Scanning probe microscopy makes it possible to image and spectroscopically characterize nanoscale objects, and to manipulate1,2,3 and excite4,5,6,7,8 them; even time-resolved experiments are now routinely achieved9,10. This combination of capabilities has enabled proof-of-principle demonstrations of nanoscale devices, including logic operations based on molecular cascades11, a single-atom transistor12, a single-atom magnetic memory cell13 and a kilobyte atomic memory14. However, a key challenge is fabricating device structures that can overcome their attraction to the underlying surface and thus protrude from the two-dimensional flatlands of the surface. Here we demonstrate the fabrication of such a structure: we use the tip of a scanning probe microscope to lift a large planar aromatic molecule (3,4,9,10-perylenetetracarboxylic-dianhydride) into an upright, standing geometry on a pedestal of two metal (silver) adatoms. This atypical and surprisingly stable upright orientation of the single molecule, which under all known circumstances adsorbs flat on metals15,16, enables the system to function as a coherent single-electron field emitter. We anticipate that other metastable adsorbate configurations might also be accessible, thereby opening up the third dimension for the design of functional nanostructures on surfaces.
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We thank L. Kronik and S. Sarkar (Weizmann Institute of Science) and M. Rohlfing (Universität Münster) for performing DFT calculations of standing molecules (not reported here).
Nature thanks T. Greber, A. Heinrich and the other anonymous reviewer(s) for their contribution to the peer review of this work.
The authors declare no competing interests.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
a, Constant-current STM image of an NTCDA (1,4,5,8-naphthalenetetracarboxylic-dianhydride) molecule and two silver adatoms, recorded before the assembly of a NTCDA + 2Ag complex. b, AFM image of a standing NTCDA molecule, recorded at a tip height of z = 13.5 Å above the surface. c, Schematic side view of standing PTCDA and NTCDA molecules. The length difference of 4.2 Å between the two molecules corresponds well with the tip-height difference Δz = 17.5 Å − 13.5 Å = 4.0 Å between the AFM images of the standing PTCDA (see Fig. 1f) and NTCDA (b) molecules.
a, Constant-current STM image of two PTCDA + 2Ag complexes that were assembled in the same way as shown in Fig. 1b. b, AFM image of the standing molecules, recorded at tip height of z = 17.5 Å above the surface (left). One of the standing molecules is then moved closer to the other by the lateral manipulation procedure demonstrated in Extended Data Fig. 3a (right).
a, Lateral movement of the standing molecule by tip approach. The white cross in the AFM image on the left indicates the tip position during manipulation (V = 2 mV). b, Rotational movement of the standing molecule by a current pulse. The white cross in the AFM image on the left indicates the tip position during manipulation (z = 17.5 Å). The molecule jumps from a red (symmetric) to a black (asymmetric) position (see Methods). c, Toppling over the standing molecule to the surface by using a positive bias-voltage sweep. The white cross in the AFM image on the left indicates the tip position during manipulation (z = 17.5 Å). The constant-current STM image on the right shows the PTCDA + 2Ag complex after the toppling.
a, Approach along the y direction as defined in Fig. 2a, b. Parameters are d = 3.25 Å, l = 12.9 Å and 2a = 4.55 Å; d + l ≠ z, because the tip height z is measured from the centre of the uppermost surface layer, whereas l is measured from the centre of the two silver adatoms in the PTCDA + 2Ag complex. b, Approach along the x direction as defined in Fig. 2a, b. The sketch on the left shows a side view, whereas on the right a perspective view onto the top of the molecule is drawn. c, Left, best fit (green line) of the experimental F x (on x axis, red circles), obtained with the model in equation (8) and κ θ = 630 zN m rad−1 (κ = 0.38 N m−1). Black data points display F y (on y axis), fitted with equation (4) (blue line). d, As in c, but for a simulated curve (green) with κ θ = 20.0 aN m rad−1 (κ = 12.02 N m−1), which is too stiff to reproduce the experimental F x (red). e, As in c, but for a simulated curve (green) with κ θ = 310 zN m rad−1 (κ = 0.19 N m−1), which is too soft. For a detailed discussion of this figure, see Methods. Tilt angles θeq and linear elongations xm are plotted in the middle and right panels in c–e.
The histogram (left) shows all evaluated orientations of standing PTCDA molecules on the Ag(111) surface. The angle is defined as in Fig. 2d and Extended Data Fig. 3b. In total, we evaluated the orientations of 128 standing PTCDA molecules. The possible orientations on the Ag(111) surface are illustrated on the right. Black and red symbols indicate the possible positions of one of the silver atoms at the surface contact, when the other sits in the centre. See also Fig. 2d and Methods.
Constant-current STM image of the atomically resolved Ag(111) surface. In all experiments, the Ag(111) lattice orientation was as shown in this image.
a–c, Successive field-emission images (without the background) recorded at z = 73.5 Å and bias voltages of V = −24.00 V (a), V = −24.35 V (b) and V = −24.70 V (c).
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Esat, T., Friedrich, N., Tautz, F.S. et al. A standing molecule as a single-electron field emitter. Nature 558, 573–576 (2018). https://doi.org/10.1038/s41586-018-0223-y
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