Photonic stop bands in quasi-random nanoporous anodic alumina structures

The existence of photonic stop bands in the self-assembled arrangement of pores in porous anodic alumina structures is investigated by means of rigorous 2D finite-difference time-domain calculations. Self-assembled porous anodic alumina shows a random distribution of domains, each of them with a very definite triangular pattern, constituting a quasi-random structure. The observed stop bands are similar to those of photonic quasicrystals or random structures. As the pores of nanoporous anodic alumina can be infiltrated with noble metals, nonlinear or active media, it makes this material very attractive and cost-effective for applications including inhibition of spontaneous emission, random lasing, LEDs and biosensors.     

Phonon emission spectra of thin metallic films

Thin metallic films evaporated on an Al₂O₃-single crystal and cooled to liquid helium temperatures are heated by short electric current pulses. The high frequency part of the emitted phonons is detected by calibrated superconductive tunneling junctions on the opposite surface of the substrate. The observed phonon detector signal amplitude is compared with theoretical models taking account of the boundary conditions for elastic waves in the film. It is found that the phonon spectrum emitted perpendicularly to the substrate-film boundary depends strongly on the thickness of the heater film.     

A method for resolving individual bands in absorption spectra

A new algorithm for resolving individual bands in absorption spectra is developed. It is assumed that the spectrum consists of absorption bands with halfwidths determined by different kinds of interactions—specific and nonspecific. The method has good accuracy in the case of the strong overlap of bands (the ratio of the distance between maxima of the peaks to the halfwidth is less than 0.2) and a high computational efficiency. Arkhangelsk State Technical University, 17, Naberezhnaya Severnoi Dviny, Arkhangelsk, 163007, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 400–404, May–June, 1997.     

Luminescence excitation spectra and characteristics of luminescence centers with overlapping absorption bands

For an ensemble of different types of luminescence centers with overlapping absorption bands, with no restrictions on the optical densities, we have obtained relations describing the luminescence excitation spectra for each type of center. We consider transformations of the relations in some limiting cases. We suggest a procedure for using the equations obtained to determine the characteristics of the luminescence centers. Some of these procedures have been experimentally implemented in study of intrinsic radiation color centers in lithium fluoride crystals. We have determined the ratios of the luminescence quantum yields for F₂ and F₃⁺ color centers, and we have observed that a major role is played by nonradiative transitions in deactivation of the first excited singlet state of F₃⁺ centers. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 365–371, May–June, 2008.     

Reconstruction of bands in metallic hydrogen

The generalized theory of normal properties of a metal for the case of the properties of the electronic band of electron–phonon systems with a variable electron density of states is used to study the normal phase of metallic hydrogen at a pressure of 500 GPa and a temperature of 200 K. We calculated the frequency dependence of the real ReΣ(ω) and imaginary ImΣ(ω) parts of the self-energy part of the electron Green’s function Σ(ω), as well as the electron density of states N(ε) of the stable phase of metallic hydrogen with the I41/amd symmetry at a pressure of 500 GPa, renormalized by the strong electron–phonon coupling. It is found that the electron conduction band of the I41/amd phase of metallic hydrogen undergoes insignificant reconstruction near the Fermi level because of the renormalization by the electron–phonon coupling.     

Measurements of absorption spectra of thin films by the waveguide technique

The waveguide technique for measuring the absorption spectra of thin films in spectral range of their transparency is considered. The error of measuring the absorption of a ～0.1 μm thick film does not exceed 5% at an absorption coefficient of less than 50 cm^–1. Capabilities and limitations of the method are discussed.     

Effect of pressure on the intensity of absorption bands in the IR spectra of compacted polyethylene powde

The investigation of the IR spectra of compacted reactor powders of ultra-high-molecular-weight polyethylene showed that the intensities of the absorption bands depend on the compaction pressure; namely, they decrease with increasing pressure. It is found that the ultimate pressure above which the absorption band intensity ceases to decrease depends on the spectral position of the band; the shorter the wavelength, the higher the ultimate pressure. This pressure is 5–10 MPa for bands in the long-wavelength spectral region (the band at 720 cm^?1) and 100 MPa for the short-wavelength region (the band at 5875 cm^?1). It is assumed that this phenomenon is related to a change in the size of pores d with pressing. Beams with wavelengths λ < d will undergo multiple diffuse reflections and reach a photodetector that is weaker than beams with λ > d. With increasing pressure, the size of pores decreases and the boundary between the two regions of the spectra shifts to short wavelengths.     

Identification of absorption bands corresponding to C-C1 stretching vibrations in the IR spectra of organic compounds

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 3, pp. 392–396, September, 1991.     

纳米多孔金薄膜显微结构分析

采用亚硫酸金钠为主盐,在阳极氧化铝模板上进行了化学镀和电镀金实验研究。通过扫描电子显微镜和X射线衍射分析测试表明:采用以上两种方法均能制备出纳米多孔金薄膜。两种方法制备的多孔金薄膜微观结构存在较大的差异。化学镀制备的多孔金薄膜微观上是枝晶状的,电镀制备的多孔金薄膜微观上由纳米线构成。     

纳米多孔金薄膜显微结构分析

 采用亚硫酸金钠为主盐,在阳极氧化铝模板上进行了化学镀和电镀金实验研究。通过扫描电子显微镜和X射线衍射分析测试表明:采用以上两种方法均能制备出纳米多孔金薄膜。两种方法制备的多孔金薄膜微观结构存在较大的差异。化学镀制备的多孔金薄膜微观上是枝晶状的,电镀制备的多孔金薄膜微观上由纳米线构成。