First principles Simulations for fullerenes and Atomic Force Microscopy: Reactivity and Manipulation at the atomic scale.

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First principles Simulations for fullerenes and Atomic Force Microscopy: Reactivity and

Manipulation at the atomic scale.

Rubén Pérez

Nanomechanics & SPM Theory Group

Departamento de Física Teórica de la Materia Condensada http://www.uam.es/ruben.perez

Projects supported by RES in BSC, October 2008

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1. “Fullerenes from Aromatic Precursors by Surface-catalysed Cyclodehydrogenation”

Nature 454, 865 (2008)

Outline

2. “Complex Patterning by Vertical

Interchange Atom Manipulation Using Atomic Force Microscopy”

Science 322, 413 (2008)

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“Fullerenes from Aromatic Precursors

by Surface-catalysed Cyclodehydrogenation”

Nature 454, 865 (2008)

Ab initio Simulations:

UAM: G. Biddau, M. Basanta, J. Ortega, R. Perez Surface Science:

ICMM (CSIC): G. Otero,C. Sanchez-Sanchez, R. Caillard, M.F.

Lopez, C. Rogero, F.J. Palomares, J. Mendez, J.A. Martin-Gago Chemistry:

ICMM (CSIC): B. Gomez-Lor

ICIQ: N. Cabello, A.M. Echevarren

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C60 C57N3

Objective and motivations Objective and motivations

OBJECTIVE:

Study and efficient synthesis fullerenes and triazafullerenes

MOTIVATIONS:

microelectronics, superconductivity, corrosion resistence, non linear optics, organic ferromagnetism...

Triazafulleres:

none

1] Scotts et al., Science 295, 1500-1503 (2002)

Available synthesis methods:

Fullerenes:

- Graphite Vaporization (uncontrolled)

- Through dehydrogenation1

(low efficiency)

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The Process The Process

VACUUM THERMAL EVAPORATION

ANNEALING (750 K)

FULLERENE AND TRIAZAFULLERENES

Efficiency ~100%

Adsorption process

Cyclodehydrogenation

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Experimental and Theoretical evidences Experimental and Theoretical evidences

PAHs

1) C60H30 2) C57N3H33

Ideal conditions:

Both are markedly twisted, Δz: 0.08 Å (polyarene 1), 0.09 Å (heteropolyarene 2).Twisting angle:

20.5º (1) and 30.5º (2)

1 2

DFT computational details:

Both Local Orbital (FIREBALL) and plane wave (CASTEP) ab- initio methods have been used in LDA and GGA approximation

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Experimental and Theoretical evidences Experimental and Theoretical evidences

PAHs: Adsorption

Experimental STM molecular shape:

• three wings (molecules do not fragment and maintain almost planar configuration)

• lobes (DFT calculations associate to external ring).

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Experimental and Theoretical evidences Experimental and Theoretical evidences

PAHs: Adsorption

Theoretical:

• As from STM images, energy landscape is complicated, many possible adsorption configurations.

• Strong variation of molecules height (Δz varies from 0.08 Ang to 0.02 Ang)

• Tendency to maxime the number of C-Pt bonds.

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Experimental and Theoretical evidences Experimental and Theoretical evidences

DFT Molecular Orbitals, confirm STM height and lengths.

~11 Angstrom

~1.3 Angstrom Molecular Orbitals of PAHs strongly

hybridize with surface, resulting in a broad DOS at Fermi level

Apparent height of 0.14 nm Base length of 2.2 nm

No dependence on bias voltage.

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Experimental and Theoretical evidences Experimental and Theoretical evidences

After annealing, molecules have:

height is 0.4 nm and diameter of 1.35 nm The low height indicates a strong covalent

adsorption.

Are they really fullerenes (triazafullerene)?

1) These values are compatible with other fullerenes adsorption datas on Pt, Si and Au.

2) We adsorbed in same experimental condition, commercial fullerenes and no difference are observed.

3) For triazafullerene, XPS 1

st

peak, shows

the nitrogen bonded with carbon with sp

2

hydridization, the 2

nd

can be

attributed to nitrogen of the carbon cage interacting with the surface in measure of 1/3. DFT calculations confirm this orientation.

ANNEALING

750 K

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Experimental and Theoretical evidences Experimental and Theoretical evidences

- height is 0.4 nm and diameter of 1.35 nm The low height indicates a strong covalent adsorption.

1)These values are compatible with other fullerenes adsorption datas on Pt, Si and Au.

2)We adsorbed in same experimental condition, commercial fullerenes and no difference are observed.

3)For triazafullerene, XPS 1

st

peak, shows

the nitrogen bonded with carbon with sp

2

nd

can be attributed to

nitrogen of the carbon cage interacting with the platinum surface.

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Experimental and Theoretical evidences Experimental and Theoretical evidences

- height is 0.4 nm and diameter of 1.35 The low height indicates a strong covalent nm

adsorption.

2) We adsorbed in same experimental condition, commercial fullerenes (2) and no difference are observed.

3) For triazafullerene, XPS 1

st

peak, shows

the nitrogen bonded with carbon with sp

2

nd

can be

attributed to nitrogen of the carbon cage interacting with the platinum surface.

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Experimental and Theoretical evidences Experimental and Theoretical evidences

- height is 0.4 nm and diameter of 1.35 The low height indicates a strong covalent nm

adsorption.

2) We adsorbed in same experimental condition, commercial fullerenes and no differences are observed.

3) For triazafullerene, XPS 1^st peak, shows the nitrogen bonded with carbon with sp² hydridization, the 2^nd can be attributed to nitrogen of the carbon cage interacting with platinum surface. DFT calculations confirm this orientation.

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Annealing and Cyclodehydrogenation Annealing and Cyclodehydrogenation

Thermal annealing (750 K) produces a serie of dehydrogenation reactions.

To exclude that activation is due to the tip, dehydrogenation signal in a mass spectrometer has been detected as a function of annealing temperature. To avoid artefacts of H desorption from apparatus, deuterated precursors have been synthesized. The mass spectrum shows:

1) No molecular shape modification or dehydrogenation under 400 K

2) Between 400 and 600 K we could have partial dehydrogenation as asymmetrical molecules are observed

3) Rapid desorption about 700K

4) Formation of HD from H₂ and D₂ is enhanced by the strong interaction molecule-surface

MASS SPECTROMETRY ON DEUTERATED PRECURSORS

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Annealing and Cyclodehydrogenation Annealing and Cyclodehydrogenation

DFT CHARACTERIZATION

Adsorbed dehydrogenation DFT calculations are computationally impossible, by the way the theoretical calculation for the free molecules provide evidence that dehydrogenation induces a strong tendency towards cyclization.

1) Removal of central H atoms, triggers structural and electronical change to induce wings to approach each other to form a hydrogenated semi-cage

2) A NEB systematic study of fully dehydrogenated mocule via ab-initio methods, shows that the different possible paths from planar precursors to fullerene cage, has barries less than 0.3 eV

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Annealing and Cyclodehydrogenation Annealing and Cyclodehydrogenation

DFT CHARACTERIZATION

Adsorbed dehydrogenation DFT calculations are computationally impossible, by the way the theoretical calculation for the free molecules provide evidence that dehydrogenation induces a strong tendency towards cyclization.

1) Removal of central H atoms, triggers structural and electronical change to induce wings to approach each other to form a hydrogenated semi-cage

2) A NEB systematic study of fully dehydrogenated mocule via ab-initio methods, shows that the different possible paths from planar precursors to fullerene cage, have barriers smaller than 0.3 eV

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Annealing and Cyclodehydrogenation

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The Process

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Conclusions and Future Developments Conclusions and Future Developments

OUR GOALS:

• In this work we have shown a very efficient synthesis process for fullerenes and triazafullerenes

• We have characterized adsorptions of PAHs, fullerenes and triazafullerenes in different adsorption sites, providing the first ab-initio calculations for all the systems studied.

• We have described the molecular orbital shape of molecules, characterizing the structural (height) and electronical contributions to DOS. Theoretical and experimental STM images are in good agreements

NEXT:

• A wide range of possible heterofullerene and endohedral fullerenes could be obtained

• Surface catalysed cyclodehydrogenation could be proposed for other metallic surfaces

“

Fullerenes from Aromatic Precursors by Surface-catalysed Cyclodehydrogenation” Nature 454, 865 (June 2008)

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“Complex Patterning by Vertical Interchange Atom Manipulation Using Atomic Force

Microscopy”

Science 322, 413 (2008)

Ab initio Simulations:

UAM: P. Pou, R. Perez FZU(Prague): P. Jelinek AFM Experiments:

Osaka University:Y. Sugimoto, M. Abe, S. Morita

NIMS (Tsukuba, Japan): O. Custance

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ATOMIC FORCE MICROSCOPY (AFM)

http://monet.physik.unibas.ch/famars/afm_prin.htm

G. Binnig, C. Gerber & C. Quate, PRL 56 (1986) 930

2nd most cited PRL: +5000 citations !!!

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Dynamic AFM

http://monet.physik.unibas.ch/famars/afm_prin.htm

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Dynamic AFM: Our Goal

Why changes observed in the dynamic properties of a vibrating cantilever with a tip that interacts with a surface make

possible to:

•Resolve atomic-scale defects in UHV.

• Obtain molecular resolution images of biological samples in ambient conditions.

AM-dAFM

FM-dAFM

R. García and R. Pérez, Surf. Sci. Rep. 47, 197 (2002)

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Tip-sample Interaction: F _V + F _vdW + F _chem

F

_chem

≡ wfs overlap

Exp: A = 340 Å !!!, R = 40 Å

Sensitivity to Short-Range Forces?

Weak singularity at

turning points !!!!

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Ad1

Ad2 Ad1 Ad2

Ad2

Re1 H3

Dynamic Force Spectroscopy: Access to F _ts

Inversion algorithms

U. Durig, APL 76, 1203 (2000) F.J. Giessibl, APL 78, 123 (2001) J. E. Sader & S. P. Jarvis, APL 84, 1801 (2004).

1 2 3 4 5 6 7 8 9

-1,8 -1,6 -1,4 -1,2 -1,0 -0,8 -0,6 -0,4 -0,2 0,0 0,2 0,4

Exp. Adatom 2 Exp. Restatom 1 Exp. H3

Short-range Force (nN)

Tip-surface Distance (Å)

SR forces amenable to

ab initio calculations

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Recent developments in FM-AFM

3. CHEMICAL IDENTIFICATION:

1. DISSIPATION: Characterizing the tip

structure and identifying a dissipation channel due to single atomic contact adhesion.

N. Oyabu et al. Phys. Rev. Lett. 96, 106101 (2006).

2. IMAGING: changes in topography: access to the real surface structure?

Y. Sugimoto et al Phys. Rev. B 73, 205329 (2006).

Y. Sugimoto et al Nature 446, 64 (2007).

1 2 3 4 5 6 7 8 9

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Exp. Adatom 2 Exp. Restatom 1 Exp. H3

Disspation (eV per Cycle)

Tip-surface Distance (Å) Ad1

Ad1

Ad1 Ad2 Ad2 Re1 Re2 H3Ad2

-6.3 fN√m -7.3 fN√m -8.4 fN√m

based on the relative interaction ratio of

the maximum attractive force measured

by dynamic force spectroscopy

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Recent developments in FM-AFM

5. VERTICAL MANIPULATION:

4. LATERAL MANIPULATION: Si vacancy on Si(111)-7x7 (tip assisted thermal hopping)

Tip/sample exchange of atoms on Sn/Si(111)

Understanding RT DFM-based single-atom manipulation

Y. Sugimoto et al. Phys. Rev. Lett. 98, 106104 (2007).

Y. Sugimoto et al., Science 322, 413 (2008).

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∆ f=-7.3 Hz

Interchange vertical manipulation: Si → Sn

M. Abe, Y. Sugimoto, O. Custance, and S. Morita, Appl. Phys. Lett. 87 (2005) 173503.

M. Abe, Y. Sugimoto, O. Custance, and S. Morita, Nanotechnology 16 (2005) 3029.

Atom tracking technique Lateral precision: ± 0.1 Å

Tip positioning over a selected Si atom

Si

Sn Sn

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0 2 4 6 8 10 12 14 16 18 20 - 25

- 20 - 15 - 10 - 5 0

∆f [Hz]

Z [Å]

γ [fN√m]

Tip approach toward the Si atom

special shape

Ref. Typical ∆ f-Z curve

Interchange vertical manipulation: Si → Sn

∆ f=-7.3 Hz

Si

Sn Sn

jump

Sn SiSn Sn

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0 2 4 6 8 10 12 14 16 18 20 - 25

- 20 - 15 - 10 - 5 0

∆f [Hz]

Z [Å]

γ [fN√m]

Tip retraction from the surface

jump

∆ f=-7.3 Hz

Interchange vertical manipulation: Si → Sn

special shape

• The Si atom on the surface was

interchanged with a Sn atom at the tip apex.

• The contrast of the images before and after manipulation are almost same.

Mechanism: Vertical Interchange Mechanism: Vertical Interchange

• Vertical manipulation as a combination of mechanical and thermal process.

• Formation of a

characteristic dimer structure along

deformation path (energetically stable).

• Atomic

rearrangements reflects in energy &

forces discontinuities.

• Local character of the tip-sample

deformation.

• Temperature effect

not included in the

simulation.

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• Explore possible dimer

rearrangement due to thermal &

mechanical movement

• Complicated configuration space;

only limited configurational space explored

• Estimated energy barriers ~ 0.4 eV (Nudged elastic band calculation).

• Dependence on the tip-sample distance, tip elasticity & structure, temperature...

Mechanism: Energy Barriers Mechanism: Energy Barriers

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Nanostructuring

by interchange vertical manipulation

Atomic “dip-pen” nanolithography

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Atomic “dip-pen” nanolithography

• 11 Interchange vertical manipulations + 1 Interchange lateral manipulation

• The construction time was reduced to 1.5 hours. Sn Si

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Conclusions Conclusions

Single-atom manipulations: atomistic insight into these processes.

• Significant reduction of activation energy due to the tip proximity

• Operating at the attractive force regime

• New manipulation method:

‘Interchange vertical manipulation’

• Characteristic mechanical deformation:

the “hybrid tip-surface” dimer structure

• Operating at the repulsive force regime

• Combination of mechanical and thermal processes

Lateral Si-vacancy manipulation

Vertical Si/Sn-exchange manipulation

Y. Sugimoto et al, Science 322, 413 (2008).

Y. Sugimoto et al, Phys. Rev. Lett. 98, 106104 (2007)

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First principles Simulations for fullerenes and Atomic Force Microscopy: Reactivity and Manipulation at the atomic scale.