22 meV for both the E₀ and E₁ thresholds. The low temperature reflectivity spectra reveal clearly several direct transitions in the range 1.5–5.5 eV. All these structures have been identified as transitions between the highest valence band and the lowest conduction band.     

几种三元过渡金属碳化物弹性及电子结构的第一性原理研究

基于密度泛函理论平面波方法研究了六方WC型Re_xW_1－xC(x=1, 0.25, 0.75, 0),Re_0.5Os_0.5C和Os_0.5W_0.5C的晶体结构、弹性和电子结构性质.研究发现Re_0.25W_0.75C晶体具有优异的弹性性能及稳定性,其剪切模量(312 GPa)超过了所有其他实验合成和     

Fundamentals and properties of zinc oxide nanostructures: Optical and sensing applications

In this paper we will give an overview of the status of catalytic growth and of low-temperature chemical growth of ZnO nanostructures performed in our laboratory. Particularly results employing different substrates will be discussed. The second part deals with structural and optical properties of ZnO nanorods. The results from high resolution transmission electron microscope (HRTEM), scanning electron microscope (SEM), photoluminescence (PL), Cathodoluminescence (CL), and Electroluminescence (EL), on single nanowires will be shown. Our results on surface morphology, bulk and the position of the catalyst as well as the optical properties including UV emission, lasing and white emission will all be presented and discussed. In the third part experimental results from electroluminescence of ZnO nanorods on different substrates in the UV in addition to excellent white light emission obtained from samples grown at low temperature are to be given and discussed. Finally the sensing of molecules in water by ZnO nanorods will be discussed from a theoretical point of view. Also fundamental properties of polaritons and excitons in ZnO nanostructures are to be highlighted.     

Optical near-fields of triangular nanostructures

We compare simulations of optical near-fields of single triangular nanostructures with experimental results from a near-field ablation technique on a periodic arrangement of triangles. We find good agreement of the lateral near-field distributions; nevertheless their dependency on the polarization of the incident light differs by 90°. Upon increasing the lateral distances of the nanotriangle arrangement in the experiment, the polarization dependence agrees with the simulation. We conclude that this at first sight unexpected behaviour stems from the coupling of near-fields by scattered surface waves and their interaction with the incoming beam. PACS 78.67.Bf; 81.07.-b     

Optical size resonances in nanostructures

The existence of optical size resonances in atomic nanostructures is proved. The properties of optical size resonances strongly depend on the interatomic distances and on the polarization of an external radiation field. The properties of linear and nonlinear size resonances are considered in the case of two-dimensional nanostructures. The linear optical size resonances are described based on a closed system of equations for dipole oscillators and nonlocal field equations taking into account the dipole-dipole interactions of atoms in the radiation field. Using a stationary solution to these equations, it is demonstrated that two isotropic atoms with definite intrinsic frequencies form an anisotropic system in the radiation field, possessing two or four size resonances depending on whether the component atoms are identical or different. The nanostructure composed of two different atoms possesses two size resonances with positive dispersion and two other resonances with negative dispersion. The frequencies of the size resonances significantly differ from the intrinsic frequencies of isolated atoms entering into the nanostructure. By changing the angle of incidence of the external wave, it is possible to excite various size resonances. The properties of nonlinear optical size resonances excited by an intense radiation field were theoretically and numerically studied using the modified Bloch equations and nonlocal field equations. Dispersion relationships for the nonlinear resonances were derived and the inversion properties of atoms in the nanostructure were studied for various polarizations of the external optical wave.     

Optical properties of Cantor nanostructures made from porous silicon: A sensing application

The fabrication and characterization of pSi based triadic Cantor multilayer structures is reported. Transfer matrix method was used to calculate the corresponding reflectivity spectrum and was compared with the experimental data. A good agreement between the theoretical and experimental reflectivity spectra is reported for the wavelengths corresponding to the non-absorbing region for silicon. The reduction in the quality of the transmission modes has been attributed to the dispersion and backscattering from the interfaces of the complete structure. As the optical response of pSi based sensor depends on the characteristics of the multilayered photonic structure, a comparison of sensitivity of 3rd order Cantor structure with a regular microcavity structure of similar optical thickness resulted in an optical response dependent on the choice of the refractive indices. An optimal choice of the refractive indices for the Cantor structures resulted in an increased red-shift (due to the enhancement of the refractive indices of the corresponding layers), after the surface modification of the photonic device. Such structures offer the possibility to improve the sensing response of the pSi-based photonic structures.     

Optical and room temperature sensing properties of highly oxygen deficient flower-like ZnO nanostructures

Oxygen deficient zinc oxide (ZnO) thin films were deposited electrochemically on glass substrates which are pre-sputtered with pure zinc (Zn) metal. Well-arranged flower-like nanostructures are observed from the SEM micrographs. The purity and crystallinity of the deposited films were confirmed from X-ray diffraction studies supported by Raman studies. The broad and intense defect induced green emission confirms the high oxygen deficiency in the nanostructures. The flower-like structures as well as the oxygen defects present in the system are indeed very suitable for gas and chemical sensing applications. These films were used for room temperature sensing of three different chemicals viz. acetone, ethanol and ammonia. The sensor was found to be insensitive to the change in different concentrations of acetone while it was found to be sensitive to different concentrations of ethanol and ammonia. The sensor is most suitable for sensing ammonia at room temperature.     

Optical functions of ternary Li-containing tellurides

First-principle calculations of electronic structures of new nonlinear nondirect-gap LiInTe ₂ and direct-gap LiGaTe ₂ chalcogenides are made within the method of density functional. The special features of the structure of valence band top and conduction band bottom are determined. The spectra of fundamental optical functions are calculated and studied using the model of direct band-to-band transitions. The pecularities of optical functions are discussed by the example of ε₂(E). __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 56–60, December, 2007.     

Optical,structural, enhanced local vibrational and fluorescence properties in K-doped ZnO nanostructures

We studied structural, optical and vibrational properties of K-doped ZnO nanostructures. X-ray diffraction studies reveal that the prepared particles are hexagonal wurtzite in structure. Increase in lattice parameters and unit cell volume is observed after K doping. Dopant influences on stress, strain of the system are studied using W–H plots. Band gap variation by doping of K is identified from optical absorption studies. Photoluminescence studies have given insight into the enhancement in blue emission observed by K doping along with the near band emission of nano ZnO. From Fourier transform infrared spectral measurements, K-related local vibration mode is observed along with the information related to influence of doping on characteristic vibrational modes of ZnO.     

Optical absorption spectroscopy of one-dimensional silicon nanostructures

During the last decade there has been a great development in nanoscience and nanotechnology. The technology of nanostructures synthesis and characterization has grown rapidly and optical spectroscopy has become a very useful characterization technique, since it provides information on the structural, electronic, optical and dynamical properties of materials. Nanostructures have unique physical properties that are different from bulk materials. A wealth of interesting and new phenomena are associated with nanometer-sized structures, such as size-dependent emission or excitation, metallic and semiconductor behavior, etc. Here we present an overview of the linear optical response of one-dimensional silicon nanostructures. In particular, we make a theoretical study of the effects of the size and shape of one-dimensional silicon structures on the absorption spectrum, focusing on the calculation of the linear optical response of clean and hydrogen-adsorbed armchair (6,6) silicon nanotubes. We discuss the changes of the absorption spectrum of silicon nanowires with different diameters and analyze the behavior of the band gap as we go from bulk silicon to one-dimensional silicon nanostructures with nanometer-size diameters.     

Optical permittivity,thermo-optical and electrical properties of nickel oxide nanostructures with heavy cupper doping

In this research, physical properties of nickel oxide nano-structured layers doped with various amount of Cu atoms (20–60 at.%) is studied using spray pyrolysis method on the glass substrate. The FESEM images show formations of nanostructures of about 20–60 nm and the XRD patterns show layers have a polycrystalline cubic structure nature with (111) as the preferred direction that its intensity reduces as the doping density increases. Analyzing transmittance UV. Vis spectra shows the variations of optical band gap of the samples are due to occurrence of doping atoms and quantum confined effects. Optical permittivity of different doped films have been compared using new numerical method and show the prominent effect of doping percent to real and imaginary parts of electrical permittivity. Also Hall effect results shows that Cu atoms substituted by Ni atoms sites play as acceptor atoms in the crystalline lattice. Finally, thermo-optical properties of the films have been studied using Nd–YAG laser illumination.