Growth Mechanisms of Octadecylphosphonic Acid Self-Assembled Monolayers on Sapphire (Corundum):  Evidence for a Quasi-equilibrium Triple Point

Abstract

Self-assembled monolayer growth of octadecylphosphonic acid on single-crystal C-face (1000) and R-face (11 h02) sapphire (corundum) has been investigated by ex situ tapping-mode atomic force microscopy, contact angle measurements, and Fourier transform infrared spectroscopy. The process of film formation is highly dependent on the temperature, a phenomenon that is explained by a three-phase model for film deposition. At low temperature, close-packed molecular islands nucleate and grow, surrounded by virtually bare substrate, analogous to a two-dimensional (2D) vapor-to-solid transition. At high temperature, on the other hand, the growth involves a 2D liquid-to-solid transition. Different growth kinetics are observed for the two crystal orientations, which can be related to the surface energetics.

Monolayer-directed Assembly and Magnetic Properties of FePt Nanoparticles on Patterned Aluminum Oxide

“…As shown below (Figure 4a), the height of the TDP features was around 1.5 nm. This is somewhat lower than the extended adsorbate length (2 nm), which indicates a tilt in the SAM layer similar to various alkylphosph(on)ate SAMs on metal oxides [31,35,40,41]. The water contact angle (CA) of oxygen plasma-cleaned Al 2 O 3 was below 10°, which increased to 70°, 60° and 115° for SAMs of ABP, PNDA and TDP, respectively.…”

“…Alkyl phosphates and alkyl phosphonates form SAMs with high ambient stability on metal oxides such as Ta 2 O 5 , Al 2 O 3 , ZrO 2 and TiO 2 without the need for controlled environmental conditions [25,31,35–40]. …”

“…The latter consist of two ferromagnetic electrodes separated by an insulating barrier, and they are promising candidates for spintronic devices, in which signal detection is achieved via tunneling magnetoresistance (TMR) [ 27 ]. The surface properties of Al 2 O 3 can easily be changed by annealing to get an ultra-smooth surface [ 31 – 32 ].…”

“…Self-assembled monolayers (SAMs), in particular thiols on gold and silanes on SiO 2 , have been studied extensively [ 33 – 34 ], but SAMs on metal oxides are relatively new. Alkyl phosphates and alkyl phosphonates form SAMs with high ambient stability on metal oxides such as Ta 2 O 5 , Al 2 O 3 , ZrO 2 and TiO 2 without the need for controlled environmental conditions [ 25 , 31 , 35 – 40 ].…”

Self‐assembly of stearic acid on aluminium: the importance of oxide surface chemistry

“…8,9 Water contact angle and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) measurements have been used to implicate this carbonaceous material in blocking decyl phosphonic acid adsorption to the surface of magnetron-sputtered aluminium. 24 A number of groups have formed self-assembled monolayers (SAMs) on alumina surfaces, some on alumina single crystals, 25,26 but more commonly on the air-formed film on metal. 4 -6,9,27 -32 Most studies aim to attain a constant surface chemistry by using a constant atmospheric exposure time or a cleaning step prior to assembly.…”