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Van Winkle M, Dowlatshahi N, Khaloo N, Iyer M, Craig IM, Dhall R, Taniguchi T, Watanabe K, Bediako DK. Engineering interfacial polarization switching in van der Waals multilayers. Nat Nanotechnol 2024:10.1038/s41565-024-01642-0. [PMID: 38504024 DOI: 10.1038/s41565-024-01642-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/28/2023] [Accepted: 02/29/2024] [Indexed: 03/21/2024]
Abstract
In conventional ferroelectric materials, polarization is an intrinsic property limited by bulk crystallographic structure and symmetry. Recently, it has been demonstrated that polar order can also be accessed using inherently non-polar van der Waals materials through layer-by-layer assembly into heterostructures, wherein interfacial interactions can generate spontaneous, switchable polarization. Here we show that deliberate interlayer rotations in multilayer van der Waals heterostructures modulate both the spatial ordering and switching dynamics of polar domains. The engendered tunability is unparalleled in conventional bulk ferroelectrics or polar bilayers. By means of operando transmission electron microscopy we show how alterations of the relative rotations of three WSe2 layers produce structural polytypes with distinct arrangements of polar domains with either a global or localized switching response. Furthermore, the presence of uniaxial strain generates structural anisotropy that yields a range of switching behaviours, coercivities and even tunable biased responses. We also provide evidence of mechanical coupling between the two interfaces of the trilayer, a key consideration for the control of switching dynamics in polar multilayer structures more broadly.
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Affiliation(s)
- Madeline Van Winkle
- Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA
| | - Nikita Dowlatshahi
- Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA
| | - Nikta Khaloo
- Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA
| | - Mrinalni Iyer
- Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA
- Department of Chemistry, University of Minnesota, Minneapolis, MN, USA
| | - Isaac M Craig
- Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA
| | - Rohan Dhall
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, Tsukuba, Japan
| | - D Kwabena Bediako
- Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA.
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
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2
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Ribet SM, Zeltmann SE, Bustillo KC, Dhall R, Denes P, Minor AM, Dos Reis R, Dravid VP, Ophus C. Design of Electrostatic Aberration Correctors for Scanning Transmission Electron Microscopy. Microsc Microanal 2023; 29:1950-1960. [PMID: 37851063 DOI: 10.1093/micmic/ozad111] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Revised: 08/29/2023] [Accepted: 09/24/2023] [Indexed: 10/19/2023]
Abstract
In a scanning transmission electron microscope (STEM), producing a high-resolution image generally requires an electron beam focused to the smallest point possible. However, the magnetic lenses used to focus the beam are unavoidably imperfect, introducing aberrations that limit resolution. Modern STEMs overcome this by using hardware aberration correctors comprised of many multipole elements, but these devices are complex, expensive, and can be difficult to tune. We demonstrate a design for an electrostatic phase plate that can act as an aberration corrector. The corrector is comprised of annular segments, each of which is an independent two-terminal device that can apply a constant or ramped phase shift to a portion of the electron beam. We show the improvement in image resolution using an electrostatic corrector. Engineering criteria impose that much of the beam within the probe-forming aperture be blocked by support bars, leading to large probe tails for the corrected probe that sample the specimen beyond the central lobe. We also show how this device can be used to create other STEM beam profiles such as vortex beams and probes with a high degree of phase diversity, which improve information transfer in ptychographic reconstructions.
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Affiliation(s)
- Stephanie M Ribet
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA
- International Institute of Nanotechnology, Northwestern University, Evanston, IL 60208, USA
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Steven E Zeltmann
- Platform for the Accelerated Realization, Analysis, and Discovery of Interface Materials (PARADIM), Cornell University, Ithaca, NY 14853, USA
- Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Karen C Bustillo
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Rohan Dhall
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Peter Denes
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Andrew M Minor
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
- Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Roberto Dos Reis
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA
- International Institute of Nanotechnology, Northwestern University, Evanston, IL 60208, USA
- The NUANCE Center, Northwestern University, Evanston, IL 60208, USA
| | - Vinayak P Dravid
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA
- International Institute of Nanotechnology, Northwestern University, Evanston, IL 60208, USA
- The NUANCE Center, Northwestern University, Evanston, IL 60208, USA
| | - Colin Ophus
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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3
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Zhang D, Dhall R, Song C, Ciston J, Schneider M, Kunwar S, Pettes M, McCabe R, Chen A. Operando STEM and EELS Study of Oxide Memristor Devices. Microsc Microanal 2023; 29:1311-1312. [PMID: 37613317 DOI: 10.1093/micmic/ozad067.671] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Affiliation(s)
- Di Zhang
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM, United States
| | - Rohan Dhall
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Lab, Berkeley, CA, United States
| | - Chengyu Song
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Lab, Berkeley, CA, United States
| | - Jim Ciston
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Lab, Berkeley, CA, United States
| | - Matt Schneider
- Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM, United States
| | - Sundar Kunwar
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM, United States
| | - Michael Pettes
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM, United States
| | - Rodney McCabe
- Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM, United States
| | - Aiping Chen
- Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM, United States
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Prabhakaran A, Dang Z, Dhall R, Camerin F, Marín-Aguilar S, Dhanabalan B, Castelli A, Brescia R, Manna L, Dijkstra M, Arciniegas MP. Real-Time In Situ Observation of CsPbBr 3 Perovskite Nanoplatelets Transforming into Nanosheets. ACS Nano 2023. [PMID: 37406164 PMCID: PMC10373526 DOI: 10.1021/acsnano.3c02477] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/07/2023]
Abstract
The manipulation of nano-objects through heating is an effective strategy for inducing structural modifications and therefore changing the optoelectronic properties of semiconducting materials. Despite its potential, the underlying mechanism of the structural transformations remains elusive, largely due to the challenges associated with their in situ observations. To address these issues, we synthesize temperature-sensitive CsPbBr3 perovskite nanoplatelets and investigate their structural evolution at the nanoscale using in situ heating transmission electron microscopy. We observe the morphological changes that start from the self-assembly of the nanoplatelets into ribbons on a substrate. We identify several paths of merging nanoplates within ribbons that ultimately lead to the formation of nanosheets dispersed randomly on the substrate. These observations are supported by molecular dynamics simulations. We correlate the various paths for merging to the random orientation of the initial ribbons along with the ligand mobility (especially from the edges of the nanoplatelets). This leads to the preferential growth of individual nanosheets and the merging of neighboring ones. These processes enable the creation of structures with tunable emission, ranging from blue to green, all from a single material. Our real-time observations of the transformation of perovskite 2D nanocrystals reveal a route to achieve large-area nanosheets by controlling the initial orientation of the self-assembled objects with potential for large-scale applications.
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Affiliation(s)
- Aarya Prabhakaran
- Istituto Italiano di Tecnologia, Via Morego, 30, 16163 Genoa, Italy
- Dipartimento di Chimica e Chimica Industriale, Università degli Studi di Genova, Via Dodecaneso, 31, 16146 Genova, Italy
| | - Zhiya Dang
- School of Materials, Shenzhen Campus of Sun Yat-sen University, No. 66, Gongchang Road, Guangming District, Shenzhen, Guangdong 518107, People's Republic of China
| | - Rohan Dhall
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Fabrizio Camerin
- Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 1, 3584CC Utrecht, The Netherlands
| | - Susana Marín-Aguilar
- Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 1, 3584CC Utrecht, The Netherlands
| | | | - Andrea Castelli
- Istituto Italiano di Tecnologia, Via Morego, 30, 16163 Genoa, Italy
| | - Rosaria Brescia
- Istituto Italiano di Tecnologia, Via Morego, 30, 16163 Genoa, Italy
| | - Liberato Manna
- Istituto Italiano di Tecnologia, Via Morego, 30, 16163 Genoa, Italy
| | - Marjolein Dijkstra
- Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 1, 3584CC Utrecht, The Netherlands
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5
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Wang X, Pettes MT, Wang Y, Zhu JX, Dhall R, Song C, Jones AC, Ciston J, Yoo J. Enhanced Exciton-to-Trion Conversion by Proton Irradiation of Atomically Thin WS 2. Nano Lett 2023; 23:3754-3761. [PMID: 37094221 DOI: 10.1021/acs.nanolett.2c04987] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Defect engineering of van der Waals semiconductors has been demonstrated as an effective approach to manipulate the structural and functional characteristics toward dynamic device controls, yet correlations between physical properties with defect evolution remain underexplored. Using proton irradiation, we observe an enhanced exciton-to-trion conversion of the atomically thin WS2. The altered excitonic states are closely correlated with nanopore induced atomic displacement, W nanoclusters, and zigzag edge terminations, verified by scanning transmission electron microscopy, photoluminescence, and Raman spectroscopy. Density functional theory calculation suggests that nanopores facilitate formation of in-gap states that act as sinks for free electrons to couple with excitons. The ion energy loss simulation predicts a dominating electron ionization effect upon proton irradiation, providing further evidence on band perturbations and nanopore formation without destroying the overall crystallinity. This study provides a route in tuning the excitonic properties of van der Waals semiconductors using an irradiation-based defect engineering approach.
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Affiliation(s)
- Xuejing Wang
- Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Michael Thompson Pettes
- Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Yongqiang Wang
- Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
- Materials Science in Radiation and Dynamics Extremes (MST-8), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Jian-Xin Zhu
- Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
- Physics of Condensed Matter and Complex Systems (T-4), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Rohan Dhall
- National Center for Electron Microscopy (NCEM), Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Chengyu Song
- National Center for Electron Microscopy (NCEM), Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Andrew C Jones
- Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Jim Ciston
- National Center for Electron Microscopy (NCEM), Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Jinkyoung Yoo
- Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
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6
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Shallcross A, Mahalingam K, Shin E, Subramanyam G, Alam MS, Taha T, Ganguli S, Bowers C, Athey B, Hilton A, Roy A, Dhall R. Transmission Electron Microscopy Study on the Effect of Thermal and Electrical Stimuli on Ge2Te3 Based Memristor Devices. Front Electron 2022. [DOI: 10.3389/felec.2022.872163] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Memristor devices fabricated using the chalcogenide Ge2Te3 phase change thin films in a metal-insulator-metal structure are characterized using thermal and electrical stimuli in this study. Once the thermal and electrical stimuli are applied, cross-sectional transmission electron microscopy (TEM) and X-ray energy-dispersive spectroscopy (XEDS) analyses are performed to determine structural and compositional changes in the devices. Electrical measurements on these devices showed a need for increasing compliance current between cycles to initiate switching from low resistance state (LRS) to high resistance state (HRS). The measured resistance in HRS also exhibited a steady decrease with increase in the compliance current. High resolution TEM studies on devices in HRS showed the presence of residual crystalline phase at the top-electrode/dielectric interface, which may explain the observed dependence on compliance current. XEDS study revealed diffusion related processes at dielectric-electrode interface characterized, by the separation of Ge2Te3 into Ge- and Te- enriched interfacial layers. This was also accompanied by spikes in O level at these regions. Furthermore, in-situ heating experiments on as-grown thin films revealed a deleterious effect of Ti adhesive layer, wherein the in-diffusion of Ti leads to further degradation of the dielectric layer. This experimental physics-based study shows that the large HRS/LRS ratio below the current compliance limit of 1 mA and the ability to control the HRS and LRS by varying the compliance current are attractive for memristor and neuromorphic computing applications.
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7
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Londoño-Calderon A, Dhall R, Ophus C, Schneider M, Wang Y, Dervishi E, Kang HS, Lee CH, Yoo J, Pettes MT. Visualizing Grain Statistics in MOCVD WSe 2 through Four-Dimensional Scanning Transmission Electron Microscopy. Nano Lett 2022; 22:2578-2585. [PMID: 35143727 DOI: 10.1021/acs.nanolett.1c04315] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Using four-dimensional scanning transmission electron microscopy, we demonstrate a method to visualize grains and grain boundaries in WSe2 grown by metal organic chemical vapor deposition (MOCVD) directly onto silicon dioxide. Despite the chemical purity and uniform thickness and texture of the MOCVD-grown WSe2, we observe a high density of small grains that corresponds with the overall selenium deficiency we measure through ion beam analysis. Moreover, reconstruction of grain information permits the creation of orientation maps that demonstrate the nucleation mechanism for new layers-triangular domains with the same orientation as the layer underneath induces a tensile strain increasing the lattice parameter at these sites.
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Affiliation(s)
- Alejandra Londoño-Calderon
- Center for Integrated Nanotechnologies (CINT), Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Rohan Dhall
- National Center for Electron Microscopy (NCEM), Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Colin Ophus
- National Center for Electron Microscopy (NCEM), Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Matthew Schneider
- Materials Science in Radiation and Dynamics Extremes (MST-8), Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Yongqiang Wang
- Center for Integrated Nanotechnologies (CINT), Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
- Materials Science in Radiation and Dynamics Extremes (MST-8), Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Enkeleda Dervishi
- Electrochemistry and Corrosion Team, Sigma Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Hee Seong Kang
- KU-KIST Graduate School of Converging Science and Technology & Department of Integrative Energy Engineering, Korea University, Seoul, 02841, Republic of Korea
| | - Chul-Ho Lee
- KU-KIST Graduate School of Converging Science and Technology & Department of Integrative Energy Engineering, Korea University, Seoul, 02841, Republic of Korea
- Advanced Materials Research Division, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea
| | - Jinkyoung Yoo
- Center for Integrated Nanotechnologies (CINT), Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Michael T Pettes
- Center for Integrated Nanotechnologies (CINT), Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
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Weng PE, Gooyandeh A, Tariq M, Li T, Godara A, Valenzuela J, Mancini S, Yeung SMT, Sosa R, Wagner DR, Dhall R, Adelstein N, Kao K, Oh D. Microbe-Assisted Nanocomposite Anodes for Aqueous Li-Ion Batteries. ACS Appl Mater Interfaces 2021; 13:39195-39204. [PMID: 34387480 DOI: 10.1021/acsami.1c07309] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
With the rapid increase in the use of lithium-ion batteries (LIBs), the development of safe LIBs has become an important social issue. Replacing flammable organic liquid electrolytes in current LIBs with water can be an alternative route to resolve this safety concern. The water-in-salt (WIS) electrolytes received great attention as next-generation electrolytes due to their large electrochemical stability window. However, their high cathodic limit remains as a challenge, impeding the use of low-potential anodes. Here, we report the first biodirected synthesis of carbonaceous layers on anodes to use them as interlayers that prevent a direct contact of water molecules to anode particles. High-aspect ratio microbes are utilized as precursors of carbonaceous layers on TiO2 nanoparticles (m-TiO2) to enhance the conductivity and to reduce the electrolysis of WIS electrolytes. We selected the cylindrical shape of microbes that offers geometric diversity, providing us a toolkit to investigate the effect of microbe length in forming the network in binary composites and their impacts on the battery performance with WIS electrolytes. Using microbes with varying aspect ratios, the optimal microbe size to maximize the battery performance is determined. The effects of storage time on microbe size are also studied. Compared to uncoated TiO2 anodes, m-TiO2 exhibited 49% higher capacity at the 40th cycle and enhanced the cycle life close to anodes made with a conventional carbon precursor while using an 11% less amount of carbon. We performed density functional theory calculations to unravel the underlying mechanism of the performance improvement using microbe-derived carbon layers. Computational results show that high amounts of pyridinic nitrogen present in the peptide bonds in microbes are expected to slow down the water diffusion. Our findings provide key insights into the design of an interlayer for WIS anodes and open an avenue to fabricate energy storage materials using biomaterials.
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Affiliation(s)
- Pei-En Weng
- Chemical and Materials Engineering Department, Charles W. Davidson College of Engineering, San José State University, One Washington Square, San José, California 95192-0080, United States
| | - Alexander Gooyandeh
- Chemical and Materials Engineering Department, Charles W. Davidson College of Engineering, San José State University, One Washington Square, San José, California 95192-0080, United States
| | - Muhammad Tariq
- Chemical and Materials Engineering Department, Charles W. Davidson College of Engineering, San José State University, One Washington Square, San José, California 95192-0080, United States
| | - Tianyu Li
- Department of Chemical Engineering, Texas A&M University, Jack E. Brown Engineering Building, 3122 TAMU, College Station, Texas 77843, United States
| | - Avinash Godara
- Department of Chemical Engineering, Texas A&M University, Jack E. Brown Engineering Building, 3122 TAMU, College Station, Texas 77843, United States
| | - Jocelyn Valenzuela
- Chemical and Materials Engineering Department, Charles W. Davidson College of Engineering, San José State University, One Washington Square, San José, California 95192-0080, United States
| | - Steven Mancini
- Chemical and Materials Engineering Department, Charles W. Davidson College of Engineering, San José State University, One Washington Square, San José, California 95192-0080, United States
| | - Samuel Ming Tuk Yeung
- Chemical and Materials Engineering Department, Charles W. Davidson College of Engineering, San José State University, One Washington Square, San José, California 95192-0080, United States
| | - Ruth Sosa
- Chemical and Materials Engineering Department, Charles W. Davidson College of Engineering, San José State University, One Washington Square, San José, California 95192-0080, United States
| | - David R Wagner
- Chemical and Materials Engineering Department, Charles W. Davidson College of Engineering, San José State University, One Washington Square, San José, California 95192-0080, United States
| | - Rohan Dhall
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley 94720, California, United States
| | - Nicole Adelstein
- Department of Chemistry and Biochemistry, San Francisco State University, 1600 Holloway Avenue, San Francisco, California 94312, United States
| | - Katy Kao
- Chemical and Materials Engineering Department, Charles W. Davidson College of Engineering, San José State University, One Washington Square, San José, California 95192-0080, United States
| | - Dahyun Oh
- Chemical and Materials Engineering Department, Charles W. Davidson College of Engineering, San José State University, One Washington Square, San José, California 95192-0080, United States
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9
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Savitzky BH, Zeltmann SE, Hughes LA, Brown HG, Zhao S, Pelz PM, Pekin TC, Barnard ES, Donohue J, Rangel DaCosta L, Kennedy E, Xie Y, Janish MT, Schneider MM, Herring P, Gopal C, Anapolsky A, Dhall R, Bustillo KC, Ercius P, Scott MC, Ciston J, Minor AM, Ophus C. py4DSTEM: A Software Package for Four-Dimensional Scanning Transmission Electron Microscopy Data Analysis. Microsc Microanal 2021; 27:712-743. [PMID: 34018475 DOI: 10.1017/s1431927621000477] [Citation(s) in RCA: 62] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Scanning transmission electron microscopy (STEM) allows for imaging, diffraction, and spectroscopy of materials on length scales ranging from microns to atoms. By using a high-speed, direct electron detector, it is now possible to record a full two-dimensional (2D) image of the diffracted electron beam at each probe position, typically a 2D grid of probe positions. These 4D-STEM datasets are rich in information, including signatures of the local structure, orientation, deformation, electromagnetic fields, and other sample-dependent properties. However, extracting this information requires complex analysis pipelines that include data wrangling, calibration, analysis, and visualization, all while maintaining robustness against imaging distortions and artifacts. In this paper, we present py4DSTEM, an analysis toolkit for measuring material properties from 4D-STEM datasets, written in the Python language and released with an open-source license. We describe the algorithmic steps for dataset calibration and various 4D-STEM property measurements in detail and present results from several experimental datasets. We also implement a simple and universal file format appropriate for electron microscopy data in py4DSTEM, which uses the open-source HDF5 standard. We hope this tool will benefit the research community and help improve the standards for data and computational methods in electron microscopy, and we invite the community to contribute to this ongoing project.
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Affiliation(s)
- Benjamin H Savitzky
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | - Steven E Zeltmann
- Department of Materials Science and Engineering, University of California, Berkeley, CA94720, USA
| | - Lauren A Hughes
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | - Hamish G Brown
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | - Shiteng Zhao
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
- Department of Materials Science and Engineering, University of California, Berkeley, CA94720, USA
| | - Philipp M Pelz
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
- Department of Materials Science and Engineering, University of California, Berkeley, CA94720, USA
| | - Thomas C Pekin
- Institut für Physik, Humboldt-Universität zu Berlin, Newtonstraße 15, 12489Berlin, Germany
| | - Edward S Barnard
- Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | - Jennifer Donohue
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
- Department of Materials Science and Engineering, University of California, Berkeley, CA94720, USA
| | - Luis Rangel DaCosta
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
- Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI48109, USA
| | - Ellis Kennedy
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
- Department of Materials Science and Engineering, University of California, Berkeley, CA94720, USA
| | - Yujun Xie
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | | | | | | | | | | | - Rohan Dhall
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | - Karen C Bustillo
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | - Peter Ercius
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | - Mary C Scott
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
- Department of Materials Science and Engineering, University of California, Berkeley, CA94720, USA
| | - Jim Ciston
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | - Andrew M Minor
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
- Department of Materials Science and Engineering, University of California, Berkeley, CA94720, USA
| | - Colin Ophus
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
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10
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Zeng L, Holmér J, Dhall R, Gammer C, Minor AM, Olsson E. Tuning Hole Mobility of Individual p-Doped GaAs Nanowires by Uniaxial Tensile Stress. Nano Lett 2021; 21:3894-3900. [PMID: 33914543 PMCID: PMC8289290 DOI: 10.1021/acs.nanolett.1c00353] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/30/2021] [Revised: 04/21/2021] [Indexed: 06/12/2023]
Abstract
Strain engineering provides an effective way of tailoring the electronic and optoelectronic properties of semiconductor nanomaterials and nanodevices, giving rise to novel functionalities. Here, we present direct experimental evidence of strain-induced modifications of hole mobility in individual gallium arsenide (GaAs) nanowires, using in situ transmission electron microscopy (TEM). The conductivity of the nanowires varied with applied uniaxial tensile stress, showing an initial decrease of ∼5-20% up to a stress of 1-2 GPa, subsequently increasing up to the elastic limit of the nanowires. This is attributed to a hole mobility variation due to changes in the valence band structure caused by stress and strain. The corresponding lattice strain in the nanowires was quantified by in situ four dimensional scanning TEM and showed a complex spatial distribution at all stress levels. Meanwhile, a significant red shift of the band gap induced by the stress and strain was unveiled by monochromated electron energy loss spectroscopy.
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Affiliation(s)
- Lunjie Zeng
- Department
of Physics, Chalmers University of Technology, 412 96 Gothenburg, Sweden
| | - Jonatan Holmér
- Department
of Physics, Chalmers University of Technology, 412 96 Gothenburg, Sweden
| | - Rohan Dhall
- National
Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Christoph Gammer
- Erich
Schmid Institute of Materials Science, Austrian Academy of Sciences, 8700 Leoben, Austria
| | - Andrew M. Minor
- National
Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Department
of Materials Science and Engineering, University
of California, Berkeley, California 94720, United States
| | - Eva Olsson
- Department
of Physics, Chalmers University of Technology, 412 96 Gothenburg, Sweden
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11
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Yang M, Li Q, Chopdekar RV, Dhall R, Turner J, Carlström JD, Ophus C, Klewe C, Shafer P, N'Diaye AT, Choi JW, Chen G, Wu YZ, Hwang C, Wang F, Qiu ZQ. Creation of skyrmions in van der Waals ferromagnet Fe 3GeTe 2 on (Co/Pd) n superlattice. Sci Adv 2020; 6:6/36/eabb5157. [PMID: 32917619 PMCID: PMC7473669 DOI: 10.1126/sciadv.abb5157] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Accepted: 07/15/2020] [Indexed: 05/27/2023]
Abstract
Magnetic skyrmions are topological spin textures, which usually exist in noncentrosymmetric materials where the crystal inversion symmetry breaking generates the so-called Dzyaloshinskii-Moriya interaction. This requirement unfortunately excludes many important magnetic material classes, including the recently found two-dimensional van der Waals (vdW) magnetic materials, which offer unprecedented opportunities for spintronic technology. Using photoemission electron microscopy and Lorentz transmission electron microscopy, we investigated and stabilized Néel-type magnetic skyrmion in vdW ferromagnetic Fe3GeTe2 on top of (Co/Pd) n in which the Fe3GeTe2 has a centrosymmetric crystal structure. We demonstrate that the magnetic coupling between the Fe3GeTe2 and the (Co/Pd) n could create skyrmions in Fe3GeTe2 without the need of an external magnetic field. Our results open exciting opportunities in spintronic research and the engineering of topologically protected nanoscale features by expanding the group of skyrmion host materials to include these previously unknown vdW magnets.
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Affiliation(s)
- M Yang
- Department of Physics, University of California, Berkeley, CA 94720, USA
| | - Q Li
- Department of Physics, University of California, Berkeley, CA 94720, USA.
| | - R V Chopdekar
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - R Dhall
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - J Turner
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - J D Carlström
- Department of Physics, University of California, Berkeley, CA 94720, USA
| | - C Ophus
- Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - C Klewe
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - P Shafer
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - A T N'Diaye
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - J W Choi
- Center for Spintronics, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea
| | - G Chen
- Department of Physics, University of California, Davis, CA 95616, USA
| | - Y Z Wu
- Department of Physics and State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China
| | - C Hwang
- Korea Research Institute of Standards and Science, Yuseong, Daejeon 305-340, Republic of Korea
| | - F Wang
- Department of Physics, University of California, Berkeley, CA 94720, USA
| | - Z Q Qiu
- Department of Physics, University of California, Berkeley, CA 94720, USA.
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12
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Dang Z, Dhanabalan B, Castelli A, Dhall R, Bustillo KC, Marchelli D, Spirito D, Petralanda U, Shamsi J, Manna L, Krahne R, Arciniegas MP. Temperature-Driven Transformation of CsPbBr 3 Nanoplatelets into Mosaic Nanotiles in Solution through Self-Assembly. Nano Lett 2020; 20:1808-1818. [PMID: 31991086 PMCID: PMC7997623 DOI: 10.1021/acs.nanolett.9b05036] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Revised: 01/25/2020] [Indexed: 05/22/2023]
Abstract
Two-dimensional colloidal halide perovskite nanocrystals are promising materials for light-emitting applications. Recent studies have focused on nanoplatelets that are able to self-assemble and transform on solid substrates. However, the mechanism behind the process and the atomic arrangement of their assemblies remain unclear. Here, we present a detailed analysis of the transformation of self-assembled stacks of CsPbBr3 nanoplatelets in solution over a period of a few months by using ex situ transmission electron microscopy and surface analysis. We demonstrate that the transformation mechanism can be understood as oriented attachment, proceeding through the following steps: (i) desorption of the ligands from the surfaces of the particles, causing the seamless atomic merging of nanoplatelet stacks into nanobelts; (ii) merging of neighboring nanobelts that form more extended nanoplates; and (iii) attachment of nanobelts and nanoplates, forming objects with an atomic structure that resembles a mosaic made of broken nanotiles. We reveal that aged nanobelts and nanoplates, which are mainly stabilized by amine/ammonium ions, link through a bilayer of CsBr, with the atomic columns of neighboring perovskite lattices shifted by a half-unit-cell, forming Ruddlesden-Popper planar faults. We also show, via in situ monitoring of the nanocrystal photoluminescence combined with transmission electron microscopy analysis, that the transformation is temperature driven and that it can take place within tens of minutes in solution and in spin-coated films. Understanding this process gives crucial information for the design and fabrication of perovskite materials, where control over the type and density of defects is desired, stimulating the development of perovskite nanocrystal structures with tailored electronic properties.
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Affiliation(s)
- Zhiya Dang
- Nanochemistry
Department and Optoelectronics, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Balaji Dhanabalan
- Nanochemistry
Department and Optoelectronics, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
- Dipartimento
di Chimica e Chimica Industriale, Università
degli Studi di Genova, Via Dodecaneso, 31, 16146 Genova, Italy
| | - Andrea Castelli
- Nanochemistry
Department and Optoelectronics, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Rohan Dhall
- National
Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Karen C. Bustillo
- National
Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Dorwal Marchelli
- Nanochemistry
Department and Optoelectronics, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Davide Spirito
- Nanochemistry
Department and Optoelectronics, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Urko Petralanda
- Nanochemistry
Department and Optoelectronics, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Javad Shamsi
- Nanochemistry
Department and Optoelectronics, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Liberato Manna
- Nanochemistry
Department and Optoelectronics, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
- E-mail:
| | - Roman Krahne
- Nanochemistry
Department and Optoelectronics, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Milena P. Arciniegas
- Nanochemistry
Department and Optoelectronics, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
- E-mail:
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13
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Grosset D, Dhall R, Gurevich T, Kassubek J, Poewe W, Rascol O, Rudzinska M, Cormier J, Sedkov A, Oh C. Long-term pulmonary safety of inhaled levodopa in parkinson’s disease subjects with motor fluctuations: interim results of a phase 3 study. Parkinsonism Relat Disord 2018. [DOI: 10.1016/j.parkreldis.2017.11.287] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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14
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Grosset D, Dhall R, Gurevich T, Kassubek J, Poewe W, Rascol O, Rudzinska M, Cormier J, Sedkov A, Oh C. Long-term efficacy of inhaled levodopa in Parkinson’s disease subjects with motor fluctuations: Interim results of a phase 3 study. Parkinsonism Relat Disord 2018. [DOI: 10.1016/j.parkreldis.2017.11.065] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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15
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Zheng Y, Fahrenholtz CD, Hackett CL, Ding S, Day CS, Dhall R, Marrs GS, Gross MD, Singh R, Bierbach U. Large-Pore Functionalized Mesoporous Silica Nanoparticles as Drug Delivery Vector for a Highly Cytotoxic Hybrid Platinum-Acridine Anticancer Agent. Chemistry 2017; 23:3386-3397. [PMID: 28122141 DOI: 10.1002/chem.201604868] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Indexed: 12/17/2022]
Abstract
Large-pore mesoporous silica nanoparticles (MSN) were prepared and functionalized to serve as a highly robust and biocompatible delivery platform for platinum-acridine (PA) anticancer agents. The material showed a high loading capacity for the dicationic, hydrophilic hybrid agent [PtCl(en)(N-[acridin-9-ylaminoethyl]-N-methylpropionamidine)] dinitrate salt (P1A1) and virtually complete retention of payload at neutral pH in a high-chloride buffer. In acidic media mimicking the pH inside the cell lysosomes, rapid, burst-like release of P1A1 from the nanoparticles is observed. Coating of the materials in phospholipid bilayers resulted in nanoparticles with greatly improved colloidal stability. The lipid and carboxylate-modified nanoparticles containing 40 wt % drug caused S-phase arrest and inhibited cell proliferation in pancreatic cancer cells at submicromolar concentrations similar to carrier-free P1A1. The most striking feature of nanoparticle-delivered P1A1 was that the payload did not escape from the acidified lysosomal vesicles into the cytoplasm, but was shuttled to the nuclear membrane and released into the nucleus.
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Affiliation(s)
- Ye Zheng
- Department of Chemistry, Wake Forest University, Winston-Salem, NC, 27109, USA
| | - Cale D Fahrenholtz
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC, 27157, USA
| | | | - Song Ding
- Department of Chemistry, Wake Forest University, Winston-Salem, NC, 27109, USA
| | - Cynthia S Day
- Department of Chemistry, Wake Forest University, Winston-Salem, NC, 27109, USA
| | - Rohan Dhall
- Analytical Instrumentation Facility, Monteith Research Center, North Carolina State University, Raleigh, NC, 27695, USA
| | - Glen S Marrs
- Department of Biology, Wake Forest University, Winston-Salem, NC, 27109, USA
| | - Michael D Gross
- Department of Chemistry, Wake Forest University, Winston-Salem, NC, 27109, USA
| | - Ravi Singh
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC, 27157, USA
| | - Ulrich Bierbach
- Department of Chemistry, Wake Forest University, Winston-Salem, NC, 27109, USA
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16
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Abstract
We report Raman and photoluminescence spectra of mono- and few-layer WSe2 and MoSe2 taken before and after exposure to a remote oxygen plasma. For bilayer and trilayer WSe2, we observe an increase in the photoluminescence intensity and a blue shift of the photoluminescence peak positions after oxygen plasma treatment. The photoluminescence spectra of trilayer WSe2 exhibit features of a bilayer after oxygen plasma treatment. Bilayer WSe2 exhibits features of a monolayer, and the photoluminescence of monolayer WSe2 is completely absent after the oxygen plasma treatment. These changes are observed consistently in more than 20 flakes. The mechanism of the changes observed in the photoluminescence spectra of WSe2 is due to the selective oxidation of the topmost layer. As a result, N-layer WSe2 is reduced to N-1 layers. Raman spectra and AFM images taken from the WSe2 flakes before and after the oxygen treatment corroborate these findings. Because of the low kinetic energy of the oxygen radicals in the remote oxygen plasma, the oxidation is self-limiting. By varying the process duration from 1 to 10 min, we confirmed that the oxidation will only affect the topmost layer of the WSe2 flakes. X-ray photoelectron spectroscopy shows that the surface layer WOx of the sample can be removed by a quick dip in KOH solution. Therefore, this technique provides a promising way of controlling the thickness of WSe2 layer by layer.
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Affiliation(s)
| | | | | | - Ewa Kosmowska
- XEI Scientific , Redwood City, California 94063, United States
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17
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White ER, Kerelsky A, Hubbard WA, Dhall R, Cronin SB, Mecklenburg M, Regan BC. Imaging interfacial electrical transport in graphene-MoS 2 heterostructures with electron-beam-induced-currents. Appl Phys Lett 2015; 107:223104. [PMID: 26648594 PMCID: PMC4670446 DOI: 10.1063/1.4936763] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Accepted: 11/17/2015] [Indexed: 06/05/2023]
Abstract
Heterostructure devices with specific and extraordinary properties can be fabricated by stacking two-dimensional crystals. Cleanliness at the inter-crystal interfaces within a heterostructure is crucial for maximizing device performance. However, because these interfaces are buried, characterizing their impact on device function is challenging. Here, we show that electron-beam induced current (EBIC) mapping can be used to image interfacial contamination and to characterize the quality of buried heterostructure interfaces with nanometer-scale spatial resolution. We applied EBIC and photocurrent imaging to map photo-sensitive graphene-MoS2 heterostructures. The EBIC maps, together with concurrently acquired scanning transmission electron microscopy images, reveal how a device's photocurrent collection efficiency is adversely affected by nanoscale debris invisible to optical-resolution photocurrent mapping.
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Affiliation(s)
- E R White
- Department of Physics and Astronomy and California NanoSystems Institute, University of California , Los Angeles, California 90095, USA
| | - Alexander Kerelsky
- Department of Physics and Astronomy and California NanoSystems Institute, University of California , Los Angeles, California 90095, USA
| | - William A Hubbard
- Department of Physics and Astronomy and California NanoSystems Institute, University of California , Los Angeles, California 90095, USA
| | - Rohan Dhall
- Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, USA
| | - Stephen B Cronin
- Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, USA
| | - Matthew Mecklenburg
- Center for Electron Microscopy and Microanalysis, University of Southern California , Los Angeles, California 90089, USA
| | - B C Regan
- Department of Physics and Astronomy and California NanoSystems Institute, University of California , Los Angeles, California 90095, USA
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18
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Liu B, Köpf M, Abbas AN, Wang X, Guo Q, Jia Y, Xia F, Weihrich R, Bachhuber F, Pielnhofer F, Wang H, Dhall R, Cronin SB, Ge M, Fang X, Nilges T, Zhou C. Black Arsenic-Phosphorus: Layered Anisotropic Infrared Semiconductors with Highly Tunable Compositions and Properties. Adv Mater 2015; 27:4423-4429. [PMID: 26112061 DOI: 10.1002/adma.201501758] [Citation(s) in RCA: 152] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Revised: 05/12/2015] [Indexed: 06/04/2023]
Abstract
New layered anisotropic infrared semiconductors, black arsenic-phosphorus (b-AsP), with highly tunable chemical compositions and electronic and optical properties are introduced. Transport and infrared absorption studies demonstrate the semiconducting nature of b-AsP with tunable bandgaps, ranging from 0.3 to 0.15 eV. These bandgaps fall into the long-wavelength infrared regime and cannot be readily reached by other layered materials.
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Affiliation(s)
- Bilu Liu
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Marianne Köpf
- Department of Chemistry, Technische Universität München, Lichtenbergstraße 4, Garching b, München, 485748, Germany
| | - Ahmad N Abbas
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Xiaomu Wang
- Department of Electrical Engineering, Yale University, New Haven, CT, 06511, USA
| | - Qiushi Guo
- Department of Electrical Engineering, Yale University, New Haven, CT, 06511, USA
| | - Yichen Jia
- Department of Electrical Engineering, Yale University, New Haven, CT, 06511, USA
| | - Fengnian Xia
- Department of Electrical Engineering, Yale University, New Haven, CT, 06511, USA
| | - Richard Weihrich
- Institut für Anorganische Chemie, Universität Regensburg, Universitätsstraße 31, Regensburg, 93040, Germany
| | - Frederik Bachhuber
- Institut für Anorganische Chemie, Universität Regensburg, Universitätsstraße 31, Regensburg, 93040, Germany
| | - Florian Pielnhofer
- Institut für Anorganische Chemie, Universität Regensburg, Universitätsstraße 31, Regensburg, 93040, Germany
| | - Han Wang
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Rohan Dhall
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Stephen B Cronin
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Mingyuan Ge
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Xin Fang
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
| | - Tom Nilges
- Department of Chemistry, Technische Universität München, Lichtenbergstraße 4, Garching b, München, 485748, Germany
| | - Chongwu Zhou
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA
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19
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Li Z, Ezhilarasu G, Chatzakis I, Dhall R, Chen CC, Cronin SB. Indirect Band Gap Emission by Hot Electron Injection in Metal/MoS₂ and Metal/WSe₂ Heterojunctions. Nano Lett 2015; 15:3977-82. [PMID: 25993397 DOI: 10.1021/acs.nanolett.5b00885] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Transition metal dichalcogenides (TMDCs), such as MoS2 and WSe2, are free of dangling bonds and therefore make more "ideal" Schottky junctions than bulk semiconductors, which produce Fermi energy pinning and recombination centers at the interface with bulk metals, inhibiting charge transfer. Here, we observe a more than 10× enhancement in the indirect band gap photoluminescence of transition metal dichalcogenides (TMDCs) deposited on various metals (e.g., Cu, Au, Ag), while the direct band gap emission remains unchanged. We believe the main mechanism of light emission arises from photoexcited hot electrons in the metal that are injected into the conduction band of MoS2 and WSe2 and subsequently recombine radiatively with minority holes in the TMDC. Since the conduction band at the K-point is 0.5 eV higher than at the Σ-point, a lower Schottky barrier exists for the Σ-point band, making electron injection more favorable. Also, the Σ band consists of the sulfur pz orbital, which overlaps more significantly with the electron wave functions in the metal. This enhancement in the indirect emission only occurs for thick flakes of MoS2 and WSe2 (≥100 nm) and is completely absent in monolayer and few-layer (∼10 nm) flakes. Here, the flake thickness must exceed the depletion width of the Schottky junction, in order for efficient radiative recombination to occur in the TMDC. The intensity of this indirect peak decreases at low temperatures, which is consistent with the hot electron injection model.
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Affiliation(s)
| | - Goutham Ezhilarasu
- ‡Department of Electrical and Electronics Engineering, College of Engineering Guindy, Anna University, Chennai Tamil Nadu 600026, India
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20
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Dhall R, Neupane MR, Wickramaratne D, Mecklenburg M, Li Z, Moore C, Lake RK, Cronin S. Direct bandgap transition in many-layer MoS2 by plasma-induced layer decoupling. Adv Mater 2015; 27:1573-8. [PMID: 25589365 DOI: 10.1002/adma.201405259] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Indexed: 05/16/2023]
Abstract
We report a robust method for engineering the optoelectronic properties of many-layer MoS2 using low-energy oxygen plasma treatment. Gas phase treatment of MoS2 with oxygen radicals generated in an upstream N2 -O2 plasma is shown to enhance the photoluminescence (PL) of many-layer, mechanically exfoliated MoS2 flakes by up to 20 times, without reducing the layer thickness of the material. A blueshift in the PL spectra and narrowing of linewidth are consistent with a transition of MoS2 from indirect to direct bandgap material. Atomic force microscopy and Raman spectra reveal that the flake thickness actually increases as a result of the plasma treatment, indicating an increase in the interlayer separation in MoS2 . Ab initio calculations reveal that the increased interlayer separation is sufficient to decouple the electronic states in individual layers, leading to a transition from an indirect to direct gap semiconductor. With optimized plasma treatment parameters, we observed enhanced PL signals for 32 out of 35 many-layer MoS2 flakes (2-15 layers) tested, indicating that this method is robust and scalable. Monolayer MoS2 , while direct bandgap, has a small optical density, which limits its potential use in practical devices. The results presented here provide a material with the direct bandgap of monolayer MoS2 , without reducing sample thickness, and hence optical density.
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Affiliation(s)
- Rohan Dhall
- Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA; Center for Electron Microscopy and Microanalysis, University of Southern California, Los Angeles, CA, 90089, USA
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21
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Mecklenburg M, Hubbard WA, White ER, Dhall R, Cronin SB, Aloni S, Regan BC. Nanoscale temperature mapping in operating microelectronic devices. Science 2015; 347:629-32. [DOI: 10.1126/science.aaa2433] [Citation(s) in RCA: 207] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Modern microelectronic devices have nanoscale features that dissipate power nonuniformly, but fundamental physical limits frustrate efforts to detect the resulting temperature gradients. Contact thermometers disturb the temperature of a small system, while radiation thermometers struggle to beat the diffraction limit. Exploiting the same physics as Fahrenheit’s glass-bulb thermometer, we mapped the thermal expansion of Joule-heated, 80-nanometer-thick aluminum wires by precisely measuring changes in density. With a scanning transmission electron microscope and electron energy loss spectroscopy, we quantified the local density via the energy of aluminum’s bulk plasmon. Rescaling density to temperature yields maps with a statistical precision of 3 kelvin/hertz−1/2, an accuracy of 10%, and nanometer-scale resolution. Many common metals and semiconductors have sufficiently sharp plasmon resonances to serve as their own thermometers.
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22
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Aykol M, Hou B, Dhall R, Chang SW, Branham W, Qiu J, Cronin SB. Clamping instability and van der Waals forces in carbon nanotube mechanical resonators. Nano Lett 2014; 14:2426-2430. [PMID: 24758201 DOI: 10.1021/nl500096p] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We investigate the role of weak clamping forces, typically assumed to be infinite, in carbon nanotube mechanical resonators. Due to these forces, we observe a hysteretic clamping and unclamping of the nanotube device that results in a discrete drop in the mechanical resonance frequency on the order of 5-20 MHz, when the temperature is cycled between 340 and 375 K. This instability in the resonant frequency results from the nanotube unpinning from the electrode/trench sidewall where it is bound weakly by van der Waals forces. Interestingly, this unpinning does not affect the Q-factor of the resonance, since the clamping is still governed by van der Waals forces above and below the unpinning. For a 1 μm device, the drop observed in resonance frequency corresponds to a change in nanotube length of approximately 50-65 nm. On the basis of these findings, we introduce a new model, which includes a finite tension around zero gate voltage due to van der Waals forces and shows better agreement with the experimental data than the perfect clamping model. From the gate dependence of the mechanical resonance frequency, we extract the van der Waals clamping force to be 1.8 pN. The mechanical resonance frequency exhibits a striking temperature dependence below 200 K attributed to a temperature-dependent slack arising from the competition between the van der Waals force and the thermal fluctuations in the suspended nanotube.
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Affiliation(s)
- Mehmet Aykol
- Ming Hsieh Department of Electrical Engineering, †Department of Physics and Astronomy and ‡Department of Materials Science, University of Southern California , Los Angeles, California 90089, United States
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23
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Amer MR, Chang SW, Dhall R, Qiu J, Cronin SB. Zener tunneling and photocurrent generation in quasi-metallic carbon nanotube pn-devices. Nano Lett 2013; 13:5129-5134. [PMID: 24127786 DOI: 10.1021/nl402334e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We investigate the electronic and optoelectronic properties of quasi-metallic nanotube pn-devices, which have smaller band gaps than most known bulk semiconductors. These carbon nanotube-based devices deviate from conventional bulk semiconductor device behavior due to their low-dimensional nature. We observe rectifying behavior based on Zener tunneling of ballistic carriers instead of ideal diode behavior, as limited by the diffusive transport of carriers. We observe substantial photocurrents at room temperature, suggesting that these quasi-metallic pn-devices may have a broader impact in optoelectronic devices. A new technique based on photocurrent spectroscopy is presented to identify the unique chirality of nanotubes in a functional device. This chirality information is crucial in obtaining a theoretical understanding of the underlying device physics that depends sensitively on nanotube chirality, as is the case for quasi-metallic nanotube devices. A detailed model is developed to fit the observed I-V characteristics, which enables us to verify the band gap from these measurements as well as the dimensions of the insulating tunneling barrier region.
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Affiliation(s)
- Moh R Amer
- Department of Electrical Engineering, ‡Department of Material Science, and §Department of Physics and Astronomy, University of Southern California , Los Angeles, California 90089, United States
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Cummings J, Isaacson S, Mills R, Williams H, Chi-Burris K, Dhall R, Ballard C. Antipsychotic efficacy and motor tolerability in a phase III placebo-controlled study of pimavanserin in patients with Parkinson's Disease psychosis (Acp-103-020). J Neurol Sci 2013. [DOI: 10.1016/j.jns.2013.07.401] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Salins N, Krishnamurthi N, Santiago A, Dhall R, Moguel-Cobos G, Sadreddin A, Husain S, Lieberman A, Pan D, Dhanani S. Gait and Posture Control Impairments Predict Falls in Parkinson's Disease (P06.049). Neurology 2012. [DOI: 10.1212/wnl.78.1_meetingabstracts.p06.049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Lieberman A, Krishnamurthi N, Santiago A, Dhall R, Moguel-Cobos G, Sadreddin A, Husain S, Salins N, Pan D, Dhanani S. Is Difficulty with Balance Different from Difficulty Walking in Parkinson's Disease? (P06.047). Neurology 2012. [DOI: 10.1212/wnl.78.1_meetingabstracts.p06.047] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Lieberman A, Krishnamurthi N, Santiago A, Dhall R, Moguel-Cobos G, Sadreddin A, Husain S, Salins N, Pan D, Dhanani S. Effects of Bradykinesia and Hypokinesia on Falls in Parkinson's Disease (P06.048). Neurology 2012. [DOI: 10.1212/wnl.78.1_meetingabstracts.p06.048] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Husain S, Krishnamurthi N, Santiago A, Dhall R, Moguel-Cobos G, Sadreddin A, Salins N, Pan D, Lieberman A, Dhanani S. The Value of the Barrow Neurological Institute Balance Scale in Predicting Falls (P06.043). Neurology 2012. [DOI: 10.1212/wnl.78.1_meetingabstracts.p06.043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Deep A, Pati S, Dhall R, Lieberman A, Horn K, Gibson A. Parvocellular Red Nucleus - A Neuromodulation Target for Medically Refractory Meige Syndrome? (P01.239). Neurology 2012. [DOI: 10.1212/wnl.78.1_meetingabstracts.p01.239] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Singh V, Sengupta S, Solanki HS, Dhall R, Allain A, Dhara S, Pant P, Deshmukh MM. Probing thermal expansion of graphene and modal dispersion at low-temperature using graphene nanoelectromechanical systems resonators. Nanotechnology 2010; 21:165204. [PMID: 20351404 DOI: 10.1088/0957-4484/21/16/165204] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
We use suspended graphene electromechanical resonators to study the variation of resonant frequency as a function of temperature. Measuring the change in frequency resulting from a change in tension, from 300 to 30 K, allows us to extract information about the thermal expansion of monolayer graphene as a function of temperature, which is critical for strain engineering applications. We find that thermal expansion of graphene is negative for all temperatures between 300 and 30 K. We also study the dispersion, the variation of resonant frequency with DC gate voltage, of the electromechanical modes and find considerable tunability of resonant frequency, desirable for applications like mass sensing and RF signal processing at room temperature. With a lowering of temperature, we find that the positively dispersing electromechanical modes evolve into negatively dispersing ones. We quantitatively explain this crossover and discuss optimal electromechanical properties that are desirable for temperature-compensated sensors.
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Affiliation(s)
- Vibhor Singh
- Department of Condensed Matter Physics, TIFR, Homi Bhabha Road, Mumbai 400005, India
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Murthy SA, Dhall R, Jain S, Yadava OP, Bana A, Shivnani G. Biatrial tuberculosis. J Assoc Physicians India 2001; 49:668-9. [PMID: 11584950] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Affiliation(s)
- S A Murthy
- Department of Medicine, Sir Ganga Ram Hospital, Old Rajinder Nagar, New Delhi
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Dhall R, das de SK. Cystoscopy in cases of carcinoma of the cervix uteri: clinical experience with 85 cases. J Indian Med Assoc 1995; 93:344-5. [PMID: 8648155] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
A retrospective study involving 85 cases of cystoscopy carried out between December, 1989 and July, 1992 in selected cases of carcinoma cervix was undertaken with the purpose of determining the place of cystoscopy in this condition. Cystoscopy was performed only when there was a clinical suspicion of the urinary bladder being involved. Of 67 cases in which cystoscopy was performed as part of staging of carcinoma cervix, one was in stage II, 48 in stage III and 18 in stage IV (stages determined prior to cystoscopy). On cystoscopy of the stage III cases, 50% showed apparent involvement of bladder, 29.17% showed suspicious findings and 20.83% showed negative findings. Of the stage IV cases, 61.11% showed apparent involvement of bladder, 33.33% showed suspicious findings and 5.56% showed negative findings. Of 13 cases in which biopsy was taken cystoscopically, 8 were histologically positive, 4 were histologically negative and one was histologically suspicious for malignancy of the urinary bladder. In the remaining 18 cases cystoscopy was performed during follow-up period.
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Affiliation(s)
- R Dhall
- Chittaranjan National Center Institute, Calcutta
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Abstract
In a patient previously operated upon for cervical adenocarcinoma, an abdominal wall swelling of identical histology developed in the surgical incision line. The skin involved was the site of external irradiation. The case is discussed and the literature reviewed.
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Affiliation(s)
- R Dhall
- Department of Obstetrics and Gynaecology, Falkirk and District Royal Infirmary, U.K
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Dhall R, Vasishta K, Majumdar S. Glycosylated haemoglobin in obstetric practice. Asia Oceania J Obstet Gynaecol 1988; 14:461-6. [PMID: 3240123 DOI: 10.1111/j.1447-0756.1988.tb00135.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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