Hybrid Organic-inorganic Thin Films: Characterization and Applications

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Phong Du¹, Anurag Jain¹, Carlos B. W. Garcia¹, Liguo Wang², Paulette Clancy², Michael O. Thompson¹, Sol M. Gruner^3,4, Detlef-M Smilgies⁴, and Ulrich Weisner^1
1Department of Materials Science & Engineering
²Department of Chemical and Biomolecular Engineering
³Department of Physics
⁴Cornell High Energy Synchrotron Source
 

Abstract:
The routine formation of nanometer size structures remains a challenge that limits advances in many fields of nanotechnology.  Increasingly, “bottom-up” self-assembly approaches for the nanometer-scale patterning of surfaces are competing with traditional “top-down” lithographic processes such as scanning probe lithography or high-resolution e-beam lithography.  Block copolymer thin films (<100nm) are among the more promising materials being examined as they offer ease of processing combined with phase-separation induced structure formation on the nanometer scale.

Here we report on the use of small molecule additives (3-glycidoxy-propyltrimethoxysilane and aluminum-tri-sec-butoxide) to a structure directing block copolymer [poly(isoprene-block-ethylene oxide)] to create organic-inorganic hybrid thin films.  In addition to retaining the self-assembling behavior of the pure polymer system, this hybrid approach allows for easy access to a wide range of morphologies and provides unique macroscopic properties (e.g. mechanical and thermal) that open up pathways for novel processing methods.  Studies of the film morphology and surface topography are carried out using atomic force microscopy (AFM), scanning electron microscopy (SEM), and grazing incidence small angle x-ray scattering (GISAXS).  AFM data are processed with a home-coded analysis program to determine angular and number of nearest neighbor distributions, grain size and defects, and translational and bond orientational correlation functions.  SEM images demonstrate control of film thickness down to the monolayer without loss of structure control.  GISAXS scattering patterns of calcined films reveal a pore geometry transformation driven, we believe, by surface area/energy minimization.  Quantitative modeling agrees well with experimental results and demonstrates successful structure formation at the nanoscale over macroscopic film dimensions.  The resultant porous films show uniformity in structure dimensions and exhibits medium-range order.

As a first application, these films serve as templates for a laser-induced capillarity-driven filling process to create large arrays of silicon nanopillars.  Surface analysis before and after laser treatment shows good registry between the pores and pillars.  This technique allows for the structuring of silicon well below current photolithographic limits without the need for time-consuming, and costly, cleanroom processes.  This method should be extendible to materials other than silicon and to generate geometrically varied structures and thus offer scientific and technological promise in a wide range of fields including nanofluidics, biosensing, and nanoelectronics.