High charge mobility in two-dimensional percolative networks of PbSe quantum dots connected by atomic bonds

Abstract

Two-dimensional networks of quantum dots connected by atomic bonds have an electronic structure that is distinct from that of arrays of quantum dots coupled by ligand molecules. We prepared atomically coherent two-dimensional percolative networks of PbSe quantum dots connected via atomic bonds. Here, we show that photoexcitation leads to generation of free charges that eventually decay via trapping. The charge mobility probed with an AC electric field increases with frequency from 150±15 cm2 V−1 s−1 at 0.2 terahertz to 260±15 cm2 V−1 s−1 at 0.6 terahertz. Gated four-probe measurements yield a DC electron mobility of 13±2 cm2 V−1 s−1. The terahertz mobilities are much higher than for arrays of quantum dots coupled via surface ligands and are similar to the highest DC mobilities reported for PbSe nanowires. The terahertz mobility increases only slightly with temperature in the range of 15–290 K. The extent of straight segments in the two-dimensional percolative networks limits the mobility, rather than charge scattering by phonons.

Structure, transport and photoconductance of PbS quantum dot monolayers functionalized with a copper phthalocyanine derivative

“…The laser system used for THz conductivity measurements has been described earlier and data acquisition and evaluation is briefly discussed in the SI unit. [16]- [18] Fig. 3a shows time-resolved THz measurements of Cu4APc functionalized PbS NC films.…”

Microscopic origin of the Drude-Smith model

“…76,77 Fitting these simulations enabled Nemȇc et al to provide approximate mathematical expressions for the Drude-Smith fit parameters 76 that have since been applied to experimental data to extract meaningful physical information. 15,26,27,33,38 Complementary experimental techniques are often also used to examine the structure 11,12,15,[17][18][19][20]22,23,25,26,29,31,[33][34][35][36][37][38][39][41][42][43][44]46,47,50 and carrier transport characteristics 11,12,19,23,26,43,57 in a sample to test the fidelity of the Drude-Smith fits. Nevertheless, in the absence of a tractable derivation that shows how weak carrier confinement yields the DrudeSmith formula with well-understood fit parameters, it is difficult for the Drude-Smith model to be more than a convenient expression for linking the conductivities of similar nanosystems to one another, and to Monte Carlo simulations.…”

Assembly and Electronic Applications of Colloidal Nanomaterials

“…Volatile ligands, such as hydrazine, [91] pyridine, [300] and alkylamine, [322] can be removed by annealing to improve interparticle interactions. [323,324] This assembly of nanocrystal arrays is realized by oriented attachment, which is a well-accepted mechanism for anisotropic growth of colloidal nanocrystals. Since the fusion of nanocrystals stems from the increased mobility of surface atoms at high temperatures, surface ligands can significantly influence the sintering behavior.…”

“…High temperatures also induce sintering of nanocrystals into large crystallites through grain growth ( Figure 5C). [5,60] Most studies have focused on oleic-acid-capped PbSe nanocrystals, [323][324][325][326][327][328] whose adjacent specific facets can lose ligands and join epitaxially together under controlled conditions. Typically, grain growth commences at ≈200 °C, [20,40] but the original nanocrystal size and phase can be maintained until 300°C with different surface ligands.…”