Influence of the Tip Shape on Scanning Tunneling Luminescence Spectra: Implications for Nanomaterial Characterization

Scanning tunneling luminescence (STL) provides a unique opportunity to determine the optical properties of nanostructures beyond the diffraction limit. However, the relationship between the STL spectra and nanoscale tip shapes remains poorly understood because of the uncertainty regarding the nanoscale tip geometry. Here, we provide direct experimental evidence supporting a relationship between the tip shapes and resulting STL spectra. We find that asymmetric nanoscale tips generated dissimilar STL spectra in different directions by simultaneously collecting STL spectra in two opposing directions. Our experiment provides an efficient way to tune the STL spectra, which can be used to characterize the optical properties of nanomaterials.11Nsciescopu

Detecting the Tip Shape Dependence of the Plasmonic Photon Emission under STM

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The tip shape dependence of the STM-induced luminescence

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Unusual Diffusion Behavior of Copper-Hexadecafluoro-Phthalocyanine Molecules on Au(111)

© 2020, The Korean Physical Society. The unusual bias-voltage dependence of copper-hexadecafluoro-phthalocyanine (F16CuPc) molecules on Au(111) was investigated by using scanning tunneling microscopy/spectroscopy (STM/STS) at low temperatures. Depending on the bias polarity, the molecules seem to cover the whole surface of Au(111) at positive bias voltages while they are apparently invisible in STM images at negative bias voltages. Here, we experimentally demonstrate that the molecular diffusivity on Au(111) varies according to the applied electric field induced between the STM tip and the Au(111) surface rather than the intrinsic molecule-substrate interaction. Such results are corroborated by STS measurements indicating that attraction/repulsion of a molecule indeed occurs under an STM tip at positive/negative bias voltages during sweeps of the bias voltage. In addition, we found that the diffusive molecules are immobilized at a temperature of 8 K at both positive and negative bias voltages due to a lack of thermal energy for diffusion11sciekc

Tunable Plasmonic Quantum Light Source with Silver Nanoclusters on a Silver Surface

Scanning tunneling luminescence (STL) can be used to investigate the optical properties of nanostructures with high spatial resolution beyond the diffraction limit of light. To get appropriate STL spectra, one needs to modify the tip repeatedly. However, such irreversible tip modification often leads to very unstable tips. Here, by using a scanning tunneling microscope (STM) tip, we demonstrate that STL spectra are tunable via silver nanocluster arrays fabricated directly on a silver surface. The silver nanoclusters are created by transferring silver atoms from the silver tip to the silver surface under STM. We found that the STL spectra were enhanced (suppressed) at higher (lower) energy on the clusters and that they showed opposite behaviors between the nanoclusters. Without relying on the irreversible tip shape modification, our findings indicate that we can tune the STL spectra simply by moving the STM tip over the nanoclusters. Our method can be used to provide a tunable light source for systematic nano-optical experiments and for nanoscale optical devices.11Nsciescopuskc

Geometric Dependence of Tip Shape on Scanning Tunneling Luminescence Spectra.

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Systematic investigation of wear-induced cold welding in ultrahigh vacuum piezoelectric motors with non-metallic coatings

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