Measuring charge trap occupation and energy level in CdSe/ZnS quantum dots using a scanning tunneling microscope
Abstract
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 ∼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.
Polina Anikeeva
Matoula S. Salapatas Professor and Head, Department of Materials Science and EngineeringProfessor, Brain and Cognitive SciencesDirector, K. Lisa Yang Brain-Body CenterAssociate Investigator, McGovern Institute for Brain ResearchAssociate Director, Research Laboratory of Electronics
My goal is to combine the current knowledge of biology and nanoelectronics to develop materials and devices for minimally invasive treatments for neurological and neuromuscular diseases.