Kawasuso A, Wada K, Miyashita A, Maekawa M, Iwamori H, Iida S, Nagashima Y
National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan.
Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan.
J Phys Condens Matter. 2020 Oct 20;33(3). doi: 10.1088/1361-648X/abbe7a.
Positronium formation at 4H SiC(0001) surfaces were investigated upon the removal of natural oxide layers by hydrofluoric acid etching and heat treatment at 1000 K in ultra-high vacuum. Two types of positronium were observed in the positronium time-of-flight (PsTOF) measurements irrespective of conduction type and surface polarity. One type formed the major part of the PsTOF spectrum with a maximum energy of 4.7 ± 0.3 eV. This energy exceeded the theoretical value calculated with valence electrons. The PsTOF spectrum shape was different from those of metal surfaces, suggesting that the surface state electrons or conduction electrons need to be considered as the positronium source. Another positronium appeared at 1000 K in the tail of the PsTOF spectrum with a maximum energy of 0.2-0.5 eV. This thermally-assisted athermal positronium may be formed via the surface state positrons and electrons.
通过氢氟酸蚀刻去除自然氧化层并在超高真空中于1000 K进行热处理后，研究了4H碳化硅（0001）表面的正电子素形成情况。在正电子素飞行时间（PsTOF）测量中观察到了两种类型的正电子素，与导电类型和表面极性无关。一种类型构成了PsTOF谱的主要部分，最大能量为4.7±0.3 eV。该能量超过了用价电子计算的理论值。PsTOF谱的形状与金属表面的不同，这表明表面态电子或传导电子需要被视为正电子素的来源。另一种正电子素在1000 K时出现在PsTOF谱的尾部，最大能量为0.2 - 0.5 eV。这种热辅助的非热正电子素可能是通过表面态正电子和电子形成的。
