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Title: Bandgap Inhomogeneity of a PbSe Quantum Dot Ensemble from Two-Dimensional Spectroscopy and Comparison to Size Inhomogeneity from Electron Microscopy

Femtosecond two-dimensional Fourier transform spectroscopy is used to determine the static bandgap inhomogeneity of a colloidal quantum dot ensemble. The excited states of quantum dots absorb light, so their absorptive two-dimensional (2D) spectra will typically have positive and negative peaks. We show that the absorption bandgap inhomogeneity is robustly determined by the slope of the nodal line separating positive and negative peaks in the 2D spectrum around the bandgap transition; this nodal line slope is independent of excited state parameters not known from the absorption and emission spectra. The absorption bandgap inhomogeneity is compared to a size and shape distribution determined by electron microscopy. The electron microscopy images are analyzed using new 2D histograms that correlate major and minor image projections to reveal elongated nanocrystals, a conclusion supported by grazing incidence small-angle X-ray scattering and high-resolution transmission electron microscopy. Lastly, the absorption bandgap inhomogeneity quantitatively agrees with the bandgap variations calculated from the size and shape distribution, placing upper bounds on any surface contributions.
Authors:
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Publication Date:
Report Number(s):
SAND-2016-12917J
Journal ID: ISSN 1530-6984; 650112
Grant/Contract Number:
AC04-94AL85000; AC02-06CH11357; FG02-07ER15912; AC02- 06CH11357
Type:
Published Article
Journal Name:
Nano Letters
Additional Journal Information:
Journal Volume: 17; Journal Issue: 2; Journal ID: ISSN 1530-6984
Publisher:
American Chemical Society
Research Org:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Univ. of Colorado, Boulder, CO (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
47 OTHER INSTRUMENTATION; Quantum dots; inhomogeneity; size dispersion; shape dispersion; 2D spectroscopy; line width; 36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; quantum dots; linewidth
OSTI Identifier:
1337889
Alternate Identifier(s):
OSTI ID: 1338409; OSTI ID: 1344807; OSTI ID: 1346934