Outline. L13. Mechanics of Nanostructures: Tensile Loading and Fracture Mechanics

Transcription

1 L13. Mechanics of Nanostructures: Tensile Loading and Fracture Mechanics Outline 1. Introduction 2. Tensile Test work overview 3. Recent work in Ruoff group Carbon nanocoil Crystalline Boron Nanowire Arc-grown MWCNT Graphene Ribbon 4. Summary

2 Part One: Tensile Test Introduction Tensile Test Gere, J., Timoshenko, S.P., Mechanics of Materials, 4 th ed, 1997, PWS Publishing Company

3 Stress-Strain Diagram necking Stress-strain diagram for a typical structure steel in tension Gere, J., Timoshenko, S.P., Mechanics of Materials, 4 th ed, 1997, PWS Publishing Company Part Two: Tensile Test Experiments Overview

4 SEM based Tensile Test: MWCNTs & SWCNT Bundles Tensile stretching of individual MWCNTs We continue to study the mechanical properties of MWCNTs with our nano-manipulator. Mechanical tensile testing schematic SEM images of tensile test Yu MF, Lourie O, Dyer MJ, Moloni K, Kelly TF, and Ruoff RS, Strength and breaking mechanism of multiwalled carbon nanotubes under tensile load, SCIENCE, 287, (2000).

5 Breaking mechanism of MWCNT The change of the MWCNT length before the break and after the break strongly suggests the pullout of MWCNT internal shells at the break and thus a swordin sheath breaking mechanism. Yu MF, Lourie O, Dyer MJ, Moloni K, Kelly TF, and Ruoff RS, Strength and breaking mechanism of multiwalled carbon nanotubes under tensile load, SCIENCE, 287, (2000). Tensile Test Results Partial tensile test results on MWCNTs. Yu MF, Lourie O, Dyer MJ, Moloni K, Kelly TF, and Ruoff RS, Strength and breaking mechanism of multiwalled carbon nanotubes under tensile load, SCIENCE, 287, (2000).

6 Tensile-Stretching of SWCNT Ropes SWCNT ropes are entangled with each other in SWCNT samples, so a different approach is used to study tensile loading of SWCNT ropes. Yu MF, Files BS, Arepalli S, and Ruoff RS, Tensile loading of ropes of single wall carbon nanotubes and their mechanical properties, Phys. Rev Lett, 84, SWCNT (con t) Yu MF, Files BS, Arepalli S, and Ruoff RS, Tensile loading of ropes of single wall carbon nanotubes and their mechanical properties, Phys. Rev Lett, 84,

7 AFM based Tensile Test: Micro/Nano Fibers Tensile Test on Polymer Fiber An AFM-based nano-indentation system was used to perform tensile tests on micro-scale polymer fiber. E.P.S. Tan and C.T. Lim, A novel approach to tensile testing of micro- and nanoscale fibers. Rev. Sci. Instrum., (8):

8 Tensile Test Results Raw data from AFM system Stress-strain plot of microfiber E.P.S. Tan and C.T. Lim, A novel approach to tensile testing of micro- and nanoscale fibers. Rev. Sci. Instrum., (8): Tensile Test on PEO Nanofiber A single electrospun polyethylene oxide (PEO) nanofiber is stretched with AFM cantilever tip with a micromanipulator. Schematic diagram of the tensile test of the nanofiber using a piezoresistive AFM tip. E.P.S. Tan, C.N. Goh, C.H. Sow, and C.T. Lim, Tensile Test of a Single Nanofiber Using an Atomic Force Microscope Tip. Appl. Phys. Lett., 86(6), 2005.

9 Result (left) single fiber manipulation (top) tensile test result E.P.S. Tan, C.N. Goh, C.H. Sow, and C.T. Lim, Tensile Test of a Single Nanofiber Using an Atomic Force Microscope Tip. Appl. Phys. Lett., 86(6) (2005). Part Three: Ruoff Group Recent Work

10 Experiment Tool: Nanomanipulator Four-degree of freedom (x,y,z linear motion and rotation) Two separate stages (X-Y stage, Z-θ stage) Sub-nanometer motion resolution In-situ EBID Clamping

11 EBID Clamping Electron beam induced deposition (EBID) is the process of using a high-intensity electron beam to deposit structures on a scanned surface. EBID is commonly used to make clamps in situ inside SEM. Carbon tube Hydrocarbon molecules AFM tip Exposure area Clamp EBID principle A carbon tube in contact with an AFM tip, before and after EBID clamping Rapid EBID Clamping EBID clamping relies on residual hydrocarbon in SEM vacuum chamber is slow and therefore clamp failure is quite common in tensile tests. Small amount of low vapor pressure hydrocarbon source was put onto AFM tip surface, and the deposition rate can be increased tens of times. Carbon Nanofiber EBID Clamp AFM tip Side view and top view of a clamp created with rapid EBID method W. Ding, D.A. Dikin, X. Chen, R. D. Piner, X. Wang, X. Li R.S. Ruoff*, E. Zussman* (2004), J. App. Phys., in press

12 Deposition Rate vs. Time & Distance Array of pillars were deposited with varied distance to the paraffin source and also varied the deposition time on a silicon wafer. Paraffin SEM image of EBID-deposited pillar array (30 o tilt). The deposition time from left to right was 2, 4, 6, 8, and 10 minutes, respectively. Pillar height versus deposition time and its linear fit Mechanical Properties- Nanoindentation The mechanical properties of the EBID material was obtained through nanoindentation study. Paraffin Paraffin (a) (b) (a) SEM image of a thin EBID film; (b) AFM image of a thin EBID film; (c) Nanoindentation results on three films deposited at 3, 12 and 20 kv accelerating voltage. (c)

13 Clamp Material Characterization Through Raman, EELS, SIMS, and TEM study, the EBID film is amorphous, has more sp 2 - than sp 3 -bonded carbon, and contains some hydrogen. Carbon (a) (b) (c) (a) High-resolution TEM image of EBID film. (b) EELS spectrum of the EBID film. (c) SIMS analysis of a EBID film. Hydrogen Application- EBID Clamping Tensile Test Resonance Test

14 Tensile Test: Carbon Nanocoil Carbon Nanocoil: Source Images of nanocoils CVD-synthesized on Fe catalyst coated ITO substrate High-yield, 95% coiled Synthesis by : Zhang et al, Jpn. J. Appl. Phys. 39 (2000) L1242

15 Carbon Nanocoil: TEM Image On lacey carbon support film: empty space Carbon Nanocoil: Tensile Test Schematic EBID clamping load SEM image of carbon nanocoils and schematic of tensile loading of an individual nanocoil.

16 a b c (a) A nanocoil was picked up by an AFM tip and clamped onto it (b) the nanocoil was extracted from the substrate and the nanocoil was extended (c) The nanocoil was detached from the substrate. Rod Ruoff Northwestern University Nanotechnology Carbon Nanocoil: General Equation F ϕ N F = F cosϕ = Bending: M F = F cosϕ R = F R h F Shear: QF TF NF d R ξ= H =H d Torsion: MF H = h/2π G= 8β H 2 R2 + H2 R=R d K ξ Nd Northwestern University FH Tension: QF = F sin ϕ = 128β H R 2 R2 + H2 β = 2(1 + υ ) + H R2 + H 2 FRH = R2 + H 2 FR R +H2 2 TF = F sin ϕ R = F R 2 + R2 + H 2 8α s R R R +H 2 2 R2 + H2 + 2 = FR 2 R2 + H 2 64 R 4 R2 + H 2 α s = (7 + 6υ ) 6(1 + υ ) G: Shear modulus K: force constant N: turns of coils Rod Ruoff Nanotechnology

17 Carbon Nanocoil: Small Pitch Nanospring R/h=4 Spring constant (N/m) (a) Relative elongation (%) Contribution of components (%) (b) Torsion Shear Bending Relative elongation (%) The force constant vs the relative elongation The contribution of the force components vs the relative elongation Carbon Nanocoil: Large Pitch Nanospring R/h=0.2 Spring constant (N/m) (c) Relative elongation (%) Contribution of components (%) 100 (d) 10 1 Torsion Bending Shear Tension Relative elongation (%) The force constant vs the relative elongation The contribution of the force components vs the relative elongation

18 Tensile Test: Crystalline Boron Nanowires Boron Nanowire: Source Boron is a unique element. The boron solids have high melting points (~2075 o C), low density (2340 kg/m 3 ), high modulus (~400 GPa) and high hardness (Knoop: ). Crystalline boron nanowires have been synthesized by the chemical vapor deposition method. SEM images of crystalline boron nanowires on an alumina substrate A boron nanowire protruding outward at the ledge of a half-cut copper TEM grid Otten et al, J.Am. Chem. Soc.,124 (17), 2002

19 Boron Nanowire: Tensile Test Boron Nanowire: Result The Young s modulus of the boron was obtained from linear data fitting of the slope of the stress-strain curve. Stress-strain diagram of a boron nanowire Tensile strength and Young s Modulus versus nanowire length W Ding, L Calabri, and RS Ruoff, to be submitted

20 Tensile Test: Arc-grown MWCNTs MWCNT: Source Arc-grown Multi-wall Carbon Nanotubes (MWCNTs) from MER Corp. AZ. were studied in this work. A simple fractionation process was used to remove some impurities and increase nanotube concentration. SEM image of powdered cathode deposit core material with 30-40% MWCNT content from MER Corp. SEM image of separated MWCNTs on a silicon wafer, after fractionation.

21 MWCNT: Sword-in-sheath Fracture Multi-wall carbon nanotubes fracture in a sword-in-sheath manner during tensile test. Inner shells Outer shell Inner shells outer shell SEM images of sword-in-sheath fracture of a MWCNT under tension MWCNT: Diameter Measurement Cantilever holders were designed to hold a shortened AFM chip for nanotube diameter measurement in TEM. (a) Gatan TEM tensile stage (c) SEM holder to hold TEM holder AFM cantilever AFM cantilevers (b) TEM cantilever holder model (d) SEM image of a cantilever chip in the holder

22 MWCNT: Diameter Measurement (con t) The nanotube diameter is measured inside TEM before and after the tensile test. SEM image of a MWCNT fragment at AFM tip TEM image of a MWCNT fragment MWCNT: Tensile Testing Result Length m Outer Diameter nm Max. Strain % Tensile Strength * GPa Young s Modulus GPa *: assuming only the outer shell sustain the tensile load. W Ding, L Calabri, and RS Ruoff, to be submitted

23 Tensile Test: Thin Graphite Film Graphite Ribbon

24 Graphite Ribbon: Tensile Test Graphite Ribbon: Deformation W Ding, L Calabri, and RS Ruoff, to be submitted

25 Graphite Ribbon: Deformation W Ding and RS Ruoff, to be submitted Northwestern University Rod Ruoff Nanotechnology