He Zhenhua, Leung K T
Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
J Phys Chem B. 2005 Aug 11;109(31):14971-8. doi: 10.1021/jp051293r.
Thermal and ion-induced reactions of 1,1-difluoroethylene (1,1-C2H2F2 or iso-DFE) on Si(111)7 x 7 and vitreous SiO2 surfaces have been investigated by vibrational electron energy loss spectroscopy and thermal desorption spectrometry. Like ethylene, iso-DFE predominantly chemisorbs via a [2 + 2] cycloaddition mechanism onto the 7 x 7 surface as a di-sigma-bonded difluoroethane-1,2-diyl adstructure, which undergoes H abstraction and defluorination, producing hydrocarbon fragments and SiF(x) (x = 1-3) upon annealing to >700 K. Ion irradiation of Si(111)7 x 7 in iso-DFE at 50 eV impact energy appears to substantially enhance the production of hydrocarbon fragments and SiF(x)(), leading to stronger SiF4 desorption products over an extended temperature range (400-900 K). The observed SiC and SiF(x) produced on the 7 x 7 surface by ion irradiation in iso-DFE are found to be similar to those obtained by ion irradiation in the fluoromethane homologues, CF4 and CH2F2. The production of higher relative concentrations for the larger SiF(x) and C2-containing fragments is evidently favored on the 7 x 7 surface. On a vitreous SiO2 surface, ion irradiation in iso-DFE, unlike that in CF4 and CH2F2, appears to produce less SiF(x) than that on the 7 x 7 surface, which indicates that surface O does not interact strongly with the C2-containing fragments. The presence or absence of a C=C bond and the relative F-to-C ratio of the sputtering gas could therefore produce important effects on the resulting surface products obtained by low-energy ion irradiation.
通过振动电子能量损失光谱和热脱附光谱研究了1,1 - 二氟乙烯（1,1 - C₂H₂F₂或异 - DFE）在Si(111)7×7和玻璃态SiO₂表面上的热诱导反应和离子诱导反应。与乙烯一样，异 - DFE主要通过[2 + 2]环加成机制化学吸附在7×7表面上，形成双σ键合的1,2 - 二氟乙烷 - 1,2 - 二基吸附结构，该结构在退火至>700 K时会发生氢提取和脱氟反应，产生烃类碎片和SiF(x)（x = 1 - 3）。在50 eV撞击能量下，在异 - DFE中对Si(111)7×7进行离子辐照似乎会大幅增强烃类碎片和SiF(x)的产生，从而在较宽的温度范围（400 - 900 K）内导致更强的SiF₄脱附产物。发现在异 - DFE中对7×7表面进行离子辐照所产生的SiC和SiF(x)与在氟甲烷同系物CF₄和CH₂F₂中进行离子辐照所得到的相似。在7×7表面上，显然有利于产生相对浓度更高的较大SiF(x)和含C₂碎片。在玻璃态SiO₂表面上，异 - DFE中的离子辐照与CF₄和CH₂F₂中的不同，似乎比在7×7表面上产生的SiF(x)更少，这表明表面O与含C₂碎片的相互作用不强。因此，溅射气体中C = C键的存在与否以及F与C的相对比例可能会对通过低能离子辐照获得的最终表面产物产生重要影响。
