Electric field mapping

Tyner, K. M., Kopelman, R. and Philbert, M. A. (2007). Nanosized voltmeter enables cellular-wide electric field mapping. Biophys. J. 93, 1163-74. 

Yang, K. Katehi, L. P. B. Whitaker, J. F., Electric field mapping system using an optical fiber based electrooptic probe, IEEE Microw. Wireless Comp. Lett. 2001, 11, 164 166... 

Figure 2. The histogram is the distribution of OH stretch frequencies for the water clusters and surrounding point charges, and the solid line is the distribution of frequencies from the quadratic electric field map.

A number of researchers [15, 38 40, 43, 113, 124 126, 128, 146] have used mixed quantum/classical models, mostly as described in Section III.A, to calculate vibrational line shapes for this system, and several are in fair agreement with experiment. Here we describe our latest work involving approaches discussed in Section III.C. Our theoretical line shapes are calculated as briefly described in previous sections and in published work [98]. From an MD simulation of SPC/E heavy water, we determine the electric field on each putative H atom. We then use electric field maps to determine the transition frequency and dipole derivative. The orientational contribution to mp(t) we... 

IR and Raman line shapes have been measured for H0D/H20. They peak near 2500 cm 1 and have line widths in the 160 to 180 cm 1 range. Corcelli et al. [151] calculated these line shapes using the approaches described in Section III.C, for the SPC/FQ model, for temperatures of 10 90°C, finding quite good agreement with experiment. More recently, we have extended the method involving the quadratic electric field map for HOD/D20 [98] to HOD/H20 [52] and have calculated IR and unpolarized Raman line shapes. These line shapes, in comparison with experimental line shapes [12, 52], are shown in Fig. 7. Agreement between theory and experiment is excellent for both the IR and Raman. 

These authors also reported theoretical calculations of this frequency-dependent rotational relaxation. The theory of Auer et al. [98] using the quadratic electric field map, originally developed for HOD/D2O, was extended to the H0D/H20 system [52]. As before [38], the orientation TCF was calculated for those molecules within specified narrow-frequency windows (those selected in the experiment) at t = 0. TCFs for selected frequency windows, up to 500 fs, are shown in Fig. 8. One sees that in all cases there is a very rapid decay, in well under 50 fs, followed by a pronounced oscillation. The period of this oscillation appears to be between about 50 and 80 fs, which corresponds most likely to underdamped librational motion [154]. Indeed, the period is clearly longer on the blue side, consistent with the idea of a weaker H bond and hence weaker restraining potential. At 100 fs the values of the TCFs show the same trend as in experiment, although the theoretical TCF loses... 

Fig. la,b. Electric field map (Volt/nm) of a water, b formic acid... 

Fig. 2a-d. Electric field maps (Volt/nm) of hydrogen bond donating molecules a (CF3)2 CHOH b CHjCHjOH c CH3N02 d (CH3)2CH2CO... 

Fig. 6.17 At a planar interface and for s-polarization, the electric field is everywhere parallel to the surface plane (a). This does not hold any longer at a rough surface [here electric-field map at a sine wave profile, with n, = 3.5 ( =12) and n2 = i...

The electric field map shown in Fig. 5b indicates where the regions of high and low electric field occur and therefore where particles move under either positive or negative DEP, shown schematically in Fig. 5c. 

As the film has a domain structure, the intrinsic nature of electrical conduction in the film may not be observed by d.c. measurements. Indeed, the distribution of the resistance in the film was investigated by electric field mapping where the grain boundaries in the film were more resistive than the insides of the grains [45]. 

Figure 6.12. Electric field map for hemispherical electrodes separated by a dielectric insert.

Despite the limitations of the DDA method, it is best suited for applications where it is important to know the local electric field on the surface, or when the nanoparticle itself has a composite structure. For example, the second feature in the two-nanoparticle absorption spectrum shown in Fig. 2 can be explained by plotting the electric field map. The map reveals that the presence of a dielectric can mediate the overlap of evanescent fields, an effect that was hitherto unknown. " ... 

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