1. . Simulated image of Ga Tetramers using SIESTA Experimental STM images of 4x3 reconstruction. PECASE: Growth and Analysis of Novel Nitride Semiconductor Systems Arthur R. Smith, Ohio University, Athens, OH, DMR-9983816 (also NIRT: DMR-0304314). Predicted tetramer unit: interatomic distances are in Angstroms. 12.8 Å Zinc-blende GaN is one of a group of cubic nitrides of interest for future technological applications in UV/blue light emitting electronic materials. The intrinsic surface structures of cubic GaN(001) are of utmost importance to the growth of device structures from this material. Shown at left is the first-ever STM image of the correct, fundamental reconstruc- tion of this surface, which has a 4x3 structure. A theoretical model predicted a 4x1 structure; however, other STM images reveal a 3x period (not seen in this image) along the row direction, which has never been predicted. 8x 4x The model at left was predicted by Neugebauer et al. 7 years ago [ Phys. Rev. Lett 80, 3097 (1998) ]. It shows one “tetramer” unit consisting of 4 Ga atoms in a row. Our new STM data agrees well with the tetramer model except for the 3x periodity observed along the row. Although seemingly a small difference between 4x1 and 4x3, this inconsistency calls for new theoretical calculations. Shown at right is an STM image of one of the more Ga-rich reconstructions on c-GaN(001), which is the c(4x16) having an 8x spacing. It consists of excess gallium adatoms on top of the (001) GaN surface. It is one of a family of similar reconstructions we have found. According to the simplest model, the c(4x16) has a Ga coverage on the surface of ~0.22 ML. These reconstructions, of this most important surface, have never before been reported. c(4x16) reconstruction

2. CAREER/PECASE: Growth and Analysis of Novel Nitride Semiconductor Systems Arthur R. Smith, Ohio University, Athens, OH, DMR-9983816. Education and Broader Impacts of This Project One of the primary products of this project is the training of students to become professional scientists. To date, the project has supported mainly 4 Ph.D. students, 1 post-doctoral researcher, and several under- graduates. These students have all received excellent training and learning opportunities. All the Ph.D. students and the post-doctoral researcher have achieved many good results and have their names on a large number of papers. In addition, they have also attended numerous conferences and have given many presentations on their research. One of the most tangible and lasting products of the research are the publications and presentations. The pie chart at right shows the distribution of publications resulting from the NSF-sponsored research under the PECASE grant which have either been published already (18) or have been accepted for publication (2). The chart shows both quantity (average 4/year) and quality (with 2 PRL’s, 3 APL’s, and 2 Surface Science papers, for example). As well, there have been a total of 55 presentations, including invited and contributed. 20 Publications Smith Group: Constantin, Yang, Haider, Al-Brithen, Yang, Smith.