Isomerization and Disorder of Polyacetylene Induced by Doping

Abstract

Raman scattering experiments are reported for cis-(CH), and cis-(CD), doped with AsF, in a concentration range between 3 and 13%. The typical cis-lines in the spectrum decreased with increasing doping concentration until they disappear completely at around 8%. Simultaneously the non-resonant trans-line a t 1291 cm-l is observed to increase and a special high-frequency mode develops around 1590 cm-l. From the experimental results it is shown that the generation of disorder and isomerization by doping is a general phenomenon. A strong increase of the scattering cross-section observed for red laser light for the heavily doped material is correlated to a band gap closure.Es wird iiber Raman-Experimente an cis-(CH), und cis-(CD), mit AsF,-Dotierung zwischen 3 und 13% berichtet. Die Linien typisch fur cis-(CH), nehmen mit zunehmender Dotierungskonzentration ab bis sie um etwa 8% vollig verschwinden. Gleichzeitig steigt die Intensitit der nicht resonanten trans-Linie bei 1291 cm-l an, und eine spezielle hochfrequente Mode urn 1590 cm-' taucht auf. Bus diesen Ergebnissen wird gezeigt, daB Dotierung generell eine Kristallstorung und eine Isomerisation bewirkt. Eine beobachtete starke Zunahme des Streuquerschnittes fur rotes Laserlicht im stark dotierten Material wird mit einer SchlieBung der Bandlucke in Zusammenhang gebracht.

Raman Study of Doped Polyacetylenes

“…For a great number of doped samples, we observe an additional shoulder i n the high frequency side o f the C =C stretch Raman band a t 2 1600 c m -I . The same observation has been previously reported (7) i n the case o f AsF5-doped (CHA. Figure 2 Table 2 -Frequency of the additional Raman band for various dopants and excitation wavelengths.…”

“…Systematic studies of doped films, as a function o f the dopant concentration, are underway. A t very low doping concentration, it may be possible that the isomerization remains limited, as it is the case of AsF5 doped films (7), the doping occuring first on amorphous parts of the material, already trans.…”