Langmuir-Blodgett film characterization in
air using surface plasmon resonance.
Introduction
The ability to assemble ordered molecular films with tailored
functionality over macroscopic lateral dimensions provides
exciting and unique opportunities in many practical and
commercial applications. Sensors, detectors, displays and
electronic circuit components are just a few examples. This
well known technique is referred to as Langmuir-Blodgett
(LB) deposition, where films of functional molecules,
nanoparticles, nanowires or microparticles are spread at the
air-water interface, compressed and transferred to a solid
substrate. Compared to other organic thin film deposition
techniques, such as thermal evaporation, sputtering,
electrodeposition, molecular beam epitaxy, layer-by-layer
or self-assembly, LB is much less limited by the molecular
structure of the functional molecule. This means that it
is often the only technique that can be used for bottom up
assembly in nanotechnology and functional materials
The Langmuir-Blodgett (LB) technique, used to deposit single and multiple
layers of molecules on a solid substrate.
applications. The aim of this note is to demonstrate that
SPR-Navi from BioNavis is ideal for the ex situ
investigation in air of mono- and multilayer films of stearic
acid deposited on a gold surface.
Experimental
The gold-coated glass slides used in the SPR
measurements were cleaned by immersion in a boiling
1:1:5 NH3OH:H2O2:H2O for ten minutes, flushed thoroughly
with ion exchanged water and blown dry with nitrogen.
Monolayers and multilayers of Cadmium Stearate (SACd,
(C17H35COO)2Cd) were deposited via the LB technique
(KSVNIMA LBtrough System 2) on cleaned gold slides,
. Complete SPR curves were
measured after depositing one, three and five layers of
SACd on separate gold slides.
Results
illustrates SPR intensity versus angle curves for
the clean gold surface, and for surfaces with one, three and
five deposited layers of SACd. There are some differences
in the absolute minimum value in the SPR curves between
different samples. This difference stems from the use of
separate gold slides, and does not affect the validity of the
measurement.Fitting the experimental data with a theoretical model (solid
curves, allows determination of the layer thickness
of the deposited LB layers (WinSPALL Software, Wolfgang
Knoll, MPI, Germany). thickness increases linearly with layer number, as expected for this
system. Meanwhile, the slope of the thickness vs. layer
number plot is 2.45 nm/deposited layer, which is in very
good agreement
