Phosphonic Acids on an Atomically Defined Oxide Surface: The Binding Motif Changes with Surface Coverage

Abstract

We have studied the anchoring mechanism of a phosphonic acid on an atomically defined oxide surface. Using time-resolved infrared reflection absorption spectroscopy, we investigated the reaction of deuterated phenylphosphonic acid (DPPA, CHPOD) with an atomically defined CoO(111) surface in situ during film growth by physical vapor deposition. We show that the binding motif of the phosphonate anchor group changes as a function of coverage. At low coverage, DPPA binds in the form of a chelating tridentate phosphonate, while a transition to a chelating bidentate occurs close to monolayer saturation coverage. However, the coverage-dependent change in the binding motif is not associated with a major change of the molecular orientation, suggesting that the rigid phosphonate linker always maintains the DPPA in a strongly tilted orientation irrespective of the surface coverage.

Aluminum Oxide at the Monolayer Limit via Oxidant‐Free Plasma‐Assisted Atomic Layer Deposition on GaN

“…Prior reports attributed the evolution from higher to lower denticities to an increasing SAM surface coverage. [ 38,39 ] Our results are consistent with this finding since we observe a relatively large phosphorus atom density of (4.5 ± 0.3) × 10 14 cm −2 , corresponding to a PA surface coverage, n , of 4.5 ± 0.3 nm −2 , as calculated from the XPS data (Figure 4c) according to the formalism introduced by Kim et al. [ 31 ] (Section S7, Supporting Information).…”

“…Prior reports attributed the evolution from higher to lower denticities to an increasing SAM surface coverage. [37][38] Our results are consistent with this finding since we observe a relatively large phosphorus atom density of (4.5 ± 0.3) × 10 14 cm -2 , corresponding to a PA surface coverage, n, of 4.5 ± 0.3 nm -2 , as calculated from the XPS data (Figure 4c) according to the formalism introduced by Kim et al [30] (Supporting Information S7). This high SAM surface coverage (4.5 ± 0.3 nm -2 ) on GaN/monolayer AlOx approaches the theoretical limits predicted for aluminum oxide (4.65 nm -2 ) [39] by DFT and estimated from the molar volume of phosphorus acid (4.25 nm -2 ), [40] and it is two times higher than reported for alkyl-PAs grafted on c-plane-Ga-polar GaN (2.3 nm -2 ).…”

Phosphonic Acid Modified ZnO Nanowire Sensors: Directing Reaction Pathway of Volatile Carbonyl Compounds

“…To confirm surface MPA modification, the FT-IR spectra of the modified ZnO nanowires were collected (Figure a,b). A set of the characteristic peaks of MPA (asymmetric stretching of CH 3 ν as (CH 3 ): 3009 cm –1 , symmetric stretching of CH 3 ν s (CH 3 ): 2942 cm –1 , symmetric umbrella bend of CH 3 δ as (CH 3 ): 1422 cm –1 , rocking of CH 3 ρ­(CH 3 ): 1323 cm –1 , stretching of PO ν­(PO): 1174 cm –1 , stretching of P–C ν­(P–C): 1160 cm –1 , and ν­(P–O) or ν­(P–OH): 1067–970 cm –1 ) − is observed in the FT-IR spectra, confirming the adsorption of MPA on the ZnO surface. These values are in good agreement with the reported values of phosphonic acids bounded on ZnO, though the stretches in the P–O and P–OH regions are not able to be absolutely verified .…”

Self-Metalation of Porphyrins by Cobalt Oxide: Photoemission Spectroscopic Investigation

“…Molecule cobalt-oxide heterostructures offer a practicable route to understand the reaction and interaction between molecules and oxide surfaces. 38 Here, we study the electronic structure of free-base porphyrin molecules on cobalt oxide and metallic Co(100) surfaces. We report the interaction of porphyrins on CoO(111) and oxygen-exposed metallic Co(100) interfaces by in situ XPS and UPS measurements.…”