Effect of surface chemical composition on the work function of silicon substrates modified by binary self-assembled monolayers
Resource
Physical Chemistry Chemical Physics, 13(33), 15122-15126
Journal
Physical Chemistry Chemical Physics
Pages
15122
Date Issued
2011
Date
2011
Author(s)
Kuo, Che-Hung
Liu, Chi-Ping
Lee, Szu-Hsian
Chang, Hsun-Yun
Lin, Wei-Chun
You, Yun-Wen
Liao, Hua-Yang
Shyue, Jing-Jong
Abstract
It has been shown that the application of self-assembled monolayers (SAMs) to semiconductors or metals may enhance the efficiency of optoelectronic devices by changing the surface properties and tuning the work functions at their interfaces. In this work, binary SAMs with various ratios of 3-aminopropyltrimethoxysilane (APTMS) and 3-mercaptopropyltrimethoxysilane (MPTMS) were used to modify the surface of Si to fine-tune the work function of Si to an arbitrary energy level. As an electron-donor, amine SAM (from APTMS) produced outward dipole moments, which led to a lower work function. Conversely, electron-accepting thiol SAM (from MPTMS) increased the work function. It was found that the work function of Si changed linearly with the chemical composition and increased with the concentration of thiol SAMs. Because dipoles of opposite directions cancelled each other out, homogeneously mixing them leads to a net dipole moment (hence the additional surface potential) between the extremes defined by each dipole and changes linearly with the chemical composition. As a result, the work function changed linearly with the chemical composition. Furthermore, the amine SAM possessed a stronger dipole than the thiol SAM. Therefore, the SAMs modified with APTMS showed a greater work function shift than did the SAMs modified with MPTMS.
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