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Visualization, Manipulation, and Verification
of Molecular Mechanical Operations
on Individual Molecules

J.K. Gimzewski*

IBM Research Division
Zurich Research Laboratory
8803 Rueschlikon, Switzerland

This is an abstract for a talk to be given at the
Fifth Foresight Conference on Molecular Nanotechnology.
There will be a link from here to the full article when it is available on the web.

 

There are two recent capabilities of scanning tunneling microscopy (STM) that have opened up the possibilities to manipulate molecules on an individual basis. First, there is the capability to image molecules at complexity levels of over 100 atoms such that molecular recognition of the orientation, integrity, and even conformation of their subcomponents is readily achievable [1]. Second, there is the capability to manipulate molecules nondestructively on an individual basis and to use the molecular recognition capabilities for verification of such operations. Using mechanical means it has been demonstrated that molecules can be controllably repositioned at room temperature using (i) specific molecular architectures, (ii) steps as guide rails for confinement of translation in one dimension [2], or (iii) using supramolecular interactions to translate one molecule over a second molecular layer [3]. We have learned some significant details of the art of molecular manipulation from these investigations and are now at the stage where design concepts for single molecular devices can be prototyped [4]. Although the actual fabrication of future molecular devices will probably involve a directed self-assembly based on molecular recognition and prepatterned receptors, STM-based techniques are unique in identifying new conceptual approaches towards these goals. The results of these experiments in themselves are not the primary goal of our work. The primary goal is to understand and thereby increase the complexity and predictability of operations that can be performed in assembly and functionality at the single molecule level. STM offers a direct probing capabilities and is in effect an interface between the molecular and macroscopic worlds. This ability to treat molecules should facilitate the incorporation of other schemes and enable validation of these approaches.

Computer simulations of quantum mechanical electron transport through molecules and molecular mechanics of manipulation processes have also allowed a better understanding of specific elements of molecular architecture that facilitate two-dimensional stabilization and nondestructive repositioning [5]. In particular the use of semiflexible legs with weak absorption characteristics mounted on a rigid chassis has been found to be suitable for two-dimensional assembly operations. The understanding gleaned from these studies has been utilized to design more complex molecular systems with specific goals in mind [6]. Recently, such a specific design approach has enabled us to observe and manipulate bistable molecular conformations as switches. Such switches may involve electromechanics. In this respect the use of virtual resonance tunneling is particularly appealing. Quantum effects such as interference can be used to switch electron transport properties through molecules. Classical-based mechanics allows direct control over such quantum phenomena in molecular systems and has been observed to result in modulations of tunneling transmission factors of 100 per 0.1 nm mechanical perturbation in molecular shape, leading to the demonstration of a electromechanical amplifier based on a single molecule [7,8]. More recently, rotational operations have been achieved [9] and, although at a preliminary stage, together with translation and vertical manipulation they complete the basic sets of operations for fabrication and operation of single-molecule devices.

The third area of research that will be discussed is the control of the diffusion barriers of single molecules using external control, field-induced self-assembly, and the observation of a single molecular type of bearing, whereby changes in the local intermolecular environment can be used for lateral stabilization or to allow the rotation of a molecule. The control of the diffusion barrier introduces certain new elements within the concept of directed self-assembly.

This talk will be based on experiments conducted on molecular systems at room temperature and under ultrahigh vacuum conditions. These results provide experimental data that can be used to test the possibilities of engineering at the level of single molecules, to utilize their internal conformational properties and their electronic structure modified by molecular mechanical transformations. I hope to convey in a fairly pragmatic manner the current state of the art in this area of research by means of selected examples. The work falls within the discipline of nanoscale science and is far from being a (nano) technology. It is nevertheless directed at the latter goal.

References
[1] T.A. Jung, R.R. Schlittler and J.K. Gimzewski, Nature 386 (1997) 696.
[2] M.T. Cuberes, R.R. Schlittler and J.K. Gimzewski, Appl. Phys. Lett. 69 (1996) 3016.
[3] M.T. Cuberes, R.R. Schlittler and J.K. Gimzewski, Surf. Sci. Lett. 371 (1997) L231.
[4] J.K. Gimzewski, V. Langlais, R.R. Schlittler and C. Joachim, unpublished data.
[5] T.A. Jung, R.R. Schlittler, J.K. Gimzewski, H. Tang and C. Joachim, Science 271 (1996) 181.
[6] J.K. Gimzewski, T.A. Jung, M.T. Cuberes and R.R. Schlittler, Surf. Sci. (1997) in press.
[7] C. Joachim and J.K. Gimzewski, Chem. Phys. Lett. 265 (1997) 353.
[8] C. Joachim, J.K. Gimzewski, R.R. Schlittler and C. Chavy, Phys. Rev. Lett. 74 (1995) 2102; C. Joachim and J.K. Gimzewski, Europhys. Lett. 30 (1995) 409.
[9] M.T. Cuberes, R.R. Schlittler and J.K. Gimzewski, Appl. Phys. A (1997) in press.

Work conducted in collaboration with Ib. Johannson, C. Joachim, R.R. Schlittler and V. Langlais.


*Corresponding Address:
J.K. Gimzewski, IBM Research Division, Zurich Research Laboratory, 8803 Rueschlikon, Switzerland, email: gim@zurich.ibm.com
For current contact information: http://www.chem.ucla.edu/dept/Faculty/gimzewski/index.html



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