Fabricating vertically ordered and etchable high aspect
ratio nanodomains
of block copolymer (BCP) thin films on diverse substrates via continuous
processing dynamic cold zone annealing (CZA) is particularly attractive
for nanomanufacturing of next-generation electronics. Previously,
we reported dynamic CZA studies with a shallow thermal gradient (maximum
∇T ∼ 14 °C/mm) that produced only
BCP cylinders oriented parallel to substrate. Here, we report a CZA
utilizing a dynamic sharp thermal gradient (∇T ∼ 45 °C/mm) (i.e., CZA-S). This method allows for production
of etchable and vertically oriented cylindrical domains of poly(styrene-b-methyl methacrylate) in 100–1000 nm thick films
on low thermal conductivity rigid (quartz) and flexible (PDMS, Kapton)
substrates. Competing substrate wetting interactions dominate BCP
orientation in films below 100 nm while broadening of the thermal
gradient profile in films thicker than 1000 nm leads to loss of vertical
orientation. An optimal dynamic sweep rate (∼5 μm/s)
produces the best vertical order. At too fast a sweep rate (>10
μm/s)
the BCP film ordering is kinetically hindered, while at too slow a
sweep rate (<1 μm/s), polymer relaxation and preferential
surface wetting dynamics favor parallel BCP orientation. Equivalent
static gradient conditions produce vertically aligned BCP cylinders
only at the maximum ∇T. CZA-S mechanism involves
propagating this vertically oriented BCP zone across the sample.
The study of the biocompatible properties of carbon microelectromechanical systems (carbon-MEMS) shows that this new microfabrication technique is a promising approach to create novel platforms for the study of cell physiology. Four different types of substrates were tested, namely, carbon-MEMS on silicon and quartz wafers, indium tin oxide (ITO) coated glass and oxygen-plasma-treated carbon thin films. Two cell lines, murine dermal fibroblasts and neuroblastoma spinal cord hybrid cells (NSC-34) were plated onto the substrates. Both cell lines showed preferential adhesion to the selectively plasma-treated regions in carbon films. Atomic force microscopy and Fourier transform infrared spectroscopy analyses demonstrated that the oxygen-plasma treatment modifies the physical and chemical properties of carbon, thereby enhancing the adsorption of extracellular matrix-forming proteins on its surface. This accounts for the differential adhesion of cells on the plasma-treated areas. As compared to the methods reported to date, this technique achieves alignment of the cells on the carbon electrodes without relying on direct patterning of surface molecules. The results will be used in the future design of novel biochemical sensors, drug screening systems and basic cell physiology research devices.
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