Molecular Orientation in Vacuum-Deposited Peralkyloligosilane Thin Films

Abstract

Linear oligosilanes (R(SiR2)10R), permethyldecasilane (R = CH3), and perpropyldecasilane (R = C3H7), were vacuum-deposited onto quartz substrates under various conditions. Molecular orientation in the deposited thin films was investigated by X-ray diffractometry and absorption spectroscopy with a varying incident angle to the substrate. Two types of highly ordered multilayered structures, one with molecular orientation normal to the substrate and the other with oblique orientation, were observed in the permethyldecasilane thin films deposited at room temperature. When deposited at −150 °C, on the other hand, the molecular orientation was largely normal to the substrates but the multilayered structure was hardly formed. For perpropyldecasilane thin films, an interdigitated structure with molecular orientation normal to the substrate was found when deposited at and above room temperatures.

Annealing-Induced Molecular Reorientation in Oligosilane Thin Films

“…Absorption spectra collected above 340 K with every 10 K step are shown in Figure . Prior to the annealing study, we confirmed that the absorption spectrum of the vacuum-deposited MS10 thin film hardly depended on the temperature from 15 to 340 K. This result is presumably explained in terms of the well-organized multilayered structure, in which the molecules were tightly packed and, hence, their conformation as well as their alignment was fixed below 340 K. The spectral profile slightly changed when heated to 350 K, because of the increase of the absorbance around 300 nm.

1 Absorption spectra of the vacuum-deposited MS10 thin film at elevated temperatures from 340 to 370 K and at 320 K after annealing.

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“…Figure exhibits an intense series of diffraction peaks labeled with 00 l ( l = 1−5), indicating the highly ordered multilayered structure with an interlayer spacing of 20.9 Å. Very recently, we have proposed normal molecular orientation in such multilayered structure on the basis of the comparison between the interlayer spacing and the molecular length with all-trans conformation . After annealing, another peak series labeled with 00 l ‘ ( l ‘ = 1−6) appeared, corresponding to another multilayered structure with an interlayer spacing of 18.5 Å.…”

“…In the case of temperatures above 340 K, we kept each temperature for an hour before each measurement to allow sufficient time for molecular reorientation. For detailed studies of the molecular orientations before and after annealing, p -polarized, varying-incident-angle absorption spectra with the spectral resolution of 2 nm were collected at room temperature using an experimental configuration described elsewhere . XRD measurements in the θ−2θ reflection mode were performed at room temperature for both as-deposited and annealed films using a Rigaku RU-300 diffractometer with Cu Kα (λ = 1.542 Å) source.…”

“…To date, molecular orientations have been investigated for vacuum-deposited thin films of permethyloligosilanes, R(Si(CH 3 ) 2 ) n R ( n = 10 and 12), where R is methyl 12,14,15 or phenyl, and perpropyldecasilane . Highly ordered multilayered structures were observed for oligosilanes with methyl end groups. ,, For oligosilanes with phenyl or propyl end groups, on the other hand, interdigitated structures with molecular orientation normal to the substrates were found. , …”

Suppression Mechanism of the Photodegradation of J-Aggregate Thin Films of Cyanine Dyes by Coating with Polysilanes

“…Nakayama et al reported that the oriented polysilane film shows higher hole transport ability than the nonoriented one . The main chain of the PDMS molecule was reported to be oriented vertically to the substrate thin film prepared by the vacuum deposition on a quartz plate. − To confirm molecular orientation of PDMS in the composite film, the absorption spectra of J O−H−Cl /PDMS composite film were measured at the angle θ of 0° and 50°, where θ is the angle between the normal to the substrate and irradiation direction (Figure a). At θ of 50°, the absorption band due to the σ−σ* transition of the main chain was observed at 295 nm.…”