Sains Malaysiana 43(2)(2014): 273–281

Synthesis and Characterization of Cu-doped ZnO Nanorods

(Sintesis dan Pencirian Cu-terdop Nanorod ZnO)

S.Y. PUNG*¹, C.S. ONG¹, K. MOHD ISHA²& M.H. OTHMAN²

¹School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, Seri Ampangan, 14300 Nibong Tebal, Pulau Pinang, Malaysia

²Advanced Materials Research Centre, SIRIM Berhad, Lot 34, Jalan Hi-Tech 2/3,

Kulim Hi-Tech Park, 09000 Kulim, Kedah, Malaysia

Received: 7 January 2013/Accepted: 17 July 2013

ABSTRACT

Cu-doped ZnO nanorods were synthesized by sol-gel method using zinc nitrate tetrahydrate, methenamine and cupric acetate monohydrate as precursors. The as-synthesized ZnO nanorods have a twin-rod structure. The polar (002) surface of ZnO nanorods, which could be either negatively charge (O-terminated) or positively charged (Zn-terminated), was responsible for the formation of twin-rod structure. The results showed that the size, aspect ratio, crystallinity and c-lattice parameter of Cu doped ZnO nanorods decreased with increasing of Cu dopant concentration. In fact, the presence of Cu retarded the growth of ZnO nanorods in its preferred growth direction, i.e. (0001). The XPS analysis indicates that Cu ions were oxidized (Cu²⁺) and substituted into the ZnO lattice at the Zn²⁺ site. The presence of Cu reduced the optical bandgap of ZnO from 3.34 eV (undoped ZnO nanorods) to 3.31 eV (20 mol% Cu doped ZnO). Besides, it induced a visible PL emission at 2.97 eV, which could be related to the transition of electrons from conduction band (E_c) to Cu acceptor energy level (E_v + 0.45 eV) radiatively.

Keywords: Copper; in-situ doping; semiconductor; sol-gel processes; ZnO nanorods

ABSTRAK

Cu-terdop nanorod ZnO telah disintesis dengan kaedah sol-gel dengan menggunakan zink nitrat tetrahidrat, metenamin dan kuprik asetat monohidrat sebagai prapenanda. Nanorod ZnO yang disintesis ini mempunyai struktur rod berkembar. Permukaan (002) nanorod ZnO yang berkutub, sama ada caj negatif (dipangkalkan oleh O) atau caj positif (dipangkalkan oleh Zn), bertanggungjawab untuk pembentukan struktur rod berkembar ini. Keputusan menunjukkan bahawa saiz, nisbah bidang, kehabluran dan parameter kekisi-c Cu-dop nanorod ZnO ini menurun dengan meningkatnya pendopan kepekatan Cu. Sebenarnya, kehadiran Cu menghalang pertumbuhan nanorod ZnO dalam halaan pertumbuhan yang diutamakan, iaitu (0001). Analisis XPS menunjukkan bahawa ion Cu telah dioksidakan (Cu²⁺) dan digantikan dalam kekisi ZnO di kedudukan Zn²⁺. Kehadiran Cu juga mengurangkan jalur tenaga optikal ZnO daripada 3.34 eV (nanorod ZnO tanpa dop) ke 3.31 eV (20 mol% ZnO Cu-terdop). Tambahan lagi, ia menghasilkan pancaran PL di 2.97 eV, yang boleh dikaitkan dengan peralihan elektron dari jalur konduksi (Ec) kepada paras tenaga Cu penerima (E_v + 0.45 eV) secara radiatif.

Kata kunci: Kuprum; nanorod ZnO; pendopan in-situ; proses sol-gel; semikonduktor

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*Corresponding author; email: sypung@eng.usm.my