X-ray Structural Analysis of the Monolayrs Adsorbed on Solid Surfaces

一些简单分子的单分子层被物理吸附在固体（如石墨）的均匀表面上，在低温下形成二维分子固体。用量热法、衍射法和中子散射法对该体系进行了研究。这种被吸附的单分子膜通常在固相中表现出相变，这与散装固体的情况类似。然而，由于该系统中分子相互作用的平衡是相当微妙的，许多相的出现取决于覆盖和温度。我们研究的体系是由同位素甲烷、新戊烷、金刚烷、硫酰氟、六氟化硫、樟脑、四（甲基）甲烷等组成的单层体系。所有的分子都呈球形，在低温下的取向顺序特别有趣。获得了金刚烷、六氟化硫、樟脑和四（甲基硫）甲烷单分子在常温和低温下的x射线衍射图。在低温下获得了全氘化新戊烷、全氘化金刚烷和六氟化硫单分子膜的中子衍射图。虽然详细的结构分析正在进行中，但相变机制似乎是定向有序-无序型。采用非弹性和准弹性中子散射方法研究了新戊烷单层膜的相变性质。用非弹性中子散射观测的旋转隧穿光谱研究了甲烷单分子膜的动力学。利用六方氮化硼作为吸附剂，对单分子膜的介电性能进行了研究，这是我们的另一个项目。

The momolayr of some simple molecules, which is physically adsorbed on a homogeneous surface of solids such as graphite, forms a two-dimensional molecular solid at low temperatures. We investigate the system by calorimetry, diffraction and neutron scattering. Such adsorbed monolayrs often exhibit phase transitions in the solid phase, which is similar to the case of the bulk solid. However, since the balance of the molecular interactions in this system is rather subtle, many phases appear depending upon the coverage and the temperature.The systems that we investigated were the monolayrs of isotopic methanes, neopentane, adamantane, sulfuryl fluoride, sulfur hexafluoride, camphor, tetrakis (methylthio) methane and others. All the molecules have globular shape and the orientational ordering at low temperatures is particularly interesting. The X-ray diffraction patterns were obtained for the monolayrs of adamantane, sulfur hexafluoride, camphor and tetrakis (methylthio) methane at ambient and low temperatures. The neutron diffraction patterns were also obtained for the monolayrs of fully-deuterated neopentane, fully-deuterated adamantane and sulfur hexafluoride at low temperatures.While the detailed structural analysis is now under way, the mechanism of the phase transitions seems to be of orientational order-disorder type. The nature of the phase transition of neopentane monolayr was investigated by inelastic and quasielastic neutron scattering. The dynamics in methane monolayrs were investigated by the rotational tunneling spectra observed by inelastic neutron scattering. Investigation of the dielectric properties of the monolayrs, which is our anotherproject, is now in progress by using hexagonal boron nitride as an adsorbent.