Micropattern generation with pulsed laser diffraction
Methods and devices for preparing microscale polymer relief structures from a thin polymer layer on an absorbing substrate are described. The described methods are ultrafast (about 8 nanoseconds) and allow formation of patterned microstructures having complex morphologies and narrow line widths that are an order of magnitude smaller than the masks used in the methods.
1. A method for preparing microscale polymer relief structures, the method comprising:
providing a substrate coated with at least one polymer layer;
exposing the substrate and the at least one polymer layer to electromagnetic radiation, the electromagnetic radiation having energy that is absorbed by the substrate;
producing heat from the energy absorbed by the substrate;
reorganizing the at least one polymer layer with the produced heat to prepare microscale polymer relief structures;
providing a periodic aperture separated by a distance from the substrate coated with at least one polymer layer; and
passing electromagnetic radiation through the periodic aperture before exposing the substrate coated with at least one polymer layer to the electromagnetic radiation, whereby a near-field diffraction pattern of electromagnetic radiation intensity maxima and minima is created on the substrate coated with at least one polymer layer.
2. The method of claim 1 , wherein reorganizing the at least one polymer layer includes: melting at least a portion of the at least one polymer layer; and cooling the melted portion of the at least one polymer layer.
3. The method of claim 1 , wherein reorganizing the at least one polymer layer includes plastic deformation of at least a portion of the at least one polymer layer.
4. The method of claim 1 , wherein the at least one polymer layer is substantially transparent to the electromagnetic radiation.
5. The method of claim 1 , wherein the at least one polymer layer comprises a polymer selected from the group consisting of polystyrene, polymethylmethacrylate, polyvinyl acetate, and combinations thereof.
6. The method of claim 1 , wherein the substrate comprises silicon, quartz, glass, indium tin oxide coated glass, a transparent conducting oxide, or combinations thereof.
7. The method of claim 1 , wherein the thickness of the at least one polymer layer is about 10 nm to about 500 micrometers.
8. The method of claim 1 , wherein exposing the substrate to electromagnetic radiation comprises irradiating the substrate and the at least one polymer layer with a laser having a fundamental emission wavelength.
9. The method of claim 8 , wherein the laser is a pulsed laser.
10. The method of claim 8 , further comprising converting the fundamental wavelength of the laser to a second, third, fourth, or fifth harmonic.
11. The method of claim 1 , wherein the electromagnetic radiation comprises light at about 355 nm.
12. The method of claim 1 , wherein the electromagnetic radiation has a fluence of about 100 mJ per cm2 to 400 mJ per cm2.
13. The method of claim 1 , further comprising adjusting the distance separating the periodic aperture from the substrate coated with at least one polymer layer.
14. The method of claim 1 , wherein the periodic aperture comprises a grid having components selected from squares, rectangles, hexagons, or combinations thereof.