1
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Bragaglia V, Jonnalagadda VP, Sousa M, Sarwat SG, Kersting B, Sebastian A. Structural Assessment of Interfaces in Projected Phase-Change Memory. NANOMATERIALS 2022; 12:nano12101702. [PMID: 35630924 PMCID: PMC9147056 DOI: 10.3390/nano12101702] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Revised: 04/27/2022] [Accepted: 05/09/2022] [Indexed: 12/04/2022]
Abstract
Non-volatile memories based on phase-change materials have gained ground for applications in analog in-memory computing. Nonetheless, non-idealities inherent to the material result in device resistance variations that impair the achievable numerical precision. Projected-type phase-change memory devices reduce these non-idealities. In a projected phase-change memory, the phase-change storage mechanism is decoupled from the information retrieval process by using projection of the phase-change material’s phase configuration onto a projection liner. It has been suggested that the interface resistance between the phase-change material and the projection liner is an important parameter that dictates the efficacy of the projection. In this work, we establish a metrology framework to assess and understand the relevant structural properties of the interfaces in thin films contained in projected memory devices. Using X-ray reflectivity, X-ray diffraction and transmission electron microscopy, we investigate the quality of the interfaces and the layers’ properties. Using demonstrator examples of Sb and Sb2Te3 phase-change materials, new deposition routes as well as stack designs are proposed to enhance the phase-change material to a projection-liner interface and the robustness of material stacks in the devices.
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2
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Dyck O, Swett JL, Evangeli C, Lupini AR, Mol JA, Jesse S. Mapping Conductance and Switching Behavior of Graphene Devices In Situ. SMALL METHODS 2022; 6:e2101245. [PMID: 35312230 DOI: 10.1002/smtd.202101245] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Revised: 11/15/2021] [Indexed: 06/14/2023]
Abstract
Graphene is proposed for use in various nanodevice designs, many of which harness emergent quantum properties for device functionality. However, visualization, measurement, and manipulation become nontrivial at nanometer and atomic scales, representing a significant challenge for device fabrication, characterization, and optimization at length scales where quantum effects emerge. Here, proof of principle results at the crossroads between 2D nanoelectronic devices, e-beam-induced modulation, and imaging with secondary electron e-beam induced currents (SEEBIC) is presented. A device platform compatible with scanning transmission electron microscopy investigations is introduced. Then how the SEEBIC imaging technique can be used to visualize conductance and connectivity in single layer graphene nanodevices, even while supported on a thicker substrate (conditions under which conventional imaging fails) is shown. Finally, it is shown that the SEEBIC imaging technique can detect subtle differences in charge transport through time in nonohmic graphene nanoconstrictions indicating the potential to reveal dynamic electronic processes.
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Affiliation(s)
- Ondrej Dyck
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
| | - Jacob L Swett
- Department of Materials, University of Oxford, Oxford, OX1 3PH, UK
| | | | - Andrew R Lupini
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
| | - Jan A Mol
- Department of Materials, University of Oxford, Oxford, OX1 3PH, UK
- School of Physics and Astronomy, Queen Mary University of London, London, E1 4NS, UK
| | - Stephen Jesse
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
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3
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He Q, Youngblood N, Cheng Z, Miao X, Bhaskaran H. Dynamically tunable transmissive color filters using ultra-thin phase change materials. OPTICS EXPRESS 2020; 28:39841-39849. [PMID: 33379525 DOI: 10.1364/oe.411874] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Accepted: 11/24/2020] [Indexed: 06/12/2023]
Abstract
Structural color filters (i.e. plasmonics and nano-cavities) provide vivid and robust color filtering in applications such as CMOS image sensors but lack simplicity in fabrication and dynamic tuning. Here we report a dynamically tunable, transmissive color filter by incorporating an ultra-thin phase change layer inside a thin-film optical resonator. The transmitted color spectrum can be designed over the entire visible range and shifted by around 50 nm after phase transition. Angle dependence shows little color variation within a ±30° viewing angle. Crucially, only film deposition is required to fabricate our phase change color filter, showing great potential for large-scale and inexpensive production. The dynamically tunable color filter, described in this paper, could be a promising component in display, CMOS sensor, and solar cell technology.
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4
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Abstract
Two-dimensional (2D) layered materials and their heterostructures have recently been recognized as promising building blocks for futuristic brain-like neuromorphic computing devices. They exhibit unique properties such as near-atomic thickness, dangling-bond-free surfaces, high mechanical robustness, and electrical/optical tunability. Such attributes unattainable with traditional electronic materials are particularly promising for high-performance artificial neurons and synapses, enabling energy-efficient operation, high integration density, and excellent scalability. In this review, diverse 2D materials explored for neuromorphic applications, including graphene, transition metal dichalcogenides, hexagonal boron nitride, and black phosphorous, are comprehensively overviewed. Their promise for neuromorphic applications are fully discussed in terms of material property suitability and device operation principles. Furthermore, up-to-date demonstrations of neuromorphic devices based on 2D materials or their heterostructures are presented. Lastly, the challenges associated with the successful implementation of 2D materials into large-scale devices and their material quality control will be outlined along with the future prospect of these emergent materials.
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5
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Sangwan VK, Hersam MC. Neuromorphic nanoelectronic materials. NATURE NANOTECHNOLOGY 2020; 15:517-528. [PMID: 32123381 DOI: 10.1038/s41565-020-0647-z] [Citation(s) in RCA: 175] [Impact Index Per Article: 43.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Accepted: 01/23/2020] [Indexed: 05/10/2023]
Abstract
Memristive and nanoionic devices have recently emerged as leading candidates for neuromorphic computing architectures. While top-down fabrication based on conventional bulk materials has enabled many early neuromorphic devices and circuits, bottom-up approaches based on low-dimensional nanomaterials have shown novel device functionality that often better mimics a biological neuron. In addition, the chemical, structural and compositional tunability of low-dimensional nanomaterials coupled with the permutational flexibility enabled by van der Waals heterostructures offers significant opportunities for artificial neural networks. In this Review, we present a critical survey of emerging neuromorphic devices and architectures enabled by quantum dots, metal nanoparticles, polymers, nanotubes, nanowires, two-dimensional layered materials and van der Waals heterojunctions with a particular emphasis on bio-inspired device responses that are uniquely enabled by low-dimensional topology, quantum confinement and interfaces. We also provide a forward-looking perspective on the opportunities and challenges of neuromorphic nanoelectronic materials in comparison with more mature technologies based on traditional bulk electronic materials.
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Affiliation(s)
- Vinod K Sangwan
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL, USA
| | - Mark C Hersam
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL, USA.
- Department of Chemistry, Northwestern University, Evanston, IL, USA.
- Department of Electrical and Computer Engineering, Northwestern University, Evanston, IL, USA.
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6
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Lee I, Kim JN, Kang WT, Shin YS, Lee BH, Yu WJ. Schottky Barrier Variable Graphene/Multilayer-MoS 2 Heterojunction Transistor Used to Overcome Short Channel Effects. ACS APPLIED MATERIALS & INTERFACES 2020; 12:2854-2861. [PMID: 31855598 DOI: 10.1021/acsami.9b18577] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
A single-layer MoS2 achieves excellent gate controllability within the nanoscale channel length of a field-effect transistor (FET) owing to an ultra-short screening length. However, multilayer MoS2 (ML-MoS2) is more vulnerable to short channel effects (SCEs) owing to its thickness and long screening length. We eliminated the SCEs in an ML-MoS2 FET (thickness of 4-13 nm) at a channel length of sub-30 nm using a Schottky barrier (SB) variable graphene/ML-MoS2 heterojunction. Although the band modulation in the ML-MoS2 channel worsens with a decrease in the channel length, which is similar to the SCEs occurring in conventional FETs, the variable Fermi level (EF) of a graphene electrode along the gate voltage allows control of the SB at the graphene/MoS2 junction and backs up the current modulation through a variable SB. Electrical measurements and a theoretical band simulation demonstrate the efficient SB modulation of our graphene nanogap (GrNG) ML-MoS2 FET with three distinct carrier transports along Vgs: a thermionic emission at a low SB, Fowler-Nordheim tunneling at a moderate SB, and direct tunneling at a high SB. Our GrNG FET shows an extremely high on-off current ratio of ∼108, which is approximately three-orders of magnitude better than a previously reported metal nanogap (MeNG) FET and a self-aligned metal/graphene nanogap FET with a similar MoS2 thickness. Our GrNG FET also exhibits a 100,000-times higher on-off ratio, 100-times lower subthreshold swing, and 10-times lower drain induced barrier.
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Affiliation(s)
- Ilmin Lee
- Department of Electrical and Computer Engineering , Sungkyunkwan University , Suwon 16419 , Republic of Korea
| | - Joo Nam Kim
- Department of Electrical and Computer Engineering , Sungkyunkwan University , Suwon 16419 , Republic of Korea
| | - Won Tae Kang
- Department of Electrical and Computer Engineering , Sungkyunkwan University , Suwon 16419 , Republic of Korea
- Center for Integrated Nanostructure Physics , Institute for Basic Science (IBS) , Suwon 16419 , Republic of Korea
| | - Yong Seon Shin
- Department of Electrical and Computer Engineering , Sungkyunkwan University , Suwon 16419 , Republic of Korea
- Center for Integrated Nanostructure Physics , Institute for Basic Science (IBS) , Suwon 16419 , Republic of Korea
| | - Boo Hueng Lee
- Department of Electrical and Computer Engineering , Sungkyunkwan University , Suwon 16419 , Republic of Korea
| | - Woo Jong Yu
- Department of Electrical and Computer Engineering , Sungkyunkwan University , Suwon 16419 , Republic of Korea
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7
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Li J, Friedrich N, Merino N, de Oteyza DG, Peña D, Jacob D, Pascual JI. Electrically Addressing the Spin of a Magnetic Porphyrin through Covalently Connected Graphene Electrodes. NANO LETTERS 2019; 19:3288-3294. [PMID: 30964303 DOI: 10.1021/acs.nanolett.9b00883] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We report on the fabrication and transport characterization of atomically precise single-molecule devices consisting of a magnetic porphyrin covalently wired by graphene nanoribbon electrodes. The tip of a scanning tunneling microscope was utilized to contact the end of a GNR-porphyrin-GNR hybrid system and create a molecular bridge between the tip and sample for transport measurements. Electrons tunneling through the suspended molecular heterostructure excited the spin multiplet of the magnetic porphyrin. The detachment of certain spin centers from the surface shifted their spin-carrying orbitals away from an on-surface mixed-valence configuration, recovering its original spin state. The existence of spin-polarized resonances in the free-standing systems and their electrical addressability is the fundamental step in the utilization of carbon-based materials as functional molecular spintronics systems.
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Affiliation(s)
- Jingcheng Li
- CIC nanoGUNE , Tolosa Hiribidea 76 , 20018 Donostia-San Sebastian , Spain
| | - Niklas Friedrich
- CIC nanoGUNE , Tolosa Hiribidea 76 , 20018 Donostia-San Sebastian , Spain
| | - Nestor Merino
- CIC nanoGUNE , Tolosa Hiribidea 76 , 20018 Donostia-San Sebastian , Spain
- Donostia International Physics Center (DIPC) , 20018 Donostia-San Sebastián , Spain
| | - Dimas G de Oteyza
- Donostia International Physics Center (DIPC) , 20018 Donostia-San Sebastián , Spain
- Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU) , 20018 Donostia-San Sebastián , Spain
- Ikerbasque, Basque Foundation for Science, 48013 Bilbao , Spain
| | - Diego Peña
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS), and Departamento de Química Orgánica , Universidade de Santiago de Compostela , 15705 Santiago de Compostela , Spain
| | - David Jacob
- Ikerbasque, Basque Foundation for Science, 48013 Bilbao , Spain
- Departamento de Física de Materiales , Universidad del País Vasco UPV/EHU , 20018 Donostia-San Sebastián , Spain
| | - Jose Ignacio Pascual
- CIC nanoGUNE , Tolosa Hiribidea 76 , 20018 Donostia-San Sebastian , Spain
- Ikerbasque, Basque Foundation for Science, 48013 Bilbao , Spain
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8
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Lee JK, Lee GD, Lee S, Yoon E, Anderson HL, Briggs GAD, Warner JH. Atomic Scale Imaging of Reversible Ring Cyclization in Graphene Nanoconstrictions. ACS NANO 2019; 13:2379-2388. [PMID: 30673212 DOI: 10.1021/acsnano.8b09211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We present an atomic level study of reversible cyclization processes in suspended nanoconstricted regions of graphene that form linear carbon chains (LCCs). Before the nanoconstricted region reaches a single linear carbon chain (SLCC), we observe that a double linear carbon chain (DLCC) structure often reverts back to a ribbon of sp2 hybridized oligoacene rings, in a process akin to the Bergman rearrangement. When the length of the DLCC system only consists of ∼5 atoms in each LCC, full recyclization occurs for all atoms present, but for longer DLCCs we find that only single sections of the chain are modified in their bonding hybridization and no full ring closure occurs along the entire DLCCs. This process is observed in real time using aberration-corrected transmission electron microscopy and simulated using density functional theory and tight binding molecular dynamics calculations. These results show that DLCCs are highly sensitive to the adsorption of local gas molecules or surface diffusion impurities and undergo structural modifications.
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Affiliation(s)
- Ja Kyung Lee
- Department of Materials , University of Oxford , Parks Road , Oxford OX1 3PH , United Kingdom
| | - Gun-Do Lee
- Department of Materials Science and Engineering , Seoul National University , Seoul 151-743 , Korea
| | - Sungwoo Lee
- Department of Materials Science and Engineering , Seoul National University , Seoul 151-743 , Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering , Seoul National University , Seoul 151-743 , Korea
| | - Harry L Anderson
- Department of Chemistry , University of Oxford , Mansfield Road , Oxford OX1 3TA , United Kingdom
| | - G Andrew D Briggs
- Department of Materials , University of Oxford , Parks Road , Oxford OX1 3PH , United Kingdom
| | - Jamie H Warner
- Department of Materials , University of Oxford , Parks Road , Oxford OX1 3PH , United Kingdom
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9
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Yuting L, Jing Z, Donghui L. Preparation of cadmium sulfide nanoparticles and their application for improving the properties of the electrochemical sensor for the determination of enrofloxacin in real samples. Chirality 2019; 31:174-184. [DOI: 10.1002/chir.23045] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2018] [Revised: 12/05/2018] [Accepted: 12/12/2018] [Indexed: 11/07/2022]
Affiliation(s)
- Liu Yuting
- Medical College; Jinzhou Medical University; Jinzhou People's Republic of China
| | - Zhang Jing
- Pharmaceutical College; Jinzhou Medical University; Jinzhou People's Republic of China
| | - Li Donghui
- Pharmaceutical College; Jinzhou Medical University; Jinzhou People's Republic of China
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10
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Sarwat SG, Youngblood N, Au YY, Mol JA, Wright CD, Bhaskaran H. Engineering Interface-Dependent Photoconductivity in Ge 2Sb 2Te 5 Nanoscale Devices. ACS APPLIED MATERIALS & INTERFACES 2018; 10:44906-44914. [PMID: 30501199 DOI: 10.1021/acsami.8b17602] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Phase-change materials are increasingly being explored for photonics applications, ranging from high-resolution displays to artificial retinas. Surprisingly, our understanding of the underlying mechanism of light-matter interaction in these materials has been limited to photothermal crystallization because of its relevance in applications such as rewritable optical discs. Here, we report a photoconductivity study of nanoscale thin films of phase-change materials. We identify strong photoconductive behavior in phase-change materials, which we show to be a complex interplay of three independent mechanisms: photoconductive, photoinduced crystallization, and photoinduced thermoelectric effects. We find that these effects also congruously contribute to a substantial photovoltaic effect, even in notionally symmetric devices. Notably, we show that device engineering plays a decisive role in determining the dominant mechanism; the contribution of the photothermal effects to the extractable photocurrent can be reduced to <0.4% by varying the electrodes and device geometry. We then show that the contribution of these individual effects to the photoresponse is phase-dependent with the amorphous state being more photoactive than the crystalline state and that a reversible change occurs in the charge transport from thermionic to tunnelling during phase transformation. Finally, we demonstrate photodetectors with an order of magnitude tunability in photodetection responsivity and bandwidth using these materials. Our results provide insights to the photophysics of phase-change materials and highlight their potential in future optoelectronics.
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Affiliation(s)
- Syed Ghazi Sarwat
- Department of Materials , University of Oxford , Oxford OX1 3PH , U.K
| | - Nathan Youngblood
- Department of Materials , University of Oxford , Oxford OX1 3PH , U.K
| | - Yat-Yin Au
- Department of Engineering , University of Exeter , Exeter EX4 4QF , U.K
| | - Jan A Mol
- Department of Materials , University of Oxford , Oxford OX1 3PH , U.K
| | - C David Wright
- Department of Engineering , University of Exeter , Exeter EX4 4QF , U.K
| | - Harish Bhaskaran
- Department of Materials , University of Oxford , Oxford OX1 3PH , U.K
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11
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Caneva S, Gehring P, García-Suárez VM, García-Fuente A, Stefani D, Olavarria-Contreras IJ, Ferrer J, Dekker C, van der Zant HSJ. Mechanically controlled quantum interference in graphene break junctions. NATURE NANOTECHNOLOGY 2018; 13:1126-1131. [PMID: 30224794 DOI: 10.1038/s41565-018-0258-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Accepted: 08/09/2018] [Indexed: 06/08/2023]
Abstract
The ability to detect and distinguish quantum interference signatures is important for both fundamental research and for the realization of devices such as electron resonators1, interferometers2 and interference-based spin filters3. Consistent with the principles of subwavelength optics, the wave nature of electrons can give rise to various types of interference effects4, such as Fabry-Pérot resonances5, Fano resonances6 and the Aharonov-Bohm effect7. Quantum interference conductance oscillations8 have, indeed, been predicted for multiwall carbon nanotube shuttles and telescopes, and arise from atomic-scale displacements between the inner and outer tubes9,10. Previous theoretical work on graphene bilayers indicates that these systems may display similar interference features as a function of the relative position of the two sheets11,12. Experimental verification is, however, still lacking. Graphene nanoconstrictions represent an ideal model system to study quantum transport phenomena13-15 due to the electronic coherence16 and the transverse confinement of the carriers17. Here, we demonstrate the fabrication of bowtie-shaped nanoconstrictions with mechanically controlled break junctions made from a single layer of graphene. Their electrical conductance displays pronounced oscillations at room temperature, with amplitudes that modulate over an order of magnitude as a function of subnanometre displacements. Surprisingly, the oscillations exhibit a period larger than the graphene lattice constant. Charge-transport calculations show that the periodicity originates from a combination of the quantum interference and lattice commensuration effects of two graphene layers that slide across each other. Our results provide direct experimental observation of a Fabry-Pérot-like interference of electron waves that are partially reflected and/or transmitted at the edges of the graphene bilayer overlap region.
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Affiliation(s)
- Sabina Caneva
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Pascal Gehring
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | - Víctor M García-Suárez
- Departamento de Física, Universidad de Oviedo, Oviedo, Spain
- Nanomaterials and Nanotechnology Research Center, CSIC - Universidad de Oviedo, Oviedo, Spain
| | | | - Davide Stefani
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
| | | | - Jaime Ferrer
- Departamento de Física, Universidad de Oviedo, Oviedo, Spain.
- Nanomaterials and Nanotechnology Research Center, CSIC - Universidad de Oviedo, Oviedo, Spain.
| | - Cees Dekker
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
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12
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Sun H, Jiang Z, Xin N, Guo X, Hou S, Liao J. Efficient Fabrication of Stable Graphene-Molecule-Graphene Single-Molecule Junctions at Room Temperature. Chemphyschem 2018; 19:2258-2265. [PMID: 29797388 DOI: 10.1002/cphc.201800220] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Indexed: 01/22/2023]
Abstract
We present a robust approach to fabricate stable single-molecule junctions at room temperature using single-layer graphene as nanoelectrodes. Molecular scale nano-gaps in graphene were generated using an optimized fast-speed feedback-controlled electroburning process. This process shortened the time for creating a single nano-gap to be less than one minute while keeping a yield higher than 97 %. To precisely control the gap position and minimize the effects of edge defects and the quantum confinement, extra-narrow grooves were pre-patterned in the graphene structures with oxygen plasma etching. Molecular junctions were formed by bridging the nano-gaps with amino-functionalized hexaphenyl molecules by taking advantage of chemical reactions between the amino groups at the two ends of the molecules and the carboxyl groups at the edges of graphene electrodes. Electronic transport measurements and transition voltage spectroscopy analysis verified the formation of single-molecule devices. First-principles quantum transport calculations show that the highest occupied molecular orbital of hexaphenyl is closer to the Fermi level of the graphene electrodes and thus the devices exhibit a hole-type transport characteristics. Some of these molecular devices remained stable up to four weeks, highlighting the potential of graphene nano-electrodes in the fabrication of stable single-molecule devices at room temperature.
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Affiliation(s)
- Hantao Sun
- Centre for Nanoscale Science and Technology, Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing, 100871, China
| | - Zhuoling Jiang
- Centre for Nanoscale Science and Technology, Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing, 100871, China
| | - Na Xin
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China
| | - Xuefeng Guo
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China
| | - Shimin Hou
- Centre for Nanoscale Science and Technology, Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing, 100871, China
| | - Jianhui Liao
- Centre for Nanoscale Science and Technology, Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing, 100871, China
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13
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Cheng Z, Ríos C, Youngblood N, Wright CD, Pernice WHP, Bhaskaran H. Device-Level Photonic Memories and Logic Applications Using Phase-Change Materials. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1802435. [PMID: 29940084 DOI: 10.1002/adma.201802435] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 05/21/2018] [Indexed: 05/24/2023]
Abstract
Inspired by the great success of fiber optics in ultrafast data transmission, photonic computing is being extensively studied as an alternative to replace or hybridize electronic computers, which are reaching speed and bandwidth limitations. Mimicking and implementing basic computing elements on photonic devices is a first and essential step toward all-optical computers. Here, an optical pulse-width modulation (PWM) switching of phase-change materials on an integrated waveguide is developed, which allows practical implementation of photonic memories and logic devices. It is established that PWM with low peak power is very effective for recrystallization of phase-change materials, in terms of both energy efficiency and process control. Using this understanding, multilevel photonic memories with complete random accessibility are then implemented. Finally, programmable optical logic devices are demonstrated conceptually and experimentally, with logic "OR" and "NAND" achieved on just a single integrated photonic phase-change cell. This study provides a practical and elegant technique to optically program photonic phase-change devices for computing applications.
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Affiliation(s)
- Zengguang Cheng
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK
| | - Carlos Ríos
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Nathan Youngblood
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK
| | - C David Wright
- Department of Engineering, University of Exeter, Exeter, EX4 4QF, UK
| | - Wolfram H P Pernice
- Institute of Physics, University of Muenster, Heisenbergstr, 11, 48149, Muenster, Germany
| | - Harish Bhaskaran
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK
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14
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Gu C, Hu C, Wei Y, Lin D, Jia C, Li M, Su D, Guan J, Xia A, Xie L, Nitzan A, Guo H, Guo X. Label-Free Dynamic Detection of Single-Molecule Nucleophilic-Substitution Reactions. NANO LETTERS 2018; 18:4156-4162. [PMID: 29874453 DOI: 10.1021/acs.nanolett.8b00949] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The mechanisms of chemical reactions, including the transformation pathways of the electronic and geometric structures of molecules, are crucial for comprehending the essence and developing new chemistry. However, it is extremely difficult to realize at the single-molecule level. Here, we report a single-molecule approach capable of electrically probing stochastic fluctuations under equilibrium conditions and elucidating time trajectories of single species in non-equilibrated systems. Through molecular engineering, a single molecular wire containing a functional center of 9-phenyl-9-fluorenol was covalently wired into nanogapped graphene electrodes to form stable single-molecule junctions. Both experimental and theoretical studies consistently demonstrate and interpret the direct measurement of the formation dynamics of individual carbocation intermediates with a strong solvent dependence in a nucleophilic-substitution reaction. We also show the kinetic process of competitive transitions between acetate and bromide species, which is inevitable through a carbocation intermediate, confirming the classical mechanism. This unique method creates plenty of opportunities for carrying out single-molecule dynamics or biophysics investigations in broad fields beyond reaction chemistry through molecular design and engineering.
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Affiliation(s)
- Chunhui Gu
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering , Peking University , Beijing 100871 , PR China
| | - Chen Hu
- Center for the Physics of Materials and Department of Physics , McGill University , Montreal , Quebec H3A 2T8 , Canada
| | - Ying Wei
- Center for Molecular Systems and Organic Devices, Key Laboratory for Organic Electronics & Information Displays and Institute of Advanced Materials , Nanjing University of Posts & Telecommunications , Nanjing 210023 , PR China
| | - Dongqing Lin
- Center for Molecular Systems and Organic Devices, Key Laboratory for Organic Electronics & Information Displays and Institute of Advanced Materials , Nanjing University of Posts & Telecommunications , Nanjing 210023 , PR China
| | - Chuancheng Jia
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering , Peking University , Beijing 100871 , PR China
| | - Mingzhi Li
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering , Peking University , Beijing 100871 , PR China
| | - Dingkai Su
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering , Peking University , Beijing 100871 , PR China
| | - Jianxin Guan
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering , Peking University , Beijing 100871 , PR China
| | - Andong Xia
- Institute of Chemistry , Chinese Academy of Sciences , Beijing 100190 , PR China
| | - Linghai Xie
- Center for Molecular Systems and Organic Devices, Key Laboratory for Organic Electronics & Information Displays and Institute of Advanced Materials , Nanjing University of Posts & Telecommunications , Nanjing 210023 , PR China
| | - Abraham Nitzan
- Department of Chemistry , University of Pennsylvania , Philadelphia , Pennsylvania 19104-6323 , United States
| | - Hong Guo
- Center for the Physics of Materials and Department of Physics , McGill University , Montreal , Quebec H3A 2T8 , Canada
| | - Xuefeng Guo
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering , Peking University , Beijing 100871 , PR China
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15
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Burzurí E, García-Fuente A, García-Suárez V, Senthil Kumar K, Ruben M, Ferrer J, van der Zant HSJ. Spin-state dependent conductance switching in single molecule-graphene junctions. NANOSCALE 2018; 10:7905-7911. [PMID: 29682641 DOI: 10.1039/c8nr00261d] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Spin-crossover (SCO) molecules are versatile magnetic switches with applications in molecular electronics and spintronics. Downscaling devices to the single-molecule level remains, however, a challenging task since the switching mechanism in bulk is mediated by cooperative intermolecular interactions. Here, we report on electron transport through individual Fe-SCO molecules coupled to few-layer graphene electrodes via π-π stacking. We observe a distinct bistability in the conductance of the molecule and a careful comparison with density functional theory (DFT) calculations allows to associate the bistability with a SCO-induced orbital reconfiguration of the molecule. We find long spin-state lifetimes that are caused by the specific coordination of the magnetic core and the absence of intermolecular interactions according to our calculations. In contrast with bulk samples, the SCO transition is not triggered by temperature but induced by small perturbations in the molecule at any temperature. We propose plausible mechanisms that could trigger the SCO at the single-molecule level.
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Affiliation(s)
- Enrique Burzurí
- Kavli Institute of Nanoscience, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands
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16
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Sarwat SG, Tweedie M, Porter BF, Zhou Y, Sheng Y, Mol J, Warner J, Bhaskaran H. Revealing Strain-Induced Effects in Ultrathin Heterostructures at the Nanoscale. NANO LETTERS 2018; 18:2467-2474. [PMID: 29510053 DOI: 10.1021/acs.nanolett.8b00036] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Two-dimensional materials are being increasingly studied, particularly for flexible and wearable technologies because of their inherent thickness and flexibility. Crucially, one aspect where our understanding is still limited is on the effect of mechanical strain, not on individual sheets of materials, but when stacked together as heterostructures in devices. In this paper, we demonstrate the use of Kelvin probe microscopy in capturing the influence of uniaxial tensile strain on the band-structures of graphene and WS2 (mono- and multilayered) based heterostructures at high resolution. We report a major advance in strain characterization tools through enabling a single-shot capture of strain defined changes in a heterogeneous system at the nanoscale, overcoming the limitations (materials, resolution, and substrate effects) of existing techniques such as optical spectroscopy. Using this technique, we observe that the work-functions of graphene and WS2 increase as a function of strain, which we attribute to the Fermi level lowering from increased p-doping. We also extract the nature of the interfacial heterojunctions and find that they get strongly modulated from strain. We observe that the strain-enhanced charge transfer with the substrate plays a dominant role, causing the heterostructures to behave differently from two-dimensional materials in their isolated forms.
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Affiliation(s)
- Syed Ghazi Sarwat
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Martin Tweedie
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Benjamin F Porter
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Yingqiu Zhou
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Yuewen Sheng
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Jan Mol
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Jamie Warner
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
| | - Harish Bhaskaran
- Department of Materials , University of Oxford , Oxford OX1 3PH , United Kingdom
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17
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Gu C, Su D, Jia C, Ren S, Guo X. Building nanogapped graphene electrode arrays by electroburning. RSC Adv 2018; 8:6814-6819. [PMID: 35540328 PMCID: PMC9078314 DOI: 10.1039/c7ra13106b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2017] [Accepted: 01/30/2018] [Indexed: 01/07/2023] Open
Abstract
Carbon nanoelectrodes with nanogap are reliable platforms for achieving ultra-small electronic devices. One of the main challenges in fabricating nanogapped carbon electrodes is precise control of the gap size. Herein, we put forward an electroburning approach for controllable fabrication of graphene nanoelectrodes from preprocessed nanoconstriction arrays. The electroburning behavior was investigated in detail, which revealed a dependence on the size of nanoconstriction units. The electroburnt nanoscale electrodes showed the capacity to build molecular devices. The methodology and mechanism presented in this study provide significant guidance for the fabrication of proper graphene and other carbon nanoelectrodes. An approach for the efficient fabrication of graphene nanoelectrodes through the combination of dash-line lithography and electroburning is demonstrated in detail.![]()
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Affiliation(s)
- Chunhui Gu
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University Beijing 100871 P. R. China
| | - Dingkai Su
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University Beijing 100871 P. R. China
| | - Chuancheng Jia
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University Beijing 100871 P. R. China
| | - Shizhao Ren
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University Beijing 100871 P. R. China
| | - Xuefeng Guo
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University Beijing 100871 P. R. China .,Department of Materials Science and Engineering, College of Engineering, Peking University Beijing 100871 P. R. China
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18
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Pósa L, El Abbassi M, Makk P, Sánta B, Nef C, Csontos M, Calame M, Halbritter A. Multiple Physical Time Scales and Dead Time Rule in Few-Nanometers Sized Graphene-SiO x-Graphene Memristors. NANO LETTERS 2017; 17:6783-6789. [PMID: 28984461 DOI: 10.1021/acs.nanolett.7b03000] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The resistive switching behavior in SiOx-based phase change memory devices confined by few nanometer wide graphene nanogaps is investigated. Our experiments and analysis reveal that the switching dynamics is not only determined by the commonly observed bias voltage dependent set and reset times. We demonstrate that an internal time scale, the dead time, plays a fundamental role in the system's response to various driving signals. We associate the switching behavior with the formation of microscopically distinct SiOx amorphous and crystalline phases between the graphene electrodes. The reset transition is attributed to an amorphization process due to a voltage driven self-heating; it can be triggered at any time by appropriate voltage levels. In contrast, the formation of the crystalline ON state is conditional and only occurs after the completion of a thermally assisted structural rearrangement of the as-quenched OFF state which takes place within the dead time after a reset operation. Our results demonstrate the technological relevance of the dead time rule which enables a zero bias access of both the low and high resistance states of a phase change memory device by unipolar voltage pulses.
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Affiliation(s)
- László Pósa
- Department of Physics, Budapest University of Technology and Economics and MTA-BME Condensed Matter Research Group , Budafoki ut 8, 1111 Budapest, Hungary
- MTA EK Institute for Technical Physics and Materials Science , Konkoly-Thege M. út 29-33, 1121 Budapest, Hungary
| | - Maria El Abbassi
- Department of Physics, University of Basel , Klingelbergstrasse 82, CH-4056 Basel, Switzerland
- Empa, Swiss Federal Laboratories for Materials Science and Technology, Transport at Nanoscale Interfaces Laboratory , CH-8600 Dübendorf, Switzerland
| | - Péter Makk
- Department of Physics, University of Basel , Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Botond Sánta
- Department of Physics, Budapest University of Technology and Economics and MTA-BME Condensed Matter Research Group , Budafoki ut 8, 1111 Budapest, Hungary
| | - Cornelia Nef
- Department of Physics, University of Basel , Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Miklós Csontos
- Department of Physics, Budapest University of Technology and Economics and MTA-BME Condensed Matter Research Group , Budafoki ut 8, 1111 Budapest, Hungary
- Empa, Swiss Federal Laboratories for Materials Science and Technology, Transport at Nanoscale Interfaces Laboratory , CH-8600 Dübendorf, Switzerland
| | - Michel Calame
- Department of Physics, University of Basel , Klingelbergstrasse 82, CH-4056 Basel, Switzerland
- Swiss Nanoscience Institute, University of Basel , CH-4056 Basel, Switzerland
- Empa, Swiss Federal Laboratories for Materials Science and Technology, Transport at Nanoscale Interfaces Laboratory , CH-8600 Dübendorf, Switzerland
| | - András Halbritter
- Department of Physics, Budapest University of Technology and Economics and MTA-BME Condensed Matter Research Group , Budafoki ut 8, 1111 Budapest, Hungary
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