Pub Date : 2024-02-13DOI: 10.1088/2053-1583/ad2525
Yuhang Hou, Hongyi Yu
We theoretically examined how the dielectric screening of two-dimensional (2D) layered materials affects the dipolar interaction between interlayer excitons (IXs) in few-layer van der Waals structures. Our analysis indicates that the dipolar interaction is largely enhanced by 2D dielectric screening at an inter-exciton separation of several nanometers or larger. The underlying mechanism can be attributed to the induced-charge densities in layered materials, which give rise to induced-dipole densities at large distances with directions parallel to that of the IX. The interaction between quadrupolar excitons in trilayer structures are found to be enhanced even larger, with a magnitude one to two orders stronger than that without 2D dielectric screening. The strengths of these dipolar and quadrupolar interactions can be further tuned by engineering the dielectric environment.
我们从理论上研究了二维（2D）层状材料的介电屏蔽如何影响少层范德华结构中层间激子（IX）之间的偶极相互作用。我们的分析表明，在激子间距为几纳米或更大时，二维介电屏蔽在很大程度上增强了偶极相互作用。其基本机制可归因于层状材料中的诱导电荷密度，这种密度会在与 IX 方向平行的大距离上产生诱导偶极子密度。研究发现，三层结构中四极激子之间的相互作用增强得更大，比没有二维电介质屏蔽时强一到两个数量级。这些二极性和四极性相互作用的强度可以通过设计电介质环境来进一步调整。
{"title":"Dipolar interactions enhanced by two-dimensional dielectric screening in few-layer van der Waals structures","authors":"Yuhang Hou, Hongyi Yu","doi":"10.1088/2053-1583/ad2525","DOIUrl":"https://doi.org/10.1088/2053-1583/ad2525","url":null,"abstract":"We theoretically examined how the dielectric screening of two-dimensional (2D) layered materials affects the dipolar interaction between interlayer excitons (IXs) in few-layer van der Waals structures. Our analysis indicates that the dipolar interaction is largely enhanced by 2D dielectric screening at an inter-exciton separation of several nanometers or larger. The underlying mechanism can be attributed to the induced-charge densities in layered materials, which give rise to induced-dipole densities at large distances with directions parallel to that of the IX. The interaction between quadrupolar excitons in trilayer structures are found to be enhanced even larger, with a magnitude one to two orders stronger than that without 2D dielectric screening. The strengths of these dipolar and quadrupolar interactions can be further tuned by engineering the dielectric environment.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"31 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140010447","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 : 2024-02-13DOI: 10.1088/2053-1583/ad2524
Giung Park, Suhan Son, Jongchan Kim, Yunyeong Chang, Kaixuan Zhang, Miyoung Kim, Jieun Lee, Je-Geun Park
Observations of emergent quantum phases in twisted bilayer graphene prompted a flurry of activities in van der Waals (vdW) materials beyond graphene. Most current twisted experiments use a so-called tear-and-stack method using a polymer called polypropylene carbonate (PPC). However, despite the clear advantage of the current PPC tear-and-stack method, there are also technical limitations, mainly a limited number of vdW materials that can be studied using this PPC-based method. This technical bottleneck has been preventing further development of the exciting field beyond a few available vdW samples. To overcome this challenge and facilitate future expansion, we developed a new tear-and-stack method using a strongly adhesive polycaprolactone. With similar angular accuracy, our technology allows fabrication without a capping layer, facilitating surface analysis and ensuring inherently clean interfaces and low operating temperatures. More importantly, it can be applied to many other vdW materials that have remained inaccessible with the PPC-based method. We present our results on twist homostructures made with a wide choice of vdW materials—from two well-studied vdW materials (graphene and MoS2) to the first-ever demonstrations of other vdW materials (NbSe2, NiPS3, and Fe3GeTe2). Therefore, our new technique will help expand moiré physics beyond few selected vdW materials and open up more exciting developments.
{"title":"New twisted van der Waals fabrication method based on strongly adhesive polymer","authors":"Giung Park, Suhan Son, Jongchan Kim, Yunyeong Chang, Kaixuan Zhang, Miyoung Kim, Jieun Lee, Je-Geun Park","doi":"10.1088/2053-1583/ad2524","DOIUrl":"https://doi.org/10.1088/2053-1583/ad2524","url":null,"abstract":"Observations of emergent quantum phases in twisted bilayer graphene prompted a flurry of activities in van der Waals (vdW) materials beyond graphene. Most current twisted experiments use a so-called tear-and-stack method using a polymer called polypropylene carbonate (PPC). However, despite the clear advantage of the current PPC tear-and-stack method, there are also technical limitations, mainly a limited number of vdW materials that can be studied using this PPC-based method. This technical bottleneck has been preventing further development of the exciting field beyond a few available vdW samples. To overcome this challenge and facilitate future expansion, we developed a new tear-and-stack method using a strongly adhesive polycaprolactone. With similar angular accuracy, our technology allows fabrication without a capping layer, facilitating surface analysis and ensuring inherently clean interfaces and low operating temperatures. More importantly, it can be applied to many other vdW materials that have remained inaccessible with the PPC-based method. We present our results on twist homostructures made with a wide choice of vdW materials—from two well-studied vdW materials (graphene and MoS<sub>2</sub>) to the first-ever demonstrations of other vdW materials (NbSe<sub>2</sub>, NiPS<sub>3</sub>, and Fe<sub>3</sub>GeTe<sub>2</sub>). Therefore, our new technique will help expand moiré physics beyond few selected vdW materials and open up more exciting developments.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"36 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140010445","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 : 2024-02-12DOI: 10.1088/2053-1583/ad2526
L H de Lima, A de Siervo
We investigated the surface structure of a NbSe2 single crystal at room temperature, using angle-scanned x-ray photoelectron diffraction (XPD) combined with multiple scattering calculations. Different stacking sequences were tested (1T, 2Ha, 2Hc, and 3R), including possible stacking faults and a mixed 2H–3R stacking proposed earlier in the literature. We confirm the capability of XPD to distinguish different proposed structural models and, unambiguously, determine the true surface structure. Also, our findings provide reliable in-plane and interlayer distances. We observed expansions of the perpendicular distances between atomic planes within the monolayer and between monolayers of 3%–5%. These results are important as accurate experimental input for the development of theoretical methods that involve a quantitative description of van der Waals systems.
{"title":"X-ray photoelectron diffraction as a modern tool for determining surface stacking sequence in layered materials","authors":"L H de Lima, A de Siervo","doi":"10.1088/2053-1583/ad2526","DOIUrl":"https://doi.org/10.1088/2053-1583/ad2526","url":null,"abstract":"We investigated the surface structure of a NbSe<sub>2</sub> single crystal at room temperature, using angle-scanned x-ray photoelectron diffraction (XPD) combined with multiple scattering calculations. Different stacking sequences were tested (1T, 2H<sub>\u0000<italic toggle=\"yes\">a</italic>\u0000</sub>, 2H<sub>\u0000<italic toggle=\"yes\">c</italic>\u0000</sub>, and 3R), including possible stacking faults and a mixed 2H–3R stacking proposed earlier in the literature. We confirm the capability of XPD to distinguish different proposed structural models and, unambiguously, determine the true surface structure. Also, our findings provide reliable in-plane and interlayer distances. We observed expansions of the perpendicular distances between atomic planes within the monolayer and between monolayers of 3%–5%. These results are important as accurate experimental input for the development of theoretical methods that involve a quantitative description of van der Waals systems.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"16 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-02-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139757274","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 : 2024-02-01DOI: 10.1088/2053-1583/ad2193
Daliang He, Bo Wang, Wang Cao, Yongjun Jiang, Sheng Dai, Wei Zhao, Xiaodong Cui, Chuanhong Jin
Self-intercalation is an efficient strategy for tailoring the property of layer structured materials like transition metal dichalcogenides (TMDCs), while the associated kinetics and mechanism remain scarcely explored. In this study, we investigate the atomic-scale dynamics and mechanism of vanadium (V) self-intercalation in multi-layer 1T-VSe2 using in situ high resolution scanning transmission electron microscopy. The results reveal that the self-intercalation of V induces structural transformation of pristine VSe2 into three V-enrich intercalated compounds, i.e. V5Se8, V3Se4 and VSe. The self-intercalated V follows an ordered arrangement of 2×2, 2×1, and 1×1 within the interlayer octahedral sites, corresponding to an intercalation concentration of 25%, 50% and 100% in V5Se8, V3Se4 and VSe, respectively. The V intercalants induced lattice distortions to the host 1T-VSe2 such as the dimerization of neighboring lattice V is observed experimentally, which are further supported by density functional theory (DFT) calculations. Finally, a superstructure model generalizing the possible structures of self-intercalated compounds in layered TMDCs is proposed and then validated by the DFT determined formation energy landscape. This study provides comprehensive insights on the kinetics and mechanism of the self-intercalation in layered TMDC materials, contributing to the precise control for the structure and stoichiometry of self-intercalated TMDC compounds.
自掺杂是调整过渡金属二钙化物（TMDCs）等层状结构材料特性的一种有效策略，但相关的动力学和机理却鲜有研究。在本研究中，我们利用原位高分辨率扫描透射电子显微镜研究了多层 1T-VSe2 中钒（V）自掺杂的原子尺度动力学和机理。结果表明，钒的自掺杂诱导原始 VSe2 结构转变为三种富钒掺杂化合物，即 V5Se8、V3Se4 和 VSe。自插层的 V 在层间八面体位点内呈 2×2、2×1 和 1×1 的有序排列，在 V5Se8、V3Se4 和 VSe 中的插层浓度分别为 25%、50% 和 100%。实验观察到 V 插层诱导宿主 1T-VSe2 晶格畸变，如相邻晶格 V 的二聚化，密度泛函理论（DFT）计算进一步证实了这一点。最后，我们提出了一个上层结构模型，概括了层状 TMDC 中自掺杂化合物的可能结构，并通过 DFT 确定的形成能谱进行了验证。这项研究全面揭示了层状 TMDC 材料中自掺杂的动力学和机理，有助于精确控制自掺杂 TMDC 化合物的结构和化学计量。
{"title":"Unraveling the mechanism of vanadium self-intercalation in 1T-VSe2: atomic-scale evidence for phase transition and superstructure model for intercalation compound","authors":"Daliang He, Bo Wang, Wang Cao, Yongjun Jiang, Sheng Dai, Wei Zhao, Xiaodong Cui, Chuanhong Jin","doi":"10.1088/2053-1583/ad2193","DOIUrl":"https://doi.org/10.1088/2053-1583/ad2193","url":null,"abstract":"Self-intercalation is an efficient strategy for tailoring the property of layer structured materials like transition metal dichalcogenides (TMDCs), while the associated kinetics and mechanism remain scarcely explored. In this study, we investigate the atomic-scale dynamics and mechanism of vanadium (V) self-intercalation in multi-layer 1T-VSe<sub>2</sub> using <italic toggle=\"yes\">in situ</italic> high resolution scanning transmission electron microscopy. The results reveal that the self-intercalation of V induces structural transformation of pristine VSe<sub>2</sub> into three V-enrich intercalated compounds, i.e. V<sub>5</sub>Se<sub>8</sub>, V<sub>3</sub>Se<sub>4</sub> and VSe. The self-intercalated V follows an ordered arrangement of <inline-formula>\u0000<tex-math><?CDATA $2 times 2$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mn>2</mml:mn><mml:mo>×</mml:mo><mml:mn>2</mml:mn></mml:math>\u0000<inline-graphic xlink:href=\"tdmad2193ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>, <inline-formula>\u0000<tex-math><?CDATA $2 times 1$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mn>2</mml:mn><mml:mo>×</mml:mo><mml:mn>1</mml:mn></mml:math>\u0000<inline-graphic xlink:href=\"tdmad2193ieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>, and <inline-formula>\u0000<tex-math><?CDATA $1 times 1$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mn>1</mml:mn><mml:mo>×</mml:mo><mml:mn>1</mml:mn></mml:math>\u0000<inline-graphic xlink:href=\"tdmad2193ieqn3.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> within the interlayer octahedral sites, corresponding to an intercalation concentration of 25%, 50% and 100% in V<sub>5</sub>Se<sub>8</sub>, V<sub>3</sub>Se<sub>4</sub> and VSe, respectively. The V intercalants induced lattice distortions to the host 1T-VSe<sub>2</sub> such as the dimerization of neighboring lattice V is observed experimentally, which are further supported by density functional theory (DFT) calculations. Finally, a superstructure model generalizing the possible structures of self-intercalated compounds in layered TMDCs is proposed and then validated by the DFT determined formation energy landscape. This study provides comprehensive insights on the kinetics and mechanism of the self-intercalation in layered TMDC materials, contributing to the precise control for the structure and stoichiometry of self-intercalated TMDC compounds.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"19 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139757437","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 : 2024-01-31DOI: 10.1088/2053-1583/ad1e78
Thomas Schmaltz, Lorenzo Wormer, Ulrich Schmoch, Henning Döscher
Graphene and related materials (GRMs) promise ample application potential throughout numerous industries. A dedicated graphene market gradually forms around emerging suppliers aspiring to satisfy future demands. Its growth critically depends on the interplay of supply stream maturation and initial utilizations to drive the demand. The present issue of Graphene Roadmap Briefs provides quantitative insights into the current state and future development of the emerging graphene market. We aggregate the underlying expectations and projections from commercial market reports and critically discuss the results. Established science and technology metrics complement our analyses and provide deeper insights into the global market landscape and key actors. In particular, we resolve composites, batteries, and electronics as major application areas likely to drive the overall development of the graphene market towards mass production.About: Graphene Roadmap BriefsGraphene Roadmap Briefs highlight key innovation areas impacted by graphene and related materials (GRMs) as well as overarching aspects of GRM innovation status and prospects. The series bases on the evolving technology and innovation roadmap process initiated by the European Graphene Flagship. It covers crucial innovation trends beyond fundamental scientific discovery and applied research on GRM utilization opportunities.
{"title":"Graphene Roadmap Briefs (No. 3): meta-market analysis 2023","authors":"Thomas Schmaltz, Lorenzo Wormer, Ulrich Schmoch, Henning Döscher","doi":"10.1088/2053-1583/ad1e78","DOIUrl":"https://doi.org/10.1088/2053-1583/ad1e78","url":null,"abstract":"Graphene and related materials (GRMs) promise ample application potential throughout numerous industries. A dedicated graphene market gradually forms around emerging suppliers aspiring to satisfy future demands. Its growth critically depends on the interplay of supply stream maturation and initial utilizations to drive the demand. The present issue of Graphene Roadmap Briefs provides quantitative insights into the current state and future development of the emerging graphene market. We aggregate the underlying expectations and projections from commercial market reports and critically discuss the results. Established science and technology metrics complement our analyses and provide deeper insights into the global market landscape and key actors. In particular, we resolve composites, batteries, and electronics as major application areas likely to drive the overall development of the graphene market towards mass production.<bold>About: Graphene Roadmap Briefs</bold>Graphene Roadmap Briefs highlight key innovation areas impacted by graphene and related materials (GRMs) as well as overarching aspects of GRM innovation status and prospects. The series bases on the evolving technology and innovation roadmap process initiated by the European Graphene Flagship. It covers crucial innovation trends beyond fundamental scientific discovery and applied research on GRM utilization opportunities.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"9 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139757180","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 : 2024-01-30DOI: 10.1088/2053-1583/ad2108
Shoaib Khalid, Bharat Medasani, John L Lyons, Darshana Wickramaratne, Anderson Janotti
Chalcogen vacancies in the semiconducting monolayer transition-metal dichalcogenides (TMDs) have frequently been invoked to explain a wide range of phenomena, including both unintentional p-type and n-type conductivity, as well as sub-band gap defect levels measured via tunneling or optical spectroscopy. These conflicting interpretations of the deep versus shallow nature of the chalcogen vacancies are due in part to shortcomings in prior first-principles calculations of defects in the semiconducting two-dimensional TMDs that have been used to explain experimental observations. Here we report results of hybrid density functional calculations for the chalcogen vacancy in a series of monolayer TMDs, correctly referencing the thermodynamic charge transition levels to the fundamental band gap (as opposed to the optical band gap). We find that the chalcogen vacancies are deep acceptors and cannot lead to n-type or p-type conductivity. Both the (0/−1) and (−1/−2) transition levels occur in the gap, leading to paramagnetic charge states S=1/2 and S = 1, respectively, in a collinear-spin representation. We discuss trends in terms of the band alignments between the TMDs, which can serve as a guide to future experimental studies of vacancy behavior.
半导体单层过渡金属二掺杂物（TMDs）中的瑀空位经常被用来解释各种现象，包括无意的 p 型和 n 型导电性，以及通过隧道或光学光谱测量的亚带隙缺陷水平。这些关于查尔根空位深浅性质的相互矛盾的解释，部分是由于之前用于解释实验观察结果的二维 TMD 半导体缺陷的第一原理计算存在缺陷。在此，我们报告了一系列单层 TMD 中胆原空位的混合密度泛函计算结果，正确地将热力学电荷转移水平引用到基带隙（而不是光带隙）。我们发现，查尔根空位是深度受体，不能导致 n 型或 p 型导电性。(0/-1)和(-1/-2)转变级都出现在带隙中，分别导致了顺磁电荷态 S=1/2 和 S = 1，采用的是准线-自旋表示法。我们讨论了 TMD 之间的带排列趋势，这可作为未来空位行为实验研究的指南。
{"title":"The deep-acceptor nature of the chalcogen vacancies in 2D transition-metal dichalcogenides","authors":"Shoaib Khalid, Bharat Medasani, John L Lyons, Darshana Wickramaratne, Anderson Janotti","doi":"10.1088/2053-1583/ad2108","DOIUrl":"https://doi.org/10.1088/2053-1583/ad2108","url":null,"abstract":"Chalcogen vacancies in the semiconducting monolayer transition-metal dichalcogenides (TMDs) have frequently been invoked to explain a wide range of phenomena, including both unintentional p-type and n-type conductivity, as well as sub-band gap defect levels measured via tunneling or optical spectroscopy. These conflicting interpretations of the deep versus shallow nature of the chalcogen vacancies are due in part to shortcomings in prior first-principles calculations of defects in the semiconducting two-dimensional TMDs that have been used to explain experimental observations. Here we report results of hybrid density functional calculations for the chalcogen vacancy in a series of monolayer TMDs, correctly referencing the thermodynamic charge transition levels to the fundamental band gap (as opposed to the optical band gap). We find that the chalcogen vacancies are deep acceptors and cannot lead to n-type or p-type conductivity. Both the (0/−1) and (−1/−2) transition levels occur in the gap, leading to paramagnetic charge states <inline-formula>\u0000<tex-math><?CDATA $S = 1/2$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mi>S</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn><mml:mrow><mml:mo>/</mml:mo></mml:mrow><mml:mn>2</mml:mn></mml:math>\u0000<inline-graphic xlink:href=\"tdmad2108ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> and <italic toggle=\"yes\">S</italic> = 1, respectively, in a collinear-spin representation. We discuss trends in terms of the band alignments between the TMDs, which can serve as a guide to future experimental studies of vacancy behavior.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"21 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139757095","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 : 2024-01-25DOI: 10.1088/2053-1583/ad1c6d
Brad M Goff, Wenyi Zhou, Alexander J Bishop, Ryan Bailey-Crandell, Katherine Robinson, Roland K Kawakami, Jay A Gupta
Introducing magnetism to the surface state of topological insulators, such as Bi2Te3, can lead to a variety of interesting phenomena. We use scanning tunneling microscopy (STM) to study a single quintuple layer (QL) of the van der Waals magnet Fe3GeTe2 (FGT) that is grown on Bi2Te3 via molecular beam epitaxy. STM topographic images show that the FGT grows as free-standing islands on Bi2Te3 and outwards from Bi2Te3 steps. Atomic resolution imaging shows triangular lattices of 390 ± 10 pm for FGT and 430 ± 10 pm for Bi2Te3, consistent with the respective bulk crystals. A moiré pattern is observed on FGT regions with a periodicity of 4.3 ± 0.4 nm that can be attributed solely to this lattice mismatch and thus indicates zero rotational misalignment. While most of the surface is covered by a single QL of the FGT, there are small double QL regions, as well as regions with distinct chemical terminations due to an incomplete QL. The most common partial QL surface termination is the FeGe layer, in which the top two atomic layers are missing. This termination has a distinctive electronic structure and a 3x3R30∘ reconstruction overlaid on the moiré pattern in STM images. Magnetic circular dichroism measurements confirm these thin FGT films are ferromagnetic with TC ∼190 K.
{"title":"Scanning tunneling microscopy study of epitaxial Fe3GeTe2 monolayers on Bi2Te3","authors":"Brad M Goff, Wenyi Zhou, Alexander J Bishop, Ryan Bailey-Crandell, Katherine Robinson, Roland K Kawakami, Jay A Gupta","doi":"10.1088/2053-1583/ad1c6d","DOIUrl":"https://doi.org/10.1088/2053-1583/ad1c6d","url":null,"abstract":"Introducing magnetism to the surface state of topological insulators, such as Bi<sub>2</sub>Te<sub>3</sub>, can lead to a variety of interesting phenomena. We use scanning tunneling microscopy (STM) to study a single quintuple layer (QL) of the van der Waals magnet Fe<sub>3</sub>GeTe<sub>2</sub> (FGT) that is grown on Bi<sub>2</sub>Te<sub>3</sub> via molecular beam epitaxy. STM topographic images show that the FGT grows as free-standing islands on Bi<sub>2</sub>Te<sub>3</sub> and outwards from Bi<sub>2</sub>Te<sub>3</sub> steps. Atomic resolution imaging shows triangular lattices of 390 ± 10 pm for FGT and 430 ± 10 pm for Bi<sub>2</sub>Te<sub>3</sub>, consistent with the respective bulk crystals. A moiré pattern is observed on FGT regions with a periodicity of 4.3 ± 0.4 nm that can be attributed solely to this lattice mismatch and thus indicates zero rotational misalignment. While most of the surface is covered by a single QL of the FGT, there are small double QL regions, as well as regions with distinct chemical terminations due to an incomplete QL. The most common partial QL surface termination is the FeGe layer, in which the top two atomic layers are missing. This termination has a distinctive electronic structure and a <inline-formula>\u0000<tex-math><?CDATA $left( {sqrt 3 {text{ }}x{text{ }}sqrt 3 } right)R{30^circ }$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mfenced close=\")\" open=\"(\"><mml:mrow><mml:msqrt><mml:mn>3</mml:mn></mml:msqrt><mml:mrow><mml:mtext> </mml:mtext></mml:mrow><mml:mi>x</mml:mi><mml:mrow><mml:mtext> </mml:mtext></mml:mrow><mml:msqrt><mml:mn>3</mml:mn></mml:msqrt></mml:mrow></mml:mfenced><mml:mi>R</mml:mi><mml:mrow><mml:msup><mml:mn>30</mml:mn><mml:mo>∘</mml:mo></mml:msup></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad1c6dieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> reconstruction overlaid on the moiré pattern in STM images. Magnetic circular dichroism measurements confirm these thin FGT films are ferromagnetic with <italic toggle=\"yes\">T</italic>\u0000<sub>C</sub> ∼190 K.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"68 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139757179","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 : 2024-01-24DOI: 10.1088/2053-1583/ad1e79
Marin Tharrault, Eva Desgué, Dominique Carisetti, Bernard Plaçais, Christophe Voisin, Pierre Legagneux, Emmanuel Baudin
Raman spectroscopy is widely used to assess the quality of 2D materials thin films. This report focuses on PtSe2, a noble transition metal dichalcogenide which has the remarkable property to transit from a semi-conductor to a semi-metal with increasing layer number. While polycrystalline PtSe2 can be grown with various crystalline qualities, getting insight into the monocrystalline intrinsic properties remains challenging. We report on the study of exfoliated 1–10 layers PtSe2 by Raman spectroscopy, featuring record linewidth. The clear Raman signatures allow layer-thickness identification and provides a reference metrics to assess crystal quality of grown films.
{"title":"Raman spectroscopy of monolayer to bulk PtSe2 exfoliated crystals","authors":"Marin Tharrault, Eva Desgué, Dominique Carisetti, Bernard Plaçais, Christophe Voisin, Pierre Legagneux, Emmanuel Baudin","doi":"10.1088/2053-1583/ad1e79","DOIUrl":"https://doi.org/10.1088/2053-1583/ad1e79","url":null,"abstract":"Raman spectroscopy is widely used to assess the quality of 2D materials thin films. This report focuses on <inline-formula>\u0000<tex-math><?CDATA $mathrm{PtSe_2}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi mathvariant=\"normal\">P</mml:mi><mml:mi mathvariant=\"normal\">t</mml:mi><mml:mi mathvariant=\"normal\">S</mml:mi><mml:msub><mml:mi mathvariant=\"normal\">e</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad1e79ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>, a noble transition metal dichalcogenide which has the remarkable property to transit from a semi-conductor to a semi-metal with increasing layer number. While polycrystalline <inline-formula>\u0000<tex-math><?CDATA $mathrm{PtSe_2}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi mathvariant=\"normal\">P</mml:mi><mml:mi mathvariant=\"normal\">t</mml:mi><mml:mi mathvariant=\"normal\">S</mml:mi><mml:msub><mml:mi mathvariant=\"normal\">e</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad1e79ieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> can be grown with various crystalline qualities, getting insight into the monocrystalline intrinsic properties remains challenging. We report on the study of exfoliated 1–10 layers <inline-formula>\u0000<tex-math><?CDATA $mathrm{PtSe_2}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi mathvariant=\"normal\">P</mml:mi><mml:mi mathvariant=\"normal\">t</mml:mi><mml:mi mathvariant=\"normal\">S</mml:mi><mml:msub><mml:mi mathvariant=\"normal\">e</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"tdmad1e79ieqn3.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> by Raman spectroscopy, featuring record linewidth. The clear Raman signatures allow layer-thickness identification and provides a reference metrics to assess crystal quality of grown films.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"79 1","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139757186","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 : 2024-01-10DOI: 10.1088/2053-1583/ad1d0c
Zhoubin Yu, Yipu Xia, H. Komsa, Junqiu Zhang, Maohai Xie, Chuanhong Jin
Interplay between defects like mirror twin boundaries (MTBs) and dopants may provide additional opportunities for furthering the research on two-dimensional monolayer (ML) transition metal dichalcogenides (TMDs). In this work, we successfully dope rhenium (Re) into molecular beam epitaxy grown ML MoSe2 and confirm the formation of a new type of MTBs, named 4|4E-M (M represents metal, Mo/Re) according to the configuration. Data from statistic atomic resolution scanning transmission electron microscopy (STEM) also reveals a preferable MTB enrichment of Re dopants, rather than intra-domain. In conjunction with density functional theory calculation results, we propose the possible routes for Re doping induced formation of 4|4E-M MTBs. Electronic structures of Re doped MTBs in ML MoSe2 are also predicted theoretically and then preliminarily tested by scanning tunnelling microscopy and spectroscopy.
镜像孪晶边界（MTB）等缺陷与掺杂剂之间的相互作用可能会为进一步研究二维单层（ML）过渡金属二钙化物（TMD）提供更多机会。在这项工作中，我们成功地在分子束外延生长的 ML MoSe2 中掺入了铼（Re），并证实形成了一种新型 MTB，根据构型命名为 4|4E-M（M 代表金属，Mo/Re）。原子分辨率扫描透射电子显微镜（STEM）的统计数据也显示，MTB 更倾向于富集 Re 掺杂物，而不是域内掺杂物。结合密度泛函理论计算结果，我们提出了掺杂 Re 诱导形成 4|4E-M MTB 的可能途径。我们还从理论上预测了 ML MoSe2 中掺杂 Re 的 MTB 的电子结构，并通过扫描隧道显微镜和光谱学进行了初步测试。
{"title":"Tuning the atomic and electronic structures of mirror twin boundaries in molecular beam epitaxy grown MoSe2 monolayers via rhenium doping","authors":"Zhoubin Yu, Yipu Xia, H. Komsa, Junqiu Zhang, Maohai Xie, Chuanhong Jin","doi":"10.1088/2053-1583/ad1d0c","DOIUrl":"https://doi.org/10.1088/2053-1583/ad1d0c","url":null,"abstract":"\u0000 Interplay between defects like mirror twin boundaries (MTBs) and dopants may provide additional opportunities for furthering the research on two-dimensional monolayer (ML) transition metal dichalcogenides (TMDs). In this work, we successfully dope rhenium (Re) into molecular beam epitaxy grown ML MoSe2 and confirm the formation of a new type of MTBs, named 4|4E-M (M represents metal, Mo/Re) according to the configuration. Data from statistic atomic resolution scanning transmission electron microscopy (STEM) also reveals a preferable MTB enrichment of Re dopants, rather than intra-domain. In conjunction with density functional theory calculation results, we propose the possible routes for Re doping induced formation of 4|4E-M MTBs. Electronic structures of Re doped MTBs in ML MoSe2 are also predicted theoretically and then preliminarily tested by scanning tunnelling microscopy and spectroscopy.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"81 13","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139440462","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 : 2024-01-09DOI: 10.1088/2053-1583/ad1c6e
Alina Valimukhametova, Olivia Fannon, Ugur C. Topkiran, Abby Dorsky, Olivia Sottile, Roberto Gonzalez Rodriguez, J. Coffer, Anton V. Naumov
Due to high tissue penetration depth and low autofluorescence backgrounds, near-infrared (NIR) fluorescence imaging has recently become an advantageous diagnostic technique used in a variety of fields. However, most of the NIR fluorophores do not have therapeutic delivery capabilities, exhibit low photostabilities, and raise toxicity concerns. To address these issues, we developed and tested five types of biocompatible graphene quantum dots (GQDs) exhibiting spectrally-separated fluorescence in the NIR range of 928 – 1053 nm with NIR excitation. Their optical properties in the NIR are attributed to either rare-earth metal dopants (Ho-NGQDs, Yb-NGQDs, Nd-NGQDs) or defect-states (NGQDs, RGQDs) as verified by Hartree-Fock calculations. Moderate up to 1.34 % quantum yields of these GQDs are well-compensated by their remarkable >4-hour photostability. At the biocompatible concentrations of up to 0.5 – 2 mg/mL GQDs successfully internalize into HEK-293 cells and enable in vitro imaging in the visible and NIR. Tested all together in HEK-293 cells five GQD types enable simultaneous multiplex imaging in the NIR-I and NIR-II shown for the first time in this work for GQD platforms. Substantial photostability, spectrally-separated NIR emission, and high biocompatibility of five GQD types developed here suggest their promising potential in multianalyte testing and multiwavelength bioimaging of combination therapies.
{"title":"Five near-infrared-emissive graphene quantum dots for multiplex bioimaging.","authors":"Alina Valimukhametova, Olivia Fannon, Ugur C. Topkiran, Abby Dorsky, Olivia Sottile, Roberto Gonzalez Rodriguez, J. Coffer, Anton V. Naumov","doi":"10.1088/2053-1583/ad1c6e","DOIUrl":"https://doi.org/10.1088/2053-1583/ad1c6e","url":null,"abstract":"\u0000 Due to high tissue penetration depth and low autofluorescence backgrounds, near-infrared (NIR) fluorescence imaging has recently become an advantageous diagnostic technique used in a variety of fields. However, most of the NIR fluorophores do not have therapeutic delivery capabilities, exhibit low photostabilities, and raise toxicity concerns. To address these issues, we developed and tested five types of biocompatible graphene quantum dots (GQDs) exhibiting spectrally-separated fluorescence in the NIR range of 928 – 1053 nm with NIR excitation. Their optical properties in the NIR are attributed to either rare-earth metal dopants (Ho-NGQDs, Yb-NGQDs, Nd-NGQDs) or defect-states (NGQDs, RGQDs) as verified by Hartree-Fock calculations. Moderate up to 1.34 % quantum yields of these GQDs are well-compensated by their remarkable >4-hour photostability. At the biocompatible concentrations of up to 0.5 – 2 mg/mL GQDs successfully internalize into HEK-293 cells and enable in vitro imaging in the visible and NIR. Tested all together in HEK-293 cells five GQD types enable simultaneous multiplex imaging in the NIR-I and NIR-II shown for the first time in this work for GQD platforms. Substantial photostability, spectrally-separated NIR emission, and high biocompatibility of five GQD types developed here suggest their promising potential in multianalyte testing and multiwavelength bioimaging of combination therapies.","PeriodicalId":6812,"journal":{"name":"2D Materials","volume":"29 3","pages":""},"PeriodicalIF":5.5,"publicationDate":"2024-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139441648","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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