Thermal Scanning Research Articles

Thermal energy storage performance of liquid polyethylene glycol in core–shell polycarbonate and reduced graphene oxide fibers

Thermal energy storage is a promising, sustainable solution for challenging energy management issues. We deploy the fabrication of the reduced graphene oxide (rGO)–polycarbonate (PC) as shell and polyethylene glycol (PEG) as core to obtain hydrophobic phase change electrospun core–shell fiber system for low-temperature thermal management application. The encapsulation ratio of PEG is controlled by controlling the core flow rate, and ~ 93% heat energy storage efficacy is apparent for 1.5 mlh−1 of core flow rate. Moreover, the prepared fiber possesses maximum latent melting and freezing enthalpy of 30.1 ± 3.7 and 25.6 ± 4.0 Jg−1, respectively. The transient dynamic temperature vs. time curve of the rGO-loaded phase change fiber demonstrates the delay of fiber surface temperature change compared to pristine fiber. We indeed show that the tunable heat transfer and thermal energy storage efficacy of phase change fiber is achieved via controlled liquid PEG delivery and the addition of rGO in shell architecture. Notably, the effectiveness of unique phase change material (PCM)–based core–shell fibers is concluded from advanced scanning thermal microscopy (SThM) and self-thermoregulation tests.

Unraveling the Impact of Boron Nitride and Silicon Nitride Nanoparticles on Thermoplastic Polyurethane Fibers and Mats for Advanced Heat Management.

The urgent challenges posed by the energy crisis, alongside the heat dissipation of advanced electronics, have embarked on a rising demand for the development of highly thermally conductive polymer composites. Electrospun composite mats, known for their flexibility, permeability, high concentration and orientational degree of conductive fillers, stand out as one of the prime candidates for addressing this need. This study explores the efficacy of boron nitride (BN) and its potential alternative, silicon nitride (SiN) nanoparticles, in enhancing the thermal performance of the electrospun composite thermoplastic polyurethane (TPU) fibers and mats. The 3D reconstructed models obtained from FIB-SEM imaging provided valuable insights into the morphology of the composite fibers, aiding the interpretation of the measured thermal performance through scanning thermal microscopy for the individual composite fibers and infrared thermography for the composite mats. Notably, we found that TPU-SiN fibers exhibit superior heat conduction compared to TPU-BN fibers, with up to a 6 °C higher surface temperature observed in mats coated on copper pipes. Our results underscore the crucial role of arrangement of nanoparticles and fiber morphology in improving heat conduction in the electrospun composites. Moreover, SiN nanoparticles are introduced as a more suitable filler for heat conduction enhancement of electrospun TPU fibers and mats, suggesting immense potential for smart textiles and thermal management applications.

Supramolecular interactions in cocrystals of benzoic acid derivatives with selective COX-2 inhibitor etoricoxib.

The structures of three 1:1 cocrystal forms of etoricoxib {ETR; systematic name: 5-chloro-2-(6-methylpyridin-3-yl)-3-[4-(methylsulfonyl)phenyl]pyridine, C18H15ClN2O2S} have been synthesized and characterized by single-crystal X-ray diffraction; these are etoricoxib-benzoic acid (1/1), C18H15ClN2O2S·C7H6O2 (ETR-Bz), etoricoxib-4-fluorobenzoic acid (1/1), C18H15ClN2O2S·C7H5FO2 (ETR-PFB), and etoricoxib-4-nitrobenzoic acid (1/1), C18H15ClN2O2S·C7H5NO4 (ETR-PNB). Powder X-ray diffraction and thermal differential scanning calorimetry-thermogravimetry (DSC-TG) techniques were also used to characterize these multicomponent systems. Due to the influence of the corresponding acids, ETR shows different conformations. Furthermore, the energetic contributions of the supramolecular motifs have been established by energy framework studies of the stabilizing interaction forces and are consistent with the thermal stability of the cocrystals.

Thermal engineering increases current density in AlGaN/GaN superlattice devices

Aluminum gallium nitride/gallium nitride multi-channel superlattice devices are receiving increasing attention as a new paradigm for driving the power density of gallium nitride based transistors toward their theoretical limit. However, the superior electrical performance of superlattice-based transistors is currently limited by excessive Joule-heating. This Letter evaluates what impact the number of superlattice channels and the buffer layer composition has on the reduction of the thermal resistance, i.e., Joule heating, of AlGaN/GaN superlattice devices. A record low thermal resistance (12.51 ± 0.34 K mm W−1) was measured via scanning thermal microscopy for non-castellated superlattice AlGaN/GaN devices with a 100 μm channel width. Overall, the use of a thin gallium nitride buffer layer, in place of a thick aluminum gallium nitride layer, reduced the buffer thermal resistance enabling the accommodation of more superlattice channels (10 vs 6), therefore augmenting the maximum power density of these devices. The superlattice device proposed here not only provides an enhanced thermal dissipation solution for high power density radio frequency electronics, but it also has the benefit of fewer fabrication steps in comparison with previously reported castellated multichannel devices.

Preparation of Hydrophobic Modified Silica with Si69 and Its Reinforcing Mechanical Properties in Natural Rubber.

The inherent large number of hydroxyl groups of silica poses strong hydrophilicity, resulting in poor dispersibility in the natural rubber matrix. Here, the silica's surface was hydrophobically modified with [3-(triethoxysiliconyl) propyl] tetrasulfide (Si69) to improve the dispersibility and reinforce the mechanical properties of silica/natural rubber composites. The structure and morphology of modified silica were characterized by Fourier infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray electron spectroscopy (XPS), nuclear magnetic resonance spectroscopy and the contact angle. Further, the mechanical properties, dynamic mechanical properties and morphology of silica/natural rubber composites were studied with a universal electronic tension machine, dynamic thermal mechanical properties analyzer (DMA) and scanning electron microscope (SEM). The experimental results show that the Si69 was successfully grafted onto the surface of silica, thereby significantly improving the water contact angle (a 158.6% increase) and enhancing the mechanical properties of modified silica/natural rubber composites.

Flexible and Thermally Insulating Porous Materials Utilizing Hollow Double-Shell Polymer Fibers.

The global climate change is mainly caused by carbon dioxide (CO2) emissions. To help reduce CO2 emissions and conserve thermal energy, sustainable materials based on flexible thermal insulation are developed to minimize heat flux, drawing inspiration from natural systems such as polar bear hairs. The unique structure of hollow double-shell fibers makes it possible to achieve low thermal conductivity in the material while retaining exceptional elasticity, allowing it to adapt to insulation systems of any shape. The layered system of porous mats reaches a thermal conductivity coefficient of 0.031 W∙m⁻¹∙K⁻¹ and enables to reduce the heat transfer. The results achieved using scanning thermal microscopy (SThM) correlate with the simulated heat flow in the case of individual fibers. This research study brings new insights into the energy efficiency of domestic environments, thereby addressing the growing demand for sustainable and high-performance insulation materials for saving energy loss and reducing pollution footprint.

Thermal characterization of thin films: A chip-based approach for in-plane property analysis

Accurate measurement of thermal properties in thin films is crucial for optimizing devices and deepening our understanding of heat transfer at nano and micro scales. This study presents a combined experimental and computational investigation on a chip-integrated technique for the assessment of in-plane thermal properties of thin films. This method stands out by incorporating inherent error cancelation to lessen the impact of radiative heat loss and allows simultaneous, independent determination of both thermal conductivity and diffusivity through straightforward linear fittings from the same dataset, reducing error propagation. We examine an 84 nm thick SiNx membrane over a temperature range from 100 K to nearly 500 K, aligning with previous studies. Further investigations into a conducting polymer film post-doping demonstrate a notable increase in both thermal conductivity and diffusivity, corroborating scanning thermal microscopy observations, confirming the technique's efficacy and reliability.

Fabrication of pesticide/LDH-LAP composite assisted by zwitterionic surfactant

Using zinc-aluminum layered double hydroxides-laponite (LDH-LAP) complex as matrix, with the assistance of zwitterionic surfactants of hexadecyl dimethyl sulfobetaine (SB) and dodecyl dimethyl carboxyl betaine (DCB), the pesticides beta-cypermethrin (BCT) and imidacloprid (IMP) were inserted into the LDH-LAP to obtain BCT/SB-LDH-LAP, BCT/DCB-LDH-LAP, BCT/SB-DCB-LDH-LAP and IMP/DCB-LDH-LAP composites, respectively. Powder X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), thermogravimetric/differential thermal analysis (TGA/DTA) and scanning electron microscope (SEM) were used to characterize the structural properties of composites. BCT/SB-LDH-LAP, BCT/DCB-LDH-LAP, BCT/SB-DCB-LDH-LAP and IMP/DCB-LDH-LAP had larger interlayer distances of 4.29, 4.33, 4.33 and 4.61 nm, which were bigger than those of SB-LDH-LAP (3.87 nm), DCB-LDH-LAP (3.83 nm) and LDH-LAP (1.65 nm). The FT-IR and TGA/DTA results further confirmed the existence of SB, DCB, BCT and IMP into LDH-LAP. The pesticide releases were investigated and analyzed in pH 5.0 and 6.8 buffer solutions. The release behaviors can be fitted by pseudo second-order and parabolic diffusion models. The composites based on LDH-LAP could be suggested to potential application for controlled-release of the pesticide.

Nanoironing van der Waals Heterostructures toward Electrically Controlled Quantum Dots.

Assembling two-dimensional van der Waals (vdW)-layered materials into heterostructures is an exciting development that sparked the discovery of rich correlated electronic phenomena. vdW heterostructures also offer possibilities for designer device applications in areas such as optoelectronics, valley- and spintronics, and quantum technology. However, realizing the full potential of these heterostructures requires interfaces with exceptionally low disorder which is challenging to engineer. Here, we show that thermal scanning probes can be used to create pristine interfaces in vdW heterostructures. Our approach is compatible at both the material- and device levels, and monolayer WS2 transistors show up to an order of magnitude improvement in electrical performance from this technique. We also demonstrate vdW heterostructures with low interface disorder enabling the electrical formation and control of quantum dots that can be tuned from macroscopic current flow to the single-electron tunneling regime.

Laser catheter ablation of atrial zones with ganglionated plexi: impact on atrial fibrillation inducibility and the risk of esophageal damage in experimental settings

Aim. To study the potential applicability of transcatheter laser ablation for the destruction of atrial ganglionated plexi (GP) zones and the safety of this technique in relation to inadvertent esophageal damage.Methods. This was a two-stage investigation: (1) ex vivo experiments: the risk of esophageal damage during ablation on the dorsal (posterior) left atrial (LA) wall was assessed; three swine organ complexes were used, which included the heart, lungs and esophagus; (2) in vivo experiments assessing the effects of laser catheter ablation of GP zones on the inducibility of atrial fibrillation (AF) and changes in atrial effective refractory period - included 13 landrace pigs (average weight 38.8±1.2 kg).Ex vivo: laser catheter ablations were performed from the endocardial surface of the LA towards the esophagus with a power of 15 watts of varying duration; ablation was performed under thermal scanning of the LA and esophagus; then a macroscopic examination of the myocardial and esophageal walls was performed.In vivo: before and after catheter laser ablation (15 W) of the GP zones in the right atrium and atrial septum, atrial ERP was assessed with programmed stimulation, and AF induction with high-frequency (33 Hz, 2 min) stimulation was evaluated. At the end of the experiment, the animals were euthanized, and the heart and lungs were collected in a single unit.Results. Ex vivo experiments: in two cases, damage to the endocardium of the LA was detected at an exposure time of 30 s. Damage to the esophagus was observed with a longer exposure time (> 30 seconds) with a 11.3-15.4°C increase in temperature. In the in vivo experiments, 78 laser applications (6±1 in one swine) were delivered to the posterior wall of the right atrium and atrial septum. Atrial effective refractory period was not altered after ablation (183±20 ms vs 186±18 ms, P=0.99). At the baseline, AF was induced in 12 out of 13 animals (92%). After ablation, AF was induced in 7 animals (54%) (P=0.03). There was a trend toward a decrease in the duration of AF after laser ablation of GP zones (18 [5; 141] vs. 2 [0; 14] s after ablation, P=0.06). Transmural damage was observed in 46% of the hearts. No damage to extra-cardiac structures was detected.Conclusion. Ex vivo, laser ablation on the dorsal (posterior) wall of the LA with a power of 15 W and duration <30 s does not lead to visible damage to the esophagus. Laser ablation of atrial GP zones is feasible and reduces the inducibility of AF. No change in atrial effective refractory period is detected following GP zones ablation, when performed from the right atrium.

Conductive polypyrrole: synthesis, characterization, thermal, and electrical properties for different applications

Pyrrole monomer (mPPy) in an aqueous solution was used to create the conductive polymer polypyrrole (a homo-PPy) using a chemical oxidative polymerization process over a period of several hours at room temperature. Ferric chloride (FeCl3) oxidant was used, and sodium dodecyl sulphate (C12H25NaO4S), a surfactant. The produced PPy samples were characterized using a variety of methods, including X-ray diffraction (XRD), the Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), Differential Thermal analysis (DTA), Thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). SEM images revealed that nanoparticles of a homo-PPy with radii of 60–90 nm were well evenly distributed in the structure. The thermal stability and electrical conductivity of homo-PPy nanoparticles were observed to rise with a solvent ethylene glycol. As temperature rises, the conductivity of homo-PPy samples is significantly raised, and electrical conductivities ranging from.0.44 to 2.2 (Ω.m)−1. Results from FTIR and XRD analysis confirmed the structural formation of a homo-polypyrrole during synthesis from pyrrole monomer. Because of their improved electrical conductivity and thermal stability, homo-PPy nanoparticles have potential applications in energy storage, adsorption and contamination elimination, electromagnetic protection, and resistance to corrosion.

Influence of Programming and Recovery Parameters on Compressive Behaviors of 4D‐Printed Biocompatible Polyvinyl Chloride or Vinyl–Poly(ε‐Caprolactone) Blends

In this article, a new class of biocompatible shape‐memory polymers (SMPs) through blending pcolyvinyl chloride or vinyl (PVC) and poly(ε‐caprolactone) (PCL) is introduced. The compressive shape‐memory behaviors of 4D‐printed SMP PVC with 5 and 10 wt% of PCL are studied in detail. In this respect, a set of experiments are carried out to understand thermomechanical responses of PVC–PCL blends under various shape‐memory parameters like programming temperature, load‐holding time, applied strain, and recovery temperature. Dynamic mechanical thermal analysis and scanning electron microscope imaging are also performed to provide thermal and morphological analyses. It is found that by raising the recovery temperature from 45 to 65 °C, the shape recovery ratio increases from 5.63 to 7.92 MPa when the PVC–PCL10 is programmed via the hot‐programming (HP) protocol. The highest level of shape fixity (100%) and the best performance of stress relaxation are achieved for HP sample, while the highest shape recovery ratio (100%) is obtained for cold programming. By applying the load‐holding time, the amount of shape fixity can reach from 88.14% to 100%. Results of this research are expected to provide an insightful understanding of the shape‐memory behaviors of PVC–PCL and be instrumental for 4D printing and programming of shape‐adaptive structures like shape‐memory intervertebral cages as spinal support devices.

Transformer bridge-based metrological unit for scanning thermal microscopy with resistive nanoprobes

Scanning probe microscopy (SPM) is a broad family of diagnostic methods. Common restraint of SPM is only surficial interaction with specimen, especially troublesome in case of complex volumetric systems, e.g. microbial or microelectronic. Scanning thermal microscopy (SThM) overcomes that constraint, since thermal information is collected from broader space. We present transformer bridge-based setup for resistive nanoprobe-based microscopy. With low-frequency (LF) (approx. 1 kHz) detection signal bridge resolution becomes independent on parasitic capacitances present in the measurement setup. We present characterisation of the setup and metrological description—with resolution of the system 0.6 mK with sensitivity as low as 5 mV K−1. Transformer bridge setup brings galvanic separation, enabling measurements in various environments, pursued for purposes of molecular biology. We present results SThM measurement results of high-thermal contrast sample of carbon fibres in an epoxy resin. Finally, we analyse influence of thermal imaging on topography imaging in terms of information channel capacity. We state that transformer bridge-based SThM system is a fully functional design along with low driving frequencies and resistive thermal nanoprobes by Kelvin Nanotechnology.

Scanning Thermal Microscopy for Localizing and Monitoring Defects in Electronics

Abstract This article presents the principles of scanning thermal microscopy (SThM) instruments and their potential uses for the local thermal analysis of passive and active electronic components and devices. Three examples are given that demonstrate the SThM’s ability to perform thermal analysis on a microscopic scale. The results suggest that SThM could be used as a powerful tool for analyzing printed circuit boards and electronic devices with high spatial resolution, during the development cycle, failure analysis during and after manufacture, and during operation.

Experimental setup for thermal measurements at the nanoscale using a SThM probe with niobium nitride thermometer.

Scanning Thermal Microscopy (SThM) has become an important measurement technique for characterizing the thermal properties of materials at the nanometer scale. This technique requires a SThM probe that combines an Atomic Force Microscopy (AFM) probe and a very sensitive resistive thermometer; the thermometer being located at the apex of the probe tip allows for the mapping of temperature or thermal properties of nanostructured materials with very high spatial resolution. The high interest of the SThM technique in the field of thermal nanoscience currently suffers from a low temperature sensitivity despite its high spatial resolution. To address this challenge, we developed a high vacuum-based AFM system hosting a highly sensitive niobium nitride (NbN) SThM probe to demonstrate its unique performance. As a proof of concept, we utilized this custom-built system to carry out thermal measurements using the 3ω method. By measuring the V3ω voltage on the NbN resistive thermometer under vacuum conditions, we were able to determine the SThM probe's thermal conductance and thermal time constant. The performance of the probe is demonstrated by performing thermal measurements in-contact with a sapphire sample.

Thermoelectric Limitations of Graphene Nanodevices at Ultrahigh Current Densities.

Graphene is atomically thin, possesses excellent thermal conductivity, and is able to withstand high current densities, making it attractive for many nanoscale applications such as field-effect transistors, interconnects, and thermal management layers. Enabling integration of graphene into such devices requires nanostructuring, which can have a drastic impact on the self-heating properties, in particular at high current densities. Here, we use a combination of scanning thermal microscopy, finite element thermal analysis, and operando scanning transmission electron microscopy techniques to observe prototype graphene devices in operation and gain a deeper understanding of the role of geometry and interfaces during high current density operation. We find that Peltier effects significantly influence the operational limit due to local electrical and thermal interfacial effects, causing asymmetric temperature distribution in the device. Thus, our results indicate that a proper understanding and design of graphene devices must include consideration of the surrounding materials, interfaces, and geometry. Leveraging these aspects provides opportunities for engineered extreme operation devices.

LaMg6Ga6S16: a chemical stable divalent lanthanide chalcogenide

Divalent lanthanide inorganic compounds can exhibit unique electronic configurations and physicochemical properties, yet their synthesis remains a great challenge because of the weak chemical stability. To the best of our knowledge, although several lanthanide monoxides epitaxial thin films have been reported, there is no chemically stable crystalline divalent lanthanide chalcogenide synthesized up to now. Herein, by using octahedra coupling tetrahedra single/double chains to construct an octahedral crystal field, we synthesized the stable crystalline La(II)-chalcogenide, LaMg6Ga6S16. The nature of the divalent La2+ cations can be identified by X-ray photoelectron spectroscopy, X-ray absorption near-edge structure and electron paramagnetic resonance, while the stability is confirmed by the differential thermal scanning, in-situ variable-temperature powder X-ray diffraction and a series of solid-state reactions. Owing to the particular electronic characteristics of La2+(5d1), LaMg6Ga6S16 displays an ultrabroad-band green emission at 500 nm, which is the inaugural instance of La(II)-based compounds demonstrating luminescent properties. Furthermore, as LaMg6Ga6S16 crystallizes in the non-centrosymmetric space group, P−6, it is the second-harmonic generation (SHG) active, possessing a comparable SHG response with classical AgGaS2. In consideration of its wider band gap (Eg = 3.0 eV) and higher laser-induced damage threshold (5×AgGaS2), LaMg6Ga6S16 is also a promising nonlinear optical material.

Preparation of MoO3 powder by hydrothermal method

Abstract Based on the raw material of ammonium tetramolybdate in the experiment, molybdenum trioxide was prepared by hydrothermal synthesis, and the effects of different pH, hydrothermal reaction time, filling degree, and calcination temperature on molybdenum trioxide powder were studied. Meanwhile, the molybdenum trioxide powder was characterized through scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and thermal analysis differential scanning calorimetry analysis so as to study the morphology and phase changes during the experiment. As is evident from the research findings, MoO3 powders with uniform and suitable size, smooth and clear surface, good dispersibility, and no adhesion can be obtained at the conditions of pH = 1, 16 h hydrothermal reaction, 90% of filling degree, and 550°C of calcination temperature. In the calcination process, MoO3 crystal undergone crystal transformation and was completely transformed from h-MoO3 to α-MoO3 at the calcination temperature of 350°C.

Thermal scanning probe and laser lithography for patterning nanowire based quantum devices

Semiconductor nanowire (NW) quantum devices offer a promising path for the pursuit and investigation of topologically-protected quantum states, and superconducting and spin-based qubits that can be controlled using electric fields. Theoretical investigations into the impact of disorder on the attainment of dependable topological states in semiconducting nanowires with large spin–orbit coupling and g-factor highlight the critical need for improvements in both growth processes and nanofabrication techniques. In this work, we used a hybrid lithography tool for both the high-resolution thermal scanning probe lithography and high-throughput direct laser writing of quantum devices based on thin InSb nanowires with contact spacing of 200 nm. Electrical characterization demonstrates quasi-ballistic transport. The methodology outlined in this study has the potential to reduce the impact of disorder caused by fabrication processes in quantum devices based on 1D semiconductors.

Synthesis and characterization of chitosan-based pH-sensitive biofilm: An experimental design approach for release of vitamin B12

Hydrogels because of their unique potentials, such as highwater content and hydrophilicity, are of interest for the controlled release of drug molecules. In the present study, a biofilm was produced using chitosan, a natural polymer. Characterization analyses of the synthesized biofilm were performed using Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis-differential thermal analysis, x-ray diffraction, and scanning electron microscopy-energy dispersive x-ray spectrometry. The analysis results of the film before loading were compared to the analysis made after adding vitamin B12 to the film. The release percentage of vitamin B12 was investigated by using ultraviolet-visible spectrophotometery. The FT-IR bands of vitamin B12 were in the range of 2,800-3,500 cm-1 and 1,000 cm-1-1,750 cm-1. When pH increased from 3 to 7, release of vitamin B12 from the biopolymer increased up to pH 5. While examining the release potential, parameters, such as pH, initial concentration of vitamin B12, release time, and solution volume, were optimized by using response surface methodology. It was determined that with the increase in release time and the initial concentration, pH contributed positively to the release of vitamin B12. The following conditions were determined for release of vitamin B12 from the biofilm: pH: 4.2, initial concentration of vitamin B12: 54.0 mg L-1, the release time: 117 min, and volume of solution: 2.1 mL. The analysis of variance results showed that the determination coefficients for the use of synthesized biofilm in vitamin B12 release were high and R2 =0.9704.