Unravelling the roles of size, ligands and pressure in the piezochromic properties of CdS nanocrystals

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Title: Unravelling the roles of size, ligands and pressure in the piezochromic properties of CdS nanocrystals
Author(s): Corsini, NRC
Hine, NDM
Haynes, PD
Molteni, C
Item Type: Journal Article
Abstract: Understanding the effects of pressure-induced deformations on the optoelectronic properties of nanomaterials is important not only from the fundamental point of view, but also for po- tential applications such as stress sensors and electromechanical devices. Here we describe the novel insights into these piezochromic ef- fects gained from using a linear-scaling den- sity functional theory framework and an elec- tronic enthalpy scheme, which allow us to ac- curately characterize the electronic structure of CdS nanocrystals with a zincblende-like core of experimentally relevant size. In particu- lar we focus on unravelling the complex inter- play of size and surface (phenyl) ligands with pressure. We show that pressure-induced de- formations are not simple isotropic scaling of the original structures and that the change in HOMO-LUMO gap with pressure results from two competing factors: (i) a bulk-like linear in- crease due to compression, which is offset by (ii) distortions/disorder and, to a lesser ex- tent, orbital hybridization induced by ligands affecting the frontier orbitals. Moreover, we observe that the main peak in the optical ab- sorption spectra is systematically red-shifted or blue-shifted, as pressure is increased up to 5 GPa, depending on the presence or absence of phenyl ligands. These heavily hybridize the frontier orbitals, causing a reduction in over- lap and oscillator strength, so that at zero pres- sure the lowest energy transition involves deeper hole orbitals than in the case of hydrogen- capped nanocrystals; the application of pressure induces greater delocalisation over the whole nanocrystals bringing the frontier hole orbitals into play and resulting in an unexpected red shift for the phenyl-capped nanocrystals, in part caused by distortions. In response to a growing interest in relatively small nanocrystals that can be difficult to accurately characterize with ex- perimental techniques, this work exemplifies the detailed understanding of structure-property re- lationships under pressure that can be obtained for realistic nanocrystals with state-of-the-art first principles methods and used for the charac- terization and design of devices based on these and similar nanomaterials.
Publication Date: 27-Jan-2017
Date of Acceptance: 23-Jan-2017
URI: http://hdl.handle.net/10044/1/44203
DOI: https://dx.doi.org/10.1021/acs.nanolett.6b04461
ISSN: 1530-6992
Publisher: American Chemical Society
Start Page: 1042
End Page: 1048
Journal / Book Title: Nano Letters
Volume: 17
Issue: 2
Sponsor/Funder: The Royal Society
Engineering & Physical Science Research Council (EPSRC)
Engineering and Physical Sciences Research Council
Funder's Grant Number: UF090007
Copyright Statement: © 2017 American Chemical Society. ACS AuthorChoice - This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited. (http://pubs.acs.org/page/policy/authorchoice_ccby_termsofuse.html)
Keywords: Science & Technology
Physical Sciences
Chemistry, Multidisciplinary
Chemistry, Physical
Nanoscience & Nanotechnology
Materials Science, Multidisciplinary
Physics, Applied
Physics, Condensed Matter
Science & Technology - Other Topics
Materials Science
II-VI nanocrystals
piezochromic properties
linear scaling methods
electronic enthalpy
time-dependent density functional theory
II−VI nanocrystals
electronic enthalpy
linear scaling methods
piezochromic properties
time-dependent density functional theory
Nanoscience & Nanotechnology
MD Multidisciplinary
Publication Status: Published
Appears in Collections:Faculty of Engineering
Faculty of Natural Sciences

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