Insitu Testing of Nanoscale Thin Films in TEM

1
In-situ Testing of Nanoscale Thin Films in TEM

• Aman Haque, Dept. of MIE
• Scott Robinson, ITG
• University of Illinois at Urbana-Champaign

2
Motivation
In-situ, quantitative studies on freestanding
films in TEM/SEM allow direct observation of
deformation mechanisms
Nanoscale Materials Modeling
Qualitative information
Bridging the gap
Quantitative information
3
In-situ Testing Challenges

• For Tensile Testing
• Freestanding specimen preparation (with known
  uniform cross-section
• Gripping
• Force (mN)/Displacement (nm) generation and
  measurement
• Bending moment prevention
• Experimental setup miniaturization to fit in 10mm
  x 3 mm x 100 mm space in TEM

4
How Small are MEMS?
100 mm
100 mm
30mm
X-section of human hair
A pin tip
Micro-STM
T-cells attacking a cancer cell
Electrostatic actuator
Red blood cells
7 mm
35mm
D 100 mm
Courtesy Taher Saif
5
MEMS-based Tensile Testing

• Right end of the chip is pulled by a
  piezo-actuator
• Displacement is transmitted to the force sensor
  beam
• Deflection of force sensor beam (read by
  displacement sensor A) gives force on specimen
• Elongation of the specimen is given by
  displacement sensors (A B)

MEMS-based Tensile Testing The freestanding
specimen is integrated with force and
displacement sensors to provide on-chip testing
capabilities inside TEM/SEM
6
Device Fabrication
7
Device Characteristics

• Dry fabrication lower prestress in specimen
• ?/? resolution 5 MPa/0.03 (calibrated by
  Nanoindenter)
• Pre-stress/Stress-relaxation measurement

• Auto gripping
• Supporting beams reduce specimen end rotation by
  5 orders of magnitude
• Small experimental setup size

8
Experimental Setup
Conventional (Gatan Model 654, 671, 672) TEM
Straining
9
Experimental Setup
A
B



Spring loading of the test chip on to the
straining stage. The test chip is gripped when
the gap A-B is closed
10
Experimental Setup
11
Aluminum Results
Grain size 50 nm lt111gt texture in Thickness
direction Random in-plane orientation
12
Aluminum Results (Contd.)
TEM micrographs of two separate areas in a 100 nm
thick specimen under zero stress and strain.
Initially, dislocations are seen in only few of
the grains.
13
Aluminum Results (Contd.)
40.5 MPa stress and 0.05 strain. Stacking faults
and twins are seen. Grain A is also shown in next
slide with changed contrast due to deformation in
the neighboring grains
14
Aluminum Results (Contd.)
94.3 MPa stress and 0.131 strain. Dislocation
activities are observed in the grain boundaries
15
Aluminum Results (Contd.)
160.8 MPa stress and 0.197 strain. Dislocations
are observed in grain boundaries and also in the
grain interior
16
Aluminum Results (Contd.)
222.3 MPa stress and 0.31 strain. Dislocations
are observed in both grain interiors and
boundaries
17
Aluminum Results (Contd.)
281.2 MPa stress and 0.403 strain. Grain A and
its neighbors are shown in next figures
18
Aluminum Results (Contd.)
(a) 338.2 MPa stress and 0.51 strain, and (b)
406.6 MPa stress and 0.53 strain. Dislocation
activities are taking place in A-B, A-H, A-G,
A-F, and F-O boundaries. Note the contrast change
in grain M
19
Aluminum Results (Contd.)
(a) 458.5 MPa stress and 0.69 strain, and (b)
509.2 MPa stress and 0.82 strain. Continued
dislocation activities in A-B, A-H, F-O
boundaries.
20
Aluminum Results (Contd.)
(a) 536.9 MPa stress and 0.90 strain, and (b)
566.2 MPa stress and 0.98 strain. Dislocation is
being generated in K and Q grain interior. L is
changing contrast due to boundary dislocations
21
Aluminum Results (Contd.)
(a) 618 MPa stress and 1.04 strain. K grain is
contrast is changes due to dislocation motions.
22
Aluminum Results (Contd.)
(a) 665 MPa stress and 1.29 strain, and (b)
680.2 MPa stress and 1.368 strain. Only grain L
contains grain boundary dislocations. Grain O has
rotated and is now free of dislocations.
23
Aluminum Results (Contd.)
680 MPa stress and 1.36 strain
The grain B changed contrast due to resulting
deformation. Grain C experienced a partial
dislocation motion in the direction shown by the
arrow, leaving a stacking fault behind.
24
Aluminum Results (Contd.)
Fractured specimen
Intragranular crack growth
25
Conclusions

• We have developed a MEMS-based technique for
  tensile testing to nanoscale freestanding thin
  films in-situ inside SEM/TEM
• For the first time, quantitative in-situ tests in
  TEM were performed on 100 nm thick Aluminum
  specimens
• Dislocation activities were observed mostly in
  the grain boundaries
• Mostly elastic deformation and brittle fracture
  were observed.