Acoustically thin film

Table 3.3 Moduli Associated with the Strain Modes (Figure 3.29) Generated by a SAW in an Acoustically Thin Film (/ < 1) [SO].

Thus, from a perturbation analysis, the change in SAW propagation arising from acoustically thin films is [50] ... 

In the somewhat rare instance that the coating (even when loaded with analyte), remains highly elastic, mass loading may be the only operative interaction mechanism. In this case, as the total coating-plus-anaiyte thickness reaches and exceeds several percent of one acoustic wavelength, the mass sensitivity deviates significantly from that derived from perturbation analyses for acoustically thin films, and is difficult to predict. 

In the case of a rigid (acoustically thin) film, the frequency shift provides film mass (Eq. 1) this will be the sum of the masses of the electroactive material (e.g. metal, polymer, or metal oxide) and the liquid that permeates it. Coulomet-ric assay-which may be based on film deposition or subsequent redox chemistry - provides the amount of electroactive... 

A flow chart demonstrating the protocol is shown in Fig. 6. The procedure has been demonstrated for poly(3-methylthiophene) films, by analysis of frequency response as a function of time during film electropolymerization short (long) time responses represent the acoustically thin (thick) film scenario [24]. Film mass (whether or not directly accessible from A/ data) defines the product hypy, so (as shown in Fig. 6 [24]) a plot of hy versus py is a hyperbola. As film mass (polymer coverage) increases, a series of hyperbolae are generated. The acoustically thin film data (A/ and Q) define the unique solution (of the infinity of solutions on the hyperbola) for p as indicated in Fig. 6 [24] this value is projected across all the hyperbolae. 

Fig. 6 Summary of data interpretation strategy (described in main text) for extracting viscoelastic parameters from film-loaded TSM resonator frequency response. Input parameters (at left of diagram) are resonator impedance and any selected parameter representative of film thickness (here, charge, interpreted using Faraday s law). Upper part of the scheme relates to acoustically thin films (yielding hf and pf). Lower part of diagram relates to acoustically thick films (yielding, with the help of hf and pf, G and C"). (Reproduced from Ref. [24] with permission from the American Chemical Society.)...

As described in Sect. 2.7.2.1, there is no sharp distinction between rigid and nonrigid behavior, but rather a continuous variation between films that are acoustically thin h < S) and acoustically thick h > S). Since the decay length, S, is a function of shear modulus and thereby of film solvent content, medium effects are critical. The discussion of poly thiophene systems above was deliberately restricted to examples of acoustically thin films, but we now move to a consideration of acoustically thick polythiophene-based films. 

This relation is only valid for acoustically thin films. Concretely, it means that the relation is not respected when thick layers are used because the influence of the viscoelastic properties of the layer may appear in the frequency change. This effect is, in general, amplified when polymer Aims are used. To determine the maximum useful thickness, electroacoustic measurements allowed a pertinent value to be evaluated. In a first step, a classical Butterworth-Van Dyke equivalent circuit of the loaded quartz (Fig. 13a) is extracted... 

Acoustic Measurements. Measurement of the propagation of ultrasonic acoustic waves has been found useful for determining the viscoelastic properties of thin films of adhesives. In this method, the specimen is clamped between transmitting and receiving transducers. The change in pulse shape between successive reverberation of the pulse is dependent on the viscoelastic properties of the transmitting material. Modulus values can be calculated (267,268). 

Vol. 144. Surface-Launched Acoustic Wave Sensors Chemical Sensing and Thin-Film Characterization. By Michael Thompson and David Stone... 

Macrocyclic Compounds in Analytical Chemistry. Edited by Yury A. Zolotov Surface-Launched Acoustic Wave Sensors Chemical Sensing and Thin-Film Characterization. By Michael Thompson and David Stone Modern Isotope Ratio Mass Spectrometry. Edited by T. J. Platzner High Performance Capillary Electrophoresis Theory, Techniques, and Applications. Edited by Morteza G. Khaledi... 

Fig. 3.4. The highest resolution ever achieved by acoustic microscopy, using pressurized superfluid helium (at 0.4 K and 2.14 MPa, at 15.4 GHz) compared with scanning electron microscopy of the same specimens coated with 10 nm carbon, at 5 keV. (a) Acoustic and (b) s.e.m. pictures of a 200 nm period titanium grating on a silicon substrate (c) acoustic and (d) s.e.m. pictures of an array of 1 [im diameter holes with 2 pm spacing in a thin film of chromium on glass (Muha et al. 1990).

Crean, G. M., Somekh, M. G., Golanski, A., and Oberlin, J. C. (1987). The influence of thin film microstructure on surface acoustic wave velocity. IEEE 1987 Ultrasonics Symposium, pp. 843-7. IEEE, New York. [220]... 

Kushibiki, J., Chubachi, N., and Tejima, E. (1989). Quantitative evaluation of materials by directional acoustic microscope. Ultrasonics Int. 89, 736-43. [56, 149, 250] Kushibiki, J., Ishikawa, T., and Chubachi, N. (1990). Cut-off characteristics of leaky Sezawa and pseudo-Sezawa wave modes for thin-film characterization. Appl. Phys. Lett. 57,1967-9. [216]... 

Thompson M, Stone DC (1997) Surface-launched acoustic wave sensors chemical sensing and thin-film characterization. Wiley, New York... 

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