An electromagnetic optimization technique based on a long short-term memory–feedforward neural network (LSTM-FNN) and transfer functions is proposed for microwave filter design. The proposed optimization method addresses the situation where a neuro-transfer function model repeatedly trains at each optimization iteration process. The proposed surrogate model combines the LSTM-FNN and polynomial model to map nonlinear relationships between geometric variables and transfer functions. Firstly, by combining the gate mechanism of LSTM with the high generalization ability of an FNN, the proposed LSTM-FNN effectively learns nonlinear relationships between geometric variables and frequency responses at specific frequencies. Secondly, the transfer functions can be accurately approximated via polynomial fitting. Frequency responses at any interesting frequency range can be accurately expressed using the transfer functions. Finally, the trained surrogate model, exploiting the trust-region algorithm, can accurately and efficiently achieve optimization convergence. An example of a low-pass filter (LPF) is adopted to validate the proposed optimization method.
{"title":"EM optimization of microwave filter based on long short-term memory–feedforward neural network and transfer functions","authors":"Xin Zhang, Jian Wu, Yong-Qiang Chai, Shui Liu, Yuan Peng","doi":"10.1088/1361-6463/ad6fb1","DOIUrl":"https://doi.org/10.1088/1361-6463/ad6fb1","url":null,"abstract":"An electromagnetic optimization technique based on a long short-term memory–feedforward neural network (LSTM-FNN) and transfer functions is proposed for microwave filter design. The proposed optimization method addresses the situation where a neuro-transfer function model repeatedly trains at each optimization iteration process. The proposed surrogate model combines the LSTM-FNN and polynomial model to map nonlinear relationships between geometric variables and transfer functions. Firstly, by combining the gate mechanism of LSTM with the high generalization ability of an FNN, the proposed LSTM-FNN effectively learns nonlinear relationships between geometric variables and frequency responses at specific frequencies. Secondly, the transfer functions can be accurately approximated via polynomial fitting. Frequency responses at any interesting frequency range can be accurately expressed using the transfer functions. Finally, the trained surrogate model, exploiting the trust-region algorithm, can accurately and efficiently achieve optimization convergence. An example of a low-pass filter (LPF) is adopted to validate the proposed optimization method.","PeriodicalId":16789,"journal":{"name":"Journal of Physics D: Applied Physics","volume":"35 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142222998","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-05DOI: 10.1088/1361-6463/ad7302
Edoardo Negri, Walter Fuscaldo, Paolo Burghignoli, Alessandro Galli
Graphene ohmic losses notably hinder the efficiency of graphene-based terahertz (THz) devices. Hybrid metal–graphene structures have recently been proposed to mitigate this issue in a few passive devices, namely waveguide and Vivaldi antennas, as well as frequency selective surfaces. In this work, such a technique is extensively investigated to optimize the radiation performance of a THz Fabry–Perot cavity leaky-wave antenna based on a hybrid metal–graphene metasurface consisting of a lattice of square metallic patches interleaved with a complementary graphene strip grating. Theoretical, numerical, and full-wave results demonstrate that, by properly selecting the unit-cell features, a satisfactory trade-off among range of reconfigurability, antenna directivity, and losses can be achieved. The proposed antenna can find application in future wireless THz communications.
{"title":"Reconfigurable THz leaky-wave antennas based on innovative metal–graphene metasurfaces","authors":"Edoardo Negri, Walter Fuscaldo, Paolo Burghignoli, Alessandro Galli","doi":"10.1088/1361-6463/ad7302","DOIUrl":"https://doi.org/10.1088/1361-6463/ad7302","url":null,"abstract":"Graphene ohmic losses notably hinder the efficiency of graphene-based terahertz (THz) devices. Hybrid metal–graphene structures have recently been proposed to mitigate this issue in a few passive devices, namely waveguide and Vivaldi antennas, as well as frequency selective surfaces. In this work, such a technique is extensively investigated to optimize the radiation performance of a THz Fabry–Perot cavity leaky-wave antenna based on a hybrid metal–graphene metasurface consisting of a lattice of square <italic toggle=\"yes\">metallic</italic> patches interleaved with a complementary <italic toggle=\"yes\">graphene</italic> strip grating. Theoretical, numerical, and full-wave results demonstrate that, by properly selecting the unit-cell features, a satisfactory trade-off among range of reconfigurability, antenna directivity, and losses can be achieved. The proposed antenna can find application in future wireless THz communications.","PeriodicalId":16789,"journal":{"name":"Journal of Physics D: Applied Physics","volume":"59 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142223001","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-05DOI: 10.1088/1361-6463/ad70c4
Wenxiong Xu, Feiyang Hou, He Zhang, Chuansheng Xia, Zhixuan Li, Yuanyuan Li, Chunxiang Xu, Qiannan Cui
Coherent acoustic phonon (CAP) oscillation of a 2D layered semiconductor/3D dielectric heterostructure generated by femtosecond laser pulse excitation can realize ultrafast photoacoustic conversion by emitting picosecond acoustic (PA) pulse; however, the photoacoustic conversion efficiency suffers from interfacial phonon scattering of simultaneously laser-induced lattice heat. Here, taking advantage of graphene’s high thermal conductivity and large acoustic impedance, we demonstrate that phonon scattering can be markedly mediated in a MoS2/graphene/glass heterostructure via femtosecond laser pump–probe measurements. The equilibrium temperatures of the MoS2 lattice have been cooled down by about 45%. As a benefit, both the lifetime of CAP oscillations and the pump pulse-picosecond acoustic pulse energy conversion efficiency have been enhanced by a factor of about 2. Our results offer insights into CAP and PA pulse manipulations via interfacial engineering that are fundamentally important for ultrafast photoacoustics based on 2D layered semiconductors.
飞秒激光脉冲激发二维层状半导体/三维电介质异质结构产生的相干声子（CAP）振荡可以通过发射皮秒声子（PA）脉冲实现超快光声转换；然而，光声转换效率却受到同时激光诱导的晶格热的界面声子散射的影响。在这里，我们利用石墨烯的高热导率和大声阻抗，通过飞秒激光泵浦探针测量证明了声子散射在 MoS2/石墨烯/玻璃异质结构中的显著介导作用。MoS2 晶格的平衡温度降低了约 45%。我们的研究结果为通过界面工程操纵 CAP 和 PA 脉冲提供了见解，这对于基于二维层状半导体的超快光声学具有根本性的重要意义。
{"title":"Mediating coherent acoustic phonon oscillation of a 2D semiconductor/3D dielectric heterostructure by interfacial engineering","authors":"Wenxiong Xu, Feiyang Hou, He Zhang, Chuansheng Xia, Zhixuan Li, Yuanyuan Li, Chunxiang Xu, Qiannan Cui","doi":"10.1088/1361-6463/ad70c4","DOIUrl":"https://doi.org/10.1088/1361-6463/ad70c4","url":null,"abstract":"Coherent acoustic phonon (CAP) oscillation of a 2D layered semiconductor/3D dielectric heterostructure generated by femtosecond laser pulse excitation can realize ultrafast photoacoustic conversion by emitting picosecond acoustic (PA) pulse; however, the photoacoustic conversion efficiency suffers from interfacial phonon scattering of simultaneously laser-induced lattice heat. Here, taking advantage of graphene’s high thermal conductivity and large acoustic impedance, we demonstrate that phonon scattering can be markedly mediated in a MoS<sub>2</sub>/graphene/glass heterostructure via femtosecond laser pump–probe measurements. The equilibrium temperatures of the MoS<sub>2</sub> lattice have been cooled down by about 45%. As a benefit, both the lifetime of CAP oscillations and the pump pulse-picosecond acoustic pulse energy conversion efficiency have been enhanced by a factor of about 2. Our results offer insights into CAP and PA pulse manipulations via interfacial engineering that are fundamentally important for ultrafast photoacoustics based on 2D layered semiconductors.","PeriodicalId":16789,"journal":{"name":"Journal of Physics D: Applied Physics","volume":"5 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142222999","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-05DOI: 10.1088/1361-6463/ad7270
Chunmin Cheng, Xiang Sun, Wei Shen, Qijun Wang, Lijie Li, Fang Dong, Kang Liang, Gai Wu
The utilization of diamond, the ultimate semiconductor, in electronic devices is challenging due to the difficulty of n-type doping. Phosphorus (P)-doped diamond, the most prevalent type of n-type diamond, is still limited by the low solubility of P dopant and undesirable compensating defects such as vacancy defects and hydrogen incorporation. In order to overcome this limitation, strain engineering is introduced to the n-type P-doped diamond theoretically in this work. Uniaxial, equibiaxial, and hydrostatic triaxial strains are applied to the P-doped diamond. The formation energy, charge transition level, defect binding energy and other physical properties of the P-doped diamond are then calculated based on first-principles calculations. The results show that uniaxial, equibiaxial, and hydrostatic triaxial tensile strain can reduce the formation energy and the donor ionization energy of P dopant, and also reduce the binding energy of phosphorus–vacancy (PV) and phosphorus–hydrogen (PH) defects. Our results indicate that under tensile strain, the solubility of the P dopant and the n-type conductivity of the P-doped diamond can be increased, and the formation of compensating defects can be suppressed. Therefore, strain engineering is anticipated to be used to enhance the n-type characteristics of the P-doped diamond, facilitating its application in electronic devices.
由于难以进行 n 型掺杂，在电子设备中利用金刚石这种终极半导体具有挑战性。磷（P）掺杂金刚石是最常见的 n 型金刚石，但仍受限于 P 掺杂剂的低溶解度以及空位缺陷和氢结合等不良补偿缺陷。为了克服这一局限性，本研究从理论上将应变工程引入 n 型 P 掺杂金刚石。对掺杂 P 的金刚石施加了单轴、等轴和静压三轴应变。然后根据第一性原理计算了掺 P 金刚石的形成能、电荷转移水平、缺陷结合能和其他物理性质。结果表明，单轴、等轴和静压三轴拉伸应变能降低掺杂 P 的形成能和供体电离能，也能降低磷-空位（PV）和磷-氢（PH）缺陷的结合能。我们的研究结果表明，在拉伸应变条件下，掺杂 P 的金刚石的 P 溶解度和 n 型电导率可以提高，补偿缺陷的形成也会受到抑制。因此，应变工程有望用于增强掺杂 P 的金刚石的 n 型特性，从而促进其在电子设备中的应用。
{"title":"Enhancing n-type doping in diamond by strain engineering","authors":"Chunmin Cheng, Xiang Sun, Wei Shen, Qijun Wang, Lijie Li, Fang Dong, Kang Liang, Gai Wu","doi":"10.1088/1361-6463/ad7270","DOIUrl":"https://doi.org/10.1088/1361-6463/ad7270","url":null,"abstract":"The utilization of diamond, the ultimate semiconductor, in electronic devices is challenging due to the difficulty of n-type doping. Phosphorus (P)-doped diamond, the most prevalent type of n-type diamond, is still limited by the low solubility of P dopant and undesirable compensating defects such as vacancy defects and hydrogen incorporation. In order to overcome this limitation, strain engineering is introduced to the n-type P-doped diamond theoretically in this work. Uniaxial, equibiaxial, and hydrostatic triaxial strains are applied to the P-doped diamond. The formation energy, charge transition level, defect binding energy and other physical properties of the P-doped diamond are then calculated based on first-principles calculations. The results show that uniaxial, equibiaxial, and hydrostatic triaxial tensile strain can reduce the formation energy and the donor ionization energy of P dopant, and also reduce the binding energy of phosphorus–vacancy (PV) and phosphorus–hydrogen (PH) defects. Our results indicate that under tensile strain, the solubility of the P dopant and the n-type conductivity of the P-doped diamond can be increased, and the formation of compensating defects can be suppressed. Therefore, strain engineering is anticipated to be used to enhance the n-type characteristics of the P-doped diamond, facilitating its application in electronic devices.","PeriodicalId":16789,"journal":{"name":"Journal of Physics D: Applied Physics","volume":"29 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142223000","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-05DOI: 10.1088/1361-6463/ad73e3
Rabia Hassan, Fei Ma, Yan Li, Rehan Hassan
Defect engineering is a powerful strategy for enhancing the catalytic properties of monolayer VSe2. In this work, we used density functional theory (DFT) to investigate the impact of point defects and hydrogen adsorption sites on the hydrogen evolution reaction (HER) activity of VSe2. We analyzed the formation energies and hydrogen adsorption behavior of single and double vacancies in VSe2. The results show that V vacancy defect (D2), consecutive V-Se double vacancy defect (D3), and separate V-Se double defect (D4) exhibit the enhanced HER activity with Gibbs free energies (ΔGH* = 0.04 eV, 0.04 eV and 0.06 eV, respectively) even surpassing that of platinum (ΔGH* = − 0.1 eV). This study highlights the potential of defect-engineered VSe2 for efficient hydrogen evolution.
{"title":"Defect engineering strategies in monolayer VSe2 for enhanced hydrogen evolution reaction: a computational study","authors":"Rabia Hassan, Fei Ma, Yan Li, Rehan Hassan","doi":"10.1088/1361-6463/ad73e3","DOIUrl":"https://doi.org/10.1088/1361-6463/ad73e3","url":null,"abstract":"Defect engineering is a powerful strategy for enhancing the catalytic properties of monolayer VSe<sub>2</sub>. In this work, we used density functional theory (DFT) to investigate the impact of point defects and hydrogen adsorption sites on the hydrogen evolution reaction (HER) activity of VSe<sub>2</sub>. We analyzed the formation energies and hydrogen adsorption behavior of single and double vacancies in VSe<sub>2</sub>. The results show that V vacancy defect (D2), consecutive V-Se double vacancy defect (D3), and separate V-Se double defect (D4) exhibit the enhanced HER activity with Gibbs free energies (Δ<italic toggle=\"yes\">G</italic><sub>H</sub>* = 0.04 eV, 0.04 eV and 0.06 eV, respectively) even surpassing that of platinum (Δ<italic toggle=\"yes\">G</italic><sub>H</sub>* = − 0.1 eV). This study highlights the potential of defect-engineered VSe<sub>2</sub> for efficient hydrogen evolution.","PeriodicalId":16789,"journal":{"name":"Journal of Physics D: Applied Physics","volume":"61 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142223003","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Liver fibrosis plays a crucial role in the progression of liver diseases and serves as a pivotal stage leading to the development of liver cirrhosis and cancer. It typically initiates from portal area with various pathological characteristics. In this article, we employed multiphoton microscopy (MPM) to characterize the pathological changes in the portal areas of liver fibrosis tissues, and subsequently, we used our developed image analysis method to extract eight collagen morphological features from MPM images and also combined a deep learning method with a cell nuclear feature extraction algorithm to perform automatic nuclei segmentation and quantitative analysis in the H&E-stained histopathology images of portal areas. Our results demonstrate that MPM can effectively identify various pathological features in portal areas, and there are significant differences in four collagen features (collagen proportionate area, number, length and width) between normal and abnormal portal areas and in four nuclear features (mean ratio of axial length, disorder of distance to 3, 5 and 7 nearest neighbors) between normal portal area, bile duct hyperplasia and periductal fibrosis. Therefore, a combination of MPM and image-based quantitative analysis may be considered as a rapid and effective means to monitor histopathological changes in portal area and offer new insights into liver fibrosis.
{"title":"Label-free characterization of pathological changes in the portal area of liver fibrosis tissue using multiphoton imaging and quantitative image analysis","authors":"Xiong Zhang, Yuan-E Lian, XunBin Yu, Xingxin Huang, Zheng Zhang, Jingyi Zhang, Jianxin Chen, Lianhuang Li, Yannan Bai","doi":"10.1088/1361-6463/ad73e6","DOIUrl":"https://doi.org/10.1088/1361-6463/ad73e6","url":null,"abstract":"Liver fibrosis plays a crucial role in the progression of liver diseases and serves as a pivotal stage leading to the development of liver cirrhosis and cancer. It typically initiates from portal area with various pathological characteristics. In this article, we employed multiphoton microscopy (MPM) to characterize the pathological changes in the portal areas of liver fibrosis tissues, and subsequently, we used our developed image analysis method to extract eight collagen morphological features from MPM images and also combined a deep learning method with a cell nuclear feature extraction algorithm to perform automatic nuclei segmentation and quantitative analysis in the H&E-stained histopathology images of portal areas. Our results demonstrate that MPM can effectively identify various pathological features in portal areas, and there are significant differences in four collagen features (collagen proportionate area, number, length and width) between normal and abnormal portal areas and in four nuclear features (mean ratio of axial length, disorder of distance to 3, 5 and 7 nearest neighbors) between normal portal area, bile duct hyperplasia and periductal fibrosis. Therefore, a combination of MPM and image-based quantitative analysis may be considered as a rapid and effective means to monitor histopathological changes in portal area and offer new insights into liver fibrosis.","PeriodicalId":16789,"journal":{"name":"Journal of Physics D: Applied Physics","volume":"5 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142223004","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-04DOI: 10.1088/1361-6463/ad714e
O D Schneble, I A Leahy, J D Zimmerman, M B Tellekamp
Transition metal oxides with insulator-metal transitions (IMTs) are uniquely suited for volatile memristor devices that mimic the spiking of biological neurons. Unlike most non-volatile memristors, which often operate via ion migration into filaments, volatile devices utilize a reversible phase change that returns to a ground state in the absence of applied stimulus. In these devices, Joule heating triggers the IMT and changes the bulk resistivity rather than influencing conduction through defects, as in previous studies. This volatile resistive switching behavior has previous been leveraged in niobium and vanadium oxides, but not in rare-earth nickelates, despite their tunable transition temperatures. This study demonstrates an electrically driven IMT in the prototypical rare-earth nickelate, NdNiO3, in large area devices. While previous work examining the electrically-driven IMT in NdNiO3 suggests defect-dominated conduction, this study shows clear s-type negative differential resistance (NDR) consistent with temperature-dependent resistivity measurements. The NDR peak-to-valley voltage scales linearly with temperature as expected for conductivity pathways dominated by bulk IMT behavior. Unlike other transition metal oxides, which are modeled using the insulator-metal phase fraction as the internal state variable, a thermoelectric model with temperature as the internal state variable is found to more accurately describe the current–voltage characteristic of NdNiO3 volatile memristors. Overall, we report the synthesis, fabrication, and characterization of NdNiO3 volatile memristors with resistivity dominated by bulk-like IMT behavior which is scalable and not dependent upon oxygen vacancy migration or defect mediated conduction pathways.
{"title":"Electrically-driven IMT and volatile memristor behavior in NdNiO3 films","authors":"O D Schneble, I A Leahy, J D Zimmerman, M B Tellekamp","doi":"10.1088/1361-6463/ad714e","DOIUrl":"https://doi.org/10.1088/1361-6463/ad714e","url":null,"abstract":"Transition metal oxides with insulator-metal transitions (IMTs) are uniquely suited for volatile memristor devices that mimic the spiking of biological neurons. Unlike most non-volatile memristors, which often operate via ion migration into filaments, volatile devices utilize a reversible phase change that returns to a ground state in the absence of applied stimulus. In these devices, Joule heating triggers the IMT and changes the bulk resistivity rather than influencing conduction through defects, as in previous studies. This volatile resistive switching behavior has previous been leveraged in niobium and vanadium oxides, but not in rare-earth nickelates, despite their tunable transition temperatures. This study demonstrates an electrically driven IMT in the prototypical rare-earth nickelate, NdNiO<sub>3</sub>, in large area devices. While previous work examining the electrically-driven IMT in NdNiO<sub>3</sub> suggests defect-dominated conduction, this study shows clear s-type negative differential resistance (NDR) consistent with temperature-dependent resistivity measurements. The NDR peak-to-valley voltage scales linearly with temperature as expected for conductivity pathways dominated by bulk IMT behavior. Unlike other transition metal oxides, which are modeled using the insulator-metal phase fraction as the internal state variable, a thermoelectric model with temperature as the internal state variable is found to more accurately describe the current–voltage characteristic of NdNiO<sub>3</sub> volatile memristors. Overall, we report the synthesis, fabrication, and characterization of NdNiO<sub>3</sub> volatile memristors with resistivity dominated by bulk-like IMT behavior which is scalable and not dependent upon oxygen vacancy migration or defect mediated conduction pathways.","PeriodicalId":16789,"journal":{"name":"Journal of Physics D: Applied Physics","volume":"7 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142223005","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-03DOI: 10.1088/1361-6463/ad7149
Qinqin Shao, Ruohan Shen, He Tian, Xiaodong Pi, Deren Yang, Rong Wang
4H silicon carbide (4H-SiC) is one of the most promising candidates in high-power and high-frequency devices, owing to its excellent properties such as wide bandgap, high electron mobility, high electric breakdown field and high thermal conductivity. The physical-vapor-transport (PVT) approach has been broadly adopted to grow 4H-SiC single-crystal boules. Because of the high-temperature growth of 4H-SiC single-crystal boules, the PVT system is a ‘black-box’ system, which decreases the yield and thus increases the cost of 4H-SiC single-crystals. Although advanced modern characterization tools, e.g. atomic force microscopy, x-ray topography, x-ray diffraction and Raman scattering spectroscopy, can provide deep insight into the structural and defect properties of 4H-SiC boules, it is rather limited to gain in-situ information of the growth process by these ex-situ methods. Therefore, the in-situ visualization on the evolution of structural morphologies and defects conducted by x-ray computed tomography (xCT) is of great importance for further development. In this topical review, the application of the xCT technology on the in-situ visualization of the evolution of the growth front, growth rate, defects, and the mass transport of the source material of 4H-SiC are reviewed. The ex-situ characterization of 4H-SiC single-crystal boules are also briefly introduced. This topical review provides insight into the growth process, structural morphology, and defect evolution of PVT-grown 4H-SiC single-crystal boules.
{"title":"In-situ and ex-situ characterizations of PVT-grown 4H-SiC single crystals","authors":"Qinqin Shao, Ruohan Shen, He Tian, Xiaodong Pi, Deren Yang, Rong Wang","doi":"10.1088/1361-6463/ad7149","DOIUrl":"https://doi.org/10.1088/1361-6463/ad7149","url":null,"abstract":"4H silicon carbide (4H-SiC) is one of the most promising candidates in high-power and high-frequency devices, owing to its excellent properties such as wide bandgap, high electron mobility, high electric breakdown field and high thermal conductivity. The physical-vapor-transport (PVT) approach has been broadly adopted to grow 4H-SiC single-crystal boules. Because of the high-temperature growth of 4H-SiC single-crystal boules, the PVT system is a ‘black-box’ system, which decreases the yield and thus increases the cost of 4H-SiC single-crystals. Although advanced modern characterization tools, e.g. atomic force microscopy, <italic toggle=\"yes\">x</italic>-ray topography, x-ray diffraction and Raman scattering spectroscopy, can provide deep insight into the structural and defect properties of 4H-SiC boules, it is rather limited to gain <italic toggle=\"yes\">in-situ</italic> information of the growth process by these <italic toggle=\"yes\">ex-situ</italic> methods. Therefore, the <italic toggle=\"yes\">in-situ</italic> visualization on the evolution of structural morphologies and defects conducted by <italic toggle=\"yes\">x</italic>-ray computed tomography (<italic toggle=\"yes\">x</italic>CT) is of great importance for further development. In this topical review, the application of the <italic toggle=\"yes\">x</italic>CT technology on the <italic toggle=\"yes\">in-situ</italic> visualization of the evolution of the growth front, growth rate, defects, and the mass transport of the source material of 4H-SiC are reviewed. The <italic toggle=\"yes\">ex-situ</italic> characterization of 4H-SiC single-crystal boules are also briefly introduced. This topical review provides insight into the growth process, structural morphology, and defect evolution of PVT-grown 4H-SiC single-crystal boules.","PeriodicalId":16789,"journal":{"name":"Journal of Physics D: Applied Physics","volume":"29 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142223017","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-03DOI: 10.1088/1361-6463/ad6e00
Yan Zhang, Zhaofu Zhang, Yuzheng Guo, John Robertson, Shijing Wu, Sheng Liu, Yunyun Sun
This review provides a comprehensive overview of recent advancements in molecular dynamics (MD) simulations of dry friction on rough substrates. While nanoscale roughness plays a crucial role in nanotribological investigations, the exploration of rough substrates remains insufficient based on MD simulations. This paper summarizes research on rough surfaces constructed from various descriptions, including the multi-asperity surface, groove-textured surface, fractal surface, Gaussian surface, stepped surface and randomly rough surface. In addition, the friction behavior of rough substrates coated with solid films is comprehensively elucidated. Present investigations on rough surfaces primarily focus on the effect of basic frictional variables, surface morphology characteristics and different motion types. The studies conducted on rough substrates exhibit a higher degree of resemblance to realistic interfaces, thereby offering valuable insight into the design of surface morphology to achieve enhanced frictional performance.
{"title":"Recent advances in molecular dynamics simulations for dry friction on rough substrate","authors":"Yan Zhang, Zhaofu Zhang, Yuzheng Guo, John Robertson, Shijing Wu, Sheng Liu, Yunyun Sun","doi":"10.1088/1361-6463/ad6e00","DOIUrl":"https://doi.org/10.1088/1361-6463/ad6e00","url":null,"abstract":"This review provides a comprehensive overview of recent advancements in molecular dynamics (MD) simulations of dry friction on rough substrates. While nanoscale roughness plays a crucial role in nanotribological investigations, the exploration of rough substrates remains insufficient based on MD simulations. This paper summarizes research on rough surfaces constructed from various descriptions, including the multi-asperity surface, groove-textured surface, fractal surface, Gaussian surface, stepped surface and randomly rough surface. In addition, the friction behavior of rough substrates coated with solid films is comprehensively elucidated. Present investigations on rough surfaces primarily focus on the effect of basic frictional variables, surface morphology characteristics and different motion types. The studies conducted on rough substrates exhibit a higher degree of resemblance to realistic interfaces, thereby offering valuable insight into the design of surface morphology to achieve enhanced frictional performance.","PeriodicalId":16789,"journal":{"name":"Journal of Physics D: Applied Physics","volume":"4 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142223015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A double-pulse femtosecond laser is used to process single-crystal silicon. Modulating the delay time was discovered to increase the ablation depth and improve the morphology of the ablated surface. The hole fabricated by a dual-pulse with a 200 ps interval is 24.4% deeper than that created by a single pulse of the same energy. Moreover, utilizing a dual pulse with an interval ranging from 100 to 1000 ps produces a considerably smoother ablation area as compared to the single pulse. The effect of the sub-pulse energy ratio of the double-pulse femtosecond laser on the size and morphology of the ablated area was also investigated. As the sub-pulse energy ratio decreases from 3:1 to 1:3, the size of the ablation area initially decreases and then increases, while the size of the ablation area is minimized when the sub-pulse ratio is 1:1, enabling precise control over the machining size. As the energy of the second sub-pulse increases, the ablation area becomes smoother due to the plasma heating of the double-pulse femtosecond laser.
{"title":"Single-crystal silicon ablation with temporally delayed femtosecond laser double-pulse trains","authors":"Zhengjie Fan, Liangtian Yi, Jing Lv, Wenjun Wang, Guoji Li, Jianlei Cui","doi":"10.1088/1361-6463/ad7300","DOIUrl":"https://doi.org/10.1088/1361-6463/ad7300","url":null,"abstract":"A double-pulse femtosecond laser is used to process single-crystal silicon. Modulating the delay time was discovered to increase the ablation depth and improve the morphology of the ablated surface. The hole fabricated by a dual-pulse with a 200 ps interval is 24.4% deeper than that created by a single pulse of the same energy. Moreover, utilizing a dual pulse with an interval ranging from 100 to 1000 ps produces a considerably smoother ablation area as compared to the single pulse. The effect of the sub-pulse energy ratio of the double-pulse femtosecond laser on the size and morphology of the ablated area was also investigated. As the sub-pulse energy ratio decreases from 3:1 to 1:3, the size of the ablation area initially decreases and then increases, while the size of the ablation area is minimized when the sub-pulse ratio is 1:1, enabling precise control over the machining size. As the energy of the second sub-pulse increases, the ablation area becomes smoother due to the plasma heating of the double-pulse femtosecond laser.","PeriodicalId":16789,"journal":{"name":"Journal of Physics D: Applied Physics","volume":"9 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142223018","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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