Localized Patterned Production and Imaging of Carbon Nanotubes in a Single Tool
Publication Date: 2005-Apr-04
The IP.com Prior Art Database
The process and instrumentation described offer the capability of in-situ CVD-based production of carbon nanotubes (CNT), applying in-situ generated metal seeds in a well controlled way. In addition to this production process the same equipment can be used to inspect the result and determine the influence of the main parameters. The whole process is achieved by switching modes of the instrument and without any exposure of the sample to air or oxygen and without need for sample handling and re-alignment of sample structures. In addition, the number of steps required to achieve the result is small--compared to lithographic techniques--because of the direct deposition using the EBID process.
Localized patterned production and imaging of CNT in a single tool
The scientific interest in Carbon Nanotubes (CNT) is still growing and is driven by the unmatched, interesting physical properties of the individual CNT. These properties range from the high electron density that can be used to flow a current through the CNT, its exceptional mechanical strength, its capability to be applied in a semi-conductor and its possible use as an electron-emitting source of high brightness. In addition to this, dedicated end-capping and lock up of specified atoms or molecules within the CNT can enhance its application of the CNT to control chemistry at the nano scale. In this way the CNT may also assist to expand AFM based microscopy with functional expansion to obtain different types of information from a surface.
Carbon Nano Tubes
Apart from its axial dimension and length, CNT are categorized in two groups: the single wall and the multi-wall type (SWCNT and MWCNT). Depending on the applied production process, one type is more abundant than the other. The most common and proven production processes are all based on the re-arrangement of carbon atoms in a defined environment:
- Arc discharge at 100 A: the yield is around 30 % and both SWCNT and MWCNT are produced simultaneously
- CVD process using a gas phase from a carbon rich gas such as methane or ethyn: the yield is 20 to 100 % mainly MWCNT
- Laser ablation of graphite with a yield up to 70 % with mainly SWCNT
All of these methods will produce carbon nano tubes in a non-structured way i.e. they are produced in bulk with a large variety of type and length and especially with random positions on the applied substrate. When produced this way, the CNT can be used in bulk particle applications such as for the reinforcement of polymers. The material property (e.g. stiffness) is then improved by the embedded presence of the CNT. In applications where CNT is used for its individual property the actual control of individual CNT becomes very important. Because the CNT's are very small, the handling of the individual CNT is not straightforward. Therefore, when the first experiments were done to characterize the CNT electrically, a procedure was followed where the local position of a diluted CNT concentration on a substrate served as the starting point. The position of an individual CNT was marked and, standard lithographic techniques were applied to generate a contact to an individual CNT with a favorable position. In this way it has been possible to characterize a single CNT electrically. However, this procedure can never be used to create actual devices because of the random position of the CNT on the substrate. Handling an individual CNT is not impossible, although directional control and fixing to a substrate is not free of artifacts. In addition this process is very slow as it is a serial, high precision movement that is required.
For this reason it is highly desired to include patterning and contr...