Yusuke Matsuda

Moisture-Insensitive Polycarbosilane Films with Superior Mechanical Properties

We report cross-linked polycarbosilane (CLPCS) films with superior mechanical properties and insensitivity to moisture. CLPCS are prepared by spin-coating and thermal curing of hexylene-bridged disilacyclobutane (DSCB) rings. The resulting films are siloxane-free and hydrophobic, and present good thermal stability and a low dielectric constant of k = 2.5 without the presence of supermicropores and mesopores. The elastic stiffness and fracture resistance of the films substantially exceed those of traditional porous organosilicate glasses because of their unique molecular structure. Moreover, the films show a remarkable insensitivity to moisture attack, which cannot be achieved by traditional organosilicate glasses containing siloxane bonds. These advantages make the films promising candidates for replacing traditional organosilicate glasses currently used in numerous applications, and for use in emerging nanoscience and energy applications that need protection from moisture and harsh environments.

Fundamental limits of material toughening in molecularly confined polymers.

The exceptional mechanical properties of polymer nanocomposites are achieved through intimate mixing of the polymer and inorganic phases, which leads to spatial confinement of the polymer phase. In this study we probe the mechanical and fracture properties of polymers in the extreme limits of molecular confinement, where a stiff inorganic phase confines the polymer chains to dimensions far smaller than their bulk radius of gyration. We show that polymers confined at molecular length scales dissipate energy through a confinement-induced molecular bridging mechanism that is distinct from existing entanglement-based theories of polymer deformation and fracture. We demonstrate that the toughening is controlled by the molecular size and the degree of confinement, but is ultimately limited by the strength of individual molecules.

Toughening Thin‐Film Structures with Ceramic‐Like Amorphous Silicon Carbide Films

A significant improvement of adhesion in thin-film structures is demonstrated using embedded ceramic-like amorphous silicon carbide films (a-SiC:H films). a-SiC:H films exhibit plasticity at the nanoscale and outstanding chemical and thermal stability unlike most materials. The multi-functionality and the ease of processing of the films have potential to offer a new toughening strategy for reliability of nanoscale device structures.

Moisture-assisted cracking and atomistic crack path meandering in oxidized hydrogenated amorphous silicon carbide films

Moisture-assisted cracking of silica-derived materials results from a stress-enhanced reaction between water molecules and moisture-sensitive SiOSi bonds at the crack tip. We report the moisture-assisted cracking of oxidized hydrogenated amorphous silicon carbide films (a-SiCO:H) consisting of both moisture-sensitive SiOSi bonds and moisture-insensitive bonds. The sensitivity of the films to moisture-assisted cracking was observed to increase with the SiOSi bond density, ρSiOSi. This sensitivity was correlated with the number of SiOSi bonds ruptured, NSiOSi, through an atomistic kinetic fracture model. By comparing these correlated NSiOSi values with those estimated by a planar crack model, we demonstrated that at the atomistic scale the crack path meanders three-dimensionally so as to intercept the most SiOSi bonds. This atomistic crack path meandering was verified by a computational method based on graph theory and molecular dynamics. Our findings could provide a basis for better underst...

Mechanical properties of hydrogenated amorphous silicon carbide thin films

The reliable fabrication of interconnects containing ultra low-k organosilicate dielectrics (ULK) has been a significant technological challenge. ULKs are inherently fragile with reduced elastic constants. In addition, their Si-O backbone makes organosilicate films prone to moisture-assisted cracking leading to serious reliability concerns. In this study, we investigated the mechanical properties of hydrogenated amorphous silicon carbide films (a-SiC:H) that do not contain Si-O bonds. The mechanical properties of a-SiC:H films are considered together with their enhanced fracture resistance and remarkable insensitivity to moisture assisted cracking.