Doping, effects

The effect of doping is first and foremost to produce a swelling of the CP, which generally leads to a large increase in the microscopically observable volume of the CP. The swelling effect however may be less pronounced if small dopants, such as BF4 or methane sulfonate are used in a nonaqueous medium. 

While different dopants may appear to impart a very different topography to a CP, the physical properties of the CP may in fact change very little this is evidenced by the case of P(Py), where different dopants show very different topographies [43], but the densities all lie in the range of 1.37 to 1.48 g/cc. 

Another important feature of doping with respect to morphology, especially in the case of post-synthesis vapor phase doping, for example re-doping with I2 of a P(Ac) sample, is diat it can be inhomogeneous. It is not only that diffusion of dopant 

Structural Aspects, Morphology and Fiber/Film Processing 

Doping also imparts a rigidization to the CP chain, as discussed in Sec. 9.1.3 above. 

In the high temperature regime for covalent crystals where the hardness drops rapidly, its values are affected by impurities (dopants). Both hardening and softening occur depending on whether the dopant is is a donor, or an accepter 

Cline and J.S. Kahn, Microhardness of Single Crystals of BeO and Other Wurtzite Compounds, Jour. Electrochem. Soc., 110,773 (1963). 

Coulson, Valence, Oxford University Press, Oxford, UK (1952). 

Donnet, J. M. Martin, Th. Le Mogne, and M. Belin, Super-low Friction of MoS2 Coatings in Various Environments, Tribology Inter., 29(2), 123 (1996). 

Feltham and R. Banerjee, Theory and Application of Microindentation in Studies of Glide and Cracking in Single Crystals of Elemental and Compound Semiconductors, Jour. Mater. Sci., 27,1626 (1992). 

Let us now quantify the situation. The incorporation reaction can be written as follows  

The excess chlorine offered by the doping with CdClj, effects the extraction of a regular Ag and hence the formation of a vacancy. The annihilation of this chlorine can (and will in a limited amount) also be carried out by an interstitial silver ion aecording to 

Other possibilities for formulating the incorporation reactions release the excess chlorine in the form of a neutral molecule, i.e. via a redox reaction 

This can be generalized to the following fundamental rule of doping. Assuming that the doping ion is introduced irreversibly (with a concentration C) and all other defects are in local equilibrium, the following statement applies for simple defect chemistry (referred to, in what follows, as the C theorem )  

The proof of Eq. (5.141) follows directly from the fact that the incorporation equations and the connecting equilibria must be electroneutral and can be formulated, in each case, with two defects of opposite charges. 

---

Dilute binary alloys of nickel with elements such as aluminium, beryllium and manganese which form more stable sulphides than does nickel, are more resistant to attack by sulphur than nickel itself. Pfeiffer measured the rate of attack in sulphur vapour (13 Pa) at 620°C. Values around 0- 15gm s were reported for Ni and Ni-0-5Fe, compared with about 0-07-0-1 gm s for dilute alloys with 0-05% Be, 0-5% Al or 1-5% Mn. In such alloys a parabolic rate law is obeyed the rate-determining factor is most probably the diffusion of nickel ions, which is impeded by the formation of very thin surface layers of the more stable sulphides of the solute elements. Iron additions have little effect on the resistance to attack of nickel as both metals have similar affinities for sulphur. Alloying with other elements, of which silver is an example, produced decreased resistance to sulphur attack. In the case of dilute chromium additions Mrowec reported that at low levels (<2%) rates of attack were increased, whereas at a level of 4% a reduction in the parabolic rate constant was observed. The increased rates were attributed to Wagner doping effects, while the reduction was believed to result from the... 

Additional information concerning the mechanisms of solid—solid interactions has been obtained by many diverse experimental approaches, as the following examples testify adsorptive and catalytic properties of the reactant mixture [1,111], reflectance spectroscopy [420], NMR [421], EPR [347], electromotive force determinations [421], tracer experiments [422], and doping effects [423], This list cannot be comprehensive. Electron probe microanalysis has also been used as an analytical (rather than a kinetic) tool [422,424] for the determination of distributions of elements within the reactant mixture. Infrared analyses have been used [425] for the investigation of the solid state reactions between NH3 and S02 at low temperatures in the presence and in the absence of water. 

In fact, an apparent doping effect was also reported by Schwan et al. [39] in a-C(N) H films deposited by the highly ionized plasma beam deposition technique in C2H2-N2 atmospheres. Schwan et al. also observed thermally activated behavior for the conductivity. As reported by Silva et al. [14], they also observed increasing optical gap, and decreasing ESR spin signal, but the Urbach energy was found to increase. 

We believe that the luminescence at 1.0 eV is due to a structural damage induced by ion implantation rather than to a chemical doping effect, since the spectrum does not depend on the chemical species of the ion. These centers may be similar to the vacancies induced by 3-MeV electron-beam irradiation, as reported by Troxell and Watkins (1979), who find donorlike and acceptorlike levels —0.1 eV from the band edges. 

T. Tiedje, Information about Band-Tail States from Time-of-Flight Experiments Arnold R. Moore, Diffusion Length in Undoped a-Si H W. Beyer and J. Overhof, Doping Effects in a-Si H H. Fritzche, Electronic Properties of Surfaces in a-Si H CR. Wronski, The Staebler-Wronski Effect... 

Codoped Single Doped Effect on Conduction Behaviors... 

Studies have demonstrated that rare-earth ion modification can greatly improve the photocatalytic activity of Ti02 [147], although recent data disclosed uncertain doping effects (even controversial results) about transition metal ion dopants [140],... 

A. R Moore, Diffusion Length in Undoped a-Si H W. Beyer and J. Overhof Doping Effects in a-Si H... 

Tanaka S, Kanai K, Kawahe E, Iwahashi T, Nishi T, Ouchi Y, Seki K (2005) Doping effect of tetrathianaphthacene molecule in organic semiconductors on their interfacial electronic structures studied by UV photoemission spectroscopy. Jpn J Appl Phys 44 3760... 

In some compounds the doping effect may be the result of charge-carrier generation brought about by an intermolecular charge-transfer transition 72,83)... 

In systems in which the charge-transfer excitation band differs from the action spectrum of photoconductivity, the doping effect may be due to a change of recombination path that results in an enhancement of carrier liefetime (e.g. holes in merocyanines and phthalocyanines). (Details on the mechanism are given in 10,11,74).)... 

Appropriate parameters should follow linear Arrhenius behavior as a function of temperature (69). The model must demonstrate oxidant pressure dependence (78), memory effects as a function of growth temperature (83), and substrate doping effects on oxidation (84). 

The parabolic rate constant, B, is affected only slightly. These results show that the doping effect only influences the interface reaction. 

The temperature dependence of the linear rate constants for various electron concentrations in phosphorus-doped silicon indicate that the doping has only a slight effect on the associated activation energy. Thus, because B/A is proportional to the rate of the interface reaction, the doping effect is buried in the chemical, electrical, or, possibly, mechanical dependence of surface rate on doping. 

Because of the potential importance for industrial-scale catalysis, we decided to check (i) whether an influence of a semiconductor support on a metal catalyst was present also if the metal is not spread as a thin layer on the semiconductor surface but rather exists in form of small particles mixed intimately with a powder of the semiconductor, and (ii) whether a doping effect was present even then. To this end the nitrates of nickel, zinc (zinc oxide is a well-characterized n-type semiconductor) and of the doping element gallium (for increased n-type doping) or lithium (for decreased n-type character) were dissolved in water, mixed, heated to dryness, and decomposed at 250°-300°C. The oxide mixtures were then pelleted and sintered 4 hr at 800° in order to establish the disorder equilibrium of the doped zinc oxide. The ratio Ni/ZnO was 1 8 and the eventual doping amounted to 0.2 at % (75). 

---