Polymer-templated mesoporous carbons synthesized in the presence of nickel nanoparticles, nickel oxide nanoparticles, and nickel nitrate

Mesoporous carbon composites, containing nickel and nickel oxide nanoparticles, were obtained by soft-templating method. Samples were synthesized under acidic conditions using resorcinol and formaldehyde as carbon precursors, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock co-polymer Lutrol F127 as a soft template and nickel and nickel oxide nanoparticles, and nickel nitrate as metal precursors. In addition, a one set of samples was obtained by impregnation of mesoporous carbons with a nickel nitrate solution followed by further annealing at 400 °C. Wide angle X-ray powder diffraction along with thermogravimetric analysis proved the presence of nickel nanoparticles in the final composites obtained using nickel and nickel oxide nanoparticles, and Ni(NO₃)₂ solution. Whereas, the impregnation of carbons with a nickel nitrate solution followed by annealing at 400 °C resulted in needle-like nickel oxide nanoparticles present inside the composites’ pores. Low-temperature (−196 °C) nitrogen physisorption, X-ray powder diffraction, and thermogravimetric analysis confirmed good adsorption and structural properties of the synthesized nickel-carbon composites, in particular, the samples possessed high surface areas (>600 m²/g), large total pore volumes (>0.50 cm³/g), and maxima of pore size distribution functions at circa 7 nm. It was found that the composites were partially graphitized during carbonization process at 850 °C. The samples are stable in an air environment below temperature of 500 °C. All these features make the synthesized nickel-carbon composites attractive materials for adsorption, catalysis, energy storage, and environmental applications.     

Magnetic resonance of metallic nanoparticles in vitreous silicon dioxide implanted with iron ions

Silica glasses exposed to steady-state and pulsed irradiation with Fe⁺ ions are studied using magnetic resonance. The irradiation doses used in experiments are equal to 1 × 10¹⁵, 1 × 10¹⁶, and 1 × 10¹⁷ cm^?2. It is found that, under both steady-state and pulsed irradiation conditions, glass samples exposed at a dose of 1 × 10¹⁷ cm^?2 exhibit a broadband orientation-dependent signal. The shape of inclusions is evaluated under the assumption that the observed spectrum is caused by the ferromagnetic resonance induced in a new phase of metallic iron.     

Third-order nonlinearity of nickel oxide nanoparticles in toluene

We report measurements of the nonlinear refractive index, n(2), of nickel oxide nanoparticles (NPs) in toluene at 532 nm. The measurements were performed using the Z-scan technique with 80 ps laser pulses at 7 Hz. Large values of n(2) in the range of 10(-13)-10(-12) cm(2)/W were measured, and negligible two-photon absorption coefficient was estimated for colloids having NP filling fractions in the range of 10(-8)-10(-7).     

Application of nickel oxide nanoparticles in electrochromic materials

This study presents the application of NiO nanoparticles in electrochromic materials field. The monodisperse NiO nanoparticles ranged from 5 to 8 nm were synthesized by hot-injection method and the NiO films were prepared by dip-coating technique on ITO glass. The structure, electrochemical as well as optical performance was investigated systematically. NiO films composing of nanoparticles maintained the porous microstructure and exhibited excellent electrochromic performance. It was clear that the film annealed at 300 °C exhibited the highest electrochemical activity and improved transmittance modulation (?T), while maintaining faster response time.     

Structural and photoluminescence properties of ZnO nanoparticles on silicon oxide

Isolated, self assembled ZnO nanoparticles are grown in two steps: by the electron beam evaporation of Zn on oxidised silicon wafers, during which isolated Zn nanodots are grown, and a subsequent annealing in oxygen that results in the desired ZnO nanodots. Low temperature PL measurements of the ZnO nanodots show that the near band edge part of the spectra is dominated by a zero phonon line near 3.36 eV which is an overlap of two emitting lines near 3.363 eV and 3.367 eV. Characterization by TEM and EELS shows that the nanoparticles are zinc oxide single crystals grown with their c-axis perpendicular to the substrate; their distribution, size and crystallinity depend on the deposition parameters of zinc and the growth substrate. We discuss the effect of these parameters on the morphology of the resulting material. Our approach demonstrates a simple method for the growth of high purity isolated ZnO nanodots of similar sizes, distributed uniformly on a large surface. PACS 61.46.Df; 81.05.Dz; 81.07.-b     

Magnetic and magneto-optical properties of ion-synthesized cobalt nanoparticles in silicon oxide

The magnetic and magneto-optical properties of ion-synthesized cobalt nanoparticles in the amorphous silicon oxide matrix are investigated as a function of the implantation dose. The analysis of the field dependences of the magnetization and the magneto-optical Faraday and Kerr effects demonstrates that, as the ion implantation dose increases, the superparamagnetic behavior of an ensemble of cobalt nanoparticles at room temperature gives way to a ferromagnetic response with the anisotropy characteristic of a thin magnetic film. The magnetization curves for the superparamagnetic and ferromagnetic ensembles of cobalt nanoparticles are simulated to determine their average sizes and the filling density in the irradiated layer of the silicon dioxide matrix. It is revealed that the spectral dependences of the Faraday and Kerr effects for ion-synthesized cobalt nanoparticles differ substantially from those for continuous cobalt films due to the localized excitations of free electrons in the nanoparticles.     

Thermoelectrics from silicon nanoparticles: the influence of native oxide

Thermoelectric materials were synthesized by current-assisted sintering of doped silicon nanoparticles produced in a microwave-plasma reactor. Due to their affinity to oxygen, the nanoparticles start to oxidize when handled in air and even a thin surface layer of native silicon oxide leads to a significant increase in the oxide volume ratio. This results in a considerable incorporation of oxygen into the sintered pellets, thus affecting the thermoelectric performance. To investigate the necessity of inert handling of the raw materials, the thermoelectric transport properties of sintered nanocrystalline silicon samples were characterized with respect to their oxygen content. An innovative method allowing a quantitative silicon oxide analysis by means of electron microscopy was applied: the contrast between areas of high and low electrical conductivity was attributed to the silicon matrix and silicon oxide precipitates, respectively. Thermoelectric characterization revealed that both, electron mobility and thermal conductivity decrease with increasing silicon oxide content. A maximum figure of merit with zT = 0.45 at 950 °C was achieved for samples with a silicon oxide mass fraction of 9.5 and 21.4% while the sample with more than 25% of oxygen clearly indicates a negative impact of the oxygen on the electron mobility.     

Nonlinear optical characteristics of CdS and ZnS nanoparticles implanted into zirconium oxide thin films

The nonlinear refractive indices γ and nonlinear absorption coefficients of ZrO₂ films doped with CdS or ZnS nanoparticles, as well as with various metals, are measured. The effects of semiconductor and metal nanoparticles and annealing on the nonlinear optical properties of films are studied. The structural parameters of films, determined by electron microscopy and x-ray dispersion spectroscopy, are compared to the optical and nonlinear optical characteristics of these media. The high magnitude of γ of the films ((3±0.6)×10^?11 cm² W^{? 1}) is attributed to the surface enhancement effect in semiconductor nanoparticles. On the basis of Z-scan data obtained at different intensities of radiation, it is shown that the variations in γ of the ZrO₂:CdS(Cr) and ZrO₂:ZnS(Mn) films are related to the generation of free carriers.     

Field emission properties of a-C and a-C:H films deposited on silicon surfaces modified with nickel nanoparticles

The a-C and a-C:H films are deposited on silicon surfaces modified with and without nickel nanoparticles by using mid-frequency magnetron sputtering. The microstructures and morphologies of the films are analyzed by Raman spectroscopy and atomic force microscopy. Field emission behaviors of the deposited films with and without nickel nanoparticles modification are comparatively investigated. It is found that the hydrogen-free carbon film exhibits a high field emission current density and low turn-on electric field compared with the hydrogenated carbon film. Nickel modifying could increase the current density, whereas it has no significant effect on the turn-on electric field. The mechanism of field electron emission of a sample is discussed from the surface morphologies of the films and nickel nanoparticle roles in the interface between film and substrate.     

Microstructure and magnetic properties of strontium titanate implanted with iron

The magnetic phase composition of strontium titanate surface layers implanted with iron ions is studied by means of Mössbauer spectroscopy, and by measuring alternating current magnetic susceptibility. It is shown that the interaction between α-Fe nanoclusters at high concentrations of the implanted admixture produces ferromagnetic order in samples at room temperature.     

Electrical measurements of boron implanted silicon on sapphire and bulk silicon

Hall effect and sheet resistivity measurements have been performed on boron implantations in 1μm silicon layers on sapphire (SOS), and in bulk silicon. The doses used were 10¹⁴, 10¹⁵ and 10¹⁶ ions/cm², and implantation energies were 150 and 300 keV. The samples were annealed at temperatures between 300 and 800°C. As a rule the effective number of carriers in SOS was found to be about twice the number of carriers in bulk silicon. However, the mobility is lower in bulk silicon, resulting in a sheet resistivity almost the same in boron implanted SOS and bulk silicon.     

Pac studies of ion implanted silicon

The annealing behaviour of radiation induced defects in ion implanted silicon is studied by the perturbed angular correlation method (PAC). Between 700 K and 1000 K the trapping and detrapping of vacancy-oxygen complexes is observed. In annealed p-Si a well defined, axially symmetric electric field gradient (EFG) appears at low temperatures. This EFG is oriented to the surface and not to any crystallographic direction. The size of the EFG depends strongly on the surface charge.     

CEMS study of silicon implanted iron

Thin layers of iron-rich Fe-Si alloys were formed by silicon implantation into iron at room temperature with different energies (100, 200, and 300 keV) and ion doses (2 × 10¹⁷ to 1×10¹⁸ cm^–2). The produced layers were investigated by⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS) to identify the phases formed by the ion implantation. Auger electron spectroscopy (AES) was used to measure the concentration depth profiles of the implanted silicon. Depending on the implantation parameters different disordered Fe-Si structures were detected. At low doses only magnetic phases were formed while at high doses a non-magnetic phase with a hitherto unknown structure appeared. Annealing of the samples resulted first in the formation of a D0₃-like short-range order and a slow decrease of the non-magnetic phase, and subsequently in the migration of Si out of the investigated depth range.     

Ellipsometric study of tellurium implanted silicon

Abstract

Ellipsometric parameters as a function of the dose (D = 2.10¹³ ? 2.10¹⁵ ions cm^?2) and annealing temperature have been measured on the silicon implanted with 30 keV Te ions. Obtained information on lattice disorder are to a great extent comparable with those of other methods, e.g. backscattering technique. Moreover optical constants of a damage surface layer may be estimated.     

Optical characteristics of implanted silicon films

The first data are presented on the change (following implantation) in the refractive index and the band structure of silicon on sapphire films. The implantation was effected with phosphor ions of 40 keV and doses from 10¹² to 10¹⁶ cm^–2. An increase following implantation of the refractive index and the energy of the first direct allowed transitions E₁ is noted, indicating changes in the second coordination sphere. The profile E₁(x) is studied pointing to heterogenization effects. The films were annealed with ruby laser pulses of 0.2 J/cm². The same laser was used to study the lux dependence of the injection level _n and surface photo-emf V. Hysteresis in the V(_n) dependence (after the use of maximum intensity of the laser beam) is noted indicating irreversible straightening of the bands at the film surface.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 40–43, May, 1984.