Abdelkader KaraUniversity 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 togenerate 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 notspread to the other part of the body.

Imaging with gold Nanorods

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 offera new tool for biological imaging.

The nanorods pump electrons from their excited state and leave a hole in the groundstate. This electron-hole recombination results in luminescence. They are dumbbellShaped 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.

BIOPHOTONICS, December 2005

Ji-Xin Cheng

Nature, vol439, 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 forNew Materials

Towards Tailored MaterialsAtom by atom fashion?

Material's Simulations

time

distance

hours

minutes

secondsmicrosecnanosec

picosec

femtosec

Å nm micron mm cm meters

MESOKMC

Continuum

QM

MD

ELECTRONS ATOMS GRAINS GRIDS

New generation reactive force fields based purely on first principlesFor metals, oxides, organics.Describes: mechanical properties, chemistry,charge transfer, etc.

Deformation and Failure (dislocations, cracks, etc.)

Transport properties(diffusion, thermal transport, etc.)

Micromechanical modeling

Continuum simulations of real devices and materials

Accurate calculations for bulk phases and molecules

“Dare I use the word nanostructure? But that is really what you want. You want almost every NiMo or CoMo sulfide-active site to be on the surface so you can maximize the activity. That has been a big challenge”

-W. ShiflettCriterion Catalysis

http://www.almaden.ibm.com/vis/stm/atomo.html

Quantum Corral Iron on Copper (111)

Stadium Corral Iron on Copper (111)

The Beginning Xenon on Nickel (110)

Carbon Monoxide Man Carbon Monoxide on Platinum (111) Iron on Copper (111)

Saw Hla et al

Ab initio

Robust Model Potentials

Data MiningMachine Learning

Artificial IntelligenceSL-KMC

MolecularDynamics

LatticeDynamics

Functional Materials by Computer Assisted Design

ChemisorptionReactivity

Structure

Dynamics

Opticalproperties

Magneticproperties

Bio-inspiredmaterials

Multi-scale & Multi-disciplinary Research

Atommanipulation

Total energy minimizationTotal energy minimization

Searching minimum

Experimental workExperimental work

L. Bartels, G. Meyer, and K.-H. Rieder, Phys. Rev. Lett. 79, 697 (1997)L. Bartels, G. Meyer, and K.-H. Rieder, Phys. Rev. Lett. 79, 697 (1997)

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, 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.

1. G. Meyer, L. Bartels, S. Zöphel, E. Henze, and K.-H. RiederPhys. 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.RiederSingle 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 modes: Pulling Pushing dragging

Manipulation types:

Lateral Vertical

Lateral Manipulation Process

attractive force (Pulling Mode)

repulsive force (Pushing Mode)Movies are obtained from www.physik.fu-berlin.de

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 stepped surface is created by The stepped surface is created by removing 1/2 the atoms of the top removing 1/2 the atoms of the top layer.layer.

•The model consists of 8 layers of The model consists of 8 layers of atoms with 10 x 12 atoms per layer.atoms with 10 x 12 atoms per layer.

•The sharp tip consists of 35 atoms, The sharp tip consists of 35 atoms, both for the (100) and the (111) both for the (100) and the (111) geometry.geometry.

•The blunt tip consists of 34 atoms in The blunt tip consists of 34 atoms in each case (4 apex atoms for the (100) each case (4 apex atoms for the (100) and 3 apex atoms for the (111)).and 3 apex atoms for the (111)).

Empirical Interaction Potential

We use Embedded Atom Method (EAM) as interaction potential

ijijji

ijijijiii

rf

rFE

)(

)(2

1)(

Ei=internal Energy

i=total electron density at position i due to the rest of the atoms

Fi(i)=the energy to embed atom i into electron density ρi.

ij=two body central potential between atom i and j.

Illustration of shift in saddle point

Hollow 1 Hollow 2

Bridge

Eb

ResultsResults

61.7 meV

Comparison of energy barriers for lateral manipulation at a tip height of 2.75Å above step edge.

Metal Barrier in the absence of tip

(meV)

Barrier in the presence of

tip(meV)

Opbarrier in the presence

of tip(meV)

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.

•At each step, the total energy of the system is minimized.

•For this height of the tip, the adatom is slowly raised in small steps from surface to tip apex.

•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.

ResultsResults

Experimental workExperimental work

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

Model System

•The stepped surface is created by The stepped surface is created by removing ½ the atoms of the top layer.removing ½ the atoms of the top layer.

•The model consists of 8 layers of The model consists of 8 layers of atoms with 10 x 12 atoms per layer.atoms with 10 x 12 atoms per layer.

•The flat surface has 7 layers.The flat surface has 7 layers.

•The kinked surface is created by The kinked surface is created by removing ½ the atoms from the step removing ½ the atoms from the step edge chain of the stepped system.edge chain of the stepped system.

Flat

Stepped

Kinked

Flat/step/kink

A. Deshpande, H. Yildirim, A. KaraD. P. Acharya, J. Vaughn, T. S. Rahman, S.-W. HlaPhys. Rev. Lett. 98, 028304 (2007)

sharp tip (35 atom)

tip apex

adatom

3D island

cluster

• substrate= 6 atomic layers in fcc (111) orientation and 8x10 atoms in each layer

• 3D island= 2D pad (25 atoms) on top of which a 3-atom cluster is adsorbed.

substrate

• adatom is placed in the 3-fold site on top of the 3- atom cluster.

Model System

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

adatom manipulation/extraction using a sharp tip

Ag(111) system

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 eV (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 eV (B to A: Climbing up).

possible path for the extraction of the adatom

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

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

Height (Å)

Energy Barrier/ Sharp Tip

(A to B)Hopping down

(B to A)Climbing up

2.43 0.032 eV 0.18 eV

2.63 0.052 eV 0.21 eV

2.83 0.12 eV 0.24 eV

3.03 0.194 eV 0.27 eV

3.23 0.28 eV 0.28 eV

3.43 0.29 eV 0.3 eV

3.63 0.3 eV 0.3 eV

Table I. The activation energy barriers for Ag(111) system in case of lateral and vertical manipulation mode.

Activation barriers in the presence of the tip (lateral and vertical manipulation processes with sharp/blunt tip)

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)

•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.

Conclusions

AcknowledgementTalat S. Rahman

Ahlam Al-RawiSondan DurukanogluWeibin FeiChandana GhoshSampyo HongAltaf KarimUlrike KurpickFaisal MehmoodJohn SpanglerPavlin StaikovSergey StolbovHandan Yildirim

Klaus-Peter BohnenJoachim ErnstThomas GreberClaude HenryRicardo Ferrando