Self-compensation

Muller R H and Farmer J C 1984 Fast self-compensating spectral-scanning ellipsometer Rev. Sol. Instrum. 55 371-4... 

A measure of self-compensation, with respect to weight rate of flow, for fluid-density changes can be introduced through the use of a float with a density twice that of the fluid being metered, in which case an increase of 10 percent in p will produce a decrease of only 0.5 percent in w for the same reading. The extent of immunity to changes in fluid viscosity depends upon the shape of the float. 

When the substituent is an ionic chain [Fig. 13(b)] with the anion on the organic side, some of the lateral anions act as counter-ions during electrochemical oxidation. The cation of the salt is expelled from, or included in, the material during oxidation or reduction, respectively. These are self-compensating or self-doping (chemical or physical terminology, respectively) materials.76... 

Since there is a slight delay between when a pulse is switched on and when it reaches full power, an error may be introduced when measuring 90° or smaller pulses directly. If the 90° pulse width is required with an accuracy of better than 0.5 fi, then it may be determined more accurately by using self-compensating pulse dusters that produce accurate flip angles even when there are small (<10%) errors in the setting of pulse widths. 

The errors in the APT spectra may arise due to (a) variation in the relaxation times of different carbons, (b) wide variation in / h values, and (c) modulations caused by long range C- H couplings. A procedure known as ESCORT (Error Self Compensation Research by Tao Scrambling) has been developed to yield cleaner subspectra with reduced / cross-talk (Madsen et ai, 1986). This involves replacing the normal APT spectral... 

The trick introduced by Meiboom and Gill (14) is to dephase all n pulses in the Carr Purcell train by an angle of 90° with respect to the initial ti/2 pulse. It is easily shown that, without this phase change, imperfections of the 71 pulses are cumulative, whereas with the 90° phase change, a self-compensation occurs for all echoes of even number. The CPMG (Carr-Purcell-Meiboom-Gill) experiment can be handled in two ways ... 

It is important to note that the good agreement achieved between the Born-Haber and calculated values for lattice energy, do not in any way prove that the ionic model is valid. This is because the equations possess a self-compensating feature in that they use formal charges on the ions, but take experimental internuclear distances. 

We now consider the nature of the transition. In compensated Si P the transition takes place in an impurity band for high concentrations of dopant this merges with the conduction band. In uncompensated Si P the many-valley structure of the conduction band leads to a kind of self-compensation so that N( F) is already finite at the transition (Chapter 5), and the transition is of Anderson type. Whether this is so for p-type material or for single-valley materials is not known. If not then the transition must be of Mott type (Chapter 4), occurring when B U. 

As we shall see below, for dilute solutions the electron is not attached to the alkali ion but is trapped in a cavity, around which the ammonia is polarized. The problem of the metal-insulator transition, then, is one of a random array of one-electron centres, as in a doped single-valley semiconductor. On the other hand, the disorder is less because the strong overlap between the wave functions of some pairs of centres characteristic of doped semiconductors is absent. In doped semiconductors there is no discontinuity in s2 at the transition. As explained in Chapter 5, this may be because of the very strong disorder or, in many-valley systems, because of self-compensation. In metal-ammonia solutions, as in the fluid alkali metals discussed in Section 4, both are absent. 

The doping can be affected by native defects such as vacancies (Vo and VN), self-interstitials (Gai and Nj) and antisites (GaN and Ng,). Such defects may cause self-compensation, e.g. when one tries to dope the material p-type, certain native defects which act as donors may spontaneously form and compensate the deliberately introduced acceptors. In GaN, a specific native defect was long believed to play an even more important role the nitrogen vacancy, which acts as a donor, was thought to occur in large concentrations, thereby causing unintentional n-type conductivity. 

The thermod3mamic and kinetic aspects of hole conduction self-compensation were analyzed in detail.It was concluded that the main reason for the monopolar conduction in the compounds under consideration is that the chalcogen is present in the vapor phase in molecular form. It was also shown that the compensation of acceptor centers in II-VI compounds can be suppressed by reducing the s mthesis or doping temperature to below a critical temperature, if the process is run in saturated chalcogen vapor. 

It can be seen that the relaxation correction decreases the Koopmans estimate, whereas the difference in the two correlation corrections increases the estimate. The errors are thus, to a certain extent, self-compensating. Transition metal d orbitals are often associated with much greater relaxation corrections than ligand orbitals, and this can lead to an inversion of ordering between an orbital energy calculation and the associated PE bands. Thus, it is not uncommon to And from a calculation a filled metal orbital to be more stable than a ligand orbital but to give rise to the first IE of a molecule. 

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