Morphology Control of Pulsed-Laser Deposited Ag Quantum Dots
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Morphology Control of Pulsed-Laser Deposited Ag Quantum Dots Kinuyo MACHI1, Sanshiro NAGARE1, Kenji HAMADA1, Mamoru SENNA2 1 Nara Machinery Co., Ltd. 2-5-7, Jonanjima, Ootaku, Tokyo 143-0002, Japan 2 Faculty of Science and Technology, Keio University, 3.14-1, Hiyoshi, Yokohama , Japan ABSTRACT Self-organized Ag nanodots were deposited on Si(100) by a pulsed laser deposition method. A compact apparatus was specially developed for this purpose with Nd:YAG-laser. Factors dominating size and morphology of the nanodots were examined by systematically varying species and pressure of the gas in the deposition chamber, deposition time, and the target – substrate distance (TSD). Pulse frequency (10Hz), pulse width (8ns) and laser wavelength (266nm) were kept constant. The dot size increased with pressure in the range between 0.005Pa to 1Pa, in Ar gas. At pressures as high as 100Pa, dot size decreased again with slightly different morphology. Increasing deposition time from 3, 5, to 10min brought about an increase in the average dot size from 5±2.1nm, 9±2.4nm, 10±3.0nm, respectively, under the constant Ar pressure, 100Pa. It is particularly to be noted that decreasing TSD from 100mm to 50mm brought about an increase in the dot size from 5±2.1nm to 9±3.3nm at Ar pressure, 100Pa, and deposition time, 3min. We discuss factors making self-organized Ag nanodots, and proposed key values to evaluate homogenize of dots assembly. INTRODUTION Quantum dots have attracted many interests because of their special electrical and optical properties. One of the major applications of quantum dots is for nonlinear-optical-devices. For this application, it is important that dots size is under about 10nm and homogeneous. In general, methods for preparing nanocomposites-thin film, including quantum dots, are sputtering [1], sol-gel [2], ion implantation [3], and pulsed laser deposition (PLD) [4-6]. Among them, PLD has a wider choice for substrates, with less contamination, and easy controlling process, such as output laser power, variety of gas, or pressure of gas in the deposition chamber [7]. In this work, self-organized Ag nanodots were deposited on Si (100) by PLD. Factors dominating size and morphology of the nanodots were examined by systematically varying species and pressure of gas in the deposition chamber, deposition time and the target – substrate distance (TSD). EXPERIMENTAL DETAILS
Nd:YAG-laser with Pulse Figure.1 shows the PLD system. Thales Laser Co.,LTD frequency of 10Hz, pulse width of 8ns, and laser wavelength of 266nm was used as the lights source. Pressure of the gas, He, N2, and Ar, in the deposition chamber was varied from 0.005 Pa to 1000Pa. Deposition time ranged between 3 and 30min, and TSD between 50mm and 100mm. Morphology of the dots were observed by transmission electron microscope (TEM;Philips, TECNAIF20).Crystallographic properties were determined by a thin film X-ray diffraction meter (Rigaku, RAD)
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Target TSD Substance
Figure 1. Pulsed Laser Deposition system RESULTS AND DIS
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