Zurich, Switzerland – IBM scientists have been able to measure the charge state of individual atoms using noncontact atomic force microscopy, opening up new possibilities in molecular electronics.
The achievement represents a fundamental step towards building computing elements at the molecular scale – computing elements that could be much smaller, faster and more energy-efficient than today’s processors and memory devices.
In collaboration with colleagues at the University of Regensburg and Utrecht University, the IBM researchers imaged and identified differently charged individual gold and silver atoms by measuring the tiny differences in the forces between the tip of an atomic force microscope and a charged or uncharged atom located immediately below it.
They used a combined scanning tunneling microscope (STM) and atomic force microscope (AFM) operated in vacuum at very low temperature (5 Kelvin) to achieve the high stability necessary for these measurements.
The AFM uses a qPlus force sensor consisting of a tip mounted on one prong of a tuning fork, the other prong being fixed. The tuning fork is activated mechanically and oscillates with amplitudes as small as 0.02 nanometer – about one-tenth of an atom’s diameter. As the AFM tip approaches the sample, the resonance frequency of the tuning fork is shifted due to the forces acting between sample and tip. By scanning the tip over a surface and measuring the differences in the frequency shift, a precise force map of the surface can be derived.
The breakthrough is a crucial advance in the field of atomic-scale science. “The AFM with single-electron-charge sensitivity is a powerful tool to explore the charge transfer in molecule complexes, providing us with crucial insights and new physics to what might one day lead to revolutionary computing devices and concepts,” said Gerhard Meyer of IBM’s Zurich Research Laboratory.
The research is reported in Science.