3-D AFM Instrumentation Development, Use,
and Nanolithography
Matthew
Johannes is a doctoral candidate in the area of AFM
instrumentation development. His research interests lie in
nanolithography, specifically working to develop nanolithography
as a high throughput industrial process. Matt is focusing on
research areas involving Dip-Pen Nanolithography (DPN) as well as
Microcontact Printing (mCP). Sept. 2006 is the start of his
sixth year and is on schedule to finish his dissertation sometime
in late 2006.
Figure 1.
The basic concept of an AFM system is shown above. A small
microfabricated cantilevered beam (~ 100-200 micrometers in
length) with an inverted pyramidal tip (curvature typically around
20-60 nm) interacts with a surface. As the tip deflects and
twists,
the motion is detected by a photo-detector and the interaction
forces and displacements are recorded.
Figure 2.
The primary instrument to be used in the research is a 3-axis AFM
setup. By having digital control algorithms implemented in real
time, the closd loop position of the cantilever tip can be located
with sub-nanometer resolution. What this enables us to do is
perform a variety of nanolithography experiments on a variety of
surfaces. Shown around the AFM is a chamber that allows the
humidity to be controlled.
Figure 3. Of primary interest is
local anodic oxidation (LAO),
which is a technique that utilizes the cantilever tip to locally
oxidize metallic and semiconducting substrates. All that is
required is a bias voltage between the tip and the substrate.
Experiments in our lab are underway to quantify and control the
current that passes from tip to samples as the process unfolds.
Figure 4.
In order to determine the result of nanolithographic experiments,
the AFM is raster scanned over an area and the resulting
cantilever deflection/twisting motion is recorded. Shown here are
two examples of substrates that have been modified using our
system and then imaged. On the left, the solid scale bar is 4
microns and the shaded scale bar is 1 nm for height. On the right,
a series of arcs and circles have been exactly duplicated from a
CAD environment and reproduced at the nanoscale.
Figure
5. Another research interest is micro-contact
printing, which uses elastomeric stamps to pattern arrays of
chemicals on surfaces over a large area (~ 1 cm^2). The nice thing
about micro-contact printing is that the stamps are reusable and
often good for a number of cycles per each `inking`.
Figure
6. Shown here is an array created with biocatalytic
microcontact
printing. The circles are 8 microns in diameter and spaced
25 microns. The confocal microscopy image is of fluorescently
tagged ssDNA at the 3' end that has been selectively removed by
the enzyme specifically bound to the surface of the stamp..
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