Interface dipoles arising from self-assembled monolayers on gold: UV-photoemission studies of alkanethiols and partially fluorinated alkanethiols

Dana M. Alloway, Michael Hofmann, Darrin L. Smith, Nadine E. Gruhn, Amy L. Graham, Ramon Colorado, Vicki H. Wysocki, T. Randall Lee, Paul A. Lee, Neal R Armstrong

Research output: Contribution to journalArticle

355 Citations (Scopus)

Abstract

Gold surfaces modified with C3-C18-alkanethiols (CH3(CH2)x-1SH; HXSH; x = 3, 8, 12, 16, 18) and C16-alkanethiols, fluorinated at the outer 1, 2, 4, and 10 methylene positions (CF3(CF2)Y-1(CH2)XSH; FyHxSH; y = 1, x = 15; y = 2, x = 14; y = 4, x = 12; y = 10, x = 6) were characterized by He(I) UV-photoelectron spectroscopy (UPS). (Detailed X-ray photoelectron spectroscopic characterization of the partially fluorinated thin films is given in the Supporting Information). Long incubation times of the gold surface with the alkanethiol solutions lead to compact monolayer films for all of the alkanethiols, as indicated by the exponential decrease in emission intensity versus alkyl chain length for both the gold Fermi edge (UPS data), and by a parallel decrease in Au(4f) photoemission intensity using X-ray photoelectron spectroscopy. Changes in the effective work function of these surfaces due to the presence of significant interfacial dipoles are observed (i) as alkyl chain length is increased, and (ii) as the fraction of fluorinated methylene groups is increased in a constant length alkyl chain. Negative shifts of the low kinetic energy photoemission edge with increasing alkyl chain length in the HxSH series are consistent with the presence of a large positive interface dipole. The largest part of this shift (ca. 1.0 eV) appears between the C3- and C8-alkyl chain lengths. Adding -CFx groups to the outer end of the C16-alkyl chain positively shifts the low-kinetic-energy photoemission edge, consistent with the presence of a large negative interface dipole that completely compensates for the positive dipole from the alkyl portion of the chain. Examining C13-C16 alkyl chains fluorinated at only the outer methyl group shows that this negative dipole depends on the orientation of the -CF3 group (i.e., "odd-even" effects in the effective work function are observed). Comparison of the shifts in gold/SAM vacuum level (changes in effective work function) as a function of the apparent dipole moment of the molecule provides an estimate of the band-edge offsets for these molecules on the gold surface, an estimate of the intrinsic shift in a vacuum level at zero dipole moment of the adsorbate, and an estimate of the intrinsic dipole moment for the gold-thiolate bond.

Original languageEnglish (US)
Pages (from-to)11690-11699
Number of pages10
JournalJournal of Physical Chemistry B
Volume107
Issue number42
StatePublished - Oct 23 2003

Fingerprint

Photoemission
Self assembled monolayers
Gold
Chain length
photoelectric emission
gold
dipoles
Dipole moment
shift
dipole moments
photoelectron spectroscopy
Photoelectron spectroscopy
Ultraviolet spectroscopy
methylene
Kinetic energy
estimates
kinetic energy
Vacuum
vacuum
Molecules

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Interface dipoles arising from self-assembled monolayers on gold : UV-photoemission studies of alkanethiols and partially fluorinated alkanethiols. / Alloway, Dana M.; Hofmann, Michael; Smith, Darrin L.; Gruhn, Nadine E.; Graham, Amy L.; Colorado, Ramon; Wysocki, Vicki H.; Lee, T. Randall; Lee, Paul A.; Armstrong, Neal R.

In: Journal of Physical Chemistry B, Vol. 107, No. 42, 23.10.2003, p. 11690-11699.

Research output: Contribution to journalArticle

Alloway, DM, Hofmann, M, Smith, DL, Gruhn, NE, Graham, AL, Colorado, R, Wysocki, VH, Lee, TR, Lee, PA & Armstrong, NR 2003, 'Interface dipoles arising from self-assembled monolayers on gold: UV-photoemission studies of alkanethiols and partially fluorinated alkanethiols', Journal of Physical Chemistry B, vol. 107, no. 42, pp. 11690-11699.
Alloway, Dana M. ; Hofmann, Michael ; Smith, Darrin L. ; Gruhn, Nadine E. ; Graham, Amy L. ; Colorado, Ramon ; Wysocki, Vicki H. ; Lee, T. Randall ; Lee, Paul A. ; Armstrong, Neal R. / Interface dipoles arising from self-assembled monolayers on gold : UV-photoemission studies of alkanethiols and partially fluorinated alkanethiols. In: Journal of Physical Chemistry B. 2003 ; Vol. 107, No. 42. pp. 11690-11699.
@article{988ec197d1e5487cbd1534d420b9346f,
title = "Interface dipoles arising from self-assembled monolayers on gold: UV-photoemission studies of alkanethiols and partially fluorinated alkanethiols",
abstract = "Gold surfaces modified with C3-C18-alkanethiols (CH3(CH2)x-1SH; HXSH; x = 3, 8, 12, 16, 18) and C16-alkanethiols, fluorinated at the outer 1, 2, 4, and 10 methylene positions (CF3(CF2)Y-1(CH2)XSH; FyHxSH; y = 1, x = 15; y = 2, x = 14; y = 4, x = 12; y = 10, x = 6) were characterized by He(I) UV-photoelectron spectroscopy (UPS). (Detailed X-ray photoelectron spectroscopic characterization of the partially fluorinated thin films is given in the Supporting Information). Long incubation times of the gold surface with the alkanethiol solutions lead to compact monolayer films for all of the alkanethiols, as indicated by the exponential decrease in emission intensity versus alkyl chain length for both the gold Fermi edge (UPS data), and by a parallel decrease in Au(4f) photoemission intensity using X-ray photoelectron spectroscopy. Changes in the effective work function of these surfaces due to the presence of significant interfacial dipoles are observed (i) as alkyl chain length is increased, and (ii) as the fraction of fluorinated methylene groups is increased in a constant length alkyl chain. Negative shifts of the low kinetic energy photoemission edge with increasing alkyl chain length in the HxSH series are consistent with the presence of a large positive interface dipole. The largest part of this shift (ca. 1.0 eV) appears between the C3- and C8-alkyl chain lengths. Adding -CFx groups to the outer end of the C16-alkyl chain positively shifts the low-kinetic-energy photoemission edge, consistent with the presence of a large negative interface dipole that completely compensates for the positive dipole from the alkyl portion of the chain. Examining C13-C16 alkyl chains fluorinated at only the outer methyl group shows that this negative dipole depends on the orientation of the -CF3 group (i.e., {"}odd-even{"} effects in the effective work function are observed). Comparison of the shifts in gold/SAM vacuum level (changes in effective work function) as a function of the apparent dipole moment of the molecule provides an estimate of the band-edge offsets for these molecules on the gold surface, an estimate of the intrinsic shift in a vacuum level at zero dipole moment of the adsorbate, and an estimate of the intrinsic dipole moment for the gold-thiolate bond.",
author = "Alloway, {Dana M.} and Michael Hofmann and Smith, {Darrin L.} and Gruhn, {Nadine E.} and Graham, {Amy L.} and Ramon Colorado and Wysocki, {Vicki H.} and Lee, {T. Randall} and Lee, {Paul A.} and Armstrong, {Neal R}",
year = "2003",
month = "10",
day = "23",
language = "English (US)",
volume = "107",
pages = "11690--11699",
journal = "Journal of Physical Chemistry B Materials",
issn = "1520-6106",
publisher = "American Chemical Society",
number = "42",

}

TY - JOUR

T1 - Interface dipoles arising from self-assembled monolayers on gold

T2 - UV-photoemission studies of alkanethiols and partially fluorinated alkanethiols

AU - Alloway, Dana M.

AU - Hofmann, Michael

AU - Smith, Darrin L.

AU - Gruhn, Nadine E.

AU - Graham, Amy L.

AU - Colorado, Ramon

AU - Wysocki, Vicki H.

AU - Lee, T. Randall

AU - Lee, Paul A.

AU - Armstrong, Neal R

PY - 2003/10/23

Y1 - 2003/10/23

N2 - Gold surfaces modified with C3-C18-alkanethiols (CH3(CH2)x-1SH; HXSH; x = 3, 8, 12, 16, 18) and C16-alkanethiols, fluorinated at the outer 1, 2, 4, and 10 methylene positions (CF3(CF2)Y-1(CH2)XSH; FyHxSH; y = 1, x = 15; y = 2, x = 14; y = 4, x = 12; y = 10, x = 6) were characterized by He(I) UV-photoelectron spectroscopy (UPS). (Detailed X-ray photoelectron spectroscopic characterization of the partially fluorinated thin films is given in the Supporting Information). Long incubation times of the gold surface with the alkanethiol solutions lead to compact monolayer films for all of the alkanethiols, as indicated by the exponential decrease in emission intensity versus alkyl chain length for both the gold Fermi edge (UPS data), and by a parallel decrease in Au(4f) photoemission intensity using X-ray photoelectron spectroscopy. Changes in the effective work function of these surfaces due to the presence of significant interfacial dipoles are observed (i) as alkyl chain length is increased, and (ii) as the fraction of fluorinated methylene groups is increased in a constant length alkyl chain. Negative shifts of the low kinetic energy photoemission edge with increasing alkyl chain length in the HxSH series are consistent with the presence of a large positive interface dipole. The largest part of this shift (ca. 1.0 eV) appears between the C3- and C8-alkyl chain lengths. Adding -CFx groups to the outer end of the C16-alkyl chain positively shifts the low-kinetic-energy photoemission edge, consistent with the presence of a large negative interface dipole that completely compensates for the positive dipole from the alkyl portion of the chain. Examining C13-C16 alkyl chains fluorinated at only the outer methyl group shows that this negative dipole depends on the orientation of the -CF3 group (i.e., "odd-even" effects in the effective work function are observed). Comparison of the shifts in gold/SAM vacuum level (changes in effective work function) as a function of the apparent dipole moment of the molecule provides an estimate of the band-edge offsets for these molecules on the gold surface, an estimate of the intrinsic shift in a vacuum level at zero dipole moment of the adsorbate, and an estimate of the intrinsic dipole moment for the gold-thiolate bond.

AB - Gold surfaces modified with C3-C18-alkanethiols (CH3(CH2)x-1SH; HXSH; x = 3, 8, 12, 16, 18) and C16-alkanethiols, fluorinated at the outer 1, 2, 4, and 10 methylene positions (CF3(CF2)Y-1(CH2)XSH; FyHxSH; y = 1, x = 15; y = 2, x = 14; y = 4, x = 12; y = 10, x = 6) were characterized by He(I) UV-photoelectron spectroscopy (UPS). (Detailed X-ray photoelectron spectroscopic characterization of the partially fluorinated thin films is given in the Supporting Information). Long incubation times of the gold surface with the alkanethiol solutions lead to compact monolayer films for all of the alkanethiols, as indicated by the exponential decrease in emission intensity versus alkyl chain length for both the gold Fermi edge (UPS data), and by a parallel decrease in Au(4f) photoemission intensity using X-ray photoelectron spectroscopy. Changes in the effective work function of these surfaces due to the presence of significant interfacial dipoles are observed (i) as alkyl chain length is increased, and (ii) as the fraction of fluorinated methylene groups is increased in a constant length alkyl chain. Negative shifts of the low kinetic energy photoemission edge with increasing alkyl chain length in the HxSH series are consistent with the presence of a large positive interface dipole. The largest part of this shift (ca. 1.0 eV) appears between the C3- and C8-alkyl chain lengths. Adding -CFx groups to the outer end of the C16-alkyl chain positively shifts the low-kinetic-energy photoemission edge, consistent with the presence of a large negative interface dipole that completely compensates for the positive dipole from the alkyl portion of the chain. Examining C13-C16 alkyl chains fluorinated at only the outer methyl group shows that this negative dipole depends on the orientation of the -CF3 group (i.e., "odd-even" effects in the effective work function are observed). Comparison of the shifts in gold/SAM vacuum level (changes in effective work function) as a function of the apparent dipole moment of the molecule provides an estimate of the band-edge offsets for these molecules on the gold surface, an estimate of the intrinsic shift in a vacuum level at zero dipole moment of the adsorbate, and an estimate of the intrinsic dipole moment for the gold-thiolate bond.

UR - http://www.scopus.com/inward/record.url?scp=0242551715&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0242551715&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0242551715

VL - 107

SP - 11690

EP - 11699

JO - Journal of Physical Chemistry B Materials

JF - Journal of Physical Chemistry B Materials

SN - 1520-6106

IS - 42

ER -