Substrate polymer coated, work function

FIGURE 2.3.11 Dependence of work function of polymer coated substrate, 4>elp/sub> on th work function of bare substrate, sub for four studied materials P3HT, TFB, poly(9-l-decylundecylidene tluorene (PIOAF), and polydioctylfluorene (PFO). (From Tengstedt, C. et al., Appl. Phys. Lett., 88, 053502, 2006. Reprinted with permission. Copyright 2006, American Institute of Physics.)... 

To conclude this section, we consider an energy band diagram (see Figure 21.15) for PFO on various substrates [78]. The Evac of the substrate and of the spin-coated polymer film is aligned (A si 0). For metal substrates with work functions varying from 3.9 eV (for Al) up to 5.4 eV (for Au), the Fermi level of the metal substrate always falls within the bandgap of PFO. This has important consequences for... 

Device fabrication requires the successive deposition of a series of layers of metal, polymer and insulators, with appropriate patterning in the case of the MISFET for the formation of the source and drain areas. We use simple metal evaporation, of gold as an ohmic contact and, typically, aluminium as a blocking contact. Thus, to fabricate a Schottky barrier diode, we deposit a bottom layer of gold onto the substrate, coat this with the polyacetylene layer, and put the low work function metal such as aluminium or indium on top of this. The Schottky barrier diode is obviously very sensitive to the presence of pin-holes in the polymer layer, and we have therefore aimed to keep the thic ess of the polyacetylene layer sufficiently high so that the chances of this failure mode are reduced to a low level. We have worked typically with polymer layer thicknesses of around 1 xm. 

Electroactive polymers may be coated on, or covalently attached to, the electrode surface. In the latter case, a facile pathrvay involving the acylation of amino groups on the el ode surface with partially derivatized activated polymer intermediates is shown in Fig. 22 [16]. Similar reactions based on the use of partially functionalized polymer intermediates provide suxess to a variety of modified surfaces with biocompatibility, substrate selectivity, fluorescence or ferromagnetic properties (proprietary work, unpublished). 

The anion-exchangers described in Tables 6.4, 6.5 and 6.6 are not latex-coated but their exchange groups are mostly in a narrow band near the outside perimeter of the spherical ion-exchange particle. In some instances the ion-exchange part of the particle consists of a functionalized polymer grafted onto the outer surfaces of the substrate. It should be emphasized that these columns work well for all forms... 

Under certain (limited) circumstances a mere physisorption of the functional polymers might work, in particular, if only transient surface coatings are employed. For example, the spin-coating of a clean Si-wafer by a photoresist is sufficient to prepare a photoreactive layer that can be used to generate a pattern by mask-illumination, etch this into the Si to laterally stmcture the substrate, and then dissolve the polymer away again. 

---