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.本数据集包含采用氦原子散射（Helium Atom Scattering，HAS）方法，对负载于钌(0001)衬底的无定形双层二氧化硅样品开展测试得到的飞行时间（Time of Flight，TOF）数据。测试在多个入射角与方位角下进行，具体细节参见附件PDF文件。TOF测试用于研究这款全球最薄玻璃样品的表面动力学特性：其记录入射氦原子经样品散射后的飞行时间。在镜面入射（45°）条件下，样品信号的主峰为弹性峰，即所有未与样品发生能量交换的散射氦原子。随着入射角改变，TOF谱中还会出现其他峰，这些峰对应声子或类声子模式——氦原子可通过激发或湮灭这类模式来损失或获得能量。层状与二维材料存在面外振动，即所谓的ZA声子模式，这类声子模式的色散关系与样品的弯曲刚度密切相关。通过测绘ZA色散曲线（即针对多个不同入射角重复开展TOF实验并识别ZA模式峰），可实验测定该样品的弯曲刚度。由于该样品为无定形材料，本数据集还被用于研究二维材料中的玻色峰现象：玻色峰是玻璃态与无定形材料中出现的一类振动异常，在太赫兹低频区间内，这类材料的振动态密度会呈现出超出德拜极限的振动模式过剩。