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Preparation and Identification of CuCr2O4 Nanoparticles and Investigation of its Microwave Absorption Characteristics at x-band Frequency using Silicone Rubber Polymeric Matrix
MDPI AG, Volume 2; 10.3390/ecms2018-05193

Lately, silicone rubber because of the desirable permittivity on the one hand and various applications in the implants, membranes, Solar cells, sensors, Semiconductor devices, high frequency devices, photothermal therapy methods, acoustic metamaterials, and insulator materials on the other hand has attracted considerable attentions. In this research, CuCr2O4 nanoparticles were prepared according to the sol-gel method and then were identified by Fourier transform infrared (FT-IR), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and vibrating sample magnetometer (VSM). Results showed that monophase crystal structure with identical morphology of CuCr2O4 nanoparticles has been synthesized. Finally, CuCr2O4 nanoparticles and silicone rubber were composited and then microwave absorbing properties of the CuCr2O4/silicone rubber nanocomposite were investigated by vector network analyzer (VNA) exhibiting 48.56 dB microwave attenuation of the CuCr2O4/silicone rubber nanocomposite with 2.6 mm thickness at 10.9 GHz frequency and more than 92.99% microwave absorption in the x-band frequency.

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Preparation and Characterization of CuFe2O4 Nanoparticles by the Sol-Gel Method and Investigation of its Microwave Absorption Properties at Ku-band Frequency using Silicone Rubber
MDPI AG, Volume 2; 10.3390/ecms2018-05218

Recently, using microwave devices emitting electromagnetic waves due to enhancing convenient life have been increased that can be harmful to the environment. In this study, CuFe2O4 nanoparticles were prepared through the conventional sol-gel procedure and then were characterized by X-ray powder diffraction (XRD), vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR), and vector network analyzer (VNA) using S parameters. Results illustrated that pure crystal structure of magnetic nanoparticles has been synthesized by the sol-gel method with 26.91 emu/g magnetic saturation (Ms). Finally, CuFe2O4 nanoparticles were composited by silicone rubber to investigate of its microwave absorption properties. Results showed that CuFe2O4/silicone rubber nanocomposite absorbed more than 94.87% of microwave at ku-band frequency with 1.7 mm thickness and the maximum reflection loss was -60.38 dB at 16.1 GHz. Magnetic and dielectric properties of the CuFe2O4 nanoparticles and silicone rubber polymeric matrix in the nanocomposite demonstrated desirable microwave absorption properties.

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Reliability of Orthodontic Miniscrews: Bending and Maximum Load of Different Ti-6Al-4V Titanium and Stainless Steel Temporary Anchorage Devices (TADs).
Published: 14 May 2018 by MDPI AG in The 3rd International Electronic Conference on Materials Sciences in The 3rd International Electronic Conference on Materials Sciences session Biomaterials
MDPI AG, 10.3390/ecms2018-05219

Temporary anchorage devices (TADs) have been introduced in orthodontic clinical practice in order to allow tooth movements avoiding side effects in the position of adjacent teeth. Miniscrews are available on the market with different diameters and materials. Accordingly, the purpose of the present report was to measure and compare the forces to bend and fracture different mini implants. Ti-6Al-4V Titanium and stainless steel TADs of different manufacturers (Spider Screw – HDC; Mini implants – Leone; Benefit – Orteam; Storm - Kristal) were evaluated. Two different diameters (1.5 mm and 2.0 mm) were tested. Ten unused specimen for each group were blocked in an Instron Universal Testing Machine and a shear load was applied at the neck of the screws. The force to bend the mini implant was measured at 0.1 mm and 0.2 mm deflections. Moreover the maximum load before screw fracture was recorded. Data were submitted to statistical analysis. 2.0 TADs showed significantly higher forces than 1.5 mm screws both at 0.1 mm and 0.2 mm deflections and at maximum load. Moreover, no significant differences were reported between titanium and stainless steel mini implants for equal diameter

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Rapid and Facile Fabrication of Wafer Scale Silicon Hierarchical Structures with Broadband Ultra High Anti-Reflection Property
Published: 15 May 2018 by MDPI AG in The 3rd International Electronic Conference on Materials Sciences in The 3rd International Electronic Conference on Materials Sciences session Optical, Electrical and Magnetic Materials
MDPI AG, 10.3390/ecms2018-05223

Nanostructuring of Silicon surface has perceived exponential growth over time due to its high demanding properties like superhydrophobicity and high anti-reflection [1]–[3]. Especially hierarchical structures (combination of micro- and nano- structures) on Silicon with significantly increased surface area has demonstrated enhanced optical and surface wettability properties, making it highly suitable for applications like self-cleaning, solar cell, photoluminescence, contamination prevention, etc [3]–[5]. Various techniques like vapour-liquid-solid (VLS), reactive ion etching (RIE), electrochemical etching and wet anisotropic electroless etching have been optimised for  micro- and nanostructuring over Silicon surface [5]–[9]. Methods like VLS and RIE are expensive and complicated. Wet electrochemical and electroless etching processes are simpler but electrochemical etching gives a very non-uniform porous structure and electroless etching only gives rise to microstructure and is also dependent on the orientation of Silicon surface. Nanostructuring of Silicon wafers using metal assisted etching has also been reported which is a rapid process [4], [10]. However, this process only results in the formation of nanostructured Silicon. There are reports where wet chemical etching and metal assisted etching process have been combined to realize hierarchical structures on Silicon but it does require longer time and large area uniformity in the formation of hierarchical structures is unpredictable [3], [11]. 

In this work, for the first time we propose an extremely fast and facile electroless method of fabricating hierarchical structures on Silicon wafer covering a large area. Added major benefits to this proposed method is that complete wafer can be textured within 3 to 8 minutes time span and is not dependent on the orientation or doping concentration of Silicon.

The unpolished side of a commercial Silicon wafer having grooved cup shaped microstructures on it was used as the base to deposit silver (Ag) nanoparticles electrolessly. After the Ag nanoparticle deposition for varied time between 30 s to 2 min, the Silicon wafer was etched for different time duration (1 min to 7 min) in dilute mixture of Hydrofluoric acid (HF) and Hydrogen peroxide (H2O2). Eventually the Ag nanoparticles were etched away in dilute Nitric acid leaving behind the hierarchical structures of Silicon unaffected. Pyramidal shaped microstructured Si surface was also used for deposition of Ag nanoparticles followed by a similar processing as mentioned above.

Diffused optical reflectance measurement on the hierarchical structured Silicon showed significant reduction by 46% in comparison to plane polished Silicon. Moreover insignificant variation in reflectance was observed over a broad wavelength range of 300 nm to 1400 nm.

It is concluded that such facile large area processing of hierarchical anti-reflecting structures on Si can be extremely beneficial for optical applications using Silicon.

References:

[1]      Y. Cao et al., “Fabrication of silicon wafer with ultra low reflectance by chemical etching method,” Appl. Surf. Sci., vol. 257, no. 17, pp. 7411–7414, 2011.

[2]      Y. Xiu, L. Zhu, D. W. Hess, and C. P. Wong, “Hierarchical silicon etched structures for controlled hydrophobicity/ superhydrophobicity,” Nano Lett., vol. 7, no. 11, pp. 3388–3393, 2007.

[3]      D. Qi et al., “Simple Approach to Wafer-scale Self-cleaning Antireflective Surfaces,” pp. 1–5.

[4]      W.-F. Kuan and L.-J. Chen, “The preparation of superhydrophobic surfaces of hierarchical silicon nanowire structures.,” Nanotechnology, vol. 20, no. 3, p. 35605, 2009.

[5]      Y. Xiu, S. Zhang, V. Yelundur, A. Rohatgi, D. W. Hess, and C. P. Wong, “Superhydrophobic and Low Light Reflectivity Silicon Surfaces Fabricated by Hierarchical Etching,” Langmuir, vol. 24, no. 18, pp. 10421–10426, Sep. 2008.

[6]      C. R. Tellier and A. Brahim-Bounab, “Anisotropic etching of silicon crystals in KOH solution,” J. Mater. Sci., vol. 29, no. 22, pp. 5953–5971, 1994.

[7]      G. Barillaro, A. Nannini, and M. Piotto, “Electrochemical etching in HF solution for silicon micromachining,” Sensors Actuators A Phys., vol. 102, no. 1–2, pp. 195–201, Dec. 2002.

[8]      V. Schmidt, S. Senz, and U. G?sele, “Diameter-Dependent Growth Direction of Epitaxial Silicon Nanowires,” Nano Lett., vol. 5, no. 5, pp. 931–935, May 2005.

[9]      F. Marty et al., “Advanced etching of silicon based on deep reactive ion etching for silicon high aspect ratio microstructures and three-dimensional micro- and nanostructures,” Microelectronics J., vol. 36, no. 7, pp. 673–677, Jul. 2005.

[10]     S. Gielis, M. H. vander Veen, S. De Gendt, and P. M. Vereecken, “Silver-assisted Etching of Silicon Nanowires S. Gielis,” ECS Trans., vol. 33, no. 18, pp. 49–58, 2011.

[11]     D. Z. Dimitrov and C.-H. Du, “Crystalline silicon solar cells with micro/nano texture,” Appl. Surf. Sci., vol. 266, pp. 1–4, 2013.

  • Open access
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Study of the Properties of Co-Substituted Ba2Mg2Fe12O22 Hexaferrites
Published: 17 May 2018 by MDPI AG in The 3rd International Electronic Conference on Materials Sciences in The 3rd International Electronic Conference on Materials Sciences session Optical, Electrical and Magnetic Materials
MDPI AG, 10.3390/ecms2018-05229

Multiferroic materials, in which long-range magnetic and ferroelectric orders coexist, have recently been of great interest in the fields of both basic and applied sciences. The Y-type hexagonal ferrite Ba2Mg2Fe12O22 is an example of a multiferroic material. Its single crystals have a relatively high spiral-magnetic transition temperature (~200 K), show multiferroic properties at zero magnetic field, and the direction of the ferroelectric polarization can be controlled by a weak magnetic field (< 0.02 T) [1]. We present a study of the influence of substituting the Mg2+ cations in the Y-type Ba2Mg2Fe12O22 hexaferrites with a magnetic cation, such as Co2+, on the structural and magnetic properties. The Ba2Mg0.4Co1.6Fe12O22 powder was synthesized by sonochemical co-precipitation. High-power ultrasound was applied to assist the co-precipitation process. The precursors produced were synthesized at 1170°С. The XRD spectra of the powders showed the characteristic peaks corresponding to the Y-type hexaferrite structure as a main phase and some CoFe2O4 impurity (< 2%) as second phase. This was also confirmed by Mössbauer spectroscopy measurements. The magnetization values at 50 kOe were 30 emu/g and 26.6 emu/g at 4.2 and 300 K, respectively. The ZFC and FC magnetization curves were obtained at a magnetic field of 500 Oe. The magnetic measurements revealed a magnetic phase transition at 200 K from ferrimagnetic-to-helical spin order. Such a transition is considered as a precondition for the material to exhibit multiferroic properties.

[1] K. Taniguchi, N. Abe, S. Ohtani, H. Umetsu, T. Arima, "Ferroelectric polarization reversal by a magnetic field in multiferroic Y-type hexaferrite Ba2Mg2Fe12O22", Appl. Phys. Express, vol. 1, art. num. 031301, 2008.

  • Open access
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Studying the Effect of PbS Film Thickness on Morphology and Optical Properties
Published: 17 May 2018 by MDPI AG in The 3rd International Electronic Conference on Materials Sciences in The 3rd International Electronic Conference on Materials Sciences session Posters
MDPI AG, 10.3390/ecms2018-05230

Lead Sulphide (PbS) is an important binary semiconductor from IV–VI group with a narrow band gap of 0.41 eV. It has a large exciton Bohr radius of 18nm which results in strong quantum confinement for electrons and holes even for large particles. PbS nanoparticles are promising in optical and photonic device applications such as solar cells, gas sensors and other optoelectronic devices and also IR detectors . When the size and shape of PbS are transferred from bulk material to nanoparticles, the optical band gap shifts from 0.41 eV to the values up to 5.2 eV which is suitable to build optical sensors with adjustable properties

In this work, PbS thin films were deposited on glass substrates by chemical bath deposition method. We observe that the film thickness was doubled by repeating the chemical reaction. The effect of varying film thickness on structure and optical properties was studied. XRD reveals that all of the films were polycrystalline with (200) preferred crystal orientation. Increasing the film thickness enhances the crystallinity as well as reduces the dislocation density and strain of the films. Optical measurements show that as the thickness of the PbS film increases, the band gap of the films decreases from 1.47eV to 0.77eV and shifts from visible region to IR region. One of the prepared samples was used as an IR detector in the range of (800 nm to 1800 nm) it shows good agreement with the commercial PbS detector .

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Effects of Silica Fume on the Pore Structure and Properties of Mortars Exposed to Sulphate Aggressive Media
Published: 17 May 2018 by MDPI AG in The 3rd International Electronic Conference on Materials Sciences in The 3rd International Electronic Conference on Materials Sciences session Materials Characterization
MDPI AG, 10.3390/ecms2018-05231

The use of additions as clinker replacement has become very popular, due to the advantages that they provide, especially regarding the improvement of cement industry sustainability. The microstructure of cement-based materials has a direct influence on their service properties. In this research, mortars with different contents of silica fume (up to 10%) have been studied. These mortars were exposed to aggressive media with presence of sodium and magnesium sulphate along 90 days. On one hand, the evolution of their pore structure was characterised using different results provided by mercury intrusion porosimetry technique, such as intrusion-extrusion curves and logarithm of differential intrusion volume versus pore size curves. On the other hand, the compressive strength and the steady-state ionic diffusion coefficient obtained from resistivity of the samples, which was measured using impedance spectroscopy, were also studied. In general, silica fume mortars showed good performance, although the greatest deterioration of these mortars was observed in a mixed magnesium and sodium sulphate solution.

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Influence of the Composition on the Environmental Impact of Soft Ferrites
Published: 17 May 2018 by MDPI AG in The 3rd International Electronic Conference on Materials Sciences in The 3rd International Electronic Conference on Materials Sciences session Optical, Electrical and Magnetic Materials
MDPI AG, 10.3390/ecms2018-05232

The aim of this paper is to better understand the influence of the composition on the environmental impact of soft ferrite magnetic materials. Magnetically soft ferrites are ceramic homogeneous materials that have a cubic crystal structure. Soft ferrites have low coercitivity with a high resistivity, low losses and high permeability, and are commonly used in high frequency applications. A life cycle assessment (LCA) has been carried out analyzing EcoInvent average ferrite dataset and updating it with material compositions of manganese-zinc (MnZn) ferrites, one of the major categories of soft ferrites. MnZn ferrites use iron oxide as their main component adding manganese oxide (17%-24.5% in weight) and zinc oxide (6.5%-14% in weight). Depending on their composition, their magnetical properties change (such as permeability, losses, Curie temperature…). The influence of the material composition has been assessed, obtaining more knowledge of their environmental impact. The main environmental problem that generates the use of soft ferrites, under ReCiPe methodology, is in the metal depletion category. Ferrites use in their composition metals that are scarce, such as Manganese. Manganese is included in the 2017 EU strategic materials list due to its high economic importance in the EU industry, and also its supply risk. The software used to develop the LCA model was SimaPro 8.4, with EcoInvent v3.4 life cycle inventory database. Both are currently the most used tools to evaluate environmental impact in the LCA scientific community. By means of the performed LCA, environmental impact values under ReCiPe methodology will be obtained to assess the influence of the composition on the overall impact. This analysis shows the large influence of material composition on the environmental impact of ferrites, allowing engineers and material scientist to choose between different ones taking also into account its sustainability.

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Analysis and reliaiblity study of luminescent materials for white lighting
MDPI AG, Volume 2; 10.3390/ecms2018-05233

With this work we report on the characterization and reliability/stability study of photoluminescent materials for lighting applications. Photoluminescent materials (phosphors) are a primary component of the white solid state lighting systems. Being based on rare earth doped Alluminate, Silicate, Garnets or Nitride compounds they offer green, yellow and red photoluminescence, when excited with a blue radiation (445 – 455 nm), typically emitted by a Gallium Nitride based LED.

With this work we report on a characterization of Phosphor materials for lighting, particularly: a) phosphors directly deposited over LED chip, b) remote phosphor solutions encapsulated in plastic medium for LED lighting, C) phosphors without binder for extreme high intensity Laser Diode white lighting.

The optical and thermal properties of phosphors have been studied to develop solution based on mix compounds to achieve different Correlated Color Temperatures and high Color Rendering Index LEDs. Thermal properties of Cerium Doped YAG phosphors materials have been evaluated in order to study the thermal quenching. A maximum phosphor operating temperature of 190-200 °C has been found to cause a sensible efficiency degeneration. Reduced efficiency and Stokes shift, also cause a localized temperature increase in the photoluminescent materials. In the case of remote phosphors, heat does not find a low thermal resistance path to the heatsink (as occurs through the GaN LED chip, for direct phosphor converted devices), thermal analysis indicate that material temperature might therefore increase up to values in excess of 60°C when a radiation of 435 mW/cm2 hits the sample template.

Reliability has also been investigated both for plastic encapsulated materials and binder free depositions: pure thermal reliability study indicate that phosphors encapsulated in Polycarbonate material are stable up to temperature of approximately 100 °C, while binder free phosphor do not show any sensible degradation up to temperatures of 525 °C.

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Preparation and Identification of BaFe2O4 Nanoparticles by the Sol-Gel Rut and Investigation of its Microwave Absorption Characteristics at Ku-Band Frequency using Silicone Rubber Medium
MDPI AG, Volume 2; 10.3390/ecms2018-05234

In the last decade, spinel structures have been widely explored due to widespread applications in the antibacterial nanocomposites, memory devices, catalysts, photocatalysts, high frequency devices, and electromagnetic absorbing materials. In this study, BaFe2O4 spinel structure were synthesized through the sol-gel method using low sintering temperature and then were identified by vibrating sample magnetometer (VSM), X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR), field emission scanning electron microscopy (FE-SEM), and vector network analyzer (VNA) analysis. Results showed that uniform and pure crystal structure of BaFe2O4 nanoparticles have been prepared base on the sol-gel method. Finally, BaFe2O4 nanoparticles were blended by silicone rubber to characterize microwave absorption properties of the nanocomposite at ku-band frequency. According to the VNA results, BaFe2O4/silicone rubber nanocomposite with 1.75 mm thickness absorbed more than 94.38% of microwave at ku-band frequency and the maximum reflection loss of the BaFe2O4/silicone rubber nanocomposite was -51.67 dB at 16.1 GHz.

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