FTIR Spectrometry as a Quality Control Method for Surface Engineering of Nanomaterials
- PDF / 92,935 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 97 Downloads / 183 Views
FTIR SPECTROMETRY AS A QUALITY CONTROL METHOD FOR SURFACE ENGINEERING OF NANOMATERIALS Marie-Isabelle BARATON SPCTS – UMR 6638 CNRS, University of Limoges, Limoges (France) e-mail: [email protected]
ABSTRACT Controlled surface engineering of nanopowders cannot be achieved without a specific characterization of the surface chemical groups and the monitoring of the reactions or interactions responsible for the surface modifications. As an example of controlled engineering of nanopowder surfaces, the surface of tin oxide nanoparticles (n-SnO2) is modified by grafting hexamethyldisilazane (HMDS) while the process leading to chemical and electrical modifications of n-SnO2 is monitored in situ by Fourier transform infrared spectrometry. It appears that the effects of the grafting reaction on the surface chemical composition are complex and that a desorption at increasing temperatures leads to strong perturbations of the chemical groups originally grafted on n-SnO2. The present work clarifies the issues related to surface engineering of nanomaterials and elucidates the case of HMDS-grafted n-SnO2. INTRODUCTION For a long time, scientists have modified surface properties of materials by adsorbing organic molecules onto their surfaces. Surface modification is indeed a very important issue which is actually at the basis of many new research topics. As non-exhaustive examples of the potentiality of surface modifications, one can quote: - self-assembly of particles (eventually nanoparticles) in a controlled way; - tailoring of surface chemistry and surface reactivity for improving material properties, such as catalysts or gas sensors; - reduction of agglomeration for optimized dispersion of nanoparticles in polymers or liquid matrices. In all these cases, the basic principle is to provoke a reaction or an interaction between an organic or organometallic molecule and the particle surface, thus creating a link of variable strength. To design and control these possible reactions or interactions, the first step is the identification of chemical groups that are present on the material surface. If the material has been kept under ultrahigh vacuum since its very first existence, the surface can be considered as “clean”, that is the first atomic layer of the material is free from foreign atoms [1]. On the contrary, if the material is exposed to regular atmosphere, the fast contamination by the atmosphere contents results in the introduction of foreign atoms in the surface layer and, therefore, in different kinds of surface chemical groups. As a consequence, it is obvious that reproducible and controlled surface modifications must begin with the control of the chemical species on the material surface. This requirement becomes critical for the processing of nanoparticles due to their high surface-to-bulk ratio. Once these surface species are identified, it is possible to foresee the reactions which can occur and eventually select the most relevant D8.1.1
molecules to graft for a given application. But, to totally control the process,