Real Time Observations of Dislocation-Mediated Plasticity in the Epitaxial AI (011)/Si(100) Thin Film System
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27 Mat. Res. Soc. Symp. Proc. Vol. 619 ©2000 Materials Research Society
tilted so that the 022 reflection of only one of the aluminum variants is in a strong diffracting condition (this variant thus appears darker). It can be seen that the grain boundaries exhibit strong faceting, and that no triple junctions are present. The inset zone axis diffraction pattern shows the orientation relationship between the grains. Additionally, cross sectional 8 micrographs show that the grain boundaries are nearly perfectly perpendicular to the substrate. It is desirable when doing in-situ thermal cycling of TEM specimens to have samples that do not have a hole etched through them. This, in general, helps to reduce anomalous strains that may arise in the sample from thin foil bending (but it does not eliminate them, as we will discuss later).9 In these experiments we have deposited the aluminum films onto pre-prepared SIMOX wafers.' 0 The buried SiO 2 layer is used as an etch stop, permitting the creation of large, uniform electron transparent regions. The SIMOX wafers consist of a silicon layer thickness of 300 nm on top of 370 nm buried SiO 2. A cross section micrograph of a portion of the SIMOX wafer following sputter deposition of a thin polycrystalline aluminum layer is shown as Figure 2. The aluminum bicrystal depositions were done using a thermal evaporation system, as described in Ref. 8. The large-area plan view TEM samples were created using a slight modification of an existing sample preparation method." The samples were cut into 3 mm discs using an ultrasonic cutter, then ground with 600 grit sandpaper from the backside to approximately 150 Pm thickness. The discs were mounted onto a glass slide with beeswax until completely covered, then a hole was scratched in the wax in the center of the sample to allow exposure to the etchant. Etching was performed in a fume hood, underneath a stereomicroscope. The etchant was 3 : 5: 3 of hydrofluoric acid : nitric acid : acetic acid. Etching was halted when the sample began to show evidence of stopping at the SiO 2 - this is visible as uniform movement of a front of silicon at the bottom of the etched pit. Following creation of a large thin area (100's of pm in diameter) with an additional etch in a more dilute 3 : 5 : 6 solution, some of the samples were submerged into
.,,Aluminum thin film
_um
Figure 1 - Plan view brightfield micrograph and diffractionpattern of the aluminumfilm
Figure 2 -Brightfield cross sectional micrographof a poly-crystalline aluminum
microstructure(silicon substrateremoved),
layer as deposited on the as-purchased SIMOX.
buffered HF (10: 1 of H20 : HF) to remove the SiO 2 layer, while others were used with the SiO 2 layer largely intact. This was done to provide additional stiffness to the sample as well as to
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investigate the role of TEM sample based relaxation in our experiments. The anneals were performed using a Gatan 622 double-tilt heating holder and a JEOL 200 CX 200 kV microscope. Because the orientation relationship between the alumi
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