Siti Meriam Ab. Gani

Effect of annealing on the optical and chemical bonding properties of hydrogenated amorphous carbon and hydrogenated amorphous carbon nitride thin films

Hydrogenated amorphous carbon (a-C:H) and hydrogenated amorphous carbon nitride (a-CNx:H) films were prepared in a custom-built radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) system with a parallel-plate configuration. Pure methane and a gas mixture of methane and nitrogen were used as gas sources to obtain these films. The films were characterized using Fourier transform infrared and optical transmission spectroscopy techniques. The incorporation of nitrogen and the effect of annealing (100–500 °C) on the film properties were studied. The films were determined to be thermally stable up to 300 °C. Upon annealing above 300 °C, the thickness and refractive index of both a-C:H and a-CNx:H films increase while the optical energy gap E04 decreases. These effects were more pronounced in a-CNx:H. From the IR spectra, these changes are considered to be due to the decreases in nitrogen and hydrogen concentrations in the films which result in their structural modification.

Influence of Hydrogen Dilution of Silane on the Properties of nc-Si:H films grown by Layer-by- Layer deposition technique

Hydrogenated nanocrystalline silicon (nc-Si:H) films produced by layer-by-layer (LBL) deposition technique were studied. The films were grown at different hydrogen to silane flow-rate ratio on crystal silicon (111) substrate. The properties of films were investigated by X-ray diffraction (XRD), micro-Raman scattering spectroscopy, Fourier transform infrared (FTIR) spectroscopy, optical transmission spectroscopy, atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). These properties showed dependence on the hydrogen dilution of silane. Appearance of XRD peaks at diffraction angles of 28.4 o and 56.1 o which correspond to silicon orientation of (111) and (311) respectively, were observed in all films indicating evidence of crystallinity in the films. Raman scattering results indicated that crystallinity in the films was due to the presence of nanocrystallites embedded in an amorphous matrix. The energy gap of the films showed dependence on the hydrogen content in the films. Increase in nanocrystallite size resulted in increase in disorder at low hydrogen dilution films but films remain homogenous with increase in nanocrystallite size for the high hydrogen dilution films.

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.

High Temperature Post-Deposition Annealing Studies of Layer-by-layer (LBL) Deposited Hydrogenated Amorphous Silicon Films

High temperature post-deposition annealing studies were done on hydrogenated amorphous silicon thin films deposited by plasma-enhanced chemical vapour deposition (PECVD) using the layer-by-layer (LBL) deposition technique. The films were annealed at temperatures of 400 o C, 600 o C, 800 o C and 1000 o C in ambient nitrogen for one hour. Auger electron spectroscopy (AES) depth profiling results showed that high concentration of O atoms were present at the substrate/film interface and at film surface. Very low concentration of O atoms was present separating silicon layers at regular intervals from the film surface and the substrate due to the nature of the LBL deposition and these silicon oxide layers were stable to high annealing temperature. Reflectance spectroscopy measurements showed that the onset of transformation from amorphous to crystalline phase in the LBL a-Si:H film structure started when annealed at temperature of 600 o C but the X-ray diffraction (XRD) and Raman scattering spectroscopy showed that this transition only started at 800 o C. The films were polycrystalline with very small grains when annealed at 800 o C and 1000 o C. Fourier transform infrared spectroscopy (FTIR), measurements showed that hydrogen was completely evolved from the film at the on-set of crystallization when annealed at 800 o C. The edge of the reflectance fringes shifted to longer wavelength decrease in hydrogen content but shifted to shorter wavelength with increase in crystallinity.

Influence of Hydrogen Plasma Treatment Time to Si:H Layer Deposition Time Ratio on the Properties of Layer‐by‐Layer Deposited Hydrogenated Silicon (Si:H) Thin Films

Hydrogenated silicon (Si‐H) thin films were deposited from a mixture of pure silane (SiH4) and hydrogen (H2) gases in a home‐built plasma enhanced chemical vapour deposition (PECVD) system using the layer‐by‐layer (LBL) deposition technique. In the LBL process, the deposition was performed by periodically alternating the deposition of Si:H layer with the hydrogen treatment process of the growth surface. In this work, the effects of the H pasma treatment time to Si‐H layer growth time ratio on the film properties were studied. The LBL deposited Si‐H films studied in this work were deposited using different Si‐H layer growth times ranging from 2 minutes to 7 minutes with the hydrogen plasma treatment time on the growth surface fixed at 3 minutes. Optical transmission spectroscopy, X‐ray diffraction (XRD), micro‐Raman scattering spectroscopy, Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) measurements were done on these films to investigate the optical, structural and morphological properties of the films. The films deposited by this technique produced the highest deposition rate of 6.3 A/s when the growth time of the Si‐H layer was fixed at 5 minutes. These films were amorphous in structure and had large optical energy gaps irrespective of the Si‐H layer deposition time. High concentration of cone‐like structures was observed in the AFM images for the films deposited using the higher Si‐H layer deposition times.Hydrogenated silicon (Si‐H) thin films were deposited from a mixture of pure silane (SiH4) and hydrogen (H2) gases in a home‐built plasma enhanced chemical vapour deposition (PECVD) system using the layer‐by‐layer (LBL) deposition technique. In the LBL process, the deposition was performed by periodically alternating the deposition of Si:H layer with the hydrogen treatment process of the growth surface. In this work, the effects of the H pasma treatment time to Si‐H layer growth time ratio on the film properties were studied. The LBL deposited Si‐H films studied in this work were deposited using different Si‐H layer growth times ranging from 2 minutes to 7 minutes with the hydrogen plasma treatment time on the growth surface fixed at 3 minutes. Optical transmission spectroscopy, X‐ray diffraction (XRD), micro‐Raman scattering spectroscopy, Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) measurements were done on these films to investigate the optical, structural and morpho...

Influence of Nitrogen/Methane Ratio on the Properties of Hydrogenated Amorphous Carbon Nitride Deposited by r.f. PECVD Technique

Hydrogenated amorphous carbon nitride (a‐CNx:H) thin films were prepared in a radio frequency plasma enhanced chemical deposition system with a parallel‐plate electrode configuration. The effects of nitrogen/methane flow rate ratio calculated on the a‐CNx:H thin films are studied in terms of the optical, bonding and photoluminescence (PL) properties. The increase in the flow rate ratio results in a decrease in the deposition rate which corresponds to an increase in ion bombardment effect and gas phase reactions. The optical energy gap E04, decreases while its PL intensity increases as the flow‐rate ratio increases up to 70%, followed by an increase in E04 and a decrease in PL intensity as the ratio is further increased. These are discussed in terms of the bonding and sp2 content in the films.Hydrogenated amorphous carbon nitride (a‐CNx:H) thin films were prepared in a radio frequency plasma enhanced chemical deposition system with a parallel‐plate electrode configuration. The effects of nitrogen/methane flow rate ratio calculated on the a‐CNx:H thin films are studied in terms of the optical, bonding and photoluminescence (PL) properties. The increase in the flow rate ratio results in a decrease in the deposition rate which corresponds to an increase in ion bombardment effect and gas phase reactions. The optical energy gap E04, decreases while its PL intensity increases as the flow‐rate ratio increases up to 70%, followed by an increase in E04 and a decrease in PL intensity as the ratio is further increased. These are discussed in terms of the bonding and sp2 content in the films.

Nanostructured silicon thin films prepared by layer-by-layer deposition technique

Nanostructured silicon thin films prepared by layer-by-layer deposition technique were studied. The films were grown at different deposition conditions such as radio-frequency (rf) power, hydrogen to silane flow-rate ratio and substrate temperature. The effect of these deposition conditions on the surface morphology, hydrogen bonding property and crystallinity of the films were studied. These properties were investigated using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), micro-Raman spectroscopy and X-ray diffraction (XRD). The results showed various morphological features of nanostructured silicon thin films which consist of clusters of nanocrystallites surrounded by grain boundaries. Raman results showed the presence of crystalline phase in these films which was contributed by the nanocrystallites. FTIR results demonstrated presence of Si-H2 bonds which we believe were present in the grain boundaries separating the nanocrystallites from each other in the clusters and also Si-H bonds which were present in the amorphous phase separating the clusters.

Morphology and electrical conductivity of copper(II) 4-fluorobenzoate

Copper(II) 4-fluorobenzoate (CFB), prepared from copper(II) acetate monohydrate and 4-fluorobenzoic acid, is a blue powder. The Fourier transform infrared spectrum of CFB, recorded as potassium bromide disc, indicates the presence of all bonds and functional groups expected of it. The X-ray diffraction pattern indicates that CFB is polycrystalline. The highest diffraction peak occurs at interplanar distance of 15.2 /spl Aring/, which corresponds to particle size of 450 /spl Aring/. Scanning electron microscopy of CFB shows that it has a layered structure. CFB conductivity at room temperature is 1.79/spl times/10/sup -11/ Scm/sup -1/. The value decreases as temperature increases in the temperature range 30-350 K, indicating metallic behaviour. The conduction mechanism obeys Motts variable range hopping (VRH) model in the temperature range 140-350 K. The density of states at Fermi level based on the VRH model is 2.9/spl times/10/sup 26/ eV/sup -1/ cm/sup -3/. The hopping distance, hopping energy and density of charge carriers at 300 K are 0.73 /spl Aring/, 0.002 eV and 7.53/spl times/10/sup 24/ cm/sup -3/, respectively.