Journal
PHYSICAL REVIEW B
Volume 81, Issue 11, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.81.115439
Keywords
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Funding
- National Science Foundation (NSF) [DMR-02-13282]
- Institute for Soldier Nanotechnologies [DAAD-19-02-0002]
- NSF through the Nanoscale Science and Engineering Center [NSF/PHY 06-46094]
- NASA-Ames Research Center [NNA04CK42A]
- DOE [DE-FG3608GO18007]
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We use a scanning tunneling microscope to probe single-electron charging phenomena in individual CdSe/ZnS (core/shell) quantum dots (QDs) at room temperature. The QDs are deposited on top of a bare Au thin film and form a double-barrier tunnel junction (DBTJ) between the tip, QD, and substrate. Analysis of room-temperature hysteresis in the current-voltage (IV) tunneling spectra, is consistent with trapped charge(s) presenting an additional potential barrier to tunneling, a measure of the Coulomb blockade. The paper describes the first direct electrical measurement of the trap-state energy on individual QDs. Manipulation of the charge occupation of the QD, verified by measuring the charging energy, (61.4 +/- 2.4) meV, and analysis of the DBTJ, show trap states similar to 1.09 eV below the QD conduction-band edge. In addition, the detrapping time, a measure of the tunneling barrier thickness, is determined to have an upper time limit of 250 ms. We hypothesize that the charge is trapped in a quantum-dot surface state.
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