Abdelkader Kara University of Central Florida kkaraphysics ucf

Abdelkader Kara University of Central Florida

kkara@physics. ucf. edu

Cancer Therapy: Photodynamic cancer therapy based on the destruction of cancer cells by laser generated atomic oxygen. A greater quantity of special dye that is used to generate the atomic oxygen is taken in by cancer cells, only cancer cells are destroyed, but the remaining dye molecules migrate to the skin and the eyes and make patient sensitive to daylight. To avoid this, the dye molecule is enclosed inside a porous nanoparticle and it did not spread to the other part of the body.

Imaging with gold Nanorods BIOPHOTONICS, December 2005 One main obstacle in biological imaging is that light does not pass through tissues very well. Researchers have shown a new imaging agent that shines 60 times brighter through tissues than conventional fluorescent dyes. The agent may offer a new tool for biological imaging. The nanorods pump electrons from their excited state and leave a hole in the ground state. This electron-hole recombination results in luminescence. They are dumbbell Shaped and almost pure gold, they produce unusually strong two photon signal (it is surface plasmon resonance effect). They can be used tumor and brain imaging in the near future. Ji-Xin Cheng

Nature, vol 439, 9 February 2006 Chameleon-like nanoparticles of gold can be used to indicate the presence of various biomolecules. Adding aptamers-DNA strands that bind only to specific Molecues-to the mix open up further possibilities.

The never ending quest for New Materials Towards Tailored Materials Atom by atom fashion?

Material's Simulations time ELECTRONS ATOMS GRAINS GRIDS Continuum simulations of real devices and materials hours Continuum minutes seconds microsec nanosec MD picosec femtosec Micromechanical modeling MESO KMC Deformation and Failure (dislocations, cracks, etc. ) QM distance Å nm micron mm Accurate calculations for bulk phases and molecules cm Transport properties (diffusion, thermal transport, etc. ) meters New generation reactive force fields based purely on first principles For metals, oxides, organics. Describes: mechanical properties, chemistry, charge transfer, etc.

“Dare I use the word nanostructure? But that is really what you want. You want almost every Ni. Mo or Co. Mo sulfideactive site to be on the surface so you can maximize the activity. That has been a big challenge” -W. Shiflett Criterion Catalysis

The Beginning Xenon on Nickel (110) Stadium Corral Iron on Copper (111) Quantum Corral Iron on Copper (111) Carbon Monoxide Man Carbon Monoxide on Platinum (111) http: //www. almaden. ibm. com/vis/stm/atomo. html Iron on Copper (111)

Saw Hla et al

Multi-scale & Multi-disciplinary Research Chemisorption Reactivity SL-KMC Data Mining Machine Learning Artificial Intelligence Structure Dynamics Ab initio Robust Model Potentials Molecular Dynamics Lattice Dynamics Magnetic properties Optical properties Bio-inspired materials Atom manipulation Functional Materials by Computer Assisted Design

Total energy minimization Searching minimum

Experimental work Detailed tip height measurements during manipulation of single atoms, molecules, and dimers on a Cu(211) surface reveal different manipulation modes depending on tunneling parameters. Both attractive (Cu, Pb dimers) and repulsive manipulation (CO) are identified. Using attractive forces, discontinuous hopping of Cu and Pb atoms from one adsorption site to the next can be induced (“pulling”). Pb dimers can be pulled with repeated single, double, and triple hops. Pb atoms can also be “slid” continuously. The occurrence of different movement patterns is shown to be a sensitive probe for surface defects. L. Bartels, G. Meyer, and K. -H. Rieder, Phys. Rev. Lett. 79, 697 (1997)

1. G. Meyer, L. Bartels, S. Zöphel, E. Henze, and K. -H. Rieder Phys. Rev. Lett. 78, 1512 (1997) 2. G. Meyer, J. Repp, S. Zöphel, K. -F. Braun, S. W. Hla, S. Fölsch, L. Bartels, F. Moresco, K. -H. Rieder Single Molecules 1, 79 (2000) 3. Saw-Wai Hla, Ludwig Bartels, Gerhard Meyer, and Karl. Heinz Rieder, Phys. Rev. Lett. 85, 2777 (2000) 4. J. Repp, F. Moresco, G. Meyer, K. -H. Rieder, P. Hyldgaard, and M. Persson, Phys. Rev. Lett. 85, 2981 (2000) 5. L. Bartels, G. Meyer, and K. -H. Rieder, Phys. Rev. Lett. 79, 697 (1997)

S. Hla, et al

Manipulation types: n n Lateral Vertical Manipulation modes: n Pulling n Pushing n dragging

Lateral Manipulation Process attractive force (Pulling Mode) repulsive force Movies are obtained from www. physik. fu-berlin. de (Pushing Mode)

Lateral Manipulation in the pulling mode C. Ghosh, A. Kara, and T. S. Rahman Theoretical aspects of vertical and lateral manipulation of atoms, Surf. Sci. 502 -503, 519, (2002).

Lateral Manipulation Model System • The model consists of 8 layers of atoms with 10 x 12 atoms per layer. • The stepped surface is created by removing 1/2 the atoms of the top layer. • The sharp tip consists of 35 atoms, both for the (100) and the (111) geometry. • The blunt tip consists of 34 atoms in each case (4 apex atoms for the (100) and 3 apex atoms for the (111)).

Empirical Interaction Potential We use Embedded Atom Method (EAM) as interaction potential Ei=internal Energy i=total electron density at position i due to the rest of the atoms Fi(fi)=the energy to embed atom i into electron density ρi. fij=two body central potential between atom i and j.

Illustration of shift in saddle point Bridge Eb Hollow 1 Hollow 2

Results 61. 7 me. V

Comparison of energy barriers for lateral manipulation at a tip height of 2. 75Å above step edge. Metal Barrier in the absence of tip (me. V) Barrier in the presence of tip (me. V) Opbarrier in the presence of tip (me. V) Shift in saddle point (Å) Tip-adatom lateral separation when barrier is lowest (Å) Cu tip on Pt surface 620. 8 1. 4 1197. 7 0. 5 2. 1 Pt tip on Cu surface 267 100 264 0. 7 2. 6 Ag 215. 5 50. 1 283. 6 0. 7 2. 6 Cu 267 61. 7 366. 5 0. 6 2. 55 Ni 308. 3 131. 3 386. 4 0. 45 2. 4 Pd 355 190. 1 426. 9 0. 4 2. 5 Au 416. 7 324. 3 414. 9 0. 12 2. 6 Pt 620. 8 462. 5 606. 2 0. 12 2. 6

Vertical Manipulation C. Ghosh, A. Kara, T. S. Rahman Comparative study of adatom manipulation on several fcc metal surfaces, J. of Nanoscience and Nanotechnology, 6, 1068 (2006).

Theoretical Details • The tip is placed at a certain height above the adatom. • For this height of the tip, the adatom is slowly raised in small steps from surface to tip apex. • At each step, the total energy of the system is minimized. • The above procedure is performed for several tip heights and for all three kinds of systems, viz. Flat, Stepped and Kinked systems. • A blunt (100) tip is used for all vertical manipulation calculations.

Results

Experimental work G. Dujardin, A. Mayne, O. Robert, F. Rose, C. Joachim, and H. Tang, Phys. Rev. Lett. 80, 3085 (1998).

Model System Flat • The model consists of 8 layers of atoms with 10 x 12 atoms per layer. • The stepped surface is created by removing ½ the atoms of the top layer. • The flat surface has 7 layers. • The kinked surface is created by removing ½ the atoms from the step edge chain of the stepped system. Stepped Kinked

Flat/step/kink

A. Deshpande, H. Yildirim, A. Kara D. P. Acharya, J. Vaughn, T. S. Rahman, S. -W. Hla Phys. Rev. Lett. 98, 028304 (2007)

Model System • adatom is placed in the 3 -fold site on top of the 3 atom cluster. • 3 D island= 2 D pad (25 atoms) on top of which a 3 -atom cluster is adsorbed. sharp tip (35 atom) tip apex adatom cluster 3 D island substrate • substrate= 6 atomic layers in fcc (111) orientation and 8 x 10 atoms in each layer

Details of the MD Simulations We monitor the time evolution of the position of each atom in the system. Our simulations are done at relatively low temperature (100 K). Simulations for several tip heights are performed for 200 ps each. The tip was given a constant lateral velocity of 10 m/s. • At relatively high positions of the tip (tip-adatom separations higher than 2. 43 Å)the adatom interacts weakly with the tip and can not be extracted !!! • For the tip height 2. 43 Å, when the tip is a few angstrom in front of the adatom, attractive forces between the tip and the adatom are so strong that the tip pulls and extracts the adatom !!!

Ag adatom manipulation/extraction using a sharp tip

Ag(111) system adatom manipulation/extraction using a sharp tip

Extraction process from MD simulation

Set-up of the calculations Energy landscapes in the absence of tip In this case, hopping down from a mound, the adatom encounters barrier of 0. 3 e. V (A to B: Hopping down) Once the adatom reaches B, the adatom could climb up to A after overcoming the same barrier of 0. 3 e. V (B to A: Climbing up). possible path for the extraction of the adatom

Energy barrier of adatom for lateral manipulation WITHOUT tip: A to B. Hopping down Energy barrier of adatom for vertical manipulation WITHOUT tip: B to A. Climbing up

Activation barriers in the presence of the tip (lateral and vertical manipulation processes with sharp/blunt tip) Height (Å) Energy Barrier/ Sharp Tip (A to B) Hopping down (B to A) Climbing up 2. 43 0. 032 e. V 0. 18 e. V 2. 63 0. 052 e. V 0. 21 e. V 2. 83 0. 12 e. V 0. 24 e. V 3. 03 0. 194 e. V 0. 27 e. V 3. 23 0. 28 e. V 3. 43 0. 29 e. V 0. 3 e. V 3. 63 0. 3 e. V Table I. The activation energy barriers for Ag(111) system in case of lateral and vertical manipulation mode.

Ag adatom manipulation/extraction using a blunt tip

Cu adatom manipulation/extraction using a sharp tip Handan Yildirim, Abdelkader Kara, and Talat S. Rahman Phys. Rev. B 75, 205409 (2007)

Conclusions • Manipulation and extraction of atoms using an STM tip is possible due to a dramatic change in the energy landscape due to the presence of the tip in the vicinity of the adatom (island). • Extraction of Ag atom from a Ag mound is found to be done through the pulling mode • For Cu system, we found that extraction was achieved through dragging mode. • The difference between the cohesive energies and bond length for Cu and Ag are the main reasons for the two extraction modes.

Acknowledgement Talat S. Rahman Ahlam Al-Rawi Sondan Durukanoglu Weibin Fei Chandana Ghosh Sampyo Hong Altaf Karim Ulrike Kurpick Faisal Mehmood John Spangler Pavlin Staikov Sergey Stolbov Handan Yildirim Klaus-Peter Bohnen Joachim Ernst Thomas Greber Claude Henry Ricardo Ferrando