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Iron powder particles were coated with a thin SiO 2 shell for protection of corrosion. Dynamic magnetic behavior of the as-synthesized material was studied in comparison with uncoated metal in terms of frequency dispersion of the microwave permeability and permittivity. A uniform 100-nm SiO 2 shell provides durable corrosion resistance to a 4.5-μm carbonyl iron powder. The shell was deposited through tetraethyl orthosilicate hydrolysis of technical grade chemicals. It was shown that the shell did not influence the magnetic properties of the iron powder. Electron microscopy, particle size analysis, and γ-resonance spectroscopy were applied in the study. The deposited SiO 2 decreased the microwave permeability value and prevented percolation conductivity in a composite with a paraffin wax dielectric matrix. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic spectra of composites filled with carbonyl iron powder were measured at frequencies of up to 30GHz. Two previously unknown intensive high-frequency peaks of magnetic absorption have been found at frequencies surpassing the ferromagnetic resonance frequency. The peaks may be attributed to Aharoni exchange resonance modes. The resonances are excited inside magnetically isolated nanocrystallites that constitute carbonyl iron grains. Features of homogeneous ferromagnetic resonance in carbonyl iron powder grains are also discussed. [Copyright &y& Elsevier]

Abstract: Results of studies in the influence of losses on the superresolution achieveability are presented. The studies involve modeling and realization of superresolution devices. It is found that rigorous electrodynamic models that are not based on homogenization of composites can be effectively used in modeling devices with metamaterials. The possibilities to compensate losses in near-optic metamaterials by means of “active” inclusions are discussed; they appear to be rather doubtful. Alternatively, new designs are suggested for applications where losses are desirable. [Copyright &y& Elsevier]

Abstract: The paper reviews recent progress in the field of microwave magnetic properties of composites. The problem under discussion is developing composites with high microwave permeability that are needed in many applications. The theory of magnetic composites is briefly sketched with the attention paid to the laws governing the magnetic frequency dispersion in magnetic materials and basic mixing rules for composites. Recent experimental reports on the microwave performance of magnetic composites, as well as data on the agreement of the mixing rules with the measured permeability of composites that are available from the literature are discussed. From the data, a conclusion is made that the validity of a mixing rule is determined by the permeability contrast in the composite, i.e., the difference between permeability of inclusions and that of the host matrix. When the contrast is low, the Maxwell Garnet mixing rule is frequently valid. When the contrast is high, which is of the most interest for obtaining high microwave permeability of a composite, no conventionally accepted theory is capable of accurately predicting the permeability of the composites. Therefore, the mixing rules do not allow the microwave properties of magnetic composites to be predicted when the permeability of inclusions is high, that is the case of the most interest. Because of that, general limitations to the microwave performance of composites are of importance. In particular, an important relation constraining the microwave permeability of composites follows from Kittel''s theory of ferromagnetic resonance and analytical properties of frequency dependence of permeability. Another constraint concerning the bandwidth of electromagnetic wave absorbers follows from the Kramers–Kronig relations for the reflection coefficient. The constraints are of importance in design and analysis of electromagnetic wave absorbers and other devices that employ the microwave magnetic properties of composites, such as magnetic substrates for microwave antennas, microwave inductors, etc. [Copyright &y& Elsevier]

Abstract: The paper touches upon the correspondence between the widely used homogenized approach and integral equation technique in simulating electromagnetic excitation of metamaterials. The attention is drawn to metamaterials with helix-type inclusions, their properties are briefly discussed. Special attention is paid to the thin metamaterial sheets as they are the primary candidates to manufacture the so-called “superlenses” that can reveal the resolution overcoming the well-known diffraction limit (about half a wavelength). Experimental results are compared to computer simulation using both homogenized model and a rigorous approach. A physical interpretation is suggested of the development of an image with superresolution in a real device. [Copyright &y& Elsevier]

Thick dielectric SiO2 shells on the surface of iron particles enhance the thermal and electrodynamic parameters of the iron. A technique to deposit thick, 500-nm, SiO2 shell to the surface of carbonyl iron (CI) particles was developed. The method consists of repeated deposition of SiO2 particles with air drying between iterations. This method allows to obtain thick dielectric shells up to 475 nm on individual CI particles. The paper shows that a thick SiO2 protective layer reduces the permittivity of the 'Fe-SiO2—paraffin' composite in accordance with the Maxwell Garnett medium theory. The protective shell increases the thermal stability of iron, when heated in air, by shifting the transition temperature to the higher oxide. The particle size, the thickness of the SiO2 shells, and the elemental analysis of the samples were studied using a scanning electron microscope. A coaxial waveguide and the Nicholson–Ross technique were used to measure microwave permeability and permittivity of the samples. A vibrating-sample magnetometer (VSM) was used to measure the magnetostatic data. A synchronous thermal analysis was applied to measure the thermal stability of the coated iron particles. The developed samples can be applied for electromagnetic compatibility problems, as well as the active material for various types of sensors. [ABSTRACT FROM AUTHOR]

Abstract: The microwave permeability of laminated composites based on thin Fe films is under study. Multi-layered films are found to possess more rigid magnetic structure and larger damping factor of ferromagnetic resonance compared to those of one-layered films. A low-weight bulk composite sample is made of multi-layered Fe films stacked together. The peak value of imaginary microwave permeability for this sample is equal to 4, with the volume fraction of Fe being equal to 5%. Composites of such kind may be used as design material for many microwave applications. [Copyright &y& Elsevier]

Abstract: The microwave permeability of regular composites filled with thin ferromagnetic discs with in-plane anisotropy is studied. The samples are made of patterned, multi-layered Fe films stacked together to comprise a bulk composite. The permeability is measured in the frequency range of 0.1–10GHz, and is discussed in terms of constraints to the microwave performance of such composites. The technology suggested allows a composite sample to be produced with the permeability of 2.8, and low magnetic loss at frequencies below 1GHz, the volume fraction of Fe is as low as 0.77%. Such composites can be useful in the design of microwave inductors, miniaturized wideband antennas, etc. [Copyright &y& Elsevier]

Hollow ferromagnetic powders of iron were obtained by means of ultrasonic spray pyrolysis. A variation in the conditions of the synthesis allows for the adjustment of the mean size of the hollow iron particles. Iron powders were obtained by this technique, starting from the aqueous solution of iron nitrate of two different concentrations: 10 and 20 wt.%. This was followed by a reduction in hydrogen. An increase in the concentration of the solution increased the mean particle size from 0.6 to 1.0 microns and widened particle size distribution, but still produced hollow particles. Larger particles appeared problematic for the reduction, although admixture of iron oxides did not decrease the microwave permeability of the material. The paraffin wax-based composites filled with obtained powders demonstrated broadband magnetic loss with a complex structure for lesser particles, and single-peak absorption for particles of 1 micron. Potential applications are 5G technology, electromagnetic compatibility designs, and magnetic field sensing. [ABSTRACT FROM AUTHOR]

Intrinsic permeability of sendust alloys is determined from the measured microwave permittivity and permeability of composites filled with either spherical or flaky sendust powders. The permittivity and permeability measurements are performed applying the coaxial reflection-transmission technique in the 0.05 to 18 GHz frequency range. The effects of the filling factor, inclusion shape, and size on composite constitutive parameters are discussed. The permeability of metal inclusion is retrieved from the measured permeability of composites using a generalized Maxwell Garnett equation that accounts for the percolation threshold. The equation parameters are found by fitting the measured dependence of composite permittivity and permeability on frequency and filling. The inclusion dimensions calculated from the found parameters agree with the results of grain-size analyses. The alloy intrinsic permeability is retrieved from inclusion permeability with the account for skinning. The fitted frequency and damping factor of ferromagnetic resonance depend on the inclusion shape. The calculated reflectivity map of the flake-filled composite shows that sendust powders are promising fillers for interference suppressors and microwave absorbers at frequencies close to 1 GHz. [ABSTRACT FROM AUTHOR]

Abstract: Microwave magnetic performance of thin ferromagnetic films is of interest in view of many technical problems. For measuring the microwave permeability, a shorted stripline technique is in common use. Recently, a coaxial technique has been developed for permeability measurements of films deposited onto a flexible substrate. The coaxial technique is reported to be advantageous over the conventional stripline method in wideband operating range and accuracy. In this paper, measurement results are presented which are obtained with these two techniques for Fe–N films. It is found that the magnetoelastic effect contributes greatly to the measured microwave permeability of the films. With the coaxial measurements under an external magnetic bias, this effect may be accounted for to estimate the permeability of a plane film sample. Additional information on the properties of the film can also be extracted from these data, such as estimations of average magnetic anisotropy field and of the magnetostriction constant of the film. [Copyright &y& Elsevier]

Original multiscale flaked silver SERS-substrate (MFSS substrate) was applied for glycated albumin (GA) biosensing. The substrate is composed from silver flakes that have three orders of magnitude size dispersion: from 50 nm to 2 μm. The multiscale silver structure refracts the incident light and various surface plasmons are excited. Some of the internal plasmons are localized and give rise of the large local electric field. It was demonstrated that Raman scattering signal strongly depends: a) on "hot spots" formation at the edges and points of contact of silver plates, and b) on the angle of incidence. As a result the silver structure operates as an effective SERS substrate. To achieve the selectivity to glycated part, the surface of SERS-substrate was modified with 4-mercaptophenylboronic acid (4-mPBA). Various saccharides (Fru, Glc, Suc, Dex) were taken as model compounds for the glycated proteins determination. The saccharides contain cis -diol groups that form five- or six-membered ethers with boronic acid. Spectrum of SERS-substrate changes after sugar/glycated albumin treatment. Main differences in the SERS-spectra of sugar/glycated albumin treated SERS-substrate and control are referred to phenylboronic acid vibrations (999, 1021, 1072 and 1589 cm−1). Principal component analysis (PCA) and Partial Least Squares Regression (PLS-R) were used to discriminate spectra and to construct calibration curve, as well as to measure GA values in real samples of human plasma. Multiscale flaked silver SERS-substrate modified with 4-mPBA allows quantitative one-step biosensing of glycated albumin in 15 μl of human plasma. Image 1 • Silver SERS-substrate was used for glycated human albumin biosensing. • The main differences in spectra are observed at 416, 470, 999, 1021, 1072, 1572 and 1589 cm−1. • SERS-effect depends on "hot spots" formation at the edges of silver plates, and on the angle of incidence. • Quantitative one-step biosensing of glycated albumin in 15 μl of human plasma had been done. [ABSTRACT FROM AUTHOR]

Metal-dielectric micro/nano-composites have surface plasmon resonances in visible and near-infrared domains. Excitation of coupled metal-dielectric resonances is also important. These different resonances can allow enhancement of the electromagnetic field at a subwavelength scale. Hybrid plasmonic structures act as optical antennae by concentrating large electromagnetic energy in micro- and nano-scales. Plasmonic structures are proposed for various applications such as optical filters, investigation of quantum electrodynamics effects, solar energy concentration, magnetic recording, nanolasing, medical imaging and biodetection, surface-enhanced Raman scattering (SERS), and optical super-resolution microscopy. We present the review of recent achievements in experimental and theoretical studies of metal-dielectric micro and nano antennae that are important for fundamental and applied research. The main impact is application of metal-dielectric optical antennae for the efficient SERS sensing. [ABSTRACT FROM AUTHOR]

The microwave permeability of nickel is determined from constitutive parameters of paraffin–bound composites filled with nickel flakes or spheres. The metal permeability is calculated with account for skinning. The measurements of constitutive parameters are performed using the reflection–transmission coaxial-line within the frequency band of 0.001–20 GHz. The effects of filling factor, particle shape, and size on permittivity and permeability spectra are analyzed. The retrieval of inclusion permeability is based on the treatment of measured dependence of composite constitutive parameters on frequency and on volume fraction of inclusions. The retrieval procedure is based on the generalized Sihvola mixing model simplified for a single-dimension composite. The model describes the wide contrast of component susceptibility, accounts for inclusion shape and the Bergman–Milton spectral linewidth. The retrieved microwave permeability is close to the values reported for measurements with thick wires and foils. [ABSTRACT FROM AUTHOR]

Abstract: Highly contrast epi‐surface‐enhanced coherent anti‐Stokes Raman scattering (SECARS) microimages of Au‐nanoparticle‐bound organic reporter molecule distributions at a surface of novel surface‐enhanced Raman scattering (SERS)‐active metamaterial junctions, based on nanoparticles spread over a nanostructured CeO2 faceted dielectric film, deposited on an Al sublayer, were recorded at two‐color picosecond excitation of the surface in the near‐infrared spectral range. For this, a scanning confocal laser‐based micro‐CARS spectrometer was employed. The investigations showed that at Raman resonant laser excitation of the molecules/Au‐NP conjugates immobilized on the surface strong SECARS signals can be generated with laser powers not deteriorating the conjugates. Coupling CARS with the plasmonic metamaterial structures under investigation provided excellent chemical imaging contrast (up to 400) for biochemically relevant 5‐thio(2‐nitrobenzoic acid) and 4‐mercaptophenylboronic acid reporter molecules. Taking into account easy handling and utmost long‐term stability of the investigated metamaterial junction at ambient conditions, it might be considered as a promising perspective for a single‐molecule‐sensitivity surface‐enhanced Raman scattering or SECARS biosensor. [ABSTRACT FROM AUTHOR]

Virus detection is often performed using antibody-based and polymerase chain reaction-based techniques. Such methods have major deficiencies, caused by time-consuming and labor-intensive incubation and purification steps. In this contribution, a novel SERS substrate for qualitative virus detection was developed and described. The substrate is composed of a thin silver film with folded surface structure containing pore-like nanoscale cavities and indentations, deposited on mica substrate by electron beam physical vapor deposition method. Pore-like structures are semi-regularly arrayed, with a rough surface in between, allowing for SERS activity, and their size and periodicity can be manipulated in the manufacturing process. It was speculated that viral particles could be trapped in these structures and would generate easily detectable enhanced Raman signals. The SERS substrate was tested against detection of four virus species – rabbit myxomatosis virus, canine distemper virus, tobacco mosaic virus and potato virus X. Specific spectra were obtained and analyzed for each virus. Data analysis demonstrated successful differentiation between tested species. The reported results demonstrate that novel SERS substrate is suitable for detection and identification of viral particles. [ABSTRACT FROM AUTHOR]

Abstract: Magnetron sputtered nanocrystalline thin Fe70Co30 metal and (Fe70Co30)95(SiO2)5 composite films show a differently broadened Mössbauer sextet, which is interpreted as an increase in CsCl-type solid solution ordering degree for the composite film. It is suggested that the effective magnetic field at iron nuclei increases by 15kOe when an Fe atom is substituted by Co in the first coordination sphere. The ordering degree and the composite structure are shown to vary the lattice parameter by up to 0.5%. [Copyright &y& Elsevier]

Abstract: The light transmission through metallic films with different types of nano-structures was studied both theoretically and experimentally. It is shown that the positions of the surface plasmon resonances depend on nano-structural details. Those can be changed from sample to sample or in given sample by applying an external dc electric or magnetic field. The dependence of transmission spectrum on the shape of holes (inclusions) and external fields can be used for manipulation of the light transmission, as well as the polarization of the transmitted light and other optical properties, by external field. Two complementary situations are considered: a metal film with dielectric holes and a dielectric film with metallic islands. A new analytical asymptotic approach for calculation of the optical properties of such plasmonic systems is developed. [Copyright &y& Elsevier]

Protective SiO2 coating deposited to iron microparticles is highly demanded both for the chemical and magnetic performance of the latter. Hydrolysis of tetraethoxysilane is the crucial method for SiO2 deposition from a solution. The capabilities of this technique have not been thoroughly studied yet. Here, two factors were tested to affect the chemical composition and the thickness of the SiO2 shell. It was found that an increase in the hydrolysis reaction time thickened the SiO2 shell from 100 to 200 nm. Moreover, a decrease in the acidity of the reaction mixture not only thickened the shell but also varied the chemical composition from SiO3.0 to SiO8.6. The thickness and composition of the dielectric layer were studied by scanning electron microscopy and energy-dispersive X-ray analysis. Microwave permeability and permittivity of the SiO2-coated iron particles mixed with a paraffin wax matrix were measured by the coaxial line technique. An increase in thickness of the silica layer decreased the real quasi-static permittivity. The changes observed were shown to agree with the Maxwell Garnett effective medium theory. The new method developed to fine-tune the chemical properties of the protective SiO2 shell may be helpful for new magnetic biosensor designs as it allows for biocompatibility adjustment. [ABSTRACT FROM AUTHOR]