Pub Date : 2023-09-18DOI: 10.1038/s41699-023-00422-z
Kartikey Thakar, Bipin Rajendran, Saurabh Lodha
Accurate, timely and selective detection of moving obstacles is crucial for reliable collision avoidance in autonomous robots. The area- and energy-inefficiency of CMOS-based spiking neurons for obstacle detection can be addressed through the reconfigurable, tunable and low-power operation capabilities of emerging two-dimensional (2D) materials-based devices. We present an ultra-low power spiking neuron built using an electrostatically tuned dual-gate transistor with an ultra-thin and generic 2D material channel. The 2D subthreshold transistor (2D-ST) is carefully designed to operate under low-current subthreshold regime. Carrier transport has been modeled via over-the-barrier thermionic and Fowler–Nordheim contact barrier tunneling currents over a wide range of gate and drain biases. Simulation of a neuron circuit designed using the 2D-ST with 45 nm CMOS technology components shows high energy efficiency of ~3.5 pJ per spike and biomimetic class-I as well as oscillatory spiking. It also demonstrates complex neuronal behaviors such as spike-frequency adaptation and post-inhibitory rebound that are crucial for dynamic visual systems. Lobula giant movement detector (LGMD) is a collision-detecting biological neuron found in locusts. Our neuron circuit can generate LGMD-like spiking behavior and detect obstacles at an energy cost of <100 pJ. Further, it can be reconfigured to distinguish between looming and receding objects with high selectivity. We also show that the spiking neuron circuit can function reliably with ±40% variation in the 2D-ST current as well as up to 3 dB signal-to-noise ratio with additive white Gaussian noise in the input synaptic current.
{"title":"Ultra-low power neuromorphic obstacle detection using a two-dimensional materials-based subthreshold transistor","authors":"Kartikey Thakar, Bipin Rajendran, Saurabh Lodha","doi":"10.1038/s41699-023-00422-z","DOIUrl":"10.1038/s41699-023-00422-z","url":null,"abstract":"Accurate, timely and selective detection of moving obstacles is crucial for reliable collision avoidance in autonomous robots. The area- and energy-inefficiency of CMOS-based spiking neurons for obstacle detection can be addressed through the reconfigurable, tunable and low-power operation capabilities of emerging two-dimensional (2D) materials-based devices. We present an ultra-low power spiking neuron built using an electrostatically tuned dual-gate transistor with an ultra-thin and generic 2D material channel. The 2D subthreshold transistor (2D-ST) is carefully designed to operate under low-current subthreshold regime. Carrier transport has been modeled via over-the-barrier thermionic and Fowler–Nordheim contact barrier tunneling currents over a wide range of gate and drain biases. Simulation of a neuron circuit designed using the 2D-ST with 45 nm CMOS technology components shows high energy efficiency of ~3.5 pJ per spike and biomimetic class-I as well as oscillatory spiking. It also demonstrates complex neuronal behaviors such as spike-frequency adaptation and post-inhibitory rebound that are crucial for dynamic visual systems. Lobula giant movement detector (LGMD) is a collision-detecting biological neuron found in locusts. Our neuron circuit can generate LGMD-like spiking behavior and detect obstacles at an energy cost of <100 pJ. Further, it can be reconfigured to distinguish between looming and receding objects with high selectivity. We also show that the spiking neuron circuit can function reliably with ±40% variation in the 2D-ST current as well as up to 3 dB signal-to-noise ratio with additive white Gaussian noise in the input synaptic current.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-10"},"PeriodicalIF":9.7,"publicationDate":"2023-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00422-z.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135103089","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 : 2023-09-13DOI: 10.1038/s41699-023-00431-y
Shayan Angizi, Lea Hong, Xianxuan Huang, P. Ravi Selvaganapathy, Peter Kruse
Understanding the performance of graphene devices in contact with highly concentrated aqueous electrolytes is key to integrating graphene into next-generation devices operating in sea water environments, biosensors, and high-density energy production/storage units. Despite significant efforts toward interpreting the structure of the electrochemical double layer at high concentrations, the interface between graphene-based materials and concentrated aqueous solutions has remained vaguely described. In this study, we demonstrate the use of graphene-based chemiresistors as a technique to indirectly quantify the experimental screening length of concentrated electrolytes that could clarify the interpretation of electrochemical measurements conducted at low ionic strength. We report a breakdown of the Debye–Hückel theory in the proximity of graphene surfaces at lower concentrations (10–50 mM) than previously reported for other systems, depending on cation size, dissolved oxygen concentration, and degree of graphene defectivity.
{"title":"Graphene versus concentrated aqueous electrolytes: the role of the electrochemical double layer in determining the screening length of an electrolyte","authors":"Shayan Angizi, Lea Hong, Xianxuan Huang, P. Ravi Selvaganapathy, Peter Kruse","doi":"10.1038/s41699-023-00431-y","DOIUrl":"10.1038/s41699-023-00431-y","url":null,"abstract":"Understanding the performance of graphene devices in contact with highly concentrated aqueous electrolytes is key to integrating graphene into next-generation devices operating in sea water environments, biosensors, and high-density energy production/storage units. Despite significant efforts toward interpreting the structure of the electrochemical double layer at high concentrations, the interface between graphene-based materials and concentrated aqueous solutions has remained vaguely described. In this study, we demonstrate the use of graphene-based chemiresistors as a technique to indirectly quantify the experimental screening length of concentrated electrolytes that could clarify the interpretation of electrochemical measurements conducted at low ionic strength. We report a breakdown of the Debye–Hückel theory in the proximity of graphene surfaces at lower concentrations (10–50 mM) than previously reported for other systems, depending on cation size, dissolved oxygen concentration, and degree of graphene defectivity.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-9"},"PeriodicalIF":9.7,"publicationDate":"2023-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00431-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135734365","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 : 2023-09-11DOI: 10.1038/s41699-023-00429-6
Mehmet Atıf Durmuş, Kaan Demiralay, Muhammad Mansoor Khan, Şeyma Esra Atalay, Ibrahim Sarpkaya
The moiré superlattices of transition metal dichalcogenide heterobilayers have a pronounced effect on the optical properties of interlayer excitons (IXs) and have been intensively studied in recent years. However, the impact of moiré potentials on the temporal coherence of the IXs has not yet been investigated in detail. Here, we systematically investigate the coherence properties of both the ensemble of delocalized and the ensemble of localized IXs trapped in moiré potentials of the hexagonal boron nitride encapsulated WSe2-MoSe2 heterostructures. Our low-temperature first-order correlation measurements show that prolonged T2 dephasing times with values up to 730 fs can be obtained from the ensemble of localized IXs under moderate pump powers. We observed up to almost a five-fold increase over the values we obtained from the delocalized IXs, while more than two-fold over the previously reported values of T2 ~ 300 fs from the delocalized IXs. The prolonged values of T2 dephasing times and narrow photoluminescence (PL) linewidths for the ensemble of moiré-trapped IXs compared to delocalized one indicate that dephasing mechanisms caused by exciton-low energy acoustic phonon and exciton-exciton scattering are significantly suppressed due to the presence of localization potentials. Our pump power-dependent T2 results show that ultra-long dephasing times can be expected if the dephasing time measurements are performed with the narrow photoluminescence emission line of a single moiré-trapped IX at a low pump power regime. The prolonged values of IX dephasing times would be critical for the applications of quantum information science and the development of two-dimensional material-based nanolasers.
{"title":"Prolonged dephasing time of ensemble of moiré-trapped interlayer excitons in WSe2-MoSe2 heterobilayers","authors":"Mehmet Atıf Durmuş, Kaan Demiralay, Muhammad Mansoor Khan, Şeyma Esra Atalay, Ibrahim Sarpkaya","doi":"10.1038/s41699-023-00429-6","DOIUrl":"10.1038/s41699-023-00429-6","url":null,"abstract":"The moiré superlattices of transition metal dichalcogenide heterobilayers have a pronounced effect on the optical properties of interlayer excitons (IXs) and have been intensively studied in recent years. However, the impact of moiré potentials on the temporal coherence of the IXs has not yet been investigated in detail. Here, we systematically investigate the coherence properties of both the ensemble of delocalized and the ensemble of localized IXs trapped in moiré potentials of the hexagonal boron nitride encapsulated WSe2-MoSe2 heterostructures. Our low-temperature first-order correlation measurements show that prolonged T2 dephasing times with values up to 730 fs can be obtained from the ensemble of localized IXs under moderate pump powers. We observed up to almost a five-fold increase over the values we obtained from the delocalized IXs, while more than two-fold over the previously reported values of T2 ~ 300 fs from the delocalized IXs. The prolonged values of T2 dephasing times and narrow photoluminescence (PL) linewidths for the ensemble of moiré-trapped IXs compared to delocalized one indicate that dephasing mechanisms caused by exciton-low energy acoustic phonon and exciton-exciton scattering are significantly suppressed due to the presence of localization potentials. Our pump power-dependent T2 results show that ultra-long dephasing times can be expected if the dephasing time measurements are performed with the narrow photoluminescence emission line of a single moiré-trapped IX at a low pump power regime. The prolonged values of IX dephasing times would be critical for the applications of quantum information science and the development of two-dimensional material-based nanolasers.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-8"},"PeriodicalIF":9.7,"publicationDate":"2023-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00429-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135980929","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 : 2023-09-11DOI: 10.1038/s41699-023-00428-7
Mahfujur Rahaman, Gwangwoo Kim, Kyung Yeol Ma, Seunguk Song, Hyeon Suk Shin, Deep Jariwala
Control of excitons in transition metal dichalcogenides (TMDCs) and their heterostructures is fundamentally interesting for tailoring light-matter interactions and exploring their potential applications in high-efficiency optoelectronic and nonlinear photonic devices. While both intra- and interlayer excitons in TMDCs have been heavily studied, their behavior in the quantum tunneling regime, in which the TMDC or its heterostructure is optically excited and concurrently serves as a tunnel junction barrier, remains unexplored. Here, using the degree of freedom of a metallic probe in an atomic force microscope, we investigated both intralayer and interlayer excitons dynamics in TMDC heterobilayers via locally controlled junction current in a finely tuned sub-nanometer tip-sample cavity. Our tip-enhanced photoluminescence measurements reveal a significantly different exciton-quantum plasmon coupling for intralayer and interlayer excitons due to different orientation of the dipoles of the respective e-h pairs. Using a steady-state rate equation fit, we extracted field gradients, radiative and nonradiative relaxation rates for excitons in the quantum tunneling regime with and without junction current. Our results show that tip-induced radiative (nonradiative) relaxation of intralayer (interlayer) excitons becomes dominant in the quantum tunneling regime due to the Purcell effect. These findings have important implications for near-field probing of excitonic materials in the strong-coupling regime.
{"title":"Tailoring exciton dynamics in TMDC heterobilayers in the ultranarrow gap-plasmon regime","authors":"Mahfujur Rahaman, Gwangwoo Kim, Kyung Yeol Ma, Seunguk Song, Hyeon Suk Shin, Deep Jariwala","doi":"10.1038/s41699-023-00428-7","DOIUrl":"10.1038/s41699-023-00428-7","url":null,"abstract":"Control of excitons in transition metal dichalcogenides (TMDCs) and their heterostructures is fundamentally interesting for tailoring light-matter interactions and exploring their potential applications in high-efficiency optoelectronic and nonlinear photonic devices. While both intra- and interlayer excitons in TMDCs have been heavily studied, their behavior in the quantum tunneling regime, in which the TMDC or its heterostructure is optically excited and concurrently serves as a tunnel junction barrier, remains unexplored. Here, using the degree of freedom of a metallic probe in an atomic force microscope, we investigated both intralayer and interlayer excitons dynamics in TMDC heterobilayers via locally controlled junction current in a finely tuned sub-nanometer tip-sample cavity. Our tip-enhanced photoluminescence measurements reveal a significantly different exciton-quantum plasmon coupling for intralayer and interlayer excitons due to different orientation of the dipoles of the respective e-h pairs. Using a steady-state rate equation fit, we extracted field gradients, radiative and nonradiative relaxation rates for excitons in the quantum tunneling regime with and without junction current. Our results show that tip-induced radiative (nonradiative) relaxation of intralayer (interlayer) excitons becomes dominant in the quantum tunneling regime due to the Purcell effect. These findings have important implications for near-field probing of excitonic materials in the strong-coupling regime.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-7"},"PeriodicalIF":9.7,"publicationDate":"2023-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00428-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135984335","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}
Inspired by massive parallelism, an increase in internet-of-things devices, robust computation, and Big-data, the upsurge research in building multi-bit mem-transistors is ever-augmenting with different materials, mechanisms, and state-of-the-art architectures. Herein, we demonstrate monolayer WS2-based functional mem-transistor devices which address nonvolatility and synaptic operations at high temperature. The ionotronic memory devices based on WS2 exhibit reverse hysteresis with memory windows larger than 25 V, and extinction ratio greater than 106. The mem-transistors show stable retention and endurance greater than 100 sweep cycles and 400 pulse cycles in addition to 6-bit (64 distinct nonvolatile storage levels) pulse-programmable memory features ranging over six orders of current magnitudes (10−12–10−6 A). The origin of the multi-bit states is attributed to the carrier dynamics under electrostatic doping fluctuations induced by mobile ions, which is illustrated by employing a fingerprint mechanism including band-bending pictures. The credibility of all the storage states is confirmed by obtaining reliable signal-to-noise ratios. We also demonstrate key neuromorphic behaviors, such as synaptic plasticity, near linear potentiation, and depression, rendering it suitable for successful implementation in high temperature neuromorphic computing. Furthermore, artificial neural network simulations based on the conductance weight update characteristics of the proposed ionotronic mem-transistors are performed to explore the potency for accurate image recognition. Our findings showcase a different class of thermally aided memories based on 2D semiconductors unlocking promising avenues for high temperature memory applications in demanding electronics and forthcoming neuromorphic computing technologies.
{"title":"Ionotronic WS2 memtransistors for 6-bit storage and neuromorphic adaptation at high temperature","authors":"Sameer Kumar Mallik, Roshan Padhan, Mousam Charan Sahu, Gopal K. Pradhan, Prasana Kumar Sahoo, Saroj Prasad Dash, Satyaprakash Sahoo","doi":"10.1038/s41699-023-00427-8","DOIUrl":"10.1038/s41699-023-00427-8","url":null,"abstract":"Inspired by massive parallelism, an increase in internet-of-things devices, robust computation, and Big-data, the upsurge research in building multi-bit mem-transistors is ever-augmenting with different materials, mechanisms, and state-of-the-art architectures. Herein, we demonstrate monolayer WS2-based functional mem-transistor devices which address nonvolatility and synaptic operations at high temperature. The ionotronic memory devices based on WS2 exhibit reverse hysteresis with memory windows larger than 25 V, and extinction ratio greater than 106. The mem-transistors show stable retention and endurance greater than 100 sweep cycles and 400 pulse cycles in addition to 6-bit (64 distinct nonvolatile storage levels) pulse-programmable memory features ranging over six orders of current magnitudes (10−12–10−6 A). The origin of the multi-bit states is attributed to the carrier dynamics under electrostatic doping fluctuations induced by mobile ions, which is illustrated by employing a fingerprint mechanism including band-bending pictures. The credibility of all the storage states is confirmed by obtaining reliable signal-to-noise ratios. We also demonstrate key neuromorphic behaviors, such as synaptic plasticity, near linear potentiation, and depression, rendering it suitable for successful implementation in high temperature neuromorphic computing. Furthermore, artificial neural network simulations based on the conductance weight update characteristics of the proposed ionotronic mem-transistors are performed to explore the potency for accurate image recognition. Our findings showcase a different class of thermally aided memories based on 2D semiconductors unlocking promising avenues for high temperature memory applications in demanding electronics and forthcoming neuromorphic computing technologies.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-12"},"PeriodicalIF":9.7,"publicationDate":"2023-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00427-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136107292","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 : 2023-09-09DOI: 10.1038/s41699-023-00426-9
Alina Mreńca-Kolasińska, Szu-Chao Chen, Ming-Hao Liu
The presence of periodic modulation in graphene leads to a reconstruction of the band structure and formation of minibands. In an external uniform magnetic field, a fractal energy spectrum called Hofstadter butterfly is formed. Particularly interesting in this regard are superlattices with tunable modulation strength, such as electrostatically induced ones in graphene. We perform quantum transport modeling in gate-induced square two-dimensional superlattice in graphene and investigate the relation to the details of the band structure. At low magnetic field the dynamics of carriers reflects the semi-classical orbits which depend on the mini band structure. We theoretically model transverse magnetic focusing, a ballistic transport technique by means of which we investigate the minibands, their extent and carrier type. We find a good agreement between the focusing spectra and the mini band structures obtained from the continuum model, proving usefulness of this technique. At high magnetic field the calculated four-probe resistance fit the Hofstadter butterfly spectrum obtained for our superlattice. Our quantum transport modeling provides an insight into the mini band structures, and can be applied to other superlattice geometries.
{"title":"Probing miniband structure and Hofstadter butterfly in gated graphene superlattices via magnetotransport","authors":"Alina Mreńca-Kolasińska, Szu-Chao Chen, Ming-Hao Liu","doi":"10.1038/s41699-023-00426-9","DOIUrl":"10.1038/s41699-023-00426-9","url":null,"abstract":"The presence of periodic modulation in graphene leads to a reconstruction of the band structure and formation of minibands. In an external uniform magnetic field, a fractal energy spectrum called Hofstadter butterfly is formed. Particularly interesting in this regard are superlattices with tunable modulation strength, such as electrostatically induced ones in graphene. We perform quantum transport modeling in gate-induced square two-dimensional superlattice in graphene and investigate the relation to the details of the band structure. At low magnetic field the dynamics of carriers reflects the semi-classical orbits which depend on the mini band structure. We theoretically model transverse magnetic focusing, a ballistic transport technique by means of which we investigate the minibands, their extent and carrier type. We find a good agreement between the focusing spectra and the mini band structures obtained from the continuum model, proving usefulness of this technique. At high magnetic field the calculated four-probe resistance fit the Hofstadter butterfly spectrum obtained for our superlattice. Our quantum transport modeling provides an insight into the mini band structures, and can be applied to other superlattice geometries.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-9"},"PeriodicalIF":9.7,"publicationDate":"2023-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00426-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136192607","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 : 2023-09-07DOI: 10.1038/s41699-023-00423-y
Talieh S. Ghiasi, Michael Borst, Samer Kurdi, Brecht G. Simon, Iacopo Bertelli, Carla Boix-Constant, Samuel Mañas-Valero, Herre S. J. van der Zant, Toeno van der Sar
Magnetic imaging using nitrogen-vacancy (NV) spins in diamonds is a powerful technique for acquiring quantitative information about sub-micron scale magnetic order. A major challenge for its application in the research on two-dimensional (2D) magnets is the positioning of the NV centers at a well-defined, nanoscale distance to the target material required for detecting the small magnetic fields generated by magnetic monolayers. Here, we develop a diamond “dry-transfer” technique akin to the state-of-the-art 2D-materials assembly methods and use it to place a diamond micro-membrane in direct contact with the 2D interlayer antiferromagnet CrSBr. We harness the resulting NV-sample proximity to spatially resolve the magnetic stray fields generated by the CrSBr, present only where the CrSBr thickness changes by an odd number of layers. From the magnetic stray field of a single uncompensated ferromagnetic layer in the CrSBr, we extract a monolayer magnetization of MCSB = 0.46(2) T, without the need for exfoliation of monolayer crystals or applying large external magnetic fields. The ability to deterministically place NV-ensemble sensors into contact with target materials and detect ferromagnetic monolayer magnetizations paves the way for quantitative analysis of a wide range of 2D magnets assembled on arbitrary target substrates.
{"title":"Nitrogen-vacancy magnetometry of CrSBr by diamond membrane transfer","authors":"Talieh S. Ghiasi, Michael Borst, Samer Kurdi, Brecht G. Simon, Iacopo Bertelli, Carla Boix-Constant, Samuel Mañas-Valero, Herre S. J. van der Zant, Toeno van der Sar","doi":"10.1038/s41699-023-00423-y","DOIUrl":"10.1038/s41699-023-00423-y","url":null,"abstract":"Magnetic imaging using nitrogen-vacancy (NV) spins in diamonds is a powerful technique for acquiring quantitative information about sub-micron scale magnetic order. A major challenge for its application in the research on two-dimensional (2D) magnets is the positioning of the NV centers at a well-defined, nanoscale distance to the target material required for detecting the small magnetic fields generated by magnetic monolayers. Here, we develop a diamond “dry-transfer” technique akin to the state-of-the-art 2D-materials assembly methods and use it to place a diamond micro-membrane in direct contact with the 2D interlayer antiferromagnet CrSBr. We harness the resulting NV-sample proximity to spatially resolve the magnetic stray fields generated by the CrSBr, present only where the CrSBr thickness changes by an odd number of layers. From the magnetic stray field of a single uncompensated ferromagnetic layer in the CrSBr, we extract a monolayer magnetization of MCSB = 0.46(2) T, without the need for exfoliation of monolayer crystals or applying large external magnetic fields. The ability to deterministically place NV-ensemble sensors into contact with target materials and detect ferromagnetic monolayer magnetizations paves the way for quantitative analysis of a wide range of 2D magnets assembled on arbitrary target substrates.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-7"},"PeriodicalIF":9.7,"publicationDate":"2023-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00423-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41921056","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 : 2023-09-06DOI: 10.1038/s41699-023-00425-w
Yong-Ju Park, Hongju Lee, Hye Leen Choi, Ma Charlene Tapia, Chong Yang Chuah, Tae-Hyun Bae
Porous materials possessing high surface areas are of paramount importance in gas separation and storage, as they can potentially adsorb a large amount of gas per unit of mass or volume. Pore structure and functionality are also important factors affecting adsorbate–absorbent interactions. Hence, efforts have been devoted to developing adsorbents with large accessible surface areas and tunable functionalities to realize improvements in gas adsorption capacity. However, the gas adsorption and storage capacities of porous materials composed of a single type of building unit are often limited. To this end, mixed-dimensional hybrid materials have been developed, as they can contain more gas storage sites within their structures than simple porous materials. In this review, we discuss (1) the methods that have been used to assemble various dimensional building blocks into a range of mixed-dimensional (zero-dimensional–two-dimensional, one-dimensional–two-dimensional, and three-dimensional–two-dimensional) hybrid materials exhibiting synergistic adsorption effects, and (2) these materials’ hydrogen and carbon dioxide adsorption properties and how they are correlated with their accessible surface areas. We conclude by outlining the challenges remaining to be surmounted to realize practical applications of mixed-dimensional hybrid materials and by providing future perspectives.
{"title":"Mixed-dimensional nanocomposites based on 2D materials for hydrogen storage and CO2 capture","authors":"Yong-Ju Park, Hongju Lee, Hye Leen Choi, Ma Charlene Tapia, Chong Yang Chuah, Tae-Hyun Bae","doi":"10.1038/s41699-023-00425-w","DOIUrl":"10.1038/s41699-023-00425-w","url":null,"abstract":"Porous materials possessing high surface areas are of paramount importance in gas separation and storage, as they can potentially adsorb a large amount of gas per unit of mass or volume. Pore structure and functionality are also important factors affecting adsorbate–absorbent interactions. Hence, efforts have been devoted to developing adsorbents with large accessible surface areas and tunable functionalities to realize improvements in gas adsorption capacity. However, the gas adsorption and storage capacities of porous materials composed of a single type of building unit are often limited. To this end, mixed-dimensional hybrid materials have been developed, as they can contain more gas storage sites within their structures than simple porous materials. In this review, we discuss (1) the methods that have been used to assemble various dimensional building blocks into a range of mixed-dimensional (zero-dimensional–two-dimensional, one-dimensional–two-dimensional, and three-dimensional–two-dimensional) hybrid materials exhibiting synergistic adsorption effects, and (2) these materials’ hydrogen and carbon dioxide adsorption properties and how they are correlated with their accessible surface areas. We conclude by outlining the challenges remaining to be surmounted to realize practical applications of mixed-dimensional hybrid materials and by providing future perspectives.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-18"},"PeriodicalIF":9.7,"publicationDate":"2023-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00425-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48657962","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 : 2023-09-05DOI: 10.1038/s41699-023-00424-x
Youngsin Park, Nannan Li, Daesung Jung, Laishram Tomba Singh, Jaeyoon Baik, Eunsook Lee, Dongseok Oh, Young Dok Kim, Jin Yong Lee, Jeongseok Woo, Seungmin Park, Hanchul Kim, Geunseop Lee, Geunsik Lee, Chan-Cuk Hwang
MoS2 has attracted intense interest in many applications. Natural MoS2 and field-effect transistors made of it generally exhibit n-type characteristics, but its origin is unknown. Herein, we show that C is the origin of the universal n-type doping of natural MoS2. Photoemission spectroscopies reveal that while many MoS2 samples with C detected are n-type, some without C exhibit p-type characteristics. The C-free, p-type MoS2 changes to n-type over time with the concurrent appearance of C that is out-diffused from bulk, indicating that C induces the n-type doping. The C-origin is verified by C-deposition and supported by theoretical calculations. This carbon appears as nanometer-scale defects frequently observed in scanning tunneling microscopy. In addition, we propose, based on the calculations, that S vacancies are responsible for the p-type characteristics, which contrasts with the widespread belief. This work provides new perspectives on MoS2 doping and presents a new direction for fabricating reliable MoS2 devices.
MoS2 在许多应用领域都引起了人们的浓厚兴趣。天然 MoS2 及其场效应晶体管通常具有 n 型特性，但其起源却不为人知。在这里，我们证明了 C 是天然 MoS2 普遍 n 型掺杂的起源。光发射光谱显示，虽然许多检测到 C 的 MoS2 样品是 n 型的，但一些未检测到 C 的 MoS2 样品却表现出 p 型特性。随着时间的推移，不含 C 的 p 型 MoS2 转变为 n 型，同时出现了从体外扩散的 C，这表明 C 诱导了 n 型掺杂。碳源通过碳沉积得到验证，并得到理论计算的支持。这种碳在扫描隧道显微镜中经常以纳米级缺陷的形式出现。此外，我们还根据计算结果提出，S 空位是产生 p 型特性的原因，这与普遍的看法不同。这项研究为 MoS2 掺杂提供了新的视角，并为制造可靠的 MoS2 器件指明了新的方向。
{"title":"Unveiling the origin of n-type doping of natural MoS2: carbon","authors":"Youngsin Park, Nannan Li, Daesung Jung, Laishram Tomba Singh, Jaeyoon Baik, Eunsook Lee, Dongseok Oh, Young Dok Kim, Jin Yong Lee, Jeongseok Woo, Seungmin Park, Hanchul Kim, Geunseop Lee, Geunsik Lee, Chan-Cuk Hwang","doi":"10.1038/s41699-023-00424-x","DOIUrl":"10.1038/s41699-023-00424-x","url":null,"abstract":"MoS2 has attracted intense interest in many applications. Natural MoS2 and field-effect transistors made of it generally exhibit n-type characteristics, but its origin is unknown. Herein, we show that C is the origin of the universal n-type doping of natural MoS2. Photoemission spectroscopies reveal that while many MoS2 samples with C detected are n-type, some without C exhibit p-type characteristics. The C-free, p-type MoS2 changes to n-type over time with the concurrent appearance of C that is out-diffused from bulk, indicating that C induces the n-type doping. The C-origin is verified by C-deposition and supported by theoretical calculations. This carbon appears as nanometer-scale defects frequently observed in scanning tunneling microscopy. In addition, we propose, based on the calculations, that S vacancies are responsible for the p-type characteristics, which contrasts with the widespread belief. This work provides new perspectives on MoS2 doping and presents a new direction for fabricating reliable MoS2 devices.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-7"},"PeriodicalIF":9.7,"publicationDate":"2023-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00424-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45680680","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 : 2023-08-23DOI: 10.1038/s41699-023-00421-0
Aviv Schwarz, Hadas Alon-Yehezkel, Adi Levi, Rajesh Kumar Yadav, Koushik Majhi, Yael Tzuriel, Lauren Hoang, Connor S. Bailey, Thomas Brumme, Andrew J. Mannix, Hagai Cohen, Eilam Yalon, Thomas Heine, Eric Pop, Ori Cheshnovsky, Doron Naveh
Recent research on two-dimensional (2D) transition metal dichalcogenides (TMDCs) has led to remarkable discoveries of fundamental phenomena and to device applications with technological potential. Large-scale TMDCs grown by chemical vapor deposition (CVD) are now available at continuously improving quality, but native defects and natural degradation in these materials still present significant challenges. Spectral hysteresis in gate-biased photoluminescence (PL) measurements of WSe2 further revealed long-term trapping issues of charge carriers in intrinsic defect states. To address these issues, we apply here a two-step treatment with organic molecules, demonstrating the “healing” of native defects in CVD-grown WSe2 and WS2 by substituting atomic sulfur into chalcogen vacancies. We uncover that the adsorption of thiols provides only partial defect passivation, even for high adsorption quality, and that thiol adsorption is fundamentally limited in eliminating charge traps. However, as soon as the molecular backbone is trimmed and atomic sulfur is released to the crystal, both bonds of the sulfur are recruited to passivate the divalent defect and the semiconductor quality improves drastically. Time-dependent X-ray photoelectron spectroscopy (XPS) is applied here together with other methods for the characterization of defects, their healing, leading energies and occupation. First-principles calculations support a unified picture of the electronic passivation of sulfur-healed WSe2 and WS2. This work provides a simple and efficient method for improving the quality of 2D semiconductors and has the potential to impact device performance even after natural degradation.
{"title":"Thiol-based defect healing of WSe2 and WS2","authors":"Aviv Schwarz, Hadas Alon-Yehezkel, Adi Levi, Rajesh Kumar Yadav, Koushik Majhi, Yael Tzuriel, Lauren Hoang, Connor S. Bailey, Thomas Brumme, Andrew J. Mannix, Hagai Cohen, Eilam Yalon, Thomas Heine, Eric Pop, Ori Cheshnovsky, Doron Naveh","doi":"10.1038/s41699-023-00421-0","DOIUrl":"10.1038/s41699-023-00421-0","url":null,"abstract":"Recent research on two-dimensional (2D) transition metal dichalcogenides (TMDCs) has led to remarkable discoveries of fundamental phenomena and to device applications with technological potential. Large-scale TMDCs grown by chemical vapor deposition (CVD) are now available at continuously improving quality, but native defects and natural degradation in these materials still present significant challenges. Spectral hysteresis in gate-biased photoluminescence (PL) measurements of WSe2 further revealed long-term trapping issues of charge carriers in intrinsic defect states. To address these issues, we apply here a two-step treatment with organic molecules, demonstrating the “healing” of native defects in CVD-grown WSe2 and WS2 by substituting atomic sulfur into chalcogen vacancies. We uncover that the adsorption of thiols provides only partial defect passivation, even for high adsorption quality, and that thiol adsorption is fundamentally limited in eliminating charge traps. However, as soon as the molecular backbone is trimmed and atomic sulfur is released to the crystal, both bonds of the sulfur are recruited to passivate the divalent defect and the semiconductor quality improves drastically. Time-dependent X-ray photoelectron spectroscopy (XPS) is applied here together with other methods for the characterization of defects, their healing, leading energies and occupation. First-principles calculations support a unified picture of the electronic passivation of sulfur-healed WSe2 and WS2. This work provides a simple and efficient method for improving the quality of 2D semiconductors and has the potential to impact device performance even after natural degradation.","PeriodicalId":19227,"journal":{"name":"npj 2D Materials and Applications","volume":" ","pages":"1-9"},"PeriodicalIF":9.7,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41699-023-00421-0.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48850049","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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