We show simultaneous molecular chemistry and bond orientation information over a large area (18 mm x 13 mm) obtained with high transmission using a novel parallel process full field secondary electron spectrometer. This unique spectrometer (LARIAT MKI) incorporates: a full field soft x-ray source (NSLS beamline U7A); electrostatic and magnetostatic electron optical elements to discriminate energy and depth of the secondary electron distribution and; a highly parallel electron detector. The rapid parallel process produces a series of two dimensional images as the incident soft X-ray energy is scanned above a K or L absorption edge.

Synthesis of the of the image stack produce spatially resolved NEXAF spectra containing information about the chemistry (including bond concentration) and orientation of the surface-bound molecules with better than 100-micron lateral resolution and sub-monolayer molecular sensitivity. Rapid image-based full field capture of NEXAFS spectra over large areas permits new combinatorial approaches to data acquisition and analysis. The power of the combinatorial imaging NEXAFS method is described through a variety of examples including:

Simultaneously probing concentration and molecular orientation of single-strand DNA micro array sensors
Semifluorinated molecular gradients
And organic electronic combinatorial device arrays.

Other possible applications described include the surface orientation and chemistry of continuously graded polymer films and graded or patterned self-assembled monolayers. We also envision combinatorial imaging NEXAFS as an in-situ probe for catalyst discovery using micro arrays to directly image catalytic chemical activity of thousands of catalysts simultaneously under reaction conditions. We will also briefly describe improvements of the second generation system (LARIAT MKII), currently in the testing phase on beam line U8 at NSLS. The MKII will be permanently installed on new Brookhaven National Laboratory synchrotron source, NSLS II to be completed in 2015. The key hardware differences in the LARIAT MKII configuration as compared to the MK I model is the use of superconducting magnet components and additional electrostatic elements in the electron optics assembly.

The use of superconducting magnets is necessary to attain the significantly higher magnetic fields required to achieve ~600X increase in areal resolution. This overall resolution improvement derives from a factor of four increase in imaging area while simultaneously improving the lateral resolution by a factor of up to twenty (~5µm). There is also the possibility to operate this instrument in a nano scale resolution modality using zone plate optics to produce a type of scanning reflection x-ray microscopy.

Edward L. Principe

University of Central Florida

Appearances