Field-penetration depths

The tuneable nature of the evanescent field penetration depth is critical to the effective operation of this sensor as it facilitates surface-specific excitation of fluorescence. This means that only those fluorophores attached to the surface via the antibody-antigen-labelled antibody recognition event... 

While planar optical sensors exist in various forms, the focus of this chapter has been on planar waveguide-based platforms that employ evanescent wave effects as the basis for sensing. The advantages of evanescent wave interrogation of thin film optical sensors have been discussed for both optical absorption and fluorescence-based sensors. These include the ability to increase device sensitivity without adversely affecting response time in the case of absorption-based platforms and the surface-specific excitation of fluorescence for optical biosensors, the latter being made possible by the tuneable nature of the evanescent field penetration depth. 

The measured intensity modulation can then be used to recover the original optical phase change Aphase shift, shown in Fig. 9.14b, is directly proportional to the density of molecules on the surface, as long as the film thickness is much less than the evanescent field penetration depth of <5 162 nm. 

It is found that for metals, low temperature field evaporation almost always produces surfaces with the (1 x 1) structure, or the structure corresponding to the truncation of a solid. A few such surfaces have already been shown in Fig. 2.32. That this should be so can be easily understood. For metals, field penetration depth is usually less than 0.5 A,1 or much smaller than both the atomic size and the step height of the closely packed planes. Low temperature field evaporation proceeds from plane edges of these closely packed planes where the step height is largest and atoms are also much more exposed to the applied field. Atoms in the middle of the planes are well shielded from the applied field by the itinerant electronic charges which will form a smooth surface to lower the surface free energy, and these atoms will not be field evaporated. Therefore the surfaces produced by low temperature field evaporation should have the same structures as the bulk, or the (lxl) structures, and indeed with a few exceptions most of the surfaces produced by low temperature field evaporation exhibit the (1 x 1) structures. 

A. Evanescent Field, Penetration Depth, and Effective Thickness... 

From the value of the resonant frequency and its change with temperature or other external parameters the permittivity of a dielectric sample and its temperature or field dependence can be determined. In case of superconductors, the temperature dependence of the magnetic field penetration depth can be determined [8], Since the mode spectrum of a resonator is controlled both its physical dimensions and by the material properties, the physical dimensions of all resonator components have to be known with tight tolerances. Relative changes of permittivity or penetration depth can be determine with much higher accuracy than absolute values. 

Figure 1. The temperature dependence of the zero-field penetration depth, Aa6(T,H=0), with...

Fig. 1 (a) Planar waveguide with refractive index on top of a substrate (refractive index n ). The evanescent field (penetration depth Az) of a guided light mode extends into the cover with refractive index c- (b) Optical fiber waveguide. The same conditions apply as to the planar waveguide... 

Gas transport in nano-confinements can significantly deviate from the kinetic theory predictions due to surface force effects. Kinetic theory-based approaches based on the assumption of dynamic similarity between nanoscale confined and rarefied flows in low-pressure environments by simply matching the Knudsen and Mach numbers are incomplete. Molecular dynamics simulations of nanoscale gas flows in the early transition and free-molecular flow regimes reveal that the wall force field penetration depth should be considered as an important length scale in nano-confined gas flows, in addition to the channel dimensions and gas mean free path. 

This entry presents the deviations of nanoscale confined shear-driven gas flows from kinetic theory predictions. Subsequently, results proved that the dynamic similarity between the rarefied and nanoscale confined gas flows is incomplete. Importance of wall force field effects is clearly indicated, and the wall force field penetration depth is introduced as an important length scale in addition to the channel dimension and gas mean free path in nano-confined gas flows. 

Overall the results show that the wall force field penetration depth is an additional length scale for gas flows in nano-channels, breaking dynamic similarity between rarefied and nanoscale gas flows solely based on the Knudsen and Mach numbers. Hence, one should define a new dimensionless parameter as the ratio of the force field penetration depth to the characteristic channel dimension, where wall effects cannot be neglected for large values of this dimensionless parameter. Additionally, the calculated tangential momentum accommodation coefficients for a specific gas-surface couple were found to be constant regardless of different base pressure, channel height, wall velocity, and Knudsen number. Results of different gas-surface couples reveal that TMAC is only dependent on the gas-surface couple properties and independent of the Knudsen number. 

Based on the discussion above, we can enhance the transmittance by increasing the Uw ratio of an ff S structure. This is because a larger Uw ratio leads to a smaller dead zone area, and meanwhile it increases the electric field penetration depth. However, the major trade-off is increased voltage because of the wider electrode gap. An effective way to overcome this problem is to employ protrusion electrodes, which enable the horizontal electric fields to penetrate more deeply into the bulk LC layer. The detailed performance depends on the protrusion height and the Uw ratio. 

A. Maeda, T. Shibauchi, N. Kondo, K. Uchinokura, M. Kobayashi Magnetic-field penetration depth... 

The magnetic field penetration depth A- in the same approximation at which equation (2) and (3) apply can be represented in the form... 

Figure 4. Calculated dependences of the magnetic field penetration depth X and critical field Hmb of niobium stannide electrolytical coatings on composition.

The specific heat measurements (Table 10.2) indicate AC/yT). is 1.50 0.15 or >2 (-2.8) for the Cu(NCS)2 salt and 2 0.5 for the Cu[N(CN)2]Br salt. These values are close to or a little higher than the BCS value. The values (215 10 K, 210 15 K) are similar to those for (TMTSF)2C104. The superconducting gaps of the CufNCSlj and Cu[N(CN)2]Br were examined by a tuimeling spectroscopic method, magnetic field penetration depth measurements by AC susceptibility, pSR, microwave in5)ed-ance, etc. The results, however, are inconsistent and controvCTsial (some claim an anisotropic gap or zero gap non-BCS type, another claims normal BCS type). 

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