Nanoscale Heterogeneity Research Articles

Visualizing nanoscale heterogeneity in perylene thin films via tip-enhanced photoluminescence with unsupervised machine learning.

We investigate the properties of ultrathin 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) films using a combination of tip-enhanced photoluminescence and unsupervised machine learning. We expose nanoscale spectral heterogeneities that can be understood on the basis of the interplay between vibronic effects, intermolecular excitons, and intramolecular excitons in PTDCI films.

Remote-Controllable Interfacial Electron Tunneling at Heterogeneous Molecular Junctions via Tip-Induced Optoelectrical Engineering.

Molecular electronics enables functional electronic behavior via single molecules or molecular self-assembled monolayers, providing versatile opportunities for hybrid molecular-scale electronic devices. Although various molecular junction structures are constructed to investigate charge transfer dynamics, significant challenges remain in terms of interfacial charging effects and far-field background signals, which dominantly block the optoelectrical observation of interfacial charge transfer dynamics. Here, tip-induced optoelectrical engineering is presented that synergistically correlates photo-induced force microscopy and Kelvin probe force microscopyto remotely control and probe the interfacial charge transfer dynamics with sub-10nm spatial resolution. Based on this approach, the optoelectrical origin of metal-molecule interfaces is clearly revealed by the nanoscale heterogeneity of the tip-sample interaction and optoelectrical reactivity, which theoretically aligned with density functional theory calculations. For a practical device-scale demonstration of tip-induced optoelectrical engineering, interfacial tunneling is remotely controlled at a 4-inch wafer-scale metal-insulator-metal capacitor, facilitating a 5.211-fold current amplification with the tip-induced electrical field. In conclusion, tip-induced optoelectrical engineering provides a novel strategy to comprehensively understand interfacial charge transfer dynamics and a non-destructive tunneling control platform that enables real-time and real-space investigation of ultrathin hybrid molecular systems.

Nanoscale structural heterogeneities in metastable refractory high-entropy alloy

Most refractory high-entropy alloys (RHEAs) with the dominant body-centered-cubic (bcc) phase are lack of room temperature tensile ductility, which strictly limits their large-scale applications in industry and aerospace. Recently, it has been found that the strategy of metastability engineering can be utilized to ductilize the TiZrHf-based RHEAs. However, up to now, a nanoscale understanding of the potential structural heterogeneities in this system remains exclusive. Herein, through performing the transmission electronic microscope (TEM) characterization on a prototype TaZrHfTa0.5 RHEA with exceptional tensile properties, we have found that this alloy contains a high density of nanoscale structural heterogeneities that are randomly distributed throughout the bcc matrix, including the hexagonal ω phase forming by the collapse of {111}bcc atomic pairs and the orthorhombic α″ phase forming by coupled shuffle-shear mechanism. It may provide a microstructural basis for manipulating the macroscopic properties of metastable RHEAs.

Synergetic strengthening through ultrafine-grained anisotropic microstructure and nanoscale heterogeneity in CoCuFeMnNi high entropy alloy wires

This study investigated the post-drawn annealed CoCuFeMnNi high-entropy wires with distinct dual phase structure and B2 nanoprecipitates. The exceptional hardness observed of the post-drawn annealed CoCuFeMnNi wires can be attributed to the synergetic effect of the ultrafine-grained (UFG) structure and nanoscale precipitation/heterogeneity in the post-drawn annealed CoCuFeMnNi wires.

Superior Energy Storage Performance in Antiferroelectric Epitaxial Thin Films via Structural Heterogeneity and Orientation Control

AbstractDielectric capacitors are desired for electronics and electrical power systems because of their fast charge–discharge speed and high‐power density. Nevertheless, dielectric capacitors typically exhibit lower energy densities in comparison to other energy storage systems like batteries or fuel cells. Among dielectrics, antiferroelectrics have shown great promise for high energy density because of their characteristic double hysteresis loops. However, current antiferroelectric capacitors still face challenges of low efficiency and low breakdown strength due to their large hysteresis, which is harmful to energy efficiency and reliability of the system. Herein, by engineering the nanoscale heterogeneity to mitigate hysteresis and controlling orientation to enhance the polarization, the exceptional energy storage performance of antiferroelectric (Pb0.97La0.02)(Zr0.55Sn0.45)O3 epitaxial thin films is demonstrated. Atomic‐resolution transmission electron microscopy and X‐ray reciprocal space mapping confirm the presence of nanoscale structural heterogeneity, characterized by fragmented antipolar nanodomains. These films exhibit remarkable energy densities, reaching up to ≈84.5 J cm−3, coupled with ultrahigh efficiencies of up to ≈98.5% and superior stability, maintaining efficiencies above 92% across a wide field range of ≈5 MV cm−1. Notably, these findings surpass the capabilities of previously reported dielectric materials, opening new avenues for advanced energy storage applications.

Multidimensional Super-Resolution Microscopy Unveils Nanoscale Surface Aggregates in the Aging of FUS Condensates.

The intracellular liquid-liquid phase separation (LLPS) of biomolecules gives rise to condensates that act as membrane-less organelles with vital functions. FUS, an RNA-binding protein, natively forms condensates through LLPS and further provides a model system for the often disease-linked liquid-to-solid transition of biomolecular condensates during aging. However, the mechanism of such maturation processes, as well as the structural and physical properties of the system, remains unclear, partly attributable to difficulties in resolving the internal structures of the micrometer-sized condensates with diffraction-limited optical microscopy. Harnessing a set of multidimensional super-resolution microscopy tools that uniquely map out local physicochemical parameters through single-molecule spectroscopy, here, we uncover nanoscale heterogeneities in FUS condensates and elucidate their evolution over aging. Through spectrally resolved single-molecule localization microscopy (SR-SMLM) with a solvatochromic dye, we unveil distinct hydrophobic nanodomains at the condensate surface. Through SMLM with a fluorogenic amyloid probe, we identify these nanodomains as amyloid aggregates. Through single-molecule displacement/diffusivity mapping (SMdM), we show that such nanoaggregates drastically impede local diffusion. Notably, upon aging or mechanical shears, these nanoaggregates progressively expand on the condensate surface, thus leading to a growing low-diffusivity shell while leaving the condensate interior diffusion-permitting. Together, beyond uncovering fascinating structural arrangements and aging mechanisms in the single-component FUS condensates, the demonstrated synergy of multidimensional super-resolution approaches in this study opens new paths for understanding LLPS systems at the nanoscale.

A Hall-Petch-like relationship linking nanoscale heterogeneity to yield stress of heterogeneous metallic glasses

Metallic glasses (MGs) undergo plastic deformation through shear transformation zones (STZs) at small deformations and shear banding at large deformations. The STZ mechanism is linked to microstructural heterogeneities, including nano-heterogeneities associated with atom clustering and their spatial distribution. Shear banding occurs due to the coalescence of STZs. In this study, we investigate the yielding behavior of heterogeneous MGs by varying the spatial correlation and standard deviation of local shear moduli associated with clustering atoms on the nanoscale. Using a mesoscale shear transformation zone (STZ) dynamics model, we compute the yielding strength and observe deformation behaviors associated with the formation and propagation of STZs. We propose a Hall-Petch-like relationship where the yield stress of the MG scales inversely with the square root of the spatial correlation length. Our results show that the yielding of MGs corresponds to the percolation of STZs from soft to hard regions. Prior to macroscopic yielding, the activated STZs tend to accumulate inside soft regions, forming a Super-STZ array, which is similar to the formation of dislocation pile-up at grain boundaries. We derive the stress concentration in the front of the Super-STZ using the Eshelby inclusion model and formulate a Hall-Petch-like equation to quantify the yield of MGs with the spatial correlation length and standard deviation of the nanoscale heterogeneity. Our results provide insights into the structure-property relationship of MGs and have important implications for the design of nanoscale MGs with tunable properties.

Tailoring the Weight of Surface and Intralayer Edge States to Control LUMO Energies.

The energies of the frontier molecular orbitals determine the optoelectronic properties in organic films, which are crucial for their application, and strongly depend on the morphology and supramolecular structure. The impact of the latter two properties on the electronic energy levels relies primarily on nearest-neighbor interactions, which are difficult to study due to their nanoscale nature and heterogeneity. Here,an automated method is presented for fabricating thin films with a tailored ratio of surface to bulk sites and a controlled extension of domain edges, both of which are used to control nearest-neighbor interactions. This method uses a Langmuir-Schaefer-type rolling transfer of Langmuir layers (rtLL) to minimize flow during the deposition of rigid Langmuir layers composed of π-conjugated molecules. Using UV-vis absorption spectroscopy, atomic force microscopy, and transmission electron microscopy, it is shown that the rtLL method advances the deposition of multi-Langmuir layers and enables the production of films with defined morphology. The variation in nearest-neighbor interactions is thus achieved and the resulting systematically tuned lowest unoccupied molecular orbital (LUMO) energies (determined via square-wave voltammetry) enable the establishment of a model that functionally relates the LUMO energies to a morphological descriptor, allowing for the prediction of the range of accessible LUMO energies.

Co-evolution of the atomic/nano scale structural heterogeneities and magnetic properties of Fe-Si-B-Cu metallic glass during relaxation with composition fluctuations

The metallic glass (MG) exhibits composition fluctuation or chemical heterogeneity during relaxation. However, the influence of this factor on the evolution of the intrinsic structural heterogeneity of MGs remains unclear. In this study, we systematically examined the co-evolution between atomic and nano-scale structural heterogeneities of Fe-Si-B-Cu MGs during relaxation. We discovered that, despite some degree of fluctuation in composition during the relaxation of Fe-Si-B-Cu MGs, it does not prevent the reduction of structural heterogeneities at the atomic/nano scale. The results demonstrate an overall increase in the number density and number of types of densely packed clusters with a high degree of local five-fold symmetry and a decrease in the number density and number of types of loosely packed clusters with a low degree of local five-fold symmetry. Furthermore, a certain degree of compositional fluctuation during relaxation of Fe-Si-B-Cu MGs facilitates the formation of uniformly distributed Fe-rich regions and Cu-rich regions.

Micro- and Nanoscale Heterogeneities in Zeolite Beta as Measured by Atom Probe Tomography and Confocal Fluorescence Microscopy.

Micro- and nanoscale information on the activating and deactivating coking behaviour of zeolite catalyst materials increases our current understanding of many industrially applied processes, such as the methanol-to-hydrocarbon (MTH) reaction. Atom probe tomography (APT) was used to reveal the link between framework and coke elemental distributions in 3D with sub-nanometre resolution. APT revealed 10-20 nanometre-sized Al-rich regions and short-range ordering (within nanometres) between Al atoms. With confocal fluorescence microscopy, it was found that the morphology of the zeolite crystal as well as the secondary mesoporous structures have a great effect on the microscale coke distribution throughout individual zeolite crystals over time. Additionally, a nanoscale heterogeneous distribution of carbon as residue from the MTH reaction was determined with carbon-rich areas of tens of nanometres within the zeolite crystals. Lastly, a short length-scale affinity between C and Al atoms, as revealed by APT, indicates the formation of carbon-containing molecules next to the acidic sites in the zeolite.

Role of Nanoscale Heterogeneity in the Mechanical Performance of Hybrid Elastomers

Silicone–organic interpenetrating polymer networks (IPNs) are hybrid materials with enhanced mechanical properties relative to pure silicones. Here, we compare structure–property relationships of graft-IPNs of polydimethylsiloxane (PDMS) made with methyl methacrylate (MMA) and isobornyl methacrylate (IBoMA). We found evidence for increased polymer–polymer mixing in the PDMS/PIBoMA graft-IPNs, which was impacted by the higher relative compatibility of these two polymers compared to PDMS/PMMA. These PDMS/PIBoMA hybrid materials possessed fracture toughness values up to 400× greater than unreinforced PDMS elastomers, contrasted by the lower toughness values and highly phase separated morphologies of the PDMS/PMMA hybrids. Increased temperature reduced the fracture and fatigue resistance of the hybrids as nanoscale mechanical heterogeneity was lost between PDMS and the methacrylate polymers, which is consistent with the behavior of existent silicone resin-filled silicone materials.

Nanoscale and functional heterogeneity of the hippocampal extracellular space

The extracellular space (ECS) and its constituents play a crucial role in brain development, plasticity, circadian rhythm, and behavior, as well as brain diseases. Yet, since this compartment has an intricate geometry and nanoscale dimensions, its detailed exploration in live tissue has remained an unmet challenge. Here, we used a combination of single-nanoparticle tracking and super-resolution microscopy approaches to map the nanoscale dimensions of the ECS across the rodent hippocampus. We report that these dimensions are heterogeneous between hippocampal areas. Notably, stratum radiatum CA1 and CA3 ECS differ in several characteristics, a difference that gets abolished after digestion of the extracellular matrix. The dynamics of extracellular immunoglobulins vary within these areas, consistent with their distinct ECS characteristics. Altogether, we demonstrate that ECS nanoscale anatomy and diffusion properties are widely heterogeneous across hippocampal areas, impacting the dynamics and distribution of extracellular molecules.

Nanoscale chemical heterogeneity enables the co-existence of opposing superhydrophobic and hygroscopic properties

Superhydrophobicity and hygroscopicity are two properties that are theoretically exclusive to each other. The fabrication of functional fabrics with these two properties remains very challenging. In this work, it is demonstrated that a non-sticky superhydrophobic and hygroscopic fabric coating can be prepared via the photo polymerization of hexadecyl acrylate and methacrylic acid. On coating surface, the phase-separation-induced chemical heterogeneity has a unique feature of possessing elevated continuous hydrophobic domain and depressed hydrophilic domain, as evidenced by atomic force microscopy measurement. The elevation of hydrophobic domain (i.e., depression of hydrophilic domain) allows the hydrophilic domain to make negligible contribution to the surface wettability to water drop, but can absorb water molecules, thus inducing the unique superhydrophobic but hygroscopic property. The coating has a very low total surface energy of 22.61 mN m−1, with its polar part (0.01 mN m−1) being negligible, thereby showing a high static water contact angle of ~112° on flat glass slide. The coated polyester fabric shows a non-sticky superhydrophobicity with a static water contact angle of ~151° and a water shedding angle of ~10°, as well as good hygroscopic and anti-static properties. We anticipate that this novel coating and the reported strategy of generating the particular chemical heterogeneity may lead to the development of advanced special wettability coatings for various applications.

Engineering of Nanoscale Heterogeneous Transition Metal Dichalcogenide-Au Interfaces.

Engineering the transition metal dichalcogenide (TMD)-metal interface is critical for the development of two-dimensional semiconductor devices. By directly probing the electronic structures of WS2-Au and WSe2-Au interfaces with high spatial resolution, we delineate nanoscale heterogeneities in the composite systems that give rise to local Schottky barrier height modulations. Photoelectron spectroscopy reveals large variations (>100 meV) in TMD work function and binding energies for the occupied electronic states. Characterization of the composite systems with electron backscatter diffraction and scanning tunneling microscopy leads us to attribute these heterogeneities to differing crystallite orientations in the Au contact, suggesting an inherent role of the metal microstructure in contact formation. We then leverage our understanding to develop straightforward Au processing techniques to form TMD-Au interfaces with reduced heterogeneity. Our findings illustrate the sensitivity of TMDs' electronic properties to metal contact microstructure and the viability of tuning the interface through contact engineering.

Formation of chemical short-range orders of two kinds and the co-existence with medium-range orders in an equiatomic VFeCoNi alloy

The chemical short-range orders (CSROs) have aroused the growing concern in the emerging multi-principal-element alloys. The CSROs as the built-in nanoscale heterogeneities cause the difference in the microstructures from conventional alloys and are expected to have an effect on mechanical properties. The formation of CSROs relates to elemental species and recent verifications of CSROs are mainly in ternary alloys. Here, the CSROs are investigated in an as-annealed, quaternary, and equiatomic VFeCoNi alloy of face-centered cubic-structured single phase before and after tensile deformation. Both the lattice structure and elemental species occupation are investigated in detail by means of electron diffraction, dark-field imaging, and atomic-resolution chemical mapping in a high-resolution transmission electron microscope. The CSROs are characterized crystallographically by two M (M: specific element)-enriched planes to sandwich one M-depleted plane. Particularly, M can be either V or Fe, instead of single elemental species reported previously. This indicates that two kinds of CSROs have been simultaneously formed in terms of the elemental species occupation, while both having the same lattice structure. Further, these two kinds of CSROs may grow up into the medium-range orders in sizes larger than 1 nm. Meanwhile, both short- and medium-range orders are mechanically stable during tensile deformation to maintain an almost unchangeable average sizes and areal fractions as well. The Moran's index analyses predict the presence of more V-enriched CSROs and CMROs than Fe-enriched ones. The present results provide the insights into understanding the production of CSROs and their growth as a result of the complex and diverse chemical species in the multi-principal-element alloys.

Toughness Amplification via Controlled Nanostructure in Lightweight Nano-Bouligand Materials.

The enhanced properties of nanomaterials make them attractive for advanced high-performance materials, but their role in promoting toughness has been unclear. Fabrication challenges often prevent the proper organization of nanomaterial constituents, and inadequate testing methods have led to a poor knowledge of toughness at small scales. In this work, the individual roles of nanomaterials and nanoarchitecture on toughness are quantified by creating lightweight materials made from helicoidal polymeric nanofibers (nano-Bouligand). Unidirectional ( = 0°) and nano-Bouligand beams ( = 2°-90°) are fabricated using two-photon lithography and are designed in a micro-single edge notch bend (µ-SENB) configuration with relative densities between 48% and 81%. Experiments demonstrate two unique toughening mechanisms. First, size-enhanced ductility of nanoconfined polymer fibers increases specific fracture energy by 70% in the 0° unidirectional beams. Second, nanoscale stiffness heterogeneity created via inter-layer fiber twisting impedes crack growth and improves absolute fracture energy dissipation by 48% in high-density nano-Bouligand materials. This demonstration of size-enhanced ductility and nanoscale heterogeneity as coexisting toughening mechanisms reveals the capacity for nanoengineered materials to greatly improve mechanical resilience in a new generation of advancedmaterials.

Ultrafast Nanoimaging of Electronic Coherence of Monolayer WSe2.

Transition-metal dichalcogenides (TMDs) have demonstrated a wide range of novel photonic, optoelectronic, and correlated electron phenomena for more than a decade. However, the coherent dynamics of their excitons, including possibly long dephasing times and their sensitivity to spatial heterogeneities, are still poorly understood. Here we implement adiabatic plasmonic nanofocused four-wave mixing (FWM) to image the coherent electron dynamics in monolayer WSe2. We observe nanoscale heterogeneities at room temperature with dephasing ranging from T2 ≲ 5 to T2 ≳ 60 fs on length scales of 50-100 nm. We further observe a counterintuitive anticorrelation between FWM intensity and T2, with the weakest FWM emission at locations of longest coherence. We interpret this behavior as a nonlocal nano-optical interplay between spatial coherence of the nonlinear polarization and disorder-induced scattering. The results highlight the challenges associated with heterogeneities in TMDs limiting their photophysical properties, yet also the potential of their novel nonlinear optical phenomena.

Small changes in lipid backbone linkages can lead to big changes in liquid-liquid phase separation in model membranes.

Cells can dynamically alter the spatial organization of lipids and proteins in the plasma membrane (PM) to regulate processes including cell signaling. The size and morphology of membrane domains, and how these depend on lipid composition, have drawn attention as potentially important variables in these processes. Model membrane studies have proven invaluable for elucidating the influence of phospholipid chains and headgroups, as well as cholesterol concentration, on membrane phase behavior. Following this approach, we have investigated simplified three- and four-component models for the PM outer leaflet to understand the role of the lipid backbone. Specifically, we replaced ester-linked DPPC and DOPC with their ether-linked counterparts to selectively change the membrane dipole potential of coexisting liquid-disordered (Ld) and liquid-ordered (Lo) phases, while titrating DOPC with POPC to control the line tension. Fluorescence imaging of GUVs gave insight into the macroscopic phase behavior, while FRET and cryo-EM of LUVs allowed us to probe nanoscale heterogeneity. Our results can be understood in terms of a model in which the tendency to minimize line tension is counteracted by dipole repulsion, which can in some cases result in stable arrays of small domains or modulated phases. These findings suggest that relatively small changes in the structure of the lipid backbone can influence domain formation and morphology in biomimetic membranes.

Revisiting metastable immiscibility in SiO2–Al2O3: Structure and phase separation of supercooled liquids and glasses

AbstractUnderstanding and controlling liquid–liquid phase separation in aluminosilicates is crucial for optimizing glass properties. However, the metastable nature of aluminosilicates’ phase separation has made it difficult to study experimentally, and uncertainty persists regarding the compositional and temperature extents of the miscibility gap. Here, we present new experimental evidence that suggests a consolute temperature between 1440 and 1590°C and endmember compositions of 7 and 62 mol.% Al2O3 for the phase‐separated glasses. Using containerless melt processing, deeply supercooled liquids over the 0–60 mol.% Al2O3 range are probed with in situ small‐ and wide‐angle X‐ray scattering, which simultaneously reveals changes in nanoscale density heterogeneity and atomic structure. Correlations between phase separation and atomic coordination environments are compared for liquids and glasses. Pair distribution function analysis shows mean O–(Si + Al) coordination increases with Al2O3 content and decreases with temperature.

Analysis of micro- and nanoscale heterogeneities within environmentally relevant thin films containing biological components, oxyanions and minerals using AFM-PTIR spectroscopy.

Minerals in groundwater interact with various chemical and biological species including organic matter, proteins, and prevalent oxyanions, resulting in surface coatings and thin films of these different components. Surface interactions and the surface adsorption of these components on both oxide and oxyhydroxide iron surfaces have been widely investigated using a variety of spectroscopic methods. Despite these numerous studies, there still remains uncertainty with respect to interactions between these individual components, as well as heterogeneities and phase segregations within these thin films. In this study, we investigate mixtures containing Fe-containing minerals, proteins, and oxyanions to better understand surface interactions and phase segregation using Atomic Force Microscopy PhotoThermal Infrared (AFM-PTIR) spectroscopy. The results of this study show that AFM-PTIR spectroscopy can identify both nano- and microscale heterogeneities present within these thin films that are difficult to discern with other more conventional techniques such as ATR-FTIR spectroscopy due to phase segregation and mineral surface interactions. Overall, AFM-PTIR spectroscopy provides insights into multi-component environmental films that are difficult to uncover using other methodologies. This method has the potential to differentiate between bound and unbound toxic species as well as biological components, including environmental DNA, which can be used to assess the fate and transport of these species in the environment.