Preparation and characterization of ultra-flat single crystal surfaces of Pd(1 1 1) and Au(1 1 1) by an in situ interference optical microscopy Rui Wen a , Abhishek Lahiri a , Mukkannan Alagurajan a , Akiyoshi Kuzume a , Shin-ichiro Kobayashi b , Kingo Itaya a,b,⇑ a World Premier International Research Center, Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Japan b Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, 6-6-04 Aoba, Sendai 980-8579, Japan article info Article history: Received 27 December 2009 Received in revised form 28 May 2010 Accepted 14 June 2010 Available online 19 June 2010 Keywords: Pd(1 1 1) Au(1 1 1) Atomic step Differential interference microscopy (DIM) abstract It is shown that the Pd(1 1 1) and Au(1 1 1) surfaces with wide atomically flat terraces having widths in a range of 2–10 lm can be prepared by annealing in an argon stream. These surfaces were investigated by a laser confocal microscope combined with a differential interference contrast microscope (LCM–DIM). It is remarkable that regularly aligned step lines are clearly discerned in electrolyte solutions. The step lines observed by LCM–DIM are monatomic steps confirmed by scanning tunneling microscopy and atomic force microscopy. It is expected that LCM–DIM is a new powerful in situ method for the investigation of electrochemical reactions with the capability of atomic layer resolution. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Scanning tunneling microscopy (STM) and atomic force micros- copy (AFM) operated at electrode surfaces in electrolyte solutions are well recognized as the premier techniques for structural inves- tigation of electrode/electrolyte interface on the atomic level [1–3]. Although those techniques have been successfully applied to reveal atomic structures of electrode surfaces in solution, observable scan areas are small, typically only a few micrometer square. This limi- tation makes it difficult to understand the overall aspect of electro- chemical reactions taking place in the entire area of a real electrode surface. Furthermore, probes such as the tunneling tip in STM and the cantilever in AFM measurements may interfere with electro- chemical processes. It is evident particularly in the case of electro- deposition that the tunneling tip disturbs the deposition and diffusion processes of metal ions [4–6]. Although the conventional optical interference microscope has been widely employed to observe steps, Sazaki’s group reported for the first time that the elementary growth steps (5.6 nm in height) on the {1 1 0} surfaces of a tetragonal lysozyme crystal in aqueous solutions can be seen by a laser confocal microscope combined with a differential interference contrast microscope (LCM–DIM) [7,8]. We have long been interested in developing an optical microscopic technique for the evaluation of electrochemical reactions on an atomic level, because of the fact that the observa- ble area is very large (more than 100 lm square) compared with that of STM and AFM. It is also noteworthy that the acquisition time of each image in LCM–DIM is very short, typically a few sec- ond [7,8], compared with those in STM and AFM. However, for the purpose of observing monatomic steps on me- tal surfaces in electrochemical environment, the vertical resolution must be increased by an order of magnitude, because the height of monatomic steps of commonly interested metals is less than 0.3 nm. We have recently demonstrated that monatomic steps with a height of 0.25 nm on ultra-flat Au(1 1 1) surfaces are clearly discerned in electrolyte solutions and the anodic dissolution of Au in an acid solution containing chloride ions can be followed by our LCM–DIM [9,10]. Such results prompted us to try to prepare ultra-flat Pd(1 1 1) surfaces. We have previously reported that the anodic dissolution at iodine modified-Pd(1 1 1) occurs exclusively at step edges in a layer-by-layer sequence without deterioration of the iodine adlat- tice structure [11,12]. It is important to note that a very flat Pd sur- faces having terrace widths greater than several micrometers is needed for the evaluation of the anodic dissolution, because the lateral resolution of the LCM–DIM method is limited by the wave-length of light as in the conventional optical microscopy. In this paper, therefore, we describe the surface structures of Pd(1 1 1) and Au(1 1 1) after annealing in a furnace in a tempera- ture range of 800–1200 °C for several hours under purified argon atmosphere in order to increase the terrace width. It is shown that 1572-6657/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2010.06.009 ⇑ Corresponding author at: Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, 6-6-04 Aoba, Sendai 980-8579, Japan. Fax: +81 22 21 214 5380. E-mail address: itaya@atom.che.tohoku.ac.jp (K. Itaya). Journal of Electroanalytical Chemistry 649 (2010) 257–260 Contents lists available at ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem