Kelvin probe microscopy of MoSe<sub>2</sub> monolayers on graphene

Borodin, Bogdan R.; Dunaevskiy, M. S.; Benimetskiy, Fedor A.; Лебедев, С. П.; Lebedev, Alexander A.; Alekseev, P. A.

doi:10.1088/1742-6596/1124/8/081031

Cited by 15 publications

(12 citation statements)

References 10 publications

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“…Additionally, it was clear that the oxidation influenced the bilayer region differently than the monolayer regions. Interestingly, bilayers atop the oxidized region showed a potential higher even than the basal plane, whereas bilayers on the basal plane showed a much lower potential consistent with literature values in pristine TMD flakes 23,61,62 . This is hypothesized to be due to potentially different oxidative states within the material such as chemisorption of oxygen to the bilayer rather than physisorption.…”

Section: Tracking Oxidation and Agingsupporting

confidence: 87%

“…KPFM measures the contact potential difference (CPD) 39 to produce a relative work function map of the surface. It is wellknown that KPFM can see changes in work function in 2D materials due to a change in layer number, grain boundaries, and chemical changes like defect densities 23,40 . The phase map is less well-studied, but can generally be considered analogous to surface dielectric properties (see Supplementary Information: KPFM Operation and Theory) 26,39,40 .…”

Section: Resultsmentioning

confidence: 99%

“…KPFM 22 , a non-contact scanning probe technique, can allow for direct measurement of surface potential and work function at a similar scale. Using this technique, the surface potential of MoSe 2 monolayers was shown to be highly thickness and environmentdependent, with an increase in work function with layer count due to interlayer screening effects 23,24 . Further surface potential and capacitance imaging of monolayer MoSe 2 flakes reveal grain boundaries and edge effects, invisible to topographic mapping, exhibit a strong contribution to the localized surface potential 25 .…”

Section: Introductionmentioning

confidence: 99%

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Uncovering topographically hidden features in 2D MoSe2 with correlated potential and optical nanoprobes

Moore

Nguyen

et al. 2020

npj 2D Mater Appl

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Developing characterization strategies to better understand nanoscale features in two-dimensional nanomaterials is of crucial importance, as the properties of these materials are many times driven by nanoscale and microscale chemical and structural modifications within the material. For the case of large area monolayer MoSe2 flakes, kelvin probe force microscopy coupled with tip-enhanced photoluminescence was utilized to evaluate such features including internal grain boundaries, edge effects, bilayer contributions, and effects of oxidation/aging, many of which are invisible to topographical mapping. A reduction in surface potential due to n-type behavior was observed at the edge of the flakes as well as near grain boundaries. Potential phase mapping, which corresponds to the local dielectric constant, depicted local biexciton and trion states in optically-active regions of interest such as grain boundaries. Finally, nanoscale surface potential and photoluminescence mapping was performed at several stages of oxidation, revealing that various oxidative states can be evaluated during the aging process. Importantly, all of the characterization performed in this study was non-destructive and rapid, crucial for quality evaluation of an exciting class of two-dimensional nanomaterials.

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Section: Tracking Oxidation and Agingsupporting

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Uncovering topographically hidden features in 2D MoSe2 with correlated potential and optical nanoprobes

Moore

Nguyen

et al. 2020

npj 2D Mater Appl

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“…From that, one can derive that Sample 1 is less p‐type conducting than Sample 2 or 3 (2 and 3 are better hole‐selective contacts), because its Fermi level is shifted away from the valence band edge. The work function of MoSe 2 was studied by Borodin et al using Kelvin probe microscopy 32 . They showed that

W_{f}

depends on the number of MoSe 2 layers with a saturating value of 4.50 eV for the bulk material, which agrees well with our results of Samples 2A/B and 3B.…”

Section: Resultssupporting

confidence: 89%

“…The work function of MoSe 2 was studied by Borodin et al using Kelvin probe microscopy. 32 They showed that W f depends on the number of MoSe 2 layers with a saturating value of 4.50 eV for the bulk material, which agrees well with our results of Samples 2A/B and 3B. All ionization potentials are equal within the measurement uncertainty of ±0.20 eV, and in particular, there is not much difference between Samples 2 and 3, although their Se/S ratio varies by almost a factor of 2.…”

Section: Electronic Propertiessupporting

confidence: 88%

Exfoliation methods for compositional and electronic characterization of interfacial Mo(Se_x,S_y) in Cu(In,Ga)(Se,S)₂ solar cells by X‐ray and UV photoelectron spectroscopy

Lange

Giesl²,

Hagendorf

et al. 2022

Surface & Interface Analysis

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Mo(SexSy) is a transition metal dichalcogenide typically applied as a back contact interlayer in Cu(In,Ga)(Se,S)2 (CIGSSe) solar cells. Band alignment at the buried Mo/CIGSSe junction mediated by Mo(SexSy) is important for current transport and enables quasi‐ohmic behavior between the CIGSSe absorber and the Mo back electrode. Furthermore, the S/(Se + S) ratio is a crucial parameter that determines the height of the valence band offset at the CIGSSe/Mo(SexSy) interface. Because the interlayer is formed during rapid thermal processing, an MoSe2 or MoS2 thin film grown on free substrate surfaces will not be representative for a realistic solar cell device. Thus, for fundamental thin‐film material analysis, as well as functional characterization and modeling, appropriate preparation and analytical techniques are required in order to prevent artifacts. In principal, the weak van der Waals forces between two‐dimensional stacked Mo(SexSy) sheets allow the implementation of exfoliation procedures to generate free Mo(SexSy) surfaces out of CIGSSe solar cell layer stacks. In this article, two different exfoliation‐based Mo(Sex,Sy) preparation methods are investigated and evaluated with respect to subsequent surface analytical characterization by X‐ray and ultraviolet photoelectron spectroscopy. A special focus is laid on an artifact‐free characterization of chemical and electronical properties of the exposed layers for a number of samples. In a first instance, the compositional Se/S and (Se + S)/Mo ratios at the surface are quantitatively analyzed on the basis of dedicated peak‐fitting routines. Artifacts from carbonaceous contamination due to different exfoliation glues can be prevented through a detailed comparative analysis of carbon 1s and KLL Auger peaks. Furthermore, a significant surface band bending is observed that can be reduced by low‐energy Ar ion in situ sputtering. A simple model for the sputter removal of a charged surface layer is presented, which allows to approximately calculate the absolute valence band maximum (VBM) positions required for band alignment and numerical device simulations. The presented exfoliation surface analysis methodology is important for the whole CIGS(Se) solar cell community and may be of general interest for emerging applications of further 2D transition metal dichalcogenides as well.

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Investigation of Doping Effects on the Local Electrochemical Activity of Transition Metal Dichalcogenides 2D Materials

Silva,

Kim,

de Oliveira

et al. 2024

Adv Funct Materials

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Finding strategies to enhance catalysts’ electrochemical activity is based on controlling the material design. Bidimensional materials (2DM) such as MoS2 are explored as catalysts for the hydrogen evolution reaction (HER). A comprehensive study of the effects of doping 2D materials with transition metals based on theoretical predictions in tandem with experimental investigation correlates the doping type to the changes in the electronic and electrochemical activity. Localized electrochemical maps obtained by scanning electrochemical cell microscopy (SECCM) reveal that Ti‐doping induces a heterogeneous increase in 2H‐MoS2 basal plane electrochemical activity, while Ni‐doping induces a homogeneous decrease. Additionally, Kelvin probe microscopy provides insight into Ti‐doping, showcasing a decline in the 2H‐MoS2 work function, therefore confirming the predictions from density functional theory simulations. In essence, the findings underscore the potential of transition metal coordination on the 2H‐MoS2 surface as an attractive method for locally doping 2D materials with minimal damage to the crystalline lattice, consequently enhancing the electrochemical activity on the material's basal plane.

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Kelvin probe microscopy of MoSe₂ monolayers on graphene

Cited by 15 publications

References 10 publications

Uncovering topographically hidden features in 2D MoSe2 with correlated potential and optical nanoprobes

Uncovering topographically hidden features in 2D MoSe2 with correlated potential and optical nanoprobes

Exfoliation methods for compositional and electronic characterization of interfacial Mo(Se_x,S_y) in Cu(In,Ga)(Se,S)₂ solar cells by X‐ray and UV photoelectron spectroscopy

Investigation of Doping Effects on the Local Electrochemical Activity of Transition Metal Dichalcogenides 2D Materials

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Kelvin probe microscopy of MoSe2 monolayers on graphene

Cited by 15 publications

References 10 publications

Uncovering topographically hidden features in 2D MoSe2 with correlated potential and optical nanoprobes

Uncovering topographically hidden features in 2D MoSe2 with correlated potential and optical nanoprobes

Exfoliation methods for compositional and electronic characterization of interfacial Mo(Sex,Sy) in Cu(In,Ga)(Se,S)2 solar cells by X‐ray and UV photoelectron spectroscopy

Investigation of Doping Effects on the Local Electrochemical Activity of Transition Metal Dichalcogenides 2D Materials

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Product

Resources

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Kelvin probe microscopy of MoSe₂ monolayers on graphene

Exfoliation methods for compositional and electronic characterization of interfacial Mo(Se_x,S_y) in Cu(In,Ga)(Se,S)₂ solar cells by X‐ray and UV photoelectron spectroscopy