Key Engineering Materials Vol. 908

Abstract: Graphene quantum dots (GQDs) is used to enhance light absorption in the visible region of DSSC by sensitising method. The used of GQDs in photoelectode may effect the N-719 dye loading on photoelectrode and the study is done by ultraviolet spectroscopy (Uv-Vis). Initially, the TiO₂ photoelectrode films is sensitised in ∼5 nm GQDs to overcome TiO₂ photoelectrode drawback such as random electron transport and short-circuit current. Then, photoelectrode films is sensitised in N-719 dye to excite the electrons in TiO₂ film. PG 7.5 adsorbed only 0.103 x 10^-7 mol cm^-2 N719 dye while PT at 0.527 x 10^-7 mol cm^-2. The pristine TiO₂ photoelectrode (PT) adsorbed more than 80.4% of N-719 dye compared to PG 7.5 photoelectrode and other TiO₂-GQDs photoeletrodes (PG 2.5, PG 5.0 and PG 10). As a result, the used of GQDs for TiO₂ photoelectrode is reduced the intake of expensive N-719 dye for DSSCs. This happened because some of the functional groups in the GQDs solution such as hydroxyl and carboxyl groups are biocompatible with TiO₂ which allows more adsorption sites of GQDs onto TiO₂ surface. Thus, after GQDs molecules were occupied on the TiO₂ surface, not many sites were available for N719 dye molecule. Therefore, it might reduce the N719-dye intake in the DSSC device, which can reduce the fabrication cost of DSSC and give good impact on environment.

Abstract: In this study, a CQDs at different concentration is used to modify the TiO₂ photoelectrode band gap which can improve light absorption of DSSC. The photoelectrode is immersed in different CQDs concentration at 2.5, 5.0, 7.5 and 10 mg/ml to study the effect on TiO₂. It was found that photoelectrode with 7.5 mg/ml CQDs was successfully narrowing the TiO₂ band gap and generated the highest photocurrent and power conversion efficiency at 17.06 mA/cm² and 7.23% respectively, compared to pristine TiO₂ (PT) at 10.94 mA/cm² and 4.63% . The band gap narrowing mechanism for CQDs- TiO₂ is obtained from the Tauc’s plot method using absorption spectra. The result shows a pristine TiO₂ photoelectrode (PT) band gap is 3.38 eV, upon existing of CQDs, the band gap of all photoelectrodes with CQDs at 2.5, 5.0, 7.5 and 10 were reduced to 3.30 eV, 3.28 eV, 3.09 eV, and 3.29 eV respectively. PG 7.5 cell with lowest band gap at 3.09 eV generates effective electron transport from N719 dye to CQDs/ TiO₂ layer compared to other photoelectrodes. The band gap narrowing effect is attributed from chemical bonds of Ti-O-C molecules between CQDs/TiO_2. Thus, extra energy states are introduced between CQDs and TiO_2. The location of these energy will present a quantum confinement effect which narrow the CQDs-TiO₂ band gap which extend the light absorption to visible region.

Abstract: In this paper, a review on the structural and morphological of nanostructured zinc oxide (ZnO) fabricated on flexible conductive substrate, mainly indium tin oxide coated on polyethylene terephthalate (ITO/PET) via various fabrication method is reported. Besides fabrication method, the effect of fabrication condition such as immersion time of ZnO-ITO/PET via hydrothermal method, concentration of modification material of precursor solution via sol-gel method, value of applied cathodic voltage and value of current densities via electrochemical deposition are also discussed. XRD analysis showed that the growth of ZnO-ITO/PET are preferred on (002) or (101) planes. SEM analysis revealed various type of nanostructured ZnO when prepared by sol-gel, spin coating, HWT and hydrothermal method, highlighting ZnO nanorods as the main morphology of ZnO-ITO/PET. The diameter of ZnO nanorods ranges from 10 nm to 830 nm.

Abstract: The different composition material of copper substrate significantly affects the intermetallic compound (IMC) formation and the solder joints durability. This study was conducted on the interfacial reaction between lead-free solder and the different copper substrates via reflow soldering. The selected substrate is copper (Cu) and copper-beryllium (Cu-Be). The lead-free solder involved is Sn-3.8Ag-0.7Cu (SAC3807) solder ball with a diameter of 700 μm. All the samples were subjected to the isothermal aging process. The material characterization and analysis on the IMC formation were examined by scanning electron microscopy (SEM), optical microscope (OM), and energy dispersive X-ray analysis (EDX). After the reflow process, the result revealed that Cu₃Sn, Cu₆Sn₅ IMC layer formed at SAC3870/Cu and SAC3870/Cu-Be interface. The changes to a rod-like shape Cu₆Sn₅ and irregular needle-shaped Cu₃Sn₄ occur after the aging treatment on SAC3870/ Cu. Meanwhile, the IMC layer for SAC3870/Cu-Be shows a rod-like shape transformed into a blocky-like shape Cu₆Sn₅ and Cu₃Sn₄ diamond-shape. This result indicates that Ag₃Sn nanosized was formed on the intermetallic surface during the aging process for both SAC3807/Cu and SAC3807/Cu-Be. The Ag₃Sn nanosized element at SAC3807/Cu-Be is many compared to SAC3807/Cu. In addition, IMC thickness for SAC3807/Cu-Be shows a thicker layer than SAC3807/Cu. Lastly, in this research, the element of Be in SAC3807/Cu-Be cannot be defined because the beryllium element is not easily detected as the percentage was very low.

Abstract: Single-layer graphene-ZnO hollow sphere (SLG-ZnO(HS)) composites were successfully prepared through facile one-step solvothermal synthesis route. The morphological structures of the samples were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Hollow spheres consisting of ZnO nanoparticles with a diameter of approximately 30 nm are decorated to both sides of the SLG sheets. The electrochemical performances were tested by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance (EIS). The SLG-ZnO(HS) composite electrode synthesized at a concentration of 0.25 mM Zn precursor exhibited an enhanced specific capacitance of 34.7 F/g at a scan rate of 1 mV/s with energy and power densities of 5.39 W h/kg and 1.73 kW/kg, respectively.

Abstract: The first principles study on the LiFePO₄ and FePO₄ crystal has been evaluated using the density functional theory encrypted in the Cambridge Serial Total Energy Package (CASTEP) computer code. The structural properties, electronic properties, and intercalation voltage of the cathode material are presented. Without the Hubbard U parameter, the conventional functional of GGA-PBE and GGA-PBEsol unable to produce the experimental open-circuit voltage (OCV) and band gap (BG) of cathode material correctly. Generally, the value of the lattice parameter, OCV, and BG will increase as the U value is increased. For OCV, the suitable U value for the GGA-PBE and GGA-PBEsol is 3 eV, whereas, for BG, the appropriate U value for both functional is around 4.3 eV to 4.5 eV. Different Hubbard U value is needed for different functional. It is found that GGA-PBEsol + U is the best parameter to calculate the electrical properties of LiFePO_{4 ­­­­}material.

Abstract: In this study, ZnO nanorods are synthesized by the means of chemical bath deposition (CBD). Further objectives, to study the effect of new parameters (oxygen and air flow) on ZnO nanorods on morphology and length of alignment of the nanorods. It was observed that 0.100M for both zinc nitrate hexahydrate and hexamethylenetetramine give a best result. Here, we added an oxygen gas pressure as others idea in chemical bath deposition method and a p-type silicon substrate to investigate the length of ZnO nanorods through their cross-section. It was found that the biggest grain sizes obtain from sample 14, which is 58.87nm produces a high crystal quality, among others. Sample 14 also has a long nanorods (1.434μm-1.451μm) compared to other samples. The hexagonal structure was observed by Field Emission Scanning Electron Microscope, FESEM and well aligned, compact and perpendicular ZnO nanorods grew on the surface of glass substrate. XRD data shows that it has a larger grain size with low lattice strain. The cross-sectional view of the samples demonstrates long nanorods with a range 2.763μm-2.844μm. Finally, the growth of ultra-long ZnO nanorods by using a modified chemical bath setup was successfully observed and recorded.Keywords: ZnO nanorods, CBD, Growth duration, FESEM images, pressure flow.

Abstract: The sensitive Electrostatic Discharge (ESD) has been found to be the major causes in semiconductor manufacturing that contributed in the event when the samples did not function properly and failed during testing. Various techniques had been studied and implemented as the ESD countermeasures. Based on the EDS event model, control measures on people, grounding and ionizations have been practiced as the main preventive measures against ESD. However, many aspects of the measures need to be customized to the specific fabrication areas. This paper conducted several experiments in the use of ionizers to tackle the ESD issue in a 12nm Gate Oxide semiconductor fabrication facility. Based on several hypotheses on the areas and operations that are prone to ESD during the back-end processes, experiments were conducted to evaluate them. The results affirm the need to individually and specifically check the effectiveness of the usage of ionizers to combat ESD as some ionizer were found to be not effective at the location or area where they are installed.

Abstract: Stability of nanolubricants is a basic requirement for heat transfer application since it is directly related to the properties of nanolubricants. However, the particle suspension is the major issue of creating a new nanolubricant. The objective of the present study is to compare the effect of different dispersion methods on the stability of graphene in polyester oil-based lubricant. Nanolubricant are prepared by different two-step method, including magnetic stirrer, overhead stirrer, and sonication. The stability of nanolubricant was measured by sedimentation observation, metallographic microscopy, and zeta potential. The results show that the overhead stirrer method was the most effective at providing a more stable suspension.

Abstract: Since the discovery of magnetocaloric effect (MCE), numbers of method in producing magnetocaloric materials has been studied. Among those methods, ball milling has been shown as a very versatile technique with several advantages compared to other preparation methods. In this work, the effect of ball milling preparation technique on the phase structural behaviour and electrical properties of MnCoGe alloys has been analysed. The changes in the structural behaviour have been studied by X-ray powder diffraction (XRD) and Raman Spectroscopy. The results suggest that the samples show significant structural changes with different method of ball milling running time. This finding has also been supported by electrical properties where the measurement found that the frequency also plays important role in the structure changes. The absolute impedance value,|Z| (Ω) suggest that structure start to change at initial frequency structure of hexagonal at point 3.22 Ω and 44.1 MHz region. The permittivity and dielectric loss (tan delta) graph that corresponds to a frequency (Hz) up to 100 kHz shown that the 2-hours milling time MnCoGe compound has the lowest permittivity value which make it had lower energy and required more frequency to react.