Laser Ionization Time of Flight Mass Spectrometry Study of Silicon Oxycarbide Glasses Gian Domenico Soraru, §, * ,† Aylin Karakuscu, §,‡ Amy Marquardt, ¶ Landon Tweeton, ¶ Prabesh Dulal, ¶ and Mario Affatigato ¶, * § Dipartimento di Ingegneria dei Materiali e Tecnologie Industriali, Universita` di Trento, Via Mesiano 77, Trento 38123, Italy ¶ Department of Physics, Coe College, Cedar Rapids, Iowa For the first time, a laser ionization time of flight mass spec- trometry (LI-TOFS) characterization has been performed on silicon oxycarbide glasses obtained by pyrolysis of sol–gel precursors. This technique allows to desorb intermediate range mesounits from the network, and to determine their mass and atomic identity precisely. It is therefore complementary to all the other analysis typically performed on SiOC glasses as it leads to collect information on a length scale which is usually difficult to probe: the medium range. The results indicate the presence, in the SiOC glasses, of mixed silicon oxycarbide units together with pure silicate mesounits (SiO 2 and SiO 3 ). I. Introduction S ILICON oxycarbide glasses have been known for more than 35 years 1 and they are still gathering a great deal of interest due to their very peculiar properties. They are much more resistant to crystallization compared with silica glass and remain predominantly amorphous above 1400°C where fused silica shows the maximum crystallization rate, 2 viscos- ity of SiOCs is from two to three order of magnitude higher than silica glass 2 and shows an unusual visco(an)elastic behavior at very high temperatures. 3 More recently, func- tional properties have been discovered in SiOCs: intense white luminescence, 4 high piezoresistivity, 5 and high capacity for Li storage which makes them suitable candidates for substituting graphite as anode materials in Li-ion batteries. 6 With the aim of relating the unusual behavior of these novel amorphous solids to their structure, silicon oxycarbides have been investigated with several techniques over the last three decades. Information on the short-range order of the amor- phous network has been attained from solid-state nuclear magnetic resonance spectroscopy (SS NMR), mainly of 29 Si and 13 C, and the bonding between Si, C, and O atoms has been studied by X-ray photoelectron spectroscopy (XPS). Details on the long-range order and on the nanostructural features were revealed by XRD and HR-TEM. Finally, Raman spectroscopy has been employed to characterize the sp 2 C phase, also known as “free C phase”, which is usually present in silicon oxycarbide glasses. Comprehensive struc- tural characterization studies of SiOCs are available in the literature. 2,7–9 Accordingly, at low pyrolysis temperature (~1000°C), silicon oxycarbides are completely amorphous and consist of a network of Si-O and Si-C bonds with C-C and aromatic C structures. In particular, Si atoms are present in mixed silicon oxycarbide units SiC x O 4x 0  x  4. At higher temperature from 1200°C up to 1500°C, the amor- phous network undergoes a structural rearrangement into mainly SiO 4 and SiC 4 units, the latter forming nanocrystal- line cubic SiC (1–3 nm in size). The network reorganization also results into the formation of nanocrystalline graphite as seen by Raman spectroscopy. All these information have been used to propose a nanostructural model for silicon oxycarbide glasses pyrolyzed above ~1200°C consisting of two interpenetrating nano-sized networks, one rich in silica and the other one formed by the sp 2 C layers and the SiC nanocrystals with mixed silicon oxycarbide units located at the interface between the two networks. 10,11 Even though this model can explain many of the unusual properties measured for the silicon oxycarbide glasses, several structural issues are still open and studies on the structure of these novel materi- als are still in progress. 12 In this work, we decided to perform a laser ionization time of flight spectrometry (LI-TOFS) characterization of silicon oxycarbide glasses. This technique is complementary with all the other analysis previously performed on SiOC glasses as it allows to collect information on a length scale which is usu- ally difficult to probe: the medium range. Indeed, with LI-TOFS it is possible to desorb intermediate range mesounits from the network, and determine their mass and atomic identity precisely. 13–15 The samples we have chosen for this inves- tigation belong to the family of sol–gel-derived silicon oxy- carbide glasses with low carbon content. These particular glasses have been previously extensively characterized in our laboratory with more standard techniques and this informa- tion will help in discussing of the LI-TOFS data. II. Experimental Procedures The Si alkoxides were purchased from ABCR (Karlsruhe, Germany) and used as-received. Gel samples were synthesized as described in detail previously. 16 The sol–gel solution was prepared dissolving triethoxysilane (TH) and methyldiethox- ysilane (DH) in ethanol with a TH:DH = 2M ratio. Hydrolysis was performed with a HCl solution at pH = 4.5 and a molar ratio H 2 O/OEt = 1. After water addition, the solution was stir- red for 20 min and then cast in test tubes for gelation. Wet gels were dried to form xerogels which were subsequently pyro- lyzed in Ar flow up to 800°C, 1200°C, and 1400°C to form the silicon oxycarbide glass. Xerogel fragments were heated at 5° C/min up to the maximum temperature and maintained for 1 h before cooling down. These samples provide a nearly stoi- chiometric silicon oxycarbide glass 7 which, being pyrolyzed at different temperatures from 800°C to 1400°C, allows studying H.-J. Kleebe—contributing editor Manuscript No. 31847. Received August 1, 2012; approved September 28, 2012. *Member, The American Ceramic Society. ‡ Present address: Sensor Lab, University of Brescia and CNR-IDASC, Brescia I- 25133, Italy. † Author to whom correspondence should be addressed. e-mail: soraru@ing.unitn.it 3729 J. Am. Ceram. Soc., 95 [12] 3729–3731 (2012) DOI: 10.1111/jace.12058 © 2012 The American Ceramic Society J ournal Rapid Communication