Heterogeneous Nanostructures Research Articles

Record-Low thermal boundary resistance at bonded GaN/diamond interface by controlling ultrathin heterogeneous amorphous layer

Thermal boundary resistance (TBR) in semiconductor-on-diamond structure bottlenecks efficient heat dissipation in electronic devices. In this study, to reduce the TBR between GaN and diamond, surface-activated bonding with a hybrid SiOx-Ar ion source was initially applied to achieve an ultrathin interfacial layer. The simultaneous surface activation and slow deposition of the SiOx binder layer enabled precise control over layer thickness (2.5–5.3 nm) and formation of an amorphous heterogeneous nanostructure comprising a SiOx region between two inter-diffusion regions. Crucially, the 2.5-nm-thick interfacial layer achieved a TBR of 8.3 m2⋅K/GW, a record low for direct-bonded GaN/diamond interface. A remarkable feature is that the TBR is extremely sensitive to the interfacial thickness; Varying from 8.3 m2⋅K/GW to 34 m2⋅K/GW with thickness difference of only 2.8 nm. Theoretical analysis revealed the origin of this phenomena: a diamond/SiOx inter-diffusion layer extend the vibrational frequency, far exceeding that of crystalline diamond, which increases the lattice vibrational mismatch and suppresses phonon transmission.

Interfacial engineering of hydrangea-like MnSe/NiSe heterostructure catalysts for methanol-assisted water splitting

Replacing the oxygen evolution reaction (OER) with the methanol oxidation reaction (MOR) is an effective strategy for energy-saving production of hydrogen in the water splitting technique. In this work, we prepared hydrangea-like heterogeneous nanostructures composed of manganese selenide and nickel selenide (denoted as MnSe/NiSe), in which heterometallic nickel can be controllably introduced into manganese selenide to promote electron transfer from manganese selenide to nickel selenide. Electronic regulation optimizes the adsorption of water and methanol by heterojunction catalysts, forming dual active sites at the MnSe/NiSe heterointerface, thereby achieving excellent hydrogen evolution and methanol oxidation performance. The two-electrode cell utilizing MnSe/NiSe as a bifunctional catalyst necessitated electrolytic potentials of 1.53 V and 1.79 V to achieve current densities of 10 and 50 mA cm−2, respectively, which are clearly lower than those of the overall water splitting. This work offers an energy-saving method for hydrogen production.

Plasmonic‐Promoted Interatomic Hot Carriers Regulation Enhanced Electrocatalytic Nitrogen Reduction Reaction

Utilizing hot carriers for efficient plasmonic‐mediated chemical reactions (PMCRs) to convert solar energy into secondary energy is one of the most feasible solutions to the global environmental and energy crisis. Finding a plasmonic heterogeneous nanostructure with a more efficient and reasonable hot carrier transport path without affecting the intrinsic plasmonic properties is still a major challenge that urgently needs to be solved in this field. Herein, the mechanism by which plasmonic‐promoted interatomic hot electron redistribution on the surface of Au3Cu alloy nanoparticles promotes the electrocatalytic nitrogen reduction reaction (ENRR) is successfully clarified. The localized surface plasmon resonance (LSPR) effect can boost the transfer of plasmonic hot electrons from Au atoms to Cu atoms, trigger the interatomic electron regulation of Au3Cu alloy nanoparticles, enhance the desorption of ammonia molecules, and increase the ammonia yield by approximately 93.9%. This work provides an important reference for rationally designing and utilizing the LSPR effect to efficiently regulate the distribution and mechanism of plasmonic hot carriers on the surface of heterogeneous alloy nanostructures.

Plasmon-Promoted Interatomic Hot Carriers Regulation Enhanced Electrocatalytic Nitrogen Reduction Reaction.

Utilizing hot carriers for efficient plasmon-mediated chemical reactions (PMCRs) to convert solar energy into secondary energy is one of the most feasible solutions to the global environmental and energy crisis. Finding a plasmonic heterogeneous nanostructure with a more efficient and reasonable hot carrier transport path without affecting the intrinsic plasmonic properties is still a major challenge that urgently needs to be solved in this field. Herein, the mechanism by which plasmon-promoted interatomic hot electron redistribution on the surface of Au3Cu alloy nanoparticles promotes the electrocatalytic nitrogen reduction reaction (ENRR) is successfully clarified. The localized surface plasmon resonance (LSPR) effect can boost the transfer of plasmon hot electrons from Au atoms to Cu atoms, trigger the interatomic electron regulation of Au3Cu alloy nanoparticles, enhance the desorption of ammonia molecules, and increase the ammonia yield by approximately 93.9 %. This work provides an important reference for rationally designing and utilizing the LSPR effect to efficiently regulate the distribution and mechanism of plasmon hot carriers on the surface of heterogeneous alloy nanostructures.

Surface mechanical rolling treatment-introduced gradient nanostructured Inconel 625 alloy with enhanced high-temperature wear resistance

Heterogeneous gradient nanostructures induced through surface treatment of nickel-based superalloys hold significant promise for enhancing wear resistance. In this study, a 700 µm ultra-thick gradient nanostructured (GNS) strengthening layer was fabricated on the surface of an Inconel 625 alloy plate via surface mechanical rolling treatment (SMRT). Subsequently, the tribological behaviors and wear resistance mechanisms of coarse-grained (CG) and GNS samples at temperatures ranging from 25 ℃ to 800 ℃ were comparatively investigated. The results indicated that the gradient nanostructures significantly enhanced the high-temperature wear resistance of the samples, which wear characterized by low coefficient of friction (COF), wear rate and thin friction layer. This enhancement was attributable to the stability and excellent hot hardness of the gradient nanostructures during friction.

Doubly resonant third-harmonic generation in near-zero-index heterogeneous nanostructures

Doubly resonant third-harmonic generation in near-zero-index heterogeneous nanostructures

Strain-rate and size dependence of gradient lamellar nickel investigated by in-situ micropillar compression

Strain rate plays a nonnegligible role in the plastic deformation behavior of metallic materials with heterogeneous nanostructure, while little research focuses on the topic. In-situ compression tests at various strain rates were conducted on the micropillars located at different depths from the gradient lamellar Ni. These tests intended to reveal the strain-rate dependence of micropillars with different lamellar thicknesses and illustrated the competitive relationship between strain rate and intrinsic grain size on the plastic deformation behavior of metallic materials. In addition, due to the strain rate sensitivity related to not only intrinsic size but also external size, single Ni micropillars with different diameters were also compressed at various strain rates in order to clarify the competitive relationship between intrinsic size and external size on the strain rate sensitivity. It is found that lamellar thickness rather than strain rate has more effect on plastic deformation, and external size exhibits a more obvious impact on the strain rate sensitivity. The plastic deformation behaviors of different micropillars are mainly explained by transitions in the effect of lamellar grain boundaries on the dislocation motion at various strain rates and over different lamellar thicknesses, resulting in the change of dislocation multiplication and annihilation rate.

Atomic-force-microscopy-based time-domain two-dimensional infrared nanospectroscopy.

For decades, infrared (IR) spectroscopy has advanced on two distinct frontiers: enhancing spatial resolution and broadening spectroscopic information. Although atomic force microscopy (AFM)-based IR microscopy overcomes Abbe's diffraction limit and reaches sub-10 nm spatial resolutions, time-domain two-dimensional IR spectroscopy (2DIR) provides insights into molecular structures, mode coupling and energy transfers. Here we bridge the boundary between these two techniques and develop AFM-2DIR nanospectroscopy. Our method offers the spatial precision of AFM in combination with the rich spectroscopic information provided by 2DIR. This approach mechanically detects the sample's photothermal responses to a tip-enhanced femtosecond IR pulse sequence and extracts spatially resolved spectroscopic information via FFTs. In a proof-of-principle experiment, we elucidate the anharmonicity of a carbonyl vibrational mode. Further, leveraging the near-field photons' high momenta from the tip enhancement for phase matching, we photothermally probe hyperbolic phonon polaritons in isotope-enriched h10BN. Our measurements unveil an energy transfer between phonon polaritons and phonons, as well as among different polariton modes, possibly aided by scattering at interfaces. The AFM-2DIR nanospectroscopy enables the in situ investigations of vibrational anharmonicity, coupling and energy transfers in heterogeneous materials and nanostructures, especially suitable for unravelling the relaxation process in two-dimensional materials at IR frequencies.

Generalized ratiometric surface-enhanced Raman scattering biosensor for okadaic acid in food based on Au-triggered signal amplification

BackgroundReliability and robustness have been recognized as key challenges for Surface-enhanced Raman scattering (SERS) analytical techniques. Quantifying the concentration of an analyte using a single characteristic peak from SERS has been a controversial topic because the Raman signal is susceptible to highly concentrated electromagnetic hotspots, inhomogeneity of SERS substrate, or non-standardization of measurement conditions. Ratiometric SERS strategies have been demonstrated as a promising solution to effectively balance and compensate for signal fluctuations caused by matrix heterogeneity. However, it is not easy to construct ratiometric SERS sensors with monitoring the ratio of two different signal intensities for target analysis. ResultsAn attempt has been made to develop a novel ratiometric biosensor that can be applied to detect okadaic acid (OA). Aptamer-anchored magnetic particles were first combined with gold-tagged short complementary DNA (Au-cDNA) to create heterogeneous nanostructures. When the target was present, the Au-cDNA was dissociated from nanostructures, and 4-nitrothiophenol (4-NTP) was initiated to reduce to 4-aminothiophenol (4-ATP) in the presence of hydrogen sources. The SERS ratio change of 4-NTP and 4-ATP was finally detected by AuNPs-coated film. OA was successfully quantified, and the detection limit was as low as 2.4524 ng/mL. The constructed biosensor had good stability and reproducibility with a relative standard deviation of less than 4.47%. The proposed method used gold nanoparticles as an intermediate to achieve catalytic signal amplification and subsequently increased the sensitivity of the biosensor. Significance and noveltyCatalytic reaction-based ratiometric SERS biosensors combine the multiple advantages of catalytic signal amplification and signal self-calibration and provide new insights into the development of stable, reproducible, and reliable SERS detection techniques. This ratiometric SERS technique offered a universal method that is anticipated to be applicable for the detection of other targets by substituting the aptamer.

Induced Diffusion Effect Realizes Heterogeneous Separation/Aggregation for In Situ Fabrication of Heterostructure with Enhanced Catalytic Activity

AbstractSpace charge transfer, which can be provided by heterogeneous structure, is the key to efficient electrocatalytic processes. However, difficulty in controlling the relative atomic diffusion rates due to different atomic radii and affinity makes heterogeneous nanostructures difficult to be accurately designed. Herein, an induced diffusion strategy based on affinity differences between elements is proposed to direct the separation/aggregation of different components in the precursor. The key to strategy in this study is the different affinity of Cu and Co to S/P in the precursor of CuCo Prussian blue analogue (PBA). By controlling the molar ratio of S and P during the phosphorization/vulcanization process, induced diffusion can be achieved and leads to directional separation/aggregation of Cu and Co species. As a result, a heterogeneous yolk‐shell Cu2S@CoP2‐C‐N‐S structure is successfully synthesized with a reticular CoP2‐C‐N‐Cu‐S as the shell and a Cu2S nanocrystal as the core. The space charge effect of the semiconductor heterojunction resulting from component separation/aggregation significantly promotes oxygen evolution reaction, resulting in an ultralow overpotential of 180 mV at 10 mA·cm−2. This work not only provides a simple method for efficient separation of key components in gas‐solid systems but also provides a method for fine‐tuning the active site in an active‐site‐engineering approach.

From 2D to 3D electrochemical microfabrication of nickel architectures at room temperature: Synthesis and characterization of microstructure and mechanical properties

Recent development in direct electrochemical 3D microprinting allows the fabrication of 3D metallic micro-components of predominantly noble metals with the positive standard reduction potentials (e.g., Cu, Au, or Pt). These pure metals (e.g., Cu, Au, or Pt) have a small shear modulus up to 60 GPa, which limits one of the important strengthening mechanisms, Taylor hardening. Hence, their mechanical strength is relatively low and limits the application in a structural component. 3D printing of mechanically high-strength metals (e.g., Ni), specifically, printing of microscale parts by direct electrodeposition using a voxel-by-voxel printing technique, is so far very challenging due to the negative standard reduction potential, which leads to hydrogen evolution and unstable printing. In this paper, we demonstrate the stable and successful room temperature (RT) electrochemical printing of Ni micro-architectures by using a newly formulated Ni ink and supporting electrolyte, which were developed through 2D voltammetry and deposition analysis. The micro manufacturing of Ni succeeds at a high deposition speed up to ∼61 nm/s, which is the fastest speed reported so far for microprinting of Ni. 3D printed micropillars feature a heterogeneous nanostructure from ∼13 nm at the center to ∼27 nm at the perimeter. By performing micropillar compression tests, the printed pillars exhibit a high compressive yield-strength of 2.3 ± 0.1 GPa, only ∼15 % lower than 2D processed samples (2.7 ± 0.1 GPa) featuring a homogeneous nanostructure of 27 ± 16 nm. Thus, by deposition of stronger, but less noble metals we show a new pathway to enhance the mechanical robustness of 3D-printed structures, opening up new applications where mechanical rigidity is essential.

Pool boiling characteristics on the micro-pillar structured surface with nanostructure and heterogeneous wettability

The nucleate boiling phenomenon is significantly affected by the wettability of the surface because it is greatly influenced by the motion of the solid–liquid–gas triplet formed by the behavior of bubbles on the heated surface. Hydrophilic surfaces have a high critical heat flux, and hydrophobic surfaces have low onset of nucleate boiling points and high heat transfer coefficients. To design an optimal boiling surface with the advantages of both hydrophilic and hydrophobic surfaces, in this study, parametric experiments were performed according to the spacing of the micropillar, the presence or absence of nanostructures, and the presence or absence of hydrophobic treatment on the surface where the nanostructure was hierarchically modified to the micropillar array structure in which the upper surface of the pillar was hydrophobic. Using the micro-pillar fabrication process and the heterogeneous hydrophobic surface fabrication process, a micro-pillar structure with hydrophobic treatment on top of the pillar was fabricated. Pool boiling experiments were conducted on uniform hydrophilic surfaces, uniform hydrophobic surfaces, hydrophobic patterns on hydrophilic surfaces, micro-pillar surfaces, micro-pillar with nanostructure surfaces, micro-pillar surfaces with heterogeneous wettability, and micro-pillar with nanostructure surfaces with heterogeneous wettability. Based on the experimental data, we analyzed the change in boiling heat transfer coefficients and critical heat flux according to the surface characteristics. Based on experimental results, it was confirmed that the optimal boiling surface should be a surface with heterogeneous wettability, microstructure, and nanostructure.

Site-Selective Bimetallic Heterogeneous Nanostructures for Plasmon-Enhanced Photocatalysis of Nitrobenzene Hydrogenation

Site-Selective Bimetallic Heterogeneous Nanostructures for Plasmon-Enhanced Photocatalysis of Nitrobenzene Hydrogenation

Crystal plasticity simulations reveal cooperative plasticity mechanisms leading to enhanced strength and toughness in gradient nanostructured metals

Heterogeneous deformation is thought to provide the strengthening in gradient nanostructured metals, but the underlying plasticity mechanisms and optimal gradient structures for attaining improved mechanical performance remain elusive. Through crystal plasticity simulations of three-dimensional heterogeneous nanostructures, we reveal the heterogeneous-deformation-induced plasticity mechanisms which evoke increased flow strength and strain hardening. We have developed a synthetic microstructure generation algorithm which replicates both the microstructural features and external geometry of experimentally characterized samples—providing a direct comparison between the mechanical response recorded in simulations and experiments. Aligning well with experiments, the simulations show synergistically enhanced mechanical properties. High strain hardening rates directly correlate to large stress gradients that emerge due to heterogeneous deformation. Samples with smooth grain size gradients exhibit the most extreme stress gradients and correspondingly higher strain hardening rates. Large increases in dislocation density—especially within larger grains—and high intra- and inter-granular crystal rotation are plasticity mechanisms common to samples which exhibit high mechanical performance. Although the nanostructural gradients have pronounced influence over the mechanical performance, samples with the same grain size and dislocation density gradients exhibit varied mechanical properties. We show that the distribution of initial grain orientations and the microstructural constraints placed on larger grains also influence the active plasticity mechanisms providing improved mechanical properties.

Comparing Surface and Bulk Curing Processes of an Epoxy Vitrimer.

We used atomic force microscopy-based infrared spectroscopy (AFM-IR) and nanomechanical mapping (AFM-NM) to image the surface of a vitrimer, specifically dicarboxylic acid-cured diglycidyl ether of bisphenol A (DGEBA), to assess the curing process of a surface layer and compared this to the process in the bulk. We identified the β-hydroxy esters with various functionalities that are the key to form the cross-links for a system, including difunctional DGEBA and carboxylic acids. The IR peaks of the carbonyl group in generated ester groups are distinguished clearly from those in acids, allowing us to quantitatively assess the curing process at the surface and in the bulk. The initial curing at the surface exhibits a gradual cross-linking and is found to be lower than a rapid cross-linking in the bulk due to a relatively lower concentration of the β-hydroxy esters with high functionalities. This curing process leads to a smaller chemically and mechanically heterogeneous nanostructure at the surface relative to the bulk. After multiple reprocessings, a substantial number of esters lacking dynamic exchange capability form in the bulk, which decrease the flowability and reprocessability of the vitrimers and therefore the mechanical properties.

Nanoscale x-ray imaging with high spectral sensitivity using fluorescence intensity correlations.

This paper introduces spectral incoherent diffractive imaging (SIDI) as a novel method for achieving dark-field imaging of nanostructures with heterogeneous oxidation states. With SIDI, shifts in photoemission profiles can be spatially resolved, enabling the independent imaging of the underlying emitter distributions contributing to each spectral line. In the x-ray domain, this approach offers unique insights beyond the conventional combination of diffraction and x-ray emission spectroscopy. When applied at x-ray free-electron lasers, SIDI promises to be a versatile tool for investigating a broad range of systems, offering unprecedented opportunities for detailed characterization of heterogeneous nanostructures for catalysis and energy storage, including of their ultrafast dynamics.

Element specific atom counting for heterogeneous nanostructures: Combining multiple ADF STEM images for simultaneous thickness and composition determination

In this paper, a methodology is presented to count the number of atoms in heterogeneous nanoparticles based on the combination of multiple annular dark field scanning transmission electron microscopy (ADF STEM) images. The different non-overlapping annular detector collection regions are selected based on the principles of optimal statistical experiment design for the atom-counting problem. To count the number of atoms, the total intensities of scattered electrons for each atomic column, the so-called scattering cross-sections, are simultaneously compared with simulated library values for the different detector regions by minimising the squared differences. The performance of the method is evaluated for simulated Ni@Pt and Au@Ag core–shell nanoparticles. Our approach turns out to be a dose efficient alternative for the investigation of beam-sensitive heterogeneous materials as compared to the combination of ADF STEM and energy dispersive X-ray spectroscopy.

Approaching theoretical strength in aluminum alloys via directional heterogeneous nanostructured design

Strengthening a material to its theoretical limit is the unremitting pursuit in the field of materials science and engineering. However, it remains extremely difficult for polycrystalline alloys to reach the theoretical limit using conventional strengthening methods. Here, we propose a directional heterogeneous nanostructured strategy (DHNS) to develop super-strong metallic materials. Based on the microstructural strategy, an aluminum-titanium alloy was developed with a yield strength up to ∼3.9 GPa approaching the theoretical limit (G/τY∼22) and a record-breaking specific strength (∼1219 KNm/kg) among metals and alloys. Microstructural characterizations showed that the DHNS alloy mainly consists of directional nanoscale columnar fcc-Al crystals surrounded by nanosized stripe amorphous phases. The columnar crystals are shown to be in hard orientation and defect free, behaving crystalline whisker-like properties. The synergistic effect of hard-orientation nano-colunmar crystals and strong nanoscale amorphous phases renders the initiation of plastic flow difficult, eventually leading to the ultrahigh yield strength of the alloy. The DHNS strategy provides a facile and effective method for developing strong metallic materials especially for fcc-type alloys where slip systems are easy to be activated.

Defect-promoted nanoparticles−nanorod Ni−NiMoO4 heterogeneous nanostructures as efficient electrocatalysts to overall water/urea splitting in fresh/sea water

The heterogeneous nanoparticles−nanorod Ni−NiMoO4nanostructures grownin situon nickel foam (Ni−NiMoO4/NF) were rationally engineered as efficient electrocatalysts. The morphological and compositionalfeatures cooperatively propel high-performance electrocatalysis to hydrogen evolution reaction (η10, η100, and η200values are 26/84/113 mV in fresh water and 27/101/132 mV in seawater), urea oxidation reaction (η10, η100, and η200values are 1.321/1.340/1.356 and 1.329/1.344/1.361 V in fresh/seawater). The Ni−NiMoO4/NF nanostructures therefore perform a low cell voltage of 1.506/1.509@10 mA cm−2in fresh/sea water. Specifically, the record cell voltage even drops to as low as 1.339/1.361 V in fresh/sea water foroverall urea splitting (OUS) reaction witha long-term stability for 240 h@100 mA cm−2toward OUS in seawater. More importantly, to realize a green manner, we also evaluated a solar-driven H2production. Even in seawater, H2gas was collected in high speed under solar illumination on a commercial solar panel.

High-speed Deformation Behavior of a SUS316LN Austenitic Stainless Steel with Heterogeneous-nano Structure

High-speed Deformation Behavior of a SUS316LN Austenitic Stainless Steel with Heterogeneous-nano Structure