Electrostatic trapping

Particle Contamination. In assembling large, high voltage equipment such as coaxial lines, contamination by metal particles may occur which may decrease the dielectric strength under various conditions by 5 to 10-fold (44—45). Metal needles are the worst contaminants and electrostatic traps or adhesive areas have been designed to cope with them (46). 

Figure 21. Cyclic voltammograms (at 20to lOOmVs-1)of [FefCNJd3"74-electrostatically trapped in polypyrrole films with an alkyl pyridinium substituent at the (A) 1 - or (B) 3-position.243 (Reprinted with permission from J. Phys. Chem. 96, 5604-5610, 1992 Copyright 1992, American Chemical Society.)...

Another technique, which allows the controlled deposition of a single nanoparticle between two metal nanoelect-odes, i.e. the technique of electrostatic trapping (ET) was reported by Schmid and Dekker [29]. A polarized metal nanoparticle is attracted to the strongest point of an electric field, which was applied to two Pt electrodes (Figure 12). 

Figure 12. Schematic representation of the setup for single particle measurements by electrostatic trapping (ET). Pt denotes two freestanding Pt electrodes (dashed region). A ligand-stabilized Pd cluster is polarized by the applied voltage and attracted to the gap between the Pt electrodes. (Reprinted with permission from Ref. [29], 1997, American Institute of Physics.)...

Fig. 16 (a) Scheme of the interface of a two Hg-drops electrochemical junction where Ru(NH3)63+ complexes red circles) are electrostatically trapped in between the electrodes, (b) I—V curves obtained by keeping constant the potential of the collector and sweeping the potential of the generator (potentials are measured against an Ag/AgCl). (c) Scheme of the operating redox cycling mechanism... 

Another measurement that follows the line of the Porath et al. [14] experiment was performed by Yoo et al. [75]. In this experiment, long poly(dG)-poly(dC) and poly(dA)-poly(dT) molecules were electrostatically trapped between two planar metal electrodes that were 20 nm apart (see Fig. 11) on a Si02 surface, such that they formed a bundle that was -10 nm wide. A planar gate electrode added another dimension to this measurement. The current-voltage curves showed a clear current flow through the bundle and both temperature and gate dependencies. The resistivity for the poly(dG)-poly(dC) was calculated to be 0.025 flcm. 

Storage has mainly been achieved in four types of traps (11 the radio frequency or Paul trap (2) the Penning trap (3) the Kingdon electrostatic trap and (4) the magnetostatic (magnetic bottle) trap. The principles, advanlages, and disadvantages of these traps are detailed by DJ. Wineland (Science, 226, 395-400, Oct. 26, 1984). 

Up to now the origin of hydration forces is not clear and several effects are discussed. Certainly the fact that one layer of water molecules is bound to the solid surfaces is important. The hydration force, however, extends over more than only two water layers. Israelachvili and Wennerstom point out that the effect of the first water layer should not even be called a hydration force because it is caused by the interaction between water molecules and the solid surface and not by water-water interactions [175], In a classical paper Marcelja and Radic proposed an elegant theory to explain the short-range repulsion by a modification of water structure near hydrophilic surfaces [178], Modern theories take additional effects into account. In fact, short-range monotonically repulsive forces observed between inorganic surfaces are probably not only due to structured water layers propagated away from the surfaces, but to the osmotic effect of hydrated ions which are electrostatically trapped between two approaching surfaces [179], This is supported by the observation that the hydration force is... 

Due to its radically different design, the latest hybrid linear ion trap FTMS instrument, the LTQ-Orbitrap (Fig. 5.6), does not suffer from the time-of-flight effect. In this instrument, the superconducting magnet and the ICR cell are replaced by an electrostatic trap (C-trap) and so distances traveled by the ions from one MS device to the other are much smaller in addition a radically different ion transfer mechanism virtually eliminates any possibility for a time-of-flight effect (Makarov,... 

The electrostatic trap or orbitrap according to the description of Makarov in [27]. An outer electrode has the shape of a barrel cut into two parts separated by a small gap. Inside is a second spindle-shaped electrode. Only DC voltages (some kilovolts) are applied. The ions turn around the central electrode while oscillating back and forth along the z axis. The resulting movement is made of intricate spirals. 

Figure 14 Effect of RH on the uptake of water by an ammonium sulfate particle. The measurements were made for a single particle suspended in an electrostatic trap. Arrows denote particle response to change in RH in the indicated direction. Temperature, 25 °C (courtesy of T. Onasch, Brookhaven National Laboratory cf. Tang (1996) and...

The recently introduced LTQ-Orbitrap is another hybrid detection instrument, where the superconducting magnet and the ICR cell in an FTICR instrument are replaced by an electrostatic trap providing performance close to that of an FTICR instrument [25,28], The LTQ-Orbitrap shows excellent performance for small molecule MS/MS. It can achieve high mass resolution up to 150,000 and mass accuracy (1 ppm) [19,29], In most cases, the sensitivity of Orbitrap detection is superior to the FTICR detection of small molecules. Low mass transmission does not appear to be an issue, as spectra are very similar to those from the LTQ. Mass accuracies did not appear to be as precise as those for the LTQ-FTMS however, with the vast majority of mass measurements falling within 3 ppm, its performance is well suited for structure elucidation. 

Figure 4-28. Classical Penning discharge with uniform magnetic induction and electrostatic trapping of electrons general schematic, distribution of electrostatic potential, and magnetie field along the diseharge axis.

The structures mentioned up to this point have represented examples of quasizero-dimensional (0-D) systems, in which self-assembly or electrostatic trapping are used to place the individual (or at least a few) partides into a nanogap for electrical transport measurements. However, the processes are not necessarily suited to electrically address a well-defined number in a desired arrangement in a reliable maimer, which in turn means that neither method can lead to strict and defect-free 1-D arrangements. In addition, inherent disorder cannot be avoided. Thus, until now, the electrical transport properties through a perfect 1-D array have been studied on a theoretical basis. 

Haimberger, C., Kleinert, J., Bhattacharya, M., and Bigelow, N.P., Formation and detection of ultracold ground-state polar molecules, Phys. Rev. A, 70, 021402, 2004. Kleinert, J., Haimberger, C., Zabawa, P.J., and Bigelow, N.P., Trapping of ultracold polar molecules with a thin-wire electrostatic trap, Phys. Rev. Lett., 99, 143002, 2007. 

Stark relaxation in collisions of ultracold polar molecules in shallow electrostatic traps will be significant enough to allow for evaporative cooling of molecular ensembles remains to be determined. 

Lara, B.L.L.M. and Bohn, J.L., Loss of molecules in magneto-electrostatic traps due to nonadiabatic transitions, 2008, arXiv 0806.2245vl. 

---