INFICON RQCM - Quartz Crystal Microbalance Research System - Manual (Page 47)

RQCM – RESEARCH QUARTZ CRYSTAL MICROBALANCE
CRYSTALS, HOLDERS AND FLOW CELL 4-9
organic solvents prior to oxidative cleaning. Polymers that are very intractable may be
particularly difficult to clean. In this case, refluxing toluene of Tetrahydrofuran helps to facilitate
the removal of the polymer. Then the following procedure is recommended:
A. Wash with Organic Solvents: Methylene Chloride, Toluene, or THF to remove most
organic material. Reflux if needed.
B. Wash with Isopropanol and dry.
C. Clean in hot piranha (70% sulfuric acid/ 30% hydrogen peroxide) for 1 – 2 minutes.
D. Rinse with DI water.
E. Rinse with isopropanol and dry.
F. O2 plasma cleaning for 5 minutes or longer if needed.
G. Rinse with ethanol.
H. O2 plasma clean for 3 minutes.
Caution
– Beware when working with piranha solution since it is a strong
oxidizer and should not be contacted with any organic solvents. Also, if you
leave the QCM crystal in the hot piranha too long it can leech the chromium or
titanium (adhesion layer) from under the gold leading to delaminating of the gold
from the crystal surface.
I. Use the crystal as soon as possible or store in a Nitrogen environment.
4.2.2 ELECTRODE SURFACE MODIFICATIONS
A QCM will response to anything that has mass. Thus, it is imperative for the QCM user to
develop a “condition” where the QCM will only responsed to the substance of interest. This
usually involves a chemically or biologically sensitive layer applied to the surface of the crystal 13 .
INFICON
offers a wide variety of standard electrode materials for you to choose from. Contact us
if you don’t see one that fits your needs. If you choose to do your own crystal surface
modification, use the following guidelines.
4.2.2.1 SPIN COATING
Thin films (nm to microns) of polymers and other materials can be applied by spin coating 14 .
Polystyrene is a common material spin-coated on QCM sensor crystals. UV/Ozone treatment can
be used to change the hydrophobicity of organic polymeric coatings 15 16 .
4.2.2.2 SELF-ASSEMBLED MONOLAYERS (SAM)
Self-assembling monolayers can be laid down on gold or silver surface by thiolization 17 18 19 or on
SiO
2
by silanization 20 to control surface properties.
4.2.2.3 PHYSICAL VACUUM DEPOSITION (PVD)
Thin films of metals or metal oxides can be applied by sputtering or thermal evaporation in a
vacuum chamber. To ensure quality and reproducible films, careful attention to cleanliness must
be observed, both in the vacuum chamber and in the preparation of the crystals prior to coating.
INFICON
is an expert in PVD. Consult us for any special needs.