Hi, TEM users and other LEXI users:
Prof. Laurence Marks of Northwestern University is going to give an invited talk today (1/28/2013, 3-4pm) in Calit2 Auditorium. Prof. Marks is a well-known TEM expert with rich research experience in materials science. This is a great opportunity for you to learn new TEM techniques and their applications in materials science research. The details of his talk are listed below.
Thanks for your attention!
Jian-Guo
Speaker: Prof. L. D. Marks
Title: NANOPARTICLES: FROM WULFF TO WINTERBOTTOM AND BEYOND
Date/time: 1/28/2013, 3pm-4pm
Venue: Calit2 Auditorium
Abstract:
NANOPARTICLES: FROM WULFF TO WINTERBOTTOM AND BEYOND
L. D. Marks
Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208
Understanding the structure of nanoparticles is a problem where electron microscopy and modeling have been partners for many years. Single crystals are simple, and can be understood by the Wulff construction1 as proved during WWII by von Laue2, with extensions for supported particles on a flat substrate by Winterbottom3 and at an edge by Taylor et al4. However, nanoparticles often have different structures as first shown by of Ino and Ogawa5-7 who published just ahead of Allpress and Sanders8. These structures, called multiply-twinned particles or MTPs remained incompletely understood until microscopy data suggested a variant of a Wulff construction which can explain their equilibrium shapes9-11. Given the growth of nanotechnology in the last decades, it is time to return to some of these topics and look further. It appears there is still a fair amount of science left to be done, ranging from Wulff shapes for alloys12 to understanding the growth shapes of nanoparticles based upon a kinetic variant of the modified Wulff construction13. Some recent results such as finite size effects for alloys and single-phase nanoparticles and how this couples with the chemical potential and substrate interfacial energy, as well as how these relate to topics such as the design of face-selective catalysis14 as well as twin-boundary steps in nanoparticles as determined by atomic-scale tomography15 will be described.
1 Wulff, G. On the question of speed of growth and dissolution of crystal surfaces. Zeitschrift fur Krystallographie und Mineralogie 34, 449 (1901).
2 von Laue, M. Der Wulffsche satz fur die gleichgewichtsform von kristallen. Z. Kristallogr. 105, 124 (1943).
3 Winterbottom, W. L. Equilibrium shape of a small particle in contact with a foreign substrate. Acta Metal. 15, 303 (1967).
4 Zia, R. K. P., Avron, J. E. & Taylor, J. E. The summertop construction: crystals in a corner. J. Stat. Phys. 50, 727 (1988).
5 Ino, S. Epitaxial Growth Of Metals On Rocksalt Faces Cleaved In Vacuum .2. Orientation And Structure Of Gold Particles Formed In Ultrahigh Vacuum. Journal of the Physical Society of Japan 21, 346 (1966).
6 Ino, S. & Ogawa, S. Multiply Twinned Particles At Earlier Stages Of Gold Film Formation On Alkalihalide Crystals. Journal of the Physical Society of Japan 22, 1365 (1967).
7 Ino, S. Stability of Multiply-Twinned Particles. Journal of the Physical Society of Japan 27, 941 (1969).
8 Allpress, J. G. & Sanders, J. V. Structure And Orientation Of Crystals In Deposits Of Metals On Mica. Surface Science 7, 1 (1967).
9 Marks, L. D. Modified Wulff Constructions for Twinned Particles. J. Cryst. Growth 61, 556 (1983).
10 Marks, L. D. Surface-Structure and Energetics of Multiply Twinned Particles. Philos. Mag. A-Phys. Condens. Matter Struct. Defect Mech. Prop. 49, 81 (1984).
11 Howie, A. & Marks, L. D. Elastic Strains and the Energy-Balance for Multiply Twinned Particles. Philos. Mag. A-Phys. Condens. Matter Struct. Defect Mech. Prop. 49, 95 (1984).
12 Ringe, E., Van Duyne, R. P. & Marks, L. D. Wulff Construction for Alloy Nanoparticles. Nano Letters 11, 3399 (2011).
13 Ringe, E., Van Duyne, R. P. & Marks, L. D. Modified Kinetic Wulff shapes for Twinned Nanoparticles. Submitted (2012).
14 Enterkin, J. A., Poeppelmeier, K. R. & Marks, L. D. Oriented Catalytic Platinum Nanoparticles on High Surface Area Strontium Titanate Nanocuboids. Nano Letters 11, 993 (2011).
15 Chen, C. et al. Three-dimensional imaging of dislocations in nanoparticles at atomic resolution. Submitted (2013).