The achievement was made by researchers in the United States

Jan 25, 2012 08:48 GMT  ·  By
Top: TEM diffraction pattern from a segment of an InGaN nanowire about 50 nm across. Bottom: Same pattern but with an overlay showing the crystallographic indexing associated with the atomic structure of the material
   Top: TEM diffraction pattern from a segment of an InGaN nanowire about 50 nm across. Bottom: Same pattern but with an overlay showing the crystallographic indexing associated with the atomic structure of the material

A group of investigators was recently able to boost a standard scanning electron microscope's (SEM) ability to resolve and measure the crystal structures of both nanoparticles and thin films, by as much as 1,000 percent. SEM imaging will from now on be used increasingly often in nanotechnology studies.

SEM imaging relies on using a high-energy beam of electrons to scan a sample in a raster patterns. When these individual particles collide with the atoms inside the sample, the resulting signals carry with them extremely important information.

The latter include data on how the topography of the sample's surface looks like, what it's made out of, if it's conductive or not, and so on. This information is very difficult to obtain through other scanning methods, and the new study ensured that their amount will continue to increase.

This work was carried out by investigators at the US National Institute of Standards and Technology (NIST), who decided to customize an SEM telescope in a way that would boost its efficiency. Right now, their instrument can study samples as small as 10 nanometers across.

According to team members, the new improvements could be used in a variety of fields, such as for example forensics science, monitoring the environment, improving control technologies in nanoscale manufacturing, and so on.

The SEM the NIST team improved is capable of determining the particular crystal structure or “phase” and orientation in the crystalline samples it's studying. “A common example is titanium dioxide, which can exist in a couple of different crystal phases,” NIST experts Robert Keller and Roy Geiss explain.

“That difference significantly affects how the material behaves chemically, how reactive it is. You need to add crystallographic identification to the chemical composition to completely characterize the material,” they add.

“You can determine the crystal structure of an isolated particle down to a size of about 100 to 120 nanometers, but below that the crystals are so small that you're getting information about the sample holder instead,” the team comments on previous SEM limitations.

Usually, samples below 50 nanometers are studied with transmission electron microscopes (TEM), but some targets are simply not suited for such investigations. The extreme energies of TEM electrons literally pierce through most samples, which means that only limited diffraction patterns are produced.

With the improved SEM, the NIST team provides a high-resolution, lower-energy alternative to TEM.