荒川 一郎

When low-energy electrons or photons (10-1000 eV) impinge on a surface of a rare-gas solid (RGS), desorption of ions, neutrals, and molecules can occur together with other processes. The desorption is due to an initial electronic excitation and a subsequent transformation of the excitation energy into kinetic energy of a desorbed atom. This phenomenon is called DIET (desorption induced by electronic transitions) : DIET by electron impact and photon impact are well known as ESD (electron-stimulated desorption) and PSD (photonstimulated desorption), respectively. Few studies of DIET of ions from RGS have been reported. In the investigation of ESD of H₂ physisorbed on condensed Xe, Arakawa and Tuzi found that ESD of ions (Xe⁺, Xe²⁺) and neutrals from condensed Xe could occur. Sakurai et al. reported the PSD of ions from the surface of solid Ar, Kr, and Xe. Dujardin et al. reported that electronically excited ions (Ar^+*) and doubly charged ions (Ar²⁺) might be primary excited states which lead to desorption of Ar⁺ from solid Ar. Menzel reported that the desorption of singly and doubly charged Kr ions occurs due to core ionization. They suggested that the kinetic energy of a desorbed ion was caused by Coulomb repulsion between adjacent ions which were formed by charge exchange between an initial multiply excited atom and its ground-state neighbor or by the deexcitation of doubly charged ionic dimers.

原子的に均一かつ平坦な表面に物理吸着した気体分子の系は,その相転移において2次元的な振舞いを示すことが知られている。吸着平衡測定,熱量測定,X線,粒子線回折などの手段を用いて,この系の熱学,統計力学の実験的な研究が行われてきた。これまでは実験上の制約から,異なる系,異なる手法での結果を互いに比較することは困難であった。偏光解析法は,測定圧力などの実験条件の制約が少なく,実験対象の選択の自由度も大きい。偏光解析法を測定手段として用いることによって,異なる吸着媒上の2次元系の広い範囲での相図を比較対照し,下地の影響などを議論することが可能となる。また,厚い物理吸着相の有力な観察手段となる。本稿では,物理吸着系の研究における偏光解析法の特徴と役割を紹介し,現在までにグラファイト単結晶表面および金属単結晶表面で得られた研究成果を紹介する。

An ellipsometric technique was applied to the study of physisorption of a rare gas on metal surfaces. In situ measurements of ellipsometric adsorption isotherms of Xe/Ag(111) and Xe/Pt(111) made it possible to compare the influences of different substrates on phase transitions. The isotherms on both metals have a stair-like shape; each step corresponds to the formation of one atomic layer in layer-by-layer growth of films. Obvious differences of the step height and the step position between two isotherms on different substrates are discussed in relation ot the induced dipole moment of adatoms on metal surfaces.

適当な条件で作成した, CO₂, 希ガスなどの凝縮層は多孔質構造をもち,活性炭などの固体吸着剤と同様に,H₂, Heに対する吸着媒となる.この性質をクライオソープション・ポンプに応用することを目的とした研究は,20年にわたって進められ,最近実用化への一歩が踏み出された.実用化にあたっては,排気の動的特性,超高真空領域における特性など,多くの問題が残されている.また,この分野の研究は,二次元相としての吸着分子層の物理という観点からも,興味深い問題を提起している.

An unidirectional vacuum gauge, which detects gas molecules coming from a certain direction in chaotic space, can be realised by means of detecting excited neutrals which are generated by electron impact. To eliminate photons and ions from detection was found to be effective measure in order to improve the performance of the gauge. The advantages of sharp directivity, small size, and high signal to background ratio were confirmed. The measured value of the gauge sensitivity is in good agreement with the expected one. This type of gauge, moreover, can measure the time of flight spectrum of gas molecules, that makes it possible to evaluate not only the anisotropy of molecular density in space but also the anisotropy and the nonequilibrium of molecular velocity distribution. © 1983, The Vacuum Society of Japan. All rights reserved.

An unidirectional vacuum gauge, which detects gas molecules coming from a certain direction in chaotic space, can be realised by means of detecting excited neutrals which are generated by electron impact. To eliminate photons and ions from detection was found to be effective measure in order to improve the performance of the gauge. The advantages of sharp directivity, small size, and high signal to background ratio were confirmed. The measured value of the gauge sensitivity is in good agreement with the expected one. This type of gauge, moreover, can measure the time of flight spectrum of gas molecules, that makes it possible to evaluate not only the anisotropy of molecular density in space but also the anisotropy and the nonequilibrium of molecular velocity distribution.

The application of an unidirectional vacuum gauge to the leak detection of a vacuum chamber is examined theoretically. The informations contained in the output signal of the gauge that sees a point gas source in a vacuum chamber are analyzed and its results are applied to the problem of the leak detection of large scale vacuum systems in numerical manner. The lower limit of detection correlates with various factors of both the performance of the unidirectional vacuum gauge and the property of the vacuum system. Sharp directivity, high signal to background ratio, and high sensitivity are desirable for the gauge. When the leak rate is far smaller than the total outgassing rate of the system, it is difficult to detect the leak even if one uses the gauge with high performances.

蒸気圧の低い気体の凝縮層は，適当な条件で作成するとH2やHeに対して大きな吸着容量を示し，クライオソープション・ポンプの吸着媒として利用することができる．この現象には，凝縮層の成長過程や構造，吸着の機構など多くの基礎的な問題が関連している事が明らかにされている．それらは単に真空技術への応用という観点からだけではなく，低温における分子間相互作用の解明という点からも研究が進められている．