The surface science of nanocrystals

Extended Surface Bands Enabled Lasing Emission and Wavelength Switch from Sulfur Quantum Dots

The development of a lasing wavelength switch, particularly from a single inorganic gain material, is challenging but highly demanded for advanced photonics. Nonetheless, all current lasing emission of inorganic gain materials arises from band-edge states, and the inherent fixed bandgap limitation of the band-edge system leads to the inaccessibility of lasing wavelength switching from a single inorganic gain material. Here the realization of a single inorganic gain material-based lasing wavelength switch is reported by proposing an alternative lasing emission strategy, that is, lasing emission from surface gain. Previous efforts to achieve surface-gain-enabled lasing emission have been hindered by the limited gain volume provided by surface states due to the broad emission bandwidth and/or low emission efficiency. This challenge is overcome by introducing extended surface bands onto the surface of sulfur quantum dots. The extended surface bands contribute to a high photoluminescence quantum yield and narrow emission bandwidth, thereby providing sufficient gain volume and facilitating stimulated emission. When combined with whispering gallery mode microcavity, surface gain enabled lasing emission manifests an ultralow threshold of 8.3 µJ cm-2. Remarkably, the reconfigurable perturbation to surface gain, facilitated by molecular affinity, allows for the realization of the lasing wavelength switch from a single inorganic gain material.

Deciphering Surface Ligand Density of Colloidal Semiconductor Nanocrystals: Shape Matters

Surface chemistry of colloidal semiconductor nanocrystals (NCs) is of paramount importance because it profoundly impacts their physical and chemical properties, processing, and performance. Herein, we report the effect of the shape of ZnS NCs in terms of nanodots, nanorods, and nanoplatelets (NPL) on the surface ligand density (LD) of the commonly used oleylamine (OLA) ligand by combining three experimental quantification techniques (e.g., thermogravimetric analysis-differential scanning calorimetry, 1H nuclear magnetic resonance spectroscopy, and inductively coupled plasma-optical emission spectrometry) with the semiempirical molecular dynamics (MD) simulations. Consistent results on the surface LD derived by the aforementioned three independent techniques were obtained, presenting an ascending order of LDdots < LDrods < LDNPLs. MD simulations reveal that the highest LD for ZnS NPLs can be attributed to their extremely flat and uniform surfaces with regular distribution of surface Zn atoms for the OLA molecules to achieve parallel and tight stacking, while for ZnS nanodots and nanorods, their surfaces may have staggered arrangement and multisteps, making it unlikely for the OLA ligand to adopt the tight ligand stacking mode. The finding revealed in this work not only sheds light on the constitution of the molecule ligand shell of NCs, which is helpful for their rational morphology control, but also provides an additional and important knob for tuning their chemical functionality.

Single-Nanometer Spinel with Precise Cation Distribution for Enhanced Oxygen Reduction

Designing spinel nanocrystals (NCs) with tailored structural composition and cation distribution is crucial for superior catalytic performance but remarkably challenging due to their intricate nature. Here, an aggregation growth restricted hot-injection method is presented by meticulously investigating the fundamental nucleation and aggregation-driven growth kinetics governing spinel NC formation to address this challenge. Through controlled collision probability of nuclei during growth, this approach enables the synthesis of spinel NCs with unprecedented, single nanometer (1.2 nm). Single-nanometer CoMn2O4 spinel via this method exhibits a highly tailored structure with a maximized population of highly active octahedral Mn atoms, thereby optimizing oxygen intermediate adsorption during oxygen reduction reaction (ORR). Consequently, it exhibits a remarkable half-wave potential of 0.88 V in ORR and leads to a superior power density (170.9 mW cm-2) in zinc-air battery, outperforming commercial Pt/C and most reported spinel oxides, revealing a clear structure-property relationship. This structure design strategy is readily adaptable for the precise synthesis and engineering of various spinel structures, opening new avenues for developing advanced electrocatalysts and energy storage materials.

Ligands of Nanoparticles and Their Influence on the Morphologies of Nanoparticle-Based Films

Nanoparticle-based thin films are increasingly being used in various applications. One of the key factors that determines the properties and performances of these films is the type of ligands attached to the nanoparticle surfaces. While long-chain surfactants, such as oleic acid, are commonly employed to stabilize nanoparticles and ensure high monodispersity, these ligands often hinder charge transport due to their insulating nature. Although thermal annealing can remove the long-chain ligands, the removal process often introduces defects such as cracks and voids. In contrast, the use of short-chain organic or inorganic ligands can minimize interparticle distance, improving film conductivity, though challenges such as incomplete ligand exchange and residual barriers remain. Polymeric ligands, especially block copolymers, can also be employed to create films with tailored porosity. This review discusses the effects of various ligand types on the morphology and performance of nanoparticle-based films, highlighting the trade-offs between conductivity, structural integrity, and functionality.

Strategies To Achieve Long-Term Stability in Lead Halide Perovskite Nanocrystals and Its Optoelectronic Applications

The lead halide perovskite (LHP) nanocrystals (NCs) research area is flourishing due to their exceptional properties and great potential for a wide range of applications in optoelectronics and photovoltaics. Yet, despite the momentum in the field, perovskite devices are not yet ready for commercialization due to degradation caused by intrinsic phase transitions and external factors such as moisture, temperature, and ultraviolet (UV) light. To attain long-term stability, we analyze the origin of instabilities and describe different strategies such as surface modification, encapsulation, and doping for long-term viability. We also assess how these stabilizing strategies have been utilized to obtain optoelectronic devices with long-term stability. This Mini-Review also outlines the future direction of each strategy for producing highly efficient and ultrastable LHP NCs for sustainable applications.

Atomic-Level Structure of the Organic-Inorganic Interface of Colloidal ZnO Nanoplatelets from Dynamic Nuclear Polarization-Enhanced NMR

Colloidal semiconductor nanoplatelets (NPLs) have emerged as a new class of nanomaterials that can exhibit substantially distinct optical properties compared to those of isotropic quantum dots, which makes them prime candidates for new-generation optoelectronic devices. Insights into the structure and anisotropic growth of NPLs can offer a blueprint for their controlled fabrication. Here, we present an atomic-level investigation of the organic-inorganic interface structure in ultrathin and stable benzamidine (bza)-supported ZnO NPLs prepared by the modified one-pot self-supporting organometallic approach. High-resolution transmission electron microscopy analysis showed a well-faceted hexagonal shape of ZnO NPLs with lateral surfaces terminated by nonpolar (101̅0) facets. The basal surfaces are flat and well-formed on one side and corrugated on the other side, which indicates that the layer-by-layer growth in the thickness of the NPLs likely occurs only in one direction via the expansion of 2D islands on the surface. The ligand coordination modes were elucidated using state-of-the-art dynamic nuclear polarization (DNP)-enhanced solid-state NMR spectroscopy supported by density functional theory chemical shift calculations. Specifically, it was found that (101̅0) nonpolar facets are stabilized by neutral L-type bza-H ligands with hydrogen bond-supported η1-coordination mode, while polar (0001) and (0001̅) facets are covered by μ2-coordinated X-type anionic bza ligands with different conformations of aromatic rings. Moreover, the ligand packing on (101̅0) lateral facets was determined using 13C natural abundance (∼1.1%) homonuclear dipolar correlation experiments. Overall, an in-depth understanding of the growth mechanism and the unique bimodal X-type/L-type ligand coordination shell of ZnO NPLs is provided, which will facilitate further design of anisotropic nano-objects.

When Metal Nanoclusters Meet Smart Synthesis

Atomically precise metal nanoclusters (MNCs) represent a fascinating class of ultrasmall nanoparticles with molecule-like properties, bridging conventional metal-ligand complexes and nanocrystals. Despite their potential for various applications, synthesis challenges such as a precise understanding of varied synthetic parameters and property-driven synthesis persist, hindering their full exploitation and wider application. Incorporating smart synthesis methodologies, including a closed-loop framework of automation, data interpretation, and feedback from AI, offers promising solutions to address these challenges. In this perspective, we summarize the closed-loop smart synthesis that has been demonstrated in various nanomaterials and explore the research frontiers of smart synthesis for MNCs. Moreover, the perspectives on the inherent challenges and opportunities of smart synthesis for MNCs are discussed, aiming to provide insights and directions for future advancements in this emerging field of AI for Science, while the integration of deep learning algorithms stands to substantially enrich research in smart synthesis by offering enhanced predictive capabilities, optimization strategies, and control mechanisms, thereby extending the potential of MNC synthesis.

Metal-phenolic network composites: from fundamentals to applications

Composites with tailored compositions and functions have attracted widespread scientific and industrial interest. Metal-phenolic networks (MPNs), which are composed of phenolic ligands and metal ions, are amorphous adhesive coordination polymers that have been combined with various functional components to create composites with potential in chemistry, biology, and materials science. This review aims to provide a comprehensive summary of both fundamental knowledge and advancements in the field of MPN composites. The advantages of amorphous MPNs, over crystalline metal-organic frameworks, for fabricating composites are highlighted, including their mild synthesis, diverse interactions, and numerous intrinsic functionalities. The formation mechanisms and state-of-the-art synthesis strategies of MPN composites are summarized to guide their rational design. Subsequently, a detailed overview of the chemical interactions and structure-property relationships of composites based on different functional components (e.g., small molecules, polymers, biomacromolecules) is provided. Finally, perspectives are offered on the current challenges and future directions of MPN composites. This tutorial review is expected to serve as a fundamental guide for researchers in the field of metal-organic materials and to provide insights and avenues to enhance the performance of existing functional materials in applications across diverse fields.

Stirring-Controlled Synthesis of Ultrastable, Fluorescent Silver Nanoclusters

This paper describes how macroscopic stirring of a reaction mixture can be used to produce nanostructures exhibiting properties not readily achievable via other protocols. In particular, it is shown that by simply adjusting the stirring rate, a standard glutathione-based method-to date, used to produce only marginally stable fluorescent silver nanoclusters, Ag NCs-can be boosted to yield nanoclusters retaining fluorescence for unprecedented periods of over 2 years. This enhancement derives not simply from increased homogenization of the reaction mixture but mainly from an appropriately timed delivery of oxygen from above the reaction mixture. In effect, oxygen serves as a reagent that dictates size, structure, stability, and functional properties of the growing nanoobjects.

Structure Distortion Endows Copper Nanoclusters with Surface-Active Uncoordinated Sites for Boosting Catalysis

The utilization of structure distortion to modulate the electronic structure and alter catalytic properties of metallic nanomaterials is a well-established practice, but accurately identifying and comprehensively understanding these distortions present significant challenges. Ligand-stabilized metal nanoclusters with well-defined structures serve as exemplary model systems to illustrate the structure chemistry of nanomaterials, among which few studies have investigated nanocluster models that incorporate structural distortions. In this work, a novel copper hydride nanocluster, Cu42(PPh3)8(RS)4(CF3COO)10(CH3O)4H10 (Cu42; PPh3 is triphenylphosphine and RSH is 2,4-dichlorophenylthiol), with a highly twisted structure has been synthesized in a simple way. Structural analysis reveals Cu42 comprises two Cu25 units that are conjoined in a nearly orthogonal manner. The dramatic distortion in the metal framework, which is driven by multiple interactions from the surface ligands, endows the cluster with a rich array of uncoordinated metal sites on the surface. The resulting cluster, as envisioned, exhibits remarkable activity in catalyzing carbonylation of anilines. The findings from this study not only provides atomically precise insights into the structural distortions that are pertinent to nanoparticle catalysts but also underscores the potential of structurally distorted NCs as a burgeoning generation of catalysts with precise structures and outstanding performances that can be tailored for specific functions.

Colloidal Quasi-2D Methylammonium Lead Bromide Perovskite Nanostructures with Tunable Shape and High Chemical Stability

Control over the lateral dimensions of colloidal nanostructures is a complex task which requires a deep understanding of the formation mechanism and reactivity in the corresponding systems. As a result, it provides a well-founded insight to the physical and chemical properties of these materials. In this work, the preparation of quasi-2D methylammonium lead bromide nanostripes and discuss the influence of some specific parameters on the morphology and stability of this material is demonstrated. The variation in the amount of the main ligand dodecylamine gives a large range of structures beginning with 3D brick-like particles at low concentrations, nanostripes at elevated and ultimately nanosheets at large concentrations. The amount of the co-ligand trioctylphosphine can alter the width of the nanostripe shape to a certain degree. The thickness can be adjusted by the amount of the second precursor methylammonium bromide. Additionally, insights are given for the suggested formation mechanism of these anisotropic structures as well as for stability against moisture at ambient conditions in comparison with differently synthesized nanosheet samples.

Ligand Controls Excited Charge Carrier Dynamics in Metal-Rich CdSe Quantum Dots: Computational Insights

Small metal-rich semiconducting quantum dots (QDs) are promising for solid-state lighting and single-photon emission due to their highly tunable yet narrow emission line widths. Nonetheless, the anionic ligands commonly employed to passivate these QDs exert a substantial influence on the optoelectronic characteristics, primarily owing to strong electron-phonon interactions. In this work, we combine time-domain density functional theory and nonadiabatic molecular dynamics to investigate the excited charge carrier dynamics of Cd28Se17X22 QDs (X = HCOO-, OH-, Cl-, and SH-) at ambient conditions. These chemically distinct but regularly used molecular groups influence the dynamic surface-ligand interfacial interactions in Cd-rich QDs, drastically modifying their vibrational characteristics. The strong electron-phonon coupling leads to substantial transient variations at the band edge states. The strength of these interactions closely depends on the physicochemical characteristics of passivating ligands. Consequently, the ligands largely control the nonradiative recombination rates and emission characteristics in these QDs. Our simulations indicate that Cd28Se17(OH)22 has the fastest nonradiative recombination rate due to the strongest electron-phonon interactions. Conversely, QDs passivated with thiolate or chloride exhibit considerably longer carrier lifetimes and suppressed nonradiative processes. The ligand-controlled electron-phonon interactions further give rise to the broadest and narrowest intrinsic optical line widths for OH and Cl-passivated single QDs, respectively. Obtained computational insights lay the groundwork for designing appropriate passivating ligands on metal-rich QDs, making them suitable for a wide range of applications, from blue LEDs to quantum emitters.

AFM-IR of Electrohydrodynamically Printed PbS Quantum Dots: Quantifying Ligand Exchange at the Nanoscale

Colloidal quantum dots (cQDs), semiconductor materials with widely tunable properties, can be printed in submicrometer patterns through electrohydrodynamic printing, avoiding aggressive photolithography steps. Postprinting ligand exchange determines the final optoelectronic properties of the cQD structures. However, achieving a complete bulk exchange is challenging, and the conventional vibrational analysis lacks the required spatial resolution. Infrared nanospectroscopy enables quantitative analysis of vibrational signals and structural topography on the nanometer scale upon ligand substitution on lead sulfide cQDs. A solution of ethanedithiol led to rapid (∼60 s) exchange of ≤90% of the ligands, in structures up to ∼750 nm thick. Prolonged exposures (>1 h) caused the degradation of the microstructures, with a systematic removal of cQDs regulated by surface:bulk ratios and solvent interactions. This study establishes a method for the development of devices through a combination of tunable photoactive materials, additive manufacturing of microstructures, and their quantitative nanometer-scale analysis.

Long-Chain Molecular Crystals Antimony(III) Alkanethiolates Sb(SCnH2n+1)3 (n ≥ 12): Synthesis, Crystal and Electronic Structures, and Supramolecular Self-Assembly via Secondary Interactions

Currently, there is not much success in solving the molecular and crystal structures of long-chain metal alkanethiolate complexes [M(SCnH2n+1)m] at the atomic level. Taking Sb(SC16H33)3 (1) as an example, we herein disclose the structural characteristics of long-chain trivalent antimony(III) alkanethiolates Sb(SCnH2n+1)3 (n ≥ 12) by single-crystal X-ray crystallography. Specifically, the Sb atom is three-coordinated by alkanethiolate ligands and a slightly distorted triangular pyramid SbS3 core is formed owing to the unique intramolecular stereochemistry of three alkyl chains, namely, two of them almost parallel aligning and the third chain extending alone around the SbS3 core. We further determine the conformation, spatial orientation and packing density of alkyl chains in 1 along with a comparison to those in other long-chain crystalline systems, and reveal the roles of intermolecular van der Waals and Sb···S secondary interactions in molecular self-assembly, which enables 1 to be a layer-structured molecular crystal with a monoclinic P21/c unit cell. The band structures and the atomic orbital contributions to the valence band maximum and conduction band minimum for 1 have also been evaluated by DFT calculations and rationally correlated with its optical absorption property. This study will help understand and discover new structures and structure-property relations of long-chain chemical systems.

Extremely Long-Lived Charge Donor States Formed by Visible Irradiation of Quantum Dots

Using cyclic voltammetry under illumination, we recently demonstrated that CdS quantum dots (QDs) form charge donor states that live for at least several minutes after illumination ends, ∼12 orders of magnitude longer than expected for free carriers. This time scale suggests that the conventionally accepted mechanism of charge transfer, wherein charges directly transfer to an acceptor following exciton dissociation, cannot be complete. Because of these long time scales, this unconventional pathway is not readily observed using time-resolved spectroscopy to probe charge transfer dynamics. Here, we investigated the chemical nature of these charge donor states using cyclic voltammetry under illumination coupled with NMR spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and optical spectroscopy. Our data reveal that charges are stored locally rather than as free carriers, and the number of charges stored is dependent on the QD surface ligation and stoichiometry. Altogether, our results confirm that electrons are stored at ligated surface Cd, these sites are competent charge donors, and this storage is charge balanced by X-type ligand desorption. We found that charge storage occurs in every QD system studied, including CdS, CdSe, and InP capped with carboxylate and phosphonate ligands.

Strongly-Confined CsPbBr3 Perovskite Quantum Dots with Ultralow Trap Density and Narrow Size Distribution for Efficient Pure-Blue Light-Emitting Diodes

The development of pure-blue perovskite light-emitting diodes (PeLEDs) faces challenges of spectral stability and low external quantum efficiency (EQE) due to phase separation in mixed halide compositions. Perovskite quantum dots (QDs) with strong confinement effects are promising alternatives to achieve high-quality pure-blue PeLEDs, yet their performance is often hindered by the poor size distribution and high trap density. A strategy combining thermodynamic control with a polishing-driven ligand exchange process to produce high-quality QDs is developed. The strongly-confined pure-blue (≈470 nm) CsPbBr3 QDs exhibit narrow size distribution (12% dispersion) and are achieved in Br-rich ion environment based on growth thermodynamic control. Subsequent polishing-driven ligand exchange process removes imperfect surface sites and replaces initial long-chain organic ligands with short-chain benzene ligands. The resulting QDs exhibit high photoluminescence quantum yield (PLQY) to near-unity. The resulting PeLEDs exhibit a pure-blue electroluminescence (EL) emission at 472 nm with narrow full-width at half-maximum (FWHM) of 25 nm, achieving a maximum EQE of 10.7% and a bright maximum luminance of 7697 cd m-2. The pure-blue PeLEDs show ultrahigh spectral stability under high voltage, a low roll-off of EQE, and an operational half-lifetime (T50) of 127 min at an initial luminance of 103 cd m-2 under continuous operation.

Suppression of Thermally Induced Surface Traps in Colloidal Quantum Dot Solids via Ultrafast Pulsed Light

Thermal annealing (TA) of colloidal quantum dot (CQD) films is considered an important process for recent high-performing CQD solar cells (SCs) due to its beneficial effects on CQD solids, including enhanced electrical conductivity, denser packing of CQD films, and the removal of organic residues and solvents. However, the conventional TA for CQDs, which requires several  minutes, leads to hydroxylation and oxidation on the CQD surface, resulting in the formation of trap states and a subsequent decline in SC performance. To address these challenges, this study introduces a flashlight annealing (FLA) technique that significantly reduces the annealing time to the millisecond scale. Through the FLA approach, it successfully suppressed hydroxylation and oxidation, resulting in decreased trap states within the CQD solids while simultaneously preserving their charge transport properties. As a result, CQD SCs treated with FLA exhibited a notable improvement, achieving an open-circuit voltage of 0.66 V compared to 0.63 V in TA-treated devices, leading to an increase in power conversion efficiency from 12.71% to 13.50%.

Towards bridging thermo/electrocatalytic CO oxidation: from nanoparticles to single atoms

Proton exchange membrane fuel cells (PEMFCs), as a feasible alternative to replace the traditional fossil fuel-based energy converter, contribute significantly to the global sustainability agenda. At the PEMFC anode, given the high exchange current density, Pt/C is deemed the catalyst-of-choice to ensure that the hydrogen oxidation reaction (HOR) occurs at a sufficiently fast pace. The high performance of Pt/C, however, can only be achieved under the premise that high purity hydrogen is used. For instance, in the presence of trace level carbon monoxide, a typical contaminant during H2 production, Pt is severely deactivated by CO surface blockage. Addressing the poisoning issue necessitates for either developing anti-poisoning electrocatalysts or using pre-purified H2 obtained via a thermo-catalysis route. In other words, the CO poisoning issue can be addressed by either thermal-catalysis from the H2 supply side or electrocatalysis at the user side, respectively. In spite of the distinction between thermo-catalysis and electro-catalysis, there are high similarities between the two routes. Essentially, a reduction in the kinetic barrier for the combination of CO to oxygen containing intermediates is required in both techniques. Therefore, bridging electrocatalysis and thermocatalysis might offer new insight into the development of cutting edge catalysts to solve the poisoning issue, which, however, stands as an underexplored frontier in catalysis science. This review provides a critical appraisal of the recent advancements in preferential CO oxidation (CO-PROX) thermocatalysts and anti-poisoning HOR electrocatalysts, aiming to bridge the gap in cognition between the two routes. First, we discuss the differences in thermal/electrocatalysis, CO oxidation mechanisms, and anti-CO poisoning strategies. Second, we comprehensively summarize the progress of supported and unsupported CO-tolerant catalysts based on the timeline of development (nanoparticles to clusters to single atoms), focusing on metal-support interactions and interface reactivity. Third, we elucidate the stability issue and theoretical understanding of CO-tolerant electrocatalysts, which are critical factors for the rational design of high-performance catalysts. Finally, we underscore the imminent challenges in bridging thermal/electrocatalytic CO oxidation, with theory, materials, and the mechanism as the three main weapons to gain a more in-depth understanding. We anticipate that this review will contribute to the cognition of both thermocatalysis and electrocatalysis.

Surface Structure of Lecithin-Capped Cesium Lead Halide Perovskite Nanocrystals Using Solid-State and Dynamic Nuclear Polarization NMR Spectroscopy

Inorganic colloidal cesium lead halide perovskite nanocrystals (NCs) encapsulated by surface capping ligands exhibit tremendous potential in optoelectronic applications, with their surface structure playing a pivotal role in enhancing their photophysical properties. Soy lecithin, a tightly binding zwitterionic surface-capping ligand, has recently facilitated the high-yield synthesis of stable ultraconcentrated and ultradilute colloids of CsPbX3 NCs, unlocking a myriad of potential device applications. However, the atomic-level understanding of the ligand-terminated surface structure remains uncertain. Herein, we use a versatile solid-state nuclear magnetic resonance (NMR) spectroscopic approach, in combination with dynamic nuclear polarization (DNP) and atomistic molecular dynamics (MD) simulations, to explore the effect of lecithin on the core-to-surface structures of CsPbX3 (X = Cl or Br) perovskites, sized from micron to nanoscale. Surface-selective (cross-polarization, CP) solid-state and DNP NMR (133Cs and 207Pb) methods were used to differentiate the unique surface and core chemical environments, while the head-groups {trimethylammonium [-N(CH3)3+] and phosphate (-PO4-)} of lecithin were assigned via 1H, 13C, and 31P NMR spectroscopy. A direct approach to determining the surface structure by capitalizing on the unique heteronuclear dipolar couplings between the lecithin ligand (1H and 31P) and the surface of the CsPbCl3 NCs (133Cs and 207Pb) is demonstrated. The 1H-133Cs heteronuclear correlation (HETCOR) DNP NMR indicates an abundance of Cs on the NC surface and an intimate proximity of the -N(CH3)3+ groups to the surface and subsurface 133Cs atoms, supported by 1H{133Cs} rotational-echo double-resonance (REDOR) NMR spectroscopy. Moreover, the 1H-31P{207Pb} CP REDOR dephasing curve provides average internuclear distance information that allows assessment of -PO4- groups binding to the subsurface Pb atoms. Atomistic MD simulations of ligand-capped CsPbCl3 surfaces aid in the interpretation of this information and suggest that ligand -N(CH3)3+ and -PO4- head-groups substitute Cs+ and Cl- ions, respectively, at the CsCl-terminated surface of the NCs. These detailed atomistic insights into surface structures can further guide the engineering of various relevant surface-capping zwitterionic ligands for diverse metal halide perovskite NCs.

Mixing Order Asymmetry in Nanoparticle-Polymer Complexation and Precipitation Revealed by Isothermal Titration Calorimetry

In recent years, there has been a renewed interest in complex coacervation, driven by concerted efforts to offer novel experimental and theoretical insights into electrostatic charge-induced association. While previous studies have primarily focused on polyelectrolytes, proteins, or surfactants, our work explores the potential of using cerium (CeO2) and iron (γ-Fe2O3) oxide nanoparticles (NPs) to develop innovative nanomaterials. By combining various charged species, such as polyelectrolytes, charged neutral block copolymers, and coated NPs, we study a wide variety of complexation patterns and compare them using isothermal titration calorimetry, light scattering, and microscopy. These techniques confirm that the titration of oppositely charged species occurs in two steps: the formation of polyelectrolyte complexes and subsequent phase (or microphase) separation, depending on the system studied. Across all examined cases, the entropic contribution to the total free energy surpasses the enthalpic contribution, in agreement with counterion release mechanisms. Furthermore, our investigation reveals a consistent asymmetry in the reaction enthalpy associated with the secondary process, with exothermic profiles observed upon the addition of cationic species to anionic ones and endothermic profiles in the reverse case.

Probing surface interactions in CdSe quantum dots with thiocyanate ligands

Surface chemistry dictates the optoelectronic properties of semiconductor quantum dots (QDs). Tailoring these properties relies on the meticulous selection of surface ligands for efficient passivation. While long-chain organic ligands boast a well-understood passivation mechanism, the intricacies of short inorganic ionic ligands remain largely unexplored. This study sheds light on the surface-passivation mechanism of short inorganic ligands, particularly focusing on SCN- ions on CdSe QDs. Employing steady-state and time-resolved infrared spectroscopic techniques, we elucidated the surface-ligand interactions and coordination modes of SCN--capped CdSe QDs. Comparative analysis with studies on CdS QDs unveils intriguing insights into the coordination behavior and passivation efficacy of SCN- ions on Cd2+ rich QD surfaces. Our results reveal the requirement of both surface-bound (strong binding) and weakly-interacting interfacial SCN- ions for effective CdSe QD passivation. Beyond fostering a deeper understanding of surface-ligand interactions and highlighting the importance of a comprehensive exploration of ligand chemistries, this study holds implications for optimizing QD performance across diverse applications.

Extremely Stable Ag-Based Photonics, Plasmonic, Optical, and Electronic Materials and Devices Designed with Surface Chemistry Engineering for Anti-Tarnish

Silver (Ag) metal-based structures are promising building blocks for next-generation photonics and electronics owing to their unique characteristics, such as high reflectivity, surface plasmonic resonance effects, high electrical conductivity, and tunable electron transport mechanisms. However, Ag structures exhibit poor sustainability in terms of device performance because harsh chemicals, particularly S2- ions present in the air, can damage their structures, lowering their optical and electrical properties. Here, the surface chemistry of Ag structures with (3-mercaptopropyl)trimethoxysilane (MPTS) ligands at room temperature and under ambient conditions is engineered to prevent deterioration of their optical and electrical properties owing to S2- exposure. Regardless of the dimensions of the Ag structures, the MPTS ligands can be applied to each dimension (0D, 1D, and 3D). Consequently, highly sustainable plasmonic effects (Δλ < 2 nm), Fabry-Perot cavity resonance structures (Δλ < 2 nm), reflectors (ΔRReflectance < 0.5%), flexible electrodes (ΔRelectrical < 0.1 Ω), and strain gauge sensors (ΔGF < 1), even in S2- exposing conditions is achieved. This strategy is believed to significantly contribute to environmental pollution reduction by decreasing the volume of electronic waste.

Engineering colloidal semiconductor nanocrystals for quantum information processing

Quantum information processing-which relies on spin defects or single-photon emission-has shown quantum advantage in proof-of-principle experiments including microscopic imaging of electromagnetic fields, strain and temperature in applications ranging from battery research to neuroscience. However, critical gaps remain on the path to wider applications, including a need for improved functionalization, deterministic placement, size homogeneity and greater programmability of multifunctional properties. Colloidal semiconductor nanocrystals can close these gaps in numerous application areas, following years of rapid advances in synthesis and functionalization. In this Review, we specifically focus on three key topics: optical interfaces to long-lived spin states, deterministic placement and delivery for sensing beyond the standard quantum limit, and extensions to multifunctional colloidal quantum circuits.

Direct visualization of ligands on gold nanoparticles in a liquid environment

The interactions between gold nanoparticles, their surface ligands and the solvent critically influence the properties of these nanoparticles. Although spectroscopic and scattering techniques have been used to investigate their ensemble structure, a comprehensive understanding of these processes at the nanoscale remains challenging. Electron microscopy makes it possible to characterize the local structure and composition but is limited by insufficient contrast, electron beam sensitivity and the requirement for ultrahigh-vacuum conditions, which prevent the investigation of dynamic aspects. Here we show that, by exploiting high-quality graphene liquid cells, we can overcome these limitations and investigate the structure of the ligand shell around gold nanoparticles and at the ligand-gold interface in a liquid environment. Using this graphene liquid cell, we visualize the anisotropy, composition and dynamics of ligand distribution on gold nanorod surfaces. Our results indicate a micellar model for surfactant organization. This work provides a reliable and direct visualization of ligand distribution around colloidal nanoparticles.

Nonequilibrium Lattice Dynamics of Individual and Attached PbSe Quantum Dots under Photoexcitation

Quantum dot (QD) solids are emerging materials for many optoelectronic applications. To enhance interdot coupling and charge transport, surface ligands can be removed, allowing individual QDs to be attached along specific crystal orientations (termed "oriented attachment"). Optimizing the electronic and optical properties of QD solids demands a comprehensive understanding of the nanoscale energy flow in individual and attached QDs under photoexcitation. In this work, we employed ultrafast electron diffraction to directly measure how oriented attachment along ⟨100⟩ directions affects the nonequilibrium lattice dynamics of lead selenide QDs. The oriented attachment anisotropically alters the ultrafast energy relaxation along specific crystal axes. Along the ⟨100⟩ directions, both the lattice deformation and atomistic random motions are suppressed in comparison with those of individual QDs. Conversely, the effects are enhanced along the unattached ⟨111⟩ directions due to ligand removal. The oriented attachment switches the major lattice thermalization pathways from ⟨100⟩ to ⟨111⟩ directions.

Ligand-Induced Size-Dependent Circular Dichroism in Quantum Dots

Recent experiments have probed the chiral properties of semiconductor nanocrystal (NC) quantum dots (QDs), but understanding the circular dichroism line shape, excitonic features, and chirality induction mechanism remains a challenge. We propose an atomistic pseudopotential method to model chiral ligand passivated QDs, computing circular dichroism (CD) spectra for CdSe QDs (2.6-3.8 nm). We find strong agreement between calculated and measured line shapes, predicting consistent bisignate line shapes with decreasing CD magnitude as size increases. Our analysis reveals the origin of bisignate line shapes, arising from nondegenerate excitons with opposing angular momenta. We also explore the impact of chiral ligand orientation on QD surfaces, observing changes in the optical activity magnitude and sign. This orientation sensitivity offers the means to distinguish ordered from disordered ligand configurations, facilitating the study of order-disorder transitions at ligand-QD interfaces.

Surface-binding molecular multipods strengthen the halide perovskite lattice and boost luminescence

Reducing the size of perovskite crystals to confine excitons and passivating surface defects has fueled a significant advance in the luminescence efficiency of perovskite light-emitting diodes (LEDs). However, the persistent gap between the optical limit of electroluminescence efficiency and the photoluminescence efficiency of colloidal perovskite nanocrystals (PeNCs) suggests that defect passivation alone is not sufficient to achieve highly efficient colloidal PeNC-LEDs. Here, we present a materials approach to controlling the dynamic nature of the perovskite surface. Our experimental and theoretical studies reveal that conjugated molecular multipods (CMMs) adsorb onto the perovskite surface by multipodal hydrogen bonding and van der Waals interactions, strengthening the near-surface perovskite lattice and reducing ionic fluctuations which are related to nonradiative recombination. The CMM treatment strengthens the perovskite lattice and suppresses its dynamic disorder, resulting in a near-unity photoluminescence quantum yield of PeNC films and a high external quantum efficiency (26.1%) of PeNC-LED with pure green emission that matches the Rec.2020 color standard for next-generation vivid displays.

Coherent Erbium Spin Defects in Colloidal Nanocrystal Hosts

We demonstrate nearly a microsecond of spin coherence in Er3+ ions doped in cerium dioxide nanocrystal hosts, despite a large gyromagnetic ratio and nanometric proximity of the spin defect to the nanocrystal surface. The long spin coherence is enabled by reducing the dopant density below the instantaneous diffusion limit in a nuclear spin-free host material, reaching the limit of a single erbium spin defect per nanocrystal. We observe a large Orbach energy in a highly symmetric cubic site, further protecting the coherence in a qubit that would otherwise rapidly decohere. Spatially correlated electron spectroscopy measurements reveal the presence of Ce3+ at the nanocrystal surface, which likely acts as extraneous paramagnetic spin noise. Even with these factors, defect-embedded nanocrystal hosts show tremendous promise for quantum sensing and quantum communication applications, with multiple avenues, including core-shell fabrication, redox tuning of oxygen vacancies, and organic surfactant modification, available to further enhance their spin coherence and functionality in the future.

Water-Soluble Lead Sulfide Nanoparticles: Direct Synthesis and Ligand Exchange Routes

Colloidal semiconductor nanoparticles (NPs) represent an emergent state of matter with unique properties, bridging bulk materials and molecular structures. Their distinct physical attributes, such as bandgap and photoluminescence, are intricately tied to their size and morphology. Ligand passivation plays a crucial role in shaping NPs and determining their physical properties. Ligand exchange (LE) offers a versatile approach to tailoring NP properties, often guided by Pearson's Hard-Soft Acid-Base theory. Lead sulfide (PbS), a semiconductor of considerable interest, exhibits size-dependent tunable bandgaps from the infrared to the visible range. Here, we present two methods for synthesizing water-soluble, polyvinylpyrrolidone (PVP)-coated PbS NPs. The first involves direct synthesis in an aqueous solution while utilizing PVP as the surfactant for the formation of nano-cubes with a crystal coherence length of ~30 nm, while the second involves LE from octadecylamine-coated PbS truncated nano-cubes to PVP-coated PbS NPs with a crystal coherence length of ~15 nm. Multiple characterization techniques, including X-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectroscopy, and thermal gravimetric analysis, confirmed the results of the synthesis and allowed us to monitor the ligand exchange process. Our findings demonstrate efficient and environmentally friendly approaches for synthesizing PVP-coated PbS NPs.

Understanding Flexdispersion: Structure-Function Relationship Studies of Organic Amphiphilic Ligands

Since inorganic nanoparticles have unique properties that differ from those of bulk materials, their material applications have attracted attention in various fields. In order to utilize inorganic nanoparticles for functional materials, they must be dispersed without agglomeration. Therefore, the surfaces of inorganic nanoparticles are typically modified with organic ligands to improve their dispersibility. Nevertheless, the relationship between the tail group structure in organic ligands and the dispersibility of inorganic nanoparticles in organic solvents remains poorly understood. We previously developed amphiphilic ligands that consist of ethylene glycol chains and alkyl chains to disperse inorganic nanoparticles in a variety of organic solvents. However, the structural requirements for amphiphilic ligands to "flexibly" disperse nanoparticles in less polar to polar solvents are still unclear. Here, we designed and synthesized several phosphonic acid ligands for structure-function relationship studies of flexdispersion. Dynamic light scattering analysis and visible light transmittance measurements revealed that the ratio of alkyl/ethylene glycol chains in organic ligands alone does not determine the dispersibility of the nanoparticles in organic solvents, but the arrangement of the individual chains also has an effect. From a practical application standpoint, it is preferable to design ligands with ethylene glycol chains on the outside relative to the particle surface.

Tailoring Plasmonic Fields with Shape-Controlled Single-Crystal Gold Metasurfaces

Geometry and crystallinity play a critical role in the wavelength-dependent optical responses and plasmonic local near-field distributions of metallic nanostructures. Nevertheless, the ability to tailor the shape and position of crystalline metal surface nanostructures has remained a challenge that limits control of their enhanced local fields and represents a barrier to harnessing their individual and collective responses. Here, we describe a solution deposition method in the presence of anionic additives, which yields shape-controlled, single-crystal plasmonic gold nanostructures on Ag(100) and Au(100) substrates. Use of SO42- ions yields smooth Au(111)-faceted square pyramids with large plasmonic Raman enhancements. Halide additives produce textured hillocks comprising edge- and screw-type dislocations (Cl-), or platelets with large-area Au(100) terraces and (110) step edges (Br-), while SO42- and Br- additive combinations provide Au(110)-faceted square pyramids. With lithographic patterning, this chemistry yields metal deposition with precise geometry and location control to provide single-crystal, plasmonic gold metasurfaces with tailored optical response. The appropriately designed metasurfaces can then generate large Raman scattering enhancements, far greater than high density gold square pyramids with random surface disposition. Shape-controlled single-crystal plasmonic metasurfaces will thus offer opportunities to tune the characteristics of nanostructures, providing enhanced optical, photocatalytic, and sensory response.

Progress in ultrasmall ferrite nanoparticles enhanced T1 magnetic resonance angiography

Contrast-enhanced magnetic resonance angiography (CE-MRA) plays a critical role in diagnosing and monitoring various vascular diseases. Achieving high-sensitivity detection of vascular abnormalities in CE-MRA depends on the properties of contrast agents. In contrast to clinically used gadolinium-based contrast agents (GBCAs), the new generation of ultrasmall ferrite nanoparticles-based contrast agents have high relaxivity, long blood circulation time, easy surface functionalization, and high biocompatibility, hence showing promising prospects in CE-MRA. This review aims to comprehensively summarize the advancements in ultrasmall ferrite nanoparticles-enhanced MRA for detecting vascular diseases. Additionally, this review also discusses the future clinical translational potential of ultrasmall ferrite nanoparticles-based contrast agents for vascular imaging. By investigating the current status of research and clinical applications, this review attempts to outline the progress, challenges, and future directions of using ultrasmall ferrite nanoparticles to drive the field of CE-MRA into a new frontier of accuracy and diagnostic efficacy.

Phase-Controlled Synthesis and Phase-Change Properties of Colloidal Cu-Ge-Te Nanoparticles

Phase-change memory (PCM) technology has recently attracted a vivid interest for neuromorphic applications, in-memory computing, and photonic integration due to the tunable refractive index and electrical conductivity between the amorphous and crystalline material states. Despite this, it is increasingly challenging to scale down the device dimensions of conventionally sputtered PCM memory arrays, restricting the implementation of PCM technology in mass applications such as consumer electronics. Here, we report the synthesis and structural study of sub-10 nm Cu-Ge-Te (CGT) nanoparticles as suitable candidates for low-cost and ultrasmall PCM devices. We show that our synthesis approach can accurately control the structure of the CGT colloids, such as composition-tuned CGT amorphous nanoparticles as well as crystalline CGT nanoparticles with trigonal α-GeTe and tetragonal Cu2GeTe3 phases. In situ characterization techniques such as high-temperature X-ray diffraction and X-ray absorption spectroscopy reveal that Cu doping in GeTe improves the thermal properties and amorphous phase stability of the nanoparticles, in addition to nanoscale effects, which enhance the nonvolatility characteristics of CGT nanoparticles even further. Moreover, we demonstrate the thin-film fabrication of CGT nanoparticles and characterize their optical properties with spectroscopic ellipsometry measurements. We reveal that CGT nanoparticle thin films exhibit a negative reflectivity change and have good reflectivity contrast in the near-IR spectrum. Our work promotes the possibility to use PCM in nanoparticle form for applications such as electro-optical switching devices, metalenses, reflectivity displays, and phase-change IR devices.

The Huge Role of Tiny Impurities in Nanoscale Synthesis

Nanotechnology is vital to many current industries, including electronics, energy, textiles, agriculture, and theranostics. Understanding the chemical mechanisms of nanomaterial synthesis has contributed to the tunability of their unique properties, although studies frequently overlook the potential impact of impurities. Impurities can show adverse effects, clouding the interpretation of results or limiting the practical utility of the nanomaterial. On the other hand, as successful doping has demonstrated, the intentional introduction of impurities can be a powerful tool for enhancing the properties of a nanomaterial. This Review examines the complex role of impurities, unintentionally or intentionally added, during nanoscale synthesis and their effects on the performance and usefulness of the most common classes of nanomaterials: nanocarbons, noble metal and metal oxide nanoparticles, semiconductor quantum dots, thermoelectrics, and perovskites.

Nanocrystal Assemblies: Current Advances and Open Problems

We explore the potential of nanocrystals (a term used equivalently to nanoparticles) as building blocks for nanomaterials, and the current advances and open challenges for fundamental science developments and applications. Nanocrystal assemblies are inherently multiscale, and the generation of revolutionary material properties requires a precise understanding of the relationship between structure and function, the former being determined by classical effects and the latter often by quantum effects. With an emphasis on theory and computation, we discuss challenges that hamper current assembly strategies and to what extent nanocrystal assemblies represent thermodynamic equilibrium or kinetically trapped metastable states. We also examine dynamic effects and optimization of assembly protocols. Finally, we discuss promising material functions and examples of their realization with nanocrystal assemblies.

Structure Effects of Ligands in Gold-Ligand Complexes for Controlled Formation of Gold Nanoclusters

Metal nanoclusters (NCs) are a special class of nanoparticles composed of a precise number of metal atoms and ligands. Because the proportion of ligands to metal atoms is high in metal NCs, the ligand type determines the physical properties of metal NCs. Furthermore, ligands presumably govern the entire formation process of the metal NCs. However, their roles in the synthesis, especially as factors in the uniformity of metal NCs, are not understood. It is because the synthetic procedure of metal NCs is highly convoluted. The synthesis is initiated by the formation of various metal-ligand complexes, which have different numbers of atoms and ligands, resulting in different coordinations of metal. Moreover, these complexes, as actual precursors to metal NCs, undergo sequential transformations into a series of intermediate NCs before the formation of the desired NCs. Thus, to resolve the complicated synthesis of metal NCs and achieve their uniformity, it is important to investigate the reactivity of the complexes. Herein, we utilize a combination of mass spectrometry, density functional theory, and electrochemical measurements to understand the ligand effects on the reactivity of AuI-thiolate complexes toward the reductive formation of Au NCs. We discover that the stability of the complexes can be increased by either van der Waals interactions induced by the long carbon chain of ligands or by non-thiol functional groups in the ligands, which additionally coordinate with AuI in the complexes. Such structural effects of thiol ligands determine the reduction reactivity of the complexes and the amount of NaBH4 required for the controlled synthesis of the Au NCs.

Active Learning of Ligands That Enhance Perovskite Nanocrystal Luminescence

Ligands play a critical role in the optical properties and chemical stability of colloidal nanocrystals (NCs), but identifying ligands that can enhance NC properties is daunting, given the high dimensionality of chemical space. Here, we use machine learning (ML) and robotic screening to accelerate the discovery of ligands that enhance the photoluminescence quantum yield (PLQY) of CsPbBr3 perovskite NCs. We developed a ML model designed to predict the relative PL enhancement of perovskite NCs when coordinated with a ligand selected from a pool of 29,904 candidate molecules. Ligand candidates were selected using an active learning (AL) approach that accounted for uncertainty quantified by twin regressors. After eight experimental iterations of batch AL (corresponding to 21 initial and 72 model-recommended ligands), the uncertainty of the model decreased, demonstrating an increased confidence in the model predictions. Feature importance and counterfactual analyses of model predictions illustrate the potential use of ligand field strength in designing PL-enhancing ligands. Our versatile AL framework can be readily adapted to screen the effect of ligands on a wide range of colloidal nanomaterials.

Next-generation all-organic composites: A sustainable successor to organic-inorganic hybrid materials

This Review presents an overview of all-organic nanocomposites, a sustainable alternative to organic-inorganic hybrids. All-organic nanocomposites contain nanocellulose, nanochitin, and aramid nanofibers as highly rigid reinforcing fillers. They offer superior mechanical properties and lightweight characteristics suitable for diverse applications. The Review discusses various methods for preparing the organic nanofillers, including top-down and bottom-up approaches. It highlights in situ polymerization as the preferred method for incorporating these nanomaterials into polymer matrices to achieve homogeneous filler dispersion, a crucial factor for realizing desired performance. Furthermore, the Review explores several applications of all-organic nanocomposites in diverse fields including food packaging, performance-advantaged plastics, and electronic materials. Future research directions-developing sustainable production methods, expanding biomedical applications, and enhancing resistance against heat, chemicals, and radiation of all-organic nanocomposites to permit their use in extreme environments-are explored. This Review offers insights into the potential of all-organic nanocomposites to drive sustainable growth while meeting the demand for high-performance materials across various industries.

Concurrent Ammonia Synthesis and Alcohol Oxidation Boosted by Glutathione-Capped Quantum Dots under Visible Light

Mother nature accomplishes efficient ammonia synthesis via cascade N2 oxidation by lightning strikes followed with enzyme-catalyzed nitrogen oxyanion (NOx -, x = 2,3) reduction. The protein environment of enzymatic centers for NOx --to-NH4 + process greatly inspires the design of glutathione-capped (GSH) quantum dots (QDs) for ammonia synthesis under visible light (440 nm) in tandem with plasma-enabled N2 oxidation. Mechanistic studies reveal that GSH induces positive shift of surface charge to strengthen the interaction between NOx - and QDs. Upon visible light irradiation of QDs, the balanced and rapid hole and electron transfer furnish GS·radicals for 2e-/2H+ alcohol oxidation and H·for 8e-/10H+ NO3 --to-NH4 + reduction simultaneously. For the first time, mmol-scale ammonia synthesis is realized with apparent quantum yields of 5.45% ± 0.64%, and gram-scale synthesis of value-added acetophenone and NH4Cl proceeds with 1:4 stoichiometry and stability, demonstrating promising multielectron and multiproton ammonia synthesis efficiency and sustainability with nature-inspired artificial photocatalysts.

Step-By-Step Standardization of the Bottom-Up Semi-Automated Nanocrystallization of Pharmaceuticals: A Quality By Design and Design of Experiments Joint Approach

Nanosized drug crystals have been reported with enhanced apparent solubility, bioavailability, and therapeutic efficacy compared to microcrystal materials, which are not suitable for parenteral administration. However, nanocrystal design and development by bottom-up approaches are challenging, especially considering the non-standardized process parameters in the injection step. This work aims to present a systematic step-by-step approach through Quality-by-Design (QbD) and Design of Experiments (DoE) for synthesizing drug nanocrystals by a semi-automated nanoprecipitation method. Curcumin is used as a drug model due to its well-known poor water solubility (0.6 µg mL-1, 25 °C). Formal and informal risk assessment tools allow identifying the critical factors. A fractional factorial 24-1 screening design evaluates their impact on the average size and polydispersity of nanocrystals. The optimization of significant factors is done by a Central Composite Design. This response surface methodology supports the rational design of the nanocrystals, identifying and exploring the design space. The proposed joint approach leads to a reproducible, robust, and stable nanocrystalline preparation of 316 nm with a PdI of 0.217 in compliance with the quality profile. An orthogonal approach for particle size and polydispersity characterization allows discarding the formation of aggregates. Overall, the synergy between advanced data analysis and semi-automated standardized nanocrystallization of drugs is highlighted.

The 2023 Nobel Prize in Chemistry: Quantum dots

The 2023 Nobel Prize in Chemistry was awarded to Aleksey I. Ekimov (prize share 1/3), Louis E. Brus (prize share 1/3), and Moungi G. Bawendi (prize share 1/3) for groundbreaking inventions in the field of nanotechnology, i.e., for the discovery and synthesis of semiconductor nanocrystals, also termed quantum dots, that exhibit size-dependent physicochemical properties enabled by quantum size effects. This feature article summarizes the main milestones of the discoveries and developments of quantum dots that paved the road to their versatile applications in solid-state lighting, display technology, energy conversion, medical diagnostics, bioimaging, and image-guided surgery.

Particle size effect on surface/interfacial tension and Tolman length of nanomaterials: A simple experimental method combining with theoretical

Surface tension and interfacial tension are crucial to the study of nanomaterials. Herein, we report a solubility method using magnesium oxide nanoparticles of different radii (1.8-105.0 nm, MgO NPs) dissolved in pure water as a targeted model; the surface tension and interfacial tension (and their temperature coefficients) were determined by measuring electrical conductivity and combined with the principle of the electrochemical equilibrium method, and the problem of particle size dependence is discussed. Encouragingly, this method can also be used to determine the ionic (atomic or molecular) radius and Tolman length of nanomaterials. This research results disclose that surface/interfacial tension and their temperature coefficients have a significant relationship with particle size. Surface/interfacial tension decreases rapidly with a radius <10 nm (while the temperature coefficients are opposite), while for a radius >10 nm, the effect is minimal. Especially, it is proven that the value of Tolman length is positive, the effect of particle size on Tolman length is consistent with the surface/interfacial tension, and the Tolman length of the bulk does not change much in the temperature range. This work initiates a new era for reliable determination of surface/interfacial tension, their temperature coefficients, ionic radius, and Tolman length of nanomaterials and provides an important theoretical basis for the development and application of various nanomaterials.

Solution processed metal chalcogenide semiconductors for inorganic thin film photovoltaics

Thin film photovoltaics are a key part of both current and future solar energy technologies and have been heavily reliant on metal chalcogenide semiconductors as the absorber layer. Developing solution processing methods to deposit metal chalcogenide semiconductors offers the promise of low-cost and high-throughput fabrication of thin film photovoltaics. In this review article we lay out the key chemistry and engineering that has propelled research on solution processing of metal chalcogenide semiconductors, focusing on Cu(In,Ga)(S,Se)2 as a model system. Further, we expand on how this methodology can be extended to other emerging metal chalcogenide materials like Cu2ZnSn(S,Se)4, copper pnictogen sulfides, and chalcogenide perovskites. Finally, we discuss future opportunities in this field of research, both considering fundamental and applied perspectives. Overall, this review can serve as a roadmap to researchers tackling challenges in solution processed metal chalcogenides to better accelerate progress on thin films photovoltaics and other semiconductor applications.

Metal-Solvent Complex Formation at the Surface of InP Colloidal Quantum Dots

The surface chemistry of colloidal semiconductor nanocrystals (QDs) profoundly influences their physical and chemical attributes. The insulating organic shell ensuring colloidal stability impedes charge transfer, thus limiting optoelectronic applications. Exchanging these ligands with shorter inorganic ones enhances charge mobility and stability, which is pivotal for using these materials as active layers for LEDs, photodetectors, and transistors. Among those, InP QDs also serve as a model for surface chemistry investigations. This study focuses on group III metal salts as inorganic ligands for InP QDs. We explored the ligand exchange mechanism when metal halide, nitrate, and perchlorate salts of group III (Al, In Ga), common Lewis acids, are used as ligands for the conductive inks. Moreover, we compared the exchange mechanism for two starting model systems: InP QDs capped with myristate and oleylamine as X- and L-type native organic ligands, respectively. We found that all metal halide, nitrate, and perchlorate salts dissolved in polar solvents (such as n-methylformamide, dimethylformamide, dimethyl sulfoxide, H2O) with various polarity formed metal-solvent complex cations [M(Solvent)6]3+ (e.g., [Al(MFA)6]3+, [Ga(MFA)6]3+, [In(MFA)6]3+), which passivated the surface of InP QDs after the removal of the initial organic ligand. All metal halide capped InP/[M(Solvent)6]3+ QDs show excellent colloidal stability in polar solvents with high dielectric constant even after 6 months in concentrations up to 74 mg/mL. Our findings demonstrate the dominance of dissociation-complexation mechanisms in polar solvents, ensuring colloidal stability. This comprehensive understanding of InP QD surface chemistry paves the way for exploring more complex QD systems such as InAs and InSb QDs.

Rational Electrochemical Design of Cuprous Oxide Hierarchical Microarchitectures and Their Derivatives for SERS Sensing Applications

Rational morphology control of inorganic microarchitectures is important in diverse fields, requiring precise regulation of nucleation and growth processes. While wet chemical methods have achieved success regarding the shape-controlled synthesis of micro/nanostructures, accurately controlling the growth behavior in real time remains challenging. Comparatively, the electrodeposition technique can immediately control the growth behavior by tuning the overpotential, whereas it is rarely used to design complex microarchitectures. Here, the electrochemical design of complex Cu2O microarchitectures step-by-step by precisely controlling the growth behavior is demonstrated. The growth modes can be switched between the thermodynamic and kinetic modes by varying the overpotential. Cl- ions preferably adhered to {100} facets to modulate growth rates of these facets is proved. The discovered growth modes to prepare Cu2O microarchitectures composed of multiple building units inaccessible with existing methods are employed. Polyvinyl alcohol (PVA) additives can guarantee all pre-electrodeposits simultaneously evolve into uniform microarchitectures, instead of forming undesired microstructures on bare electrode surfaces in following electrodeposition processes is discovered. The designed Cu2O microarchitectures can be converted into noble metal microstructures with shapes unchanged, which can be used as surface-enhanced Raman scattering substrates. An electrochemical avenue toward rational design of complex inorganic microarchitectures is opened up.

Nanosurface-reconstructed perovskite for highly efficient and stable active-matrix light-emitting diode display

Perovskite quantum dots (QDs) are promising for various photonic applications due to their high colour purity, tunable optoelectronic properties and excellent solution processability. Surface features impact their optoelectronic properties, and surface defects remain a major obstacle to progress. Here we develop a strategy utilizing diisooctylphosphinic acid-mediated synthesis combined with hydriodic acid-etching-driven nanosurface reconstruction to stabilize CsPbI3 QDs. Diisooctylphosphinic acid strongly adsorbs to the QDs and increases the formation energy of halide vacancies, enabling nanosurface reconstruction. The QD film with nanosurface reconstruction shows enhanced phase stability, improved photoluminescence endurance under thermal stress and electric field conditions, and a higher activation energy for ion migration. Consequently, we demonstrate perovskite light-emitting diodes (LEDs) that feature an electroluminescence peak at 644 nm. These LEDs achieve an external quantum efficiency of 28.5% and an operational half-lifetime surpassing 30 h at an initial luminance of 100 cd m-2, marking a tenfold improvement over previously published studies. The integration of these high-performance LEDs with specifically designed thin-film transistor circuits enables the demonstration of solution-processed active-matrix perovskite displays that show a peak external quantum efficiency of 23.6% at a display brightness of 300 cd m-2. This work showcases nanosurface reconstruction as a pivotal pathway towards high-performance QD-based optoelectronic devices.

HsGDY 3D Framework-Encapsulated Cu2O Quantum Dots for High-Efficiency Energy Storage

Nanostructured electrode materials become a vital component for future electrode materials because of their short electron and ion transport distances for fast charge and discharge processes and sufficient space between particles for volume expansion. So, achieving a smaller size of the nanomaterial with stable structure and high electrode performance is always the pursuit. Herein, the hybrid electrode material system hydrogen-substituted graphdiyne (HsGDY)/Cu2O-quantum dots (QDs) composed of an active carbon substrate and vibrant metal oxide QD load was established by HsGDY and cuprous oxide. The HsGDY frame with conjugated structure not only delivers impressive capacity by a self-exchange mechanism but also characterizes a matrix to forge strong connections with numerous active Cu2O-QDs for the prevention of aggregation, leading to a homogeneous storage and transport of charge in a bulk material of crisscross structural pores. QD-based electrode materials would exhibit desired capacities by their large surface area, abundant active surface atoms, and the short diffusion pathway. The hybrid system of HsGDY/Cu2O-QDs delivers an ultrahigh capacity of 1230 mA h g-1 with loading density reaching up to 1 mg cm-2. In the meantime, the electrode exhibits a long cycle stability of over 8000 cycles. The synergistic effect endows the hybrid system electrode with an approximately theoretical energy density, suggesting the great potential of such carbon/QD hybrid material system applied for high-performance batteries.

Microwave-assisted synthesis of polyoxometalate-Dy2O3 monolayer nanosheets and nanotubes

Two-dimensional (2D) materials have shown unique chemical and physical properties; however, their synthesis is highly dependent on the layered structure of building blocks. Herein, we developed monolayer Dy2O3-phosphomolybdic acid (PMA) nanosheets and nanotubes based on microwave synthesis. Microwave-assisted synthesis with high-energy input gives a faster and dynamically driven growth of nanomaterials, resulting in high-purity nanostructures with a narrow size distribution. The reaction times of the nanosheets and nanotubes under microwave synthesis are significantly reduced compared with oven-synthesis. Dy2O3-PMA nanosheets and nanotubes exhibit enhanced activity and stability in photoconductance, with higher sensitivities (0.308 μA cm-2 for nanosheets and 0.271 μA cm-2 for nanotubes) compared to the individual PMA (0.12 μA cm-2) and Dy2O3 (0.025 μA cm-2) building blocks. This work demonstrates the promising application potential of microwave-synthesized 2D heterostructures in superconductors and photoelectronic devices.

Ferroelectric Properties of Polymer-Semiconductor Hybrid Material or Composite under Optical Excitation

Polymer-semiconductor hybrid materials or composites have been investigated with respect to their microstructure, optical, photoconductive, and ferroelectric properties. For this purpose, either CdSe quantum dots or (Cd:Zn)S microparticles were dispersed in poly(vinylidenefluoride-trifluoroethylene) solution and hot pressed to films. In both material systems, the electrical conductivity and the polarization behavior could be controlled by the intensity of the optical excitation. The simultaneous high optical transparency of the CdSe quantum-dot-based hybrid materials makes them particularly interesting for applications in the field of flexible, high-resolution sensors.

Versatile Prepolymer Platform for Controlled Tailoring of Quantum Dot Surface Properties

Quantum dots (QDs) hold immense promise for bioimaging, yet technical challenges in surface engineering limit their wider scientific use. We introduce poly(pentafluorophenyl acrylate) (PPFPA) as a user-friendly prepolymer platform for creating precisely controlled multidentate polymeric ligands for QD surface engineering, accessible to researchers without extensive synthetic expertise. PPFPA combines the benefits of both bottom-up and prepolymer approaches, offering minimal susceptibility to hydrolysis and side reactions for controlled chemical composition, along with simple synthetic procedures using commercially available reagents. Live cell imaging experiments highlighted a significant reduction in nonspecific binding when employing PPFPA, owing to its minimal hydrolysis, in contrast to ligands synthesized by using a conventional prepolymer prone to uncontrolled hydrolysis. This observation underscores the distinct advantage of our prepolymer system. Leveraging PPFPA, we synthesized biomolecule-conjugated QDs and performed QD-based immunofluorescence to detect a cytosolic protein. To effectively label cytosolic targets in such a dense and complex environment, probes must exhibit minimal nonspecific binding and be compact. As a result, QD-immunofluorescence has focused primarily on cell surface targets. By creating compact QD-F(ab')2, we sensitively detected alpha-tubulin with a ∼50-fold higher signal-to-noise ratio compared to organic dye-based labeling. PPFPA represents a versatile and accessible platform for tailoring QD surfaces, offering a pathway to realize the full potential of colloidal QDs in various scientific applications.