Properties of the defect mode in one-dimensional ferroelectric Si/C60 photonic crystals

In the present paper, a novel photonic crystal (PC) defect mode is designed by inserting a ferroelectric material layer (LiNbO₃) into Si/C₆₀ one-dimensional PCs. The band structure of the ferroelectric PCs is numerically analyzed by the transfer matrix method (TMM). The width of the photonic band gap increases by 80 nm and a defect mode appears at a central wavelength of 680 nm when a 150 nm LiNbO₃ layer is inserted into the Si/C₆₀ PC structure. The defect mode in the band gap shifts linearly with the change in electric field. The defect mode shifts by 11.2 nm toward shorter wavelengths when the thin film is subjected to a DC voltage of 1 KV.     

Comparative study of optical parameters of fullerene C60 film at different temperatures

Fullerene C₆₀ thin films on glass substrate (around 2000 ? thickness) were prepared by thermal evaporation technique. The structural, surface morphology and optical properties of the films were studied. The optical properties of fullerene C₆₀ were investigated in the spectral range 200 nm to 900 nm using a UV-Vis spectrophotometer at room temperature as well as at liquid nitrogen temperature (77 K). The optical band gap at room temperature is found to be 2.30 eV, which gradually decreases with lowering the temperature and reaches to 2.27 at 77 K. The thickness and refractive index of fullerene C₆₀ film were calculated by ellipsometry. From the X-ray analysis, we have calculated the grain size, dislocation density, number of crystallite per unit area, and strain of the film at room temperature. The surface morphology of film was analyzed by scanning electron microscope (SEM). The present result show that the fullerene C₆₀ film becomes more conducting at low temperature.     

Organic Photovoltaic Cells with Improved Performance Using Bathophenanthroline as a Buffer Layer

采用Bphen作为缓冲层,研究Bphen处在电子受体材料C₆₀和阴极Ag之间对有机薄膜光伏电池(OPV)性能的影响．通过引入2.5nm厚的Bphen,在100 mW/cm²光照下,CuPc/C₆₀结构的器件效率从0.87%提高到2.25%． 对光生电流-电压的分析表明,Bphen缓冲层可以有效的提高电子从C₆₀层向Ag阴极的传输能力和平衡器件中载流子的传输能力．系统研究了Bphen厚度对OPV器件性能的影响,发现随着Bphen厚度的增加,电导率的降低是限制器件性能的主要原因．此外,采用紫外-可见光分光光度计测试了器件的吸收光谱,发现Bphen缓冲层可以增强CuPc/C₆₀的光吸收能力．     

Analysis and design of optically transparent antenna on photonic band gap structures

An optically transparent microstrip patch antenna is designed on photonic bandgap structures and its radiation characteristics are computed and analyzed in the visible spectrum region. The proposed antenna consists of indium tin oxide, a transparent conducting material used both as a radiating patch and a ground plane separated by the 5 μm thin glass substrate. The introduction of periodic cylindrical air cavity structures in the glass substrate leads to the formation of photonic band gap. The patch thickness is carefully selected based on the analysis of the optical transmission coefficient with respect to patch thickness. The effective dielectric constant of the photonic band gap loaded glass substrate is computed using the effective medium approach. The refractive index of the proposed antenna is presented and discussed. The radiation efficiency of the antenna is shown to improve significantly due to insertion of proposed photonic band gap structures. The proposed design has yielded a bandwidth of 2–2.3 THz for a return loss (S₁₁) of less than −15dB and achieved a peak gain of 4.97dB at 2.27 THz.     

Theoretical investigation of the reflectivity of fullerene-(C60, C70)/AlN multilayers in UV region

Theoretical calculations via a transfer matrix method (TMM) were performed to investigate the possibility of fullerene/AlN multilayer films acting as one-dimensional (1D) photonic band gap (PBG) crystals. The response within and out of the periodic plane of (C₆₀, C₇₀)/AlN multilayers was studied. (C₆₀, C₇₀)/AlN multilayer films presented incomplete PBG behavior in UV region. C₆₀/AlN multilayers with two pairs of 49 nm-C₆₀ and 21 nm-AlN layers exhibited a high reflectivity of 90.4% at a wavelength of about 200 nm. As a consequence, this photonic crystal may be important for achieving materials with an incomplete band gap in the UV region.     

Direct observation of the optical anisotropy of C70 fullerene molecules in the Shpol’skii spectra

Linear optical absorption and emission spectra of C₇₀ fullerene molecules in single-crystal toluene are investigated. It is established that the lines of purely electronic S ₀-S ₁ transitions are significantly polarized. The degree of linear polarization of the spectral lines depends on the position of the fullerene molecule in the toluene matrix and can be as high as 100%. The polarization characteristics of the lines can be understood in the context of a model in which the S ₀ → S ₁ electronic transition is represented by the excitation of a planar oscillator whose axis is oriented along the principal axis of the C₇₀ molecule. The relationship between the polarization of the spectral lines and the position of the fullerene molecule in the matrix is consistent with the conclusions drawn from a theoretical analysis of different configurations possible upon the embedding of C₇₀ molecules into crystalline toluene.     

Investigation of one-dimensional photonic crystals composed of dispersive materials

One-dimensional photonic crystals (1DPCs) composed of dispersive materials (including negative refractive index materials, negative μ materials, and negative ? materials) are proposed. The dependence of the band gaps on the angle of incidence and thickness scale are investigated by using the transfer matrix method. Simulation results show that the band gaps of these dispersive material 1DPC are insensitive to the thickness scale. The defect modes of these doped 1DPCs behave specially when the thickness of the defect layer, the angle of incidence and the thickness scale of PC change.     

Influence of superalkali oxides on structural,electrical and optical properties of C24 fullerene nanocluster: A theoretical study

The influence of superalkali oxides on structural, electrical and the optical properties of 6-5 isomer of C₂₄ fullerene nanocluster was investigate using DFT calculations. It was shown that the structure of fullerene was drastically affected by adsorption of M₃O on its surface and as a result of all bonding lengths, was subsequently changed. DOS results showed that the E_g of C₂₄ in presence of M₃O (M=Li, Na, K) was fairly changed so that the electronic properties and electrical conductance of C₂₄ were not affected by M₃O adsorption. Based on the results of NBO calculations, specifically on MEP surfaces and HOMO-LUMO distribution, the charge was transferred from M₃O to C₂₄ fullerene; therefore, the M₃O is the positive head of complexes and in an electric field it is oriented toward the negative pole. The calculated polarisability(α) and the first hyperpolarisability(β₀) values indicated that the adsorption of M₃O on exterior surface of C₂₄ fullerene has had a drastic effect on the optical response of C₂₄ fullerene and caused a large increase in α and β₀ values. TD-DFT calculations were also carried out in order to confirm the β₀ values. This work theoretically devises novel C₂₄-based nanostructures via interaction with Superalkali Oxides in order to promote, their potential applications in electronic devices and high-performance NLO materials.     

Junction characteristics of C60/polycarbonate blend on Si substrate

We report a study of the interface between fullerene (C₆₀) doped polycarbonate (PC) blends and n-type Si substrate. C₆₀ is usually an electron acceptor in interpenetrated networks and an electron transport in photovoltaic cells. We have studied that the guest-host approach to prepare C₆₀ doped polycarbonate blend. In this article, we report the I-V characteristics of C₆₀ doped polycarbonate/n-type Si junction and the annealing effect on these characteristics. In this junction, a nanocomposite of organic semiconductor fullerene (C₆₀), used as the active medium, with an inert polycarbonate matrix was spin coated on n-type Si substrate. We found that the C₆₀ shows the junction characteristics with n-type Si substrate. The knee voltage and dynamic resistance varies with concentration of C₆₀ as well as temperature. Ellipsometry studies showed the annealing effect on the refractive index and thickness of C₆₀ doped polycarbonate blend on n-type Si substrate. The optical micrographs show that fullerene (C₆₀) is spherical molecule and it is blend in the form of crystallites having size of micron order.     

New method for determining refractive index and thickness of fluorescent thin films

The optical parameters of homogeneous, isotropic, and fluorescent thin films are determined by comparing measured with calculated angular intensity distributions of the s- and p-polarized light emitted into the substrate. The method also yields information about the multipole nature of the emitted radiation. The theory is presented for electric and magnetic dipole transitions. For extremely thin layers of optical thickness n₀d₀ ? λ/8 (where λ is the emission wavelength) analytic expressions for the angular intensity distributions are given. For between 25–30 nm thick evaporated layers of an europium-benzoyltrifluoro-acetone- chelate the refractive index was determined to be n₀ = 1.57 at λ = 612 nm. The fluorescent light emitted by these layers in an about 6 nm wide band centered at λ = 612 nm is emitted by randomly oriented electric dipoles.     

Novel approaches to high-density perpendicular recording media

Two different approaches to reduce the intermediate layer (IL) thickness in perpendicular recording media are proposed. Such a reduction in IL thickness could lead to improvement in writability and recording performance. The first approach involved the introduction of a magnetic intermediate layer (MIL), to obtain C-axis growth. Media with CoCr alloy layer as the MIL were studied. Reasonably good C-axis growth with a Δθ₅₀ of about 3.8° could be obtained for MIL thickness of about 10 nm. Noise could be controlled by introducing exchange-breaking layers. The other approach involved the use of crystalline soft underlayers (SUL) to obtain suitable growth conditions for the recording layers. For this purpose, CoFeTaCr alloys with a FCC(1 1 1) texture were prepared. A good C-axis dispersion in the recording layer with a Δθ₅₀ of about 3.1° could be obtained for IL thickness of about 5 nm. The present study indicates that the recording medium deposited on crystalline SUL is relatively noisier than that deposited on amorphous SUL. Reducing the noise of the crystalline SUL is a way towards higher areal densities.     

异质三周期光子晶体的光子带隙特性

利用传输矩阵法研究了由TiO₂和SiO₂两种材料构成的异质三周期一维光子晶体的传光特性,发现该结构能在波长为200~ 2 000 nm的范围内形成7处比较明显的光子带隙,并且波长越大,带隙的宽度越大。重点研究了这种结构的光子晶体的透射谱线与入射角度、介质层数及介质层厚度的关系,发现该结构形成的光子带隙的大小和位置对介质层的循环周期数不敏感,但对入射角度和介质层的厚度很敏感。     

Effect of bismuth nanolayers on the oriented growth of fullerene C<Subscript>60</Subscript> on an amorphous substrate

The effect of a bismuth sublayer with an effective thickness of 0.5 to 4 nm on the structure of C₆₀ fullerene films grown on amorphous substrates (silicon covered with a natural oxide layer; glass) using the quasi-closed-volume method is studied. An x-ray diffraction study of fullerene films showed that the intensity ratio between the (220) and (111) peaks depends nonmonotonically on the sublayer thickness. In the bismuth sublayer thickness range 0.5–2.0 nm, fullerene films are found to exhibit a growth texture with the 〈110〉 axis; the average crystallite size was ～20 µm. The quality of the texture can be improved by varying the fullerene growth temperature.     

Study on complete band gap of two-dimensional photonic crystal with quadrangular rods

The plane wave expansion method (PWM) was employed to study the relation between the photonic band gap (PBG) of 2D triangular lattice photonic crystal (PC) and the shapes of rods and dielectric constant. It is shown that the PBG of PC with quadrangular rods is the widest one, compared with the other case with cross section shapes of triangular, circular and hexagon under the same filling ratio, and a peak value appears when the side length ratio of l_x/l_y is equal to 1.21 approximately to any filling ratio. In the aspect of the effects of dielectric constant, the PBG width does not increase monotonically with the increase permittivity ?₂ of the background material to certain permittivity ?₁ of the quadrangular rods, but has a peak value instead. However, the larger the permittivity ?₁ is, the narrower the band width is and the lower the central frequency is, and the dispersion Δ? = ?₂ − ?₁ is larger also.     

Optical gain spectra of unstrained graded GaAs/AlxGa1 − xAs quantum well laser

We have calculated the optical gain spectra in unstrained graded GaAs/Al_xGa_1 − xAs single quantum well lasers as a function of the energy of the radiation, the quantum well width and the interface thickness. The optical gain spectra were calculated using the density matrix approach (Luttinger–Kohn method), considering the parabolic band model (conduction band), all subband mixing between the heavy and light holes (valence band), and the transversal electrical light polarization. Our results show that the optical peak gain is sensitive to the width and the graded profile of the interfaces, and is blue-shifted as a function of the interface width.     

Optical properties of one-dimensional photonic crystals containing graded materials

The optical properties of an one-dimensional photonic crystal containing graded materials are studied theoretically. The graded layers have space dispersive permittivity and magnetic permeability which vary along the direction perpendicular to the surface of the layer. The gradation profiles of permittivity are studied in detail. We show that the structure possesses forbidden band gaps in its transmission spectra and the gradation profiles of permittivity affect the band gaps significantly. For the exponential gradation profile ε₁(x) = α e^βx, the number of the band gaps increases and the total frequency region corresponding to the gaps becomes large with increasing parameter β. On the other hand, the position of band gaps can be changed by the adjustment of the gradation profiles even if possessing same volume-average permittivity in the graded layers. Therefore, we can achieve suitable photonic band gaps by choosing gradation profiles of permittivity.     

Laser synthesis of semiconductor nanostructures with narrow band gap

Semiconductor nanostructures with narrow band gap were synthesized by means of laser chemical vapor deposition (LCVD) of elements from iron carbonyl vapors [Fe(CO)₅] under the action of Ar⁺ laser radiation (λ_L = 488 nm) on the Si substrate surface. The temperature dependence of the specific conductivity of these nanostructures in the form of thin films demonstrated typical semiconductor tendency and gave the possibility to calculate the band gap for intrinsic conductivity (E_g) and the band gap assigned for impurities (E_i), which were depended upon film thickness and applied electrical field. Analysis of deposited films with scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrated their cluster structure with average size not more than 100 nm. Semiconductor properties of deposited nanostructures were stipulated with iron oxides in different oxidized phases according to X-ray photoelectron spectroscopy (XPS) analysis.These deposited nanostructures were irradiated with Q-switched YAG laser (λ_L = 1064 nm) at power density about 6 × 10⁷ W/cm². This irradiation resulted in the crystallization process of deposited films on the Si substrate surface. The crystallization process resulted in the synthesis of iron carbide-silicide (FeSi_2−xC_x) layer with semiconductor properties too. The width of the band gap E_g of the synthesized layer of iron carbide-silicide was less than for deposited films based on iron oxides Fe₂O_3−x (0 ≤ x ≤ 1).     

双波长垂直腔面发射激光器及特性研究

基于光子晶体技术在一维光子晶体带隙内引入缺陷态模式,并对激光器谐振腔内部电磁场分布和共振波长进行调制,从而将单一波长分裂为双波长输出.最终制备出了一种新的具有双波长光谱输出特性的垂直腔面发射激光器,缺陷层为Al_0.8Ga_0.2As材料,厚度为5λ/4.所得到的双波长输出光谱具有低吸收损耗、输出波长容易控制及同方向垂直输出特性.同时,通过调整一维光子晶体的折射率差和缺陷层厚度可以有效调谐双波长的间距及输出波段.所设计的双波长垂直腔面发射激光器结构同样 关键词： 垂直腔面发射激光器 光子带隙 双波长     

The modulation on the optical responses of one-dimensional photonic crystals based on the ordered porous TiO2 films

The optical responses of the 1D porous TiO₂/SiO₂ complete and defect PCs formed with the ordered porous TiO₂ film prepared by using the spin coating and annealing techniques have been systematically studied with FDTD simulation technique. The whole photonic band gap can be easily linearly modulated by the structure parameters, such as thickness, porosity, the filled materials, and so on. The defect layer thickness and porosity only modulate the defect state, and have little effects on the whole PBG. It is more important that the 1D porous TiO₂/SiO₂ complete and defect PCs have no omnidirectional photonic band gap and defect state.     

Rotational relaxation of the 0001 level of CO2 including radiative transfer in the 4.3-μm band of planetary atmospheres

Accurate numerical solutions have been obtained for a model problem of rotational relaxation within the 00⁰1 vibrational level of C¹²O₂¹⁶ accounting for the transfer of radiation in the lines of the fundamental transition 00⁰1-00⁰0 of the 4.3-μm band. Intramolecular exchange of vibrational energy with the reservoir of v₂ quanta and absorption of solar radiation in the 00⁰1- 00⁰0 band are accounted for. A plane-parallel isothermal atmosphere of pure CO₂ with the barometric pressure distribution and solar illumination is assumed. The line opacity is represented by nonoverlapping Voigt profiles depending on temperature and pressure. The transfer problem, which is equivalent to that of a multiplet with a large number of lines with a common lower level, was solved by a generalization of the Rybicki method. We find significant deviations from ratational LTE (local thermodynamic equilibrium) in regions in which the harmonic average of the optical depth over the band is of order 10³-10⁴. Absorption of solar radiation can affect significantly the source functions of lines at the centers of the P and R branches. Deviations from rotational LTE are shown to influence the intensity and shape of the 4.3-μm band of CO₂ in the spectra of Mars and Venus, and should be taken into account in the interpretation of the observations in which the rotational structure is resolved, especially in limb measurements, where these effects are particularly apparent.