Electroless Deposition and Patterning of Morphologically Complex Precious Metal Films on Semiconductor Surfaces
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Electroless Deposition and Patterning of Morphologically Complex Precious Metal Films on Semiconductor Surfaces Lon A. Porter, Jr., Hee Cheul Choi, Alexander E. Ribbe, and Jillian M. Buriak Department of Chemistry, 1393 Brown Laboratories, Purdue University, West Lafayette, IN 47907-1393, U.S.A. ABSTRACT Precious metals are choice materials for a myriad of applications due their high electrical conductivity, resistance to corrosion, and ligand binding specificity. Indispensable in modern electronics fabrication, precious metals also enjoy widespread use as catalysts, support substrates, and sensor elements. Recent progress towards metallization on diminishing size regimes has imposed increasingly stringent demands upon thin film preparation methodologies. Metallization techniques employed in ultra large scale integration (ULSI) device fabrication, nanoelectromechanical systems (NEMS), and arrayed nanosensors will require unparalleled control of surface morphology, deposition rate, and substrate adhesion without sacrificing throughput or cost effectiveness. Furthermore, precious metal films of this type are essential for fundamental investigations aimed at elucidating the intricate nature of interfacial topics ranging from self-assembled monolayers (SAMs) to heterogeneous catalysis. In contrast to complex and expensive vacuum methods of metallization, research in our laboratory has focused on the preparation of precious metal thin films on semiconductor substrates via electroless deposition. Thin and thick films of gold, platinum, and palladium nanoparticles have been prepared as a result of the immersion of germanium and gallium arsenide substrates into dilute, aqueous solutions of tetrachloraurate (III), tetrachloroplatinate (II), and tetrachloropalladate (II), respectively. This methodology yields nanostructured precious metal films with control over surface morphology and deposition rate. Moreover, metal films prepared in this manner exhibit excellent adhesion to the underlying semiconductor substrate. The resultant films were characterized utilizing scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and scanning probe microscopy (SPM). This method provides for the facile interfacing of metal nanostructures with group (IV) and III-IV compound semiconductor surfaces. INTRODUCTION In contrast to complex and expensive vacuum methods of metallization [1,2], research in our laboratory has focused on the preparation of gold and other precious metal thin films on semiconductor substrates via electroless deposition [3]. Herein, we report the implementation of this facile methodology to prepare nanostructured precious metal films with control over surface morphology and deposition rate. Deposition proceeds via galvanic displacement in the absence of fluoride (HF, NH4F) [4], pH adjusters [1], complexing agents [1], or external reducing agents [1]. Furthermore, nanoparticle films prepared in this facile manner exhibit excellent adhesion to the underlying semiconductor
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