ELSEVIER Synthetic Metals 69 (1995) 59.5-596 Photoelectron spectroscopy of polysilaneqpolygermanes and related compounds H. Ishiia, A. Yuyamaa, S. Nariokaa, K. Sekia, S. Hasegawab, M. Fujinoc, H. Isakac, M. Fujik?, and N. MatsumotoC aDepartment of Chemistry, Faculty of Science, Nagoya University, Chikusa-ku, Nagoya 464-O 1, Japan l?nstitute for Molecular Science, Myodaiji, Okazaki 444, Japan ‘Basic Research Laboratories, Nippon Telegraph and Telephone Corporation, Morinosato, Atsugi 243-01, Japan Abstract Ultraviolet photoelectron spectra were measured for five polysilanes, two polygermanes, three Si-Ge copolymers and feti- butyloctasilacubane. The UPS spectra of the polyalkylsilanes and polyalkylgermanes indicate that the valence electronic structure can be regarded as an overlap of those of the backbone and substituents. On the other hand, the spectra of polyarylsilanes imply that the uppermost part of the valence band structure is slightly different from the superposition of those of the Si backbone and substituents due to o-?c interaction The results of copolymers and reti-butyloctasilacubane are also discussed 1.INTRODUCTION Silicon-backbone materials, whose electronic structure is characterized by o-conjugation along the Si backbone instead of n-conjugation in carbon-based polymers, have attracted attention as a new class of conducting polymers, and photoresists.[l,2]. Several studies have been made on the valence electronic structure of polysilanes using ultraviolet photoelectron spectroscopy (UPS)[3-51, but the reported spectra were not sufficient in two points; (i) they did not cover the whole valence states due to the low photon energy used. (ii) In a part of the spectra, fine structures were smeared out probably due to sample degradation by air exposure or due to charging effect. In the present study, we report the whole valence UPS spectra using synchrotron radiation for a series of polysilanes, polygermanes, Si-Ge copolymers and reti-butyloctasilacubane prepared in air-free condition, with fine details lacking in the previous report[3]. By the comparison of the observed spectra with the spectra of the constituent parts, the whole valence electronic structure is discussed. 2.EXPERIMENTAL The WS spectra were measured by using angle-resolved UPS system at the beamline 8B2 of UVSOR at IMS[6]. All the sample were synthesized at NIT. The sample films were prepared by spin-coating of 0.4 weight % toluene solution of each compounds onto Cu substrates in a glove bag under nitrogen gas flow. These films were transferred into the vacuum chamber without exposure to air, evacuated and measured. 3.RESULTS AND DISCUSSION Polyalkylsilanes The UPS spectrum (hv=40eV) of poly(methylpropylsilane) (SiMePr), is shown in figure l(a). The abscissa is the binding energy relative to the vacuum level. In order to assign the spectral features, we also show the UPS and XPS spectra of CH4[7,8], C3H8[8,9], and Si4(CH3)10[10] as model compounds of the side group and the Si backbone in fig.(b)-(f). The spectrum has better quality than the reported one [3] and enables detailed analysis of the spectrum. As seen in the figure, the spectrum of (SiMePr), corresponds well to the superposition of those of model compounds. This indicates that the valence electronic structure can be regarded as an overlap of those of the constituent parts, Similar results were obtained for poly(dibutylsilane) and poly(dihexylsilane). It should be noted that the bands from alkyl group does not overlap with those of Si 3p derived states. This result indicates that the states of alkyl side group scarcely contribute to the uppermost valence electronic structure which mainly dominates the various properties of polysilanes. Polyarylsilanes The UPS spectrum of poly(methylphenylsilane),(SiMePh)n is shown in figure 2(a) with the UPS and XPS spectra of Si4(CH3)10[10] , c&[ll] and CH4[7,8] in Iig.2(b)-(e). The spectrum has better quality than the reported one again [3]. Fig.2 shows that all bands of (SiMePh), except those in the uppermost energy region correspond one by one to each band in the spectra of the substituents. Similar result was obtained in 0379~6779/95/$09.50 0 1995 Elsevier Science S.A. All rights reserved SSDI 0379-6779(94)02585-M