The Russian Thistle—A Scourge to Agriculture

Hofer, Elza

doi:10.1038/scientificamerican12291894-406

Cited by 7 publications

(9 citation statements)

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“…Within this barrier, the interaction between electrons is negligible; for typical tunneling conditions of ϳ1 nA, the time scale of processes is about 10 −10 s-two or three orders of magnitude longer than the typical time scale of lattice relaxations. 25 With this in mind the STM can be simplified to the study of tunneling current between two leads ͑in thermal equilibrium͒ separated by a vacuum barrier. The applied bias potential modifies the chemical potential of surface ͑ S ͒ and tip ͑ T ͒, thus the tunneling current can be expressed through the LandauerBütticker formula, 26…”

Section: Calculating the Currentmentioning

confidence: 99%

Detailed scanning probe microscopy tip models determined from simultaneous atom-resolved AFM and STM studies of theTiO2(110)surface

et al. 2008

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The atomic-scale contrast in noncontact atomic force microscopy ͑nc-AFM͒ images is determined by the geometry and exact atomic structure of the tip apex. However, the tip state is an experimentally unknown parameter, and the lack of insight into the tip apex often limits the possibilities of extracting precise quantitative and qualitative atomistic information on the surface under inspection. From an interplay between simultaneously recorded nc-AFM and scanning tunneling microscopy ͑STM͒ data, and atomistic STM simulations based on multiple scattering theory, we demonstrate how the state of the scanning probe microscopy ͑SPM͒ tip in the experiments may be determined. The analysis of a large number of experimental SPM images recorded with different tips reveals that no general correlation exists between the contrast observed in the nc-AFM and the tunneling current ͑I t ͒ images on TiO 2 ͑110͒ surface. The exact state of the SPM tip must, therefore, be determined for each specific case, which is normally a very difficult endeavor. However, our analysis of the AFM contrast on TiO 2 ͑110͒ surface allows us to considerably reduce the number of tips to be considered in a full simulation. By carefully evaluating the contrast of a handpicked library of SPM tips, we manage to determine a very accurate model of the SPM tip used in an experiment for the first time. It is envisioned that the approach presented here may eventually be used in future studies to screen for and select a SPM tip with a special functionalization prior to imaging an unknown sample, and in that way facilitate precise modeling and chemical identification of surface species.

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Section: Calculating the Currentmentioning

confidence: 99%

Detailed scanning probe microscopy tip models determined from simultaneous atom-resolved AFM and STM studies of theTiO2(110)surface

et al. 2008

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“…A step beyond the TH model is the transfer-Hamiltonian approach in which the matrix elements are computed from the wave functions of the sample and the tip. 15,16 In order to distinguish unequivocally the tip wave function from the sample wave function, the entire tunnel junction is divided into two subsystems, namely, the sample and tip, and the electronic structures of these subsystems are calculated separately. Therefore, tip-sample interactions, which might be significant for small tip-sample distances, are not included.…”

Section: Introductionmentioning

confidence: 99%

Multiple-scattering theoretical approach to scanning tunneling microscopy

et al. 2008

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An approach for computing scanning tunneling microscopy from first principles is proposed. Within the framework of Landauer-Büttiker theory, the conductance of a scanning tunneling microscope ͑STM͒ is obtained in terms of real-space Green functions, thereby taking into account incoherent tunneling processes and the tip-sample interaction but avoiding repeated STM tips as in a supercell approach. The approach is formulated within multiple-scattering theory, especially in the Korringa-Kohn-Rostoker method, but can be implemented in any Green-function method for electronic-structure calculations. Extensive tests are presented for planar and STM tunnel junctions involving Au͑111͒ electrodes.

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“…Possible explanations of this attenuation in the small gap resistance range were given in the literature. 14,21 The corrugations could be reduced when the tip atom is very close to the surface atoms because of the apex atom motion 21 or quenching of the surface states 14 due to high electric fields.…”

Section: Cu(014)-omentioning

confidence: 99%

“…[1][2][3][4][5][6][7] In the meantime, the origin of atomic resolution in each particular case still cannot be easily deduced in a straightforward manner despite substantial experimental and theoretical efforts. [8][9][10][11][12][13][14][15][16][17][18][19][20][21] In the early years of STM, the concept of atomic resolution on metals was understood in terms of a single tip orbital of s-like character being responsible for the surface images. 8,9 However, this concept was unable to explain tip electronic structure effects reported in the literature for the first time by Tromp et al 10 as well as giant atomic corrugations frequently observed in real experiments on various metal surfaces including close-packed surfaces.…”

Section: Introductionmentioning

confidence: 99%

“…8,9 However, this concept was unable to explain tip electronic structure effects reported in the literature for the first time by Tromp et al 10 as well as giant atomic corrugations frequently observed in real experiments on various metal surfaces including close-packed surfaces. Elastic deformation of the tip apex [11][12][13][14][15] and electronic structure effects [17][18][19][20][21] were mainly considered in the literature as two possible mechanisms of corrugation enhancement in STM experiments. One of the explanations of the experimentally observed atomic features with large corrugation heights was given by Chen [18][19][20] in terms of the actual electronic states on realistic tips.…”

Section: Introductionmentioning

confidence: 99%

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Asymmetry effects in atomically resolved STM images of Cu(014)-O and W(100)-O surfaces measured with MnNi tips

et al. 2007

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We report on scanning tunneling microscopy ͑STM͒ studies of the Cu͑014͒-O and W͑100͒-O surfaces using MnNi tips. The STM data demonstrate asymmetry effects in atomically resolved images of W͑100͒-O as well as a regular apparent doubling of surface atomic features along the ͕110͖ direction in Cu͑014͒-O surface images. A qualitative explanation of the observed features based on tight-binding ͑TB͒ and density functional theory ͑DFT͒ calculations of the electronic structure of the MnNi tip is presented. The experimentally observed tip-sample distance dependence of atomically resolved images of Cu͑014͒-O surface and results of DFT and TB calculations show a significant role of different electron orbitals on both the tip and the surface atoms in the STM image formation.

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The Russian Thistle—A Scourge to Agriculture

Cited by 7 publications

References 0 publications

Detailed scanning probe microscopy tip models determined from simultaneous atom-resolved AFM and STM studies of theTiO2(110)surface

Detailed scanning probe microscopy tip models determined from simultaneous atom-resolved AFM and STM studies of theTiO2(110)surface

Multiple-scattering theoretical approach to scanning tunneling microscopy

Asymmetry effects in atomically resolved STM images of Cu(014)-O and W(100)-O surfaces measured with MnNi tips

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