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Nanotechnology ; 28(25): 255301, 2017 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-28548051


Focused ion beam (FIB) systems have become powerful diagnostic and modification tools for nanoscience and nanotechnology. Gas field ion sources (GFISs) built from atomic-size emitters offer the highest brightness among all ion sources and thus can improve the spatial resolution of FIB systems. Here we show that the Ir/W(111) single-atom tip (SAT) can emit high-brightness Xe+ ion beams with a high current stability. The ion emission current versus extraction voltage was analyzed from 150 K up to 309 K. The optimal emitter temperature for maximum Xe+ ion emission was ∼150 K and the reduced brightness at the Xe gas pressure of 1 × 10-4 torr is two to three orders of magnitude higher than that of a Ga liquid metal ion source, and four to five orders of magnitude higher than that of a Xe inductively coupled plasma ion source. Most surprisingly, the SAT emitter remained stable even when operated at 309 K. Even though the ion current decreased with increasing temperature, the current at room temperature (RT) could still reach over 1 pA when the gas pressure was higher than 1 × 10-3 torr, indicating the feasibility of RT-Xe-GFIS for application to FIB systems. The operation temperature of Xe-SAT-GFIS is considerably higher than the cryogenic temperature required for the helium ion microscope (HIM), which offers great technical advantages because only simple or no cooling schemes can be adopted. Thus, Xe-GFIS-FIB would be easy to implement and may become a powerful tool for nanoscale milling and secondary ion mass spectroscopy.

Nanotechnology ; 24(30): 305702, 2013 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-23807471


In this work, we present a design based on Lorentz force induction to excite pure torsional resonances of different types of cantilevers in air as well as in water. To demonstrate the atomic force microscopy imaging capability, the phase-modulation torsional resonance mode is employed to resolve fine features of purple membranes in a buffer solution. Most importantly, force-versus-distance curves using a relatively stiff cantilever can clearly detect the characteristic oscillatory profiles of hydration layers at a water-mica interface, indicating the high force sensitivity of the torsional mode. The high resonance frequencies and high quality-factors for the torsional mode may be of great potential for high-speed and high-sensitivity imaging in aqueous environment.

Nanotechnology ; 21(5): 055702, 2010 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-20023321


In this study, we demonstrate a high-resolution friction profiling technique using synchronous atomic/lateral force microscopy (AFM/LFM). The atomic resolution is achieved by our special carbon nanotube (CNT) probes made via in situ tailoring and manipulation inside an ultra-high vacuum transmission electron microscope (UHV TEM). The frictional pattern mapped on graphite displays a periodic distribution similar to the atomic (0001)-oriented graphite lattice structure. Furthermore, the electrothermal process in the UHV TEM renders a graphite-capped CNT tip, which delivers the nanotribology study within two graphite layers by the LFM measurement on graphite. The synchronous AFM and LFM images can discern a spatial shift between the atomic points and local friction maxima. We further interpret this shift as caused by the lattice distortion, which in turn induces irreversible energy dissipation. We believe this is the origin of atomic friction on the sub-nanonewton scale.