Professor Maria Hepel

Electrochemical Quartz Crystal Nanobalance (EQCN) technique utilizes quartz vibrations and piezoelectric effect to measure mass changes as small as a fraction of a monolayer of atoms

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CHEMISTRY Dept.

The Electrochemical Quartz Crystal Nanobalance (EQCN) technique uses quartz crystal vibrations to detect minute changes in the mass attached to the crystal.

The frequency of vibrations is characteristic to the piezoelectric material (quartz), cut direction of the crystal, and physical dimensions. For instance, the AT-cut quartz crystal wafers (35⁰15' angle from c-axis) with thickness of 0.166 mm have the fundamental frequency: 10 MHz.

The AT-cut quartz crystals oscillate in the thickness shear mode.

The AT-cut quartz crystal wafers show a negligible temperature coefficient at room temperature, which makes it a convenient choice for routine measurements.

	The oscillations of a quartz crystal wafer are maintained by an electrical oscillation circuit tuned broadly to the band of the fundamental frequency of the crystal.
	Any mass attached to the faces of a quartz crystal wafer influences the oscillation frequency, which can be measured. The frequency shift is proportional to the mass rigidly attached to the crystal according the Sauerbrey equation:

where

Δf - change in the resonant frequency

Δm - interfacial mass

n - overtone number

f_o - oscillation frequency at the fundamental mode

A - surface area

μ_q = 2.947 x 10¹¹ g cm^-1 s^-2 is the shear modulus

r_q = 2.648 g/cm³ is the density of quartz

	For f₀ = 10 MHz:
		k = 0.8673 ng/Hz

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