Thomas W. Tombler

Reversible electromechanical characteristics of carbon nanotubes underlocal-probe manipulation

The effects of mechanical deformation on the electrical properties of carbonnanotubes are of interest given the practical potential of nanotubes in electromechanicaldevices, and they have been studied using both theoreticaland experimental approaches. One recent experiment used the tip of an atomic force microscope (AFM) to manipulate multi-wallednanotubes, revealing that changes in the sample resistance were small unlessthe nanotubes fractured or the metal–tube contacts were perturbed. Butit remains unclear how mechanical deformation affects the intrinsic electricalproperties of nanotubes. Here we report an experimental and theoretical elucidationof the electromechanical characteristics of individual single-walled carbonnanotubes (SWNTs) under local-probe manipulation. We use AFM tips to deflectsuspended SWNTs reversibly, without changing the contact resistance; insitu electrical measurements reveal that the conductance of an SWNT samplecan be reduced by two orders of magnitude when deformed by an AFM tip. Ourtight-binding simulations indicate that this effect is owing to the formationof local sp3 bonds caused by the mechanical pushingaction of the tip.

Molecular photodesorption from single-walled carbon nanotubes

Probing the photoelectrical properties of single-walled carbon nanotubes (SWNTs) led to the discovery of photoinduced molecular desorption phenomena in nanotube molecular wires. These phenomena were found to be generic to various molecule–nanotube systems. Photodesorption strongly depends on the wavelength of light, the details of which lead to a fundamental understanding of how light stimulates molecular desorption from nanotubes. The results have important implications to nanotube-based molecular electronics, miniature chemical sensors, and optoelectronic devices.

Integration of suspended carbon nanotube arrays into electronic devices and electromechanical systems

A synthetic strategy is devised for reliable integration of long suspended single-walled carbon nanotubes into electrically addressable devices. The method involves patterned growth of nanotubes to bridge predefined molybdenum electrodes, and is versatile in yielding various microstructures comprised of suspended nanotubes that are electrically wired up. The approach affords single-walled nanotube devices without any postgrowth processing, and will find applications in scalable nanotube transistors (mobility up to 10 000 cm2/V s) and nanoelectromechanical systems based on nanowires.

Carbon nanotube arrays on silicon substrates and their possible application

Abstract A method to grow regular arrays of oriented carbon nanotubes on silicon substrates is presented. It has been found that porous silicon is an ideal substrate for growing self-oriented carbon nanotubes on large surfaces. The growth mechanism of nanotube arrays has been discussed. The potential applications of carbon nanotube arrays in flat panel display and in synthesizing of other semiconducting nanorods on silicon substrates through the carbon nanotube-confined reaction have also been studied.

Gating individual nanotubes and crosses with scanning probes

Atomic force microscopy tips are used to apply point-like local gates to manipulate the electrical properties of individual single-walled carbon nanotubes (SWNT) contacted by Ti electrodes. Depleting a semiconducting SWNT at a local point along its length leads to orders of magnitude decrease of the nanotube conductance, whereas local gating to metallic SWNTs causes no change in the conductance of the system. These results shed light into gating effects on metal-tube contacts. Electrical properties of SWNT crosses are also investigated. Scanning-probe gating is used to identify the metallic or semiconducting nature of the nanotube components in the crosses.