Koch Sascha, Kaiser Christopher D, Penner Paul, Barclay Michael, Frommeyer Lena, Emmrich Daniel, Stohmann Patrick, Abu-Husein Tarek, Terfort Andreas, Fairbrother D Howard, Ingólfsson Oddur, Gölzhäuser Armin
Physics of Supramolecular Systems and Surfaces, Bielefeld University, 33613 Bielefeld, Germany.
Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Beilstein J Nanotechnol. 2017 Nov 30;8:2562-2571. doi: 10.3762/bjnano.8.256. eCollection 2017.
The determination of the negative ion yield of 2'-chloro-1,1'-biphenyl (2-Cl-BP), 2'-bromo-1,1'-biphenyl (2-Br-BP) and 2'-iodo-1,1'-biphenyl (2-I-BP) upon dissociative electron attachment (DEA) at an electron energy of 0 eV revealed cross section values that were more than ten times higher for iodide loss from 2-I-BP than for the other halogenides from the respective biphenyls (BPs). Comparison with dissociative ionization mass spectra shows that the ratio of the efficiency of electron impact ionization induced fragmentation of 2-I-BP, 2-Br-BP, and 2-Cl-BP amounts to approximately 1:0.7:0.6. Inspired by these results, self-assembled monolayers (SAMs) of the respective biphenyl-4-thiols, 2-Cl-BPT, 2-Br-BPT, 2-I-BPT as well as BPT, were grown on a Au(111) substrate and exposed to 50 eV electrons. The effect of electron irradiation was investigated by X-ray photoelectron spectroscopy (XPS), to determine whether the high relative DEA cross section for iodide loss from 2-I-BPT as compared to 2-Br-BP and 2-Cl-BP is reflected in the cross-linking efficiency of SAMs made from these materials. Such sensitization could reduce the electron dose needed for the cross-linking process and may thus lead to a significantly faster conversion of the respective SAMs into carbon nanomembranes (CNMs) without the need for an increased current density. XPS data support the notation that DEA sensitization may be used to achieve more efficient electron-induced cross-linking of SAMs, revealing more than ten times faster cross-linking of 2-I-BPT SAMs compared to those made from the other halogenated biphenyls or from native BPT at the same current density. Furthermore, the transfer of a freestanding membrane onto a TEM grid and the subsequent investigation by helium ion microscopy (HIM) verified the existence of a mechanically stable CNM created from 2-I-BPT after exposure to an electron dose as low as 1.8 mC/cm. In contrast, SAMs made from BPT, 2-Cl-BPT and 2-Br-BPT did not form stable CNMs after a significantly higher electron dose of 9 mC/cm.
在电子能量为0 eV时，通过解离电子附着（DEA）测定2'-氯-1,1'-联苯（2-Cl-BP）、2'-溴-1,1'-联苯（2-Br-BP）和2'-碘-1,1'-联苯（2-I-BP）的负离子产率，结果显示，2-I-BP中碘化物损失的截面值比相应联苯（BP）中其他卤化物的截面值高十多倍。与解离电离质谱的比较表明，电子碰撞电离诱导2-I-BP、2-Br-BP和2-Cl-BP碎片化的效率之比约为1:0.7:0.6。受这些结果启发，在Au(111)衬底上生长了相应的联苯-4-硫醇、2-Cl-BPT、2-Br-BPT、2-I-BPT以及BPT的自组装单分子层（SAMs），并使其暴露于50 eV电子下。通过X射线光电子能谱（XPS）研究了电子辐照的影响，以确定与2-Br-BP和2-Cl-BP相比，2-I-BPT中碘化物损失的高相对DEA截面是否反映在由这些材料制成的SAMs的交联效率中。这种敏化作用可以降低交联过程所需的电子剂量，从而可能导致相应的SAMs在不需要增加电流密度的情况下显著更快地转化为碳纳米膜（CNM）。XPS数据支持这样一种观点，即DEA敏化可用于实现SAMs更有效的电子诱导交联，结果表明，在相同电流密度下，2-I-BPT SAMs的交联速度比由其他卤化联苯或天然BPT制成的SAMs快十多倍。此外，将独立的膜转移到透射电子显微镜（TEM）网格上，随后通过氦离子显微镜（HIM）进行研究，证实了在暴露于低至1.8 mC/cm的电子剂量后，由2-I-BPT形成了机械稳定的CNM。相比之下，由BPT、2-Cl-BPT和2-Br-BPT制成的SAMs在9 mC/cm的显著更高电子剂量后并未形成稳定的CNM。
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