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Introduction


Group III nitrides have attracted much attention recently because of their wide spectrum of potential applications ranging from optoelectronic devices for the blue ultraviolet spectral region [1] to high temperature devices [2]. The high bond strength of gallium to nitrogen presents a challenge to achieving good etching characteristics in GaN. A number of methods have been employed to etch GaN and its related compounds, including photochemical wet etching [3] dry etching utilizing high density plasmas [4] and conventional reactive ion etching [5]. However, to fabricate GaN-based optoelectronic devices successfully, reproducible etching processes with high etch rate and vertical etch profile are required. Recently, dry etching techniques using high density electron cyclotron resonance (ECR) plasmas or chemically assisted ion beams (CAIBE) have been employed to define device features with controlled profiles and etch depths [6-8]. While most studies on dry etching are focused on the etch properties related to the etch equipment and etch process parameters such as plasma chemistry, source power, bias voltage, etc., detailed studies on the dry etching characteristics of GaN-based materials based on the plasma diagnostic and surface analysis have been little reported.


Materials and Methods


The material used here is nominally n-type GaN wafers. Four samples were used and prepared using similar photolithographic process. Before patterning, the samples were cleaned, dipped in DI water and dried using N2 gas. Photo resist was spin coated onto all samples, forming ~ 1.5 µm layer. After that, all of them were etched by inductively coupled plasma etching using various gases in Oxford Plasma 80 system. The gallium was etched using combination of Cl2/Ar at operational pressure for 20 mTorr while ICP power, substrates temperature and RF power were fixed at 100 W, 17C and 600 W, respectively. For this experiment, the Ar flow rate was varied from 0 sccm to 60 sccm meanwhile the Cl2 flow rates at 60 sccm. After that, an individual sample was loaded into the chamber, centered on platters with the oxidized side exposed to the upper electrode. Immediately after samples removed from etching system, they were dipped into acetone to remove the photoresist. The etch rates were measured from the depth of the etched features with a scanning electron microscope (SEM) after the removal of the PR layer. Surface morphology, etch anisotropy, wall angle and sidewalls undercutting of the etched GaN was evaluated with SEM model JSM-6460 LV while ULTRAObjective AFM is used to measure the surface roughness.
Results and Discussion

For these experiments, etch rates were studied as a function of addition of Ar and DC bias. Prior to etching patterned samples, a simple set of experiments were conducted to get an understanding of how changes in Ar affect the etch rate. It was found that the etch rates were found to increase significantly between 0 sccm to 60 sccm of Ar, peaking around 20 sccm and then dropping off slightly around 24 sccm. For gas Ar flow rates of 24 sccm and higher, it was found that the etch process decrease.





Fig. 3 Cross-sectional SEM micrograph of the etched patterns; (a) 20 mTorr. Process condition: Cl2/Ar = 60/20 sccm, RIE power = 100 W, RF Power = 600 W, electrode temperature = 17 C.

Conclusion

We have shown the effects of Ar to Cl2 interaction in ICP process. The highest etch rate obtained at 20 sccm of Ar. It was explained as if the Ar concentration is high (> 30%) polymerization occurs on all surfaces and etching stops. We have also shown that DC voltage decreased as the flow rate of Ar increased. Furthermore, the etched surface is of anisotropic type and has smooth sidewalls.


Acknowledgements

This work was conducted under IRPA RMK8 strategic research grant. The support from Universiti Sains Malaysia is gratefully acknowledged.



References

  1. S. Nakamura and G. Fasol, The Blue Laser Diode: GaN Based Light Emitters and Lasers (Springer, Berlin, 1997).

  2. Q. Chen, M. Gaska, M. Asif Khan, M. S. Shur, A. Ping, I. Adesida, J. Burm, W. J. Schaff, and L. F. Eastman, (1997), Electron. Lett. 33, 637.

  3. C. Youtsey, I. Adesida, and G. Bulman, Appl. Phys. Lett. 71, 2151 (1997).

  4. R. J. Shul, G. B. McClellan, S. J. Pearton, C. R. Abernathy, C. Constantine, and C. Barratt, (1996), Electron. Lett. 32, 1408.

  5. D. Basak, M. Verdu, M. T. Montojo, M. A. Sanchez-Garcia, F. J.Sanchez, E. Munoz, and E. Callej, (1997), Semicond. Sci. Technol. 12, 1654.

  6. C. Caillat et. al, Solid State Electronics, 46 (2002).

  7. P.J Matuso, B.E.E Kasteimeier, J.J. Buelens, and G.S Oehrlein, (1997), J. Vac. Sci. Sci. Technol. A, 15, 4.

  8. I. Hassan, C.A. Pawlowics, L.P Berndt, and N.G. Tarr, (2002), J. Vac. Sci. Sci. Technol. A, 20, 3.

RO24


Interactions and Characterizations of Shorea Collina Spp. and Parashorea Sp. using CO2 Laser
Nor Fadhlin Jaafar, Mohamad Suhaimi Jaafar, Khalid M. Omar and Izyani Karudin
Medical Physics Research, School of Physics, Universiti Sains Malaysia,

11800 Minden, Pulau Pinang

Carbon dioxide laser (CO2 laser) was one of the most efficient infrared lasers. In this study, CO2 laser is used to penetrate the balau (Shorea Collina Spp.) and gerutu (Parashorea Sp.).Correlation between average surface diameter and average depth penetration with time, incident angles and power density is obtained. Lasing process occurred between 9 to 12 minutes, 0° to 50° incident angles and power density range from 10 W/cm2 to 23 W/cm2. After laser exposure, each of the wood samples is immersed in water and ultrasound technique is used to measure the surface diameter and depth penetration of the burned portion. For both samples, the time of exposure is varies linearly with depth penetration non-linearly with surface diameter. Power density of the laser is inversely proportional to the surface diameter and depth penetration.Layer of charcoal appeared only on Parashorea Sp. surface. This is due to the fact that Shorea Collina Spp. has a high density of 800-880 kg/m3 compared to Parashorea Sp. with 640-770 kg/m3. The finding shows that the most suitable angle for fine cutting with smallest surface diameter and deepest depth penetration is 0˚. This is due to the angular divergence in the laser beam, formed within the near and far zone. In the far zone, angular divergence increases with diameter. The findings obtained can be utilized in the selection of laser parameters for fine cutting of Shorea Collina Spp. and Parashorea Sp.



RO25


Plasmid Library Production from Local Medicinal Plant, Gardenia jasminoides
Zaidah Rahmat, Nor Kamila Kamaruzaman and Siti Intan Rosdianah Damis
Biology Department, Faculty of Science, Universiti Teknologi Malaysia, 81310 UTM Skudai,

Johor, Malaysia.

Attributing approximately 90% of the newly discovered pharmaceuticals, medicinal plants continue to be a powerful source of new drugs. One such local medicinal plant, Gardenia jasminoides, is gaining use in therapeutic aid for alleviating human ailments. Advancement in biotechnological methods of DNA-based study facilitates the determination of the suitable restriction enzyme for genomic DNA digestion and comparison of transformation method towards the plasmid library construction and subsequently, the screening procedure. Partial digestion of genomic DNA was achieved with HindIII restriction enzyme after 1 hour and 15 minutes digestion. Chemical transformation was a better method for library construction compared to Magic E.coli transformation method, giving higher transformation efficiency at 4 x 106 as compared to 8 x 104 for the latter method. PCR was used to evaluate the library in which 77% clone of various sizes were obtained from the library.




RO26


Engineering the Maltose Binding Protein for Biosensing Application
Shafinaz Shahir1, Tony Cass2
1 Biology Department, Faculty of Science, Universiti Teknologi Malaysia, 81310 Skudai, Johor 2 Institute of Biomedical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom

The aim of this work is to the develop a reagentless fluorescent sensing system for the detection of metal ions using genetically engineered metal binding variants of the maltose binding protein (MBP) as the biorecognition element. MBP is a member of the periplasmic binding proteins that typically adopt two conformations: an open form in the absence of ligand and a closed form upon ligand binding. This ligand-mediated conformational change forms the basis of the sensing system. In developing such as sensor system this work will demonstrate the use of rational protein engineering techniques to (1) adapt the MBP as reagentless fluorescent sensors by coupling the binding characteristics of the protein to a single environmentally sensitive fluorescent group and (2) change the specificity of the MBP by introducing metal-binding sites based on the designs previously described in the literature into the receptor pocket of the protein. Protein engineering is defined as the ensemble of methods that allow the modification of the gene that codifies for a protein with the purpose of generating mutants or variants with the desired properties. The immobilisation of biomolecules is also a crucial aspect in the design and construction of biosensors. Hence, the use of biotin as a tag will be investigated as a method for site-specific attachment of the proteins onto a solid support. The resulting tagged metal-binding MBP variants will be assessed for their ligand binding properties via metal ion dependent fluorescence intensity changes in solution. The possibility of extending the sensor system to a solid platform will then be examined by site-specifically immobilising the tagged metal-binding MBP variants onto glass slides in a microarray format.



RO27


Photocatalytic Degradation of Dye Pollutants using SiO2/TiO2 Catalyst
Nazwin Ahmad
Mineral Research Centre, Department of Mineral and Geosdence,

Jalan Sultan Azlan Shah, 31400 Ipoh. Perak, Malaysia.

The photocatalytic degradation of methylene blue (MB) and methyl orange (MO) in aqueos solution with SiO2/TiO2 as catalyst have been carried out using UV light. The SiO2/TiO2 catalyst was prepared by deposition of titanium dioxide (TiO2) aver a silica gel as a support by hydrolysis and condensation reaction of TiO2, There are significant differences in adsorption of dyes on SiO2/TiO2 catalyst. The effect of various parameters such as catalyst loading and pH has been determined. The photocatalytic degradation rate of MB and MO using SiO2/TiO2 catalyst were faster than using pure TiO2. The effects of the calcination temperature and the TiO2 loading on the phdtooatalytic activity of SiO2/TiO2 catalyst were also discussed.




RO28


Optical Characterization of Au Thin Film Using Surface Plasmon Resonance Technique
I. Nurul Izrini, M.Y.W.Mahmood, A.T. Zainal, A.W. Zaidan
Department of Physics, Faculty of Science,

Universiti Putra Malaysia, 43400 UPM Serdang,

Selangor, Malaysia

The optical constant for various thickness of Au thin film was studied using Kretschmann method of Surface Plasmon Resonance (SPR) technique. The optical properties of very thin Au films have been evaluated by Fresnel analysis with optical boundary condition pertaining to the SPR at the gold-air interface. It is observed that the optical constants of real part (εr) not dependent to the Au film. For the thickness below 45 nm, εr values are at the range of -8.854 to -8.678 while the thickness above 45 nm, the values of εr is at the range of -10.448 to -10.057. For the imaginary part (εi), the values are constant with the thickness which is between 1.227 and 2.110. The optimum SPR excitation conditions and instrumental sensitivity was achieved at a sharply defined thickness of 49.32 nm. With decreasing film thickness below 45 nm, the resonance angle starts to shift to larger values. A substantial increased of the intrinsic resonance broadening parameter is observed below 61nm associated with an increasingly asymmetric SPR line shape.



RO29



Acidity Study of Mesoporous Alumina containing para-toluenesulfonic Acid Stabilized by n-octadecyltrichlorosilane
Sheela Chandren1, Zainab Ramli1 and Hadi Nur2
1Department of Chemistry, Faculty of Science,

Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia

2Ibnu Sina Institute for Fundamental Science Studies,

Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia

Aluminas are extensively used as catalyst, catalyst support and adsorption applications. With the development of large molecule hydrocarbon processes, mesoporous alumina which possesses high surface area with narrow pore size distribution has received a great deal of attention. Although mesoporous alumina possesses high mechanical and thermal stability, but its acid properties lack Bronsted acidity and showed only Lewis acid sites. In this study, para-toluenesulfonic acid (TsOH) is impregnated on mesoporous alumina in order to introduce Bronsted acidity. In order to avoid the leeching of TsOH from the mesoporous alumina, the surface of the samples were modified by the alkylsilylation of n-ocatdecyltrichlorosilane (OTS). The acidity of the samples that were coated and not coated with OTS were then determined using FTIR-Pyridine. The acidity study shows that only the sample coated with OTS showed the presence of Bronsted acidity, while samples without the surface modification by OTS displayed only Lewis acid sites. This proved that by modifying the surface of the TsOH impregnated on mesoporous alumina with OTS, the Bronsted acidity on mesoporous alumina by impregnation of TsOH is preserved.




RO30


The effect of Attachment of Polyaniline on Stannic Oxide-Titanium Dioxide Coupled Semiconductor in Photocatalytic Oxidation of 1-Octene
Hadi Nur, Izan Izwan Misnon, Lim Kheng Wei
Ibnu Sina Institute for Fundamental Science Studies,

Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia

Stannic oxide-titanium dioxide (SnO2-TiO2) coupled semiconductor photocatalyst loaded with polyaniline (PANI), a conducting polymer, possesses a high photocatalytic activity in oxidation of 1- octene to 1,2-epoxyoctane in the presence of aqueous hydrogen peroxide. The photocatalyst was prepared by impregnation of SnO2 and followed by attachment of PANI onto a TiO2 powder to give sample PANI-SnO2-TiO2. The electrical conductivity of the system becomes high in the presence of PANI. Enhanced photocatalytic activity was observed in the case of PANI-SnO2-TiO2 compared to PANI-TiO2, SnO2-TiO2 and TiO2. A higher photocatalytic activity in the oxidation of 1-octene on PANI-SnO2-TiO2 than SnO2-TiO2, PANI-TiO2 and TiO2 can be considered as an evidence of enhanced charge separation of PANI-SnO2-TiO2 photocatalyst as confirmed by photoluminescence spectroscopy. It suggests that photoinjected electrons are tunneled from TiO2 to SnO2 and then to PANI in order to allow wider separation of excited carriers.




RO31


15N Nitroxide Free Radicals Imaged by Field-Cycled Proton-Electron

Double-Resonance Imaging (FC-PEDRI) at Low Magnetic Field

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