short communications 446 doi:10.1107/S0909049507029809 J. Synchrotron Rad. (2007). 14, 446–448 Journal of Synchrotron Radiation ISSN 0909-0495 Received 24 November 2006 Accepted 18 June 2007 # 2007 International Union of Crystallography Printed in Singapore – all rights reserved In situ synchrotron far-infrared spectromicroscopy of a copper electrode at grazing incidence angle F. Hahn, a Y.-L. Mathis, b A. Bonnefont, c F. Maillard d and C. A. Melendres e * a UMR 6503, CNRS, Universite ´ de Poitiers, 40 avenue du Recteur Pineau, F-86022 Poitiers, France, b Synchrotron Light Source ANKA/Institute for Synchrotron Radiation (ISS), Forschungszentrum Karlsruhe, PO Box 3640, D-76021 Karlsruhe, Germany, c Laboratoire d’Electrochimie et de Chimie Physique du Corps Solide, UMR 7177, CNRS/ULP, 4 rue Blaise Pascal, BP 1032, F-67070 Strasbourg, France, d Laboratoire d’Electrochimie et de Physico-chimie des Mate ´riaux et des Interfaces, UMR 5631 CNRS/INPG/UJF, 1130 rue de la Piscine, BP 75, F-38402 Saint Martin d’He `res, France, and e The SHD Institute, 216 F Street, PMB 114, Davis, CA 95616, USA. E-mail: camelendres@shdinstitute.org Synchrotron far-infrared spectroscopy in situ was successfully carried out on a copper microelectrode using a grazing-angle objective attached to a Bruker IRscope II microscope. The thin-layer spectroelectrochemical cell was constructed out of Teflon and fitted with a 20 mm-thick Mylar window; the copper electrode was 500 mm in diameter. Measurements were carried out in 0.1 M NaOH solution as a function of applied potential between 1.4 and 0 V versus a Hg/Hg 2 SO 4 reference electrode. Results demonstrate that with the present technique it is possible to obtain in situ spectra with excellent signal-to- noise ratio for surface oxide films formed electrochemically with less than 1 nL of active solution volume. The surface film on copper at 0 V consisted mainly of CuO with possibly some Cu(OH) 2 also present. This interpretation is consistent with previous works and thermodynamic calculations. Keywords: far-infrared spectromicroscopy; electrochemistry; oxide film on copper. 1. Introduction Synchrotrons provide a novel source of well collimated infrared (IR) radiation which is about a thousand times brighter than conventional laboratory globar sources (Melendres & Tadjeddine, 1994). This increase in intensity has opened up new opportunities for investi- gating classic problems in various areas of science and technology. In interfacial electrochemistry, for example, the in situ measurements of low-frequency vibrations in the far IR for surface oxide films on copper (Melendres et al. , 1998) and halide (Melendres & Hahn, 1999) as well as oxyanions (Melendres et al. , 2000) adsorbed on gold elec- trode surfaces have been demonstrated and are now possible, despite the strong attenuation of the IR beam by interfacial water. The first experiments (Melendres et al. , 1998) made use of a conventional copper rod electrode using a silicon window; the second set (Melendres & Hahn, 1999; Melendres et al. , 2000) involved a gold film vacuum evaporated on a silicon hemicylinder as electrode using the attenuated total reflection technique. The finely focused synchrotron beam is particularly well suited for the study of small particles and areas. Advantage of this has been made use of in IR microscopy (Dumas & Tobin, 2003). We have explored the use of the technique of IR spectromicroscopy for the investigations of microelectrodes. We report here our results on the identification of the oxide film on copper in situ in an aqueous solution environment using an IR microscope fitted with a grazing- angle objective (Bruker Hyperion 2000 IR microscope). We believe that this is the first time the experiment has been successfully carried out and will open new applications in other fields of interface science and technology. Microelectrodes have found extensive use in electrochemistry (Montenegro et al. , 1991) owing to a number of advantages, e.g. they allow the use of very small amounts of solution (thin layers, small volume), the measurement of fast electrode processes, and electro- chemical studies in very dilute electrolyte and highly resistive solu- tions (including organic solvents). We envisage the use of IR spectromicroscopy with solutions so thin and approaching monolayer amounts of material to study adsorbed molecules under the influence of an applied electrical potential. This form of ‘electrochemical surface science’ could bridge the gap between UHV surface science and conventional electrochemistry. We have already carried out far-IR synchrotron spectromicroscopy of a Pt microelectrode in perchloric acid solution and initial results have been presented (Hahn & Melendres, 2005). The IR detection of very thin layers of materials (e.g. oxide film, adsorbed molecules, ions) can be carried out with highest sensitivity at glancing angles of incidence (approaching 90  with respect to the surface normal) and using p-polarized radiation (the plane of polarization of the incident radiation being perpendi- cular to the electrode surface). With the micrometer-size synchrotron IR beam, the use of a grazing-angle objective (GAO), attached to a microscope, allows high angles of incidence (75–85  ) to be achieved. In situ spectromicroscopic measurements in an electro- chemical cell are rather difficult because of the very short working distance between the objective and the electrode surface (less than 1 mm), the presence of solution, and the need to use an IR window of suitable material for the cell. We have constructed a suitable thin-layer spectromicroelectrochemical cell made of Teflon and have successfully carried out measurements to identify the