KSV QCM-Z500 FREQUENTLY ASKED QUESTIONS
Q. Can QCM-Z500 measure dissipation or monitor dissipation changes?
A. YES ! The QCM-Z500 instrument can measure dissipation and also monitor dissipation changes.
The measurement principle of QCM-Z500 is based on impedance (Z) analysis of the quartz crystal
properties, which enables the determination of the Quality factor of resonance of the crystal, i.e. the
Q-factor. The Q-factor is a characteristic property of quartz crystals, and actually dissipation is
defined as D = 1/Q.
The Q-factor contains all the information about how well the quartz crystal is resonating in the
surrounding media. This means that the influence of all kind of adsorbed layers on the quartz crystal
or liquids in contact with the quartz crystal surface are reflected in the Q-factor, especially if the
surrounding media damps the oscillation of the quartz crystal i.e. energy is dissipated into the
surrounding media or adsorbed layer. An example of how the Q-factor of a quartz crystal is affected
by the surrounding media is shown in the figure below.
Admittance (A) spectra of a quartz crystal in contact with different surrounding media.
Admittance = 1/Impedance.
The sharper and higher the admittance peak the higher the Q-factor and less energy dissipates into
the surrounding media. Dissipation is reflected in the admittance peak as a broadening of the peak
and lowering of the peak height.

Q. What is the difference between KSV QCM-Z500 and other QCM instruments on the market?
A. The QCM-Z500 (Quartz Crystal Microbalance with Impedance (Z) Analysis) extracts the frequency
and Q-factor (dissipation) of a quartz crystal by making use of impedance analysis. To our knowledge
this is one of the few if not even the only commercial QCM instrument on the market making use of
impedance analysis. In a simplified description one could say that by using impedance analysis it is
possible to extract a series of electrical components of the quartz crystal that reflects the acoustic
properties of the quartz crystal and its surrounding media. These electrical components can then be
used for calculating the frequency and Q-factor (dissipation), even at several overtone frequencies.
Most of the other QCM instruments on the market are based on connecting the quartz crystal to a
simple electronic oscillator circuit to extract the frequency of the quartz crystal. However, the
disadvantages of using an electronic oscillator are a) you only measure one frequency and are not
capable of measuring overtone frequencies or Q-factors (dissipation) as can be done by the QCMZ500
instrument, b) the frequency shift of an oscillator circuit always contains some admixture from
the energy supplying elements which can interfere with the “true” frequency shift due to a mass
increase*, and c) the measured change in frequency depends on the phase shift introduced by the
electronic oscillator, which is in most cases unknown.*
The use of impedance analysis enables unique features of the QCM-Z500 instrument:
- Avoids the problems induced by using an electronic oscillator mentioned above as
impedance analysis enables the measurements of impedance magnitude and phase of the
QCM.*
- It enables the measurement of frequency and Q-factors not only for the fundamental
resonance frequency of the crystal but also for a series of overtone frequencies. For
example, for a 5 MHz crystal the QCM-Z500 can measure the frequencies and Q-factors up
to the 11th overtone frequency i.e. 15, 25, 35, 45, 55 MHz. By measuring overtones it is
possible to determine the validity of the Sauerbrey equation, as well as it gives an indication
of the softness of the adsorbed layer.
- It enables fast jumps between different overtones and therefore also quick measurements
i.e. 1 data point/second. The data collection rate can be increased up to 5 data
points/second if you allow for a lower signal/noise ratio. However, to our experience so far a
faster acquisition time is only needed in 1 case of 100, if even that often.
- The QCM-Z500 can be used as a conventional network impedance analyzer i.e. it is not
restricted to only Quartz Crystal Microbalance application. For example, it can be utilized for
impedance spectroscopy used a lot in corrosion science, and to determine the characteristic
impedance of other kind of solid substrates used in coating industries.
Furthermore, impedance analysis is a very well established technique and has been used for several
decades for characterizing fundamental quartz crystal properties. Hence, it is very well known and
the theories and treatment of the obtained data are well accepted.

Q. What exactly is Q-factor?
A. The Q-factor reflects how purely elastic the oscillation of the crystal is. If there is something that
resists this purely elastic oscillation for example a liquid in contact with the crystal it will damp the
crystal and the crystal oscillation will loose some energy i.e. dissipation occurs. Hence, damping is
then the sum of all energy losses in the system per oscillation cycle. A soft film adsorbed to the
quartz crystal is deformed during the oscillation, which gives a low Q-factor (high dissipation) while a
rigid film gives a high Q-factor (low dissipation).
Q. Why measure Q-factors (dissipation) and overtones?
A. There are several reasons for this, and they all contribute to the fact that by combining the
measurement of frequency and Q-factors obtained at different overtones one can obtain valuable
information about the properties of the adsorbed layer that cannot be extracted by only measuring
the frequency.
The measurement of the Q-factor (dissipation) is important as the frequency signal reflects the total
mass of the adsorbed layer on the quartz crystal, while the Q-factor reflects the softness of the film
formed on the surface. For example, the amount of the surrounding liquid in the film may vary
between 10-90% depending on the type of molecule and the way the molecules adsorbs on the
quartz crystal surface. In this kind of situations a soft film (liquid rich) and a rigid film (less liquid) may
give close to the same frequency change, while they induces completely differences changes in the
Q-factor. The measurement of Q-factor (dissipation) also can provide information about structural
differences between different adsorbed systems, or structural changes in the same film during the
actual adsorption process because it is reflects the shear viscous losses induced by the adsorbed
films.
The measurement at several overtones is very useful in such cases where the adsorbed film is so
soft that the upper region far away from the quartz crystal surface, do not couple to the oscillation of
the quartz crystal sensor. If one would try to use the normal Sauerbrey relation to calculate the mass
of the adsorbed film directly from the frequency change one would underestimate the mass.
However, by measuring both dissipation and frequency at several harmonics it becomes possible to
estimate visco-elastic properties and even film thickness and film density in the case of soft films.
Furthermore, the different overtones give information about the homogeneity of the adsorbed films,
because the detection range out from the quartz crystal surface decreases with increasing overtone
number. Hence, often an abnormal frequency behavior is the reason for variations in the film
properties in the thickness direction. The fact that the detection range decreases with increasing
overtone number can also be used to estimate the thickness of films that do not fully couple to the
oscillation of the crystal.
Another advantage of using higher overtones is the increased sensitivity and signal-to-noise ratio at
higher overtones, which is good when better sensitivity is required.
There is a vast amount of scientific publications available dealing with the modeling of data obtained
from impedance analysis of quartz crystals coated with soft films. These articles are readily available
for everybody that is interested in using the data from impedance analysis for modeling of the viscoelastic
properties of soft films adsorbed to quartz crystals.

Q. How can I make a stable and good QCM measurement in a liquid environment?
A. The most important things we have found out for making a stable measurement is the type of
crystal used and a stress-free mounting of the quartz crystal to the measuring chamber. If these are
not optimized there may be strange jumps in the frequency. In QCM-Z500 this is obtained by using
optically polished quartz crystals with a little bit thicker edges combined with a good design of gentle
mounting of the crystal into the measuring chamber.
Secondly, it is important to control the temperature of the measuring chamber in order to avoid
influences from changes in the bulk liquid viscosity and the quartz crystal frequency as the
temperature is fluctuating. The QCM-Z500 can be equipped with a temperature control unit for
controlling the temperature between 15 and 60 oC with a resolution of 0.1oC.
Furthermore, sophisticated electronics is needed to make a good impedance analysis of the quartz
crystal, and especially building an impedance analyzer for the QCM application. This has been
enabled by the well over 20-years of experience that KSV has as a company of designing electronics
for sophisticated measurement instruments, complete developments and manufacturing of laboratory
instruments, and of course a careful choice of the components for the impedance analyzer.
Q. How is the temperature of the measurement controlled?
A. The temperature of the bypass and the actual compartment holding the quartz crystal is controlled
by a temperature controller connected to a peltier element that on the other hand is attached to a
large aluminum block that holds both the bypass and the compartment with the quartz crystal. The
bypass is used for exchange and pre-temperaturize the sample liquid before it is flushed into the
compartment holding the quartz crystal. The temperature can be controlled between 15 and 60 oC
with a resolution of 0.1oC.
Q. What kind of crystals in terms of manufacturer, size and frequency can be used?
A. There are a range of manufacturers of quartz crystals out on the market and the standard
measuring chamber for the QCM-Z500 hold quartz crystals that are max 14 mm in diameter (min. 13
mm), has the connection electrodes on one side of the crystal, and the frequency is in the range of 3-
55 MHz. KSV of course provides standard 5 MHz crystals for the instrument, but if you find any other
supplier that can supply you similar crystals and you would like to try them out, then be free to do so!
Furthermore, we have a wide experience of customizing instruments, so if there is a need for using a
special size quartz crystal, then please contact us for more discussions.
Note also that the large frequency range of the QCM-Z500 instrument is an important feature, which
enables the determination of several overtones for crystals in the frequency range 3-10 MHz.

Q. What kind of coating or surfaces can be used on the quartz crystals?
A. A quartz crystal can be coated with almost any material as long as it can be deposited firmly as a
thin homogenous film to the quartz crystal surface. The layer thickness normally used is in the range
50-100 nm, but can vary depending on the properties of the applied material. KSV has a
subcontractor that can coat the quartz crystals with the following materials:
Metals: Ag, Al, Ca, Cr, Cu, Li, Mg, Ni, Sn, Pt
Inorganics: ITO, LiF, MgF2, SiO, SiO2, TiO2, ZnS, Ti3NO
Polymers: PANi, Teflon, PMMA, PS, PC, PE, PP, AKD
Q. How many times can the quartz crystal be re-used?
A. The number of times the quartz crystal can be re-used is totally dependent on the system you
study. We have experience of re-using the same quartz crystal up to 10 times in a vesicle adsorption
study, but in that case a very good and gentle cleaning procedure was available. For re-use purposes
careful handling and cleaning procedures that do not harm the crystal or its coating is required.
However, for other situations like covalently bound self-assembled monolayers or polyelectrolyte
adsorption studies it can be difficult to find proper cleaning procedures and the quartz crystals used
tend to be disposable.
Q. What amount of sample liquid volumes is needed for the measurements?
A. The standard flow through measuring chamber contains a bypass that takes 2.5 ml of liquid, while
the actual compartment holding the quartz crystal takes 1 ml of liquid measured from the 3-valve
point that separates the bypass and the inlet to the compartment. So, in principle if working very
carefully 2-2.5 ml is enough for each exchange, but 4-5 ml is recommended for optimal results.
Additionally, the QCM-Z500 instrument can be equipped with an open air/open beaker measurement
probe that can be immersed in any open beaker for measurements. This measurement probe might
require large amounts of sample liquid, but it has the advantage that it is not closed into any
compartment and the quartz crystal surface can easily be viewed or illuminated with light for example
through the bottom of a glass/quartz beaker.
Q. What kind of fluids can I use for my measurements ?
A. The tubes and O-rings used in the standard measuring chamber for the QCM-Z500 instrument is
made of Viton. Many different kind of fluids can be used with these tubes and O-rings ranging from
water, water based inorganic salt solutions and buffers, most alcohols and organic solvents.
For example, the manufacturer for Viton tubes and O-rings claims that at least the following different
fluids and organic solvents can be used with Viton; water, inorganic salt solutions, Butanol, Carbon

tetrachloride, Chloroform, Cyclohexane, Ethanol, Hydrochloric acid (dilute), Hydrogen peroxide
(dilute), Methyl chloride, Nitric acid (dilute and medium), Toluene, Trichloroethylene, Xylene, just to
mention a few of the most fluids used in the laboratory.
Q. How thick layers can I use with the QCM-Z500 instrument?
A. The maximum thickness of the layer that can be deposited on the quartz crystal depends on the
visco-elastic and density properties of the material deposited on the quartz surface. As a thumb of
rule one can say that the more rigid the layer that is deposited on the quartz is, the larger thickness is
possible. One can estimate the maximum thickness of the layer from the approximate penetration
length of the shear waves induced by the oscillatory movement of the quartz crystal i.e.
d = (h/prf)½ , where h = shear viscosity of the layer, r = density of the layer,
and f = resonance frequency
For example for water (h = 1 Pa s, and r = 1 g/ml) and a 5 MHz crystal one obtains as the
penetration depth 250 nm, and for a 10 MHz crystal the penetration depth reduces to about 178 nm.
However, by applying a very rigid film on the quartz surface such as a metal will still give the same
detection range in a liquid i.e. a pre-coated metal or other high density solid do not affect the
detection range as long as the rigid film have been coated on the quartz surface prior to the
measurements.
Q. What is the smallest mass change I can detect with the QCM-Z500?
A. First of all this depends on the frequency of the quartz crystal used. The higher the frequency the
smaller changes can be detected. The mass sensitivity of a standard 5 MHz (optional 10 MHz)
crystal used in the QCM-Z500 instrument is 17.5 ng/cm2 (4.24 ng/cm2) per 1 Hz change in the
frequency. This means that as the QCM-Z500 instrument can detect frequency changes down to
0.03 Hz in air the mass sensitivity become around 0.5 ng/cm2 (0.15 ng/cm2) for a 5 MHz (10 MHz)
crystal. In the case of liquid measurements the QCM-Z500 can detect changes down to 0.2 Hz
meaning that the mass sensitivity become around 4 ng/cm2 (1 ng/cm2). Furthermore, the sensitivity
increases with the overtone number, so if higher sensitivity is needed one can always use the
overtone measurements in the calculations.

Q. What is the noise level of the measurement data and how much can it drift on a long term
scale?
A. The noise level of the measured data is dependent on the mounting of the quartz crystal into the
measuring chamber, the electronics and the software algorithms used for running the instrument.
Due to KSV:s proprietary electronic design, innovative measuring chamber design and software
algorithms the noise level of the QCM-Z500 instrument is superior compared to other QCM
instruments on the market. This is illustrated by the measurement below. The frequency of the crystal
monitored in air is shown in figure A and the crystal monitored in a water solution is shown in figure
B. Note, the small scales in the images.
Figure A. Figure B.
The RMS values of the noise level for air and the water solution are 0.005 Hz and 0.08 Hz,
respectively.
The drift of the measurement data is largely dependent on if the measurement cell is temperature
controlled or not. The data in figures A and B above have been measured with the QCM-Z500 in air
and water, respectively, by using the temperature control unit controlling the temperature with a
resolution of 0.1 oC. The drift of the signal in air is less than 1 Hz/hour and hardly anything in liquid as
can be seen from the figures above. Generally the signal measured with the QCM-Z500 drifts less
than 1 Hz/hour in both air and liquid if the temperature control unit is used to control the temperature
of the measuring chamber.