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Increasing demand for accurate, reliable and highly sensitive pH sensors has led researchers to explore various materials for this reason. Metal oxide (MOx) pH sensors have received considerable attention due to their high degree of accuracy and great sensitivity to hydrogen ions. Additionally, this MOx pH sensor overcomes the shortcomings of the glass electrode. Thus, a comparative experimental study on various metal oxides (MOx) of TiO2, ZnO, CuO, and NiO thin films as sensing electrodes for extended-gate field effect transistor (EGFET)-pH sensor was carried out via a facile sol–gel spin-coating method. Here, the thin films were tested as pH sensors in pH 2, 4, 7, 10 and 12 and hysteresis stability for 25 min in pH 7 → 4 → 7 → 10 → 7. The pH measurements were repeated several times to confirm the sensitivity behaviour. The surface morphology and surface roughness of the films were characterized using field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM), respectively. The TiO2thin films showed the highest sensitivity (53.4 mV/pH, R2= 0.992) and lowest hysteresis value (1 mV) compared to the other sensing electrodes. Moreover, the thin film showed drift rates of 6.74, 3.52 and 41.18 mV/h for pH 10, 7 and 4. The experimental findings suggested that both surface morphology and surface roughness affect the sensitivity performance of these devices since a smooth surface morphology and low roughness value were observed for TiO2thin films. Besides, the basic mechanism of MOx pH sensor was presented in this study.

Polyvinyl alcohol (PVA) nanofibers were fabricated using the electrospinning method. The nanofibers were embedded with zinc oxide (ZnO) particles by mixing PVA liquid with the ZnO powders during the solution preparation stage. The FESEM images showed an increase in the amount of ZnO particles embedded in the PVA nanofibers as the powder content was increased. Other than that, there are no significant changes in other physical properties of the nanofibers caused by the increasing number of ZnO particle content. This means that ZnO nanopowders (with concentration in the range of 1.63 wt% - 8.14 wt%) can be effectively integrated and embedded into PVA nanofibers without negative consequences on the fibers formation and structure. This will facilitate the fabrication of ZnO embedded PVA nanofibers in some applications that may require it such as drug delivery, filtration, and biomedical application.

Conductive and flexible electronics have attracted great demands and attention in the field of stretchable and wearable electronic devices. In this work, polydimethylsiloxane (PDMS) was composited with different drops of graphene solution to produce flexible, conductive and optically transparent PDMS/Graphene composite using the drop-cast method. The dielectric constants of PDMS and PDMS/Graphene composite were measured using Agilent dielectric probe. I-V characterization was used to measure the conductivity of the flexible substrate in flat and bending conditions. The UV-VIS was used to measure the transmittance properties of the substrate. Comparing the electrical properties of the pristine PDMS substrate with graphene composited PDMS substrates, the current shows a slight decrease due to the physical morphology of PDMS/Graphene composite that creates a small hole on the surface. No significant changes can be found between 1 drop, 2 drops, 3 drops and 4 drops of graphene in PDMS solution. For the dielectric measurement, the result of composited PDMS/Graphene sample had shown a lower value of dielectric constant (1.1 F/m) compared to pure PDMS (2.33 F/m). This shows that the existence of graphene in PDMS reduces the dielectric constant of pristine PDMS. The result of UV-VIS shows the samples with 4 drops of graphene having the lowest visible transmittance. The PDMS/Graphene composite can be concluded as a dielectric material with a lower dielectric constant. It has the potential to be used as a conductive substrate for further flexible interconnect materials since it has a unique electrical feature and robust mechanical strength.

This study presents an investigation on copper oxide (CuO) composited with polyethylene glycol (PEG) thin film. The main objective for this compositing thin film is to explore and determine the characteristic of the thin film when the value of PEG is varied. In this study, PEG plays a role as phase change material (PCM), where this type of material has the capability to absorb and release heat based on its surrounding condition. Due to this characteristic, the amount of PEG is vary from 0.5, 1.0, 1.5 and 2.0 ml to confirm its influence towards CuO thin film. As for comparison, CuO thin film without PEG is also fabricated. Both of the materials used were prepared using sol-gel route and deposited onto indium tin oxide (ITO) substrate using spin coating method. The influences of the PEG values on CuO thin film were investigated using field emission scanning electron microscope (FESEM), x-ray diffraction (XRD), ultra-violet visible microscope (UV-Vis), and current-voltage (IV) measurement. Based on the investigation conducted, the characteristics of CuO thin film produced in this study are affected with the different value of PEG.

Two types of memristor sensor were fabricated using two different TiO2deposition methods of sputtering and sol-gel spin coating. The surface morphology of the sensors and the behaviour of the sensors were analysed by using scanning electron microscopy with energy dispersive x-ray system and I-V characterisation system respectively. The sensors were applied with liquid with hydroxyl group to check the capability of this sensor in sensing different concentration of hydroxyl ion inside the liquid. For that purpose, d-glucose liquid with four concentrations of 10mM, 20mM, 30mM and 40mM were chosen. The liquids dispensed onto the TiO2surface to act as sensing material. The TiO2surface was initially covered with polydimethylsiloxane to control the liquid. The sensing capability of the sensors was determined via the current-voltage measurement and off-on resistance ratio. The sensitivity of the sensors was analysed from the off-on resistance ratio analysis. Type II memristor sensor which was fabricated using sol-gel spin coating technique recorded high sensitivity of 120.65 (mM)−1, while Type I sensor fabricated using the sputtering technique recorded low sensitivity of 0.035 (mM)−1. However, SEM-EDX image illustrated that the sputtering technique produced more uniform TiO2thin film than sol-gel spin coating technique with larger atomic number of oxygen through the sol-gel spin coating technique. This indicates Type II sensor that has large number of oxygen atom produced more reaction with hydroxyl ion inside the liquid. While, Type I sensor produced less reaction compared with Type II and thus produced smaller off-on resistance ratio.

Single layer of titanium dioxide (TiO2) is common metal oxide in fabricating memristor device. In this study, two types of memristor with composite metal oxide thin films will be demonstrated. The two types of memristor are titanium dioxide (TiO2) thin film coated on zinc oxide (ZnO) thin film and ZnO coated on TiO2 thin film. Sol-gel spin coating method was to coat metal oxide thin film and sputtering method for depositing the metal contact. Platinum (Pt) was selected as the top electrode and indium tin oxide (ITO) as the bottom electrode. The electrical characteristics were defined by performing I-V measurement using two point probe equipment. I-V characteristics showed shape of pinched hysteresis loop for both samples. Sample with TiO2 coated on ZnO has slightly higher Roff/Ron ratio than sample ZnO coated on TiO2 which means it more memristive than another one. The cross-section of sample with TiO2 coated on ZnO had been performed as well by using Field-Emission Scanning Electron Microscopy (FESEM).

This paper presents an investigation on titanium dioxide (TiO2) thin film, which is used as sensing membrane for Extended-Gate Field Effect Transistor (EGFET) for pH sensing application. TiO2 thin films were deposited using sol-gel spin coating method on indium tin oxide (ITO) substrates. After the deposition, the thin films were annealed at 300 °C for 10 and 15 min, while another sample was annealed at 400 °C for 15 min. The sensitivity measurement was taken using the EGFET setup equipment with constant-current (100 μA) and constant-voltage (0.5 V) biasing interfacing circuit. TiO2 thin film as the pH-sensitive membrane and the working electrode was connected to a commercial metal-oxide semiconductor FET (MOSFET). The MOSFET then was connected to the interfacing circuit. The sensitivity of the TiO2 thin film towards pH buffer solution was measured by dipping the sensing membrane in pH4, pH7 and pH10 buffer solution. For comparison, a sample of bare-ITO was also tested to see its sensitivity. We found that the TiO2 thin film annealed at 400 °C for 15 min gave the highest sensitivity compared to other annealing conditions and also compared to the bare ITO substrate with the value of 44.30 mV/pH. This showed that TiO2 thin film can be used for pH sensing and the post-deposition treatment of the thin film can influence the sensing ability. We also measured the TiO2 thin films’ current – voltage (I-V) characteristics. Relating the I-V characteristic of the thin films and sensitivity, the sensing membrane with higher conductivity gave better sensitivity.

The paper presents the memristive behavior of sputtered titania thin films on ITO substrate. Titania thin films were deposited by RF magnetron sputtering method while varying the oxygen flow rate of (O2/ (O2 + Ar) x100 = 10, 20 and 30 %) during deposition process. The effect of oxygen flow rate to the structural properties was studied including the physical thickness, and also the effect towards switching behavior. It was found that sample deposited at 20 % oxygen flow rate gave better memristive behavior compared to other samples, with larger ROFF/RON ratio of 9. The characterization of memristive behavior includes the effect of electroforming process and successive of I-V measurements are discussed.

This paper reports the results of zinc oxide (ZnO) nanostructure growth on different types of metal catalysts, namely gold and platinum, and also the effect of annealing time of the metal catalysts prior to the deposition of ZnO nanostructures. The metal catalysts layers with 15 nm thickness were deposited on glass substrates by sputter coater and then annealed in air ambient for 15 and 30 min at 500 °C. ZnO nanostructure was then deposited on the metal catalysts by thermal chemical vapour deposition (TCVD) method. We found that the Au catalyst morphologies varied with the annealing time, and the growth morphology of the ZnO followed the morphology of the Au catalyst. The morphology of the metal catalysts and ZnO nanostructures were characterized using field emission scanning electron microscopy (FESEM). The grown ZnO nanostructures were tested for their ability for extended gate field effect transistor (EGFET) sensor application. The samples were attached to the gate of an NFET and were dipped in acid and alkali buffer solutions while the gate voltage was measured. We found that the extended gate gave different voltage in buffer solutions with different pH which indicated that the samples can act as the extended gate of an EGFET sensor.

The paper presents the memristive behaviour of spin-coated titania thin films on ITO substrate. The sample was annealed in air ambient at different annealing temperature and duration of 250 and 450 °C for 20 and 60 min. The effect of post-annealing process to the physical thickness and crystallinity of the films towards switching behaviour was studied. It was found that the thickness and crystallinity of the films increases as the post annealing process increases. Sample annealed at 250 °C for 20 min with thinner film showed better switching behaviour even though the sample is still in amorphous form. Thus, in our work, we believed that the crystallinity of the films does not affect the switching behaviour of the sample. The reliability of device performance was studied by repeating the measurement for three times.

The resistive switching or memristive behavior of sputtered titania thin films sandwiched in between of three types of metal electrodes (Au, Pt and Ti) was investigated. The active region of the device consisted of two titania thin films, in which, the first layer was exposed to a plasma treatment to create the oxygen vacancies, before the deposition of the second layer. The whole active layer sputtering deposition process was conducted in a one-flow process without exposing the sample to the room ambient. From the I-V measurements, titania thin films in between Ti and Au did not show any resistive switching, but those sandwiched between Pt electrodes exhibit a noticeable memristive behavior. This may due to the metal work function of the platinum itself.

TiO2 nanostructures were successfully grown on TiO2 thin film by solution-based method at low temperature. TiO2 thin film as a seed layer for the nanostructures growth was deposited on ITO substrate by RF magnetron sputtering method at 40 and 60 nm thicknesses. Then the TiO2 nanostructures were synthesized on the samples by keeping them floating with TiO2 layer facing down the vessel in 10M NaOH solution at 80°C for 45 min. Effect of seed layer thickness to the growth of TiO2 nanostructure and its memristive behaviour were investigated. Surface morphology and current-voltage measurement for its memristive behaviour were measured by FESEM image and Keithley 4200 semiconductor characterization system. It was found that 60 nm-TiO2 thin film result in the formation of dandelion-like morphology of TiO2 nanowires and gives better memristive behavior with larger switching loops when positive voltage was applied to the sample.

Zinc oxide (ZnO) thin films were deposited on teflon substrates by RF magnetron sputtering at different substrate temperature. The effect of substrate temperature on ZnO thin films electrical and structural properties were examined using current-voltage (I-V) measurement, and x-ray diffraction (XRD) It was found that the electrical conductivity and resistivity of the ZnO thin film deposited at 40oC was the highest and lowest intensity accordingly. This was supported by the crystalline quality of the films from the x-ray diffraction (XRD) results. The XRD pattern showed that the ZnO thin film deposited at 40oC has the highest intensity with the narrowest full-width-at-half-maximum indicating that the film has the highest quality compared to other thin film.

Titania films were deposited on glass substrates by RF magnetron sputtering method at different substrate temperatures which are room temperature, 50oC, 100oC, 150oC, 200oC, 250oC and 300oC. The surface morphology and cross section of the particles structure were studied using Field Emission Scanning Electron Microscope. It is shown that the increase in substrate temperature during the sputtering process up to 300oC will make the film become more dense and grown in a columnar structure. Significant changes occur on the titania thin film structure at 250oC due to the significant changes in the surface thermal energy and the surface diffusion.

The electrical characteristics of metal--insulator--semiconductor (MIS) capacitor employing nanocomposite poly(methyl methacrylate):titanium dioxide (PMMA:TiO2) as insulator and zinc oxide (ZnO) as the semiconductor were discussed. The capacitance of the MIS devices was found to be 0.42 and 0.29 nF at frequency of 1 kHz and 1 MHz respectively. Meanwhile, the dielectric loss values are constant (${\sim}60\times 10^{-3}$) in the frequency range from 100 Hz to 100 kHz. Current--voltage ($I$--$V$) results for MIS are much higher than MIM is due to there is a trapped holes/electron located at the semiconductor--insulator interface which contributes to high leakage current in the MIS device. We conclude, although interposing the PMMA:TiO2nanocomposite insulator layer between the semiconductor and Al electrodes degrades the MIS device performance, nevertheless, they remain sufficiently good for use in organic electronic devices.

ZnO thin films were deposited on Teflon substrates by RF magnetron sputtering at different substrate temperature and different RF power. In this work, we investigated the dependence of the deposition rate and also the ZnO physical and electrical properties on the substrate temperature and RF power. It is observed that the deposition rate increased as the temperature and RF power increased. FE-SEM images confirmed that microstructure of the thin films consists of nanoparticles. XRD data confirmed that the ZnO thin films at various RF power and substrate temperature have (002) structure.

This paper reports on the dielectric properties of multilayer PVDF-TrFE/PMMA:TiO2 thin film. Two samples were fabricated on ITO substrates; one with PVDF-TrFE only and another PMMA:TiO2 on PVDF-TrFE on (PVDF-TrFE/PMMA:TiO2). Both samples were produced by spin coating method. Dielectric properties were characterized using impedance spectroscopic. Dielectric constant, k, capacitance and dielectric loss, tan δ values of PMMA:TiO2/PVDF-TrFE were measured in the frequency range 0 – 50 kHz. The result for dielectric loss did not show any significant different between the samples with and without nanocomposite PVDF-TrFE layer. However, the dielectric constant are affected when depositing a nanocomposite PVDF-TrFE layer on PMMA:TiO2. The dielectric constant is decreased by 0.3 from 7.9 to 7.6.

Silicon thin film was successfully deposited on glass substrate using Radio frequency (RF) magnetron sputtering. The effect of deposition pressure on the physical and structural properties of thin films on the glass substrate was studied. The film thickness and deposition rate decreased with decreasing deposition pressure. Field emission scanning electron microscopy (FESEM) shows as the deposition pressure increased, the surface morphology transform from concise structured to not closely pack on the surface. Raman spectroscopy result showed that the peak was around 508 cm-1, showing that the thin film is nanocrystalline instead of polycrystalline silicon.

Nanocrystalline silicon (nc-Si) thin films were deposited on glass and polytetrafluoroethylene (PTFE, teflon) substrates using Radio frequency (RF) magnetron sputtering. The effect of RF power and deposition temperature on the physical and structural properties of nc-Si on the glass and Teflon substrate was studied. The thin films properties were examined by Raman spectroscopy and field emission scanning electron microscopy (FESEM). We found that the thickness of thin films increased with increased RF power and deposition temperature. Raman spectroscopy results it showed that, with increasing RF power and deposition temperature can cause the changing of crystallinity on both glass and Teflon substrate.

Alloys for high temperature application always rely on their ability to form protective, dense Cr2O3 and Al2O3 scales. In case of Ni-Cr binary alloy, a minimum composition of Cr is required for the formation of continuous protective scale. However, addition of small amount of third element such as Al may results in decrease of required Cr composition to form protective scale. This study aims to clarify the effect of ternary element on the formation of protective scale quantitatively. Ni-Cr alloys composed with 2 mass% and 4 mass% of Al were exposed in oxidizing environment under Cr/Cr2O3, Fe/FeO and Ni/NiO oxygen partial pressure. The oxidation of all samples is following parabolic rate’s law. XRD and SEM results show that Al2O3 and Cr2O3 are formed internally. Parabolic rate’s constant of samples oxidized in Ni/NiO oxygen partial pressure is higher by few magnitude orders. Higher Al concentration decreases the parabolic rate’s constant. It is concluded that the formation of protective scale is enhanced by the addition of Al as ternary element in Ni-Cr alloys.

Fe - 9 to 12%Cr alloys are a material for the thick sections boiler components and steam lines of a power plant. The role Fe - 9 to 12%Cr alloys is becoming more prominent in the development of a new generation of Ultra-Supercritical (USC) Power Plant due to the target operating temperature is reaching 620 °C (893 K), in 100% steam condition as well as pressure in excess of 300 bar (30 × 106 Pa). In such condition, the integrity of Fe - 9 to 12%Cr alloys relies on the oxide scale formed during the time of exposure. However due to the high temperature and water vapor condition, it is a well known fact that, the formation of oxide scale is accelerated thus depleting the structural integrity of the Fe - 9 to 12%Cr alloys over the time. Studies show that not only the formation of protective oxide scale was suppressed but the formation of non-protective oxide scale was accelerated instead. Decades of studies done by various groups around the globe has yet to have consensual on the exact mechanism of this phenomenon. Initial stage oxidation of these alloys plays great roles in hope to understand the formation of oxide scale in water vapor condition at high temperature. This paper reviews previous research works to understand the initial stage oxidation of Fe - 9 to 12%Cr alloys at high temperature in water vapor condition.

Nanoparticles ZnO thin films have been deposited using sol-gel spin coating technique. A 0.4M sol of ZnO had been prepared by dissolving zinc acetate dihydrate in monoethanolamine (MEA), and 2-methoxyethanol as a stabilizer. Thin films are then spin coated onto quartz substrate with rotation speed of 3000rpm. After each layer, the samples were heated at 150 oC and annealed at 550 oC; which are defined as layer-by-layer process. The aim of this paper is to study the effect of annealing time to the structural, electrical and optical properties of the films. XRD result shows highest peak observed from sample annealed for 1 hour at (102) and (002) orientation. Calculation shows that the film annealed for 1 hour gives lower resistivity at 92.29Ω.cm which is due to the oxygen adsorption and good crystalline quality. Photoluminescence measurements exhibit UV emission centred at 380 nm and yellow-orange emission centred at 580 nm. Optical transmittance of the films show transparency above 70% for sample annealed for 30 minutes.

Sol-gel spin coated PMMA:TiO2 nanocomposite thin films on glass substrates were studied by comparing two types of the sol-gel solutions. Two types of PMMA:TiO2 nanocomposite sol-gel solutions were prepared; one using Degusa (P25), and the other one is using self-prepared TiO2 powder. The self-prepared nanosized TiO2 powder is obtained by drying the TiO2 sol-gel using solvothermal method followed by grinding the TiO2 crystal using ball miller. Triton-X was used as surfactant to stabilize the composite. Besides comparing the nanocomposite solution, we also studied the effect of the thin films thickness on the optical properties and their surface morphology. The optical properties and surface morphology were measured with UV-VIS spectrometer and atomic force microscopy (AFM). The result showed that nanocomposite PMMA with self-prepared TiO2 give high optical transparency than that of with Degusa (P25). The results also indicate that as the thickness is increased the optical transparency are decreased. Both AFM images showed that the agglomerations of TiO2 particles occurred on top of the thin film and the surface roughness increased when the thickness is increased. AFM results show that nanocomposited PMMA with P25 has high agglomeration particles compared to the other one.

Transparent nanoparticles ZnO thin films have been deposited on glass substrates using sol-gel spin coating technique. 0.35M sol were prepared by dissolving zinc acetate dehydrate in 2-methoxyethanol with monoethanolamine as the stabilizer. In this paper, a novel method called layer-by-layer is introduced, where the thin film is not only dried after each layer is spin-coated, but also directly annealed at 500oC to improve the electrical and optical properties of the films. Samples without annealing were also prepared as the reference sample. ZnO thin films were characterized using current-voltage measurement, UV-Vis spectroscopy and photoluminescence spectroscopy. The results revealed that layer-by-layer ZnO thin films have lower resistivity compared to the reference samples with a maximum value of 0.77Ω.cm for ZnO films deposited with 2 layers. Transmittance spectra show that the films were transparent in the visible range above 400nm with range of 86%-98% for the layer-by-layer ZnO films. The optical band gaps were between 3.2 to 3.3eV for both layer-by-layer and the reference samples. PL spectra indicate that layer-by-layer method improves the crystallinity of the films.

A poly(methyl methacrylate)-doped titanium dioxide (PMMA:TiO2) nanocomposite film was obtained by spin coating the nanocomposite solution onto a silicon substrate. The nanocomposite solutions were prepared by dissolving the PMMA and TiO2nanopowder in three different types of organic solvent, namely, toluene, tetrahydrofuran (THF), and acetone. We found that the dielectric properties of the PMMA:TiO2nanocomposite are dependent on the type of solvent used. The dielectric properties measured at a frequency of 1 kHz showed that acetone gives the highest dielectric constant and capacitance compared with toluene and THF. Toluene gives the lowest dielectric loss among the three. The topography and roughness of the PMMA:TiO2nanocomposite indicate that a particular solvent results in a different kind of surface morphology.