B. K. Yap

Enhancement of the work function of indium tin oxide by surface modification using caesium fluoride

The work function of indium tin oxide (ITO) was modified using caesium fluoride (CsF). Various concentrations of CsF was spin-coated on top of ITO and baked while the residual CsF was washed away with DI water. The work function of all the ITO samples was measured using ultraviolet photoelectron spectroscopy and it was found that the work function of ITO reaches as high as 5.75 eV. The work function rapidly increases with small concentrations of CsF solution and then decreases for higher concentrations. Using atomic force microscopy and x-ray photoelectron spectroscopy, the cause was determined to be the change in surface roughness and the oxygen concentration, with the former having a much greater influence on the work function than the latter. The current density of ITO/poly(vinylcarbazole)/Al hole-only devices using the modified ITO increases by more than seven orders of magnitude compared with the control device.

Effect of mixed hole transporting host on the mobility, Gaussian density of states and efficiencies of a heterojunction phosphorescent organic light emitting diode

We present an in-depth study of the hole transport in poly(vinylcarbazole) PVK films blended with small molecule tris(4-carbazoyl-9-ylphenyl)amine (TcTa). Doping TcTa in PVK introduces shallow hole traps when the doping concentration is lower than 20 wt%. It becomes percolative at higher concentrations. The energetic disorder σ of the blended system reduces from ~72 meV at 0 wt% TcTa to ~41 meV at 50 wt% TcTa. A correlation between σ and the film morphologies suggests that the blending of TcTa molecules in the film does not only change the film homogeneity and roughness but also the energetic disorder. In addition to the mobility study, we fabricated a red phosphorescent organic light emitting diode with the same blending system. By doping merely 5 wt% of TcTa into PVK as mixed hole-transporting hosts, the efficiency of the deep red heterojunction phosphorescent organic light emitting diode increased from 2 cd A−1 to 4 cd A−1, suggesting that TcTa molecules assist in hole injection.

Highly efficient processable molybdenum trioxide as a hole blocking interlayer for super-yellow organic light emitting diode

By inserting lithium fluoride (LiF) between solution-processed MoO3 with optimal thickness on top of super yellow poly-(p-phenylenevinylene) (SY-PPV), the efficiency of the SY-PPV fluorescent-based devices can be significantly improved by more than two-fold. Despite the increased driving voltage, the device showed a current and a luminance efficiency up to 22.8 cd A−1 and 14.3 lm W−1 respectively, which is a more than a two-fold increase in efficiency compared to the control device using LiF/Al at a brightness of 1000 cdm−2. Ultraviolet photoelectron spectroscopy (UPS) is used to analyze the energy alignment between SY-PPV and the solution processed MoO3 and MoO3/LiF/Al interfaces. We found that the solution processed MoO3 using diluted sodium hydroxide has relatively low ionization energy (IA), electron affinity (EA) and work function decreasing with increasing thickness of MoO3. However, the optical bandgap increases with increasing spin-speed. A large energetic barrier is always present between the SY-PPY and deep lying valence band of MoO3. This is supported by suppression of hole current in hole dominating devices. The ability of thin MoO3 (~2 nm) acting as a hole blocking layer while allowing electrons to be transported across the layer and a large upward vacuum shift appeared to be the origin of efficiency enhancement of SY-PPV light-emitting diode when MoO3/LiF/Al is used.

Characterization study for polymer core solder balls under AC and TC reliability test

Since Restriction of Hazardous Substance (RoHS) Regulation came into effect in year 2006 due to the hazardous effects of lead to humans health and toxicity for environment, Ball Grid Array (BGA) semiconductor chip are widely used for many electronic applications including portable, automotive and telecommunication products that require stringent thermal and mechanical requirements. However, dropped balls in lead-free BGA products due to poor solder joint strength caused by reliability stress are a major concern in the semiconductor industries. A new technology with polymer core inside the solder ball (polymer core/Cu/Sn) is integrated to improve the solder joint strength. The polymer core inside the solder ball is function to dissipate the stress better as compared to the lead-free solder ball. The diffusion rate of Cu is faster than the diffusion rate of Sn, thus Kirkendall voids are tends to form in between the interface at the Cu and Sn layer, especially after subjected to the high temperature reliability stress. This would affect the solder joint strength and causing drop ball issue. To overcome this, an additional of 1 μm Ni layer is coated on the Cu (polymer core/Cu/Sn/Ni) to reduce the diffusion from Cu to Sn, to avoid Kirkendall voids formation. This research work studies the performance of the solder ball shear strength and IMC thickness of two types of polymer core solder balls applied to BGA device. In this research, polymer core solder balls were went through under AC (Autoclave) and TC (Temperature Cycle) reliability test up to 144 hours and 1000 cycles, respectively. Solder ball shear strength test was conducted via Dage 4000 series bond tester and IMC thickness measurement via cold mount cross-section. From the results of the two types of polymer core solder ball, observed that, the ball shear strength were decreased with increased of aging time, while IMC thicknesses were increased with increase of aging time. This is probably due to the rapid Cu diffusion into the Cu core interface resulting in lower shear strength and thicker IMC. From this research work, it can be concluded that the polymer core solder ball with an additional Ni layer showed better performance than the polymer core solder ball without Ni layer, after subjected to the AC and TC reliability test. This is due to the Ni layer could limit the Cu diffusion into the solder thus resulting in good solder joint strength and drop reliability performance as well as reduced crack issues caused from Kirkendall voids.

Novel assay for efficient iron release from ferritin

Ferritin plays an important role in iron detoxification and iron storage by converting soluble iron(II) to insoluble iron(III) inside the protein cage. Mechanism of in vitro ferritin iron release occurs more readily under reducing conditions, whereby reducing agents may enter into the ferritin cage through the protein pores to convert insoluble iron(III) into soluble iron(II), after accepting an electron from reducing agents. The soluble iron(II) then liberates outside the protein cage and forms coloured and stable complexes in the presence of chromophore, an iron(II) chelating agent, to be quantified by spectrophotometry. However, iron(II) is readily converted back to iron(III) in the presence of oxygen. Thus, oxygen scavenger compounds were used to remove any dissolved oxygen. Studies suggested that low concentration of chaotropic agents regulate the protein pore opening and result in protein unfolding that is therefore accessible by reducing agents more effectively. According to in vivo studies, iron exit from ferritin for recycling or meeting the cells need via lysosomal and/or proteasomal pathways. We designed an assay to determine the total iron available inside the ferritin by first using the commercially available iron(II) or iron(III) compounds as a substrate to optimize the concentration of reactants involved. Apart from chromophore and reducing agents, oxygen scavenger compounds, chaotropic agents and enzymes were added in order to induce ferritin iron release effectively. Linear calibration curve of the iron(II)-chromophore complex were obtained and was used as a reference to correlate absorbance readings to concentration of iron level. Reducing agents was able to reduce the iron(III) to iron(II) and oxygen scavenger A seems to be more effective in removing any dissolved oxygen to avoid oxidation of both the reducing agents and iron(III). Taken altogether, this experiment setup will be beneficial for the improvement of efficiency in quantifying the total iron level inside the ferritin.

Stitch bond strength study in insulated Cu wire bonding

Abstract The market demands for higher pin counts and more chips functionality pose challenges in conventional wire bonding. However, insulated Cu wire technology enables fine and ultra-fine pitch wire bonding as the insulator coating on the bare wire prevents wires shorting problem. This paper presents the study on the stitch-bonding process optimisation and its challenges for the insulated Cu wire with a diameter of 20 µm. Insulated Cu stitch bond samples show 37% lower stitch pull strength than that of bare Cu. The cross-sectioned insulated Cu stitch bond shows that there is an insulation residue between the Cu stitch and the Au-plated substrate, potentially resulting in lower stitch pull performance. However, after isothermal aging at 225°C for up to 78 hours, the stitch pull results for insulated Cu wire passed the industry reliability standard, without any lifted bond. A detailed comparison study was performed for the insulated Cu and the bare Cu stitch bonding.

Influence of Magnesium Doping in Hydroxyapatite Bioceramics Sintered by Short Holding Time

In the present research, nano hydroxyapatite (HA) powder doped with magnesia (MgO) was studied. The dopant was added to pure HA powder and ball milling was done for 1 hour. Green samples, in the form of discs and rectangular bars, were prepared and consolidated in air at temperatures ranging from 1000°C to 1300°C. The sintered samples were characterized to determine the phase stability, relative density, hardness, fracture toughness and Young’s modulus. The phase analysis revealed that the HA phase was not disrupted regardless of dopant additions and sintering temperature. It has been revealed that all HA samples achieved > 98% relative density when sintered between 1100oC–1300oC. However, the addition of 0.5 wt% MgO when sintered at 1100°C was found to be most beneficial in aiding sintering with samples exhibiting the highest Young’s modulus of 122.15 GPa and fracture toughness of 1.64 MPam1/2 as compared to 116.57 GPa and 1.18 MPam1/2 for the undoped HA.

Calcination Effects on the Sinterability of Hydroxyapatite Bioceramics

The sinterability of calcined synthesized HA (700oC to 1000oC) was investigated over the temperature range of 1050oC to 1350oC in terms of phase stability, bulk density, Young’s modulus and Vickers hardness. Calcination has resulted in higher crystallinity of the starting synthesized HA powder. Decomposition of HA phase to form secondary phases was not observed in the present work for the calcined powders. The results also indicated that calcination of the HA powder prior to sintering has negligible effect on the sinterability of the HA compacts (up to 900oC). Further treatment at 1000oC was found to be detrimental to the properties of sintered HA.

Potential Point-of-Care Microfluidic Devices to Diagnose Iron Deficiency Anemia

Over the past 20 years, rapid technological advancement in the field of microfluidics has produced a wide array of microfluidic point-of-care (POC) diagnostic devices for the healthcare industry. However, potential microfluidic applications in the field of nutrition, specifically to diagnose iron deficiency anemia (IDA) detection, remain scarce. Iron deficiency anemia is the most common form of anemia, which affects billions of people globally, especially the elderly, women, and children. This review comprehensively analyzes the current diagnosis technologies that address anemia-related IDA-POC microfluidic devices in the future. This review briefly highlights various microfluidics devices that have the potential to detect IDA and discusses some commercially available devices for blood plasma separation mechanisms. Reagent deposition and integration into microfluidic devices are also explored. Finally, we discuss the challenges of insights into potential portable microfluidic systems, especially for remote IDA detection.

Iron deficiency anaemia: with the conclusion of a need for iron reader

In our bloodstream, there are plenty of red blood cells (RBC), which function as an important oxygen carrier in our bodies. Each RBC consists of millions of haemoglobin (Hb), which is made up from globin and iron. If any deficiency/malfunction of any globin, it will lead to anaemia as indicated in low Hb level while iron deficiency anaemia (IDA) is anaemic due to the lacking of iron as indicated in low Hb and ferritin levels. IDA affects almost two billion people globally while anaemia without iron deficiency, such as thalassaemia, affects almost 4.5% in Malaysian population. These anaemic conditions have similar clinical symptoms like fatigue, dizziness, in which disturb their cognitive development and productivity in workplace. In areas without proper medical access, many anaemic individuals were misdiagnosed and treated with iron tablets because they were thought to have iron deficiency anaemia due to low Hb content. But, excess iron is toxic to the body. Misdiagnosis can be avoided by iron status assessment. We hereby review the currently available iron status parameters in laboratory and field study with the conclusion of demonstrating the importance of a need for iron reader, in the effort to reduce the prevalence of IDA globally.