Photonic metamaterials by direct laser writing and silver chemical vapour deposition

Rill, Michael S.. “Photonic metamaterials by direct laser writing and silver chemical vapour deposition.” Nature materials 7.7 (2008):543-546.

Purpose

Photonic metamaterials exhibit fascinating magnetic properties at optical frequencies.  Functional devices will ultimately require large-scale three-dimensional systems.  However, current 3D device fabrication is usually limited to pattering two-dimensional systems via electron-beam lithography and metal film evaporation followed by repeated stacking.  This work investigates a faster and more direct method of laser writing and metallic chemical vapour deposition (CVD) for the purpose of rapidly prototyping 3D photonic metamaterials. 

Method

A 3D polymeric template is fabricated by standard methods of direct laser writing (DLW) a thin film of SU-8 photoresist (on glass substrate).  Post-bake and developing are performed after exposure.  Next, a thin layer of SiO2 is applied in order to increase mechanical stability and to serve as a backbone for the subsequent deposition of silver.  Following activation of the oxide layer with O2 plasma, a metal-organic precursor is added and CVD cycles are applied.  Ten cycles of silver CVD generate a silver thickness of 50nm.  Electron micrographs are used to examine the quality of the structure.  Optical properties are determined via normal-incidence transmittance measurements in a Fourier-transform microscope spectrometer.

Key findings

1. Electron imaging revealed a uniform silver coating.  This was noted to be in sharp contrast to the typical 2D evaporation method.
2. Optical transmittance measurements corresponded well with theory.
3. Overall, this method was successfully demonstrated to be a quick and reliable way of achieving 3D photonic metamaterials.  The authors note that they have approached a bottleneck in the theory of such devices.  They hope that this work spurs further theoretical investigation and research in this emerging field.

Key terms

CVD – chemical vapor deposition; DLW – direct laser writing.