Ph.D Thesis

Ph.D StudentPozner Roni
SubjectModeling Charge Transport Induced Phenomena in
Colloidal Double Quantum Dots and Developing New
Probes for Inter-Dot Interactions
DepartmentDepartment of Energy
Supervisors PROF. Efrat Lifshitz
PROF. Uri Peskin
Full Thesis textFull thesis text - English Version


Colloidal quantum dots (CQDs) are free-standing nanostructures surrounded by capping ligands with chemically tunable electronic properties. The properties of single CQD and the extent to which electrical and mechanical interactions between dots in an array are significant in relation to observed transport properties are highly important. However, it is difficult to assess those interactions because they are controlled by the dots surface chemistry and by the organic ligands that link between separate dots. To date only a few studies have accounted for the ligands structure at the atomistic level and their effect on the mechanical forces between dots was yet to be considered.

In this work, we consider a new scanning tunneling microscopy (STM) tip - double quantum dot (DQD) - surface setup, for measuring ligand-mediated effective inter-dot forces, for inducing motion of individual CQDs within an array, and for exploring the unique connectivity of this setup in which the tip is coupled to a single dot while the coupling to the surface is shared by two dots.

The theoretical analysis of the DQD structure within this setup reveals for the first time voltage-induced inter-dot recoil and dissociation of the dots with pronounced changes in the current. By considering realistic microscopic parameters, our approach enables correlating the onset of mechanical motion under bias voltage with the effective ligand-mediated binding forces. The analysis also reveals a unique negative differential resistance (NDR) effect attributed to destructive interference during charge transfer from the DQD to the surface electrode.

Finally we consider a novel concept of nano-electromechanical nonvolatile memory device incorporating a triple quantum dot (TQD) cluster. The device operation is based on the bias induced motion of a floating quantum dot (FQD) located between two bound quantum dots (BQD). The mechanical motion capability of the FQD is used for switching between two stable states, "ON" and "OFF" states, while the ligand-mediated effective inter-dot forces between the BQDs and the FQD serve to hold the FQD in each stable position under zero bias. Considering realistic microscopic parameters, our theoretical treatment of the TQD reveals the characteristics of the device. Based on this analysis, the operation frequency of the device is estimated to be higher than current non-volatile memory devices.