Quartz Crystal Microbalance (QCM)
The Quartz Crystal Microbalance (QCM) is the sample substrate on which
the molecular ice films are deposited.
The QCM contains two gold coated quartz crystals, (a sample and a reference).
When driven by a small electric current, each crystal has a resonant frequency
around 15MHz (dependant on the crystal temperature). As matter is deposited
on the sample crsytal its resonant frequency changes. According to the
Sauerbrey equation this frequency change is directly proportional to the
mass change. This technology is typically used in the semiconductor industry
for thin film deposition and semiconductor growth.
For even greater sensitivity, the sample and reference frequencies in
this QCM are heterodyned together to give a single beat frequency in the
kHz regime. The nominal sensitivity of this instrument is 1.97x10-9
g cm-2 Hz-1.
The image below shows how the QCM sample is positioned in the chamber
relative to the rest of the surface probes.
Consequently, it is possible to measure;
-
the amount of ice deposited during film growth
-
the amount of molecular species adsorbed onto the ice film during adsorbate
dosing
-
the amount of ice film and/or adsorbate that has desorbed from the surface
as the sample is heated
The QCM was designed by and purchased from 
Oxford Applied Research
and modified in house by the Electronics Department in the School of
Chemistry.
The Surface Astrophysics experiment is part of 
Nottingham Astronomy Research Forum
and is based in the Surface
Science Group in the School
of Chemistry at the University
of Nottingham
These pages were last updated 14/10/01