Increased crystallinity of octadecylphosphonic acid Langmuir–Blodgett films with an increasing number of layers

• Published in: Thin solid films 2013-06, Vol.537, p.242-246
• Main Authors: Zhao, F.Z., Dey, R., Nie, H.-Y., Lau, W.M.
• Format: Article
• Language: English
• Subjects: Arrays; Atomic force microscopy; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Crystallinity; even-numbered LB films; Exact sciences and technology; increased crystallinity; Langmuir-Blodgett films; Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids); Materials science; Methods of deposition of films and coatings; film growth and epitaxy; molecular headgroups; molecular-resolution images; Multilayers; Octadecylphosphonic acid; Oxides; Physics; Si wafer; Stopping; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2013.04.117

We report that contact mode atomic force microscopy (AFM) imaging is useful in revealing crystallinity of octadecylphosphonic acid (OPA) Langmuir–Blodgett (LB) films. On a monolayer OPA LB film prepared on the native oxide of a Si wafer, no molecular-resolution could be obtained. However, molecular-resolution images were obtained on a bilayer surface, a reflection that molecules in the top layer adjust their alkyl chains to accommodate those from below to form a closely packed, OPA headgroup-terminated surface. We demonstrate that with an increasing number of layers, the crystallinity of multilayer OPA LB films improves as molecular-resolution AFM images obtained on even-numbered multilayers reveal that the terminating OPA headgroups form a sheet of hexagonal array. •Langmuir–Blodgett (LB) films of octadecylphosphonic acid (OPA) on SiO2.•Atomic force microscopy (AFM) imaging of OPA LB films.•Molecular-resolution AFM images on even-numbered OPA multilayers.•OPA headgroups form a sheet-like crystalline structure.•OPA molecules in monolayer LB film are weakly bonded to substrate.