المؤلفون: Rizzo, Daniel J, Zhang, Jin, Jessen, Bjarke S, Ruta, Francesco L, Cothrine, Matthew, Yan, Jiaqiang, Mandrus, David G, Nagler, Stephen E, Taniguchi, Takashi, Watanabe, Kenji, Fogler, Michael M, Pasupathy, Abhay N, Millis, Andrew J, Rubio, Angel, Hone, James C, Dean, Cory R, Basov, DN

المصدر: Nano Letters. 23(18)

مصطلحات موضوعية: Quantum Physics, Physical Sciences, Condensed Matter Physics, phonon polaritons, charge transfer, & alpha, -RuCl3, scanning near-field optical microscopy, two-dimensional (2D) materials, heterostructures, α-RuCl3, Nanoscience & Nanotechnology

الوصف: The use of work-function-mediated charge transfer has recently emerged as a reliable route toward nanoscale electrostatic control of individual atomic layers. Using α-RuCl3 as a 2D electron acceptor, we are able to induce emergent nano-optical behavior in hexagonal boron nitride (hBN) that arises due to interlayer charge polarization. Using scattering-type scanning near-field optical microscopy (s-SNOM), we find that a thin layer of α-RuCl3 adjacent to an hBN slab reduces the propagation length of hBN phonon polaritons (PhPs) in significant excess of what can be attributed to intrinsic optical losses. Concomitant nano-optical spectroscopy experiments reveal a novel resonance that aligns energetically with the region of excess PhP losses. These experimental observations are elucidated by first-principles density-functional theory and near-field model calculations, which show that the formation of a large interfacial dipole suppresses out-of-plane PhP propagation. Our results demonstrate the potential utility of charge-transfer heterostructures for tailoring optoelectronic properties of 2D insulators.

وصف الملف: application/pdf

الوصول الحر: https://escholarship.org/uc/item/248338d0Test

المؤلفون: Chen, Xinzhong, Xu, Suheng, Shabani, Sara, Zhao, Yueqi, Fu, Matthew, Millis, Andrew J, Fogler, Michael M, Pasupathy, Abhay N, Liu, Mengkun, Basov, DN

المصدر: Advanced Materials. 35(34)

مصطلحات موضوعية: Quantum Physics, Physical Sciences, artificial intelligence, machine learning, scanning near-field microscopy, scattering-type scanning near-field optical microscopy, Chemical Sciences, Engineering, Nanoscience & Nanotechnology, Chemical sciences, Physical sciences

الوصف: The ability to perform nanometer-scale optical imaging and spectroscopy is key to deciphering the low-energy effects in quantum materials, as well as vibrational fingerprints in planetary and extraterrestrial particles, catalytic substances, and aqueous biological samples. These tasks can be accomplished by the scattering-type scanning near-field optical microscopy (s-SNOM) technique that has recently spread to many research fields and enabled notable discoveries. Herein, it is shown that the s-SNOM, together with scanning probe research in general, can benefit in many ways from artificial-intelligence (AI) and machine-learning (ML) algorithms. Augmented with AI- and ML-enhanced data acquisition and analysis, scanning probe optical nanoscopy is poised to become more efficient, accurate, and intelligent.

وصف الملف: application/pdf

الوصول الحر: https://escholarship.org/uc/item/75f000mvTest

المؤلفون: Victor Wong, Sabastine Ezugwu, Giovanni Fanchini

المصدر: Advanced Materials Interfaces, Vol 11, Iss 12, Pp n/a-n/a (2024)

مصطلحات موضوعية: nanogranular materials, scanning‐near field optical microscopy (SNOM), thermal expansion coefficient, thermoreflecance, Physics, QC1-999, Technology

الوصف: Abstract To date, there are very few experimental techniques, if any, that are suitable for the purpose of acquiring quantitative maps of the thermal expansivity of 2D materials and nanostructured thin films with nanoscale lateral resolution in spite of huge demand for nanoscale thermal management, for example in designing integrated circuitry for power electronics. Besides, contactless analytical tools for determining the thermal expansion coefficient (TEC) are highly desirable because probes in contact with the sample significantly perturb any thermal measurements. Here, ω‐2ω near‐field thermoreflectance imaging is presented as a novel, all‐optical, and contactless technique to map the TEC at the nanoscale with precision. Testing of this technique is performed on nanogranular films of gold and multilayer graphene (ML‐G) platelets. With ω‐2ω near‐field thermoreflectance, it is demonstrated that the TEC of Au is higher at the metal‐insulator interface, with an average of (17.12 ± 2.30) ×10−6 K−1 in agreement with macroscopic techniques. For ML‐G, the average TEC is (−5.77 ± 3.79) x10−6 K−1 and is assigned to in‐plane vibrational bending modes. A vibrational‐thermal transition from graphene to graphite is observed, where the TEC becomes positive as the ML thickness increases. The nanoscale method here reported demonstrates results in excellent agreement with its macroscopic counterparts, as well as superior capabilities to probe 2D materials and interfaces.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/2196-7350Test

الوصول الحر: https://doaj.org/article/32ffbdd0bb1b476b8b097eed6669f3adTest

المؤلفون: Vincent, Tom

مصطلحات موضوعية: Graphene, 2D materials, scanning near-field optical microscopy, Raman, light-matter interaction, van der Waals heterostructures, van der Waals materials

الوصف: In this thesis, I study nanoscale light-matter interactions in two-dimensional (2d) and van der Waals (vdW) materials, with a particular focus on graphene and graphene-based heterostructures. In part I, I begin by reviewing some key background information, with an overview of the physics of graphene and bilayer graphene (BLG) in chapter 1, and an overview of the wider family of 2d materials and vdW heterostructures in chapter 2. Then in part II, I follow this with a review of the characterisation techniques used in the rest of this thesis, with a discussion of laser-coupled scanning probe microscopy (SPM) methods in chapter 3, and of optical spectroscopy in chapter 4. Finally in part III, I present several original research chapters based on work I conducted during my PhD: Chapter 5 demonstrates spatial mapping of nanoscale strains and doping in graphene heterostructures with Raman vector decomposition analysis, in which I reveal that variations in Raman spectra correlate with nanoscale features such as cracks, bubbles and wrinkles. In chapter 6, I build upon this by investigating bubbles in boron nitride-encapsulated graphene with scanning near-field optical microscopy (SNOM), and reveal strongly absorbing subwavelength domains for infrared light, which relate to the complex strain configurations of the bubbles. Chapter 7 focuses on a different vdW material indium selenide, and I use Raman and photoluminescence (PL) spectroscopy to probe strains induced by depositing the material on a patterned substrate. Lastly, in chapter 8 I showcase different ways that data cluster analysis, a machine learning tool, can accelerate the identification and analysis of twisted bilayer graphene from Raman spectra. The research presented here demonstrates that the combination of advanced microscopy and spectroscopy with modern computational techniques, such as vector decomposition and machine learning, can reveal a wealth of important material properties. With these techniques, I show that nanoscale features of vdW materials and heterostructures, such as fractures folds and bubbles, play a significant role in determining their optoelectronic properties, particularly via their local effects on strain and doping. This is fundamentally important for both the design and characterisation of 2d material-based optoelectronic devices.

الوصول الحر: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.860607Test

المؤلفون: Zhang Songtian S., Rajendran Anjaly, Chae Sang Hoon, Zhang Shuai, Pan Tsai-Chun, Hone James C., Dean Cory R., Basov D. N.

المصدر: Nanophotonics, Vol 12, Iss 14, Pp 2841-2847 (2023)

مصطلحات موضوعية: phase transition, scanning near-field optical microscopy, transition metal dichalcogenides, Physics, QC1-999

الوصف: Among the family of transition metal dichalcogenides, 1T-TaS2 stands out for several peculiar physical properties including a rich charge density wave phase diagram, quantum spin liquid candidacy and low temperature Mott insulator phase. As 1T-TaS2 is thinned down to the few-layer limit, interesting physics emerges in this quasi 2D material. Here, using scanning near-field optical microscopy, we perform a spatial- and temperature-dependent study on the phase transitions of a few-layer thick microcrystal of 1T-TaS2. We investigate encapsulated air-sensitive 1T-TaS2 prepared under inert conditions down to cryogenic temperatures. We find an abrupt metal-to-insulator transition in this few-layer limit. Our results provide new insight in contrast to previous transport studies on thin 1T-TaS2 where the resistivity jump became undetectable, and to spatially resolved studies on non-encapsulated samples which found a gradual, spatially inhomogeneous transition. A statistical analysis suggests bimodal high and low temperature phases, and that the characteristic phase transition hysteresis is preserved down to a few-layer limit.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/2192-8606Test; https://doaj.org/toc/2192-8614Test

الوصول الحر: https://doaj.org/article/4c033cbb1e16471399d0a46a35df0cb8Test

المؤلفون: Rizzo, Daniel J, Jessen, Bjarke S, Sun, Zhiyuan, Ruta, Francesco L, Zhang, Jin, Yan, Jia-Qiang, Xian, Lede, McLeod, Alexander S, Berkowitz, Michael E, Watanabe, Kenji, Taniguchi, Takashi, Nagler, Stephen E, Mandrus, David G, Rubio, Angel, Fogler, Michael M, Millis, Andrew J, Hone, James C, Dean, Cory R, Basov, DN

المصدر: Nano Letters. 20(12)

مصطلحات موضوعية: Physical Sciences, Engineering, Nanotechnology, Condensed Matter Physics, Mott insulators, graphene, plasmon polaritons, scanning near-field optical microscopy, two-dimensional (2D) materials, α-RuCl3, Nanoscience & Nanotechnology

الوصف: Nanoscale charge control is a key enabling technology in plasmonics, electronic band structure engineering, and the topology of two-dimensional materials. By exploiting the large electron affinity of α-RuCl3, we are able to visualize and quantify massive charge transfer at graphene/α-RuCl3 interfaces through generation of charge-transfer plasmon polaritons (CPPs). We performed nanoimaging experiments on graphene/α-RuCl3 at both ambient and cryogenic temperatures and discovered robust plasmonic features in otherwise ungated and undoped structures. The CPP wavelength evaluated through several distinct imaging modalities offers a high-fidelity measure of the Fermi energy of the graphene layer: EF = 0.6 eV (n = 2.7 × 1013 cm-2). Our first-principles calculations link the plasmonic response to the work function difference between graphene and α-RuCl3 giving rise to CPPs. Our results provide a novel general strategy for generating nanometer-scale plasmonic interfaces without resorting to external contacts or chemical doping.

وصف الملف: application/pdf

الوصول الحر: https://escholarship.org/uc/item/2423z0gwTest

المؤلفون: Muller, Eric A, Gray, Thomas P, Zhou, Zhou, Cheng, Xinbin, Khatib, Omar, Bechtel, Hans A, Raschke, Markus B

المصدر: Proceedings of the National Academy of Sciences of the United States of America. 117(13)

مصطلحات موضوعية: Macromolecular and Materials Chemistry, Chemical Sciences, Physical Chemistry, Theoretical and Computational Chemistry, Engineering, Materials Engineering, infrared spectroscopy, molecular vibrations, scattering-scanning near-field optical microscopy, vibrational exciton, molecular energy transport

الوصف: Much of the electronic transport, photophysical, or biological functions of molecular materials emerge from intermolecular interactions and associated nanoscale structure and morphology. However, competing phases, defects, and disorder give rise to confinement and many-body localization of the associated wavefunction, disturbing the performance of the material. Here, we employ vibrational excitons as a sensitive local probe of intermolecular coupling in hyperspectral infrared scattering scanning near-field optical microscopy (IR s-SNOM) with complementary small-angle X-ray scattering to map multiscale structure from molecular coupling to long-range order. In the model organic electronic material octaethyl porphyrin ruthenium(II) carbonyl (RuOEP), we observe the evolution of competing ordered and disordered phases, in nucleation, growth, and ripening of porphyrin nanocrystals. From measurement of vibrational exciton delocalization, we identify coexistence of ordered and disordered phases in RuOEP that extend down to the molecular scale. Even when reaching a high degree of macroscopic crystallinity, identify significant local disorder with correlation lengths of only a few nanometers. This minimally invasive approach of vibrational exciton nanospectroscopy and -imaging is generally applicable to provide the molecular-level insight into photoresponse and energy transport in organic photovoltaics, electronics, or proteins.

وصف الملف: application/pdf

الوصول الحر: https://escholarship.org/uc/item/05z002tnTest

المؤلفون: Chen, Xinzhong, Liu, Xiao, Guo, Xiangdong, Chen, Shu, Hu, Hai, Nikulina, Elizaveta, Ye, Xinlin, Yao, Ziheng, Bechtel, Hans A, Martin, Michael C, Carr, G Lawrence, Dai, Qing, Zhuang, Songlin, Hu, Qing, Zhu, Yiming, Hillenbrand, Rainer, Liu, Mengkun, You, Guanjun

المصدر: ACS Photonics. 7(3)

مصطلحات موضوعية: scattering-type scanning near-field optical microscopy, near-field, THz, nanoimaging, Schottky diodes, Optical Physics, Quantum Physics, Electrical and Electronic Engineering

الوصف: Modern scattering-type scanning near-field optical microscopy (s-SNOM) has become an indispensable tool in material research. However, as the s-SNOM technique marches into the far-infrared (IR) and terahertz (THz) regimes, emerging experiments sometimes produce puzzling results. For example, "anomalies" in the near-field optical contrast have been widely reported. In this Letter, we systematically investigate a series of extreme subwavelength metallic nanostructures via s-SNOM near-field imaging in the GHz to THz frequency range. We find that the near-field material contrast is greatly impacted by the lateral size of the nanostructure, while the spatial resolution is practically independent of it. The contrast is also strongly affected by the connectivity of the metallic structures to a larger metallic "ground plane". The observed effect can be largely explained by a quasi-electrostatic analysis. We also compare the THz s-SNOM results to those of the mid-IR regime, where the size-dependence becomes significant only for smaller structures. Our results reveal that the quantitative analysis of the near-field optical material contrasts in the long-wavelength regime requires a careful assessment of the size and configuration of metallic (optically conductive) structures.

الوصول الحر: https://escholarship.org/uc/item/6654h3v6Test

المؤلفون: Vasconcelos, TL, Archanjo, BS, Oliveira, BS, Valaski, R, Cordeiro, RC, Medeiros, HG, Rabelo, C, Ribeiro, A, Ercius, P, Achete, CA, Jorio, A, Cançado, LG

المصدر: Advanced Optical Materials. 6(20)

مصطلحات موضوعية: electron energy loss spectroscopy, localized surface plasmon resonance, monopole nanoantennas, scanning near-field optical microscopy, tip-enhanced Raman spectroscopy, Electrical and Electronic Engineering, Optical Physics, Materials Engineering

الوصف: Squeezing optical fields into nanometer scale is the key step to perform spatially resolved near-field optics. In scattering-type near-field optical microscopy, this task is accomplished by nanoantennas that convert propagating radiation to local near-fields and vice versa. The usual nanoantenna is composed by an elongated metal structure whose longitudinal dimension is scaled to support dipole modes of localized surface plasmon resonances. However, monopole modes can also be explored if the elongated metal nanoparticle is electrically grounded on a flat metallic plateau that acts like a mirror providing the monopole's image that closes the dipole system. Here, a method for batch production of monopole nanoantennas for scattering-type near-field scanning optical microscopy is presented. The nanoantennas are composed of a micropyramidal body with a nanopyramidal end whose lateral dimension can be scaled to fine-tune localized surface plasmon resonance modes. The monopole character of the nanoantennas is revealed by electron energy loss spectroscopy, and their efficiency and reproducibility are tested in tip-enhanced Raman spectroscopy experiments performed on single-layer graphene and single-walled carbon nanotubes.

وصف الملف: application/pdf

الوصول الحر: https://escholarship.org/uc/item/010464ztTest

المؤلفون: Zhaomin Peng, Dehai Zhang, Shuqi Ge, Jin Meng

المصدر: Applied Sciences, Vol 13, Iss 6, p 3400 (2023)

مصطلحات موضوعية: terahertz technology, scattering-scanning near-field optical microscopy, finite element model, near-field interactions, edge effect, antenna effect, Technology, Engineering (General). Civil engineering (General), TA1-2040, Biology (General), QH301-705.5, Physics, QC1-999, Chemistry, QD1-999

الوصف: Terahertz scattering-scanning near-field optical microscopy (THz s-SNOM), combining the best features of terahertz technology and s-SNOM technology, has shown unique advantages in various applications. Consequently, building a model to characterize near-field interactions and investigate practical issues has become a popular topic in THz s-SNOM research. In this study, a finite element model (FEM) is proposed to quantify the near-field interactions, and to investigate the edge effect and antenna effect in THz s-SNOM. Our results indicate that the proposed model can give us a better understanding of the near-field interactions and direct the parameter design of the probe for THz s-SNOM.

العلاقة: https://www.mdpi.com/2076-3417/13/6/3400Test; https://doaj.org/toc/2076-3417Test; https://doaj.org/article/c404d587ba334847ac002f8381e1bd3aTest

الإتاحة: https://doi.org/10.3390/app13063400Test
https://doaj.org/article/c404d587ba334847ac002f8381e1bd3aTest