Probing Lattice Vibrations at SiO_2/Si Surface and Interface with Nanometer Resolution

Recent advances in monochromatic aberration corrected electron microscopy make it possible to detect the lattice vibrations with both high-energy resolution and high spatial resolution. Here, we use sub-10 meV electron energy loss spectroscopy to investigate the local vibrational properties of the SiO_2/Si surface and interface. The energy of the surface mode is thickness dependent, showing a blue shift as z-thickness(parallel to the fast electron beam)of SiO_2 film increases, while the energy of the bulk mode and the interface mode keeps constant. The intensity of the surface mode is well-described by a Bessel function of the second kind. The mechanism of the observed spatially dependent vibrational behavior is discussed and compared with dielectric response theory analysis. Our nanometer scale measurements provide useful information on the bonding conditions at the surface and interface.     

对甲氧基苯甲腈的单色共振双光子电离光谱

对甲氧基苯甲腈是一种重要的化学化工原料,本文采用超声分子束技术和共振多光子电离方法获得了对甲氧基苯甲腈的单色共振双光子电离光谱,基态S0到电子激发态S1的0←0跃迁被确定为(35549±2)cm~(-1),结合含时密度泛函理论计算结果对观察到的光谱进行了振动模式标识和描述.实验发现呼吸振动模非常易于激活,其基频和二次泛频光谱很强,三次泛频也可明确标识,观察到大量呼吸振动与其他正则模的结合振动,这是对甲氧基苯甲腈不同于常见的多原子分子的一个重要特性.这些结果为研究对甲氧基苯甲腈的里德堡态、动力学和零动能光谱等提供了重要的参考数据.     

Effects of Localized Interface Phonons on Heat Conductivity in Ingredient Heterogeneous Solids

Phonons are the primary heat carriers in non-metallic solids. In compositionally heterogeneous materials, the thermal properties are believed to be mainly governed by the disrupted phonon transport due to mass disorder and strain fluctuations, while the effects of compositional fluctuation induced local phonon states are usually ignored.Here, by scanning transmission electron microscopy electron energy loss spectroscopy and sophisticated calculations, we identify the vibrational properties of in...