updates of iowa state university
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Updates of Iowa State University . S. Dumpala , S. Broderick and K. Rajan Sep – 18, 2013 . Summary . Refinements in Environmental chamber set up for in-situ gas reactions Oxidation studies of Al using new set up of E-cell - PowerPoint PPT PresentationTRANSCRIPT
Updates of Iowa State University
S. Dumpala, S. Broderick and K. Rajan
Sep – 18, 2013
Summary • Refinements in Environmental chamber set up for in-situ gas reactions
• Oxidation studies of Al using new set up of E-cell
• Preliminary analysis of silicon oxidation results in comparison with ReaxFF simulations (Adri’s papers)
• Further analysis of silicon oxidation growth mechanisms and sub oxide species at different temperatures
• Study of Si tips from Maryland using APT
E-Cell APT Results
Bulk Alumina Phase Bulk Al Phase
Aluminum Oxidation
3D atomic scale interfacial analysis (structural and chemical)
Stoichiometry of different phases observed Inter-diffusional characteristics of elements
Reduced Contamination with In-situ E-Cell Oxidation
In-situ E-cell Oxidation
• Numerous additional peaks representing contamination that were detected in ex-situ oxidation were absent in in-situ oxidation results.
Unkown peaks.
Ex-situ Oxidation
Increased Mass Resolution with In-situ E-Cell Oxidation
• Lower mass resolution with longer tails of the peaks were seen in ex-situ
Unkown peaks.
In-situ E-cell OxidationEx-situ Oxidation
APT of Si Tips from Maryland : Anode Voltage: 250 V of Argon exposure
50 monolayers 150 monolayers Bare Si Tip
• Laser APT – 1nj (laser power)
• Higher Ar content in beam exposed tips compared to bare Si tip
Mass Spectra
1. Small peak of Ar
2. Check other condition tips (Different beam currents)
3. Different deposition thickness of monolayers
4. FIM studies
50 monolayers
150 monolayers
Bare Si Tip
Oxidation of Silicon
ReasFF Simulations APT- Experimental
• Hyper thermal oxidation (atomic and molecular oxygen beam source)
• Dynamic study
• Smaller time scales (3pc)
• Monolayer detection
• Plasma oxidation (ambient oxygen)
• Static study (post deposition study)
• Longer time scales (minutes)
• Sub nano scale detection
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Conc
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(at%
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Distance (nm)
2 nm
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Conc
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(at%
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Distance (nm)
2.5 nm
-2-4 2 40
-22
0
-2-4 2 40
-22
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Interfacial Diffusion – Interfacial Width383 K 548 K
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Conc
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(at%
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Distance (nm)
2.5 nm
Region III Region IRegion II
383 K 548 K
Diffusion Profiles – Sub Oxides
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Si2O %
SiO2
SiO
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Si2O %
SiO
SiO2
Conc
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(at%
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Distance (nm)
0
2
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Si2O %
SiO
SiO2
0
2
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Si2O %
SiOSiO2
Conc
entr
ation
(at%
)
Distance (nm)
0
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-5 -4 -3 -2 -1 0 1 2 3 4 5
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(at%
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Distance (nm)
2 nm
Region IRegion III Region II
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383 K 548 K
Si2O
SiO
SiO2
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500
Region I Region II Region III
Si2OSiOSiO2
• Interface region – Between bulk Si, and bulk silica (region II from proxigrams)
• The total number of sub oxide species increase with increase temperature, observed similar trend in APT results
• Relative amounts/ratio of Si+1 (Si2O), Si+2 (SiO) at two different temperatures agrees with simulations
• Silica layer – 1. Surface, 2. Bulk (Si+4 components in interface)
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383 K 548 K
Si2O
SiO
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Region I Region II Region III
Si2OSiOSiO2
Aver
age
Conc
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ation
(at%
)Av
erag
e Co
ncen
trati
on (a
t%)
Analysis of Interfacial Sub Oxides – Comparison of Simulations with APTAtom Probe (Interfacial Region) ReaxFF Simulation
• For 8 ML, the number of Si4+ components is much higher at low temperatures than at high temperatures, indicating that the initial growth of the silica (SiO2) layer occurs much faster at low than at high temperature
• After 32 ML, number of Si4+ components is almost same at all temperatures indicating that the silica layer now grows faster at higher temperatures, but its nucleation started later
• APT results also indicate the presence of almost same number of Si4+(SiO2) components at both the temperatures
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383 K 548 K
Si2O
SiO
SiO2
Aver
age
Conc
entr
ation
(at%
)0
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100
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Region I Region II Region III
Si2OSiOSiO2
Analysis of Si+4 (SiO2) Oxides – Comparison of Simulations with APT
Atom Probe (Silica Region) ReaxFF Simulation
Growth Mechanism - Low Temperature
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Si2O %
SiO2
SiO
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Si2O %
SiO
SiO2
Conc
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ation
(at%
)
Distance (nm)
0
2
4
6
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14
Region I Region II Region III
Si2OSiOSiO2
0
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Region I Region II Region III
Si2OSiOSiO2
Aver
age
Conc
entr
ation
(at%
)
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Conc
entr
ation
(at%
)
Distance (nm)
2 nm
Region IRegion III Region II
APT - 383 K
• Stage I - Growth of sub oxides and an incipient silica layer growth• Stage II -1) Continued growth of sub oxides and also growth of silica observed, 2) Inward
growth rate of sub oxides drops (high activation energy) (mainly Si2O) due to fast conversion of Si+1 Si+2 Si+4
• Stage III, IV - Growth of sub oxides and silica slowed down
ReaxFF - 300 K
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Conc
entr
ation
(at%
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Distance (nm)
2.5 nm
Region III Region IRegion II
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Si2O %
SiO
SiO2
Conc
entr
ation
(at%
)
Distance (nm)
0
2
4
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16
Region I Region II Region III
Si2OSiOSiO2
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Region I Region II Region III
Si2OSiO
SiO2
Aver
age
Conc
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ation
(at%
)
0
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Si2O %
SiO
SiO2
0
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Si2O %
SiO
SiO2
Conc
entr
ation
(at%
)
Distance (nm)
• Stage I - Growth of sub oxides and an incipient silica layer growth• Stage II -1) Continued growth of sub oxides and also growth of silica observed, 2) Inward
growth rate of sub oxides still continues does not drop as in lower temperature case• Stage III, IV – 1) Continued growth of sub oxides (interstitial neutral oxygen atoms
surmount the activation energy barrier at threshold T of 500 K), 2) Interface (consisting of sub oxides) is thicker than low T and 3) Inward growth of silica slows down
APT - 548 K
ReaxFF - 1300 KGrowth Mechanism - High Temperature
Effect of Temperature on Growth Mechanism
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Si2O %
SiO2
SiO
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Si2O %SiO
SiO2
Conc
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ation
(at%
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Distance (nm)
0
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Region I Region II Region III
Si2OSiOSiO2
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Region I Region II Region III
Si2OSiOSiO2
Aver
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Conc
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(at%
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Conc
entr
ation
(at%
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Distance (nm)
2 nm
Region IRegion III Region II
APT - 383 K
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Conc
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Distance (nm)
2.5 nm
Region III Region IRegion II
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SiO
SiO2
Conc
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(at%
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Distance (nm)
0
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Region I Region II Region III
Si2OSiOSiO2
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Region I Region II Region III
Si2OSiO
SiO2
Aver
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Conc
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(at%
)0
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Si2O %
SiO
SiO2
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-5 -4 -3 -2 -1 0 1 2 3 4 5
Si2O %
SiO
SiO2
Conc
entr
ation
(at%
)
Distance (nm)
APT - 548 K
ReaxFF
Future
• Study of thermal oxidation (silicon) case
• Analysis of bonding information in different regions (bulk, interface) from APT data that could offer complimentary information to the bond length and bong angle analysis by ReaxFF.