Microrelief dependent on the temperature and external field on the free surface of a smectic-<Emphasis Type="Italic">A</Emphasis> liquid crystal

A homeotropically oriented smectic-A film on the surface of a solid substrate with a periodic microrelief is considered. Relationships are derived for describing the dependences of the microrelief-induced deformation of the free surface of the film on the film thickness, the temperature, and the external magnetic (electric) field strength. It is shown that, for a specific choice of the microrelief shape on the substrate surface, a variation in the sample temperature and the external magnetic (electric) field strength makes it possible to control not only the microrelief depth but also the shape of the microrelief formed on the free surface of the smectic-A film.     

Some features of the electrical forming of MDM systems based on silicon oxynitride films

Results are given in this paper of a study of the electrical forming process in thin-film MDM systems based on films of silicon oxynitride of varying compositions. It was observed that the forming voltage and forming rate of a thin-film Al-Si_xN_yO_z-Al system depends essentially on the composition of the dielectric film while the characteristics of the formed structures depend weakly on the oxygen/nitrogen ratio in the film. The results obtained are in good agreement with Shnurov's model of forming.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 71–74, May, 1976.     

Temperature and external field-driven microrelief at free surface of smectic-A liquid crystal

A homeotropically oriented smectic-A film on a solid substrate with periodical microrelief is considered. Periodical distortions of the free surface of the film induced by this microrelief are theoretically investigated. The dependence of these distortions on the film thickness, the temperature, and external magnetic (electric) field is obtained. It is shown that, for a certain choice of the shape of the substrate surface microrelief, one can realize a temperature and external magnetic (electric) field control on the microrelief at the free surface of the smectic-A film.     

The technology of fabricating focusators of infrared laser radiation

The possibility of fabricating focusators of infrared laser radiation, based on photolithographic technology, is analysed. The realizability of focusator fabrication is based on the possibility of producing a set of binary photomasks and achieving the necessary depth of etching the substrate of the pattern while forming the microrelief. The possibility of producing these photomasks is evaluated with regard to the focusator's extremal zone width and the appearance of photomasks displayed on the screen. Forming of step-by-step microrelief is achieved using plasma etching or wet etching and depends on the minimum element's dimension and the etching depth. Examples of the microrelief's profiles, of focusators fabricated using photolithography, and the result of the transformation of a focusator's radiation into a straight line segment, are discussed.     

Surface plasmon optical sensor with enhanced sensitivity using top ZnO thin film

Surface plasmon resonance (SPR) is one of the most sensitive label-free detection methods and has been used in a wide range of chemical and biochemical sensing. Upon using a 200 nm top layer of dielectric film with a high value of the real part ε′ of the dielectric function, on top of an SPR sensor in the Kretschmann configuration, the sensitivity is improved. The refractive index effect of dielectric film on sensitivity is usually ignored. Dielectric films with different refractive indices were prepared by radio frequency magnetron (RF) sputtering and measured with spectroscopic ellipsometry (SE). The imaginary part ε′′ of the top nanolayer permittivity needs to be small enough in order to reduce the losses and get sharper dips. The stability of the sensor is also improved because the nanolayer is protecting the Ag film from interacting with the environment. The response curves of the Ag/ZnO chips were obtained by using SPR sensor. Theoretical analysis of the sensitivity of the SPR sensors with different ZnO film refractive indices is presented and studied. Both experimental and simulation results show that the Ag/ZnO films exhibit an enhanced SPR over the pure Ag film with a narrower full width at half maximum (FWHM). It shows that the top ZnO layer is effective in enhancing the surface plasmon resonance and thus its sensitivity.     

Photonic band-structure effects in soft X-ray spectrum for SBA-15 ordered mesoporous structures

The photonic band gap of SBA-15 ordered mesoporous structure is investigated when used as photonic crystals. The filling fraction has more significant effects on the width and attenuation length of PBG than does the dielectric contrast, whereas the PBG position is strongly dependent on both the filling fraction and dielectric contrast. Since the position of PBG occurs between 30–40 nm and the width is about 4–5 nm, SBA-15 with such a narrow gap is expected to be applied as filters in soft X-ray spectrum.     

Combustion synthesis of high-quality diamond film suitable for application in electronic devices

The purpose of this research is to elucidate the electrical characteristics of a diamond film synthesized by combustion flame and synthesize a diamond film suitable for application in electronic devices. When the film contains amorphous carbon, the dielectric loss increases, i.e., the electrical characteristics of the diamond film are degraded. We employed three methods to decrease the amorphous carbon in the diamond film—the detection of the optimal equivalence ratio, addition of hydrogen into synthesizing gas, and heat treatment (annealing) of the diamond film. All these methods can decrease the amount of amorphous carbon effectively, thus systematically changing the factors influencing the optimal synthesis for improving the electric characteristics of the film. We have successfully developed a method for preparing a high-quality diamond film with excellent electrical characteristics that has no dielectric loss in the wide frequency range (10²–10⁸ Hz).     

Electrical forming of thin-film MDM systems

The influence of dielectric silicon dioxide film density and upper-electrode material on the electrical forming and puncture of thin-film MDM systems is investigated. It is shown that forming is controlled by destruction of weakly bound hydrogen-containing complexes by hot electrons. Tomsk State Academy of Control Systems and Radioelectronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 55–59, October, 1996.     

The optical properties of thin erbium films

The effective dielectric constant, ε′₂, of very thin films of erbium on sodium chloride substrates was determined from measurements of normal incidence reflectance and transmittance in the visible spectrum. ε′₂ showed a maximum which moved to longer wavelengths as the film thickness increased. Electron microscopy revealed that the film islands grew flatter and more irregular with thickness. The shape factor of the islands, F, was calculated by a modified Maxwell-Garnett method and became smaller as the film thickness increased.     

On resonance absorption of electromagnetic radiation in finely dispersed media

It is shown that the statistical spread of the particle parameters of the dispersed phase of a finely dispersed medium that affect the frequency of quasi-static dipole resonance results in the appearance of an absorption band whose frequency width is determined only by the corresponding distribution function and in the case of small losses is not a function of the specific mechanism of field attenuation in the material. Dissipation is caused by the presence of a group of resonance particles and in this sense is similar to Landau collisionless attenuation in plasma. Examples of numerically calculated reflection, transmission, and absorption spectra are provided for finely dispersed media consisting of suspensions of silver particles frozen into a dielectric matrix.Institute of Applied Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 10, pp. 892–900, October, 1993.     

Effect of polymer relaxation on dielectric spectroscopic study of polymer–ferroelectric liquid crystal composites

Polymethylmethacrylate (PMMA) and ferroelectric liquid crystal (P–FLC) composite films (~ 4 μm) with varying proportions of ferroelectric liquid crystal have been prepared and the dielectric response of the composite films as a function of wide frequency (100 Hz–10 MHz) and temperature (127–40 °C) have been analyzed. The dielectric spectra of such composite systems are considerably modified compared to those of the corresponding pure LC or PMMA materials. The observed paraelectric to ferroelectric transition temperature of the composites is found to be lower (~ 85 °C) compared to that of the pure LC system (~ 98 °C), which makes these composites technologically more significant. The P–FLC composites also exhibit higher relaxation frequency and smaller dielectric strength for the Goldstone mode compared to those of the corresponding pure FLC. Depending on the percentage of the constitute materials, the molecular dynamics of the composite materials changes. Dielectric contributions of both liquid crystal and PMMA matrix forming the composites have been analyzed on the basis of Havriliak and Negami function.     

Effects of microstructure on the properties of ferroelectric lead zirconate titanate (PZT) thin films

Lead zirconate titanate (PZT) thin films were prepared with pulsed laser deposition and sol–gel techniques. The PZT films fabricated by these two techniques have similar randomly oriented single perovskite phases, but the film derived from the pulsed laser deposition exhibits a more compact and flat morphology. The dielectric, ferroelectric, and piezoelectric properties of the two kinds of films are comparatively characterized and discussed. It is observed that a denser microstructure would lead to a significantly higher dielectric constant and remanent polarization and a much lower coercive electric field, but only a relatively slight enhancement on the piezoelectric constant. The film with a looser microstructure could have a substantially higher piezoelectric voltage constant g₃₃ due to the much lower dielectric constant. Our results and discussion provide a better understanding of the relationship between the microstructure and the film properties, which is essential in order to tailor the microstructure and hence determine the performance aiming at a specific application. PACS 68.55.Jk; 77.22.-d; 77.65.-j     

Effects of texture on the dielectric properties of Ba(Zr0.2Ti0.8)O3 thin films prepared by pulsed laser deposition

Ba(Zr_0.2Ti_0.8)O₃ (BZT) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a pulsed laser deposition process. The BZT thin films directly grown on annealed and un-annealed Pt/Ti/SiO₂/Si substrates exhibited random and high (100) orientations, respectively. The dielectric constant of a 400-nm-thick BZT film with (100) orientation was 331, which was higher than that of a BZT film with random orientation (∼236). This result is attributed to the fact that the polar axis of the (100)-oriented films was more tilted away from the normal to the film surface than that of the randomly oriented films. Also, the tunabilities of BZT thin films with random and (100) orientations were ∼50% and ∼59% at an applied field of 400 kV/cm, respectively. Improved tunability has been attributed to the (100) texture of the film leading to an enhancement of the in-plane-oriented polar axis. PACS 77.22.-d; 77.55.+f; 77.80.-e; 77.84.-s     

Structural and optical properties of thermally evaporated thin films

Chalcogenide glass Se₅₅Ge₃₀As₁₅ have amorphous structure in both as-deposited and annealed conditions. The optical properties of the as-deposited and annealed films were studied using spectrophotometric measurements of transmittance, T(λ), and reflectance, R(λ), at normal incidence of light in the wavelength range 200–2500 nm. Neither annealing temperature nor film thickness can influence spectral response on refractive index and absorption index of films. The type of electronic transition responsible for optical properties is indirectly allowed transition with energy gap of 1.94 eV and phonon energy of 40 meV. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple–Didomenico (WD) model. The width of band tails of localized states into the gap (ΔE), the single oscillator energy (E_o), the dispersion energy (E_d), the optical dielectric constant (ε_∞), the lattice dielectric constant (ε_L), the plasma frequency (ω_p) and the free charge carrier concentration (N) were estimated.     

Design of MMICs employing whispering-gallery mode dielectric resonators at microwave and millimeter wave frequencies

A simple theoretical model for predicting the resonant frequencies of the modes of the whispering — gallery (WG) mode dielectric resonators MICs (Microwave Integrated Circuits) at microwave and millimetre wave frequencies is presented. The unsymmetric field distribution for WGE mode in the axial direction is taken into account. The theoretical results are found to be in good agreement with the practical results taken at microwaves C-X bands. In addition, the variation of resonant modes against dielectric resonator's dimensions and dielectric constant is modelled. The effect of the width of dielectric substrate on resonant modes is also illustrated.     

Dielectric property of CaCu3Ti4O12 thin film grown on Nb-doped SrTiO3(100) single crystal

Thin film of CaCu₃Ti₄O₁₂ (CCTO) has been deposited on Nb-doped SrTiO₃(100) single crystal using pulsed laser deposition. The dielectric constant and AC conductivity of CCTO film in the metal–insulator–metal capacitor configuration over a wide temperature (80 to 500 K) and frequency (100 Hz to 1 MHz) range have been measured. The small dielectric dispersion with frequency observed in the lower temperature region (<300 K) indicates the presence of small defects in the deposited CCTO thin film. The frequency-dependent AC conductivity at lower temperature indicates the hopping conduction. The dielectric dispersion data has been analyzed in the light of both conductivity relaxation and Debye type relaxation with a distribution of relaxation times. Origin of dielectric dispersion is attributed to the distribution of barrier heights such that some charge carriers are confined between long-range potential wells associated with defects and give rise to dipolar polarization, while those carriers which do not encounter long-range potential well give rise to DC conductivity.     

Improvement of plasmonic field-matter interaction by subwavelength dielectric gratings

We experimentally and theoretically investigate that detection sensitivity in surface plasmon resonance (SPR) biosensors can be significantly enhanced by employing subwavelength dielectric gratings deposited on a gold film. The enhancement originates from an improvement of field-matter interaction: enhanced evanescent field intensity at the binding region and increased surface reaction area. Using a large-area SiO₂ grating array fabricated by nanoimprint lithography, experimental sensor performance measured by parylene film coating shows that the SPR substrates combined with a dielectric grating provide a notable sensitivity improvement compared to a conventional bare gold film. We also demonstrate that plasmon field can be more confined and enhanced at the dielectric gratings with a larger width. The proposed SPR structure could potentially be useful in a variety of plasmonic applications including high-sensitivity biosensors.     

Changes in conductivity of metal-dielectric-metal and metal-dielectric-semiconductor structures under the action of radiation

This study is an experimental investigation of the effects of radiation on conductivity of metal-dielectric-metal (MDM) and metal-dielectric-semiconductor (MDS) structures. A brief theoretical analysis of current flow mechanisms in the dielectric layer of an MDS structure is given. A physical interpretation of the experimental results obtained is offered. It is shown that the change in conductivity of MDM and MDS structures upon irradiation is dependent on the type of dielectric film used and the type of radiation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 26–33, November, 1973.     

Discrete velocity modelling of gaseous mixture flows in MEMS

The need of developing advanced micro-electro-mechanical systems (MEMS) has motivated the study of fluid-thermal flows in devices with micro-scale geometries. In many MEMS applications the Knudsen number varies in the range from 10⁻² to 10². This flow regime can be treated neither as a continuum nor as a free molecular flow. In order to describe these flows it is necessary to implement the Boltzmann equation (BE) or simplified kinetic model equations.The aim of the present work is to propose an efficient methodology for solving internal flows of binary gaseous mixtures in rectangular channels due to small pressure gradients over the whole range of the Knudsen number. The complicated collision integral term of the BE is substituted by the kinetic model proposed by McCormack for gaseous mixtures. The discrete velocity method is implemented to solve in an iterative manner the system of the kinetic equations. Even more the required computational effort is significantly reduced, by accelerating the convergence rate of the iteration scheme. This is achieved by formulating a set of moment equations, which are solved jointly with the transport equations.The velocity profiles and the flow rates of three different binary mixtures (He–Ar, Ne–Ar and He–Xe) in 2D micro-channels of various height to width ratios are calculated. The whole formulation becomes very efficient and can be implemented as an alternative methodology to the classical method of solving the Navier–Stokes equations with slip boundary conditions, which in any case is restricted by the hydrodynamic regime.     

Micromachining of a thin film by laser ablation using femtosecond laser with masks

A gold thin film was machined by laser ablation using a femtosecond laser with mask patterns in the shape of lines and numbers. The patterns were successfully transferred with proper focusing and laser fluence. The optimal femtosecond laser fluence to keep the line width was about 5.2 mJ/cm² on the mask, and 99 mJ/cm² on the film. The processing resolution was 13 μm, and the narrowest line width was about 4 μm.