Update ISU Feb 26 th 2013

JOAUIN PERALTARUPA DUMPALA

SCOTT BRODERICKKRISHNA RAJAN

Update ISU Feb 26th 2013

Summary

- DFT

- Ab-Initio molecular dynamics and energetic.

- Simulation of Si9 atomic cluster with Oxygen atom.

- Comparison with ReaxFF simulation by Ali's simulation.

-Atom Probe

- Oxidation of Si at two different temperatures is studied and compared to ReaxFF simulations

- The increase of interface thickness at higher temperatures and inward growth of other silicon oxides except SiO2 observed is in close approximation with simulation results

Computational Simulations

VASP 4.6Si9/O

Initial settings and velocities from Ali. Rescaling simulation cell to reduce vacuum space at

16Å. Original cell size was 80Å.Two simulation types

Energies from Ali’s trajectory file Simulation from scratch.

Initial structure

Trajectory file results

Original results 1000 simulation steps. 5 [ps] using a time step dt=0.1 [fs] / 50000 steps Energies evaluated using VASP, each 20 simulation

steps.Energy of each atomic configuration

Not kinetic energy associated. Techincal settings :

Precision Accurate Spin polarization Energy cutoff 500 eV

From scratch simulation

Using microcanonical ensemble NVESimulation speed (vasp 4.6 and 8 CPU)

Initial rate 0.2 MD steps/min Highest rate 0.6 MD steps/min

Time scale dt = 1[fs].Total simulation steps 5000 steps.Total simulation time ~8 days.Energies / TemperatureStrange behavior of electronic convergence

after 4.8[ps].

Temperature

Kinetic and Potential Energy

Ali’s data from ReaxFF

Left results from Ali’s simulation using ReaxFF.Right results from ISU, using DFT.

Ali’s data from ReaxFF

Left results of potential energy from Ali’s simulation using ReaxFF.Right results from DFT using simulations with Ali’s data and from scratch.

• Inward and outward growth of SiOx (x < 2) and only outward growth of SiO2

SiO2

Si

O

SiO

Si2O

Si and Oxygen System at 373 K

10 5 0 -5 - 10 10 5 0 -5 - 10

10 5 0 -5 - 10 10 5 0 -5 - 10 10 5 0 -5 - 10

10 5 0 -5 -10

SiO2

Si

O

SiO

Si2O

Si and Oxygen System at 548 K

• Inward and outward growth of SiOx (x < 2) and only outward growth of SiO2

Si and Oxygen System at 548 K

~ 1 nm

~ 1 nm

• The interface thickness before growth of SiO2 starts is in close approximation with simulation results

SiO2

Si

O

SiO

Si2O

1.8 nm 2.6 nm

Study of Interfaces373 K 548 K

• Increase of interface thickness with the temperature was noticed similar to simulation results with close approximation of interface thickness values.

700 K300 K

1 nm2 nm

Our wafers are ( 100) wafers.The two edges of the tip rows are aligned along the intersection of the(111) crystal planeswith the ( 100) surface.”

Silicon Coupon – Si tips Orientation

Future Steps

- Provide Si, O atomic positions for ReaxFF simulations

- Analysis of Al and oxygen system with varying temperature similar to silicon system

- Gas solid reactions of near space environment condition