Gating Method Research Articles

A clustering algorithm based on jet algorithms for cross-talk events in neutron detector arrays

A clustering algorithm based on the jet (cascade of particles descendant from a single particle due to hadronization) algorithms used in High Energy Physics is presented for identification of neutron cross-talk events in neutron detector arrays with one layer by defining a temporal distance function, instead of transverse energy. Detector simulations on an array of neutron detectors show a significant improvement when compared with neighbor rejection technique and the method of gating with time-of-flight difference.

PervasiveFL: Pervasive Federated Learning for Heterogeneous IoT Systems

Federated learning (FL) has been recognized as a promising collaborative on-device machine learning method in the design of Internet of Things (IoT) systems. However, most existing FL methods fail to deal with IoT applications that contain a variety of IoT devices equipped with different types of neural network (NN) models. This is because traditional FL methods assume that local models on devices should have the same architecture as the global model on cloud. To address this problem, we propose a novel framework named PervasiveFL that enables efficient and effective FL among heterogeneous IoT devices. Without modifying original local models, PervasiveFL installs one lightweight NN model named modellet on each device. By using the deep mutual learning (DML) and our entropy-based decision gating (EDG) method, modellets and local models can selectively learn from each other through soft labels using locally captured data. Meanwhile, since modellets are of the same architecture, the learned knowledge by modellets can be shared among devices in a traditional FL manner. In this way, PervasiveFL can be pervasively applied to any heterogeneous IoT system. Comprehensive experimental results on four well-known datasets show that PervasiveFL can not only pervasively enable FL among heterogeneous devices within a large-scale IoT system, but also significantly enhance the inference accuracy of heterogeneous IoT devices with low communication overhead.

Clinical utility of a new protocol of cardiac computed tomography in dogs.

The characteristics of non-electrocardiography- and electrocardiography-gated multidetector computed tomography have not been extensively studied in veterinary clinics but it can be useful for cardiac imaging. This study aimed to ascertain the differences between non-electrocardiography and electrocardiography gating methods and to establish their clinical utility based on patient history. Six client-owned dogs (two with patent ductus arteriosus, two with heart base tumour, one with pericardial mesothelioma, and one with normal health) were included in this study. All the dogs were examined using a non-electrocardiography-gated scan, followed by a retrospective electrocardiography-gated scan. Images were reviewed to determine the optimal scan timing and R-R interval in non-electrocardiography- and electrocardiography-gated images, respectively, for detailed coronary artery imaging, diagnostic quality of the best coronary artery visualisation in non-electrocardiography- and electrocardiography-gated images through visual assessment of the main coronary artery branches, and branching patterns of the left coronary artery. Further, we compared the size and margin demarcation of the heart or pericardial lesions in non-electrocardiography- and electrocardiography-gated images obtained from patients with heart or pericardial tumours. The optimal scan timing and R-R interval were the second-scan timing and end-diastole (70%-90%), respectively. Second-scan non-electrocardiography-gated images allowed coronary artery evaluation, indicating high-grade quality in visual assessment, except for the septal branch. Electrocardiography-gated images, but not non-ECG-gated images, clearly revealed pericardial nodules in two dogs. Our findings suggest the respective clinical utilities of non-electrocardiography- or electrocardiography-gated imaging using high-slice cardiac computed tomography based on patient history.

Evaluation of the feasibility of cardiac gating for SBRT of ventricular tachycardia based on real-time ECG signal acquisition.

To investigate the feasibility of cardiac synchronized gating in stereotactic body radiation therapy (SBRT) of ventricular tachycardia (VT) using a real-time electrocardiogram (ECG) signal acquisition. Stability of beam characteristics during simulated ECG gating was examined by developing a microcontroller interface to a Varian Clinac iX linear accelerator allowing gating at frequencies and duty cycles relevant to cardiac rhythm. Delivery accuracy was evaluated by measuring dose linearity with an ionization chamber, and flatness and symmetry with a two-dimensional detector array, for different gating windows within typical human cardiac cycle periods. To establish a practical method of gating based on actual ECG signals, an AD8232 Heart Monitor board was used to acquire the ECG signal and synchronize the beam delivery. Real-time cardiac gated delivery measurements were performed for a single 10×10cm2 field and for a VT-SBRT plan using intensity-modulated radiation therapy (IMRT). Dose per monitor unit (MU) values were found to be linear within most gating windows investigated with maximum differences relative to non-gated delivery of <2% for gating windows ≥200ms and for >10MUs. Beam profiles for both gated and non-gated modes were also found to agree with maximum differences of 0.5% relative to central axis dose for all sets of beam-on/beam-off combinations. Comparison of dose distributions for intensity-modulated SBRT plans between non-gating and cardiac gating modes provided a gamma passing rate of 97.2% for a 2% 2mm tolerance. Beam output is stable with respect to linearity, flatness, and symmetry for gating windows within cardiac cycle periods. Agreement between dose distributions for VT-SBRT using IMRT in non-gated and cardiac cycle gated delivery modes shows that the proposed methodology is feasible. Technically, gating for delivery of SBRT for VT is possible with regard to beam stability.

A transparent virtual channel power gating method for on-chip network routers

Since static power gradually dominates on-chip network power, power gating has been widely studied as a way to mitigate this trend. Even though many power gating methods reduce static power, they introduce new problems such as higher latency and hardware overhead, network disconnections, and low scalability. A new power gating method is therefore needed that can effectively reduce static power without sacrificing the benefits of the on-chip network. In this paper, we propose an efficient power gating method for virtual channels. Firstly, neighboring routers no longer exchange and store each other’s power states with handshake signals, and each router independently decides when to sleep or wake up based on traffic loads. Secondly, in order to eliminate flit stalls and reduce network latency, we propose a modified credit-based flow control and provide a detailed hardware implementation. Finally, bypasses allow packets to reach processing elements (PEs) or downstream routers without waking up sleeping virtual channels, which reduces breakeven time (BET) violations and cumulative wake-up latency while ensuring network connectivity. Based on the evaluation, under real applications, the proposed power gating method reduces static energy by an average of 82.5% compared to the baseline, while increasing latency overhead by 13.7% and area overhead by 6.48%.

System requirements to improve adaptive 4-dimensional computed tomography (4D CT) imaging

Four-Dimensional Computed Tomography (4D CT) is of increasing importance in stereotactic body radiotherapy (SBRT) treatments affected by respiratory motion. However, 4D CT images are commonly impacted by irregular breathing, causing image artifacts that can propagate through to treatment, negatively effecting local control. REspiratory Adaptive CT (REACT) is a real-time gating method demonstrated to reduce motion artifacts by avoiding imaging during irregular respiration. Despite artifact reduction seen through in silico and clinical phantom-based studies, REACT has not been able to remove all artifacts. Here, we explore several hardware and software latencies (gantry rotation time, couch shifts, acquisition delays and phase calculation method) inherently linked to REACT and 4D CT in general and investigate their contribution to artifacts beyond those caused by irregular breathing. Imaging was simulated using the digital extended cardiac-torso (XCAT) phantom for fifty patient-measured respiratory traces. Imaging protocols included conventional cine 4D CT and five REACT scans with systematically varied parameters to test the effect of different latencies on artifacts. Artifacts were quantified by comparing the image normalized cross correlation across couch transition points and determining the volume error compared to a static phantom ground truth both as a total error and individually across pixel rows in the main plane of motion. Artifacts were determined for each lung, the whole heart and lung tumour and were compared back to conventional 4D CT and REACT with standard clinical scanning parameters. The gantry rotation time and acquisition delay were found to have the largest impact on reducing image artifacts and should be the focus of future development. The phase calculation method was also found to influence motion artifacts and should potentially be assessed on a patient-to-patient basis. Finally, the correlation between an increase in artifacts and baseline drift suggests that longer scan times allowing drift to occur may impact image quality.

Clockless skyrmion logic gate based on voltage-controlled skyrmion propagation

Magnetic skyrmions are nanoscale topologically nontrivial spin texture that offer great promise as information carriers for the next-generation spintronic computing schemes. However, the current skyrmion-based logic gates require precise control of skyrmion collisions through clocked synchronizers, which leads to the complexity of logic implementation. To address this challenge, we propose a clockless skyrmion logic gate that can be implemented into large-scale computing networks without skyrmions synchronization. The clockless operations are achieved in a cross-shaped skyrmion track based on the skyrmion gating method with the aid of the voltage-controlled magnetic anisotropy gate. A complete set of Boolean operations and a cascaded full adder can be realized through the different combinations of inputs and interconnections of these logic gates. This computing paradigm paves the way for the design of a highly efficient and robust computing architecture using fully skyrmion-based logic devices.

All-optical sampling of ultrashort laser pulses based on perturbed transient grating.

We propose and demonstrate an all-optical pulse sampling technique based on the transient grating (TG) procedure with perturbation, which provides a simple and robust manner to characterize an ultrashort laser pulse without employing a retrieval algorithm. In our approach, a two-orders weaker perturbation pulse perturbs the diffracted pulse from the TG, which is generated by another strong fundamental pulse. The modulation of the diffracted pulse energy directly represents the temporal profile of the perturbation pulse. We have successfully characterized few-cycle and multi-cycle pulses, which is consistent with the results verified by the widely employed frequency-resolved optical gating (FROG) method. Our method provides a potential way to characterize ultrashort laser waveform from the deep-UV to far-infrared region.

(CRISPR/Cas9 Cassette Construction for OsARF2 Gene Editing and Development of Transgenic Rice Nipponbare Containing CRISPR/Cas9-OsARF2

&lt;p&gt;High Affinity K+ transporter 5 (HAK5) is one of the K + channel that involves in K + uptake. HAK5 gene expression is repressed under K + sufficient condition by the Auxin Response Factor 2 (ARF2) transcription factor. K + absorption can be increased by inactivation of ARF2 gene, e.g. by directed mutation using CRISPR/Cas9 method. The aims of this study were to create CRISPR/Cas9 construct carrying gRNA of OsARF2 gene and obtain transgenic rice Nipponbare containing CRISPR/Cas9- gRNAOsARF2. Two different sites in OsARF2 gene were succesfully designed as gRNA of the gene. Both oligo duplex RNA guides, gRNAOsARF2-A and gRNAOsARF2-B, were ligated into pDIRECT_21A plasmid using Golden Gate method. CRISPR/Cas9-gRNAOsARF2-A and CRISPR/Cas9-gRNAOsARF2-B cassettes were succesfully introduced separately into japonica rice cv. Nipponbare genome via Agrobacterium-mediated transformation, resulting putative transgenic lines. Analysis of Cas9 gene integration by PCR showed that 11 of 28 N-ARF-2-A putative transgenic lines contained Cas9 transgene. The sequencing analysis of the two selected lines showed that the OsARF2 gene of the CRISPR/Cas9-gRNAOsARF2 construct had not been mutated. Further studies are needed to determine the presence of mutations in the OsARF2 gene from other T0 transgenic lines obtained in this study together with that of the T1 transgenic lines.&lt;/p&gt;

A Monopole-Based Wideband Absorber for Ultralarge Angles

This article develops a broadband absorber by fully using the radiation features of monopole antennas for ultrawide-angle absorption application. A unit cell (UC) based on monopole antennas is proposed, and its working polarization is analyzed with the antenna reciprocity method and image theory. A wide-angle impedance matching layer is also introduced to further enhance the absorption at large angles. The optimized monopole-based UC reveals 90% absorptivity from 5.5–14.76 GHz at the incident angle of 80°. To the best of our knowledge, this is the first time to report an absorber that can work perfectly under such ultrawide angles in a broadband manner. An 11 × 36 array is configured and simulated to verify the effectiveness of the monopole-based UC. The monostatic and bistatic scattering are both reduced significantly as well as other diffuse scattering directions from the simulated results. A prototype of 110 mm × 360 mm is fabricated and measured. Time gating methods are adopted to diminish the direct coupling effect. The measurements are in good agreement with the full-wave simulation results.

Volumetric Fetal Flow Imaging With Magnetic Resonance Imaging.

Fetal development relies on a complex circulatory network. Accurate assessment of flow distribution is important for understanding pathologies and potential therapies. In this paper, we demonstrate a method for volumetric imaging of fetal flow with magnetic resonance imaging (MRI). Fetal MRI faces challenges: small vascular structures, unpredictable motion, and inadequate traditional cardiac gating methods. Here, orthogonal multislice stacks are acquired with accelerated multidimensional radial phase contrast (PC) MRI. Slices are reconstructed into flow sensitive time-series images with motion correction and image-based cardiac gating. They are then combined into a dynamic volume using slice-to-volume reconstruction (SVR) while resolving interslice spatiotemporal coregistration. Compared to prior methods, this approach achieves higher spatiotemporal resolution ( 1×1×1 mm3, ~30 ms) with reduced scan time - important features for the quantification of flow through small fetal structures. Validation is demonstrated in adults by comparing SVR with 4D radial PCMRI (flow bias and limits of agreement: -1.1 ml/s and [-11.8 9.6] ml/s). Feasibility is demonstrated in late gestation fetuses by comparing SVR with 2D Cartesian PCMRI (flow bias and limits of agreement: -0.9 ml/min/kg and [-39.7 37.8] ml/min/kg). With SVR, we demonstrate complex flow pathways (such as parallel flow streams in the proximal inferior vena cava, preferential shunting of blood from the ductus venosus into the left atrium, and blood from the brain leaving the heart through the main pulmonary artery) for the first time in human fetal circulation. This method allows for comprehensive evaluation of the fetal circulation and enables future studies of fetal physiology.

Generation of Intense Low-Divergence Isolated Soft-X-Ray Attosecond Pulses in a Gas-Filled Waveguide Using Three-Color Synthesized Laser Pulses

Isolated attosecond pulses (IAPs) in the soft-x-ray (SXR) region have been successfully produced via high-order harmonic generation in a gas medium at several laboratories, but pulse energies are much lower compared to the IAPs in the extreme ultraviolet. Here, we show that in a gas-filled hollow waveguide, an efficient gating method using a few-cycle three-color synthesizer is able to generate stronger SXR IAPs. We show that an 104-as IAP in the SXR region (central energy of 210 eV) with a higher pulse energy (0.9 nJ) and a lower divergence (within 1.5 mrad) can be generated with a three-color laser beam for input pulse energy at 0.62 mJ, under the condition of optimal gas pressure and waveguide length. The enhancement of the IAP is attributed to favorable phase matching of SXR high harmonics caused by the evolution of the three-color waveform during its propagation in the waveguide, which can be understood by analyzing the time shift of the waveform due to the interplay of the waveguide mode, atomic dispersion, and plasma dispersion. We check that the gating method is quite robust with respect to the phase jitter in the waveform. The advantage of this method is further demonstrated by comparing the generation of SXR high harmonics and attosecond pulses with two other schemes: the three-color waveform in a gas cell and a previously optimized two-color waveform in a gas-filled waveguide.

Accurate identification of cell doublet profiles: Comparison of light scattering with fluorescence measurement techniques.

Doublet discrimination is usually based on pulse analysis of light scatter parameters. A combination of two pulse parameters (Area, A; Height, H; or Width, W) can be used to discriminate a pulse originated in a single cell from a pulse originated from cells stuck together. Fluorescence signals can be also used to discriminate aggregates, being essential to identify cells in the G2/M phase from doublets in the G0/G1 phase in cell cycle/DNA applications. The most used method combines FSC-A versus FSC-H, whereas other strategies combine FSC-H versus FSC-W, SSC-H versus SSC-A and SSC-H versus SSC-W. However, when studying activated or proliferating cells, scatter discrimination can be difficult. In this study, we have compared the use of light scattering with fluorescence measurement techniques for successful doublet discrimination for single cells. Effective use of FSC and SSC height, area and width are commonly used to eliminate aggregates. However, fluorescence-based methods using viable DNA stains provide a good compromise between performance and accurate manual gating methods, especially for highly concentrated cell products and pathological specimens. Viable DNA dyes, such as Vybrant™ DyeCycle™ Violet stain or Hoechst 33342, can be used to detect nucleated cells in blood and in bone marrow, or to discriminate cell aggregates and debris based on no-lyse no-wash assays, where scatter degradation is a dominant component of the measured data, which increases with event rate.

Relative superiority of the revised Lund-Malmö equation over 22 other equations used for glomerular filtration rate estimation in undialyzed patients with end-stage renal disease.

The glomerular filtration rate (GFR) is an important indicator of renal function, and its precise measurement is essential for guiding clinical management. However, studies evaluating the performance of GFRestimation equations in undialyzed patients with end‑stage renal disease (ESRD) remain scarce. Our work sought to identify a relatively accurate equation for estimating the residual renal function in undialyzed patients with ESRD. We used the revised Gates method as the gold standard to measure GFR in 101 undialyzed patients with ESRD. We used a total of 23 equations (CKD‑EPIScr, MDRDII, FASScr, EKFC, revised Lund‑Malmö (LMR), Mayo, XiangYa, XiangYa‑s, Vilar, Shafiβ2M, CKD‑EPISCysC, FASSCysC, CAPA, Hoek, Yang, CKD‑EPIScr‑SCysC, FASScr‑SCysC, Adachi, ShafiβTP, ShafiβTP‑β2M, Wong, CKD‑EPI_3M, and CKD‑EPI_4M) to estimate the patients' GFR. The GFR measured by the dual plasma sampling method (dGFR) and the revised Gates method (rGFR) showed high agreement. The median dGFR and rGFR were 13.1 ml/min/1.73 m2 and 10.7 ml/min/1.73 m2, respectively. In the investigated population, the LMR equation showed a low bias (median, 0.6), high precision (interquartile range [IQR], -3.25 to 1.05), and the highest accuracy (P30, defined as the percentage of eGFR within 30% [70%-130%] of rGFR, 65.3%). Based on comparison of 23 equations, we recommend using the LMR equation, despite its large deviations, to estimate GFR in undialyzed patients with ESRD.

Fetal Cardiovascular MRI - A Systemic Review of the Literature: Challenges, New Technical Developments, and Perspectives.

Fetal magnetic resonance imaging (MRI) has become a valuable adjunct to ultrasound in the prenatal diagnosis of congenital pathologies of the central nervous system, thorax, and abdomen. Fetal cardiovascular magnetic resonance (CMR) was limited, mainly by the lack of cardiac gating, and has only recently evolved due to technical developments. A literature search was performed on PubMed, focusing on technical advancements to perform fetal CMR. In total, 20 publications on cardiac gating techniques in the human fetus were analyzed. Fetal MRI is a safe imaging method with no developmental impairments found to be associated with in utero exposure to MRI. Fetal CMR is challenging due to general drawbacks (e. g., fetal motion) and specific limitations such as the difficulty to generate a cardiac gating signal to achieve high spatiotemporal resolution. Promising technical advancements include new methods for fetal cardiac gating, based on novel post-processing approaches and an external hardware device, as well as motion compensation and acceleration techniques. Newly developed direct and indirect gating approaches were successfully applied to achieve high-quality morphologic and functional imaging as well as quantitative assessment of fetal hemodynamics in research settings. In cases when prenatal echocardiography is limited, e. g., by an unfavorable fetal position in utero, or when its results are inconclusive, fetal CMR could potentially serve as a valuable adjunct in the prenatal assessment of congenital cardiovascular malformations. However, sufficient data on the diagnostic performance and clinical benefit of new fetal CMR techniques is still lacking. · New fetal cardiac gating methods allow high-quality fetal CMR.. · Motion compensation and acceleration techniques allow for improvement of image quality.. · Fetal CMR could potentially serve as an adjunct to fetal echocardiography in the future.. · Knapp J, Tavares de Sousa M, Schönnagel BP. Fetal Cardiovascular MRI - A Systemic Review of the Literature: Challenges, New Technical Developments, and Perspectives. Fortschr Röntgenstr 2022; 194: 841 - 851.

Range Intensity Profiles of Multi-Slice Integration for Pulsed Laser Range-Gated Imaging System

Pulsed laser range-gated imaging (PLRGI) is one of the most effective methods to achieve underwater high-resolution imaging. When searching target, there are two methods can be used: fixed gate and sliding gate. In practice, fixed gate has a small depth of field of view and sliding gate cannot meet the need of real time. In order to overcome these problems, multi-slice integration (MSI) method is proposed in this paper. First, the laser energy received by the PLRGI system is derived from radiative transfer theory. In addition, range intensity profiles (RIP) of MSI method is established. Experiments are carried out in lab to validate the RIP model and results show that theoretical data and experimental data are in good coincidence. Then the gate width and the number of pulse assigned to each slice are discussed. Finally, to prove the effectiveness of the MSI method, experiments are carried out in a boat tank. Results show that the MSI method is better than the fixed gate method for surveillance, and can acquire a clear image of the target at 18 m (4.5 times of the attenuation length) in the water with attenuation coefficient of 0.25 m−1.

Dynamic mass loss from Greenland's marine-terminating peripheral glaciers (1985–2018)

AbstractGlobal glacier mass balance decreased rapidly over the last two decades, exceeding mass loss from the Greenland and Antarctic Ice Sheets. In Greenland, peripheral glaciers and ice caps (GICs) cover only ~5% of Greenland's area but contributed ~20% of the island's ice mass loss between 2000 and 2018. Although Greenland GIC mass loss due to surface meltwater runoff has been estimated using atmospheric models, mass lost to changes in ice discharge into oceans (i.e., dynamic mass loss) remains unquantified. We use the flux gate method to estimate discharge from Greenland's 585 marine-terminating peripheral glaciers between 1985 and 2018, and compute dynamic mass loss as the discharge anomaly relative to the 1985–98 period. Greenland GICs discharged between 2.94 ± 0.23 and 4.03 ± 0.23 Gt a−1from 1985 to 1998, depending on the gap-filling method, and abruptly increased to 5.10 ± 0.21 Gt a−1from 1999 to 2018. The resultant ~1–2 Gt a−1dynamic mass loss was driven by synchronous widespread acceleration around Greenland. The mass loss came predominantly from the southeast region, which contains 39% of the glaciers. Although changes in discharge over time were small relative to surface mass-balance changes, our speed and discharge time series suggest these glaciers may quickly accelerate in response to changes in climate.

Bi-Static Radar Cross-Section Test Method by using Historic Marconi Set-up and Time Gating

In this paper, a low-cost, simple, and reliable bi-static radar cross-section (RCS) measurement method by using a historic Marconi set-up is presented. It uses a transmitting (Tx) antenna (located at a constant position, at a reference angle of θ=0∘θ=0∘) and a moving receiver (Rx) antenna. A time gating method is used to extract the information from the reflection in the time domain; applying time filter allows removing the antenna side-lobe effects and other ambient noises. In this method, the Rx antenna (on the movable arm) is used to measure the reflected field in the angular range from 1∘1∘ to 90∘90∘ from the structure (printed circuit board, PCB) and the reference configuration represented by a ground (GND) plane of the same dimension. The time gating method is then applied to each pair of PCB/GND measurements to extract the bi-static RCS pattern of the structure at a given frequency. Here, a comparison of measurement results is carried out at 18 and 32 GHz with simulation ones indicating successful performance of the proposed method. It can be used as a low-cost, reliable, and available option in future measurement and scientificresearch.

Deep regression using 99mTc-DTPA dynamic renal imaging for automatic calculation of the glomerular filtration rate.

To develop and evaluate an artificial intelligence (AI) system that can automatically calculate the glomerular filtration rate (GFR) from dynamic renal imaging without manually delineating the regions of interest (ROIs) of kidneys and the corresponding background. This study was a single-center retrospective analysis of the data of 14,634 patients who underwent 99mTc-DTPA dynamic renal imaging. Two systems based on convolutional neural networks (CNN) were developed and evaluated: sGFRa predicts the radioactive counts of ROIs and calculates GFR using the Gates equation and sGFRb directly predicts GFR from dynamic renal imaging without using other information. The root-mean-square error (RMSE), mean absolute error (MAE), mean absolute percentage error (MAPE), and R2 were used to evaluate the performance of our approach. sGFRa achieved an RMSE of 5.05, MAE of 4.03, MAPE of 6.07%, and R2 of 0.93 for total GFR while sGFRb achieved an RMSE of 7.61, MAE of 5.92, MAPE of 8.92%, and R2 of 0.85 for total GFR. The accuracy of sGFRa and sGFRb in determining the stage of chronic kidney disease was 87.41% and 82.44%, respectively. The findings of sGFRa show that automatic GFR calculation based on CNN and using dynamic renal imaging is feasible and efficient and, additionally, can aid clinical diagnosis. Furthermore, the promising results of sGFRb demonstrate that CNN can predict GFR from dynamic renal imaging without additional information. • Our CNN-based AI systems can automatically calculate GFR from dynamic renal imaging without manually delineating the ROIs of kidneys and the corresponding background. • sGFRa accurately predicted the radioactive counts of ROIs and calculated GFR using the Gates method. • sGFRb-predicted GFR directly without any parameters related to the Gates equation.

(Invited, Digital Presentation) Ultra-Low Thermal Conductance across Hetero-Structured Four-Layered Van Der Waals Materials

Tuning the thermal properties of materials and exploring their heat transport mechanisms are of critical significance for optimizing the performance of current electronic and thermoelectric devices. Regarding flexible thermoelectric, recently, gigantic power factor is achieved in carbon nanotube fibers with tuned Fermi energy level [1]. Thus, control of heat transport across van der Waals (vdW) interfaces, which are the origins of flexibility, is very important for improvement of thermoelectric conversion efficiency. Considering that thermal transport is mainly affected by phonon-boundary scattering, development a route to tune such scattering at vdW interfaces is important. Ultrathin two-dimensional (2D) materials have been widely studied in electronic and photonic fields due to the distinctly unique geometrical and electronic structures of such materials. Regarding thermal transport properties, they have a lot of degrees of freedom in their integration, and the layered vdW integrated structure of these materials, in which building blocks are physically assembled together through weak vdW interactions, provides a strategy to reduce thermal conductance. The rich interfacial lattice mismatch in layered vdW structures is promising for enhancing phonon-boundary scattering at interfaces. For instance, Vaziri et al. studied the thermal boundary resistance of various heterointerfaces via the stacking of exfoliated several-micron-sized graphene, MoS2, and WSe2 monolayers using Raman thermometry, suggesting great potential for controlling heat flow by using the interfaces of vdW heterostructures [2]. However, there has been no systematic study on how homo- and hetero-interfaces with or without lattice matches influence heat flow. Therefore, a systematic study on the thermal conductance (G) of vdW structures with various comparable interfaces is urgently required to understand how homo- and heterointerfaces and the coupling effect influence thermal transport. Here we demonstrate the thermal conductance across four layered (4L) homo- and hetero-structured MoS2 and MoSe2 using time-domain thermo-reflectance method. Compared with the thermal conductance of homo-structured sample, the thermal conductance across hetero-structured 4L sample was significantly reduced, indicating that hetero-interface is an efficient way to reduce thermal conductance [3]. In addition, we have combined electrochemical gating method and TDTR measurements, and employed our technique on the 4L sample and investigated how the intercalation can influence the thermal conductance on the 4L sample. In this presentation, I would like to discuss our recent results.