Scanning tunneling microscopy current from localized basis orbital density functional theory

Gustafsson, Alexander; Paulsson, Magnus

doi:10.1103/physrevb.93.115434

Cited by 18 publications

(35 citation statements)

References 27 publications

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“…In contrast to the metallic tips investigated here, for the case of a CO-functionalized tip, the symmetry of the tip state is drastically changed from σ to π , which results in the inversion of the STM image contrast for a CO molecule on the Cu(111) surface from dip to bump [31,35]. This change of the tip state is predicted to decrease the efficiency of the IETS considerably for a CO molecule on a metal surface [19], in contrast to the present case.…”

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confidence: 95%

“…The IETS calculations are then performed at the point. [35,36], where the current on top of the CO molecule is larger for the four-atom tip than for the single-atom tip owing to the larger tip area from which electrons can tunnel. Figure 1(e) shows the IETS for CO molecules obtained with the singleatom tip [37] and the four-atom tip, where identical current set points are used for both tips.…”

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confidence: 99%

“…165415-3 basis set, causing the calculated tunneling current to preferentially pass through the CO molecule regardless of the opposite-electrode geometry [35], i.e., the direct tunneling between the tip and the substrate is underestimated. Thus the calculated IETS dominantly reflects the contribution of γ inel rather than that of I CO /I total .…”

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Influence of atomic tip structure on the intensity of inelastic tunneling spectroscopy data analyzed by combined scanning tunneling spectroscopy, force microscopy, and density functional theory

et al. 2016

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Achieving a high intensity in inelastic scanning tunneling spectroscopy (IETS) is important for precise measurements. The intensity of the IETS signal can vary by up to a factor of 3 for various tips without an apparent reason accessible by scanning tunneling microscopy (STM) alone. Here, we show that combining STM and IETS with atomic force microscopy enables carbon monoxide front-atom identification, revealing that high IETS intensities for CO/Cu(111) are obtained for single-atom tips, while the intensity drops sharply for multiatom tips. Adsorption of the CO molecule on a Cu adatom [CO/Cu/Cu(111)] such that the molecule is elevated over the substrate strongly diminishes the tip dependence of IETS intensity, showing that an elevated position channels most of the tunneling current through the CO molecule even for multiatom tips, while a large fraction of the tunneling current bypasses the CO molecule in the case of CO/Cu(111). DOI: 10.1103/PhysRevB.93.165415 Inelastic electron tunneling spectroscopy (IETS) with scanning tunneling microscopy (STM) is an effective method to analyze the vibrational modes of a single adsorbed molecule with subnanometer lateral resolution [1,2]. The vibrational energy of a molecule on a substrate strongly depends on the surrounding environment, such as the substrate structure and composition [3]. By studying these subtle changes of the vibrational energy using STM-IETS with a molecularfunctionalized tip, it has been demonstrated that STM-IETS can provide information on the inner structure of a molecule [4,5] similarly to atomic force microscopy (AFM) [6]. These advantages of STM-IETS have accelerated research in related fields [7][8][9][10][11][12][13][14][15][16]. Owing to recent progress in the theoretical description of IETS [17][18][19][20][21][22], the qualitative understanding has been improved considerably: the symmetry of the wave functions of a tip and a molecule on a substrate and a vibrational mode of the molecule are predicted to influence the efficiency of the inelastic process (γ inel ) for the tunneling current involving the molecule. In order to discuss γ inel on the basis of the intensity of IETS, we have to consider that IETS intensity is described by the multiplication of two factors: (1) the ratio of the tunneling current passing through a molecule to the total tunneling current (I molecule /I total ) and (2) the efficiency of the inelastic process (γ inel ). These factors should in principle be affected by the geometrical structure of the substrate and of the tip.The geometrical structure of a metal tip apex can be determined by using carbon monoxide (CO) front-atom identification (COFI) provided by AFM [23,24], where the tip apex of a force sensor is probed by a CO molecule that stands upright on a metal surface [inset of Fig. 1(e)]. The metallic tip apex atom has a dipole moment induced by the Smoluchowski effect [25], whose direction is the same as that of the CO molecule adsorbed on the surface [26]. Thus in the distance regime where the electrostatic int...

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Influence of atomic tip structure on the intensity of inelastic tunneling spectroscopy data analyzed by combined scanning tunneling spectroscopy, force microscopy, and density functional theory

et al. 2016

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“…In our previous development [9,25] of calculating STM images from localized-orbital DFT, we used the Bardeen's approximation [11] for the real-space propagated wave functions in the vacuum region. The wave functions are calculated on an equidistant discrete lattice utilizing a simple nearest-neighbour finite difference (FD) scheme.…”

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confidence: 99%

“…Upon using the Bardeen's approximation we introduce a separation surface [9,25], S, in vicinity of the middle of the vacuum gap (where the total DFT potential reaches its maximum) and set the potential away from this slice as the average of the potential at S. The wave functions from the substrate, ϕ s , and the tip, ϕ t , are then computed equivalently, but separately from each side of the vacuum region.…”

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STM contrast of a CO dimer on a Cu(1 1 1) surface: a wave-function analysis

Gustafsson¹,

Paulsson²

2017

J. Phys.: Condens. Matter

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We present a method used to intuitively interpret the STM contrast by investigating individual wave functions originating from the substrate and tip side. We use localized basis orbital density functional theory, and propagate the wave functions into the vacuum region at a real-space grid, including averaging over the lateral reciprocal space. Optimization by means of the method of Lagrange multipliers is implemented to perform a unitary transformation of the wave functions in the middle of the vacuum region. The method enables (i) reduction of the number of contributing tip-substrate wave function combinations used in the corresponding transmission matrix, and (ii) to bundle up wave functions with similar symmetry in the lateral plane, so that (iii) an intuitive understanding of the STM contrast can be achieved. The theory is applied to a CO dimer adsorbed on a Cu(111) surface scanned by a single-atom Cu tip, whose STM image is discussed in detail by the outlined method.

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Attenuation of Redox Switching and Rectification in Azulenequinones/Hydroquinones after B and N Doping: A First‐Principles Investigation

Haidar

Tawfik

Stampfl

et al. 2020

Advcd Theory and Sims

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The redox switching of doped 1,5-azulenequinones/hydroquinones wired between gold electrodes is investigated using density functional theory and the nonequilibrium Green's function. Their electronic transport properties when separately doped with nitrogen and boron as well as co-doping of these atoms are examined. The results illustrate a significant enhancement of the current at low bias voltage in some of the 12 doped studied systems, leading to "switching on" the transmission, where the greatest switching ratio is 18. These systems also exhibit a modest rectification in which the greatest rectification ratio is 4. The significance of the position of the doped atom and the functional group on the switching behavior is analyzed through the transmission spectra and molecular orbitals. The present study broadens knowledge of organic redox switching bringing in potential diverse options for future molecular electronic circuit components.

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Scanning tunneling microscopy current from localized basis orbital density functional theory

Cited by 18 publications

References 27 publications

Influence of atomic tip structure on the intensity of inelastic tunneling spectroscopy data analyzed by combined scanning tunneling spectroscopy, force microscopy, and density functional theory

Influence of atomic tip structure on the intensity of inelastic tunneling spectroscopy data analyzed by combined scanning tunneling spectroscopy, force microscopy, and density functional theory

STM contrast of a CO dimer on a Cu(1 1 1) surface: a wave-function analysis

Attenuation of Redox Switching and Rectification in Azulenequinones/Hydroquinones after B and N Doping: A First‐Principles Investigation

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