Effect of annealing temperature on the structure of pyrolysates of diphthalocyanines of rare-earth elements: Neutron research

Small-angle neutron scattering is used to study the structure of carbon matrices—the pyrolysis products of diphthalocyanines with embedded metal atoms (Y, La, and Ce), synthesized at annealing temperatures of 800–1700°C. It is shown that the structure of the porous matrix on the scale of ～10⁰–10² nm is characterized by a level of small pores (3–10 nm in radius) and the next level of the structure is associated with the formation of their aggregates (above 100 nm in size). The quantity and size of the scattering objects increases sharply at annealing temperatures above 1000°C. The results are consistent with X-ray diffraction data.     

Small-angle neutron scattering investigation of the nanostructure of the SAV-1 alloy irradiated with fast neutrons to high fluences

The supra-atomic structure in samples of the SAV-1 alloy (unirradiated and irradiated with fast neutron fluences of 3.48 × 10²² n/cm²) has been investigated using small-angle neutron scattering. It has been found that, in the irradiated material, the volume fraction of scattering structures (pores) with a radius of 40–50 nm significantly decreases, which is compensated to a large extent by an increase in the total fraction of these objects with a radius of less than 20 nm. The results of neutron scattering investigations correlate with the data of mechanical tests of the irradiated alloys and with the changes in their elemental composition.     

Atomic mobility in a ternary liquid Ga–In–Sn alloy of the eutectic composition

The nuclear spin–lattice relaxation and Knight shift of ⁷¹Ga, ⁶⁹Ga, and ¹¹⁵In nuclei in a ternary liquid gallium–indium–tin alloy of the eutectic composition, which was introduced into pores of an opal matrix and porous glasses with pore sizes of 18 and 7 nm, have been investigated and compared with those for the bulk melt. It has been found that longitudinal relaxation is accelerated and the Knight shift is decreased, depending on the size of pores. The correlation time of the atomic motion has been calculated for the nanostructured melt in porous matrices. It has been shown that the atomic mobility in the melt decreases with decreasing size of pores in the glasses.

     

Structure of aluminum alloys irradiated with reactor neutrons

Samples of the CAB-1 alloy in the initial state and irradiated with fast neutrons at an fluence of 2 × 10²¹ neutrons/cm² have been studied by small-angle neutron scattering. It has been demonstrated that the observed large scattering cross sections are associated with the presence of nanosized pores with radii R ∼ 5–50 nm in the alloy, whereas for possible inclusions of the Mg₂Si and Si phases, the contrast factors and limiting volume fractions lead to the estimated cross sections that are two orders of magnitude smaller than those observed in the experiment. As a result of the irradiation, the volume fraction of scattering objects (pores) 40–50 nm in radius decreases by a factor of more than two. This is compensated, to a large extent, by an increase in the total fraction of particles with radii of 5–8 and 20–25 nm as the total surface area of the scattering objects increases by 40%.     

Surface‐enhanced Raman spectra of individual multiwalled carbon nanotubes with small innermost diameters

The Raman spectra of individual multiwalled carbon nanotubes (MWCNTs) with the innermost diameters of 0.6–0.9 nm are studied by surface‐enhanced Raman scattering. The influences of small innermost diameters to Raman features are investigated. A clear and relatively sharp Raman peak appears at 1510 cm⁻¹ when the innermost diameter is close to 0.6 nm. Lorentzian fits of G band indicate that its splitting is affected by the small innermost diameter of MWCNT. Moreover, the splitting of 2iTO mode is also observed at 2800–3000 cm⁻¹. Copyright © 2012 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering and fluorescence emission of gold nanoparticle–multiwalled carbon nanotube hybrids

Multiwalled carbon nanotubes (MWCNTs) are grafted with gold (Au) nanoparticles of different sizes (1–12 and 1–20 nm) to form Au–MWCNT hybrids. The Au nanoparticles pile up at defect sites on the edges of MWCNTs in the form of chains. The micro‐Raman scattering studies of these hybrids were carried using visible to infrared wavelengths (514.5 and 1064 nm). Enhanced Raman scattering and fluorescence is observed at an excitation wavelength of 514.5 nm. It is found that the graphitic (G) mode intensity enhances by 10 times and down shifts by approximately 3 cm⁻¹ for Au–MWCNT hybrids in comparison with pristine carbon nanotubes. This enhancement in G mode due to surface‐enhanced Raman scattering effect is related to the interaction of MWCNTs with Au nanoparticles. The enhancement in Raman scattering and fluorescence for large size nanoparticles for Au–MWCNTs hybrids is corroborated with localized surface plasmon polaritons. The peak position of localized surface plasmons of Au nanoparticles shifts with the change in environment. Further, no enhancement in G mode was observed at an excitation wavelength of 1064 nm. However, the defect mode (D) mode intensity enhances, and peak position is shifted by approximately 40 cm⁻¹ to lower side at the same wavelength. The enhanced intensity of D mode at 1064 nm excitation wavelength is related to the double resonance phenomenon and shift in the particular mode occurs due to more electron phonon interactions near Fermi level. Copyright © 2012 John Wiley & Sons, Ltd.     

金原子团簇的分频散射光谱研究

液相金原子团簇是一种非线性光学介质.它在580nm处产生一个最强共振散射峰.当激发波长为290nm(1.03×10¹⁵Hz)时,液相金原子团簇在580nm(1/2×1.03×10¹⁵Hz)和870nm(1/3×1.03×10¹⁵Hz)分别产生一个1/2分频和1/3分频散射峰;当激发波长为580nm(5.02×10¹⁴Hz)时在290nm(2×5.02×10^-14Hz)和870nm(2/3×5.02×10¹⁴Hz)分别产生一个2倍频和2/3分频散射峰;当激发波长为870nm(3.34×10¹⁴Hz)时在580nm(3/2×3.34×10¹⁴Hz)和290nm(3×3.34×10¹⁴Hz)分别产生一个3/2分频和3倍频散射峰.分频散射和倍频散射峰与共振散射峰具有相似的散射行为.从激励光与液相金原子团簇相互作用的运动方程出发,根据傅氏变换理论,较好地解释了液相金原子团簇产生的一些非线性散射光谱.     

The Formation of Helium Bubbles in Silicon Surface Layers via Plasma Immersion Ion Implantation

The surface layers of single-crystal silicon Si(001) substrates subjected to plasma-immersion implantation with 2- and 5-keV helium ions to a dose of 5 × 10¹⁷ cm^–2 were probed via grazing incidence small-angle X-ray scattering and transmission electron microscopy. A surface layer formed by helium ions was found to possess a multilayer structure, wherein the upper layer is amorphous silicon, being on top of a sublayer with helium bubbles and a sublayer with a disturbed crystal structure. The in-depth electron density distribution, as well as the concentration and pore-size distribution, were established. The average pore sizes of bubbles at the above implantation energies are 4 nm and 8 nm, respectively.     

Small angle neutron scattering and small angle X-ray scattering studies of platinum-loaded carbon foams

The morphology of carbon nanofoam samples comprising platinum nanoparticles dispersed in the matrix was characterized by small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) techniques. Results show that the structure of pores of carbon matrix exhibits a mass (pore) fractal nature and the average radius of the platinum particles is about 2.5 nm. The fractal dimension as well as the size distribution parameters of platinum particles varies markedly with the platinum content and annealing temperature. Transmission electron micrographs of the samples corroborate the SANS and SAXS results.      

Additional Nonreciprocity Effects in the Magneto-Optics of Asymmetric Layer Structures

The structure of the adsorbed layer of alkali ions on the surface of colloidal silica solutions with a particle size of 27 nm has been studied by reflectometry and diffuse scattering of synchrotron radiation with a photon energy of about 71 keV. Electron density profiles in the direction perpendicular to the surface have been reconstructed from experimental data and spectra of the correlation function of heights in the surface plane have been obtained. The revealed deviation of the integral and frequency characteristics of the roughness spectra of the silica sol surface from predictions of the capillary-wave theory is of a fundamental character. This deviation is due to the contribution from roughnesses with low spatial frequencies ν < 10^?4 nm^–1 and to the interference of diffuse scattering from different layer interfaces of the surface structure.     

Linear and nonlinear dielectric properties of nanocomposites based on the organic ferroelectric of diisopropylammonium bromide

ABSTRACT

The present work aims at investigating linear and nonlinear dielectric properties of nanocomposites based on diisopropylammonium bromide (C₆H₁₆NBr, DIPAB) embedded into Al₂O₃ films having honeycomb structure with pores of 100?nm in diameter, and into opal matrices with three-dimensional structure containing pores of 100 and 60?nm. The obtained results indicated the shift of Curie point toward lower temperatures for DIPAB in porous aluminum oxide and the appearance of two phase transitions, detected upon heating and cooling for DIPAB in opal matrices. In addition, a ferroelectric phase was found to form between these two phase transitions without significant change of Curie temperature.     

Laser operated elasto-optical features of La2CaB10O19:Pr3+ polymer nanocomposites

We have discovered a principal role of the polymer matrices on the spectral dependences of piezooptical coefficients of La₂CaB₁₀O₁₉:Pr³⁺ (LCBO:Pr) nanocomposites formed by polymethylmethacrylate (PMMA) and polycarbonate (PC) matrices. It was established that the optical treatment by the 10 ns Nd:YAG laser can cause substantial changes of the dispersion of the piezooptical coefficients within the spectral wavelength 1400–1600 nm. The optimal content of the LCBO:Pr with sizes ranging from 40 to 110 nm corresponds to 4–6% in weighing units. Following the performed quantum chemical simulations, the observed changes are caused by different polarizabilities of the polymer matrices.     

Peculiarities of Er3+ photoluminescence in halogen-doped amorphous silica

The spectra and photoluminescence kinetics of Er³⁺ ions embedded in amorphous fluorine- and chlorine-doped silica matrices synthesized by surface-plasma chemical vapor deposition were investigated at 27–300 K. Luminescence was excited with an Ar⁺ laser at a wavelength of 514.5 nm and with a diode laser at a wavelength of 975 nm. Narrow and well-expressed components of Stark sublevels with a small contribution of inhomogeneous broadening intrinsic to Er³⁺ ions in crystalline rather than amorphous matrices were revealed and identified in photoluminescence spectra. The structure of Stark sublevels was well-resolved at low temperatures. The presence of the well-resolved Stark structure in spectra was indicative of stable anion complex formation in Er³⁺ environment presumably associated with halogen incorporation. This environment was formed at a stage of the low-temperature plasma-chemical synthesis and was destroyed at glass fusion.     

Technical Reports: A Single-photon Counting Pixel Detector for Surface Diffraction Experiments

The intense flux delivered by third-generation synchrotron sources has opened up exciting new possibilities in surface diffraction (SD) studies [1–3]. Nonetheless, practical SD experiments are plagued by several technical problems. Because the crystalline surface is typically probed down to a depth of approximately 1 or 2 nm when using subcritical-angle incident X-ray beams, the scattering volume is only about 10^-12 cm³. This is further exacerbated by the fact that the most interesting information on the surface structure is generally obtained from those regions of diffraction features known as crystal truncation rods (CTRs) where scattering is weakest, i.e., in between Bragg peaks.     

Small-angle neutron scattering study of the nano-sized features in an oxide dispersion-strengthened Fe12Cr alloy

Small-angle neutron scattering experiments, along with positron lifetime measurements and transmission electron microscopy observations, were performed on samples of an oxide dispersion-strengthened (ODS) Fe12Cr alloy and its non-ODS counterpart in order to characterize their nano-sized features. The nuclear and magnetic scattering data were analysed using the maximum entropy approach for obtaining the size distribution of the scattering centres in these materials. The positron annihilation results and the TEM information have made possible an interpretation of the volume distribution of the scattering centres having sizes below ~16 nm and their proper quantitative analyses. The smaller scattering centres in the ODS alloy exhibit distributions with modal values at ~6–7 and 12–14 nm. The peak at ~6–7 nm appears to be due to the overlapping of more than one type of scattering centres, while the one at ~12–14 nm can be exclusively attributed to the Y-rich centres. The quantitative analysis of the magnetic scattering data yields a volume fraction and number density of the Y-rich particles estimated in 0.70?±?0.03% and 0.77 × 10²² m^?3, respectively.     

Properties of a surface contaminated by gaseous products of polymer composition materials under vacuum conditions

Optical properties and chemical composition of a surface that is contaminated by molecular flows consisting of gaseous products of polymer composition materials (e.g., EKOM-2 enamel) are experimentally studied. The polymer materials are irradiated using a short-wavelength source with a luminous intensity of 6 × 10^?4 W/cm² sr in the wavelength interval 90–320 nm in a vacuum chamber that is evacuated to a pressure of 10^?4–10^?3 Pa. An analytical solution is obtained for the problem of radiation fluxes in scattering and absorbing medium of precipitate on a mirror surface, and a relation of model absorption and scattering coefficients for optical radiation in such medium and transport coefficients of the Gurevich theory of turbid medium is demonstrated.     

Dependence of the threshold voltage in indium-phosphide pore formation on the electrolyte composition

Results of the experimental determination of the threshold voltage of pore formation for n-InP (100) crystals with a charge-carrier density of 2.3 × 10¹⁸ cm^?3 are presented. The threshold voltage of pore formation is shown to be a function of the electrolyte composition, in particular, of the acid concentration in the electrolyte solution. A 5% solution of hydrochloric acid is the most suitable etchant for obtaining high-quality porous indium phosphide films. It is possible to obtain a nanoporous layer that consists of pores 40 nm in diameter spaced by 5–10 nm. The porosity in this case is 45%.     

Two-dimensional spatially ordered Al2O3 systems: Small-angle neutron scattering investigation

The structure of anodized aluminum oxide films has been investigated by the small-angle neutron scattering method. A theoretical solution is obtained for describing neutron scattering from the Al₂O₃ ordered porous structure. Analysis of the neutron-experiment data shows the possibility of obtaining porous membranes with ideally periodic hexagonal packed pores on a large area (～0.5 cm²).     

Fabrication of composite based on GeSi with Ag nanoparticles using ion implantation

Comparative analysis of the structural and optical properties of composite layers fabricated with the aid of implantation of single-crystalline silicon (c-Si) using Ge⁺ (40 keV/1 × 10¹⁷ ions/cm²) and Ag⁺ (30 keV/1.5 × 10¹⁷ ions/cm²) ions and sequential irradiation using Ge⁺ and Ag⁺ ions is presented. The implantation of the Ge⁺ ions leads to the formation of Ge: Si fine-grain amorphous surface layer with a thickness of 60 nm and a grain size of 20–40 nm. The implantation of c-Si using Ag⁺ ions results in the formation of submicron porous amorphous a-Si structure with a thickness of about 50 nm containing ion-synthesized Ag nanoparticles. The penetration of the Ag⁺ ions in the Ge: Si layer stimulates the formation of pores with Ag nanoparticles with more uniform size distribution. The reflection spectra of the implanted Ag: Si and Ag: GeSi layers exhibit a sharp decrease in the intensity in the UV (220–420 nm) spectral interval relative to the intensity of c-Si by more than 50% owing to the amorphization and structuring of surface. The formation of Ag nanoparticles in the implanted layers gives rise to a selective band of the plasmon resonance at a wavelength of about 820 nm in the optical spectra. Technological methods for fabrication of a composite based on GeSi with Ag nanoparticles are demonstrated in practice.     

Formation of nanoparticles containing zinc in Si(001) by ion-beam implantation and subsequent annealing

The formation of nanoparticles containing zinc in Si(001) substrates by the implantation of ⁶⁴Zn⁺ ions and subsequent annealing in dry oxygen at 800 and 1000°C for 1 h is studied. The structure of the samples is studied by high-resolution transmission electron microscopy, X-ray diffraction, and photoluminescence spectroscopy. 20-nm zinc nanoparticles located at a depth of about 50 nm are revealed in the as-implanted sample. 10–20-nm pores are observed in the surface layer. Annealing leads to oxidation of the Zn nanoparticles to the Zn₂SiO₄ state. It is shown that the oxidation of Zn nanoparticles begins on their surface and at an annealing temperature of 800°C results in the formation of nanoparticles with the “соre–shell” structure. The X-ray diffraction technique shows simultaneously two Zn and Zn₂SiO₄ phases. ZnO nanoparticles are not formed under the given implantation and annealing conditions.