Seminars are Wednesdays at 11¹⁵ AM in S5 Osmond unless otherwise noted.
Refreshments are served at 11 AM.

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Progress in nanochemistry requires the characterization of ever smaller numbers of molecules. We approach the problem with variants of Secondary Ion Mass Spectrometry, SIMS, using keV-MeV mono and polyatomic “cluster” ions as projectiles. Sputtered secondary ions, SIs, are identified via time-of-flight MS. A first issue is to select an efficient projectile. keV polyatomic ions can significantly improve the yield of SIs. However, they can concurrently promote prompt fragmentation, recombination/rearrangement processes and metastable decay. Thus the challenge is to tune the projectile characteristics for maximum yield of analyte-specific SIs while minimizing the production of non specific SIs. The scope of “cluster-SIMS” will be illustrated with data from different types of samples.

A further aim is to extract a maximum of information from a vanishingly small analytical signal. One approach is to identify coincidental SIs, i.e., two or more SIs emitted from a single projectile impact. These coincidental SIs can only originate from atoms and molecules colocated within nanometric dimensions; i.e., they can reveal chemical composition on a small scale. The concept of “coincidence-MS” has been validated with mass spectra from ~ 30 nm diameter particles. A recent breakthrough in coincidence-MS methodology holds promise for further advances in nanophase characterization.

A large research effort is currently being focused on the development of organic electroluminescent technology for organic light-emitting devices (OLEDs). Since the report of efficient green electroluminescence from aluminum tris(8-quinolinato) (Alq3), significant improvements in OLEDs have been reported. However, despite more than a decade of research, a consistent picture of the nature of charge injection, migration and recombination processes in organic heterostructure devices is not well established. In addition thermal (morphological) and chemical stability of organic materials has been a limiting factor in their practical use for some applications. These material properties are interrelated and dependent on the molecular and electronic structure of the molecules and their packing in the solid-state. The best method for understanding these structure-property relationships is to conduct systematic studies of similar materials. In this seminar, an investigation of the molecular and electronic structure and their relationship to photophysical and physical (i.e., thermal stability) properties for methylated metal 8-quinolinato chelates (Al+3, Ga+3, and Zn+2) is presented. These results are related to differences in device performance when these materials are used as the emitting layer in OLEDs.

(Hosts: Mary Beth Williams, x5-8859 and Paul Weiss, x5-3693 )

(Host: Paul Weiss, x5-3693 )