Unravelling the roles of size, ligands and pressure in the piezochromic properties of CdS nanocrystals
File(s)
Published version
Author(s)
Corsini, NRC
Hine, NDM
Haynes, PD
Molteni, C
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 potential applications such as stress sensors and electromechanical devices. Here, we describe the novel insights into these piezochromic effects gained from using a linear-scaling density functional theory framework and an electronic enthalpy scheme, which allow us to accurately characterize the electronic structure of CdS nanocrystals with a zincblende-like core of experimentally relevant size. In particular, we focus on unravelling the complex interplay of size and surface (phenyl) ligands with pressure. We show that pressure-induced deformations 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 increase due to compression, which is offset by (ii) distortions and disorder and, to a lesser extent, orbital hybridization induced by ligands affecting the frontier orbitals. Moreover, we observe that the main peak in the optical absorption 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 overlap and oscillator strength, so that at zero pressure, the lowest energy transition involves deeper hole orbitals than in the case of hydrogen-capped nanocrystals; the application of pressure induces greater delocalization 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 experimental techniques, this work exemplifies the detailed understanding of structure–property relationships under pressure that can be obtained for realistic nanocrystals with state-of-the-art first-principles methods and used for the characterization and design of devices based on these and similar nanomaterials.
Date Issued
2017-02-08
Date Acceptance
2017-01-23
Citation
Nano Letters, 2017, 17 (2), pp.1042-1048
ISSN
1530-6992
Publisher
American Chemical Society
Start Page
1042
End Page
1048
Journal / Book Title
Nano Letters
Volume
17
Issue
2
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)
License URL
Sponsor
The Royal Society
Engineering & Physical Science Research Council (EPSRC)
Engineering and Physical Sciences Research Council
Grant Number
UF090007
EP/J015059/1
EP/G036888/1
Subjects
Science & Technology
Physical Sciences
Technology
Chemistry, Multidisciplinary
Chemistry, Physical
Nanoscience & Nanotechnology
Materials Science, Multidisciplinary
Physics, Applied
Physics, Condensed Matter
Chemistry
Science & Technology - Other Topics
Materials Science
Physics
II-VI nanocrystals
piezochromic properties
linear scaling methods
electronic enthalpy
time-dependent density functional theory
INDUCED STRUCTURAL TRANSFORMATIONS
DENSITY-FUNCTIONAL THEORY
SEMICONDUCTOR NANOCRYSTALS
INDUCED AMORPHIZATION
MOLECULAR-DYNAMICS
QUANTUM DOTS
ELECTRONIC EXCITATIONS
OPTICAL-PROPERTIES
SI35H36 CLUSTER
AB-INITIO
II−VI nanocrystals
MD Multidisciplinary
Publication Status
Published
Date Publish Online
2017-01-27