Surface Tamm states in a photonic crystal slab with asymmetric termination

The reflection and transmission spectra of a finite thickness 2D photonic crystal slab (PCS) based on macroporous silicon are investigated. Periodic photonic crystal region is separated from air by homogeneous silicon interfacial layers. These interfacial layers at the silicon/air boundary being defects of the photonic crystal lattice, define the properties of surface Tamm states in the photonic stop‐bands (PSBs). It is demonstrated experimentally and theoretically that the reflection spectra of a structure with different thicknesses of the interfacial layers on both sides of the PCS depend on the illuminated side. At the same time, the transmission spectra are identical for both light directions in agreement with the reciprocity principle. Analysis shows that the dependence of the reflection spectrum on the side of light entrance is due to scattering losses in the real structure. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High resolution x-ray diffractometry of the structural characteristics of a semiconducting (InGa)As/GaAs superlattice

A statistical approach is used to construct a kinematic theory of x-ray diffraction on a semiconducting superlattice with a two layer period. This theory takes two types of structural deformations into account: crystal lattice defects caused by microdefects distributed chaotically over the thickness of the superlattice, and periodicity defects of an additional superlattice potential owing to random deviations in the thicknesses of the layers of its period from specified values. Numerical simulation is used to illustrate the effect of structural defects on the development of the diffraction reflection curve. The theory is used to analyze experimental x-ray diffraction spectra of semiconducting In_xGa_1−x As/GaAs superlattices. Zh. Tekh. Fiz. 69, 44–53 (February 1999)     

Ultrasoft X-ray spectroscopy investigation of the model system Si-SiO2

SiO₂ surface films with different thicknesses (ranging from 20 to 630 Å), grown on a crystal silicon substrate, have been investigated by the method of reflection and scattering of ultrashoft X-rays. It is shown on the basis of a simultaneous analysis of the SiL _{2, 3} reflection spectra and the scattering indicatrix that the critical angle θ_c for total external reflection for SiO₂ at λ = 57 Å lies in the range 4.5 °–°. The angular dependence of the thickness of the surface layer that forms the specular reflection is obtained. It is shown that the surface layer, whose thickness corresponds to the penetration depth of the radiation into the material with glancing angle close to the critical value θ_c, plays a large role in the formation of the anomalous scattering peak (Yoneda peak).     

Optical properties of grooved silicon microstructures: Theory and experiment

The reflection spectra of grooved silicon structures consisting of alternating silicon walls and grooves (air channels) with a period of a = 4–6 μm are studied experimentally and theoretically in the mid-IR spectral range (2–25 μm) upon irradiation of samples by normally incident light polarized along and perpendicular to silicon layers. The calculation is performed by the scattering matrix method taking into account Rayleigh scattering losses in a grooved layer by adding imaginary parts to the refractive indices of silicon and air in grooved regions. The experimental and calculated reflection spectra are in good agreement in the entire spectral range studied. The analysis of experimental and calculated spectra gave close values of the effective refractive indices and birefringence of the studied structures in the long-wavelength spectral region. The values calculated in the effective medium model in the long-wavelength approximation (λ ≫ a) gave considerably understated values. The obtained results confirm the efficiency of the scattering matrix method for describing the optical properties of silicon microstructures.     

Efficiency of Si L 2,3 x-ray generation in the SiO2/Si system by electron impact

The paper reports a study of the depth profile of the generation efficiency and escape of the ultrasoft silicon L _2,3 x-ray radiation excited by electrons of various energies. The generation function describing the excitation efficiency is the kernel of an integral equation determining the dependence of x-ray emission intensity on primary-electron energy. To determine the form of this function, a study was made of the dependence of the Si L _2,3 x-ray spectral intensity and of its silicon L _2,3 component bands, from crystalline silicon and amorphous dioxide SiO₂, on primary-electron energy in samples made from dioxide layers of various thicknesses grown on crystalline silicon. These experiments permitted investigation of the generation-function cross sections at the depth of the Si-SiO₂ interface. The theoretical simulation of the generation function made use of the simplest laws governing electron interaction with solids and of the cross section of the inner-level ionization by electron impact in its most general form. A comparison of the experimentally obtained relative contributions of the Si and SiO₂ emissions with the calculations shows them to be in good agreement up to primary-electron energies of 2–3 keV. Fiz. Tverd. Tela (St. Petersburg) 40, 1932–1936 (October 1998)     

X-ray-diffractometry of structural changes occurring in surface layers of silicon in the process of laser diffusion of boron

The effect of laser diffusion of boron on the structure of surface layers in silicon single crystals was investigated by diffracted-reflection curve and three-crystal x-ray diffractometry methods. Deformation and static Debye-Waller factor distribution profiles were determined numerically by varying the parameters of the problem. Fiz. Tverd. Tela (St. Petersburg) 40, 156–160 (January 1998)     

Synchrotron investigations of the specific features in the electron energy spectrum of silicon nanostructures

The Si L _{2, 3} x-ray absorption near-edge structure (XANES) spectra of porous silicon nanomaterials and nanostructures with epitaxial silicon layers doped by erbium or containing germanium quantum dots are measured using synchrotron radiation for the first time. A model of photoluminescence in porous silicon is proposed on the basis of the results obtained. According to this model, the photoluminescence is caused by interband transitions between the energy levels of the crystalline phase and oxide phases covering silicon nanocrystals. The stresses generated in surface silicon nanolayers by Ge quantum dots or clusters with incorporated Er atoms are responsible for the fine structure of the spectra in the energy range of the conduction band edge and can stimulate luminescence in these nanostructures.     

Parametric x-ray radiation of a relativistic electron under conditions of asymmetric reflection

Coherent x-ray radiation of a relativistic electron crossing a single-crystal plate in the Laue scattering geometry is considered in a two-wave approximation of the dynamic diffraction theory [1]. Analytical expressions describing the spectral-angular distribution of parametric x-ray radiation (PXR) and diffraction transition radiation (DTR) formed on the atomic planes located at an angle δ to the crystal plate surface (asymmetric scattering) are derived. Dependence of the spectral-angular density of PXR, DTR, and their interference term on the angle δ is investigated. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 80–89, August, 2008.     

X-ray diffraction studies of silicon implanted with high-energy erbium ions

Silicon crystals after implantation of erbium ions with energies in the range 0.8–2.0 MeV and doses in the range 1×10¹²–1×10¹⁴ cm⁻² have been studied by two-and three-crystal x-ray diffraction. Three types of two-crystal reflection curves are observed. They correspond to different structural states of the implanted layers. At moderate doses (1×10¹²–1×10¹³ cm⁻²) a positive strain is observed, due to the formation of secondary radiation defects of interstitial type. An increase of the implantation dose is accompanied by the formation of an amorphous layer separating the bulk layer and a thin monocrystalline surface layer. At an implantation dose of 1×10¹⁴ cm⁻² the monocrystalline surface layer is completely amorphized. Parameters of the implantation layers are determined. A model of the transformation of structural damage is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 853–857 (May 1997)     

X-ray luminescence of disperse SiO2 and porous silicon

We carry out a comparison between the luminescence spectra (photo-and x-ray luminescence) of porous silicon and disperse SiO₂, which by its physical characteristics is most similar to oxide films on porous silicon. The photoluminescence of porous silicon was also investigated using fluorescence (excitation by a nitrogen laser) and metallographic microscopes. We found that the natures of the luminescence centers of porous silicon and disperse SiO₂ are identical. A porous layer on single-crystal silicon ensures the creation of a highly branched surface of oxide film. Luminescence centers are located on its inner (as viewed from the porous silicon) surface. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 247–251, March–April, 1998.     

Features of X-ray diffraction in thick perfect crystals with deformed subsurface layers

Diffraction of X-rays in thick perfect crystals with deformed subsurface layers has been investigated. It is shown that in deformed layers kinematic scattering occurs, while in the bulk of perfect part dynamic scattering takes place. It is revealed that in the beams diffracted on surface defects, an essential role plays the second harmonic of the employed characteristic MoK_α1 radiation.     

Room-temperature ferromagnetism in lightly Cr-doped ZnO nanoparticles

Zn_1−x Cr _x O (0≤x≤0.15) nanoparticles were synthesized by an auto-combustion method and characterized by x-ray diffraction and Raman scattering techniques. The solubility limit for Cr in ZnO was determined as x≈0.03. Room-temperature ferromagnetism (RT-FM) was observed in lightly Cr-doped ZnO nanoparticles with x=0.01 and 0.02. Raman scattering spectra of the lightly Cr-doped and Co-doped ZnO were studied and compared. The enhancement of both the magnetization and the intensity of Raman scattering peak associated with donor defects (Zn_i and/or V_O) and carriers indicates that light Cr doping in ZnO could be an effective way to achieve pronounced RT-FM and the ferromagnetism is closely related to the dopant-donor hybridization besides the ferromagnetic Cr–O–Cr superexchange interactions.     

Depth of formation of a reflected soft x-ray beam under conditions of specular reflection

Over a wide range of glancing-incidence angles, bremsstrahlung from an x-ray tube was used to measure the reflection spectra of an Si-SiO₂ system with different dioxide thickness near the Si L _2,3 ionization threshold. The angular dependence of the depth of formation of the reflected soft x-ray beam was determined experimentally and compared with that obtained from a theoretical analysis of the interaction between electromagnetic radiation and the surface of an isotropic solid. Fiz. Tverd. Tela (St. Petersburg) 40, 1360–1363 (July 1998)     

Backscattering of low-energy (0–8 eV) electrons by a silicon surface

An experimental apparatus and method for investigating elastic and inelastic backscattering (180°) of low-energy (0–8 eV) monoenergetic electrons by a solid surface are described and the first results are presented for the reflection of electrons by samples of pure single-crystalline silicon with a polished surface (Si), doped p-type single-crystalline silicon with a porous surface (Si-p) as well as H₂O and H₂O₂ passivated porous samples, Si-p + H₂O and Si-p + H₂O₂. A structure due to the excitation of surface plasmons has been observed for the first time in the loss spectra. Features corresponding to a resonance excited state of molecular nitrogen adsorbed on the surface of porous silicon have been observed in the constant residual energy spectra. Zh. Tekh. Fiz. 67, 103–108 (May 1997)     

Parametric x-ray radiation along the velocity of relativistic electron in a Bragg scattering geometry

Based on the dynamic scattering theory, forward parametric x-ray radiation (FPXR) of a relativistic electron is investigated in a single crystal plate in a Bragg scattering geometry. Analytical expressions for the spectral-angular distribution of FPXR and transition radiation (TR) including the crystal surface orientation with respect to a system of diffracting atomic planes are derived, which allow one to identify the conditions under which a contribution from FPXR is considerable even in the case of a thick absorbing crystal. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 48–56, June, 2007.     

Observation of ions with energies above 100 keV produced by the interaction of a 60-fs laser pulse with clusters

The x-ray spectra of a plasma generated by heating CO₂ and Ar clusters with high-intensity femtosecond laser pulses with q _las≃10¹⁸ W/cm² are investigated. Spatially resolved x-ray spectra of a cluster plasma are obtained for the first time. Photoionization absorption is observed to influence the spectral line profiles. The recorded features of the x-ray emission spectra definitely indicate the existence of a large relative number of excited ions (≃10⁻²–10⁻³) with energies of 0.1–1 MeV in such a plasma. Possible mechanisms underlying the acceleration of ions to high energies are discussed. It is shown that the experimental results can be attributed to the influence of ponderomotive forces in standing waves generated by the reflection of laser radiation from the clusters. Zh. éksp. Teor. Fiz. 115, 2051–2066 (June 1999)     

Thermoluminescence of corundum containing anion defects following ultraviolet laser and x irradiation

The thermoluminescence of single crystals of corundum containing anion defects following x-ray and laser excitation is investigated. Its features in the luminescence bands of F, F⁺, and Cr³⁺ centers are studied. Synchronous measurements of the thermoluminescence and thermally stimulated exoelectron emission are performed by the fractional glow technique following x-ray and laser excitation of the samples. It follows from the results obtained that several traps are active in the temperature range of the principal dosimetric peak (400–500 K). The spectral sensitivity curve contains maxima corresponding to absorption bands of F, F⁺, and Al _i ⁺ centers. A possible mechanism for the recombination luminescence of F centers is discussed. It is found that the material exhibits high sensitivity to small doses of ultraviolet laser radiation. Zh. Tekh. Fiz. 67, 72–76 (July 1997)     

Dependence of the spectral characteristics of quartz on the fluence of neutrons

The influence of radiation on the change in the optical properties of a crystalline quartz is investigated. The results of the measurement of the optical spectra of luminescence, reflection, and scattering in specimens irradiated with different fluences of neutron radiation are presented. It is shown that the corresponding spectral characteristics experience substantial changes in the region of fluences that are associated with rearrangement of the crystalline structure. The results of approximation of some radiation kinetics are given, and the trend in the process of accumulation of disordered zones is established. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 543–545, July–August, 2000.     

Detection of surface defects under low-energy scattering

Computer simulation of Ga⁺ ion (E ₀ = 40–100 eV) scattering on a GaAs film with defects in the form of vacancies and K⁺ ions (E ₀ = 40–300 eV) on a V-target containing cerium has been carried out in the framework of the multiparticle interaction model. The simulation results show that low-energy scattering can be used as a tool for detection of surface defects.     

Formation of SERS-active silver structures on the surface of mesoporous silicon

We have optimized the procedure for preparation of nanostructured silver films on the surface of mesoporous silicon (PSi) to use them as active substrates in surface-enhanced Raman scattering (SERS) spectroscopy. The greatest enhancement of the SERS signal was observed for samples obtained when the silver was deposited on PSi from an aqueous AgNO₃ solution with concentration 1⋅10^–2 M over a 10–15 minute period. The detection limit for rhodamine 6G on SERS-active substrates prepared by the optimized procedure was 1⋅10^–10 M. The enhancement factor for the SERS signal on these surfaces was estimated as ≈2⋅10⁸. We have shown that SERS-active substrates based on mesoporous silicon are promising for detection and study of complex organic compounds, in particular tetrapyrrole molecules. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 298–306, March–April, 2009.