Spatial variation in local work function as an origin of moiré contrast in scanning tunneling microscopy images of Pb thin films/Si(111)

Kim, Howon; Hasegawa, Yukio

doi:10.7567/jjap.55.08na03

Cited by 3 publications

(3 citation statements)

References 37 publications

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“…Electrons in metallic films with free-electron property, atomic-scale flatness, and nanometer thickness can lead to the quantization of the electron wave vector to form the quantum well (QW) states in the surface normal [4][5][6][7][8][9][10][11][12][13][14]. Yang et al demonstrated that the image potential in vacuum provides a phase contribution on empty QW states, causing the energy spacing between adjacent states to shrink [16].…”

Section: Introductionmentioning

confidence: 99%

Sharpness-induced energy shifts of quantum well states in Pb islands on Cu(111)

Chan

et al. 2017

Nanotechnology

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We elucidate that the tip sharpness in scanning tunneling microscopy (STM) can be characterized through the number of field-emission (FE) resonances. A higher number of FE resonances indicates higher sharpness. We observe empty quantum well (QW) states in Pb islands on Cu(111) under different tip sharpness levels. We found that QW states observed by sharper tips always had lower energies, revealing negative energy shifts. This sharpness-induced energy shift originates from an inhomogeneous electric field in the STM gap. An increase in sharpness increases the electric field inhomogeneity, that is, enhances the electric field near the tip apex, but weakens the electric field near the sample. As a result, higher sharpness can increase the electronic phase in vacuum, causing the lowering of QW state energies. Moreover, the behaviors of negative energy shift as a function of state energy are entirely different for Pb islands with a thickness of two and nine atomic layers. This thickness-dependent behavior results from the electrostatic force in the STM gap decreasing with increasing tip sharpness. The variation of the phase contributed from the expansion deformation induced by the electrostatic force in a nine-layer Pb island is significantly greater, sufficient to effectively negate the increase of electronic phase in vacuum.

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Section: Introductionmentioning

confidence: 99%

Sharpness-induced energy shifts of quantum well states in Pb islands on Cu(111)

Chan

et al. 2017

Nanotechnology

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“…Determining work function variations in nanoscale structures by field emission resonance (FER) spectroscopy has been widely used in STM. − ,− Briefly, in FER the bias voltage between the STM tip and the sample surface is chosen such that the Fermi level of the STM tip lies above the vacuum level of the sample. In this Fowler–Nordheim tunneling regime, the drop in the potential at the tunnel junction causes a potential well between the tip and the sample surface.…”

Section: Resultsmentioning

confidence: 99%

“…To accomplish strong work function modulations in the moiré structures, the interlayer charge redistribution must depend on local interlayer atom coordination within the moiré unit cell. This has been shown for monolayer materials deposited on crystalline supports such as NaCl, FeO, , or Pb monolayers on silver, platinum, or silicon crystals, respectively. More prominently this effect has been also explored for graphene on Rh or h-BN on various transition metals (e.g., Rh, Ru, Cu, , Ir) where the varying coordination of the BN atoms with respect to the surface metals gives rise to strongly variable chemical interactions, causing large corrugation of the h-BN layer and consequently modulations of interlayer dipoles and the local work function .…”

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confidence: 99%

A van der Waals Heterostructure with an Electronically Textured Moiré Pattern: PtSe₂/PtTe₂

Ghorbani‐Asl

Lasek

et al. 2023

ACS Nano

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The interlayer interaction in Pt-dichalcogenides strongly affects their electronic structures. The modulations of the interlayer atom-coordination in vertical heterostructures based on these materials are expected to laterally modify these interlayer interactions and thus provide an opportunity to texture the electronic structure. To determine the effects of local variation of the interlayer atom coordination on the electronic structure of PtSe 2 , van der Waals heterostructures of PtSe 2 and PtTe 2 have been synthesized by molecular beam epitaxy. The heterostructure forms a coincidence lattice with 13 unit cells of PtSe 2 matching 12 unit cells of PtTe 2 , forming a moirésuperstructure. The interaction with PtTe 2 reduces the band gap of PtSe 2 monolayers from 1.8 eV to 0.5 eV. While the band gap is uniform across the moiréunit cell, scanning tunneling spectroscopy and dI/dV mapping identify gap states that are localized within certain regions of the moiréunit cell. Deep states associated with chalcogen p z -orbitals at binding energies of ∼ −2 eV also exhibit lateral variation within the moiréunit cell, indicative of varying interlayer chalcogen interactions. Density functional theory calculations indicate that local variations in atom coordination in the moiréunit cell cause variations in the charge transfer from PtTe 2 to PtSe 2 , thus affecting the value of the interface dipole. Experimentally this is confirmed by measuring the local work function by field emission resonance spectroscopy, which reveals a large work function modulation of ∼0.5 eV within the moiréstructure. These results show that the local coordination variation of the chalcogen atoms in the PtSe 2 /PtTe 2 van der Waals heterostructure induces a nanoscale electronic structure texture in PtSe 2 .

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Nano-modulated Electronic States Induced by Structural Strain in a Moiré Pattern on an Iron-nitride Atomic Layer

Ienaga

Komori

2018

Vac. Surf. Sci.

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Strain-induced modulation of electronic states in a Moiré pattern on a hexagonal-type FeN monoatomic layer has been studied using scanning tunneling microscopy and spectroscopy. The hexagonal FeN film is stabilized by a strong Fe-N bond even on the square Cu(001) substrate and shows a strip structure comprising regular and deformed hexagonal lattices. By analyzing the atomically resolved images, we have found that the lattice is periodically deformed along a hypothetical Moiré pattern between a perfect hexagonal lattice and the square Cu(001) lattice. Moreover, dI/dV spectra exhibit spatial change of the unoccupied local density of states, which is attributed to an energy shift of the antibonding states due to the periodic compressive lattice strain.

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Spatial variation in local work function as an origin of moiré contrast in scanning tunneling microscopy images of Pb thin films/Si(111)

Cited by 3 publications

References 37 publications

Sharpness-induced energy shifts of quantum well states in Pb islands on Cu(111)

Sharpness-induced energy shifts of quantum well states in Pb islands on Cu(111)

A van der Waals Heterostructure with an Electronically Textured Moiré Pattern: PtSe₂/PtTe₂

Nano-modulated Electronic States Induced by Structural Strain in a Moiré Pattern on an Iron-nitride Atomic Layer

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Spatial variation in local work function as an origin of moiré contrast in scanning tunneling microscopy images of Pb thin films/Si(111)

Cited by 3 publications

References 37 publications

Sharpness-induced energy shifts of quantum well states in Pb islands on Cu(111)

Sharpness-induced energy shifts of quantum well states in Pb islands on Cu(111)

A van der Waals Heterostructure with an Electronically Textured Moiré Pattern: PtSe2/PtTe2

Nano-modulated Electronic States Induced by Structural Strain in a Moiré Pattern on an Iron-nitride Atomic Layer

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A van der Waals Heterostructure with an Electronically Textured Moiré Pattern: PtSe₂/PtTe₂