Fast, Nondestructive Test for Two-Dimensional Materials

In the test, red light is emitted from the edges where defects are located. Image courtesy of Penn State.

Pennsylvania State University (Penn State) (University Park, Pennsylvania) researchers are using a fast, nondestructive optical method to analyze defects in two-dimensional materials.

Their technique utilizes fluorescent microscopy, in which a laser of a specific wavelength is shined on a sample. Excited electrons, pushed to a higher energy level, emit photons of a longer wavelengths when they drop to a lower energy state. The longer wavelengths can be measured by spectroscopy, giving information about the defect type and location.

The sample goes in a specimen holder with a 77 °K (-196 °C) temperature, where the electron-hole pairs producing the fluorescence are bound to the defect—emitting a stronger signal than in pristine areas.

“For the first time, we have established a direct relationship between the optical response and the amount of atomic defects in two-dimensional materials,” says researcher Victor Carozo.

The team correlates results visually with a high-powered electron microscope known as transmission electron microscopy (TEM). Theoretical simulations are also used for validation. Without the optical method, the TEM imaging process would take much longer, researchers say, while also posing more risk of damaging the sample.

The team identifies the semiconductor industry as one potential beneficiary.

“In the semiconductor industry, defects are important because you can control properties through defects," says Mauricio Terrones, a Penn State professor and researcher. “This is known as defect engineering. Industry knows how to control defects and which types are good for devices.”

Source: Penn State,