Novel Synthesis of Metal Nanowhiskers: High-temperature Glancing Angle Deposition
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1058-JJ03-09
Novel Synthesis of Metal Nanowhiskers: High-temperature Glancing Angle Deposition Motofumi Suzuki, Kenji Hamachi, Koji Nagai, Ryo Kita, Kaoru Nakajima, and Kenji Kimura Department of Micro Engineering, Kyoto University, Yoshida, Sakyo, Kyoyo, 606-8501, Japan ABSTRACT We demonstrate the high-temperature glancing angle deposition (HT-GLAD) of metals on a heated substrate. It has been found that Al, Ag, Au, Fe nanowhiskers can grow on the substrates of Si, SiO2, and glass. The robustness in the selection of materials suggests that HTGLAD is a universally accepted method for growing nanowhiskers of various metals. We also demonstrate the selective growth of nanowhiskers on a substrate with microtrench patterns. Metal nanowhiskers are useful for the fabrication of nanoelectromechanical devices and in vacuum microelectronics.
INTRODUCTION Very recently, we have found that the unusual Al nanowhiskers grow by glancing angle deposition on a high-temperature substrate (HT-GLAD) [1, 2]. The key requirement for producing nanowhiskers is that the glancing angle during deposition should be typically greater than 80°. It semms that the growth of nanowhiskers on a flat substrate by HT-GLAD is closely related to the growth of nanowhiskers on a hot tungsten wire, as demonstrated by Melmed and Gomer [3]. This is because a significant amount of Al atoms can be incident on the substrate from the oblique direction during deposition on the tungsten wire. If this hypothesis is correct, the growth of nanowhiskers of various metals, other than Al, on hot tungsten wires is expected by using HT-GLAD and this will lead to the development of the metal hetero-nanowhiskers. Moreover, HT-GLAD enables the selective growth of nanowhiskers on nanostructured substrates since the growth of nanowhiskers strongly depends on the deposition geometry [1]. Therefore, nanowhiskers grown by HT-GLAD are potential candidates for the fabrication of novel nanoelectromechanical devices and for use in vacuum microelectronics. In this paper, we report some examples of nanowhiskers, other than those of Al, and describe their selective growth on patterned substrates. We also discuss the possible applications of these nanowhiskers.
EXPERIMENT All deposition processes were carried out using an electron-beam (EB) evaporation apparatus specially designed for HT-GLAD. Prior to HT-GLAD, a 50-nm thick SiO2 layer was deposited on a surface-oxidized Si substrate at a room temperature in the normal direction. Subsequently, the substrate was irradiated with a halogen lamp for heating up to a substrate temperature Ts of 300–500 ºC; and the temperature of the substrate was maintained at a constant value during HT-GLAD. On the heated SiO2 layer, Al, Ag, Au, and Fe were deposited at a deposition angle α of 82°–85° with an average thickness (weight thickness) d of 5–100 nm. During the deposition of metals, the deposition rate was maintained constant typically at 0.05 nm/s, and the pressure was maintained in the range of 10–4 Pa. RESULTS AND DISCUSSION Examples of metal
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