Orientation-dependent imaging of electronically excited quantum dots.

Area of Science:

• Nanoscience and Nanotechnology
• Quantum Physics
• Surface Science

Background:

• Single-molecule absorption scanning tunneling microscopy (SMA-STM) images electronic excitations in quantum dots.
• The technique involves modulating a laser to saturate electronic transitions, with current modulation mapping the image.

Purpose of the Study:

• To derive the theory for calculating SMA-STM signals in the one-electron approximation.
• To experimentally demonstrate imaging of excited state electronic structure of quantum dots at different orientations.
• To model orbital density maps (ODMs) for comparison with experimental results.

Main Methods:

• Derivation of basic theory for SMA-STM signal calculation.
• Experimental manipulation of quantum dots on a surface to change orientation.
• Density functional theory (DFT) modeling of ODMs at various orientations.

Main Results:

• SMA-STM signal is proportional to the electron density of the excited orbital, approximating an orbital density map (ODM).
• Quantum dots were successfully repositioned to image excited states at different orientations.
• DFT models qualitatively matched experimental SMA-STM observations.

Conclusions:

• SMA-STM provides sub-nanometer super-resolution imaging of excited electronic states.
• The technique is sensitive to defect-localized electronic states within nanomaterials.
• This method holds potential for mapping 3D excited state structures in nanomaterials.