Presentation on theme: "Manifestation of external size reduction effects on the yield point of nanocrystalline rhodium using nanopillars approach By: Omar Alshehri Winter 2012."— Presentation transcript:
Manifestation of external size reduction effects on the yield point of nanocrystalline rhodium using nanopillars approach By: Omar Alshehri Winter 2012 Waterloo, ON
Why rhodium? Has not been fabricated nor studied in the nanoscale. Has promising applications in catalysis and optics.
Why Nanomechanical Properties? We are the first ever to investigate the nanomecahnical properties of Rh. To assure usefulness for being incorporated in a device.
Methods of Studying Nanomecahnics Nanoindentation. Uniaxial tension. Uniaxial compression. Three/four point bending. Plane-strain bulge testing. Crack propagation testing.
Why Choosing Electroplating? High quality deposits. Low cost. Process simplicity. Provides the possibility of fabricating sub 100nm pillars [1, 2].
Electroplate Rh for size X (size = diameter) Check the pillars under SEM. Do they have proper aspect ratio? Are they free of defects (no cracks, no bent pillars, etc.)? Compression test Check the compressed pillars under SEM. Have they got compressed properly (no buckling, no barrelling, etc.)? Choose some pillars from the array (from for example) and draw a map for them to be able to find them easily under the indenter microscope Report the results, then send the sample to HR- TEM and other tests Yes No Yes The Steps Followed
1 st : Electroplating The nanopillars were fabricated using a template. The templates were fabricated at the ECTI at the University of Toronto. To show the size effect, four sizes were chosen : 1135, 535, 205, and 125nm.
Silicon substrate Titanium deposition Gold deposition PMMA deposition E-beam development Etching of exposed areas 1 st : Electroplating (cont.) Rh electroplating
Silicon substrate Titanium deposition Gold deposition PMMA deposition E-beam development Etching of exposed areas 1 st : Electroplating (cont.) Rh electroplating PMMA etching
2 nd : SEM checking A pillar to be suitable has to be 1- Crack free. 2- Has 3:1(or lower) aspect ratio. BucklingFalling down
Remark In characterization, report the unsuccessful tests because you may benefit from them more than the successful ones.
SEM checking (cont.) SEM images showed that the pillars have a nanocrystalline structure.
3 rd : Compression test (Substrate Effect) We face a problem of substrate effect: Au and Ti are weaker than Rh. Silicon substrate The compression tip
Compression test (Substrate Effect) This effect makes it hard to find the yield point of the pillar. We dealt with this effect by using the two lines method for finding the yield point.
4 th : HR-TEM test HR-TEM was used for two purposes: 1- To check the nanocrystallinity. 2- To check the substrate effect.
HR-TEM test (cont) TEM images of 1000 nm Rh pillars at di ﬀ erent magniﬁcations, before and after compression. (Top left) Rh nanopillar before compression. (Top right) Rh nanopillar after compression. (Bottom left) high-magniﬁcation image of the top of an uncompressed pillar. (Bottom right) high-magniﬁcation image of the top of a compressed pillar.
HR-TEM test: yes; nanocrystalline HRTEM nanograph of a 1000 nm Rh nanopillar after compression. The white, black and gray regions indicate di ﬀ erent grains. The color di ﬀ erence is due to di ﬀ erent orientations of these grains.
HR-TEM test: yes; substrate effect A 1135nm pillar before (left) and after (right) compression. Note how the adhesion layer has popped up, or bulges, from both sides of the bottom of the pillar. For small pillars, the bulge height almost equal to the pillar height.
5 th : EDX test Energy Dispersive X-Ray Analysis (EDX) was used to find out the impurities present in the pillars.
EDX test: Tl + Cu impurities Using Energy Dispersive X-Ray Analysis (EDX), the spectrum of the 1000nm rhodium pillars after compression indicating the presence of mainly the thallium impurities.
6 th : Ebeam diffraction test Ebeam diffraction test was used to further check the if the miscrostructure has changed after compression. NO CHANGE. Different brightness is due to different slicing thickness. After compression Before compression
Results’ preliminaries: The Size Effect There are two deformation modes that act simultaneously for this nanosized and nanocrystalline pillars: 1- Dislocation-driven mode. A B C D
The Size Effect Which one prevails the other? Depends on the size: Large pillars dislocation mode. Small pillars grain boundary sliding
The Results The size-yield point for each size is as follows: Size 1135nm535nm205nm125nm Yield Point 4200 MPa4600 MPa2400 MPa2100 MPa Bulk 67 MPa
The results (cont) There are three ways the data can be interpreted. Size 1135nm535nm205nm125nm Yield Point 4200 MPa4600 MPa2400 MPa2100 MPa Bulk 67 MPa
The Results (cont.) As seen in all three scenarios, the Rh “eventually” get weakened as size get reduced, an effect consistent with literature for nanocrystalline materials [3,4]. The chosen one is neglecting the 500nm test due to the difference in the people who did the experiment + fabrication mistake.
The Grand Conclusion We have demonstrated for the first time in the field of nanotechnology that size effect is not only: strengthening or weakening. We found a third case: strengthening-then-weakening.
Future Work: Recommendations Future work should: 1- Use FIB fabricated pillars. Reprinted with permissions from  and .
Future Work: Recommendations (cont) 2- Use harder-than-Rh conduction + adhesion layer. 3- Study the strain rate sensitivity.
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