Matthew Asplund

We report on the design, construction, and testing of a high-speed rotor intended for use in hypervelocity microparticle impact studies. The rotor is based on a four-wing design to provide rotational stability and includes flat “paddle” impact surfaces of ∼0.5 cm2 at the tips of each wing. The profile of each wing minimizes the variation in tensile forces at any given rotational speed. The rotor was machined using titanium (grade 5) and operated in high vacuum using magnetically levitated bearings. Initial experiments were run at several speeds up to 100 000 rpm (revolutions per minute), corresponding to a tip speed of 670 m/s. Elongation at the wing tips as a function of rotational speed was measured with a precision of several micrometers using a focused diode laser and found to agree with an elastic modulus of 1.16 GPa for the rotor material. Applications to microparticle impact experiments are discussed.

Modifying active species loading, particle size, and distribution on a support is an effective method for tuning catalyst activity. In this work, a copper catalyst anchored on titania was synthesized using the deposition‐precipitation method at low weight % in order to obtain a highly dispersed catalyst ( 1‐Cu/TiO 2 ). The interactions between the copper and TiO 2 support contribute to the physical and chemical properties of the catalyst. Transmission electron micrographs indicate copper nanoparticles with ∼2 nm diameter with a fairly uniform distribution across the TiO 2 particles. This synthetic approach yields a catalyst that is more active than similar precious metal catalysts, and therefore is a possible approach for creating highly efficient catalysts from economic materials.

Proper analysis of vibrational sum-frequency generation (VSFG) spectra requires that the nonresonant contribution be dealt with correctly. This work shows that the temporal profile of the nonresonant SFG response varies with crystal facing and sample orientation for single-crystal Si and is significantly different than what is observed with polycrystalline Au. These considerations will affect the use of time-delay methods to experimentally suppress the nonresonant signal in broadband SFG measurements. Time-resolved or phase-sensitive SFG measurements will also need to properly account for these effects in post-processing.