thickness of the film, surface tension cannot be used to give the absolute
film thickness or the absolute mass of the monolayer. Fortunately, film
thicknesses as low as a fraction of a nanometer can be measured using
optical methods such as ellipsometry (Section 8.3) or dual-beam polarization interferometry (Section 8.5). Gravimetric techniques also exist that
can measure the mass of a monolayer on solid surfaces. The quartz
crystal microbalance is a popular method used to determine the mass of a
monolayer.
8.2 QUARTZ CRYSTAL MICROBALANCE
All gravimetric analyses rely on the determination of the mass of a material, or in our context, the mass of a nanofilm that has been deposited
on a solid support. Gravimetric analysis is generally a precise analytical
method when performed with well-calibrated balances. However, when
working with nanofilms, the mass in question may well be as low as a few
nanograms per square centimeter, and traditional methods for weighing
such samples are not possible. The next few sections discuss methods that
allow the direct measurement of the mass and the thickness of a nanofilm
(or, more often, the measurement of mass-related and thickness-related
parameters). These methods are the quartz crystal microbalance with
dissipation monitoring (QCM-D), ellipsometry, dual beam polarization
interferometry (DPI), and surface plasmon resonance (SPR). These techniques are routinely used in many research laboratories and can measure
the changes in mass and thickness during nanofilm growth.
First, let’s focus on the quartz crystal microbalance (QCM). QCM is a
powerful technique that can measure the mass of material as small as a
few nanograms adsorbed to a surface. What makes this technique particularly appealing is that modern QCM instruments allow one to follow the mass deposition process as a function of time. In other words,
the formation of a thin nanofilm, such as a model membrane, can be
observed in real time. The quartz crystal microbalance is based on the
piezoelectric characteristics of quartz, so in order to properly understand
how QCM operates, let us first discuss the piezoelectric effect.
8.2.1 The piezoelectric effect
Since early times it has been known that an electric field could be induced
in certain types of crystals if they underwent a change in temperature (i.e.,
were heated or cooled). This phenomenon was named pyroelectricity.
QUARTZ CRYSTAL MICROBALANCE 259
film thickness or the absolute mass of the monolayer. Fortunately, film
thicknesses as low as a fraction of a nanometer can be measured using
optical methods such as ellipsometry (Section 8.3) or dual-beam polarization interferometry (Section 8.5). Gravimetric techniques also exist that
can measure the mass of a monolayer on solid surfaces. The quartz
crystal microbalance is a popular method used to determine the mass of a
monolayer.
8.2 QUARTZ CRYSTAL MICROBALANCE
All gravimetric analyses rely on the determination of the mass of a material, or in our context, the mass of a nanofilm that has been deposited
on a solid support. Gravimetric analysis is generally a precise analytical
method when performed with well-calibrated balances. However, when
working with nanofilms, the mass in question may well be as low as a few
nanograms per square centimeter, and traditional methods for weighing
such samples are not possible. The next few sections discuss methods that
allow the direct measurement of the mass and the thickness of a nanofilm
(or, more often, the measurement of mass-related and thickness-related
parameters). These methods are the quartz crystal microbalance with
dissipation monitoring (QCM-D), ellipsometry, dual beam polarization
interferometry (DPI), and surface plasmon resonance (SPR). These techniques are routinely used in many research laboratories and can measure
the changes in mass and thickness during nanofilm growth.
First, let’s focus on the quartz crystal microbalance (QCM). QCM is a
powerful technique that can measure the mass of material as small as a
few nanograms adsorbed to a surface. What makes this technique particularly appealing is that modern QCM instruments allow one to follow the mass deposition process as a function of time. In other words,
the formation of a thin nanofilm, such as a model membrane, can be
observed in real time. The quartz crystal microbalance is based on the
piezoelectric characteristics of quartz, so in order to properly understand
how QCM operates, let us first discuss the piezoelectric effect.
8.2.1 The piezoelectric effect
Since early times it has been known that an electric field could be induced
in certain types of crystals if they underwent a change in temperature (i.e.,
were heated or cooled). This phenomenon was named pyroelectricity.
QUARTZ CRYSTAL MICROBALANCE 259