Amplitude sweep curves

The one exception in which phase contrast is not due to the dissipation arises when the tip jumps between attraction phases (>90°) and repulsion phases (<90°). Since sine is a symmetric function about 90°, the phase changes symmetric even if there are no losses in the tip-sample interaction. The relative contribution of the repulsive and attractive forces can be estimated experimentally from the frequency-sweep curves in Fig. lib by measuring the effective quality factor as Qe=co0/Ao)1/2, where Ago1/2 is the half-width of the amplitude curve. The relative contribution of the attractive forces was shown to increase with increasing the set-point ratio rsp=As/Af. Eventually, this may lead to the inversion of the phase contrast when the overall force becomes attractive [110,112]. The effect of the attractive forces becomes especially prominent for dull tips due to the larger contact area [147]. 

Fig. 3.41 Left Frequency sweep in water (silicon nitride lever) right amplitude distance curve recorded in water on a glass sample...

Interpretation of IC-AFM images is complicated by the fact that the tip-sample force is a nonlinear function of tip-sample separation. The tip-surface interactions in IC-AI have been modeled extensively and have been recently reviewed [109, 143]. Two important conclusions have come from the modeling. First, the nonlinear interaction of the dynamic tip with the surface can lead to two stable oscillation states one that follows a net attractive path and the other that follows a net repulsive path [147, 148]. A hint of this is seen in the phase versus frequency plot (see Fig. 3.32) where the cantilever initially oscillates along an adhesive path and then abruptly transitions to the repulsive path. Simulated amplitude and phase (z-sweep) curves can reproduce those determined experimentally. These have been interpreted in terms of force based interaction models that include the effect of capillary forces and adhesive forces when they are known or can be estimated. The transition between the bistable states depends on a number of factors including the cantilever Q, Ao, and r p, and the drive frequency as well as the surface properties [149]. In general high Q cantilevers or small Ao favor the net attractive path. 

Figure 14.7 (a) Amplitude sweeps and (b) flow curves of a suspoemulsion comprised of 23% sunflower oil, 23% Chlorothalonil, 4% lignosulfonate and biocide, wetting agent and xanthan gum for stablllzaton. The plateau value of the complex viscosity increases slightly with time, but the yield stress remains similar for the duration of the trial. From measurements of the shear viscosity, no changes are discerned in the flow curves (b). 

The diagrams in Fig. 1 lb can be obtained by the so-called frequency-sweep method, where the lateral position and the distance Zc are fixed, while the frequency is varied around (O0. The Zc value corresponds to a given set-point ratio of the amplitude in contact to the free amplitude, rsp=Asp/Af. Depending on the tip-sample interaction, both the amplitude and the phase curve shifts in a certain direction. When the overall force is repulsive, the resonance frequency moves to higher values and results in a positive phase shift A(p=90 °-(p>0, where the phase shift of 90 ° corresponds to the free cantilever oscillations at ks=0 in Eq. 12. When the force is attractive the resonance frequency decreases compared to the free cantilever and Acp becomes negative. The situation in Fig. lib corre-... 

FIG. 27 Reduction peak.s of the surface oxide species on CWN2—Ox (a), CWZ—Ox (b), and RKD3—Ox (c) recorded for different sweep amplitudes (anodic potential limits) in 0.05 M H1SO4. On the ordinate axis only 0 is marked, indicating vertical shift of the curves. (From Ref. 28.)... 

OLED was switched to a pulsed mode, and t (corresponding to the 21% O2 in air) was determined. In this pulsed mode, the pulse amplitude, width, and repetition rate were 20 V, 100 ps, and 50 Hz, respectively. The displayed value of T was determined by averaging the decay curves over 1,000 sweeps. 

Ionization efficiency curves can also be easily obtained in the ion cyclotron resonance spectrometer. As mentioned earlier, the most common modulation techniques now center around some form of electron energy or beam modulation. If the electron beam is amplitude-modulated (switched on and off), it is only necessary to sweep the electron energy to obtain such a curve. With the restriction that the ion residence times are much longer (so that some fragmentation patterns may be different from those obtained in more conventional instruments), the ionization efficiency curves thus obtained should be comparable to those obtained in other mass spectrometers. 

The characterizations which we shall present below are the plot of the polarization curve, impedance spectroscopy response to current value steps and responses to large amplitude current sweepings. These are all non-intrusive characterizations on the scale of the component (or of each cell), and are intended to characterize its electrical behavior in the static and dynamic states in real operating conditions. These characterizations will enable us, on the one hand, to appreciate the performances of the electrolyzer, and on the other, if we cross them, to parameterize the different models presented above. 

As Figure 2.33 illustrates, this technique involves subjecting the electrolyzer to a very-low-frequency sinusoidal current whose amplitude is equal to the range of current which we wish to characterize. Unlike the stairway plot, the plot for the current sweeping is a continuous curve. 

Figure 3.34. Amplitude and phase z-sweep data for the PMMA and crosslinked PBA domains imaged in Fig. 3.33. As before, the free amplitude, Ao = 38 nm. The imaging set point for Fig. 3.33, Asp = 30 nm, is marked on the curves.

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