John DiNardo
Vibrational Dynamics at Semiconductor Surfaces and Interfaces
Funding NSF-DMR (N. J. DiNardo and E. J. Mele)
NSF-DMR Instrumentation for Materials Research
This is a combined experimental and theoretical study of the vibrational dynamics of reconstructed Si surfaces to be extended to homo-epitaxial and hetero-epitaxial growth on Si surfaces. Experimentally, a new Ibach-designed ultra-high resolution LK-300
0 HREELS spectrometer is being used to measure surface phonon band structure. At the outset, the premise is that the surface phonons of Si(100) should exhibit a temperature-dependent phase transition correlated with the observed 4x2>2x1 structural trans
ition. After testing this hypothesis and making comparisons with theory, vibrational studies of epitaxially-grown metal and semiconductor overlayers will proceed.
Diamond-like Carbon Thin Films
Funding: DOE-CRADA via Sandia National Laboratory (Albuquerque)
Drexel - U Maryland
This project involves a collaboration between Sandia National Laboratory, an industrial partner, DiNardo, and Martinez-Miranda (U. Maryland) to characterize thin carbon films grown on various substrates by laser ablation. Although the films are amorphous
, they appear to have a comparatively large sp3 content. AFM and STM are being used to characterize the surface morphology of films of varying thicknesses under an array of processing conditions. In addition, Raman spectroscopy, photoemission, and elect
ron microscopy are being used to correlate bulk and surface structure and preparation with the sp3/sp2 ratios.
Metal-Semiconductor Interfaces
Funding: NSF-DMR - Penn (W. R. Graham and N. J. DiNardo)
NSF-MRL - Penn (N. J. DiNardo)
This project, involving a collaboration is comprised of two components which are merging towards an improved understanding of the relation of microscopic and macroscopic physical phenomena occurring at atomically-abrupt buried interfaces. A wide variety
of surface techniques have been employed to study structure, coverage, and electronic properties of model alkali-metalsemiconductor (Si, GaAs) interfaces. A case for electron localization on non-metallic ultra-thin films has been established and the con
ditions and signatures of the development of metallization in films as a function of thickness have been shown and analyzed. In addition, a new model for the alkali-metal-induced Si(111)-3x1 surface structure has been proposed. The work is currently bei
ng extended to explore these properties on epitaxial metal layers of sub-monolayer > few layer coverages. The second component of these studies have established new insights into the role of inhomogeneity in the Schottky-barrier heights of abrupt epitax
ial interfaces.
Polymer Surfaces and Interfaces
Funding: NSF-DMR Instrumentation for Materials Research
This project involves a collaboration between DiNardo and J. M. Vohs (Penn,ChemE). The new LK3000 HREELS spectrometer is being used to study vibrational modes and electronic excitations at polymer surfaces and interfaces and compare these to nanoscale st
ructures as measured by AFM and STM. DiNardo previously published one of the first HREELS studies of polymer surfaces and the first HREELS study of polymer-metal interfaces One focus will be on conducting polymeric materials such as polyaniline under di
fferent doping conditions. HREELS is currently being used to study aniline adsorption (chemisorption and physisorption) on metal surfaces. In addition, preliminary studies have been performed on polyaniline films as a test of the instrument and our capa
bilities. A new sample introduction system is being constructed to allow rapid sample turnaround and ex-situ preparation of polymer samples.
Quantum Structure of Materials
Funding: NSF-Gateway - Drexel-Penn
This project involves a collaboration between DiNardo, Vallires (Drexel,Physics/AtmosSci.), Vohs (Penn,ChemE), Graham (Penn,MatSciE), and Composto (Penn,MatSciE) to develop new undergraduate courses including (1) quantum mechanical phenomena taught in th
e context of nanoscale systems directed to materials scientists and engineers and (2) modern techniques in materials science. The centerpiece of this project is the development of new undergraduate laboratory experiments based on modern, state-of-the-art
instrumentation. These experiments are centered around a Burleigh Instructional STM at Drexel and a medium/high energy ion scattering undergraduate beamline attached to a thin-film growth chamber at Penn. In light of the proximity of the two campuses,
we plan to share the facilities to maximize the opportunities for students at both Universities.
Atomic Structure of Semiconductor Surfaces
NSF-DMR Instrumentation for Materials Research
DiNardo is co-PI on a project involving the acquisition of a JEOL variable temperature STM which is housed at Oak Ridge National Laboratory. Access to this instrument will allow the study of the geometric and electronic structure of semiconductor surface
s as a function of temperature from <50K to >1000K. A locally-housed custom-built UHV-STM is accessible for more routine studies or for preliminary studies before utilizing the JEOL instrument.