Sequential infiltration
synthesis (SIS) into poly(styrene)-
block
-maltoheptaose
(PS-
b
-MH) block copolymer
using vapors of trimethyl aluminum and water was used to prepare nanostructured
surface layers. Prior to the infiltration, the PS-
b
-MH had been self-assembled into 12 nm pattern periodicity. Scanning
electron microscopy indicated that horizontal alumina-like cylinders
of 4.9 nm diameter were formed after eight infiltration cycles, while
vertical cylinders were 1.3 nm larger. Using homopolymer hydroxyl-terminated
poly(styrene) (PS–OH) and MH films, specular neutron reflectometry
revealed a preferential reaction of precursors in the MH compared
to PS–OH. The infiltration depth into the maltoheptaose homopolymer
film was found to be 2.0 nm after the first couple of cycles. It reached
2.5 nm after eight infiltration cycles, and the alumina incorporation
within this infiltrated layer corresponded to 23 vol % Al
2
O
3
. The alumina-like material, resulting from PS-
b
-MH infiltration, was used as an etch mask to transfer
the sub-10 nm pattern into the underlying silicon substrate, to an
aspect ratio of approximately 2:1. These results demonstrate the potential
of exploiting SIS into carbohydrate-based polymers for nanofabrication
and high pattern density applications, such as transistor devices.
Here we present a method to control the size of the openings in hexagonally organized BCP thin films of poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) by using surface reconstruction. The surface reconstruction is based on selective swelling of the P4VP block in ethanol, and its extraction to the surface of the film, resulting in pores upon drying. We found that the BCP pore diameter increases with ethanol immersion temperature. In our case, the temperature range 18 to 60 °C allowed fine-tuning of the pore size between 14 and 22 nm. A conclusion is that even though the molecular weight of the respective polymer blocks is fixed, the PS-b-P4VP pore diameter can be tuned by controlling temperature during surface reconstruction. These results can be used for BCP-based nanofabrication in general, and for vertical nanowire growth in particular, where high pattern density and diameter control are of importance. Finally, we demonstrate successful growth of indium arsenide InAs vertical nanowires by selective-area metal-organic vapor phase epitaxy (MOVPE), using a silicon nitride mask patterned by the proposed PS-b-P4VP surface reconstruction lithography method.
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