Copper Chalcogenide Nanocrystals Research Articles

Redox Chemistries for Vacancy Modulation in Plasmonic Copper Phosphide Nanocrystals.

Copper phosphide (Cu3-xP) nanocrystals are promising materials for nanoplasmonics due to their substoichiometric composition, enabling the generation and stabilization of excess delocalized holes and leading to localized surface plasmon resonance (LSPR) absorption in the near-IR. We present three Cu-coupled redox chemistries that allow postsynthetic modulation of the delocalized hole concentrations and corresponding LSPR absorption in colloidal Cu3-xP nanocrystals. Changes in the structural, optical, and compositional properties are evaluated by powder X-ray diffraction, electronic absorption spectroscopy, 31P magic-angle spinning solid-state nuclear magnetic resonance spectroscopy, and elemental analysis. The redox chemistries presented herein can be used to access nanocrystals with LSPR energies of 660-890 meV, a larger range than has been possible through synthetic tuning alone. In addition to utilizing previously reported redox chemistries used for copper chalcogenide nanocrystals, we show that the largest structural and LSPR modulation is achieved using a divalent metal halide and trioctylphosphine. Specifically, nanocrystals treated with zinc iodide and trioctylphosphine have the smallest unit-cell volume (295.2 Å3) reported for P63cm Cu3-xP, indicating more Cu vacancies than have been previously observed. Overall, these redox chemistries present valuable insight into controlling the optical and structural properties of Cu3-xP.

Recent advances in heavily doped plasmonic copper chalcogenides: from synthesis to biological application

Copper-based chalcogenide compounds have emerged as alternative materials to Cd- or Pb-based traditional semiconductors and have drawn significant attention. Compared with widely reported semiconductors, copper chalcogenide nanocrystals (NCs) with abundant copper defects and vacancies present p-type features. Additionally, the migration of free hole carriers in copper-based chalcogenide NCs produced a metal-like local surface plasmon resonance (LSPR) effect. In this review, we focused on the plasmonic copper chalcogenide NCs achieved through a heavily doped strategy. The copper sulfur compounds with versatile atomic ratios and complex crystal structures exhibit rich electrical, optical, and magnetic properties, making them highly promising for a broad range of applications, from energy conversion to biomedical fields. Therefore, our main focus is on the classification of copper chalcogenide synthesis strategies, theoretical studies of doping, doping strategies, and biological applications. We aim to analyze the trends of copper-based chalcogenide nanomaterials for clinical applications by summarizing previous studies and presenting designs and concepts in a brief manner.

Insights into Nucleation and Growth of Colloidal Quaternary Nanocrystals by Multimodal X-ray Analysis.

Copper chalcogenide nanocrystals find applications in photovoltaic inks, bio labels, and thermoelectric materials. We reveal insights in the nucleation and growth during synthesis of anisotropic Cu2ZnSnS4 nanocrystals by simultaneously performing in situ X-ray absorption spectroscopy (XAS) and small-angle X-ray scattering (SAXS). Real-time XAFS reveals that upon thiol injection into the reaction flask, a key copper thiolate intermediate species is formed within fractions of seconds, which decomposes further within a narrow temperature and time window to form copper sulfide nanocrystals. These nanocrystals convert into Cu2ZnSnS4 nanorods by sequentially incorporating Sn and Zn. Real-time SAXS and ex situ TEM of aliquots corroborate these findings. Our work demonstrates how combined in situ X-ray absorption and small-angle X-ray scattering enables the understanding of mechanistic pathways in colloidal nanocrystal formation.

Multifunctional CuBiS2 Nanoparticles for Computed Tomography Guided Photothermal Therapy in Preventing Arterial Restenosis After Endovascular Treatment.

Chronic inflammation mediated by artery infiltrated macrophages plays critical role in artery restenosis after endovascular therapy. Evidence has demonstrated the potential ability of photothermal therapy (PTT) in eliminating chronic inflammation by targeting inflammatory cells including macrophages. Recently, increasing attention has been payed to copper chalcogenide nanocrystals doped of radiocontrast agent, e.g., bismuth (Bi) for computed tomography (CT) guided PTT. However, the application of imaging guided PTT in preventing artery restenosis is lacking and limited. Herein, a novel multifunctional CuBiS2 nanoparticles (CuBiS2 NPs) were synthesized for CT imaging guided PTT in artery re-stenosis prevention. The optimum amount and other conditions of CuBiS2 NPs were optimized to exert the maximum ablation effect on macrophages with good biocompatibility. In vivo carotid injury model revealed that CuBiS2 NPs exhibited promising therapeutic effect on inhibition of artery stenosis by eliminating macrophages with excellent CT imaging ability. The recent study highlights a new cost-effective metal nanostructures-based nanotechnology in prevention of artery restenosis after endovascular therapy.

Rational design of multinary copper chalcogenide nanocrystals for photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution is one of the most promising ways to solve environmental problems and produce a sustainable energy source. To date, different types of photocatalysts have been developed and widely used in photocatalytic hydrogen evolution. Recently, multinary copper chalcogenides have attracted much attention and exhibited potential applications in photocatalytic hydrogen evolution due to their composition-tunable band gaps, diverse structures and environmental-benign characteristics. In this review, some progress on the synthesis and photocatalytic hydrogen evolution of multinary copper chalcogenide nanocrystals (NCs) was summarized. In particular, considerable attention was paid to the rational design and dimensional or structural regulation of multinary copper chalcogenide NCs. Importantly, the photocatalytic hydrogen evolution of multinary copper chalcogenide NCs were reviewed from the aspects of energy level structures, crystal facets, morphology as well as composition. Finally, the current challenges and future perspectives of copper chalcogenide were proposed.

Localized surface plasmon resonances in self-doped copper chalcogenide binary nanocrystals and their emerging applications

Cartoon overview of plamsonic copper chalcogenide (Cu 2−x E; E = S, Se, and Te) binary NCs: their synthesis, LSPR tuning, and applications. • The review devoted to self-doped plasmonic copper chalcogenide binary NCs. • The factors that impact their localized surface plasmon resonances (LSPRs) and the synthesis methods for tuning the LSPRs were summarized. • We emphasize the underlying mechanisms of LSPR generation and the unique roles and advantages of the copper chalcogenide NCs. Owing to their extraordinary surface plasmon and semiconductor properties, copper chalcogenide nanocrystals (NCs) have experienced a steeply increased interest for various types of applications since the first discovery of their plasmonic property in 2009. This article critically and comprehensively reviews the decade long research effort devoted to doped plasmonic copper chalcogenide binary NCs with respect to their synthesis methods, their theoretical description and various applications. In particular, we focus on factors that impact their localized surface plasmon resonances (LSPRs) and on methods used for tuning the LSPRs. We emphasize the underlying mechanisms of LSPR generation and the unique roles and advantages of the copper chalcogenide NCs with respect to the commonly attended plasmonic metal nanoparticles. Finally, we review current challenges in the field of copper chalcogenide NCs and give a perspective for further research. We believe that this review provides a timely and concise summary of the field of plasmonic copper chalcogenide NCs for the benefit and inspiration of its rapid and formulated development.

Hetero-epitaxial growth of Cu2ZnSn(S1−x,Sex)4-Au nanocomposites: Microstructures and corresponding impacts on optoelectronic properties

Coupling plasmonic gold nanoparticles to sub-stoichiometric copper chalcogenide nanocrystals tends to generate promising nano-heterostructures. We report the research on plasmon-enhanced Cu2ZnSn(S1−x,Sex)4-Au nanocomposites (CZTSSe for 0 < x < 1, and CZTS if x = 0), emphasizing on exploring how hetero-epitaxial relationship at Cu2ZnSn(S1−x,Sex)4//Au interfaces affects their optoelectronic properties. Digital image processing tools, fast Fourier transform/Fourier inversion, are utilized to extract interfacial epitaxial orientations. We demonstrate that nonnegligible lattice mismatch in short-range order could be equivalently compensated by coincident lattice-matching at certain periodic intervals in a long-range order. By exploring polytypic CZTSSe, we further provide reasonable interpretation of abnormal symmetrical distribution of Au on CZTSSe, which induces lower gold coverage rate and accordingly moderates their localized surface plasmon resonance effect, compared to that of CZTS. It indicates that the shape and phase of CZTSSe should be elaborately controlled to realize optimal multi-site nucleation of heterostructured nanocomposites. As a result, by testing optoelectronic response of solar cells with Cu2ZnSn(S1−x,Sex)4-Au films as counter electrodes (CEs), we confirm that a superior hetero-epitaxial interconnection between Au and Cu2ZnSn(S1−x,Sex)4 can availably restrain interfacial defects of the junction and thus contribute efficient hole transfer/transportation in cathode region. The corresponding balanced electron and hole migration plays a quite significant role in the improvement of open-circuit voltage (Voc) and fill factor of photovoltaic devices.

Dye-Sensitized Ternary Copper Chalcogenide Nanocrystals: Optoelectronic Properties, Air Stability, and Photosensitivity

We report on the effect of ligand exchange of copper sulphide selenide as well as copper selenide nanocrystals with the organic pi-system Cobalt beta-tetraaminophthalocyanine and analyse changes in the structural, optical as well as electric properties of thin films of these hybrid materials. A strong ligand interaction with the surface of the nanocrystals is revealed by UV-vis absorption and Raman spectroscopy. Grazing-incidence small-angle X-ray scattering studies show a significant contraction in the interparticle distance upon ligand exchange. For copper-deficient copper selenide, this contraction has a negligible effect on electric transport, while for copper-deficient copper sulphide selenide, the conductivity increases by eight orders of magnitude and results in metal-like temperature-dependent transport. We discuss these differences in the light of varying contributions of electronic vs. ionic transport in the two materials and highlight their effect on the stability of the transport properties under ambient conditions. With photocurrent measurements, we demonstrate high optical responsivities of 200-400 A W-1 for the phthalocyanine-capped copper sulphide selenide and emphasize the beneficial role of the organic pi-system in this respect, which acts as an electronic linker and an optical sensitizer at the same time.

Synthesis of Wurtzite Cu2ZnSnS4 Nanosheets with Exposed High-Energy (002) Facets for Fabrication of Efficient Pt-Free Solar Cell Counter Electrodes

Two-dimensional (2D) semiconducting nanomaterials have generated much interest both because of fundamental scientific interest and technological applications arising from the unique properties in two dimensions. However, the colloidal synthesis of 2D quaternary chalcogenide nanomaterials remains a great challenge owing to the lack of intrinsic driving force for its anisotropic growth. 2D wurtzite Cu2ZnSnS4 nanosheets (CZTS-NS) with high-energy (002) facets have been obtained for the first time via a simple one-pot thermal decomposition method. The CZTS-NS exhibits superior photoelectrochemical activity as compared to zero-dimensional CZTS nanospheres and comparable performance to Pt counter electrode for dye sensitized solar cells. The improved catalytic activity can be attributed to additional reactive catalytic sites and higher catalytic reactivity in high-energy (002) facets of 2D CZTS-NS. This is in accordance with the density functional theory (DFT) calculations, which indicates that the (002) facets of wurtzite CZTS-NS possess higher surface energy and exhibits remarkable reducibility for I3− ions. The developed synthetic method and findings will be helpful for the design and synthesis of 2D semiconducting nanomaterials, especially eco-friendly copper chalcogenide nanocrystals for energy harvesting and photoelectric applications.

Multifunctional Cu1.94S-Bi2S3@polymer nanocomposites for computed tomography imaging guided photothermal ablation

The doping of radiocontrast agent such as bismuth (Bi) in copper chalcogenide nanocrystals for computed tomography (CT) imaging guided photothermal therapy (PTT) has drawn increasing attention. However, the doping of Bi often suffers from the weak CT signal due to the low Bi doping concentration and deteriorates the PTT efficacy of copper chalcogenides. Here we report a multifunctional nanoprobe by encapsulating both Cu1.94S and Bi2S3 nanocrystals into a biocompatible poly(amino acid) matrix with size of ~85 nm for CT imaging guided PTT. The amount of nanocrystals and the ratio of Cu1.94S-to-Bi2S3 in the multifunctional nanocomposites (NCs) are tunable toward both high photothermal conversion efficiency (~31%) and excellent CT imaging capability (27.8 HU g L−1). These NCs demonstrate excellent effects for photothermal ablation of tumors after intratumoral injection on 4T1 tumor-bearing mice. Our study may provide a facile strategy for the fabrication of multifunctional theranostics towards simultaneous strong CT signal and excellent PTT.

Q-switching Yb3+: YAG lasers based on plasmon resonance nonlinearities of Cu2-xSe@Cu2-xS nanorods.

Copper(II) chalcogenide nanocrystals, including Cu2-xY (Y=S, Se, and Te), have an intense localized surface plasmon resonance (LSPR) band in the near-infrared (NIR) region. In this research, colloidal Cu2-xSe@Cu2-xS nanorods were synthesized using the organometallic colloidal and cation-exchange methods. The dynamics of LSPR were investigated using ultrafast laser pulses via pump-probe experiments in the NIR region. Investigation of the transient absorption spectra revealed an LSPR spectral band from approximately 850 to 1350nm, with a center wavelength of 1030nm. The kinetics of the recovering plasmon maximum, probed at the peak wavelength of 1030nm, exhibited a strong nonlinear response for plasmonic absorption, with a modulation depth exceeding 25% in the transmitted signal under a pump fluence of 3.97 mJ/cm2. The ultrafast nonlinear optical properties of these plasmonic nanoparticles could be used as excellent saturable absorbers (SAs) in ultrafast lasers. A compact passively Q-switched Yb3+:YAG microchip laser with a Cu2-xSe@Cu2-xS SA was investigated. Furthermore, a maximum average output power of 187mW was obtained, with a pulse energy of 4.11μJ, pulse duration of 8.5μs, and repetition rate of 45.45KHz at a pump power of 8.7W.

Prospects of Colloidal Copper Chalcogenide Nanocrystals.

Over the past few years, colloidal copper chalcogenide nanocrystals (NCs) have emerged as promising alternatives to conventional Cd and Pb chalcogenide NCs. Owing to their wide size, shape, and composition tunability, Cu chalcogenide NCs hold great promise for several applications, such as photovoltaics, lighting and displays, and biomedical imaging. They also offer characteristics that are unparalleled by Cd and Pb chalcogenide NCs, such as plasmonic properties. Moreover, colloidal Cu chalcogenide NCs have low toxicity, potentially lower costs, and excellent colloidal stability. This makes them attractive materials for the large-scale deployment of inexpensive, sustainable, and environmentally benign solution-processed devices. Nevertheless, the synthesis of colloidal Cu chalcogenide NCs, especially that of ternary and quaternary compositions, has yet to reach the same level of mastery as that available for the prototypical Cd chalcogenide based NCs. This review provides a concise overview of this rapidly advancing field, sketching the state of the art and highlighting the key challenges. We discuss recent developments in the synthesis of size-, shape-, and composition-controlled NCs of Cu chalcogenides, with emphasis in strategies to circumvent the limitations arising from the need to precisely balance the reactivities of multiple precursors in synthesizing ternary and quaternary compositions. In this respect, we show that topotactic cation-exchange reactions are a promising alternative route to complex multinary Cu chalcogenide NCs and hetero-NCs, which are not attainable by conventional routes. The properties and potential applications of Cu chalcogenide NCs and hetero-NCs are also addressed.

Selective cation exchange in the core region of Cu2-xSe/Cu2-xS core/shell nanocrystals.

We studied cation exchange (CE) in core/shell Cu2–xSe/Cu2–xS nanorods with two cations, Ag+ and Hg2+, which are known to induce rapid exchange within metal chalcogenide nanocrystals (NCs) at room temperature. At the initial stage of the reaction, the guest ions diffused through the Cu2–xS shell and reached the Cu2–xSe core, replacing first Cu+ ions within the latter region. These experiments prove that CE in copper chalcogenide NCs is facilitated by the high diffusivity of guest cations in the lattice, such that they can probe the whole host structure and identify the preferred regions where to initiate the exchange. For both guest ions, CE is thermodynamically driven as it aims for the formation of the chalcogen phase characterized by the lower solubility under the specific reaction conditions.

Monodisperse Copper Chalcogenide Nanocrystals: Controllable Synthesis and the Pinning of Plasmonic Resonance Absorption.

Controllable synthesis of copper chalcogenide nanocrystals (NCs), including desired geometry, composition and surrounding environment, is of high significance for the modulation of their optoelectronic response and the corresponding applications. Herein, copper nitride nanoparticles have been used as "uncontaminated" copper precursors to synthesize copper chalcogenide NCs with high monodispersity through a one-pot strategy. In this protocol, the sizes and compositions of NCs can be readily controlled by varying the ratio of the precursors. For Cu(2-x)S NCs with different diameters, the size variations are all smaller than 5.6%. Furthermore, the plasmonic properties of the copper chalcogenide NCs are investigated under a steady state by tuning the plasmonic resonance absorption band to a limiting condition (denoted "pinning" phenomena). It is observed that the pinning frequency increases (from 1.09 to 1.23 eV) with the increment of the NC size (from 5.4 ± 0.3 to 11.1 ± 0.4 nm), explained by introducing surface scattering. Meanwhile, the frequencies of ternary alloyed copper sulfide selenide NCs blue-shift from 0.90 to 1.00 eV with the increase of selenium content from 11% to 66%, which is related to the effective mass of free carriers. Additionally, the plasmonic absorption bands of Cu(2-x)S NCs encapsulated by two single-layer graphene pin at 1525-1550 nm during the oxidation process, which is influenced by both the dielectric constant and redox potential of the surrounding environment. This study demonstrates the controllable synthesis and precise fundamental plasmonic properties of the copper chalcogenide NCs, ensuring the potential plasmonic-related techniques with high efficiency, accuracy and excellent spatial resolution.

Occurrence of Polytypism in Compound Colloidal Metal Chalcogenide Nanocrystals, Opportunities, and Challenges

This Perspective will look at the occurrence of polytypism in colloidal nanocrystals of metal chalcogenides. The low energy barrier between growth in wurtzite and zincblende crystal phases allows the occurrence of both in a single particle which has a dramatic influence on shape control. To date, various strategies have been employed to understand and control this phenomenon leading to a range of particle shapes across a wide range of semiconductor compositions from the archetypal cadmium selenide to the more recently studied compound copper chalcogenide nanocrystals such as dicopper–zinc–tin tetrasulfide and copper indium gallium selenide systems. The Perspective will also look at the control factors for polytypism in colloidal nanocrystals and the impact of polytypism on end-use applications.

Synergistic role of dopants on the morphology of alloyed copper chalcogenide nanocrystals.

The presence of antimony, as a dopant in the colloidal growth reaction for CuIn(1-x)Ga(x)S2 (CIGS) nanocrystals, causes end-to-end fusion of nanorod pairs into nanodumbbells at high yield. The influence of the dopant on shape is indirect; antimony catalyzes the incorporation of gallium, which is found in high concentration at the junction between the fused nanorods.

Generalized One-Pot Synthesis of Copper Sulfide, Selenide-Sulfide, and Telluride-Sulfide Nanoparticles

Here we report a facile approach to synthesize copper chalcogenide (Cu2–xS, Cu2–xSeyS1–y and Cu2–xTeyS1–y) nanocrystals without employing hot-injection, at moderate reaction temperatures (200–220 °C) and free of phosphines. Scaling up of the synthesis yields monodisperse nanoparticles without variations in their morphology. We have observed the formation of alloyed copper selenide-sulfide and telluride-sulfide nanocrystals due to the incorporation of sulfur by using 1-dodecanethiol as a ligand along with oleic acid. The materials obtained possess localized surface plasmon resonances in the near-infrared region, which are demonstrated to be widely tunable via a controlled oxidation generating copper vacancies. Copper sulfide nanoparticles with well-defined initial chalcocite crystal phase were subjected to oxidation followed by structural characterization. Structural rearrangement of the oxidized chalcocite Cu2–xS crystal lattice to roxbyite by aging is proven to release the copper vacancies. Further oxidation again can create new copper vacancies in the roxbyite lattice, however its structure does not evolve into covellite CuS. These findings suggest that besides nonstoichiometry (i.e., the value of x) induced by oxidation, crystal structure is an important factor responsible for plasmonic properties of copper chalcogenide nanocrystals. Furthermore, successful water solubilization of Cu2–xTeyS1–y nanoparticles with preservation of their plasmon band has been realized via a ligand exchange approach employing a mPEG-SH stabilizer.

Colloidal Synthesis of Cu2SnSe3 Tetrapod Nanocrystals

The formation of Cu2SnSe3 tetrapod nanocrystals is reported using a hot injection colloidal synthesis. The ternary copper chalcogenide nanocrystals nucleate with a cubic core with four short wurzite arms.

Shedding Light on Vacancy-Doped Copper Chalcogenides: Shape-Controlled Synthesis, Optical Properties, and Modeling of Copper Telluride Nanocrystals with Near-Infrared Plasmon Resonances

Size- and shape-controlled synthesis of copper chalcogenide nanocrystals (NCs) is of paramount importance for a careful engineering and understanding of their optoelectronic properties and, thus, for their exploitation in energy- and plasmonic-related applications. From the copper chalcogenide family copper telluride NCs have remained fairly unexplored as a result of a poor size-, shape-, and monodispersity control that is achieved via one-step syntheses approaches. Here we show that copper telluride (namely Cu(2-x)Te) NCs with well-defined morphologies (spheres, rods, tetrapods) can be prepared via cation exchange of preformed CdTe NCs while retaining their original shape. The resulting copper telluride NCs are characterized by pronounced plasmon bands in the near-infrared (NIR), in analogy to other copper-deficient chalcogenides (Cu(2-x)S, Cu(2-x)Se). We demonstrate that the extinction spectra of the as-prepared NCs are in agreement with theoretical calculations based on the discrete dipole approximation and an empirical dielectric function for Cu(2-x)Te. Additionally we show that the Drude model does not appropriately describe the complete set of Cu(2-x)Te NCs with different shapes. In particular, the low-intensity longitudinal plasmon bands for nanorods and tetrapods are better described by a modified Drude model with an increased damping in the long-wavelength interval. Importantly, a Lorentz model of localized quantum oscillators describes reasonably well all three morphologies, suggesting that holes in the valence band of Cu(2-x)Te cannot be described as fully free particles and that the effects of localization of holes are important. A similar behavior for Cu2-xS and Cu(2-x)Se NCs suggests that the effect of localization of holes can be a common property for the whole class of copper chalcogenide NCs. Taken altogether, our results represent a simple route toward copper telluride nanocrystals with well-defined shapes and optical properties and extend the understanding on vacancy-doped copper chalcogenide NCs with NIR optical resonances.

Tuning the Excitonic and Plasmonic Properties of Copper Chalcogenide Nanocrystals

The optical properties of stoichiometric copper chalcogenide nanocrystals (NCs) are characterized by strong interband transitions in the blue part of the spectral range and a weaker absorption onset up to ~1000 nm, with negligible absorption in the near-infrared (NIR). Oxygen exposure leads to a gradual transformation of stoichiometric copper chalcogenide NCs (namely, Cu(2-x)S and Cu(2-x)Se, x = 0) into their nonstoichiometric counterparts (Cu(2-x)S and Cu(2-x)Se, x > 0), entailing the appearance and evolution of an intense localized surface plasmon (LSP) band in the NIR. We also show that well-defined copper telluride NCs (Cu(2-x)Te, x > 0) display a NIR LSP, in analogy to nonstoichiometric copper sulfide and selenide NCs. The LSP band in copper chalcogenide NCs can be tuned by actively controlling their degree of copper deficiency via oxidation and reduction experiments. We show that this controlled LSP tuning affects the excitonic transitions in the NCs, resulting in photoluminescence (PL) quenching upon oxidation and PL recovery upon subsequent reduction. Time-resolved PL spectroscopy reveals a decrease in exciton lifetime correlated to the PL quenching upon LSP evolution. Finally, we report on the dynamics of LSPs in nonstoichiometric copper chalcogenide NCs. Through pump-probe experiments, we determined the time constants for carrier-phonon scattering involved in LSP cooling. Our results demonstrate that copper chalcogenide NCs offer the unique property of holding excitons and highly tunable LSPs on demand, and hence they are envisaged as a unique platform for the evaluation of exciton/LSP interactions.