Role of copper sulfide seeds in the growth process of CuInS2 nanorods and networks

Anisotropic Heavy-Metal-Free Semiconductor Nanocrystals: Synthesis, Properties, and Applications

Heavy-metal (Cd, Hg, and Pb)-containing semiconductor nanocrystals (NCs) have been explored widely due to their unique optical and electrical properties. However, the toxicity risks of heavy metals can be a drawback of heavy-metal-containing NCs in some applications. Anisotropic heavy-metal-free semiconductor NCs are desirable replacements and can be realized following the establishment of anisotropic growth mechanisms. These anisotropic heavy-metal-free semiconductor NCs can possess lower toxicity risks, while still exhibiting unique optical and electrical properties originating from both the morphological and compositional anisotropy. As a result, they are promising light-emitting materials in use various applications. In this review, we provide an overview on the syntheses, properties, and applications of anisotropic heavy-metal-free semiconductor NCs. In the first section, we discuss hazards of heavy metals and introduce the typical heavy-metal-containing and heavy-metal-free NCs. In the next section, we discuss anisotropic growth mechanisms, including solution-liquid-solid (SLS), oriented attachment, ripening, templated-assisted growth, and others. We discuss mechanisms leading both to morphological anisotropy and to compositional anisotropy. Examples of morphological anisotropy include growth of nanorods (NRs)/nanowires (NWs), nanotubes, nanoplatelets (NPLs)/nanosheets, nanocubes, and branched structures. Examples of compositional anisotropy, including heterostructures and core/shell structures, are summarized. Third, we provide insights into the properties of anisotropic heavy-metal-free NCs including optical polarization, fast electron transfer, localized surface plasmon resonances (LSPR), and so on, which originate from the NCs' anisotropic morphologies and compositions. Finally, we summarize some applications of anisotropic heavy-metal-free NCs including catalysis, solar cells, photodetectors, lighting-emitting diodes (LEDs), and biological applications. Despite the huge progress on the syntheses and applications of anisotropic heavy-metal-free NCs, some issues still exist in the novel anisotropic heavy-metal-free NCs and the corresponding energy conversion applications. Therefore, we also discuss the challenges of this field and provide possible solutions to tackle these challenges in the future.

Kinetic Analysis of the Cation Exchange in Nanorods from Cu2-xS to CuInS2: Influence of Djurleite's Phase Transition Temperature on the Mechanism

In the syntheses of ternary I-III-VI₂ compounds, such as CuInS₂, it is often difficult to balance three precursor reactivities to achieve the desired size, shape, and atomic composition of nanocrystals. Cation exchange reactions offer an attractive two-step alternative, by producing a binary compound with the desired morphology and incorporating another atomic species postsynthetically. However, the kinetics of such cation exchange reactions, especially for anisotropic nanocrystals, are still not fully understood. Here, we present the cation exchange reaction from Cu-deficient djurleite Cu_2-xS nanorods to wurtzite CuInS₂, with size and shape retention. With reaction parameters in a broad temperature range between 40 °C and 160 °C, we were able to obtain various intermediates. Djurleite has a bulk phase transition temperature at 93 °C, which influences the cation exchange considerably. Below the phase transition temperature, indium is only incorporated into the surface of the nanorods, while, at temperatures above the phase transition temperature, we observe a Janus-type exchange mechanism and the formation of CuInS₂ bands in the djurleite nanorods. The findings suggest that the diffusion above the phase transition temperature is strongly favored along the copper planes of the copper sulfide nanorods over the diffusion through the sulfur planes. This results in a difference of 37 kJ mol^-1 in the activation energy of the cation exchange below and above the phase transition temperature.

Phonon Raman spectroscopy of nanocrystalline multinary chalcogenides as a probe of complex lattice structures

Ternary (I-III-VI) and quaternary (I-II-IV-VI) metal-chalcogenides like CuInS₂or Cu₂ZnSn(S,Se)₄are among the materials currently most intensively investigated for various applications in the area of alternative energy conversion and light-emitting devices. They promise more sustainable and affordable solutions to numerous applications, compared to more developed and well understood II-VI and III-V semiconductors. Potentially superior properties are based on an unprecedented tolerance of these compounds to non-stoichiometric compositions and polymorphism. However, if not properly controlled, these merits lead to undesirable coexistence of different compounds in a single polycrystalline lattice and huge concentrations of point defects, becoming an immense hurdle on the way toward real-life applications. Raman spectroscopy of phonons has become one of the most powerful tools of structural diagnostics and probing physical properties of bulk and microcrystalline I-III-VI and I-II-IV-VI compounds. The recent explosive growth of the number of reports on fabrication and characterization of nanostructures of these compounds must be pointed out as well as the steady use of Raman spectroscopy for their characterization. Interpretation of the vibrational spectra of these compound nanocrystals (NCs) and conclusions about their structure can be complicated compared to bulk counterparts because of size and surface effects as well as emergence of new structural polymorphs that are not realizable in the bulk. This review attempts to summarize the present knowledge in the field of I-III-VI and I-II-IV-VI NCs regarding their phonon spectra and capabilities of Raman and IR spectroscopies in the structural characterizations of these promising families of compounds.

Design Principles of Colloidal Nanorod Heterostructures

Anisotropic heterostructures of colloidal nanocrystals embed size-, shape-, and composition-dependent electronic structure within variable three-dimensional morphology, enabling intricate design of solution-processable materials with high performance and programmable functionality. The key to designing and synthesizing such complex materials lies in understanding the fundamental thermodynamic and kinetic factors that govern nanocrystal growth. In this review, nanorod heterostructures, the simplest of anisotropic nanocrystal heterostructures, are discussed with respect to their growth mechanisms. The effects of crystal structure, surface faceting/energies, lattice strain, ligand sterics, precursor reactivity, and reaction temperature on the growth of nanorod heterostructures through heteroepitaxy and cation exchange reactions are explored with currently known examples. Understanding the role of various thermodynamic and kinetic parameters enables the controlled synthesis of complex nanorod heterostructures that can exhibit unique tailored properties. Selected application prospects arising from such capabilities are then discussed.

Oleic acid/oleylamine ligand pair: a versatile combination in the synthesis of colloidal nanoparticles

A variety of colloidal chemical approaches has been developed in the last few decades for the controlled synthesis of nanostructured materials in either water or organic solvents. Besides the precursors, the solvents, reducing agents, and the choice of surfactants are crucial for tuning the composition, morphology and other properties of the resulting nanoparticles. The ligands employed include thiols, amines, carboxylic acids, phosphines and phosphine oxides. Generally, adding a single ligand to the reaction mixture is not always adequate to yield the desired features. In this review, we discuss in detail the role of the oleic acid/oleylamine ligand pair in the chemical synthesis of nanoparticles. The combined use of these ligands belonging to two different categories of molecules aims to control the size and shape of nanoparticles and prevent their aggregation, not only during their synthesis but also after their dispersion in a carrier solvent. We show how the different binding strengths of these two molecules and their distinct binding modes on specific facets affect the reaction kinetics toward the production of nanostructures with tailored characteristics. Additional functions, such as the reducing function, are also noted, especially for oleylamine. Sometimes, the carboxylic acid will react with the alkylamine to form an acid-base complex, which may serve as a binary capping agent and reductant; however, its reducing capacity may range from lower to much lower than that of oleylamine. The types of nanoparticles synthesized in the simultaneous presence of oleic acid and oleylamine and discussed herein include metal oxides, metal chalcogenides, metals, bimetallic structures, perovskites, upconversion particles and rare earth-based materials. Diverse morphologies, ranging from spherical nanoparticles to anisotropic, core-shell and hetero-structured configurations are presented. Finally, the relation between tuning the resulting surface and volume nanoparticle properties and the relevant applications is highlighted.

Subsuming the Metal Seed to Transform Binary Metal Chalcogenide Nanocrystals into Multinary Compositions

Direct colloidal synthesis of multinary metal chalcogenide nanocrystals typically develops dynamically from the binary metal chalcogenide nanocrystals with the subsequent incorporation of additional metal cations from solution during the growth process. Metal seeding of binary and multinary chalcogenides is also established, although the seed is solely a catalyst for nanocrystal nucleation and the metal from the seed has never been exploited as active alloying nuclei. Here we form colloidal Cu-Bi-Zn-S nanorods (NRs) from Bi-seeded Cu_2-xS heterostructures. The evolution of these homogeneously alloyed NRs is driven by the dissolution of the Bi-rich seed and recrystallization of the Cu-rich stem into a transitional segment, followed by the incorporation of Zn²⁺ to form the quaternary Cu-Bi-Zn-S composition. The present study also reveals that the variation of Zn concentration in the NRs modulates the aspect ratio and affects the nature of the majority charge carriers. The NRs exhibit promising thermoelectric properties with very low thermal conductivity values of 0.45 and 0.65 W/mK at 775 and 605 K, respectively, for Zn-poor and Zn-rich NRs. This study highlights the potential of metal seed alloying as a direct growth route to achieving homogeneously alloyed NRs compositions that are not possible by conventional direct methods or by postsynthetic transformations.

Photoluminescent, "ice-cream cone" like Cu-In-(Zn)-S/ZnS nanoheterostructures

Copper based ternary and quaternary quantum confined nanostructures have attracted huge attention over recent years due to their potential applications in photonics, photovoltaics, imaging, sensing and other areas. However, anisotropic nanoheterostructures of this type are still poorly explored to date, despite numerous predictions of the distinctive optical properties of these highly fluorescent heavy metal free nanostructures. Here, we report new fluorescent multicomponent Cu-In-(Zn)-S/ZnS nanoheterostructures with a unique anisotropic "ice-cream cone" like morphology. These nanostructures have been prepared with a seeded growth technique and exhibit distinct photophysical properties with maximum emission in the visible range (≈ 640 nm) and long photoluminescence lifetimes (τ_average ≥ 300 ns). In depth time interval studies have been carried out to better understand the step by step growth mechanism of this distinct "ice-cream cone" like geometry. We have demonstrated that the crystal structure evolution from the zinc blende Cu-In-S core to the wurtzite "ice cream cone" like Cu-In-(Zn)-S/ZnS nanocrystals plays a key role in the origin of this morphology. This research opens new possibilities to produce unique fluorescent Cu-based multicomponent anisotropic heteronanostructures, while also offering a distinctive insight into the design of bespoke nanostructures, which could find a range of potential applications.

Phase-Controlled Synthesis and Quasi-Static Dielectric Resonances in Silver Iron Sulfide (AgFeS2 ) Nanocrystals

Ternary metal-chalcogenide semiconductor nanocrystals are an attractive class of materials due to their tunable optoelectronic properties that result from a wide range of compositional flexibility and structural diversity. Here, the phase-controlled synthesis of colloidal silver iron sulfide (AgFeS₂ ) nanocrystals is reported and their resonant light-matter interactions are investigated. The product composition can be shifted selectively from tetragonal to orthorhombic by simply adjusting the coordinating ligand concentration, while keeping the other reaction parameters unchanged. The results show that excess ligands impact precursor reactivity, and consequently the nanocrystal growth rate, thus deterministically dictating the resulting crystal structure. Moreover, it is demonstrated that the strong ultraviolet-visible extinction peak exhibited by AgFeS₂ nanocrystals is a consequence of a quasi-static dielectric resonance (DR), analogous to the optical response observed in CuFeS₂ nanocrystals. Spectroscopic studies and computational calculations confirm that a negative permittivity at ultraviolet/visible frequencies arises due to the electronic structure of these intermediate-band (IB) semiconductor nanocrystals, resulting in a DR consisting of resonant valence-band-to-intermediate-band excitations, as opposed to the well-known localized surface plasmon resonance response typically observed in metallic nanostructures. Overall, these results expand the current library of an underexplored class of IB semiconductors with unique optical properties, and also enrich the understanding of DRs in ternary metal-iron-sulfide nanomaterials.

Synthesis and Formation Mechanism of Colloidal Janus-Type Cu2-xS/CuInS2 Heteronanorods via Seeded Injection

Colloidal heteronanocrystals allow for the synergistic combination of properties of different materials. For example, spatial separation of the photogenerated electron and hole can be achieved by coupling different semiconductors with suitable band offsets in one single nanocrystal, which is beneficial for improving the efficiency of photocatalysts and photovoltaic devices. From this perspective, axially segmented semiconductor heteronanorods with a type-II band alignment are particularly attractive since they ensure the accessibility of both photogenerated charge carriers. Here, a two-step synthesis route to Cu_2-xS/CuInS₂ Janus-type heteronanorods is presented. The heteronanorods are formed by injection of a solution of preformed Cu_2-xS seed nanocrystals in 1-dodecanethiol into a solution of indium oleate in oleic acid at 240 °C. By varying the reaction time, Janus-type heteronanocrystals with different sizes, shapes, and compositions are obtained. A mechanism for the formation of the heteronanocrystals is proposed. The first step of this mechanism consists of a thiolate-mediated topotactic, partial Cu⁺ for In³⁺ cation exchange that converts one of the facets of the seed nanocrystals into CuInS₂. This is followed by homoepitaxial anisotropic growth of wurtzite CuInS₂. The Cu_2-xS seed nanocrystals also act as sacrificial Cu⁺ sources, and therefore, single composition CuInS₂ nanorods are eventually obtained if the reaction is allowed to proceed to completion. The two-stage seeded growth method developed in this work contributes to the rational synthesis of Cu_2-xS/CuInS₂ heteronanocrystals with targeted architectures by allowing one to exploit the size and faceting of premade Cu_2-xS seed nanocrystals to direct the growth of the CuInS₂ segment.

Seeded Growth Combined with Cation Exchange for the Synthesis of Anisotropic Cu2-x S/ZnS, Cu2-x S, and CuInS2 Nanorods

Colloidal copper(I) sulfide (Cu_2-x S) nanocrystals (NCs) have attracted much attention for a wide range of applications because of their unique optoelectronic properties, driving scientists to explore the potential of using Cu_2-x S NCs as seeds in the synthesis of heteronanocrystals to achieve new multifunctional materials. Herein, we developed a multistep synthesis strategy toward Cu_2-x S/ZnS heteronanorods. The Janus-type Cu_2-x S/ZnS heteronanorods are obtained by the injection of hexagonal high-chalcocite Cu_2-x S seed NCs in a hot zinc oleate solution in the presence of suitable surfactants, 20 s after the injection of sulfur precursors. The Cu_2-x S seed NCs undergo rapid aggregation and coalescence in the first few seconds after the injection, forming larger NCs that act as the effective seeds for heteronucleation and growth of ZnS. The ZnS heteronucleation occurs on a single (100) facet of the Cu_2-x S seed NCs and is followed by fast anisotropic growth along a direction that is perpendicular to the c-axis, thus leading to Cu_2-x S/ZnS Janus-type heteronanorods with a sharp heterointerface. Interestingly, the high-chalcocite crystal structure of the injected Cu_2-x S seed NCs is preserved in the Cu_2-x S segments of the heteronanorods because of the high-thermodynamic stability of this Cu_2-x S phase. The Cu_2-x S/ZnS heteronanorods are subsequently converted into single-component Cu_2-x S and CuInS₂ nanorods by postsynthetic topotactic cation exchange. This work expands the possibilities for the rational synthesis of colloidal multicomponent heteronanorods by allowing the design principles of postsynthetic heteroepitaxial seeded growth and nanoscale cation exchange to be combined, yielding access to a plethora of multicomponent heteronanorods with diameters in the quantum confinement regime.

Morphology Controlled Synthesis of Composition Related Plasmonic CuCdS Alloy Nanocrystals

Cu-based ternary alloy nanocrystals have emerged for extensive applications in solar cells, light-emitting devices (LEDs), and photoelectric detectors because of their low-toxicity, tunable band gaps, and large absorption coefficients. It is still an enormous challenge that regulating optical and electrical properties through changing their compositions and shapes in alloy nanocrystals. Herein, we present a facile method to synthesize CuCdS alloy nanocrystals (NCs) with tunable compositions and shapes at relatively low temperature. Different morphologies of monodisperse CuCdS nanocrystals are tailored successfully by simply adjusting the reaction temperature and Cu:Cd precursor molar ratio. The as-synthesized nanocrystals are of homogeneous alloy structures with uniform obvious lattice fringes throughout the whole particles rather than heterojunction structures. The localized surface plasmon resonance (LSPR) absorption peaks of CuCdS NCs are clearly observed and can be precisely tuned by varying the Cu:Cd molar ratio. Moreover, current-voltage (I-V) behaviors of different shaped CuCdS nanocrystals show certain rectification characteristics. The alloy CuCdS NCs with tunable shape, band gap, and compositionpossess a potential application in optoelectronic devices.

Optical Properties, Synthesis, and Potential Applications of Cu-Based Ternary or Quaternary Anisotropic Quantum Dots, Polytypic Nanocrystals, and Core/Shell Heterostructures

This review summaries the optical properties, recent progress in synthesis, and a range of applications of luminescent Cu-based ternary or quaternary quantum dots (QDs). We first present the unique optical properties of the Cu-based multicomponent QDs, regarding their emission mechanism, high photoluminescent quantum yields (PLQYs), size-dependent bandgap, composition-dependent bandgap, broad emission range, large Stokes’ shift, and long photoluminescent (PL) lifetimes. Huge progress has taken place in this area over the past years, via detailed experimenting and modelling, giving a much more complete understanding of these nanomaterials and enabling the means to control and therefore take full advantage of their important properties. We then fully explore the techniques to prepare the various types of Cu-based ternary or quaternary QDs (including anisotropic nanocrystals (NCs), polytypic NCs, and spherical, nanorod and tetrapod core/shell heterostructures) are introduced in subsequent sections. To date, various strategies have been employed to understand and control the QDs distinct and new morphologies, with the recent development of Cu-based nanorod and tetrapod structure synthesis highlighted. Next, we summarize a series of applications of these luminescent Cu-based anisotropic and core/shell heterostructures, covering luminescent solar concentrators (LSCs), bioimaging and light emitting diodes (LEDs). Finally, we provide perspectives on the overall current status, challenges, and future directions in this field. The confluence of advances in the synthesis, properties, and applications of these Cu-based QDs presents an important opportunity to a wide-range of fields and this piece gives the reader the knowledge to grasp these exciting developments.

From one-dimensional to two-dimensional wurtzite CuGaS2 nanocrystals: non-injection synthesis and photocatalytic evolution

Multinary copper-based chalcogenides exhibit significant performance in photocatalytic hydrogen evolution due to their suitable optical bandgap for visible light absorption and environmentally friendly character. Herein, high-quality wurtzite CuGaS2 (CGS) nanocrystals (NCs) were synthesized by using a one-step heating-up process without any injection, and the morphology could be tuned from one-dimensional (1D) to two-dimensional (2D) by precise choice of surface ligands and gallium precursors. The formation mechanism of CGS NCs was studied comprehensively by means of the temporal-evolution of the morphology, crystal structure and optical absorption results. The reaction started from djurleite Cu31S16 NCs, and then proceeded with the formation of Cu31S16-CGS heteronanostructures (HNS), and finally the transformation from HNS to monophasic CGS nanorods took place with prolonging of the synthesis time. The optical bandgap and the energy level of the different-dimensional CGS NCs exhibited a strong dependence on the morphology change, which correlated with the percentage of the exposed {001} and {100} facets. The theoretical calculation based on density functional theory (DFT) revealed that the (001) surface facilitated the charge transport rather than the (100) surface, which was consistent with the electrochemical impedance spectroscopy (EIS) results. As a result, the 2D CGS nanoplates with more exposed {001} facets exhibited an attractive photocatalytic hydrogen production activity under simulated solar illumination as compared to 1D and quasi-2D counterparts. This study demonstrates that control over the dimension of I-III-V group semiconductor NCs could lead to a significant improvement of the photocatalytic hydrogen evolution.

Selective formation of ternary Cu–Ge–S nanostructures in solution

Selective formation of ternary Cu–Ge–S nanostructures was achieved by manipulating the solvent environment, leading to either faceted Cu₈GeS₆ nanostructures or fragmented Cu₂GeS₃ nanocrystals.

Formation of uniform carrot-like Cu31S16-CuInS2 heteronanostructures assisted by citric acid at the oil/aqueous interface

A simple two-phase strategy was developed to prepare Cu₃₁S₁₆-CuInS₂ heterostructures (HNS) at the oil/aqueous interface, in which the In(OH)₃ phase was often obtained in the products due to the reaction between indium ions and hydroxyl ions in the aqueous phase. To prevent the formation of the In(OH)₃ phase, citric acid was incorporated into the aqueous phase to assist in the synthesis of uniform carrot-like Cu₃₁S₁₆-CuInS₂ semiconductor HNS at the oil/aqueous interface for the first time. By manipulating the dosage of citric acid and Cu/In precursor ratios, the morphology of the Cu₃₁S₁₆-CuInS₂ HNS could be tailored from mushroom to carrot-like, and the presence of citric acid played a critical role in the synthesis of high-quality Cu₃₁S₁₆-CuInS₂ HNS, which inhibited the formation of the In(OH)₃ phase due to the formation of the indium(iii)-citric acid complex. The formation mechanism was studied by monitoring the morphology and phase evolution of the Cu₃₁S₁₆-CuInS₂ HNS with reaction time, which revealed that the Cu₃₁S₁₆ seeds were first formed and then the cation-exchange reaction directed the subsequent anisotropic growth of the Cu₃₁S₁₆-CuInS₂ HNS.

Facile solvothermal approach to pristine tetrahedrite nanostructures with unique multiply-voided morphology

Tetrahedrite (Cu₁₂Sb₄S₁₃) is a highly promising environmentally friendly material for energy conversion applications but its synthesis generally requires several days of heating at high temperature conditions. To fabricate tetrahedrite in a more rapid way and under milder conditions, solvothermal synthesis has been recently explored. However, a common problem faced when using this technique is the formation of significant amounts of other ternary Cu-Sb-S phases along with the desired tetrahedrite phase. Here, we present an optimized solvothermal procedure for synthesizing high-purity samples of tetrahedrite at moderate temperatures and reasonable heating times. The as-prepared samples are single-crystalline nanometer-sized structures having multiple voids or pores. By modifying certain experimental parameters such as the reaction temperature and heating time, we have shown that we can alter the nanocrystal architecture. The formation mechanism was investigated and it was found that these porous tetrahedrite nanostructures are a product of the non-classical oriented aggregation growth process. Porosity in nanomaterials is known to improve material properties and is desirable in many important applications so the construction of void-containing tetrahedrite nanostructures will potentially extend the utility of tetrahedrite to a wider range of applications. In this work, we explore its possible use as a photothermal-responsive drug delivery vehicle.

Controlled Synthesis of CuInS2/ZnS Nanocubes and Their Sensitive Photoluminescence Response toward Hydrogen Peroxide

We synthesized uniform CuInS₂/ZnS nanocubes by adjusting reaction parameters at the ZnS growth stage. Higher temperature and zinc concentration were shown to drive resultant crystals to have cubic morphology, which could be ascribed to the facet-dependent ligand dynamics on the crystal surface and concomitantly preferred directions of crystal growth. It was found that these nanocubes exhibit sensitive responses, as of photoluminescence quenching, toward hydrogen peroxide, compared to pyramid-shaped nanocrystals. The origin of quenching was further analyzed to be the oxidation of thiolate ligands that leaves the quenching center on the surface. It was noted that the quenched photoluminescence could be fully recovered by introducing additional ligand molecules into the system. Being adopted in the shape-controlled crystal growth, the ligand-to-crystal interaction was shown to still govern the interfacial reaction, the oxidation by hydrogen peroxide, of faceted crystals in our system. It turns out that the reactivity at the crystal surface depends on the exposed facets, especially induced by shape control, and the weak ligand-binding nature of the nanocube renders it vulnerable to the surface reaction.

Diversified copper sulfide (Cu2-xS) micro-/nanostructures: a comprehensive review on synthesis, modifications and applications

As a significant metal chalcogenide, copper sulfide (Cu_2-xS, 0 < x < 1), with a unique semiconducting and nontoxic nature, has received significant attention over the past few decades. Extensive investigations have been employed to the various Cu_2-xS micro-/nanostructures owing to their excellent optoelectronic behavior, potential thermoelectric properties, and promising biomedical applications. As a result, micro-/nanostructured Cu_2-xS with well-controlled morphologies, sizes, crystalline phases, and compositions have been rationally synthesized and applied in the fields of photocatalysis, energy conversion, in vitro biosensing, and in vivo imaging and therapy. However, a comprehensive review on diversified Cu_2-xS micro-/nanostructures is still lacking; therefore, there is an imperative need to thoroughly highlight the new advances made in function-directed Cu_2-xS-based nanocomposites. In this review, we have summarized the important progress made in the diversified Cu_2-xS micro-/nanostructures, including that in the synthetic strategies for the preparation of 0D, 1D, 2D, and 3D micro-/nanostructures (including polyhedral, hierarchical, hollow architectures, and superlattices) and in the development of modified Cu_2-xS-based composites for enhanced performance, as well as their various applications. Furthermore, the present issues and promising research directions are briefly discussed.

Compound Copper Chalcogenide Nanocrystals

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), energy storage (lithium-ion batteries, hydrogen generation), emissive materials (plasmonics, LEDs, biolabelling), sensors (electrochemical, biochemical), biomedical devices (magnetic resonance imaging, X-ray computer tomography), and medical therapies (photochemothermal therapies, immunotherapy, radiotherapy, and drug delivery). The confluence of advances in the synthesis, assembly, and application of these NCs in the past decade has the potential to significantly impact society, both economically and environmentally.

Shape-controlled synthesis of Cu31S16-metal sulfide heteronanostructures via a two-phase approach

A series of different-shaped Cu31S16-metal sulfide (ZnS, CdS and CuInS2) heteronanostructures have been synthesized using a simple two-phase approach for the first time. This two-phase approach may shed light on the synthesis of Cu31S16-based heteronanostructures.

Recent developments in the synthesis of nanostructured chalcopyrite materials and their applications: a review

Nanostructured chalcopyrites: synthesis and applications.

The phase transformation of CuInS2 from chalcopyrite to wurtzite

In the present work, CuInS2 nanoparticles have been successfully synthesized by water-bath method with deionized water as solvent and thioglycolic acid as complexing agent at 80°C. The phase transition of CuInS2 from chalcopyrite to wurtzite was realized by adjusting the pH value of reaction solution. The emergence of Cu2S in the condition of higher pH value of reaction solution led to the formation of wurtzite CuInS2. This facile method that controls the phase structure by adjusting the solution pH value could open a new way to synthesize other I-III-VI2 ternary semiconductor compounds.

Complete study of the composition and shape evolution in the synthesis of Cu2ZnSnS4 (CZTS) semiconductor nanocrystals

This article describes a complete study of the evolution of composition (from binary to quaternary) and shape (0D–1D) during the synthesis of CZTS nanocrystals.

Critical size for the β- to α-transformation in tin nanoparticles after lithium insertion and extraction

The formation of the α-Sn phase in Sn/SnO_x core/shell nanoparticles after lithium insertion and extraction was investigated for the first time and a critical size for the transformation was determined.

Synthesis, optical properties, and photochemical activity of zinc-indium-sulfide nanoplates

Colloidal zinc-indium-sulfide nanoplates with varying Zn content were synthesized and their optical, structural and photochemical properties were studied.