Part IV : 2-Dimensional Chiral Effect of the Organic Molecule on the Configuration of Organic Self-assembly on the Reactive Metal Surface.

Transcription

1 Part IV : 2-Dimensional Chiral Effect of the rganic Molecule on the Configuration of rganic Self-assembly on the eactive Metal Surface. Byung-Il Kim Department of Chemistry University of Houston

2 Motivation of rganic Self-assembly: - Potential anoscale Device - Formation Mechanism in Biology system esearch bjective: - To determine factors influencing the configuration of organic self-assembled nanostructures with High stability. System with High Stability at oom Temperature: - Strong Intermolecular Interaction and adsorbatesubstrate interaction - PVBA/Pd(111)

3 4-trans-2-(pyrid-4-yl-vinyl) benzoic acid : PVBA - Planar and Stiff - Conjugated System with π-electron - Conjugated Chain - Hydrogen Bonding Head 6.7 Å Tail 12.7 Å H

4 Intermolecular Interaction:Hydrogen Bonding - Head - Head interaction :Unfavorable - Head - Tail interaction : -10 kcal/mole - Tail - Tail interaction : -15kcal/mole

5 Substrate: Pd(111) - Size : 1cm dia 1mm -Step height = 2.24Å - Melting Temp: 1550 C -Terrace width:~1000å - Structure : fcc(111) -Defect free surface -..D.: 2.75Å - Most reactive metal of Group 8B(10)

6 UHV-STM/AFM Surface Analysis System

7 rganic Molecular Beam Deposition -Deposition of PVBA Pd(111) PVBA < Torr -Substrate Temp.: T -Deposition Temp. of PVBA: 128 C

8 STM on PVBA/Pd(111) - inear and Y shape Statistics Dimer ~ 85.0% Trimer ~8.6 % thers ~6.4% It=100pA Vt~1V ( T > 1GW ) at T

9 Straight Dimer Peaksfiings 11Å ~7Å H H p-conjugate chain fi I t ~ 1Å

10 Bent Dimer ~ 1Å H H

11 2-Dimensional chirality High Contrast STM Image - Molecular beam : 2-dimensional racemic mixture. - ot superimposed by translation and rotation

12 2-Dimensional Chirality Effect on Dimer Shape same chiral symmetry different chiral symmetry

13 rientation of Dimer ~20 - [011] - : ~ n - : ~ n 60 ~40 - [011] rientational Preference of Single PVBA : ~ n : ~ n

14 rientation of Trimer Type A(, ) : ~ 20, ~ , ~ : ~ 40, ~ , ~ Type B(,,,,,) Type B : ~0, ~120, ~240 lattice rows STM Statistics Type A ~ 2.2% Type B ~ 6.4% A : B ~ 1 : 3

15 Interaction Energy due to verlap between Aromatic ings and Hollow sites d 0 =6.7Å At θ ~ 0 or 60, d=6.92å, d-d 0 / d 0 =3.2% d At θ ~ 20 or 40, d=7.27å, d-d 0 /d 0 =7.8% verlap Interaction E overlap Angle(degree)

16 verall Interaction due to Symmetry and verlap - E symmetry > E overalp to have global minimum at ~40 ( 20 ) + 60 n for ( ) ~ n x1 x2 ~ n ~ n x Angle(degree)

17 Competition between verlap and Symmetry E tot =1 E symmetry + 3 E overlap 3 E overlap > 1 E symmetry to have a global minimum at ~ n ~ n Angle(degree) -E symmetry /E overlap 3 for Trimer - E symmetry /E overlap 1 for Dimer 1 E symmetry /E overlap 3 for PVBA/Pd(111)

18 3x(E symmetry + E overlap ) ~ n Angle(degree) 1xE symmetry + 3xE overlap ~ n Angle(degree)

19 Comparison to other Systems PVBA/Pd (110) Monomers with two distinct orientations J. Weckesser, J. V. Barth, C. Cai, B. Muller and K. Kern, Surf. Sci. 431(1999) PVBA/Ag (111) 1-D nano-grating structure J. V. Barth, J. Weckesser, C. Cai, P. Gunter,. Burgi,. Jeandupeux, and K. Kern. Angew. Chem. Int. Ed. 2000, 39, PVBA on / Pd(111) Intermediate adsorbate-substrate interaction

20 Manipulation: Two Dimers ne Trimer Scanning direction

21 Medium Coverage -Self-assembled nanostructure with orientational preference -o preferential growth near the step edge Strong π bonding or weak lateral interaction. -Head-to-Tail bonding

22 High coverage -Self-assembled chain structures-annealing Effect on rdering Competition between inter-molecular hydrogen bonding and molecules substrate interaction

23 High coverage H H H H H H H H H H

24 Conclusions 1. PVBA molecules were deposited on clean Pd(111) to form selfassembled nanostrucutres with organic molecular beam epitaxy system. 2. Dimer and trimer structures formed with strong hydrogen bond strongly depend on molecular chiral symmetry and the substrate orientation. 3. Interaction energy due to molecular symmetry with lattice competes with the one due to overlap between aromatic rings and hollow sites. 4. The orientation and configuration of self-assembly could be modified by applying strong force on single molecules during tip scanning.

25 Acknowledgement - Prof. Scott S. Perry - Prof. Chengzhi Cai ( PVBA ) - Texas Advanced esearch Program - Air Force ffice of Scientific esearch