Microwave-Assisted Fabrication of Carbon Nanotube AFM Tips Tamara S. Druzhinina, † Stephanie Hoeppener* ,†,‡,§ and Ulrich S. Schubert* ,†,‡,§ † Laboratory of Macromolecular Chemistry and Nanoscience, Eindhoven University of Technology, Den Dolech 2, 5600 MB Eindhoven, The Netherlands, ‡ Dutch Polymer Institute, P.O. Box 902, 5600 AX Eindhoven, The Netherlands, and § Laboratory of Organic and Macromolecular Chemistry (IOMC), Friedrich-Schiller-University Jena, Humboldtstrasse 10, D-07743 Jena, Germany ABSTRACT A new, fast, alternative approach for the fabrication of carbon nanotube (CNT) atomic force microscopy (AFM) tips is reported. Thereby, the tube material is grown on the apex of an AFM tip by utilizing microwave irradiation and selective heating of the catalyst. Reaction times as short as three minutes allowed the fabrication of CNT AFM tips in a highly efficient process. This method represents a promising approach toward a cheaper, faster, and straightforward synthesis of CNT AFM tips. KEYWORDS Carbon nanotubes, microwave, AFM tip, carbon nanotube synthesis, catalyst S canning force microscopy has developed into a stan- dard tool in material research and represents a fre- quently used technique in nearly all fields of science, including, e.g., chemistry, physics, biology, and others. 1-4 The resolution of this technique is, however, strongly related to the quality of the available tip material, which limits not only the lateral resolution but also implies limitations with respect to the investigation of, e.g., steep edges. 5,6 While commercially available atomic force microscopy (AFM) tips are fabricated by using silicon microfabrication techniques reaching a typical resolution of approximately 10 nm, tailor- made tip layouts have been proposed to improve the tip performance. The tip quality depends mainly on the dimen- sions and shape of the probe, the durability of the tip apex, and the nature of the interaction between sample and probe. In this respect, in particular, AFM tips functionalized with a carbon nanotube (CNT) have attracted considerable atten- tion. Due to the high Young’s modulus of the CNTs and their excellent aspect ratio, 7 attempts have been made to use them as probes for AFM experiments. Not only their unique mechanical but also their chemical and electronic proper- ties 8-12 open attractive possibilities that might result in improving imaging performance 13,14 or in measuring the properties of CNTs. 15 Due to the high resolution of CNT AFM tips, they can be used to image very fine structures, such as biological and molecular materials. Several studies have been performed where CNT AFM tips were used to image biological materials, such as, DNA or proteins. 16-18 Different methods have been developed either to directly grow CNTs on AFM tips 19-23 or to place CNTs on tips. 24-27 The place- ment of the CNT on the AFM tip is usually performed by using scanning electron microscope (SEM) manipulators, where individual tubes are picked and stabilized on the AFM tip with locally deposited carbon. This process is time- consuming and requires a rather expensive experimental infrastructure and is also difficult to be used for a scale-up of the manufacturing process. Alternatively, the direct growth of CNTs onto AFM tips can be used. For this purpose different methods can be utilized, e.g., surface or pore growth. In particular the chemical vapor deposition (CVD) is frequently used and yields thin CNTs grown directly on the tip apex. Besides a relatively fast production time, still dedicated equipment as well as rather harsh reaction condi- tions are required using these conventional CVD approaches. Due to the fact that all these methods are time-consuming and costly, there is a demand for alternative methods for the formation of AFM CNT-tips, which makes them afford- able and allows their use not only for very specialized applications. Here we introduce an alternative approach that allows the fabrication of carbon nanotube AFM probes utilizing the microwave-assisted growth of CNTs directly on the apex of a commercially available AFM tip. This approach benefits from the selective heating of tip mounted catalyst particles due to a preferential absorption of the microwave irradia- tion, which results in a strong, local increase of the temper- ature that is sufficient to grow multiwall carbon nanotubes in the presence of ethanol vapor within very short time scales of a few minutes only. Different aspects of the fabrication process are discussed, and an optimized proce- dure to fabricate CNT tips is presented. The microwave-assisted synthesis of CNTs on AFM tips was performed according to a previously reported method. 30 For the microwave irradiation in a synthetic laboratory single mode microwave (Emrys Liberator, Biotage) was used. * Corresponding authors. E-mail: s.hoeppener@uni-jena.de (S.H.), ulrich.schubert@uni-jena.de (U.S.S.). Telephone: +49 (0)3641 948261 (S.H.), +49 (0)3641 948202 (U.S.S.). Received for review: 06/1/2010 Published on Web: 09/24/2010 pubs.acs.org/NanoLett © 2010 American Chemical Society 4009 DOI: 10.1021/nl101934j | Nano Lett. 2010, 10, 4009–4012