Local Electric Field Intensity Research Articles

Localized surface plasmon nanolithography with ultrahigh resolution

A localized surface plasmon nanolithography (LSPN) technique is proposed and demonstrated to produce patterns with a sub-20nm line width. High transmission efficiency is realized by adjusting the period of grating. The well-regulated grating structures in metallic mask are employed to excite surface plasmon polaritons (SPPs) on the illuminated side. The SPP waves propagate toward the tip along the taper surfaces which cause most of energy accumulation at the tip and give rise to high local field enhancements in a near-field region around the tip. The amplitude of local electric field intensity is quite large and the line width can be confined within sub-20nm, at the same time, the contrast and spatial resolution are greatly enhanced, which can facilitate nanolithography efficiently with simple ultraviolet light sources.

Local structure of Ag nano-clusters deposited on silicon wafer by total conversion electron yield XAFS

We have investigated the local structure of Ag nano-clusters deposited as thin films on silicon substrate by using a total conversion electron yield XAFS (x-ray absorption fine structure) method at Ag K-edge. High quality spectra were obtained from samples with thicknesses of 1–10 nm. We have found that these clusters have an fcc structure and that the interatomic distance does not depend on the thickness. The coordination number, N, however, changes with the thickness of the film. The N value for the first nearest shell as a function of the film thickness is compared with the theoretically expected value by taking account of the surface effect. For thinner films, the observed N values are smaller than the expected values. We have observed a correlation between the N value and the electromagnetic field intensity at the surface evaluated from IR measurement. The morphology of Ag nano-cluster particles must affect the local electric field intensity at the surface.

Mobility-based selective on-line preconcentration of proteins in capillary electrophoresis by controlling electroosmotic flow

A simple method to perform selective on-line preconcentration of protein samples in capillary electrophoresis (CE) is described. The selectivity, based on protein electrophoretic mobility, was achieved by controlling electroosmotic flow (EOF). A short section of dialysis hollow fiber, serving as a porous joint, was connected between two lengths of fused silica capillary. High voltage was applied separately to each capillary, and the EOF in the system was controlled independently of the local electric field intensity by controlling the total voltage drop. An equation relating the EOF with the total voltage drop was derived and evaluated experimentally. On-line preconcentration of both positively charged and negatively charged model proteins was demonstrated without using discontinuous background electrolytes, and protein analytes were concentrated by approximately 60–200-fold under various conditions. For positively charged proteins, positive voltages of the same magnitude were applied at the free ends of the connected capillaries while the porous joint was grounded. This provided a zero EOF in the system and a non-zero local electric field in each capillary to drive the positively charged analytes to the porous joint. CE separation was then initiated by switching the polarity of the high voltage over the second capillary. For negatively charged proteins, the procedure was the same except negative voltages were applied at the free ends of the capillaries. Mobility-based selective on-line preconcentration was also demonstrated with two negatively charged proteins, i.e. β-lactoglobulin B and myoglobin. In this case, negative voltages of different values were applied at the free ends of the capillaries with different values, which provided a non-zero EOF in the system. The direction of EOF was the same as that of the electrophoretic migration velocities of the protein analytes in the first capillary and opposite in the second capillary. By controlling the EOF, β-lactoglobulin B, which has a higher mobility, could be concentrated over 150-fold with a 15 min injection while myoglobin, which has a lower mobility, was eliminated from the system.

Examination of the core field uniformity for 3-layer power-law nonlinear slab waveguides

Uniform electric field in waveguide core may have some importance in application for various waveguide devices. It has been shown that uniform electric field can occur in and only in nonlinear waveguide structures with Kerr-like or saturable media. In this paper, three-layer slab optical waveguide for which the nonlinear permittivity of film and claddings take the same power-law form ε∼| E| δ , where E is the local electric field intensity and δ can be an arbitrary positive number ( δ=2 for Kerr-like media), has been analyzed to find out the structures in which the core electric field profile can become uniform at appropriate optical power. It is shown that there are five kinds of such structures. Numerical calculations for electric field profiles at different optical powers for various δ are made and the results are plotted for several realistic waveguide models. The results show that stronger nonlinearity is beneficial for occurrence of uniform core field at a lower optical power.

Levy's distributions of local fields intensities in metal-dielectric systems

Levy's distributions are involved in many physical phenomena. Their main characteristics are a very wide spreading and a long tail. The aim of our study is to use these Levy's distributions to understand optical measurements on metal-dielectric systems. Giant fluctuations of the local electric field intensity in metal-dielectric granular films in visible and infrared range have been recently studied. By using previously developed methods, we calculate the intensities of the local fields at each point of the sample surface for Au/TiO 2 cermets. We study the field intensities distributions, which show up non-negligible height in giant field values. We interpret these distributions in terms of Levy's law. In such cases, because of the long tail decay, the most important characteristic is the decisive participation of rare events. We then conclude that high-intensities values are high enough to govern the statistical properties when the metal concentration is around 10%.

Ionisation probabilities in gas field ion sources

Ionisation probabilities per unit of time, for a gas atom in the close vicinity of a supertip-gas field ion source, are analytically calculated and interpreted accordingly with the operational conditions of these devices. The results obtained for realistic values of the local electric field intensities are significantly smaller than the ones said to be expected and necessary for an “instantaneous” ionisation of a gas atom. Considerations about the effect of the local electric field and ionisation probabilities on the beam narrowness and intensity are also done when discussing their dependence on position and direction at the vicinity of the emitter.

Infrared external reflection spectroscopy of self-assembled monolayer films on Si substrate with a buried metal layer (BML) structure

This paper reports a study of the signal behavior of IR reflection spectra on the flat Si substrate with a buried metal layer (BML) and MBE-grown Si overlayer. A self-assembled monolayer of octadecyltrichlorosilane on the surface was used as a typical sample of a well-oriented layer. The signal intensities strongly depend on the orientation of surface vibration, the polarization of IR radiation and the angle of incidence. The dependence is quite different from that seen on metal and normal (without BML) semiconductor surfaces and can be explained by local electric field intensity based on classical electromagnetic treatment. On a relatively thin Si overlayer (typically 700–1200Å), vibration modes only with the transition moment in the vertical direction were observed for p-polarization and modes only in the lateral direction were observed for s-polarization. On a relatively thick Si overlayer (typically 2000A˚), modes with lateral as well as vertical components show significant signals for p-polarization, and only lateral modes could be detected at significant intensity for s-polarization. These results show that the orientation of surface species can be determined by analyzing the spectral dependence on polarization, angle of incidence and the thickness of the Si overlayer.

Composite papers with enhanced electrical strength

A theoretical analysis of the possibility of increasing the electrical strength, E s, of solid dielectrics has been carried out. It is shown that the local electric field intensity in regions of defect (pores) aggregation can be about 5 times larger than the average field applied to the paper dielectric. This is one reason for the fact that the electrical strength of ‘large-porous’ electrical capacitor papers (CPs) are only a fifth to a third of those of ‘fine-porous’ dielectrics such as hydrated cellulose films. To enhance the value of E s of CPs noticeably it is necessary either to prevent the pores exceeding some critical size or to provide a sufficiently small dispersion of the pore sizes. Simple fabrication methods of dielectric composite papers with CPs as a main component—referred to as composite papers—give materials with values of E s exceeding 110 kV/mm, which is higher than the values reached previously.

Spin-Lattice Relaxation Time of Co2+Ion in Yttrium Aluminum Garnet

Spin-lattice relaxation times of Co 2+ spins in yttrium aluminum garnet (YAG) are investigated below 100 K. Co 2+ impurities in YAG have the octahedral, tetrahedral and interstitial sites and these spins have considerably different local crystalline electric field symmetries and intensities. The observed relaxation times well reflect the local fields and it is found that the octahedral and interstitial spins show the Orbach relaxation process with the energy gap Δ / k of 280 K and 95 K, respectively, while the tetrahedral spin shows simple direct- and Raman-processes.

Bubble dielectrophoresis

The force due to polarization exerted on dielectric particles, vapor or gas bubbles, and voids in insulating dielectric liquids is an example of dielectrophoresis. This force is directly proportional to the gradient of the electric field intensity. Bubbles and voids are attracted into regions of lower electric field intensity, while dielectric particles (with higher relative polarizability) are attracted into regions of higher electric field intensity. It is shown that local electric field intensity maxima cannot exist in space-charge-free electrostatic fields, while examples such as the three-dimensional quadrupole demonstrate the existence of local electric field intensity minima. Experimental investigation of the dielectrophoretic force on small gas bubbles (up to ∼1.0 mm in diameter) in insulating dielectric liquids shows that a simple model, which neglects bubble elongation effects, adequately describes the static and dynamic behavior. Experimental demonstration of a simple bubble trap which levitates and positions bubbles using dielectrophoresis is also provided. Applications of these bubble traps in laser target fabrication and zero-gravity space processing are envisioned.