Microstructures Properties and Characterization

Although the body of work collected so far on TPP has demonstrated how valuable this technique is in many applications, several fundamental aspects of TPP still remain ambiguous. For example, how do scanning patterns influence 

CARS microscopy derives its analytical capability from the Raman active modes of molecules [75]. There are two specific vibrational modes in the Raman spectra of acrylic based polymers that can give insights on the polymerization process and the structural integrity of microstructures fabricated via TPP. One is around 3000 cm and arises from the stretching of both aliphatic and aromatic carbon-hydrogen bonds. The other one is around 1640 cm and is due to the carbon-carbon double bond resonant vibration with the carbonyl group present in the acrylic units of the starting materials [73, 76]. 

From the SEM images of this structures it is noticeable that the shape of the last cantilever was distressed during the washing process of the unsolidified resin. 

CARS microscopy unveils how inhomogeneous is the density of polymer in some parts the microstructure. Since density is related to the polymer cross-linking and polymer total conversion, CARS microscopy in the 3000 cm range can be used to optimize the microfabrication experimental conditions. 

3D photonic crystals. Lastly, through a double inversion process, a pure silicon 3D photonic crystal was produced starting from a SU-8 master [91], Because of the high refractive index of silicon, a full bandgap was created and it was centered at 2.35 pm. 

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