Laboratory of Organic Chemistry, Wageningen University, Dreijenplein 8, 6703 HB Wageningen, The Netherlands.
Langmuir. 2010 Apr 6;26(7):4790-5. doi: 10.1021/la9035503.
On H-Si(111), monolayer assembly with 1-alkenes results in alkyl monolayers with a Si-C-C linkage to the silicon substrate, while 1-alkynes yield alkenyl monolayers with a Si-C=C linkage. To investigate the influence of the different linkage groups on the final monolayer structure, organic monolayers were prepared from 1-alkenes and 1-alkynes with chain lengths from C(12) to C(18), and the final monolayer structures were studied in detail by static water contact angles measurements, ellipsometry, attenuated total reflectance infrared (ATR-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The thicknesses, tilt angles, and packing densities of the alkyl monolayers are in good agreement with literature values, whereas increased thicknesses, reduced tilt angles, and improved packing densities were observed for the alkenyl monolayers. Finally, the surface coverages for alkyl monolayers were determined to be 50-55% (in line with literature values), while those for the alkenyl monolayers increased with the chain length from 55% for C(12) to as high as 65% for C(18)! The latter value is very close to the theoretical maximum of 69% obtainable on H-Si(111). Such enhanced monolayer quality and increased surface coverage of the alkenyl monolayers, in combination with the oxidation-inhibiting nature of the Si-C=C linkage, significantly increases the chance of successful implementation of organic monolayers on oxide-free silicon in molecular electronic and biosensor devices, especially in view of the importance of a defect-free monolayer structure and the corresponding stability of the monolayer-silicon interface.
在 H-Si(111)表面，1-烯烃的单层组装导致与硅衬底的 Si-C-C 键合的烷基单层，而 1-炔烃则生成具有 Si-C=C 键合的烯基单层。为了研究不同键合基团对最终单层结构的影响，我们使用具有从 C(12)到 C(18)的链长的 1-烯烃和 1-炔烃制备了有机单层，并通过静态水接触角测量、椭圆光度法、衰减全反射红外光谱（ATR-IR）和 X 射线光电子能谱（XPS）详细研究了最终的单层结构。烷基单层的厚度、倾斜角度和堆积密度与文献值非常吻合，而烯基单层的厚度增加、倾斜角度减小和堆积密度提高。最后，确定烷基单层的表面覆盖率为 50-55%（与文献值一致），而烯基单层的表面覆盖率随链长的增加而增加，从 C(12)的 55%增加到 C(18)的 65%！后一个值非常接近 H-Si(111)上可获得的 69%的理论最大值。这种增强的单层质量和增加的烯基单层表面覆盖率，结合 Si-C=C 键的抗氧化性质，大大增加了在无氧化物硅上成功实施有机单层的机会，特别是考虑到无缺陷单层结构的重要性和单层-硅界面的相应稳定性在分子电子和生物传感器设备中。
