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1
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3142667327
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(Cornell Univ. Press, Ithaca, New York, ed. 2), chap. 11
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L. C. Pauling, The Nature of the Chemical Bond (Cornell Univ. Press, Ithaca, New York, ed. 2, 1948), chap. 11.
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(1948)
The Nature of the Chemical Bond
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Pauling, L.C.1
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4
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35949017776
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M. Posternak, H. Krakauer, A. J. Freeman, D. D. Koelling, Phys. Rev. B 21, 5601 (1980).
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Phys. Rev. B
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Posternak, M.1
Krakauer, H.2
Freeman, A.J.3
Koelling, D.D.4
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6
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34848919386
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G. Binnig, H. Rohrer, Ch. Gerber, E. Weibel, Phys. Rev. Lett. 49, 57 (1982).
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Phys. Rev. Lett.
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Binnig, G.1
Rohrer, H.2
Gerber, Ch.3
Weibel, E.4
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8
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3142742093
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note
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F (20). The images of single metal atoms are paraboloids with apex radii on the order of 0.5 nm. The exact value depends on tip-sample distance and the electronic states (20) with a possible influence of mechanical deformations (26). STM operation at smaller tip-sample distances would result in sharper atomic images (20, 29). However, in standard STM, the tip-sample distance must exceed a lower threshold to prevent tip instabilities (26), and extremely small tip-sample distances require the use of oscillating STM tips (30).
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3142776013
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After the introduction of the AFM in 1986, the first clear proof of its capability to image single atoms was obtained by imaging the calcite surface in a liquid environment (27) in 1993. Reactive surfaces that require imaging in an ultrahigh vacuum, such as the Si (111)-(7×7) surface, were imaged 2 years later (31, 32) with FM-AFM (33) with a lateral resolution of ≈0.6 nm. Now, FM-AFM is a routine method (34, 12) for imaging conductive and insulating surfaces with atomic resolution that even enables the direct measurement of chemical-bonding forces (35) by using deconvolution techniques (36). An optimized sensing technology has led to the observation of subatomic features within a single atom spaced by 220 pm (37), related to the orbital structure of a Si atom (38). The rest atoms on Si (111)-(7×7) were imaged by low-temperature AFM (39) and small-amplitude techniques (40), demonstrating a lateral resolution of 384 pm. Repulsive forces vary more strongly with distance than attractive forces and thus offer better spatial resolution (29, 41). FM-AFM probing repulsive interactions can achieve a lateral resolution of 142 pm, demonstrated by resolving the nearest neighbor atoms in graphite (42).
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13
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3142673227
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ts (Eq. 1).
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3142692284
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thesis, Augsburg University, Augsburg, Germany
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S. Hembacher, thesis, Augsburg University, Augsburg, Germany (2003).
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(2003)
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Hembacher, S.1
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3142753854
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Because the coefficients of thermal expansion are greatly reduced at temperatures near absolute zero, the thermal drift (i.e., a slow drift of the probe with respect to the sample), a common nuisance in scanning probe experiments, is reduced to 25 pm/hour. The resulting accuracy and time stability permits measurements at very slow scanning speeds and in a constant-height mode, during which the z feedback can be turned off for at least 3 hours while remaining in the tunneling distance regime.
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18
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3142726013
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We attempted to prepare tips made of doped diamond, but the electrical conductivity of these tips was insufficient for simultaneous AFM/STM operation. Carbon nanotubes might also appear promising as AFM tips, but we require very stiff tips to avoid artifacts from elastic tip deflections.
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19
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3142687954
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thesis, Stanford University, Stanford, CA
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H. Mizes, thesis, Stanford University, Stanford, CA (1987).
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(1987)
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Mizes, H.1
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22
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3142676196
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dB = 65 kHz.
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23
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3142711283
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In addition to the tunneling current and higher harmonic signal, the frequency shift and the dissipation signal were recorded in parallel (43). The frequency shift data are similar to the higher harmonic data in the right column of Fig. 2, yet with much less contrast and a substantially smaller signal-to-noise ratio. The resolution of the dissipation data is similar to that of the current data.
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24
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3142690872
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Notably, the W tip is not an oriented single crystal but the apex of a polycrystalline W wire. The orientation of the tip was not known beforehand in our experiment. However, a tip that provides good STM images exposes a single W atom at the tip apex, and it is reasonable to assume that high-symmetry orientations provide stable tips. The geometry of the next neighbor atoms of the tip could be determined by field ion microscopy (FIM) (44), but space constraints prevent the implementation of FIM in our low-temperature AFM/STM.
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28
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3142762799
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The atomic radii of W and C are taken as half the nearest neighbor distance in bulk W [bcc, cubic lattice constant 316 pm (2)] and graphite (142 pm), respectively.
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33
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0038981463
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T. R. Albrecht, P. Grutter, H. K. Horne, D. Rugar, J. Appl. Phys. 69, 668 (1991).
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(1991)
J. Appl. Phys.
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Albrecht, T.R.1
Grutter, P.2
Horne, H.K.3
Rugar, D.4
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35
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0035970899
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M. Lantz et al., Science 291, 2580 (2001).
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(2001)
Science
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, pp. 2580
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Lantz, M.1
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37
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0034698297
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F. J. Giessibl, S. Hembacher, H. Bielefeldt, J. Mannhart, Science 289, 422 (2000).
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(2000)
Science
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, pp. 422
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Giessibl, F.J.1
Hembacher, S.2
Bielefeldt, H.3
Mannhart, J.4
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42
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0242363188
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S. Hembacher, F. J. Giessibl, J. Mannhart, C. F. Quate, Proc. Natl. Acad. Sci. U.S.A. 100, 12539 (2003).
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(2003)
Proc. Natl. Acad. Sci. U.S.A.
, vol.100
, pp. 12539
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Hembacher, S.1
Giessibl, F.J.2
Mannhart, J.3
Quate, C.F.4
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45
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3142692283
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We thank G. Binnig, M. Herz, and C. Quate for valuable discussions and comments and C. Quate for encouraging us to perform experiments on graphite. Supported by the Bundesministerium für Bildung und Forschung (project no. 13N6918).
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