Ultrathin Highly Luminescent Two‐Monolayer Colloidal CdSe Nanoplatelets

Surface effects in atomically flat colloidal CdSe nanoplatelets (NLPs) are significantly and increasingly important with their thickness being reduced to subnanometer level, generating strong surface related deep trap photoluminescence emission alongside the bandedge emission. Herein, colloidal synthesis of highly luminescent two‐monolayer (2ML) CdSe NPLs and a systematic investigation of carrier dynamics in these NPLs exhibiting broad photoluminescence emission covering the visible region with quantum yields reaching 90% in solution and 85% in a polymer matrix is shown. The astonishingly efficient Stokes‐shifted broadband photoluminescence (PL) emission with a lifetime of ≈100 ns and the extremely short PL lifetime of around 0.16 ns at the bandedge signify the participation of radiative midgap surface centers in the recombination process associated with the underpassivated Se sites. Also, a proof‐of‐concept hybrid LED employing 2ML CdSe NPLs is developed as color converters, which exhibits luminous efficacy reaching 300 lm W_opt^?1. The intrinsic absorption of the 2ML CdSe NPLs (≈2.15 × 10⁶ cm^?1) reported in this study is significantly larger than that of CdSe quantum dots (≈2.8 × 10⁵ cm^?1) at their first exciton signifying the presence of giant oscillator strength and hence making them favorable candidates for next‐generation light‐emitting and light‐harvesting applications.     

Regulating Ag Wettability via Modulating Surface Stoichiometry of ZnO Substrates for Flexible Electronics

A novel and highly efficient methodology to regulate (enhance or suppress) the Volmer–Weber 3D growth mode of ultra-thin (<10 nm) Ag layers by modulating the surface stoichiometry of ZnO substrates prior to Ag deposition is presented. Relative to pristine ZnO layers, oxygen-deficient surface states formed by preferential removal of surface oxygen atoms remarkably improve Ag layer wettability, whereas oxygen-excessive surface states formed by oxygen atom incorporation strongly facilitate Ag agglomeration. The dissimilar nucleation and coalescence dynamics are elucidated via combined molecular dynamics and force-bias Monte Carlo simulations. The improved wettability results in significantly lower sheet resistance in the ultra-thin (6–10 nm) Ag layers, for example, 6.03 Ωsq⁻¹ at 8 nm, than the previously reported values from numerous other approaches in the equal thickness range. When this unique methodology is applied to ZnO/Ag/ZnO transparent electrodes, simultaneous improvement in electrical conductivity and visible transparency is realized, with a resultant Haacke figure of merit value of 0.139 Ω⁻¹ that is >50% higher than the best reported value for an identically structured electrode. We select transparent heating devices as a model system to confirm that the superior optoelectronic properties are highly sustainable under simultaneous and severe electrical, mechanical, and thermal stresses.     

Quasi‐2D Colloidal Semiconductor Nanoplatelets for Narrow Electroluminescence

The first functional light‐emitting diodes (LEDs) based on quasi 2D colloidal core/shell CdSe/CdZnS nanoplatelets (NPLs). The solution‐processed hybrid devices are optimized with respect to their electroluminescent characteristics, first, by improving charge injection through exchanging the as‐synthesized NPL long‐chain ligands to shorter ones such as 3‐mercaptopropionic acid, and second, by comparing different hole‐transporting layers. NPL‐LEDs exhibit a maximum luminance of 4499 cd m^‐2 and external quantum efficiencies of 0.63%. In particular, over different applied voltages, systematically narrow electroluminescence of full width at half maximum (FWHM) in the range of 25–30 nm is observed to be independent from the choice of device configuration and NPL ligands. As spectrally narrow electroluminescence is highly attractive in terms of color purity in the context of LED applications, these results emphasize the unique potential of this new class of colloidal core/shell nanoplatelet in achieving bright and functional LEDs of superior color purity.     

Mixed‐Dimensional 1D ZnO–2D WSe2 van der Waals Heterojunction Device for Photosensors

2D layered van der Waals (vdW) atomic crystals are an emerging class of new materials that are receiving increasing attention owing to their unique properties. In particular, the dangling‐bond‐free surface of 2D materials enables integration of differently dimensioned materials into mixed‐dimensional vdW heterostructures. Such mixed‐dimensional heterostructures herald new opportunities for conducting fundamental nanoscience studies and developing nanoscale electronic/optoelectronic applications. This study presents a 1D ZnO nanowire (n‐type)–2D WSe₂ nanosheet (p‐type) vdW heterojunction diode for photodetection and imaging process. After amorphous fluoropolymer passivation, the ZnO–WSe₂ diode shows superior performance with a much‐enhanced rectification (ON/OFF) ratio of over 10⁶ and an ideality factor of 3.4–3.6 due to the carbon–fluorine (C? F) dipole effect. This heterojunction device exhibits spectral photoresponses from ultraviolet (400 nm) to near infrared (950 nm). Furthermore, a prototype visible imager is demonstrated using the ZnO–WSe₂ heterojunction diode as an imaging pixel. To the best of our knowledge, this is the first demonstration of an optoelectronic device based on a 1D–2D hybrid vdW heterojunction. This approach using a 1D ZnO–2D WSe₂ heterojunction paves the way for the further development of electronic/optoelectronic applications using mixed‐dimensional vdW heterostructures.     

Solution‐Processed Silicane Field‐Effect Transistor: Operation Due to Stacking Defects on the Channel

2D silicon nanomaterials have unique potential for use in applications owing to their many different exotic electronic properties. Field‐effect transistors are fabricated based on free‐standing silicanes through a solution process. Owing to the sensitive surface and the nanometer thickness, the devices require the use of fabrication conditions similar to those of lithium‐ion batteries to prevent oxidation of the sheets. Reliable transistor performance is observed at room temperature in a channel thinner than 3 nm, as drain voltage dependent transfer curves current modulation, depending on the edge effect of the silicane, although the transistor property is modest (hole mobility of 1.8 cm² V^?1 s^?1). The results suggest the feasibility of other air‐sensitive 2D nanomaterials for applications in nanoelectronic devices.     

Platelet‐in‐Box Colloidal Quantum Wells: CdSe/CdS@CdS Core/Crown@Shell Heteronanoplatelets

Here, the CdSe/CdS@CdS core/crown@shell heterostructured nanoplatelets (NPLs) resembling a platelet‐in‐box structure are developed and successfully synthesized. It is found that the core/crown@shell NPLs exhibit consistently substantially improved photoluminescence quantum yield compared to the core@shell NPLs regardless of their CdSe‐core size, CdS‐crown size, and CdS‐shell thickness. This enhancement in quantum yield is attributed to the passivation of trap sites resulting from the critical peripheral growth with laterally extending CdS‐crown layer before the vertical shell growth. This is also verified with the disappearance of the fast nonradiative decay component in the core/crown NPLs from the time‐resolved fluorescence spectroscopy. When compared to the core@shell NPLs, the core/crown@shell NPLs exhibit relatively symmetric emission behavior, accompanied with suppressed lifetime broadening at cryogenic temperatures, further suggesting the suppression of trap sites. Moreover, constructing both the CdS‐crown and CdS‐shell regions, significantly enhanced absorption cross‐section is achieved. This, together with the suppressed Auger recombination, enables the achievement of the lowest threshold amplified spontaneous emission (≈20 μJ cm^?2) from the core/crown@shell NPLs among all different architectures of NPLs. These findings indicate that carefully heterostructured NPLs will play a critical role in building high‐performance colloidal optoelectronic devices, which may even possibly challenge their traditional epitaxially grown thin‐film based counterparts.     

Filling the Gaps between Graphene Oxide: A General Strategy toward Nanolayered Oxides

Despite extraordinary developments in the research of 2D inorganic nanomaterials, a scalable and generalized synthetic method toward 2D oxide materials that lack layered lattice structures is still challenging. Herein, an easy and versatile solution‐based route to synthesize oxides with layered nanostructures by combining sol–gel method with graphene oxide (GO) paper templates is reported. GO can stack together to form a paper‐like membrane, the gap between two GO layers provides ideal 2D space to template the growth of oxide nanolayers. By this simple strategy, the gaps are filled successfully with polycrystalline TiO₂, ZnO, Fe₂O₃, and amorphous SiO₂ nanolayers with thickness of 1–5 nm. Single or multilayers of the oxide‐based ceramic/glass nanolayers for applications in electronics, catalysts, energy storage, and gas separation can be expected; as an example, it is shown that layered Fe₂O₃ electrodes exhibit high performance for lithium‐ion battery due to enhanced electrical connections between the 2D nanolayers.     

Tandem adsorption-photodegradation activity induced by light on NiO-ZnO p–n couple modified silica nanomaterials

Well dispersed mono and coupled NiO, ZnO oxides modified silica, with a narrow size distribution, less than 10 nm, have been synthesized by “one–pot” microemulsion assisted sol–gel procedure. The composites exhibited significantly enhanced tandem adsorption–photodegradation activity for the degradation of Methylene Blue dye over 90% (under UV light) and 97% (under sun light). These highly homogeneous oxides modified silica, with very low content of NiO (0.01÷1.14%) and ZnO (0.09%) oxides dispersed in silica, are generating a size effect that leads to nanomaterials with superior properties like higher specific surface area (308 m² g⁻¹), smaller band-gaps energy (2.5 eV) and, consequently, extended light absorption range from UV to natural light. A synergistic effect of mixed n–type ZnO and p–type NiO oxides incorporated in silica has been noticed on the tandem adsorption and photodegradation process. Several influencing process parameters, such as the material and dye loading, stirring speed, NiO/ZnO ratio and light source on the photodegradation performance of NiO-ZnO modified silica related to Methylene Blue cationic dye, were also investigated.     

Sub-2 nm Ultrathin and Robust 2D FeNi Layered Double Hydroxide Nanosheets Packed with 1D FeNi-MOFs for Enhanced Oxygen Evolution Electrocatalysis

Water oxidation is a critical process for electrochemical water splitting due to its inherent sluggish kinetics. In spite of the high catalytic activities of noble metal-based electrocatalysts for water oxidation, their high cost, rare reserves, and low stabilities drive researchers to exploit efficient but low-cost electrocatalysts. Ultrathin 2D nanomaterials are considered efficient electrocatalysts for oxygen evolution reaction (OER) in water splitting. Herein, a facile strategy is proposed to fabricate 2D FeNi layered double hydroxide (FeNi-LDH) nanosheets packed with the in situ produced 1D sword-like FeNi-MOFs by using FeNi-LDH as a semi-sacrificial template. In the composite, the thickness of the formed nanosheets is only 1.34 nm, much thinner than that of most previously reported 2D materials. The 1D porous sword-like MOF nanorods have a long length of around 1.3 µm. Due to the unique 2D/1D combined structure, the as-prepared FeNi LDH/MOF is directly used as electrocatalyst for the OER displays enhanced OER electrocatalytic performance with a low overpotential of 272 mV@100 mA cm^–2, a small Tafel slope of 34.1 mV dec^–1, high long-term durability. This work provides a new way to fabricate integrated ultrathin 2D nanosheets and MOFs as advanced catalysts for electrochemical energy conversion.     

One‐Step Preparation of Biocompatible Gold Nanoplates with Controlled Thickness and Adjustable Optical Properties for Plasmon‐Based Applications

The ability to synthesize plasmonic nanomaterials with well‐defined structures and tailorable size is crucial for exploring their potential applications. Gold nanoplates (AuNPLs) exhibit appealing structural and optical properties, yet their applications are limited by difficulties in thickness control. Other challenges include a narrow range of tunability in size and surface plasmon resonance, combined with a synthesis conventionally involving cytotoxic cetyltrimethylammonium (CTA) halide surfactant. Here, a one‐step, high‐yield synthesis of single‐crystalline AuNPLs is developed, based on the combined use of two structure‐directing agents, methyl orange and FeBr₃, which undergo preferential adsorption onto different crystalline facets of gold. The obtained AuNPLs feature high shape homogeneity that enables mesoscopic self‐assembly, broad‐range tunability of dimensions (controlled thickness from ≈7 to ≈20 nm, accompanied by modulation of the edge length from ≈150 nm to ≈2 µm) and plasmonic properties. These merits, coupled with a preparation free of CTA‐halide surfactants, have facilitated the exploration of various uses, especially in bio‐related areas. For example, they are demonstrated as biocompatible photothermal agents for cell ablation in NIR I and NIR II windows. This work paves the way to the innovative fabrication of anisotropic plasmonic nanomaterials with desired attributes for wide‐ranging practical applications.     

Room‐Temperature Metallic Fusion‐Induced Layer‐by‐Layer Assembly for Highly Flexible Electrode Applications

To fabricate flexible electrodes, conventional silver (Ag) nanomaterials have been deposited onto flexible substrates, but the formed electrodes display limited electrical conductivity due to residual bulky organic ligands, and thus postsintering processes are required to improve the electrical conductivity. Herein, an entirely different approach is introduced to produce highly flexible electrodes with bulk metal–like electrical conductivity: the room‐temperature metallic fusion of multilayered silver nanoparticles (NPs). Synthesized tetraoctylammonium thiosulfate (TOAS)‐stabilized Ag NPs are deposited onto flexible substrates by layer‐by‐layer assembly involving a perfect ligand‐exchange reaction between bulky TOAS ligands and small tris(2‐aminoethyl)amine linkers. The introduced small linkers substantially reduce the separation distance between neighboring Ag NPs. This shortened interparticle distance, combined with the low cohesive energy of Ag NPs, strongly induces metallic fusion between the close‐packed Ag NPs at room temperature without additional treatments, resulting in a high electrical conductivity of ≈1.60 × 10⁵ S cm^?1 (bulk Ag: ≈6.30 × 10⁵ S cm^?1). Furthermore, depositing the TOAS–Ag NPs onto cellulose papers through this approach can convert the insulating substrates into highly flexible and conductive papers that can be used as 3D current collectors for energy‐storage devices.     

Enhanced and Engineered d0 Ferromagnetism in Molecularly‐Thin Zinc Oxide Nanosheets

Molecularly‐thin nanosheets are ultimate two‐dimensional (2D) nanomaterials potentially giving unusual physical and chemical properties due to the strong 2D quantum and surface effects. Here, it is demonstrated that 1.5‐nm‐thick ZnO nanosheets exhibit greatly enhanced room‐temperature ferromagnetism. Saturation magnetization value of the nanosheets with intercalated dodecyl sulfate layers is approximately 100 times that of ZnO mesocrystals. Anion exchange with dodecyl phosphate layers strongly suppresses ferromagnetic ordering as a result of surface defect passivation while maintaining bulk‐like n‐type semiconducting properties, which reveals significance of interfacial states to engineer functional properties of nanosheet‐based hybrid materials.     

Self-assembly fabrication of ZnO hierarchical micro/nanospheres for enhanced photocatalytic degradation of endocrine-disrupting chemicals

ZnO hierarchical micro/nanospheres were successfully synthesized via a facile and surfactant-free chemical solution route. The field emission scanning electron microscopy and transmission electron microscopy observations showed that the ZnO micro/nanospheres were assembled by large amounts of interleaving nanosheets with the thickness of about 17 nm. The X-ray diffraction, energy dispersion X-ray and Raman results revealed that the as-synthesized products were well-crystalline and possessing wurtzite hexagonal phase pure ZnO. Under UV irradiation, the ZnO micro/nanospheres showed an enhanced photocatalytic performance compared with the ZnO nanorods and commercial TiO₂ in the degradation of phenol. The photocatalytic enhancement of ZnO micro/nanospheres was attributed to their unique hierarchical porous surface structure and large surface area which can enhance the electron–hole separation and increased the yield of hydroxyl radical quantities as evidenced by the photoluminescence spectra. By using a certain of radical scavengers, hydroxyl radical was determined to play a pivotal role for the phenol degradation. Moreover, the as-synthesized ZnO micro/nanospheres could be easily recycled without any significant loss of the photocatalytic activity. Other endocrine-disrupting chemicals such as resorcinol, bisphenol A and methylparaben were also successfully photodegraded under identical conditions. These characteristics showed the practical applications of the ZnO micro/nanospheres in environmental remediation.     

Direct Holographic Patterning of ZnO

Zinc oxide thin films are holographically patterned on submicronic scale by direct photodissolution method. The photodissolution process in solution is highly sensitive in the UV range (355 nm). 1D and 2D nanostructures are successfully obtained by this photoresist‐free process. The kinetic of the reaction is studied by recording the transmitted intensity through the evolution of the ZnO film thickness along the reaction time. Application of an electrical potential strongly increases the dissolution rate (1.5 μm min^?1) and decreases the pattern formation time. As a first demonstration of the potential of all‐in liquid direct ZnO heterostructuring, selective growth of ZnO nanorods is performed by chemical bath deposition using holographically patterned ZnO films as a substrate.     

Functionalized Gold Nanoclusters Identify Highly Reactive Oxygen Species in Living Organisms

Surface engineering of nanomaterials allows fine tuning of their interactions with biological systems, and thus can benefit their applications in monitoring intracellular events. Herein, the facile synthesis of ligand‐functionalized gold nanoclusters (AuNCs) as intracellular probes targeting highly reactive oxygen species (hROS, such as ?OH, ClO^?, and ONOO^?) is demonstrated. Selected ligands such as quaternary ammonium and oligopeptides are utilized to modulate the surface chemistry of AuNCs. It is shown that AuNCs decorated with the cell‐penetrating oligoarginine peptide facilitate cellular uptake and intracellular imaging of hROS in living cells and the zebrafish, with high stability and selectivity.     

Hollow Spherical Nanoshell Arrays of 2D Layered Semiconductor for High‐Performance Photodetector Device

Well‐defined hollow spherical nanoshell arrays of 2D transitional metal dichalcogenide (TMDC) nanomaterials for MoSe₂ and MoS₂ are grown via chemical vapor deposition technique for the first time. The hollow sphere arrays display the uniform dimensions of ≈450 nm with the shell thickness of ≈10 nm. The unique hollow sphere architecture with increased active surface area is forecasted to supply more efficient route to improve light‐harvesting efficiency through repeated light reflection and scattering inside the hollow structure without decay of response and recovery speed, because exceptional “SP–SP” junction barriers conducting mechanism can facilitate carriers tunneling and transport during the electron transfer procedure within the present particular structure. The MoSe₂ hollow sphere photodetector exhibits an outstanding responsivity (8.9 A W^?1), which is tenfold higher than that for MoSe₂ compact film (0.9 A W^?1), fast response and recovery speed, and good durability under illumination wavelength of 365 nm. Meanwhile, MoSe₂ hollow sphere arrays on flexible polyethylene terephthalate substrates reveal excellent bending stability. Therefore, this research indicates that unique hollow sphere architecture of 2D TMDC materials will be an anticipated avenue for efficient photodetector devices with far‐ranging capability.     

Surfactant free hydrothermally derived ZnO nanowires,nanorods, microrods and their characterization

ZnO nanowires, nanorods and microrods have been prepared by an organic-free hydrothermal process using ZnSO₄ and NaOH/NH₄OH solutions. The powder X-ray diffraction (PXRD) patterns reveal that the ZnO nano/microrods are of hexagonal wurtzite structure. The Fourier transform infrared (FT-IR) spectrum of ZnO powder shows only one significant spectroscopic band at around 417 cm^?1 associated with the characteristic vibrational mode of Zn–O bonding. The thickness 75–300 nm for ZnO nanorods and 0.2–1.8 μm for microrods are identified from SEM/TEM images. UV–visible absorption spectra of ZnO nano/microrods show the blue shift. The UV band and green emission observed in photoluminescence (PL) spectra are due to free exciton emission and singly ionized oxygen vacancy in ZnO. Finally, the mechanism for organic-free hydrothermal synthesis of the ZnO nano/microrods is discussed.     

Photoelectric phenomena in ZnO:Al-<Emphasis Type="Italic">p</Emphasis>-Si heterostructures

Al-doped zinc-oxide (ZnO:Al) films are obtained by magnetron sputtering. Based on an investigation of electrical properties of the films, it is shown that the electron density in these films is as high as 5×10²⁰ cm⁻³ and is practically constant in the temperature range 77–300 K, which indicates high efficiency of doping ZnO with an Al impurity. It is found that the deposition of thin films (d≈1 μm) on the p-Si(111) surface leads to the formation of heterostructures with the highest photosensitivity of ∼400 V/W at T=300 K, which oscillates in the spectral range 1.3–3.5 eV. With the oblique incidence of linearly polarized radiation, induced pleochroism emerges in such heterostructures. The magnitude of pleochroism oscillates in the range 5–40% (θ≈75°), which is associated with the interference phenomena in the ZnO films. The prospects of using the heterostructures obtained as highly selective photosensors of natural and linearly polarized radiation are considered. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 11, 2003, pp. 1329–1333. Original Russian Text Copyright ? 2003 by Nikitin, Nikolaev, Polushina, V. Rud’, Yu. Rud’, Terukov.     

Polarized Optoelectronics of CsPbX3 (X = Cl,Br, I) Perovskite Nanoplates with Tunable Size and Thickness

Low dimensional semiconductor nanomaterials have shown their tailorable properties for a variety of promising applications in decades. Here a general strategy to synthesize all‐inorganic CsPbX₃ (X = Cl, Br, I or their mixture) perovskite 2D nanoplates by introducing additional metal halides MX'₂ or MX'₃ (M = Cu, Zn, Al or Pb, etc.; X' = Cl, Br or I) is reported. These CsPbX₃ perovskite nanoplates have uniform thickness and tunable size, which can be feasibly controlled by the component and ratio of the metal halides, temperature, time, and ligands. The well‐defined morphology of the nanoplates makes them ideal building blocks for the self‐assembly in the face‐to‐face and column‐by‐column arrangement. Compared to the optically isotropic CsPbX₃ nanocubes, the 2D CsPbX₃ nanoplates exhibit remarkable polarized UV–vis absorption and photoluminescence not only in liquid solvent and solid resin matrix, but also in self‐assembled films. An optoelectronic photodetector sensitive for linear polarized light is fabricated to demonstrate the proof‐of‐concept.