2D Nanocrystals Research Articles

Unveiling the Mysterious Structure Growth of 2D and 3D All-Inorganic Perovskite Nanocrystals in Solution Phase Dynamically by Using Small-Wide Angle X-Ray Scattering Spectroscopy.

Real-time analysis of the structural formation of 2D and 3D perovskites in solution is challenging due to the sensitivity of perovskite intermediates to environmental conditions and their rapid growth. Conventional techniques often require stringent sample preparation, limiting the ability to study dynamic behaviors in solution. In this study, small- and wide-angle X-ray scattering (SWAXS) is employed to analyze the morphology and dynamics of 2D and 3D perovskite nanostructures in their native colloidal state. Unlike previous studies that attribute CsPbI3 degradation to delta-phase formation, SWAXS revealed preexisting 2D Cs7Pb6I19 nanosheets in pristine CsPbI3 colloidal solutions. In situ SWAXS tracked the dynamic transformation of these structures during recrystallization in diluted solutions. Adding bis(trimethylsilyl)sulfide (TMS) disassembled the 2D nanosheets, while subsequent recrystallization in a poor solvent formed highly crystalline Cs7Pb6I19 nanosheets. The recrystallization dynamics aligned with crystal growth theory, with TMS concentration playing a critical role. Higher TMS concentrations slowed recrystallization, promoting stable lattice formation and enhanced crystallinity, resulting in bright yellow emission. Conversely, lower concentrations accelerated recrystallization, causing structural damage and limiting high-crystallinity growth. This study highlights the importance of controlling recrystallization rates through TMS concentration to optimize the crystallinity and optoelectronic properties of perovskites, offering insights into improving their performance.

Oleylammonium fluoride passivated blue-emitting 2D CsPbBr3 nanoplates with near-unity photoluminescence quantum yield: safeguarding against threats from external perturbations.

Quantum-confined, two-dimensional (2D) CsPbBr3 (CPB) nanoplates (NPLs) have emerged as exceptional candidates for next-generation blue LEDs and display technology applications. However, their large surface-to-volume ratio and detrimental bromide vacancies adversely affect their photoluminescence quantum yield (PLQY). Additionally, external perturbations such as heat, light exposure, moisture, oxygen, and solvent polarity accelerate their transformation into three-dimensional (3D), green-emitting CPB nanocrystals (NCs), thereby resulting in the loss of their quantum confinement. Until now, no reported strategies have successfully addressed all these issues simultaneously. In this study, for the first time, we prepared oleylammonium fluoride (OAmF) salt and applied it post-synthetically to CPB NPLs with thicknesses of n = 3 and n = 4. Steady state and time-resolved photoluminescence (TRPL) measurements like fluorescence upconversion and TCSPC confirmed the elimination of detrimental deep trap states by fluoride ions, resulting in an unprecedented improvement in PLQY to 85% for n = 3 and 98% for n = 4. Furthermore, the formation of robust Pb-F bonds, coupled with strong electrostatic and hydrogen-bonding interactions, resulted in a highly stable NPL surface-ligand interaction. This concrete surface architecture restricts the undesired phase transition of 2D NPLs into 3D NCs under various external perturbations, including heat up to 363 K, strong UV irradiation, water, atmospheric conditions, and solvent polarity. Also, the temperature dependent TRPL measurements provide an insight into the charge carrier dynamics under thermal stress conditions and reveal the location of shallow trap states, which lie below 7 meV from the conduction band edge. In brief, our innovative OAmF salt has effectively addressed all the critical issues of 2D CPB NPLs, paving the way for next-generation LED applications. This breakthrough not only enhances the stability and PLQY of CPB NPLs but also offers a scalable solution for the advancement of perovskite-based technologies.

Controlled synthesis of branched 2D polytypic CdS quantum nanostructures

Controlled synthesis of branched 2D polytypic CdS quantum nanostructures

Growth of novel tin oxide nanocrystals under different pH: Structure evolution, broad spectrum response and photocatalytic activity

Growth of novel tin oxide nanocrystals under different pH: Structure evolution, broad spectrum response and photocatalytic activity

Enhancing thermal stability of one-dimensional poly(ethylene oxide) nanocrystals via matrix chemical crosslinking

Enhancing thermal stability of one-dimensional poly(ethylene oxide) nanocrystals via matrix chemical crosslinking

Nucleation-Controlled Doping of II-VI Semiconductor Nanocrystals Mediated by Magic-Sized Clusters.

Doping quantum-confined semiconductor nanocrystals offers an effective way to tailor their unique properties. However, the inherent challenges of nanoscale doping processes, such as the low probability of successful doping, have hindered their practical applications. Nucleation-controlled doping has emerged as a potential solution, but a comprehensive mechanistic understanding of this process is lacking. Herein, the nucleation-controlled doping process facilitated by magic-sized cluster intermediates is elucidated. This approach enables the synthesis of 2D ZnSe quantum nanoribbons with two distinct doping sites. Remarkably, the identity of the dopants plays a critical role in determining the chemical pathways of nucleation-controlled doping. Substitutional doping of magic-sized clusters with Mn2+ ions leads to successful substitutional doping of the final 2D nanocrystals. Conversely, Co2+ ions, initially occupying substitutional positions in the magic-sized cluster intermediates, relocate to alternative sites, such as interstitial sites, in the final nanocrystals. First-principle calculations of dopant formation energies support these experimental findings, demonstrating the thermodynamic favorability of specific dopant site preferences. Moreover, a consistent tendency is observed in CdSe nanocrystals, suggesting that the proposed doping mechanism is generally applicable to II-VI semiconductors. This study will advance the controlled synthesis of various doped semiconductor nanocrystals using nucleation-controlled doping processes.

Chiral Inorganic Nanomaterials Characterized by Advanced TEM: A Qualitative and Quantitative Study.

Chiral inorganic nanomaterials (CINMs) have garnered significant interest due to their exceptional optical, electronic, and catalytic properties, offering promising advancements in energy conversion, data storage, catalysis, and biomedicine. While traditional optical spectrophotometers reveal the chiroptical performance of CINMs on an ensemble level, the direct structural visualization for the qualitative and quantitative discernment of their chiral features has become increasingly distinct with the advancements of transmission electron microscopy (TEM) techniques. The need for reasonable and high-standard discrimination requirements of CINMs has driven the progress of chirality-based TEM technologies. Therefore, this review in the good season takes the initiative to summarize the current advancements in TEM technologies for CINMs characterization, emphasizing a qualitative analysis of chiral atomic-level features, 0D, 1D, and 2D nanocrystals, and assembled nanomaterials. Then, the quantitative methods for determining chirality is also highlighted, such as 3D electron tomography, and further address the evolution of chiral structures monitored by the Ex-situ and In-situ TEM technologies. By providing a roadmap for the current challenges and proposing future advancements in TEM technologies for the qualitative, quantitative, and real-time analysis of CINMs, it can drive innovations in the field of chiral nanomaterials as well as the development of TEM technologies.

Chirality and Curvature on Protein Adsorption and Osteogenesis

AbstractHere we designed enantiomeric lipid‐mimetic glutamic acid derivatives (L/D‐UG) and investigated their self‐assembled chiral nanostructures’ interaction with the protein adsorption as well as the osteogenesis. It was found that L or D‐UG molecules can self‐assemble into vesicle bilayers and two‐dimensional (2D) nanocrystals via a kinetic and thermodynamic control, respectively. These chiral vesicles and 2D crystals showed differentiated adsorption of proteins, determined by their curvature and chirality. Specifically, fibronectin constituted by L‐amino acids adsorbed preferentially on L‐UG 2D crystal in a semi‐random pattern and L‐2D nanocrystal show as the most effective structures to promote bone regeneration. The controlled vesicle and 2D crystal assemblies with different chirality and curvature helps to clarify their determine roles in protein adsorption and osteogenesis.

Chirality and Curvature on Protein Adsorption and Osteogenesis.

Here we designed enantiomeric lipid-mimetic glutamic acid derivatives (L/D-UG) and investigated their self-assembled chiral nanostructures' interaction with the protein adsorption as well as the osteogenesis. It was found that L or D-UG molecules can self-assemble into vesicle bilayers and two-dimensional (2D) nanocrystals via a kinetic and thermodynamic control, respectively. These chiral vesicles and 2D crystals showed differentiated adsorption of proteins, determined by their curvature and chirality. Specifically, fibronectin constituted by L-amino acids adsorbed preferentially on L-UG 2D crystal in a semi-random pattern and L-2D nanocrystal show as the most effective structures to promote bone regeneration. The controlled vesicle and 2D crystal assemblies with different chirality and curvature helps to clarify their determine roles in protein adsorption and osteogenesis.

Synthesis Route to Single-Walled Zeolite Nanotubes Enabled by Tetrabutylammonium Hydroxide.

Single-walled zeolite nanotubes (ZNT) were recently synthesized in a narrow compositional window. ZNT structural features-thin zeolitic walls and large mesopores-can allow for easy access of small molecules to zeolite micropores, but they also impart processing limitations for these materials, such as challenges with conventional aqueous ion-exchange conditions. Conventional solid- and liquid-phase ion exchange of calcined NaOH-derived ZNT (NaH-ZNT) results in structural degradation to either 2D sheet-like phases, 3D nanocrystals, or amorphous phases, motivating different direct synthesis routes and unconventional ion-exchange procedures of uncalcined ZNT precursors. Here, a modified synthesis route for ZNT synthesis is introduced that facilitates facile ion exchange as well as incorporation of additional non-Al heteroatoms in the zeolite framework. Tetrabutylammonium hydroxide (TBAOH) is used as a hydroxide source and co-OSDA, enabling synthesis of new compositions of ZNT, otherwise unachievable by post-modification of previously reported NaH-ZNT. By varying the gel composition, synthesis temperature, crystallization time, hydroxide source, silicon source, and aluminum source, productive conditions for the new TBAOH synthesis are developed, leading to increased strong acid site density in the ZNT. The collected results demonstrate the sensitivity of the ZNT synthesis to many key parameters and show that the ZNT forms only when Si/(Al + T) ∼ 30 in these synthesis gels and with specific Si and Al sources, and always in the presence of trace Na+. Catalytic testing, via the tandem CO2 hydrogenation to methanol and methanol to aromatics reaction, shows that ZNTs provide adequate catalytic activity (acidity), relative to their conventional 3D counterparts in converting methanol to aromatic compounds.

Versatile stochastic model for predictive KMC simulation of fcc metal nanostructure evolution with realistic kinetics.

Stochastic lattice-gas models provide the natural framework for analysis of the surface diffusion-mediated evolution of crystalline metal nanostructures on the appropriate time scale (often 101-104s) and length scale. Model behavior can be precisely assessed by kinetic Monte Carlo simulation, typically incorporating a rejection-free algorithm to efficiently handle the broad range of Arrhenius rates for hopping of surface atoms. The model should realistically prescribe these rates, or the associated barriers, for a diversity of local surface environments. However, commonly used generic choices for barriers fail, even qualitatively, to simultaneously describe diffusion for different low-index facets, for terrace vs step edge diffusion, etc. We introduce an alternative Unconventional Interaction-Conventional Interaction formalism to prescribe these barriers, which, even with few parameters, can realistically capture most aspects of behavior. The model is illustrated for single-component fcc metal systems, mainly for the case of Ag. It is quite versatile and can be applied to describe both the post-deposition evolution of 2D nanostructures in homoepitaxial thin films (e.g., reshaping and coalescence of 2D islands) and the post-synthesis evolution of 3D nanocrystals (e.g., reshaping of nanocrystals synthesized with various faceted non-equilibrium shapes back to 3D equilibrium Wulff shapes).

CsPbBr3 Perovskite Crack Platelet Nanocrystals and Their Biexciton Generation.

Lead halide perovskite nanocrystals have been extensively studied in recent years as efficient optical materials for their bright and color-tunable emissions. However, these are mostly confined to their 3D nanocrystals and limited to the anisotropic nanostructures. By exploring the Cs-sublattice-induced metal(II) ion exchange with Pb(II), crack CsPbBr3 perovskite platelet nanocrystals having polar surfaces in all three directions are reported here, which remained different than reported standard square platelets. The crack platelets are also passivated with halides to enhance their brightness. Further, as these crack and passivated crack platelets have defects and polar surfaces, the exciton and biexciton generation in these platelets is investigated using femtosecond photoluminescence and transient absorption measurement at ambient as well as cryogenic temperatures, correlated with time-resolved single-particle photoluminescence spectroscopy, and compared with standard square platelets having nonpolar facets. These investigations revealed that the crack platelets and passivated crack platelets possess enhanced biexciton emission compared to square platelets due to the presence of polar surfaces in all three directions. These results provide insights into not only the design of the anisotropic nanostructures of ionic nanocrystals but also the possibility of tuning the single exciton to biexciton generation efficiency, which has potential applications in optoelectronic systems.

Two-dimensional crystallization of precise side-chain giant molecules with constant building blocks ratio

Two-dimensional crystallization of precise side-chain giant molecules with constant building blocks ratio

Exciton control enables high-performance colloidal quantum well light-emitting diodes

Two-dimensional (2D) nanocrystals are promising for optoelectronic and microelectronic technologies. However, the performance of 2D nanocrystal light-emitting diodes (LEDs) remains limited. Here, exciton dynamics are rationally controlled by both shell engineering and device engineering, obtaining colloidal quantum well LEDs (CQW-LEDs) with superior performance. The formation of CQW films on charge transport layers shows an excellent photoluminescence quantum yield of 76.63%. An unreported relationship among Auger lifetime, electron confinement energy, and external quantum efficiency (EQE) in 2D nanocrystal devices is directly observed. The optimized CQW-LEDs possess a maximum power efficiency of 6.04 lm W−1 and a current efficiency of 9.20 cd A−1, setting record efficiencies for 2D nanocrystal red LEDs. Additionally, a remarkable EQE of 13.43% has been achieved, accompanied by an exceptionally low efficiency roll-off. Significantly, EQE for flexible CQW-LEDs is 42-fold higher than the previous best results. Furthermore, active-matrix CQW-LEDs on printed circuit boards are developed. The findings not only unlock new possibilities for controlling exciton dynamics but also provide an alternative strategy to achieve high-performance 2D nanocrystal based applications.

Charge Transfer from Quantum-Confined 0D, 1D, and 2D Nanocrystals.

The properties of colloidal quantum-confined semiconductor nanocrystals (NCs), including zero-dimensional (0D) quantum dots, 1D nanorods, 2D nanoplatelets, and their heterostructures, can be tuned through their size, dimensionality, and material composition. In their photovoltaic and photocatalytic applications, a key step is to generate spatially separated and long-lived electrons and holes by interfacial charge transfer. These charge transfer properties have been extensively studied recently, which is the subject of this Review. The Review starts with a summary of the electronic structure and optical properties of 0D-2D nanocrystals, followed by the advances in wave function engineering, a novel way to control the spatial distribution of electrons and holes, through their size, dimension, and composition. It discusses the dependence of NC charge transfer on various parameters and the development of the Auger-assisted charge transfer model. Recent advances in understanding multiple exciton generation, decay, and dissociation are also discussed, with an emphasis on multiple carrier transfer. Finally, the applications of nanocrystal-based systems for photocatalysis are reviewed, focusing on the photodriven charge separation and recombination processes that dictate the function and performance of these materials. The Review ends with a summary and outlook of key remaining challenges and promising future directions in the field.

Mechanical Properties of Small Quasi-Square Graphene Nanoflakes

The rise of straintronics—the possibility of fine-tuning the electronic properties of nanosystems by applying strain to them—has enhanced the interest in characterizing the mechanical properties of these systems when they are subjected to tensile (or compressive), shear and torsion strains. Four parameters are customarily used to describe the mechanical behavior of a macroscopic solid within the elastic regime: Young’s and shear moduli, the torsion constant and Poisson’s ratio. There are some relations among these quantities valid for elastic continuous isotropic systems that are being used for 2D nanocrystals without taking into account the non-continuous anisotropic nature of these systems. We present in this work computational results on the mechanical properties of six small quasi-square (aspect ratio between 0.9 and 1.1) graphene nanocrystals using the PM7 semiempirical method. We use the results obtained to test the validity of two relations derived for macroscopic homogeneous isotropic systems and sometimes applied to 2D systems. We show they are not suitable for these nanostructures and pinpoint the origin of some discrepancies in the elastic properties and effective thicknesses reported in the literature. In an attempt to recover one of these formulas, we introduce an effective torsional thickness for graphene analogous to the effective bending thickness found in the literature. Our results could be useful for fitting interatomic potentials in molecular mechanics or molecular dynamics models for finite carbon nanostructures, especially near their edges and for twisted systems.

Hydrothermally grown pure and Er-doped ZnS nanocrystals based flexible piezoelectric nanogenerator for energy harvesting and sensing applications

Hydrothermally grown pure and Er-doped ZnS nanocrystals based flexible piezoelectric nanogenerator for energy harvesting and sensing applications

Energy transfer enhanced photoluminescence of 2D/3D CsPbBr3 hybrid assemblies.

Energy transfer has been proven to be an effective method to optimize optoelectronic conversion efficiency by improving light absorption and mitigating nonradiative losses. We prepared 2D/3D CsPbBr3 hybrid assemblies at different reaction temperatures using the hot injection method and found that the photoluminescence quantum yields (PLQYs) of these hybrids were greatly enhanced from 53.4% to 72.57% compared with 3D nanocrystals (NCs). Femtosecond transient absorption measurements were used to study the PLQY enhancement mechanisms, and it was found that the hot carrier lifetime improved from 0.36 to 1.88ps for 2D/3D CsPbBr3 hybrid assemblies owing to the energy transfer from 2D nanoplates to 3D NCs. The energy transfer benefits the excited carrier accumulation and prolonged hot carrier lifetime in 3D NCs in hybrid assemblies, as well as PLQY enhancement in materials.

Rewritable Photoluminescence and Structural Color Display for Dual-Responsive Optical Encryption.

Optical encryption using coloration and photoluminescent (PL) materials can provide highly secure data protection with direct and intuitive identification of encrypted information. Encryption capable of independently controlling wavelength-tunable coloration as well as variable light intensity PL is not adequately demonstrated yet. Herein, a rewritable PL and structural color (SC) display suitable for dual-responsive optical encryption developed with a stimuli-responsive SC of a block copolymer (BCP) photonic crystal (PC) with alternating in-plane lamellae, of which a variety of 3D and 2D perovskite nanocrystals is preferentially self-assembled with characteristic PL, is presented. The SC of a BCP PC is controlled in the visible range with different perovskite precursor doping times. The perovskite nanocrystals developed in the BCP PC are highly luminescent, with a PL quantum yield of ≈33.7%, yielding environmentally stable SC and PL dual-mode displays. The independently programmed SC and PL information is erasable and rewritable. Dual-responsive optical encryption is demonstrated, in which true Morse code information is deciphered only when the information encoded by SCs is properly combined with PL information. Numerous combinations of SC and PL realize high security level of data anticounterfeiting. This dual-mode encryption display offers novel optical encryption with high information security and anti-counterfeiting.

Revealing Two Distinct Formation Pathways of 2D Wurtzite‐CdSe Nanocrystals Using In Situ X‐Ray Scattering

AbstractUnderstanding the mechanism underlying the formation of quantum‐sized semiconductor nanocrystals is crucial for controlling their synthesis for a wide array of applications. However, most studies of 2D CdSe nanocrystals have relied predominantly on ex situ analyses, obscuring key intermediate stages and raising fundamental questions regarding their lateral shapes. Herein, the formation pathways of two distinct quantum‐sized 2D wurtzite‐CdSe nanocrystals — nanoribbons and nanosheets — by employing a comprehensive approach, combining in situ small‐angle X‐ray scattering techniques with various ex situ characterization methods is studied. Although both nanostructures share the same thickness of ≈1.4 nm, they display contrasting lateral dimensions. The findings reveal the pivotal role of Se precursor reactivity in determining two distinct synthesis pathways. Specifically, highly reactive precursors promote the formation of the nanocluster‐lamellar assemblies, leading to the synthesis of 2D nanoribbons with elongated shapes. In contrast, mild precursors produce nanosheets from a tiny seed of 2D nuclei, and the lateral growth is regulated by chloride ions, rather than relying on nanocluster‐lamellar assemblies or Cd(halide)2–alkylamine templates, resulting in 2D nanocrystals with relatively shorter lengths. These findings significantly advance the understanding of the growth mechanism governing quantum‐sized 2D semiconductor nanocrystals and offer valuable guidelines for their rational synthesis.