Materials Science Forum Vol. 1055

Abstract: Integration of low bandgap antimonide based nanowires on Si substrate has been attracting huge attention for opto-electronic applications. In this work we demonstrated InAs/InSb and InAs/GaSb heterostructure nanowires on Si substrate by metal organic chemical vapor deposition. We grew high quality axial InSb heterostructure segment on InAs stem by self-catalyzed growth technique, which paves a way to tune the crystal structure of InSb. In case of InAs-GaSb core-shell architecture, GaSb crystal quality highly depends on InAs core. We successfully demonstrated basic electrical characteristics of InAs-GaSb core-shell nanowire which exhibits negative differential resistance at 0.8 V and peak-to-valley current ratio of 3.84.

Abstract: In this study, the results indicate that a method combining fully-recessed wet etching and regrown channel by MOCVD is capable of obtaining high quality interface in GaN MIS-HEMT. A low V_th hysterisis GaN MIS-HEMT of 0.3V is demonstrated in this work. The GaN MIS-HEMT has a V_th of-1.5 V, a high I_d,max of 771mA/mm and a R_ON of 13.5 Ω·mm. The wet etching shows good uniformity while the MOCVD grown AlN enhances the maximum drain current. The concept provides new insights to gate recess fabrication and MOCVD grown high quality dielectrics.

Abstract: Global energy consumption is increasingly becoming high due to industrial activity and advances both in developed and developing countries. Fossil fuels such as coal, natural gas, and oil are used to meet the energy demands all over the world. However, there is a concern about depletion of these resources and rise in greenhouse gas such as carbon dioxide emissions. Therefore, some alternative ways are needed to satisfy the energy demand and decrease the greenhouse emissions. Renewable energy, such as solar energy, wind energy, hydropower, and so on, is a promising source to satisfy the future energy requirements. As to solar cells, there is no need to concern about energy source because it uses solar rays, and it never emits CO₂ when generating electricity.

Abstract: In this study, the Multi-Walled Carbon Nanotube (MWCNT) and polydimethylsiloxane (PDMS) were prepared by using simple solution mixing method. However, the MWCNT have an issue to achieve stable polymer composite because the nanotubes can easily agglomerate and causes bundling when dispersed in polymer. Thus, the MWCNT was dispersed in toluene using mechanical stirring and sonication process. As a result, sonication process shows excellent dispersion of MWCNT with toluene compared to mechanical stirring method. To prepare conductive polymer composite, MWCNT with 2, 4, 6, 8, and 10 wt% concentrations were used. The dispersion processes of MWCNT in PDMS were characterized using Raman Spectroscopy. The intensity of D-band and G-band, I_D/I_G band decreases from 1.20 to 1.10 as the MWCNT content (6 wt% to 10 wt%) increases. This indicates less MWCNT defect occurred during dispersion process. Besides, the electrical conductivity of MWCNT/PDMS composite was investigated by using two point probe method. The conductivity of fabricated MWCNT/PDMS composite is in the range of 10⁹ to 10⁶ S/cm and a low percolation threshold is achieved at 4 wt% of MWCNT concentration in PDMS. Extension of this study is needed to improve the electrical conductivity of MWCNT/PDMS composite.

Abstract: This paper aims to review the methodologies used to conduct microstructure evaluation of the photovoltaic (PV) interconnection. This analysis is important to identify the microstructural properties of the interconnection for failure analysis purposes. The interconnection becomes a major concern towards the efficiency and reliability of PV technology. In this paper, the common techniques used for the interconnection technology such as soldering, conductive adhesive and ultrasonic were presented with the assessment method to identify the failure mode and failure mechanism at the bonding interface. The identification of the failure mode and failure mechanism through visual analysis and conformation of failure phenomenon was important to highlight the risks and develop the countermeasures. The evaluation of microstructure characterization techniques in the electronics and PV industry has been presented by identifying the outcomes of each technique with different reliability tests. The discoveries of failure analysis in the electronics industry were more matured and becomes the reference to the PV development. The outcomes from this review could be beneficial to improve the interconnection bond in the PV industry by eliminating or minimizing the failure through design modification at the earliest point in the development process.

Abstract: Most wearable electronics widely incorporate metal electrodes for parameter detection but these electrodes possess drawbacks due to corrosion and performance degradation. Therefore, in this work, pH sweat sensor is fabricated by using highly conductive, stable and non-toxic PEDOT:PSS/GO nanocomposite on flexible cotton fibre substrate. This work is aimed to determine the effects of fabrication techniques and durability performance on pH sensitivity of fibre-based PEDOT:PSS/GO sensor via resistance measurements. In this work, a wearable fibre-based sensor is developed by using Poly (3,4 ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT:PSS), and Graphene Oxide (GO) nanocomposite. Sample characterisations are completed by analysing absorbance spectrums, FESEM images and XRD spectra. One layer PEDOT:PSS/GO of 4:2 ratio is fabricated on cotton fabric by using dip coating and screen-printing techniques. Lower resistance of 105 Ω and higher conductivity are achieved by using dip coating technique compared to screen printing, as better absorption of nanocomposite into fiber strands via this method, leads to excellent charge distribution on coated fabric. Resistance increases proportionally with pH values. Resistance of 1.547 kΩ, 3.791 kΩ and 9.18 kΩ are measured for pH 4.00, 6.86 and 9.18 respectively. Nanocomposite layer fabricated with dip coating is also stable, durable and remained intact on the coated fabric after soaking test in distilled (DI) water for 45 minutes. On the other hand, resistance values are 3.11 Ω, 4.81 Ω and 6.54 Ω when the sensor bends at 30°, 60° and 90° respectively. This is due to additional introduced strain and redistribution of charges on the fabric after repeated movements. Based on excellent chemiresistive response towards sweat pH detection, several health conditions such as hyperhidrosis, normal state and cystic fibrosis associated with sweat pH of 4.00, 6.86 and 9.18 respectively, could be possibly identified. These promising results open up possibilities for future studies in the development of nanocomposite-based health monitoring wearable devices.

Abstract: Out of the perovskite material used in Perovskite Solar Cells, methylammonium lead triiodide (MAPbI₃) is the most studied, proving to yield a device with high power conversion efficiency. However, this perovskite material has a high tendency to degrade, especially when exposed to high humidity and ambient atmosphere. The degradation issue has led to its poor morphology, which eventually affects the device's power conversion efficiency based on this perovskite material. Therefore, this study aims to enhance the morphological property of the perovskite thin film by incorporating sulfonated reduced graphene oxide (srGO) as a dopant. The reduced graphene oxide is synthesized through modified Hummer's method and further sulfonated before being incorporated into the perovskite thin film deposited under relative humidity above 80% in ambient conditions. The srGO has successfully assisted the nucleation growth of MAPbI₃ with the increment of grain size is approaching micron-sized. In this work, the optimized weight percentage of srGO in methylammonium iodide (MAI) precursor is found to be 20% resulting in grain size in the diameter range of 300 to 1000 nm. Hence, this perovskite doped srGO would be incorporated as the active layer for further application, especially in inverted planar perovskite solar cells.

Abstract: Nitrogen-doped TiO₂ (N-TiO₂)/polytetrafluoroethylene (PTFE) has been prepared by optimization of nitrogen and polytetrafluoroethylene. N-TiO₂ has been modified by optimizing doping concentration in two-step process synthesis via solvothermal treatment, by mixing TiO₂ and variation ammonium carbonate as a nitrogen source at 0.5 M, 1.0 M, 1.5 M. Synthesized materials denoted as N-TiO₂, were characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared ( FTIR), Scanning Electron microscopy (SEM), and spectrophotometer UV Vis. Based on the XRD pattern, a shift diffraction pattern was assigned to [101] that indicated the nitrogen successfully doped. The functional group identified by FTIR shown an O-Ti-N bond seems to influence the energy gap of TiO₂. The presence of nitrogen as an impurity in semiconductor TiO₂ was decreased the amount of bandgap energy from 3.10 eV to 2.95 eV. Synthesized N-TiO₂ is a nanosphere morphology. Glass substrate containing N-TiO₂/PTFE has excellent self-cleaning in a ratio N-TiO₂/PTFE (1:3) and based on optical properties, show that each coating on the glass substrate has high transmittance for composition N-TiO₂/PTFE (1:3) > 90%. The contact angle before and after oleic acid contaminant under visible light are 97.68 and 94.16º, respectively. The discoloration of methylene blue (MB) coated on the glass performed under visible light shown 60.32% degradation.

Abstract: This paper presents a simulation of three different types of lead-free piezoelectric materials for energy harvesting. Polyvinylidene Fluoride (PVDF), Zinc Sulfide (ZnS), and Cadmium Sulfide (CdS) are simulated using COMSOL Multiphysics to evaluate the frequency response and electrical potential for each materials. The simulation consisted of two parts which is 3D block cantilever for simulating frequency response and total displacement. The second part is 2D block bimorph to simulate power generated by varying frequency responses. The simulated result for the first shows that frequency response for each materials is differents for ZnS, PVDF and CdS which 30.897 kHz, 8.517 kHz, and 22.118 kHz. For total displacement is 303 µm which same for each materials. Each material is simulated for various cantilever beam thicknesses ranging from 1-4 µm and result ZnS having the greatest frequency response. For 2D block bimorph model, the highest electric potential is 0.75 V at 60 Hz frequency for ZnS. Meanwhile for CdS and PVDF has less electric potential which 0.6 V and 0.4V at 60 Hz frequency response. For power disspation, ZnS generate 10% more power compare to CdS and PVDF. In the end of the paper, ZnS is excellent lead free material compared to CdS and PVDF in term of aforementioned parameter studied.