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Title: Dipole-like electrostatic asymmetry of gold nanorods

The symmetry of metallic nanocolloids, typically envisaged as simple geometrical shapes, is rarely questioned. However, the symmetry considerations are so essential for understanding their electronic structure, optical properties, and biological effects that it is important to reexamine these foundational assumptions for nanocolloids. Gold nanorods (AuNRs) are generally presumed to have nearly perfect geometry of a cylinder and therefore are centrosymmetric. We show that AuNRs, in fact, have a built-in electrostatic potential gradient on their surface and behave as noncentrosymmetric particles. The electrostatic potential gradient of 0.11 to 0.07 V/nm along the long axes of nanorods is observed by off-axis electron holography. Kelvin probe microscopy, secondary electron imaging, energy-filtered transmission electron microscopy, and plasmon mapping reveal that the axial asymmetry is associated with a consistently unequal number of cetyltrimethylammonium bromide moieties capping the two ends of the AuNRs. Electrostatic field maps simulated for the AuNR surface reproduce the holography images. The dipole-like surface potential gradient explains previously puzzling discrepancies in nonlinear optical effects originating from the noncentrosymmetric nature of AuNRs. Furthermore, similar considerations of symmetry breaking are applicable to other nanoscale structures for which the property-governing symmetry of the organic shell may differ from the apparent symmetry of inorganic core observedmore » in standard electron microscopy images.« less
Authors:
ORCiD logo [1] ;  [2] ;  [1] ;  [3] ; ORCiD logo [2] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1]
  1. Univ. of Michigan, Ann Arbor, MI (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
  3. SPM Labs LLC, Tempe, AZ (United States)
Publication Date:
Report Number(s):
BNL-203570-2018-JAAM
Journal ID: ISSN 2375-2548
Grant/Contract Number:
SC0012704
Type:
Accepted Manuscript
Journal Name:
Science Advances
Additional Journal Information:
Journal Volume: 4; Journal Issue: 2; Journal ID: ISSN 2375-2548
Publisher:
AAAS
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
OSTI Identifier:
1434778