Shafinaz Sobihana Shariffudin

Effects of annealing environments on the solution-grown, aligned aluminium-doped zinc oxide nanorod-array-based ultraviolet photoconductive sensor

We have fabricated metal-semiconductor-metal- (MSM-) type ultraviolet (UV) photoconductive sensors using aluminium- (Al-) doped zinc oxide (ZnO) nanorod arrays that were annealed in different environments: air, oxygen, or a vacuum. The Al-doped ZnO nanorods had an average diameter of 60 nm with a thickness of approximately 600nm that included the seed layer (with thickness ∼200 nm). Our results show that the vacuum-annealed nanorod-array-based UV photoconductive sensor has the highest photocurrent value of 2.43 × 10-4 A. The high photocurrent is due to the high concentration of zinc (Zn) interstitials in the vacuum-annealed nanorod arrays. In contrast, the oxygen-annealing process applied to the Al-doped ZnO nanorod arrays produced highly sensitive UV photoconductive sensors, in which the sensitivity reached 55.6, due to the surface properties of the oxygen-annealed nanorods, which have a higher affinity for oxygen adsorption than the other samples and were thereby capable of reducing the sensors dark current. In addition, the sensor fabricated using the oxygen-annealed nanorod arrays had the lowest rise and decay time constants. Our result shows that the annealing environment greatly affects the surface condition and properties of the Al-doped ZnO nanorod arrays, which influences the performance of the UV photoconductive sensors.

Optical and Electrical Characteristic of Layer-by-Layer Sol-Gel Spin Coated Nanoparticles ZnO Thin Films

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 500°C 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.

Self-Catalyzed Thermal Chemical Vapor Deposited ZnO Nanotetrapods

ZnO in various nanostructures forms have been widely studied for the application such as in solar cells, light emitting diodes, UV sensors and so on. In this paper, we have successfully deposited ZnO nanotetrapods using thermal chemical vapour deposition (TCVD) technique on layer-by-layer ZnO seeded catalyst, with Zn powder and O2 gas as source materials. We demonstrate that by using double furnace TCVD system, ZnO nanotetrapods can be deposited at lower temperature than the vapour temperature of the Zn powder. In this paper we report the effect of different deposition temperature (450 °C to 600 °C) on the surface morphologies, crystalline structure and optical properties of the ZnO nanotetrapods. FE-SEM micrographs show that the length of the nanotetrapods arms decreases with the increase of the deposition temperature. PL spectra show that the visible emission are very low compared to the UV emission which indicates that the ZnO tetrapod have very low intrinsic defect. The highest UV emission intensity is given by the sample deposited at 500 °C.

Hybrid organic-inorganic light emitting diode using ZnO nanorods as electron transport layer

We have successfully synthesized hybrid organic-inorganic light emitting diode using ZnO nanorods as the electron transport layer and MEH-PPV as the emitting layer. The ZnO nanorods were synthesized using self-catalyzed thermal chemical vapor deposition method. The current density-voltage curves prove that the conductivity of the ZnO nanorods was improved. The turn on voltage was reduced from 2V to 0.4V with the insertion of ZnO nanorods between the cathode and emissive layer. Sharp visible emissions centred at 540 and 580 nm were observed from the electroluminescence spectra under forward biasing. A broad emission at 590 nm with a shoulder peak at 640 nm was also detected.

Influence of metal catalyst for zinc oxide nanostructures grown by TCVD method for extended-gate FET sensor application

In this work, zinc oxide (ZnO) nanostructure was synthesized by thermal vapor deposition (TCVD) on various kinds of metal catalyst namely, gold (Au) and platinum (Pt). The thicknesses of the metal catalyst were varied (10 nm and 15 nm) to investigate the shape of the ZnO nanostructures. The metal catalyst was used as seed layer to facilitate the nucleation site for nanostructured growth. FESEM images showed that different shape of ZnO nanostructures were produced on the different type of metal catalyst with different thicknesses. We found that those on Pt catalyst were in the form of nanotetrapod and those on Au catalyst were nanorods. The ZnO nanostructure on Au was tested for its sensitivity in pH measurement for application in extended-gate field effect transistor sensor and a sensitivity of 38.2 mV/pH was achieved.

Characteristics of layer-by-layer ZnO nanoparticles thin films prepared with different deposition layer

Layer-by-layer ZnO nanoparticles thin films were deposited using sol-gel spin coating technique. Zinc acetate dihydrate, 2-methoxyethanol and monoethanolamine were used in the ZnO solution. Different numbers of film layers were employed to study their effects to the physical, electrical and optical properties of the thin films. XRD patterns showed that the films were single crystalline with highly c-axis orientation for films with higher numbers of deposition layers. Morphology studies revealed that the grain sizes increased with the number of layers. Resistivity of the film decreased with the increased number of layers with minimum value of 15.5 Ω.cm given by 6 layers film. The PL spectra exhibit highest UV emission for 6 layers film due to high crystalline quality of the thin film.

A study on ohmic contact of different metal contact materials on nanostructured Titanium Dioxide (TiO 2 ) Thin Film

Three different type of materials i.e Au, Pt, and Pd have been investigated as metal contact on Titanium Dioxide (TiO2) thin films. These metal contacts have been deposited using sputter coating method. Meanwhile sol-gel spin coating method has been chosen to deposits TiO2 thin film. The ohmic contact characteristic of the three materials has been studied using Current-Voltage measurement.

Influence of drying temperature on the structural, optical, and electrical properties of layer-by-layer ZnO nanoparticles seeded catalyst

Layer-by-layer zinc oxide (ZnO) nanoparticles have been prepared using sol-gel spin coating technique. The films were dried at different temperature from 100°C to 300°C to study its effect to the surface morphology, optical and electrical properties of the films. Film dried at 200°C shows the highest (0 0 2) peak of X-ray diffraction pattern which is due to complete decomposition of zinc acetate and complete vaporization of the stabilizer and solvent. It was found that the grain size increased with the increased of drying temperature from 100 to 200°C, but for films dried at above 200°C, the grain size decreased. Photoluminescence measurements show a sharp ultraviolet emission centred at 380nm and a very low intensity visible emission. Blue visible emission was detected for sample dried at temperature below 200°C, while for films dried above 250°C, the visible emission is red shifted. The films were transparent in the visible range from 400 to 800nm with average transmittance of above 85%. Linear IV characteristics were shown confirming the ohmic behaviour of the gold contacts to the films. A minimum resistivity was given by 5.08Ωċ cm for the film dried at 300°C.

Post annealing temperature effect on photoluminescence spectroscopy of ZnO thin film

This paper reports on the effect of annealing temperature on the photoluminescence (PL) properties of ZnO thin film. Sol-gel spin coating method was used to prepare the ZnO templates on silicon substrate. ZnO thin films were then deposited by thermal chemical vapor deposition technique by using Zinc Acetate dihydrate as a precursor. Deposited films are annealed at various temperatures; from 650°C to 850°C for 1 hour. The effect of annealing on the optical, structure and electrical properties is investigated. FE-SEM images shows sizes of ZnO nanothorn encapsulate in balls changes as the annealing temperature increased. The optical properties were characterized using photoluminescence (PL) spectrometer with 325nm UV light from a He-Cd laser at room temperature and the electrical properties were characterized using Current-Voltage (I–V) measurement.

Electrical & optical properties of nanocomposite MEH-PPV/ZnO thin film

Nanocomposite thin films consist of conjugated polymer; MEH-PPV and inorganic material; ZnO were deposited using low cost spin coating method. The thin films characteristics were investigated in term of their electrical and optical properties; as each of it were heated at different temperature. The electrical properties of the thin films were studied to identify whether the nanocomposite thin films have ohmic capability or vice versa. Optical properties of the thin films were characterized by photoluminescence measurement. This study will provide the evidence that the nanocomposite thin films produced give better performance and suitable for several applications especially in optoelectronic devices.