Microwave-assisted synthesis of c -axis oriented ZnO nanorods on a glass substrate coated with ZnO film
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1035-L08-16
Microwave-assisted synthesis of c-axis oriented ZnO nanorods on a glass substrate coated with ZnO film Ken-ichi OGATA, Kazuto Koike, Shigehiko Sasa, Masataka Inoue, and Mitsuaki Yano Nanomaterials Microdevices Research Center, Osaka Institute of Technology, Osaka, 535-8585, Japan ABSTRACT ZnO nanorod synthesis on a glass substrate coated with ZnO film was performed by means of microwave-assisted heating. Nanorod structure was dependent on the underlying ZnO films; slightly tilted nanorods about 800nm diameter were synthesized on an as-sputtered ZnO film while highly c-axis oriented ones about 100nm diameter were developed on the ZnO film after annealing. Photoluminescence spectra of the ZnO nanorods at 6K showed a badedge excitonic emission with comparable intensity to a visible defect related emission, suggesting the existence of many radiative defects which would be originated from insufficient quality of the underlying ZnO layer. Pattered photoresist layer can successfully be utilized for synthesis of the ZnO nanolods in selective area. INTRODUCTION ZnO nanostructures, such as nanorings, nanohelixes, or nanorods, [1] are of great interest because of their unique shapes and properties and until now various techniques were employed for the nanofabrication [2]. Owing to the recent progress of those techniques, novel devices based on ZnO nanostructures, for instance, piezoelectric nanogenerators [3] and ring-shaped wireless biocompatible nanoheaters for targeted drug delivery [4] are proposed. Toward the combining of nanostructure devices with layered structure ones, such as field effect transistors (FETs) with a high transconductance (gm) value of 71mS/mm [5] or a high pH sensitivity of 20µA/pH [6], ZnO nanostructures should be grown at low temperatures in order to inhibit the deterioration of the underlying devices properties. Synthesis of ZnO nanostructures from an aqueous solution [7] is one of the suitable techniques for that purpose, which also enables the deposition on thermally labile substrates. In addition to that, attentions are paid to the heating system, namely, instead of conventional thermal conduction, microwave irradiation heating was utilized. Since microwave heating is related with the dielectric loss in the materials, synthesis can be performed rapidly, energyefficiently and area-selectively [8, 9]. Despite of many researches on ZnO nanorod synthesis [2], reports of microwave-assistance [10, 11] or that on ZnO underlying templates [12, 13] were not so many. Therefore in this contribution, a microwave irradiation technique was applied for fabrication of c-axis oriented ZnO nanorods on ZnO film coated glass substrates, aiming at the linking with ZnO layered structures, such as FETs mentioned above. EXPERIMENT As the substrates, 300nm-thick ZnO films sputtered on boronsilicate glass plates at room temperature by means of radio frequency (RF) magnetron sputtering using a high purity ZnO target (5N, Furuuchi) were utilized. During the sputtering of ZnO films, the RF power and
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