Alkylphosphonate Modified Aluminum Oxide Surfaces

Abstract

The surface properties of aluminum, such as chemical composition, roughness, friction, adhesion, and wear, can play an important role in the performance of micro-/nano-electromechanical systems, e.g., digital micromirror devices. Aluminum substrates chemically reacted with octadecylphosphonic acid (ODP/Al), decylphosphonic acid (DP/Al), and octylphosphonic acid (OP/Al) have been investigated and characterized by X-ray photoelectron spectroscopy (XPS), contact angle measurements, and atomic force microscopy (AFM). XPS analysis confirmed the presence of alkylphosphonate molecules on ODP/Al, DP/Al, and OP/Al. No phosphonates were found on bare Al as a control. The sessile drop static contact angle of pure water on ODP/Al and DP/Al was typically more than 115 degrees and on OP/Al typically less than 105 degrees indicating that all phosphonic acid reacted Al samples were highly hydrophobic. The root-mean-square surface roughness for ODP/Al, DP/Al, OP/Al, and bare Al was less than 15 nm as determined by AFM. The surface energy for ODP/Al and DP/Al was determined to be approximately 21 and 22 mJ/m2, respectively, by the Zisman plot method, compared to 25 mJ/m2 for OP/Al. ODP/Al and OP/Al were studied by friction force microscopy, a derivative of AFM, to better understand their micro-/nano-tribological properties. ODP/Al gave the lowest coefficient of friction values while bare Al gave the highest. The adhesion forces for ODP/Al and OP/Al were comparable.

Organic corrosion inhibitors: where are we now? A review. Part IV. Passivation and the role of mono- and diphosphonates

“…Hoque et al [43] 18 provided > 125°, which indicates strong hydrophobization of the Al/Si surface. In the following work [44], studies were carried out on oxidized Al, and APhC 8 was studied instead of APhC 10 F 17 . After treatment of the sample surface by a 0.1% APhC 8 solution in THF,  was < 105°, although in the case of similar treatment with APhC 10 or APhC 18 solution with the same concentration,  was >115°.…”

The fabrication and surface functionalization of porous metal frameworks – a review

“…In addition, as opposed to silanes where Si-O-Si reactions can occur, phosphonates will not cause homo-condensations that has the advantage of increasing the grafting yield 197 . Alumina, tin oxide, zirconia and magnetite were also shown to be readily functionalized with phosphonate groups 6,214,[216][217][218] . In addition, due to larger steric hindrance effects, phosphonate groups may also form multiple anchorages onto metal oxide surfaces, further stabilizing the structure 219 .…”

Influence of chain ordering on frictional properties of self-assembled monolayers (SAMs) in nano-lubrication

“…Alkylphosphonic acids are also an important class of SAM molecules because of their ability to assemble on a number of oxide surfaces, such as tantalum oxide, aluminum oxide, silicon oxide, iron oxide, copper oxide, and mica, and to form robust surface films [78][79][80][81][82][83][84][85][86][87][88][89][90][91][92]. Compared to SAMs of fatty acids, alkanethiols, and alkylsilanes, which have been studied extensively, phosphonic acid-based SAMs have not received much attention [84].…”

“…Compared to SAMs of fatty acids, alkanethiols, and alkylsilanes, which have been studied extensively, phosphonic acid-based SAMs have not received much attention [84]. There has been increasing interest in forming monolayer lubricants with alkylphosphonate SAMs for Al-based substrates recently, particularly with the development of digital micromirror devices used in optical projection displays [81][82][83][84]93,94]. The phosphonic acid head group binds more strongly to metal oxide surfaces than carboxylic acid head group [85], and the increased binding stability leads to significant interest in phosphonic acid SAMs for applications in electronics and MEMS/NEMS.…”