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Molecular Transistor Built From a Single Molecule and Atoms

Molecular Transistor Built From a Single Molecule and Atoms

by Giulio PriscoJuly 15, 2015

Scientists have used a scanning tunneling microscope to build a tiny transistor with a single molecule and a small number of atoms. The development will open the way to more and more precise control of molecular electronics.

The impressive research result, achieved by physicists at the Paul-Drude-Institut für Festkörperelektronik (PDI) and the Freie Universität Berlin (FUB), Germany, the NTT Basic Research Laboratories (NTT-BRL), Japan, and the U.S. Naval Research Laboratory (NRL), has been published in Nature Physics with the title “Gating a single-molecule transistor with individual atoms.”

Atomically Precise Control of Molecular Transistor Properties

Molecular Transistor with AtomsThe scientists used a highly stable scanning tunneling microscope (STM) to create a transistor consisting of a single organic molecule and positively charged metal atoms, positioning them with the STM tip on the surface of an indium arsenide (InAs) crystal. The technique allows atomically precise control of the gate, which is crucial to transistor operations at molecular scales.

The STM image shows a phthalocyanine molecule centered within a hexagon assembled from twelve indium atoms on an indium arsenide surface. The positively charged atoms provide the electrostatic gate of the single-molecule transistor. Using the STM, the researchers assembled electrical gates from the charged atoms with atomic precision, and then placed the molecule at various desired positions close to the gates.

“When we bring the STM tip very close to the molecule and apply a bias voltage to the tip-sample junction, single electrons can tunnel between template and tip by hopping via nearly unperturbed molecular orbitals, similar to the working principle of a quantum dot gated by an external electrode,” said PDI physicist Stefan Fölsch. “In our case, the charged atoms nearby provide the electrostatic gate potential that regulates the electron flow and the charge state of the molecule.”

The scientists observed that the molecule adopts different rotational orientations, depending on its charge state. This behavior, which can be predicted by computational models, has important effects on the electron flow across the molecule. “This intriguing behavior goes beyond the established picture of charge transport through a gated quantum dot. Instead, we developed a generic model that accounts for the coupled electronic and orientational dynamics of the molecule,” said FUB physicist Piet Brouwer.

The model reproduces the experimentally observed single-molecule transistor characteristics.

The STM-generated molecular transistors will enable researchers to explore elementary processes involving current flow through single molecules at a fundamental level. Understanding and controlling these processes will be important for integrating molecule-based devices with existing semiconductor technologies.

Images from U.S. Naval Research Laboratory and Wikimedia Commons.

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