Multidimensional Morphology Control for PS‐b‐P₄VP Templated Mesoporous Iron (III) Oxide Thin Films

Abstract

nanostructured α-Fe 2 O 3 exhibits more size-dependent properties induced by the high surface area and quantum confinement. [5][6][7][8] Assembly of α-Fe 2 O 3 nanoparticles (NPs) into periodic arrays has attracted high attention due to their potential applications in photoelectrochemical conversion, [9,10] photovoltaic devices, [11][12][13][14] lithium-ion batteries, [4,7,8,[15][16][17] gas sensors, [6,18,19] and high-density nanoelectronic technologies. [20,21] Here the morphology is of particular relevance. For example, when used as the electron transport layer for photovoltaic devices, the nanoscale morphology will affect the charge carrier transport and thereby the device efficiency. [22] Current lithographic techniques employed in the microelectronic industry face the escalating production cost by further decreasing the feature size. [23][24][25] As an inexpensive alternative, the block copolymer templated sol-gel method can achieve various nanoscale structures with the assistance of selfassembly of block copolymers. [2,20,[26][27][28][29][30] Typically, nanopatterning of the Fe 2 O 3 NPs through block copolymer templates can be categorized into two types: directly accommodating the NPs inside the block copolymer matrix or in situ reducing block copolymer coordinated metal precursors into NPs. To accommodate the NPs, a special surface treatment of the NPs Mesoporous α-Fe 2 O 3 thin films with large area homogeneity demonstrate tremendous potential in multiple applications. In the present work, the synthesis of morphology-controlled α-Fe 2 O 3 thin films is realized with polystyrene-blockpoly(4-vinyl pyridine) (PS-b-P 4 VP) diblock copolymer assisted sol-gel chemistry. The solvent category (DMF and 1,4-dioxane) and polymer-to-FeCl 3 ratio used for the solution preparation are systematically varied to tune the morphology of the thin films. For both solvents, DMF and 1,4-dioxane, nanocluster structures are obtained with low PS-b-P 4 VP concentration. When the concentration of PS-b-P 4 VP reaches the critical micelle concentration, spherical and wormlike porous structures are specifically formed in the DMF and 1,4-dioxane solvent system, respectively. Further increasing the polymer-to-FeCl 3 ratios leads to the enlargement of the spherical pore sizes in the DMF system, whereas the center-to-center distances of the wormlike structures in the 1,4-dioxane system decrease. Moreover, DMF/1,4-dioxane solvent mixtures with different volume ratios are applied for the sol-gel solution preparation to gain more insight into how the solvent selectivity affects the thin film morphology. By adjusting the preferential affinity of the solvent mixture to the polymer blocks, a spherical to wormlike pore shape transition is observed with a critical Δχ value of around 0.77.

Toluene‐Mediated Morphology Tuning of Diblock Copolymer‐Templated Porous Si/Ge/K/C Thin Films for Li‐Ion Batteries

“…[1,16,17] Importantly, other porous metal oxides also gained attention as promising energy materials like porous iron, tin, and zinc oxides. [18][19][20] Contrary, studies about porous mixed semimetal films are relatively rare up to now. [21][22][23] In this regard, especially Si and germanium (Ge) as anodes in Li-ion batteries (LIBs) show huge benefits such as high theoretical specific capacities (Si: 4200 mAh g À1 , Ge: 1600 mAh g À1 ) and high diffusion coefficient paired with good cycling performance compared to graphite (372 mAh g À1 ).…”

Liquid Phase Infiltration of Block Copolymers

“…The following polymer removal and simultaneous reduction or oxidation of the metal precursor, whether by O 2 plasma, thermal degradation or UV/ozone treatment, reveals a nanostructured inorganic material (typically metals or metal oxides) whose morphology replicates that of the BCP template [ 34 ] ( Figure 1 ). The selective incorporation of the precursor could be achieved either prior to the BCP self-assembly process, by mixing the BCP and metal salt solution [ 28 ], or afterwards, by soaking the self-assembled nanostructures into the precursor-containing solution [ 17 ]. Alternatively, the metal salt solution can be directly spin-coated on top of the polymeric film [ 32 ].…”

“…Compared to SIS, LPI offers a wider range of metallic elements (Au, Pt, Pd, Fe, Co, Cu, Ni) [ 15 , 22 , 23 ], metal alloys (FePt, AuAg) [ 24 , 25 , 26 ], multicomponent nanopatterns (Pd/Pt, Au/Pt) [ 27 ], metal oxides (Fe 2 O 3 , Fe 3 O 4 , NiO, Cr 2 O 3 ) [ 16 , 20 , 28 ] as well as metal halide perovskites (MAPbBr 3 ) [ 21 ] that can be incorporated inside BCPs commonly used in nanopatterning applications such as poly(styrene)- b -poly(2-vinylpyridine) (PS- b -P2VP), poly(styrene)- b -poly(4-vinylpyridine) (PS- b -P4VP) and poly(styrene)- b -poly(ethylene oxide) (PS- b -PEO). Although LPI was initially exploited for lithographic purposes [ 29 , 30 , 31 ], recent developments in infiltration design have led to the synthesis of materials with added functionalities, widening its application to plasmonics [ 32 ] and electronics [ 33 ].…”

Organic‐Inorganic Phenolic/POSS Hybrids Provide Highly Ordered Mesoporous Structures Templated by High Thermal Stability of PS‐b‐P4VP Diblock Copolymer

“…As a consequence, the preparation of mesoporous materials templated by PS‐ b ‐P4VP has been generally interesting in recent years. Incorporating inorganic materials into phenolic resins could be considered a simple way to achieve this goal [47–51] …”