Patterning PETN and HMX using Dip Pen Nanolithography
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0896-H05-06.1
Patterning PETN and HMX using Dip Pen NanolithographyTM (DPNTM) a
Omkar A. Nafdaya, Brandon L.Weeksa, Jason Haaheimb and Ray Ebyb Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409. b NanoInk Inc., 1335 W Randolph St. Chicago, IL 60607.
ABSTRACT Recently there has been a focused effort to develop reliable nanoscopic writing and reading capabilities. Dip-pen nanolithography (DPN) has emerged as a convenient method to deliver nanoscale materials onto a substrate by leveraging scanning probe microscopy capability. A new application for the DPN method is the field of microdetonics which is the micro scale decomposition and study of reactions of explosives. Results are presented for patterning pentaerythritol tetranitrate (PETN) and cyclotetramethylene tetranitramine (HMX) on silicon and mica substrates. The ultimate goal is to pattern both energetic materials in nanoscale registry and investigate their reaction and decomposition at the nanoscale due to heating or shock initiation. In addition to patterning of high explosives, a discussion on the effect of surface energy on patterning rates is investigated. This knowledge will be applicable to inks beyond high explosives. Keywords: Dip Pen Nanolithography, PETN, HMX. 1 INTRODUCTION Direct write methods such as dip pen nanolithography (DPN) are emerging as the method of choice for patterning soft organic molecules on different substrates at the nanoscale. Mirkin et al. [1] were the first to document and describe a working example of DPN and since then, this method has found numerous patterning applications. This method gives better resolution in comparison to other deposition methods like nano-transfer printing [2], electron beam lithography [3], nanoimprint lithography [4] and ion-beam lithography [5] for patterning of soft molecules. The DPN method has found numerous applications in patterning thiols [1, 6-9], dendrimers [10], gold nanostructures [11], DNA [12], proteins [13], luminescent nanowires [14], sol-gels [15] and solid-inks. [16]. DPN is an application of the atomic force atomic force microscope (AFM). Since its invention [17], the AFM has been a primary tool for nanoscale investigations due to its ability to image surfaces at high resolution. A sharp AFM tip (silicon nitride (Si3N4), silicon or diamond, radius ~ 10-20 nm) is coated with chemical inks in the DPN method and used to deposit ink on a suitable substrate to form a stable nanoscale pattern. As the tip scans the surface, deviations of the piezo scanner due to surface features are registered as changes in the photodetector and a high resolution image of the patterned features is registered. The lateral force microscopy (LFM) image shows the difference in friction force between the inked tip and the substrate. 1a
1b 2 µm
Figure 1: Schematic representation of the DPN method (1a) and the LFM (1b) image of text patterned with MHA in acetonitrile on evaporated gold.
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The LFM mode image is used to highlight the patterned features as there is little
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