Transient tunneling current in laser-assisted scanning tunneling microscopy

Lyubinetsky, Igor; Dohnálek, Zdenek; Ukraintsev, Vladimir A.; Yates, John T.

doi:10.1063/1.366251

Cited by 44 publications

(31 citation statements)

References 20 publications

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“…The exact value of this relaxation time varies from tip to tip, but nevertheless all values observed in our experiments were above the time resolution of the amplifier (30 µs). Similar values for tungsten tips have also been observed by Lyubinetsky et al [7].…”

Section: Resultssupporting

confidence: 78%

“…On one hand field enhancement in the vicinity of the tip and subsequent field evaporation is proposed, while thermal effects are ruled out [1][2][3][4][5]. On the other hand mechanical contact as a result of thermal expansion is discussed as well [6][7][8]. Such thermal effects have also been observed in other combinations of pulsed laser light with scanning microscope tips [9][10][11].…”

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confidence: 82%

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The mechanism of nanostructuring upon nanosecond laser irradiation of a STM tip

Boneberg

Münzer

Tresp

et al. 1998

Applied Physics A: Materials Science & Processing

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Abstract. The mechanism of nanostructuring by illumination of scanning probe tips is examined. For that purpose the tip of a scanning tunneling microscope is illuminated with nanosecond and femtosecond laser pulses. The observation of a transient increase of the tunneling current on the timescale of µs is indicative of thermal expansion, which amounts to several nm for the energy density necessary for the purpose of nanostructuring. Furthermore, quantized electrical resistance can be observed upon illumination, which shows the formation of mechanical contact between tip and surface. Thus it is concluded that the appearance of nanostructures (craters or mounds) is dominated by the cohesion properties of the tip/sample combination. Finally it is shown that even a huge increase of the involved electromagnetic field, reached by the reduction of the pulse length from 10 ns to 100 fs, does not change this scenario. 61.16.Ch; 65.70.+y Recent experiments have shown the possibility of surface nanostructuring by illumination of a scanning microscope tip with ns laser pulses [1][2][3][4][5]. This seems to be a promising method since a high degree of reproducibility has been reported [3][4][5]. Furthermore this method is applicable to different materials (for example Au, Au/Pd, Ti, PMMA, polycarbonate, organic media) as well as with different kinds of microscopes (AFM and STM) [3][4][5]. However, the responsible mechanism is controversial. On one hand field enhancement in the vicinity of the tip and subsequent field evaporation is proposed, while thermal effects are ruled out [1][2][3][4][5]. On the other hand mechanical contact as a result of thermal expansion is discussed as well [6][7][8]. Such thermal effects have also been observed in other combinations of pulsed laser light with scanning microscope tips [9][10][11]. PACS:We performed transient measurements of the tunneling current during such experiments, which should enable us to distinguish between these two models due to the different time scales involved. Whereas a field evaporation mechanism should take place on the time scale of the laser pulse (ns), a thermal effect occurs with a typical cooling time in the order of µs (from τ = d 2 /2D one can estimate a relaxation time of 73 µs for a tungsten tip with a thermal diffusivity D of 0.68 cm 2 /s and a focus diameter d = 100 µm). Following the thermal model it might also be possible to observe indications of the mechanical contact, for example quantized conductance of the junction formed upon illumination. Therefore we present measurements of the gap resistance of a STM upon illumination with a ns laser pulse. Finally a comparison of current transients after illumination with ns and fs laser pulses, respectively, is shown.

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Section: Resultssupporting

confidence: 78%

mentioning

confidence: 82%

The mechanism of nanostructuring upon nanosecond laser irradiation of a STM tip

Boneberg

Münzer

Tresp

et al. 1998

Applied Physics A: Materials Science & Processing

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“…Hence, as the concepts of low-energy electron holography are compatible with ultrafast nanofocused SPP-driven electron sources, the prospective combination of sub-10 fs temporal and 1 nm spatial resolutions would enable the investigation of ultrafast charge transport on electronic time and molecular length scales. At tip-sample distances in the sub-nanometer range, SPP-driven electron point sources are promising probes for timeresolved scanning tunneling microscopy (STM), which has been pursued for more than two decades [36,38,55,56] but remains challenging due to laser-induced thermal expansion [57][58][59] and contribution of the transient hot electrons to the tunneling currents [39]. The non-local excitation of the optical near-field in the tip-sample junction via nanofocused SPPs may help to overcome these limitations.…”

Section: Resultsmentioning

confidence: 99%

Nanofocused Plasmon-Driven Sub-10 fs Electron Point Source

et al. 2016

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Progress in ultrafast electron microscopy relies on the development of efficient laser-driven electron sources delivering femtosecond electron pulses to the sample. In particular, recent advances employ photoemission from metal nanotips as coherent point-like femtosecond low-energy electron sources. We report the nonlinear emission of ultrashort electron wave packets from a gold nanotip generated by nonlocal excitation and nanofocusing of surface plasmon polaritons. We verify the nanoscale localization of plasmon-induced electron emission by its electrostatic collimation characteristics. With a plasmon polariton pulse duration below 8 fs at the apex, we identify multiphoton photoemission as the underlying emission process. The quantum efficiency of the plasmon-induced emission exceeds that of photoemission from direct apex illumination. We demonstrate the application for plasmon-triggered point-projection imaging of an individual semiconductor nanowire at 3 µm tip-sample distance. Based on numerical simulations we estimate an electron pulse duration at the sample below 10 fs for tip-sample distances up to few micrometers. Plasmon-driven nanolocalized electron emission thus enables femtosecond point-projection microscopy with unprecedented temporal and spatial resolution, femtosecond low-energy electron in-line holography, and opens a new route towards femtosecond scanning tunneling microscopy and spectroscopy.

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“…[1][2][3][4][5][6][7] In many of these experiments, in which generally visible or infrared wavelengths are used, it is frequently considered that the various photoinduced effects such as electron-phonon coupling, 8,9 photovoltage, 10 thermovoltage, 11 photoelectron emission, 12 hot electron formation, 13 and tunnel current rectification 14 are decoupled. Thus, in many experiments, the optical-field confinement and enhancement that may be created underneath the STM-tip apex 15,16 is regularly considered as an independent optical process separated from the other photoinduced effects.…”

Section: Introductionmentioning

confidence: 99%

Very low thermally induced tip expansion by vacuum ultraviolet irradiation in a scanning tunneling microscope junction

et al. 2009

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The thermal and photoelectronic processes induced when a vacuum ultraviolet ͑VUV͒ laser irradiates the junction of a scanning tunneling microscope ͑STM͒ are studied. This is performed by synchronizing the VUV laser shots with the STM scan signal. Compared to other wavelengths, the photoinduced thermal STM-tip expansion is not observed when the VUV radiation is freed from spurious emissions. Furthermore, we demonstrate that the purified VUV photoinduced transient signal detected in the tunnel current is entirely due to photoelectronic emission and not combined with thermionic processes. The ensuing photoelectron emission is shown to be independent of the tip-surface distance while varying linearly with the pure VUV laser intensity. These results illustrate a strong decoupling between phonons and photoelectrons which allows a very weak STM-tip expansion.

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Transient tunneling current in laser-assisted scanning tunneling microscopy

Cited by 44 publications

References 20 publications

The mechanism of nanostructuring upon nanosecond laser irradiation of a STM tip

The mechanism of nanostructuring upon nanosecond laser irradiation of a STM tip

Nanofocused Plasmon-Driven Sub-10 fs Electron Point Source

Very low thermally induced tip expansion by vacuum ultraviolet irradiation in a scanning tunneling microscope junction

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