Photoconductivity in trans (CH)x: A proof for the existence of solitons?

The optical absorption spectrum has been measured on trans (CH)_x upon simultaneous illumination of the sample with a second light source. No additional mid-gap absorption has been observed nor have the characteristic i.r. peaks been found which are known to show up at 0.11 and 0.17 eV upon doping. On the other hand photoconductivity has been detected, and, from its size, one would expect that the i.r. features should appear provided that the electron-hole pairs preferentially decay into soliton-antisoliton pairs, as predicted by theory. The negative results thus suggests that photo-generated carriers do not relax into solitonic states.     

On the decay of the polarization charge on zinc oxide induced by the pyroelectric effect

Using a method which was mainly developed to measure surface charges on insulators, the decay of pyroelectrically induced polarization charges on zinc oxide was studied. If no charge carriers were injected into the crystal, the decay of the charge was found to obey a logarithmic time law. Since field dependent processes could be ruled out to cause the decay, this law is indicative for processes, the thermal activation energies of which are continuously distributed.     

Spectroscopic evidence for polarons in poly(3-methylthiophene)

We present the results of an in-situ spectroscopic study of poly(3-methylthiopene) electrochemically doped with BF₄^?. It is concluded that polarons are the primary elementary excitations in the dilute doping regime.     

Electrical and Optical Properties of Oriented (CH)x

We have measured the optical and electrical properties of both graphoepitaxially grown and shear-flow polymerized polyacetylene filmzs. The former show a pronounced optical anisotrop;y whereas the latter do not. This result is is correlated with the orientation of the chain axes relative to the fibra axes relative to the fibre axis, which is preferentially parallel in graphoepitaxially grown films. The electrical anisotropy was found to be rather weak. Optical measurements on doped (CH)_x indicate that both the characteristic IR modes at 0.11 eV and 0.17 eV and the mid-gap absorption around 0.5 eV, which have been attributed to solitonic defects, persist up to the metallic level. This result shows that both the IR modes and the mid-gap absorption are not necessarily signatures for solitonic defects. furthermore we conclude that the impurity potential is more effective than hitherto assumed.     

ESR and optical measurement on poly(3-methylthiophene)

The elementary excitations of poly(3-methyl-thiophene) in a doping range up to 7.5% have been found to be polarons as evidenced by ESR-measurements. Above 7.5% doping Pauli susceptibility indicates metallic behaviour. In contrast, at 5% doping the optical absorption spectra show a transition from the three peak structure due to polarons to one with two peaks and commonly assigned to the formation of bipolarons. It is argued that a widening of the polaron levels gives rise to this phenomenon and not the induction of bipolarons. Above 20% doping the formation of a new phase of the material is observed, which is characterized by the disappearance of the peak at 1.6 eV and a well defined isosbestic point at 1.4 eV.     

Preparation of polymer nanocomposites with “ultrahigh” refractive index

Nanocomposites of lead sulfide and several polymers, especially poly(ethyleneoxide), were prepared by coprecipitation of lead sulfide and polymer, followed by a drying and pressing procedure. Such nanocomposites consist of ca. 90% w/w (or ca. 50% v/v) lead sulfide, of particle dimensions of 2–40 nm. The refractive index of these materials is on the order of 3 and therefore, to the authors' best knowledge, is the highest reported for any polymer composite.