TY - JOUR
T1 - Comparative study of structural order, thermal desorption behavior, and work function change of self-assembled monolayers of pentafluorobenzenethiols and tetrafluorobenzenethiols on Au(1 1 1)
AU - Kang, Hungu
AU - Seong, Sicheon
AU - Ito, Eisuke
AU - Isoshima, Takashi
AU - Hara, Masahiko
AU - Yoon, Hyo Jae
AU - Noh, Jaegeun
N1 - Funding Information:
This work was supported by the National Research Foundation of Korea (NRF) (NRF-2019R1A2C2011003 and NRF-2019R1A6A1A11044070 for H. J. Yoon, NRF-2012R1A6A1029029, NRF-2018R1D1A1B07048063, and NRF-2021R1A2C2010917 for J. Noh).
Publisher Copyright:
© 2021 Elsevier B.V.
PY - 2021/7/30
Y1 - 2021/7/30
N2 - The surface and interface structures, thermal desorption behaviors, and electronic properties of pentafluorobenzenethiol (PFBT) and tetrafluorobenzenethiol (TFBT) self-assembled monolayers (SAMs) on Au(1 1 1) formed at different vapor deposition temperatures (298, 323, and 348 K) were examined to understand the effect of dipole directions in fluorinated aromatic thiol SAMs using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), thermal desorption spectroscopy (TDS), and Kelvin probe (KP) measurements. Molecular-scale STM observations revealed that PFBT SAMs on Au(1 1 1) had a well-ordered phase with a c(2 × √3) structure at 348 K, whereas TFBT SAMs showed a well-ordered phase with a (2√3 × 8√2)R30° structure at 323 K. TDS and XPS measurements also demonstrated that PFBT and TFBT SAMs showed significantly different thermal desorption behaviors and interface structures due to opposite directions of molecular dipole moments. The KP measurements showed that the extent of the work function change of SAM-modified Au substrates was lowest in most highly-ordered PFBT and TFBT SAMs formed at 348 K and 323 K, respectively, regardless of chemisorbed surface coverage. These findings revealed that the degree of structural order of SAMs is a more significant factor in causing the depolarization effect rather than chemisorbed surface coverage.
AB - The surface and interface structures, thermal desorption behaviors, and electronic properties of pentafluorobenzenethiol (PFBT) and tetrafluorobenzenethiol (TFBT) self-assembled monolayers (SAMs) on Au(1 1 1) formed at different vapor deposition temperatures (298, 323, and 348 K) were examined to understand the effect of dipole directions in fluorinated aromatic thiol SAMs using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), thermal desorption spectroscopy (TDS), and Kelvin probe (KP) measurements. Molecular-scale STM observations revealed that PFBT SAMs on Au(1 1 1) had a well-ordered phase with a c(2 × √3) structure at 348 K, whereas TFBT SAMs showed a well-ordered phase with a (2√3 × 8√2)R30° structure at 323 K. TDS and XPS measurements also demonstrated that PFBT and TFBT SAMs showed significantly different thermal desorption behaviors and interface structures due to opposite directions of molecular dipole moments. The KP measurements showed that the extent of the work function change of SAM-modified Au substrates was lowest in most highly-ordered PFBT and TFBT SAMs formed at 348 K and 323 K, respectively, regardless of chemisorbed surface coverage. These findings revealed that the degree of structural order of SAMs is a more significant factor in causing the depolarization effect rather than chemisorbed surface coverage.
KW - Pentafluorobenzenethiol
KW - Scanning tunneling microscopy
KW - Self-assembled monolayers
KW - Surface structure
KW - Tetrafluorobenzenethiol
KW - Work function
UR - http://www.scopus.com/inward/record.url?scp=85103982141&partnerID=8YFLogxK
U2 - 10.1016/j.apsusc.2021.149671
DO - 10.1016/j.apsusc.2021.149671
M3 - Article
AN - SCOPUS:85103982141
VL - 555
JO - Applied Surface Science
JF - Applied Surface Science
SN - 0169-4332
M1 - 149671
ER -