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Overview

Scanning-probe microscopes (SPMs) allow the investigation and manipulation of surfaces down to the atomic scale. The nanoManipulator (nM) system provides an improved, natural interface to SPMs, including Scanning Tunneling Microscopes (STMs) and Atomic Force Microscopes (AFMs). The nM couples the microscope to a virtual-reality interface that gives the scientist virtual telepresence on the surface, scaled by a factor of about a million to one. It provides new ways of interacting with materials and objects at the nanometer scale, placing the scientist on the surface, in control, while an experiment is happening.

The nM system is a continually evolving tool, and is a collaborative project between the Departments of Computer Science, Physics and Astronomy, Chemistry, the School of Information and Library Science, and the School of Education at the University of North Carolina at Chapel Hill. This tool is continually being developed in close collaboration with real users. It has led to new results in the study of biology, materials science, carbon nanotubes, and electrical engineering.

In the image above right (photo by Larry Ketchum), biology postdoctoral student Martin Guthold uses the nM to examine carbon nanotubes. The nanoManipulator is also being used at UNC to examine and manipulate adeno virus particles, fibrin, DNA/protein complexes, and mucin. Adeno virus particles are used as vectors in gene therapy, traveling into cells and then releasing the genetic material contained in their hollow core. Fibrin makes up the strands that capture blood cells to form blood clots. Martin directly controls the lateral position of the AFM tip; real-time force feedback indicating surface height allows him to guide the motion of the nanotubes during manipulation, when the tip cannot scan the surface.

From Conception to Current

The nanoManipulator interface was conceived by Warren Robinett at the UNC-CH Department of Computer Science and Stan Williams, then at the UCLA Department of Chemistry, now at HP Basic Science labs. Collaboration between the departments began in 1991 with the development of a system to control an STM. In 1993, Sean Washburn of the UNC Physics Department joined the project, leading experiments that led to our discovery of nanoWelding . He leads our investigation into the design and fabrication of quantum devices. Richard Superfine of the UNC Physics Department joined our team in the Spring of 1994, bringing expertise in AFM and leading our work on biological samples.

Since that time, the project has expanded rapidly, now including graduate and undergraduate students in Computer Science, Physics, Materials Science, Chemistry, Information Science, Psychology, and Education. The team includes a full-time biology postdoctoral student (Tim O'Brien) who provides outreach to biologists wanting to use the Resource.

The nM also provides access to the CORES image-processing software developed by the MIDAG medical image group. This software provided the center tracing for the data analysis done on carbon nanotubes described in our Nature article, the Tobacco-Mosaic Virus work described in our Biophysical Journal article, as well as mucin, fibring and DNA.

Biologists interested in coming to use our facility in its capacity as an NIH National Research Resource should check out our visitor web page.

How it works

Scanning Probe Microscopes (SPMs) work by rastering a tip across a surface, sampling its height at locations on a regular grid. The data is typically viewed in real time as a grayscale map viewed from above, (left image). The nM interface tiles the surface with triangles and uses a highly-parallel graphics supercomputer to render the image as a shaded surface (right image). Specular highlights bring out features in the data that are missed in the grayscale image.

SPMs can modify the surface using either voltage pulses or by physically pressing the tip into the surface. This modification is normally done under program control, with experiments consisting of scanning the surface before and after a change. Normally, there is no feedback during the modification event. The nM uses a force-feedback probe to allow the user to directly control tip motion during modification and feel the changes as they are occurring. This provides much finer control over modification and enables new and fruitful types of experiments.

Modern SPMs can acquire multiple data sets (conductance, lateral force, temperature) at the same time they sample the height of the surface. These are normally displayed as several side-by-side grayscale images, one per data set. The nM is investigating the use of color and programmable shading to display these data sets overlaid on the topography, allowing the scientist to naturally view correlations between topography and other data. We are also exploring richer force-feedback models (including adhesion and friction) and the use of auditory feedback to convey information.

More information

Click here for our most recent 2-page summary.

Click here for a 2-page summary of the distributed nanoManipulator that was handed out at the Internet 2 conference in April '99.

Questions and comments should be sent via email to taylorr@cs.unc.edu