Imaging and manipulating molecular orbitals

Ima gi ng a nd m an ip ul at in g m ol ec ul ar o rb it al s

AtMol International Workshop 2012 September 24-25 Berlin Germany

2012 AtMol International Workshop 2012, September 24-25 Berlin-Germany

[IMAGING AND MANIPULATING MOLECULAR ORBITALS]

Index

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Foreword

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Scientific Program

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Abstracts

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Abstracts Index (Invited Speakers)

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Abstracts Index (Oral Contributions)

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Abstracts Index (Alphabetical Order)

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Imaging and manipulating molecular orbitals AtMol International Workshop 2012 Berlin-Germany September 24-25

Real space imaging of the electronic cloud of a single atom or molecule is now of prime importance in the field of quantum information transmission, manipulation and storage and in the field of single molecule mechanics. One can also be simply interested by the intramolecular electronic and magnetic phenomena inside a single molecule.

This workshop will bring together groups from all around the world which are working on the theory or the experimental recording of the electronic cloud of a single atom or molecule and when possible its description and detail experimental capture on the basis of the molecular orbitals concept. Manipulation techniques to change the spatial distribution or quantum properties of those by interacting with this single molecule will also be discussed.

It will be the occasion to celebrate the first recording of the image of a single molecule by E. Muller 60 years ago.

Sponsors This workshop is open for contributors in the fields of single atom and molecule atomic and molecular orbitals imaging using for example the FEM, TEM, PE, Attosecond Tomography, NC-AFM or LT-UHV-STM instruments.

Experimental demonstrations of a technical way to manipulate reproductively single orbitals on a single molecule are also welcome. Contributors to the field of image calculations and interpretations for all the above mentions microscopy or techniques are also invited to contribute.

Organisers: • • • • •

Christian Joachim (CEMES-CNRS, France) Leonhard Grill (Fritz Haber Institute - Max Planck Gesellschaft, Germany) Antonio Correia (Phantoms Foundation, Spain) Marie Hervé (CEMES/CNRS, France) Philip Moriarty (University Nottingham, UK)

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[SCIENTIFIC PROGRAM]

Scientific Program Monday September 24, 2012

08:50-09:00

09:00-09:40

09:40-10:20 10:20-10:50

10:50-11:30

11:30-12:10

12:10-12:30 12:30 -14:00

14:00-14:40

14:40-15:00

Imaging and manipulating molecular orbitals Opening (Christian Joachim and Leonhard Grill) FEM Moh'd Rezeq (Khalifa University, UAE) "62 years after the first observation of individual molecules with the field emission microscope and p. 49 prospective improvements for a single molecule microscopy" Carlos Manzano (IMRE, Singapore) "High voltage STM imaging of single Copper p. 35 Phthalocyanine" Coffee Break STEM Masanori Koshino (AIST, Japan) "Atomic level imaging and spectroscopy of nano materials" Photo-emission (PE) Mike G. Ramsey (University of Graz, Austria) "Valence band tomography and the reconstruction of molecular orbitals from angle resolved photoemission" Benoit Mignolet (UniversitÊ de Liège, Belgium) "Theoretical study of the superatom molecular orbitals of C60-C70"

p. 31

p. 45

p. 37

Lunch break LT-UHV-STM Christophe Nacci (FHI-MPG, Germany) "Manipulation and spectroscopy of individual phthalocyanine molecules on InAs ( 111)A with a low-temperature scanning tunnelling microscope" Matthias Koch (Fritz-Haber Institut, Germany) "Electronic structure of single graphene nanoribbons determined by scanning tunnelling microscopy and spectroscopy"

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p. 19

p. 29

9

15:00-15:20

Robin Ohmann (Technische Universität Dresden, Germany) "Imaging and manipulation of molecular orbitals on metal surfaces with scanning tunneling microscopy"

p. 41

Coffee Break

15:20-15:50

STM Theory and image interpretation 15:50-16:30

16:30-17:10

17:10-17:50

17:50-18:30

Mikaël Képénékian (CIN2, Spain) "Simulations of constant current images of openshell systems" Mathilde Portais (CNRS-CEMES, France) "Multi-configuration electronic Scattering matrix calculations for electron tunneling through a metal-molecule-metal junction" Martin Verot (ENS-Lyon, France) "Transport through a molecular tunnel junction: Some Insights From a Multiconfigurational Point of View" Massimo Rontani (Università di Modena e Reggio Emilia , Italy) "Alteration of scanning-tunnelling-spectroscopy images of molecular orbitals as a probe of electron correlation"

Invited Speakers (40 min. including discussion time) Oral (20 min. including discussion time)

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AtMol International Workshop 2012, Berlin-Germany

p. 27

p. 43

p. 57

p. 51

Scientific Program Tuesday September 25, 2012

Imaging and manipulating molecular orbitals LT-UHV-STM 09:00-09:40

We Hyo Soe (IMRE, Singapore) "Mapping the electronic resonances of single molecule STM tunnel junction"

p. 55

09:40-10:20

Cornelius Krull (ICN, Spain) "Characterizing chiral, electronic and magnetic properties of molecular adsorbates by Scanning Tunneling Microscopy"

p. 33

10:20-10:50

Coffee Break LT-UHV-STM

10:50-11:30

Olivier Guillermet (CNRS-CEMES, France) "STM characterization of molecular states on thin insulating films"

p. 25

11:30-12:10

Szymon Godlewski (Jagiellonian University, Poland) "Molecular orbital imaging and spectroscopy on hydrogen passivated semiconductors"

p. 21

12:10-13:30

13:30-14:10

14:10-14:50

14:50-15:20

Lunch break Attosecond Tomography Pascal Salières (IRAMIS CEA, France) "Imaging orbitals with attosecond and Angström resolutions" Françoise Remacle (Université de Liège, Belgium) "Attosecond electron dynamics in molecular systems: probing of electron density and molecular orbitals by sudden photoionization"

p. 53

p. 47

Coffee Break

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NC-AFM 15:20-16:00

16:00-16:40

16:40

Philip Moriarty (University of Nottingham, UK) "Combining orbital imaging with atomic resolution for tip-adsorbed molecules" Leo Gross (IBM Zurich, Switzerland) "Molecules investigated with atomic resolution using scanning probe microscopy with functionalized tips" Conclusions and Coffee Break

Invited Speakers (40 min. including discussion time) Oral (20 min. including discussion time)

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p. 23

[ABSTRACTS]

Abstracts (Invited Speakers)

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Szymon Godlewski (Jagiellonian University, Poland) "Molecular orbital imaging and spectroscopy on hydrogen passivated semiconductors"

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Leo Gross (IBM Zurich, Switzerland) "Molecules investigated with atomic resolution using scanning probe microscopy with functionalized tips"

23

Olivier Guillermet (CNRS-CEMES, France) "STM characterization of molecular states on thin insulating films"

25

Mikaël Képénékian (CIN2, Spain) "Simulations of constant current images of open-shell systems"

27

Masanori Koshino (AIST, Japan) "Atomic level imaging and spectroscopy of nano materials"

31

Cornelius Krull (ICN, Spain) "Characterizing chiral, electronic and magnetic properties of molecular adsorbates by Scanning Tunneling Microscopy"

33

Carlos Manzano (IMRE, Singapore) "High voltage STM imaging of single Copper Phthalocyanine"

35

Philip Moriarty (University of Nottingham, UK) "Combining orbital imaging with atomic resolution for tipadsorbed molecules"

39

Mathilde Portais (CNRS-CEMES, France) "Multi-configuration electronic Scattering matrix calculations for electron tunneling through a metalmolecule-metal junction"

43

Mike G. Ramsey (University of Graz, Austria) "Valence band tomography and the reconstruction of molecular orbitals from angle resolved photoemission"

45

Françoise Remacle (Université de Liège, Belgium) "Attosecond electron dynamics in molecular systems: probing of electron density and molecular orbitals by sudden photoionization"

47

Moh'd Rezeq (Khalifa University, UAE) "62 years after the first observation of individual molecules with the field emission microscope and prospective improvements for a single molecule microscopy"

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Massimo Rontani (Università di Modena e Reggio Emilia , Italy) "Alteration of scanning-tunnelling-spectroscopy images of molecular orbitals as a probe of electron correlation"

51

Pascal Salières (IRAMIS CEA, France) "Imaging orbitals with attosecond and Angström resolutions"

53

We Hyo Soe (IMRE, Singapore) "Mapping the electronic resonances of single molecule STM tunnel junction"

55

Martin Verot (ENS-Lyon, France) "Transport through a molecular tunnel junction: Some Insights From a Multiconfigurational Point of View"

Abstracts (Oral Contributions)

57

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Matthias Koch (Fritz-Haber Institut, Germany) "Electronic structure of single graphene nanoribbons determined by scanning tunnelling microscopy and spectroscopy"

29

Benoit Mignolet (Université de Liège, Belgium) "Theoretical study of the superatom molecular orbitals of C60-C70"

37

Christophe Nacci (FHI-MPG, Germany) "Manipulation and spectroscopy of individual phthalocyanine molecules on InAs ( 111)A with a lowtemperature scanning tunnelling microscope"

Robin Ohmann (Technische Universität Dresden, Germany) "Imaging and manipulation of molecular orbitals on metal surfaces with scanning tunneling microscopy"

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Abstracts (Alphabetical Order)

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Szymon Godlewski (Jagiellonian University, Poland) "Molecular orbital imaging and spectroscopy on hydrogen passivated semiconductors"

21

Leo Gross (IBM Zurich, Switzerland) "Molecules investigated with atomic resolution using scanning probe microscopy with functionalized tips"

23

Olivier Guillermet (CNRS-CEMES, France) "STM characterization of molecular states on thin insulating films"

25

Mikaël Képénékian (CIN2, Spain) "Simulations of constant current images of open-shell systems"

27

Matthias Koch (Fritz-Haber Institut, Germany) "Electronic structure of single graphene nanoribbons determined by scanning tunnelling microscopy and spectroscopy"

29

Masanori Koshino (AIST, Japan) "Atomic level imaging and spectroscopy of nano materials"

31

Cornelius Krull (ICN, Spain) "Characterizing chiral, electronic and magnetic properties of molecular adsorbates by Scanning Tunneling Microscopy"

33

Carlos Manzano (IMRE, Singapore) "High voltage STM imaging of single Copper Phthalocyanine"

35

Benoit Mignolet (Université de Liège, Belgium) "Theoretical study of the superatom molecular orbitals of C60-C70"

37

Philip Moriarty (University of Nottingham, UK) "Combining orbital imaging with atomic resolution for tip-adsorbed molecules"

39

Christophe Nacci (FHI-MPG, Germany) "Manipulation and spectroscopy of individual phthalocyanine molecules on InAs ( 111)A with a lowtemperature scanning tunnelling microscope"

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Robin Ohmann (Technische Universität Dresden, Germany) "Imaging and manipulation of molecular orbitals on metal surfaces with scanning tunneling microscopy"

41

Mathilde Portais (CNRS-CEMES, France) "Multi-configuration electronic Scattering matrix calculations for electron tunneling through a metalmolecule-metal junction"

43

Mike G. Ramsey (University of Graz, Austria) "Valence band tomography and the reconstruction of molecular orbitals from angle resolved photoemission"

45

Françoise Remacle (Université de Liège, Belgium) "Attosecond electron dynamics in molecular systems: probing of electron density and molecular orbitals by sudden photoionization"

47

Moh'd Rezeq (Khalifa University, UAE) "62 years after the first observation of individual molecules with the field emission microscope and prospective improvements for a single molecule microscopy"

49

Massimo Rontani (Università di Modena e Reggio Emilia , Italy) "Alteration of scanning-tunnelling-spectroscopy images of molecular orbitals as a probe of electron correlation"

51

Pascal Salières (IRAMIS CEA, France) "Imaging orbitals with attosecond and Angström resolutions"

53

We Hyo Soe (IMRE, Singapore) "Mapping the electronic resonances of single molecule STM tunnel junction"

55

Martin Verot (ENS-Lyon, France) "Transport through a molecular tunnel junction: Some Insights From a Multiconfigurational Point of View"

57

AtMol International Workshop 2012, Berlin-Germany

Manipulation and spectroscopy of individual phthalocyanine molecules on InAs(111)A with a low-temperature scanning tunneling microscope

Ch. Nacci1,*, S. C. Erwin2, K. Kanisawa3 and S. Fölsch1 1

Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany 2 Center for Computational Materials Science, Naval Research Laboratory, Washington, D.C. 20375, United States 3 NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0198, Japan * Present address: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany

Phthalocyanine is a promising class of organic molecules to explore new functionality concepts within a molecule-semiconductor hybrid scheme. We report on single free-base phthalocyanine (H2Pc) molecules on the weakly binding III-V semiconductor surface InAs(111)A studied by low-temperature scanning tunneling microscopy (STM) at 5 K. InAs(111)A is an In-terminated surface characterized by completely saturated surface dangling bonds due to its intrinsic (2 × 2) In vacancy reconstruction [1]. H2Pc adopts a planar adsorption geometry on InAs(111)A with the molecular center located at the In vacancy site. When probed by the STM tip, the discrete molecule performs in-plane rotational jumps between three equivalent in-plane orientations excited by inelastic electron tunneling (IET) [2]. STM-based molecule and atom manipulation techniques at low temperature [2,3] have been applied to quench the rotation and stabilize H2Pc at the surface using native individual In adatoms (Inad). This allows us to explore the intrinsic molecular switching behavior given by the tautomerization switching of the two inner hydrogen atoms. STM imaging of the Inad-H2Pc-Inad complex reveals the presence of a left-handed and a right-handed conformer, suggesting that the adatominduced single-molecule pinning leaves the tautomerization reaction unperturbed, and that it can be excited by IET. Density functional theory calculations reveal these experimental observations and show that the energetics of the switching process remains largely unaffected by both the surface and the stabilizing atoms [2].

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The IET-induced in-plane rotation observed for discrete H2Pc proves to be a generic property of phthalocyanines on InAs(111)A and was observed also for metal phthalocyanines (MPc, M: Cu, Sn) [4]. Finally, STM imaging of largely unperturbed frontier molecular orbitals of naphthalocyanine (NPc) molecules on InAs(111)A indicates that the molecule is in a physisorbed state. The molecular electronic structure of NPc is preserved to a large extent, indicating a weak electronic coupling to the semiconductor template [5].

This research was supported by the Deutsche Forschungsgemeinschaft (SFB658).

References: [1] [2] [3] [4] [5]

A. Taguchi, K. Kanisawa, Appl. Surf. Sci. 252, 526 (2006) Ch. Nacci, S. C. Erwin, K. Kanisawa, S. Fölsch, ACS Nano 6, 4190 (2012) S. Fölsch , J. Yang, Ch. Nacci, K. Kanisawa, Phys. Rev. Lett. 103, 096104 (2009) C. Nacci, K. Kanisawa, S. Fölsch, J. Phys.: Condens. Matter 24, 354008 (2012) G. Münnich, F. Albrecht, C. Nacci, D. Schuh, K. Kanisawa, S. Fölsch, J. Repp, J. Appl. Phys. 112, 034312 (2012)

20 AtMol International Workshop 2012, Berlin-Germany

Molecular orbital imaging and spectroscopy on hydrogen passivated semiconductors

Szymon Godlewski1, Marek Kolmer1, Bartosz Such1, Hiroyo Kawai2, Mark Saeys2,3, Paul McGonigal4, Paula de Mendoza4, Claudia De Le贸n4, Antonio M. Echavarren4 and Marek Szymonski1 1

Department of Physics of Nanostructures and Nanotechnology, Institute of Physics, Jagiellonian University, Reymonta 4, PL 30-059, Krakow, Poland 2 Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602, Singapore 3 Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117576, Singapore 4 Institute of Chemical Research of Catalonia (ICIQ), Avenida Pa茂sos Catalans 16, 43007 Tarragona, Spain

In order to facilitate molecular orbital imaging and spectroscopy based on the state-of-the-art use of modern nanotechnology tools, such as STM and NCAFM, electronic decoupling of the molecule in question from the underlying substrate is required. It is expected that proper isolation of such molecular entities could be achieved by application of passivated semiconductor surfaces, e.g., Si(001):H and Ge(001):H. Following the first experiments with pentacene molecules on the Si(001):H surface we performed measurements of trinaphthylene molecules (Y molecules) on the hydrogenated Ge(001):H substrate with the application of tuning fork based sensors. They facilitate simultaneous STM and NC-AFM measurements and thus molecular orbitals could be probed by both tunneling current and atomic forces concurrently. In the presentation we will discuss also the role of surface dangling bonds (DBs) on the adsorption, immobilization and imaging of the molecules.

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Molecules investigated with atomic resolution using scanning probe microscopy with functionalized tips

L. Gross, F. Mohn, N. Moll and G. Meyer IBM Research - Zurich, 8803 R端schlikon, Switzerland lgr@zurich.ibm.com

Single organic molecules adsorbed on ultrathin insulating films were investigated using scanning tunnelling microscopy (STM), noncontact atomic force microscopy (NC-AFM), and Kelvin probe force microscopy (KPFM). With all of these techniques submolecular resolution was obtained due to tip functionalization by atomic manipulation. The techniques yield complementary information regarding the molecular structural and electronic properties.

Using NC-AFM with CO terminated tips, atomic resolution on molecules has been demonstrated and the contrast mechanism was assigned to the Pauli repulsion [1]. On the other hand, by using STM the molecular frontier orbitals, i.e., the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO), were mapped [2]. Using a CO terminated tip for orbital imaging with the STM, the resolution can be increased and the images correspond to the gradient of the molecular orbitals due to the p-wave character of the tip states [3]. Finally, KPFM reveals information about the distribution of charges within molecules by measuring the z-component of the electrostatic field above the molecule, as demonstrated on the hydrogen tautomerization switch naphthalocyanine [4].

The possibilities of extracting additional information from AFM measurements on molecules, especially concerning intramolecular bonds, e.g. bond order and bond length, will be discussed.

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References: [1] [2] [3] [4]

L. Gross et al. Science 325, 1110 (2009) J. Repp et al. Phys. Rev. Lett. 94, 026803 (2005) L. Gross et al. Phys. Rev. Lett. 107, 086101 (2011) F. Mohn et al. Nature Nanotechnol. 7, 227 (2012)

Figures:

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AtMol International Workshop 2012, Berlin-Germany

STM characterization of molecular states on thin insulating films

Olivier Guillermet GNS-CEMES-CNRS 29 rue Jeanne Marvig, BP 94347 31055 Toulouse Cedex 4, France

In 2005, J. Repp and al. [1] reported the use of a NaCl thin insulating layer to decouple molecular states from the substrate. In this case, the STM images greatly vary with the applied bias voltage and show great similarity with the calculations of the frontier orbitals of the free molecule. The capacity of a thin NaCl layer to decouple molecules from the substrate was confirmed in our laboratory for some terrylene derivatives, indigo and starphene molecules.

The indigo dye molecule presents two tautomeric forms which only differ in the position of one hydrogen atom. By using a thin insulating layer, it has been possible to evaluate the change in the electronic states associated with the propotropy process. When this molecule was deposited on a thin NaCl layer, we show that an electrostatic field is locally induced by the NaCl. This electrostatic field is able to shift the electronics states of the molecule and different states are observed for the same bias voltage. A monolayer of indigo was consequently used to obtain reproducible pictures before and after the prototropy process.

For starphene molecule, we could clearly associate electronics states with the calculated HOMO and LUMO of the free molecule [2]. In the case of the LUMO state, a functionalized tip allowed us to reveal nodal planes inaccessible to a clean metal tip.

In addition, localized applications of current pulses allowed us to identify inelastic processes associated with the energy of unoccupied states. This ability gives us a perfect, but limited, control on the molecular position and will be discussed.

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References: [1] [2]

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J. Repp et al. Phys. Rev. Lett. 94, 026803 (2005) O. Guillermet et al. Chem. Phys. Lett. 511, 482 (2011)

AtMol International Workshop 2012, Berlin-Germany

Simulations of constant current images of open-shell systems

Mikaël Kepenekian1, Richard Korytár1,2, Roberto Robles1 and Nicolás Lorente1 1

CIN2, Consejo Superior de Investigaciones Científicas, 08193 Bellaterra, Spain 2 Karlsruhe Institut of Technology, Karlsruhe, Germany

Open-shell systems are challenging objects. For scanning tunneling microscopy (STM) imaging, matters become complex when the open-shell structure involves a multiconfigurational electronic structure. In this contribution, we will show results on STM imaging simulations of a copper phthalocyanine (CuPc) on a Ag (100) substrate, as motivated by the experiments of Mugarza et al. [1]. CuPc is an open-shell molecule with a magnetic moment of S=½. It is thus a rather simple molecule. However, when adsorbed an extra electron is captured giving rise to a S=1 ground state configuration which is then openshell and multiconfigurational. This leads to exotic behavior such as Kondo correlations.

We first study the system using typical theoretical tools such as density functional theory (DFT) and different levels of transport calculations. We compare the simple approach by Tersoff and Hamman [2] with the more involved of Landauer [3]. However, present forms of DFT imply a mean-field approach that erases the multiconfigurational study. For this we have developed a non-crossing approximation (NCA) approach [4] based on the Baym-Kadanoff formalism in the limit where we keep the full multiconfigurational Hilbert space but we reduced the Fock space to infinite correlation.

We find that while Tersoff-Hamman gives a good qualitative picture, DFTbased methods fail in reproducing the experimental conductance behavior and only NCA can give an account of the Kondo phenomena.

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References: [1] [2] [3] [4]

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A. Mugarza, C. Krull, R. Robles, S. Stepanow, G. Ceballos, P. Gambardella, Nature Comm. 2, 490 (2011).

J. Tersoff, D. R. Hamann, Phys. Rev. B 31, 805 (1985).

M. Brandbyge, J.-L. Mozos, P. Ordej贸n, J. Taylor, K. Stokbro, Phys. Rev. B 65, 165401 (2002).

R. Koryt谩r, N. Lorente, J. Phys.: Condens. Matter 23, 355009 (2011).

AtMol International Workshop 2012, Berlin-Germany

Electronic structure of single graphene nanoribbons determined by scanning tunnelling microscopy and spectroscopy

Matthias Koch¹, Francisco Ample³, Christian Joachim², and Leonhard Grill¹ 1

Fritz-Haber Institut Berlin Nanosciences Group, CEMES-CNRS, Toulouse, France 3 Institute of Materials Research and Engineering (IMRE), Singapore Koch@fhi-berlin.mpg.de 2

Due to the high carrier mobility graphene nanoribbons (GNR) are promising candidates for molecular wires in future nanotechnology. The electronic properties of a GNR are controlled by its edge-structure and width [1].

Bottom-up approaches like on-surface synthesis allow the formation of extended conjugated electronic systems [2]. Moreover, they lead to atomically defined edges which are required for charge transport studies as structural defects have been predicted to modify the electronic structure and to reduce the conductance. We have used low temperature scanning tunneling microscopy (STM) to investigate the formation, adsorption properties and electronic structure of graphene nanoribbons. 10,10'-Dibromo-9,9'-bianthryl molecules were used as molecular building blocks to form GNR’s after linking of the monomers and subsequent cyclodehydrogenation [3]. In addition to intact ribbons, the influence of various defects on the electronic states is also investigated.

References: [1] [2] [3]

Louie et al., Phys. Rev. Lett. 99, 186801 (2007) L. Grill et al., Nature Nanotech., 2 (2007) 687 J. Cai et al, Nature, 466 (2009) 470

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Atomic level imaging and spectroscopy of nano materials

Masanori Koshino Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565 Japan m-kosihno@aist.go.jp

High-resolution transmission electron microscopy (HRTEM) plays an important role to characterize atomic structures of carbon-based materials. Recently, it has been demonstrated that the motional behaviors of single molecules can be characterized by HRTEM [1, 2]. The bimolecular reactions of fullerene and metallo fullerene molecules in carbon nanotube were studied by TEM, proving that the atomic resolution imaging of chemical reaction is indeed possible with moderate experimental conditions [3]. More recent advances is found in scanning transmission electron microscopy combined with electron energyloss spectroscopy (STEM-EELS) on the basis of single atomic imaging and spectroscopy, unveiling intrinsic electronic states of edge atoms in graphene [4] and modulated electronic states of nitrogen atom adjacent to a boron vacancy in hexagonal boron nitride (h-BN) [5]. Although it has been believed impossible, we have provided enough evidences of ultimate single atomic analysis. The topic may cover some of the advantages in the instrumentations: small and bright electron probe and less damage system, attained by newly developed aberration correctors operated at low voltage (30 - 60 eV).

A part of the study is supported by Kakenhi from MEXT (23681026 and 22000008), JST-Kenkyu Kasoku, and JST-S-innovation.

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References: [1] [2] [3] [4] [5]

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[1] Koshino M. et al. Science 316, 853 (2007).

[2] Koshino, M., et al. Nat. Nano. 3, 595 (2008).

[3] Koshino, M., et al. Nat. Chem. 2, 117 (2010).

[4] Suenaga, K., & Koshino, M., Nature, 468, 1088–1090 (2010).

[5] Suenaga, K., et al., M. Phys. Rev. Lett., 108, 075501 (2012).

AtMol International Workshop 2012, Berlin-Germany

Characterizing chiral, electronic and magnetic properties of molecular adsorbates by Scanning Tunneling Microscopy

C. Krull, A. Mugarza, R. Robles and P. Gambardella Institut CatalĂ de Nanotecnologia (ICN) UAB Campus, Facultat de Ciencies Edifici CM7 E-08193 Bellaterra (Barcelona), Spain cornelius.krull@icn.cat

Scanning Tunneling Microscopy (STM) /Spectroscopy (STS) is a versatile tool to investigate the electronic structure of molecular adsorbates on (semi)conducting substrates. Particularly its local probe approach allows correlation between molecular states and their spatial distributions and symmetries. At low energies, transport through molecules is often determined by many-body phenomena such as the Kondo effect, and inelastic channels where the electron charge appears coupled to the vibrational and magnetic degrees of freedom of the molecule.

We use STS to study the charge and spin configuration of copper and nickel phthalocyanines (Cu, NiPc) deposited on Ag(100). Based on spatial distributions and DFT calculations we are able to assign spectroscopic resonances to molecular orbitals (MO) of the organic ligand or the central ion of the molecules. We discuss possible origins for the differences observed between constant current dI/dV maps and calculated charge densities of MO. Further we characterize the changes induced in the molecular electronic structure by the interaction with the substrate. They manifest in (i) a chiral intensity distribution of only some of the frontier MO [1] and (ii) an additional spin originated from the charge transfer of one electron to the molecule, showing a Kondo interaction. From the spatial distribution of the Kondo resonance we can pinpoint the singly occupied MO where the induced spin is localized [2,3]. In the case of CuPc, the interaction between the molecular and metallic spins results in a Kondo effect that couples to vibrational and magnetic excitations inside the molecule with pronounced intramolecular variations of the conductance and spin dynamics [2,3]. Finally, we explore AtMol International Workshop 2012, Berlin-Germany

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different methods to manipulate the charge and spin states of the molecules, such as controlling intermolecular bonds in artificially fabricated molecular clusters (see Fig. 1).

References: [1] [2] [3]

A. Mugarza, C. Krull, et al., Phys. Rev. Lett. 105, 115702 (2010).

A. Mugarza, R. Robles, C. Krull et al., Phys. Rev. B 85, 155437 (2012).

A. Mugarza , C. Krull et al., Nat. Comm. 2:490 (2011).

Figures:

Figure 1: Tuning the charge and spin state with intermolecular interactions. (a) Topography of a 3x3 cluster of CuPc on the Ag(100) surface. (b-d) Spectroscopic (dI/dV) maps of the lowest unoccupied molecular orbital (LUMO). Its energy in each molecule depends on the number of intermolecular bonds (e) Spectroscopic map of the Kondo resonance, which reveals the spin that interacts with electrons from the metallic surface. The presence/absence of the resonance can be correlated with the behavior of the LUMO.

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High voltage STM imaging of single Copper Phthalocyanine

C Manzano1, W–H Soe1 and C Joachim1, 2 1

IMRE, A*STAR, 3 Research Link, 117602, Singapore 2 GNS-CEMES, CNRS, 29 rue J. Marvig, 31055 Toulouse Cedex, France

Sixty years ago, Erwin Müller used his newly developed electron microscopy technique (the Field Emission Microscopy) to image for the first time and in real space the electronic cloud of a large organic molecule [1]. By using voltages in the range of 10 kilovolts to reach a FEM regime, E. Müller observed and “photograph” single Cu-Phthalocyanine (CuPc) molecules previously deposited on the emitting tungsten tip. From this period of time, CuPc became a molecule of choice for new microscopy techniques. For example, CuPc was used to test the capabilities to image the electronic cloud of organic molecules in real space with the Transmission Electron Microscope (TEM) which is another microscopy technique using electrons accelerated via a high voltage potential.

In our days, the possibility of imaging molecules in real space is not restricted to the use of highly accelerated ballistic electrons. With the Scanning Tunneling Microscope (STM) and with a tunneling junction bias voltages of a few volts (± 3 V), tunneling electrons give access to a map of molecule electronic states near the substrate’s Fermi level [2,3], of molecules weakly coupled i.e. physisorbed on a metal surface.

Herein, we have used a low temperature STM to image single CuPc molecules deposited on Au(111) with a junction bias voltage larger than the normally used voltage window. Bias voltages up to 10.0 V were used. In this STM field emission regime [4], our interpretation of the process enabling the visualization of electronic cloud of a single CuPc molecule under these conditions will be presented.

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References: [1] [2] [3] [4]

36

Melmed A. J. and Muller E. W. 1958 J. Chem. Phys. 29 1037-1041.

Jascha Repp, Gerhard Meyer, Sladjana M. Stojković, André Gourdon, and Christian Joachim, Phys. Rev. Lett. 94, 026803 (2005).

W.-H. Soe, C. Manzano, A. De Sarkar, N. Chandrasekhar, and C. Joachim, Phys. Rev. Lett. 102, 176102 (2009).

G. Binnig, K. H. Frank, H. Fuchs, N. Garcia, B. Reihl, H. Rohrer, F. Salvan, and A. R. Williams, Phys. Rev. Lett. 55, 991–994 (1985).

AtMol International Workshop 2012, Berlin-Germany

Theoretical study of the superatom molecular orbitals of C60-C70

Benoit Mignolet1, J. Olof Johansson2, Eleanor E. B. Campbell2 and Françoise Remacle1 1

Département de Chimie, B6c, Université de Liège, B4000 Liège, Belgium 2 EaStCHEM, School of Chemistry, University of Edinburgh, West Mains Road, EH9 3JJ, Scotland bmignolet@ulg.ac.be fremacle@ulg.ac.be

Recent scanning tunneling microscopy study of C60 on metal surface [1] shows the presence of superatom molecular orbitals (SAMOs). The SAMOs are diffuse hydrogen like orbitals bound to the core of the C60 cage.

Photoelectron angular distributions (PADs) of gas-phase C60 and C70 have been obtained by Rydberg fingerprint spectroscopy and angular resolved photoelectron spectroscopy [2]. A rich structure of peaks at low kinetic energies is observed and the angular distributions of these peaks are compared with theoretical PADs. From the Dyson orbital of a large band of 500 excited states of C60 and C70 computed in time dependent density functional theory, we computed the energy dependence of the PADs of the randomly oriented excited states with respect to the electron kinetic energy (fig. 1). The excited states composed of the SAMOs have high ionization probabilities and specific angular distributions that are in good agreement with the experimental results.

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References: [1] [2]

M. Feng, J. Zhao, and H. Petek, Science, 320 (2008) 359.

J. O. Johansson, G. G. Henderson, F. Remacle, and E. E. B. Campbell, Physical Review Letters, 108 (2012) 173401.

Figures:

Figure 1: (a) Dyson orbital of the excited state 287 of C60. (b)-(c) Computed photoelectron angular distribution of the randomly oriented band of excited states close in energy of the exited state 287 for a kinetic energy of 0.1eV (b) and 1.3eV(c).

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AtMol International Workshop 2012, Berlin-Germany

Combining orbital imaging with atomic resolution for tip-adsorbed molecules

Philip Moriarty School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK www.nottingham.ac.uk/physics/research/nano

Tip functionalization via the controlled transfer of an adsorbed species from a substrate has played a central role in recent remarkable advances in submolecular resolution scanning probe microscopy. In a series of pioneering experiments, Gross and coworkers [1,2] have shown that a CO-functionalized dynamic force microscope tip could be used to image the internal atomic structure of organic molecules with unprecedented resolution. Given that the contrast attained in any scanning probe microscope image is critically dependent on the tip state [3], and that single-molecule functionalization of the probe will play an increasingly important role in state-of-the-art scanning probe microscope imaging, the development of strategies to determine molecular orientation with the highest possible resolution *at the tip* is essential.

By exploiting the 'inverse imaging' technique pioneered by Giessibl and coworkers a decade ago [4], I will discuss how it is possible to ascertain the precise orientation (rotation/tilt) of a C60 molecule terminating the tip of a qPlus sensor [5]. A combination of dynamic STM (dSTM) and non-contact atomic force microscopy (NC-AFM) enables images of molecular orbital structure to be correlated with atomic resolution images. We show that not only is simple Huckel molecular orbital theory more than adequate to determine molecular orientation through comparison with experimental dSTM images but that weakly attractive tip-sample interactions are sufficient to provide atomic resolution images of the structure of the tip-adsorbed C60 cage. Thus, in this case, operation within the Pauli exclusion regime of the potential is not a prerequisite for atomic resolution NC-AFM imaging of submolecular structure.

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References: [1] [2] [3] [4] [5]

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L. Gross, F. Mohn, N. Moll, P. Liljeroth, and G. Meyer, Science 325, 1110 (2009).

L. Gross, F. Mohn, N. Moll, G. Meyer, R. Ebel, W. Abdel-Mageed, and M. Jaspars, Nature Chem. 2, 821(2010).

For a recent example, see Joachim Welker and Franz J. Giessibl, Science 336 444 (2012).

F. Giessibl, S. Hembacher, H. Bielefeldt, and J. Mannhart, Science 289, 422 (2000).

"Precise orientation of a single C60 molecule on the tip of a scanning probe microscope", C. Chiutu, A. M. Sweetman, A. J. Lakin, A. Stannard, S. Jarvis, L. Kantorovich, J. L. Dunn, and P. Moriarty, Phys. Rev. Lett., in press (2012).

AtMol International Workshop 2012, Berlin-Germany

Imaging and manipulation of molecular orbitals on metal surfaces with scanning tunneling microscopy

Robin Ohmann1,2, Lucia Vitali1, Klaus Kern1, Anja Nickel2, Jörg Meyer2, Francesca Moresco2and Gianaurelio Cuniberti2 1

Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569, Stuttgart, Germany 2 Institute for Materials Science and Max Bergmann Center of Biomaterials, Technische Universität Dresden, D-01062 Dresden, Germany robin.ohmann@nano.tu-dresden.de

Scanning tunneling microscopy (STM) allows to image molecular orbitals close to the Fermi energy by acquiring conductance maps. Furthermore, the STM can be employed to manipulate such molecular orbitals. Here, several mechanisms for such control for molecules adsorbed on a metal surface are presented. In the first, an additional Cu adatom is moved with the tip of the STM towards the molecule 4-[trans-2-(pyrid-4-yl-vinyl)] benzoic acid (PVBA) adsorbed on Cu(111). The local density of states is mapped before and after the manipulation indicating a change in the molecular orbitals upon attachment of the adatom to the molecule. In the second case, a selfassembled metal-organic complex composed of two PVBA molecules and a central Cu atom is excited by an electrical bias. This acts as an external stimulus causing the metal-ligand bond to alternate on a time-scale of milliseconds between a bonded and a non-bonded configuration. These two configurations reveal different molecular orbitals, which can be visualized by taking conductance maps. The quantum yield per tunneling electron to trigger a transition between the two states varies spatially and is related to the local density of states of the bonded and non-bonded configuration. Finally, the control of molecular orbitals by different binding geometries of molecules within a supramolecular structure will be presented.

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References: [1]

Ohmann R., Vitali L., Kern K. Nano Letters, 10 (2010) 2995-3000.

Figures: (a)

(b)

(c)

Figure 1: (a) Schematic of the electrically induced bond breaking and forming of a metal-ligand bond of Cu(PVBA)2. (b) Current as a function of time indicating the alternation between the bonded and the non-bonded configuration. (c) Corresponding conductance maps of a bonded and non-bonded PVBA molecule (image sizes 18 x 20 Ų).

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AtMol International Workshop 2012, Berlin-Germany

Multi-configuration electronic Scattering matrix calculations for electron tunneling through a metalmolecule-metal junction

Mathilde Portais GNS-CEMES-CNRS 29 rue Jeanne Marvig, BP 94347 31055 Toulouse Cedex 4, France

Lately, the inclusion of Coulomb and exchange interactions for tunnel current intensity calculations has become an important challenge. For example, some experimental results disagree with the common mono-electronic interpretation that an STM image of a molecule at a given electronic tunneling resonance is representative of the spatial electronic density of one (or a few) molecular orbitals of this molecule [1,2]. So, it is now important to describe the corresponding metal-molecule-metal junction as a many-body electronic system using a full Slater determinant basis set instead of mono-electronic states of this junction.

Here we present a method to calculate the scattering matrix and the corresponding electronic transmission spectrum of a metal-molecule-metal tunnel junction described using an electronic multi-configuration basis set.

This new elastic scattering calculation (ESQC) like method is applicable to nano-scale systems where the interconnection electrodes can be considered in a ballistic regime of transport and where the N-electrons electronic structure of the central metal-molecule-metal nano-junction is taken into account. Simple applications demonstrate that the resonances of the electronic transmission spectrum of such a junction can be interpreted as instantaneous multi-electronic states fluctuations. They are created by the multiple possible virtual excitations of the metal-molecule-metal junction electronic structure induced by the tunneling electrons transferred through this junction.

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References: [1] [2]

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Soe W.H, Manzano C., De Sarkar A., Chandrasekar N. and C. Joachim; Phys. Rev. Lett., 102, 176102 (2009) Soe W.H, Wong H.S, Manzano C, Grisolia M, Hliwa M, Feng X, Mullen K and Joachim C, ACS Nano, 6, 3230 (2012).

AtMol International Workshop 2012, Berlin-Germany

Valence band tomography and the reconstruction of molecular orbitals from angle resolved photoemission

Michael G. Ramsey Institute of Physics Karl-Franzens University Graz A-8010 Austria

With examples of chain- and plate-like molecules it will be shown that the combination of studies of conjugated molecules with modern electron energy spectrometers has led to advances in understanding valence band photoemission in general and the electronic structure of “organic semiconductors� in particular. Angle resolved valence band photoemission will be focused upon and it will be shown that the hitherto apparently complex angular distribution can be simply understood making it a very powerful tool.

Examples of intra- and inter-band dispersion will demonstrate how a simple Fourier transform of molecular orbitals predicts the angular/momentum distribution of emitted photoelectrons. For adsorbate monolayers it will be shown how this can be used to reconstruct orbitals in real space, determine molecular geometries and gain insight into the nature of the surface chemical bond. Finally we show that momentum maps allow the orbital energy ordering to be unambiguously determined providing important bench marks for the selection of functionals for DFT calculations. Acknowledgment: This work was supported through the Austrian Science Foundation FWF national research network: Interface controlled and functionalized organic films.

AtMol International Workshop 2012, Berlin-Germany

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Attosecond electron dynamics in molecular systems: probing of electron density and molecular orbitals by sudden photoionization

F. Remacle Department of Chemistry University of Liège B4000 Liège, Belgium

Ultrafast UV excitation can prepare nonstationary electronic states that are a coherent superposition. In molecules it is of interest to probe such states both before the onset of nuclear motion and in the very early stages of the unfolding of chemistry. A suitable probe can be a sudden XUV ionization of the coherent excited electronic states. We discuss the ultrafast electron dynamics for the LiH and ABCU (C10H19N) molecules computed at the many electron level solving the time-dependent Schrödinger equation. Specifically we generate molecular frame photoelectron angular distributions (MFPAD) resulting from the sudden XUV ionization. We are able to relate the angular patterns of the MFPAD to the spatial localization of the electronic states that participate in the coherent superposition of states that is ionized and the corresponding Dyson molecular orbitals.

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62 years after the first observation of individual molecules with the field emission microscope and prospective improvements for a single molecule microscopy

Moh’d Rezeq Khalifa University of Science, Technology & Research, Abu Dhabi, UAE

The remarkable invention of the field emission microscope in 1936 by E. W. Muller enabled him some years later to turn it into a powerful instrument for imaging and characterizing individual molecules. He succeeded to report the first observations of organic molecules, namely phthalocyanine molecules, in 1950. Since then very few publications have been seen about this method of molecular characterization. For instance, the Cu_Phthalocyanine (Cu-Pc) molecule was observed in different configurations, namely two and four-leaf patterns, where these various apparent shapes were linked to the location of the molecule on particular atomic planes. Other investigations have been done for metal tips covered with such molecules, like field emission current (IV) measurements. In fact, in these publications a group of individual molecules can be seen distributed randomly on a metal tip apex of 50-100 nm, which makes the analyses of a single molecule infeasible. Therefore, no quantitative investigations have been made to explain either the reason of the molecular appearance or the detailed mechanism of electron emission through a molecule. Currently, the development of new methods for fabrication of extremely sharp tips with an apex in the size of a single molecule provides a unique opportunity to study the behavior of one molecule, adsorbed on the tip apex, at a time. We briefly review some of the common methods for the fabrication of those extremely sharp tips with an apex in the range of 1 nm.

We present preliminary data where two molecular adsorption states have been observed from the electronic cloud of a molecule: One arises from a very stable two-leaf pattern and the other case from a variable structure of single,

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two, three and four-leaf configurations. As the atomic structure of the tip is identified from the field ion microscope the interaction of the molecule with surface atoms, and thus the adsorption and electronic states, can be readily modeled.

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AtMol International Workshop 2012, Berlin-Germany

Alteration of scanningtunnelling-spectroscopy images of molecular orbitals as a probe of electron correlation

Massimo Rontani CNR-NANO, Research Center S3; Via Campi 213a 41125 Modena, Italy

Scanning tunnelling spectroscopy (STS) allows to image single molecules decoupled from the supporting substrate. The obtained images are routinely interpreted as the square moduli of molecular orbitals, dressed by the meanfield electron-electron interaction. Here we demonstrate that the effect of electron correlation beyond mean field qualitatively alters the uncorrelated STS images. Our evidence is based on the ab-initio many-body calculation of STS images of planar molecules with metal centers. We find that many-body correlations alter significantly the image spectral weight close to the metal center of the molecules. This change is large enough to be accessed experimentally, surviving to molecule-substrate interactions.

This work is done together with S. Corni and D. Toroz. We acknowledge support from projects Fondazione Cassa di Risparmio di Modena COLD and FEW and CINECA-ISCRA IscrB_FERMIFEW, IscrC_FEW1D, IscrC_QUASIPAR.

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Imaging orbitals with attosecond and Angström resolutions

Pascal Salières CEA-Saclay, Service des Photons Atomes et Molécules 91191 Gif sur Yvette, France pascal.salieres@cea.fr

An intense short (few-femtosecond) laser pulse interacting with a molecule in the gas phase may liberate by tunnel ionization an attosecond electron wave packet (EWP). This EWP is then accelerated by the laser field and made to recollide with the core one laser cycle later. The attosecond XUV emission resulting from the recombination encodes rich information on the possibly transient electronic [1,2] and nuclear [3,4] configuration of the core. The recolliding EWP may be seen as a probe of the core in the direction of the laser field. By characterizing the attosecond emission (in intensity, phase and polarization) for different molecular alignment angles, one can access the recombination dipole moment in the molecular frame. The spectral phase of this transition dipole is a unique quantity that cannot be accessed through other means, like photoionization experiments. It encodes the structure of the radiating molecular orbital and allows the reconstruction of the orbital amplitude and phase using a tomographic procedure [1,5,6]. It thereby becomes possible to image orbitals with a spatial resolution in the ångström range, and a temporal resolution in the attosecond range [5]. This paves the way to monitoring deformations of these orbitals during chemical reactions [7].

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References: [1] [2] [3] [4] [5] [6] [7]

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J. Itatani et al., ”Tomographic imaging of molecular orbitals”, Nature 432, 867-871 (2004).

W. Boutu et al., ”Coherent control of attosecond emission from aligned molecules”, Nature Physics 4, 545 (2008).

S. Baker et al., ”Probing Proton Dynamics in Molecules on an Attosecond Time Scale”, Science 312, 424 (2006).

S. Haessler et al., ”Attosecond chirp encoded dynamics of light nuclei”, J. Phys. B 42, 134002 (2009).

S. Haessler et al., ”Attosecond imaging of molecular electronic wavepackets”, Nature Physics 6, 200 (2010).

C. Vozzi et al., ”Generalized molecular orbital tomography”, Nature Physics 7, 822 (2011).

P. Salières et al., ”Imaging orbitals with attosecond and angstrom resolutions: toward attochemistry?”, Rep. Prog. Phys. 75, 062401 (2012).

AtMol International Workshop 2012, Berlin-Germany

Mapping the electronic resonances of single molecule STM tunnel junction

W – H Soe1, C Manzano1 and C Joachim1,2 1

IMRE, A*STAR, 3 Research Link, 117602, Singapore 2 GNS-CEMES, CNRS, 29 rue J. Marvig, 31055 Toulouse Cedex, France

A low-temperature scanning tunneling microscope (STM) differential conductance (dI/dV) measurement is a very effective technique to gain access to the low lying electronic states of a molecule weakly coupled to the surface of an STM tunnel junction. By accessing those states, the electron probability distribution of the ground and first excited states of a pentacene molecule had been imaged in real space [1]. Here pentacene was electronically decoupled from the metal substrate by an ultrathin insulating layer and the corresponding STM images are found to be very close to the mono-electronic HOMO and LUMO maps [1]. To have access to more states and therefore to more MO maps, a metal surface where the molecule is physisorbed on the surface of the STM tunnel junction can be used to reduce the energy gap between STM junction tunneling resonances and to get more molecular electronic states inside the STM bias voltage range without destroying the molecule.

First, we show that aside from the two frontier MOs (HOMO and LUMO), the second (HOMO-1) and third (HOMO-2) occupied MOs of a pentacene molecule lying directly on a Au(111) surface can be also imaged [2]. The way to disentangle those MO components from the contribution of higher resonance molecular electronic states will be discussed.

Second, the case of the Cu-phthalocyanine molecule characterized by a double-degenerated LUMO will be presented. An MOs basis set decomposition of the electronic cloud of this molecule does not correspond to AtMol International Workshop 2012, Berlin-Germany

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the one provided by the STM dI/dV conductance mapping: during scanning, the tip apex-molecular cloud electronic interactions capture the molecular orbital components of the molecular electronic states located in the dI/dV energy range as a complex mixture of different phases and weight contributions [3].

Finally, the hexabenzocoronene molecule, and some of its oligomers (monomer, dimer, trimer, and tetramer) prepared by an on-surface synthesis on Au(111) were imaged. From the tunneling spectra and the dI/dV maps of these molecules, a given STM dI/dV electronic resonance results from a complex contribution to the local conductance of many molecular states. This makes difficult to reconstruct an apparent molecular orbital electron probability density map in a straightforward manner using the standard quantum superposition of Slater determinants constructed with those monoelectronic molecular orbitals [4].

References: [1] [2] [3] [4]

56

J Repp et al. Phys. Rev. Lett. 94, 026803 (2005) W – H Soe et al. Phys. Rev. Lett. 102, 176102 (2009) W – H Soe et al. J. Phys.: Condens. Matter in press (2012) W – H Soe et al. ACS Nano 6, 3230 (2012)

AtMol International Workshop 2012, Berlin-Germany

Transport through a molecular tunnel junction: some insights from a multiconfigurational point of view

Martin Verot ENS Lyon, Laboratoire de Chimie 69364 Lyon CEDEX 07, France martin.verot@ens-lyon.fr

We demonstrate how a few key parameters, extracted from wavefunction-based based methods (post Hartree-Fock) control the electron transport through a simple molecular system. The transport of molecules ranging from lowly correlated systems (H2-like) to highly correlated ones (O2-like) is investigated.

For magnetic systems where several spin states are involved, we will show that both the energy spectrum and the wavefunction structure have an impact on the conductance observed. With this toy model, further properties (“spin-valve� behavior, Zeeman effect) can also be investigated to see the importance of the multiconfigurational description of such molecular filters.

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º

Cover image: The first ever recorded image of a few isolated molecules in real space by Erwin W. Müller in 1950 with a Field Emission Microscope. The imaged molecules are CuPhthalocyanines deposited on a broad tungsten tip with about a 200 nm radius of curvature. This image was first submitted the 7 August 1950 and published in the journal Zeitschrift für Naturforschung 5a, 473 (1950). At that time E. Müller was at the Kaiser-Wilhelm-Institut für Physikalische Chemie und Elektrochemie in Berlin. Before this direct space image, molecules were only known indirectly via a Fourier analysis of the Röntgen X-Ray diffraction pattern recorded through a crystal of Cu-Phthalocyanine molecules as obtained for the first time by J.M. Robertson in 1935 (J. Chem. Soc, 615 (1935))

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