Photoluminescence properties of dye-doped polymer multilayer films with periodic structure

We report the photoluminescence properties of polymer alternating multilayer films containing a fluorescent dye in one component. The alternating multilayer film with periodicity in both refractive indices and dye distribution showed 6 times higher intensity of amplified spontaneous emission than the multilayer film with periodicity in dye distribution only. Multilayer films that have a structure of Fabry-Perot resonator showed a lasing threshold of approximately 1.7 mJ cm^− 2.     

Photonic and omnidirectional band gap engineering in stack of exponential graded index material and negative index material

We have investigated the photonic band gaps (PBG) and omnidirectional band gaps in one-dimensional photonic crystals made up of alternate layer of exponential graded index material and negative index material. We have considered the influence of material properties, geometrical parameters and material composition on the PBG and omnidirectional band gap. Results show that the parameters of exponential graded index material and negative index material can change the photonic and omnidirectional band structures remarkably. Number and bandwidth of PBG increases with increasing the negative index material layer thicknesses while thicknesses of graded index layer only have an effect on the bandwidth of PBGs. The bandwidth of PBG also depends on grading profile parameter of exponential graded index layers and bandwidth can be tuned with increase the value of grading profile parameter. This work can facilitate the design of filters and reflectors, and provide the basic understanding of the influence of graded index materials and metamaterials on the PBG properties.     

Measurement of valence band structure in arbitrary dielectric films

A new way of measuring the band structure of various dielectric materials using the secondary electron emission from Auger neutralization of ions is introduced. The first example of this measurement scheme is the magnesium oxide (MgO) films with respect to the application of the films in the display industries. The density of state in the valence bands of MgO film and MgO film with a functional layer (FL) deposited over a dielectric surface reveals that the density peak of film with a FL is considerably less than that of film, thereby indicating a better performance of MgO film with functional layer in display devices. The second example of the measurement is the boron-zinc oxide (BZO) films with respect to the application of the films to the development of solar cells. The measurement of density of state in BZO film suggests that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film. Secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials.     

Full-band absorption enhancement in ultrathin-film solar cells through the excitation of multiresonant guided modes

We demonstrate the optimization of plasmonic thin-film solar cells with broadband absorption enhancements. The solar cells model system consists of a three-dimensional, periodic array of Ag/silica cylinders on a Si film supported by a silica substrate. Particle swarm optimization (PSO) and the finite-difference time domain (FDTD) are combined to achieve the maximum absorption enhancement (Ehm). Through optimization, the optimal system parameters, such as the height and diameter of Ag and the silica cylinder, and the period of periodic array, were obtained. Following this approach, we can attain a 321% enhancement in the integrated quantum efficiency as compared to a cell without metallic structures. The full-band absorption enhancement arises from the near-field enhancement and multiresonant guided modes in the Si waveguide.     

Optical constants in the ultraviolet region of evaporated high index thin films

A suitable method to determine the optical constants of high index thin films is essential for developing high efficiency dielectric thin film devices in theuv region from 240 nm to 400 nm. A quick and accurate method is established to determine these constants. Using this method the optical losses, refractive index, absorption coefficient and extinction coefficient of ZrO₂ films prepared by the method of reactive evaporation were evaluated in theuv region.     

Change in characteristics of the band structure of oxide materials at high temperatures

The integral emissivity of oxide materials at high temperatures are evaluated by means of the band model; its behavior is explained. A simplified model of the band structure at high temperatures is proposed, and the expression for the calculation of the relative population of the states under thermodynamic equilibrium is obtained. The urgency of the measurements of absorption and emission of oxide materials for the determination of the density-of-states distribution and the band structure of substances at high temperatures and melting is demonstrated.     

Effect of two organic contamination modes on laser-induced damage of high reflective films in vacuum

The impact of two organic contamination modes of toluene on the damage characteristics of a high reflective film (HR) at 1064 nm is investigated. The laser-induced damage modifications of HR films are locally analyzed by the Raman techniques, optical microscopy and scanning electron microscopy (SEM). It is found that liquid phase toluene decreases laser-induced damage threshold (LIDT) and gaseous phase toluene seems to be benign and increases the LIDT of the HR film. A possible damage mechanism is analyzed and discussed.     

Quantum size effect in films and new methods for investigating the band structure of solids

The results of theoretical and experimental investigations of the quantum size effect in thin films are presented. The locations of the extrema of the size sub-bands and of the Tamm surface states are calculated as functions of the film thickness. A new length R is introduced which characterizes the crystal surface properties and allows the behaviour of the Tamm levels and of levels connected with the size quantization to be determined. Experimental results for the tunnel effect in the size-quantized film-dielectric-metal system, for conductivity oscillations in quantizing magnetic fields normal to the film and for magneto-optical absorption are discussed. It is shown from these experiments that new information about the electron spectrum in solids can be obtained using the quantum size effect, i.e. without using a priori theoretical models it is possible to determine the electron dispersion law in a direction normal to the film and to determine the topology of the isoenergetic surfaces located both above and below the Fermi level.     

Set of modes for the description of wave propagation through slabs with a transverse variation of the refractive index

The scattering of electromagnetic waves by a slab whose refractive index is changing along its boundary planes is exactly calculated in a closed analytical form. The key feature of the calculation is the introduction of a new set of modes. As a specific example, we calculate the reflected and transmitted fields generated by the interaction of an incoming plane wave with an N-layered medium, the layers of which are perpendicular to the boundary planes of a slab.     

导波在多损伤板结构中的散射

对导波在含有单个损伤和两处损伤的板结构中时形成的散射波场进行了理论分析,利用附加Bessel理论推导了含两处损伤板的结构中任意一点处的叠加散射位移场。通过数值计算对比了含单损伤板和含两处损伤板以及两处损伤的相对位置变化时散射位移场在损伤周围的分布情况,得到的分析结果是进一步进行多损伤板结构健康监测的基础。     

Thickness-dependence of stoichiometry and microstructure characteristics in correlation with conductivity type of CdTe films

CdTe films were prepared by physical vapour deposition on a substrate at room temperature (RT) as well as on a cold (LT) one using low deposition rate. The thickness-dependence of stoichiometry revealed an abrupt decrease in the Cd/Te ratio as the thickness increases. Change of thickness did not affect the type of observed (111) crystallographic texture, only the degree of preferred orientation is enhanced as the film grows. The internal strain was negligible while the crystallite size increased rapidly at small thickness (up to 400 nm), and less thickness dependence was observed with further film growth. However, thickness dependence of lattice parameters showed a minimum and a maximum at approximately 300 nm in the case of RT and LT, respectively. The observed change in conductivity from n- to p-type and its vital correlation with the stoichiometry and structural characteristics were presented. Based on thickness dependence of stoichiometry and lattice parameters as well as the conductivity type, formation and annihilation of lattice defects were considered.     

Analytical extraction of leaky modes in circular slab waveguides with arbitrary refractive index profile

Circular slab waveguides are conformally transformed into straight inhomogeneous waveguides, whereupon electromagnetic fields in the core are expanded in terms of Legendre polynomial basis functions. Thereafter, different analytical expression of electromagnetic fields in the cladding region, viz. Wentzel-Kramers-Brillouin solution, modified Airy function expansion, and the exact field solution for circular waveguides, i.e., Hankel function of complex order, are each matched to the polynomial expansion of the transverse electric field within the guide. This field matching process renders different boundary conditions to be satisfied by the set of orthogonal Legendre polynomial basis functions. In this fashion, the governing wave equation is converted into an algebraic and easy to solve eigenvalue problem, which is associated with a matrix whose elements are analytically given. Various numerical examples are presented and the accuracy of each of the abovementioned different boundary conditions is assessed. Furthermore, the computational efficiency and the convergence rate of the proposed method with increasing number of basis functions are briefly discussed.     

A link between the coercivity and microstructure of high moment Fe films and their use in magnetic tunnel junctions

Magnetron sputtered single Fe films have been “softened” magnetically by controlled N-doping during the sputter deposition. This technique allows a reduction in grain size and coercivity of the Fe films, without decreasing the saturation magnetization and without the formation of any crystalline FeN phases. We describe this effect through a modification of the random magnetocrystalline anisotropy model, by taking the film thickness into account. The coercivities calculated in this way are in good agreement with those obtained experimentally.It is demonstrated that N-doping can be applied beneficially to control the switching field of the ‘free’ layer in magnetic trilayer films of the MTJ type. It is thus possible to construct an all Fe-electrode magnetic tunnel junction (MTJ) that displays the tunneling magnetoresistance (TMR) effect by altering the switching field of one Fe layer using N-doping. The ability to control the magnetic softness of high magnetic moment materials is important in regard to their incorporation into TMR devices.     

Variations in microstructure and composition of indium tin oxide films with the deposition technique

Indium tin oxide (ITO) films have been deposited by reactive d.c.-sputtering and also by the reactive thermal evaporation technique onto glass substrates. The relationship between the microstructure and composition of the ITO films was found to strongly depend on the deposition technique. In addition the application of pure water vapour as the reactive sputtering atmosphere and its influence on the structural and compositional properties of the ITO films has been studied.X-ray diffraction investigations showed that all the films exhibited the bixbite structure of In₂O₃. No other crystalline phases were observed. Highly crystallized ITO films have been obtained using the reactive thermal evaporation technique. These films show a large average grain size of about 80 nm and a very homogeneous morphology. In contrast the d.c.-sputtered ITO films have a smaller average grain size and a characteristic texture. All deposited ITO films show an enlarged lattice constant compared to that of In₂O₃. A strong dependence of the chemical composition of the ITO films on the deposition technique and parameters was detected.     

Combination of e-beam lithography and of high velocity AIN/diamond-layered structure for SAW filters in X band

In this work, we report on the fabrication results of surface acoustic wave (SAW) devices operating at frequencies up to 8 GHz. In previous work, we have shown that high acoustic velocities (9 to 12 km/s) are obtained from the layered AIN/diamond structure. The interdigital transducers (IDTs) made of aluminium with resolutions up to 250 nm were successfully patterned on AIN/diamond-layered structures with an adapted technological process. The uniformity and periodicity of IDTs were confirmed by field emission scanning electron microscopy and atomic force microscopy analyses. A highly oriented (002) piezoelectric aluminum nitride thin film was deposited on the nucleation side of the CVD diamond by magnetron sputtering technique. The X-ray diffraction effectuated on the AIN/diamond-layered structure exhibits high intensity peaks related to the (002) AIN and (111) diamond orientations. According to the calculated dispersion curves of velocity and the electromechanical coupling coefficient (K2), the AIN layer thickness was chosen in order to combine high velocity and high K2. Experimental data extracted from the fabricated SAW devices match with theoretical values quite well.     

Defects in epitaxial films of semiconducting compounds with the sphalerite structure

The crystallography of point defects, dislocations, grain boundaries, misfit dislocation networks, and polytypes in semiconducting compounds with the sphalerite (zincblende) structure is outlined. The methods available for depositing films of compounds are reviewed with reference to the problem of non-stoichiometry. The variation of film structure with substrate temperature is considered, and the few published results of studies of the phase structures and the defect content of epitaxial films of semiconducting compounds are described. The experimental methods available for more detailed analysis of these features are then pointed out.     

Use of gold island films in design of reflectors with high luminosity

We describe the optical properties of gold island films embedded between SiO2 and/or TiO2 layers. Plasmonic properties of gold films have been characterized using spectrometry and variable angle spectroscopic ellipsometry for various combinations of the embedding media. The obtained refractive indices of embedded gold island films have been used in the design of several types of multilayer reflectors.     

Intensity of the absorption lines of spin wave resonance modes in garnet films with nanometer-thick pinning layers

We have studied the influence of the thickness of the spin-pinning layer on the intensity of spin wave resonance (SWR) modes in two-layer garnet ferrite films. For pinning layers with thicknesses in the nanometer range, the SWR mode absorption lines exhibit periodic variations for a certain orientation of the magnetic field relative to the film plane. At thicknesses equal to a quarter of the wavelength of the spin wave in the pinning layer, the intensity of SWR mode absorption lines exhibits a sharp (approximately 3.5-fold) increase.     

Resonant interaction of periodic pulsed energy source with shock-wave structure in transonic flow past airfoil

The interaction of a periodic pulsed energy source with a closing shock wave that arises near an airfoil in transonic flight regimes has been studied. The evolution of the shock-wave structure near a symmetric airfoil is analyzed based on a numerical solution of two-dimensional nonstationary equations of gasdynamics. A resonance interaction mechanism is established that leads to a significant (by an order of magnitude) decrease in the wave drag of the airfoil.     

The structure and phase change of a molybdenum grid coated with silicon and carbon composite thin films annealed at high temperature

Si-C composite thin films were deposited onto molybdenum substrates by radio-frequency magnetron sputtering. In order to simulate the working conditions of a grid contaminated by the active electron emission substance BaO from the hot cathode of a pulse-controlled grid travelling-wave tubes (TWTs), BaO layers were chemically deposited on the surface of the Si-C films. The structure and phase changes of BaO/Si-C/Mo systems were investigated using Raman scattering and XRD analysis after annealing at temperatures from 973 to 1273 K. The results show that high temperature annealing leaves only the high work function materials, SiC (about 4.4 eV) and SiO₂ (about 3.1 eV), remaining on the surface. The results are discussed in terms of chemical reactions believed to occur during annealing and the importance of these for electron suppression from grids in working TWT devices.