Design of an extremely stable low-temperature ultrahigh vacuum scanning tunneling microscope

Koslowski, B.; Dietrich, Ch.; Tschetschetkin, Anna; Ziemann, P.

doi:10.1063/1.2213171

Cited by 13 publications

(8 citation statements)

References 15 publications

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“…The green, blue, and red lines indicate within a diagram (dashed) the position of the peaks and between the diagrams (solid) the correspondence of the two diagrams. with SERS data taken from the literature 13,14 is excellent, especially keeping in mind that the experimental situation is different in each case. The agreement of our IETS results with theory is good, with a mean absolute deviation (MAD) close to the combined accuracy of experiment and theory (see Table 1).…”

Section: Resultsmentioning

confidence: 73%

Vibrations of a single adsorbed organic molecule: anharmonicity matters!

Ulusoy

Scribano

Benoit

et al. 2011

Phys. Chem. Chem. Phys.

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Vibrational spectroscopy is a powerful tool to identify molecules and to characterise their chemical state. Inelastic electron tunnelling spectroscopy (IETS) combined with scanning tunnelling microscopy (STM) allows the application of vibrational analysis to a single molecule. Up to now, IETS was restricted to small species due to the complexity of vibration spectra for larger molecules. We extend the horizon of IETS for both experiment and theory by measuring the STM-IETS spectra of mercaptopyridine adsorbed on the (111) surface of gold and comparing it to theoretical spectra. Such complex spectra with more than 20 lines can be reliably determined and computed leading to completely new insights. Experimentally, the vibrational spectra exhibit a dependence on the specific adsorption site of the molecules. Theoretically, this dependence is only accessible if anharmonic contributions to the interaction potentials are included. These joint experimental and theoretical advances open new perspectives for structure determination of organic adlayers.

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Section: Resultsmentioning

confidence: 73%

Vibrations of a single adsorbed organic molecule: anharmonicity matters!

Ulusoy

Scribano

Benoit

et al. 2011

Phys. Chem. Chem. Phys.

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“…After introduction into ultra-high vacuum (UHV), these films were further annealed at temperatures up to 700 °C to remove contaminants from the surface. After a routine check of the gold surface by STM at low temperature ( p < 1 × 10 −10 mbar, T ≈ 5.5 K) [ 13 ], the samples were quickly transferred to the preparation chamber under UHV conditions and, there, 0.2 to 0.7 monolayers (ML) of 3T (obtained from Sigma Aldrich and further purified) were deposited onto the gold film at a rate of about 0.01 nm/s from a home-built Knudsen-type cell. After deposition, the samples were immediately transferred back to the low-temperature STM.…”

Section: Methodsmentioning

confidence: 99%

Terthiophene on Au(111): A scanning tunneling microscopy and spectroscopy study

Koslowski¹,

Tschetschetkin²,

Maurer³

et al. 2011

Beilstein J. Nanotechnol.

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SummaryTerthiophene (3T) molecules adsorbed on herringbone (HB) reconstructed Au(111) surfaces in the low coverage regime were investigated by means of low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) under ultra-high vacuum conditions. The 3T molecules adsorb preferentially in fcc regions of the HB reconstruction with their longer axis oriented perpendicular to the soliton walls of the HB and at maximum mutual separation. The latter observation points to a repulsive interaction between molecules probably due to parallel electrical dipoles formed during adsorption. Constant-separation (I-V) and constant-current (z-V) STS clearly reveal the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals, which are found at −1.2 eV and +2.3 eV, respectively. The HOMO–LUMO gap corresponds to that of a free molecule, indicating a rather weak interaction between 3T and Au(111). According to conductivity maps, the HOMO and LUMO are inhomogeneously distributed over the adsorbed 3T, with the HOMO being located at the ends of the linear molecule, and the LUMO symmetrically with respect to the longer axis of the molecule at the center of its flanks. Analysis of spectroscopic data reveals details of the contrast mechanism of 3T/Au(111) in STM. For that, the Shockley-like surface state of Au(111) plays an essential role and appears shifted outwards from the surface in the presence of the molecule. As a consequence, the molecule can be imaged even at a tunneling bias within its HOMO–LUMO gap. A more quantitative analysis of this detail resolves a previous discrepancy between the fairly small apparent STM height of 3T molecules (1.4–2.0 nm, depending on tunneling bias) and a corresponding larger value of 3.5 nm based on X-ray standing wave analysis. An additionally observed linear decrease of the differential tunneling barrier at positive bias when determined on top of a 3T molecule is compared to the bias independent barrier obtained on bare Au(111) surfaces. This striking difference of the barrier behavior with and without adsorbed molecules is interpreted as indicating an adsorption-induced dimensionality transition of the involved tunneling processes.

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“…In the following we apply the above-described scheme to experimental data obtained on Nb(110) [ 21 ]. The measurements were performed on a home-built low-temperature STM operated at a base pressure of ~10 −10 mbar and a base temperature of 5.2 K [ 22 ]. The ∂ V I–V curves were recorded at different set currents by employing a lock-in technique with a modulation frequency of ~500 Hz, which is well above the bandwidth of the topographic feedback loop.…”

Section: Resultsmentioning

confidence: 99%

Deconvolution of the density of states of tip and sample through constant-current tunneling spectroscopy

Pfeifer¹,

Koslowski²,

Ziemann³

2011

Beilstein J. Nanotechnol.

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SummaryWe introduce a scheme to obtain the deconvolved density of states (DOS) of the tip and sample, from scanning tunneling spectra determined in the constant-current mode (z–V spectroscopy). The scheme is based on the validity of the Wentzel–Kramers–Brillouin (WKB) approximation and the trapezoidal approximation of the electron potential within the tunneling barrier. In a numerical treatment of z–V spectroscopy, we first analyze how the position and amplitude of characteristic DOS features change depending on parameters such as the energy position, width, barrier height, and the tip–sample separation. Then it is shown that the deconvolution scheme is capable of recovering the original DOS of tip and sample with an accuracy of better than 97% within the one-dimensional WKB approximation. Application of the deconvolution scheme to experimental data obtained on Nb(110) reveals a convergent behavior, providing separately the DOS of both sample and tip. In detail, however, there are systematic quantitative deviations between the DOS results based on z–V data and those based on I–V data. This points to an inconsistency between the assumed and the actual transmission probability function. Indeed, the experimentally determined differential barrier height still clearly deviates from that derived from the deconvolved DOS. Thus, the present progress in developing a reliable deconvolution scheme shifts the focus towards how to access the actual transmission probability function.

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Design of an extremely stable low-temperature ultrahigh vacuum scanning tunneling microscope

Cited by 13 publications

References 15 publications

Vibrations of a single adsorbed organic molecule: anharmonicity matters!

Vibrations of a single adsorbed organic molecule: anharmonicity matters!

Terthiophene on Au(111): A scanning tunneling microscopy and spectroscopy study

Deconvolution of the density of states of tip and sample through constant-current tunneling spectroscopy

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