The Focused Ion Beam – All Grown Up?
The initial combination of a scanning electron microscope column and a focused ion beam column in the early 1990s, which gave birth to the FIB-SEM, has found wide application in the semiconductor and electronic sectors. The possibility for sectioning and imaging areas of interest must have been tantalising to the first souls lucky enough to use a FIB-SEM and the technology has steadily been gaining momentum.
For those who might not be familiar with it, the focused ion beam scanning electron microscope (FIB-SEM) combines a scanning electron column with a second column in the same chamber of the instrument that emits a beam of gallium ions (in most cases). The microscope may be used as a traditional SEM mode and some variants can operate in low vacuum, or environmental modes as well as at high vacuum. This alone makes the instrument quite versatile, but it doesn’t stop there. The FIB allows removal of material from specific locations allowing sub-surface features to be observed. This combination of beams and steadily improving resolution (from both columns) offers access to nanometre imaging and sample preparation in the instrument.
FIB-SEM instruments are now available from all the major EM manufacturers (in alphabetical order FEI, JEOL, Hitachi, Tescan and Zeiss ) and modern variants employ the principle of having the stage at a eucentric point, where the beams can be aligned on a coincident point, to allow milling and imaging. However, these instruments can now be adorned with all manner of attachments; from the traditional gas injectors (for deposition of protective, conductive, insulating substrates or etching gasses), to electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS) detectors, cryogenic / heating stages, micro manipulators and scanning transmission (STEM) or X-ray tomography detectors. Given the in-situ preparation possibilities and the bolt on options available, the FIB is an increasingly sound investment for stretched, multi-disciplinary institutions as it has such a wide appeal.
The major attraction of the FIB is the coincident beams that are used to mill and image samples. This means it is relatively simple (after some alignment) to obtain a sequence of 2 dimensional images that can be processed to some very visually impressive 3 dimensional videos, a fact that has led to the uptake of FIB by a range of users from biological disciplines who wish to perform serial block face (SBF) imaging or simple cross-sectioning into fixed stained cells with the sub-250 nm resolution than EM offers. Other areas that have seen major uptake are the materials community, and more recently, those interested in natural resources exploration.
A video showing the use of information obtained by FIB which can be used to create a 3-dimensional representation of the sample of shale rock. Courtesy of VSG
For those researchers in materials science, a common option is TEM lamella preparation. Thin samples can be prepared from bulk samples and transferred to a support grid using the FIB and gas injector, which deposits a metal to attach the lamella to a manipulator. The Omniprobe (now Oxford Instruments) micromanipulator system, solutions from Kleindiek or Klocke Nanotechnik and more recently FEI’s ‘Easy lift’ system allow the sample transfer to the TEM.
A micromanipulator preparing to remove a TEM lamella from a bulk sample, courtesy of Klocke Nanotechnik
In my previous posts (Is your sample preparation holding you back and I want one of those, but do I need it?) I discussed the need for corrected EM and improved sample preparation. The current generation of FIB instruments allow preparation of TEM lamellae at sub-kilovolt accelerating voltages (FIB-column), which reduces surface amorphisation to less than 1 nm, something which is absolutely essential for corrected TEM sample preparation of a 30 nm sample.
The biggest innovation from the manufacturers is an increase in ion column currents such as the recently unveiled Zeiss Crossbeam or the FEI Helios range, both with a maximum 100 nA current. For the needs of the customer who requires pre-preparation of samples where the regions of interest must first be exposed , the Zeiss Auriga Laser offers a laser for just this purpose. If you don’t quite require a laser, but need large volume removal from your FIB, the FEI Vion ‘plasma’ FIB from FEI or Tescan Fera3, which uses a Xenon plasma, should be up to the job. The Fera3 offers a staggering current of up to 2 µA, which can mill at around 50 times the rate of a traditional FIB.
Via either of these solutions it is possible for the first time to perform large scale removals of material in the SEM chamber (or prep-chamber) quickly, which is perhaps one of the most common limitations of the instruments. The FE-SEM resolution that is nowadays more-or-less guaranteed with a new system allows effortless imaging as we have become accustomed to.
Image of a FIB prepared ballistics residue particle, courtesy of TESCAN
Finally, we shouldn’t forget the other type of FIB instruments that use helium or neon in place of or alongside gallium. The three-beam Zeiss Orion NanoFab, which was launched around the time of EMC meeting in Sept 2012 offers the user the traditional cutting rate and performance of gallium and then offers the prospect of the smaller interaction volume (and removal rate) of either neon or helium, to make near nm scale modifications to a surface or nano-fabricated structure you may be creating. In case the need for a triple beam instrument isn’t quite there, the newest galium FIB-SEM instruments are capable of prototyping, nano-patterning and creating nanoscale structures for the emerging technologies and challenges of the nano-age. Whilst at MC2013 this year, I attended both the FEI and Zeiss presentations at which their instruments were outlined as able to create such structures with ease within a matter of hours. The possibility to create these complex designs within the microscope are yet a further selling point of these tools and reinforce the versatility of the platform.
A microfluidic device created using the Helios FIB, courtesy of FEI.
All things considered the FIB-SEM has come a long way in its short life and promises much for those lucky enough to have one. In my next post, we’ll look at the future of the FIB and ask whether the King of the EM world, the TEM, is set to be toppled by this twenty-something year old upstart- the FIB-SEM. Do you have a comment? If so let me know.