We have studied electron tunneling characteristics across an aqueous STM capacitor junction by measuring the tunneling current and local barrier height as functions of junction distance and applied bias voltage for HOPG, Au and TaTe 2 surfaces in air. The electron tunneling distance ranges from 7-20 Å when the junction resistance is of the order of 10 8 Ω. We suggest that the unusually low value of the barrier height (< 1.5 eV) originates from the three-dimensional nature of the electron tunneling through the interfacial water layer present inside the junction. An asymmetric variation in barrier height is observed with respect to the applied bias voltage at a junction distance of water monolayer thickness, which reflects the polarization of the water layer on the surface.The nature of the interfacial water layer and its response to electron transmission are related to many important phenomena in the physical sciences. However, current knowledge on this subject is far from complete. Theoretical considerations [1-3] predict that water molecules are polarized at a charged interface by breaking the bulk structure maintained by hydrogen bonding network under an interfacial electric field of the order of 10 7 V/cm. Spectroscopic studies [4,5] give evidence for a disrupted hydrogen bonding network in the first layer of water on a metal electrode. X-ray scattering studies [6,7] have measured the spacing between the Ag electrode surface and the first layer of water and found that water molecules flip their average dipole orientation upon changing the polarity of the electrode potential.Scanning tunneling microscopy (STM) can, in principle, be used to characterize the interfacial water and its electron transmission property. An electrochemical environment [8][9][10] or humid atmosphere [11][12][13][14] provides an STM junction filled with water, in the latter case condensed from atmospheric moisture [13,14]. In the aqueous STM studies, however, many aspects are still not well resolved or perhaps have not been given enough detailed consideration. For example, * To whom correspondence should be addressed water inside an STM junction greatly increases the tunneling distance compared with that in ultrahigh vacuum (UHV) [8]. The local barrier height for electron tunneling (φ) is unusually low in water [8][9][10][11][12]15] compared with UHV [16][17][18][19]. These phenomena should somehow be related to the physics of electron transfer across interfacial water, but this remains uncertain at present. In this work, we examine electron tunneling across the interfacial water layer present inside a capacitor junction composed of an STM tip and sample surface in air. The junction distance is accurately controlled to water monolayer thickness, and the tunneling current (I) and φ are investigated as functions of junction distance and applied bias voltage.

We show that ultrahigh-vacuum low-energy electron microscopy and scanning tunneling microscopy can be used to image residual uniaxial strain fields on (001) surfaces of SiGe heterostructures. We find that the surface crosshatch morphology on these films is highly correlated with large spatial variations in the residual uniaxial strain fields, confirming the importance of local strain fields in the formation of crosshatch.