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Neutron Scattering Study on Low-Energy Excitations in Vapor-Deposited Molecular Glasses

气相沉积分子玻璃低能激发的中子散射研究

基本信息

批准号：
08640486
负责人：
YAMAMURO Osamu
金额：
$ 1.41万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08640486/
关键词：
Neutron Scattering Vapor-Deposition Molecular Glass Low-Energy Excitation Boson Peak Debye-Waller Factor

项目摘要

We have developed a novel cryostat designed for the neutron scattering experiments on vapor-deposited glassy samples. By using this cryostat, glassy propylene of 0.15mm thickness was prepared at 20 K taking 5h. Neutron scattering spectra of this sample was measured with LAM-40 spectrometer (omega<10 meV,DELTAomega=0.2 meV) at High Energy Accelerator Research Organization (KEK). A broad inelastic peak, which is called a boson peak, was found at around 3 meV in dynamic structure factor S (Q,omega). The low energy part of this peak was reduced by annealing the sample at around the glass transition temperature (55 K). The phonon density of states calculated from S (Q,omega) was reproduced well by the soft potential model. The present results indicate that the low-energy excitation of molecular glasses is associated with the local potential softened by disorder and/or strain in the structure of glass.The neutron scattering spectra of vapor-deposited glassy propylene and benzene was measured by LAM-80ET spectrometer (omega<1.5 meV,DELTAomega=15 mueV). The elastic peak intensity was measured in the temperature range 16-70K to investigate the temperature dependence of the Debye-Waller factor. The logarithmic peak intensity, proportional to the mean square displacement<u^2>, of the glassy sample was more than two times larger than that of the crystalline sample. This result indicates that the vibrations of the glass is much softer than that of the crystal.

我们开发了一种新型低温恒温器，专为气相沉积玻璃样品的中子散射实验而设计。通过使用该低温恒温器，在20 K、5小时内制备出0.15mm厚度的玻璃状丙烯。该样品的中子散射光谱由高能加速器研究组织（KEK）的LAM-40光谱仪（omega<10meV，DELTAomega=0.2meV）测量。在动态结构因子 S (Q,omega) 的 3 meV 附近发现了一个宽的非弹性峰，称为玻色子峰。通过在玻璃化转变温度 (55 K) 附近对样品进行退火，可以降低该峰的低能量部分。软势模型很好地再现了从 S (Q,omega) 计算的声子态密度。结果表明，分子玻璃的低能激发与玻璃结构中无序和/或应变软化的局部势有关。采用LAM-80ET能谱仪测量了气相沉积玻璃态丙烯和苯的中子散射光谱（omega<1.5 meV，DELTAomega=15 mueV）。在 16-70K 温度范围内测量弹性峰强度，以研究德拜-沃勒因子的温度依赖性。玻璃状样品的对数峰值强度与均方位移<u^2>成正比，比结晶样品的对数峰值强度大两倍以上。该结果表明玻璃的振动比晶体的振动要柔和得多。