Reply briefly to the following questions: a) Which lithographic methods are capa
ID: 702539 • Letter: R
Question
Reply briefly to the following questions: a) Which lithographic methods are capable of making surface features smaller than 100 nm? b) Suggest a few techniques for making protein patterns on surfaces. c) Which method is slower: e-beam lithography or photolithography and why? d) Which techniques can be used for making microfluidic channels in PDMS? e) Discuss the advantages or disadvantages in using conventional polymer 3D printing two-photon photopolymerization for making of 3D structures in the range of 100 nm-1Explanation / Answer
(a) Microelectronics:
This is very important photolithography, bit more expansive but cpable of making surface features <100nm. It can not be used widely because in some processes cost is really dominent factor. In this type of lithography Cu supported on quartz plate pattern used which can directly pattern polymers with photosensitive aditives. This lithography can be replaced with Soft lithography due to its less cost and minimum feature size between 10-100 nm. This soft lithography produce selfassembled micropatterns (SAMs) by imprinting, molding (replica) and cantact printing.
(b) Fabrication techniques:
(1) Photochemical modification technique:
In this technique high energy photons (mostly UV) is used to break the chemical bond at surface and releases free radicals. To improve surface adhesion different functional group like -OH, -CONH2 attached to the surface, These groups are better than -COOH due to thier wetting properties.
In this technique a mask applied on the surface to provide selective surface modification.
(2) Composites and graft formation technique
In this technique ratio of glycolic acid and lactic acid added which improves the hydrophilic nature of surface. By controlling (mainly glycolic acid) this ratio hydrophobicity of surface.
(3) Plasma treatment
In this technique glow discharge plasma is crated with the help of low pressure ( ammonia, argon etc.) gases filled in vaccum. The gas is then ionized by microwave or current due to excitation. this ionized gas is then bombarded on surface at a very high velocity due to which energy created modifies the surface.
(c) E-beam lithography is slower than photolithography.
Reason: E-beam lithography is as maskless techniques used in number of applications because it fabricate ultrahigh resolution masks but the patterns it writes in successive manner which make it more slower than photolithography.
(d) A research shows that these channels can be created by water soluble molds:
In this techniques a cutting machine used to cut channels from a water-soluble starch sheet, which produces our
master mold. This cutting and plotter machine has a linear resolution of approximately 100 ?m, which is not as fine as that obtained from photolithography, but is typical for simple chemical and biological experiments. Then put the prepared designed sheet onto the semi-cured PDMS surface, and then add PDMS to cover the film. PDMS is then degas using a portable vacuum sealer that is normally used to preserve foods. We cure the PDMS in a microwave oven, which we found to be surprisingly simple and efficient cure times are typically about 3 - 6 min