Surface Derivatization of Amorphous Silicon by Grignard Reagents
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Surface Derivatization of Amorphous Silicon by Grignard Reagents
Takashi Ehara* and Arata Maruyama School of Science and Engineering, Ishinomaki Senshu University, 1 Shinmito, Minamisakai, Ishinomaki, Miyagi 986-8580, Japan
ABSTRACT Substitution reactions of surface hydrogen in amorphous silicon at room temperature have been studied. After wet treatment of hydrogenated amorphous silicon thin films with Grignard reagent, surface hydrogen atoms have been substituted by organic groups. Wet treatment of amorphous silicon thin films in CH3(CH2)9-MgBr ether solution followed by quenching by diluted HCl changes infrared absorption spectra. After the treatment, new three peaks of C–H have been observed. In addition, the peaks did not disappeared after rising by hydrofluoric acid or various kinds of organic solvent. The spectra indicate that the Grignard reagent is enough reactive to form new covariant bonding of C and Si at the amorphous silicon surface by substitution reaction.
INTRODUCTION Hydrogenated amorphous silicon (a-Si:H) has been recognized as a useful material for solar cells or thin film transistors [1,2]. As the a-Si:H films have been prepared by plasma enhanced chemical vapor deposition (PECVD), the films contain hydrogen atoms to terminate dangling bonds [3]. The termination of dangling bond defects makes possible to use a-Si:H for device by impurity doping [4]. Hydrogen atoms have been also observed in the porous Si [5]. In the case of porous Si, Si-H2 bonds are formed while the anordization of crystalline Si using HF-EtOH mixed solution. Some workers have reported derivatization of the porous Si surface by wet chemical treatments [6-8]. Kim and co-workers used Grignard reagent and achieved substitution of surface hydrogen with alkyl group at room temperature [6]. The reaction does not require low temperature treatment that induces peering off of the films. In the present work, we investigate the surface modification of a-Si:H by chemical reaction using Grignard reagents at room temperature. The effect of surface modification to optical and electrical properties of the a-Si:H will be discussed.
A20.4.1
EXPERIMENTAL DETAILS a-Si:H thin films with thickness of 0.5 µm were prepared by PECVD. The silicon source gas was hydrogen diluted SiH4 (10%) at a feed rate of 50 sccm. Rf power, substrate temperature and deposition pressure were 30W, 370ºC and 133 Pa, respectively. The structure of a-Si:H is confirmed by Raman spectra by a broad peak at 480 cm-1 [8]. We used high resistive Si (100) as the substrate. We also used Corning 7059 glass substrate for measurement of optical absorption and conductivity. The surface modification was carried out by the wet treatment described as follows. 3.0 g of Mg (0.12 mol) was put in a dried 300 ml round flask. Then, a solution of 36.6 g of 1-bromodecane (0.15 mol) in 80 ml of dried diethylether was added dropwise with stirring. The solution of decylmagnesium bromide with 1.2 M of concentration was synthesized and used in the following procedure. Surface derivatization of
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