A Picture of Pentacene

August 31, 2009

Scientists from IBM Research used an atomic force microscope to create the first-ever close-up image of a single molecule.

Scientists from IBM Research (Zurich, Switzerland) used an atomic force microscope to create the first-ever close-up image of a single molecule. The researchers focused on a single molecule of pentacene, which is commonly used in solar cells. Pentacene is made up of 22 carbon atoms and 14 hydrogen atoms. In the image, the hexagonal shapes of the five carbon rings are clear, and the positions of the hydrogen atoms around them can be seen.

The earliest images of individual atoms were taken in the 1970s by transmission electron microscopy, but it was not possible to image larger molecules at the same level of detail because their structure is more fragile and would break apart when bombarded by electrons.

The IBM researchers used a modified version of atomic force microscopy (AFM) to image the pentacene molecule. Typically, AFM uses a sharp metal tip to measure the tiny forces between the tip and the molecule. The technique requires extreme precision because the tip moves within a nanometer of the sample. This would usually result in the tip of the microscope sticking to the pentacene molecule because of electrostatic attraction, so the researchers fixed a single molecule of carbon monoxide to the end of the probe so that only one atom of relatively inactive oxygen came into contact with the pentacene. This created weaker electrostatic attractions with the pentacene and enabled the researchers to capture a higher resolution image.

The experiment was performed inside a high vacuum at the extremely cold temperature of -268 °C to keep stray gas molecules or atomic vibrations from affecting the results.

The results of this research could have a huge impact on the field of nanotechnology.