Effect of the chemical composition on the work function of gold substrates modified by binary self-assembled monolayers.
This study demonstrated that the work function (Φ) of Au substrates can be fine-tuned by using series ratios of binary self-assembled monolayers (SAMs). By using pure amine- and carboxylic acid-bearing alkanethiol SAM on gold substrates, Φ of Au changed from 5.10 to 5.16 and 5.83, respectively, as determined by ultra-violet photoelectron spectrometry (UPS). The shift in Φ due to the use of different functional groups was rationalized by considering the dipole moments of the molecules anchored on the Au surface. A series of binary SAMs were fabricated by mixing carboxylic acid- and amine-terminated alkanethiols in the deposition solution. By mixing these functional groups in SAMs, a linear correlation between Φ with respect to chemical composition (hence the effective dipole moment on the Au surface) was observed. It was found that arbitrary Φ between extremes (5.16 and 5.83) controlled by respective functional groups can be obtained by changing the chemical composition of SAMs. The Scanning Kelvin Probe (SKP) was also used to measure the contact potential difference (CPD) between SAMs and referencing Au on a patterned substrate prepared by photo-lithography. It was found that the CPD of SAMs with different chemical compositions correlates to their Φ. However, the magnitude of the CPD was smaller than the difference in Φ measured by UPS that was possibly due to the adsorption of contaminants in air.
Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan 106, Republic of China.
Szu-Hsian
SH
Lee
Wei-Chun
WC
Lin
Chi-Jen
CJ
Chang
Chih-Chieh
CC
Huang
Chi-Ping
CP
Liu
Che-Hung
CH
Kuo
Hsun-Yun
HY
Chang
Yun-Wen
YW
You
Wei-Lun
WL
Kao
Guo-Ji
GJ
Yen
Ding-Yuan
DY
Kuo
Yu-Ting
YT
Kuo
Meng-Hung
MH
Tsai
Jing-Jong
JJ
Shyue