Structural Chemistry of Self-Assembled Monolayers of Octadecylphosphoric Acid on Tantalum Oxide Surfaces

Abstract

Octadecylphosphoric acid ester is shown to self-assemble on amorphous/nanocrystalline tantalum oxide (Ta2O5) layers deposited by physical vapor deposition onto glass substrates. Three complementary surfaceanalytical techniques (angle-dependent X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and atomic force microscopy in lateral force mode), showed that a 2.2 nm thick, "tailsup"-oriented adlayer is formed, which displays local near-hexagonal order, strong P-O-Ta bonding, and the presence of (-P-O-)2Ta species. A model for the binding and the structural organization of the octadecyl phosphate molecules on the tantalum oxide surface is proposed involving direct coordination of the terminal phosphate headgroup to Ta(V) cations forming a strong complexation bond, two types of bonding of the octadecyl phosphate with both monodentate and bidentate phosphate-Ta(V) coordinative interactions, and, locally, the formation of a coincidence lattice of approximately hexagonal structure defined by both the location of Ta(V) cation sites and an intermolecular spacing between the octadecyl phosphate ligands of approximately 0.5 nm. This is very similar to the self-assembled monolayer structure of long-chain alkanethiols on gold. The use of phosphoric acid ester derivatives is believed to have potential for designing specific interface architectures in sensor technology, in surface modification of oxide-passivated metallic biomaterials, and in composite metal (oxide)-polymer interfaces.

Electrically-Assisted Formation and Desorption of Dodecyl Phosphate Self-Assembled Monolayers on Indium Tin Oxide Surfaces

“…The O1s peak intensity consisted of three components with contributions from: (i) O1s(a) at 530.1 eV ((Sn-In)O x ), (ii) O1s(b) ((In-Sn)-O-P, P=O) at 531.3 eV and (iii) O1s(c) at 532.6 eV (P-O-H, P-O-R). The binding energies of the different O1s subpeaks as well as the higher C1s(a) and lower O1s(a) intensities of the DDPO 4 -coated surface (in comparison to those of the clean substrate) are consistent with the presence of a DDPO 4 monolayer and a phosphate-substrate interaction based on both monodentate and bidentate binding as has been proposed earlier for octadecylphosphate SAMs on tantalum oxide substrates [10].…”

“…This electro-active platform was then used to control the specific attachment of cells to the surface. Although alkanethiols produce strongly bound monolayers with a high degree of packing density and order on gold, the necessity to employ gold (or silver) as a substrate excludes applications where high optical transparency is required [10] 2 has the further advantage of eliminating the risk associated with organic solvent contamination of cell culture substrates [13]. ITO is an opto-electronic material of high optical transparency and electrical conductivity.…”

Spectroscopic and Theoretical Study of the Grafting Modes of Phosphonic Acids on ZnO Nanorods

“…This shift toward lower BE (0.9 eV) compared to free acids is associated with the deprotonation of −POH terminations, as it is generally accepted that P 2p BE value of [PO n (OH) m ] x− groups depends on the number of O bonded to P and on the n/m ratio. 52,53 A shift of about 0.5 eV has been associated, in previous papers, 54 with the deprotonation of one P−OH termination since the n/m ratio increases from 1/2 in PO(OH) 2 to 2 in [PO 2 OH] − . The greater shift observed in this work can be associated with the deprotonation of both −POH terminations 54 with the occurrence of two P−O−Zn bonds.…”

Surface modification of titanium, titanium alloys, and related materials for biomedical applications

“…Protein adsorption and cell adhesion are reduced on the phosphorylcholine-assembled surfaces. With the intention of producing well-controlled surfaces on oxide, chlorosilanes [204], hydroxamic acid [205], carboxylic acids [206], and phosphoric and phosphonic acids [207][208][209][210] have been proposed as SAMs molecules.…”