Cross-linked and chemically functionalized polymer supports by reactive reversal nanoimprint lithography

Direct nanoimprinting of nanoporous organosilica films consisting of covalently crosslinked photofunctional frameworks

Nanoimprinting methods have been used widely to prepare various patterned or nanostructured thin films from inorganic or organic components. However, the accumulation of large functional aromatic groups in covalently crosslinked nanoimprints is challenging, due to the difficulty in controlling the fluidity and reactivity of the precursor films. In this work, nanoimprinting of naphthalimide-silica sol-gel films results in vertically oriented nanoporous structures consisting of covalently crosslinked UV-absorbing frameworks. The nanoimprinted films demonstrate potential as robust analytical substrates for laser desorption/ionization mass spectrometry (LDI-MS). The sol-gel polycondensation behavior of the precursors is examined using 29Si NMR spectroscopy to determine reaction conditions suitable for nanoimprinting. The inorganic-organic hybrid frameworks containing a high density of naphthalimide groups exhibit small volume shrinkage during the polycondensation reactions, which leads to desired nanoimprinting. Various bio-related compounds on the order of picomole to femtomole quantities are detectable by LDI-MS measurements using the nanoimprinted substrates. To improve their user-friendliness and signal intensity in LDI-MS analysis, the nanoimprinted substrates are patterned with surface-modified silica nanoparticles. The direct formation of surface nanostructures by nanoimprinting of functional organosilica films may open a new path to developing optically and electronically functional materials, thereby widening their utility.

Selective growth of silver nanoparticle arrays on nanoimprinted sol-gel silica patterns

Selective growth of silver nanoparticles on ~100 nm thick silica patterns produced by nanoimprint method has been successfully demonstrated using either (1) thermo-induced reduction or (2) room temperature electroless deposition (ELD) without removing the ~25 nm thick residual layer left by nanoimprint process. This selectivity was achieved by silane additive, (3-mercaptopropyl)trimethoxysilane (3-MTS), which was added to the silica matrix to control nucleation and growth of silver. The presence of silver nanoparticles was confirmed by EDX and UV-vis spectrum, and the density, distribution, and size of silver particles were examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Silica film heat-treated between 400 and 600 °C resulted in silver particles of 100-120 nm diameter with a linear density of 2.63-3.36 μm(-1), while the film treated by room temperature ELD produced silver particles of 67 nm diameter with a linear density of 5.65 μm(-1). The selective growth ratio based on particle density on pattern area versus residual layer is 12.92 and 20.31 for high- and room-temperature processes, respectively, whereas the samples without 3-MTS shows low selective growth ratio of 1.22 and 1.04. These results prove that both approaches are fast and effective, suggesting their potential to produce other type of nanoparticle arrays directly on nanoimprinted patterns.