| AVS 59th Annual International Symposium and Exhibition | |
| Helium Ion Microscopy Focus Topic | Wednesday Sessions |
| Session HI+AS+NS-WeA |
| Session: | Basics of Helium Ion Microscopy |
| Presenter: | I.-S. Hwang, Academia Sinica, Taiwan, Republic of China |
| Authors: | I.-S. Hwang, Academia Sinica, Taiwan, Republic of China H.-S. Kuo, Academia Sinica, Taiwan, Republic of China T.-Y. Fu, National Taiwan Normal University, Taiwan, Republic of China J.-L. Hou, Academia Sinica, Taiwan, Republic of China C.-Y. Lin, Academia Sinica, Taiwan, Republic of China Y.-H. Lu, Academia Sinica, Taiwan, Republic of China W.-T. Chang, Academia Sinica, Taiwan, Republic of China T.T. Tsong, Academia Sinica, Taiwan, Republic of China |
| Correspondent: | Click to Email |
Thermally and chemically stable single-atom tips (SAT) or nanotips are highly desirable for emission of high-brightness gas field ion beams. In 2001, Fu et al. demonstrated a Pd-covered W(111) SAT through vacuum deposition of an ultra-thin Pd film on a clean W tip surface followed by thermal annealing [1]. Later, Kuo et al. further simplified the preparation process by replacing the tip cleaning and the vacuum deposition with electrochemical processes and successfully prepared several different types of noble metal-covered W(111) SATs [2]. This type of SATs is thermally stable and chemically inert, and thus can be regenerated through a gentle annealing if the apex is contaminated.
We have successfully generated hydrogen, helium, argon, and oxygen ion beams using a Ir/W SAT and characterized these ion sources [3]. The first two lightest ions provide the lowest sputtering rates, which is beneficial for scanning ion microscopy. The argon ion has a large mass and can provide a high sputtering rate, suitable for ion milling. Due to the high secondary ion yields, an oxygen ion beam may be applied to secondary ion mass spectrometry. The ion beam profiles indicate that the half opening angle is ~0.5°. This single spot indicates that emission occurs only from the topmost atom. This small source size and the small opening angle are particularly favorable for achieving high angular intensity, high brightness, and low spherical aberration, which are important characteristics for a focused ion beam system. The ion current of these gas ion beams are very stable and the tip does not show any degradation under fields above 5 V/Å after a total operation time of 80 hours. Since the SAT can be regenerated for more than 50 times, therefore its lifetime is long enough for most practical applications.
In addition, we have also prepared a pure iridium SAT based on oxygen-induced crystal faceting of the Ir(210) [4]. We have shown that the Ir-SAT can be a good field ion emitter, capable of emitting a variety of gas ion beams, including He+, H2+, N2+, and O2+, with high brightness and stability. In particular, nitrogen is a very corrosive gas for metal tips under strong positive electric fields. If we can achieve a stable emission of nitrogen ion, it also means many other gas field ion beams may also be emitted from this Ir-SAT. This may greatly broaden the application of focused ion beam technology.
[1] T.-Y. Fu et al., Phys. Rev.B 64 (2001), 113401.
[2] H.-S. Kuo et al., Nano Lett. 4 (2004), 2379.
[3] H.-S. Kuo et al., Appl. Phys. Lett. 92 (2008), 063106.
[4] H.-S. Kuo et al., Nanotechnology 20 (2009), 335701.