Maryland NIRT

PIs: Michael Fuhrer, Chris Lobb, Ellen Williams, Larry Sita

Overview

The Maryland Nanoscale Interdisciplinary Research Team ("NIRT") is funded by the National Science Foundation under the Nanotechnology Initiative.  The goal of the NIRT is to investigate the effects of fluctuations in atomic structure or electric charge on the electronic properties of nanoscale devices.  As electronic device dimensions become smaller, two issues become increasingly important: the discreteness of atomic matter becomes significant in determining structural stability, and the discreteness of charge causes significant sensitivity of the device to fluctuations in the local electrostatic environment.  Both issues are of fundamental importance to the design of any working nanoscale device.  The Maryland NIRT brings together researchers with significant experience in studying charge fluctuations (Lobb) and structure fluctuations (Williams) with researchers who are constructing radically new molecular-scale electronic devices (Sita, Fuhrer). 

To accomplish this goal, the Maryland NIRT team has set out to construct a range of model nanoscale devices in which to study the effects of changes in atomic structure and/or electrostatic potential on electronic properties.  These devices include (1) semiconducting carbon nanotube transistors, (2) single-electron transistors constructed from Al/Al₂O₃/Al or carbon nanotubes, (3) single molecules bonded to metal electrodes, and (4) clean ultrathin metal films and wires prepared in ultra-high vacuum. 

A range of experimental techniques will be employed, often synergistically, to investigate the electronic properties of the devices mentioned above.  Electronic transport measurements will be performed at room temperature and at cryogenic temperatures.  These will include conductance measurements as well as characterization of the anomalous (1/f) noise in these systems.  Transport measurements will be coupled with scanned probe techniques to probe the local electronic properties of the devices.  For example, scanning tunneling microscopy (STM) will be used to monitor the atomic structures of thin metal films during electromigration; electrostatic force microscopy (EFM) will be used to locate and study individual defects in carbon nanotubes; scanned gate microscopy (SGM) will be used to study the effects of local electrostatic potential variations on nanotubes and molecular devices. 

Unique facilities are being developed to perform these measurements on samples in a range of environments.  An environmental atomic-force microscope (AFM) has been modified to perform electronic measurements (EFM, SGM) in a range of environments, from pure gases to high vacuum, and from cryogenic temperatures (100 K) to high temperature (800 K).  An ultra-high vacuum scanned-probe microscope is being developed which will feature a cantilever-type AFM, a field-emission scanning electron microscope, and in situ electrical measurement capability.  This facility will allow preparation of clean samples in UHV, and the study of their electronic and structural properties without breaking vacuum.

The proposed research will have a significant impact on nanoscale science and technology.  Nanoscale memory elements will require the control of charge and structure at the level of a single charge or defect.  Understanding the sensitivity of devices to their structural and electrostatic environments will allow the design of new nanoscale sensors of charge and structure, which may be used as sensitive detectors of defects, dopants, electric fields, or chemical species.  Understanding how nanoscale devices interact through electrostatic and structural fluctuations may guide the development of new nanoscale logic elements.  The interdisciplinary nature of the proposed research will also offer unique educational opportunities to the undergraduate and graduate students who will have the opportunity to perform research with collaborating investigators from nominally separate fields.

Personnel

Research

Please also see the following homepages:

    Fuhrer Research Group

    Lobb Research Group

    Sita Research Group

    Williams Research Group

Publications

"High-Mobility Nanotube Transistor Memory" M. S. Fuhrer, B. M. Kim, T. Dürkop, and T. Brintlinger, Nano Letters 2, 755 (2002).

"Rapid Imaging of Nanotubes on Insulating Substrates" T. Brintlinger, Yung-Fu Chen, T. Dürkop, Enrique Cobas, M. S. Fuhrer, John D. Barry, and John Melngailis, Applied Physics Letters 81, 2454 (2002).

"Nanotubes are High Mobility Semiconductors," T. Dürkop, T. Brintlinger, and M. S. Fuhrer in Structural and Electronic Properties of Molecular Nanostructures, pp. 242-6, H. Kuzmany, J. Fink, M. Mehring, and S. Roth, Editors (AIP Conference Proceedings, New York, 2002).