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The emergence of band structure in nanoscale insulators Jay A. Gupta, Ohio State University Research Foundation, DMR 0645451
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A detailed understanding of nanometer-scale structures is becoming increasingly important for next-generation information and energy technologies. Due to their small size, such structures represent a crossroads between bulk materials and isolated atoms. We have used a scanning tunneling microscope (STM) to study the emergence of electronic structure in few atom nanoislands.
Our prior work demonstrated that despite being only one atomic layer thick, Cu2N acts as a wide-gap insulator. We recently found that the area of Cu2N islands could be varied from few-atom islands to monolayer sheets by adjusting growth conditions. Electrons can be confined within the islands, leading to a direct visualization of the canonical particle-in-a-box problem from quantum mechanics. These electronic states shift toward higher energy in smaller islands, consistent with quantum confinement. More novel however, is that the states themselves first emerge in islands comprising only 48 atoms (16 N and 32 Cu), and are absent in smaller 12 atom islands.
These data provide insight into how band structure evolves from the atomic scale in nanoscale solids.
(A) STM topographic image of a single Cu2N island. (B) Spectroscopic image of the same island, showing a pronounced peak in state density at the center. The inset is the calculated probability density for the corresponding particle-in-a-box state. (C) Tunneling spectroscopy showing that these quantum states first emerge in ~2nm2 islands, representing only 48 atoms.
Ruggiero et al., in preparation (2009).
Scientific impact: Prof. Gupta has used a scanning tunneling microscope (STM) to study the electronic and atomic structure of ultrathin insulating films, a class of materials that represent a fundamental limit for the scaling of transistors in computer chips. These results and techniques will aid in the search for new materials for next-generation technologies.
Outreach and educational impact: The imaging and manipulation of atoms with the STM is both a profound example of the frontier in nanoscience, and a simple exercise that can be intuitively understood by anyone. Prof. Gupta’s STM studies are communicated to a broad and diverse audience of high school students through the Columbus Center for Science and Innovation‘s Electronic Experts program. In this program, students across the country can interact with research experts through real-time videoconferencing technologies. The hour-long experience comprises a 20 min presentation on current research, followed by a 40 min Q&A session. Prof. Gupta’s semi-annual lectures have so far been attended by 600+ students in 7 states (c.f. map at left). Students ask wide-ranging questions related to nanoscience research, potential applications, and life as a scientist in general.
COSI’s video conferencing studio connects K-12
students with experts at the frontiers of research.
600+ students in 7 states have participated in Gupta’s presentations on nanoscience research at the atomic scale.