- Post Doctoral
MIT Unit Affiliation:
- Materials Science and Engineering
Post Doc Sponsor / Advisor:
Date PhD Completed:
Top 3 Areas of Expertise:
My research as a Fulbright and MIT-Technion Postdoctoral Fellow is now underway at the Department of Materials Science and Engineering, Massachusetts Institute of Technology, in the group of Prof. Christopher A Schuh.
I am a scientist and an engineer, and the fields of Materials and Nanotechology are closest to my heart. Performing research in these fields is my broad objective, and teaching others what I've learned is another (and also a passion).
Currently I'm interested in "interface engineering" - structural and/or chemical modifications of interfaces (surface, grain boundaries, etc.) in materials, to better understand their complex nature and improve engineering properties. My preferred method to tackling this is harnessing thermodynamics as an ally - various interfacial phenomena may be employed to create stable, modified interfaces even in nanomaterials (where the surface/volume ratio is very large).
Expected End Date of Post Doctoral Position:
Title: Stability of nanocrystalline metallic alloys: interface engineering with nature's blessing
Description: This research is focused on the design, fabrication and characterization of thermodynamically-stable nanocrystalline metallic alloys. Nanocrystalline metallic alloys are metallic materials which are made of up of many nano-scale crystallites (“grains”), typically ranging in size between 1-50 nanometers. These materials exhibit significantly improved properties over their conventional coarse-grained counterparts, yet their nanostructure is a double-edged sword as their thermal stability as inherently poor.
The main challenge of this project is to "tame the nanostructure" and my approach differs from the mainstream since it is based on thermodynamic, rather than kinetic principles. In other words, by careful interface engineering I attempt to alter the fundumental "desires" of the material to favor a nanostructure as its most-stable configuration. In that sense, it can be referred to as interface engineering with nature's blessing.
This research thesis revolves around a chronological journey through the “life” of a thin bilayer on a substrate (gold/iron/sapphire). Three main “stops” in this journey, each relies on the conclusions of the previous, lead to an applicative research goal - obtaining core(iron)-shell(gold) nanoparticles by annealing the films at elevated temperatures (600-1100°C).
1. As-deposited microstructure of thin films: we obtained single-crystalline gold thin films on sapphire, having exceptional crystal quality and thermal stability, by using the iron layer as a “seed”. The seed layer accommodates the large difference between the lattice parameters of gold and sapphire, which would otherwise result in a typical polycrystalline film containing many structural defects.
2. Anisotropic dewetting: upon annealing, the films agglomerate into particles due to poor adhesion between metals (gold, iron) and the ceramic substrate (sapphire - aluminum oxide). At temperatures lower than the films’ melting temperature, this is termed ‘solid-state dewetting’. The unique microstructure of the films leads to a unique dewetting behavior, which had not been observed before. We developed a quantitative model which accounts for surface-energy and diffusion anisotropies (dependence of those properties on crystallographic direction), and described the dewetting kinetics in the films well.
3. Phase transformations in micro- and nanoparticles: when dewetting of a single-crystalline film is complete, structurally-perfect particles are obtained. Phase transformations in alloy particles (gold/iron) are expected to proceed differently from bulk systems due to the “size effect”. We explored two transformations: (1) precipitation of iron from a gold solid-solution; (2) the a?g transformation of iron and iron-gold alloys. Our main conclusion was that, contrary to the current paradigm, phase transformation proceed differently even in sub-micrometer-sized particles, and not only in nanometer-sized particles, where capillary forces dominate. Particularly, segregation (migration of a solute atom to a surface/interface to reduce its energy) of gold to all surfaces and interfaces of iron nanoparticles greatly affected the kinetics and morphology of the phase transformations.
We capitalized on the latter main result to fulfil the applicative research goal by employing a segregated gold layer as the shell, demonstrated the ability to bind organic molecules to their surfaces, and explored their magnetic properties. Such nanoparticles could find promising uses in bio-medical, data storage and catalytic applications, due to the unique combination of a magnetic iron core and an inert gold shell. Compared to other fabrication methods, we suggested a simple process which leads to nanoparticles with a high degree of purity and structural perfection.
Top 5 Awards and honors (name of award, date received):
5 Recent Papers:
Amram D., Barlam D., Rabkin E., Shneck R.Z. (2016), “Coherency strain reduction in particles on a substrate as a driving force for solute segregation”, Scripta Materialia 122, 89-92.
Amram D., Rabkin E. (2016), “Phase transformations in Au-Fe particles and thin films: size effects at the micro- and nano-scales”, JOM 68, 1335-1342.
Amram D., Amouyal Y., Rabkin E. (2016), “Encapsulation by segregation – a multifaceted approach to gold segregation in iron particles on sapphire”, Acta Materialia 102, 342-351 (2016).
Amram D., Kovalenko O., Rabkin E. (2015), “The a<->g transformation in Fe and Fe–Au thin films, micro- and nanoparticles – an in situ study”, Acta Materialia 98, 343-354.
Amram D., Rabkin E. (2014), “Core(Fe)-shell(Au) nanoparticles obtained from thin Fe/Au bilayers employing surface segregation”, ACS Nano 8, 10687-10693.