Sains Malaysiana 43(6)(2014): 833–842

Characteristics of Nanostructured Ca_xZn_(1-x)Al₂O₄ Thin Films Prepared by Sol-Gel Method

for GPS Patch Antennas

(Ciri Filem Nipis Ca_xZn(_1-x)Al₂O₄ Berstruktur Nano yang Dihasilkan Melalui Kaedah

Sol-Gel untuk GPS Tampalan Antena)

WAN NASARUDIN WAN JALAL¹, HUDA ABDULLAH¹*, MOHD SYAFIQ ZULFAKAR¹, SAHBUDIN SHAARI², MOHAMMAD THARIQUL ISLAM³& BADARIAH BAIS¹

¹Department of Electrical, Electronic and System Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

²Institute of Microengineering and Nanoelectronics (IMEN), Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

³The Institute of Space Science (ANGKASA), Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

Received: 28 March 2013/Accepted: 2 February 2014

ABSTRACT

Ca_xZn_(1-x)Al₂O₄ thin films (x = 0.00; 0.05; 0.10; 0.15 and 0.20) were prepared by sol-gel method with the substitution of Zn²⁺ by Ca²⁺ in the framework of ZnAl₂O₄. The effect of Ca addition on the structure and morphology of CaZnAl₂O₄ thin films was investigated by x-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), energy-dispersive x-ray spectroscopy (EDX), ultra-violet visible (UV-Vis) and atomic force microscope (AFM). The XRD patterns showed the characteristic peaks of face-centred cubic (fcc) ZnAl2O4 and CaZnAl₂O₄. The addition of Ca increased the crystallite size from 8.9 to 30.2 nm. The bandgap of Ca_xZn_(1-x)Al₂O₄ thin film was found in the range of 3.40 to 3.84 eV. SEM micrograph shows the morphology of all thin films is sphere-like, with the grain size increased from 33 to 123 nm. The AFM images show the roughness of surface morphology increased. The substitution of Zn²⁺ by Ca²⁺ increased the crystallite size, grain size and surface roughness which evidently increased the density (4.59 to 4.64 g/cm³) and dielectric constant (8.48 to 9.54). The composition of

Ca_xZn_(1-x)Al₂O₄ is considered as suitable material for GPS patch antennas.

 Keywords: Band gap; Ca-ZnAl₂O₄; GPS patch antena; nanostructures

ABSTRAK

Filem nipis Ca_xZn_(1-x)Al₂O₄(x = 0.00; 0.05; 0.10; 0.15 dan 0.20) telah dihasilkan dengan kaedah sol-gel iaitu menggantikan Zn²⁺ dengan Ca²⁺ di dalam bahan utama ZnAl₂O₄. Kesan terhadap penambahan Ca pada struktur dan morfologi filem nipis CaZnAl₂O₄ telah dianalisis dengan menggunakan pembelauan sinar-x (XRD), mikroskopi imbasan pancaran medan elektron (FESEM), x-ray serakan tenaga spektroskopi (EDX), cahaya nampak ultra lembayung (UV-Vis) dan mikroskopi daya atomik (AFM). Corak pembelauan XRD menunjukkan ciri-ciri puncak berpusat muka padu pada bahan ZnAl₂O₄ dan CaZnAl₂O₄. Penambahan Ca telah meningkatkan saiz kristal daripada 8.9 kepada 30.2 nm. Jalur tenaga bagi filem nipis Ca_xZn_(1-x)Al₂O₄ ialah antara 3.40 hingga 3.84 eV. Graf mikro SEM menunjukkan morfologi bagi kesemua filem nipis adalah berbentuk butiran dengan saiz butiran meningkat daripada 33 kepada 123 nm. Imej AFM menunjukkan berlakunya peningkatan pada permukaan morfologi Ca_xZn_(1-x)Al₂O₄. Penggantian Zn²⁺ dengan Ca²⁺ telah meningkatkan saiz butiran dan peningkatan kekasaran permukaan yang seterusnya memberi kesan terhadap ketumpatan bahan (4.59 kepada 4.64 g/cm³) dan pemalar dielektrik (8.48 kepada 9.54). Komposisi Ca_xZn_(1-x)Al₂O₄ dianggap sebagai bahan yang sesuai untuk penghasilan GPS tampalan antena.

Kata kunci: Ca-ZnAl₂O₄; GPS tampalan antena; jalurtenaga; strukturnano

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*Corresponding author; email: huda@vlsi.eng.ukm.edu.my