Pub Date : 2023-10-12DOI: 10.1088/2053-1583/acff08
Chaofan Chen, Albert de Kogel, Mark Weijers, Lars J. Bannenberg, Xuehang Wang
Abstract The growing demand for safe, cost-efficient, high-energy and high-power electrochemical energy storage devices has stimulated the development of aqueous-based supercapacitors with high capacitance, high rate capability, and high voltage. 2D titanium carbide MXene-based electrodes have shown excellent rate capability in various dilute aqueous electrolytes, yet their potential window is usually narrower than 1.2 V. In this study, we show that the potential window of Ti 3 C 2 T x MXene can be efficiently widened to 1.5 V in a cost-effective and environmentally benign polyethylene glycol (PEG) containing molecular crowding electrolyte. Additionally, a pair of redox peaks at −0.25 V/−0.05 V vs. Ag (cathodic/anodic) emerged in cyclic voltammetry after the addition of PEG, yielding an additional 25% capacitance. Interestingly, we observed the co-insertion of the molecular crowding agent PEG-400 during the Li + intercalation process based on in-situ x-ray diffraction analysis. As a result, Ti 3 C 2 T x electrodes presented an interlayer space change of 4.7 Å during a complete charge/discharge cycle, which is the largest reversible interlayer space change reported so far for MXene-based electrodes. This work demonstrates the potential of adding molecular crowding agents to improve the performance of MXene electrodes in aqueous electrolytes and to enlarge the change of the interlayer spacing.
对安全、高性价比、高能量、大功率的电化学储能装置的需求日益增长，刺激了高电容、高倍率、高电压的水基超级电容器的发展。2D碳化钛mxene基电极在各种稀水电解质中表现出优异的倍率性能，但其电位窗口通常小于1.2 V。在这项研究中，我们证明了在一种具有成本效益和环境友好的聚乙二醇(PEG)分子拥挤电解质中，Ti 3 C 2 T x MXene的电位窗口可以有效地扩大到1.5 V。此外，在循环伏安法中，添加PEG后，在−0.25 V/−0.05 V vs. Ag(阴极/阳极)处出现一对氧化还原峰，产生额外25%的电容。有趣的是，基于原位x射线衍射分析，我们在Li +嵌入过程中观察到分子拥挤剂PEG-400的共插入。结果表明，在一个完整的充放电循环中，ti3c2tx电极的层间空间变化为4.7 Å，这是迄今为止报道的基于mxene电极的最大可逆层间空间变化。这项工作证明了添加分子拥挤剂可以改善MXene电极在水溶液中的性能，并扩大层间距的变化。
{"title":"Enhancing pseudocapacitive intercalation in Ti3C2Tx MXene with molecular crowding electrolytes","authors":"Chaofan Chen, Albert de Kogel, Mark Weijers, Lars J. Bannenberg, Xuehang Wang","doi":"10.1088/2053-1583/acff08","DOIUrl":"https://doi.org/10.1088/2053-1583/acff08","url":null,"abstract":"Abstract The growing demand for safe, cost-efficient, high-energy and high-power electrochemical energy storage devices has stimulated the development of aqueous-based supercapacitors with high capacitance, high rate capability, and high voltage. 2D titanium carbide MXene-based electrodes have shown excellent rate capability in various dilute aqueous electrolytes, yet their potential window is usually narrower than 1.2 V. In this study, we show that the potential window of Ti 3 C 2 T x MXene can be efficiently widened to 1.5 V in a cost-effective and environmentally benign polyethylene glycol (PEG) containing molecular crowding electrolyte. Additionally, a pair of redox peaks at −0.25 V/−0.05 V vs. Ag (cathodic/anodic) emerged in cyclic voltammetry after the addition of PEG, yielding an additional 25% capacitance. Interestingly, we observed the co-insertion of the molecular crowding agent PEG-400 during the Li + intercalation process based on in-situ x-ray diffraction analysis. As a result, Ti 3 C 2 T x electrodes presented an interlayer space change of 4.7 Å during a complete charge/discharge cycle, which is the largest reversible interlayer space change reported so far for MXene-based electrodes. This work demonstrates the potential of adding molecular crowding agents to improve the performance of MXene electrodes in aqueous electrolytes and to enlarge the change of the interlayer spacing.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135922862","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-11DOI: 10.1088/2053-1583/ad024c
Sandra Schiemenz, Samuel Froeschke, Marco Naumann, Marco Rosenkranz, Bernd Büchner, Andreas Koitzsch, Martin Knupfer, Silke Hampel, Stanislav M Avdoshenko, Alexey Popov
Abstract Covalent bonding between transition metal atoms is a common phenomenon in honeycomb lattices of layered materials, which strongly affects their electronic and magnetic properties. This work presents a detailed spectroscopic study of α-MoCl3, 2D van der Waals material with covalently bonded Mo2 dimers, with a particular focus on the Mo–Mo bonding. Raman spectra of α-MoCl3 were studied with multiple excitation laser lines chosen in different parts of the absorption spectrum, while polarization measurements aided in the symmetry assignment of the observed modes. Furthermore, far-IR measurements and DFT phonon computations were performed to complete vibrational assignment. Polarized absorption, photoluminescence, and photoelectron spectroscopy supported by DFT calculations were employed to understand the consequences of the Mo–Mo bonding for the electronic structure and the localization/delocalization balance in d3–d3 interactions. A coupling of dimerization-related structural and electronic properties was revealed in the strong resonance Raman enhancement of the Mo–Mo stretching mode at 153 cm−1 when the excitation laser matched the electronic transition between σ-bonding and antibonding orbitals of the Mo2 dimer (σ→σ*). The deeper understanding of the metal-metal bonding and identification of the vibrational and electronic spectroscopic signatures of the dimerization will be of great use for the studies of electron delocalization in magnetic van der Waals materials.
{"title":"Metal-metal bonding, electronic excitations, and strong resonance Raman effect in 2D layered α-MoCl3","authors":"Sandra Schiemenz, Samuel Froeschke, Marco Naumann, Marco Rosenkranz, Bernd Büchner, Andreas Koitzsch, Martin Knupfer, Silke Hampel, Stanislav M Avdoshenko, Alexey Popov","doi":"10.1088/2053-1583/ad024c","DOIUrl":"https://doi.org/10.1088/2053-1583/ad024c","url":null,"abstract":"Abstract Covalent bonding between transition metal atoms is a common phenomenon in honeycomb lattices of layered materials, which strongly affects their electronic and magnetic properties. This work presents a detailed spectroscopic study of α-MoCl3, 2D van der Waals material with covalently bonded Mo2 dimers, with a particular focus on the Mo–Mo bonding. Raman spectra of α-MoCl3 were studied with multiple excitation laser lines chosen in different parts of the absorption spectrum, while polarization measurements aided in the symmetry assignment of the observed modes. Furthermore, far-IR measurements and DFT phonon computations were performed to complete vibrational assignment. Polarized absorption, photoluminescence, and photoelectron spectroscopy supported by DFT calculations were employed to understand the consequences of the Mo–Mo bonding for the electronic structure and the localization/delocalization balance in d3–d3 interactions. A coupling of dimerization-related structural and electronic properties was revealed in the strong resonance Raman enhancement of the Mo–Mo stretching mode at 153 cm−1 when the excitation laser matched the electronic transition between σ-bonding and antibonding orbitals of the Mo2 dimer (σ→σ*). The deeper understanding of the metal-metal bonding and identification of the vibrational and electronic spectroscopic signatures of the dimerization will be of great use for the studies of electron delocalization in magnetic van der Waals materials.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136062760","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-06DOI: 10.1088/2053-1583/acfe88
Miguel Abraham Mojarro Ramirez, Sergio E Ulloa
Abstract We study effects of strain on the electronic properties of the kagome lattice in a tight-binding formalism with spin–orbit coupling (SOC). The degeneracy at the Γ point evolves into a pair of emergent tilted Dirac cones under uniaxial strain, where the anisotropy and tilting of the bands depend on the magnitude and direction of the strain field. SOC opens gaps at the emergent Dirac points, making the flatband topological, characterized by a nontrivial Z2 index. Strains of a few percent drive the system into trivial or topological phases. This confirms that moderate strain can be used to engineer anisotropic Dirac bands with tunable properties to study new phases in kagome lattices.
{"title":"Strain-induced topological transitions and tilted Dirac cones in kagome lattices","authors":"Miguel Abraham Mojarro Ramirez, Sergio E Ulloa","doi":"10.1088/2053-1583/acfe88","DOIUrl":"https://doi.org/10.1088/2053-1583/acfe88","url":null,"abstract":"Abstract We study effects of strain on the electronic properties of the kagome lattice in a tight-binding formalism with spin–orbit coupling (SOC). The degeneracy at the Γ point evolves into a pair of emergent tilted Dirac cones under uniaxial strain, where the anisotropy and tilting of the bands depend on the magnitude and direction of the strain field. SOC opens gaps at the emergent Dirac points, making the flatband topological, characterized by a nontrivial <?CDATA $mathbb{Z}_2$?> <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" overflow=\"scroll\"> <mml:msub> <mml:mrow> <mml:mi mathvariant=\"double-struck\">Z</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:math> index. Strains of a few percent drive the system into trivial or topological phases. This confirms that moderate strain can be used to engineer anisotropic Dirac bands with tunable properties to study new phases in kagome lattices.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135302190","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ti3C2Tx MXene is emerging as the enabling material in a broad range of wearable and implantable medical technologies, thanks to its outstanding electrical, electrochemical, and optoelectronic properties, and its compatibility with high-throughput solution-based processing. While the prevalence of Ti3C2Tx MXene in biomedical research, and in particular bioelectronics, has steadily increased, the long-term stability and degradation of Ti3C2Tx MXene films have not yet been thoroughly investigated, limiting its use for chronic applications. Here, we investigate the stability of Ti3C2Tx films and electrodes under environmental conditions that are relevant to medical and bioelectronic technologies: storage in ambient atmosphere (shelf-life), submersion in saline (akin to the in vivo environment), and storage in a desiccator (low-humidity). Furthermore, to evaluate the effect of the MXene deposition method and thickness on the film stability in the different conditions, we compare thin (25 nm), and thick (1.0 μm) films and electrodes fabricated via spray-coating and blade-coating. Our findings indicate that film processing method and thickness play a significant role in determining the long-term performance of Ti3C2Tx films and electrodes, with highly aligned, thick films from blade coating remarkably retaining their conductivity, electrochemical impedance, and morphological integrity even after 30 days in saline. Our extensive spectroscopic analysis reveals that the degradation of Ti3C2Tx films in high-humidity environments is primarily driven by moisture intercalation, ingress, and film delamination, with evidence of only minimal to moderate oxidation.
{"title":"Effect of the deposition process on the stability of Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> MXene films for bioelectronics.","authors":"Sneha Shankar, Brendan B Murphy, Nicolette Driscoll, Mikhail Shekhirev, Geetha Valurouthu, Kateryna Shevchuk, Mark Anayee, Francesca Cimino, Yury Gogotsi, Flavia Vitale","doi":"10.1088/2053-1583/ace26c","DOIUrl":"10.1088/2053-1583/ace26c","url":null,"abstract":"<p><p>Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> MXene is emerging as the enabling material in a broad range of wearable and implantable medical technologies, thanks to its outstanding electrical, electrochemical, and optoelectronic properties, and its compatibility with high-throughput solution-based processing. While the prevalence of Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> MXene in biomedical research, and in particular bioelectronics, has steadily increased, the long-term stability and degradation of Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> MXene films have not yet been thoroughly investigated, limiting its use for chronic applications. Here, we investigate the stability of Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> films and electrodes under environmental conditions that are relevant to medical and bioelectronic technologies: storage in ambient atmosphere (shelf-life), submersion in saline (akin to the <i>in vivo</i> environment), and storage in a desiccator (low-humidity). Furthermore, to evaluate the effect of the MXene deposition method and thickness on the film stability in the different conditions, we compare thin (25 nm), and thick (1.0 μm) films and electrodes fabricated via spray-coating and blade-coating. Our findings indicate that film processing method and thickness play a significant role in determining the long-term performance of Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> films and electrodes, with highly aligned, thick films from blade coating remarkably retaining their conductivity, electrochemical impedance, and morphological integrity even after 30 days in saline. Our extensive spectroscopic analysis reveals that the degradation of Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> films in high-humidity environments is primarily driven by moisture intercalation, ingress, and film delamination, with evidence of only minimal to moderate oxidation.</p>","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"10 4","pages":""},"PeriodicalIF":4.5,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10373437/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"10276654","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-29DOI: 10.1088/2053-1583/acfb20
Martin von Helversen, Lara Greten, Imad Limame, Ching-Wen Shih, Paul Schlaugat, Carlos Anton-Solanas, Christian Schneider, Bárbara Rosa, Andreas Knorr, Stephan Reitzenstein
Abstract In recent years, much research has been undertaken to investigate the suitability of two-dimensional materials to act as single-photon sources with high optical and quantum optical quality. Amongst them, transition-metal dichalcogenides, especially WSe 2 , have been one of the subjects of intensive studies. Yet, their single-photon purity and photon indistinguishability remain the most significant challenges to compete with mature semiconducting systems such as self-assembled InGaAs quantum dots. In this work, we explore the emission properties of quantum emitters in a WSe 2 monolayer which are induced by metallic nanoparticles. Under quasi-resonant pulsed excitation, we verify clean single-photon emission with a g (2) (0) = 0.036 ± 0.004. Furthermore, we determine the temperature dependent coherence time via Michelson interferometry, where a value of (13.5 ± 1.0) ps is extracted for the zero-phonon line at 4 K, which reduces to (9 ± 2) ps at 8 K. Associated time-resolved photoluminescence experiments reveal a decrease of the decay time from (2.4 ± 0.1) ns to (0.42 ± 0.05) ns. This change in decay time is explained by a model which considers a Förster-type resonant energy transfer process which yields a strong temperature induced energy loss from the single-photon emitters to the nearby Ag nanoparticle.
{"title":"Temperature dependent temporal coherence of metallic-nanoparticle-induced single-photon emitters in a WSe<sub>2</sub> monolayer","authors":"Martin von Helversen, Lara Greten, Imad Limame, Ching-Wen Shih, Paul Schlaugat, Carlos Anton-Solanas, Christian Schneider, Bárbara Rosa, Andreas Knorr, Stephan Reitzenstein","doi":"10.1088/2053-1583/acfb20","DOIUrl":"https://doi.org/10.1088/2053-1583/acfb20","url":null,"abstract":"Abstract In recent years, much research has been undertaken to investigate the suitability of two-dimensional materials to act as single-photon sources with high optical and quantum optical quality. Amongst them, transition-metal dichalcogenides, especially WSe 2 , have been one of the subjects of intensive studies. Yet, their single-photon purity and photon indistinguishability remain the most significant challenges to compete with mature semiconducting systems such as self-assembled InGaAs quantum dots. In this work, we explore the emission properties of quantum emitters in a WSe 2 monolayer which are induced by metallic nanoparticles. Under quasi-resonant pulsed excitation, we verify clean single-photon emission with a g (2) (0) = 0.036 ± 0.004. Furthermore, we determine the temperature dependent coherence time via Michelson interferometry, where a value of (13.5 ± 1.0) ps is extracted for the zero-phonon line at 4 K, which reduces to (9 ± 2) ps at 8 K. Associated time-resolved photoluminescence experiments reveal a decrease of the decay time from (2.4 ± 0.1) ns to (0.42 ± 0.05) ns. This change in decay time is explained by a model which considers a Förster-type resonant energy transfer process which yields a strong temperature induced energy loss from the single-photon emitters to the nearby Ag nanoparticle.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135131730","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The family of 2D ferromagnets is in the center of research for novel spintronics applications. Among the various 2D ferromagnets, Fe 3 GeTe 2 has drawn significant attention since it combines a high Curie temperature with a van der Waals structure, which allows easy exfoliation, and a high spin polarization/large spin–orbit coupling. The presence of interfacial DMI in 2D ferromagnets have a significant impact on the behavior of magnetic domain walls, which are fundamental in magnetic memory and logic devices. By controlling the interfacial DMI, it is possible to manipulate the motion of domain walls and the magnetic domain configuration, which is essential for the development of efficient and reliable magnetic devices. In this study, we investigate the effect of an, inversion symmetry breaking, oxidized layer on the magnetic domain structure of Fe 3 GeTe 2 flakes due to the emergence of interfacial DMI. By combining magneto-optical Kerr effect microscopy images and micromagnetic simulations, we study the formation of a circular double wall (CDW) domain lattice in oxidized flakes under specific field cooling and magnetic field sweeping protocols. Their formation is attributed to a competition between the exchange interaction both symmetric and antisymmetric (associated to interfacial DMI), magnetocrystalline anisotropy and the external magnetic field. The CDW domains have a diameter of several microns, a magnetic structure resembling that of a skyrmionium and are arranged in regular lattice that survives thermal fluctuations close to T c . Our results suggest that these CDW domains transition to Néel type skyrmions after a magnetic field threshold. These findings could have important implications for the design and optimization of 2D ferromagnetic materials for spintronic applications.
{"title":"Magnetic field assisted stabilization of circular double wall domain lattice in oxidized Fe<sub>3</sub>GeTe<sub>2</sub> flakes","authors":"Panagiotis Pappas, Elli Georgopoulou-Kotsaki, Akylas Lintzeris, Athanasios Dimoulas","doi":"10.1088/2053-1583/acfb1f","DOIUrl":"https://doi.org/10.1088/2053-1583/acfb1f","url":null,"abstract":"Abstract The family of 2D ferromagnets is in the center of research for novel spintronics applications. Among the various 2D ferromagnets, Fe 3 GeTe 2 has drawn significant attention since it combines a high Curie temperature with a van der Waals structure, which allows easy exfoliation, and a high spin polarization/large spin–orbit coupling. The presence of interfacial DMI in 2D ferromagnets have a significant impact on the behavior of magnetic domain walls, which are fundamental in magnetic memory and logic devices. By controlling the interfacial DMI, it is possible to manipulate the motion of domain walls and the magnetic domain configuration, which is essential for the development of efficient and reliable magnetic devices. In this study, we investigate the effect of an, inversion symmetry breaking, oxidized layer on the magnetic domain structure of Fe 3 GeTe 2 flakes due to the emergence of interfacial DMI. By combining magneto-optical Kerr effect microscopy images and micromagnetic simulations, we study the formation of a circular double wall (CDW) domain lattice in oxidized flakes under specific field cooling and magnetic field sweeping protocols. Their formation is attributed to a competition between the exchange interaction both symmetric and antisymmetric (associated to interfacial DMI), magnetocrystalline anisotropy and the external magnetic field. The CDW domains have a diameter of several microns, a magnetic structure resembling that of a skyrmionium and are arranged in regular lattice that survives thermal fluctuations close to T c . Our results suggest that these CDW domains transition to Néel type skyrmions after a magnetic field threshold. These findings could have important implications for the design and optimization of 2D ferromagnetic materials for spintronic applications.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"131 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135131729","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-26DOI: 10.1088/2053-1583/acf945
gowtham polumati, Barbara A Muñiz Martínez, Chandra Sekhar Reddy Kolli, Venkatarao Selamneni, mario flores, David Emanuel Sanchez, Andres fest Carreno, Mauricio Terrones, Dr. Andrés de Luna Bugallo, Parikshit Sahatiya
Abstract This work demonstrates the band-type engineering and the detailed charge transport mechanism upon visible light illumination for various configurations of vertically stacked monolayers of MoS 2 -ReS 2 grown by a two-step chemical vapour deposition method. In order to understand the stacking order of both materials has a direct impact on the band alignment arrangements, we investigate the optical properties of both ReS 2 –MoS 2 stacking configurations using micro-photoluminescence and interestingly observed the change in the band alignment upon changing the stacking order (ReS 2 –MoS 2 and MoS 2 –ReS 2 ). The formation of the vertically stacked heterostructure is further validated by observing its morphology by HR-TEM. The MoS 2 on top of ReS 2 yielded Type II and ReS 2 on top of MoS 2 yielded type I band alignment. The fabricated photodetector exhibits responsivities of 152 A W −1 for pristine ReS 2 , 72 A W −1 for MoS 2 on top, and 400 A W −1 for ReS 2 on top respectively for visible light illumination of 554 nm suggesting that the stacking configuration of the monolayer TMDs play a vital role in the performance of the optoelectronic properties. The detailed study of such configurations of vertically stacked 2D heterostructure is essential to better understand the optimal configuration for the development of highly responsive photodetectors.
摘要:本文研究了两步化学气相沉积法生长的MoS 2 - re2垂直堆叠单层在可见光照射下的带型工程和详细的电荷输运机制。为了了解两种材料的堆叠顺序对能带排列的直接影响，我们利用微光致发光技术研究了两种材料的堆叠结构的光学性质，并观察了堆叠顺序改变后的能带排列变化(res2 -MoS 2和MoS 2 - res2)。通过透射电镜观察其形貌，进一步证实了垂直堆叠异质结构的形成。在res2之上的MoS 2产生II型，而res2之上的MoS 2产生I型波段对准。制备的光电探测器在554 nm的可见光照射下，对原始ReS 2的响应率为152 A W−1，对顶部MoS 2的响应率为72 A W−1，对顶部ReS 2的响应率为400 A W−1，这表明单层tmd的堆叠结构对光电性能起着至关重要的作用。对这种垂直堆叠的二维异质结构的详细研究对于更好地理解高响应光电探测器的最佳配置是必不可少的。
{"title":"Band Type Engineering Using Different Stacking Configurations of Anisotropic and Isotropic Monolayer Transition Metal Dichalcogenides","authors":"gowtham polumati, Barbara A Muñiz Martínez, Chandra Sekhar Reddy Kolli, Venkatarao Selamneni, mario flores, David Emanuel Sanchez, Andres fest Carreno, Mauricio Terrones, Dr. Andrés de Luna Bugallo, Parikshit Sahatiya","doi":"10.1088/2053-1583/acf945","DOIUrl":"https://doi.org/10.1088/2053-1583/acf945","url":null,"abstract":"Abstract This work demonstrates the band-type engineering and the detailed charge transport mechanism upon visible light illumination for various configurations of vertically stacked monolayers of MoS 2 -ReS 2 grown by a two-step chemical vapour deposition method. In order to understand the stacking order of both materials has a direct impact on the band alignment arrangements, we investigate the optical properties of both ReS 2 –MoS 2 stacking configurations using micro-photoluminescence and interestingly observed the change in the band alignment upon changing the stacking order (ReS 2 –MoS 2 and MoS 2 –ReS 2 ). The formation of the vertically stacked heterostructure is further validated by observing its morphology by HR-TEM. The MoS 2 on top of ReS 2 yielded Type II and ReS 2 on top of MoS 2 yielded type I band alignment. The fabricated photodetector exhibits responsivities of 152 A W −1 for pristine ReS 2 , 72 A W −1 for MoS 2 on top, and 400 A W −1 for ReS 2 on top respectively for visible light illumination of 554 nm suggesting that the stacking configuration of the monolayer TMDs play a vital role in the performance of the optoelectronic properties. The detailed study of such configurations of vertically stacked 2D heterostructure is essential to better understand the optimal configuration for the development of highly responsive photodetectors.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"150 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134903937","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-25DOI: 10.1088/2053-1583/acfa0f
Sabeeh Irfan Ahmad, Arpit Dave, Emmanuel Sarpong, Hsin-Yu Yao, Joel M. Solomon, Jing-Kai Jiang, Chih-Wei Luo, Wen-Hao Chang, Tsing-hua Her
Abstract Hexagonal boron nitride (hBN) has emerged as a promising two-dimensional (2D) material for many applications in electronics and photonics. Although its linear and nonlinear optical properties have been extensively studied, the interaction of hBN with high-intensity laser pulses, which is important for realizing high-harmonic generation, creating deterministic defects as quantum emitters, and resist-free patterning in this material, has not been investigated. Here we report the first systematic study of dielectric breakdown in chemical vapor deposition (CVD)-grown hBN monolayers induced by single femtosecond laser pulses. We report a breakdown fluence of 0.7 J cm −2 , which is at least 7× higher than that of other monolayer 2D materials. A clean removal of hBN without leaving traces behind or causing lateral damage is demonstrated. The ablation features exhibit excellent fidelity with very small edge roughness, which we attribute to its ultrahigh fracture toughness due to its heterogeneous nature with three-fold symmetry. Moreover, even though defects are known to be abundant in CVD-grown hBN, we show experimentally and theoretically that its nonlinear optical breakdown is nearly intrinsic as defects only marginally lower the breakdown threshold. On top of this, we observe that hBN monolayers have a 4–5× lower breakdown threshold than their bulk equivalent. The last two observations can be understood if the carrier generation in monolayers is intrinsically enhanced due to its 2D nature. Finally, we demonstrate laser patterning of array of holes and lines in hBN with sub-wavelength feature sizes. Our work advances the fundamental knowledge of light-hBN interaction in the strong field regime and firmly establishes femtosecond lasers as novel and promising tools for resist-free patterning of hBN monolayers with high fidelity.
{"title":"Dielectric breakdown and sub-wavelength patterning of monolayer hexagonal boron nitride using femtosecond pulses.","authors":"Sabeeh Irfan Ahmad, Arpit Dave, Emmanuel Sarpong, Hsin-Yu Yao, Joel M. Solomon, Jing-Kai Jiang, Chih-Wei Luo, Wen-Hao Chang, Tsing-hua Her","doi":"10.1088/2053-1583/acfa0f","DOIUrl":"https://doi.org/10.1088/2053-1583/acfa0f","url":null,"abstract":"Abstract Hexagonal boron nitride (hBN) has emerged as a promising two-dimensional (2D) material for many applications in electronics and photonics. Although its linear and nonlinear optical properties have been extensively studied, the interaction of hBN with high-intensity laser pulses, which is important for realizing high-harmonic generation, creating deterministic defects as quantum emitters, and resist-free patterning in this material, has not been investigated. Here we report the first systematic study of dielectric breakdown in chemical vapor deposition (CVD)-grown hBN monolayers induced by single femtosecond laser pulses. We report a breakdown fluence of 0.7 J cm −2 , which is at least 7× higher than that of other monolayer 2D materials. A clean removal of hBN without leaving traces behind or causing lateral damage is demonstrated. The ablation features exhibit excellent fidelity with very small edge roughness, which we attribute to its ultrahigh fracture toughness due to its heterogeneous nature with three-fold symmetry. Moreover, even though defects are known to be abundant in CVD-grown hBN, we show experimentally and theoretically that its nonlinear optical breakdown is nearly intrinsic as defects only marginally lower the breakdown threshold. On top of this, we observe that hBN monolayers have a 4–5× lower breakdown threshold than their bulk equivalent. The last two observations can be understood if the carrier generation in monolayers is intrinsically enhanced due to its 2D nature. Finally, we demonstrate laser patterning of array of holes and lines in hBN with sub-wavelength feature sizes. Our work advances the fundamental knowledge of light-hBN interaction in the strong field regime and firmly establishes femtosecond lasers as novel and promising tools for resist-free patterning of hBN monolayers with high fidelity.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"2013 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135769124","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-25DOI: 10.1088/2053-1583/acf944
Yann in 't Veld, Mikhail I Katsnelson, Andrew J. Millis, Malte Rösner
Abstract Two-dimensional (2D) metals can host gapless plasmonic excitations that strongly couple to electrons and thus may significantly affect superconductivity. To investigate the dynamical interplay of the electron–electron and electron–phonon interactions in the theory of 2D superconductivity, we apply a full momentum- and frequency-dependent one-loop theory treating electron–phonon, electron–plasmon, and phonon–plasmon coupling with the same accuracy. We tune the strength of the Coulomb interaction by varying the external screening εext to the layered superconductor and find three distinct regions. At weak screening, superconductivity is mediated by plasmons. In the opposite limit conventional electron–phonon interactions dominate. In between, we find a suppressed superconducting state. Our results show that even in conventional electron–phonon coupled layered materials, superconductivity can be significantly enhanced by the electron–plasmon coupling in a manner that can be controlled by the external screening.
{"title":"Screening Induced Crossover between Phonon- and Plasmon-Mediated Pairing in Layered Superconductors","authors":"Yann in 't Veld, Mikhail I Katsnelson, Andrew J. Millis, Malte Rösner","doi":"10.1088/2053-1583/acf944","DOIUrl":"https://doi.org/10.1088/2053-1583/acf944","url":null,"abstract":"Abstract Two-dimensional (2D) metals can host gapless plasmonic excitations that strongly couple to electrons and thus may significantly affect superconductivity. To investigate the dynamical interplay of the electron–electron and electron–phonon interactions in the theory of 2D superconductivity, we apply a full momentum- and frequency-dependent one-loop theory treating electron–phonon, electron–plasmon, and phonon–plasmon coupling with the same accuracy. We tune the strength of the Coulomb interaction by varying the external screening <?CDATA $varepsilon_mathrm{ext}$?> <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" overflow=\"scroll\"> <mml:msub> <mml:mi>ε</mml:mi> <mml:mrow> <mml:mi mathvariant=\"normal\">e</mml:mi> <mml:mi mathvariant=\"normal\">x</mml:mi> <mml:mi mathvariant=\"normal\">t</mml:mi> </mml:mrow> </mml:msub> </mml:math> to the layered superconductor and find three distinct regions. At weak screening, superconductivity is mediated by plasmons. In the opposite limit conventional electron–phonon interactions dominate. In between, we find a suppressed superconducting state. Our results show that even in conventional electron–phonon coupled layered materials, superconductivity can be significantly enhanced by the electron–plasmon coupling in a manner that can be controlled by the external screening.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135769280","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Niobium chloride (Nb 3 Cl 8 ) is a layered two-dimensional semiconducting material with many exotic properties including a breathing kagome lattice, a topological flat band in its band structure, and a crystal structure that undergoes a structural and magnetic phase transition at temperatures below 90 K. Despite being a remarkable material with fascinating new physics, the understanding of its phonon properties is at its infancy. In this study, we investigate the phonon dynamics of Nb 3 Cl 8 in bulk and few layer flakes using polarized Raman spectroscopy and density-functional theory (DFT) analysis to determine the material’s vibrational modes, as well as their symmetrical representations and atomic displacements. We experimentally resolved 12 phonon modes, five of which are A 1 g modes while the remaining seven are E g modes, which is in strong agreement with our DFT calculation. Layer-dependent results suggest that the Raman peak positions are mostly insensitive to changes in layer thickness, while peak intensity and full width at half maximum are affected. Raman measurements as a function of excitation wavelength (473–785 nm) show a significant increase of the peak intensities when using a 473 nm excitation source, suggesting a near resonant condition. Temperature-dependent Raman experiments carried out above and below the transition temperature did not show any change in the symmetries of the phonon modes, suggesting that the structural phase transition is likely from the high temperature P 3mˉ 1 phase to the low-temperature R 3mˉ phase. Magneto-Raman measurements carried out at 140 and 2 K between −2 and 2 T show that the Raman modes are not magnetically coupled. Overall, our study presented here significantly advances the fundamental understanding of layered Nb 3 Cl 8 material which can be further exploited for future applications.
{"title":"Raman Study of Layered Breathing Kagome Lattice Semiconductor Nb3Cl8","authors":"Dylan A. Jeff, Favian Gonzalez, Kamal Harrison, Yuzhou Zhao, Tharindu Fernando, Sabin Regmi, Zhaoyu Liu, Humberto Rodriguez Gutierrez, Madhab Neupane, Jihui Yang, Jiun-Haw Chu, Xiaodong Xu, Ting Cao, Saiful Khondaker","doi":"10.1088/2053-1583/acfa10","DOIUrl":"https://doi.org/10.1088/2053-1583/acfa10","url":null,"abstract":"Abstract Niobium chloride (Nb 3 Cl 8 ) is a layered two-dimensional semiconducting material with many exotic properties including a breathing kagome lattice, a topological flat band in its band structure, and a crystal structure that undergoes a structural and magnetic phase transition at temperatures below 90 K. Despite being a remarkable material with fascinating new physics, the understanding of its phonon properties is at its infancy. In this study, we investigate the phonon dynamics of Nb 3 Cl 8 in bulk and few layer flakes using polarized Raman spectroscopy and density-functional theory (DFT) analysis to determine the material’s vibrational modes, as well as their symmetrical representations and atomic displacements. We experimentally resolved 12 phonon modes, five of which are A 1 g modes while the remaining seven are E g modes, which is in strong agreement with our DFT calculation. Layer-dependent results suggest that the Raman peak positions are mostly insensitive to changes in layer thickness, while peak intensity and full width at half maximum are affected. Raman measurements as a function of excitation wavelength (473–785 nm) show a significant increase of the peak intensities when using a 473 nm excitation source, suggesting a near resonant condition. Temperature-dependent Raman experiments carried out above and below the transition temperature did not show any change in the symmetries of the phonon modes, suggesting that the structural phase transition is likely from the high temperature P <?CDATA $bar {text{3}m}$?> <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" overflow=\"scroll\"> <mml:mover> <mml:mrow> <mml:mtext>3</mml:mtext> <mml:mi>m</mml:mi> </mml:mrow> <mml:mo>ˉ</mml:mo> </mml:mover> </mml:math> 1 phase to the low-temperature R <?CDATA $bar {3m}$?> <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" overflow=\"scroll\"> <mml:mover> <mml:mrow> <mml:mn>3</mml:mn> <mml:mi>m</mml:mi> </mml:mrow> <mml:mo>ˉ</mml:mo> </mml:mover> </mml:math> phase. Magneto-Raman measurements carried out at 140 and 2 K between −2 and 2 T show that the Raman modes are not magnetically coupled. Overall, our study presented here significantly advances the fundamental understanding of layered Nb 3 Cl 8 material which can be further exploited for future applications.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135769125","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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