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.

The effect of heat treatment on the grain size, phase assemblage, and mechanical properties of a 3 mol% Y‐TZP ceramic was investigated. Specimens were initially sintered for 2 h at 1450°C to near theoretical density; some specimens were then heat‐treated at 1550°, 1650°, 1750°, or 1850°C to coarsen the microstructure. The average grain size increased with heat treatment from <0.5 to ∼10 μ‐m. Phase analyses revealed predominantly tetragonal and cubic phases below 1750°C, with a significant decrease in tetragonal content and increase in monoclinic content for temperatures >1750°C. The maximum fraction of tetragonal phase that transformed during fracture corresponded with the largest tetragonal grain size of ∼5–6 μm. Strength was on the order of 1 GPa, and was surprisingly insensitive to heat‐treatment temperature and grain size, contrary to previous studies. The fracture toughness increased from 4 to 10 MPa.m1/2 with increasing grain size, owing to an increasing transformation zone size. Grain sizes larger than 5–6 μm spontaneously transformed to monoclinic phase during cooling. Such critical grain sizes are much larger than those found in past investigations, and may be due to the greater fraction of cubic phase present which decreases the strain energy arising from crystallographic thermal expansion anisotropy of the tetragonal phase.

Octadecyl phosphoric acid ester has been found to produce oriented, well-ordered monolayers on a flat tantalum(V) oxide surface, via self-assembly from a heptane/propan-2-ol solution. By means of contact angle, optical waveguide lightmode spectroscopy (OWLS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and X-ray photoelectron spectroscopy (XPS) measurements, it has been shown that these layers closely resemble those formed by the corresponding thiol−gold system, with respect to packing density, inclination, and order. The system shows promise as an approach to functionalizing oxide surfaces with well-ordered organic monolayers, with potential applications in the fields of biochemical analysis and sensors.

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