Super scopes (part 1)
In the latest issue of the Berkeley Science Review, we profiled the exciting development of graphene liquid cell technology at Lawrence Berkeley National Lab and UC Berkeley. This technique allows microscopists to visualize real-time nanocrystal growth in a transmission electron microscope. You may have caught us bragging a little bit in that article about the specific microscope Cal researchers used in that work. We usually try to be humble but when it comes to electron microscopes at Berkeley, that’s extremely hard to do. In fact, our extraordinary microscopy was one of the reasons I was so excited to start graduate school here in the first place. In this multi-part post, I’ll be giving you a whirlwind tour of a few amazing microscope systems around campus. Hopefully, I’ll be able to convince you that these amazing instruments should be yet another reason to walk around campus with some serious Cal pride.
Whether or not you’re a scientist, chances are that if you’ve ever taken a biology class you’ve seen your fair share of transmission electron micrographs—the black and white photos with the arrows pointing at the different components, remember? Those images were showing you images of individual cells. Well, today that should seem huge because we’re taking a trip way down to the bottom, as Feynman would say. The electron microscope I’ll be talking about is capable of producing directly interpretable images of individual atomic columns with picometer spatial resolution.
This is possible because our friendly, local, national lab is home to one of the most cutting-edge electron microscopy facilities in the world, the National Center for Electron Microscopy (NCEM). The headliner of this facility is certainly the TEAM or Transmission Election Aberration-Corrected Microscope. TEAM was built up from a national scientific effort and international collaborations to push the frontiers of nanoscience and electron optics into the future. Depending on your perspective on life, the TEAM (photo above) probably seems like either a very large box or, as I see it, clearly a contraption from the Hitchhiker’s Guide to the Galaxy.
The design of every minute detail of the room and environment that houses this remarkable instrument was deliberate: from the temperature, to the air flow, to the foundation of the floor, to the padding on the walls, to the protective casing, and finally to the remote control station for microscopy operation. Controlling these conditions is highly important because any fluctuations in these external conditions could impact the quality of the data acquired on the scope. This care is usually not necessary with standard electron microscopes because they are limited by other factors before mechanical floor vibrations, for instance, can have a significant impact on data quality. But the TEAM I is not like other electron microscopes.
Notably, the TEAM I is at the top of the heap of an elite class of microscopes that have CEOS correctors to improve the spherical aberration of the objective lens which is the critical limiting factor in directly interpretable resolution in the electron microscope. You may already be familiar with another famous microscope that required some corrective action for spherical aberration…the Hubble microscope. Correction of spherical aberration is extremely challenging in electron microscopy because there are theoretical limitations, outlined by the Scherzer theorem, which make these aberrations fundamentally unavoidable element of electromagnetic lens design. The best solution is to break the rotational symmetry condition of the Scherzer theorem (some history by Harald Rose himself here), achieved by installing a multipole corrector. The TEAM microscope takes aberration correction to a new level given its integration of not one but two sets of correctors for different parts of the system (both the objective and condenser lenses). This is one of the most important reasons why the TEAM is able to achieve such amazing resolution.
There are other crucial elements that push the TEAM I to the limit of what’s possible in modern electron microscopy. Some of its notable attributes include:
- An extraordinary stage that can perform extreme 180 degree tilts of individual TEM sample grids for atomic-resolution electron tomography.
- An ability to align the instrument at variable accelerating voltages that allows for imaging samples that are sensitive to knock-on damage from the electron-beam.
- A corrector for the chromatic aberration that is resolution limiting at low operating voltages.
- A novel high-brightness electron source.
Of late, the TEAM has helped scientists make critical advancements in understanding the fundamental physical properties of hard nanomaterials. Understanding ferroelectric behavior, as well as visualizing the atomic-level of graphene, are two of the many research areas where the TEAM has been found to be incredibly useful. The graphene liquid cell also continues to be employed as a strategy to visualize real-time growth properties and molecular assembly by researchers at LBNL and Berkeley. There is no doubt that this extraordinary tool is pushing new frontiers in imaging materials for researchers at Cal and nationwide.
Photo source: ncem.lbl.gov