Acquisition of a Near Field Microscopy System for Materials Research and Education at North Carolina Central University

This proposal requests funding for a scanning near field optical microscopy (SNOM) platform to increase the impact and scope of nanoscale materials research at North Carolina Central University (NCCU). This new instrument, when integrated with existing millimeter wave and ultrafast optical capabilities, will form a powerful tool capable of performing correlated measurements of chemical composition, crystalline structure, carrier dynamics, carrier densities and carrier mobilities with nanometer-scale spatial resolution. The proposed system will employ probes from the visible to terahertz regions of the spectrum to characterize materials across broad temporal (femtosecond to second) and spatial (nanometer to centimeter) scales. The system will initially be used in the following areas: À Effects of compositional inhomogeneity, grain boundaries and ion migration on carrier dynamics in doped hybrid organic Ð inorganic perovskites: Our previous research has shown initial evidence for shifts in the peak wavelength and decay time for photoluminescence (PL) collected from the edges of micron sized grains in polycrystalline thin films of alkali metal doped perovskites. The improved spatial resolution of this instrument (~ 10 nm vs. 200 nm for confocal microscopy) would allow us to clearly discriminate between PL and ultrafast transient absorption (TA) responses from the edges and centers of the grain, and enable infrared (IR) and mm-wave/THz measurements to determine local carrier mobilities that could only be performed over mm-size regions encompassing many grains. Correlation of optoelectronic properties with dopant concentration variations within or between grains, as well as grain size, can easily be discerned from this data along with effects of ion migration under illumination. À Charge and energy transfer nanostructure heterojunctions: o CdSxSe1-x nanoribbons: Confocal PL and TA measurements in CdSxSe1-x nanoribbons with laterally varying compositions have revealed significant differences in PL emission intensity and carrier lifetimes in the different regions of the system, suggesting efficient charge transfer in these type I heterojunctions. This instrument enables characterization of the diffusion length in these materials by precisely controlling photoexcitation distance on one side of the interface, while monitoring PL or TA on the other side. THz o Hybrid organic semiconductor Ð inorganic nanostructure systems: Chemical composition and orientation of organic small molecule or polymer domains determined with near field infrared spectroscopy can be correlated with local THz mobility measurements, and with charge transfer efficiencies determined using the pump- probe methods described above. Research in this area will focus on combining 2D (WS2, MoS2) and 1D (CdSxSe1-x) nanostructures with copper phthalocyanine, pentacene, and polymer PTB7. The high spatial resolution combined with the broad spectral range offered by this instrument represent a significant upgrade to NCCUÕs ability to perform competitive research and to provide students with productive research experiences. This instrument provides a rare set of capabilities that will allow NCCU to develop new areas of nanoscience research and strengthen existing research collaborations. The requested system will also significantly impact NCCUÕs STEM education and training missions by offering undergraduate, graduate and high school students hands-on opportunities with cutting edge instrumentation and scientific concepts.