Sains Malaysiana 49(6)(2020): 1461-1470

http://dx.doi.org/10.17576/jsm-2020-4906-24

Komposisi Ikatan Kimia dan Mekanisme Pertumbuhan Filem Nipis a-CN_x oleh Teknik rf-PECVD Suhu Rendah

(Chemical Bonding Composition and Growth Mechanism of a-CN_x Thin Films by Low-Temperature rf-PECVD Technique)

SITI AISYAH ABD AZIZ & ROZIDAWATI AWANG*

Program Fizik, Fakulti Sains dan Teknologi, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor Darul Ehsan

Malaysia

Received: 4 November 2019/Accepted: 13 February 2020

ABSTRAK

Dalam kajian ini, filem nipis karbon nitrida amorfus (a-CN_x) telah dimendapkan menggunakan teknik pemendapan wap kimia secara peningkatan plasma berfrekuensi radio, (radio-frequency plasma enhanced chemical vapor deposition, rf-PECVD). Sampel disediakan pada suhu substrat yang berbeza iaitu pada 80, 100, 120, 150 dan 180 ℃ dan kesannya ke atas morfologi, kadar pemendapan serta komposisi ikatan kimia sampel dikaji. Seterusnya, mekanisme pertumbuhan filem nipis a-CNx daripada campuran gas asetilena (C2H2) dan nitrogen (N2) dicadangkan. Ketebalan filem nipis dan morfologi filem nipis a-CNx diciri menggunakan mikroskop elektron imbasan pancaran medan (field emission scanning electron microscopy, FESEM). Manakala komposisi ikatan kimia diperoleh daripada pencirian menggunakan spektroskopi infra-merah jelmaan Fourier (Fourier transform infrared spectroscopy FTIR). Morfologi filem nipis a-CN_x kelihatan seperti kobis bunga yang padat dan butiran yang seragam. Manakala sampel yang dimendapkan pada suhu 100 dan 180 ℃ menunjukkan struktur butiran bersaiz nano pada keseluruhan permukaan filem. Kadar pemendapan filem nipis a-CN_x maksimum pada suhu pemendapan 120 ℃ dan minimum pada 180 ℃. Secara keseluruhannya, semua sampel menunjukkan kehadiran ikatan C-N, C=C, C=N, C≡N, C-H dan N-H/O-H iaitu ikatan yang berpadanan wujud dalam filem nipis a-CN_x. Dalam kajian ini, mekanisme pertumbuhan filem nipis a-CNx membincangkan pembentukan C-H, C-N dan keluaran sampingan HCN hasil daripada penguraian gas C₂H₂ dan N₂. Pertumbuhan filem a-CN_x juga disebabkan tindak balas kinetik semasa proses pemendapan iaitu penjerapan spesies karbon dan nitrogen pada permukaan pertumbuhan filem dan nyahjerapan spesies nitrida tepu, kesan daripada spesies bertenaga serta mobiliti spesies yang tinggi pada permukaan pertumbuhan. Maka, komposisi ikatan kimia dan kadar pemendapan filem dipengaruhi oleh keseimbangan antara molekul CN dengan atom C dan N mencapai permukaan pertumbuhan filem.

Kata kunci: FTIR; morfologi; saiz nano

ABSTRACT

In this study, amorphous carbon nitride (a-CN_x) thin films were deposited using radio-frequency plasma enhanced chemical vapor deposition (rf-PECVD) technique. Samples were prepared at different substrate temperatures of 80, 100, 120, 150, and 180 ℃ and the effect on morphology, deposition rate and chemical bonding composition were studied. Next, the growth mechanism of a- CN_x thin films using acetylene (C₂H₂) and nitrogen (N₂) as gas precursor. Film thickness and morphology of a-CN_x thin film were characterized using field emission scanning electron microscopy, (FESEM), while the chemical bonding composition was obtained using Fourier transform infrared spectroscopy (FTIR). The morphology of the a-CN_x thin film looks like a uniform structural shape of a cauliflower. Whereas samples deposited at 100 and 180 ℃ show nanosize granular structure on the entire surface of the film. Maximum deposition rate of a-CNx thin films at deposition temperature of 120 ℃ and minimum at 180 ℃. Overall, all samples show the presence of C-N, C = C, C = N, C≡N, C-H and N-H /O-H bonds, which are the corresponding bonds present in a-CN_x thin films. In this study, the growth mechanism of a-CN_x thin films discusses the formation of C-H, C-N and HCN by-products resulting from the decomposition of C₂H₂ and N₂ gas. The growth of a- CN_x films was also due to the kinetic reactions during the deposition process: the adsorption of carbon and nitrogen species on the surface of the film growth and the desorption of saturated nitride species, caused by energetic species, and the high mobility of the species on the growth surface. Thus, the chemical bonding composition and deposition rate of the film is influenced by the equilibrium between the CN molecules and the C and N atoms reaching the film growth surface.

Keywords: FTIR; morphology; nano size

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*Corresponding author; email: rozida@ukm.edu.my