Modified Semiconductor Surfaces

The ISFET, developed from the fabrication techniques of semiconductor devices, is an important sensor device used in potentiometry. The main advantages are the extremely small size, solid-state structure and the ability to fabricate multi-ion sensors. More than 30 years ago, methods have been proposed to work with a differential arrangement, i.e. the integration of an ion-sensitive and an ion-insensitive structure, the later one working as the reference element (R(E)FET). The main problem is that semiconductor-modified surfaces required for R(E)FET are also not always in thermodynamical equilibrium with the test solution and can be sensitive to aggressive or interfering dissolved species or not well characterised aging phenomena. 

Like XPS, the application of AES has been very widespread, particularly in the earlier years of its existence more recently, the technique has been applied increasingly to those problem areas that need the high spatial resolution that AES can provide and XPS, currently, cannot. Because data acquisition in AES is faster than in XPS, it is also employed widely in routine quality control by surface analysis of random samples from production lines of for example, integrated circuits. In the semiconductor industry, in particular, SIMS is a competing method. Note that AES and XPS on the one hand and SIMS/SNMS on the other, both in depth-profiling mode, are complementary, the former gaining signal from the sputter-modified surface and the latter from the flux of sputtered particles. 

Plasma treatment is widely used commercially for polymer surface modification. Plasma discharge treatments are used to improve adhesiveness and printing properties, to improve cell adhesion to tissue culture substrates (1 ) and to etch or clean the surfaces of materials (removal of photoresist materials on semiconductors, for example ( ). The surface characterization of plasma-modified surfaces is important in order to provide greater insight into how the properties are changed. 

The strategy to modify surface states, and thus the Vg and SRV, is based on interaction of chemically grafted molecules with these states. The key is to find molecules that will modify the semiconductor surface chemistry in a way that involves the surface states. In this respect, the origin of the surface states should be considered. Intrinsic surface states originate from the termination of the crystal bulk and the breaking of chemical bonds at the surface, whereas extrinsic surface states originate from crystal imperfections, such as missing surface atoms, line defects, or... 

Lacaze, P.C., J.E. DuBois, A. Desbene-Monvernay, P.L. Desbene, J.J. Basselier, and D. Richard. 1983. Polymer-modified electrodes as electrochromic material. Part III. Formation of poly-N-vinylcar-bazole films on transparent semiconductor ITO surfaces by electropolymerization of NVK in acetonitrile. / Electroanal Chem 147 107-121. 

Van Duyne, R.P. and Haushalter, J.P. (1983) Surface-enhanced resonance Raman-speciroscopy of adsorbates on semiconductor electrode surfaces - Tris(bipyridine)Ruthenium(II) adsorbed on silver-modified N-Gaas(lOO). The Journal of Physical Chemistry, 87, 2999-3003. 

The potential advantages of photoelectrosynthesis over photovol-taics coupled to dark electrosynthesis are in higher net conversion efficiency, better engineering designs for solar reactors, and unique catalytic effects possible with modified semiconductor electrode surfaces. 

There are many other experiments in which surface atoms have been purposely moved, removed or chemically modified with a scanning probe tip. For example, atoms on a surface have been induced to move via interaction with the large electric field associated with an STM tip [78]. A scaiming force microscope has been used to create three-dimensional nanostructures by pushing adsorbed particles with the tip [79]. In addition, the electrons that are tunnelling from an STM tip to the sample can be used as sources of electrons for stimulated desorption [80]. The tuimelling electrons have also been used to promote dissociation of adsorbed O2 molecules on metal or semiconductor surfaces [81, 82]. 

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