Rozidawati Awang

Characterization of multilayer graphene prepared from short-time processed graphite oxide flake

Multilayer graphene has been prepared by thermal reduction of graphene oxide film. The graphite oxide flake was first synthesized by using modified Hummers method with a relatively small amount of oxidizing agent and short-time processing at ambient temperature. The graphite oxide flake was dispersed in deionized water and deposited on quartz substrates to form graphene oxide film. The red shift of absorption peak and decrease of interlayer distance as interpreted from the X-ray diffraction spectrum indicate the formation of multilayer graphene. The resultant multilayer graphene has been successfully used as counter electrode in FTO/ZnO nanorods/electrolyte/multilayer graphene dye sensitized solar cell.

Influence of radio frequency power on thermal diffusivity of plasma enhanced chemical vapor deposition-grown hydrogenated amorphous carbon thin-films

Thermal diffusivity (α) of hydrogenated amorphous carbon (a-C:H) thin-films was characterized using the picosecond thermoreflectance measurement technique in the present study. The samples were fabricated in a plasma enhanced chemical vapor deposition system with varying radio frequency (RF) discharge powers from 15 to 70 W. Chemical bonding properties of the a-C:H films were determined from the Fourier transform infrared spectra and Raman spectroscopy. Results show that α is enhanced from 0.07 to 0.20 mm2 s−1 as the RF power increases. It attributes to the dehydrogenation of film resulting from the bombardment of high-energy ion species that breaks C–H bonds at the lower power regime. Particularly at the highest RF power, however, the increase of α is more influenced by the restructuring of bonding configuration associated with the breaking up of sp2 clusters into smaller ones.

Effects of Deposition Time Duration on Thermal Diffusivity of Hydrogenated Amorphous Carbon Films

In the present investigation we study the effects of film-deposition time duration on thermal diffusivity (α) of hydrogenated amorphous carbon (a-C:H) thin-films grown in a radio-frequency (RF) plasma enhanced chemical vapor deposition system. A set of films was deposited at 50 W RF power for 40, 60, 80, and 100 min. Film characteristics were determined from the optical transmission spectroscopy, Fourier Transform Infrared spectroscopy, and Raman spectroscopy. Thermal diffusivity of a-C:H films was evaluated using the optical pump-and-probe technique on the aluminum-coated samples. Results show a trend of increase in α as the deposition time increases due to the microstructural changes associated with longer exposure to ion bombardment effects on the growth surface of the films.

Formation of chemical bonds and morphological studies of a-CNx : Effects of PECVD deposition pressure

We report the structural difference and film properties of amorphous carbon nitride (a-CNx) thin films as a function of PECVD deposition pressure using precursor gases of ethane (C2H6) and nitrogen (N2). The Fourier transform infra-red (FTIR) spectra reveal peaks of single C-N (1100 cm−1), double C=C (1500 cm−1), double C=N (1670 cm−1) and triple C≡N (2340 cm−1). A systematic change in the preferential peaks correspond to the C=N and C≡N triple bonds were found to increase as deposition pressure increased. Field emission scanning electron microscopy (FESEM) provides morphological structure of the film. From the samples prepare at low deposition pressure, the particles tend to agglomerate into clusters with non-homogenous grains distributed over the surface. Higher deposition pressure results in coalescence process of the film, reflecting the formation of grains evenly distributed on the film. The film morphology is increased in voids structure with increase in deposition pressure. Finally, the samples were successfully prepared by PECVD technique with deposition pressure in varied, and the effect of deposition pressure on the chemical bonding and the morphology of the films had been studied.We report the structural difference and film properties of amorphous carbon nitride (a-CNx) thin films as a function of PECVD deposition pressure using precursor gases of ethane (C2H6) and nitrogen (N2). The Fourier transform infra-red (FTIR) spectra reveal peaks of single C-N (1100 cm−1), double C=C (1500 cm−1), double C=N (1670 cm−1) and triple C≡N (2340 cm−1). A systematic change in the preferential peaks correspond to the C=N and C≡N triple bonds were found to increase as deposition pressure increased. Field emission scanning electron microscopy (FESEM) provides morphological structure of the film. From the samples prepare at low deposition pressure, the particles tend to agglomerate into clusters with non-homogenous grains distributed over the surface. Higher deposition pressure results in coalescence process of the film, reflecting the formation of grains evenly distributed on the film. The film morphology is increased in voids structure with increase in deposition pressure. Finally, the samples wer...

Optimizing rf Power for Preferential C≡N Bond Formation in a-CNx Thin Films Prepared by rf-PECVD Technique

Effects of rf power on the chemical bonding in carbon nitride films deposited using radio-frequency (rf) plasma enhanced chemical vapor deposition in pure methane and nitrogen gas mixtures were investigated. The rf power was varied from 60 to 100 W. The deposition rate of the films increased constantly with increasing rf power up to 80W, before saturating with further increase in rf power. Fourier transform infra-red spectroscopy (FTIR) studies showed a systematic change in the spectra and revealed three main peaks namely the G-peak, D-peak and C≡N triple bond. This work showed that rf power has significant effects on the chemical bonding of the a-CNx films and the optimum rf power for the high C≡N absorption intensity is 80 W.

Influence of Power and Film Thickness on the Properties of Rf PECVD Hydrogenated Amorphous Carbon Films

Two sets of hydrogenated amorphous carbon (a‐C:H) films were deposited with different thicknesses at rf powers of 15 W and 50 W by varying the deposition time from the rf discharge of pure methane using our home‐built plasma enhanced chemical vapour deposition (PECVD) system. The growth rate, optical energy gap, bonded hydrogen and the sp2 content in the films were obtained from the optical transmission and Fourier transform infrared (FTIR) of the films. The growth rate, hydrogen content and optical energy gap were found to be strongly dependent on rf power. The higher rf power reduced hydrogen content in the film which resulted in increase in sp2 content in the film structure with increase in film thickness. The optical energy gap decreased with increase in film thickness for both the higher and lower rf power films.

Photoacoustic measurements on thermal properties of hydrogenated amorphous carbon films: the effect of hydrogen dilution

Thermal properties of hydrogenated amorphous carbon (a-C:H) thin-films are measured using an ultrafast optical pump-probe technique. The a-C:H samples were grown in a home-built direct-current (DC) plasma enhanced chemical vapor deposition (PECVD) system with varying hydrogen (H2) diluents to methane (CH4) flow-rate ratios. Thermal diffusivities of samples are extracted by comparing thermoreflectance measurements with numerical calculations so that thermal conductivities (k) can be determined. Although the dependence of thermal property on H2 dilution was not significant, our films show lower k (0.10–0.15 W/mK ± 20%) compared to the results of previous studies.

Dependence of Radio Frequency Power on Optical, Chemical Bonding and Photoluminescence Properties of Hydrogenated Amorphous Carbon Nitride Films

Hydrogenated amorphous carbon nitride films (a-CNx:H) were prepared in a radio-frequency plasma enhanced chemical vapour deposition (r.f. PECVD) system with a parallel-plate configuration. The gas sources of CH4 and N2 were fixed at CH4:N2 ratio of 1:3. The films were grown on glass and Si substrates on the grounded electrode at 100degC. The effect of r.f. power (varied between 0.71 - 3.54 W/cm2) on the optical, infrared (IR) absorption spectra and photoluminescence (PL) spectra of the a- CNx:H films were studied. It was observed that the deposition rate increases linearly up to the r.f. power of 2.83 W/cm2 , while the optical band gap (E04) decrease exponentially in the whole range. This is proposed to be the effect of an increase in nitrogen incorporation into the sp2 carbon clusters, as indicated by FTIR. The PL spectra consist of a band in the region of 2.10-2.40 eV, with peaks at approximately 2.23, 2.27 and 2.33 eV. The PL intensity of the films increases as the r.f. deposition power increases and is related to the increase of the sp2 clusters with increasing nitrogen incorporation.

Effect of graphite oxide solution concentration on the properties of multilayer graphene

This paper reports the influence of graphite oxide (GO) solution concentration on the optical and electrical properties of multilayer graphene (MLG) films. Graphene oxide (GrO) films were deposited on the glass substrates by spin coating aqueous solutions of GO with different concentrations (7, 8, 9, 10 and 11 mg/ml). The GrO films were then thermally reduced at temperature of 500°C in argon flow for half an hour to form MLG films. Both the transmittance and sheet resistance decreased with the GO concentration from 8 mg/ml to 9 mg/ml, possibly due to thicker and uniform coverage of MLG over the substrate. However, the transmittance and sheet resistance increased rapidly as the GO concentration reached 11 mg/ml, which can be attributed to poor film quality. The MLG film obtained at concentration of 10 mg/ml showed the highest transmittance/sheet resistance ratio with 69 % transmittance and sheet resistance of 292 ± 63 kΩ/sq. The optimum MLG film was utilized as counter electrode in dye sensitized solar cells based on ZnO nanorods.

The Effects of Deposition Pressure on the Optical and Structural Properties of d.c. PECVD Hydrogenated Amorphous Carbon Films

A direct-current plasma enhanced chemical vapour deposition (PECVD) system was designed and built in-house for the deposition of hydrogenated amorphous carbon(a-C:H) thin films. In this work, a-C:H thin films prepared using this system at different deposition pressures were studied. The influence of deposition pressure on the deposition rate, energy gap, bonded hydrogen content and structure of the film has been investigated. The characterization techniques were determined from optical transmission spectroscopy, Fourier transform infrared spectroscopy and Xray diffraction measurements. The results demonstrated that the deposition pressure had strong influence on the deposition rate, optical energy gap and the bonded H content in the film. Evidence of crystallinity was observed in films prepared at low deposition pressure.