Microstructure and Mechanical Properties of Surfactant Templated Nanoporous Silica Thin Films: Effect of Methylsilylation

Abstract

Microstructural and mechanical properties of organic surfactant templated nanoporous thin silica films have been studied by X-ray diffraction, Fourier transform infrared spectroscopy, and nanoindentation. Compared with many other porous low-k dielectrics, the self-assembled molecularly templated nanoporous silica films demonstrate better mechanical properties. This is ascribed to the presence of a well-ordered pore channel structure in the nanoporous silica thin films. Hardness and elastic modulus are strongly dependent on film preparation and modification methods. Trimethylsilylation by hexamethylsilazane vapor treatment effectively enhances the mechanical strength of the nanoporous silica films. When the sol precursor solution is mixed with trimethylchlorosilane ͑TMCS͒, the resulting nanoporous films have a weaker mechanical strength. The pore channel structure of the nanoporous silica film becomes less ordered for the TMCS derivatized nanoporous films. In addition, the chemical structure in the silica solid matrix of the TMCS derivatized films is more disordered than those without TMCS modification. The nanoindentation measurement results are discussed in terms of the pore microstructure of the nanoporous silica network and the springback effect due to the presence of trimethylsilyl groups in the nanopores.

Long-term durability of sol–gel porous coatings for solar glass covers

“…The cause of this deterioration has often been attributed to the absorption of airborne contaminants and overall water vapour in the film pores, leading to an increase in the refractive index [8][9][10][11]. Additionally, it has been reported that, this adsorption degrades not only the optical properties but also the electrical properties of porous silica films [12,13].…”

A Novel Organosiloxane Vapor Annealing Process for Improving Elastic Modulus of Porous Low-k Films

“…The drawbacks of these porous films include the presence of hydrophilic silanol groups on the internal wall surfaces and the lack of mechanical strength (e.g., elastic modulus, hardness). Although the silanol groups can be transformed to the hydrophobic moieties by treatment with hexamethyldisilazane (HMDS) [1][2][3][4], the mechanical strength of the resulting films is insufficient as ULSI interconnects.…”

Probing the Effects of Nanoscale Architecture on the Mechanical Properties of Hexagonal Silica/Polymer Composite Thin Films

“…Periodic surfactant-templated film systems with large degrees of nanoscale order have shown moduli in the range of 10±13 GPa. [6,27] Although some of these numbers have been derived from nanoindentation experiments that may overestimate moduli, [28±30] it is clear that these numbers are lower than the thin films in the parallel orientation in this study. This comparison shows that the alignment effects observed in this work must be central in determining the modulus of the films.…”

“…Furthermore, surfactanttemplated porous silica films with large degrees of nanoscale order have shown moduli in the range of 10±13 GPa. [6,27] Although many of the moduli discussed above should be treated with caution because nanoindentation experiments can overestimate elastic moduli owing to the viscoelasticity of the film, substrate stiffening, and film±tip interactions, [28±30] the average moduli for ordered systems are clearly larger than those of the disordered systems addressed above. This trend is clear whether the material is present in bulk or thin-film forms, indicating that nanoscale architecture is an important variable that contributes to the mechanical properties in these systems.…”