Laser Micromachining for Polymer Surface Topography Design

We are researching new applications and capabilities of laser micromachining. We are working on determining the conditions and the parameter space for processing different types of materials. Currently, our main focus is surfaces of polymers, in particular, magnetoactive elastomers that can be difficult to process using other techniques due to their stickiness.

Our protocol describes a maskless structuring of surfaces, which enables rapid prototyping. It also allows for the creation of slanted structures that are not possible with other techniques. To begin, place the cured magnetoactive elastomer sample on the working area of the scanning head, ensuring it is positioned in the focal plane and tilted to the preselected angle.

Using the laser control software, design the scanning trajectory by tracing the area where material should be removed. For optical microscopy, clean the sample using pressurized nitrogen gas to gently blow away any dust or debris particles. Place the clean sample on the microscope table and switch on the reflective microscopy light source.

Select the 10x subjective lens to measure lateral dimensions such as the pitch between lamellae. Then switch to the 40x objective lens to capture data on the height of the structures. Then open the field aperture on the microscope to reduce the depth of the field.

Adjust the height of the micrometer stage to focus on the top surface of the structures. And record the reading on the micrometer screw. Afterward, gradually raise the stage by turning the micrometer screw until the substrate surface comes into focus.

Then record this new value. Wear gloves, and using a scalpel, cut the samples to match the size of the scanning electron microscopy sample holder pins. With the help of plastic tweezers, attach the trimmed samples to the pins, taking care not to damage them.

Then clean the mounted samples with pressurized nitrogen gas to remove any dust or debris. Place the pins with the attached samples into the stage and record their positions. Next, to perform backscattered electron measurements, first, evacuate air from the vacuum chamber to reach a high vacuum state.

Capture an optical navigation image of the samples and use it to guide the stage, positioning the sample of interest at the correct distance from the detector edge. Activate the electron beam and display the image from the concentric backscatter detector. To set the beam parameters, select a 30-kilovolt accelerating voltage, a spot size of 4.0, and a dwell time of five microseconds.

For secondary electron measurements, adjust the chamber to a low vacuum of 0.70 millibar. Move the samples to a working distance of approximately 3.5 millimeters. Then switch on the electron beam and view the image captured by the low vacuum secondary electron detector.

Next, attach a piece of double-sided adhesive tape to the center of the sample holder between the poles of the electromagnet. Place the sample on the adhesive tape, ensuring it is centered between the poles. While capturing images, apply a 4.5 ampere direct current to the electromagnet to generate a homogeneous magnetic field of approximately 340 millitesla in the 20-millimeter pole gap.

Optical microscopy confirmed the defect-free pattern of the magnetoactive elastomer surface with clear lateral structuring, and focus adjustments validating vertical profile visibility. Scanning electron microscopy revealed that the structured pillars have a coarse surface texture with distinct microparticles embedded throughout the side profile. Secondary electron imaging revealed a rugged and irregular polymer surface structure at high resolution.

Magnetic manipulation resulted in visible tilting of the microstructures over time, as observed in the side views under different field exposures.