Structure of Self-Assembled Monolayers of Partially Fluorinated Alkanethiols with a Fluorocarbon Part of Variable Length on Gold Substrate

Lu, Hao; Zeysing, Daniela; Kind, Martin; Terfort, Andreas; Zharnikov, Michael

doi:10.1021/jp405475h

Cited by 36 publications

(109 citation statements)

References 93 publications

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“…Further evidence of the grafting of the perfluoroalkyl layer at the surface of Alnp was given by the high-resolution C 1s spectra (shown in the inset of Figure 5b), which display two new intense components after functionalization, C CF 2 at 291.3 eV and C CF 3 at 293.0 eV, corresponding to the perfluoro chain (−CF 2(n) −CF 3 ). 31 3.3.2. TGA.…”

Section: Resultsmentioning

confidence: 99%

Powerful Surface Chemistry Approach for the Grafting of Alkyl Multilayers on Aluminum Nanoparticles

et al. 2015

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The synthesis of aluminum nanoparticles (Alnp) has raised promising perspectives these past few years for applications in energetic materials. However, because of their high reactivity, it is crucial to functionalize them before their use. In this work, we propose an original and simple chemical approach to graft spontaneously alkyl layers derived from alkyl halides at the surface of Alnp, by relying on the highly reductive character of these nanoparticles, when they are in the unoxidized form. Alnp were prepared in a glovebox and reacted with alkyl halides (RI and RBr) to give modified Alnp-R, as shown by infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction, thermogravimetric analysis (TGA), and microscopy. The coating is made of alkyl multilayers, which were found to be strongly anchored at the Alnp surface, as it resisted 2 h of rinsing in toluene. An electrocatalytic electron transfer promoted by Alnp is proposed to describe the mechanism of this grafting reaction.

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Section: Resultsmentioning

confidence: 99%

Powerful Surface Chemistry Approach for the Grafting of Alkyl Multilayers on Aluminum Nanoparticles

et al. 2015

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“…This potential favors a preferable GaAs−S−C bond angle of ∼104°, 44,56 and predefines, thus, the orientation of the alkyl linker, which, as far as the all-trans conformation is maintained, "transfers" this preferable orientation to the adjacent biphenyl moiety. Accordingly, a small inclination of these moieties is favored at an odd n, as illustrated in Figure 6, allowing the energetically preferred high packing density, so that the bending potential works cooperatively with the other The Journal of Physical Chemistry C Article structure-building interactions.…”

Section: ■ Discussionmentioning

confidence: 99%

Structure-Building Forces in Biphenyl-Substituted Alkanethiolate Self-Assembled Monolayers on GaAs(001): The Effect of the Bending Potential

Zharnikov

2015

J. Phys. Chem. C

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Molecular assembly on a technologically relevant GaAs substrate is an important and application-related issue. In this context, self-assembled monolayers (SAMs) formed from a series of ω-(4′-methylbiphenyl-4-yl)alkanethiols, CH 3 (C 6 H 4 ) 2 (CH 2 ) n SH (BPn, n = 1−6), were prepared on GaAs(001) and characterized in detail by highresolution X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The resulting films exhibited pronounced, "odd−even" variation in molecular orientation and packing density with the number (n) of methylene groups in the alkyl linker; viz., smaller molecular inclination, associated with a higher packing density, was observed for an odd n, while the opposite was the case for an even n. Such an odd−even behavior confirms once again the existence of a bending potential for GaAs(001), which is equivalent to the analogous potential for the Au(111) substrate, where similar odd−even behavior has been observed. This potential plays an important role in the balance of the structure-building interactions, predefining the orientation of the alkyl linker, transferred in an odd−even fashion, depending on the parity of n, to the adjacent biphenyl spacer. The above effects were found to be superimposed onto pronounced dependence of the film quality on the length of the BPn precursor. This occurred due to proneness of the GaAs substrate to oxidation, hindering an efficient self-assembly, as well as due to a limited ability of the shortchain monolayers to protect this sensitive substrate from the postpreparation oxide regrowth. A proper selection of the parameters is, thus, very important for the design of functional monomolecular films on GaAs. ■ INTRODUCTIONSelf-assembled monolayers (SAMs) of organic molecules on solid substrates attract significant attention due to their technological relevance and as important test systems for fundamental research. 1 The lateral density and structure of these films stem from a complex interplay of several factors, viz., intermolecular interaction, the anchor group−substrate interaction, corrugation of the binding energy hypersurface, and mismatch between the optimal molecular lattice and the structural template provided by the substrate. 2 At a given mismatch and the corrugation of the binding energy hypersurface, the intermolecular interaction is frequently believed to play a dominant role as compared to the anchor group− substrate interaction, as was in particular assumed for SAMs of nonsubstituted alkanethiolates (ATs) on coinage metal substrates. These films exhibit intermolecular lattice spacing of ∼5 and ∼4.67−4.77 Å on Au(111) and Ag(111), respectively, accompanied by a molecular tilt of ∼27−35°on Au(111) and ∼10−12°on Ag(111). 1−9 The tilt can then be considered as the only means to achieve the optimal interchain spacing (∼4.4 Å), characteristic of the respective bulk materials, whereas the substrate−S−C moiety is assumed to behave as a "free joint", adapting to an optimal geometrical configuration and enabling the nece...

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“…In general, the voltammetric traces of the Pt film electrode in supporting electrolyte 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 vibration of the trifluoromethyl group 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 adsorption. It should be noted, however, that the integral band intensities of the different anions do not represent their absolute coverage.…”

Section: Cyclic Voltammetry Measurementsmentioning

confidence: 99%

Perfluoroalkyl-Phosphonic Acid Adsorption on Polycrystalline Platinum and Its Influence on the Oxygen Reduction Reaction

et al. 2015

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Motivated by the need for a better understanding of the oxygen reduction reaction (ORR) in high temperature proton exchange membrane fuel cells (HTPEM-FC), we have investigated the impact of anion adsorption on the ORR activity and selectivity for small concentrations of perfluoroalkylated phosphorus based model compounds.A polycrystalline Pt surface was used to evaluate the adsorption behaviour of trifluoromethyl-phosphonic acid (TFMPA) and pentafluoroethyl-phosphonic acid (PFEPA) by means of cyclic voltammetry (CV), a rotating disc electrode (RDE), and a spectro-electrochemical flow cell. In-situ Fourier transform infrared spectroscopy in the attenuated total reflection (ATR-FTIRS) configuration was performed to study the impact of the adsorbed species on the ORR activity and selectivity employing simultaneous detection of hydrogen peroxide formation during the ORR.Electrochemical impedance spectroscopy (EIS) was applied to determine the charge transfer resistance R CT under ORR conditions. The presence of TFMPA, PFEPA or H 3 PO 4 had significant effects on the cyclic voltammograms in the H upd and oxide formation potential region. The ORR activity, measured under well-defined mass transport conditions, revealed a doubling of the kinetic current densities for TFMPA and PFEPA compared with H 3 PO 4 , suggesting a weaker adsorption tendency for these model compounds. The ORR selectivity was found to be dependent on the nature of the adsorbed species. These observations are consistent with ATR-FTIRS and EIS results, where the reduced interaction of perfluoroalkylated compounds with the Pt surface was observed compared to H 3 PO 4 . . IntroductionSustainable energy sources are of growing interest due to environmental regulations and increasing energy consumption worldwide. To satisfy the need for clean energy, fuel cells, which convert chemical energy directly into electrical energy, are promising for both stationary and mobile applications, where high power densities are required.Compared with conventional proton exchange membrane fuel cells (PEM-FC) operated below 100 °C 1 , high-temperature operation (150 -180°C) holds certain advantages, including an increased overall efficiency, a reduced sensitivity to catalyst poisoning, and simplified water management 2 .Under such operating conditions, concentrated phosphoric acid is usually used as the common electrolyte because of its favorable physical and chemical properties at high temperatures. However, the slow ORR in phosphoric acid electrolyte causes a relatively high overpotential on the cathode side 3 , which limits the performance and practical applications of high temperature proton exchange membrane fuel cells (HTPEM-FC). The anions adsorbed at the electrode surface are known to strongly affect the ORR kinetics by occupying catalyst surface sites and hindering the dissociative adsorption of molecular oxygen 4-7 . Hence, they act as site-blocking spectator species. The anions also affect the ORR selectivity by changing the ORR pathway and promote the productio...

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Structure of Self-Assembled Monolayers of Partially Fluorinated Alkanethiols with a Fluorocarbon Part of Variable Length on Gold Substrate

Cited by 36 publications

References 93 publications

Powerful Surface Chemistry Approach for the Grafting of Alkyl Multilayers on Aluminum Nanoparticles

Powerful Surface Chemistry Approach for the Grafting of Alkyl Multilayers on Aluminum Nanoparticles

Structure-Building Forces in Biphenyl-Substituted Alkanethiolate Self-Assembled Monolayers on GaAs(001): The Effect of the Bending Potential

Perfluoroalkyl-Phosphonic Acid Adsorption on Polycrystalline Platinum and Its Influence on the Oxygen Reduction Reaction

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