High In-plane Research Articles

Multilayered nacre-mimetic inspired flexible PEI film with high thermal conductivity and reliable dielectric performances

It is critically desired to integrate high in-plane thermal conductivity (TC) and distinguished electric insulation for thermal conductive film in modern electronic devices. Herein, integration of high TC and electric insulation in sandwich-like BNNSs@MWCNTs/PEI (S-BNNSs@MWCNTs/PEI) composite film has been successfully achieved by layer-by-layer spin coating and hot pressing inspired by highly ordered structure of natural nacre. The covalently bonded connections between BNNSs and MWCNTs are beneficial to create more efficient heat conduction path, which can partly decrease the interfacial thermal resistance and phonon scattering. The resultant S-BNNSs@MWCNTs/PEI composite films possess a high in-plane TC of 6.88 W m−1K−1. Meantime, benefiting from the alternating multilayer structure, the composite films exhibit satisfactory reliable dielectric performances with flexibility, which shows great potential in ceramics-filled polymer composite TIMs.

Giant anisotropic in-plane thermal conduction induced by Anomalous phonons in pentagonal PdSe2

In two-dimensional materials, different atomic stacking induces anisotropic atomic interactions and phonon dispersions, leading to the anisotropy of in-plane thermal transport. Here, we report an exceptional case in layered pentagonal PdSe2, where the bonds, force constants, and lattice constants are nearly-equal along the in-plane crystallographic axis directions, while the thermal conductivity is surprisingly much greater along b-axis than along a-axis with a ratio up to 1.8. Such strong anisotropy is not only unexpected in in-plane uniform structured materials, but also comparable to the record high in-plane anisotropic thermal conductivity in the nonuniform structured material reported to date (the ratio is ∼2.0 in TiS3). By combining the inelastic X-ray scattering measurement and the first-principles calculations, we attribute such high anisotropy to the low-energy phonons along a-axis, particularly their lower group velocities and “avoided-crossing” behavior. The different buckling structures between a- (zigzag-type) and b-axis (flat-type) are mainly responsible for such unique phonon dynamics properties of PdSe2. This finding helps to discover materials with high anisotropic in-plane thermal conductivity in uniform structures and reveals new physics of anisotropy of in-plane thermal conduction. Due to the unique features in structure and thermal transport properties, PdSe2 may serve as a new platform for designing novel devices to route heat flow precisely at the nanoscale.

Tunable Performance of Quantum Dot-MoS2 Hybrid Photodetectors via Interface Engineering.

Heterostructures of quantum dots (QDs) and two-dimensional (2D) materials show promising potential for photodetection applications owing to their combination of high optical absorption and good in-plane carrier mobility. In this work, the performance of QD-2D photodetectors is tuned by band engineering. Devices are fabricated by coating MoS2 nanosheets with InP QDs, type-I core-shell InP/ZnS QDs, and type-II core-shell InP/CdS QDs. Comparative spectroscopic and photoelectric studies of different hybrids show that the energy band alignment and shell thickness can influence the efficiency of charge transfer (CT), energy transfer (ET), and defect-related processes between QDs and MoS2. Benefiting from efficient CT between the QDs and MoS2, a significant enhancement of responsivity and detectivity is observed in thick-shell InP/CdS QD-MoS2 devices. Our results demonstrate the feasibility of using core-shell QDs for regulating the ET and CT efficiency in heterostructures and highlight the importance of interface band design in QD-2D and other low-dimensional photodetectors.

The emergence of high room temperature in-plane and out-of-plane magnetostriction in polycrystalline CoFe2O4 film

The polycrystalline CoFe2O4 (CFO) film on cantilever substrate of silicon was grown using pulsed laser deposition (PLD) method and investigated its in-plane and out-of-plane magnetostrictive strain at room temperature (300 K) using the indigenous optical Cantilever Beam Magnetometer (CBM). The film shows a high compressive magnetostrictive strain of ‒ 387 ppm and ‒ 708 ppm for in-plane and out-of-plane configurations, respectively. Considerably, the magnetostrictive strain loops (λ‒H) possess a certain degree of hysteresis with a symmetric butterfly shape. The origin of large compressive magnetostriction of CFO film is attributed to the non-180° domain wall motion followed by 90° domain rotation. The large values of saturation magnetostrictive strain make CFO film a suitable candidate in sensor design for different purposes.

Impregnation of Cellulose Fibers with Copper Colloids and Their Processing into Electrically Conductive Paper

The use of biodegradable and nontoxic cellulose as a renewable alternative to plastic in electronics is a promising way to decrease the environmental pollution. Unfortunately, cellulose lacks one of the key properties for such applications, namely, electrical conductivity. Here, we report the complete impregnation of macroscopic cellulose fibers with copper colloids using a simple, fast, gram-scalable, electroless, and noble metal catalyst-free liquid-phase approach. By varying the stepwise addition of a precursor to the ongoing reaction, the amount of copper colloids inside the cellulose fibers and thus the electrical conductivity of the final product can be controlled. A simple vacuum filtration makes it possible to process the copper-impregnated fibers into self-supporting, paper-like membranes, whose electrical conductivity can be further improved by slight pressing. The fiber-like morphology in these papers is fully preserved after pressing, leading to a high in-plane conductivity of 10′105 ± 751 S/m. By equipping cellulose with electrical conductivity, the functional properties of this renewable material are significantly extended, making it now attractive for a wide range of emerging applications in electronics and electrocatalysis.

An inductively coupled plasma metal organic chemical vapor deposition based on showerhead structure for low temperature growth

An inductively coupled plasma metal organic chemical vapor deposition (ICP-MOCVD) based on showerhead structure is proposed for the low temperature growth of thin solid films including GaN. The flow field of precursors in the chamber of ICP-MOCVD was analyzed and the structure of showerhead was optimized by changing the showerhead diameter to obtain uniform velocity field above the substrate. The thickness non-uniformity of GaN films grown at 600 °C was improved from 5.14% to 1.86% after the optimization of showerhead. On that basis, the influence of triethylgallium (TEG) and trimethylgallium (TMG) on low-temperature GaN growth were investigated and TEG was proved to be the more appropriate Ga source in this case. Finally, GaN film with high c-axis and in-plane orientations was obtained on sputtered AlN/sapphire template and the full width half maximums of (002) and (102) x-ray rocking curves are 0.45° and 0.57° respectively. Our results provide a practicable method for the optimization of low-temperature MOCVD, which has potential to obtain large-scale crystalline films at low temperature.

Hybrid carbon filled thermoplastic composites: synergistic effect of synthetic graphite and graphene nanoplatelets on thermal and mechanical properties of polyamide 4.6

ABSTRACT In comparison with conventional polyamides, polyamide 4.6 is known as one of the high-temperature polyamides due to polymer chain constituents which also enhances its dimensional stability, creep resistance, and chemical resistance. The effect of hybrid synthetic graphite and graphene nanoplatelets fillers on thermal conductivity of polyamide 4.6 based composites was investigated in this study. Synthetic graphite and graphene nanoplatelets filled polyamide 4.6 based composites were fabricated using a twin-screw extruder. The variations on electrical, mechanical, thermal, and morphological properties were also examined. The highest in-plane and through-plane thermal conductivity values were obtained for hybrid 40 wt.% synthetic graphite and 5 wt.% graphene nanoplatelets filled composites as 21.65 and 4.04 W/mK, respectively. It was reported that the usage of hybrid carbon fillers in polyamide 4.6 leads to better thermal conductivity value..

Grafting of epoxidized natural rubber chains with BN platelets to obtain flexible and thermally conductive papers

Owing to the rapid development of high-power and minimized electronic devices, the materials with ultra-flexibility and effective heat dissipation have attracted much interest. Herein, the high thermally conductive epoxidized natural rubber (ENR) papers with layered structures based on boron nitride (BN) platelets are reported. First, polyrhodanine (PRd) was coated on the surface of BN platelets via oxidative polymerization of rhodanine (Rhd), which was initiated by the absorbed (S2O8)2- ions. Then, BN-PRd platelets were grafted with ENR chains using a mechanochemical method due to the presence of N–CS groups in PRd, allowing the combination of PRd and ENR chains with stable covalent bonds. Moreover, the grafted ENR chains acted as bridges between adjacent BN platelets and improved the heat transfer ability of BN-PRd/ENR thermally conductive composite papers. The as-prepared ultra-flexible 30 wt% BN-PRd/ENR thermally conductive composite papers rendered high in-plane (λ∥) and through-plane (λ⊥) thermal conductivity of 14.57 and 0.52 W/(mK), respectively, which were correspondingly 8094% and 289% of pure ENR paper (0.18 W/(mK)). Also, Young's modulus of the 30 wt% BN-PRd/ENR thermally conductive composite paper was 25.90 MPa. Overall, the as-fabricated BN-PRd/ENR thermally conductive composite papers demonstrated high flexibility, excellent mechanical robustness, outstanding thermal conductivity, and superior electronic illustration, indicating potential applications in areas of electronic components as thermal interface materials.

Brain volumetric and fractal analysis of synthetic MRI: A comparative study with conventional 3D T1-weighted images

PurposeThe estimation of brain volumetric measurements based on Synthetic MRI (SyMRI) is easy and fast, however, the consistency of brain volumetric and morphologic measurements based on SyMRI and 3D T1WI should be further addressed. The current study evaluated the impact of spatial resolution on brain volumetric and morphologic measurements using SyMRI, and test whether the brain measurements derived from SyMRI were consistent with those resulted from 3D T1WI. MethodBrain volumetric and fractal analysis were applied to thirty healthy subjects, each underwent four SyMRI acquisitions with different spatial resolutions (1 × 1 × 2 mm, 1 × 1x3mm, 1 × 1 × 4 mm, 2 × 2 × 2 mm) and a 3D T1WI (1 × 1 × 1 mm isotropic). The consistency of the SyMRI measurements was tested using one-way non-parametric Kruskal-Wallis test and post hoc Dwass-Steel-Critchlow-Fligner test. The association between SyMRI and 3D T1WI derived measurements was evaluated using linear regression models. ResultsOur results demonstrated that both in- and through-plane resolutions show an impact on brain volumetric measurements, while brain parenchymal volume showed high consistency across the SyMRI acquisitions, and high association with the measurements from 3D T1WI. In addition, SyMRI with 1 × 1 × 4 mm resolution showed the strongest association with 3D T1WI compared to other SyMRI acquisitions in both volumetric and fractal analyses. Moreover, substantial differences were found in fractal dimension of both gray and white matter between the SyMRI and 3D T1WI tissue segmentations. ConclusionsOur results suggested that the measurements from SyMRI with relatively higher in-plane and lower through-plane resolution (1 × 1 × 4 mm) are much closer to 3D T1WI.

Improving thermal conductivity of polybutylene terephthalate composites with hybrid synthetic graphite and carbon fiber

Polybutylene terephthalate (PBT) is a semi-crystalline engineering thermoplastic polyester. PBT offers rapid molding cycles, high heat resistant, crystallinity, fatigue resistance, strength and rigidity, excellent electrical properties, creep resistance, reproducible mold shrinkage and chemical resistance. In this study, PBT was loaded with synthetic graphite and carbon fiber at different weight fractions (10–40 wt.%). PBT-based composites were fabricated by the melt mixing process by using a co-rotating twin screw extruder then thermal, mechanical and morphological properties of filled PBT composites was investigated. Weight fraction of carbon fiber (up to 30 wt.%) increases the tensile strength and flexural strength of PBT, but synthetic graphite loading decreases the tensile strength and flexural strength of PBT. The highest in-plane and through-plane thermal conductivity values were obtained as 9.24 for 40 wt.% synthetic graphite filled composite and 3.41 W/mK for 40 wt.% carbon fiber reinforced composite, respectively. Carbon fiber was found to be more effective in increasing the through-plane thermal conductivities than synthetic graphite.

Graphitized-rGO/Polyimide Aerogel as the Compressible Thermal Interface Material with Both High In-Plane and Through-Plane Thermal Conductivities.

Reduced graphene oxide (rGO) aerogels with a three-dimensional (3D) interconnected network provides continuous heat transport paths in multi-directions. However, the high porosity of rGO aerogels commonly leads to very low thermal conductivity (TC), and defects and grain boundaries of rGO sheets result in a high extent of phonon scattering, which is far from satisfying the requirement of thermal interface materials (TIMs). Here, a compressible graphitized-rGO/polyimide (g-rGO/PI) aerogel was prepared by the ice-template method and “molecular welding” strategy. The regular cellular structure and closely packed cell walls bring the g-rGO/PI aerogel high compressibility, which made the aerogel can maintain the continuous thermal transport paths well even in highly compacted status. The rGO sheets in the cell wall surface are welded up by g-PI during imidization and graphitization treatment, providing efficient channels for phonon transportation in the 3D network. The g-rGO/PI aerogel in a compressive strain of 95% has a high TC in the plane of 172.5 W m−1k−1 and a high TC through the plane of 58.1 W m−1k−1, which is superior to other carbon-based TIMs previously reported.

Effect of Energy and Temperature on Tetrahedral Amorphous Carbon Coatings Deposited by Filtered Laser-Arc.

In this study, both the plasma process of filtered laser-arc evaporation and the resulting properties of tetrahedral amorphous carbon coatings are investigated. The energy distribution of the plasma species and the arc spot dynamics during the arc evaporation are described. Different ta-C coatings are synthesized by varying the bias pulse time and temperature during deposition. An increase in hardness was observed with the increased overlapping of the bias and arc pulse times. External heating resulted in a significant loss of hardness. A strong discrepancy between the in-plane properties and the properties in the film normal direction was detected specifically for a medium temperature of 120 °C during deposition. Investigations using electron microscopy revealed that this strong anisotropy can be explained by the formation of nanocrystalline graphite areas and their orientation toward the film’s normal direction. This novel coating type differs from standard amorphous a-C and ta-C coatings and offers new possibilities for superior mechanical behavior due to its combination of a high hardness and low in-plane Young’s Modulus.

Synergetic integration of thermal conductivity and flame resistance in nacre‐like nanocellulose composites

Highly thermally conductive and flame resistant nanocellulose-based composites can synchronously achieve efficient thermal dissipation and low fire hazards of electronic devices, which shows great promise in next-generation green and flexible electronics. However, it has long been intractable to optimize the high thermal conductivity (TC) and flame resistance simultaneously. Herein, synergetic integration of high TC and flame resistance in nacre-like nanocellulose composites has been successfully achieved by the vacuum-assisted filtration of cellulose nanofibers (CNFs) and functionalized boron nitride nanosheets (BNNS-p-APP). Benefiting from the highly oriented hierarchical microstructure, strong hydrogen-bonding interaction, and successful immobilization of ammonium polyphosphate (APP), the as-obtained CNFs/BNNS-p-APP composite film achieves a high in-plane TC of 9.1 W m−1 K−1 and outstanding flame resistance. Meantime, this eco-friendly nanocellulose-based composite also exhibits remarkable flexibility, folding endurance, and mechanical robustness, robustness, which may open up a new opportunity for the thermal management of flexible electronics.

Design of 3D printed bioinspired nacre-like structured materials with significantly enhanced thermal conductivity

In this Letter, we report a simple approach for the preparation of bioinspired nacre-like structured materials with achievable high in-plane or through-plane thermal conductivity via digital light processing 3D printing under optimized printing parameters. Based on the 3D layer-by-layer formation, a vertical force exerted on each printing layer during the 3D printing process makes 2D platelets well-ordered in ultraviolet curable resin (hereafter UV resin), which is proved by the images of the scanning electron microscope and spectra of x-ray diffraction. It is found that a lower printing layer thickness leads to a higher orientation of Al2O3 platelets in the UV resin and greater thermal conductivity of the composites. The thermal conductivity of the structured composites reaches up to 2.622 W m−1 K−1 along the oriented direction at the loading of 30 wt. % of 2D Al2O3 platelets under the designed 3D printing layer thickness of 15 μm, which is about 14 times greater than that of pure UV resin. The surface temperature variations of the composites with time during heating and cooling, observed from the infrared thermograph, indicate the great potential of the 3D-printed structured materials for thermal management applications in electronic devices and electric equipment. It is predicted that fillers with greater intrinsic thermal conductivity and a larger diameter than the 3D printing layer thickness will lead to composites with greater thermal dissipation capability.

Resonator-Based Bidirectional Lorentz Force Magnetic Sensor

We present a low power high sensitive in-plane resonant bidirectional Lorentz-force magnetic micro-sensor operating in air at ambient pressure. The concept is based on the detection of the resonance frequency shift of an electrothermally straight micro-beam resonator operated near the buckling point. Powered at 20 $\mu \text{W}$ , the micro-sensor shows a measured sensitivity (S) of 3.32/(mA.T), which is very high compared to the state of the art. The proposed method is simple in design making it promising for achieving practical low-cost magnetometer.

High In-Plane Seebeck Coefficients of Bi–Sb–Te Alloy Thin Films with Growth Texture and Their Field-Controlled Seebeck Coefficients

Bismuth antimony telluride (BixSb2–xTe3, BST) is an alloy that has widely been used over the past 5 decades for excellent p-type thermoelectric (TE) materials that operate around 300 K, for example...

The electronic structures, elastic constants, dielectric permittivity, phonon spectra, thermal properties and optical response of monolayer zirconium dioxide: A first-principles study

Zirconium dioxide (ZrO2) with great mechanical and dielectric properties can be widely used in both structural and functional material fields. In this paper, the first-principles calculations are performed to investigate the geometrical and electronic structures, elastic constants and mechanical stability, Born effective charges and dielectric permittivity, phonon spectra and thermal properties, as well as optical response of monolayer ZrO2. A wide indirect bandgap of 4.41 eV and a p-d hybridized ionic bond are presented in monolayer ZrO2, instead of a zero bandgap and a sp2 hybridized covalent bond in grapheme. Both the large in-plane stiffness of 209.59 N/m and small Poisson's ratio of 0.24 imply monolayer ZrO2 a high strength in-plane and good flexibility out-plane. A strong dynamic charge transfer from Zr to O is existed in monolayer ZrO2. The large bandgap and dielectric permittivity, mechanical and dynamical stability show monolayer ZrO2 a promising two dimensional dielectric material. The high and sharp absorption peaks in the ultra-violet spectral region suggest monolayer ZrO2 a potential application as a ultra-violet detector.

Flexible and alternant-layered cellulose nanofiber/graphene film with superior thermal conductivity and efficient electromagnetic interference shielding

Inspired by sedimentary rock structure, we demonstrate a flexible heterogeneous multilayered film with high thermal conductivity (TC) and excellent electromagnetic interference (EMI) shielding performance by stacking and concentrating graphene nanosheets (GNS) into alternating conductive layers. Typically, the multilayered film with alternating cellulose nanofiber (CNF) layers and conductive CNF/GNS layers was fabricated by alternating vacuum filtration. Arising from the unique nacre-like oriented structure and highly concentrated conductive filler, high-efficiency phonon and electron transmission paths can be formed in the obtained multilayered CNF@GNS film. As a result, the optimal film with only 25 wt% GNS reveal a high in-plane TC of 33.55 W/(m·K), which increases by 144.6% comparing to the homogeneous CNF/GNS film. Simultaneously, the multilayered films exhibit the effective EMI shielding performance with the highest shielding effectiveness (SE) of 27.4 dB, which is mainly attributed to the enhancing impedance matching and multiple microwave reflections induced by the unique alternating multilayer structure.

Mechanical and thermal conduction properties of carbon/carbon composites with different carbon matrix microstructures

Four carbon/carbon composites with densities of 1.75–1.81 g/cm3were produced with matrix carbons derived from (a)coal tar pitch and furfural acetone resin by impregnation-carbonization, (b) natural gas by isothermal chemical vapor infiltration and (c) xylene by film-boiling chemical vapor infiltration. Theirmechanical properties and thermal conductivities (TC) were compared and correlated to the matrix carbon microstructures. Results showed that the strength of the composites decreased as thecarbon matrix changed from natural gas pyrocarbon (PyCN), to resin-derived carbon, to xylene PyC (PyCX), and to pitch-derived carbon. The highest flexural and interlaminar shear strengths of 208.7 and 26.4MPa, respectively, were obtained for the PyCN matrix. The large amount of fiber pull-out and step-like matrix fracture contributed to a high toughness of composites with PyCN and PyCX matrices. Relatively low strength and toughness were obtained for the pitch-derived carbon. The change of TC with the matrix type was consistent with the graphitization degree and apparent crystallite height. The highest in-plane and out-of-plane TC reached 148.2 and 75.4 W/(m·K), respectively, for the PyCX matrix, which was due to its carbon layers having the highest preferred orientation. The chaotic structure and large number of defects of the resin-derived carbon produced a relatively low TC. PyCN was the most suitable matrix for composites with excellent mechanical properties. PyCXshould be used to improve the TC and toughness of the low-cost composites.

High Surface Phonon-Polariton in-Plane Thermal Conductance along Coupled Films.

Surface phonon-polaritons (SPhPs) are evanescent electromagnetic waves that can propagate distances orders of magnitude longer than the typical mean free paths of phonons and electrons. Therefore, they are expected to be powerful heat carriers capable of significantly enhancing the in-plane thermal conductance of polar nanostructures. In this work, we show that a SiO/Si (10 m thick)/SiO layered structure efficiently enhances the SPhP heat transport, such that its in-plane thermal conductance is ten times higher than the corresponding one of a single SiO film, due to the coupling of SPhPs propagating along both of its polar SiO nanolayers. The obtained results thus show that the proposed three-layer structure can outperform the in-plane thermal performance of a single suspended film while improving significantly its mechanical stability.