1. Impurity sites in a semiconductor discovered through their localized vibrational signatures in the infrared Anant K. Ramdas and Sergio Rodriguez, Purdue University, DMR-0405082 Research goal: To discover and delineate impurity sites of impurities diffused into a tetrahedrally coordinated semiconductor exploiting high resolution Fourier-transform spectroscopy of the impurity and its neighbors. Fig 1 In the course of the growth of ZnTe epilayers on GaSb substrates by molecular beam epitaxy and their spectroscopic characterization with ultrahigh resolution Fourier Transform Spectroscopy, we discovered that Zn impurities diffuse into the substrate and manifest a fascinating fine structure in their local vibrational mode (LVM) [Fig. 1]. The frequency of the LVM and its fine structure components are demonstrated to be the infrared active modes of 64 Zn substitutionally replacing a Sb anion ( 64 Zn Sb ) rather than an Ga cation ( 64 Zn Ga ). The choice is compelled by the frequencies, relative intensities and spacings of the fine structure components produced by the vibrations of the four, tetrahedrally bonded nearest neighbor Ga cations.

2. Education/Broader Impact: The research for the nugget is based on an intense collaborations between A. K. Ramdas [PI], Sergio Rodriguez [co-PI], R. L. Gunshor [Emeritus Professor, Purdue], H. Kim [Sogang Uni., Korea], E. Tarhan [Izmir Institute of Technology, Turkey], M. D. Sciacca [IBM, Hopewell Junction, NY] and G. Chen, a current graduate student. Collaborations with I. Miotkowski (Senior scientist in charge of crystal growth), S. Tsoi [NRL], M. Cardona [Max-Planck Institute, Germany], Harald Pascher [Bayreuth Uni., Germany], T. R. Anthony [formerly of GE], RamMohan [WPI], and Haller [UCB] are further examples of the intensely interactive ambience in which our current graduate students (G. Chen, X. Lu, and J. Bhosale) work. The entire research experience prepares the younger participants for an exciting future in universities and national and industrial laboratories. Similarly, undergraduates who work in our group for “Research Experience” also benefit in defining and making their career choices. Future Plans: The results highlighted in this nugget has opened a new avenue of research on interface diffusion in the context of combinations of epilayers, quantum wells, quantum dots or quantum wires, on the one hand, and the surrounding host material, on the other, fabricated with molecular beam epitaxy for example. These opportunities will be pursued with different combinations of nanostructure / host. Fig 2 Impurity sites in a semiconductor discovered through their localized vibrational signatures in the infrared Anant K. Ramdas and Sergio Rodriguez, Purdue University, DMR-0405082 On the basis of an XY 4 quasimolecule model (X  64 Zn and Y  69 Ga and 71 Ga) for the 64 Zn Sb impurity (the natural abundance for 69 Ga and 71 Ga being 60.11% and 39.89%, respectively) and 64 Zn Ga (with the natural abundance of 121 Sb of 57.3% and 123 Sb of 42.7%), together with stretching and bending force constants, the agreement of the experimental results with the calculations distinctly favor Zn Sb, the anti- site substitution (Fig. 2).