The characterization of organic monolayers at gold surfaces using scanning tunneling microscopy and atomic force microscopy correlation with macrostructural properties
Monolayer films formed by self-assembly of organothiols at epitaxially grown Au(111) films at mica were examined in air using scanning tunneling (STM) and atomic force microscopies (AFM). n-Alkanethiolate monolayers exhibit a hexagonal packing arrangement with nearest-neighbor and next-nearest-neighbor spacings of 0.50 and 0.87 nm. This arrangement is consistent with the ([radical]3 [times] [radical]3)R30[degrees] adlayer structure at Au(111). STM reveals the structure of the Au-bound sulfur, while AFM details the structure at the monolayer/air interface, revealing that the order at the Au-S interface is retained up to the monolayer/air interface. The investigation of the self-assembled CF[sub 3](CF[sub 2])7(CH[sub 2])[sub 2]SH monolayer at Au(lll) by AFM reveals a (2 [times] 2) adlayer structure, with nearest-neighbor and next-nearest-neighbor spacings of 0.58 [plus minus] 0.02 nm and 1.0 [plus minus] 0.02 nm, respectively. This is consistent with the larger van der Waals diameter of the fluorinated chain. Coverage of this fluorinated thiolate monolayer is (6.3[plus minus]0.8) [times] 10[sup [minus]10] mol/cm[sup 2], consistent with the expected 0.25 monolayer coverage of the (2 [times] 2) adlayer structure at Au(l11). Infrared reflection spectroscopy also confirm this. Upon prolonged exposure to air, the thiolate species is oxidized to elemental sulfur in the forms of cyclooctasulfur (cyclo-S[sub 8]) and other allotropes. STM reveals square structures on aged thiolate monolayers. Dimensions of these squares (0.40--0.50 rum per side) are close to those of cyclo-S[sub 8]. Electrochemical reductive desorption experiments also reveal a change in the surface species with time, with a second desorption wave.
- Research Organization:
- Ames Lab., IA (United States)
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 7181124
- Report Number(s):
- IS-T-1628; ON: DE93001218
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
GOLD
SORPTIVE PROPERTIES
ORGANIC FLUORINE COMPOUNDS
ADSORPTION
THIOLS
AIR
ELECTROCHEMISTRY
INFRARED SPECTRA
ION MICROSCOPY
LAYERS
MICROSCOPY
OXIDATION
REFLECTION
SURFACES
TUNNEL EFFECT
CHEMICAL REACTIONS
CHEMISTRY
ELEMENTS
FLUIDS
GASES
METALS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
SORPTION
SPECTRA
SURFACE PROPERTIES
TRANSITION ELEMENTS
400201* - Chemical & Physicochemical Properties