Seeing is Believing – In situ TEM Pioneer Khalid Hattar, Sandia National Labs

Materials scientists are known for pushing the limits of research, but Khalid Hattar is a pioneer in his field. A principal member of the technical staff at Sandia National Laboratories’ Center for Integrated Nanotechnology in Albuquerque, NM, Khalid has mastered in situ Transmission Electron Microscopy allowing him to conduct some extreme experiments requiring a variety of techniques.

“Seeing is believing,” Khalid says of using in situ TEM to test out the dynamics of a material’s behavior in the microscope. “The benefit is you get to see what really happens inside material with nanometer resolution. Oftentimes it’s not what you would expect.” His work sometimes challenges the textbook and accepted simulations of how a material evolves under different conditions. “When you go to use it in the real world it may not do what you expect. Maybe it’s something more complicated or something even more beautiful, and that is really nice to be able to watch those dynamics in real time - and then provide feedback to the models and know what's going on and how the dynamics are different and how we can get a greater understanding of it.”

To set the stage for his experiments, he has outfitted the TEM column to its capacity for detectors, and he often swaps out one for another because he has even more to choose from. He has no less than 20 different sample holders, ranging from electron tomography to cryogen to quantitative mechanical testing. Visitors to the lab are impressed to see this workhorse TEM in full regalia, with a high-tilt pole piece designed for high contrast imaging, his choice for looking at structural defects caused by radiation damage or line dislocation motion due to mechanical deformation.

The many modifications were done after the TEM installation and acceptance, making this a one-of-a-kind microscope that is still under a service contract. Khalid listed the attachments, in order from the top of the column:

All of this capability allows for a lot of fun conducting some extreme experiments to benefit materials science. “I would say our microscope is constantly being evolved and changed,” he says. Khalid’s lab was also an alpha and beta test site for the IDES technology. This opened up a new capability for another extreme experiment. “We ran a typical in situ TEM cryogenic experiment using the Gatan cryo stage and cooled the sample down to liquid nitrogen temperatures. Then using the IDES 1064 nm laser system with up to 20 Watts of power, we just blasted one area. We found we can do everything from melting tungsten to taking ceramics and turning them into silly putty. We can rapidly heat that area with just a single pulse then watch how it rapidly cools. So, for rapid temperature changes, whether heating or cooling, we can now explore with that combination.

With all this instrumentation, what exactly does the Sandia team look at in the TEM?

“Pretty much anything you can put into the TEM, we've tried it. We’ve done everything from looking at liposomes to show how much cholesterol is in them and how it hardens or shapes them, to looking at rubber for tires to structural metals to uranium alloys out of a nuclear reactor,” he says. Nuclear or explosive samples, when prepared at the size needed for TEM analysis, are so small that the danger of these materials is of no concern, he explains. By the time you get the sample at that tiny size needed for a TEM sample, “you can actually eat that sample and it would be less radioactive than a banana,” he says. (Radioactive potassium in a banana is naturally occurring.)

“We've also done a lot for advanced reactor designs, whether fusion or fission. There’s a limitation in materials that can survive the high temp environment, the corrosive environment, and the radioactive environment. Our work allows us to explore those environments at the nanometer scale, which then allows the data to be fed into modeling without taking the decades that would be required in an actual reactor environment type of experiment. It’s not a direct surrogate for testing materials in a reactor but an amazingly fast process to screen a material to determine if it’s good for that combination of radiation, temperature, or mechanical loading.” The modeling information allows real world applications to be refined.

Studying rapid heating and cooling, or thermal shock, is important in applications like satellites exposed to the sun then the backside (shadow?) of the moon – undergoing temperature changes by hundreds of degrees Celsius in very short periods of time. “We can now look at these types of mechanisms faster than any conventional approach.”

Additionally, they have adapted their JEOL IT300HRLV Scanning Electron Microscope to study the materials at the SEM scale.

Khalid got his start in TEM 19 years ago while working on his PhD with Ian M. Robertson at the University of Illinois where the emphasis was on in situ TEM experiments. He and other former group mates honored his advisor at a TMS symposium Anaheim earlier this year with a symposium called “Seeing Is Believing”. Since his earliest days using in situ TEM, he has witnessed many changes in this field.

“When I first started in grad school, I trained on a JEOL 4000 EX, a 1980-1990s vintage microscope. We initially did our image processing by film. You got about 40 images then had to process the film and start your experiments again.” Eventually the then-new technology called ImageJ processing came along.

“Things have changed drastically. Now the problem is too much data. As opposed to having just a few films that you could process, now with the new cameras you have terabytes of data that you have to somehow figure out how to process.

“Up until a year ago, we were still using a 1k camera – it’s amazing how robust that CCD camera is considering the abuse we put it through. Now, we have a Direct Electron DE16 camera that has been amazing. We have been able to integrate it with our precession electron diffraction (PED) automated crystallographic orientation mapping (ACOM). It also can be triggered by the IDES system - which has been really nice when we initiate a laser experiment or an ion radiation experiment.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE’s National Nuclear Security Administration Khalid is the lead microscopist for mostly hard materials at the Center for Integrated Nanotechnologies user facility. As a user facility, there are researchers bringing in a variety of materials to study everything from solar wind in space to the stability of nuclear reactors, he says. The access to the TEM allows researchers to try out all the latest “toys” and beta test a feature of the TEM for their own applications.