Inelastic Electron Tunneling Spectroscopy of an Alkanethiol Self-Assembled Monolayer Using Scanning Tunneling Microscopy

Okabayashi, Norio; Konda, Youhei; Komeda, Tadahiro

doi:10.1103/physrevlett.100.217801

Cited by 68 publications

(87 citation statements)

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“…An important issue is the appearance of inelastic effects where energy is taken from the electron flow into the different degrees of freedom of the system. Inelasticities lead to new regimes of transport that contain relevant information on the atomic contact and have been thus used to develop single atom and molecule spectroscopies [2,3,4].Inelastic electron tunneling spectroscopy (IETS) where electrons excite vibrations leading to conductance steps at certain voltage thresholds [2] has been extensively studied in the last years [5,6,7,8,9]. The inelastic change in conductance is within a few percent of the elastic conductance, mainly due the smallness of the electron-vibration coupling [10,11].…”

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confidence: 99%

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Efficient Spin Transitions in Inelastic Electron Tunneling Spectroscopy

2009

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The excitation of the spin degrees of freedom of an adsorbed atom by tunneling electrons is computed using a strong coupling theory. The excitation process is shown to be a sudden switch between the initial state determined by the environmental anisotropy to an intermediate state given by the coupling to the tunnelling electron. This explains the observed large inelastic currents. Application is presented for Fe and Mn adsorbates on CuN monolayers on Cu(100). First-principles calculations show the dominance of one collisional channel, leading to a quantitative agreement with the experiment.PACS numbers: 68.37. Ef, The way electrons flow through atomic contacts has important fundamental and technological implications [1]. Electronic transport is a quantal process in which charge, spin and vibrational degrees of freedom are entangled leading to problems of intrinsic fundamental interest. Technologically, the quest for minutarization is pushing the limits of devices to the atomic scale, where the above transport properties will determine the actual device functionalities. An important issue is the appearance of inelastic effects where energy is taken from the electron flow into the different degrees of freedom of the system. Inelasticities lead to new regimes of transport that contain relevant information on the atomic contact and have been thus used to develop single atom and molecule spectroscopies [2,3,4].Inelastic electron tunneling spectroscopy (IETS) where electrons excite vibrations leading to conductance steps at certain voltage thresholds [2] has been extensively studied in the last years [5,6,7,8,9]. The inelastic change in conductance is within a few percent of the elastic conductance, mainly due the smallness of the electron-vibration coupling [10,11]. Recently, Heinrich and co-workers have been able to develop a spin-resolved spectroscopy using an STM [4,12,13,14]. In magnetic IETS [4], the tunneling electron yields energy to the spin of an adsorbed magnetic atom and in this way changes its orientation by overcoming the magnetic anisotropy barrier of the atom on the surface. Magnetic transitions in the meV range could be observed in adsorbates partly decoupled from a metal substrate [4,12,13,14,15]. As in vibrational IETS, the conductance presents a step at the energy threshold however the changes in conductance at inelastic threshold can reach several hundreds percent. This is at odds with previous treaments [13,16,17] where first-order perturbation theory is used.In this letter, we present an all-order theory of the spin transitions IETS and apply it to the cases of Fe and Mn adsorbates on a CuN monolayer on Cu, experimentally studied in Refs. [13,14]. We compute the relative weights of both elastic and inelastic channels, leading to a quantitative account of the inelastic currents in the experimental observations. The theory reveals the nature of the inelastic transitions and explains the extremely large inelastic currents in these magnetic systems.The general idea of our approach is the following. ...

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confidence: 99%

“…Inelastic electron tunneling spectroscopy (IETS) where electrons excite vibrations leading to conductance steps at certain voltage thresholds [2] has been extensively studied in the last years [5,6,7,8,9]. The inelastic change in conductance is within a few percent of the elastic conductance, mainly due the smallness of the electron-vibration coupling [10,11].…”

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confidence: 99%

Efficient Spin Transitions in Inelastic Electron Tunneling Spectroscopy

2009

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“…Within the context of the STM, this technique is denoted as inelastic electron tunneling spectroscopy (STM-IETS) and is extensively employed to characterize the molecule's vibrational spectra. [9][10][11][12][13][14][15] From the theoretical side, a wealth of formalisms dealing with the inelastic transport have been developed in parallel to these delicate experiments. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] The earliest models for IETS employed a multiple scattering formalism (multichannels) with simplified semiempirical Hamiltonians 16 or a Tersoff-Hamman-(TH-) type approach.…”

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confidence: 99%

Lowest order in inelastic tunneling approximation: Efficient scheme for simulation of inelastic electron tunneling data

2013

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We have developed an efficient and accurate formalism which allows the simulation at the ab initio level of inelastic electron tunneling spectroscopy data under a scanning tunneling microscope setup. It exploits fully the tunneling regime by carrying out the structural optimization and vibrational mode calculations for surface and tip independently. The most relevant interactions in the inelastic current are identified as the inelastic tunneling terms, which are taken into account up to lowest order, while all other inelastic contributions are neglected. As long as the system is under tunneling regime conditions and there is no physisorbed molecule on the surface or tip apex, this lowest order in inelastic tunneling (LOIT) approach reduces drastically the computational cost compared to related approaches while maintaining a good accuracy. Adopting the wide-band limit for both tip and surface further reduces calculation times significantly, and is shown to give similar results to when the full energy dependence of the Green's functions is taken into account. The LOIT is applied to the Cu(111) + CO system probed by a clean and a CO contaminated tip to find good agreement with previous works. Different parameters involved in the calculations such as basis sets, k sampling, tip-sample distance, or temperature, among others, are discussed in detail.

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“…1 The STM is thus conferred with the ability to chemically analyze surfaces on the atomic scale. 2,3 IETS has rapidly become a mature technique and multimode analyses on molecular substrates have been accomplished 4 as well as analyses of extended vibrations or phonons. 5 The characterization and control of single-molecule reactivity through the excitation of a specific vibrational mode is a challenging area for the STM-based IETS technique.…”

Section: Introductionmentioning

confidence: 99%

Role of molecular electronic structure in inelastic electron tunneling spectroscopy:O2on Ag(110)

2010

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Density-functional theory ͑DFT͒ simulations corrected by the intramolecular Coulomb repulsion U are performed to evaluate the vibrational inelastic electron tunneling spectroscopy ͑IETS͒ of O 2 on Ag͑110͒. In contrast to DFT calculations that predict a spinless adsorbed molecule, the inclusion of the U correction leads to the polarization of the molecule by shifting a spin-polarized molecular orbital toward the Fermi level. Hence, DFT+ U characterizes O 2 on Ag͑110͒ as a mixed-valent system. This has an important implication in IETS because a molecular resonance at the Fermi level can imply a decrease in conductance while in the off-resonance case, an increase in conductance is the expected IETS signal. We use the lowest-order expansion on the electron-vibration coupling in order to evaluate the magnitude and spatial distribution of the inelastic signal. The final IET spectra are evaluated with the help of the self-consistent Born approximation and the effect of temperature and modulation-voltage broadening are explored. Our simulations reproduce the experimental data of O 2 on Ag͑110͒ ͓J. R. Hahn, H. J. Lee, and W. Ho, Phys. Rev. Lett. 85, 1914 ͑2000͔͒ and give extra insight of the electronic and vibrational symmetries at play. This ensemble of results reveals that the IETS of O 2 is more complicated that a simple decrease in conductance and cannot be ascribed to the effect of a single molecular-orbital resonance.

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Inelastic Electron Tunneling Spectroscopy of an Alkanethiol Self-Assembled Monolayer Using Scanning Tunneling Microscopy

Cited by 68 publications

References 30 publications

Efficient Spin Transitions in Inelastic Electron Tunneling Spectroscopy

Efficient Spin Transitions in Inelastic Electron Tunneling Spectroscopy

Lowest order in inelastic tunneling approximation: Efficient scheme for simulation of inelastic electron tunneling data

Role of molecular electronic structure in inelastic electron tunneling spectroscopy:O2on Ag(110)

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