Updates of Iowa State University

S. Dumpala, S. Broderick and K. Rajan

May – 14 - 2013

Summary of Previous Results

Atom probe experimentation-Atomic scale measurement of gas-solid reactions of Al and Oxygen and Si and O systems

- Compound formation- Study of Interfacial chemistry

-Environmental chamber for in-situ gas reactions – Unique features and capabilities

-Collaborations:- Maryland – Sample prepared by Maryland by reacting Si

microtips; analysis of samples by ISU- Van Duin group – Use of atom probe results for

experimental inputs into ReaxFF simulations

Progress

Atom probe experimentation

-Refinements in Environmental chamber set up for in-situ gas reactions

- Oxidation studies of Al using new set up of E-cell

- Study of Si tips from Maryland using APT

E-Cell : Modifications/Improvements1. Cooling water lines were installed for

turbo pump

2. Burst disk valve is added (prevent any accidental excess pressure build up of the chamber)

3. Mass flow controller and pressure regulator is added with flow sensor bypassed with pressure sensor to be able to regulate the flow with desired pressure set point very close to the main reaction cell (small chamber)

4. Prssures as low as 0.1 milli torr can be regulated with the new setup.

5. Digital reader/regulator of the pressure is included.

6. Base pressures is as low as 1 x 10-5 torr

1. 4 tip holder was used.2. All the four tips were cleaned using laser atom probe

runs prior to oxidation reaction to remove the contamination and native oxide layer

3. Oxidation was done using the E-cell at 450 C (sample temperature), 20 milli torr for 30 min

4. Laser atom probe ( 0.5 nj) was used to study the oxidized needles.

Al – Oxidation with New set up of E-cell

Study of InterfacesDiffusion Profiles - APT

Al- Iso surface 82.39%

Si Tips from Maryland :

Sample 2 (Anode Voltage: 250 V, 50 monolayers of Argon exposure) – Tip 1

1. Laser Atom probe was employed

2. Laser energy – 1 nj

Sample 2 (Anode Voltage: 250 V, 50 monolayers of Argon exposure) – Tip 2

Sample 2 (Anode Voltage: 250 V, 50 monolayers of Argon exposure) – Tip 7

1. No SEM done

2. Was able to collect 2.8 million data

3. Thick oxide layer at the very tip and higher Argon content observed here

Bare Si tip

1. No SEM done

2. Lower oxide content

Mass Spectra Comparison

1. More background noise

2. Detection of Argon

3. Higher hydrogen content

Base Si tip

After exposed to Ar beam

Future

• More experiments as function of temperature and pressures

• Testing the Si tips from Maryland using FIM

1. Check other condition tips (Different beam currents)

2. Different deposition thickness of monolayers

3. FIM studies