INFICON PLO-10i Phase Lock Oscillator - Manual (Page 43)

PLO-10 PHASE LOCK OSCILLATOR
CRYSTALS, HOLDERS AND FLOW CELL 7-9
7.2.1.5 Polystyrene removal
To clean polystyrene (PS) off a crystal, immerse the crystal into a 1:1 solution of hexane
and deionized water and treat it in an ultrasonic bath for 1 minute. Rinse thoroughly with
deionized water and blow dry with filtered nitrogen gas.
7.2.2 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.
7.2.2.1 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 .
7.2.2.2 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.
7.2.2.3 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.
7.3 CRYSTAL HOLDERS
Figure 14 shows a INFICON CHC-100 Crystal Holder (without a crystal, the crystal
retainer or the retainer cover). It has a cavity for a 1-inch diameter crystal. Inside the
cavity there are two Pogo® pins providing connections to the crystal’s front and rear
electrodes. Note the locations of the Pogo® pins. These pins are internally connected to
the BNC connector (SMB Jack for CHT-100 and CHK-100 holders) via an internal
coaxial cable.