Power of Mass Spectrometry for Analyzing Organometallic Molecules as Precursor of Nanomaterials
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Department of Chemistry, UCSB, Santa Barbara, CA 93106-9510, [email protected] LSMCL, Universit6 de Metz, IPC, I bd Arago, 57078 Metz Cedex 03 France, gaumet @lsnicl.sciences.univ-metz.fi
ABSTRACT A mass spectrometry method (Electrospray Mass Spectrometry [ESMS]) for analyzing organometallic precursors of nano-materials is described. We show that application of lowcone voltage ESMS is a useful technique for the rapid analysis of intact organometallic precursor molecules when both positive and negative ionic modes are analyzed. This method shows promise for extrapolation to analysis of the dynamics of growth in nano-scale materials. INTRODUCTION The development of nanoscale science has arisen from the observation of fascinating size dependent optical and electronic properties of these materials [1, 2]. Nanoparticles represent a boundary where a gradual transition from solid-state to molecular properties occurs as the particle size decreases [3, 4]. Such compounds are a class of materials whose properties are amenable to chemical tuning by manipulating particle size, cristallinity, dopant level, and surface tuning via ligand capping. Development of technology for analysis of such materials has centered on traditional solid state methods requiring efficient isolation of the samples after their syntheses. While TEM, X-ray diffraction, UV/Visible and IR spectroscopies, photoluminescence, Raman spectroscopy and TGA techniques are excellent tools for structure analysis. they do not specifically address the compositional integrity of the materials in an -on-line >> fashion required for process control. Consequently, a significant disadvantage
arises due to the inability to probe the real-time dynamics of nanomaterial growth. An alternative pathway for real time analysis of particle size and composition is the
application of mass spectrometry. More specially, we present herein the results from a soft mass spectrometry technique: the Electrospray Mass Spectrometry (ESMS). The main advantage of ESMS over other mass spectrometry techniques is the capabilities for direct analyses of mixtures and solvated molecules. ESMS ionization methods have been largely applied to molecules in biochemistry which due to their chemical composition and their bonding are susceptible to damage [5, 6]. We present in this paper the analysis of chalcogenide cadmium clusters of discrete size by positive and negative ion mode ESMS under lows-cone voltage. Such ionic mode allows a small fragmentation and the observation of the parent ion [7-8]. The first study illustrates how ESMS allows differentiation of the physical properties of the precursor molecules arising from variability of the chalcogenide core and the surface capping of the cluster (S or Se). The second study illustrates the application of ESMS to the analysis of a binary metal chalcogenide nano-material precursor (Cd-Co). Analysis of the mass spectra for such materials provides insight into the applicability of ESMS methods to structure analysis, composition and stability of nano-se
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