Surface ion-induced

In addition to the electron energy bands and impurity levels in the semiconductor interior, which are three-dimensional, two-dimensional localized levels in the band gap exist on the semiconductor surface as shown in Fig. 2-28. Such electron levels associated with the surface are called surface states or interfacial states, e . The siuface states are classified according to their origin into the following two categories (a) the surface dangling state, and (b) the surface ion-induced state. 

Fig. 2-30. Surface dangling states and surface ion-induced states (a) surface dangling donor (DL-B) and acceptor (DL-AB) leveb on covalent bonding semiconductors, (b) surface cation-induced acceptor (SCL) and surface anion-induced donor (SAL) levels on ionic bonding semiconductors.

On semiconductors that are partially ionic and partially covalent, such as transition metal oxides, the surface ion-induced and the surface dangling states may coexist together. 

The dangling and the surface ion-induced states are intrinsic surface states that are characteristic of individual semiconductors. In addition, there are extrinsic surface states produced by adsorbed particles and siuface films that depend on the enviromnent in which the siuface is exposed. In general, adsorbed particles in the covalently bonded state on the semiconductor surface introduce the danglinglike surface states and those in the ionically bonded state introduce the adsorption ion-induced surface states. In electrochemistiy, the adsorption-induced surface states are important. 

An electron or photon incident on a surface can induce an electroiuc excitation. When the electroiuc excitation decays, an ion or neutral particle can be emitted from the surface as a result of the excitation. Such processes are known as desorption induced by electroiuc transitions (DIET) [82]. The specific teclmiques are known as electron-stimulated desorption (ESD) and photon-stimulated desorption (PSD), depending on the method of excitation. 

Zalm P C, Kolfschoten A W, Sanders F H M and Vischer P 1987 Surface processes in ion-induced etching Nud. Instrum. Methods B 18 625-8... 

In the ion induced damage mechanism energetic ions break crystal bonds on the film surface thereby making the film more accessible and more reactive to the active chemical etchant. However, the side walls remain relatively unperturbed, and etching proceeds at the nominal chemical etch rate. Consequently, material removal proceeds far more rapidly in the ion flux direction, resulting in anisotropy. In actuality, the surfaces exposed to the plasma are likely to be composed of a chemisorbed coating of etchant... 

In summary, the importance of ion-induced secondary-electron emission in plasma environments is demonstrated by, among other things, the fact that it produces a substantial fraction of the ions, generates significant heating of surrounding surfaces, and modifies the properties of deposited films. 

Ion pairing with the polar micelle surface can induce pronounced effects on the observed excited state chemistry. 

Auger emission to neutralize incoming ions leaves the solid surface in an excited state relaxation of the surface results in secondary electron generation (23, 24). Secondary electrons are ejected when high-energy ions, electrons, or neutral species strike the solid surface. These electrons enhance the electron density in the plasma and can alter the plasma chemistry near a solid surface. Radiation impingement on a surface can induce a number of phenomena that depend upon the bombardment flux and energy. 

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