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Cu3-x P Nanocrystals as a Material Platform for Near-Infrared Plasmonics and Cation Exchange Reactions.

De Trizio L, Gaspari R, Bertoni G, Kriegel I, Moretti L, Scotognella F, Maserati L, Zhang Y, Messina GC, Prato M, Marras S, Cavalli A, Manna L - Chem Mater (2015)

Bottom Line: Also, thermoelectric measurements point to a p-type behavior of the majority carriers from films of Cu3-x P NCs.It is likely that both the LSPR and the p-type character of our Cu3-x P NCs arise from the presence of a large number of Cu vacancies in such NCs.We demonstrate here that Cu3-x P NCs can be easily cation-exchanged to hexagonal wurtzite InP NCs, with preservation of the anion framework (the anion framework in Cu3-x P is very close to that of wurtzite InP).

View Article: PubMed Central - PubMed

Affiliation: Department of Nanochemistry, CONCEPT Lab, Department of Nanostructures, and CompuNet, Istituto Italiano di Tecnologia (IIT) , via Morego, 30, 16163 Genova, Genova, Italy.

ABSTRACT

Synthesis approaches to colloidal Cu3P nanocrystals (NCs) have been recently developed, and their optical absorption features in the near-infrared (NIR) have been interpreted as arising from a localized surface plasmon resonance (LSPR). Our pump-probe measurements on platelet-shaped Cu3-x P NCs corroborate the plasmonic character of this absorption. In accordance with studies on crystal structure analysis of Cu3P dating back to the 1970s, our density functional calculations indicate that this material is substoichiometric in copper, since the energy of formation of Cu vacancies in certain crystallographic sites is negative, that is, they are thermodynamically favored. Also, thermoelectric measurements point to a p-type behavior of the majority carriers from films of Cu3-x P NCs. It is likely that both the LSPR and the p-type character of our Cu3-x P NCs arise from the presence of a large number of Cu vacancies in such NCs. Motivated by the presence of Cu vacancies that facilitate the ion diffusion, we have additionally exploited Cu3-x P NCs as a starting material on which to probe cation exchange reactions. We demonstrate here that Cu3-x P NCs can be easily cation-exchanged to hexagonal wurtzite InP NCs, with preservation of the anion framework (the anion framework in Cu3-x P is very close to that of wurtzite InP). Intermediate steps in this reaction are represented by Cu3-x P/InP heterostructures, as a consequence of the fact that the exchange between Cu(+) and In(3+) ions starts from the peripheral corners of each NC and gradually evolves toward the center. The feasibility of this transformation makes Cu3-x P NCs an interesting material platform from which to access other metal phosphides by cation exchange.

No MeSH data available.


Related in: MedlinePlus

(a-b) HRTEM images and the correspondingFFT (of platelet-shaped InP NCs). The WZ structure can be directlyinferred from the top (a) and the side (b) views. (c) Atomic sketchesrepresenting (left panel) [11̅0] and [001] lattice slabs ofhexagonal Cu3-xP and (right panel)[100], [001] lattice slabs of WZ InP. The structural isomorphism ofthe two phases is evident, with preservation of the anion sublattice.The projection of the primitive unit cell is depicted with a solidblack line in both structures.
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fig6: (a-b) HRTEM images and the correspondingFFT (of platelet-shaped InP NCs). The WZ structure can be directlyinferred from the top (a) and the side (b) views. (c) Atomic sketchesrepresenting (left panel) [11̅0] and [001] lattice slabs ofhexagonal Cu3-xP and (right panel)[100], [001] lattice slabs of WZ InP. The structural isomorphism ofthe two phases is evident, with preservation of the anion sublattice.The projection of the primitive unit cell is depicted with a solidblack line in both structures.

Mentions: Further insights over the cation exchange processcould be deduced from the optical absorption spectra of solutionscontaining initial Cu3-xP NCs,the intermediate sample, and the final InP NCs, respectively. As shownin Figure 4e, the initial copper phosphideNCs (black curve) were characterized by a LSPR absorption peak (asalready discussed earlier). A weaker NIR absorption in the intermediatesample (blue curve in Figure 4e), with a maximumstill at about 1500 nm, most likely arose from the residual Cu3-xP domains in the partially exchangedheterostructures. The final InP NCs (red curve) did not show any featurein the NIR region and exhibited instead an absorption edge havingits maximum at ∼800 nm from which we extrapolated a bandgapof 1.55 eV. This value is slightly larger than the bulk band gap ofWZ InP (832 nm, 1.49 eV),39−43 thus we believe that a quantum confinement of carriers might takeplace in our InP NCs. Since the Bohr radius of bulk zinc-blende InPis around 110 Å (11 nm),44 the confinementin our InP nanoplatelets should be along their (001) direction (theone perpendicular to the basal facets). This is reasonable, as thethickness of some NCs could be as low as 5 nm (see Figure 6b), while the lateral dimensions were much larger.


Cu3-x P Nanocrystals as a Material Platform for Near-Infrared Plasmonics and Cation Exchange Reactions.

De Trizio L, Gaspari R, Bertoni G, Kriegel I, Moretti L, Scotognella F, Maserati L, Zhang Y, Messina GC, Prato M, Marras S, Cavalli A, Manna L - Chem Mater (2015)

(a-b) HRTEM images and the correspondingFFT (of platelet-shaped InP NCs). The WZ structure can be directlyinferred from the top (a) and the side (b) views. (c) Atomic sketchesrepresenting (left panel) [11̅0] and [001] lattice slabs ofhexagonal Cu3-xP and (right panel)[100], [001] lattice slabs of WZ InP. The structural isomorphism ofthe two phases is evident, with preservation of the anion sublattice.The projection of the primitive unit cell is depicted with a solidblack line in both structures.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4419285&req=5

fig6: (a-b) HRTEM images and the correspondingFFT (of platelet-shaped InP NCs). The WZ structure can be directlyinferred from the top (a) and the side (b) views. (c) Atomic sketchesrepresenting (left panel) [11̅0] and [001] lattice slabs ofhexagonal Cu3-xP and (right panel)[100], [001] lattice slabs of WZ InP. The structural isomorphism ofthe two phases is evident, with preservation of the anion sublattice.The projection of the primitive unit cell is depicted with a solidblack line in both structures.
Mentions: Further insights over the cation exchange processcould be deduced from the optical absorption spectra of solutionscontaining initial Cu3-xP NCs,the intermediate sample, and the final InP NCs, respectively. As shownin Figure 4e, the initial copper phosphideNCs (black curve) were characterized by a LSPR absorption peak (asalready discussed earlier). A weaker NIR absorption in the intermediatesample (blue curve in Figure 4e), with a maximumstill at about 1500 nm, most likely arose from the residual Cu3-xP domains in the partially exchangedheterostructures. The final InP NCs (red curve) did not show any featurein the NIR region and exhibited instead an absorption edge havingits maximum at ∼800 nm from which we extrapolated a bandgapof 1.55 eV. This value is slightly larger than the bulk band gap ofWZ InP (832 nm, 1.49 eV),39−43 thus we believe that a quantum confinement of carriers might takeplace in our InP NCs. Since the Bohr radius of bulk zinc-blende InPis around 110 Å (11 nm),44 the confinementin our InP nanoplatelets should be along their (001) direction (theone perpendicular to the basal facets). This is reasonable, as thethickness of some NCs could be as low as 5 nm (see Figure 6b), while the lateral dimensions were much larger.

Bottom Line: Also, thermoelectric measurements point to a p-type behavior of the majority carriers from films of Cu3-x P NCs.It is likely that both the LSPR and the p-type character of our Cu3-x P NCs arise from the presence of a large number of Cu vacancies in such NCs.We demonstrate here that Cu3-x P NCs can be easily cation-exchanged to hexagonal wurtzite InP NCs, with preservation of the anion framework (the anion framework in Cu3-x P is very close to that of wurtzite InP).

View Article: PubMed Central - PubMed

Affiliation: Department of Nanochemistry, CONCEPT Lab, Department of Nanostructures, and CompuNet, Istituto Italiano di Tecnologia (IIT) , via Morego, 30, 16163 Genova, Genova, Italy.

ABSTRACT

Synthesis approaches to colloidal Cu3P nanocrystals (NCs) have been recently developed, and their optical absorption features in the near-infrared (NIR) have been interpreted as arising from a localized surface plasmon resonance (LSPR). Our pump-probe measurements on platelet-shaped Cu3-x P NCs corroborate the plasmonic character of this absorption. In accordance with studies on crystal structure analysis of Cu3P dating back to the 1970s, our density functional calculations indicate that this material is substoichiometric in copper, since the energy of formation of Cu vacancies in certain crystallographic sites is negative, that is, they are thermodynamically favored. Also, thermoelectric measurements point to a p-type behavior of the majority carriers from films of Cu3-x P NCs. It is likely that both the LSPR and the p-type character of our Cu3-x P NCs arise from the presence of a large number of Cu vacancies in such NCs. Motivated by the presence of Cu vacancies that facilitate the ion diffusion, we have additionally exploited Cu3-x P NCs as a starting material on which to probe cation exchange reactions. We demonstrate here that Cu3-x P NCs can be easily cation-exchanged to hexagonal wurtzite InP NCs, with preservation of the anion framework (the anion framework in Cu3-x P is very close to that of wurtzite InP). Intermediate steps in this reaction are represented by Cu3-x P/InP heterostructures, as a consequence of the fact that the exchange between Cu(+) and In(3+) ions starts from the peripheral corners of each NC and gradually evolves toward the center. The feasibility of this transformation makes Cu3-x P NCs an interesting material platform from which to access other metal phosphides by cation exchange.

No MeSH data available.


Related in: MedlinePlus