Pub Date : 2024-01-12DOI: 10.1038/s41699-024-00440-5
Oleksiy Kovalchuk, Sungjae Lee, Hyowon Moon, Andrea M. Armani, Yong-Won Song
Generation of high-speed laser pulses is essential for sustaining today’s global, hyper-connected society. One approach for achieving high spectral and temporal purity is to combine optical nonlinear materials with spectral filtering devices. In this work, a graphene-coated microresonator integrates a nonlinear material and a spectral filtering platform into a single device, creating a tunable GHz repetition rate mode-locked fiber laser. The graphene is directly synthesized on the non-planar surface of microresonator, resulting in a uniform, conformal coating with minimal optical loss in the device. The whispering gallery modes of the resonator filter the propagating modes, and the remaining modes from the interaction with graphene lock their relative phases to form short pulses at an elevated repetition rate relying on inter-modal spectral distance. Additionally, by leveraging the photo-thermal effect, all-optical tuning of the repetition rate is demonstrated. With optimized device parameters, repetition rates of 150 GHz and tuning of 6.1 GHz are achieved.
{"title":"Non-planar graphene directly synthesized on intracavity optical microresonators for GHz repetition rate mode-locked lasers","authors":"Oleksiy Kovalchuk, Sungjae Lee, Hyowon Moon, Andrea M. Armani, Yong-Won Song","doi":"10.1038/s41699-024-00440-5","DOIUrl":"10.1038/s41699-024-00440-5","url":null,"abstract":"Generation of high-speed laser pulses is essential for sustaining today’s global, hyper-connected society. One approach for achieving high spectral and temporal purity is to combine optical nonlinear materials with spectral filtering devices. In this work, a graphene-coated microresonator integrates a nonlinear material and a spectral filtering platform into a single device, creating a tunable GHz repetition rate mode-locked fiber laser. The graphene is directly synthesized on the non-planar surface of microresonator, resulting in a uniform, conformal coating with minimal optical loss in the device. The whispering gallery modes of the resonator filter the propagating modes, and the remaining modes from the interaction with graphene lock their relative phases to form short pulses at an elevated repetition rate relying on inter-modal spectral distance. Additionally, by leveraging the photo-thermal effect, all-optical tuning of the repetition rate is demonstrated. With optimized device parameters, repetition rates of 150 GHz and tuning of 6.1 GHz are achieved.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-9"},"PeriodicalIF":9.7,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-024-00440-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139431108","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-01-12DOI: 10.1038/s41699-023-00439-4
José D. Mella, Muralidhar Nalabothula, Francisco Muñoz, Karin M. Rabe, Ludger Wirtz, Sobhit Singh, Aldo H. Romero
In this work, we introduce a 2D materials family with chemical formula MX2 (M={As, Sb, Bi} and X={S, Se, Te}) having a rectangular 2D lattice. This materials family has been predicted by systematic ab-initio structure search calculations in two dimensions. Using density-functional theory and many-body perturbation theory, we study the structural, vibrational, electronic, optical, and excitonic properties of the predicted MX2 family. Our calculations reveal that the predicted SbX2 and BiX2 monolayers are stable while the AsX2 layers exhibit an in-plane ferroelectric instability. All materials display strong excitonic effects and good optical absorption within the infrared-to-visible range. Hence, these monolayers can harvest solar energy and serve in optoelectronics applications. Furthermore, our results indicate that exfoliation of the predicted MX2 monolayers from their bulk counterparts is experimentally viable.
{"title":"Prediction of BiS2-type pnictogen dichalcogenide monolayers for optoelectronics","authors":"José D. Mella, Muralidhar Nalabothula, Francisco Muñoz, Karin M. Rabe, Ludger Wirtz, Sobhit Singh, Aldo H. Romero","doi":"10.1038/s41699-023-00439-4","DOIUrl":"10.1038/s41699-023-00439-4","url":null,"abstract":"In this work, we introduce a 2D materials family with chemical formula MX2 (M={As, Sb, Bi} and X={S, Se, Te}) having a rectangular 2D lattice. This materials family has been predicted by systematic ab-initio structure search calculations in two dimensions. Using density-functional theory and many-body perturbation theory, we study the structural, vibrational, electronic, optical, and excitonic properties of the predicted MX2 family. Our calculations reveal that the predicted SbX2 and BiX2 monolayers are stable while the AsX2 layers exhibit an in-plane ferroelectric instability. All materials display strong excitonic effects and good optical absorption within the infrared-to-visible range. Hence, these monolayers can harvest solar energy and serve in optoelectronics applications. Furthermore, our results indicate that exfoliation of the predicted MX2 monolayers from their bulk counterparts is experimentally viable.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-8"},"PeriodicalIF":9.7,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00439-4.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139435318","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-01-10DOI: 10.1038/s41699-023-00438-5
M. Zinkiewicz, M. Grzeszczyk, T. Kazimierczuk, M. Bartos, K. Nogajewski, W. Pacuski, K. Watanabe, T. Taniguchi, A. Wysmołek, P. Kossacki, M. Potemski, A. Babiński, M. R. Molas
Raman scattering excitation (RSE) is an experimental technique in which the spectrum is made up by sweeping the excitation energy when the detection energy is fixed. We study the low-temperature (T = 5 K) RSE spectra measured on four high quality monolayers (ML) of semiconducting transition metal dichalcogenides (S-TMDs), i.e. MoS2, MoSe2, WS2, and WSe2, encapsulated in hexagonal BN. The outgoing resonant conditions of Raman scattering reveal an extraordinary intensity enhancement of the phonon modes, which results in extremely rich RSE spectra. The obtained spectra are composed not only of Raman-active peaks, i.e. in-plane E $${}^{{prime} }$$ and out-of-plane A $${}_{1}^{{prime} }$$ , but the appearance of 1st, 2nd, and higher-order phonon modes is recognized. The intensity profiles of the A $${}_{1}^{{prime} }$$ modes in the investigated MLs resemble the emissions due to neutral excitons measured in the corresponding PL spectra for the outgoing type of resonant Raman scattering conditions. Furthermore, for the WSe2 ML, the A $${}_{1}^{{prime} }$$ mode was observed when the incoming light was in resonance with the neutral exciton line. The strength of the exciton-phonon coupling (EPC) in S-TMD MLs strongly depends on the type of their ground excitonic state, i.e. bright or dark, resulting in different shapes of the RSE spectra. Our results demonstrate that RSE spectroscopy is a powerful technique for studying EPC in S-TMD MLs.
拉曼散射激发（RSE）是一种在探测能量固定的情况下通过扫描激发能量来构成光谱的实验技术。我们研究了封装在六方 BN 中的四种高质量过渡金属二钙化物（S-TMDs）单层（ML）（即 MoS2、MoSe2、WS2 和 WSe2）的低温（T = 5 K）RSE 光谱。拉曼散射的外向共振条件显示了声子模式的非凡强度增强，从而产生了极其丰富的 RSE 光谱。所获得的光谱不仅由拉曼活性峰（即面内 E ${}^{prime} }$$和面外 A ${}_{1}^{prime} }$$）组成，而且出现了一阶、二阶和更高阶的声子模式。在所研究的 ML 中，A $${}_{1}^{{prime} }$ 模式的强度曲线类似于在相应的出射型共振拉曼散射条件下的聚光光谱中测量到的中性激子发射。此外，对于 WSe2 ML，当入射光与中性激子线共振时，观察到 A $${}_{1}^{{prime} }$$ 模式。S-TMD ML 中激子-声子耦合（EPC）的强度在很大程度上取决于其地面激子态的类型，即亮态或暗态，从而导致 RSE 光谱的不同形状。我们的研究结果表明，RSE 光谱是研究 S-TMD ML 中 EPC 的一种强大技术。
{"title":"Raman scattering excitation in monolayers of semiconducting transition metal dichalcogenides","authors":"M. Zinkiewicz, M. Grzeszczyk, T. Kazimierczuk, M. Bartos, K. Nogajewski, W. Pacuski, K. Watanabe, T. Taniguchi, A. Wysmołek, P. Kossacki, M. Potemski, A. Babiński, M. R. Molas","doi":"10.1038/s41699-023-00438-5","DOIUrl":"10.1038/s41699-023-00438-5","url":null,"abstract":"Raman scattering excitation (RSE) is an experimental technique in which the spectrum is made up by sweeping the excitation energy when the detection energy is fixed. We study the low-temperature (T = 5 K) RSE spectra measured on four high quality monolayers (ML) of semiconducting transition metal dichalcogenides (S-TMDs), i.e. MoS2, MoSe2, WS2, and WSe2, encapsulated in hexagonal BN. The outgoing resonant conditions of Raman scattering reveal an extraordinary intensity enhancement of the phonon modes, which results in extremely rich RSE spectra. The obtained spectra are composed not only of Raman-active peaks, i.e. in-plane E $${}^{{prime} }$$ and out-of-plane A $${}_{1}^{{prime} }$$ , but the appearance of 1st, 2nd, and higher-order phonon modes is recognized. The intensity profiles of the A $${}_{1}^{{prime} }$$ modes in the investigated MLs resemble the emissions due to neutral excitons measured in the corresponding PL spectra for the outgoing type of resonant Raman scattering conditions. Furthermore, for the WSe2 ML, the A $${}_{1}^{{prime} }$$ mode was observed when the incoming light was in resonance with the neutral exciton line. The strength of the exciton-phonon coupling (EPC) in S-TMD MLs strongly depends on the type of their ground excitonic state, i.e. bright or dark, resulting in different shapes of the RSE spectra. Our results demonstrate that RSE spectroscopy is a powerful technique for studying EPC in S-TMD MLs.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-7"},"PeriodicalIF":9.7,"publicationDate":"2024-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00438-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139407002","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-01-05DOI: 10.1038/s41699-023-00437-6
Yifei Guan, Oleg V. Yazyev
Real-world samples of graphene often exhibit various types of out-of-plane disorder–ripples, wrinkles and folds–introduced at the stage of growth and transfer processes. These complex out-of-plane defects resulting from the interplay between self-adhesion of graphene and its bending rigidity inevitably lead to the scattering of charge carriers thus affecting the electronic transport properties of graphene. We address the ballistic charge-carrier transmission across the models of out-of-plane defects using tight-binding and density functional calculations while fully taking into account lattice relaxation effects. The observed transmission oscillations in commensurate graphene wrinkles are attributed to the interference between intra- and interlayer transport channels, while the incommensurate wrinkles show vanishing backscattering and retain the transport properties of flat graphene. The suppression of backscattering reveals the crucial role of lattice commensuration in the electronic transmission. Our results provide guidelines to controlling the transport properties of graphene in presence of this ubiquitous type of disorder.
{"title":"Electronic transport in graphene with out-of-plane disorder","authors":"Yifei Guan, Oleg V. Yazyev","doi":"10.1038/s41699-023-00437-6","DOIUrl":"10.1038/s41699-023-00437-6","url":null,"abstract":"Real-world samples of graphene often exhibit various types of out-of-plane disorder–ripples, wrinkles and folds–introduced at the stage of growth and transfer processes. These complex out-of-plane defects resulting from the interplay between self-adhesion of graphene and its bending rigidity inevitably lead to the scattering of charge carriers thus affecting the electronic transport properties of graphene. We address the ballistic charge-carrier transmission across the models of out-of-plane defects using tight-binding and density functional calculations while fully taking into account lattice relaxation effects. The observed transmission oscillations in commensurate graphene wrinkles are attributed to the interference between intra- and interlayer transport channels, while the incommensurate wrinkles show vanishing backscattering and retain the transport properties of flat graphene. The suppression of backscattering reveals the crucial role of lattice commensuration in the electronic transmission. Our results provide guidelines to controlling the transport properties of graphene in presence of this ubiquitous type of disorder.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-9"},"PeriodicalIF":9.7,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00437-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139102714","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2023-11-21DOI: 10.1038/s41699-023-00435-8
Cheol-Yeon Cheon, Zhe Sun, Jiang Cao, Juan Francisco Gonzalez Marin, Mukesh Tripathi, Kenji Watanabe, Takashi Taniguchi, Mathieu Luisier, Andras Kis
Sunlight is widely seen as one of the most abundant forms of renewable energy, with photovoltaic cells based on pn junctions being the most commonly used platform attempting to harness it. Unlike in conventional photovoltaic cells, the bulk photovoltaic effect (BPVE) allows for the generation of photocurrent and photovoltage in a single material without the need to engineer a pn junction and create a built-in electric field, thus offering a solution that can potentially exceed the Shockley–Queisser efficiency limit. However, it requires a material with no inversion symmetry and is therefore absent in centrosymmetric materials. Here, we demonstrate that breaking the inversion symmetry by structural disorder can induce BPVE in ultrathin PtSe2, a centrosymmetric semiconducting van der Waals material. Homogenous illumination of defective PtSe2 by linearly and circularly polarized light results in a photoresponse termed as linear photogalvanic effect (LPGE) and circular photogalvanic effect (CPGE), which is mostly absent in the pristine crystal. First-principles calculations reveal that LPGE originates from Se vacancies that act as asymmetric scattering centers for the photo-generated electron-hole pairs. Our work emphasizes the importance of defects to induce photovoltaic functionality in centrosymmetric materials and shows how the range of materials suitable for light sensing and energy-harvesting applications can be extended.
{"title":"Disorder-induced bulk photovoltaic effect in a centrosymmetric van der Waals material","authors":"Cheol-Yeon Cheon, Zhe Sun, Jiang Cao, Juan Francisco Gonzalez Marin, Mukesh Tripathi, Kenji Watanabe, Takashi Taniguchi, Mathieu Luisier, Andras Kis","doi":"10.1038/s41699-023-00435-8","DOIUrl":"10.1038/s41699-023-00435-8","url":null,"abstract":"Sunlight is widely seen as one of the most abundant forms of renewable energy, with photovoltaic cells based on pn junctions being the most commonly used platform attempting to harness it. Unlike in conventional photovoltaic cells, the bulk photovoltaic effect (BPVE) allows for the generation of photocurrent and photovoltage in a single material without the need to engineer a pn junction and create a built-in electric field, thus offering a solution that can potentially exceed the Shockley–Queisser efficiency limit. However, it requires a material with no inversion symmetry and is therefore absent in centrosymmetric materials. Here, we demonstrate that breaking the inversion symmetry by structural disorder can induce BPVE in ultrathin PtSe2, a centrosymmetric semiconducting van der Waals material. Homogenous illumination of defective PtSe2 by linearly and circularly polarized light results in a photoresponse termed as linear photogalvanic effect (LPGE) and circular photogalvanic effect (CPGE), which is mostly absent in the pristine crystal. First-principles calculations reveal that LPGE originates from Se vacancies that act as asymmetric scattering centers for the photo-generated electron-hole pairs. Our work emphasizes the importance of defects to induce photovoltaic functionality in centrosymmetric materials and shows how the range of materials suitable for light sensing and energy-harvesting applications can be extended.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-8"},"PeriodicalIF":9.7,"publicationDate":"2023-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00435-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138537006","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2023-11-03DOI: 10.1038/s41699-023-00436-7
Thomas Pucher, Pablo Bastante, Federico Parenti, Yong Xie, Elisabetta Dimaggio, Gianluca Fiori, Andres Castellanos-Gomez
This work demonstrates the fabrication and characterization of single-layer MoS2 field-effect transistors using biodegradable albumen (chicken eggwhite) as gate dielectric. By introducing albumen as an insulator for MoS2 transistors high carrier mobilities (up to ~90 cm2 V−1 s−1) are observed, which is remarkably superior to that obtained with commonly used SiO2 dielectric which we attribute to ionic gating due to the formation of an electric double layer in the albumen MoS2 interface. In addition, the investigated devices are characterized upon illumination, observing responsivities of 4.5 AW−1 (operated in photogating regime) and rise times as low as 52 ms (operated in photoconductivity regime). The presented study reveals the combination of albumen with van der Waals materials for prospective biodegradable and biocompatible optoelectronic device applications. Furthermore, the demonstrated universal fabrication process can be easily adopted to fabricate albumen-based devices with any other van der Waals material.
{"title":"Biodegradable albumen dielectrics for high-mobility MoS2 phototransistors","authors":"Thomas Pucher, Pablo Bastante, Federico Parenti, Yong Xie, Elisabetta Dimaggio, Gianluca Fiori, Andres Castellanos-Gomez","doi":"10.1038/s41699-023-00436-7","DOIUrl":"10.1038/s41699-023-00436-7","url":null,"abstract":"This work demonstrates the fabrication and characterization of single-layer MoS2 field-effect transistors using biodegradable albumen (chicken eggwhite) as gate dielectric. By introducing albumen as an insulator for MoS2 transistors high carrier mobilities (up to ~90 cm2 V−1 s−1) are observed, which is remarkably superior to that obtained with commonly used SiO2 dielectric which we attribute to ionic gating due to the formation of an electric double layer in the albumen MoS2 interface. In addition, the investigated devices are characterized upon illumination, observing responsivities of 4.5 AW−1 (operated in photogating regime) and rise times as low as 52 ms (operated in photoconductivity regime). The presented study reveals the combination of albumen with van der Waals materials for prospective biodegradable and biocompatible optoelectronic device applications. Furthermore, the demonstrated universal fabrication process can be easily adopted to fabricate albumen-based devices with any other van der Waals material.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-6"},"PeriodicalIF":9.7,"publicationDate":"2023-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00436-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135819026","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2023-10-19DOI: 10.1038/s41699-023-00434-9
Fangzhu Xiong, Jie Sun, Penghao Tang, Weiling Guo, Yibo Dong, Zaifa Du, Shiwei Feng, Xuan Li
A technique for the transfer-free growth of 2-inch wafer-scale patterned graphene directly on GaN LED epilayers is introduced. High-quality graphene as transparent electrodes and heat spreaders is synthesized directly on GaN by PECVD at only 600 °C deposition temperature and within 3 min growth time. Co acts as both the catalyst for graphene growth and the dry etching mask for GaN mesas, which greatly improves the efficiency of the semiconductor device process. Elegantly, the graphene growth is in accordance with the shape of Co, which offers a lithography-free patterning technique of the graphene. Afterward, using our penetration etching method through the PMMA and graphene layers, the Co is peacefully removed, and in-situ Ohmic contact is achieved between the graphene and p-GaN where the contact resistivity is only 0.421 Ω cm2. The graphene sheet resistance is as low as 631.2 Ω sq−1. The device is also superior to the counterpart graphene-free LED in terms of heat spreading behavior, as evidenced by the lower junction temperature and thermal resistance. Most importantly, the developed technique produces graphene with excellent performance and is intrinsically more scalable, controllable, and semiconductor industry compatible than traditionally transferred graphene.
本文介绍了一种直接在氮化镓发光二极管外延层上无转移生长 2 英寸晶圆级图案化石墨烯的技术。通过 PECVD 技术，只需 600 °C 沉积温度和 3 分钟生长时间，就能直接在 GaN 上合成高质量的石墨烯，用作透明电极和热传播器。钴既是石墨烯生长的催化剂，又是 GaN 中层的干蚀刻掩模，从而大大提高了半导体器件工艺的效率。优雅的是，石墨烯的生长与 Co 的形状一致，这提供了一种无光刻的石墨烯图案化技术。之后，利用我们的穿透蚀刻方法，通过 PMMA 和石墨烯层，Co 被顺利去除，石墨烯和 p-GaN 之间实现了原位欧姆接触，接触电阻率仅为 0.421 Ω cm2。石墨烯片电阻低至 631.2 Ω sq-1。从较低的结温和热阻可以看出，该器件的散热性能也优于无石墨烯 LED。最重要的是，所开发的技术生产出的石墨烯性能卓越，与传统的转移石墨烯相比，具有更高的可扩展性、可控性和半导体工业兼容性。
{"title":"Transfer-free rapid growth of 2-inch wafer-scale patterned graphene as transparent conductive electrodes and heat spreaders for GaN LEDs","authors":"Fangzhu Xiong, Jie Sun, Penghao Tang, Weiling Guo, Yibo Dong, Zaifa Du, Shiwei Feng, Xuan Li","doi":"10.1038/s41699-023-00434-9","DOIUrl":"10.1038/s41699-023-00434-9","url":null,"abstract":"A technique for the transfer-free growth of 2-inch wafer-scale patterned graphene directly on GaN LED epilayers is introduced. High-quality graphene as transparent electrodes and heat spreaders is synthesized directly on GaN by PECVD at only 600 °C deposition temperature and within 3 min growth time. Co acts as both the catalyst for graphene growth and the dry etching mask for GaN mesas, which greatly improves the efficiency of the semiconductor device process. Elegantly, the graphene growth is in accordance with the shape of Co, which offers a lithography-free patterning technique of the graphene. Afterward, using our penetration etching method through the PMMA and graphene layers, the Co is peacefully removed, and in-situ Ohmic contact is achieved between the graphene and p-GaN where the contact resistivity is only 0.421 Ω cm2. The graphene sheet resistance is as low as 631.2 Ω sq−1. The device is also superior to the counterpart graphene-free LED in terms of heat spreading behavior, as evidenced by the lower junction temperature and thermal resistance. Most importantly, the developed technique produces graphene with excellent performance and is intrinsically more scalable, controllable, and semiconductor industry compatible than traditionally transferred graphene.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-7"},"PeriodicalIF":9.7,"publicationDate":"2023-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00434-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135730402","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2023-10-05DOI: 10.1038/s41699-023-00432-x
Michele Gastaldo, Javier Varillas, Álvaro Rodríguez, Matěj Velický, Otakar Frank, Martin Kalbáč
Nanobubbles naturally formed at the interface between 2D materials and their substrate are known to act as exciton recombination centers because of the reduced bandgap due to local strain, which in turn scales with the aspect ratio of the bubbles. The common understanding suggests that the aspect ratio is a universal constant independent of the bubble size. Here, by combining scanning tunneling microscopy and molecular dynamics, we show that the universal aspect ratio breaks down in MoS2 nanobubbles below a critical radius (≈10 nm), where the aspect ratio increases with increasing size. Accordingly, additional atomic-level analyses indicate that the strain increases from 3% to 6% in the sub-critical size range. Using scanning tunneling spectroscopy, we demonstrate that the bandgap decreases as a function of the size. Thus, tunable quantum emitters can be obtained in 2D semiconductors by controlling the radius of the nanobubbles.
{"title":"Tunable strain and bandgap in subcritical-sized MoS2 nanobubbles","authors":"Michele Gastaldo, Javier Varillas, Álvaro Rodríguez, Matěj Velický, Otakar Frank, Martin Kalbáč","doi":"10.1038/s41699-023-00432-x","DOIUrl":"10.1038/s41699-023-00432-x","url":null,"abstract":"Nanobubbles naturally formed at the interface between 2D materials and their substrate are known to act as exciton recombination centers because of the reduced bandgap due to local strain, which in turn scales with the aspect ratio of the bubbles. The common understanding suggests that the aspect ratio is a universal constant independent of the bubble size. Here, by combining scanning tunneling microscopy and molecular dynamics, we show that the universal aspect ratio breaks down in MoS2 nanobubbles below a critical radius (≈10 nm), where the aspect ratio increases with increasing size. Accordingly, additional atomic-level analyses indicate that the strain increases from 3% to 6% in the sub-critical size range. Using scanning tunneling spectroscopy, we demonstrate that the bandgap decreases as a function of the size. Thus, tunable quantum emitters can be obtained in 2D semiconductors by controlling the radius of the nanobubbles.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-9"},"PeriodicalIF":9.7,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00432-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135481059","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2023-09-27DOI: 10.1038/s41699-023-00433-w
Abdelrahman M. Askar, Paula Palacios, Francisco Pasadas, Mohamed Saeed, Mohammad Reza Mohammadzadeh, Renato Negra, Michael M. Adachi
The research of two-dimensional (2D) Tellurium (Te) or tellurene is thriving to address current challenges in emerging thin-film electronic and optoelectronic devices. However, the study of 2D-Te-based devices for high-frequency applications is still lacking in the literature. This work presents a comprehensive study of two types of radio frequency (RF) diodes based on 2D-Te flakes and exploits their distinct properties in two RF applications. First, a metal-insulator-semiconductor (MIS) structure is employed as a nonlinear device in a passive RF mixer, where the achieved conversion loss at 2.5 GHz and 5 GHz is as low as 24 dB and 29 dB, respectively. Then, a metal-semiconductor (MS) diode is tested as a zero-bias millimeter-wave power detector and reaches an outstanding linear-in-dB dynamic range over 40 dB, while having voltage responsivities as high as 257 V ⋅ W−1 at 1 GHz (up to 1 V detected output voltage) and 47 V ⋅ W−1 at 2.5 GHz (up to 0.26 V detected output voltage). These results show superior performance compared to other 2D material-based devices in a much more mature technological phase. Thus, the authors believe that this work demonstrates the potential of 2D-Te as a promising material for devices in emerging high-frequency electronics.
{"title":"Two-dimensional tellurium-based diodes for RF applications","authors":"Abdelrahman M. Askar, Paula Palacios, Francisco Pasadas, Mohamed Saeed, Mohammad Reza Mohammadzadeh, Renato Negra, Michael M. Adachi","doi":"10.1038/s41699-023-00433-w","DOIUrl":"10.1038/s41699-023-00433-w","url":null,"abstract":"The research of two-dimensional (2D) Tellurium (Te) or tellurene is thriving to address current challenges in emerging thin-film electronic and optoelectronic devices. However, the study of 2D-Te-based devices for high-frequency applications is still lacking in the literature. This work presents a comprehensive study of two types of radio frequency (RF) diodes based on 2D-Te flakes and exploits their distinct properties in two RF applications. First, a metal-insulator-semiconductor (MIS) structure is employed as a nonlinear device in a passive RF mixer, where the achieved conversion loss at 2.5 GHz and 5 GHz is as low as 24 dB and 29 dB, respectively. Then, a metal-semiconductor (MS) diode is tested as a zero-bias millimeter-wave power detector and reaches an outstanding linear-in-dB dynamic range over 40 dB, while having voltage responsivities as high as 257 V ⋅ W−1 at 1 GHz (up to 1 V detected output voltage) and 47 V ⋅ W−1 at 2.5 GHz (up to 0.26 V detected output voltage). These results show superior performance compared to other 2D material-based devices in a much more mature technological phase. Thus, the authors believe that this work demonstrates the potential of 2D-Te as a promising material for devices in emerging high-frequency electronics.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-11"},"PeriodicalIF":9.7,"publicationDate":"2023-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00433-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135535617","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2023-09-21DOI: 10.1038/s41699-023-00430-z
Joshua J. P. Thompson, Marina Gerhard, Gregor Witte, Ermin Malic
Hybrid van der Waals heterostructures of organic semiconductors and transition metal dichalcogenides (TMDs) are promising candidates for various optoelectronic devices, such as solar cells and biosensors. Energy-transfer processes in these materials are crucial for the efficiency of such devices, yet they are poorly understood. In this work, we develop a fully microscopic theory describing the effect of the Förster interaction on exciton dynamics and optics in a WSe2/tetracene heterostack. We demonstrate that the differential absorption and time-resolved photoluminescence can be used to track the real-time evolution of excitons. We predict a strongly unidirectional energy transfer from the organic to the TMD layer. Furthermore, we explore the role temperature has in activating the Förster transfer and find a good agreement to previous experiments. Our results provide a blueprint to tune the light-harvesting efficiency through temperature, molecular orientation and interlayer separation in TMD/organic heterostructures.
{"title":"Optical signatures of Förster-induced energy transfer in organic/TMD heterostructures","authors":"Joshua J. P. Thompson, Marina Gerhard, Gregor Witte, Ermin Malic","doi":"10.1038/s41699-023-00430-z","DOIUrl":"10.1038/s41699-023-00430-z","url":null,"abstract":"Hybrid van der Waals heterostructures of organic semiconductors and transition metal dichalcogenides (TMDs) are promising candidates for various optoelectronic devices, such as solar cells and biosensors. Energy-transfer processes in these materials are crucial for the efficiency of such devices, yet they are poorly understood. In this work, we develop a fully microscopic theory describing the effect of the Förster interaction on exciton dynamics and optics in a WSe2/tetracene heterostack. We demonstrate that the differential absorption and time-resolved photoluminescence can be used to track the real-time evolution of excitons. We predict a strongly unidirectional energy transfer from the organic to the TMD layer. Furthermore, we explore the role temperature has in activating the Förster transfer and find a good agreement to previous experiments. Our results provide a blueprint to tune the light-harvesting efficiency through temperature, molecular orientation and interlayer separation in TMD/organic heterostructures.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-7"},"PeriodicalIF":9.7,"publicationDate":"2023-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00430-z.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136101789","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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