Manipulation of individual carbon nanotubes: towards scanning probe applications

Carbon nanotubes the long, cylindrical carbon molecules are the most exciting material discovered lately. They offer the possibility for a large number of applications. My task was to explore the way how we can use multi-walled carbon nanotubes (MWNT) in scanning probe applications: Atomic Force Microscopy (AFM) and Scanning Nearfield Optical Microscopy (SNOM). Carbon nanotubes (CNTs) are potentially ideal atomic force microscopy probes because they can have diameters as small as one nanometer, they have robust mechanical properties, and can be specifically functionalized with chemical and biological probes at the tip ends. CNTs will not wear, because they buckle elastically under applied load and thus will stay sharp. They also show exceptional field emission properties, and remarkably enough, the field emission at high currents is accompanied by light emission. This phenomenon offers the possibility to use CNTs as nanometer-size light sources for SNOM. In order to test CNTs for AFM and SNOM applications a mounting method has been elaborated. Two nanomanipulators have been designed and constructed for operations inside a Transmission and Scanning Electron Microscopes (TEM and SEM). This latter one with large work space and available electrical contacts allowed versatile use of nanomanipulator, including in situ field emission, and photon counting measurements using a photodiode. Hundreds of individual MWNT and double-wall nanotubes (DWNT) bundles, produced by arc-discharge (AD) or chemical vapour deposition (CVD) method, have been mounted, one-by-one, on either commercial AFM probes or sharpened metallic wires (W, Au, Pt). The tests show that in both case, AFM and SNOM probes, the weakest point is the attachment of the nanotube to the support. Amorphous carbon deposit is good for attaching nanotubes for limited time and limited applications, but it deforms under the forces that it has been submitted to during AFM scans. This weak bonding of nanotubes is the source of failure in AFM. In field/light emission the high contact resistance, which can change during the mechanical stress exerted by the applied electric field, will lead to a Joule heating of the nanotube/contact area and results a thermal breakdown of the tip. Attempts were made to elaborate a good mechanical and electrical attachment of the carbon nanotubes to the Si/metallic cantilever by using indium as bonding agent.


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