SCANNING TUNNELING MICROSCOPE SCANNING TUNNELING SPECTROSCOPY INVESTIGATION OF THE STRUCTURAL MODULATION ON THE SURFACE OF CLEAVED BI2SR2CACU2OY SINGLE-CRYSTAL

The surface of cleaved Bi2Sr2 CaCu2Oy (Bi2212) single crystals has bee n studied by means of scanning tunneling microscope (STM) and scanning tunneling spectroscopy (STS) at room temperature in ultrahigh vacuum. We obtain atomic images of the BiO surface using logarithmic current mode and conventional mode. It is demonstrated that the Bi atoms in th e BiO plane are not missing. Some Bi atoms are depressed down below th e BiO surface. STS obtained at different places of the surface shows m ore or less the same feature, indicating that local electronic density of states does not change much due to the depression or the well-know n structural modulation. The possible origins of the variation in the period of the structural modulation in the BiO plane of cleaved Bi2212 single crystals extracted from STM images are also studied.