Creation of Patterned Gold Nanostructures via Electron-Beam-Induced Deposition
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Creation of Patterned Gold Nanostructures via Electron-Beam-Induced Deposition Anastasia V. Riazanova,1 Johannes J. L. Mulders2 and Lyubov M. Belova1,2 1 Department of Materials Science and Engineering, KTH – Royal Institute of Technology, Brinellvägen 23, Stockholm, 100 44, Sweden. 2 FEI Electron Optics, Achtseweg Noord 5, Eindhoven, 5600 KA, The Netherlands. ABSTRACT One of the methods to grow nanoscale three-dimensional (3D) Au patterns is to perform local electron-beam-induced deposition (EBID) using the Me2Au(acac) precursor inside the chamber of a scanning electron microscope (SEM). However, due to the organometallic nature of the chemical, the concentration of the metallic constituent in the as-deposited structure is dramatically low, at around 10 at. % of Au. Ex-situ post-annealing of Me2Au(acac) EBIDs is a very promising purification approach, resulting in an Au content of > 92 at. % after annealing at 600 °C. However, in most of the cases it also distorts the geometrical shape of the heat-treated structure, preserving of which is essential for the application. In this paper we present a systematic study of the dependence between the annealing parameters and resulting purity in combination with the shape of the Au structure. Optimized heat treatment conditions for the creation of well-purified high aspect ratio Au pillar array are presented; and for planar continuous structures, the importance of the parameter height to area ratio is identified. INTRODUCTION Nano- to microscale Au patterned structures are of great interest nowadays for use in a number of fields, such as electronics, plasmonics, biotechnology, biosensing and life science applications, e.g. lab-on-chip architectures. A superb way to create such small site-specific threedimensional (3D) Au structures of precise shape and location is to write them directly on a substrate with an electron beam via electron-beam-induced deposition (EBID) [1-3]. This technique is mask-free and is compatible with a multitude of substrates and patterns. It could be performed in the chamber of any transmission electron microscope (TEM), scanning electron microscope (SEM) or a combined focused ion beam (FIB)/SEM Dual Beam, equipped with a gas injection system (GIS). In our case, we worked with one of the most commonly used Au organometallic precursors – the dimethyl gold acetylacetonate [Me2Au(acac)]. It is known that direct writing of gold structures from this chemical results in very low concentration of gold, only 8 – 12 at. %, the rest being carbon [4]. Thus, in order to increase the amount of metallic content in the EBID structures, we performed ex-situ post-deposition annealing of the created samples. This purification method is rather widely applicable to a number of different gas chemistries [5,6]; and in our previous work [4] we established that annealing of Me2Au(acac) EBID structures for 1 hour at 600 °C in air leads to a spectacular purity improvement: above 92 at. % of Au. However, during the heat treatment of gold patterns the undesirable reconfiguration
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