NEUTRON-DIFFRACTION STUDY OF THE SOLID LAYERS AT THE LIQUID-SOLID BOUNDARY IN HE-4 FILMS ADSORBED ON GRAPHITE
NEUTRON-DIFFRACTION STUDY OF THE SOLID LAYERS AT THE LIQUID-SOLID BOUNDARY IN HE-4 FILMS ADSORBED ON GRAPHITE
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DOI：
10.1103/physrevb.24.1170
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发表时间：
1981-01-01
影响因子：
3.7
通讯作者：
TAUB, H
中科院分区：
文献类型：
--
作者：
CARNEIRO, K;PASSELL, L;TAUB, H
用中子散射法研究了石墨表面吸附的He 4膜的结构.从氦单分子膜在1.2 K的温度下的衍射表明，形成一个无公度，三角晶格固体的高密度。当覆盖率增加到两层以上时，衍射图案改变，表明第二层的固化。所观察到的两层图案可以与一对不相称的，不同密度的三角形晶格固体层或紧密堆积的双层索引;现有的实验信息不足以进行更精确的识别。还测量了石墨基面上方的第一氦层的高度。这是通过确定石墨（002）衍射峰位置的覆盖率依赖性位移（假设由膜和基底散射之间的干涉引起）并将其拟合到简单的结构模型来完成的。给出了石墨平面以上的单层高度和可能的双层结构的晶格常数的值。
A neutron scattering study of the structure of He 4 films adsorbed on graphite is reported. Diffraction from helium monolayers at a temperature of 1.2 K shows the formation of an incommensurate, triangular-lattice solid of high density. As the coverage is increased above two layers, the diffraction pattern changes indicating solidification of a second layer. The observed two-layer patterns can be indexed with either a pair of incommensurate, triangular-lattice solid layers of different densities or a close-packed bilayer; the experimental information available is not sufficient to make a more precise identification. A measurement of the height of the first helium layer above the graphite basal plane was also made. This was done by determining the coverage-dependent shift in the position of the graphite (002) diffraction peak (assumed to arise from interference between film and substrate scattering) and fitting it to a simple structural model. Values for the monolayer height above the graphite plane and for the lattice constants of the possible bilayer structures are given.