3 Things to Consider when Purchasing a Quartz Crystal Microbalance

A quartz crystal microbalance or QCM measures a mass per unit area by measuring the change in frequency of a quartz crystal resonator. The sensor, which is the crystal, oscillates at a constant frequency and as the mass on the crystal changes, so does the resonance frequency. The addition or abstraction of the mass is due to oxide growth or film deposition at the surface of the acoustic resonator. The QCM works under vacuum, in gas and even in liquid environments. Under vacuum, it is useful for monitoring the rate of deposition in thin film deposition system and in liquid; it is effective at determining the affinity of molecules to surfaces functionalised with recognition sites. Simply put, QCM is the mass measurement standard, just as laser diffraction is essential for the measurement of particle size.

A basic QCM includes a source of alternating current — the oscillator, a quartz crystal, two metal electrodes on opposite sides of the thin crystal wafer and a frequency counter. According to most experts, choosing a QCM is a matter of finding the right match for the analytical objective and sample conditions. There are however, three important things that play critical roles in the equipment’s functionality that you should consider.

1. The Crystal

There are a few parameters that you have to determine when purchasing QCM crystals.

Frequency

Although higher frequencies will provide better resolution, these crystals will be more difficult to handle. A crystal’s frequency ranges from 1.00 to 30.000MHz.

Blank Diameter

The standard blank diameters are .538”, .340” and .318”.

Electrode Diameter

The electrode diameters available include aluminium, carbon, chromium, cobalt, copper, molybdenum, nickel, palladium, platinum, silicon, silver, tin oxide, titanium, tungsten, zinc.

Mounting and Bonding

While most crystals will be bonded to a base that provides a physical and electrical connection, you may request for the crystals to be un-bonded and coated with material from your facility.

2. Crystal Accessories

For a QCM crystal to work, you must have some type of oscillator circuit to enable a connection. In most cases, an enclosure or liquid/static cell for the crystal is necessary. There are two main types of high-quality oscillators specially designed for use with QCM crystals. They are standard (clock) oscillators used in gaseous applications and lever oscillators used in liquid applications.

3. QCM Components

In addition to the crystals, there are also a variety of components to complement the QCM. Some components are limited to manual control while others have different levels of electronic module. A QCM with the additional measurement of dissipation is called QCM-D. Dissipation provides information about the structure and viscoelasticity of the film. The measurement of particle size which can be done with a particle size analyzer and the study of surface properties are essential for a better understanding of the way in which materials interact, making the QCM-D very useful and effective as it is a real-time, label-free, surface-sensitive technique.

Microscopy

QCM-D can be combined with light microscopy using the window module. This visual entry allows correlation of real-time microscopy to changes in mass and viscoelastic properties. Studies of light-induced reactions and cell adhesion are also enabled.

Electrochemistry

As electrochemistry and QCM-D are surface techniques, they form an ideal pair. Electrochemistry can be the stimulus of an interaction or provide information about interfacial charge transfer while QCM-D can provide real-time information on mass and structure of these films. One such application is electrostatic interactions of biomolecules with surfaces.

Make an informed purchase

Do you need a Quartz Crystal Microbalance for your processes? ATA Scientific offers quality scientific instruments and can help you decide which instrument best fits your needs. Contact ATA Scientific today.