Interface, types abrupt

In compositional analysis of very small precipitates, or in interface segregation studies, using a probe-hole type atom-probe, one is always faced with the fact that the probe-hole may cover both the matrix and the precipitate phases, or the interface as well as the matrix. Thus any abrupt compositional changes will be smeared out by the size of the probe-hole and also by the effect of ion trajectories. A similar uncertainty seems to exist in the compositional analysis of nitride platelets formed in nitrided Fe-3 at.% Mo alloy, aged between 450 and 600°C, where Wagner ... 

In solid-state devices semiconductors are interfaced with other materials and junctions are formed. A junction between two semiconductors of opposite polarity is called a pn-junction. If the concentration of one type of dopant is much higher than that of the other (e.g., N > > Afo) it is called an abrupt junction (Fig. C.3). For the approximately equal doping levels we talk about, we use the term two-sided junction. A gradient of dopants is found in graded junctions. The concentrations of carriers on the two sides of the junction (subscripted) are... 

The interface obtained by sputtering is not abrupt but on the contrary, it is a region of strong mixing of Al with Si, O and C atoms over a depth of several tens of A, as observed from the chemical shifts. This finding is also evidenced by another type of measurements related to the intensity measurements. Figure 8 shows for instance, the comparison of the variation of Al/O and C/O atomic ratios determined for the two types of interfaces as a function of Al thickness. The Al/O ratio increases with a smaller slope for sputtered interfaces when compared to evaporated interfaces. Furthermore, the O/C ratio is constant (= 0.55) for evaporated film indicating that the attenuation of... 

The type II isotherm is associated with solids with no apparent porosity or macropores (pore size > 50 nm). The adsorption phenomenon involved is interpreted in terms of single-layer adsorption up to an inversion point B, followed by a multi-layer type adsorption. The type IV isotherm is characteristic of solids with mesopores (2 nm < pore size < 50 nm). It has a hysteresis loop reflecting a capillary condensation type phenomenon. A phase transition occurs during which, under the eflcct of interactions with the surface of the solid, the gas phase abruptly condenses in the pore, accompanied by the formation of a meniscus at the liquid-gas interface. Modelling of this phenomenon, in the form of semi-empirical equations (BJH, Kelvin), can be used to ascertain the pore size distribution (cf. Paragr. 1.1.3.2). 

Interface analysis is one field of special interest for LIBS. The analytical aim is usually the description of a sample or zone thereof where an abrupt change in the identity or concentration of its components occurs. The suitability of LIBS for this type of application lies in the ability to associate spectral data to the spatial coordinates of the sample. 

Figure 3 shows plots of thermoelectromotive force against position across the joint interface in the p-n junction. The conduction type at the boundary of p-n jimction was found to change abruptly within 1 mm. This result shows that a well-defined joint boundary can be prepared by PAS process without a long distance of diffusion of the dopant in matrix material. Figure 4 shows the I-V characteristic of the p-n junction. The current is foimd to depend upon the forward and reverse bias and the... 

This Interface is characterized by an abrupt transition from the film material to the substrate material. The transition region has a thickness of 0.2 - 0.5 nm. Interfaces of this type form when no diffusion occurs there is little or no chemical reaction and the substrate surface is supposed to be dense and smooth. 

Should the changes in distribution of electrons (majority carriers) in w-type be abrupt at the interface as compared to the bulk or should it change linearly or exponentially The most reasonable assumption would be that the change in concentration of majority carrier between the bulk and interface is exponential. This situation can be illustrated by an exponential bending in the conduction band (Fig. 4). Similarly, the valence band must also bend in a similar fashion to maintain the difference between the conduction band and valence band, which is equal to the band gap of the semiconductor. Since difference between the Fermi level and conduction band is related to the magnitude of dopant s concentration, this difference must be maintained even after the formation of band bending. However, it is difficult to present it pictorially. Hence, we compromise by depicting it as a horizontal broken line. 

Rather little work has been reported on the use of conducting polymers in active semiconductor devices. A problem in organic pn-junctions is the interdiffusion of dopants destroying the abrupt interface. In Schottky junctions made of (the more stable) p-type polymers, metals with low work functions must be used. These metals, such as aluminium (work function 4 3 eV) are typically reactive and oxidize easily. 

So far we have only considered the case of abrupt junctions where dopant concentration changes abruptly across the interface. Example of this type is when the doping material is implanted into the substrate by means of a high-energy ion source and then annealed at high temperatures over a relatively short period. On the other hand, heating for long period of time... 

For semiconductors, the most important junction is the p-n junction, i.e. the interface between AT-type and P-type doped materials. Such a junction can be abrupt (if, for example, two dishes of different materials are pressed together). More important, however, are dijfuse junctions, which are formed, for example, when a P-dopant diffuses from the gas phase into a piece of N-type silicon forming around it a region of P-type material. 

The abrupt interface is characterized by an abrupt change from the film material to the substrate material in a distance on the order of the atomic spacing (i.e. 2-5 A) with concurrent abrupt changes in material properties. This type of interface is formed when there is no bulk diffusion and generally signifies weak chemical reaction between the depositing atoms and the substrate, a low deposition temperature, surface contamination, or no solubility between the film and substrate materials. Some systems such as silver on iron and indium or gallium... 

---