STM and TEM studies of a model catalyst: Pd/MoS2(0001)

Perrot, E.; Humbert, A.; Piednoir, Agnès; Chapon, C.; Henry, Claude R.

doi:10.1016/s0039-6028(99)01107-3

Cited by 28 publications

(31 citation statements)

References 30 publications

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“…They find that chalcogen atoms are imaged at usual tunneling conditions, in good agreement with other theoretical works, but at small tip-sample distances the contrast is governed by electronic interference effects and the STM images show a honeycomb lattice with contributions from metal atoms and hollow sites. This prediction was corroborated in the past 39 and also is in qualitative agreement with our STM observations. STM images of monolayer MoSe 2 on graphene reveal a superlattice on top of the atomic lattice with periodicity varying from approximately 9.9 Å down to 9.3 Å.…”

Section: Supplementary Text 1 Stm Imaging Of Monolayer Mose 2 On Bilsupporting

confidence: 93%

Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor

et al. 2014

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The remarkable properties of atomically-thin semiconducting TMD layers include an indirect-to-direct bandgap crossover 1, 2, 9 , field-induced transport with high on-off ratios 16 , 3 valley selective circular dichroism [3][4][5][6] , and strong photovoltaic response 17,18 . Fundamental understanding of the electron/hole quasiparticle band structure and many-body interactions in 2D TMDs, however, is still lacking. Enhanced Coulomb interactions due to low-dimensional effects are expected to increase the quasiparticle bandgap as well as to cause electron-hole pairs to form more strongly bound excitons [10][11][12][13] . Untangling such many-body effects in single-layer TMDs requires measurement of both the electronic bandgap and the optical bandgap, the most fundamental parameters for transport and optoelectronics, respectively. The electronic bandgap (E g ) characterizes single-particle (or quasiparticle) excitations and is defined by the sum of the energies needed to separately tunnel an electron and a hole into monolayer MoSe 2 . The optical bandgap (E opt ), on the other hand, describes the energy required to create an exciton, a correlated two-particle electron-hole pair, via optical absorption. The difference in these energies (E g -E opt ) directly yields the exciton binding energy (E b ) (Fig. 2a). Here we provide evidence for Coulomb driven quasiparticle bandgap renormalization and unusually strong exciton stability in 2D TMD through direct determination of both E g and E opt via STS and PL spectroscopy, respectively. STS and PL measurements were carried out on the same high-quality sub-monolayer MoSe 2 films grown on epitaxial bilayer graphene (BLG) on a 6H-SiC(0001) substrate.Because the MoSe 2 surface coverage for our sample was ~ 0.8 ML, we were able to simultaneously image the MoSe 2 monolayer and the underlying graphene substrate using scanning tunneling microscopy (STM). We experimentally investigated both the electronic structure and the optical transitions in monolayer MoSe 2 /BLG by combining STS and PL spectroscopy. Fig. 2b shows a typical STM dI/dV spectrum acquired on monolayer MoSe 2 /BLG. The observed electronic structure is dominated by a large electronic bandgap surrounded by features labeled V 1-4 in the valence band (VB) and C 1 in the conduction band (CB). The MoSe 2 band edges are best determined by taking the logarithm of dI/dV, as shown in Fig. 2d.There the VB maximum (VBM) for monolayer MoSe 2 is seen to be located at -1.55 ± 0.03 V and the CB minimum (CBM) at 0.63 ± 0.02 V. The relative position of E F (V bias = 0 V) with respect to the band edges reveals n-type doping for our samples, although with 5 a very low carrier concentration. We tentatively attribute the n-doping of our MoSe 2 samples to intrinsic point defects such as vacancies and/or lattice antisites, which have been found to be responsible for n-doping in similar materials 20 . Our STS measurements yield a value for the single-particle electronic bandgap of E g = E CBM -E VBM = 2.18 eV ± 0.04 eV. The uncertainty ...

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Section: Supplementary Text 1 Stm Imaging Of Monolayer Mose 2 On Bilsupporting

confidence: 93%

Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor

et al. 2014

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“…The corresponding atomically resolved STM images in Figure h,i show honeycomb and hexagonal lattices, respectively, with the specific morphology dependent on the tip conditions . The atomic lattices possess the same lattice constant of ≈3.20 Å, agreeing well with the value for the bulk MoS 2 .…”

Section: Resultsmentioning

confidence: 47%

Temperature‐Triggered Sulfur Vacancy Evolution in Monolayer MoS₂/Graphene Heterostructures

Liu

Shi

et al. 2017

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The existence of defects in 2D semiconductors has been predicted to generate unique physical properties and markedly influence their electronic and optoelectronic properties. In this work, it is found that the monolayer MoS prepared by chemical vapor deposition is nearly defect-free after annealing under ultrahigh vacuum conditions at ≈400 K, as evidenced by scanning tunneling microscopy observations. However, after thermal annealing process at ≈900 K, the existence of dominant single sulfur vacancies and relatively rare vacancy chains (2S, 3S, and 4S) is convinced in monolayer MoS as-grown on Au foils. Of particular significance is the revelation that the versatile vacancies can modulate the band structure of the monolayer MoS , leading to a decrease of the bandgap and an obvious n-doping effect. These results are confirmed by scanning tunneling spectroscopy data as well as first-principles theoretical simulations of the related morphologies and the electronic properties of the various defect types. Briefly, this work should pave a novel route for defect engineering and hence the electronic property modulation of three-atom-thin 2D layered semiconductors.

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“…According to previous studies, [27][28][29][30][31] chalcogen atoms at a TMD surface are imaged in STM measurements at usual tunneling conditions, showing a hexagonal lattice. Therefore, the majority of vacancies observed in our studies are centered on the tungsten sites.…”

Section: The Inset Inmentioning

confidence: 74%

Engineering Point-Defect States in Monolayer WSe₂

et al. 2019

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Defect engineering is a key approach for tailoring the properties of the emerging two-dimensional semiconductors. Here, we report an atomic engineering of the W vacancy in monolayer WSe 2 by single potassium atom decoration. The K decoration alters the energy states and reshapes the wave-function such that previously hidden mid-gap states become visible with well-resolved multiplets in scanning tunneling spectroscopy. Their energy levels are in good agreement with first principle calculations. More interestingly, the calculations show that an unpaired electron donated by the K atom can lead to a local magnetic moment, exhibiting an onoff switching by the odd-even number of electron filling. Experimentally the Fermi level is pinned above all defect states due to the graphite substrate, corresponding to an off state. The close agreement between theory and experiment in the off state, on the other hand, suggest a possibility of gate-programmable magnetic moments at the defects.

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STM and TEM studies of a model catalyst: Pd/MoS2(0001)

Cited by 28 publications

References 30 publications

Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor

Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor

Temperature‐Triggered Sulfur Vacancy Evolution in Monolayer MoS₂/Graphene Heterostructures

Engineering Point-Defect States in Monolayer WSe₂

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STM and TEM studies of a model catalyst: Pd/MoS2(0001)

Cited by 28 publications

References 30 publications

Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor

Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor

Temperature‐Triggered Sulfur Vacancy Evolution in Monolayer MoS2/Graphene Heterostructures

Engineering Point-Defect States in Monolayer WSe2

Contact Info

Product

Resources

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Temperature‐Triggered Sulfur Vacancy Evolution in Monolayer MoS₂/Graphene Heterostructures

Engineering Point-Defect States in Monolayer WSe₂