Temporal Profile of Nonresonant Sum-Frequency Signal from Single-Crystal Silicon Depends on Crystal Orientation.

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.

Surface Spectroscopic Signatures of Mechanical Deformation in High-Density Polyethylene (HDPE).

High-density polyethylene (HDPE) has been extensively studied, both as a model for semi-crystalline polymers and because of its own industrial utility. During cold drawing, crystalline regions of HDPE are known to break up and align with the direction of tensile load. Structural changes due to deformation should also manifest at the surface of the polymer, but until now, a detailed molecular understanding of how the surface responds to mechanical deformation has been lacking.

Polarization and phase characteristics of nonresonant sum-frequency generation response from a silicon (111) surface.

Silicon (111) [Si(111)] surfaces both with and without a thin film of polystyrene are investigated with sum-frequency generation (SFG) spectroscopy with s-polarized visible and p-polarized infrared inputs. On uncoated Si, the nonresonant polarization changes from s to p, with the maximum signal in each polarization component repeating every 60° of sample rotation. With polystyrene on Si(111), the resonant features go in and out of phase with the nonresonant signal every 120°.