Awardee Interviews | Ivan Petrov - 2013 John A. Thornton Memorial Award Winner - Interview

Ivan Petrov

2013 John A. Thornton Award Winner

Interviewed by Paul Holloway and Jack Rowe, 2013
 
HOLLOWAY:  My name is Paul Holloway.  I’m a member of the AVS History Committee.  I’m joined today for the interview by Dr. Jack Rowe, also a member of the AVS History Committee.  Today is Thursday, October 31, 2013, and we’re at the 60th annual International Symposium of the AVS in Long Beach, California.  We have the privilege and pleasure of interviewing Dr. Ivan Petrov from the University of Illinois.  He is the 2013 John Thornton Memorial Award winner, and his citation reads: “For seminal contributions in determining the role of low-energy ion/surface interactions for controlling the microstructure evolution during low-temperature growth of transition-metal nitride layers.”  So Ivan, congratulations on the Thornton Award.
 
PETROV:  Thank you, Paul.  It’s a great honor for me to talk to you and Jack. Shall we start from the beginning..?
 
HOLLOWAY:  Yes, Please give us your place and date of birth.
 
PETROV:  I was born on September 6, 1949 in a town called Shumen in Bulgaria.
 
HOLLOWAY:  Good.  Can we continue with you telling us something about your educational background?
 
PETROV:  Yes.  I grew up in the northeastern part of Bulgaria.  My father was a professor on wheat selection, an agronomist.  He knew the importance of the English language for science, and I wanted to be a scientist.  So in 1963, at the age of 14 I went to a town called Rousse at the Danube River to study in an English language high school.  We studied one year mostly English  and then four years high school where we had physics, chemistry, history, biology, and English literature in English.  We were lucky to have teachers from England and US.
 
HOLLOWAY:  Very good.
 
PETROV:  There was a questionnaire at that time: why do you study English?  I know I answered because I want to work as a scientist, and indeed that helped me a lot to be here and speak to you in that language.  For University, I won one of the two slots in a nation-wide entrance exam competition to study Electrical Engineering in Moscow. However I wanted to study physics and chose the Faculty of Physics at Sofia University “Saint Kliment Ohridski,” which is the leading university in Bulgaria.  That’s where I met my wife Vania; we were both studying physics.  During the course of six years I specialized in theoretical physics.  We had a Professor Ivan Todorov who was at age 33 had already the highest rank at the Academy.  He was a professor in Princeton, and also co-wrote a book on quantum field theory with the leading Soviet experts Bogoliubov and Logunov.  He had a very active group, working on quantum field theory, and many from our generation wanted to emulate him. That’s where I did my master’s diploma.
 
HOLLOWAY:  What year did you get your master’s diploma?
 
PETROV:  In 1974. I was under one of Todorov’s assistants, but I attended all his weekly seminars.  It was a very exciting, interesting time. But then we graduated 14 people from the faculty of physics with a degree in quantum field theory, and obviously we couldn’t all work in the field in a small country.  So I had contacted a group of experimentalists at the Bulgarian Academy of Sciences and helped them write papers in English because I knew English and Physics.
 
HOLLOWAY:  Knew it very well.
 
PETROV:  They happened to be in the Institute of Electronics, and at that time, that meant physical electronics, or the science that made vacuum tubes work.  I was struck when I came to the U.S. that the Coordinated Science Lab that was headed by Daniel Alpert was very much the same background.  We had a glass-blowing shop, and they were making a lot of experimental devices in vacuum tubes for studies of emission of electrons and ions from surfaces.  So all that science then expanded into the areas of which AVS is active now. Physical electronics expanded in thin film physics, surface science, gave birth to many analytical techniques, XPS, Auger, SIMS and others. Many of these fields were active areas of the research at the Institute.

HOLLOWAY:  So what year was this?

PETROV:  That was in 1976 after an army service for a year and a half.  That was mandatory.
 
HOLLOWAY:  And you had a master’s degree at this time?
 
PETROV:  A master’s degree, yes.
 
HOLLOWAY:  What year did you get your master’s degree?
 
PETROV:  In ’74 and then was in the army.  In the meantime I married, and then I joined the Center for Physics, Institute of Electronics at the Bulgarian Academy of Science (IE-BAS) as a physicist.
 
HOLLOWAY:  In Sofia.
 
PETROV:  In Sofia as a physicist.  I started working in a group on sputter deposition—or we called it ion technology because sputtering, at least in the ’50s and before was investigated as an undesirable phenomenon limiting the cathodes in electron tubes.  So most of the theory and experimentation was how to minimize sputtering and so on.  But at that time, of course already semiconductor electronics had dominated.  So people who were knowledgeable in physical electronics made the transition to thin films, surface analysis, radiophysics, etc. That was the strength of the Institute.  I benefited from this climate of fundamental understanding of ion and electron interactions with solids and physics of gas discharges from this institute. I was also influenced by the ideas from the Kaischew Institute of Physical-Chemistry at BAS on the atomistics of film growth.
 
HOLLOWAY:  So did you use the sputtering for depositing thin films?
 
PETROV:  Yes.
 
HOLLOWAY:  Or you were just studying the physical phenomenon itself?
 
PETROV:  I was using the sputtering for deposition of thin films.  In ’76, there were no magnetrons yet.  We had DC and RF reactive sputtering.  My first job was to look at reactive sputtering of aluminum.
 
HOLLOWAY:  Oh yeah, to produce aluminum oxide.
 
PETROV:  Aluminum oxide. But I want to mention two names from IE-BAS who were my mentors in the new for me field of Physical Electronics: Prof. V. Orlinov who was the head of the division (or section as we called it) on ion technologies, and B.  Goranchev who was the younger scientist, let me see - a docent-type rank. They really introduced me into sputter-deposition and thin films physics.  They had developed a model of reactive sputtering monitoring the change of the secondary electron emission on the target when a target is poisoned or reaction on the target occurs.  That is very sensitive to the state of the target reaction. You can measure the discharge voltage and deduce what happens on the target; with relatively simple means we tried to look into the physics that goes on in the process.  So I used that technique and I came across the fact that you can have a same reactive partial pressure and the target could be either metallic or oxidized. My first paper was called “DC Reactive Sputtering in Aluminum.”  It was published in Thin Solid Films in ’78.  Somewhere on the third or fourth page we wrote, “This phenomenon of hysteresis effect is due to the gettering action of the sputter deposit.” To my knowledge this is the first description of this important effect.
 
HOLLOWAY:  On the target.
 
PETROV:  Yes.  But it was buried somewhere in this paper.  It was only two or three years later that they really showed in magnetrons very clearly how the total pressure of the chamber varies with, let’s say, the increase/decrease of the flow of reactive gas.  But I’m personally quite excited by my unnoticed “discovery”.  This was published in Thin Solid Films.  Two years later I became a research scientist at the Institute, and I began compiling my PhD thesis which I defended in 1986.
 
HOLLOWAY:  In Sofia?
 
PETROV:  In Sofia. But in the meantime, I had the chance to go to Sweden, which was, in part, facilitated by the International Union Vacuum Science, Technology, and Applications.
 
HOLLOWAY:  IUVSTA.
 
PETROV:  Yes.  Bulgaria was one of the founding members, and the director of our institute, Emil Djakov, was active in IUVSTA as well as in the International Committee for Weights and Measures (in French Comité international des poids et mesures (CIMP)). By the way, now the Institute today is named after him -  Emil Djakov Institute of Electronics.
 
 To my knowledge, through his participation in IUVSTA and CIMP, Djakov established a collaboration between the Bulgarian Academy of Sciences and the Swedish Royal Academy of Science.  The Swedish representative of IUVSTA was Sven-Eric Karlsson who was a professor in Linköping University (LiU). That is how, through these international organizations, a collaboration between IE-BAS and LiU was established. It was crucial for my career.
 
HOLLOWAY:  Is that right?
 
PETROV:  So through this collaboration, I got a short time visit to Sweden for three months.
 
HOLLOWAY:  Three months.  What year was this now roughly?
 
PETROV:  ’81.  I wanted to explore two institutions, which my senior colleagues G. Mladenov and V. Orlinov had visited.  One was Linköping University where Sven-Eric Karlsson was.  The other was the Manne Siegbahn Institute of Atomic Physics in Stockholm where we had another contact group.  
 
ROWE:  He was a very famous person.
 
PETROV:  Yes.  He was a Nobel laureate in the ’20s, and at that time, they gave Nobel laureates the right to build an institute.  So it was just across the Swedish Royal Academy.
 
ROWE:  And he was the father of Kai Siegbahn who also won the Nobel Prize for XPS.
 
PETROV:  Exactly.  Exactly.  His son moved to Uppsala and did that.  So I met Jan-Eric Sundgren who was a graduate student in his last year. I spent most of the time in the Institute of Atomic Physics where I had access to RBS.  I had one planned experiment by Orlinov, which was to measure the sputtering yield of aluminum because that was…
 
HOLLOWAY:  As a function of ion energy?
 
PETROV:  We had one ion energy, but we wanted to measure—and we had a collector using two ion-beams in one chamber.  Of course, there was quite a high background pressure.  So we measured the sputtering yield at 40 keV, but I think it was more aluminum oxide.  We published one paper in Vacuum.  But I also joined the work with one other professor, Edward Thomas from Georgia Tech, who was a sabbatical there.
 
ROWE:  Oh yeah.  I know him.
 
PETROV:  He then became the Head of the Physics Department at Georgia Tech immediately after that.
 
HOLLOWAY:  So may I ask you— 
 
ROWE:  He actually was at Bell Labs before he went to Georgia Tech.
 
PETROV:  Is that right?  So I helped him process the data in his project on recombination of Deuterium implanted in stainless steel which was published in J. Appl. Phys. 
 
HOLLOWAY:  Your sputtering was DC or RF (the yield)?
 
PETROV:  In Bulgaria, I was using DC.  This was an ion beam experiment in Stockholm.
 
HOLLOWAY:  Oh, it was an ion beam experiment.
 
PETROV:  So there were two accelerators, an ion beam accelerator which was an ion implanter in fact, so where we had 40 keV Ar ion beam on Al target and then we had a carbon collector of the sputtered material. 
 
HOLLOWAY:  How did you quantitate the neutrals coming off?
 
PETROV:  After sputtering with a known dose, we turn the collector to the RBS beam and measured the quantitatively the deposited layer in atoms/cm2.
 
ROWE:  Yeah.  You measure the mass of what’s deposited.
 
PETROV:  Yes.  But I was interested in reactive sputtering, so I had one of my colleague, T. Donchev who was visiting at the same time KTH Royal Institute of Technology, deposit a series of titanium nitride films with varying N content.  I measured them by RBS. As you know RBS is not sensitive to the light film component.  So I developed a technique to measure the relative height of the heavy element signal to the substrate signal, and deduce the composition of the films using well-known formulas.  I published that paper in Journal of Applied Physics in ’83, which for me was a big breakthrough.  I was very proud that I could publish a paper with my idea and me being the first author.
 
HOLLOWAY:  So this was a paper in Journal of Applied Physics— 
 
PETROV:  On quantitative RBS on two-component films.
 
HOLLOWAY:  I see.  Now who was your mentor?  Were there other people you worked with at Linköping?
 
PETROV:  At Linköping I just met Jan-Eric and but did most of the initial work in Stockholm.
 
HOLLOWAY:  Oh, in Stockholm.  Okay.
 
PETROV:  Manuel Braun was my host, coauthor of this.  He taught me the RBS and ion beam techniques.  As I mention, Edward Thomas from Georgia Tech invited me to join his project.  So for me, this was very important that I could publish early in my career two papers in Journal of Applied Physics.
 
HOLLOWAY:  So after the three-month stay in Sweden you went back to Bulgaria?
 
PETROV:  Yes, of course.  I went back.  It was a short time visit but I continued the work with processing the data and writing the papers. These papers went into my thesis, which I defended later.
 
HOLLOWAY:  Oh, I see.  Yeah.
 
PETROV:  Then the second time when I could go to Sweden, I contacted Jan-Eric and ask him to join his lab for sputter deposition experiments. It was the time before emails and faxes even, and I didn’t get an answer for two or three months.  I said, “Okay, I’ll have to think of something else.”  But suddenly he responded very enthusiastically from Urbana.
 
HOLLOWAY:  From Urbana!
 
PETROV:  He was a post-doc with Joe Greene.  He wrote back “Ivan, I’m finishing my post-doc.  Come to Linköping and we’ll do sputter deposition and thin film growth experiments.”  I had some ideas which I brought from the Institute of Electronics because as I mentioned, we had very good experts in vacuum, ion-solid interaction, electron-solid interaction.  In particular, in creating vacuum, we had one scientist, G. Grigorov, who had invented an ion getter pump with evaporation and very nice ionization system to implant the gas ions.  His idea was that the gettering action depends on the amount of ions to the deposited titanium getter flux.  So the more you bombard with ions, the more efficiently you capture them.  He quantified that by the ratio of the flux of the gas ions to the Ti metal ion flux.  At that time, we were all studying bias sputtering, but we didn’t actually use the atomistics of fluxes reaching the substrate.  At the best, the voltage was used as a parameter while the exact ion to metal flux ratio was not measured.  That wasn’t generally in the sputtering papers before that.  So I went to Linköping and wanted to explore this idea for bias sputtering. The second idea, I wanted to explore, is the effect of the mass of the ions, so to have some information on the momentum transfer.  So we worked with Jan-Eric and his graduate students U. Helmersson and L. Hultman.  We designed experiments where we controlled the ion energy but first of all I made very careful characterization of the plasma so that we know what the ion and the metal fluxes were. Then we studied the effect of the ion energy with known gas- ions/metal flux ratios by cross-sectional TEM.
 
HOLLOWAY:  What sort of energy range did you encounter?
 
PETROV:  We used from 20 volts to 2,000 volts.  We really did study a wide range because I wanted to test also an idea of “recoil implantation” to improve film adhesion which was promoted by ion-beam sputtering folks.  That, by the way, did not prove a productive route and later on we showed that metal ion etch is the best way to improve adhesion in hard coatings. It took us five years to publish a couple of papers. The process was slow because I had to write the text, send it my airmail to Joe Greene in Urbana and Jan-Eric in Linköping. 
 
HOLLOWAY:  And then you wait forever to get something back.  [Laughter]
 
PETROV:  Yes.  [Overlapping voices]  Then Joe goes over the text with a red pen and then I had to re-write etc.  But the first paper, which was published in 1989, is one of my most cited papers, over 200 times.  Today I showed in the beginning how when you increase the ion energy at normal plasma conditions, you get a very sharp interface when ions begin to get trapped into the film.  That causes densification but also stresses.  So that was something that has continued to be cited, so that paper is, I think, an important one.  It happened with this collaboration between IE-BAS, LiU (Jan-Eric, Ulf, and Lars) and University of Illinois (Joe).
 
HOLLOWAY:  Now the other name that comes to mind immediately about sputtering is Fred Wehner.
 
PETROV:  I can tell you my experience with Fred.  I met him when I came to the U.S. in ’89.  He was a tall, distinguished gentleman in his 90s – worked most of his life with Mercury diffusion pumps. In the late 80’s there were 5-6 empirical formulas for the sputtering yield introducing threshold energy as a correction to Sigmund’s high-energy theoretical expression. I wrote a review article comparing these expressions and recommending one which is best suited for sputter-deposition, i.e. the low energy interval. In any case, in the course of this work I came to realize that the sputtering world, to this day, relies on the only systematic data on the low-energy sputtering yield obtained by Fred. His papers from the early 60’s are masterpieces, full of ideas and deep insights. It is remarkable that he did this work for General Mills, a cereals company.
 
HOLLOWAY:  And your thesis you submitted to the Bulgarian Academy?
PETROV:  Academy of Sciences, yes.
 
HOLLOWAY:  And you were awarded a PhD…
 
PETROV:  Yeah, a PhD.
 
HOLLOWAY:  …equivalent from the Academy?
 
PETROV:  Yes.  They call it a Candidate of Physical Sciences.   But the requirements are similar: you have to write a thesis which contained the content of four to six papers.  The papers that I did in Sweden were the core of my work.  So this international collaboration gave me the opportunity to make some good science with some ideas generated at IE-BAS.
 
HOLLOWAY:  That’s wonderful.  Good.
 
PETROV:  In the meantime, the young people in our institute started a School of Vacuum, Electron and Ion Technologies, as we called it at that time, 1978.  We got some a small amount of seed money from the institute.  I was the “organizing secretary”, sort of local-arrangements-chair, for the first five editions. We invited famous people from around the world to come and give lectures, and surprisingly they came.  We paid them the local expenses.  We couldn’t afford much more.  We took some resorts at the Black Sea, very nice areas, after the season.  But it was still warm and you could go to the beach.  We had a lot of famous people come.  From Russia, Jurasova, Pleshivtsev; George Carter from UK, K. Reichelt from West Germany, Christian Weissmantel from GDR, Phil Martin from Australia and many others – a dozen major names each meeting. Also Joe Greene came, Jan-Eric,   Dieter Münz, Lars, and Ulf...  The latter five are future major collaborators of mine.  So these forums of international interaction were crucial for me and for many others.  So that is very, very important even today – we should try to encourage scientific interactions across the world. Another award winner yesterday spoke about how important the international exchange in science is, and we shouldn’t have any roadblocks. 
 
HOLLOWAY:  So you now got your degree at the Academy.
 
PETROV:  I got my degree and became a research scientist at the Institute of Electronics.    With Dieter, Jan-Eric and Joe, we continued the study of ion-assisted growth with careful characterization of the plasma and very careful characterization then of the microstructure of the deposited films trying to understand the atomistics of the process.  In the meantime, then Joe invited me to University of Illinois as a visiting professor.
 
HOLLOWAY:  Right.  What year was that?
 
PETROV:  ’89.  We arrived in the U.S. on March 2, 1989, and I started working with Joe continuing very intensively on the path which led me to this award.  In the meantime, communism collapsed the same year.  To that point science was funded very much like a prestige activity, but in the 90s funding really dropped because it became clear how poor the country was.  In contrast, I had such wonderful conditions to work as a scientist at the Frederick Seitz Materials Research Lab.  We have one of the best characterization facilities that gave us unlimited access to the best techniques.  We had, in our group with Joe, very nice sputtering equipment: one of the first UHV, very well-characterized systems, with unique control of the plasma around the substrate.  Eventually we acquired scanning tunneling microscopy which my wife was running, and we used to the fullest.  We had one of the first LEEMs, low-energy electron microscope. We used these instruments for dynamic surface studies of titanium nitride. As a refractory material, it requires very-high temperatures for in-situ observations of surface diffusion.  Most people studied semiconductors and metals where diffusion occurs at much lower temperatures.  So the Frederick Seitz Materials Research Lab, the group of Joe was the place where I did most of my science that lead to the award.  I think it is fair to say that Joe and I have had an extraordinarily productive collaboration and friendship over 30 years which has been central for my success. The links to Linköping continued throughout.  I was visiting Linköping periodically.  We would go there, and then they would send post-docs and students in Urbana.  Lars came on a sabbatical in the mid-2000s. We have perhaps over hundred joint papers. Based on the sustained interaction, LiU conferred a Doctor Honoris Causa on me in 2009. The other person I need to mention is Dieter Münz.  Do I go in too much detail?  We can shorten.
 
HOLLOWAY:  Maybe just shorten it a little bit, but not too bad.  Go ahead.  We’ll take a short break.
 
PETROV:  I think we can edit out most of it.
 
ROWE:  I was particularly interested because my research interests over the years have been in silicon-based electronic materials, and of course titanium nitride has been very important in that technology.  Then more recently, I’ve gotten involved with LEEM and STM, so you had that.  So everything connected to my interests.  I was surprised at that.  [Interruption]
 
PETROV:  Dieter Münz funded a graduate student, Greger Håkansson in Jan-Eric’s group in Linköping to study TiAlN coatings and the effects of ion bombardment on adhesion in steel tools.  Dieter was in industry, and he was a sputter deposition champion, the sputtering man.  But sputter-deposited coatings on tools were not as good as the ion plating were, and he wanted to understand why.  So he proposed and we did cross-section electron microscopy analysis of the interfaces of different commercial coatings. To complete the study, we analyzed these samples with sub-nanometer resolution using STEM-EDS in Urbana with Lars Hultman, when he was in Northwestern. Lars succeeded Jan-Eric in his group and remained a major collaborator. 
 
HOLLOWAY:  I see.  Succeeded him as the director and professor of the group.
 
PETROV:  As professor of ThinFilm group in late ’90s.  Sputter-deposited samples had a poor interface.  Obviously the cleaning was not good.   Ion plating, and especially cathodic arc, had very clean interfaces.  With cathodic arc, with metal ion irradiation we found some intermixing, so the adhesion was superior.  This analysis led Dieter to develop the so-called arc bond sputtering combining metal ion cleaning and sputter deposition.  He became a professor in Sheffield, and we continued the collaboration.  He would send me samples prepared by his new technique to study the interfaces by XTEM. 
I just want to mention that we made some discoveries that I’m most proud of in this applied area that I didn’t have time to talk about today.  For example, Dieter initial thinking was that heavy metal ions, such as Nb or Mo, which have multiple charge, will penetrate deeper into the substrate and result in better adhesion.  In fact, we found out that heavy metal ion amorphize the surface and promote random nucleation. In contrast, the use light metal ions, such as Ti-Al or Cr, provide a very active, clean metal surface which promotes epitaxy during nucleation and thus a very good adhesion of transition metal nitride coating on both steel and WC substrate. We introduced the notion of local epitaxy for hard coatings on tools. XTEM also showed that Dieter was producing nanolayers which expanded into the whole field of his research.  Based on this collaboration with Dieter and later with his successor, Papken Hovsepian, Sheffield Hallam University appointed me as an honorary visiting professor from 2000-2012.
 
HOLLOWAY:  At Illinois.
 
PETROV:  At Sheffield, but we had of exchange of joint students from Sheffield Hallam University who visited the University of Illinois.
 
HOLLOWAY:  I see.  So you were made an honorary professor at Sheffield Hallam.
 
HOLLOWAY:  Okay.  I want to come back to the ion plating.  Who invented that term?  I know that Don Mattox did a lot of that at Sandia in the timeframe.
 
PETROV:  I think no doubt that he is the inventor of the term.  I think he has the patents.
 
HOLLOWAY:  Yeah, I think so.
 
PETROV:  He combined evaporation with a discharge – a high voltage abnormal glow discharge on the substrate - the same type used in sputter-deposition. Don Mattox defined ion plating as PVD deposition with ion bombardment.  So in that sense, all bias sputtering is ion plating. But commercial titanium nitride was deposited by—they called it then reactive…
 
HOLLOWAY:  Reactive arcs ion deposition, right?
 
PETROV:  Activated reactive ion plating. It’s electron beam evaporation in nitrogen atmosphere which induces ionization while applied bias at the substrates attracts ions.  With this system pre-cleaning was carried out in a thermionic arc, which produced a transitional layer enriched in tungsten which. However, the good adhesion was very good.
 
HOLLOWAY:  Good.   Now where are we at? What else is important in your career?
 
PETROV:  Well, I want to mention a milestone. In 1997, the director of the Center for Microanalysis of Materials, Alwyn Eades resigned and went to become professor at Lehigh University.  There was a world-side a search for the director at Illinois, with some 80 candidates.  After six months they could not find a suitable candidate. Howard Birnbaum, the director of the Frederick Seitz MRL then offered me the position. The fact that our group with Joe was the heaviest user of the facilities and that I personally used most of the techniques had something to do with the offer. I was also included as a principal investigator in the Surface Science Cluster in the DOE-funded project in FS-MRL and an adjunct professor at the Materials Science Department.  I was the director for 12 years, and that opened me to the whole characterization field and collaborations with the other DOE electron microscopy centers (EMC).  Because we (the EMCs) were so small compared to synchrotrons, we decided to invent a synchrotron-like project.  We proposed a build the first chromatic-aberration-corrected TEM. Chromatic aberration correction would permit to analyze thick samples. Another advantage is that we could open the space between the poles and have maybe two or three centimeters for in-situ experiments.  Users can come and put their in-situ modules in the microscope.  The project got funded for about $25 million, which was a very big project, (so called TEAM project) and that took a lot of my time in the 2000s.  We built that microscope with half an Ångstrom resolution, which is operating in Berkeley.  Our job at CMM was to make an in-situ stage.  Our center was leading in in-situ science.  We had high-temperature STM, LEEM, several environmental TEMs, XPS with an electrochemical cell etc. We developed, together with Berkley, the stage for the new microscope which is a five-axis stage based on piezo-motion. The stage was built on the same principle as the stages used in the STMs but it was miniaturized.  The stage is inside the microscope, the vacuum provides vibration isolation.  So that took a lot of my effort which is not in the area of thin films.
 
ROWE:  Yeah.  That’s mentioned, though, in the booklet.
 
PETROV:  We got a patent and an R&D 100 Award.
 
ROWE:  Right.  That’s very prestigious.
 
PETROV:  And it is something that I put a lot of time as director of the center.
 
HOLLOWAY:  So are you still director of the center?
 
PETROV:  I stepped down three years ago.
 
HOLLOWAY:  So in 2010.
 
PETROV:  In 2010 and decided to concentrate on science. Partly, because Lars Hultman offered me a visiting professorship at Linkoping.  I could not travel over long periods of time if I was the director.  So I stepped down and now I am a visiting professor for four years.  I go there and their students came to Urbana.
 
HOLLOWAY:  At Linköping.

PETROV:  At Linköping.
 
ROWE:  I see.

HOLLOWAY:  Let me ask.  You’re an adjunct faculty at the Seitz Laboratory, right?
 
PETROV:  At Seitz Laboratory, I have a position of principal research scientist with zero time, which means I am not paid.  But I have grants still from Argonne National Lab.  That is another sustained interaction; we studied failure mechanisms in batteries for a decade.  That grant is going on.  My lab is working.  I have one graduate student, and two of my other chambers are used by other groups to deposit thin film lithium ion batteries.
 
HOLLOWAY:  Is that right?
 
PETROV:  So I’m active with them.  That’s about my story.
 
HOLLOWAY:  That’s quite a story.
 
ROWE:  It is.  Very impressive.
 
ROWE:  So let me ask a question.  You mentioned about the Doctor Honoris Causa from physics in Linköping.  What year was that?
 
PETROV:  2009.
 
ROWE:  2009.  Okay.  I think you said that, but I wasn’t sure.
 
PETROV:  They gave me that, and then they offered me the visiting position.
 
ROWE:  I see.
 
PETROV:  And I didn’t… 
 
ROWE:  And took a year to decide and work there.
 
PETROV:  That was incompatible with my administrative work, and I preferred to go back to science.
 
ROWE:  I understand.  I did something similar in my career.  It’s more fun doing science.
 
PETROV:  Yes.  I enjoy it.  It had become too much of a hassle to deal with personalities…
 
ROWE:  Yeah.  That’s right.
 
PETROV:  …staff, hiring, firing.  [Laughs] The lab went through turmoil, cuts in funding, so that created tensions and I didn’t enjoy that part.
 
ROWE:  That’s right.
 
HOLLOWAY:  No, that’s not enjoyable.  Now you’re well-known because of your work with nitrides.  What’s the most significant accomplishment in all of that?  Why are nitrides important?
 
PETROV:  Well, we like to say that we use them as model systems to study fundamentals of thin film growth and ion-assisted thin film growth.  The important thing is that they are very high melting point materials, refractory materials, so at normal deposition temperatures they have poor microstructure.  Ion-bombardment is crucial for high quality films. They have such a wide range of applications including as diffusion barriers in semiconductors.
 
ROWE:  Yeah.  They’re very important, diffusion barriers.
 
PETROV:  That’s a huge field.  They have special machines that deposit a nitrides uniformly over large substrate.  I mean, Steve Rossnagel invented ionized deposition for this purpose.
 
ROWE:  That of course is all very important to AVS.
 
PETROV:  Other application include decorative coating, wear-resistant coatings on cutting tools, etc.
 
HOLLOWAY:  Right.  That’s a tremendous business.
 
PETROV:  It’s a big business.  So I think that’s the interest in nitrides. However, Joe and I have been interested in fundamental studies of the properties of nitrides. The applications were done through collaboration, for example with Dieter, Papken, and others.
 
ROWE:  Very good.
 
HOLLOWAY:  Now you worked with students in all of this.
 
PETROV:  Yes.
 
HOLLOWAY:  Did they graduate under you or did they graduate under Joe?  What was the arrangement?
 
PETROV:  Both.  In the 90’s Joe had a very large group which had roughly two parts – transition-metal nitrides and semiconductors.

HOLLOWAY:  Right.  Yeah, he’s done a lot of semiconductor.
 
ROWE:  That’s right.
 
PETROV:  Yes, and he got very big awards in that area – gas-source MBE of Si-GE, and I was not part of that area until 2003 when Joe moved to Wyoming.  So, I would say I helped him build the hard coatings area in the 90s. Since 1998 I had my own DOE funding.
 
ROWE:  But of course, as you point out that they have so many applications, they overlap into some of these other areas as well.  So I think that’s part of the importance of—
 
PETROV:  Yes.  We have had, for a long time funding, from SRC (Semiconductor Research Consortium).  That was a diffusion barrier project.  So we had several graduate students working on diffusion barrier applications of nitrides, titanium nitride, titanium-tungsten nitride, tantalum nitride.
 
HOLLOWAY:  So do you go back to Bulgaria periodically and visit the— 
 
PETROV:  I go there—I still have family—once or twice a year. 
 
ROWE:  That’s nice.
 
PETROV:  I still participate in the conference that we started many years ago.  It’s still going, although this year I had a conflict and could not attend.  I have had visiting scientists from Bulgaria in FS-MRL. But from other countries as well: Austria, Switzerland, Japan, Korea, France...  Many have become professors now and we continue working.  So it’s been very rewarding.  I began with the international collaboration, and it is very important for science and it is fun.
 
HOLLOWAY:  Do you teach in the classroom at Illinois or do you…
 
PETROV:  I have taught classes on materials characterization, but most of my work was in fact research and administrative as a director.
 
HOLLOWAY:  Yeah.  That covers quite a range of topics.  Do you have any topics that we haven’t covered that you would like to add?
 
PETROV:  I pretty much poured my soul.  [Laughter]  I don't know what else.  I think I mentioned all the important people that I collaborated with. There are, of course, the students— 
 
HOLLOWAY:  Do some students and post-docs come to mind as being particularly important?
 
PETROV:  Yes, they do.  My first graduate student from Bulgaria is Ivan Ivanov.  He then went to Linköping, then came to University of Nebraska, and is now very successful in industry here. From Illinois there are a couple of dozen, but some stand out – Farshid Adibi, Young Kim, Daniel Bergstrom, Daniel Gall, Chansoo Shin, Suneel Kodamaka, Javier Bareno, Brandon Howe, Martin Bettge, and now Antonio Mei. K. Masak from Linköping and A. Ehiasarian from Sheffield with whom we have done a lot in the HiPIMS area.
 
HOLLOWAY:  That’s one question I wanted to ask.  What does HiPIMS stand for?
 
PETROV:  Okay.  We called it High-Pulsed Power Magnetron Sputtering.  HiPIMS came later, as high impulse power. In late 1997, when I happened to be visiting Sweden, Jan-Eric brought Volodya Kouznetzov to LiU. Volodya had developed the pulsed power supply and together with Ulf Helmersson and his students we began to study the discharge. With very high DC power density, the magnetron target will melt.  But if you apply the power in pulses, you can reach very high current densities and then let it cool.  During the high power pulse, the gas is driven away because there’s a momentum transfer, so called sputtering wind.  In the latter part of the pulse, there is a discharge in metal plasma, and that creates metal ions.  It doesn't have the drawback of cathodic arc which produces droplets.   It’s just something that became very popular in the past 15 years. The paper, we published in 1999, was the first show that this discharge produces metal ions and is heavily cited.
 
HOLLOWAY:  So what is your advice to a young scientist coming out with a first degree in Bulgaria as to how to interact with the world and achieve the same stellar career that you have achieved?
 
PETROV:  Well, English is important.  [Laughs] Do not burry your best idea on the fifth page of your paper – put it in the title. Then international collaborations are important.  But in each collaboration, you have to prove yourself.  I mean you have to be useful and have ideas and contribute.  It’s not a one-way street.   To any scientist, I think you need to work hard and not despair when results do not turn out as expected.  Good ideas don’t always come because you are very bright.  Good ideas come if you work a lot and you explore many, many routes, some of which may lead to nothing.  But if you collect a lot of data, then you suddenly discover something that is unusual.  Always look for the unexpected.  I don't know if I put it the right way.  But you need to— 
 
HOLLOWAY:  I understand.  I think you did a wonderful job.
 
ROWE:  Yeah, I think so, too.
 
HOLLOWAY:  Any other questions, Jack?
 
ROWE:  No, I don't have any further questions.
 
HOLLOWAY:  Well, congratulations on the Thornton Award for 2013, Ivan.  Well-deserved.
 
ROWE:  That’s right.
 
PETROV:  Thank you for your attention.  I am really humbled. 


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