iMechanica - nanomaterials - Comments

How can we use the concept of temperature for few atoms

Teng zhang — Tue, 21 Oct 2008 05:35:48 -0400

Very interesting topic!

I read the first parts of the book Thermal physics written by C.Kittel under the suggestion of Prof. Suo. I post this comment to explain what I learn form that book.

First, the thermal contact plays a signifcant role in the definition of the temperature and entropy. As for two systems, we can obtain the total degeneracy of all the accessible configurations after the thermal contact. If the number of particles in at least one of the two systems is very large, the numbers of that total configurations can be replaced by the number of the states in the most probable configuration. Only in this case, the additivity of the entropy is valid.

As defined in the lectures of Prof. Suo:1/T = change in the logarithm of the number of quantum states divided by the change in the energy of the system, everything else being fixed. The introduction of temperature is to describe the equilibrium state of two systems under thermal contact. It is noted that this equilibrium state is just the most probable configuration. The formalism of T is also derived from the maximum of total degeneracy of all the accessible configurations. In this sense, we can think T is corresponding to the most probable configuration. However, the states expect the most probable configuration can be observed only when the number of particles in at least one of the two systems is very large. If the two systems are both small, then we can see that many different states expect of the most probable configuration which can be represented by the temperature.

Thus, for a small system with only few atoms, we can define the temperature of this kind system via letting it contact with a very large system. However, when we make two small systems together, how can we obtain the final temperature of these two systems, even though we know the temperature of them before contact. If we make they contact with a large system, this may destroy the states of the real systems and make them have the same temperature of the large system itself.

I am not sure whether my understanding is reasonable or not, however, I hope this can make any help for this topic.

Best regards

Teng Zhang

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

time-temperature equivalence for a viscouselastic material

Henry Tan — Sat, 08 Sep 2007 15:59:24 -0400

How does the time-temperature equivalence for a viscouselastic material be viewed at molecular scale?

How temperature affects the viscoelastic behaviour?

Henry Tan — Sat, 08 Sep 2007 15:56:04 -0400

How temperature affects the viscoelastic behaviour? especially viewed from the behaviour of molecular movements?

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

Yuefei Zhang — 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.