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Sutter E, Komsa HP, Sutter P. Valley-selective carrier transfer in SnS-based van der Waals heterostructures. NANOSCALE HORIZONS 2024. [PMID: 39171396 DOI: 10.1039/d4nh00231h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/23/2024]
Abstract
Valleytronics, i.e., use of the valley degree of freedom in semiconductors as an information carrier, is a promising alternative to conventional approaches for information processing. Transition metal dichalcogenides with degenerate K/K' valleys have received attention as prototype 2D/layered semiconductors for valleytronics, but these systems rely on exotic effects such as the valley-Hall effect for electrical readout of the valley occupancy. Non-traditional valleytronic systems hosting sets of addressable non-degenerate valleys could overcome this limitation. In the van der Waals semiconductor Sn(II) sulfide (SnS), for instance, different bandgaps and band edges may allow manipulating the population of the X- and Y-valleys via charge transfer across interfaces to other layered semiconductors. Here, we establish this concept by comparing SnS flakes and SnS-based heterostructures. Cathodoluminescence spectroscopy shows a striking reversal of the luminescence intensity of the two valleys in SnS-GeS van der Waals stacks, which stems from a selective electron transfer from the Y-valley into GeS while X-valley electrons remain confined to SnS. Our results suggest that non-traditional systems, embodied here by SnS-based van der Waals heterostructures, open avenues for valley-selective readout relying on design parameters such as heterostructure band offsets that are among the core concepts of semiconductor technology.
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Affiliation(s)
- E Sutter
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA.
| | - H-P Komsa
- Microelectronics Research Unit, University of Oulu, FI-90014 Oulu, Finland
| | - P Sutter
- Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA.
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2
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Sutter E, Kisslinger K, Unocic RR, Burns K, Hachtel J, Sutter P. Photonics in Multimaterial Lateral Heterostructures Combining Group IV Chalcogenide van der Waals Semiconductors. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2024; 20:e2307372. [PMID: 38054819 DOI: 10.1002/smll.202307372] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2023] [Revised: 11/25/2023] [Indexed: 12/07/2023]
Abstract
Lateral heterostructures combining two multilayer group IV chalcogenide van der Waals semiconductors have attracted interest for optoelectronics, twistronics, and valleytronics, owing to their structural anisotropy, bulk-like electronic properties, enhanced optical thickness, and vertical interfaces enabling in-plane charge manipulation/separation, perpendicular to the trajectory of incident light. Group IV monochalcogenides support propagating photonic waveguide modes, but their interference gives rise to complex light emission patterns throughout the visible/near-infrared range both in uniform flakes and single-interface lateral heterostructures. Here, this work demonstrates the judicious integration of pure and alloyed monochalcogenide crystals into multimaterial heterostructures with unique photonic properties, notably the ability to select photonic modes with targeted discrete energies through geometric factors rather than band engineering. SnS-GeS1-xSex-GeSe-GeS1-xSex heterostructures with a GeS1-xSex active layer sandwiched laterally between GeSe and SnS, semiconductors with similar optical constants but smaller bandgaps, were designed and realized via sequential vapor transport synthesis. Raman spectroscopy, electron microscopy/diffraction, and energy-dispersive X-ray spectroscopy confirm a high crystal quality of the laterally stitched components with sharp interfaces. Nanometer-scale cathodoluminescence spectroscopy provides evidence for a facile transfer of electron-hole pairs across the lateral interfaces and demonstrates the selection of photon emission at discrete energies in the laterally embedded active (GeS1- xSex) part of the heterostructure.
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Affiliation(s)
- Eli Sutter
- Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
| | - Kim Kisslinger
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973, USA
| | - Raymond R Unocic
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
| | - Kory Burns
- Department of Materials Science & Engineering, University of Virginia, Charlottesville, VA, 22904, USA
| | - Jordan Hachtel
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37830, USA
| | - Peter Sutter
- Department of Electrical & Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
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3
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Khanmohammadi S, Kushnir Friedman K, Chen E, Kastuar SM, Ekuma CE, Koski KJ, Titova LV. Tailoring Ultrafast Near-Band Gap Photoconductive Response in GeS by Zero-Valent Cu Intercalation. ACS APPLIED MATERIALS & INTERFACES 2024; 16:16445-16452. [PMID: 38528798 DOI: 10.1021/acsami.3c19251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/27/2024]
Abstract
Zero-valent intercalation of atomic metals into the van der Waals gap of layered materials can be used to tune their electronic, optical, thermal, and mechanical properties. Here, we report the impact of intercalating ∼3 atm percent of zero-valent copper into germanium sulfide (GeS). Advanced many-body calculations predict that copper introduces quasi-localized intermediate band states, and time-resolved THz spectroscopy studies demonstrate that those states have prominent effects on the photoconductivity of GeS. Cu-intercalated GeS exhibits a faster rise of transient photoconductivity and a shorter lifetime of optically injected carriers following near-gap excitation with 800 nm pulses. At the same time, Cu intercalation improves free carrier mobility from 1100 to 1300 cm2 V-1 s-1, which we attribute to the damping of acoustic phonons observed in Brillouin scattering and consequent reduction of phonon scattering.
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Affiliation(s)
- Sepideh Khanmohammadi
- Department of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, United States
| | - Kateryna Kushnir Friedman
- Department of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, United States
| | - Ethan Chen
- Department of Chemistry, University of California Davis, Davis, California 95616, United States
| | - Srihari M Kastuar
- Department of Physics, Lehigh University, Bethlehem, Pennsylvania 18015, United States
| | - Chinedu E Ekuma
- Department of Physics, Lehigh University, Bethlehem, Pennsylvania 18015, United States
| | - Kristie J Koski
- Department of Chemistry, University of California Davis, Davis, California 95616, United States
| | - Lyubov V Titova
- Department of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, United States
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4
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Ribeiro TC, Fonseca DHS, Barreto RR, Pereira-Andrade E, Miquita DR, Malachias A, Magalhaes-Paniago R. Scanning Tunneling Spectroscopy Method for the Prediction of Semiconductor Heterojunction Performance as a Prequel for Device Development. ACS APPLIED MATERIALS & INTERFACES 2024; 16:1650-1658. [PMID: 38117664 DOI: 10.1021/acsami.3c11876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2023]
Abstract
The prediction of semiconductor device performance is a persistent challenge in materials science, and the ability to anticipate useful specifications prior to construction is crucial for enhancing the overall efficiency. In this study, we investigate the constituents of a solar cell by employing scanning tunneling microscopy (STM) and spectroscopy (STS). Through our observations, we identify a spatial distribution of the dopant type in thin films of materials that were designed to present major p-doping for germanium sulfide (GeS) and dominant n-doping for tin disulfide (SnS2). By generating separate STS maps for each semiconductor film and conducting a statistical analysis of the gap and doping distribution, we determine intrinsic limitations for the solar cell efficiency that must be understood prior to processing. Subsequently, we fabricate a solar cell utilizing these materials (GeS and SnS2) via vapor phase deposition and carry out a characterization using standard J-V curves under both dark/illuminated irradiance conditions. Our devices corroborate the expected reduced efficiency due to doping fluctuation but exhibit stable photocurrent responses. As originally planned, quantum efficiency measurements reveal that the peak efficiency of our solar cell coincides with the range where the standard silicon solar cells sharply decline. Our STS method is suggested as a prequel to device development in novel material junctions or deposition processes where fluctuations of doping levels are retrieved due to intrinsic material characteristics such as the occurrence of defects, roughness, local chemical segregation, and faceting or step bunching.
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Affiliation(s)
- Thiago C Ribeiro
- Departament of Physics, Federal University of Minas Gerais, Belo Horizonte, MG 30123-970, Brazil
| | - Daniel H S Fonseca
- Departament of Physics, Federal University of Minas Gerais, Belo Horizonte, MG 30123-970, Brazil
| | - Rafael Reis Barreto
- Departament of Physics, Federal University of Minas Gerais, Belo Horizonte, MG 30123-970, Brazil
| | - Everton Pereira-Andrade
- Departament of Physics, Federal University of Minas Gerais, Belo Horizonte, MG 30123-970, Brazil
| | - Douglas R Miquita
- Microscopy Center, Federal University of Minas Gerais, Belo Horizonte, MG 30123-970, Brazil
| | - Angelo Malachias
- Departament of Physics, Federal University of Minas Gerais, Belo Horizonte, MG 30123-970, Brazil
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Sutter E, Sutter P. Self-Assembly of Mixed-Dimensional GeS 1- x Se x (1D Nanowire)-(2D Plate) Van der Waals Heterostructures. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2023; 19:e2302592. [PMID: 37312407 DOI: 10.1002/smll.202302592] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 05/09/2023] [Indexed: 06/15/2023]
Abstract
The integration of dissimilar materials into heterostructures is a mainstay of modern materials science and technology. An alternative strategy of joining components with different electronic structure involves mixed-dimensional heterostructures, that is, architectures consisting of elements with different dimensionality, for example, 1D nanowires and 2D plates. Combining the two approaches can result in hybrid architectures in which both the dimensionality and composition vary between the components, potentially offering even larger contrast between their electronic structures. To date, realizing such heteromaterials mixed-dimensional heterostructures has required sequential multi-step growth processes. Here, it is shown that differences in precursor incorporation rates between vapor-liquid-solid growth of 1D nanowires and direct vapor-solid growth of 2D plates attached to the wires can be harnessed to synthesize heteromaterials mixed-dimensional heterostructures in a single-step growth process. Exposure to mixed GeS and GeSe vapors produces GeS1- x Sex van der Waals nanowires whose S:Se ratio is considerably larger than that of attached layered plates. Cathodoluminescence spectroscopy on single heterostructures confirms that the bandgap contrast between the components is determined by both composition and carrier confinement. These results demonstrate an avenue toward complex heteroarchitectures using single-step synthesis processes.
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Affiliation(s)
- Eli Sutter
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
- Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
| | - Peter Sutter
- Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
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6
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Sutter P, Komsa HP, Kisslinger K, Sutter E. Lateral Integration of SnS and GeSe van der Waals Semiconductors: Interface Formation, Electronic Structure, and Nanoscale Optoelectronics. ACS NANO 2023; 17:9552-9564. [PMID: 37144978 DOI: 10.1021/acsnano.3c02411] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The emergence of atomically thin crystals has allowed extending materials integration to lateral heterostructures where different 2D materials are covalently connected in the plane. The concept of lateral heterostructures can be generalized to thicker layered crystals, provided that a suitably faceted seed crystal presents edges to which a compatible second van der Waals material can be attached layer by layer. Here, we examine the possibility of integrating multilayer crystals of the group IV monochalcogenides SnS and GeSe, which have the same crystal structure, small lattice mismatch, and similar bandgaps. In a two-step growth process, lateral epitaxy of GeSe on the sidewalls of multilayer SnS flakes (obtained by vapor transport of a SnS2 precursor on graphite) yields heterostructures of laterally stitched crystalline GeSe and SnS without any detectable vertical overgrowth of the SnS seeds and with sharp lateral interfaces. Combined cathodoluminescence spectroscopy and ab initio calculations show the effects of small band offsets on carrier transport and radiative recombination near the interface. The results demonstrate the possibility of forming atomically connected lateral interfaces across many van der Waals layers, which is promising for manipulating optoelectronics, photonics, and for managing charge- and thermal transport.
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Affiliation(s)
- Peter Sutter
- Department of Electrical & Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Hannu-Pekka Komsa
- Microelectronics Research Unit, University of Oulu, FI-90014 Oulu, Finland
| | - Kim Kisslinger
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Eli Sutter
- Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
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7
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Mohammadzadeh MR, Hasani A, Jaferzadeh K, Fawzy M, De Silva T, Abnavi A, Ahmadi R, Ghanbari H, Askar A, Kabir F, Rajapakse R, Adachi MM. Unique Photoactivated Time-Resolved Response in 2D GeS for Selective Detection of Volatile Organic Compounds. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2023; 10:e2205458. [PMID: 36658730 PMCID: PMC10074048 DOI: 10.1002/advs.202205458] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Revised: 12/19/2022] [Indexed: 06/17/2023]
Abstract
Volatile organic compounds (VOCs) sensors have a broad range of applications including healthcare, process control, and air quality analysis. There are a variety of techniques for detecting VOCs such as optical, acoustic, electrochemical, and chemiresistive sensors. However, existing commercial VOC detectors have drawbacks such as high cost, large size, or lack of selectivity. Herein, a new sensing mechanism is demonstrated based on surface interactions between VOC and UV-excited 2D germanium sulfide (GeS), which provides an effective solution to distinguish VOCs. The GeS sensor shows a unique time-resolved electrical response to different VOC species, facilitating identification and qualitative measurement of VOCs. Moreover, machine learning is utilized to distinguish VOC species from their dynamic response via visualization with high accuracy. The proposed approach demonstrates the potential of 2D GeS as a promising candidate for selective miniature VOCs sensors in critical applications such as non-invasive diagnosis of diseases and health monitoring.
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Affiliation(s)
| | - Amirhossein Hasani
- School of Engineering ScienceSimon Fraser UniversityBurnabyBritish ColumbiaV5A 1S6Canada
| | - Keyvan Jaferzadeh
- Department of Computer Science and Software EngineeringConcordia UniversityMontrealQuebecH3G 1M8Canada
| | - Mirette Fawzy
- Department of PhysicsSimon Fraser UniversityBurnabyBritish ColumbiaV5A 1S6Canada
| | - Thushani De Silva
- School of Engineering ScienceSimon Fraser UniversityBurnabyBritish ColumbiaV5A 1S6Canada
| | - Amin Abnavi
- School of Engineering ScienceSimon Fraser UniversityBurnabyBritish ColumbiaV5A 1S6Canada
| | - Ribwar Ahmadi
- School of Engineering ScienceSimon Fraser UniversityBurnabyBritish ColumbiaV5A 1S6Canada
| | - Hamidreza Ghanbari
- School of Engineering ScienceSimon Fraser UniversityBurnabyBritish ColumbiaV5A 1S6Canada
| | - Abdelrahman Askar
- School of Engineering ScienceSimon Fraser UniversityBurnabyBritish ColumbiaV5A 1S6Canada
| | - Fahmid Kabir
- School of Engineering ScienceSimon Fraser UniversityBurnabyBritish ColumbiaV5A 1S6Canada
| | - R.K.N.D. Rajapakse
- School of Engineering ScienceSimon Fraser UniversityBurnabyBritish ColumbiaV5A 1S6Canada
| | - Michael M. Adachi
- School of Engineering ScienceSimon Fraser UniversityBurnabyBritish ColumbiaV5A 1S6Canada
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8
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Nörenberg T, Álvarez-Pérez G, Obst M, Wehmeier L, Hempel F, Klopf JM, Nikitin AY, Kehr SC, Eng LM, Alonso-González P, de Oliveira TVAG. Germanium Monosulfide as a Natural Platform for Highly Anisotropic THz Polaritons. ACS NANO 2022; 16:20174-20185. [PMID: 36446407 PMCID: PMC9799068 DOI: 10.1021/acsnano.2c05376] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Accepted: 11/08/2022] [Indexed: 05/17/2023]
Abstract
Terahertz (THz) electromagnetic radiation is key to access collective excitations such as magnons (spins), plasmons (electrons), or phonons (atomic vibrations), thus bridging topics between optics and solid-state physics. Confinement of THz light to the nanometer length scale is desirable for local probing of such excitations in low-dimensional systems, thereby circumventing the large footprint and inherently low spectral power density of far-field THz radiation. For that purpose, phonon polaritons (PhPs) in anisotropic van der Waals (vdW) materials have recently emerged as a promising platform for THz nanooptics. Hence, there is a demand for the exploration of materials that feature not only THz PhPs at different spectral regimes but also host anisotropic (directional) electrical, thermoelectric, and vibronic properties. To that end, we introduce here the semiconducting vdW-material alpha-germanium(II) sulfide (GeS) as an intriguing candidate. By employing THz nanospectroscopy supported by theoretical analysis, we provide a thorough characterization of the different in-plane hyperbolic and elliptical PhP modes in GeS. We find not only PhPs with long lifetimes (τ > 2 ps) and excellent THz light confinement (λ0/λ > 45) but also an intrinsic, phonon-induced anomalous dispersion as well as signatures of naturally occurring, substrate-mediated PhP canalization within a single GeS slab.
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Affiliation(s)
- Tobias Nörenberg
- Institut für
Angewandte Physik, Technische Universität
Dresden, Dresden 01187, Germany
- Würzburg-Dresden
Cluster of Excellence - EXC 2147 (ct.qmat), Dresden 01062, Germany
- Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, Dresden 01328, Germany
| | - Gonzalo Álvarez-Pérez
- Department of Physics, University
of Oviedo, Oviedo 33006, Spain
- Center of Research
on Nanomaterials and Nanotechnology CINN (CSIC−Universidad
de Oviedo), El Entrego 33940, Spain
| | - Maximilian Obst
- Institut für
Angewandte Physik, Technische Universität
Dresden, Dresden 01187, Germany
| | - Lukas Wehmeier
- Institut für
Angewandte Physik, Technische Universität
Dresden, Dresden 01187, Germany
- Würzburg-Dresden
Cluster of Excellence - EXC 2147 (ct.qmat), Dresden 01062, Germany
| | - Franz Hempel
- Institut für
Angewandte Physik, Technische Universität
Dresden, Dresden 01187, Germany
- Collaborative Research
Center 1415, Technische Universität
Dresden, Dresden 01069, Germany
| | - J. Michael Klopf
- Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, Dresden 01328, Germany
| | - Alexey Y. Nikitin
- Donostia International
Physics Center (DIPC), Donostia-San
Sebastián 20018, Spain
- IKERBASQUE, Basque Foundation for Science, Bilbao 48013, Spain
| | - Susanne C. Kehr
- Institut für
Angewandte Physik, Technische Universität
Dresden, Dresden 01187, Germany
| | - Lukas M. Eng
- Institut für
Angewandte Physik, Technische Universität
Dresden, Dresden 01187, Germany
- Würzburg-Dresden
Cluster of Excellence - EXC 2147 (ct.qmat), Dresden 01062, Germany
- Collaborative Research
Center 1415, Technische Universität
Dresden, Dresden 01069, Germany
| | - Pablo Alonso-González
- Department of Physics, University
of Oviedo, Oviedo 33006, Spain
- Center of Research
on Nanomaterials and Nanotechnology CINN (CSIC−Universidad
de Oviedo), El Entrego 33940, Spain
| | - Thales V. A. G. de Oliveira
- Institut für
Angewandte Physik, Technische Universität
Dresden, Dresden 01187, Germany
- Würzburg-Dresden
Cluster of Excellence - EXC 2147 (ct.qmat), Dresden 01062, Germany
- Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, Dresden 01328, Germany
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9
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Sutter E, French JS, Komsa HP, Sutter P. 1D Germanium Sulfide van der Waals Bicrystals by Vapor-Liquid-Solid Growth. ACS NANO 2022; 16:3735-3743. [PMID: 35147417 DOI: 10.1021/acsnano.1c07349] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Defects in two-dimensional and layered materials have attracted interest for realizing properties different from those of perfect crystals. Even stronger links between defect formation, fast growth, and emerging functionality can be found in nanostructures of van der Waals crystals, but only a few prevalent morphologies and defect-controlled synthesis processes have been identified. Here, we show that in vapor-liquid-solid growth of 1D van der Waals nanostructures, the catalyst controls the selection of the predominant (fast-growing) morphologies. Growth of layered GeS over Bi catalysts leads to two coexisting nanostructure types: chiral nanowires carrying axial screw dislocations and bicrystal nanoribbons where a central twin plane facilitates rapid growth. While Au catalysts produce exclusively dislocated nanowires, their modification with an additive triggers a switch to twinned bicrystal ribbons. Nanoscale spectroscopy shows that, while supporting fast growth, the twin defects in the distinctive layered bicrystals are electronically benign and free of nonradiative recombination centers.
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Affiliation(s)
- Eli Sutter
- Department of Mechanical and Materials Engineering and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588, United States
| | - Jacob S French
- Department of Electrical and Computer Engineering, University of Nebraska, Lincoln, Nebraska 68588, United States
| | - Hannu-Pekka Komsa
- Faculty of Information Technology and Electrical Engineering, University of Oulu, FI-90014 Oulu, Finland
| | - Peter Sutter
- Department of Electrical and Computer Engineering, University of Nebraska, Lincoln, Nebraska 68588, United States
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10
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Sutter E, Unocic RR, Idrobo J, Sutter P. Multilayer Lateral Heterostructures of Van Der Waals Crystals with Sharp, Carrier-Transparent Interfaces. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2022; 9:e2103830. [PMID: 34813175 PMCID: PMC8787400 DOI: 10.1002/advs.202103830] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 10/14/2021] [Indexed: 05/16/2023]
Abstract
Research on engineered materials that integrate different 2D crystals has largely focused on two prototypical heterostructures: Vertical van der Waals stacks and lateral heterostructures of covalently stitched monolayers. Extending lateral integration to few layer or even multilayer van der Waals crystals could enable architectures that combine the superior light absorption and photonic properties of thicker crystals with close proximity to interfaces and efficient carrier separation within the layers, potentially benefiting applications such as photovoltaics. Here, the realization of multilayer heterstructures of the van der Waals semiconductors SnS and GeS with lateral interfaces spanning up to several hundred individual layers is demonstrated. Structural and chemical imaging identifies {110} interfaces that are perpendicular to the (001) layer plane and are laterally localized and sharp on a 10 nm scale across the entire thickness. Cathodoluminescence spectroscopy provides evidence for a facile transfer of electron-hole pairs across the lateral interfaces, indicating covalent stitching with high electronic quality and a low density of recombination centers.
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Affiliation(s)
- Eli Sutter
- Department of Mechanical & Materials Engineering and Nebraska Center for Materials and NanoscienceUniversity of Nebraska‐LincolnLincolnNE68588USA
| | - Raymond R. Unocic
- Center for Nanophase Materials SciencesOak Ridge National LaboratoryOak RidgeTN37831USA
| | - Juan‐Carlos Idrobo
- Center for Nanophase Materials SciencesOak Ridge National LaboratoryOak RidgeTN37831USA
| | - Peter Sutter
- Department of Electrical & Computer EngineeringUniversity of Nebraska‐LincolnLincolnNE68588USA
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11
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Sutter E, Sutter P. Ultrathin Twisted Germanium Sulfide van der Waals Nanowires by Bismuth Catalyzed Vapor-Liquid-Solid Growth. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2021; 17:e2104784. [PMID: 34655159 DOI: 10.1002/smll.202104784] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 09/18/2021] [Indexed: 06/13/2023]
Abstract
1D nanowires of 2D layered crystals are emerging nanostructures synthesized by combining van der Waals (vdW) epitaxy and vapor-liquid-solid (VLS) growth. Nanowires of the group IV monochalcogenide germanium sulfide (GeS) are of particular interest for twistronics due to axial screw dislocations giving rise to Eshelby twist and precision interlayer twist at helical vdW interfaces. Ultrathin vdW nanowires have not been realized, and it is not clear if confining layered crystals into extremely thin wires is even possible. If axial screw dislocations are still stable, ultrathin vdW nanowires can reach large twists and should display significant quantum confinement. Here it is shown that VLS growth over Bi catalysts yields vdW nanowires down to ≈15 nm diameter while maintaining tens of µm length. Combined electron microscopy and diffraction demonstrate that ultrathin GeS nanowires crystallize in the orthorhombic bulk structure but can realize nonequilibrium stacking that may lead to 1D ferroelectricity. Ultrathin nanowires carry screw dislocations, remain chiral, and achieve very high twist rates. Whenever the dislocation extends to the nanowire tip, it continues into the Bi catalyst. Eshelby twist analysis demonstrates that the ultrathin nanowires follow continuum predictions. Cathodoluminescence on individual nanowires, finally, shows pronounced emission blue shifts consistent with quantum confinement.
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Affiliation(s)
- Eli Sutter
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
- Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
| | - Peter Sutter
- Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
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12
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Abstract
Two-dimensional crystals provide exceptional opportunities for integrating dissimilar materials and forming interfaces where distinct properties and phenomena emerge. To date, research has focused on two basic heterostructure types: vertical van der Waals stacks and laterally joined monolayer crystals with in-plane line interfaces. Much more diverse architectures and interface configurations can be realized in the few-layer and multilayer regime, and if mechanical stacking and single-layer growth are replaced by processes taking advantage of self-organization, conversions between polymorphs, phase separation, strain effects, and shaping into the third dimension. Here, we highlight such opportunities for engineering heterostructures, focusing on group IV chalcogenides, a class of layered semiconductors that lend themselves exceptionally well for exploring novel van der Waals architectures, as well as advanced methods including in situ microscopy during growth and nanometer-scale probes of light-matter interactions. The chosen examples point to fruitful future directions and inspire innovative developments to create unconventional van der Waals heterostructures beyond stacking.
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13
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Sutter P, French JS, Khosravi Khorashad L, Argyropoulos C, Sutter E. Optoelectronics and Nanophotonics of Vapor-Liquid-Solid Grown GaSe van der Waals Nanoribbons. NANO LETTERS 2021; 21:4335-4342. [PMID: 33955765 DOI: 10.1021/acs.nanolett.1c00891] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
2D/layered semiconductors are of interest for fundamental studies and for applications in optoelectronics and photonics. Work to date focused on extended crystals, produced by exfoliation or growth and investigated by diffraction-limited spectroscopy. Processes such as vapor-liquid-solid (VLS) growth carry potential for mass-producing nanostructured van der Waals semiconductors with exceptionally high crystal quality and optoelectronic/photonic properties at least on par with those of extended flakes. Here, we demonstrate the synthesis, structure, morphology, and optoelectronics/photonics of GaSe van der Waals nanoribbons obtained by Au- and Ag-catalyzed VLS growth. Although all GaSe ribbons are high-quality basal-plane oriented single crystals, those grown at lower temperatures stand out with their remarkably uniform morphology and low edge roughness. Photoluminescence spectroscopy shows intense, narrow light emission at the GaSe bandgap energy. Nanophotonic experiments demonstrate traveling waveguide modes at visible/near-infrared energies and illustrate approaches for locally exciting and probing such photonic modes by cathodoluminescence in transmission electron microscopy.
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Affiliation(s)
- Peter Sutter
- Department of Electrical & Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Jacob S French
- Department of Electrical & Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Larousse Khosravi Khorashad
- Department of Electrical & Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Christos Argyropoulos
- Department of Electrical & Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Eli Sutter
- Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
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Sarkar AS, Stratakis E. Dispersion behaviour of two dimensional monochalcogenides. J Colloid Interface Sci 2021; 594:334-341. [PMID: 33773385 DOI: 10.1016/j.jcis.2021.02.081] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2020] [Revised: 02/03/2021] [Accepted: 02/18/2021] [Indexed: 11/15/2022]
Abstract
Solution processable two-dimensional (2D) materials have provided an ideal platform for both fundamental studies and wearable electronic applications. Apart from graphene and 2D dichalcogenides, IVA-VI metal monochalcogenides (MMCs) has emerged recently as a promising candidate for next generation electronic applications. However, the dispersion behavior, which is crucial for the quality, solubility and stability of MMCs, has been quite unexplored. Here, the exfoliation and the dispersion behavior of Germanium (II) monosulfide (GeS) and Tin (II) monosulfide (SnS) nanosheets has been investigated in a wide range of organic solvents. Nine different organic solvents were examined and analyzed, considering the solvent polarity, surface tension, and Hansen solubility parameters. A significant yield of isolated GeS and SnS flakes, namely ~16.4 and ~23.08 μg/ml in 2-propanol and N-Methyl-2-pyrrolidone respectively were attained. The isolated flakes are few-layers nanosheets with lateral sizes over a few hundreds of nanometers. The MMC colloids exhibit long-term stability, suggesting the MMCs applicability for scalable solution processable printed electronic device applications.
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Affiliation(s)
- Abdus Salam Sarkar
- Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, Heraklion, 700 13 Crete, Greece.
| | - Emmanuel Stratakis
- Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, Heraklion, 700 13 Crete, Greece; Physics Department, University of Crete, Heraklion, 710 03 Crete, Greece.
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Sutter P, Khorashad LK, Argyropoulos C, Sutter E. Cathodoluminescence of Ultrathin Twisted Ge 1- x Sn x S van der Waals Nanoribbon Waveguides. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2006649. [PMID: 33283337 DOI: 10.1002/adma.202006649] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Revised: 11/09/2020] [Indexed: 06/12/2023]
Abstract
Ultrathin van der Waals semiconductors have shown extraordinary optoelectronic and photonic properties. Propagating photonic modes make layered crystal waveguides attractive for photonic circuitry and for studying hybrid light-matter states. Accessing guided modes by conventional optics is challenging due to the limited spatial resolution and poor out-of-plane far-field coupling. Scanning near-field optical microscopy can overcome these issues and can characterize waveguide modes down to a resolution of tens of nanometers, albeit for planar samples or nanostructures with moderate height variations. Electron microscopy provides atomic-scale localization also for more complex geometries, and recent advances have extended the accessible excitations from interband transitions to phonons. Here, bottom-up synthesized layered semiconductor (Ge1- x Snx S) nanoribbons with an axial twist and deep subwavelength thickness are demonstrated as a platform for realizing waveguide modes, and cathodoluminescence spectroscopy is introduced as a tool to characterize them. Combined experiments and simulations show the excitation of guided modes by the electron beam and their efficient detection via photons emitted in the ribbon plane, which enables the measurement of key properties such as the evanescent field into the vacuum cladding with nanometer resolution. The results identify van der Waals waveguides operating in the infrared and highlight an electron-microscopy-based approach for probing complex-shaped nanophotonic structures.
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Affiliation(s)
- Peter Sutter
- Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
| | | | - Christos Argyropoulos
- Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
| | - Eli Sutter
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
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Sutter E, Wang J, Sutter P. Lateral Heterostructures of Multilayer GeS and SnS van der Waals Crystals. ACS NANO 2020; 14:12248-12255. [PMID: 32886477 DOI: 10.1021/acsnano.0c05978] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Engineered heterostructures derive distinct properties from materials integration and interface formation. Two-dimensional crystals have been combined to form vertical stacks and lateral heterostuctures with covalent line interfaces. While thicker vertical stacks have been realized, lateral heterostructures from multilayer van der Waals crystals, which could bring the benefits of high-quality interfaces to bulk-like layered materials, have remained much less explored. Here, we demonstrate the integration of anisotropic layered Sn and Ge monosulfides into complex heterostructures with seamless lateral interfaces and tunable vertical design using a two-step growth process. The anisotropic lattice mismatch at the lateral interfaces between GeS and SnS is relaxed via dislocations and interfacial alloying. Nanoscale optoelectronic measurements by cathodoluminescence spectroscopy show the characteristic light emission of joined high-quality van der Waals crystals. Spectroscopy across the lateral interface indicates valley-selective luminescence in the bulk SnS component that arises due to anisotropic electron transfer across the interface. The results demonstrate the ability to realize high-quality lateral heterostructures of multilayer van der Waals crystals for diverse applications, e.g., in optoelectronics or valleytronics.
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Affiliation(s)
- Eli Sutter
- Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Jia Wang
- Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Peter Sutter
- Department of Electrical & Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
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Sutter E, French JS, Sutter S, Idrobo JC, Sutter P. Vapor-Liquid-Solid Growth and Optoelectronics of Gallium Sulfide van der Waals Nanowires. ACS NANO 2020; 14:6117-6126. [PMID: 32369332 DOI: 10.1021/acsnano.0c01919] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Nanowires of layered van der Waals (vdW) crystals are of interest due to structural characteristics and emerging properties that have no equivalent in conventional 3D crystalline nanostructures. Here, vapor-liquid-solid growth, optoelectronics, and photonics of GaS vdW nanowires are studied. Electron microscopy and diffraction demonstrate the formation of high-quality layered nanostructures with different vdW layer orientation. GaS nanowires with vdW stacking perpendicular to the wire axis have ribbon-like morphologies with lengths up to 100 μm and uniform width. Wires with axial layer stacking show tapered morphologies and a corrugated surface due to twinning between successive few-layer GaS sheets. Layered GaS nanowires are excellent wide-bandgap optoelectronic materials with Eg = 2.65 eV determined by single-nanowire absorption measurements. Nanometer-scale spectroscopy on individual nanowires shows intense blue band-edge luminescence along with longer wavelength emissions due to transitions between gap states and photonic properties such as interference of confined waveguide modes propagating within the nanowires. The combined results show promise for applications in electronics, optoelectronics, and photonics, as well as photo- or electrocatalysis owing to a high density of reactive edge sites, and intercalation-type energy storage benefiting from facile access to the interlayer vdW gaps.
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Affiliation(s)
- Eli Sutter
- Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Jacob S French
- Department of Electrical & Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Stephan Sutter
- Department of Electrical & Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Juan Carlos Idrobo
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Peter Sutter
- Department of Electrical & Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
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Sutter E, Zhang B, Sun M, Sutter P. Few-Layer to Multilayer Germanium(II) Sulfide: Synthesis, Structure, Stability, and Optoelectronics. ACS NANO 2019; 13:9352-9362. [PMID: 31305983 DOI: 10.1021/acsnano.9b03986] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Among 2D/layered semiconductors, group IV monochalcogenides such as SnS(e) and GeS(e) have attracted attention as phosphorene/black phosphorus analogues with anisotropic structures and predicted unusual properties. In contrast to SnS, for which bottom-up synthesis has been reported, few-layer GeS has been realized primarily via exfoliation from bulk crystals. Here, we report the synthesis of large (up to >20 μm), faceted single crystalline GeS flakes with anisotropic properties using a vapor transport process. In situ electron microscopy is used to identify the thermal stability and sublimation pathways, and demonstrates that the GeS flakes are self-encapsulated in a thin, sulfur-rich amorphous GeSx shell during growth. The shell provides exceptional chemical stability to the layered GeS core. In contrast to exfoliated GeS, which rapidly degrades during exposure to air, the synthesized GeS-GeSx core-shell structures show no signs of chemical attack and remain unchanged in air for extended time periods. Measurements of the optoelectronic properties by photoluminescence spectroscopy show a tunable bandgap due to out-of-plane quantum confinement in flakes with thickness below 100 nm. Cathodoluminescence (CL) spectroscopy with nanoscale excitation provides evidence for interfacial charge transfer due to a type II heterojunction between the crystalline core and amorphous shell. Measurements by locally excited CL yield a minority carrier (electron) diffusion length in the p-type GeS core ldiff = 0.27 μm, on par with diffusion lengths in the highest-quality layered chalcogenide semiconductors.
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Affiliation(s)
- Eli Sutter
- Department of Mechanical and Materials Engineering , University of Nebraska-Lincoln , Lincoln , Nebraska 68588 , United States
| | - Bo Zhang
- Department of Mechanical and Materials Engineering , University of Nebraska-Lincoln , Lincoln , Nebraska 68588 , United States
| | - Muhua Sun
- Department of Mechanical and Materials Engineering , University of Nebraska-Lincoln , Lincoln , Nebraska 68588 , United States
| | - Peter Sutter
- Department of Electrical and Computer Engineering , University of Nebraska-Lincoln , Lincoln , Nebraska 68588 , United States
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Sutter P, Wang J, Sutter E. Wrap-Around Core-Shell Heterostructures of Layered Crystals. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1902166. [PMID: 31157467 DOI: 10.1002/adma.201902166] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Revised: 05/08/2019] [Indexed: 06/09/2023]
Abstract
Engineered heterostructures create new functionality by integrating dissimilar materials. Combining different 2D crystals naturally produces two distinct classes of heterostructures, vertical van der Waals (vdW) stacks or 2D sheets bonded laterally by covalent line interfaces. When joining thicker layered crystals, the arising structural and topological conflicts can result in more complex geometries. Phase separation during one-pot synthesis of layered tin chalcogenides spontaneously creates core-shell structures in which large orthorhombic SnS crystals are enclosed in a wrap-around shell of trigonal SnS2 , forcing the coexistence of parallel vdW layering along with unconventional, orthogonally layered core-shell interfaces. Measurements of the optoelectronic properties establish anisotropic carrier separation near type II core-shell interfaces and extended long-wavelength light harvesting via spatially indirect interfacial absorption, making multifunctional layered core-shell structures attractive for energy-conversion applications.
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Affiliation(s)
- Peter Sutter
- Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
| | - Jia Wang
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
| | - Eli Sutter
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
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Sutter P, Wimer S, Sutter E. Chiral twisted van der Waals nanowires. Nature 2019; 570:354-357. [DOI: 10.1038/s41586-019-1147-x] [Citation(s) in RCA: 74] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Accepted: 01/25/2019] [Indexed: 11/10/2022]
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Kennedy OW, White ER, Howkins A, Williams CK, Boyd IW, Warburton PA, Shaffer MSP. Mapping the Origins of Luminescence in ZnO Nanowires by STEM-CL. J Phys Chem Lett 2019; 10:386-392. [PMID: 30614706 DOI: 10.1021/acs.jpclett.8b03286] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
In semiconductor nanowires, understanding both the sources of luminescence (excitonic recombination, defects, etc.) and the distribution of luminescent centers (be they uniformly distributed, or concentrated at structural defects or at the surface) is important for synthesis and applications. We develop scanning transmission electron microscopy-cathodoluminescence (STEM-CL) measurements, allowing the structure and cathodoluminescence (CL) of single ZnO nanowires to be mapped at high resolution. Using a CL pixel resolution of 10 nm, variations of the CL spectra within such nanowires in the direction perpendicular to the nanowire growth axis are identified for the first time. By comparing the local CL spectra with the bulk photoluminescence spectra, the CL spectral features are assigned to internal and surface defect structures. Hyperspectral CL maps are deconvolved to enable characteristic spectral features to be spatially correlated with structural features within single nanowires. We have used these maps to show that the spatial distribution of these defects correlates well with regions that show an increased rate of nonradiative transitions.
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Affiliation(s)
- Oscar W Kennedy
- London Centre for Nanotechnology , University College London , London WC1H 0AH , United Kingdom
- Department of Electronic and Electrical Engineering , University College London , London WC1E 7JE , United Kingdom
| | - Edward R White
- Department of Chemistry , Imperial College London , London SW7 2AZ , United Kingdom
| | - Ashley Howkins
- Experimental Techniques Centre , Brunel University London , Uxbridge UB8 3PH , United Kingdom
| | | | - Ian W Boyd
- Experimental Techniques Centre , Brunel University London , Uxbridge UB8 3PH , United Kingdom
| | - Paul A Warburton
- London Centre for Nanotechnology , University College London , London WC1H 0AH , United Kingdom
- Department of Electronic and Electrical Engineering , University College London , London WC1E 7JE , United Kingdom
| | - Milo S P Shaffer
- Department of Chemistry , Imperial College London , London SW7 2AZ , United Kingdom
- Departmental of Materials , Imperial College London , London , SW7 2AZ , United Kingdom
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