SMA-STM microscopy reveals 3D laser-excited quantum dot structure

April 1, 2018
Quantum-dot excited states in 3D have been imaged using a single-molecule absorption scanning-tunneling microscope.

Researchers from the University of Illinois at Urbana-Champaign and the University of Washington, Seattle have collaborated to image quantum-dot excited states in three dimensions (3D) for the first time using a single-molecule absorption scanning-tunneling microscope (SMA-STM). A modulated laser beam excites localized electronic transitions (green atoms, as shown in the figure) in a single quantum dot and SMA-STM produces a two-dimensional (2D) projected image of the excited state. The dot is then “rolled” by a single-atom-thick needle to image different orientations in 2D. By comparing different orientations with a full quantum-mechanical calculation of a quantum dot, the 3D electronically excited structure can be reconstructed.

Unlike cryogenic electron tomography methods that create an image using an average of thousands of cryogenically cooled particles that are in different orientations, SMA-STM requires only one particle that is reoriented and does not require cryogenic freezing of the particle, improving understanding of its behavior in the excited state at room temperature. The actual image obtained is a representation of the orbital-density map of the transition excited by the laser and has subnanometer resolution in a field of view of tens of nanometers. Reference: D. Nguyen et al., J. Chem. Phys., 148, 6, 064701 (2018).

About the Author

Gail Overton | Senior Editor (2004-2020)

Gail has more than 30 years of engineering, marketing, product management, and editorial experience in the photonics and optical communications industry. Before joining the staff at Laser Focus World in 2004, she held many product management and product marketing roles in the fiber-optics industry, most notably at Hughes (El Segundo, CA), GTE Labs (Waltham, MA), Corning (Corning, NY), Photon Kinetics (Beaverton, OR), and Newport Corporation (Irvine, CA). During her marketing career, Gail published articles in WDM Solutions and Sensors magazine and traveled internationally to conduct product and sales training. Gail received her BS degree in physics, with an emphasis in optics, from San Diego State University in San Diego, CA in May 1986.

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