Raman Spectroscopy Research Articles

The chlorite adduct of aquacobalamin: contrast with chlorite dismutase.

In the reaction of aquacobalamin (aquaCbl) with chlorite, a stable species is detected and assigned as a Co(III)-chlorite complex, Co(III)-OClO-. Its UV-Vis spectrum is almost identical to that of aquaCbl, except for some minor differences at ~ 430nm; cyanide can eliminate and prevent these changes. The 1H-NMR spectra reveal strong influences of chlorite on the B2 and B4 protons of the cobalt-bound dimethyl benzimidazole ligand. Together, the UV-Vis and NMR titrations suggest a Kd of 10mM or higher for chlorite on Cbl. Resonance Raman spectra reveal minor changes in the spectrum of aquaCbl to chlorite-as well as a disappearance of the free chlorite signals, consistent with Cbl-chlorite complex formation. Corroboration for these interpretations is also offered from mass spectrometry and DFT calculations. This Co(III)-OClO- complex would be a stable analogue of the first reaction intermediate in the catalytic cycle of chlorite dismutase, or in the reaction of chlorite with a number of other heme proteins. The differences in reactivity between Co(III) cobalamin and Fe(III) heme towards chlorite are analyzed and rationalized, leading to a reconciliation of experimental and computational data for the latter.

Characterization of ultramarine blue in Roman wall paintings: case study from Volsinii (Bolsena, Italy).

The identification of blue pigments in Roman wall paintings provides crucial insights into the materials, artistic techniques, and trade routes in the antiquity. The present study focuses on the analysis of a blue pigment lump discovered at Ponticello (Bolsena, Italy) initially thought to be Egyptian blue. The lump pigment is compared with two synthetic ultramarine pigments (Poggi and Divolo), "Herculaneum blue," Egyptian blue, and natural lapis lazuli from Monte Somma, Italy. Through a multi-analytical approach that comprehends energy-dispersive X-ray fluorescence (ED-XRF) spectroscopy, micro-Raman spectroscopy, and X-ray powder diffraction (XRPD), the pigment was univocally identified as natural lazurite, the primary component of lapis lazuli. Chemometrics, including principal component analysis (PCA), was applied to the ED-XRF data to reveal patterns in the elemental composition of the samples. This finding is significant as ultramarine blue was a rare and expensive material in Roman times, which was traditionally sourced from distant regions like Afghanistan. While this study does not aim to determine the geographical provenance of the pigment, it offers important insights into Roman artistic practices, economic resources, and trade networks. Future research will explore the chemical composition of the pigments present in the frescoes from the archaeological area of Volsinii to provide important further insights into ancient material exchanges.

Understanding the impact of plasma functionalized MWCNTs on the structure, physicochemical and mechanical properties of PEMA

In this study, plasma functionalized multiwalled carbon nanotubes, f-MWCNTs, were incorporated into a poly(ethyl methacrylate), PEMA, polymer matrix at different wt.% (0.005, 0.01, and 0.02 wt.%) to prepare nanocomposite films using the traditional solution casting method. The XRD, Raman spectroscopy, XPS, TGA, mechanical analysis and UV–Vis spectroscopy techniques were employed to investigate the effects of the wt.% of f-MWCNTs on the structure, spectroscopic and other physiochemical properties of the synthesized films. XRD analysis showed a monotonic change in the PEMA structure upon incorporation of f-MWCNTs at different wt.%. The XPS results showed an increase of oxygen-based functional groups C-O and O-C-O on the PEMA/f-MWCNTs/ composite films compared to pure PEMA. Raman spectroscopy results consistent with the XRD and XPS findings, confirming the homogeneous distribution of f-MWCNTs in the PEMA matrix. Thermal stability of f-MWCNTs/PEMA improved as the f-MWCNTs content increased. Optical studies showed a reduction in the bandgap energy as the f-MWCNTs content increased, accompanied by significant improvements in optical properties such as refractive index (n), extinction coefficient (k), dielectric constants (ε′ and ε″), and optical conductivity (σopt). Mechanical testing revealed enhancements in breaking strength, Young’s modulus, yield stress, and elongation at break with increasing f-MWCNTs concentrations. Furthermore, the AC electrical conductivity of the films also improved, demonstrating better charge transport capabilities. These synergistic enhancements in optical, thermal, mechanical, and electrical properties make PEMA/f-MWCNTs nanocomposites promising candidates for advanced applications, including optoelectronic devices, optical components, and conductive packaging materials.

Changes in morphofunctional parameters of erythrocytes and oxygen-binding capacity of hemoglobin under the influence of microorganisms of various types.

When bacteria interact with red blood cells, the plasma membrane receives signals from the microorganism adhesins, and the functional work of the erythrocyte as a whole depends on the biomembrane phospholipid condition. However, the microorganism effect on the structural and functional properties of the red blood cell membrane, as well as on the hemoglobin oxygen-binding ability has not been studied enough. Given the foregoing, we sought to study these issues in our work. The study used the "bacteria-red blood cells" model, using archival microbial strains (Staphylococcus aureus, Escherichia coli, Mycolicibacterium rutilum, and M. iranicum) and donor erythrocytes. The structural and functional properties of the red blood cell membrane phospholipids and the spectral characteristics of the hemoglobin molecule were studied using Raman spectroscopy. To study changes in red blood cell (RBC) morphology under the impact of microorganisms, laser interference microscopy was used. The results show that various types of microorganisms affected the conformational structure of the RBCs membrane phospholipid bonds, which contributed to changes in the morphological characteristics of cells, resulting in functional changes in both the red blood cell as a whole and the main RBC oxygen transport protein-hemoglobin.

Surface-Enhanced Raman Spectroscopy for the Characterization of Blood Serum Samples of Chronic Kidney Disease by Using 100 kDa

Surface-Enhanced Raman Spectroscopy for the Characterization of Blood Serum Samples of Chronic Kidney Disease by Using 100 kDa

Exploring the properties of engineered biosorbents from rice straw for effective and economical remediation of Fe (II) and Ni (II) ions

Industrial effluents, agricultural runoff, and even waste disposal also contribute to the maximum loading of potentially toxic elements into freshwater ecosystems- the root cause being humans. These pollutants reach the water bodies due to runoff, soil erosion, or deposition from the atmosphere. Recent technological advancements have even proposed more benign methods for potentially toxic elements analysis in the water. In particular, it has been shown that agricultural or industrial waste, when converted into nanocomposites, can adsorb heavy metal ions more efficiently. Biomass-defined nanocomposites comprising metal ion complexes are developed for potentially toxic element ions’ binding and subsequent desorption. This new method eliminates a significant amount of potentially harmful elements from water, which is already ready for discharge as it meets environmental standards and is inexpensive compared to conventional high-temperature methods. Rice straw-derived nanowaste has mainly helped outgoing metal ions by synthesizing 40-60nm nanoparticles. XRD was used to describe the arrangement of atoms within the Rise Straw (RS) and its nanoparticles (RSNP), while the chemical identification was addressed by Raman spectroscopy and FTIR. This is supported by the FESEM, HRTEM, BET, and Zeta analyses. Fe2+ and Ni2+ ions removal efficiencies obtained for RSNP were 90% and 89%, respectively. Critical parameters such as contact time and pH were investigated when contact adsorption of potentially toxic elements to aquatic environments was tested, and thanks to these studies, the parameters were optimized.

Degradation of polyvinyl chloride (PVC) microplastics employing the actinobacterial strain Streptomyces gobitricini.

The disposal of plastic materials has resulted in the huge increase of microplastics in the environment. One of the most hazardous plastic waste is polyvinyl chloride (PVC) due to its durability. A tool to remediate PVC microplastic polluted environment might be offered by microorganisms such as Actinobacteria, which has been proven to degrade PVC. Streptomyces gobitricini was isolated from soil polluted by heavy metals and plastic debris and used in a PVC microplastics degradation experiment. Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, and scanning electron microscopy (SEM) were used to study the characteristics of microplastic particles. For the incubation, the optimal pH 7.5 was determined in a preliminary experiment where also pH 5.5 and pH 9.5 were included. Three PVC concentrations (200, 400, and 800mg/L) were incubated in Luria-Bertani broth with S. gobitricini for 90days. After the incubation, PVC-MP particles were recovered by filtering. The percentual weight loss of microplastics was highest (66%) in 200mg/L treatment. Relatively high reductions were observed for the higher microplastic concentrations as well (400mg/L; 65% and 800mg/L; 60%). The bacterial growth decreased in order 200mg/L (3.1 ± 0.1CFU × 105/mL), 400mg/L (3.0 ± 0.0CFU × 105/mL) and 800mg/L treatment (2.7 ± 0.0CFU × 105/mL). High hydrophobicity was observed in all treatments at the end of the incubation indicating the formation of bacterial biofilm on the surfaces of plastic particles. The highest hydrophobicity (84%) associated with the bacterial strain was observed in 200mg/L microplastics treatment. The results show that the bacterium S. gobitricini suits for further studies to reduce PVC microplastic waste in the environment.

Raman spectroscopy investigation of strain evolution in relaxed and pseudomorphic layers of Si0.4Ge0.6 films grown on (001) Si substrates

Abstract In this study, the laminated strain of relaxed and the pseudomorphic layer in the Si0.4Ge0.6 films grown on (001) Si substrates are studied by Raman spectroscopy. With the SiGe films ranging from 20 nm to 1200 nm in thickness, biaxial strains are revealed through room-temperature Raman peak analysis. Notably, a highly strained layer named the pseudomorphic layer is observed in the 30-nm sample. The peak broadening induced by the scattering of phonons at the thickness of 30 nm suggests dense dislocations at the substrate-pseudomorphic layer interface. The study also finds that the relaxed layer has a much more dramatic relaxation compared to that of the pseudomorphic layer, while the pseudomorphic layer maintains a high degree of strain. These findings contribute to the understanding of the SiGe alloy growth, enhancing the fabrication of intricate SiGe-based devices with improved strain control and relaxation dynamics.

Cobalt titanate nanocatalyst for enhanced photodegradation of atrazine: kinetics, degradation efficiency, and mechanistic analysis

In this study, cobalt titanate nanoparticles (CoTiO₃ NPs) were synthesized and applied as a photocatalyst to degrade atrazine. Scanning electron microscopic (SEM) analysis showed irregularly shaped particles prone to agglomeration, while X-ray diffraction (XRD) confirmed the formation of a rhombohedral CoTiO₃ phase with a crystallite size of 3.76 nm. Raman spectroscopic analysis showed vibrations typical for Ti–O and Co–O bonds and confirmed a well-defined cobalt titanate structure. Thermogravimetric analysis (TGA) showed that the nanoparticles remained stable up to 800 °C. The photocatalytic activity of CoTiO₃ NPs was tested under sunlight irradiation and the results obtained demonstrated excellent efficiency compared to the photolysis reaction. The efficiency was influenced by concentration (20–50 ppm), catalyst dosage (0.5–2.0 mg/L), pH (4.21–10.22), and irradiation time (0–120 min). The synthesized nanoparticles exhibited a surface area of 32.5 m2/g (DFT) and 828.03 m⁻1 (BET), a pore volume of 0.03925 m3/g, and a bandgap energy of 2.66 eV. Kinetic studies demonstrated that the degradation followed the Langmuir–Hinshelwood model, with the photocatalytic reaction being the rate-determining step. Adsorption rate constants were found to range from 0.03828 to 0.166528 min⁻1, while photocatalytic rate constants ranged from 0.373692 to 0.977135 min⁻1. The CoTiO₃ NPs also showed excellent recyclability, maintaining high degradation efficiency after five cycles. Scavenger experiments confirmed that hydroxyl radicals (HO•) are responsible for atrazine degradation while GCMS analysis confirmed the complete mineralization of atrazine with carbon dioxide (CO₂) and water (H₂O) as the final degradation products.

Optimizing Electro-Oxidation Kinetics via Constructing Built-In Electric Field on Pd-Ni(OH)2 Heterostructures for Selective Oxidation of Benzylamine to Benzonitrile.

Rationally regulating redox properties of electrocatalysts is highly essential to accomplish selective electro-oxidation of benzylamine (BA) to benzonitrile (BN) and concurrently promote hydrogen evolution reaction (HER) at cathode. Herein, a facile built-in electric field (BIEF) engineering strategy to optimize the electrocatalytic kinetics for the BA oxidation reaction (BOR) on Pd-Ni(OH)2 heterostructures, is presented. Both experimental and theoretical results confirm the construction of BIEF with the direction from α-Ni(OH)2 nanosheet to Pd nanoparticle at the heterointerface. It is unequivocally found that the creation of BIEF is favorable for not only the generation of electroactive Ni(OH)O species, but also the adsorption and dehydrogenation of BA molecules, achieving significantly promoted BOR kinetics. As expected, the Pd-Ni(OH)2 catalyst shows excellent electrocatalytic performance toward selectively oxidizing BA to BN, which is further coupled with cathodic H2 production. The faradaic efficiency (FE) for BN production can approximate to 85% in a two-electrode electrolyzer. In situ Raman spectroscopy and electrochemical measurements disclose that the activity origin for the BOR is dehydronated Ni(OH)O intermediate, clarifying a direct electro-oxidation mechanism over the Pd-Ni(OH)2 electrode. This work highlights an effective insight into design and synthesis of highly active electrocatalysts for organic upgrading.

Water Is Cool: Advanced Phonon Dynamics in Ice Ih and Ice XI via Machine Learning Potentials and Quantum Nuclear Vibrations.

Low-dimensional water, despite the relative simplicity of its constituents, exhibits a vast range of phenomena that are of central importance in natural sciences. A large number of bulk as well as nanoscale polymorphs offer engineering possibilities for technological applications such as desalinization, drug delivery, or biological interfacing. However, little is known about the stability of such structures. Therefore, in this study, we employ an array of state-of-the-art computational techniques to study the vibrational properties of ice Ih and XI in their bulk and thin film forms in order to elucidate their structural stability and dynamic behavior. An efficient workflow, consisting of quantum mechanical simulations (based on density functional theory) and machine learning interatomic potentials (MTPs) coupled to temperature-dependent effective potentials (TDEP) and classical molecular dynamics, was verified necessary to capture the temperature-dependent stabilization of the phonons in bulk ice Ih and XI. Anharmonicity and nuclear quantum effects, incorporated in an efficient way through a quantum thermal bath technique, were found crucial to dynamically stabilize low-frequency lattice modes and high-frequency vibrational stretching involving hydrogen. We have identified three novel thin film structures that retain their stability up to at least 250 K and have shed light on their phonon characteristics. In addition, our examination of the Raman spectrum of ice underscores the shortcomings of predicting vibrational properties when relying entirely on the harmonic approximation or purely anharmonic effects. The corrected redistribution of vibrational intensities is found to be achieved only upon inclusion of quantum nuclear vibrations. This was found to be even more crucial for low-dimensional thin film (2D) structures. Overall, our findings demonstrate the significance of joining advanced computational methodologies in unraveling the intricate vibrational dynamics of crystalline ice materials, offering valuable insights into their thermodynamic and structural properties. Furthermore, we suggest a procedure based on MTPs coupled to a quantum thermal bath for the computationally efficient probing of nuclear effects in ice structures, although equally applicable to any other system.

Single compound data supplementation to enhance transferability of fermentation specific Raman spectroscopy models.

Raman spectroscopy is a valuable analytical tool for real-time analyte quantification in fermentation processes. Quantification is performed with chemometric models that translate Raman spectra into concentration values, which are typically calibrated with process data from multiple comparable fermentations. However, process-specific models underperform for minor process variation(s) or different operation modes due to the integration of cross-correlations, resulting in low target analyte specificity. Thus, model transferability is poor and labor-intensive (re-)calibration of models is required for related processes. In this work, partial least-squares models for glucose, ethanol, and biomass were calibrated with Saccharomyces cerevisiae batch fermentation data and subsequently transferred to a fed-batch operation. To enhance model transferability without additional process runs, single compound data supplementation was performed. The supplemented models increased overall target analyte specificity and demonstrated sufficient prediction accuracy for the fed-batch process (root-mean-square errors of prediction (RMSEP) of 3.06mM, 8.65mM, and 0.99g/L for glucose, ethanol, and biomass), while maintaining high prediction accuracy for the batch process (RMSEP of 1.71mM, 4.20mM, and 0.17g/L for glucose, ethanol, and biomass). This work showcases that process data in combination with single compound spectra is a fast and efficient strategy to apply Raman spectroscopy for real-time process monitoring across related processes.

Biofunctionalization of Magneto-Plasmonic Fe3O4@SiO2-NH2-Au Heterostructures with the Cellulase from Trichoderma reesei

The study focuses on the synthesis of Fe3O4@SiO2-NH2-Au heterostructures with magneto-plasmonic properties composed of well-defined cubic Fe3O4 cores (79 nm) covered with 10 nm silica shell and gold nanoparticles (8 nm) fabricated on silica shell. The surface-anchored MHDA (16-mercaptohexadecanoic acid) linker facilitated cellulase bioconjugation, which was confirmed through Raman spectroscopy. The presence of gold nanoparticle islands on the heterostructure enabled surface-enhanced Raman scattering (SERS), demonstrating the potential for bioactive substance identification. Immobilization of cellulase allowed for pH enhancement and enzyme thermal stability. The optimal pH shifted from 4.0 (free enzyme) to 6.0 while thermal stability increased by 20 °C. The immobilized cellulase kept its 49% activity after five hydrolysis cycles, compared to significantly lower activity for free cellulase. The proposed heterostructures for cellulase immobilization demonstrate potential for practical applications.

The role of α-RuCl3 flat bands in G peak splitting in graphene/α-RuCl3 heterostructures

Abstract α-RuCl3 is known for its potential to realize a Kitaev quantum spin liquid by tuning
the competing interactions, such as doping effects. Here, we investigated the doping
effect of α-RuCl3/graphene heterostructures and observed a G peak splitting related
to different spins, as revealed by Raman spectroscopy. The deliberate disruption of the
heterostructure led to a transition from a double G peak to a single peak, underscoring
the significance of interface quality. This finding was corroborated by density functional
theory calculations. Additionally, we distinguished the contributions of doping
and strain by employing Raman mapping, drawing comparisons to CrCl3/graphene
heterostructures. These findings present a high-resolution technique for assessing the
uniformity of similar heterostructure surfaces and investigating the behavior of distinct
spins in Raman scattering influenced by magnetic proximity effects.

Ultralow-Resistance Contacts to Heavily Doped p-Type NbxW1-xSy Thin Films Grown by Atomic Layer Deposition.

Transition metal dichalcogenides (TMDs) are an important class of materials for future microelectronics. Of particular interest are TMDs deposited by atomic layer deposition (ALD) since this technique allows both back-end-of-line (BEOL) compatible deposition and the ability to create heavily doped regions for contact formation. In this work, we characterize ∼3 nm-thick heavily doped NbxW1-xSy thin films grown by plasma-enhanced ALD using gated transfer-length measurement (TLM) structures. An analysis of films with different Nb concentrations, x, found that films with x = 0.22 had the lowest sheet resistivity of 86 kΩ/sq along with an ultrahigh carrier concentration of 4.2 × 1020 cm-3. The contact resistance, RC, of different metals to NbxW1-xSy thin films was also analyzed. Among Pd, Ni, and Ti contacts, Pd was found to have the lowest RC, whereas Ni (Ti) had an average RC that was 6× (20×) higher than Pd. Physical analysis of the films using Raman spectroscopy and transmission electron microscopy shows that the crystal quality degrades going from x = 0.08 to 0.33, while Kelvin probe force microscopy, complemented by density functional theory, is used to explain the Nb concentration of the extracted work function. The best TLM structures have an RC value as low as 0.30 ± 0.26 kΩ-μm and a mean specific contact resistivity, ρC, of 11 ± 27 nΩ-cm2. Even after accounting for experimental error, this value is lower than the other values reported for p-type TMD contacts in the literature. These results suggest that NbxW1-xSy can be a promising intermediate layer between metal contacts and monolayer WSe2 in future scaled-down TMD MOSFETs.

Bioaerosol Characterization with Vibrational Spectroscopy: Overcoming Fluorescence with Photothermal Infrared (PTIR) Spectroscopy.

Aerosols containing biological material (i.e., bioaerosols) impact public health by transporting toxins, allergens, and diseases and impact the climate by nucleating ice crystals and cloud droplets. Single particle characterization of primary biological aerosol particles (PBAPs) is essential, as individual particle physicochemical properties determine their impacts. Vibrational spectroscopies, such as infrared (IR) or Raman spectroscopy, provide detailed information about the biological components within atmospheric aerosols but these techniques have traditionally been limited due to the diffraction limit of IR radiation (particles >10 μm) and fluorescence of bioaerosol components overwhelming the Raman signal. Herein, we use photothermal infrared spectroscopy (PTIR) to overcome these limitations and characterize individual PBAPs down to 0.18 μm. Both optical-PTIR (O-PTIR) and atomic force microscopy-PTIR (AFM-PTIR) were used to characterize bioaerosol particles generated from a cyanobacterial harmful algal bloom (cHAB) dominated by Planktothrix agardhii. PTIR spectra contained modes consistent with traditional Fourier transform infrared (FTIR) spectra for biological species, including amide I (1630-1700 cm-1) and amide II (1530-1560 cm-1). The fractions of particles containing biological materials were greater in supermicron particles (1.8-3.2 μm) than in submicron particles (0.18-0.32 and 0.56-1.0 μm) for aerosolized cHAB water. These results demonstrate the potential of both O-PTIR and AFM-PTIR for studying a range of bioaerosols with vibrational spectroscopy.

2D Quantum Spin-Liquid Candidate Including a Chiral Anion: κ-(BEDT-TTF)2[BR/S(salicylate)2

The quantum spin-liquid state was first theorized by Anderson 50 years ago and the challenge remains to realize a quantum spin-liquid material. A handful of two-dimensional molecular candidates have attracted huge attention over the past 30 years owing to their triangular lattice possessing S = 1/2 spin systems. We present a new quantum spin-liquid candidate in 2D Mott insulator κ-(BEDT-TTF)2[BR/S(salicylate)]2. The structure has a double-width anion layer giving it a strong 2D character. The spiroborate anion is chiral and the salt is an inversion twin, having no inversion symmetry center and crystallizing in space group P21. This offers the possibility of novel behavior owing to the low symmetry not previously seen in molecular spin-liquid candidates. The peak height of the 6K anomaly of κ-(BEDT-TTF)2[BR/S(salicylate)2] is 2 or 3 times larger than that of κ-(BEDT-TTF)2Cu2(CN)3 and EtMe3Sb[Pd(dmit)2]2. The structure presents many opportunities for crystal engineering through atom-by-atom changes to the ligands on the spiroborate anion to produce a family of materials which lie in and around the QSL region of the phase diagram for these salts. This gives the prospect of an experimental playground to deepen understanding of the QSL state. Electrical resistivity, SQUID magnetometry, band calculations, heat capacity, Infrared and Raman spectroscopy are reported for κ-(BEDT-TTF)2[BR/S(salicylate)2].

Comparative Study Into the Effect of Detector Noises and Sensitivity on the Serum SERS Analysis: Example of Non-Communicable Diseases Discrimination.

The aim of the study is to compare the performance of surface-enhanced Raman spectroscopy (SERS) analysis of serum using a non-cooled detector (EnSpectr R785) and a high spectral resolution detector (Renishaw) in the task of discrimination between the patients with chronic heart failure and the patients with chronic obstructive pulmonary disease. The SERS-based solution of the classification problem demonstrates an insignificant relationship between the disease classification accuracy and detector quality (classification accuracy for the high-resolution setup is 0.84 and for the low-cost setup is 0.81). In the data recorded on Renishaw setup, the most significant bands are 611, 675, 720, 804, 1187, 1495, and 1847 cm-1; for the EnSpectr setup-721, 1051, and 1665 cm-1. The results have revealed equal discrimination capabilities in the EnSpectr and the Renishaw setups; however, the Renishaw setup has more prospects for identifying the spectral contribution of pathologically associated analytes.

Insights into the Morphological Effects of 1D, 2D, and 3D CoV-Layered Double Hydroxides on Their Electrochemical Performance in Supercapacitors.

In this study, bimetallic cobalt-vanadium-based layered double hydroxide (CoV-LDH) systems were developed by varying the Co/V molar ratios (1:1 and 2:1) and hydrothermal temperatures (120 and 180 °C). Structural analysis by X-ray diffraction (XRD), Raman, and Fourier-transform infrared (FTIR) spectroscopy indicated the successful formation of CoV-LDH with a unique structure and lattice distortions, reflecting the influence of both the metal concentrations and temperature on the crystal and chemical structures of the developed bimetallic systems. Similarly, the field-emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) images revealed a flaky 2D nanosheet-like structure for the bimetallic CoV-LDH with a 1:1 ratio prepared at 120 °C (CVL1-120), whereas one-dimensional (1D) and three-dimensional (3D) morphologies were observed for other bimetallic CoV-LDH systems prepared with a different molar ratio (2:1) and/or temperature (180 °C). Electrochemical analysis performed in a three-electrode setup demonstrated a specific capacitance of 314.4 F g-1 at 1 A g-1 current density for CVL1-120, which is ∼4.5 and 5.2 times higher than those of monometallic Co and V-LDH, respectively. In addition, CVL1-120 exhibited an excellent capacitance retention of ∼97% over 5000 charge-discharge cycles with 100% Coulombic efficiency at 10 A g-1. Furthermore, the developed asymmetric device delivered an energy density of 36.5 Wh kg-1 and a power density of 1208.2 W kg-1. This enhanced performance of CVL1-120 was attributed to its two-dimensional (2D) flaky structures, with rich intercalated ions serving as electroactive sites, facilitating enhanced charge storage efficiency and improved stability, making it suitable as an electrode material for sustainable supercapacitors.

Accurate operando measurement of AlGaN/GaN HEMTs channel temperature and optimization of thermal design

The accurate estimation of the temperature distribution of the GaN based power devices and optimization of the device structure is of great significance to possibly solve the self-heating problem, which hinders the further enhancement of the device performances. We present here the operando temperature measurement with high spatial resolution using Raman spectroscopy of AlGaN/GaN high electron mobility transistors (HEMTs) with different device structures and explore the optimization of the device thermal design accordingly. The lateral and depth temperature distributions of the single-finger HEMT were characterized. The channel temperature and self-heating effect of the device under different bias voltages were investigated. By incorporating the two-dimensional electrothermal simulation, the hotspot position can be clearly observed under the gate edge near the drain side. The channel temperature of the multi-finger HEMT was further measured and the experiment results were in agreement with the three-dimensional finite element analysis simulation results. The device structure of the multi-finger device, including the gate width, gate pitch, structure layout, substrate materials, and thickness, were then theoretically optimized to improve the heat dissipation. The peak channel temperature of the device can be reduced by 70 °C when the substrate is substituted from silicon carbide to a single crystalline diamond. These results are of great interest for the thermal management of GaN HEMT power devices and further device performance improvement.