The plastic deformation of the nanocolumns arises due to defect formation caused by the energetic ions. It enables the complete tuning of the photonic and plasmonic properties of the grating through the slant angle. The slant angle of the nanocolumns in the periodically patterned columnar thin films (PP-CTFs) arises during the deposition process. This is due to a self-shadowing effect and is controlled by the angle of the collimated vapour flux.

Fixing the slant angle

The slant angle in a given sample is thus a quantity fixed during fabrication. The slant angle is a very crucial parameter that determines the photonic properties, like the diffraction and coupling efficiencies. The reorientation can be uniformly carried over large areas of 0.2 mm2 with the focussed ion beam (FIB). The diffraction patterns from the reoriented grating show large changes in the diffraction efficiencies.

Electromagnetic simulations of the grating structures reveal large changes in the photonic properties with the slant angle e.g. diffraction efficiencies and electromagnetic near fields. The nanocolumns can be reoriented back to the original configuration by simply changing the direction of the incident ion beam flux. These gratings give rise to highly asymmetric diffraction and surface plasmon coupling due to blazing effects. They can be flexibly controlled by reorienting the slanted metallic nanocolumns uniformly over large areas.

Reorientation

The actuation of the nanocolumns results in a reorientation of the columns. They move from a slanted configuration to being perpendicular (upright) to the substrate in a continuous manner, as a function of the irradiation time. Ga ions from the FIB at 30 keV energy and a current of 0.3 nA are made incident on the CTF. This is such that the ion beam is almost normal to the substrate.

Watching the bending

A video clip of the bending of metallic nanocolumnar rods is obtained from the Field Emission Scanning Electron Microscope (FESEM). This reveals more details showing the gradual bending of nanocolumns. They rise up to an angle that is almost directly proportional to the time of irradiation until they are oriented in a direction parallel to the ion beam direction.

More information about this research can be found in the journal Nanotechnology 26 205301.

Further reading

Focused-ion-beam-deposition contamination destabilises nanoelectronics (Jan 2015)
Achieving continuous metal film with broadband optical transparency (Apr 2015)
Patterning technique prepares graphene nanoribbons for photodetector applications (Jan 2014)