Key Engineering Materials Vol. 843

Abstract: The microfluidic Lab-On-Chip (LOC) systems, based on the CMOS technology, today grow rapidly based on requirement of the Point-of-care-testing (POCT). It is a need for a high sensitive biotransducers, as a part of biosensors to be integrated on LOC system. To detect low-level of light emitted by an analyte, promising material and devices are a p-i-n a-Si:H photodiodes. The observed absorbance of blue light in human cells HeLa (cervical carcinoma) induct H₂O₂ in same cells and consequently, chemical reaction with NO, detected as chemiluminescence signal by the photodiode, as well as formation of cytotoxic singlet oxygen. On the other side a-Si:H p-i-n photodiode has a high sensitivity on blue light at low-light intensity, good spectral responsivity and small reflectance for blue light, low dark current, low-noise in the range of low reverse bias voltages. The photoconductivity of a-Si:H p-i-n photodiode is influenced by the native and light induced localized state density and their energy distribution in the energy gap of intrinsic a-Si:H. It is observed that the defect states of i-layer at various bias voltages contribute to the detection of HeLa cells chemiluminescence. The optical bias dependence of modulated photocurrent method (OBMPC) using the blue LED light is applied to clarify the energy gap density of state nature and energy distribution, respectively in a-Si:H p-i-n photodiode i-layer.

Abstract: In this work, fabrication and characterization of a nanostructured rare-earth-doped ZnMoO₄ will be reported. Photoluminescence properties and quantum efficiency of the rare-earth-doped ZnMoO₄ with different dopant concentrations have been investigated. These samples were synthesized by sol-gel method. Lattice structure of the fabricated samples was characterized by X-ray powder diffraction (XRD); absorption spectrum was performed on UV-2600 photo spectrometer; PL excitation and emission spectra were recorded by Fluorescence Spectrometers; quantum efficiency was measured by an integrating sphere photoluminescence (PL) system. The results showed that the optimized doping concentration of Eu³⁺ was around 10 mol% for the highest quantum efficiency at 616 nm emission peak and 465 nm excitation peak. The highest internal quantum efficiency was 91% at low power density excitation (around 50 μW/mm²). Introduction of Mn²⁺ to Eu³⁺-doped ZnMoO₄ lead to reduced quantum efficiency and electronic lifetime, which can be attributed to defects inside the crystal lattice and energy transfer from Eu³⁺ to Mn²⁺ (more non-radiative transition occur).

Abstract: This work focused on the printing of semiconductor TiO₂ thin films for solar cell applications by 3D printing system. We demonstrate a Liquid Deposition Modeling (LDM) type for controlling the pattern of TiO₂ electrode. The advantage of this type of printer is able to vary the numbers of printed layer as well as different levelling pattern of TiO₂ thin films by one time operation. Our aim was to study the effects of operating parameters of the 3D printer, such as nozzle size, speed and pressure on the thickness and uniformity of the printed TiO₂ films. Using a commercial TiO₂ paste, TiO₂ precursor films were deposited on a conductive F-doped SnO₂ glass by adjusting nozzle size, speed and pressure. The precursor films with different printed layers and levelling pattern were sintered using oven to produce porous TiO₂ electrodes. The thickness and surface roughness of obtained TiO₂ electrodes were characterized using Scanning Electron Microscope (SEM) and 3D Measuring Laser Microscope. The printed TiO₂ substrates were applied to dye-sensitized solar cells as electrodes. Our LDM type 3D printing will provide a new way of levelling design of device components for versatile optoelectronic applications.

Abstract: Acetylcholine (ACh) is a main neurotransmitter functioning in smooth muscle and cardiovascular system control. It also plays a key role in memory and learning. While excessive acetylcholine level results in decreased heart rates, depleted level of acetylcholine in human brains can lead to Alzheimer disease. Therefore, detection of acetylcholine is clinically vital. This study aimed at examining potential usage of titanium dioxide (TiO₂) doped with 2.5 mol% Zn as electrochemical sensors for acetylcholine detection. Zn-doped TiO₂ powder was synthesized by a solution combustion technique. Phase identification, microstructural examination, as well as electrocatalytic activity evaluation of the synthesized powder were conducted. The synthesized powder showed anatase phase with fine particle sizes ranging from 9.3 to 11.4 nanometers on average. Specific surface area of 75.48 m²/g was observed. Electrocatalytic activities of the powder in cholin acetate solutions with concentrations ranging from 0.05 to 0.1 μM and 1 to 10 μM were evaluated via cyclic voltammetry technique. At applied voltage of 0.05 V, peak currents corresponding to oxidation reactions between ACh and Zn-doped TiO₂ were detected. Sensitivity values of 3.13x10^-4 and 1.32 μA/(μMmm²), which is in an acceptable range, were evident.

Abstract: Hexagonal boron nitride (hBN) films were epitaxially grown on (100)-Oriented silicon and c-plane sapphire (α-Al2O3) substrates via a low-pressure chemical vapor deposition (LPCVD) method with boron trichloride (BCl3) and ammonia (NH3) as the boron source and nitrogen source. Crystalline quality differences between hBN films grown on different substrates are studied and discussed by XPS, Raman spectroscopy, XRD and SEM characterizations. All the characterization results indicate that the sapphire substrate is more suitable for epitaxial growth of hBN films than silicon substrates.

Abstract: Benefit from the gradient distribution of microstructure, gradient nanograined (GNG) metals have broad application prospect owing to their advantages of both high strength and good tensile ductility. Meanwhile, the fracture behavior of gradient nanograined metals is different from that of traditional homogeneous materials. Using molecular dynamics (MD) method, we simulated the propagation of a crack in a pre-cracked GNG Cu. Voronoi method was adopted to generate the polycrystalline topology with gradient grain size, and FCC copper atoms were filled into the topological structure. The crack was introduced by removing three layers of atoms. Then, the MD specimen was loaded to simulate the crack growth and/or blunting. The micro-defects were identified by the common neighbor analysis parameter. The effects of the grain size gradient and the crack tip initial position on the crack growth were also investigated.

Abstract: Magentic separation generally required strong magnetic forces induced in ferromagnetic or strong paramagnetic particles; in order to realize the separation in diamagnetic or weak paramagnetic particles, it was necessary to attach magnetic beads or magnetic ions to induce the strong magnetic force. A method to separate mixture of weak magnetic particles by its concentration of paramagnetic ferrous ion is newly proposed, which does not require the abovementioned magnetic attachments. The efficiently of the new method is experimentally examined using a pocketsize magnetic circuit (4.5 cm x2.0 cm x 1.0 cm) and a piece of cross sectional paper (5.0 cm x1.0cm). The separation is based on a principle that velocity of a translating particle, induced by a magnetic volume force in an area of monotonically decreasing field, is uniquely determined only by its magnetic susceptibility (per unit mass) of the particle; the velocity is independent to mass of particle. By examining the spectra of the separated particles recovered on the cross sectional paper, a histogram on Fe concentration is easily obtained for the particles without the need of consuming them.

Abstract: Zirconia has a number of remarkable properties, including a very low thermal conductivity. In this research, the phonon thermal conductivity of two phases (cubic and monoclinic) of zirconia (ZrO₂) are calculated. For this purpose, an equilibrium molecular dynamics simulation employing the Green-Kubo formalism is used. The results are presented in detail over a wide temperature range, from 100 K to 2400 K and 100 K to 1400 K for the above-mentioned structures, respectively, with a 100K temperature step. The temperature dependence of the equilibrium atomic volume demonstrated a reasonable agreement with the experimental data. Moreover, the lattice thermal conductivity was calculated by analysing the heat current autocorrelation function. The results showed that zirconia has a low thermal conductivity that is dependent on the temperature. It was also shown that the lattice thermal conductivity of the two phases of zirconia can be decomposed into three contributions due to the acoustic shortrange and long-range phonon and optical phonon modes. Finally, the results from this research are compared with the available experimental data.

Abstract: Titania pillared clay membranes exhibit unique charge characteristics which are dependent on the solution pH. Doping of such membranes with precious metal like Pt induces a positive charge on the surface of the membranes, thus increasing its resistance against fouling. X-ray Diffraction (XRD) and Fourier Transform Infra-Red Spectroscopy (FT-IR) confirm the complete intercalation of anatase titania in the interlayer spaces of Montmorillonite in the present work. These membranes efficiently removed 83% of the dye from the real textile effluent in a one filtration cycle.

Abstract: Due to the large number of stainless steels with different chemical composition and different microstructure the selection of the suitable material represents a huge challenge. In order to facilitate the appropriate grade selection, in the current European standard EN 1993-1-4 a procedure is defined based on the use of a look-up table considering the key variables that influence the selection of stainless steels. The table uses descriptions that competent designers should be able to readily understand or define without prior knowledge. The output from the look-up table is used to select alloys based on a Corrosion Resistance Class (CRC) from I to V. The advantage of this approach is that the designer simply specifies the relevant CRC and does not need to consider in detail which of the many (very similar) alloys to specify.