Following an experiment to optimize annealing conditions on a silicon substrate by CW laser irradiation, the scientists found asymmetric sheet resistance on the surface of the wafer. After studying the surface to look for the reasons, the team located bumpy nanostructures.

The researchers introduced a high-speed scanning CW laser as a versatile approach to building up these self-organized nanostructures along the trace of a scanning laser. The scanning CW laser extends the irradiated spot over the whole area of the target, and carves periodic nanostrip grating lines (nano-SGL) along the trace of a single scanning laser beam at a speed of 300 m/min, while a femtosecond laser irradiating a target forms a periodic structure in the irradiated spot typically after hundreds of laser shots.

Although the structure formed by a femtosecond laser is called a grating structure, it is rather a fibre-like structure; it has granularity, relief, ripples or grooves with some periodic structure.

As an example of the versatility of this method, a computer cooling fan was used for rotating the target sample to draw concentric circles, resulting in structural colour from the formed nano-SGL, as shown in the photo above.

Additional information can be found in the journal Nanotechnology.