Mass Spectrometry Analysis of Organic-Inorganic Nanomaterials and their Precursors
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Mass Spectrometry Analysis of Organic-Inorganic Nanomaterials and their Precursors Jean-Jacques Gaumet1 and Geoffrey Strouse2 1 LSMCL, Metz University, IPEM, Technopôle 2000, 57078 Metz Cedex 03, FRANCE 2 UCSB, Department of Chemistry, Santa Barbara, CA 93106-9510, U.S.A. ABSTRACT We report in this paper how electrospray mass spectrometry (ESMS) and nanospray mass spectrometry (NMS) are promising for analyzing precursors and nano-scale semiconductor (IIVI) materials up to 1.5 nm and mixed valence clusters (Co/Cd). We show that both ion modes in ESMS and NMS provide insight concerning the structure analysis, the composition and the stability of these materials. INTRODUCTION The study of nanometer sized crystallites provides an opportunity to observe the evolution of material properties depending on their size. Concerning semiconductors, this evolution is easily noticeable. II/VI compound semiconductors have been a favorite subject for such studies because of the evolution of their electronic properties during the consolidation process. As a result, these compounds are of considerable interest and have been studied extensively due to their potential applications in future technology [1-4]. These materials can be prepared in the form of dispersed colloids or trapped and stabilized within micelles, polymers, zeolites or glasses. An other major pathway for building nanomaterials is the synthesis of singlesized (monodisperse) clusters with well defined surfaces. The growth of the II-VI clusters is analogous to the growth of a polymer chain as long as the surfaces are not covered by a terminating agent. The process involves precipitation of a semiconductor in the presence of a capping species, such as thiols, or growth of larger clusters from molecular precursors which already incorporate the capping ligands [5-7]. Current methods have centered on physical methods, such as NMR, TEM, X-ray diffraction, XPS, UV/Visible, Infrared, Raman and photoluminescence spectroscopies. All these analytical tools are excellent for average analysis of a cluster or a nanomaterial. However, with these techniques, specific distributions in the composition and structure of individual nanomaterials are not addressed. The use of soft ionization mass spectrometry techniques, such as electrospray (ESMS) is an alternative way to better understand their composition, size, surface and stability when analyzing nanoparticles that are often generated from organometallic precursors. We report in this paper the analyses of one CdS precursor and one nanosized material (1.5 nm diameter) using nanospray mass spectrometry. Then, we will show the potential ESMS has as an analytical tool to better understand the structure of mixed valence nanoclusters containing Co(II)/Co(III) and cadmium atoms. EXPERIMENTAL DETAILS The cadmium thiophenolate clusters [(CH3)4N]2[Cd4(SPh)10], [(CH3)4N]4[S4Cd10(SPh)16] and [S14Cd32(SPh)36.DMF4] (Ph = C6H5, DMF = dimethylformamide) named in the paper as Cd4, Cd10 and Cd32 (see its structure in figure 1), respectively, were prepared
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