Thermal fabrication of gold nanocages
The purpose of this research project was to test and characterize a new method for gold nanoparticle production. The main idea was based on the preliminary observations made in earlier work, which had suggested that small amounts of gold deposited onto a silicon substrate will spontaneously reshape into gold nanoparticles when treated to controlled high-temperature heating for a sufficient period of time. This idea for a fabrication process was extended to incorporate Electron Beam Lithography (EBL) gold patterning. The full fabrication method consisted of the following steps: (1) Preparation of clean silicon substrates, (2) Addition of a Poly(methyl methacrylate) (PMMA) Coat via spin coating, (3) Design of gold patterns for the EBL, (4) Gold patterning via EBL, (5) Gold deposition via electron beam evaporation, (6) PMMA mask removal via acetone wash, and (7) High-Temperature furnace heating, as well as plans for a final step (8) Isolation of the gold nanocages via HF etching. The project research required the use of the photolithographic facilities of the Vanderbilt Institute of Nanoscale Science and Engineering (VINSE), as well as the use of the high-temperature furnace and other basic needs supplied by the research group of Professor Dickerson. Some of the VINSE equipment required relatively extensive operational training. The research project has demonstrated that the described thermal fabrication method can uniformly and repeatedly produce Au nanoparticles of about 400 nm in diameter from Au deposits of 1 um2 area and 20 nm thickness. Larger areas displayed structural fragmentation into multiple nanoparticles, and this fragmentation effect increased proportionally with increasing area size. Due to time constraints, the many available parameters prevented a complete characterization of this fabrication method; however, useful insights were obtained for several of the parameters of the fabrication process. In particular, it can be expected that smaller nanoparticles may be fabricated in a straightforward manner by reducing the patterned area sizes of the gold deposits. Results suggested an intrinsic limitation to the method: for the requirement of product uniformity, each Au-area deposit had to produce only a single nanoparticle.