Cu2Se and Cu Nanocrystals as Local Sources of Copper in Thermally ActivatedIn SituCation Exchange (original) (raw)
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Alloyed copper chalcogenide nanoplatelets via partial cation exchange reactions
ACS nano, 2014
We report the synthesis of alloyed quaternary and quinary nanocrystals based on copper chalcogenides, namely, copper zinc selenide-sulfide (CZSeS), copper tin selenide-sulfide (CTSeS), and copper zinc tin selenide-sulfide (CZTSeS) nanoplatelets (NPLs) (∼20 nm wide) with tunable chemical composition. Our synthesis scheme consisted of two facile steps: i.e., the preparation of copper selenide-sulfide (Cu2-xSeyS1-y) platelet shaped nanocrystals via the colloidal route, followed by an in situ cation exchange reaction. During the latter step, the cation exchange proceeded through a partial replacement of copper ions by zinc or/and tin cations, yielding homogeneously alloyed nanocrystals with platelet shape. Overall, the chemical composition of the alloyed nanocrystals can easily be controlled by the amount of precursors that contain cations of interest (e.g., Zn, Sn) to be incorporated/alloyed. We have also optimized the reaction conditions that allow a complete preservation of the size,...
Journal of Materials Chemistry C, 2014
Rod-shaped CdTe-Cu 2Àx Te nano-heterostructures with tunable dimensions of both sub-units and a type II band alignment were prepared by Cd 2+ /Cu + cation exchange. The light absorption properties of the heterostructures are dominated by the excitonic and plasmonic contributions arising, respectively, from the CdTe and the Cu 2Àx Te sub-units. These results were confirmed over a wide range of sub-unit length fractions through optical modelling based on the discrete dipole approximation (DDA). Although assuming electronically independent sub-units, our modelling results indicate a negligible ground state interaction between the CdTe exciton and the Cu 2Àx Te plasmon. This lack of interaction may be due to the low spectral overlap between exciton and plasmon, but also to localization effects in the vacancydoped sub-unit. The electronic interaction between both sub-units was evaluated with pump-probe spectroscopy by assessing the relaxation dynamics of the excitonic transition. In particular, the CdTe exciton decays faster in the presence of the Cu 2Àx Te sub-unit, and the decay gets faster with increasing its length. This points towards an increased probability of Auger mediated recombination due to the high carrier density in the Cu 2Àx Te sub-unit. This indication is supported through length-fraction dependent band structure calculations, which indicate a significant leakage of the CdTe electron wavefunction into the Cu 2Àx Te sub-unit that increases along with the shortening of the CdTe sub-unit, thus enhancing the probability of Auger recombination. Therefore, for the application of type II chalcogenide-chalcogenide heterostructures based on Cu and Cd for photoenergy conversion, a shorter Cu-based sub-unit may be advantageous, and the suppression of high carrier density within this sub-unit is of high importance.
A facile chemical route for the synthesis of copper sulfide (CuS) nanocrystallites consists of the reaction between Cu(CH3COO)2 .H2O and Na2S2O3 .5H2O. In this reaction the influence of the following factors was pursued: pH value, reaction time, molar ratios, temperature and others. In this article we tried to establish the evolution of the morphology and the shape of the CuS nanocrystallites with the pH value. The CuS nanocrystallites obtained were studied by X ray diffraction, IR spectrometry, TEM – transmission electron microscopy and SAED selected area electron diffraction. The CuS crystallites are formed in spherical or “discoidal” particles which are bonded in bigger aggregates. The reaction pH value was varied from a slightly acid value to an alkali value. In case of alkali medium the crystallites dimensions were smaller than their value in slightly acid medium.
Nano Letters, 2010
The growth behavior of cadmium chalcogenides (CdE ) CdS, CdSe, and CdTe) on sphalerite Cu 2-x Se nanocrystals (size range 10-15 nm) is studied. Due to the capability of Cu 2-x Se to undergo a fast and quantitative cation exchange reaction in the presence of excessive Cd 2+ ions, no Cu 2-x Se/CdE heterostructures are obtained and instead branched CdSe/CdE nanocrystals are built which consist of a sphalerite CdSe core and wurtzite CdE arms. While CdTe growth yields multiarmed structures with overall tetrahedral symmetry, CdS and CdSe arm growth leads to octapod-shaped nanocrystals. These results differ significantly from literature findings about the growth of CdE on sphalerite CdSe particles, which until now had always yielded tetrapod-shaped nanocrystals.
Nano letters, 2014
We demonstrate dual interface formation in nanocrystals (NCs) through cation exchange, creating epitaxial heterostructures within spherical NCs. The thickness of the inner-disk layer can be tuned to form two-dimensional (2D), single atomic layers (<1 nm). During the cation exchange reaction from copper sulfide to zinc sulfide (ZnS), we observe a solid-solid phase transformation of the copper sulfide phase in heterostructured NCs. As the cation exchange reaction is initiated, Cu ions replaced by Zn ions at the interfaces are accommodated in intrinsic Cu vacancy sites present in the initial roxbyite (Cu1.81S) phase of copper sulfide, inducing a full phase transition to djurleite (Cu1.94S)/low chalcocite (Cu2S), a more thermodynamically stable phase than roxbyite. As the reaction proceeds and reduces the size of the copper sulfide layer, the epitaxial strain at the interfaces between copper sulfide and ZnS increases and is maximized for a copper sulfide disk ∼ 5 nm thick. To minimiz...
Journal of Cluster Science, 2013
Cu 2 S nanostructures were synthesized successfully via hydrothermal approach with new precursor. The precursor was characterized via thermal gravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). The products were characterized with X-ray diffraction, scanning electron microscopy, transition electron microscopy, energy-dispersive X-ray spectroscopy, FT-IR, room temperature photoluminescence spectroscopy and ultraviolet-visible spectroscopy. The effect of different parameters such as Cu 2? /TGA mole ratio, reaction time and temperature were investigated on product size and morphology. Keywords Cu 2 S Á Hydrothermal Á Nanostructures Á Polymeric precursor Introduction Recently, transition metals chalcogenide semiconductors have been attracted due to potential application in catalyst, solar cells, field emission, photoluminescence, and photo electronic device [1, 2]. Synthesis methods for fabrication of transition metals chalcogenide such as CdS, CdTe, CdSe, ZnS and ZnSe have been developed significantly [3-8]. But, despite of the application of copper sulfide in solar cells, cold cathode and nanoscale switches [9-12], controlled synthesis methods for preparation of this material with good quality and purity has not been done widely due to formation of copper sulfide as mixture phases. Copper sulfide (Cu 2-x S) has various phases such as Cu 2 S (b,c-chalcocite), Cu 1.96 S (djurleite), Cu 1.8 S (digenite) and CuS (covellite). All of these phases are p-semiconductor due to presence of copper vacancies in their lattice [12]. These phases show stoichiometry-dependent
Electrically driven cation exchange for in situ fabrication of individual nanostructures
Nature communications, 2017
Cation exchange (CE) has been recognized as a particularly powerful tool for the synthesis of heterogeneous nanocrystals. At present, CE can be divided into two categories, namely ion solvation-driven CE reaction and thermally activated CE reaction. Here we report an electrically driven CE reaction to prepare individual nanostructures inside a transmission electron microscope. During the process, Cd is eliminated due to Ohmic heating, whereas Cu(+) migrates into the crystal driven by the electrical field force. Contrast experiments reveal that the feasibility of electrically driven CE is determined by the structural similarity of the sulfur sublattices between the initial and final phases, and the standard electrode potentials of the active electrodes. Our experimental results demonstrate a strategy for the selective growth of individual nanocrystals and provide crucial insights into understanding of the microscopic pathways leading to the formation of heterogeneous structures.