• PDF / 1,494,954 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 14 Downloads / 193 Views

DOWNLOAD

REPORT

---

The Novel Synthesis of Silicon and Germanium Nanocrystallites Susan M. Kauzlarich, Qi Liu, Shih-Chieh Yin, Howard W. H. Lee1, and Boyd Taylor1 Department of Chemistry University of California at Davis One Shields Ave Davis, CA 95616, U.S.A. 1 Lawrence Livermore National Laboratory P. O. Box 808 Mail Stop L-174 Livermore, CA 94551 ABSTRACT Interest in the synthesis of semiconductor nanoparticles has been generated by their unusual optical and electronic properties arising from quantum confinement effects. We have synthesized silicon and germanium nanoclusters by reacting Zintl phase precursors with either silicon or germanium tetrachloride in various solvents. Strategies have been investigated to stabilize the surface, including reactions with RLi and MgBrR (R = alkyl). This synthetic method produces group IV nanocrystals with passivated surfaces. These nanoparticle emit over a very large range in the visible region. These particles have been characterized using HRTEM, FTIR, UV-Vis, solid state NMR, and fluorescence. The synthesis and characterization of these nanoclusters will be presented. INTRODUCTION There is currently a great deal of interest in exploring the synthesis and characterization of nanocrystalline Si and Ge. Visible emission has been observed from porous Si and Si nanocrystal produced by a variety of techniques including solution [1-6], gas phase decomposition of silanes [7-12], and thermal vaporization of silicon [13]. In all cases presented above, there is little size control during the synthesis step of any of the processes other than what can be achieved by changes in the initial reactant concentrations and the length of time over which agglomeration is allowed to take place. This results in a comparatively wide size distribution that can be greatly narrowed through use of size-selective precipitation. This group has been interested in exploring the solution chemistry route.[14-19] This work demonstrated that both silicon and germanium nanoclusters with functionalized surfaces can be formed in solution at low temperatures and ambient pressures. This approach to form nanocrystalline silicon or germanium utilizes the high reactivity of metal silicides with either silicon or germanium tetrachloride to form chloride capped group IV nanocluster. Subsequent reaction of this product with either RLi or RMgCl (R = –methyl, –ethyl, –butyl, and –octyl) terminates the particles with alkyl groups forming R capped nanocluster. This work provides the groundwork for an exciting new area of research, exploring the surface functionalization of Si and Ge nanoclusters: the next generation nanoparticles. F6.5.1

EXPERIMENTAL The synthesis of KSi, Mg2Si and Mg2Ge has been published previously [14, 1719]. The nanoclusters were prepare by reacting the metal silicide or germinide with the respective tetrachloride in excess, in ethylene glycol dimethyl ether (glyme) or dimethylene glycol dimethyl ether (diglyme) solvent under anerobic conditions. The reaction mixture was heated to reflux overnight and then cooled to room