I know that a thin film deposition is required on the quartz crystal to measure the in situ etch rates by QCM. I would like to know how this film effect the accuracy of etch rates measurement? Are there any other factors? Thanks.
Hallo, the accuracy of the QCM will depend on the film's viscoelastic properties as well as its thickness. If the coating is rigid i.e. purely elastic and its mass (thickness) is less than 0.02% of the QCM's mass (thickness), then you should be able to measure the rates with an accuracy of ng/cm^2. However, if the film is viscoelastic and thick, then your accuracy will depend on the overall mass loading and insertion loss increase that the film will induce. Hope this helps.
Dear Mr. Galib,
Colleague Esmeryan is correct.
One correction though; to calculate the film mass from the difference in resonant frequency via the Sauerbrey relation, the mass of the film coating should not exceed 2% of the crystal's mass [1].
Furthermore, the Sauerbrey equation or related formulations [2], are accurate for coating thicknesses up to 1μm. Beyond that thickness, the error in thickness determination becomes substantial (even for glassy coatings), and independent film thickness measuring techniques, should be implemented [3]. Through numerical simulations with the transmission line model [2], I verified the previously mentioned errors in (polymer) film thickness, by comparing the frequency and electrical response of glassy polymer coatings of varying thickness (0-6μm), to that of a uncoated QCM substrate, and using the formulations mentioned in [2].
In conclusion, be sure that in view of the conditions of your experiment, the viscoelastic nature (if any) of your material, is toned down as much as possible. If that's not the case, tune your film thickness well below 1μm, so as to dampen the effect of viscoelasticity on the frequency and electrical response.
Good luck.
[1] Buttry, D.A., Ward, M.D., "Measurement of Interfacial Processes at Electrode Surfaces with the Electrochemical Quartz Crystal Microbalance", Chem. Rev. 92 (1992) 1355-1379 (page 1365).
[2] Lucklum, R., Behling, C., Hauptmann, P., "Error Analysis of Material Parameter Determination with Quartz-Crystal Resonators", Sens. Actuators A 66 (1998) 184-192.
[3] Hossenlopp, J., Jiang, L., Cernosek, R., Josse, F., "Characterization of Epoxy Resin (SU-8) Film Using Thickness-Shear Mode (TSM) Resonator under Various Conditions", J. Polym. Sci. B: Polym. Phys. 42 (2004) 2373-2384.
Yes, i agree with colleague Kakalis, my mistake. Indeed the mass of the film should not exceed 2% of the crystal's mass. What i was trying to say is that the ratio of the frequency deviation towards the resonance frequency should not exceed 0.02 (deltaF/F - 0.02), otherwise the Z-match method must be applied [1-3].
[1] O. Lewis C. Lu. Investigation of film thickness determination by oscillating
quartz resonators with large mass load. J. Appl. Phys., 43(11):4385–4390, 1972.
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[2] D. Johannsmann. Viscoelastic analysis of organic thin films on quartz resonators.
Macromolecular Chemistry and Physics, 200(3):501–516, 1999. 10
[3] D. Johannsmann. Viscoelastic, mechanical, and dielectric measurements on complex samples with the quartz crystal microbalance. Physical Chemistry Chemical
Physics, 10:4516–4534, 2008. 8, 10
Dear Karekin and Athanasios, thank you for your replies. I got the answer I needed.
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