Double Negative Electromagnetic Properties of NiZn Ferrite/Cu Granular Composite Materials
1Graduate School of Education, Hiroshima University, Japan; 2National Institute of Technology, Tokuyama College, Japan; 3Graduate School of Engineering, University of Hyogo, Japan
Left handed materials (LHMs) with simultaneously negative values of permittivity (ENG) and permeability (MNG) have been extensively investigated by use of artificial composite structures with transmission line theory as well as the composite materials including metallic, dielectric or magnetic particles. We have been investigating the electromagnetic properties of hybrid granular composite materials combining magnetic and conductive particles from RF to microwave frequency range with the aim to achieve the double negative characteristic (DNG) [1-3]. In this study the relative complex permeability μr and permittivity εr spectra as well as the low frequency electrical conductivity s have been measured for the hybrid granular composite materials combined NiZn Ferrite (NiZnF) with Cu, i.e. (CuxNiZnF1-x)0.8PPS0.2. Where, the x is the volume fraction of embedded Cu particles; the volume fraction of whole particle was fixed at 0.8. The PPS is the Polyphenylenesulfide resin at the volume fraction of 0.2.
The electrical conductivity s shows insulating properties in the particle content below x = 0.18. The percolation threshold φC, where the transition from insulating to metallic state, takes place at around x = 0.17. The low frequency plasmonic state was observed above x = 0.18 where the composite shows a negative permittivity spectrum. Meanwhile, negative permeability mr was observed for x = 0.20, 0.24 and 0.30 at the same time; the DNG characteristic was realized for these particle contents.
 T. Tsutaoka, et.al, Appld Phys Lett. 103, 261906 (2013)
 T. Tsutaoka, H. Massango et.al, Appl. Phys. Lett. 108 (2016) 191904
 H. Massango, T. Tsutaoka et.al, Mater. Res. Express. 3, 095801 (2016).
Effect of Metal Doped Reduced Graphene Oxide on Thermomechanical Behaviour of Graphene/Acrylonitrile-Butadiene-Styrene Composites
1Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, India; 2Centre of Nanotechnology, Indian Institute of Technology Roorkee, India
Graphene is a unique nanomaterial which possesses unique mechanical properties, but it has two major drawbacks, i.e., the tendency of agglomeration and absence of functional groups required for good bonding between the filler and polymer chains, which restricts its use in amorphous polymer composites for structural or consumer applications. Reduced graphene oxide (rGO) is one of its derivatives which overcome both these drawbacks. However, the synthesis of rGO via top-down approach creates valencies during the ultra-sonication processes and thermal treatment which degrades its reinforcing ability in polymer composites. In this work, we have synthesized rGO doped with two different metals and studied the tensile, morphological and thermomechanical properties of metal-doped rGO reinforced acrylonitrile-butadiene-styrene composites. It has been found that 2-4 wt% of doping in rGO resulted in about 30% increase in tensile strength and 54% improvement in storage modulus of the composites. However, there was no significant effect of doping on the glass transition and thermal decomposition temperatures of these composites. This shows that the addition of metal dopants in rGO can be very useful for the preparation of light weight graphene/polymer composites having excellent stress absorption ability.
Electromagnetic Interference Shielding Effectiveness of Sulfur-Doped Graphene
1Korea Institute of Science and Technology, South Korea; 2University of Science and Technology, South Korea
Electrically conductive thin carbon materials have attracted remarkable interest as a shielding material to mitigate the electromagnetic interference (EMI) produced by many telecommunication devices. Herein, we developed sulfur-doped reduced graphene oxide (SrGO) with high electrical conductivity through using different sulfur based precursors. Experimental results demonstrate, that sulfur can be successfully doped into the graphene lattice by using different types of sulfur precursors. The resultant SrGO product exhibited excellent electrical conductivity, with maximum of 311 S cm−1, which is 52% larger than 205 S cm−1 for undoped rGO. SrGO also exhibited an excellent EMI shielding effectiveness of 38.6 dB, which is 61% larger than 24.4 dB measured for undoped rGO. Analytical examinations indicate that a sulfur content of 1.95 atom % acts as n-type dopant, increasing the electrical conductivity and, therefore the EMI shielding of doped graphene.
Electromagnetic Properties of Acicular Fe-Co Nanoparticle Composite Materials
1National Institute of Technology, Tokuyama College, Japan; 2Graduate School of Education, Hiroshima University, Japan; 3Graduate School of Engineering, University of Hyogo, Japan
Electromagnetic properties of acicular Fe-Co nanoparticle composite materials have been studied in the microwave frequency range up to 20 GHz considering the application for the EMC devises and the left-handed metamaterials. Commercially available acicular Fe76Co24 nanoparticles with an approximate length and diameter respectively 100 and 25 nm were used for preparing nanocomposites. In the magnetization measurement of nanoparticles, the magnetic hysteresis with a coercive force of 3.5 kOe was observed; the magnetization value at 17 kOe was 136 emu/g. The Fe-Co nanocomposites were prepared by mixing the Fe76Co24 nanoparticles with Polyphenylene sulfide (PPS) resin.
The ac electrical conductivity measurement revealed a drastic variation at around 65 vol.%; the conductivity value of the 70 vol.% composite at 1 kHz becomes approximately 3.7×10-4 S/cm. The complex permittivity εr = εr’ - jεr” and permeability μr = μr’ - jμr” of the Fe-Co nanocomposites were measured by the conventional S-parameter method. Both the εr’ and εr” showed a dielectric property even in the percolated state at 78 vol.%; it is difficult to realize the metallic electrical conduction as well as the low frequency plasmonic state in the Fe-Co nanocomposite due to the surface oxidation of nanoparticles. Meanwhile, a negative μr’ spectrum caused by the gyromagnetic resonance was observed above 10 GHz in the 78 vol.% composite; the μr” shows a maximum at around 9 GHz. In our previous studies, the spherical Fe-Co microparticle composites with almost the same particle content showed a negative μr’ spectrum above 6 GHz . Hence the resonance frequency of the acicular Fe-Co nanocomposites tends to locate higher than that of the spherical Fe-Co ones. This difference can be attributed to the effects of the shape magnetic anisotropy of embedded particles.
 T. Kasagi et al., J. Korean Phys. Soc., 62(2) (2013) 2113.
Fabrication and Analyses of a Novel Polymer Nanocomposite Material Suitable for Electronic Components and Devices
1Raffles Institution, Singapore; 2Republic Polytechnic, Singapore
Polymer nanocomposites have attracted considerable attention from both fundamental research and application points of view, because it exhibited much better mechanical, thermal, and multifunctional properties in comparison with the polymer matrices and their conventional microcomposite and macrocomposite counterparts. This is related to the specific properties of the nanoparticles incorporated into the polymer matrix, such as small size effect and high surface activity and energy. In this project, it is proposed to fabricate polymer nanocomposite materials using Hot-melt mixing and Injection moulding techniques with improved functional properties suitable for integration into electronic components and devices.
Structural, Dielectric and Impedance Characteristics of (Sm0.5Li0.5)(Fe0.5V0.5)O3 Multiferroics
1National Institute of Technology, Silchar, India; 2Siksha ‘O’ Anusandhan University, India; 3National University of Singapore, Singapore
A single phase multiferroicmagnetoelectric compound, (Sm0.5Li0.5)(Fe0.5V0.5)O3, is found at room temperature. This sample is fabricated using solid state reaction route. Analysis of the structural properties of the sampleby X-ray diffraction method confirmed the fabrication of the desired compound with orthorhombic unit cell structure.Morphological property of the sample is recorded by field emission scanning electron microscopy (FE-SEM). Impedance spectroscopy is employed to determine the various electrical parameters such as dielectric constant, loss tangent, impedance, electric modulus etc. at different temperature (RT-4000C) within a frequency range of (1kHz-1MHz). Furthermore, the bulk resistance as function of temperature and J–E characteristic showed the semiconducting behavior of sample with negative temperature coefficient of resistance (NTCR) type nature of the compound.The M-H loop of this sample indicates the ferromagnetic nature with very low cohesive field. A dedicated magnetoelectric set up is used to measure the ME coefficient as a function of magnetic field and found a significant ME coefficient of 2.99 mV.Cm-1.Oe-1 at room temperature.
Generation of High Transmittance Anti-Fogging TiO2 Nanotubes with Sol-Gel TiO2 Seed Layer and Hydrothermal Technique
Singapore Institute of Technology, Singapore
Titania (TiO2) suspension solutions were made with the sol-gel method using isopropanol as dispersants to prevent premature hydrolysis of Titanium (IV) Isopropoxide. A seed layer of TiO2 film was deposited on FTO glass by dip coating and annealed at 450oC.
Hydrothermal process was carried out to grow TiO2 nanotubes on TiO2 seed layer. Varying hydrothermal growth duration was done to achieve nanotubes of different length and diameter. The dimension and transmittance of the nanotubes were determined by cross-sectional Scanning Electron Microscope (SEM) and UV-VIS respectively. Water vapor treatment was done to convert the as-grown amorphous TiO2 nanotubes to crystalline anatase phase. High transmittance TiO2 nanotubes on FTO glass was achieved with antifogging and self-cleaning property. This has potential application for panels of building architecture.
Millimeter Wave Properties of Ferromagnetic Cobalt Particles Prepared by Hydrothermal Synthesis
University of Electronic Science and Technology of China, China
Ferromagnetic metal particles usually have resonance peaks in the micrometer/millimeter wave bands for EM wave shielding or absorption applications. However, it still remains a big challenge to improve the loss factor of the ferromagnetic metal particles at such high frequencies. In this study, ferromagnetic cobalt particles were prepared by hydrothermal method and the electromagnetic parameters of cobalt particles were studied with different hydrothermal temperature, time, alkali concentration and formula. It is found that hydrothermal time and formula plays a vital role on the surface morphology and electromagnetic absorption properties of the sample. In detail, we can gain the ferromagnetic cobalt particles with high loss factor in different formulations. When the content of sodium tartrate increased from 1.104 g to 3.312 g, the surface morphology of the particles changed from the peak shape to the spherical bulge, and then to the small sheet shaped bulge. Therefore, sodium tartrate can agglomerate the samples and inhibit the growth of the particles on the surface of the sample.
It is worth noticed that the magnetic metal powder, in millimeter wave band (26-40 GHz) have resonance absorption peak, and magnetic loss factor is greater than 0.3. At the same time, the experimental results show that the material has a strong resonance absorption peak around 1.2 GHz of centimeter wave band, and magnetic loss factor greater than 0.3.
The main novelty of this paper is that the as-prepared ultrafine Co particles realize the double magnetic resonances in the centimeter and millimeter wave band respectively, and this effect can be effectively controlled by the morphology of the powders.
 EGUCHI.T, NAKAGAWA.N, et al.. High-frequency magnetic properties of (FeCoNbB)-(SiO2) nanocolumnar films[J]. J. Appl. Phys. 2014, 17(115)
Optically Transparent Film of BaTiO3 – TiO2 and Fe3O4 – TiO2 on Acrylic Substrate with Water Vapor Treatment
Singapore Institute of Technology, Singapore
Surveillance drones face the threat of detection by defensive radar system, especially for its payload housed in a transparent acrylic dome. In this work, an optically transparent film stack in the visible and infra-red regime which consists of BaTiO3 – TiO2 and Fe3O4 – TiO2 was successfully deposited on acrylic substrates. A seed layer of TiO2 (7nm) was first deposited by atomic layer deposition (ALD) followed by dip coating of absorbent layers of TiO2 and BaTiO3 / Fe3O4. These as-prepared oxide layer stacks were found to compromise the transmittance of the acrylic in the visible spectrum. However, when exposed to water vapor, the TiO2 film experienced a significant surface morphology and phase transformation, causing the film to be optically transparent. The scanning electron microscopy (SEM) and EDX imaging confirmed that the BaTiO3 and Fe3O4 coat remained on the acrylic. Further testing was done using an ultraviolet-visible spectroscopy and a 10 – 20% improvement in the transmittance for the Fe3O4 film was observed. The stacked oxide absorbent layers also demonstrated a significant reduction in the reflectance of microwave signals based on arc reflectivity measurements.
Reduction in Electromagnetic Interference with BaTiO3 and Fe3O4 Thin Film Grown by Unbalanced Magnetron (UBM) Sputtering
1Engineering Cluster, Singapore Institute of Technology, Singapore; 2Newcastle University, United Kingdom; 3Institute Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore; 4Low Energy Electronic Systems (LEES) IRG, Singapore-MIT Alliance for Research and Technology (SMART) Centre, Singapore
Electromagnetic Interference (EMI) is an undesirable form of electrical-noise pollution that can impact the performance of sensitive electronic equipment, especially in intensive care unit of hospital and control unit of the aircraft. EMI originates from man-made electronic devices such as cellular phones which can cause interference in telecommunication and healthcare unit systems. Multi-stacked structure of high permittivity and permeability Barium Titanium Trioxide (BaTiO3) and Iron Ferrite (Fe) and Yttrium Trioxide (Y2O3) have been sputtered on the glass substrate. The complex permittivity (Ɛ' and Ɛ'') and permeability (μ' and μ'') of these oxide-coated substrates are verified through measurement of their Scattering (S-) parameters (S11 and S21) using Vector Network Analyzer (VNA) in the range of 300MHz to 18GHz regime. Computer Simulation Technology (CST) software was used to optimize the thickness of oxide deposition needed for EMI shielding. PASCO source kit with 10.5GHz horn transmitter and receiver in microwave regime revealed significant reduction of EM signal at 10.5GHz. With the coating of these stacked of oxides frequency absorber on electronic sensitive device, it would potentially open a new frontier into future EM shield design and allow mobile communication in frequency sensitive zone.
The Influence of Microstructure on the Microwave Absorbing Properties of U-type Hexaferrite
1Department of Physics, Indian Institute of Technology Delhi, India; 2Department of Physics, Bhaskaracharya College of Applied Sciences, University of Delhi, India
The effect of grain size on the microwave (MW) absorbing properties of U-type hexaferrite has been studied. In this work, the hexaferrites were prepared through solid state reaction and chemical methods with optimized growth parameters to obtain the varying grain sizes (~3-4 μm to ~100 nm). X-ray diffraction (XRD) studies have confirmed the formation of U-type hexaferrite phase in the prepared samples. Le Bail refinement of XRD patterns have been used to calculate the lattice parameters ‘a’ and ‘c’. Scanning electron microscopy (SEM) has been exploited in determination of microstructure of the prepared samples. The complex permittivity and permeability measurement were carried out using vector network analyser (VNA) in 2-18 GHz frequency range. Further, the reflection loss (RL), in decibels (dB), is calculated, to characterize the MW absorbing properties of single-layered plane wave absorber, by using Naito and Suetake model and transmission line theory. The samples prepared through chemical and solid state reaction methods have shown the minimum reflection loss of -22.3 dB and -27.6 dB, respectively. The results demonstrate that MW absorption properties get affected significantly with varying grain size.
The Microwave Permeability of Sendust Deduced from Measured Effective Permeability of Composites Filled with Sendust Powder
1Institute for Theoretical and Applied Electromagnetics, Russian Federation; 2Moscow State University, Russian Federation
The presentation considers the microwave performance of composites containing sendust powder with either spherical or platelet-shaped particles. The composites comprising various fractions of the powder are fabricated with paraffin wax as the host matrix. The frequency dependences of microwave permittivity and permeability are measured in the frequency range of 0.1 to 20 GHz by the coaxial Nicolson-Ross technique. The validity of various mixing rules for the measured data is checked and the intrinsic permeability of sendust is extracted. With the account for the effect of eddy currents, the intrinsic permeability values for different powders are in reasonable agreement. The data on the intrinsic permeability of ferromagnetic metals may be useful for design of composite materials for various technical applications, such as radar absorbing materials and electromagnetic shields.
Tunable Plasmonic Response from Embedded Silver Nanoparticles
1Institute of Physics, Bhubaneswar, India; 2Department of Physics, Indian Institute of Technology Delhi, India
The phenomena of Localized Surface Plasmon Resonance (LSPR) in noble metal nanoparticles has found applications in a wide variety of application ranging from high resolution optical imaging (beyond the diffraction limit), for Surface Enhanced Raman Spectroscopy, for enhanced light trapping in Solar Cells, for enhancement in luminescence yield. Crucial to these applications is the ability to synthesise material systems in which the surface plasmon resonance can be tuned as per the requirements of a particular application. Essentially, it is desirable to have a strong resonant absorption, along with a control on the wavelength at which this absorption occurs.
We report on tuning the localised plasmon resonance in silver nanoparticles, by embedding silver nanoparticles in dielectric matrices of different refractive indices. Ion beam implantation with 40keV was employed to introduce negative silver ions into amorphous hydrogenated silicon nitride (a-SiNx:H) with an excellent control over the depth and fluence of ions. The ion energy had been chosen to obtain an implantation depth of 25 nm from the film surface.Further, the refractive index of a-SiNx:H is tuned with stoichiometry, thereby making possible the tuning of the LSPR. The formation of silver clusters in the films is confirmed by XRD. The red-shifting of Plasmon peak is confirmed by UV-Vis reflectance measurements, wherein the LSPR peak is found to shift from 400 nm to 500nm.
Structural Modification and Electron Emission Characteristics in Few Layers of Graphene by Ion Induced Irradiation
1Doon University, India; 2Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, India; 3Inter University Accelerator Centre, India
Graphene is the monolayer of carbon atoms that are tightly packed into a two-dimensional (2D) honeycomb lattice that is projected as the mother of all carbon allotropes. Few and multilayered-layered graphene, which are composed of several individual graphene layers, are now also under intensive investigation and are found to be a good electron emitters. The electron emission property of graphene can be improved by various post treatments such as metal or metal oxide doping etc. Ion irradiation is also one of the means to modify the structure of graphene and hence its electron emission properties.
In the present study, we have grown few graphitic layers by microwave plasma enhanced CVD system. The high energy irradiation was carried out using 100 MeV silver (Ag) ion beam provided by the IUAC Pelletron accelerator. These studies were carried out at three different fluences, in the range of 1 x 1010 ions/cm2 to 1x 1013 ions/cm2. The structural studies of graphene were carried out using high resolution transmission electron microscope. Micro Raman spectroscopy is used an essential tool to investigate the number of graphene layers in the structure, which is confirmed by calculating ID/IGand I2D/IGratio. The electron emission studies were carried out using diode set up, with the anode and cathode distance of 200 mm. It is found that the turn on (Eon) value for as deposited sample is 2.9 V/mm which improves on irradiation at 1 x 1010 ions/cm2 (2.2 V/mm). The improved emission properties can be related to modified localized density of states due to irradiation, thereby affecting the local work function of graphene layers. However, these values increases for high dose of irradiation, confirming damage in the graphene layers.
Synthesis, Characterization and Catalytic Application of Pt-Au Alloy Nanoparticles
Department of Chemistry, School of Physical Sciences, Doon University, India
Bimetallic alloy nanoparticles (BNPs) have their unique electronic catalytic and optical properties. Such fascinating characteristics properties of BNP are different from the single component metallic nanoparticles. Moreover, these properties of the BNP can be tailored according to the specific application by controlling the size, shape and metallic composition of the particles. It has been observed that the incorporation of even a little content of the other metal changes the catalytic activity significantly. Herein, we report a single pot facile and versatile method for synthesis of bimetallic Au-Pt alloy nanoparticles (size < 10 nm) using long chain quaternary ammonium salt as stabilizer. The synthesis procedure demonstrated here is quite robust and can be adopted for synthesis of monometallic and bimetallic nanoparticles with different chemical compositions. The physical characterization of the synthesized nanoparticles confirms the alloying of Au and Pt in the nanoparticles without phase segregation. The application of the alloy nanoparticles as a catalyst has been established by investigating the 4-NP reduction in aqueous medium. The bimetallic alloy nanoparticles exhibit superior catalytic activity towards reduction of 4-NP and the efficiency of the nanoparticles increases with the increase in the Pt content. The results suggest that the expensive Pt metal can be replaced by Au-Pt alloy nanoparticles in the catalytic process.