Soft electronics

Reproduced with permission of the American Institute of Physics from 

3 PDLCs comprise LC droplets dispersed in a polymer matrix. Random director orientation leads to the scattering of light due to refractive index mismatch between LC and polymer. A field applied across the film orients the LC so that the refractive indices match and the scattering is reduced, rendering the film transparent. 

4 E-ink consists of microcapsules of oppositely charged black and white particles in a fluid matrix. The microcapsules are dispersed in a polymer film with an upper transparent electrode and an electrode array on the lower surface. The white particles are attracted to the visible surface of the display by an applied field of one polarity the black particles are attracted to the surface when the polarity of the field is reversed. 

The use of polymers with a low relative permittivity, see Section 2.7, as the FET gate insulator has been found to result in higher carrier mobility and improved device performance (Veres et al., 2003). The authors developed stable semiconductive polymers, poly(triarylamines), and used them to fabricate FETs with silicon dioxide and poly(methylmethacrylate) gate insulators. Values of the carrier mobilities measured in the FETs were about 10 times smaller than those determined by TOF experiments. A dramatic increase in FET mobility was observed when a low permittivity fluoropolymer (e = 2.1) was employed as gate insulator. The FET mobilities for devices with gate insulators with relative permittivities in the range 2-18 are shown in Fig. 10.12(a). The devices were made with two different poly(triarylamines) 

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CROSSED MOLECULAR BEAM REACTIVE SCATTERING TOWARDS UNIVERSAL PRODUCT DETECTION BY SOFT ELECTRON-IMPACT IONIZATION... 

The future prospects opened up by soft electron-impact ionization for product detection in CMB studies of atom/radical reactions with polyatomic molecules/radicals are briefly examined. 

Soft Electron-Impact Ionization by Low-Energy Electrons 337... 

Reactive Scattering by Soft Electron Impact Ionization... 

What are the future opportunities in CMB reactive scattering studies opened up by the soft electron-impact ionization ... 

Earlier it was described how PH3 is a much weaker base than NH3. That is certainly true when the interaction of these molecules with H+ is considered. However, if the electron pair acceptor is Pt2+, the situation is quite different. In this case, the Pt2+ ion is large and has a low charge, so it is considered to be a soft (polarizable) Lewis acid. Interaction between Pt2+ and PH3 provides a more stable bond that when NH3 bonds to Pt2+. In other words, the soft electron acceptor, Pt2+, bonds better to the softer electron donor, PH3, than it does to NH3. The hard-soft interaction principle does not say that soft Lewis acids will not interact with hard Lewis bases. In fact, they will interact, but this is not the most favored type of interaction. 

However, with soft electron pair acceptors such as Pt2+, Ag+, and Ir+, phosphines are stronger Lewis bases than are NH3 and amines, so phosphines and arsines interact better with class B metals than do amines. Generally, phosphines and arsines form stable complexes with second- and third-row transition metals in low oxidation states. 

Although the subject of stability of complexes will be discussed in greater detail in Chapter 19 it is appropriate to note here some of the general characteristics of the metal-ligand bond. One of the most relevant principles in this consideration is the hard-soft interaction principle. Metal-ligand bonds are acid-base interactions in the Lewis sense, so the principles discussed in Sections 9.6 and 9.8 apply to these interactions. Soft electron donors in which the donor atom is sulfur or phosphorus form more stable complexes with soft metal ions such as Pt2+ or Ag+, or with metal atoms. Hard electron donors such as H20, NH3( or F generally form stable complexes with hard metal ions like Cr3+ or Co3+. 

The thiocyanate ion provides an interesting test of these ideas. In the SCN ion, the sulfur atom is considered to be a soft electron donor, whereas the nitrogen atom is a much harder electron donor. Accordingly, Pt2+ bonds to SCN- at the sulfur atom, whereas Cr3+ bonds to the nitrogen atom. Uncharged metal atoms are considered to be soft electron acceptors, and they form complexes with soft ligands such as CO, 11, and PR3. We will see many examples of such complexes in later chapters. On the other hand, we would not expect complexes between uncharged metal atoms and NH3 to be stable. 

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