Experimental Characterization Research Articles

Size-Dependent Thresholds in CuO Nanowires: Investigation of Growth from Microstructured Thin Films for Gas Sensing

An experimental characterization of cupric oxide nanowire (CuO NW) growth from thermally oxidized, microstructured Cu thin films is performed. We have systematically studied the influence of the thickness and dimension of Cu layers on the synthesis of CuO NW. The objective was to determine the optimum Cu geometries for increased CuO NWs growth to bridge the gap between adjacent Cu structures directly on the chip for gas sensing applications. Thresholds for CuO-NW growth regarding film thickness and lateral dimensions are identified based on SEM images. For a film thickness of 560 nm, NWs with lengths > 500 nm start to grow from the edges of Cu structures with an area ≥ 4 µm2. NWs growing from the upper surface were observed for an area ≥ 16 µm2. NW growth between adjacent thermally oxidized thin films was analyzed. The study provides information on the most relevant parameters of CuO NWs growth, which is mandatory for integrating CuO NWs as gas sensor components directly on microchips. Based on this result, the gap size of the structure was varied to find the optimum value of 3 µm.

Large anomalous Nernst conductivity of L10-ordered CoPt in CoPt composition-spread thin films

We demonstrate a high-throughput experimental characterization of anomalous Nernst conductivity ( αxyA ) of L10-ordered CoPt using Co1–x Pt x composition-spread thin films on MgO(100) substrates. The compositional dependence of the anomalous Nernst effect, anomalous Hall effect (AHE) and Seebeck effect is systematically measured. As increasing the Pt concentration, the crystal structure in the composition-spread film grown at 500 °C changes from face-centered cubic (fcc) Co, A1-disordered CoPt, L10-ordered CoPt, A1-CoPt to fcc Pt. The largest αxyA of 2.52 A m–1 K–1 is obtained in L10-CoPt for Pt-rich composition of x = 70%, which is larger than that for an additionally fabricated nearly stoichiometric L10-Co48Pt52 reference uniform film. The contribution from direct conversion of a temperature gradient to a transverse charge current through αxyA is dominant to the total anomalous Nernst coefficient compared to the AHE-related contribution. From a scaling analysis of the AHE, the intrinsic contribution is found to be dominant for x = 70%. A theoretical calculation for αxyA of L10-Co50Pt50 agrees with the experimental αxyA value for the nearly stoichiometric reference film by considering on-site Coulomb interaction for Co atoms. We also point out the possible electron doping effect by the addition of Pt in L10-CoPt, which could explain the larger αxyA for the off-stoichiometric Pt-rich composition than that for the nearly stoichiometric one. Our experimental and theoretical results suggest the potential of L10-CoPt with a large αxyA originating from the intrinsic mechanism for future thermoelectric applications.

The Effect of Chopped Carbon Fibers on the Mechanical Properties and Fracture Toughness of 3D-Printed PLA Parts: An Experimental and Simulation Study

The incorporation of fiber reinforcements into polymer matrices has emerged as an effective strategy to enhance the mechanical properties of composites. This study investigated the tensile and fracture behavior of 3D-printed polylactic acid (PLA) composites reinforced with chopped carbon fibers (CCFs) through experimental characterization and finite element analysis (FEA). Composite samples with varying CCF orientations (0°, 0°/90°, +45°/−45°, and 0°/+45°/−45°/90°) were fabricated via fused filament fabrication (FFF) and subjected to tensile and single-edge notched bend (SENB) tests. The experimental results revealed a significant improvement in tensile strength, elastic modulus, and fracture toughness compared to unreinforced PLA. The 0°/+45°/90° orientation exhibited a 3.6% increase in tensile strength, while the +45°/−45° orientation displayed a 29.9% enhancement in elastic modulus and a 29.9% improvement in fracture toughness (259.12 MPa) relative to neat PLA (199.34 MPa√m). An inverse correlation between tensile strength and fracture toughness was observed, attributed to mechanisms such as crack deflection, fiber bridging, and fiber pull-out facilitated by multi-directional fiber orientations. FEA simulations incorporating a transversely isotropic material model and the J-integral approach were conducted using Abaqus, accurately predicting fracture toughness trends with a maximum discrepancy of 8% compared to experimental data. Fractographic analysis elucidated the strengthening mechanisms, highlighting the potential of tailoring CCF orientation to optimize mechanical performance for structural applications.

Experimental and numerical characterization of screw elements used in twin-screw extrusion

Hot melt extrusion by a co-rotating twin screw extruder is an important process in the pharmaceutical industry. Especially for quality by design aspects, a comprehensive process understanding is indispensable. The performance of conveying elements was determined as critical process parameter, and therefore an experimental and numerical framework was developed to analyze and compare variations. A test rig capable of measuring volume flow, pressure and torque with high accuracy and precision was designed and built. The 3D simulation was performed using computational fluid dynamics (CFD). A stationary model with impulse transmission and an apparent motion of the screws was applied. The experimental data were fitted to the model of Pawlowski, and parameters for the pressure (A1, A2) and power characteristics (B1, B2) were determined. Good agreement between experimental data and the model was observed. The simulation was significantly faster compared to common methods, and the results were consistent with the literature. Systematic investigations of a native and worn screw were performed with CFD resulting in a transport capacity increase and a pressure build up decrease for all tested screw elements. An experimental and simulation setup was generated to assess the performance of co-rotating twin screw elements. The experiments provided high-quality data, and the simulations exhibited high flexibility with low computational effort.

Geometric and electronic properties of anionic precious metal gold doped boron clusters AuBn - (n = 10-20)

Abstract Recently, the Au-B covalent bonds in gold doped boron clusters has attracted great attention. However, there are fewer theoretical reports on exploration their ground state structures and stabilities, especially for The medium sizes. Here, we study the structural evolution and electronic properties of the anionic Au doped boron clusters with medium sizes of n from 10 to 20 using the unbiased cluster structural searches combined with density functional theory (DFT) calculations. The results reveal that the quasi-planar AuB18 - (1A, C1) cluster shows excellent stability and a large vertical separation energy (VDE) of 4.25 eV. The good consistency between the computationally simulated photoelectron spectra and the experimental spectra strongly supports the correctness of our low-lying structures. Further bonding analyses show that the well-stabilized aromatic AuB18 - cluster is due to the active σ interactions between Au atom (6s orbitals) and B units (2p orbitals), as well as the large number of σ-bonds in the B18 - moiety with π-aromaticity. These findings enriched the family of Au-B alloy clusters and metal-doped boron-based aromatic clusters, which provide valuable information for the experimental characterization and preparation of boron-rich alloy nanoclusters in the future.

Photoluminescence Enhancement of 0D Organic-Inorganic Metal Halides via Aggregation-Induced Emission and Halide Substitution.

0D organic-inorganic metal halides (OIMHs) provide unprecedented versatility in structures and photoluminescence properties. Here, a series of bluish-white emissive 0D OIMHs, (TPE-TPP)2Sb2BrxCl8-x (x = 1.16 to 8), are prepared by assembling the 1-triphenylphosphonium-4-(1,2,2-triphenylethenyl)benzene cation (TPE-TPP)+ with antimony halides anions. Based on experimental characterizations and theoretical calculations, the emission of the 0D OIMHs are attributed to the fluorescence of the organic cations with aggregation-induced emission (AIE) properties. The 0D structure minimized the molecular motion and intermolecular interactions between (TPE-TPP)+ cations, effectively suppressing the non-radiative recombination processes. Consequently, the photoluminescence quantum efficiency (PLQE) of (TPE-TPP)2Sb2Br1.16Cl6.84 is significantly enhanced to 55.4% as compared to the organic salt (TPE-TPP)Br (20.5%). The PLQE of (TPE-TPP)2Sb2BrxCl8-x can also be readily manipulated by halide substitution, due to the competitive processes between non-radiative recombination on the inorganic moiety and the energy transfer from inorganic to organic. In addition, electrically driven light-emitting diodes (LEDs) are fabricated based on (TPE-TPP)2Sb2Br1.16Cl6.84 emitter, which exhibited bluish-white emission with a maximum external quantum efficiency (EQE) of 1.1% and luminance of 335cdm-2. This is the first report of electrically driven LED based on 0D OIMH with bluish-white emission.

Computational thermodynamics-guided alloy design and phase stability in CoCrFeMnNi-based medium-and high-entropy alloys: An experimental-theoretical study

A computational thermodynamics approach has been employed to design CoCrFeMnNi-based medium- and high-entropy alloys (M/HEAs) with systematically varied compositions (Co((80-X)/2)Cr((80-X)/2)FeXMn10Ni10 with x = 30, 40, and 50 at.%) and phase stability. Since the formation of sigma phase, usually brittle and undesirable, is a common concern, when this class of alloys is subjected to elevated temperatures (600–1000 °C), predicting its formation becomes essential. Thus, its formation and the phase equilibria were studied using the CALPHAD method, and two empirical methods, namely, valence electron concentration (VEC) and paired sigma-forming element (PSFE). Isothermal aging treatments at 900–1100 °C for 20 h were performed, since CALPHAD and VEC/PSFE predictions diverged. Both prediction methods were compared with experimental characterization by a combination of scanning electron microscopy and high-energy synchrotron X-ray diffraction. The predictions from the VEC/PSFE and CALPHAD calculations (depending on the database used) were shown to be quite accurate.

Optical fiber LSPR sensor for SARS-CoV-2 N gene detection based on AuNRs

A novel SARS-CoV-2 N gene optical fiber biosensor based on ASO-coated gold nanorods is proposed in this work. A fiber probe prepared by AuNRs self-assembly was used to detect N gene by complementary base pairing method. The detected material was processed into AuNRs-ASO2-N gene coupler by cross-linking, and the pairing of N gene with ASO1 connected to AuNRs on the surface of the optical fiber formed the hydrogen bonding. The coupling of AuNRs resulted in a left shift of the peak position and a decrease in absorbance in the LSPR spectrum. In this manuscript, it is verified for the first time by simulation and experimental characterization that the coupling mode of AuNRs on the surface of the optical fiber is side by side, which leads to a left shift of the peak position of the LSPR absorption peak on the optical fiber. It is also proved that sandwich method is superior to the traditional method of changing the refractive index. The response time of the sensor is 10 min, and the detection limit is 1 pM, and the results show that the optical fiber sensor based on ASO-coated AuNRs has excellent RNA detection performance in artificial body fluids and is very suitable for RNA detection.

Thermal Management of Lithium-Ion Battery Pack Using Equivalent Circuit Model

The design of an efficient thermal management system for a lithium-ion battery pack hinges on a deep understanding of the cells’ thermal behavior. This understanding can be gained through theoretical or experimental methods. While the theoretical study of the cells using electrochemical and numerical methods requires expensive computing facilities and time, the Equivalent Circuit Model (ECM) offers a more direct approach. However, upfront experimental cell characterization is needed to determine the ECM parameters. In this study, the behavior of a cell is characterized experimentally, and the results are used to build a second-order equivalent electrical circuit model of the cell. This model is then integrated with the cooling system of the battery pack for effective thermal management. The Equivalent Circuit Model estimates the internal heat generation inside the cell using instantaneous load current, terminal voltage, and temperature data. By extrapolating the heat generation data of a single cell, we can determine the heat generation of the cells in the pack. With the implementation of the ECM in the cooling system, the coolant flow rate can be adjusted to ensure the attainment of a safe operating cell temperature. Our study confirms that 14% of pumping power can be reduced when compared to the conventional constant flow rate cooling system, while still maintaining the temperature of the cells within safe limits.

Polarized Raman, infrared and dielectric spectra of lead-free K0.5Na0.5NbO3piezoelectric system: insights from ab-initio theoretical and experimental studies.

The K0.5Na0.5NbO3(KNN) system has emerged as one of the most promising lead-free piezoelectric over the years. In this work, we perform a comprehensive investigation of electronic structure, lattice dynamics and dielectric properties of room temperature phase of KNN by combining ab-initio DFT based theoretical analysis and experimental characterization. We assign the symmetry labels to KNN vibrational modes and obtain ab-initio polarized Raman spectra, Infrared (IR) reflectivity, Born-effective charge tensors, oscillator strengths etc. The KNN ceramic samples are prepared using conventional solid-state method and Raman and UV-Vis diffuse reflectance spectra are obtained. The computed Raman spectrum is found to agree well with the experimental spectrum. In particular, the results suggest that the mode in range ~840-870 cm-1 reported in the experimental studies is longitudinal optical (LO) with A_1 symmetry. The Raman mode intensities are calculated for different light polarization set-ups that suggests the observation of different symmetry modes in different polarization set-ups. The electronic structure of KNN is investigated and optical absorption spectrum is obtained. Further, the performances of DFT semi-local, meta-GGA and hybrid exchange-correlations (XC) functionals, in the estimation of KNN band gaps are investigated. The KNN bandgap computed using GGA-1/2 and HSE06 hybrid functional schemes are found to be in excellent agreement with the experimental value. The COHP, electron localization function and Bader charge analysis is also performed to deduce the nature of chemical bonding in the KNN. Overall, our study provides several bench-mark important results on KNN that have not been reported so far.

Polarized Raman, infrared and dielectric spectra of lead-free K0.5Na0.5NbO3piezoelectric system: insights from ab-initio theoretical and experimental studies.

The K0.5Na0.5NbO3(KNN) system has emerged as one of the most promising lead-free piezoelectric over the years. In this work, we perform a comprehensive investigation of electronic structure, lattice dynamics and dielectric properties of room temperature phase of KNN by combining ab-initio DFT based theoretical analysis and experimental characterization. We assign the symmetry labels to KNN vibrational modes and obtain ab-initio polarized Raman spectra, Infrared (IR) reflectivity, Born-effective charge tensors, oscillator strengths etc. The KNN ceramic samples are prepared using conventional solid-state method and Raman and UV-Vis diffuse reflectance spectra are obtained. The computed Raman spectrum is found to agree well with the experimental spectrum. In particular, the results suggest that the mode in range ~840-870 cm-1 reported in the experimental studies is longitudinal optical (LO) with A_1 symmetry. The Raman mode intensities are calculated for different light polarization set-ups that suggests the observation of different symmetry modes in different polarization set-ups. The electronic structure of KNN is investigated and optical absorption spectrum is obtained. Further, the performances of DFT semi-local, meta-GGA and hybrid exchange-correlations (XC) functionals, in the estimation of KNN band gaps are investigated. The KNN bandgap computed using GGA-1/2 and HSE06 hybrid functional schemes are found to be in excellent agreement with the experimental value. The COHP, electron localization function and Bader charge analysis is also performed to deduce the nature of chemical bonding in the KNN. Overall, our study provides several bench-mark important results on KNN that have not been reported so far.

Dilute Electrolytes with Fluorine-free Ether Solvents for 4.5 V Lithium Metal Batteries.

The limited oxidation stability of ether solvents has posed significant challenges for their applications in high-voltage lithium metal batteries (LMBs). To tackle this issue, the prevailing strategy either adopts a high concentration of fluorinated salts or relies on highly fluorinated solvents, which will significantly increase the manufacturing cost and create severe environmental hazards. Herein, an alternative and sustainable salt engineering approach is proposed to enable the utilization of dilute electrolytes consisting of fluorine (F)-free ethers in high-voltage LMBs. The proposed 0.8 M electrolyte supports stable lithium plating-stripping with a high Coulombic efficiency of 99.47% and effectively mitigates the metal dissolution, phase transition, and gas release issues of the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode upon charging to high voltages. Consequently, the 4.5 V high-loading Li||NCM 811 cell shows a capacity retention of 75.2% after 300 cycles. Multimodal experimental characterizations coupled with theoretical investigations demonstrate that the boron-containing salt plays a pivotal role in forming the passivation layers on both anode and cathode. The present simple and cost-effective electrolyte design strategy offers a promising and alternative avenue for using commercially mature, environmentally benign, and low-cost F-free ethers in high-voltage LMBs.

Dilute Electrolytes with Fluorine‐free Ether Solvents for 4.5 V Lithium Metal Batteries

The limited oxidation stability of ether solvents has posed significant challenges for their applications in high‐voltage lithium metal batteries (LMBs). To tackle this issue, the prevailing strategy either adopts a high concentration of fluorinated salts or relies on highly fluorinated solvents, which will significantly increase the manufacturing cost and create severe environmental hazards. Herein, an alternative and sustainable salt engineering approach is proposed to enable the utilization of dilute electrolytes consisting of fluorine (F)‐free ethers in high‐voltage LMBs. The proposed 0.8 M electrolyte supports stable lithium plating‐stripping with a high Coulombic efficiency of 99.47% and effectively mitigates the metal dissolution, phase transition, and gas release issues of the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode upon charging to high voltages. Consequently, the 4.5 V high‐loading Li||NCM 811 cell shows a capacity retention of 75.2% after 300 cycles. Multimodal experimental characterizations coupled with theoretical investigations demonstrate that the boron‐containing salt plays a pivotal role in forming the passivation layers on both anode and cathode. The present simple and cost‐effective electrolyte design strategy offers a promising and alternative avenue for using commercially mature, environmentally benign, and low‐cost F‐free ethers in high‐voltage LMBs.

Specific wavelength peak emulation with amorphous metastructures.

The conventional design process for metasurfaces is time-consuming and computationally expensive. To address this challenge, we utilize a deep convolutional generative adversarial network (DCGAN) to generate new nanohole metastructure designs that match a desired transmittance spectrum in the visible range. The trained DCGAN model demonstrates an exceptional performance in generating diverse and manufacturable metastructure designs that closely resemble the target optical properties. The proposed method provides several advantages over existing approaches. These include its capability to generate new designs without prior knowledge or assumptions regarding the relationship between metastructure geometries and optical properties, its high efficiency, and its generalizability to other types of metamaterials. The successful fabrication and experimental characterization of the predicted metastructures further validate the accuracy and effectiveness of our proposed method.

Dilute Electrolytes with Fluorine-free Ether Solvents for 4.5 V Lithium Metal Batteries.

The limited oxidation stability of ether solvents has posed significant challenges for their applications in high-voltage lithium metal batteries (LMBs). To tackle this issue, the prevailing strategy either adopts a high concentration of fluorinated salts or relies on highly fluorinated solvents, which will significantly increase the manufacturing cost and create severe environmental hazards. Herein, an alternative and sustainable salt engineering approach is proposed to enable the utilization of dilute electrolytes consisting of fluorine (F)-free ethers in high-voltage LMBs. The proposed 0.8 M electrolyte supports stable lithium plating-stripping with a high Coulombic efficiency of 99.47% and effectively mitigates the metal dissolution, phase transition, and gas release issues of the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode upon charging to high voltages. Consequently, the 4.5 V high-loading Li||NCM 811 cell shows a capacity retention of 75.2% after 300 cycles. Multimodal experimental characterizations coupled with theoretical investigations demonstrate that the boron-containing salt plays a pivotal role in forming the passivation layers on both anode and cathode. The present simple and cost-effective electrolyte design strategy offers a promising and alternative avenue for using commercially mature, environmentally benign, and low-cost F-free ethers in high-voltage LMBs.

Biomimetic Phthalocyanine-Based Covalent Organic Frameworks with Tunable Pendant Groups for Electrocatalytic CO2 Reduction.

Electrocatalytic carbon dioxide reduction reaction (CO2RR) is an effective way of converting CO2 into value-added products using renewable energy, whose activity and selectivity can be in principle maneuvered by tuning the microenvironment near catalytic sites. Here, we demonstrate a strategy for tuning the microenvironment of CO2RR by learning from the natural chlorophyll and heme. Specifically, the conductive covalent organic frameworks (COFs) linked by piperazine serve as versatile supports for single-atom catalysts (SACs), and the pendant groups modified on the COFs can be readily tailored to offer different push-pull electronic effects for tunable microenvironment. As a result, while all the COFs exhibit high chemical structure stability under harsh conditions and good conductivity, the addition of -CH2NH2 can greatly enhance the activity and selectivity of CO2RR. As proven by experimental characterization and theoretical simulation, the electron-donating group (-CH2NH2) not only reduces the surface work function of COF, but also improves the adsorption energy of the key intermediate *COOH, compared with the COFs with electron-withdrawing groups (-CN, -COOH) near the active sites. This work provides insights into the microenvironment modulation of CO2RR electrocatalysts at the molecular level.

Characterization Of Cryogenic Sloshing Via Image Velocimetry, Free Surface Tracking And Data Assimilation

Cryogenic fuels such as liquid hydrogen (LH_2 ) and liquified natural gas (LNG) are promising energy carriers for the future. Their thermal management is significantly challenged by the liquid sloshing induced by external acceleration because sloshing strongly impacts the evaporation rate and, thus, the reservoir’s pressure control. This work presents a unique experimental characterization of liquid sloshing in cryogenic conditions combining interface tracking, image velocimetry and physics-constrained data assimilation. The experiments were conducted in a reduced-scale cryogenic tank partly filled with liquid nitrogen undergoing lateral harmonic sloshing. A combination of floating and neutrally buoyant seeding particles was used to simultaneously carry out interface tracking using a moving-window Radon transform and image velocimetry using Particle Tracking Velocimetry (PTV). The data assimilation was carried out using constrained radial basis function (RBF) regression, imposing kinematic boundary conditions at the walls and interface. The assimilation allows for unprecedented super-resolution of the velocity field.

Functional guanine superstructures derived superior sodiophilic porous carbonaceous metamaterial for anodic-sodium-metal-free sodium metal batteries

Metamaterials, owing to their engineered building blocks, are considered as easily functionalized composites with designed nano-properties, sparking widespread research interest. However, the scalable synthesis and programmatically derived metamaterials into the designed nano-to-macro functionalized structure still pose significant challenges. Here, we report a fast and scalable synthesized Sn-guanine superstructures derived 1D porous carbonaceous metamaterial frameworks (Sn-NCS) that self-assembled by atomic Sn doping high nitrogen content carbon nanosheets. Due to the unique bottom-up designed nano-to-macro functionalized structural characteristics, Sn-NCS exhibited superior sodiophilic property. Using density functional theory (DFT) analysis and in-situ/ex-situ experimental characterization, we reveal that Sn-NCS can not only provide abundant Sn-N4 functional sites to minimize sodium nucleation overpotential and favors a uniform Na nucleation, but also effectively guide sodium deposition within the self-assembled porosity framework of Sn-NCS along the surface of carbon nanosheets to accommodate the volume variation and stress fluctuations within the anode, even under the extremely high current density of 120 mA/cm2 with a deposition/stripping capacity of 20 mAh/cm2. Moreover, the fabricated anode-sodium-metal-free sodium metal batteries (ASM-free SMB), using Cu-Sn-NCS (Sn-NCS coated Cu foil with a mass loading of 0.1 mg/cm2) as anodic current collector, exhibit highlighted energy density and excellent cycling reliability.

Experimental characterization of epoxy/quartz composite material exposed to PDs

Failures due to the degradation of polymeric insulation in components of electrical power systems are difficult to predict. Partial discharges (PDs) are one of the main phenomena that contribute to polymeric insulators’ aging. Therefore, a better understanding of the aging process due to PDs is crucial to develop effective models that predict degradation, optimize materials and propose diagnostic indicators. Here we present an experimental characterization, via Fourier-transform Infrared spectroscopy (FTIR), of a composite material exposed to PDs. The material consisted of cured epoxy resin mixed with silica (quartz). Aging tests with surface discharges, using a needle-plate configuration, were conducted considering two atmospheres (air and CO2) and four exposition times (6, 24, 72 and 120 hours). To aid the interpretation of spectroscopic data, we included a series of simulation results. The main effect observed was the erosion and removal of epoxy resin from the surface of the samples, proportionally to treatment time and distance from the needle. Along with erosion, new chemical species (possibly oxalate salts) were detected on the surface exposed to air-plasma. These species were likely formed and then removed due to plasma activity over time. On the other hand, samples aged in CO2 atmosphere underwent only epoxy resin erosion.

Dual modulation of electrolyte inner solvent structure and anode interface for high performance alkaline Al-air battery

In this work, we propose a Water-in-salt electrolyte based on concentrated ionic additive for Al-air batteries, aiming at inhibiting the unexpected severe hydrogen evolution self-corrosion. Computing calculations and experimental characterizations consistently confirm that the additive can significantly affect both the solvent structure and anode interface. A stronger H-bonding network is reconfigured and formed in the electrolyte, thus leading to a dramatic decrease in free water content and activity. Besides, the adsorption behavior of used additive molecules on Al anode surface plays an activating and stabilizing role, which is conducive to promoting the uniform dissolution of Al anode and improving the electrochemical performance. Owing to this dual modulation, the electrolyte system endows Al-air battery with extremely low self-corrosion rate (reduced by 89.6%) and remarkable discharge capacity of 2623 mAh/g.