Manufacturing Bits: July 21

Graphene metrology; spinning spectroscopy.


Graphene metrology
Harvard University, Monash University and the U.S. Department of Energy’s Lawrence Berkeley National Laboratory have developed a new technique that provides atomic-scale images of colloidal nanoparticles.

The technique, dubbed SINGLE, stands for 3D Structure Identification of Nanoparticles by Graphene Liquid Cell Electron Microscopy. Using the technology, researchers have reconstructed the three dimensional structures of two individual platinum nanoparticles in a solution. Platinum nanoparticles have a high electron scattering strength. And its atomic structure is important to develop catalysis.

TEM imaging of platinum nanocrystals. (Source: Berkeley Lab)

TEM imaging of platinum nanocrystals (Source: Berkeley Lab)

Colloidal nanoparticles are clusters of hundreds to thousands of atoms, which are suspended in a solution. Traditional imaging techniques can’t be applied to suspended nanomaterials. This is because the particles in a solution are not static.

To solve the problem, researchers developed SINGLE, which is based on a previously developed technology. At one time, researchers devised a technique called “single-particle cryo-electron microscopy.” In this method, a number of 2D transmission electron microscope (TEM) images are recorded and then combined into three dimensional reconstructions.

A TEM uses a beam of electrons to image a sample. TEM is also a destructive technique. So, samples must be hermetically sealed in special containers or cells. In the cell, there is a thin, silicon-based viewing window. But at times, the sample material becomes perturbed in the process.

To solve the problem, researchers developed a graphene liquid cell (GLC). The viewing window is made from a graphene sheet that is only a single atom thick. “The GLC provides us with an ultra-thin covering of our nanoparticles while maintaining liquid conditions in the TEM vacuum,” said Peter Ercius of Berkeley Lab, on the agency’s Web site. “Since the graphene surface of the GLC is inert, it does not adsorb or otherwise perturb the natural state of our nanoparticles.

“Our earlier GLC studies of platinum nanocrystals showed that they grow by aggregation, resulting in complex structures that are not possible to determine by any previously developed method,” Ercius said. “Since SINGLE derives its 3D structures from images of individual nanoparticles rotating freely in solution, it enables the analysis of heterogeneous populations of potentially unordered nanoparticles that are synthesized in solution, thereby providing a means to understand the structure and stability of defects at the nanoscale.”

Spinning spectroscopy
The National Institute of Standards and Technology (NIST) has put a new twist on an older technology called electron spin resonance (ESR) spectroscopy. Using the technology, a tiny probe can detect defects in chips down to the atomic level, according to NIST.

Traditionally, ESR has been used in chemistry, biology and other fields. The technology can be used to find out how molecules stick together.

ESR has its limits, as the technology can only analyze materials in bulk. In a system, samples must be placed in a small resonant chamber. This, in turn, forces microwaves into the system. And like a microwave oven, the chamber is unable to handle anything metallic or conductive, including semiconductors, according to NIST.

In response, NIST has developed an ESR spectrometric method, based on a near-field, nonresonant, and X-band technology. With the technology, ESR sensitivities have been improved by greater than 20,000 times over previous methods.

NIST has made electron spin resonance useful for exploring tiny objects. (Source: NIST)

NIST has made electron spin resonance useful for exploring tiny objects. (Source: NIST)

NIST also eliminated the resonant chamber. Microwave energy is introduced through a high-frequency current via a microscopic wire. The wire acts like a tiny probe tip. The tip can be moved within a few micrometers of a sample material. “Combined with other techniques, we can imagine seeing atom-sized defects in chips,” said NIST’s Jason Campbell, on the agency’s Web site. “But we’re also excited for the huge number of people who can now use this technique in chemistry and biology. It’s a simple, elegant solution to a longstanding problem.”