Reconstructing Laser-Structured Surfaces in 3D with SEM Imaging

Ultrashort femtosecond lasers are known for their ability to fabricate complex devices and nanostructures efficiently for a huge scope of applications including:

  • Biomedical engineering
  • Micro-optical components
  • Gratings

Recently, in two studies on either side of the Atlantic, the properties of femtosecond laser-structured surfaces were observed using a unique SEM image reconstruction method, in cases where other characterization techniques were unable to yield valid results.

Cavity machined with a femtosecond laser.

Cavity machined with a femtosecond laser.

Recently, Mickaël Le Barh, a materials science student, performed a study on femtosecond laser micromachining optimization for the Department of Mechanical Engineering at the University of Ottawa, Canada.

Deep cavities (500 µm x 500 µm x 100 µm) were machined with a femtosecond laser (see image above) and our goal was to get the smoothest surfaces possible on the bottom and sides of the cavities. To achieve this, we adjusted machining parameters using visual quantification but found it was also useful to be able to perform roughness measurements.

 

Mickaël Le Barh, Materials Science Student

Le Barh continued, “Initially I attempted to do this using an atomic force microscope (AFM) but the complex geometry of the sample prevented the microscope from accessing the bottom of the cavity. Using a Zeiss scanning electron microscope equipped with Mountains® software, we were able to obtain the desired result.”

3D reconstruction of cavity base with roughness parameters.

3D reconstruction of cavity base with roughness parameters. 

“Obtaining smooth surfaces using ultrafast lasers is relevant in many applications where slower processes are currently used such as in sample preparation for electron microscopy, fabrication of microfluidic channels, 3D serial sectioning, micro-electro-mechanical systems and micro-optical elements,” added Le Barh.

Surface Wettability in Biomedical Applications

Ph.D. Researcher in Laser Material Processing at the FEMTO-ST Institute in Besançon, France, Vahan Malkhasyan, has been examining the femtosecond laser-matter interaction of metals and transparent materials.

This interaction was studied for fabricating super-hydrophilic (super-wetting) and super-hydrophobic (water-repellent) surfaces for biomedical devices in a similar application. Again, in order to achieve reliable results, the 3D reconstruction of SEM images was vital.

3D model of a laser ablated micro-line reconstructed from two SEM images obtained at different tilt angles.

3D model of a laser ablated micro-line reconstructed from two SEM images obtained at different tilt angles.

In this study, it was important to measure the depth of crater impacts & lines ablated on different surfaces. The depths to be quantified were situated in the 5-60µm range. we compared topographies obtained by stereo reconstruction of SEM images and by optical and mechanical measurements.

 

Vahan Malkhasyan, PhD Researcher, Laser Material Processing, FEMTO-ST Institute in Besançon, France

Malkhasyan continued, “Using our 3D profilometer, it was difficult to obtain profile depth values of the impacts. In some cases, the values found were inaccurate. However using our FEI SEM to obtain two images of the sample which were then built into a 3D model using Mountains® software gave much more credible values.”

Automatic step height measurement performed on reconstructed SEM data.

Automatic step height measurement performed on reconstructed SEM data.

This information has been sourced, reviewed and adapted from materials provided by Digital Surf.

For more information on this source, please visit Digital Surf.

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