Abstract
Semiconductors with chiral geometries at the nanoscale and mesoscale provide a rich materials platform for polarization optics, photocatalysis, and biomimetics. Unlike metallic and organic optical materials, the relationship between the geometry of chiral semiconductors and their chiroptical properties remains, however, vague. Homochiral ensembles of semiconductor helices with defined geometries open the road to understanding complex relationships between geometrical parameters and chiroptical properties of semiconductor materials. We show that semiconductor helices can be prepared with an absolute yield of ca 0.1% and an enantiomeric excess (e.e.) of 98% or above from cysteine-stabilized cadmium telluride nanoparticles (CdTe NPs) dispersed in methanol. This high e.e. for a spontaneously occurring chemical process is attributed to chiral self-sorting based on the thermodynamic preference of NPs to assemble with those of the same handedness. The dispersions of homochiral self-assembled helices display broadband visible and near-infrared (Vis-NIR) polarization rotation with anisotropy (g) factors approaching 0.01. Calculated circular dichroism (CD) spectra accurately reproduced experimental CD spectra and gave experimentally validated spectral predictions for different geometrical parameters enabling de novo design of chiroptical semiconductor materials. Unlike metallic, ceramic, and polymeric helices that serve predominantly as scatterers, chiroptical properties of semiconductor helices have nearly equal contribution of light absorption and scattering, which is essential for device-oriented, field-driven light modulation. Deconstruction of a helix into a series of nanorods provides a simple model for the light-matter interaction and chiroptical activity of helices. This study creates a framework for further development of polarization-based optics toward biomedical applications, telecommunications, and hyperspectral imaging.
| Original language | English |
|---|---|
| Article number | e1601159 |
| Journal | Science advances |
| Volume | 3 |
| Issue number | 3 |
| DOIs | |
| State | Published - Mar 2017 |
| Externally published | Yes |
Bibliographical note
Publisher Copyright:© 2017 The Authors, some rights reserved.
Funding
We would like to thank W. Zhang for assistance with indexing electron diffraction patterns, E. Mutlugun for providing the refractive index data for individual CdTe NPs, and the University of Michigan’s Michigan Center for Materials Characterization for assistance with electron microscopy. The central part of this work was supported by the NSF project “Energy- and Cost-Efficient Manufacturing Employing Nanoparticles” (NSF 1463474). Partial support of this work was also made by the Center for Photonic and Multiscale Nanomaterials funded by the NSF Materials Research Science and Engineering Center program DMR-1120923, as well as NSF projects 1403777 and 1411014, and the University of Michigan’s Michigan Center for Materials Characterization for the NSF grant DMR-9871177 for the funding of the JEOL 2100F and 3011 analytical electron microscope used in this work. Author contributions: W.F. and J.-Y.K. carried out CdTe NP synthesis, assembly, and characterization. W.F., X.W., and H.A.C. performed Lumerical simulations. W.F. and Z.Q. studied 3D tomography of helices. L.M. carried out TEM studies on CdTe NPs. N.A.K. supervised the project. W.F. and N.A.K. analyzed the data and co-wrote the paper. All authors discussed the results and commented on the manuscript. Competing interests: The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from N.A.K. ([email protected]).
| Funders | Funder number |
|---|---|
| National Science Foundation | 1403777, 9871177, 1120923 |
| University of Michigan | |
| National Science Foundation | DMR-9871177, DMR-1120923, 1411014, JEOL 2100F, 1463474 |