iMechanica - Journal Club Theme of May 2007: Experimental Mechanics of Nanobuilding Blocks - Comments

Re: Stress jump in compression of single crystals

Xiaodong Li — Wed, 07 Jan 2009 22:41:00 -0500

Thanks a lot Caizhi for your message. Yes, it will be of great interest to see large samples. I think that in addition to dislocation, surface also plays a very important role. Recent publications on the surface effects on the mechanical properties of nanosized samples give an in-depth underdtanding of the mechanisms that work at the samll scale. Below may you please see the papers that may be of interest to you.

Guofeng Wang and Xiaodong Li, "Predicting the Elastic Modulus of
Nanowires from First-principles Calculations on Their Surface and Bulk
Materials," Journal of Applied Physics (in press).

Guofeng Wang and Xiaodong Li, "Size Dependency of the Elastic Modulus
of ZnO Nanowires: Surface Stress Effect," Applied Physics Letters, 9
(2007) 231912.

Stress jump in compression of single crystals

Caizhi Zhou — Fri, 02 Jan 2009 17:04:09 -0500

Experimental micro-compression studies showed the staircase stress–strain behavior. However this behavior is not obvious in larger samples and the polycrystals. ‘Dislocation starvation’ mechanism often used to describe this behavior. However, in-situ TEM experiment just could verify this mechanism in small samples with diameter smaller then 200nm (Z.W. Shan on Nature Mater., 2008). In larger samples, dislocations could not be fully eliminated. And the measured flow stresses of micropillars are much lower than those of nanowires. That means the plastic deformation of micropillars not nucleation controlled.Currently, there are several explanations on staircase stress–strain behavior as following:One is that the moving dislocations was trapped by the junction and caused the intermittency of plastic deformation (S.I. Rao on Acta Mater., 2008). So the applied stress must be increased to sustain the applied strain rate. Actually, how often of the moving dislocations could be trapped by the junctions and whether the junctions are strong enough to cause such high stress jump in the stress–strain curves are two major questions on this explanation.The second explanation is the cross-slip of the moving dislocations divided them into several shorter segments, and then the stress need to be increased to bow out the shorter dislocation segment (J.A. El-Awad on JMPS, 2008). But this explanation could not be verified by atomistic simulation at this time. The above two explanations are both based on 3D dislocation dynamics simulation.The third explanation based on FEM simulation is that the rotation of sample after yielding could change the Schmid factor on slip planes and then cause the change of flow stress (Y.S. Choi on Scripta Mater, 2007). Actually, the rotated sample under bending may also trap moving dislocations at the neutral plane where there isn’t share stress and the applied stress need to be increased to bow out new dislocations. In addition, even the rotation of sample is not obvious, there must be some surface steps caused by the slip out of upper part of the sample. This surface steps decreased the original area of the slip planes on which active dislocations are moving, and then shortened the effective length of dislocation arms. This also might case the increase of applied stress. However, the underlying mechanisms are still under debate. More sophisticated modeling and simulations are still needed to determine which conjecture would take the dominate role on the stress jump in compression of single crystals.

Playing with nanotubes.

Karen Peterson — Sun, 16 Mar 2008 20:52:15 -0400

That's true, there is still so much to discover about nanotubes. Hopefully computational modeling will help us improve what we know about the CNT. The Lieber group is doing amazing and i really hope things will work out well.

Karen, rpg games.. in tubes

Manipulation of individual

Jianyu Huang — Thu, 04 Oct 2007 22:48:49 -0400

Manipulation of individual SWCNT has not been possible. Using 200 kV TEM, the SWCNT is likely to be burned rapidly by e-beam irradiation. 80 kV or 120 kV is ideal. At such low kV, your resolution is not that great, hopeless to image point defects. However, if you have a Cs-corrector, it is possible to image point defects, such as 5/7, or individual vacancies. Iiijima's group published some papers in this regard recently.

imechanica get together at MRS

Rohit Khanna — Thu, 04 Oct 2007 00:42:30 -0400

Prof. Oyen,

Regarding imechanica get-together at MRS Fall meeting, i will be happy to volunteer.

Sorry, i checked your post on imechaica today only. let me know if i can help you.

Best Regards,

Rohit

individual SWNT Manipulation

gurpreet — Thu, 06 Sep 2007 03:06:44 -0400

Great website. Great to see all the biggies!!

I was curious if there any group who has done 3-d manipulation of individual SWNTs? is it possible at all? Also is it possible (or how difficult) to see defects in an individual SWNT using 200 kV TEM (F-20)? Please note that I am not talking about a SWNT Rope. Thank You.

Gurpreet Singh

Seeking volunteers for MRS get together planning

MichelleLOyen — Mon, 03 Sep 2007 05:31:54 -0400

I would very much like to have an iMechanica get-together at the MRS fall meeting in Boston (26-30 Nov. 2007). I am seeking at least a few volunteers to help with organization and running of such an event; please reply here or email me if you are willing to get involved!

Michelle

Get-together at MRS FAll 2007

Rohit Khanna — Fri, 31 Aug 2007 02:31:50 -0400

hi,

May i know if you have any plans to organize imechanica get-together during MRS Fall 2007 meeting.

Best wishes,

Rohit

Re: gold nanopillars

Xiaodong Li — Sun, 10 Jun 2007 12:25:42 -0400

Thanks, Fred. I just read this paper and found that this is paper of great interest to experimental community. I like the paper a lot. Excellent! I believe that you will see a lot of follow up papers soon.

Strengthening in gold nanopillars with nanoscale twins

Fred Sansoz — Tue, 05 Jun 2007 22:01:16 -0400

Food for (experimental) thought: A new size effect in metallic nanowires due to interfacial plasticity predicted by molecular dynamics simulation.

To learn more, read the following article:

K. A. Afanasyev and F. Sansoz, Strengthening in gold nanopillars with nanoscale twins, Nano Letters, 2007 (ASAP article)

Size-dependent strengthening effects in nanowires

yfzhang — Sun, 03 Jun 2007 06:37:06 -0400

Dear Fred Sansoz

I fully agree with your comments about microstructure size effects in nanowires.The mechanics propertie of one dimensional nanomaterials may be closely related to the microstructre, such as stacking faults, dislocations, and twins. The anisotropic performance of mechanical properties is also very strong in nanowires and tubes. So, the experimental datum is scattered. Obviously, experimental studies are required to clarify the true deformation features and mechanisms of the nanowires. Researchers have investigated the mechanical properties of various nanowire systems using different techniques, such as nanoindentation, atomic force microscopy (AFM) and transmission electron microscopy . In situ experiments provide direct visualization and description of the events as they happen and give qualitative information about the structure of deformation. It is need develop some new in situ experimental technology in nano and atomic scale to clear some basic deformation mechanism. Recent some paper show a good development in this fields. The paper list is following:

1.Y. Huang, S. Chen, S. H. Jo, Z. Wang, D. X. Han, G. Chen, M. S. Dresselhaus, and Z. F.Ren, Phys. Rev. Lett. 94, 236802 (2005).2.Y. Huang, S. Chen, S. H. Jo, Z. Wang, D. X. Han, G. Chen, M. S. Dresselhaus, and Z. F.Ren,Nature, 439,281(2006).3. F. Yu, O. Lourie, M. J. Dyer, K. Moloni, T. F. Kelly and R. S. Ruoff, Science, 287, 637-640 (2000).4. Ding, L. Calabri, X. Chen, K. M. Kohlhaas, and R. S. Ruoff, Composites Science and Technology, 66, 1109-1121 (2006).5. C-H. Ke and H.D. Espinosa. Small, 2, 1484(2006).

6. Zhu, A. Corigliano and H.D. Espinosa. Journal of Micromechanics and Microengineering, 16, 242(2006).

7.D.Han, Y.F. Zhang, K. Zheng, Z. Zhang, Y.J. Hao, X.Y. Guo, J. Yuan and Z.L. Wang, Nano letter. 7, 452 (2007).

Yuefei zhang

iMech Get-together at MRS Fall 2007

MichelleLOyen — Thu, 31 May 2007 16:58:13 -0400

Thanks. Let's have a best-ever showing in this symposium and a comprehensive proceedings volume to document the current state-of-the-art!

In conjunction with this symposium, we will definitely be planning an iMech get-together for the MRS Fall 2007 meeting! Details to come closer to the time.

A journal special issue bridging simulation and experiments

Xiaodong Li — Thu, 31 May 2007 14:05:43 -0400

One more. Dr. Jun Lou and Dr. Junlan Wang are co-editing a special issue on Nanomechanics and Nanostructured Multifunctional Materials: Experiments, Theories, and Simulations for Journal of Nanomaterials. This will be a good opportunity to promote bridging nanomechanics simulation and experiments.

MRS Fall meeting 2007

Xiaodong Li — Thu, 31 May 2007 11:25:30 -0400

Thanks. This symposium - Fundamentals of Nanoindentation and Nanotribology IV is timely and of great interest. Hope we can have sessions on bridging simulation and experiments. We may have another Imechanica get-together meeting.

Load and depth control versus limits

MichelleLOyen — Thu, 31 May 2007 05:55:15 -0400

These comments are primarily focused not on load- or depth- control of indentation experiments but really on whether comparisons are made based on a load- or depth-limit (maximum value). I suspect the simple response to these questions would include the idea that no good comparison would involve only a single data point for comparison of widely different materials; the data from different materials should (with modern automation of nanoindenters) be compared over a range of values in terms of the load- or depth-limits. If I did have to choose one single comparison to make, it would be for different loads and comparable depths.

A separate issue entirely is the control mode of the experiment itself, in terms of load- or displacement-control or even hybrid conditions (spring loading). For polymers and PMCs, of course, this matters a great deal as the data analysis is wholly dependent on the control mode in terms of the viscoelastic responses, and it goes without saying that an Oliver-Pharr approach for making hardness and modulus measurements is insufficient for any control mode!

Journal Club Theme of May 2007: Experimental Mechanics of Nanobuilding Blocks

Xiaodong Li — Mon, 30 Apr 2007 21:07:59 -0400

Welcome to the May 2007 issue. This issue focuses on experimental nanomechanics of nanobuilding blocks. The extremely small dimensions of nanobuilding blocks (for instance, nanoparticles, nanotubes, and nanowires) have imposed great challenges to many existing instruments, methodologies, and even theories. In this issue, we will discuss – (1) experimental techniques and (2) size-effects.

The methods that have been developed and used for measuring the mechanical properties of isolated individual nanobuilding blocks include uniaxial tensile loading using a nanomanipulation stage, in-situ compression of nanoparticles and nanopillars, mechanical/electric-field induced resonance, AFM bending, and nanoindentation. The following is a brief summary of these methods for discussion.

Can one perform tensile tests on a nanowire as we normally do on a big dog-bone sample? Prof. Rod Ruoff’s group realized such challenging tests on individual multiwalled carbon nanotubes (MWCNTs) using a testing stage based on a nanomanipulation tool operating inside a SEM. The nanomanipulation stage makes 3-D manipulation possible – picking, positioning, and clamping of individual 1-D nannomaterials. The individual 1-D nanomaterials were attached and clamped to AFM probes by a localized electron beam induced deposition of carbonaceous materials inside the SEM. A single 1-D nanomaterial so clamped between two AFM probes was then tensile loaded by displacement of the rigid AFM probe and the applied force was measured at the other end by the AFM cantilever deflection of the other, compliant AFM probe. The measured force-elongation data were converted, by SEM measurement of the nanomaterial geometry, to obtain a stress-strain curve. In addition to the Young’s modulus, breaking strength can be measured by this method. Prof. Rod Ruoff’s paper is the first one under discussion in the present issue of journal club.

Yu MF, Lourie O, Dyer MJ, Moloni K, Kelly TF, Ruoff RS, Strength and breaking mechanism of multiwalled carbon nanotubes under tensile load, Science, 287 (2000) 637-640.

Compression tests on small pillars inside a SEM provide a new way to study the sample size effects. To mimic the conventional compression tests, FIB was used to cut a bulk sample to a smaller size (top-down approach). A flat nanoindenter was then used to perform uniaxial compression tests on the FIB cut sample in situ. Engineering stress-strain curves can be obtained. Sample’s morphology change such as slip bands can be studied by SEM. The second paper selected for discussion is:

Uchic MD, Dimiduk DM, Florando JN, Nix WD, Sample dimensions influence strength and crystal plasticity, Science, 305 (2004) 986-989.

Prof. C. M. Lieber’s group used an AFM operating in lateral-force mode to bend cantilevered MWCNTs that were deposited on a low-friction MoS2 surface and pinned down at one end by overlaying SiO2 pads using lithography. The bending modulus of individual MWCNTs was calculated from deflection of a cantilevered MWCNT and the lateral force applied by the AFM probe. Another approach is to use AFM to perform indentation three point bending tests on the 1-D nanomaterials deposited on a membrane having nanopores. The suspended 1-D nanomaterial was considered as a double-clamped simple beam that was clamped to the membrane by its high surface energy at the ambient humidity condition. By positioning the AFM tip directly on the center of the 1-D nanomaterial spanning the pore and applying an indentation force, the Young’s modulus of individual 1-D nanomaterials can be obtained from the AFM tip force-deflection curve. Below please find Prof. C. M. Lieber’s paper:

Wong EW, Sheehan PE, and Lieber CM, Nanobeam mechanics: elasticity, strength, and toughness of nanorods and nanotubes, Science, 277 (1997) 1971-1975.

To study the size-effects of nanoparticles is extremely difficult. Prof. Bill Gerberich’s group performed compression tests on individual silicon nanospheres using in situ nanoindentation techniques. In situ TEM provides insightful information such as dislocation initiation and motion, onset of plasticity, and fracture mechanisms. Here I would like to use one of Prof. Bill Gerberich’s papers for discussion:

Deneen J, Mook WM, Minor A, Gerberich WW, Carter CB, In situ deformation of silicon nanospheres, Journal of Materials Science, 41 (2006) 4477-4483.

In a cantilever vibration test, individual cantilevered 1-D nanomaterials are thermally oscillated using a variable-temperature sample holder in a TEM or oscillated by directly inducing the mechanical resonance using an electric field. Using continuum beam mechanics, the bending modulus of 1-D nanomaterials can be calculated from the measured resonance frequency and the selected nanomaterial geometry. Below, please find the two representative papers:

Treacy MMJ, Ebbesen TW, and Gibson JM, Exceptionally high young's modulus observed for individual carbon nanotubes, Nature, 381 (1996) 678-680.

Wang ZL, Poncharal P, and de Heer W A, Measuring physical and mechanical properties of individual carbon nanotubes by in situ TEM, Journal of Physics and Chemistry of Solids, 61 (2000) 1025-1030.

Nanoindentation techniques and theories have been well established for the mechanical characterization of solid surfaces and thin films. The major challenge we are facing is: can we extend application of traditional nanoindentation approaches to 0-D (nanoparticles) and 1-D nanomaterials (nanowires/nanobelts) for directly measuring their mechanical properties? The early work includes:

Mao SX, Zhao MH, and Wang ZL, Nanoscale mechanical behavior of individual semiconducting nanobelts, Applied Physics Letters, 83 (2003) 993-995.

Li XD, Hao HS, Murphy CJ, and Caswell KK, Nanoindentation of silver nanowires, Nano Letters, 3 (2003) 1495-1498.

The mechanisms (physics/science) of size-effects are still, to a large extent, unknown. One of the basic debates is size-dependency of Young’s modulus. The reported Young’s modulus of many nanobuilding blocks exhibits a large variation relative to the corresponding values of the bulk materials. For many metallic nanowires or small-scale samples, the strength was reported to increase as size decreases. The above selected papers cover the mechanisms of size-effects. Insightful discussion on this topic is greatly needed.

Previous discussions and selected papers on experiemntal mechanics can be found in this forum and may help stimulate further discussions.

Please note that due to space restrictions, I am not able to include all the papers that I know of. I sincerely apologize for any omission of papers that should be included in this post.