# Presentation: 736377

## Metal Electrochemical Atomic Layer Epitaxy 

**(EC-ALE); John Stickney/U. GA, DMR-0312130**

*** ******15 *****x15 nm****2**

- EC-ALE is the electrochemical equivalent of atomic layer epitaxy (ALE).  Until now EC-ALE has only been used to form compound semiconductors.  We recently demonstrated a derivative of the EC-ALE method based on exchange of a surface limited atomic layer of one metal for another, achieving formation of nanometer thick metal films in spite of a greatly reduced electrochemical (thermodynamic) driving force for direct EC-ALE of a second layer of the same metal. Nanometer layers of Cu and Pt have been formed, with atomic level control of thickness.  The STM Images above show the structure evolution as a gold single crystal surface is converted to a Pt surface.
- *UPD-underpotential deposition (lower electrochemical potential than that needed to deposit an element on itself.)

- Cu monolayer formed by
- UPD*, I atom coated.

- Cu UPD* exchanged for Pt
- One time, and I atom coat.

- Three EC-ALE cycles of Cu
- UPD replaced by Pt, I coated.
- PtI4 species adsorbed on top.

**Notes:**
Research Results:
EC-ALE is the formation of nano films an atomic layer at a time, the electrochemical analog of atomic layer epitaxy (ALE) and atomic layer deposition (ALD).  All three techniques are based on the use of surface limited reactions.  In EC-ALE, the electrochemical surface limited reactions are referred to as underpotential deposits (UPD; under potential refers to a lower electrochemical potential than that needed to deposit an element on itself).  UPD is the electrochemical deposition of an atomic layer of one element on a second, at a potential independent of the formation of the first element on itself.  The process is the result of the free energy of formation of a surface compound.  The net result is that an atomic layer of one element can be formed at equilibrium on a second, without the formation of any bulk deposit.  This promotes layer by layer growth, and epitaxy, creating  well ordered atomic layers, and through EC-ALE, well ordered epitaxial nanofilms of a material, with atomic layer control. 
It has long been felt by the PI that metals could not be formed, as you cannot get the thermodynamic driving force for a second atomic layer that you get for the formation of the first atomic layer, UPD.  However, work by Adzic et al. has pointed the way.  The idea was to use an exchange reaction.  That is, if you want to make a Cu film, you use a more reactive element, say Pb, and form a UPD layer of Pb on the growing Cu film.  Then you simply do a chemical step, exposing the Pb atomic layer to a solution of Cu ions.  As Cu has a higher deposition potential then Pb, the surface limited quantity of Pb will be replaced by a surface limited amount of Cu.  Adzic showed that this worked in the deposition of Pt by exchanging it for a Cu UPD layer.  He showed that you could repeat the process for a few cycles.  We have added the use of an iodine atom protection layer, which keep the surface clean, and provide some surface annealing, resulting in a smoother surface, with better order.   We are the first to show that this results in an atomically well ordered surface. We have also extended the process to the deposition of Cu nano films.  
Significance of this work:
The importance can be seen for catalytic metals, as a way of forming well controlled nano films of catalytic metals, and alloys, as well as structured deposits, as Adzic intended.   However, by extending this process to Cu, we can see the broader implications of the methodology.  Cu is of great interest in the formation of ULSI, as presently on-chip conductors are electrodeposited Cu.  However the process for forming these conductors involves the use of a seed layer.  As the electronics industry goes to the 70 nm and 35 nm nodes, the thickness of the seed layer will become critical, and must be very uniform, and less then 5 nm thick. Metal EC-ALE should be a viable option for forming such thin layer with atomic layer control.   Further, magnetic materials will benefit from the controlled growth of alloy and metal nano films.  
I believe this is a very important breakthrough for our group, and nano science in general, as now there is a method for controlling the formation of metal nano films with atomic level control, that has no equivalent gas phase process. 
Future Plans:
In order that Metal EC-ALE can become widely applicable, the fundamentals of the process must be investigated.  What elements can be deposited, and what elements should be used as the sacrificial elements.  What are the problems?  What hardware is best suited for transfer of the technology to industry.  Discussions are underway with SemiTool, the first company to build tools for the electrodeposition of Cu by the ULSI companies.  
The catalytic metals are the easiest to do, and I think we will see broad applications in that area.  In the case of magnetic materials, the elements of interest, such as Fe, have relatively complex electrochemistry, and will require study.  Presently, Pt has been formed, and some work at its extension will continue.  Cu is at the stage where we can grow films, but the process shows sensitivity to oxygen, and must be optimized.  In the area of magnetic materials, there are some very interesting PtFe compounds, which will allow us to examine Pt deposition along with the more challenging deposition of Fe.  
A couple of designs are being worked on that will scale the process up to wafer size, and that should be adaptable to existing tools used by SemiTool, as well as Applied Materials. 

## Increasing Diversity; John Stickney/U. GA, DMR-0312130

- I seek to increase diversity at every level. This process is of so much importance in this state given our minority population. Currently I am working on a mentoring program for undergraduate minority chemistry majors at UGA. Presently, my research group has two African graduate students, Dhego Banga, from the Congo, and Tim Hayes, an African American.
- I am also continuing to build “Drum Majors for Science”,  a program to help out predominantly minority grammar schools in the area, build interest in science.  Work is continuing with Fourth Street Elementary school, which is over 95% minority, and currently on probation.
- As department head of Chemistry at UGA for the last two years, I have been aggressively pursuing diversity, starting with the faculty.  This last year, I was able to retain Greg Robinson, who was aggressively sought by other major universities. I was also able to hire a new African American assistant professor, Marcus Lay.

- Franklin Professor:
- Gregory Robinson

- First Year Assistant Professor:
- Marcus Lay

**Notes:**
Results:
I have been the department head of Chemistry for the past two years.  As such, my job has changed significantly.  The positive side is that I have a lot more control over hiring.  I have found the upper administration open to my interest in increasing diversity.  Last year we had one African American Full Professor in the physical sciences at Georgia.  That professor, Greg Robinson, was considering an offer from another major University.  I was able to secure a package to keep him at Georgia, my most important accomplishment so far.  
In general, my faculty do not like to hire their own.  I was able to convince them that we had an opportunity with Marcus Lay, to hire a bright young African American who was intent on becoming a faculty member at a major research university.  He had offers from 5 other major schools.  The problem was that he had been my student, supported by your program.  I first convinced the faculty that we needed to be proactive, and not just give lip service to this problem, changing the demographics of Chemistry on this campus.  As I noted, the administration backed me up, and we were able to make a competitive offer, and get Marcus to come to Georgia, where his research will be in the area of bio nano materials.   
Significance of this work:
We were able to double the number of African American faculty in Chemistry.  This is a state where a quarter of the population is African American, our program and the University should reflect it.  However, without aggressive work on our part, this is not going to happen in the near term.  
Future Plans:
I have requested that the administration provide us with an extra position if we can identify a strong candidate who is a minority or woman.  Our department has only two women on the faculty.  I requested that the area be open, as I wanted to enlist the faculty in this process.  If they want someone in their area, or to collaborate with, all they have to do is go and find one.  The idea is to get them working and thinking outside the box.  
I continue to take any and all minority students with any interest in my area, and presently have two black students.  One is from the Congo, and is working out well.  He has a green card, and thus will be staying in the US.  A second student, an African American, Tim Hayes, joined by group last spring.  I introduced him to Marcus Lay, and he has decided to work for Marcus; he is switching groups this fall.  I encouraged this process, as I feel Marcus will be a better mentor, and Marcus will need students to get his program off the ground.  
My work on “Drum Majors for Science”, has been slowed by my change in jobs to department head, but is still on going.  I still work with one school, and am working on the structure of the program.  I still feel that the grammar school level, 4th and 5th grades, is the place to spark the interest in science, that will hold them in years to come.  I am enlisting  Marcus in the process, as well as my graduate students. 
As department head, I have access to the list of minority students who are majoring in chemistry.  My plan for this fall is to contact them all, and develop a mentoring system for them.  I am collecting faculty members who have an interest, and will split the students up, so that they all have a faculty member to talk to in the department, from the time they come though the door as freshmen.  At large universities, these students can get lost, and a little help goes a long way.