STM and TS Study of InAs Quantum Dots Immobilized on Au and Pt Surfaces

Abstract

The first study of the electrical properties of nanometer-size InAs particles is presented. InAs quantum dots (Q-InAs) deposited as films onto Pt and Au electrodes are examined using scanning tunneling microscopy (STM), tunneling spectroscopy (TS), and macroscopic conductivity measurements. In addition, single Q-InAs particles adsorbed on Au-covered mica substrates are examined by STM. The following results are reported in this study: (1) The size distribution of Q-InAs obtained from cross sections of STM images agreed with previous XRD and TEM size measurements, and the measured size was well below the exciton diameter estimated for InAs. (2) The TS I-V curves for Q-InAs films on Au show a larger zero-current region than that obtained for sulfide-passivated, bulk single crystal p-InAs; consistent with the magnitude of strong confinement predicted for particles of this size by the effective mass model. (3) Macroscopic I-V measurements acquired under vacuum for Q-InAs films deposited onto Au interdigitated array electrodes show the absence of an effect of charge transport at either the Q-InAs/Q-InAs or the Q-InAs/Au interfaces on TS energy gap measurements. These results supported our conclusion that the zero-current region in the TS spectra of Q-InAs is reflective of a wider HOMO-LUMO gap in the quantum dots. These I-V plots also showed that the conductivity of the Q-films is only 2 orders of magnitude lower than bulk InAs.

Atomic Layer Deposition of Lead Sulfide Thin Films for Quantum Confinement

“…At a fixed tip−sample separation, the tunneling current was monitored while the voltage was swept over a given range. d I /d V tunneling spectra were numerically calculated from this I − V tunneling spectra, allowing the bandgap to be extracted from the zero-conductivity region of the curve. − Under these conditions, we were able to achieve a resolution of ∼0.1 eV. The bandgap of the bulk PbS film was measured as 0.46 ± 0.02 eV.…”

Nanoparticle characterization based on STM and STS

“…This result indicates that the chemisorption of NPs can be attributed to the stable electrical characteristics of NPs. 81,83 Electrical characteristics of various synthesized NPs have been reported in addition to Au NPs: Ag, 85,[190][191][192][193] Pt, 137 Co, 156,194 Pd, 168,169,185 Au-Ag alloy, 195 InAs, 85,[196][197][198] CdS, 199 and CdSe. 78,[200][201][202] Tuning the bandgap of InAs NPs linked to an Au surface by hexanedithiol molecules has been demonstrated between 0.9 and 1.9 eV by changing the diameter of the NPs between 1.0 and 3.5 nm ( Fig.…”