Ahmad Shuhaimi

Effects of graphene oxide concentration on optical properties of ZnO/RGO nanocomposites and their application to photocurrent generation

The effects of different concentrations of graphene oxide (GO) on the structure and optical properties of ZnO nanoparticles (NPs) were investigated. The nanocomposites were synthesized via the sol-gel method in a gelatin medium. X-ray diffraction patterns (XRD) and Fourier transform infrared spectroscopy indicated that the GO sheets were reduced and changed to reduced GO (RGO) during the calcination of the nanocomposites at 400 °C. In addition, the XRD patterns of the NPs indicated a hexagonal (wurtzite) structure for all the products. Microscopic studies showed that the NPs were decorated and dispersed on the RGO sheets very well. However, these studies revealed that the RGO concentration had an effect on the crystal growth process for the ZnO NPs. Furthermore, these studies showed that the NPs could be grown with a single crystal quality in an optimum RGO concentration. According to the XRD results that were obtained from pure ZnO NPs, the calcinations temperature was decreased by the RGO. UV–vis and room temperature photoluminescence studies showed that the optical properties of the ZnO/RGO nanocomposite were affected by the RGO concentration. Finally, the obtained ZnO/RGO nanocomposite was used to generate a photocurrent. Observations showed that the photocurrent intensity of the nanocomposite was significantly increased by increasing the RGO, with an optimum RGO concentration.

One-pot sol–gel synthesis of reduced graphene oxide uniformly decorated zinc oxide nanoparticles in starch environment for highly efficient photodegradation of Methylene Blue

ZnO NPs + reduced graphene oxide (rGO) nanocomposites were synthesized using a sol–gel method with starch as the polymerisation agent. Long-chain starch compounds were used to terminate the growth of the ZnO NPs on rGO and stabilise them. The resulting products were annealed at 350 °C to remove the starch and produce a reduced graphene oxide (rGO) sheet in one-pot without any post-annealing processes. Microscopic studies showed that the NPs were dispersed on the rGO sheet. They had a spherical shape and a size of approximately 25 ± 10 nm. In addition, these studies revealed that the NPs were single crystals. The X-ray diffraction pattern of the NPs indicated a hexagonal (wurtzite) structure. The results of Fourier transform infrared spectrum analysis (FTIR) revealed that the GO sheet was transformed into rGO via the sol–gel method in the starch environment. The results of photoluminescence spectroscopy demonstrated that the incorporation of reduced graphene oxide (rGO) sheets with ZnO NPs suppressed the electron–hole recombination of the composite. Therefore, a significant enhancement in the photocatalytic degradation of methylene blue (MB) was observed with the ZnO NPs + rGO nanocomposite compared to the bare ZnO nanoparticles.

Crystalline quality assessment, photocurrent response and optical properties of reduced graphene oxide uniformly decorated zinc oxide nanoparticles based on the graphene oxide concentration

Zinc oxide-nanoparticles (ZnONPs)–reduced graphene oxide (rGO) composites with a high degree of crystallinity and a high dispersity were successfully synthesized via a one-pot, facile sol–gel method in a starch environment, during which the formation of zinc oxide nanoparticles, the reduction of graphene oxide and the loading of the ZnONPs onto the rGO surface occur simultaneously. Starch, as a natural capping agent, plays a significant role in controlling the degree of dispersion and coverage of the ZnONPs. The effect of rGO on the crystalline structure and optical properties of the ZnONPs was determined via X-ray diffraction, UV-visible diffused reflectance spectroscopy and photoluminescence spectroscopy. The ZnONPs+rGO composites exhibit excellent potential for photocurrent generation compared with pure ZnONPs under visible light irradiation, provided that efficient photo-induced charge separation and transportation can be achieved at the interface. The maximum photocurrent response, crystalline quality and factor optical properties (NBE/DLE ratio) were obtained for the ZnONPs+rGO composite with a 1.7% mass fraction of rGO, which is twice that achieved on pure ZnONPs.

PEDOT:PSS Thin Film as Transparent Electrode in ITO-Free Organic Solar Cell

Two types of polar solvent materials; namely glycerol and ethylene glycol (EG) were used in this study as dopants for PEDOT:PSS. The 2 to 10% of doped PEDOT:PSS were synthesized using sol-gel technique and were spin-coated onto glass substrate. The optical, conductivity and morphological characteristics of the doped PEDOT:PSS thin films were measured via UV-VIS spectrometer, two-point probes technique and AFM measurement, respectively. All films show direct band gap behavior and compared to the pristine thin film, the doped PEDOT:PSS show higher transparency in visible range. Furthermore, the conductivity of glycerol and EG doped PEDOT:PSS thin films were also improved due to the changes in molecule alignment and interchain interaction in the thin films.

Effects of Pressure Dependence on Nanocolumnar Zinc Oxide Deposited by RF Magnetron Sputtering

Nanocolumnar zinc oxide (ZnO) was deposited on glass substrates by RF magnetron sputtering.It was performed with a ZnO target at RF power of 200 W. The deposition wascarried out in argon and oxygen ambient at the ratio of 10 and 5 sccmrespectively, with total deposition time of 1 hour. The growth temperature wasfixed at 500°C and deposition pressure specified at 3, 5 and 10 mTorr. It wasobserved that the morphological and photoluminescence properties of ZnOstrongly dependent on the deposition pressure. The ZnO mean grain area was inverselyrelated with the surface roughness. The best morphological andphotoluminescence properties was found to be associated with ZnO grown at 10mTorr. Smooth ZnO surface and lowest defects related emission in PL wasobtained for the respective sample.

Study of Annealed Nickel (Ni)/Indium Tin Oxide (ITO) Nanostructures Prepared by RF Magnetron Sputtering

Nickel (Ni) / indium tin oxide (ITO) nanostructures were deposited on glass and silicon (111) substrates by RF magnetron sputtering using a nickel target and ITO (In-Sn, 90%-10%) targets. The post-deposition annealing has been performed for Ni/ITO films in air and the effect of annealing temperature on the electrical, optical and structural properties on ITO films was studied. We found the appearance of (411) and (622) peaks in addition to (400) and (222) major peaks, which indicates an improvement of the film crystallinity at high annealing temperature of 650°C. The samples show higher transmittance of more than 90% at 460 nm after annealing. In addition, increasing the annealing temperatures also improve the film electrical properties. The resistivity decreases to 6.67×10-6 Ωcm when annealed at 500°C as opposed to 6.75×10-5 Ωcm in as-deposited film.

Post-Annealing Effects on ITO Thin Films RF Sputtered at Different Thicknesses on Si and Glass

We report on electrical, optical and surface morphological characteristics of indium tin oxide (ITO) thin films. The ITO was deposited by radio frequency (RF) magnetron sputtering on Si and glass substrates at different thicknesses of 125 nm and 239 nm. Post-annealing treatment was conducted on the samples at temperature of 500°C and 600°C. From Hall Effect measurement, the lowest resistivity was measured as 4.4 × 10-4 Ωcm and 4.5 × 10-4 Ωcm corresponding to the 239 nm and 125 nm ITO sample, respectively, after post-annealed at 600°C. Using UV-Vis spectrophotometer, the highest transmittance of ~84% at 470 nm was observed with respect to the 125 nm ITO thin films after post-annealed at 500°C. Furthermore, the 500°C post-annealed 125 nm thin film shows highest carrier concentrations of more than 1021 cm-3 and smoothest surface morphology of 0.5 nm root-mean-square, RMS. It is clearly shown that post-annealing treatment on ITO thin films is able to enhance the electrical and optical transmittance properties as compared to the as deposited films.

Structural and Optical Properties of Nickel (Ni)/indium Tin Oxide (ITO) Thin-Films Deposited by RF Magnetron Sputtering

Nickel (Ni)/ indium tin oxide (ITO) thin-films have been deposited on silicon (Si) and glass substrates using radio-frequency (RF) magnetron sputtering at 200°C temperature. ITO layer was deposited on top of Ni layer with various deposition parameter. The material and optical properties of the ITO samples with and without Ni seed layer were analyzed. X-ray diffraction studies shows that the films are crystalline with the typical ITO diffraction peaks of (222), (400) and (411). The FESEM and AFM images shows that the grains have uniform shapes and sizes. FESEM results reveal that the grain size along the sample surface decreases when the Ni seed layer is added. Both the samples shows higher transmittance of more than 95% in UV-vis spectrometer.

Structural and Optical Properties of Nickel-Doped Zinc Oxide Thin Film on Nickel Seed Layer Deposited by RF Magnetron Sputtering Technique

Nickel (Ni)-doped zinc oxide (ZnO) layers were deposited simultaneously by radio frequency (RF) magnetron sputtering from a Ni and ZnO target. A Ni seed layer was used as catalyst prior to the deposition of Ni-doped ZnO. The Ni seed layer was grown with 15 sccm of Ar flow rate while the Ni-doped ZnO was grown with mixture of Ar:O2 at 25:5 sccm gas flow rate ratio. The deposition pressure is 5 mTorr for both Ni seed layer and Ni-doped ZnO layer. This paper studies the influence of deposition temperature to the Ni seed layer and Ni-doped ZnO layer at temperature range from room temperature (RT) until 500°C with an increment of every 100°C. The sample was characterized using field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD) and UV visible spectroscopy (UV-vis) to determine the structural, crystallinity and optical properties of the deposited layer. FESEM surface analysis shows that uniformity of the nanocolumns is improved when deposition temperature is increased. The transmittance of the deposited nanocolumns was improved when temperatures are increased to 500°C.

Effects of Growth Temperature on the Structural Properties of Zinc Oxide Nanograins Deposited by RF Magnetron Sputtering

Nanograins zinc oxide (ZnO) with c-axis preferred orientation was deposited on glass substrates by RF magnetron sputtering. It was performed with a ZnO target with 99.999% purity at RF power of 200 W. The deposition was carried out in argon and oxygen ambient at the ratio flow-rates of 10 and 5 sccm respectively, with total deposition time of 1 hour. The films were grown atgrowth temperatures were specified at RT, 100, 200, 300, 400 and 500°C. The effects of the growth temperature on the ZnO structural property was investigated by x-ray diffraction (XRD). The best ZnO crystalline quality obtained at growth temperature, TG of 300°C was further characterized by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM).