Surfaces and Interfaces in Nanoscale Electronic Materials: from Understanding to Engineering – Pengpeng Zhang

Date: Mon. February 2nd, 2009, 4:15 pm-5:15 pm
Location: Rockefeller 301

Surfaces and interfaces play a critical role in determining properties and functions of nanomaterials, in many cases simply dominating bulk properties, owing to the large surface- and interface-to-volume ratio. One can further engineer and improve the performance of nanoscale devices through the control of surface and interface chemistry. Using Si nanomembranes as a model system, we have investigated how surfaces and interfaces influence electrical transport properties at the nanoscale by means of scanning tunneling microscopy (STM) and four-probe measurements. We show that electronic conduction in Si nanomembranes is not determined by bulk dopants but by the interplay of surface and interface electronic structures with the “bulk” band structure of the thin Si membrane, which can be thought of as “surface transfer doping.” Additionally, we characterize self-assembled alkanethiolate monolayers (SAMs) on Au{111} with embedded static dipole groups in the adsorbate molecules using Kelvin probe force microscopy (KPFM), X-ray photoelectron spectroscopy (XPS) and quantitative infrared vibrational spectroscopy (IR) techniques. We have modulated the metal work function by adjusting the orientation of the embedded dipole and the geometric structures of the SAMs, which will facilitate applications in charge injection in organic electronic devices. Recently, we have also studied divergent dipoles and intermolecular interactions in geometrically identical adsorbates, finding that differing orientations of molecular dipole moments influence SAM properties, including the stability of the monolayers in competitive binding and exchange environments. These studies demonstrate that a thorough physical understanding of emerging phenomena at the nano- or molecular scale can advance technologies in nanoelectronics and molecular electronics.