Scanning tunneling spectroscopy of InAs nanocrystal quantum dots

Scanning tunneling spectroscopy is used to investigate single InAs nanocrys tals, 20-70 Angstrom in diameter, in a highly asymmetric double barrier tun nel junction configuration. The I-V characteristics reflect contributions o f both single-electron charging and the atomiclike level structure of the q uantum dots. The spectra are simulated and well described within the framew ork of the "orthodox model" for single-electron tunneling. The peaks in the tunneling spectra display a systematic broadening with the reduction of do t diameter, from 40 to 150 meV over the studied quantum dot size range. Thi s is assigned to a decreased electron dwell time on the dot, due to reducti on of the barrier height, induced by the blueshift of the quantum-confined levels. The distribution of peak spacings within charging multiplets in the tunneling spectra is found to be Gaussian, resembling observations on meta llic quantum dots.