Carbon nanotubes (CNTs) have many spectacular properties and thus have been proposed as building material for applications in a number of different fields. One of the special properties is the ability of single-walled carbon nanotubes (SWNTs) to have different electrical properties for different tube chirality and diameter. This property in combination with the inherent small dimensions of SWNTs, smaller than 1 nm in diameter, makes them promising for use in future miniaturized transistors. Still, a complete understanding of the growth mechanism of CNTs has been lacking. Nor is there any known method to control the properties of SWNTs, such as diameter or chirality, as they are grown. For growth of CNTs on chip, chemical vapour deposition (CVD) using predefined metal nanoparticles as catalysts is the preferred growth method. Nonetheless the correlation between the size of the nanoparticle and the diameter of the SWNT grown from it is still controversial and it is not yet possible to control the chirality. In order to obtain more detailed information concerning the important parameters during growth, it is essential to combine a number of powerful characterisation methods.
We have used microfabrication methods for the making of a chip forming the platform for combined TEM and Raman characterization of SWNT. A thin film of amorphous silicon-nitride (SiN) is deposited by low pressure CVD on silicon wafers. The catalyst nanoparticles are then deposited on positions defined by electron-beam lithography (EBL). Close to the catalyst sites a narrow trench-pattern is defined by EBL and transferred into the silicon by deep-reactive-ion-etching (DRIE). Next larger openings are defined on the backside of wafer using photolithography with backside alignment. Using DRIE the larger openings are etched until they meet the narrow trenches, thus forming a trench going all the way through the wafer. Then selective wet-etching is used to remove the part of the silicon under catalysts, thus forming an electron-transparent SiN-membrane. The result is a wafer full of chips, which after CNT-growth form the platform for characterization of individual single-walled carbon nanotubes.
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