Atomic force microscopy (AFM) and scanning tunnel microscopy (STM) observations have been performed on the surfaces of a hydrotalcite (HT) crystal (Mg6Al2(OH)(16)(CO3)(1/2). Cl . 2H(2)O) and HT crystals ion-exchanged with Fe(CN)(6)(3-) and Fe(CN)(6)(4-) (denoted by HT-Fe(CN)(6)(3-) and HT-Fe(CN)(6)(4-), respectively). The AFM image of a HT crystal surface in contact with an aqueous solution of 0.1 M Na2SO4 shows two-dimensional periodicity with the unit lattice of a = 0.31 +/- 0.02 nm, b = 0.31 +/- 0.02 nm, and alpha = 58 +/- 3 degrees. This corresponds to the lattice made by the external hydroxyl groups on a basal plane. No ion exchanged anion was observed by the AFM method, indicating that an external anion is so weakly bound to a surface that it is removed under the scanning operation of an AFM tip. The STM image of the same crystal under air shows a two-dimensional lattice with a = 0.75 +/- 0.04 nm, b = 1.10 +/- 0.03 nm, and alpha = 70 +/- 3 degrees. One bright spot in the image exists at every 1.1 Mg6Al2(OH)(16)(2+) unit, leading to the conclusion that the spot represents a chloride ion adsorbed on a surface. The STM image of the same crystal at less negative bias voltage exhibits a different two-dimensional lattice with a = 0.62 +/- 0.03 nm, b = 0.62 +/- 0.03 nm, and alpha = 65 +/- 3 degrees. This is ascribed to the lattice made by the aluminum atoms at the octahedral sites inside a layer. The STM images of HT-Fe(CN)(6)(3-) and HT-Fe(CN)(6)(4-) crystals in contact with an aqueous solution of 0.1 M Na2SO4 show the two-dimensional lattices of a = 1.43 +/- 0.06 nm, b = 1.86 +/- 0.06 nm, and alpha = 90 +/- 4 degrees and a = 2.20 +/- 0.06 nm, b = 2.20 +/- 0.06 nm, and alpha = 75 +/- 3 degrees, respectively. These are ascribed to the molecular layers of Fe(CN)(6)(3-) and Fe(CN)(6)(4-) on a surface, respectively. The causes for the ordered molecular adsorption are discussed. References: 14
展开▼
