Investigations of Electronic Structures of Defects Introduced by Ar Ion Bombardments on MoS<sub> 2</sub> by Scanning Tunneling Microscopy

Sengoku, Naohisa; Ogawa, Keiichi

doi:10.1143/jjap.34.3363

Cited by 22 publications

(28 citation statements)

References 12 publications

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“…The increase in electron doping can be explained by an increasing concentration of sulfur vacancies acting as electron donors, but it is perhaps surprising that the field-effect mobility also increases. 9 , 10 Below we examine whether the PL data are also consistent with the proposed variation in sulfur vacancy concentration, and then consider possible explanations for the trends in field effect mobility.…”

Section: Resultsmentioning

confidence: 99%

Influence of Stoichiometry on the Optical and Electrical Properties of Chemical Vapor Deposition Derived MoS₂

et al. 2014

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Ultrathin transition metal dichalcogenides (TMDCs) of Mo and W show great potential for digital electronics and optoelectronic applications. Whereas early studies were limited to mechanically exfoliated flakes, the large-area synthesis of 2D TMDCs has now been realized by chemical vapor deposition (CVD) based on a sulfurization reaction. The optoelectronic properties of CVD grown monolayer MoS2 have been intensively investigated, but the influence of stoichiometry on the electrical and optical properties has been largely overlooked. Here we systematically vary the stoichiometry of monolayer MoS2 during CVD via controlled sulfurization and investigate the associated changes in photoluminescence and electrical properties. X-ray photoelectron spectroscopy is employed to measure relative variations in stoichiometry and the persistence of MoOx species. As MoS2−δ is reduced (increasing δ), the field-effect mobility of monolayer transistors increases while the photoluminescence yield becomes nonuniform. Devices fabricated from monolayers with the lowest sulfur content have negligible hysteresis and a threshold voltage of ∼0 V. We conclude that the electrical and optical properties of monolayer MoS2 crystals can be tuned via stoichiometry engineering to meet the requirements of various applications.

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Section: Resultsmentioning

confidence: 99%

Influence of Stoichiometry on the Optical and Electrical Properties of Chemical Vapor Deposition Derived MoS₂

et al. 2014

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“…Changes of surface structure and tunneling spectra was observed at edges and grain boundaries with presence of mid-gap electronic states 23 , 24 . This led to observation of both p-type and n-type doping with varying contact resistance in molybdenite and synthetic MoS 2 12 , 15 , 16 , 19 , 22 . Strong interactions with the substrate could also induce local spatial modulation of the density of states via local strain or local charge accumulation 25 .…”

Section: Introductionmentioning

confidence: 99%

Evolution of Metastable Defects and Its Effect on the Electronic Properties of MoS2 Films

Precner

Polakovic

Qiao

et al. 2018

Sci Rep

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We report on structural and electronic properties of defects in chemical vapor-deposited monolayer and few-layer MoS2 films. Scanning tunneling microscopy, Kelvin probe force microscopy, and transmission electron microscopy were used to obtain high resolution images and quantitative measurements of the local density of states, work function and nature of defects in MoS2 films. We track the evolution of defects that are formed under heating and electron beam irradiation. We observe formation of metastable domains with different work function values after annealing the material in ultra-high vacuum to moderate temperatures. We attribute these metastable values of the work function to evolution of crystal defects forming during the annealing. The experiments show that sulfur vacancies formed after exposure to elevated temperatures diffuse, coalesce, and migrate bringing the system from a metastable to equilibrium ground state. The process could be thermally or e-beam activated with estimated energy barrier for sulfur vacancy migration of 0.6 eV in single unit cell MoS2. Even at equilibrium conditions, the work function and local density of states values are strongly affected near grain boundaries and edges. The results provide initial estimates of the thermal budgets available for reliable fabrication of MoS2-based integrated electronics and indicate the importance of defect control and layer passivation.

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“…28 Ar + bombardments of WSe 2 , at the energies between 5 and 10 keV, produced nanostructures with diameters less than a͒ Author to whom correspondence should be addressed; electronic mail: bruce.parkinson@colostate.edu 10 nm as imaged with STM. 29 They proposed that the bright features contained negatively charged sulfur atoms and the dark regions were attributed to electron depletion due to the Coulomb repulsion around the negatively charged species. 29 They proposed that the bright features contained negatively charged sulfur atoms and the dark regions were attributed to electron depletion due to the Coulomb repulsion around the negatively charged species.…”

Section: Introductionmentioning

confidence: 99%

Scanning tunneling microscopy investigation of nanostructures produced by Ar+ and He+ bombardment of MoS2 surfaces

Park¹,

France²,

Parkinson³

2005

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

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Nanostructures were fabricated on natural MoS 2 crystals by bombardment with low doses of Ar + and He + with energies ranging from 100 to 5 keV. The bombarded surfaces were investigated with x-ray photoemission spectroscopy ͑XPS͒ and scanning tunneling microscopy ͑STM͒ in an ultrahigh vacuum environment. The ion exposures were low enough to ensure that the observed nanostructures can be associated with individual ion impacts. Argon ions ͑Ar + ͒ with energies of 100 eV or less remove very few, if any, sulfur atoms from the surface but STM and XPS studies reveal that the electronic structure of the MoS 2 surface is altered. Ar + with energies greater than 100 eV has a higher probability of sputtering sulfur atoms from the surface. The apparent size of the nanostructures in the STM images increased with Ar + energies up to about 1 keV and was dependent on the angle of incidence of the Ar + . Helium ion ͑He + ͒ sputtering of MoS 2 produced similar but smaller nanostructures when compared to Ar + at the same impinged ion energy. STM images showed bright ring-shaped features were created with He + energies greater than 500 eV. On the basis of XPS and current imaging tunneling spectroscopy investigations, the features are assigned to sulfur atom vacancies. A change in the surface doping type from n to p was observed upon light sputtering of the surface.

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Investigations of Electronic Structures of Defects Introduced by Ar Ion Bombardments on MoS₂ by Scanning Tunneling Microscopy

Cited by 22 publications

References 12 publications

Influence of Stoichiometry on the Optical and Electrical Properties of Chemical Vapor Deposition Derived MoS₂

Influence of Stoichiometry on the Optical and Electrical Properties of Chemical Vapor Deposition Derived MoS₂

Evolution of Metastable Defects and Its Effect on the Electronic Properties of MoS2 Films

Scanning tunneling microscopy investigation of nanostructures produced by Ar+ and He+ bombardment of MoS2 surfaces

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Investigations of Electronic Structures of Defects Introduced by Ar Ion Bombardments on MoS 2 by Scanning Tunneling Microscopy

Cited by 22 publications

References 12 publications

Influence of Stoichiometry on the Optical and Electrical Properties of Chemical Vapor Deposition Derived MoS2

Influence of Stoichiometry on the Optical and Electrical Properties of Chemical Vapor Deposition Derived MoS2

Evolution of Metastable Defects and Its Effect on the Electronic Properties of MoS2 Films

Scanning tunneling microscopy investigation of nanostructures produced by Ar+ and He+ bombardment of MoS2 surfaces

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Investigations of Electronic Structures of Defects Introduced by Ar Ion Bombardments on MoS₂ by Scanning Tunneling Microscopy

Influence of Stoichiometry on the Optical and Electrical Properties of Chemical Vapor Deposition Derived MoS₂

Influence of Stoichiometry on the Optical and Electrical Properties of Chemical Vapor Deposition Derived MoS₂