Microscopy Investigations of Nanostructured Materials

S. Leone, Principal Investigator

Nanostructured materials offer great potential for novel ways to generate, utilize, store and transport energy for the nation's economy.  Investigations related to solar energy utilization are made with state-of-the-art optical characterization microscopies that provide higher spatial, spectroscopic, and time resolutions than are afforded by conventional techniques.  Laser sources are coupled with a variety of scanned probe and confocal microscopies to obtain high performance apertureless near field microscopy to enhance spatial resolution, single-molecule or single-nanostructure spectroscopies for fluorescence intermittency studies, coherent anti-Stokes Raman microscopy for greatly improved spectral resolution, and ultrafast pump-optical injection probing microscopies for time dynamics studies.  These techniques are applied to problems in semiconductor nanostructured materials, such as the measurement of carrier lifetimes under stimulated emission conditions, the optical identification and energy transfer between dissimilar materials of nanodots and islands, and the full spectral characterization of soft matter.  A parallel growth effort for processing semiconductor materials by molecular beam epitaxy with in situ scanning tunneling microscopy is used to study growth properties and provide some materials for this effort.

Near field images of small and large nanoparticles.

CURRENT PROJECTS

Studies of the photophysics of single semiconductor nanoparticles, the fabrication of novel layered structures
and band gap engineered materials, and the probing of these materials by near field and related spectroscopic
tools.  

Investigations of the excitation wavelength effects of CdSe and core shell quantum dot materials, seeking a detailed understanding of the response of excited nanoparticles to a host of fundamental nanoscale photophysics related to nanoparticle-inspired photovoltaic devices.  

Application of the apertureless near field microscopy technique, along with AFM and STM, to investigate InxGa1-xN samples grown in a variety of conditions,observing dielectric properties of nanoisland morphologies and chemical composition to identify the growth parameters.

Growth of ternary and quaternary nitride alloys from (I+II) or (II+IV) elements by molecular beam epitaxy.

Coherent anti-Stokes microscopy investigations combined with ultrafast UV pump excitation to study the Raman surface bands of ZnO nanostructures under high carrier conditions.