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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.


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Low resolutionTEM images of hexagonal platelet-shaped (a) Cu3-xP and (b) InP NCs after cation exchange. The scalebar in each image is 50 nm. (c) XRD patterns and (d) Raman spectraobtained from dropcast solutions of Cu3-xP, Cu3-xP/InP, and InP NCs.In (c) the bulk reflections of Cu3-xP (ICSD card no. 15056) and WZ InP, the latter calculated from theICSD card no. 180911, are also reported. From the Raman spectra in(d), labeled as Cu3-xP/InP andInP, it can be noticed the presence of transverse optical (TO, at304 cm–1) and longitudinal optical (LO, at 343 cm–1) phonon first order modes and of the LO phonon secondorder mode at 687 cm–1 of InP, in accordance withliterature data.36 At a deeper analysis,it is possible to note that the LO peak, even if characterized bya narrow profile (fwhm = 5 cm–1), shows an asymmetricbroadening at lower frequencies, associated with contributions fromthe surface modes of the crystals.36 (e)UV–vis-NIR absorption curves of solutions of Cu3-xP, Cu3-xP/InP,and InP NCs dispersed in TCE.
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fig4: Low resolutionTEM images of hexagonal platelet-shaped (a) Cu3-xP and (b) InP NCs after cation exchange. The scalebar in each image is 50 nm. (c) XRD patterns and (d) Raman spectraobtained from dropcast solutions of Cu3-xP, Cu3-xP/InP, and InP NCs.In (c) the bulk reflections of Cu3-xP (ICSD card no. 15056) and WZ InP, the latter calculated from theICSD card no. 180911, are also reported. From the Raman spectra in(d), labeled as Cu3-xP/InP andInP, it can be noticed the presence of transverse optical (TO, at304 cm–1) and longitudinal optical (LO, at 343 cm–1) phonon first order modes and of the LO phonon secondorder mode at 687 cm–1 of InP, in accordance withliterature data.36 At a deeper analysis,it is possible to note that the LO peak, even if characterized bya narrow profile (fwhm = 5 cm–1), shows an asymmetricbroadening at lower frequencies, associated with contributions fromthe surface modes of the crystals.36 (e)UV–vis-NIR absorption curves of solutions of Cu3-xP, Cu3-xP/InP,and InP NCs dispersed in TCE.

Mentions: The Cu3-xP NCs resulting from our synthetic route are typicallypolydispersed hexagonal shaped platelets with a diameter ranging from∼10 nm to ∼50 nm. Higher reaction times (i.e., morethan 50 min) result in larger NCs that can be grown as large as 100nm, albeit with a broader size distribution.8 The XPS analysis of the as-synthesized Cu3-xP NCs is consistent with the presence of Cu+ andP3– species (giving a rough estimation of the Cu:Pratio of 2.9:1) and excludes any trace of Cu2+ ions (seethe SI and Figure S7 for further details).According to their XRD pattern (reported later in this work in Figure 4c and in Figure S8),the NCs crystallize in a hexagonal phase (space group P63cm, see Figure 1a-b). Refinementof the structural parameters using the fundamental parameter (FP)method19 yielded the following latticeparameters: a = 6.9507 Å and c = 7.1428 Å (see Figure S8) thatare consistent with a Cu3P structure substoichiometricin copper, as shown by Olofsson.7


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)

Low resolutionTEM images of hexagonal platelet-shaped (a) Cu3-xP and (b) InP NCs after cation exchange. The scalebar in each image is 50 nm. (c) XRD patterns and (d) Raman spectraobtained from dropcast solutions of Cu3-xP, Cu3-xP/InP, and InP NCs.In (c) the bulk reflections of Cu3-xP (ICSD card no. 15056) and WZ InP, the latter calculated from theICSD card no. 180911, are also reported. From the Raman spectra in(d), labeled as Cu3-xP/InP andInP, it can be noticed the presence of transverse optical (TO, at304 cm–1) and longitudinal optical (LO, at 343 cm–1) phonon first order modes and of the LO phonon secondorder mode at 687 cm–1 of InP, in accordance withliterature data.36 At a deeper analysis,it is possible to note that the LO peak, even if characterized bya narrow profile (fwhm = 5 cm–1), shows an asymmetricbroadening at lower frequencies, associated with contributions fromthe surface modes of the crystals.36 (e)UV–vis-NIR absorption curves of solutions of Cu3-xP, Cu3-xP/InP,and InP NCs dispersed in TCE.
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fig4: Low resolutionTEM images of hexagonal platelet-shaped (a) Cu3-xP and (b) InP NCs after cation exchange. The scalebar in each image is 50 nm. (c) XRD patterns and (d) Raman spectraobtained from dropcast solutions of Cu3-xP, Cu3-xP/InP, and InP NCs.In (c) the bulk reflections of Cu3-xP (ICSD card no. 15056) and WZ InP, the latter calculated from theICSD card no. 180911, are also reported. From the Raman spectra in(d), labeled as Cu3-xP/InP andInP, it can be noticed the presence of transverse optical (TO, at304 cm–1) and longitudinal optical (LO, at 343 cm–1) phonon first order modes and of the LO phonon secondorder mode at 687 cm–1 of InP, in accordance withliterature data.36 At a deeper analysis,it is possible to note that the LO peak, even if characterized bya narrow profile (fwhm = 5 cm–1), shows an asymmetricbroadening at lower frequencies, associated with contributions fromthe surface modes of the crystals.36 (e)UV–vis-NIR absorption curves of solutions of Cu3-xP, Cu3-xP/InP,and InP NCs dispersed in TCE.
Mentions: The Cu3-xP NCs resulting from our synthetic route are typicallypolydispersed hexagonal shaped platelets with a diameter ranging from∼10 nm to ∼50 nm. Higher reaction times (i.e., morethan 50 min) result in larger NCs that can be grown as large as 100nm, albeit with a broader size distribution.8 The XPS analysis of the as-synthesized Cu3-xP NCs is consistent with the presence of Cu+ andP3– species (giving a rough estimation of the Cu:Pratio of 2.9:1) and excludes any trace of Cu2+ ions (seethe SI and Figure S7 for further details).According to their XRD pattern (reported later in this work in Figure 4c and in Figure S8),the NCs crystallize in a hexagonal phase (space group P63cm, see Figure 1a-b). Refinementof the structural parameters using the fundamental parameter (FP)method19 yielded the following latticeparameters: a = 6.9507 Å and c = 7.1428 Å (see Figure S8) thatare consistent with a Cu3P structure substoichiometricin copper, as shown by Olofsson.7

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