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Cation Exchange-Mediated Synthesis of Library of Plasmomagnetic Nanoheterostructures: Transformation of 2‑Dimensional-Shaped Fe7S8 Nanoplates to Cu–Fe–S-Based Ternary Compound
journal contribution
posted on 2018-07-31, 00:00 authored by Dulal Barman, Sirshendu Ghosh, Sumana Paul, Biswajit Dalal, Subodh Kumar DeCation
exchange mediated synthesis of nanoheterostructures (NHSs),
core–shell structure or segmented nanostructures are gaining
high interest in nanoscience research as the process gives a wide
window of opportunity to tune and enhance the photophysical properties
of semiconductors. Presence of point defects or layered structure
of the material accelerates cation exchange process, which is well
established for copper chalcogenide system. Here, we are reporting
facile synthesis of high-quality Fe7S8 hexagonal
nanoplate by colloidal synthesis route and studied the effect of Cu(I)
ion addition by in situ and ex situ condition. The addition and consequent
increase of Cu(I) precursor concentration to presynthetic Fe7S8 nanocrystals (ex situ) leads to successive compositional
and morphological transformations as follows: Fe7S8 (hexagonal nanoplate) → Fe7S8@Cu5FeS4 (multigrained heterostructure) →
Cu1.97S/Cu5FeS4/Cu1.97S (nanodumbbell) → Cu1.97S/Cu5FeS4 (segmented nanohat) → Cu1.97S (nanodisk).
Native Fe vacancies in layered crystalline structure of original Fe7S8 drive intercalation and cation exchange processes
to stabilize a particular NHS. Different diffusion rates and channels
of incoming Cu and outgoing Fe ions result in linear and bent nanodumbbells.
The position of strong localized surface plasmon resonance (LSPR)
band in NHSs is shifted from visible region to infrared region of
the spectrum due to the variation of hole concentration originating
from intrinsic Cu vacancy. The LSPR bands in NHS are further tuned
by generating more holes through oxidation of Cu(I) → Cu(II)
reaction in oxygen atmosphere. Shape anisotropy in NHS gives rise
to multiple plasmon modes. Fe7S8 (hexagonal
nanoplate) and Cu1.97S/Cu5FeS4/Cu1.97S (nanodumbbell) exhibit features of ferrimagnetism with
transition temperature of above 300 and 320 K, respectively. In situ
chemical synthesis using same Cu and Fe precursors as that of ex situ
process yields CuFeS2 and Cu5FeS4 phases under Cu-deficit and Cu-rich environment. The LSPR resonance
bands with high plasmonic sensitivity are also tuned by controlling
the hole concentration.
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Keywords
Fe 7 S 8 drive intercalation1.97Cu 5 FeS 4 phasesprocess yields CuFeS 2Fe ions resulthole concentrationcation exchange processesFe 7 S 8Different diffusion ratesCation Exchange-Mediated Synthesissurface plasmon resonanceNative Fe vacanciescation exchange processCu 5 FeS 4NHScopper chalcogenide systemLSPR resonance bandspresynthetic Fe 7 S 8 nanocrystals
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