NANOSCIENCE
A molecular “template” for self-assembling atomic wires

Paris, April 11, 2002

Researchers of the molecular electronics group of the CEMES-CNRS center in Toulouse, France (Centre d’élaboration de matériaux et d’études structurales) and the Department of Physics and Astronomy of the University of Aarhus (Denmark) have described in the April 12, 2002 issue of Science a specially designed nano-template(1) molecule which enables the self-assembly(2) of atomic wires on a copper substrate. These results will pave the way for the electric interconnection of molecular components, and eventually enable mono-molecular circuits.

The molecule synthesized and developed at the CEMES-CNRS center by André Gourdon, Ping Jiang and Christian Joachim resembles a four-legged table: its top is a molecular wire that is maintained .36 nm above the copper substrate by four molecular legs. After placing the molecule on the surface of a copper crystal, Federico Rosei, Michael Schunack and Flemming Besenbacher of the University of Aarhus observed its behavior with a scanning tunneling microscope (STM). This microscope not only provided atomic scale images of the surface of the molecule, it was also used to move individual molecules at will. A combination of microscopy and molecular manipulation enabled the researchers to observe that each molecule acted like a nano-template. Laterally confined by its four “legs”, the nanoscopic molecular cavity formed underneath the molecule’s “tabletop” captures copper atoms from the copper substrate, which are trapped between the four legs. An atomic wire is formed during the displacement of the molecule over the copper substrate as the molecule leaves a line of copper atoms behind it. The theoretical work of the CEMES-CNRS group in Toulouse also led to a precise description of the process involved in the formation of these atomic wires and a better understanding of the small variations (about .01 nm) in the size of the molecular template required in the assembly of an atomic wire.

This Franco-Danish collaboration was conducted within the framework of the “Bottom Up Nanomachines” (BUN) project, of which one of the primary objectives is the development of new nanofabrication methods for the development of components and circuits in molecular electronics. The objective is to provide a viable technological alternative to the traditional top-down(3) approach used by the semi-conductor industry in which lithographic techniques are employed to produce increasingly miniaturized electronic components. The BUN project explores the “Bottom-up”(4) approach, based on the fabrication of functional units from atomic building blocks or prefabricated molecular structures, that would, for example, be capable of acting as electric wires or switches. Molecules are considered the ultimate limit in the miniaturization of computer and electronic components at a nanometric dimension. Though this approach may seem visionary, it should be remembered that only 20 years ago, today’s microelectronics standards were considered unrealistic.

(1) Nano-template: shape at a nanometric scale (1 nm = 10-9 meter) that can be used to form a string of atoms.
(2) Auto-assembly: assembly without need of external stimulus. The atoms are lodge and organize themselves inside the cavity formed between the molecule and the substrate. Auto-assembly presupposes that the elements that are about to be joined possess the necessary shape and interactions that would enable them to recognize each other and bind together.
(3) Top-down: Wires, components, and circuits are fabricated from solid materials like silicon to make conventional electronic chips.
(4) Bottom-up: This method employs as few atoms as possible in constructing electronic components or circuits.

References: F. Rosei, M. Schunack, P. Jiang, A. Gourdon, E. Laegsgaard, I. Stensgaard,
C. Joachim, F. Besenbacher. Organic Molecules Acting as Templates on Metal Surfaces. Science, vol. 296, no 5566 – April 12, 2002.

Researcher contact:
Christian Joachim
CEMES-CNRS
Tel: + 33 5 62 25 78 35
e-mail: joachim@cemes.fr

Chemical Sciences Department contact:
Laurence Mordenti
Tel: + 33 1 44 96 41 09
e-mail: laurence.mordenti@cnrs-dir.fr

Press contact :
Martine Hasler
Tel : +33 1 44 96 46 35
e-mail : martine.hasler@cnrs-dir.fr