Paper by: Leo Gross, Fabian Paper by: Leo Gross, Fabian MohnMohn, , NikolajNikolaj Moll, Moll, Peter Peter LiljerothLiljeroth, Gerhard Meyer, Gerhard Meyerjj yy
Presented by : Florencia Paredes
Soah LeeTim Burke
M ti ti Motivation Background Scanning Tunneling Microscopy (STM)Scanning Tunneling Microscopy (STM) Atomic Force Microscopy (AFM)
IntroductionCh ll Challenges Why is it difficult to get atomic resolution?
ResultsResults Images and force fields obtained Comparison with ab initio calculations C l i /F W k Conclusions/Future Work
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l l f f Ultimate goal of surface microscopy??
D t i i i di id l t i fi ti !! Determining individual atomic configurations!!
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(Image adapted from original by the National Institute for Materials Science)
STMSTM
Fine probe tip scanning Measures density of states on
sample near Fermi Surface Conductive tip and samplep p
High vacuum with very clean surfaceclean surface
Can damage sample
4(Image courtesy of Institut für Angewandte Physik)
AFMAFM
Fine probe tip scanning Measures force interaction Can be performed
on insulatorson insulators
Ambient conditions(possible)(possible)
Noncontact scanning (possible)
5(Image courtesy of Angewandte Physik)
Imaging of single atomson molecules
With AFM using CO tip
Image complete chemical structure of an individual molecule with atomic resolutionresolution
Noncontact Atomic Force Microscopy (NC‐AFM)Microscopy (NC AFM)
6(Image courtesy of IBM Research, Zurich)
High contrast STMSTM
Tip Geometry Atomic composition Atomic composition Stability
Forces measured Neglect long range forces
▪ van derWaals
AFMAFM
▪ van derWaals▪ Electrostatic
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(A) Ball‐and‐stick model of the pentacene molecule(B) Constant‐current STM image of pentacene(C &D) Constant‐height AFM images of pentacene
acquired with a CO‐modified tip8
Constant‐height AFM images of pentacene on NaCl(2ML)/Cu(111) Constant height AFM images of pentacene on NaCl(2ML)/Cu(111) using different tip modifications
Cu NaCl/CuCu NaCl/Cu
(A) Ag, (B) CO, (C) Cl, and (D) pentacene
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“M f d f hift Δf (A) d t t d “Maps of measured frequency shift Δf (A) and extracted vertical force FZ (B) at different tip heights z. Corresponding line profiles of Δf (C) and FZ (D) along the long molecular axis.” 10
Calculated
Measured
“Calculated energy map (A) for a CO‐pentacene distance of d = 4 5 Å Calculated line profiles of Calculated energy map (A) for a CO pentacene distance of d 4.5 Å. Calculated line profiles of the energy (B), the vertical force (C), and Δf (D) above the long molecular axis for different molecular distances. (E and F) force‐distance curves above different molecular sites. The inset in (E) shows a measured Δf map with the different molecular sites indicated.” 11
EXPERIMENTAL DATAEXPERIMENTAL DATA CALCULATIONSCALCULATIONS
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l l l Atomic resolution in NC‐AFM imaging on molecules requires entering repulsive force regime
Precise information about the probe tip is necessary for interpreting the force measurementsp g
With a CO tip, it was possible to achieve single atom resolution for an entire molecule on both conducting and insulating substrates
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Optimize tip molecule for range of target samples Optimize tip molecule for range of target samples
Use technique to calculate quantitative molecular parametersparameters
Characterize stability issues for easier future applicationapplication
Extend to ambient conditions
Use to investigate single‐electron transport and charge distributions in metal‐molecule systems on the atomic scalescale
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G L M h F M ll N Lilj th P & M G ( ) Th h i l Gross, L., Mohn, F., Moll, N., Liljeroth, P., & Meyer, G. (2009). The chemical structure of a molecule resolved by atomic force microscopy. Science (New York, N.Y.), 325(5944), 1110‐4. doi:10.1126/science.1176210
Sader, J. E., & Jarvis, S. P. (2004). Accurate formulas for interaction force and energy in frequency modulation force spectroscopy. Applied Physics Letters, 84(10), 1801. doi:10.1063/1.1667267
Giessibl, F. J. (2003). Advances in atomic force microscopy. Reviews of Modern Physics, 75(3), 949‐983. doi:10.1103/RevModPhys.75.949
Unattributed pictures and quotes are from the first listed reference.
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