Atomic level studies of step dynamics in the homogeneous growth of metal crystals

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NON-TECHNICAL ABASTRACT:The growth of crystalline materials is the first step in the manufacture of numerous electronic devices including microprocessors for computers, chemical sensors for human health, and biological detectors to counter terrorism threats. Today, individual atoms are being manipulated in attempts to create such processors and sensors at the atomic scale. Improvement in our understanding of atomic scale surface processes, such as atom transport and its role in the growth of crystalline materials, is required so that the manipulation of individual atoms can be routinely employed to enhance the performance of existing devices, as well as develop new devices. This project uniquely combines the ability to view the motion of individual atoms using a microscope with the capability of identifying the atomic species in motion using a mass spectrometer. It thereby allows for a detailed atomic level study of the growth of an elemental crystalline material. This research is serving as the Ph.D. thesis project for one graduate student and employing an undergraduate science major to assist with the experiments. The inherent interdisciplinary nature of the project is training the students in a wide variety of technical areas and thereby helping to thoroughly prepare them to begin a career in the physical sciences. Underrepresented groups have a good opportunity to fill the student positions on this research effort because the University of New Mexico is exceptional in combining a highly rated research program and designated as both a Minority-serving institution and a Hispanic-serving institution. TECHNICAL ABSTRACT: The dynamics of steps on crystal surfaces is one of the most important processes governing atom transport and the resulting crystal growth. In this project, step dynamics at the atomic scale in the prototypic case, elemental crystals, is being investigated for the first time. To enable the study of such homogeneous systems we are employing a novel approach - the use of an adatom that is a stable isotope of the elemental substrate. This preserves the chemical nature of the homogeneous system, yet the isotope adatom is distinguishable due to its known mass and isotopic abundance. The field ion microscope is being used for atomic resolution surface imaging. Possible isotope adatom-substrate atom exchange processes that occur during atom transport are detected by the removal of individual atoms as ions with field evaporation and subsequent time-of-fight-based atom-probe microanalysis to determine their mass. The project is investigating step dynamics on various transition metal surfaces by studies of: Year 1 - The descent of isotope adatoms over steps and the diffusion of isotope adatoms along step edges, Year 2 - Nanosecond-time-scale diffusion initiated by laser pulses to capture any 'non-equilibrium' isotope adatom-substrate configurations, and Year 3 - The impact of the proximity of steps to one another on isotope adatom-step dynamics.