Noble metal nanostructures are known for their unique optical property as localized surface plasmon resonance (LSPR), which electromagnetic radiation interacts with the free electrons of the metallic nanostructure, resulting in collective oscillations and thus to a significant strengthening of the local electric field surrounding the particles [1]. Although noble metal such as Ag and Au have been widely known for their plasmonic properties, Cu has often been overlooked due to surface oxidation problems, which significantly reduces the excitation intensity [2]. We present in this paper a systematic study of Cu nanoparticles assembled by direct current (DC) magnetron sputtering on quartz substrates. The effect of deposition time on the optical properties, particle size, and particle spacing has been investigated.

The Cu nanoparticles were deposited in Argon atmosphere with a pressure of 19 mTorr, DC power of 200W, and a substrate temperature of 400°C. Additionally, the Cu nanoparticles were annealed at 400°C in vacuum for 6 hours following deposition. A photograph of the Cu nanoparticles on quartz is seen in Figure 1. From left to right, the color of the samples changes from dark blue with a green hue to a light blue color as the deposition time decreases. Absorbance spectra (250-850 nm) in Figure 2 show that increased deposition time lead to higher absorbance and a slight red shift of the LSPR peak. SEM images indicated that particle size for the individual samples was not uniform, which is seen in Figure 3 (particle size ~8 – 28 nm).

In conclusion, we have demonstrated the fabrication of Cu nanoparticles by DC magnetron sputtering. The particle sizes ranged from ~8 – 28 nm when depositing for 45 seconds. Particle size, geometry, height, and spacing, which are directly responsible for the optical response, are to be investigated on quartz substrates using scanning electron microscope (SEM) and atomic force microscope (AFM).

References

1. Christy L. Haynes and Richard P. Van Duyne* The Journal of Physical Chemistry B2001 105 (24), 5599-5611 DOI: 10.1021/jp010657m
2. George H. Chan,Jing Zhao,Erin M. Hicks,George C. Schatz,* and, and Richard P. Van Duyne* Nano Letters 2007 7 (7), 1947-1952 DOI: 10.1021/nl070648a