Formation and characterization of swelled nano-porous structures on ion-irradiated Ge surfaces
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0908-OO11-04.1
Revised Formation and characterization of swelled nano-porous structures on ion-irradiated Ge surfaces Junichi Yanagisawa1,2, Keiji Ogushi1, Kentaro Takarabe1, Kenji Gamo1,3, and Yoichi Akasaka1,2 Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan 2 Research Center for Materials Science at Extreme Conditions, Osaka University, Toyonaka, Osaka, Japan 3 Kansai Advanced Research Center, National Institute of Information and Communications Technology, Kobe, Hyogo, Japan 1
ABSTRACT Single crystal germanium (Ge) surfaces were irradiated with 100 keV Ga ions at room temperature at doses up to 3x1017 cm-2 and were observed by a scanning electron microscope (SEM) and an atomic force microscope (AFM). It is found that the Ga-irradiated regions swelled and nano-porous structures were formed on the surface after the Ga irradiation up to a dose of about 2x1017 cm-2, but the region was etched by the Ga irradiation for larger doses. The atomic composition of the swelled and etched surfaces was investigated by an Auger electron spectroscopy (AES), but no Ga signal was observed, indicating that the precipitation of Ga did not influence on these characteristics of the Ga-irradiated Ge surfaces. To investigate the water resistance of such nano-porous structures, the sample was dipped in water up to 10 hours, and the surface was observed using SEM and AFM. It is found that the swelled structures were maintained, but the etched region formed by larger-dose irradiation was partially peeled off. This indicates that the nano-porous structures can be used under water environments as a functional surface, such as filters, and deep etching can be performed by larger dose irradiations and dipping the sample in water.
INTRODUCTION It is known that the topography of germanium (Ge) surfaces is easily affected by ion irradiation. For example, formation of swelled and/or porous structures with nano-meter size by 30-200 keV Ge ion irradiation on Ge (111) [1], by 280 keV Bi ion irradiation on Ge (111) [2], by 1.5 MeV Kr ion irradiation on amorphous Ge [3], and by 75 MeV Ni ion irradiation on Ge (111) [4] are reported. Such nano-porous structures have remarkable characteristics of the very large surface area compared with its volume and a large number of holes with nm size. The swelled structures are useful to, for example, bury micro flow channels with shallow depth, forming a nano-filter in biochips and sensors. However, characteristics of such swelled nano-porous structures, as well as formation mechanisms of them, have not been clarified so far. In the present paper, a focused Ga ion beam (Ga FIB) at an energy of 100 keV was irradiated on Ge (110) surfaces at ion doses of 3x1015 - 3x1017 cm-2, and the composition of the Ga irradiated regions and the solubility of such nano-porous structures in water were investigated to obtain some information about the formation mechanisms and the characteristics of such structures, respectively.
0908-OO11-04.2
EXPERIMENTAL Ga FIB with a beam diameter of 100 nm w
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