Solid State Phenomena Vol. 307

Abstract: Perovskite manganites have always been the research interest attributed to its intriguing colossal magnetoresistive (CMR) properties. Incorporation of an insulating secondary phase into the manganite composites has proven as an effective measure to enhance the low field magnetoresistance (LFMR). This paper reports the structural, microstructural and magnetic properties of (1-x) Pr_0.7Sr_0.3MnO₃ (PSMO): x Al₂O₃ composites synthesized by the solid-state reaction method. Different compositions of nano-sized Al₂O₃ (x = 0.00, 0.05, 0.10, 0.15 and 0.20) were appended into the samples to investigate its effect on the physical properties. X-ray diffraction patterns show all samples exhibit polycrystalline PSMO as the major phase and strong orientation along (121) direction throughout the series. The crystal structural parameter is presented by Rietveld refinement. Nano-sized of Al₂O₃ has distorted the pure PSMO as changes have been observed in bond length and bond angle observed. Surface roughness and particle size show the increment along with increasing Al₂O₃ composition from the atomic force microscope (AFM) analysis. All samples possess the narrow hysteresis loop with weak ferromagnetic nature. The PSMO: Al₂O₃ presented in this study is a promising manganite composite which can be utilized in the magnetic sensor applications.

Abstract: Colossal magnetoresistive (CMR) materials have been widely studied because of their huge potential in spintronic technology. An introduction of secondary phase to the manganite matrix is able to improve the low field magnetoresistance (LFMR). This method is favoured by recent research works as it requires a lower magnetic field compared to intrinsic magnetoresistance. Structural, magnetic properties and magnetotransport properties of polycrystalline (1-x) La_0.67Ca_0.33MnO₃ (LCMO): x TiO₂ composites where x = 0.00, 0.05, 0.10, 0.15 and 0.20 were investigated in this work. Polycrystalline La_0.67Ca_0.33MnO₃ (LCMO) was synthesized via sol-gel method and pre-sintered at 800 °C before appending with nano-sized TiO₂. All samples are in LCMO phase having an orthorhombic structure with space group Pnma. The crystal structural parameter is studied by using Rietveld refinement. As TiO₂ content increases, the magnetization is getting higher as observed via vibrating sample magnetometer (VSM) analysis at room temperature. Magnetotransport properties of the pure LCMO sample have been studied from 80 – 220 K. The LFMR is enhanced as the temperature drops. The results have shown LCMO: TiO₂ manganite composite is an excellent candidate for future magnetic sensors and memory devices.

Abstract: Coloured solders offer wide range of possible application on top of conventional usage related to solder and soldering. Coloured solder can be produced by adding colour pigment into solder formulation to form coloured solder composite. The performance of coloured solder joint typically determined by good solderability, which influenced by wetting properties. The objectives of this paper is to investigate the solderability of coloured lead free solder composite with different formulation type of colour pigment and variation of colour pigment composition. Green and “glow in the dark pigment” with composition of 5% and 10% respectively were added into the lead free solder paste. Each coloured solder paste was stencil printed on the PCB and then reflowed using reflow soldering process. The wettability of the solder composite was measured and observed using Infinite Focus Measurements (IFM). The results demonstrated that coloured lead free solder composite have a good wettability. This finding also indicates that use of green pigment into the solder composite has shown greater wettability as compared to glow in the dark pigment. Higher percentage of added colour pigment of 10% has significantly reduced the wettability of solder composite. Wettability of coloured solder composite with small amount of added pigment is in the acceptable range of contact angle, showing good solderability of joining.

Abstract: A single layer of BiFeO₃ (BFO)/epoxy resin composite with thickness of 3 mm was fabricated by polymerized 70 wt% of sintered BFO as fillers and 30 wt% of epoxy resin polymer as matrix. The electromagnetic and the microwave absorption properties of BFO/epoxy resin composite were reported. The reflection loss (RL) of the same composite sample was measured by two different techniques of measurement, S_11a parameter (without metal backed reflector) and S_11b parameter (with metal backed reflector) in the range of 8-18 GHz using a network analyzer. Minimum RL (RL_min) from S_11b parameter for BFO/epoxy resin composite with metal backed is lower than the RL_min from S_11a composite without metal backed reflector. In details, the results showed BFO/epoxy resin composite with metal backed can achieve a strong absorption with RL_min of -40.5 dB over a 1.31 GHz bandwidth.

Abstract: Evaluating the growth kinetics is one of the most important characteristic in assessing the quality and reliability of metallurgical joining, especially in electronics packaging such as soldering and wire bonding technology. The growth kinetics is normally assessed using Arrhenius equation that involves diffusion activities due to thermally activated process. The well-known factors of thermal and time together with generally accepted growth exponent have been widely used for this assessment. The intermetallic compound layer which is the by-product of metallurgical reaction during soldering process has been exposed to high temperature to accelerate its growth. The cross-section of the joining was observed using optical microscope to quantify the layer of intermetallic compound. Morphological effect and shape factor of the layer have been analysed in complement with the effect of temperature and time on the growth behaviour. Directional growth and irregularities shape of the intermetallic layer show some inconsistency on the selection of growth exponent. The effect of initial size of intermetallic layer must also be considered in this assessment. This study suggests that the morphological effect must be analysed prior to the selection the growth exponent in assessing growth behaviour and kinetics of intermetallic layer in metallurgical joining.

Abstract: Tin-Silver-Copper (SnAgCu) lead-free solder on Electroless Nickel Immersion Gold (ENiG) and Immersion Tin (ImSn) surface finish printed circuit board was subjected to blast test. A variation of intermetallic compounds (IMC) layer, hardness and reduced modulus of soldered sample exposed to blast test were intensively investigated using optical microscope and nanoindentation machine. Formation of IMCs due to reaction between solder and substrate during blast test provided deleterious effect of metallurgical bond strength and reliability on the solder joint. Microstructural analysis was evaluated via Infinite Focused Microscope (IFM). The findings of these studies indicate that best surface finished for blast test performance was not necessarily the best surface finish for optimum reliability. ENiG and ImSn surface finish can be advantage or a disadvantage depending on the application, package and reliability requirements. As a result, most component assemblers are using ENiG and ImSn in order to improve solderability as well as the wettability between solder and the substrate and to meet various package requirements.

Abstract: Multilayers zinc oxide thin films were synthesized by the sol–gel spin coating process to fabricate sensing membranes in an electrolyte-insulator-semiconductor (EIS) sensor for pH detection. The effect of various layers (single, three and five layers) on the crystallinity, morphological and optical properties of ZnO films were investigated by XRD, FE-SEM, and Photoluminescence respectively. The ZnO thin films grown were polycrystalline with hexagonal wurtzite structure. The films were not smooth, with grains and porosity in between them, and become denser as film thickness increased. The PL spectra exhibit two main emission peaks at near band edge 360-380 nm region (strong and sharp UV radiation) and 450–600 nm region (broad blue, green, and yellow radiation). Sensitivity, linearity was measured to determine the sensing and reliability performance of fabricated devices. The result confirmed that, the sensitivity for the three samples increased with increased layer from 48.3 mV/pH to 82.58 mV/pH. Compared to single and three layers of the ZnO electrolyte-insulator-semiconductor (EIS), ZnO grown with five layers exhibits a higher sensitivity of 82.58 mV/pH in solutions from pH 2–12 and linearity of 99.015 %. This is due to the increased of ZnO thickness, which produces dense surface and a well-crystallized grain structure.

Abstract: We explore the structural and electronic properties of a single layer arsenene using the state of art, first principle approach from density functional theory (DFT). All the calculation was conducted using an open source DFT code, adopted the planewaves (PWs) method by Quantum Espresso (QE). The calculation utilized an exchange correlation potential of electron parametrized by Perdew-Burke-Ernzerhof (PBE) under generalized gradient approximation (GGA) functional scheme. Meanwhile, the pseudopotential assigned for the core electron is the projector typed augmented-wave with the core potential correction, generated using "atomic" code. All those parameters resulted an optimized structure of the honeycomb arsenene with lattice constant of 4.4971 Ǻ. The arsenene layer occupy a bond length value of 2.5964 Ǻ as measured between its neighbouring bonded atoms. From an optimized structure, we explore its electronic bandstructure plotted from 3 highly symmetries point for 2-dimensional (2D) material known as ‘’, ‘’ and ‘’ with 3 electron pathways. The total number of bands considered in bandstruture plotting is 10, where 5 bands will consider as valance bands while another 5 is conduction bands. The bandstructure shows that a single layer flat arsenene exhibits the characteristics of a conductor due to the overlapping of band near to Fermi level. Dirac cone were also noticed near to the Fermi energy level of the bandstructure. Lastly, we study the total electron density for the whole structure to reveal its bonding characteristics. The contour plot of electron densities between two bounded atoms displayed a pure covalent bond characteristic. The findings of this work is expected to contribute to the key of the electronic devices development, optoelectronics, and sensor devices based on 2D material technology.Keywords: flat layer arsenene, density of state, electron density, electronic band structure

Abstract: ZnO thin films have been prepared by the dip coating sol gel method. Zinc acetate dihydrate, 2-methoxyethanol and monoethanolamine (MEA) were used as precursor, solvent and stabilizer respectively. The synthesized sample was coated on glass substrate as the molarity of the solution was kept constant at 0.1 M. The structural properties and surface morphologies of ZnO thin film were characterized by XRD and FESEM. The optical properties such as transmittance, absorbance, reflectance and refractive index were studied by using UV-Vis. The functional group of the synthesized sample were verified by using FTIR. Average crystallite sizes of the samples were calculated by using Debye-Scherrer's formula. Next, ZnO is coated on POF in order to examine the reaction towards UV light.