Adsorption particles

To a certain extent one can consider an approach to describe non-Langmuir features accounting for probable interaction between adsorption particles as an alternate theory of inhomogeneous surface. Moreover... 

T v exp +Eq / kT) is the average time of contact of adsorption particle with the surface. Integrating equation (1.10) one gets... 

Assume, that there are adsorption particles with concentration Nt on the surface of semiconductor which is in adsorption equilibrium with a certain gas. A fraction of adsorption particles is charged with concentration designated as w<. Apart from them, on the surface there are various biographic surface states with concentration of the charged particles ng controlling the degree of an a priori band bending qUso-... 

Solution of equations (1.26) and (1.27) for above two limiting cases differing in the value of the surface concentration of adsorption particles brings about different dependencies of the value of the surface band bending as a function of parameters of the absorbate-adsorbent system. Thus, in case of adsorption of acceptors we obtain from (1.26) that... 

Expression (1.28) gives the equilibrium height of the surface barrier caused by the total transition of chemisorbed particles into the charged form. In case when expression (1.29) is valid the equilibrium height of the barrier is determined by the leveling-off of energy state of adsorption particle with the Fermi level of adsorbent. In case... 

Consequently, for high concentration of adsorption particles (which is directly linked either with their high partial pressure in gaseous phase or with high value of their adsorption heat) all kinetic curves ait) whose shape (as it will be showed below) is notably dependent on concentration of adsorption particles Nt tend (at long times) to a specific value of (Tp dependent on the nature and history of adsorbent and independent on the value of Nt-... 

As it has been already mentioned in numerous cases one should take into account the dipole component in the adsorption — caused change in the work function stemming from availability of dipole moment in adsorption particles. This component alters the value of micropotential of the surface. As it has been already mentioned in section 1.2, the origin of these dipoles can differ ranging from inherent to quantum mechanical one [4]. 

If acceptor adsorption particles with concentrations Nta possessing a value of affinity to electron Eta appear on the surface of adsorbent characterized by pre-adsorption band bending (1.49), then the condition of their transition into the charged form is provided by inequality... 

Therefore, the theoretical analysis and numerous experimental data enable one to assume that charging of the surface of adsorbent occurring during adsorption can result in relaxation of the charge state of an a priori existing BSS and influence the kinetics of transition of adsorption particles into the charged form. However, during chemisorption of ac-... 

To determine correlation between (t) and nd, therefore, to find out the type of dependence f let us consider the occupation kinetics for ASS levels by free charge carriers. The capturing of charge carriers occurring during transition of adsorption particles into the charged form will be considered, as usual, in adiabatic approximation, i.e. assuming that at any moment of time there is a quasi-equilibrium and the system of crystallites is characterized by immediate equilibrium values and L inside the conduction (valence) band. 

The adsorption-caused change in concentration of critical barriers f(4c>0 is also different for various relationships between parameters Nt, co sud a. Thus, in case of small concentration of adsorption particles Nt<-Ja-... 

When concentration of adsorption particles exceeds the limiting one... 

One can deduce from these profiles that in case of small concentrations of adsorption particles that an additional notable change in ohmic electric conductivity takes place for the case of small concentration of adsorption particles during change of t in vicinity of tg,. This happens... 

As for equilibrium values of as and P they are mainly dependent on relations between such parameters of the systems as initial electric conductivity of adsorbent, concentration of chemisorbed particles, reciprocal position of the energy levels of absorbate and adsorbent. Thus, during acceptor adsorption in case of small concentration of adsorption particles one can use (1.82) and (1.84) to arrive to expressions for equilibrium values of ohmic electric conductivity and the tangent of inclination angle of VAC ... 

Therefore, the activation energy of quasi-equilibrium conductivity changes as a logarithm of concentration of adsorption particles which, when the linear dependence between Nt and P is available, corresponds to situation observed in experiment [155]. We should note that due to small value m function (1.91) satisfactorily approximates the kinetics oit) A - B n(i + t/t>) observed in experiments [51, 167, 168]. Moreover, substantially high partial pressures of acceptor gas, i.e. at high concentrations of Nt expression (1.81) acquires the shape ait) Oait/toc) it,Nty " when t>toc>. This suggests that for... 

In case when the concentration of adsorption particles increases t > -j4co ) formulas (1.108) and (1.109) become valid only for times t < tee, where tee is the characteristic time determined from equation > which is the condition of leveling-off of criti-... 

During the studies of adsorption-caused response in a and p by donor particles we monitored both kinetics of the change in above characteristics and dependence of their stationary values on concentration of adsorption particles. The partial pressure in gaseous phase (and in case of atom particles the time of treatment of the surface of adsorbent by the flux of above particles) used to be the measure of the quantity of absorbed particles during adsorption of molecular particles. 

Adopting the current standpoint that the process of chemisorption can be treated as chemical reaction of adsorption particle with adsorption center accounting for effect of both the reaction on the whole adsorbent and adsorbent on the reaction proper, i.e. accounting for the... 

In conjunction with latest progress in quantum chemistry the availability of vast experimental data makes it possible to anal)rze the character of possible centers of adsorption of particles of various gases as well as type, chemical and electron properties of surface compounds formed during interaction of adsorption particles with adsorption centers. 

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