Exploring shaped focused ion beams for lamella preparation.

Area of Science:

• Materials Science and Engineering
• Microscopy and Imaging
• Nanotechnology

Background:

• Focused ion beam (FIB) milling is a standard technique for transmission electron microscopy (TEM) sample preparation.
• Conventional FIB milling typically produces non-isometric lamellae with dimensions significantly different in thickness versus width and length.
• The standard Gaussian-like ion probe limits precise control over material ablation geometry.

Purpose of the Study:

• To investigate an alternative ion probe shape for improved FIB milling.
• To characterize the 'ion knife' probe for enhanced material removal and lamella geometry control.
• To demonstrate the utility of the 'ion knife' for cryogenic sample preparation.

Main Methods:

• Utilized the stigmator as a quasi-cylindrical lens to create a highly astigmatic ion probe, termed 'ion knife'.
• Characterized probe dimensions and material removal patterns using spot burn cross-sections.
• Developed a method for rapid imaging-based approximation of probe shapes for parameter alignment.
• Applied the 'ion knife' for milling cellular lamellae and sectioning cryo-lift-out volumes.

Main Results:

• The 'ion knife' probe spreads ion current over a larger area, altering material removal dimensions compared to Gaussian probes.
• A method for rapid probe shape approximation via imaging was successfully demonstrated.
• The 'ion knife' proved feasible for milling cellular lamellae and sectioning cryo-lift-out volumes in cryogenic preparation.

Conclusions:

• The astigmatic 'ion knife' probe offers a novel approach to FIB milling for TEM sample preparation.
• This technique allows for modified material removal characteristics and improved control over lamella geometry.
• The 'ion knife' shows significant potential for advancing cryogenic sample preparation in microscopy.