Novel catalysts: Indium implanted SiO2 thin films
Introduction
Indium (In) has been of much interest in various research fields such as semiconductor technologies and catalytic applications [1], [2], [3]. Recently it has been pointed out that interaction between In and silicon (Si) shows high catalytic ability [1], [2]. However, it is difficult for a conventional chemical method to synthesize such catalyzers. In this study, we use a more “physical” approach to prepare materials that contain both In and Si atoms in close proximity as potential candidates for catalyzers, i.e., In implantation into a Si containing material by ion beam injection.
In conventional experiments of In ion beam injection [4], [5], [6], the solid-state In is heated to produce liquid or gaseous In atoms and then In ions are produced [7]. However, in this study, we modified a Freeman-type ion source so that a solid-state material can be set inside the ion source chamber as a sputtering target. In this experiment, we used In2O3 as the target in the ion source. The melting temperature of In2O3 is much higher than that of In metal. In the ion source, In ions can be obtained from sputtering of the In2O3 target by Ar ions generated from an Ar plasma. In ions thus obtained were injected into a SiO2 thin film that had been formed thermally on a Si substrate (SiO2/Si substrate). The typical thickness of the SiO2 layer used in this study is 0.1 μm.
After In implanted SiO2/Si substrates were prepared under different implantation conditions, we analyzed the substrate surfaces by X-ray diffraction (XRD) and atomic force microscopy (AFM). Catalytic abilities of the In implanted SiO2/Si substrates were also examined for a particular organic chemical reaction.
Section snippets
Experimental setup
The In ion production experiment was carried out in a low-energy mass-selected ion beam system. The system consists of an ion source, an extractor electrode, a mass selector, a decelerator, and a process chamber [8]. The configuration of the Freeman-type hybrid ion source was shown in Fig. 1, Fig. 2 of Ref. [9]. In this experiment, an In2O3 target was set in the ion source as a sputtering target. The procedure of In ion beam production is as follows: The arc chamber (25.4 mm in diameter, 50.8 mm
Preparation of In implanted SiO2 thin films
By changing the electric current to generate the magnetic field of the mass selector, the mass spectrum of ions extracted from the ion source was measured by a Faraday cup installed just after the mass selector. Fig. 1 shows the dependence of ion beam intensity (i.e., Faraday cup current) on the mass selector current. In Fig. 1, several ion peaks are seen. The mass numbers of some peaks were identified by the mass-energy analyzer PPM-421. It was found that N+, O+, Ar2+, Ar+, In+, and W+ ions
Conclusions
We have used In ion beam injection into a SiO2 thin film to create a material that has both In and Si in close proximity, which exhibits a catalytic effect on an organic chemical reaction. It has been known that a Si compound/Indium catalyst system shows strong catalytic effects on various organic chemical reactions. With the use of conventional chemical reactions, it is known to be difficult to synthesize single-molecule catalysts containing both Si and In. By the ion injection method, In can
Acknowledgments
The work is partially supported by a Grant-in-Aid for Scientific Research from Ministry of Education, Culture, Sports, Science and Technology (MEXT) Japan. The authors would like to thank Messrs. K. Ikuse and Y. Tsukazaki for their assistance in the ion beam experiments.
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