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.
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].
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