Electrostatic-Directed Deposition of Nanoparticles on a Field Generating Substrate
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Electrostatic-Directed Deposition of Nanoparticles on a Field Generating Substrate De-Hao Tsai1,2, Takumi Hawa1,2, Hung-Chih Kan3, Raymond J Phaneuf3, and Michael R Zachariah1,2 1 Department of Mechanical Engineering and Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, 20742 2 National Institute of Standards and Technology, Gaithersburg, MD, 20899 3 Department of Material Science and Engineering, University of Maryland, College Park, MD, 20742 ABSTRACT In this paper we develop a Brownian dynamics model applied to position metal nanoparticles from the gas phase onto electrostatic-patterns generated by biasing P-N junction substrates. Brownian motion and fluid convection of nanoparticles, as well as the interactions between the charged nanoparticles and the patterned substrate, including electrostatic force, image force and van der Waals force, are accounted for in the simulation. Using both experiment and simulation we have investigated the effects of the particle size, electric field intensity, and the convective flow on coverage selectivity. Coverage selectivity is most sensitive to electric field, which is controlled by the applied reverse bias voltage across the p-n junction. A nondimensional analysis of the competition between the electrostatic and diffusion force is found to provide a means to collapse a wide range of process operating conditions and an effective indicator or process performance. INTRODUCTION Functional nanoparticles have been widely considered as the building blocks of potential electronic, optoelectronic, and sensing devices [1-2]. For many applications of nanoparticles, in for example sensors or other electronic devices precise positioning for integration into a working device becomes a considerable challenge. The production of nanoparticles using gas phase methods has the advantage of a clean, continuous process which can be operated at atmospheric conditions without requiring any vacuum environment or solvent medium [1]. An additional advantage is that charge can be readily placed on nanoparticles, which can be used both to conduct size selection or filtration, and to direct deposition through the implementation of electric fields. Electrostatic-directed methods have been used previously with some success [3-6] and suggest a good strategy to achieve this alignment. In our previous work [6], we directed the deposition of particles using a substrate with lateral and vertical tunable fields. This was achieved by using an array of biased p-n junction patterned substrate to generate a pattern of tunable electric fields, which enabled us to form stable charge patterns on the substrate. The success of this work suggested further investigation into the particle size dependence of coverage selectivity, and some consideration of the ultimate resolution that could be achieved in this patterning approach. In this paper we discuss an expanded set of experiments using sizeselected particles. This data forms the basis for the development of a validated Bro
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