ACS Nanoscience Au最新文献

Since the isolation of graphene in 2004, two-dimensional (2D) materials research has rapidly evolved into an entire subdiscipline in the physical sciences with a wide range of emergent applications. The unique 2D structure offers an open canvas to tailor and functionalize 2D materials through layer number, defects, morphology, moiré pattern, strain, and other control knobs. Through this review, we aim to highlight the most recent discoveries in the following topics: theory-guided synthesis for enhanced control of 2D morphologies, quality, yield, as well as insights toward novel 2D materials; defect engineering to control and understand the role of various defects, including in situ and ex situ methods; and properties and applications that are related to moiré engineering, strain engineering, and artificial intelligence. Finally, we also provide our perspective on the challenges and opportunities in this fascinating field.

Although multicomponent inorganic thin films (metal-oxides, -carbides, -nitrides, and -chalcogenides) have been synthesized by polymer-assisted deposition (PAD), synthesis of high-performance transparent conducting oxides (TCOs) has been rarely reported. TCO requires (i) removal of impurities, (ii) high-density oxide film, (iii) homogeneity in crystal structures and film morphology, and (iv) controllable elemental doping. This study performs a systematic investigation on preparation of stable multicomponent metal–polymer complex solutions by removing the counteranions in the solution. This study also proposes accurate acid–base titration for each metal species in order to minimize the amount of PEI, thus maximizing the density of the film. As a representative TCO, Sn-doped In₂O₃ (ITO) films have been achieved. The ITO film has an excellent sheet resistance (24.5 Ω/sq) at 93% optical transparency, with a figure of merit of 2.1 × 10^–2 Ω^–1, which is comparable to the best.

Au-seeded semiconductor nanowires have classically been considered to only grow in a layer-by-layer growth mode, where individual layers nucleate and grow one at a time with an incubation step in between. Recent in situ investigations have shown that there are circumstances where binary semiconductor nanowires grow in a multilayer fashion, creating a stack of incomplete layers at the interface between a nanoparticle and a nanowire. In the current investigation, the growth behavior in ternary InGaAs nanowires has been analyzed in situ, using environmental transmission electron microscopy. The investigation has revealed that multilayer growth also occurs for ternary nanowires and appears to be more common than in the binary case. In addition, the size of the multilayer stacks observed is much larger than what has been reported previously. The investigation details the implications of multilayers for the overall growth of the nanowires, as well as the surrounding conditions under which it has manifested. We show that multilayer growth is highly dynamic, where the stack of layers regularly changes size by transporting material between the growing layers. Another observation is that multilayer growth can be initiated in conjunction with the formation of crystallographic defects and compositional changes. In addition, the role that multilayers can have in behaviors such as growth failure and kinking, sometimes observed when creating heterostructures between GaAs and InAs ex situ, is discussed. The prevalence of multilayer growth in this ternary material system implies that, in order to fully understand and accurately predict the growth of nanowires of complex composition and structure, multilayer growth has to be considered.

Transition metal phosphides (TMPs) are a highly investigated class of nanomaterials due to their unique magnetic and catalytic properties. Although robust and reproducible synthetic routes to narrow polydispersity monometallic phosphide nanoparticles (M₂P; M = Fe, Co, Ni) have been established, the preparation of multimetallic nanoparticle phases (M_2–xM′_xP; M, M′ = Fe, Co, Ni) remains a significant challenge. Colloidal syntheses employ zero-valent metal carbonyl or multivalent acetylacetonate salt precursors in combination with trioctylphosphine as the source of phosphorus, oleylamine as the reducing agent, and additional solvents such as octadecene or octyl ether as “noncoordinating” cosolvents. Understanding how these different metal precursors behave in identical reaction environments is critical to assessing the role the relative reactivity of the metal precursor plays in synthesizing complex, homogeneous multimetallic TMP phases. In this study, phosphorus incorporation as a function of temperature and time was evaluated to probe how the relative rate of phosphidation of organometallic carbonyl and acetylacetonate salt precursors influences the homogeneous formation of bimetallic phosphide phases (M_2–xM′_xP; M, M′ = Fe, Co, Ni). From the relative rate of phosphidation studies, we found that where reactivity with TOP for the various metal precursors differs significantly, prealloying steps are necessary to isolate the desired bimetallic phosphide phase. These insights were then translated to establish streamlined synthetic protocols for the formation of new trimetallic Fe_2–x–yNi_xCo_yP phases.

Optimizing the synthesis of atomically precise metal nanoclusters by virtue of molecular tools is highly desirable but quite challenging. Herein we report how ¹⁹F NMR spectroscopy can be used to guide the high-yield synthesis of N-heterocyclic carbene (NHC)-stabilized gold nanoclusters. In spite of little difference, ¹⁹F NMR signals of fluoro-incorporated NHCs (^FNHC) are highly sensitive to the tiny change in their surrounding chemical environments with different N-substituents, metals, or anions, thus providing a convenient strategy to discriminate species in reaction mixtures. By using ¹⁹F NMR, we first disclosed that the one-pot reduction of ^FNHC-Au-X (X is halide) yields multiple compounds, including cluster compounds and also a large amount of highly stable [Au(^FNHC)₂]⁺ byproduct. The detailed quantitative ¹⁹F NMR analyses over the reductive synthesis of NHC-stabilized Au nanoclusters reveal that the formation of the di-NHC complex is deleterious to the high-yield synthesis of NHC-stabilized Au nanoclusters. With the understanding, the reaction kinetic was then slowed by controlling the reduction rate to achieve the high yield of a [Au₂₄(^FNHC)₁₄X₂H₃]³⁺ nanocluster with a unique structure. The strategy demonstrated in this work is expected to provide an effective tool to guide the high-yield synthesis of organic ligand-stabilized metal nanoclusters.

In plasmonic photothermal therapy (PPTT), illuminated gold nanoparticles are locally heated to produce selective damage in cells. While PPTT is expected to strongly depend on the cell line, available data are sparse and critical parameters remain unclear. To elucidate this pivotal aspect, we present a systematic study of diseased and nondiseased cells from different tissues to evaluate cytotoxicity, uptake of gold nanorods (AuNRs), and viability after PPTT. We identified differences in uptake and toxicity between cell types, linking AuNR concentrations to toxicity. Furthermore, the cell death mechanism is shown to depend on the intensity of the irradiated light and hence the temperature increase. Importantly, the data also underline the need to monitor cell death at different time points. Our work contributes to the definition of systematic protocols with appropriate controls to fully comprehend the effects of PPTT and build meaningful and reproducible data sets, key to translate PPTT to clinical settings.

Controlling the flow of broadband electromagnetic energy at the nanoscale remains a critical challenge in optoelectronics. Surface plasmon polaritons (or plasmons) provide subwavelength localization of light but are affected by significant losses. On the contrary, dielectrics lack a sufficiently robust response in the visible to trap photons similar to metallic structures. Overcoming these limitations appears elusive. Here we demonstrate that addressing this problem is possible if we employ a novel approach based on suitably deformed reflective metaphotonic structures. The complex geometrical shape engineered in these reflectors emulates nondispersive index responses, which can be inverse-designed following arbitrary form factors. We discuss the realization of essential components such as resonators with an ultrahigh refractive index of n = 100 in diverse profiles. These structures support the localization of light in the form of bound states in the continuum (BIC), fully localized in air, in a platform in which all refractive index regions are physically accessible. We discuss our approach to sensing applications, designing a class of sensors where the analyte directly contacts areas of ultrahigh refractive index. Leveraging this feature, we report an optical sensor with sensitivity two times higher than the closest competitor with a similar micrometer footprint. Inversely designed reflective metaphotonics offers a flexible technology for controlling broadband light, supporting optoelectronics’ integration with large bandwidths in circuitry with miniaturized footprints.

We demonstrate the use of white-light spectral interferometry as an effective technique involving only linear optical interactions and a partially coherent light source to measure the complex transmission response function of optical resonance and to determine the corresponding variation in the refractive index relative to a reference. We also discuss experimental arrangements to increase the accuracy and sensitivity of the technique. The superiority of the technique over single-beam absorption measurements is demonstrated by the accurate determination of the response function of the chlorophyll-a solution. The technique is then applied to chlorophyll-a solutions of varying concentrations and gold nanocolloids to characterize inhomogeneous broadening. Results on the inhomogeneity of gold nanocolloids are also supported by transmission electron micrographs, showing distributions of the size and shape of the constituent gold nanorods.

MXenes are a growing family of 2D transition-metal carbides and nitrides, which display excellent performance in myriad of applications. Theoretical calculations suggest that manipulation of the MXene surface termination (such as ═O or −F) could strongly alter their functional properties; however, experimental control of the MXene surface termination is still in the developmental stage. Here, we demonstrate that annealing MXenes in an Ar + O₂ low-power plasma results in increased ═O functionalization with minimal formation of secondary phases. We apply this method to two MXenes, Ti₂CT_x and Mo₂TiC₂T_x (T_x represents the mixed surface termination), and show that in both cases, the increased ═O content increases the electrical resistance and decreases the surface transition-metal’s electron count. For Mo₂TiC₂O_x, we show that the O content can be reversibly altered through successive vacuum and plasma annealing. This work provides an effective way to tune MXene surface functionalization, which may unlock exciting surface-dependent properties.