IBM scientists claim to have been able to image the chemical structure inside a molecule with unprecedented resolution, using a technique known as non-contact atomic force microscopy (AFM).
According to IBM, the results of its research push the exploration of using molecules and atoms at the smallest scale and could greatly impact the field of nanotechnology.
"Though not an exact comparison, if you think about how a doctor uses an x-ray to image bones and organs inside the human body, we are using the atomic force microscope to image the atomic structures that are the backbones of individual molecules," said IBM Researcher Gerhard Meyer in a statement. "Scanning probe techniques offer amazing potential for prototyping complex functional structures and for tailoring and studying their electronic and chemical properties on the atomic scale."
IBM continued to state that understanding the charge distribution at the atomic scale is "essential for building smaller, faster, and more energy-efficient computing components than today’s processors and memory devices." Such components, IBM said, could one day contribute to a "smarter planet" by helping instrument and interconnect the physical world.
IBM Research Zurich Scientists Leo Gross, Fabian Mohn, Nikolaj Moll, and Meyer, in collaboration with Peter Liljeroth of Utrecht University, used an AFM operated in an ultrahigh vacuum and at very low temperatures ( -268°C or -451°F) to image the chemical structure of individual pentacene molecules, oblong organic molecules consisting of 22 carbon atoms and 14 hydrogen atoms measuring 1.4nm in length. With the AFM, the IBM scientists were able to look through the electron cloud and see the atomic backbone of an individual molecule. IBM claimed that the act was the first of its kind.
Offering more detail, IBM said the AFM uses a sharp metal tip to measure the forces between the tip and the sample, such as a molecule, to create an image. The spacing between neighboring carbon atoms is only 0.14nm, roughly 1 million times smaller then the diameter of a grain of sand, IBM said. In the experimental image, the hexagonal shapes of the five carbon rings as well as the carbon atoms in the molecule were clearly resolved, IBM claimed, adding that even the positions of the hydrogen atoms of the molecule can be deduced from the image.
“The key to achieving atomic resolution was an atomically sharp and defined tip apex as well as the very high stability of the system,” said Gross in the statement. “We prepared our tip by deliberately picking up single atoms and molecules and showed that it is the foremost tip atom or molecule that governs the contrast and resolution of our AFM measurements.”
IBM said that a tip terminated with a carbon monoxide molecule yielded the optimum contrast at a tip height of approximately 0.5nm above the molecule being imaged and resolved the individual atoms within the pentacene molecule, revealing its exact atomic-scale chemical structure. Furthermore, the scientists said they were able to derive a complete 3-D force map of the molecule investigated.
IBM's Moll performed first-principles density functional theory calculations of the system investigated. “The calculations helped us understand what caused the atomic contrast," he said in the statement. "In fact, we found that its source was Pauli repulsion between the CO and the pentacene molecule.” The Pauli exclusion principle states that two identical electrons can not approach each other too closely.
The research was reported on in a scientific paper entitled
“The Chemical Structure of a Molecule Resolved by Atomic Force Microscopy” that appears in the August 28 issue of Science.
The current publication follows an experiment published in the June 12 issue of Science where IBM scientists measured the charge states of atoms using an AFM.
IBM
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