Substrate photoelectron enhancement of carbonaceous overlayer Auger emission: effect of the substrate on carbon overlayer thickness determination in XPS

Brizzolara, Robert A.; Beard, Bruce C.

doi:10.1002/(sici)1096-9918(199908)27:8<716::aid-sia565>3.0.co;2-r

Cited by 9 publications

(3 citation statements)

References 18 publications

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“…The similarity of these compositional profiles indicates that neither reversible deformations nor the curvature of the electrode affects the composition or the average thickness of the oxide layer; angstrom-scale differences in the average thickness of the oxide layer would result in observable differences in the ratios between the intensities of the Ga 3+ and Ga 0 XPS signals. 75,76 While deformations have an effect on the mechanical properties of the surface, 54 and might plausibly have a macroscopic effect on its roughness (and thus on the effective contact area of the junctions), the nanoscopic characteristics (i.e., composition and thickness of the layer of oxides and contaminants) of the surface, and thus of the junctions, are-according to these XPS results-unaffected by the history of handling and by the shape of the electrode.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Electrical Resistance of Ag^TS–S(CH₂)_n−1CH₃//Ga₂O₃/EGaIn Tunneling Junctions

et al. 2012

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Tunneling junctions having the structure Ag TS −S(CH 2 ) n−1 CH 3 // Ga 2 O 3 /EGaIn allow physical−organic studies of charge transport across selfassembled monolayers (SAMs). In ambient conditions, the surface of the liquid metal electrode (EGaIn, 75.5 wt % Ga, 24.5 wt % In, mp 15.7°C) oxidizes and adsorbs-like other high-energy surfaces-adventitious contaminants. The interface between the EGaIn and the SAM thus includes a film of metal oxide, and probably also organic material adsorbed on this film; this interface will influence the properties and operation of the junctions. A combination of structural, chemical, and electrical characterizations leads to four conclusions about Ag TS −S(CH 2 ) n−1 CH 3 // Ga 2 O 3 /EGaIn junctions. (i) The oxide is ∼0.7 nm thick on average, is composed mostly of Ga 2 O 3 , and appears to be self-limiting in its growth. (ii) The structure and composition (but not necessarily the contact area) of the junctions are conserved from junction to junction. (iii) The transport of charge through the junctions is dominated by the alkanethiolate SAM and not by the oxide or by the contaminants. (iv) The interface between the oxide and the eutectic alloy is rough at the micrometer scale. ■ INTRODUCTIONWe, and others, are developing procedures with which to study charge transport across self-assembled monolayers (SAMs). 1−32We have explored two systems, both based on electrodes made of liquid metals (Hg, and a eutectic alloy of gallium and indium, which we abbreviate as EGaIn) and focused on the latter. The latter system has two major components: (i) a SAM supported by a template-stripped silver (Ag TS ) electrode and contacted by (ii) a "top" electrode of EGaIn (75.5 wt % Ga, 24.5 wt % In, mp 15.7°C 33 ) that is a liquid at room temperature and covered with a thin metal oxide film; we refer to these junctions by a nomenclature defined earlier 1 as Ag TS −SR//Ga 2 O 3 /EGaIn, where R is an organic group (which may range in structure from simple n-alkyl groups to more complex functionalities, e.g., aromatics 28 or ferrocenes 13,34,35 ). These junctions are typically formed, characterized, and used in contact with ambient laboratory atmosphere. In these conditions, the surface of EGaIn oxidizes rapidly and spontaneously (for convenience we indicate the composite structure-oxide skin and metal electrode-as "Ga 2 O 3 / EGaIn") and it-as do all other surfaces-adsorbs adventitious contaminants (e.g., water, organic molecules, particles). The electrical resistance, thickness, and heterogeneity of the composite films of metal oxide and contaminants on the surface (and their variability from electrode to electrode, and from junction to junction) have not been characterized: the most serious ambiguity affecting the measurement of charge transport through Ag TS −SR//Ga 2 O 3 /EGaIn junctions is currently the effect of the oxide skin and adventitious contaminants.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Electrical Resistance of Ag^TS–S(CH₂)_n−1CH₃//Ga₂O₃/EGaIn Tunneling Junctions

et al. 2012

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“…XPS is a surface sensitive technique that has become widely used for studying properties of atoms, molecules, solids, and surfaces. − Generally speaking, intensities of core level photoelectron peaks are used for quantitative analysis, and binding energies of core level photoelectrons exhibit chemically induced shifts. The main success of the XPS technique is associated with studies of the physical and chemical phenomena on the surface of solids (see for instance refs and and refs therein).…”

Section: Introductionmentioning

confidence: 99%

Surface Analysis by X-ray Photoelectron Spectroscopy of Sol−Gel Silica Modified with Covalently Bound Peptides

2007

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Chemical surface characterization of biologically modified sol-gel derived silica is critical but somewhat limited. This work demonstrates the ability of x-ray photoelectron spectroscopy (XPS) to characterize the surface chemistry of peptide modified sol-gel thin films based on the example of four different free peptide-silanes, denoted RGD, NID, KDI ,and YIG. The N 1s and C 1s peaks were found to be good fingerprints of the peptides, whereas O 1s overlapped with the signal of substrate oxygen and, therefore, the O 1s peak was not informative in the case of the thin films. The C 1s peak was fitted and the contribution of the residual hydrocarbons was sorted out. The curve-fitting procedure of the C 1s peak accounted for the different chemical states of carbon atoms in the peptide structure. The curve-fitting procedure was validated by analyzing free peptides in the powder form and was then applied to the characterization of the peptide-modified thin films. The XPS measured ratio between nitrogen and carbon for the peptide thin film was similar to the corresponding value calculated from the peptide structures. Angle resolved XPS confirmed the surface nature of peptides in modified thin films. The coverage and thickness of the peptides on the thin film surface depended on the peptide sequence. The coverage was in the range of 10% of a monolayer, and the layer thickness varied from 10 to 30 A. We believe that the different thicknesses and surface coverage are due to the local structure of the peptides, with the RGD and NID peptides taking a globule conformation and the YIG and KDI peptides adopting a more linear structure.

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“…The variability of the photoelectron attenuation length can be used to determine whether an adsorbate has formed a monolayer on a surface . A number of methods have been proposed to model the attenuation of the photoelectrons through solids and through an overlayer. , …”

Section: Resultsmentioning

confidence: 99%

Variable Energy X-ray Photoemission Studies of Alkylsilane Based Monolayers on Gold

2003

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Gaseous n-hexylsilane (C 6 H 13 SiH 3 ), n-octylsilane (C 8 H 17 SiH 3 ), and n-octadecylsilane (C 18 H 37 SiH 3 ) have been vapor deposited in ultrahigh vacuum (UHV) on freshly evaporated gold surfaces to form monolayers. Surface sensitive X-ray photoemission studies utilizing synchrotron radiation in the 160-360 eV range have been used to characterize these systems. Analyses of the C 1s, Si 2p, and Au 4f and valence band regions permit a structural assessment of the monolayer. The full width at half-maximum of the Si 2p and C 1s core levels, 0.4 and 1.2 or 1.1 eV, respectively, suggest the monolayers are chemically homogeneous. The intensity variation of the Au 4f and Si 2p core levels at different photon energies indicate the surface coverage of the monolayer is ∼96% and the chain orientation is upright on the surface, not parallel to the surface. The valence band of the alkylsilane monolayers exhibit features at ∼-13.2, -14.6, -16.3, -17.6, and -18.9 eV that agree well with those observed for alkyl chains of the same length.

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Substrate photoelectron enhancement of carbonaceous overlayer Auger emission: effect of the substrate on carbon overlayer thickness determination in XPS

Cited by 9 publications

References 18 publications

Electrical Resistance of Ag^TS–S(CH₂)_n−1CH₃//Ga₂O₃/EGaIn Tunneling Junctions

Electrical Resistance of Ag^TS–S(CH₂)_n−1CH₃//Ga₂O₃/EGaIn Tunneling Junctions

Surface Analysis by X-ray Photoelectron Spectroscopy of Sol−Gel Silica Modified with Covalently Bound Peptides

Variable Energy X-ray Photoemission Studies of Alkylsilane Based Monolayers on Gold

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Substrate photoelectron enhancement of carbonaceous overlayer Auger emission: effect of the substrate on carbon overlayer thickness determination in XPS

Cited by 9 publications

References 18 publications

Electrical Resistance of AgTS–S(CH2)n−1CH3//Ga2O3/EGaIn Tunneling Junctions

Electrical Resistance of AgTS–S(CH2)n−1CH3//Ga2O3/EGaIn Tunneling Junctions

Surface Analysis by X-ray Photoelectron Spectroscopy of Sol−Gel Silica Modified with Covalently Bound Peptides

Variable Energy X-ray Photoemission Studies of Alkylsilane Based Monolayers on Gold

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Electrical Resistance of Ag^TS–S(CH₂)_n−1CH₃//Ga₂O₃/EGaIn Tunneling Junctions

Electrical Resistance of Ag^TS–S(CH₂)_n−1CH₃//Ga₂O₃/EGaIn Tunneling Junctions