Wafer Scale Nanopatterning and Nanomaterials Synthesis of Functional Nano Probes for Atomic Force Microscopy
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Wafer Scale Nanopatterning and Nanomaterials Synthesis of Functional Nano Probes for Atomic Force Microscopy Qi Laura Ye*, Alan M. Cassell, Hongbing Liu, and M. Meyyappan Center For Nanotechnology, NASA Ames Research Center, Moffett Field, CA 94035, USA *Corresponding author: e-mail: [email protected], phone: (650) 604-0497, fax: (650) 604-0987 ABSTRACT The key hurdle in nanoscience and nanotechnology is the large-scale integration of nanoscale materials with micron scale electronics and structures to form functional devices and sensors. We have developed an innovative bottom-up wafer scale fabrication method that combines nanopatterning and nanomaterials synthesis with traditional silicon micromachining technologies. We have achieved nano-micro integration through catalyst nanopatterning and registration at wafer scale and through effective nanocatalyst protection and release before and after microfabrication. Our wafer scale fabrication process has produced 244 carbon nanotube (CNT) probes per 4-inch silicon wafer with control over the CNT location, diameter, length, orientation, and crystalline morphology. CNT probes with diameters of 40-80 nm and lengths of 2-6 µm are found to be functional nano probes for atomic force microscopy (AFM) imaging. In this paper, we will address our nano probe design and fabrication considerations in detail. CNT tip locations and diameters are defined by e-beam lithography. CNT length, orientation, and crystalline quality are controlled by the plasma enhanced chemical vapor deposition (PECVD) method. With effective catalyst protection schemes, this fabrication process is very similar to the conventional approach for fabricating wafer-scale silicon AFM probe tips. Process control is feasible and the overall yield is greatly improved. Our method and technology can be easily adapted to many other nanomaterials (nanotubes and nanowires) synthesis and processes for their rational design, fabrication, and integration in their applications. INTRODUCTION Carbon nanotubes (CNTs) possess remarkable electrical, mechanical, and thermal properties [1]. The idea of using carbon nanotubes as nano probes in scanning probe microscopy was first introduced by Dai et al. in 1996 [2]. The intrinsic nanometer scale diameter, high aspect ratio, and strong mechanical robustness of CNTs make them ideal for high lateral resolution imaging [3,4] and deep trench/via critical dimension imaging [5] in semiconductor in-line processing applications. CNT probes are also highly desired in biological and chemical applications [6-8] where gentle probe-sample interactions are required. When CNT probes approach the sample surface during AFM tapping mode imaging, the CNT buckles elastically which restricts the maximum force that can be applied to soft samples. CNT probes can also be functionalized at the tube open ends [9,10]. They can be made into multi-purpose nano probes by imaging and sensing at the same time, and probing and manipulating materials at the same time. Therefore, CNT probes may be the ultima
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