Tomography

About a month ago I posted an entry about the microscopes in my lab. In this previous post, I briefly described a technique called Electron Tomography. Here is great video that describes in detail the process of making a tomogram. The section used for this was 500 nanometers thick. This is extremely thick for an electron microscope. The data taken for this tomogram was gathered on one of the world's three 1 Million kV transmission electron microscopes! Most microscopes only have the capability to gather images on sections no thicker than 200 nanometers.
About a year ago I was in a class at the New York Structural Biology Center about electron microscopy techniques. The lesson about electron tomography was taught by the person who made this particular tomogram.

Sciatic Nerve

The sciatic nerve is a critical branch of the central nervous system. It connects the legs to the dorsal root nerve, which then connects to the spinal cord. The sciatic nerve is crucial to everyday movement and sensation and is the largest nerve in the body. Here are some highly magnified images from sciatic nerve. This tissue was taken from a mouse, but looks similar in humans and other mammals. The nerve itself is composed of small bundles called Axons (see image right, click to enlarge). Each of these bundles is wrapped a membrane-like material called Myelin, or the Myelin Sheath. The Myelin, made by a specific cell called a Schwan Cell, is crucial to conducting electrical impulses that travel through the nerve (there are two Schwan cells visable on the left side of the right image). The image on the left shows the different layers of myelin as they wrap around the axon (click to enlarge). Multiple Sclerosis (MS) degrades the Myelin Sheath, interfering with signaling. MS can result in a plethora of debilitating neurological problems ranging from muscle weakness to speech problems.
This sample was provided by Hasna Baloui of the Salzer lab in the Smilow Institute of the NYU School of Medicine Neurology Department. The images were gathered on a Philips CM-12 TEM.

1950 RCA Tabletop Electron Microscope

Check out this beautiful example of Atomic Age design from RCA. This microscope was marketed as an affordable alternative to a typical Scanning Electron Microscope. "So simplified is the new instrument that a high school student or unskilled laboratory technician can quickly learn to use it!"
This is the cover from a twelve page brochure detailing the features of the RCA EMT Tabletop. The advertisement boasts a maximum magnification of 6,000x. Today's SEMs are capable of magnifications beyond 100,000x.

Focused Ion Beam H-Bar Technique

Back in school, I learned how to use a Focused Ion Beam (FIB) workstation (taught by Bill Carmichael at MATC Madison). This interesting technology uses a Gallium source to create a beam capable of milling away at very small objects. This machine is used by technology companies such as Intel to aid in the creation of everything from computer chips and data storage devices to LCD displays and C-MOS digital camera detectors.

One technique commonly used by the industry for looking at and editing errors that occurred in the lithography is called the H-Bar technique. The H-bar technique produces an electron transparent cross-section (image top right click to enlarge) of an integrated circuit.
The microchip is polished to an approximate thickness of 20um and mounted to a grid (a 3mm circular piece of metal that can support a sample and is be placed into a Transmission Electron Microscope for examination (image left click to enlarge)). After putting the sample into the FIB, a small Tungsten strip is deposited to protect the circuits and then the sides of the microchip are milled away with the Gallium Ion beam. This results in an H-shaped cross-section of circuits, hence the name, "H-Bar." The sample can then be put into a TEM and the circuits imaged.
The above image was taken on a Hitachi H-800 TEM. The image below (click to enlarge) was taken with an FEI 610 Focused Ion Beam Workstation. Illustrations were made with AppleWorks 6.

Carbon Atoms in Motion!

Here's some amazing footage of Carbon atoms moving around. The movie was captured with a Transmission Electron Microscope called TEAM 0.5. This microscope (cross-sectioned on the left) uses special lenses to correct for chromatic and spherical aberration, one of the limitations of a typical TEM. This is one of the key features that allows researchers to clearly view atoms and atomic lattices.
From the Article:
"Researchers with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), working with TEAM 0.5, the world's most powerful transmission electron microscope, have made a movie that shows in real-time carbon atoms repositioning themselves around the edge of a hole that was punched into a graphene sheet. Viewers can observe how chemical bonds break and form as the suddenly volatile atoms are driven to find a stable configuration. This is the first ever live recording of the dynamics of carbon atoms in graphene."