Rational Design and Fabrication of Block Copolymer Templated Hafnium Oxide Nanostructures

Abstract

The ability to fabricate hafnium oxide (HfO 2 ) nanostructures is central to the performance of computation devices, non-volatile memories, capacitors, biosensors, and optical devices. Sequential infiltration synthesis (SIS) has emerged in recent years as a new platform for nanostructure fabrication via the growth of inorganic materials within polymer templates using vapor phase precursors. However, the SIS materials library is currently still limited. In this study, we expand the SIS library with the development of hafnium oxide SIS and demonstrate HfO x nanostructure fabrication via SIS within block copolymer (BCP) templates. Insights into the infiltration behavior of tetrakis(dimethylamino)hafnium (TDMAHf), the Hf precursor, in various homopolymers, were obtained by in situ quartz crystal microgravimetry (QCM) measurements. These insights guided us to judiciously choose BCP systems for HfO x nanofabrication, where polystyrene-block-poly(epoxyisoprene) (PS-b-EPI) and HfO x SIS at 95 °C showed exceptional selective growth of HfO x in the EPI domains. Density functional theory (DFT) calculations supported the experimental observation that TDMAHf exhibits higher reactivity with the EPI domain compared to the PS domain. Detailed investigation of the templated HfO x nanostructures using scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) further validates the presence and distribution of Hf and O elements, as well as two oxidation states of the oxide. Our work presents the first report of HfO x SIS in BCPs, providing a method for HfO x nanostructure fabrication with tuned morphology and precise control over the HfO x growth. Furthermore, it contributes to the growing SIS library and its new avenues for functional nanomaterials with customizable properties fabrication.

The Development and Atomic Structure of Zinc Oxide Crystals Grown within Polymers from Vapor Phase Precursors

“…SIS provides an alternative to common nanofabrication techniques as it enables a controlled, step-by-step conversion of organic nanostructures into hybrid and inorganic nanostructures. Over the past 15 years, the SIS materials library has been greatly expanded to include precursors for growth of metal oxides like AlO x , − TiO 2 , − ZnO, ,,− In 2 O 3 and more, − and even metals like W, , and Ru . The scope of polymers has been greatly broadened over this time period, as well, and SIS has been used to alter the inherent properties of both natural , and synthetic polymers, ,− including block copolymers (BCPs) and block terpolymers .…”

Sequential Infiltration Synthesis of Al2O3 in PMMA Thin Films: Temperature Investigation by Operando Spectroscopic Ellipsometry

“…The SIS process for infiltration of Al 2 O 3 into poly­(methyl methacrylate) (PMMA) films via trimethyl aluminum (TMA) and H 2 O has been widely studied, and it is considered as the reference system in the field. Several in situ characterization techniques including quartz crystal microgravimetry (QCM), ,− Fourier transform infrared (FTIR) ,,− spectroscopy, spectroscopic ellipsometry (SE), ,, and X-ray photoelectron spectroscopy (XPS) ,, have been employed to investigate the different phenomena occurring during the SIS process. These characterization techniques provide complementary information that contributed to advancing the effective understanding of the interplay among these fundamental phenomena.…”