Structural and nanomechanical properties of a zeolite membrane measured using nanoindentation C.A. Charitidis a, ⁎, E.P. Koumoulos a , V. Nikolakis b, c , D.A. Dragatogiannis a a School of Chemical Engineering, Department of Materials, Science and Engineering, National Technical University of Athens, Zografou Campus, 15780 Athens, Greece b Foundation for Research and Technology Hellas, Institute of Chemical Engineering Sciences, P.O. Box 1414, GR-26504 Patras, Greece c Catalysis Center for Energy Innovation, Department of Chemical & Biomolecular Engineering, University of Delaware, Newark DE19716, USA abstract article info Article history: Received 27 October 2011 Received in revised form 15 October 2012 Accepted 16 October 2012 Available online 23 October 2012 Keywords: Nanoindentation Zeolite membrane Hardness Modulus Creep Deformation Pile-up/sink-in Knowledge of the elastic constants of zeolite films is of great practical interest, due to its main applications. The structural and nanomechanical properties of a faujasite-type zeolite film have been measured using nanoindentation. The hardness and elastic moduli of the film are estimated from creep and non-creep nanoindentation measurements. The deformation mechanism was analyzed using a pile-up/sink-in analysis, revealing a switch of dominant deformation mechanism at ~250 nm of displacement. Wear analysis (hardness to elastic modulus ratio) provided information about the structural integrity and mechanical reliability of the film. Hardness and elastic modulus values were found to decrease with increasing penetration depth. In particular, the elastic modulus decreased from ~60 GPa (at displacement of 20–30 nm) to ~7 GPa (at displacement of 200 nm), and the hardness from ~8 GPa (at displacement of 20–30 nm) to ~0.8 GPa (at displacement of 500 nm). © 2012 Elsevier B.V. All rights reserved. 1. Introduction Zeolites are crystalline, microporous materials that are formed by corner linked aluminosilicate tetrahedral frameworks. They have channel and cages with dimensions similar to those of several indus- trially important molecules. As a result they are widely used in catal- ysis, in ion exchange and in gas separations. Zeolites are also used as cracking catalysts and water softening additives for detergents. Dur- ing the last decades, there has been an increasing interest in develop- ing novel zeolite based applications. Most efforts focused on the synthesis of permselective zeolite membranes for the separation of gas or liquid mixtures [1–4]. However, there has been a considerable amount of work toward the development of other types of applica- tions such as modified electrodes [5], optical devices [6], films of low dielectric constant for the replacement of dense silica in the semi- conductor industry [7] and gas sensors [8]. A solid knowledge of the zeolite crystal and film mechanical properties would be of great help in the design of engineering applications (especially in the case of permselective membranes, gas sensors, and low dielectric constant films) [7,9,10] as well as for the performance improvements in tradi- tional zeolite based applications (i.e., zeolite catalysts) [11–13]. For example, several recent publications in the field of zeolite membranes have mentioned that the enhancement or loss of the membrane permselective performance might be attributed to changes of the zeo- lite polycrystalline film mechanical properties as a result of the adsorp- tion of gas or vapor molecules [14,15]. Finally, a prerequisite for the utilization of zeolite layers as low dielectric constant films in the semi- conductor industry is their ability to withstand the chemical and me- chanical conditions encountered during the fabrication processes [7]. Thus, knowledge of the elastic constants of zeolite films is of great prac- tical interest. The knowledge of the mechanical properties of zeolites is scarce [7,9,11–13,16–20] mainly because of the difficulty of measuring these properties [12]. The elastic modulus (frequently also referred as Young modulus) of zeolites can be measured using either mechan- ical (nanoindentation, microdeformation, or three point bending) [11–13,19–21] or spectroscopic methods (Brilllouin or Synchrotron X-ray spectroscopy) [10,18,22]. Unfortunately, the mechanical methods often require samples having sizes of at least several millimeters that are much larger than the usual maximum size of the synthetic zeolite crystals (100–200 μm). In the case of spectroscopic techniques, the experimental procedures and the analysis of the data are rather complicated. Wang et al. [21,23] measured the Young's modulus of a ~200 μm Zeolite Socony Mobil (ZSM)-5, (structure type MFI — mordenite framework inverted) zeolite single crystal using a homemade microdeformation tester. Lin et al. [12,24] measured the hardness (H) and elastic modulus (E) of zeolites (ferrierite (FER) and sodalite (SOD)) of smaller sizes than ZSM-5 by nanoindentation experiments. Thin Solid Films 526 (2012) 168–175 ⁎ Corresponding author. E-mail address: charitidis@chemeng.ntua.gr (C.A. Charitidis). 0040-6090/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.tsf.2012.10.021 Contents lists available at SciVerse ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf