Nur Syafinaz Ridhuan

Structural and Morphology of ZnO Nanorods Synthesized Using ZnO Seeded Growth Hydrothermal Method and Its Properties as UV Sensing

In this study, zinc oxide (ZnO) nanorod arrays were synthesized using a simple hydrothermal reaction on ZnO seeds/n-silicon substrate. Several parameters were studied, including the heat-treatment temperature to produce ZnO seeds, zinc nitrate concentration, pH of hydrothermal reaction solution, and hydrothermal reaction time. The optimum heat-treatment temperature to produce uniform nanosized ZnO seeds was 400°C. The nanorod dimensions depended on the hydrothermal reaction parameters. The optimum hydrothermal reaction parameters to produce blunt tip-like nanorods (770 nm long and 80 nm in top diameter) were 0.1 M zinc nitrate, pH 7, and 4 h of growth duration. Phase analysis studies showed that all ZnO nanorods exhibited a strong (002) peak. Thus, the ZnO nanorods grew in a c-axis preferred orientation. A strong ultraviolet (UV) emission peak was observed for ZnO nanorods grown under optimized parameters with a low, deep-level emission peak, which indicated high optical property and crystallinity of the nanorods. The produced ZnO nanorods were also tested for their UV-sensing properties. All samples responded to UV light but with different sensing characteristics. Such different responses could be attributed to the high surface-to-volume ratio of the nanorods that correlated with the final ZnO nanorods morphology formed at different synthesis parameters. The sample grown using optimum synthesis parameters showed the highest responsivity of 0.024 A/W for UV light at 375 nm under a 3 V bias.

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

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.

Formation of ZnO Nanorods via Seeded Growth Hydrothermal Reaction

In this study, ZnO nanorods was formed on a seeded substrates prepared by thermal oxidation of Zn foil followed by hydrothermal reaction. ZnO seed was prepared via thermal oxidation process at 300°C for 10 minutes to form uniform circular nanosize grains that were suitable as a seeded template for the growth of ZnO nanorods via hydrothermal reaction. Several hydrothermal reaction parameters were studied; hydrothermal reaction temperature, ratio of zinc nitrate to hexamethylamine and pH. In hydrothermal reaction, the formation of ZnO nanorods occurs due to thermal degradation of hexamethylamine (HMT) which released hydroxyl ions that react with Zn ions in the precursor solution. Well aligned, ZnO nanorods with length of ~700 nm, base diameter of ~200 nm and top diameter of less than 30 nm needle-like structure were formed on seeded Zn substrate with concentration ratio of zinc nitrate to hexamethylamine 0.1M:0.1M, pH 6-7 at hydrothermal reaction temperature of 80°C

Properties of ZnO Nanorods Arrays Growth via Low Temperature Hydrothermal Reaction

This work describes properties of 1-D ZnO nanorods arrays growth using low temperature hydrothermal method on a seeded substrate. The properties of ZnO seed were studied by varying thermal oxidation temperature from 250-450°C. The formation of ZnO nanorods was studied by varying the growth time during hydrothermal process. The optimum oxidation temperature to produce seeded ZnO template was 400°C. The formation of ZnO nanorods was further studied by varying hydrothermal reaction growth time from 1 to 24 hours. The optimum hydrothermal growth time of 4 hours produced blunt tip-like nanorods with length of ~735 nm and top diameter of ~66 nm. I-V characteristics of ZnO nanorods photodetector in dark, ambient light and UV light were also studied. The change in the photoconductivity under UV illumination was found to be 1 order of magnitude higher compared to dark and ambient light. With an incident wavelength of 370 nm and applied bias of 3V, the responsivity of photodetector was 5.0 mA/W, which was higher compared to other reported works. The increase of photosensitivity indicated that the produced ZnO nanorods were suitable for UV photodetector applications.

Synthesis of tunable size gold nanoparticles using seeding growth method and its application in glucose sensor

This work describes synthesis of gold nanoparticles (AuNPs) of tunable size using the seeding growth method. High concentration of AuNPs of various sizes was synthesized by varying synthesis parameters. The properties were observed using transmission electron microscope (TEM), zetasizernanoZS, X-ray diffractometer (XRD) and UV Vis spectrophotometers. The produced AuNPs were then used in fabrication of glucose sensors with the following structure; Nafion/GOx/AuNPs/ITO. The effect of AuNPs size on glucose sensor properties was studied by measuring electrocatalytic activity of the prepared AuNPs/ITO electrodes using cyclic voltammetry in the range of -0.5 to 0.5 V versus Ag/AgCl reference electrode. Cyclic voltammograms of various sizes of AuNPs tested in 10 mM glucose in 0.01 M PBS. UV-Vis analysis shows the wavelength of AuNPs increases from 518, 519, 523, 525 and 529 for 15 (Au seed), 20, 30, 40 and 50 nm, respectively. Particle size analysis using the zetasizer gave z-average for expected size 20, 30, 40...

Fabrication and Characterization of Glucose Biosensors by Using Hydrothermally Grown ZnO Nanorods

Highly oriented ZnO nanorod (NR) arrays were fabricated on a seeded substrate through a hydrothermal route. The prepared ZnO nanorods were used as an amperometric enzyme electrode, in which glucose oxidase (GOx) was immobilised through physical adsorption. The modified electrode was designated as Nafion/GOx/ZnO NRs/ITO. The morphology and structural properties of the fabricated ZnO nanorods were analysed using field-emission scanning electron microscope and X-ray diffractometer. The electrochemical properties of the fabricated biosensor were studied by cyclic voltammetry and amperometry. Electrolyte pH, electrolyte temperature and enzyme concentration used for immobilisation were the examined parameters influencing enzyme activity and biosensor performance. The immobilised enzyme electrode showed good GOx retention activity. The amount of electroactive GOx was 7.82 × 10−8 mol/cm2, which was relatively higher than previously reported values. The Nafion/GOx/ZnO NRs/ITO electrode also displayed a linear response to glucose ranging from 0.05 mM to 1 mM, with a sensitivity of 48.75 µA/mM and a low Michaelis–Menten constant of 0.34 mM. Thus, the modified electrode can be used as a highly sensitive third-generation glucose biosensor with high resistance against interfering species, such as ascorbic acid, uric acid and L-cysteine. The applicability of the modified electrode was tested using human blood samples. Results were comparable with those obtained using a standard glucometer, indicating the excellent performance of the modified electrode.

The effect of gold nanoparticles modified electrode on the glucose sensing performance

In this work, 20 nm, 30 nm, 40 nm, 50 nm and 60 nm colloidal gold nanoparticles (AuNPs) were synthesized using the seeding growth method. AuNPs produced had spherical shape with uniform size. The AuNPs also are well dispersed in colloidal form that was proven by low polydispersity index. The produced AuNPs were used to modify electrode for glucose sensor. The produced AuNPs were deposited on indium tin oxide substrate (ITO), followed by immobilization of glucose oxidase (GOx) on it. After that, Nafion was deposited on the GOx/AuNPs/ITO. Electrooxidation of glucose with AuNPs-modified electrode was examined by cyclic voltammeter (CV) in 15 mM glucose mixed with 0.01 M PBS. The optimum size of AuNPs was 30 nm with optical density 3.0. AuNPs were successfully immobilized with glucose oxidase (GOx) and proved to work well as a glucose sensor. Based on the high electrocatalytic activity of Nafion/GOx/AuNPs/ITO, the sensitivity of the glucose sensors was further examined by varying the concentration of glucose solution from 2 mM to 20 mM in 0.01 M phosphate buffer solution (PBS) solution. Good linear relationship was observed between the catalytic current and glucose concentration in the range of 2 mM to 20 mM. The sensitivity of the Nafion/GOx/AuNPs/ITO electrode calculated from the slope of linear square calibration was 0.909 µA mM−1 cm−2 that is comparable with other published work. The linear fitting to the experimental data gives R-square of 0.991 at 0.9 V and a detection limit of 2.03 mM. This detection range is sufficient to be medically useful in monitoring human blood glucose level in which the normal blood glucose level is in the range of 4.4 to 6.6 mM and diabetic blood glucose level is above 7 mM.In this work, 20 nm, 30 nm, 40 nm, 50 nm and 60 nm colloidal gold nanoparticles (AuNPs) were synthesized using the seeding growth method. AuNPs produced had spherical shape with uniform size. The AuNPs also are well dispersed in colloidal form that was proven by low polydispersity index. The produced AuNPs were used to modify electrode for glucose sensor. The produced AuNPs were deposited on indium tin oxide substrate (ITO), followed by immobilization of glucose oxidase (GOx) on it. After that, Nafion was deposited on the GOx/AuNPs/ITO. Electrooxidation of glucose with AuNPs-modified electrode was examined by cyclic voltammeter (CV) in 15 mM glucose mixed with 0.01 M PBS. The optimum size of AuNPs was 30 nm with optical density 3.0. AuNPs were successfully immobilized with glucose oxidase (GOx) and proved to work well as a glucose sensor. Based on the high electrocatalytic activity of Nafion/GOx/AuNPs/ITO, the sensitivity of the glucose sensors was further examined by varying the concentration of glucose ...

Properties of Al-Doped ZnO Nanorods Synthesized Using Low Temperature Hydrothermal Method

This work describes the growth of 1-D Al-doped ZnO nanorods via low temperature hydrothermal reaction on seeded substrates. The amount of Al doped ZnO nanorods were tuned by using different concentration of aluminum nitrate from 1-20 mM. The optimum 5 mM Al doping produced an arrays of sharp-tip nanorods with average length of ~1.16 μm and average diameter of ~118 nm. I-V characteristic of the Al-doped ZnO nanorods fabricated onto Al electrodes were observed under UV illumination and dark condition. The change in photoconductivity of Al-doped ZnO nanorods under UV light was found two orders of times higher compared to ZnO nanorods. Different concentrations of aluminium doped ZnO nanorods UV sensing showed response to UV light but with different sensing value. 5 mM Al-doped ZnO showed high responsivity of fabricated UV sensing at 3V with 23.56 A/W which was higher compared to other concentrations. This suggested that the responsivity of Al-doped ZnO NRs UV sensing could be controlled to some extent by controlling the percentage of Al-doped.