| 1. |
- Ogorzalek, Zuzanna, et al.
(författare)
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Charge transport in MBE-grown 2H-MoTe(2)bilayers with enhanced stability provided by an AlO(x)capping layer
- 2020
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 12:31, s. 16535-16542
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Tidskriftsartikel (refereegranskat)abstract
- Thin layers of transition metal dichalcogenides have been intensively studied over the last few years due to their novel physical phenomena and potential applications. One of the biggest problems in laboratory handling and moving on to application-ready devices lies in the high sensitivity of their physicochemical properties to ambient conditions. We demonstrate that novel,in situcapping with an ultra-thin, aluminum film efficiently protects thin MoTe(2)layers stabilizing their electronic transport properties after exposure to ambient conditions. The experiments have been performed on bilayers of 2H-MoTe(2)grown by molecular beam epitaxy on large area GaAs(111)B substrates. The crystal structure, surface morphology and thickness of the deposited MoTe(2)layers have been precisely controlledin situwith a reflection high energy electron diffraction system. As evidenced by high resolution transmission electron microscopy, MoTe(2)films exhibit perfect arrangement in the 2H phase and the epitaxial relation to the GaAs(111)B substrates. After the growth, the samples werein situcapped with a thin (3 nm) film of aluminum, which oxidizes after exposure to ambient conditions. This oxide serves as a protective layer to the underlying MoTe2. Resistivity measurements of the MoTe(2)layers with and without the cap, exposed to low vacuum, nitrogen and air, revealed a huge difference in their stability. The significant rise of resistance is observed for the unprotected sample while the resistance of the protected one is constant. Wide range temperature resistivity studies showed that charge transport in MoTe(2)is realized by hopping with an anomalous hopping exponent ofx similar or equal to 0.66, reported also previously for ultra-thin, metallic layers.
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| 2. |
- Pacuski, Wojciech, et al.
(författare)
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Narrow Excitonic Lines and Large-Scale Homogeneity of Transition-Metal Dichalcogenide Monolayers Grown by Molecular Beam Epitaxy on Hexagonal Boron Nitride
- 2020
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 20:5, s. 3058-3066
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Tidskriftsartikel (refereegranskat)abstract
- Monolayer transition-metal dichalcogenides(TMDs) manifest exceptional optical properties related to narrow excitonic resonances. However, these properties have been so far explored only for structures produced by techniques inducing considerable large-scale inhomogeneity. In contrast, techniques which are essentially free from this disadvantage, such as molecular beam epitaxy (MBE), have to date yielded only structures characterized by considerable spectral broadening, which hinders most of the interesting optical effects. Here, we report for the firsttime on the MBE-grown TMD exhibiting narrow and resolved spectral lines of neutral and charged exciton. Moreover, our material exhibits unprecedented high homogeneity of optical properties, with variation of the exciton energy as small as ±0.16 meV over a distance of tens of micrometers. Our recipe for MBE growth is presented for MoSe2 and includes the use of atomically flat hexagonal boron nitride substrate. This recipe opens a possibility of producing TMD heterostructures with optical quality, dimensions, and homogeneity required for optoelectronic applications.
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| 3. |
- Sadowski, Janusz, et al.
(författare)
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Structural Properties of TaAs Weyl Semimetal Thin Films Grown by Molecular Beam Epitaxy on GaAs(001) Substrates
- 2022
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 22:10, s. 6039-6045
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Tidskriftsartikel (refereegranskat)abstract
- Thin crystalline layers of TaAs Weyl semimetal are grown by molecular beam epitaxy on GaAs(001) substrates. The (001) planes of the tetragonal TaAs lattice are parallel to the GaAs(001) substrate, but the corresponding in-plane crystallographic directions of the substrate and the layer are rotated by 45 degrees. In spite of a substantial lattice mismatch (about 19%) between the GaAs(001) substrate and TaAs epilayer, no misfit dislocations are observed at the GaAs(001)/TaAs(001) interface. Only stacking fault defects in TaAs are detected by transmission electron microscopy. Thorough X-ray diffraction measurements and analysis of the in situ reflection high-energy electron diffraction images indicate that TaAs layers are fully relaxed already at the initial deposition stage. Atomic force microscopy imaging reveals the columnar structure of the layers, with lateral (parallel to the layer's surface) columns about 20 nm wide and 200 nm long. Both X-ray diffraction and transmission electron microscopy measurements indicate that the columns share the same orientation and crystalline structure.
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| 4. |
- Seredynski, Bartlomiej, et al.
(författare)
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Molecular Beam Epitaxy of a 2D Material Nearly Lattice Matched to a 3D Substrate : NiTe2 on GaAs
- 2021
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 21:10, s. 5773-5779
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Tidskriftsartikel (refereegranskat)abstract
- The lattice mismatch between interesting 2D materials and commonly available 3D substrates is one of the obstacles in the epitaxial growth of monolithic 2D/3D heterostructures, but a number of 2D materials have not yet been considered for epitaxy. Here, we present the first molecular beam epitaxy growth of a NiTe2 2D transition-metal dichalcogenide. Importantly, the growth is realized on a nearly lattice-matched GaAs(111)B substrate. Structural properties of the grown layers are investigated by electron diffraction, X-ray diffraction, and scanning tunneling microscopy. Surface coverage and atomic-scale order are evidenced by images obtained with atomic force, scanning electron, and transmission electron microscopy. Basic transport properties were measured confirming that the NiTe2 layers are metallic, with a Hall concentration of 10(20) to 10(23) cm(-3), depending on the growth conditions.
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