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Fulltext Direct formation of gold nanoparticles on substrates using a novel ZnO sacrificial templated-growth hydrothermal approach and their properties in organic memory device

Goh LP, Razak KA, Ridhuan NS, Cheong KY, Ooi PC, Aw KC

Nanoscale Res Lett, 2012;7(1):563.
PMID: 23046949 DOI: 10.1186/1556-276X-7-563

This study describes a novel fabrication technique to grow gold nanoparticles (AuNPs) directly on seeded ZnO sacrificial template/polymethylsilsesquioxanes (PMSSQ)/Si using low-temperature hydrothermal reaction at 80°C for 4 h. The effect of non-annealing and various annealing temperatures, 200°C, 300°C, and 400°C, of the ZnO-seeded template on AuNP size and distribution was systematically studied. Another PMMSQ layer was spin-coated on AuNPs to study the memory properties of organic insulator-embedded AuNPs. Well-distributed and controllable AuNP sizes were successfully grown directly on the substrate, as observed using a field emission scanning electron microscope followed by an elemental analysis study. A phase analysis study confirmed that the ZnO sacrificial template was eliminated during the hydrothermal reaction. The AuNP formation mechanism using this hydrothermal reaction approach was proposed. In this study, the AuNPs were charge-trapped sites and showed excellent memory effects when embedded in PMSSQ. Optimum memory properties of PMMSQ-embedded AuNPs were obtained for AuNPs synthesized on a seeded ZnO template annealed at 300°C, with 54 electrons trapped per AuNP and excellent current-voltage response between an erased and programmed device.
Wafer-Scale Fabrication of Nitrogen-Doped Reduced Graphene Oxide with Enhanced Quaternary-N for High-Performance Photodetection

Mohammad Haniff MAS, Zainal Ariffin NH, Hafiz SM, Ooi PC, Syono MI, Hashim AM

ACS Appl Mater Interfaces, 2019 Jan 30;11(4):4625-4636.
PMID: 30618229 DOI: 10.1021/acsami.8b19043

We demonstrated a simple and scalable fabrication route of a nitrogen-doped reduced graphene oxide (N-rGO) photodetector on an 8 in. wafer-scale. The N-rGO was prepared through in situ plasma treatment in an acetylene-ammonia atmosphere to achieve an n-type semiconductor with substantial formation of quaternary-N substituted into the graphene lattice. The morphology, structural, chemical composition, and electrical properties of the N-rGO were carefully characterized and used for the device fabrication. The N-rGO devices were fabricated in a simple metal-semiconductor-metal structure with unconventional metal-on-bottom configuration to promote high-performance photodetection. The N-rGO devices exhibited enhanced photoresponsivity as high as 0.68 A W-1 at 1.0 V, which is about 2 orders of magnitude higher compared to a pristine graphene and wide-band photoinduced response from the visible to the near-infrared region with increasing sensitivity in the order of 785, 632.8, and 473 nm excitation wavelengths. We also further demonstrated a symmetric characteristic of the photoinduced response to any position of local laser excitation with respect to the electrodes. The excellent features of wafer-scale N-rGO devices suggest a promising route to merge the current silicon technology and two-dimensional materials for future optoelectronic devices.
Fulltext Knowledge, attitude, and practice regarding atrial fibrillation among primary care physicians: the potential role of postgraduate training

Ooi PC, Ramayah G, Omar SR, Rajadorai V, Nadarajah T, Ting CH, et al.

Malays Fam Physician, 2021 Mar 25;16(1):39-49.
PMID: 33948141 DOI: 10.51866/oa0002

Introduction: Atrial fibrillation (AF) is known to lead to stroke and thromboembolism, causing a five-fold increase in the risk of stroke and almost doubling the mortality rate. Optimal anticoagulant therapy is effective in reducing AF-related death. However, prescription of anticoagulants in AF in East Asian countries has been low, ranging from 0.5% to 28%. This study aimed to determine whether vocational training in family medicine improves primary care physicians' knowledge, attitude, and practice in the management of AF.
Method: This investigation was a cross-sectional study carried out during centralized workshops for two groups of trainees using a validated questionnaire: (i) junior trainees were newly enrolled postgraduate trainees in the Graduate Certificate in Family Medicine (GCFM) program, and (ii) senior trainees were postgraduate trainees in Advance Training in Family Medicine (ATFM) programs of the Academy of Family Physicians of Malaysia (AFPM).
Results: A total of 223 trainees (127 junior and 96 senior) participated in this study. Only 55.2% of the trainees passed the knowledge test; senior trainees were more likely to pass the knowledge test compared to junior trainees (69.8% vs. 44.1%, p < 0.001). Female trainees were significantly more likely to pass the knowledge test than male trainees. While the attitude of senior and junior trainees was similar, more of the latter group worked in public clinic that provide better support where there is better support for outpatient anticoagulation treatment (e.g., same-day INR test, direct access echocardiogram, and warfarin in in-house pharmacy).
Conclusion: Vocational training in family medicine appears to improve primary care physicians' knowledge regarding the management of AF. Better knowledge will help vocationally trained primary care physicians to provide anticoagulation treatment for AF within primary care clinics. More optimal AF management within primary care can take place if the identified barriers are addressed and a shared care plan can be implemented.
Fulltext Ultraviolet Light-Assisted Copper Oxide Nanowires Hydrogen Gas Sensor

Sihar N, Tiong TY, Dee CF, Ooi PC, Hamzah AA, Mohamed MA, et al.

Nanoscale Res Lett, 2018 May 15;13(1):150.
PMID: 29766297 DOI: 10.1186/s11671-018-2566-6

We fabricated copper oxide nanowires (CuO NWs) ultraviolet (UV) light-assisted hydrogen gas sensor. The fabricated sensor shows promising sensor response behavior towards 100 ppm of H2 at room temperature and elevated temperature at 100 °C when exposed to UV light (3.0 mW/cm2). One hundred-cycle device stability test has been performed, and it is found that for sample elevated at 100 °C, the UV-activated sample achieved stability in the first cycle as compared to the sample without UV irradiation which needed about 10 cycles to achieve stability at the initial stage, whereas the sample tested at room temperature was able to stabilize with the aid of UV irradiation. This indicates that with the aid of UV light, after some "warming up" time, it is possible for the conventional CuO NW sensor which normally work at elevated temperature to function at room temperature because UV source is speculated to play a dominant role to increase the interaction of the surface of CuO NWs and hydrogen gas molecules absorbed after the light exposure.
Fulltext Solid-State Limited Nucleation of NiSi/SiC Core-Shell Nanowires by Hot-Wire Chemical Vapor Deposition

Alizadeh M, Binti Hamzan N, Ooi PC, Bin Omar MF, Dee CF, Goh BT

Materials (Basel), 2019 Feb 24;12(4).
PMID: 30813502 DOI: 10.3390/ma12040674

This work demonstrated a growth of well-aligned NiSi/SiC core-shell nanowires by a one-step process of hot-wire chemical vapor deposition on Ni-coated crystal silicon substrates at different thicknesses. The NiSi nanoparticles (60 to 207 nm) acted as nano-templates to initially inducing the growth of these core-shell nanowires. These core-shell nanowires were structured by single crystalline NiSi and amorphous SiC as the cores and shells of the nanowires, respectively. It is proposed that the precipitation of the NiSi/SiC are followed according to the nucleation limited silicide reaction and the surface-migration respectively for these core-shell nanowires. The electrical performance of the grown NiSi/SiC core-shell nanowires was characterized by the conducting AFM and it is found that the measured conductivities of the nanowires were higher than the reported works that might be enhanced by SiC shell layer on NiSi nanowires. The high conductivity of NiSi/SiC core-shell nanowires could potentially improve the electrical performance of the nanowires-based devices for harsh environment applications such as field effect transistors, field emitters, space sensors, and electrochemical devices.
Fulltext High sensitivity and wide response range artificial synapse based on polyimide with embedded graphene quantum dots

Kou L, Ye N, Waheed A, Auliya RZ, Wu C, Ooi PC, et al.

Sci Rep, 2023 May 20;13(1):8194.
PMID: 37210533 DOI: 10.1038/s41598-023-35183-8

Artificial electronic synapses are commonly used to simulate biological synapses to realize various learning functions, regarded as one of the key technologies in the next generation of neurological computation. This work used a simple spin coating technique to fabricate polyimide (PI):graphene quantum dots(GQDs) memristor structure. As a result, the devices exhibit remarkably stable exponentially decaying postsynaptic suppression current over time, as interpreted in the spike-timing-dependent plasticity phenomenon. Furthermore, with the increase of the applied electrical signal over time, the conductance of the electrical synapse gradually changes, and the electronic synapse also shows plasticity dependence on the amplitude and frequency of the pulse applied. In particular, the devices with the structure of Ag/PI:GQDs/ITO prepared in this study can produce a stable response to the stimulation of electrical signals between millivolt to volt, showing not only high sensitivity but also a wide range of "feelings", which makes the electronic synapses take a step forwards to emulate biological synapses. Meanwhile, the electronic conduction mechanisms of the device are also studied and expounded in detail. The findings in this work lay a foundation for developing brain-like neuromorphic modeling in artificial intelligence.
Fulltext Electrical transportation mechanisms of molybdenum disulfide flakes-graphene quantum dots heterostructure embedded in polyvinylidene fluoride polymer

Ooi PC, Mohammad Haniff MAS, Mohd Razip Wee MF, Goh BT, Dee CF, Mohamed MA, et al.

Sci Rep, 2019 May 01;9(1):6761.
PMID: 31043694 DOI: 10.1038/s41598-019-43279-3

In the interest of the trend towards miniaturization of electronic gadgets, this study demonstrates a high-density data storage device with a very simple three-stacking layer consisting of only one charge trapping layer. A simple solution-processed technique has been used to fabricate the tristable non-volatile memory. The three-stacking layer was constructed in between two metals to form a two-terminal metal-insulator-metal structure. The fabricated device showed a large multilevel memory hysteresis window with a measured ON/OFF current ratio of 107 that might be attributed to the high charge trapped in molybdenum disulphide (MoS2) flakes-graphene quantum dots (GQDs) heterostructure. Transmission electron microscopy was performed to examine the orientation of MoS2-GQD and mixture dispersion preparation method. The obtained electrical data was used further to speculate the possible transport mechanisms through the fabricated device by a curve fitting technique. Also, endurance cycle and retention tests were performed at room temperature to investigate the stability of the device.
Silver Nanowire Networks with Moisture-Enhanced Learning Ability

Qiu J, Li J, Li W, Wang K, Xiao T, Su H, et al.

ACS Appl Mater Interfaces, 2024 Feb 28;16(8):10361-10371.
PMID: 38362885 DOI: 10.1021/acsami.3c17438

The human brain possesses a remarkable ability to memorize information with the assistance of a specific external environment. Therefore, mimicking the human brain's environment-enhanced learning abilities in artificial electronic devices is essential but remains a considerable challenge. Here, a network of Ag nanowires with a moisture-enhanced learning ability, which can mimic long-term potentiation (LTP) synaptic plasticity at an ultralow operating voltage as low as 0.01 V, is presented. To realize a moisture-enhanced learning ability and to adjust the aggregations of Ag ions, we introduced a thin polyvinylpyrrolidone (PVP) coating layer with moisture-sensitive properties to the surfaces of the Ag nanowires of Ag ions. That Ag nanowire network was shown to exhibit, in response to the humidity of its operating environment, different learning speeds during the LTP process. In high-humidity environments, the synaptic plasticity was significantly strengthened with a higher learning speed compared with that in relatively low-humidity environments. Based on experimental and simulation results, we attribute this enhancement to the higher electric mobility of the Ag ions in the water-absorbed PVP layer. Finally, we demonstrated by simulation that the moisture-enhanced synaptic plasticity enabled the device to adjust connection weights and delivery modes based on various input patterns. The recognition rate of a handwritten data set reached 94.5% with fewer epochs in a high-humidity environment. This work shows the feasibility of building our electronic device to achieve artificial adaptive learning abilities.
Fulltext Practical Route for the Low-Temperature Growth of Large-Area Bilayer Graphene on Polycrystalline Nickel by Cold-Wall Chemical Vapor Deposition

Shazni Mohammad Haniff MA, Zainal Ariffin NH, Ooi PC, Mohd Razip Wee MF, Mohamed MA, Hamzah AA, et al.

ACS Omega, 2021 May 11;6(18):12143-12154.
PMID: 34056368 DOI: 10.1021/acsomega.1c00841

We report a practical chemical vapor deposition (CVD) route to produce bilayer graphene on a polycrystalline Ni film from liquid benzene (C6H6) source at a temperature as low as 400 °C in a vertical cold-wall reaction chamber. The low activation energy of C6H6 and the low solubility of carbon in Ni at such a low temperature play a key role in enabling the growth of large-area bilayer graphene in a controlled manner by a Ni surface-mediated reaction. All experiments performed using this method are reproducible with growth capabilities up to an 8 in. wafer-scale substrate. Raman spectra analysis, high-resolution transmission electron microscopy, and selective area electron diffraction studies confirm the growth of Bernal-stacked bilayer graphene with good uniformity over large areas. Electrical characterization studies indicate that the bilayer graphene behaves much like a semiconductor with predominant p-type doping. These findings provide important insights into the wafer-scale fabrication of low-temperature CVD bilayer graphene for next-generation nanoelectronics.
Stress and Deformation of Optimally Shaped Silicon Microneedles for Transdermal Drug Delivery

Zainal Abidin HE, Ooi PC, Tiong TY, Marsi N, Ismardi A, Mohd Noor M, et al.

J Pharm Sci, 2020 Aug;109(8):2485-2492.
PMID: 32380181 DOI: 10.1016/j.xphs.2020.04.019

In this study, we demonstrated the fabrication of the concave conic shape microneedle with the aid of COMSOL Multiphysics simulation. The stress and buckling of the microneedle structure were simulated by applying various loads ranging from 50 to 800 g perpendiculars to the tip in order to predict the occurrence of microneedles structure deformation. The simulation study indicated that the surface buckling deformation does not occur to the microneedle structure with the increment of the load. The microneedles with dimensions of height and diameter tip ranging from 60 to 100 μm and 1 to 4 μm, respectively had been fabricated via an etching process in a mixture of hydrofluoric acid, nitric acid, and acetic acid. Three optimized microneedles but different in the structures were fabricated via the acidic etching process. The reproducibility of 3 different microneedle structures was 15, 20, and 60%, respectively. Stress and buckling analyses of the fabricated microneedles were further carried out on the rat skin. The obtained experimental results show promising applications for the deep dermis, stratum corneum to epidermis layer penetration.
Fulltext Exploration of 2D Ti3C2 MXene for all solution processed piezoelectric nanogenerator applications

Auliya RZ, Ooi PC, Sadri R, Talik NA, Yau ZY, Mohammad Haniff MAS, et al.

Sci Rep, 2021 Aug 31;11(1):17432.
PMID: 34465806 DOI: 10.1038/s41598-021-96909-0

A new 2D titanium carbide (Ti3C2), a low dimensional material of the MXene family has attracted remarkable interest in several electronic applications, but its unique structure and novel properties are still less explored in piezoelectric energy harvesters. Herein, a systematic study has been conducted to examine the role of Ti3C2 multilayers when it is incorporated in the piezoelectric polymer host. The 0.03 g/L of Ti3C2 has been identified as the most appropriate concentration to ensure the optimum performance of the fabricated device with a generated output voltage of about 6.0 V. The probable reasons might be due to the uniformity of nanofiller distribution in the polyvinylidene difluoride (PVDF) and the incorporation of Ti3C2 in a polymer matrix is found to enhance the β-phase of PVDF and diminish the undesired α-phase configuration. Low tapping frequency and force were demonstrated to scavenge electrical energy from abundant mechanical energy resources particularly human motion and environmental stimuli. The fabricated device attained a power density of 14 µW.cm-2 at 10.8 MΩ of load resistor which is considerably high among 2D material-based piezoelectric nanogenerators. The device has also shown stable electrical performance for up to 4 weeks and is practically able to store energy in a capacitor and light up a LED. Hence, the Ti3C2-based piezoelectric nanogenerator suggests the potential to realize the energy harvesting application for low-power electronic devices.

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