Collaborative Research: Connecting Mesoscale Dynamics of Metallic Films on Semiconductors to Nanoscale Phenomena

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Nontechnical AbstractElectronic devices, such as computers and smartphones, are at the heart of our technological society. Such devices currently are based on semiconductor technology, which involves making electrical contacts between metals and semiconductors. By studying and understanding the details of how metals can be deposited onto semiconductor materials, this project will allow the development of novel methods to grow low dimensional nanostructures, such as extremely thin wires and very thin films. The project connects state-of-the-art experiments to observe the growth properties of the materials with sophisticated theoretical techniques using models consisting of tens to millions of atoms to explore the physics governing the predicted properties of the fabricated nanostructures. Working in conjunction, these methods will facilitate the optimal design and creation of these low dimensional nanostructures. Such structures could be very useful in making future electronic devices, thus maintaining the technological leadership of the U.S. in nanotechnology. Students working on the project will not only gain in-depth physical understanding in the exciting research areas involving metal-semiconductor interfaces but also will engage in outreach activities with local K-12 students and teachers with whom the PIs have on-going interactions, especially through the American Physical Society Physics Teacher Education Coalition (APS PhysTEC). All PIs regularly mentor undergraduate researchers and are actively engaged in recruiting women and underrepresented minority students, particularly through the APS Bridge Program.Technical AbstractThis project will study the growth mechanisms of several metal on semiconductor systems. The objectives of this project are controlling the growth of low-dimensional (1D and 2D) nanostructures, elucidating the novel and complex collective diffusion behavior which has been observed for these systems, and understanding how quantum behavior can influence epitaxial growth in order to facilitate the optimal design and fabrication of novel materials. A complementary set of experimental and theoretical techniques will be applied to examine systematically the initial growth stages and structural evolution of Ag, Au, and Pb nanostructures on single crystal surfaces of Ge and Si. The atomic ordering and adatom binding sites, as well as sizes and shapes of formed islands, will be determined by scanning tunneling microscopy (STM) and low energy electron microscopy/diffraction (LEEM/LEED) and compared with predictions from density functional theory (DFT)-based simulations. Unusual collective behavior of millions of atoms and quantum size effects (QSE) will be investigated to elucidate details of the mechanisms. Scanning tunneling spectroscopy (STS) and angle-resolved photoemission spectroscopy (ARPES) will be used to measure local density of states, k-resolved band structure, and quantum well states; these results will be compared with DFT calculations to understand the factors controlling the nanostructure characteristics and to formulate the physical picture about the basic mechanisms and processes for future growth. Bond order potentials (BOP) will be determined for metals bound to semiconductor surfaces and used for self-learning kinetic Monte Carlo (SLKMC) simulations of the growth and movement of islands. These large-scale simulations will improve understanding of the physical origin of the collective motions and suggest additional experimental systems that may display unusual physical phenomena. The use of Si and Ge-based materials would enable rapid development of technological applications for electronic devices.