Helium atom scattering on amorphous bilayer silica

This dataset contains time of flight (TOF) measurements obtained using helium atom scattering (HAS) on an amorphous bilayer silica sample supportend on a Ru(0001) substrate. TOF measurements are taken at several incident angles and azimuthal angles, as described in the attached pdf file. TOF measurements are used to study the surface dynamics of the sample, which is the world's thinnest glass. TOF measurements record the flight time of incident helium atoms scattered of the sample. At specular incidence (45 degrees) the largest peak in the sample is the elastic peak, which are all the helium atoms that scatter without exchanging energy with the sample. As the incident angle is varied, other peaks are also visible in the TOF specra. These are phonons, or other phonon like modes, that the helium atom can either excite or annihilate to loose or gain energy. Layered and 2D materials exhibit out of plane vibrations, so called ZA phonon modes. These phonon modes have a dispersion relation that involves the bending rigidity of the sample. By mapping out the ZA dispersion, i.e. repeating the TOF experiment for several different incident angles and identifying the ZA mode peaks, one can experimentally measure the bending rigidity of the sample. As the sample is amorphous, it has also been used to study the boson peak phenomenon in a 2D material. The boson peak is a vibrational anomaly that occurs in glassy and amorphous materials, where the vibrational density of states exhibits an excess of vibrational modes above the Debye level in the low terahertz regime.