Dead layers

From this equation It Is clear that a plot of M/Mg versus MgpH/3kT will yield a line with slope v /v. The only unknown In this equation Is the value of Mg. Assuming that this does not change as a function of particle size (no dead layers) this can be determined for magnetite from the formula of Pauthenet (23) ... 

Mix together 1 1/2 oz. each of ground, dried elder blossoms and peppermint leaves. Add to 2 oz. of ground oatmeal and 2 oz. corn meal. Use one oz. a week to gently scrub and remove dead layers of skin. It can also be mixed... 

In 1984, the AMPTE mission launched the first carbon-foil TOF-MS into space, which would have been the second, had the Challenger shuttle disaster not delayed the Ulysses launch until 1991 (Fig. 11.2) [23]. The photons were filtered out by a traditional blackened deflection system, which directed the ions toward the 2 p,g/cm2 thick foil mounted on an 85% transparent grid almost a square centimeter in area. The grid provided the support needed to survive the launch. The foil thickness permitted >2keV/nuc ions to pass through and hit a SSD some 10 cm away. To ensure that the ions made it through the foil and also through the dead layer on the SSD (caused by the upper electrode), the foil and the entire TOF section were floated at 20 kV to post-accelerate the ions. Electrons sputtered off the carbon foil became the start, whereas electrons sputtered off the SSD became the stop pulse for the TOF. 

The depletion width can play a role in analyte-induced modulation of the semiconductor PL [4]. As molecules adsorb onto the surface of the semiconductor, the dead-layer thickness can change, resulting in what can be described as a luminescent litmus test When Lewis bases adsorb onto the semiconductor surface, they donate electron density to the solid, which decreases the electric field and thus decreases the dead-layer thickness. The reduction in D causes an enhancement in the PL intensity from the semiconductor. Figures 2a and 2b present typical PL enhancements observed from an etched n-CdSe substrate Relative to a nitrogen reference ambient, adsorption of the Lewis bases ammonia and trimethylamine cause a reversible increase in PL intensity. In contrast, when Lewis acids adsorb onto the surface, they can withdraw additional electron density, causing the electric field to increase and the PL intensity to decrease. Such effects have been observed with gases like sulfur dioxide [5]. 

The quantitative form of the dead-layer model relates PL intensity to dead-layer thickness, which is assumed to approximate the depletion width W [6,7] ... 

Photoluminescence experiments with ni-V wafers of Ino.5o(Gao.9o A1o.io)o.5oP were conducted 114]. The Lewis basic gaseous analytes ammonia, methylamine, dimethyl amine, and trimethylamine all yielded reversible PL enhancements. The Lewis acid sulfur dioxide, in contrast, caused reversible quenching of the semiconductor s PL intensity. These PL intensity changes were consistent with analyte-induced modifications of the dead-layer thickness. 

Fig. 9.21 Change of the dead-layer thickness Dd = Di -D2 upon exposure of Pd to hydrogen in the photoluminescent Schottky junction...

The presence in the cluster of a positively charged impurity has also been considered, analyzing, by first principles, the screening due to the Si-NCs [123,124]. A reduction of screening in Si nanostructures with respect to bulk Si has been already observed [52] and predicted [125]. This reduction is a fundamental process at the basis of the enhancement of both the electron-hole interaction and the impurity activation energies in nanosized objects, and is due to the fact that close to the surface there is a dielectric dead layer, with a finite-range reduction of the dielectric constant due to the dielectric mismatch at the nanocrystal-environment interface. 

In addition, the dielectric constant at the pzt top surface was found to be dramatically reduced compared to the bulk value. Our measurements therefore suggest a dead layer to be present. Similar experiments of deducing the local dielectric constant are now necessary for the inner interface. 

The major barrier of the skin is the outermost dead layer, the stratum corneum. A number of routes of penetration of a drug, across this region can be identified. First, the appendages, the pilosebaceous and eccrine glands, form a potential shunt route across the stratum corneum. The relative surface area of these is very small (<0.1%) and there has been little conclusive evidence to suggest that this is a major route. Second, the penetrant could diffuse across the entire stratum corneum through the dead cells, the corneocytes. A large surface area is available but the... 

The browning of skin occurs in the stratum corneum—the outermost, dead layer—where the DHA reacts with free amino (—NH2) groups of the proteins found there. 

A dead layer usually exists on the surface of phosphor particles, which degrades the phosphors due to crystal defects, residues, oxidation, contamination, etc. A surface treatment with an acid wash is widely used in industry to improve the quality of oxide and sulfide phosphors. Chemical etching on phosphors can also be used to investigate the microstructure properties of the phosphor particles. " ... 

The collimator impact for 81 keV is shown in Fig. 11. The counts are normalized to the counts at 90°. The 81 keV lines are almost completely absorbed by either the steel or tungsten. The upturn in the uncollimated curve at 0° and 180° is due to the difference in absorption by the endcap, cup and germanium dead layer for the 0° angle of incidence and the 10° angle of incidence. The combined circular (front face) and cylindrical surface area of the detector perpendicular to the gamma ray flux has a maximum at about 45°, but this is reduced by the change in... 

Fig. 5.17. Penetrating powers of ionizing radiation in tissue y and n radiation penetrates easily P-particles penetrate a few centimetres at max. a-particles do not penetrate the dead layer of the skin.

---