Sequential infiltration synthesis (SIS) is an emerging method for vapor-phase growth of inorganic materials within polymers that is utilized for hybrid organic–inorganic and inorganic nanostructure fabrication. The range of SIS applications has been continuously expanding for the past decade. A fundamental understanding of precursor–polymer interactions is, however, essential to expand the use of SIS to additional chemistries and move beyond thin film polymer templates. This work utilizes density functional theory (DFT) calculations and in situ gravimetric analysis to probe the growth mechanism of trimethyl­aluminum (TMA) within poly­(methyl methacrylate) (PMMA) and poly­(2-vinylpyridine) (P2VP). The theoretical and experimental analyses reveal that each precursor–polymer pair is characterized by a balance point temperature at which rates of forward and reverse precursor–polymer binding enable maximum mass gain at thermodynamic equilibrium. At short exposure times, mass gain is significantly influenced by the pressure profile of the process chamber. Mechanism comprehension enabled nanopatterning of a previously unsuitable block copolymer (BCP), polystyrene-block-P2VP (PS-b-P2VP), at elevated temperatures. It was proven possible to grow significant mass while maintaining the pattern by stabilizing the morphology via a single cycle at low-temperature SIS, thus overcoming self-assembly sensitivity to temperature.

Nanofabrication is continuously searching for new methodologies to fabricate 3D nanostructures with 3D control over their chemical composition. A new approach for heterostructure nanorod array fabrication through spatially controlled–growth of multiple metal oxides within block copolymer (BCP) templates is presented. Selective growth of metal oxides within the cylindrical polymer domains of polystyrene‐block‐poly methyl methacrylate is performed using sequential infiltration synthesis (SIS). Tuning the diffusion of trimethyl aluminum and diethyl zinc organometallic precursors in the BCP film directs the growth of AlOx and ZnO to different locations within the cylindrical BCP domains, in a single SIS process. BCP removal yields an AlOx‐ZnO heterostructure nanorods array, as corroborated by 3D characterization with scanning transmission electron microscopy (STEM) tomography and a combination of STEM and energy‐dispersive X‐ray spectroscopy tomography. The strategy presented here will open up new routes for complex 3D nanostructure fabrication.

Inorganic nanofibers are advantageous materials in a variety of applications such as gas sensing and catalysis due to their 1D morphology, high surface area, and versatile properties. Here, we present a new approach for high-precision ceramic fiber fabrication of AlO x , ZnO, and AlO x -ZnO core–shell fibers, with programmable dimensions, morphology, and surface structure, through controlled growth of metal oxides within electrospun polymer fibers using sequential infiltration synthesis (SIS). Designed growth profiles within the fiber are achieved through controlled diffusion of the SIS gaseous precursors; moderate growth gradients lead to spherical fibers after polymer removal, while sharp growth gradients result in fiber buckling into nanobelt morphology. To move towards complex inorganic fiber architectures, we extend single-metal-oxide SIS into spatially controlled, multi-material SIS and demonstrate AlO x -ZnO core–shell fibers with tunable core and shell thicknesses. The core–shell fibers are fabricated in a single SIS process, where the location of each metal oxide is controlled by its diffusion time. This study opens up new possibilities for high-precision, complex architecture and composition ceramic fibers fabrication process.

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