Paper TF1-ThM10
Investigating the Local Physical Structure of Amorphous Hydrogenated Boron Carbide

Thursday, November 3, 2011, 11:00 am, Room 109

The unique physical structure of boron-rich carbides, based on an extended molecular network of covalently bound icosahedral cages, has distinguished this material with an exceptional set of thermal, electrical, and mechanical properties. Technologically, boron carbide has generated interest for applications in solid-state neutron detectors, interlayer low-k dielectrics for ultra-large-scale integrated circuits, and high-temperature thermoelectric power convertors. A method that has proven amenable to thin-film heterostructure device fabrication is the plasma-enhanced chemical vapor deposition (PECVD) of high-resistivity amorphous hydrogenated boron carbide (a-B_xC:H_y; x ≈ 2–5) from the single-source precursor orthocarborane (C₂B₁₀H₁₂). However, although the physical structure of bulk crystalline boron carbide (e.g., B_4.3C) is nowadays well-understood, the short-range physical structure of the hydrogenated material (e.g., the number and types of atoms/bonds) has remained unsatisfactorily characterized, likewise for the intermediate-range physical structure of the amorphous lattice (e.g., how molecular subunits are bound together and arranged on a short sub-nm length scale)—structural modifications which have important consequences on the properties of the a-B_xC:H_y films. Herein, we investigate the short- and intermediate-range physical structure of a-B_xC:H_y films using solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared (FTIR) spectroscopies, backed by density functional theory (DFT) molecular structure calculations. The comparison of experimentally observed spectral features with theoretical predictions for model molecular compounds provides valuable insight into the different local chemical environments and intermediate-range networks that make up the a-B_xC:H_y films. We demonstrate how applying these combined analyses provides an important stepping stone to understanding and optimizing the chemical, electrical, and mechanical properties of a-B_xC:H_y films for next-generation device fabrication.