Visualization, Manipulation, and Verification
of Molecular Mechanical Operations
on Individual Molecules
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: [email protected]
For current contact information: http://www.chem.ucla.edu/dept/Faculty/gimzewski/index.html
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