AVS Historical Persons | Peter Hobson - 1990

Peter Hobson - 1990

Oral History Interview with Peter Hobson

Interviewed by Paul Redhead & Jim Lafferty, October, 1990
 
hobson.JPGREDHEAD: Could you tell us about the early days of the development of ultra-high vacuum at the National Research Council in Canada?

HOBSON: Yes. I'll do what I can about that. I arrived in your laboratory in 1954, and you were pretty well under way. You knew, in general, that you wanted to go into the field. Your first suggestion to me was to do some surface science on reflection of electrons, metal surfaces and LEED tubes, and LEED work later on. But the major thrust, I think, took place when you proposed the inverted magnetron gauge. You recall that, I'm sure. 

REDHEAD: I don't remember the date, though.

HOBSON: No? And I sort of undertook the task of seeing whether it really would measure a low pressure. So we built, essentially together, this little sealed-off apparatus with one Bayard-Alpert gauge, one inverted magnetron gauge, and a little finger that we could put into liquid nitrogen.

REDHEAD: This was an all-glass system, as I remember.

HOBSON: That's right. It was an all-glass system, and our own glass blowers had put it together for us. The idea was to prepare it as an ultra-high vacuum system with all the modern outgassing techniques, baking and so forth, and then to immerse this finger in liquid helium in order to get the pressure down a little bit more. This was my idea, to immerse the finger in liquid helium. I must confess in retrospect that I really didn't have any good idea of exactly what I expected to happen. I don't know whether you recall what you thought of this experiment at the time.

REDHEAD: I remember we had doubts, yes. 

HOBSON: [Laughs] Well, I think these were quite legitimate. But the experiment itself was executed on January 11, 1957. You were out of town that morning. The experiment was over in about 30 seconds. The sealed-off system had pumped down to its base level; both gauges were reading something steady. And just as soon as you put that liquid helium around that finger, the Bayard-Alpert gauge reading dropped by tens of percent, and the inverted magnetron gauge reading dropped by two orders of magnitude. I think it's a fair assumption that the Bayard-Alpert gauge had just dropped right onto its X-ray limit. Who knows exactly what had happened to the inverted magnetron gauge? When we removed the liquid helium after something like half an hour, both gauges went back to what they were before. So we had done nothing irreversible to the inverted magnetron gauge. We didn't know at the time. Well, it was very clear that it was sensitive at these levels. But what wasn't so clear was had we snuffed it out entirely? Had we just destroyed it as a gauge? 

REDHEAD: Why wasn't this clear? Was it that the current amplifiers weren't adequate?

HOBSON: No, it was just the current just dropped by such an enormous amount that maybe we had just snuffed out the discharge. It took us some time - weeks and months - to satisfy ourselves that it really was measuring something down there. It wasn't snuffed out. And indeed, you will recall your own gauge developments after that. 

REDHEAD: Can you remember what sort of pressures we estimated were achieved in those systems?

HOBSON: Yes. I don't recall the paper. You sprung this interview on me without the proper reference to those papers! But it was well below 10-10[Torr]. I think it might have been into the upper 10-12s, was our estimate. Somewhere about that. 

So the gauge part of it was on its way. The thing that interested me, and concerned me from there on, was what had the liquid helium really done? I calculated from perfect gas laws and so forth. These were not adequate to explain such a huge drop. I remember going to my friend, Derek Manchester, who was a PDF in physics at NRC at the time. 

REDHEAD: Solid-state group, I think, wasn't it D.K.C's1 group?

HOBSON: That's right. He [Manchester] later became a professor here at the University of Toronto. I explained the observation. I said, "I can't explain this. If indeed that gauge is telling the truth, I cannot explain why the pressure dropped so much." "Oh," he says, "that's physical adsorption of helium on your Pyrex glass." It was the first time I'd ever heard those words. 

REDHEAD: I presume by this time we had a fair idea that the residual gas was mainly helium.

HOBSON: Yes, we assumed that, essentially on the basis of Alpert's work. Absolutely, yes. That was our assumption, and I think a fairly good one. But even if it hadn't - well, that's a later story, in hindsight. We assumed it was helium, yes. And you referred me to a paper that recently had been published called "The First Adsorbed Layer of Helium" by - one of the authors was Meyer2, and I just forget the second one. These people had done some physical adsorption work with helium and had arrived at the conclusion that, indeed, the first layer of helium and adsorbed helium was formed at a very low pressure. My response to all this was to go chase down a book by Brunauer called The Physical Adsorption of Gases, a classic. In that book was a diagram of the physical adsorption of nitrogen at liquid nitrogen temperatures. It seemed to me it was a lot easier, if one wanted to explore this a little further, to do it with nitrogen gas at liquid nitrogen temperatures. It was just simply easier to manipulate the experiment. I recall that I stayed up; I got this thing set up to do essentially the adsorption isotherm of nitrogen on Pyrex at 77 [Kelvin] with ultra-high vacuum apparatus so I could watch the thing right down to the lowest levels. And I stayed up all night doing that experiment. In those days, it was normal to work through the night. 

REDHEAD: In your youth?

HOBSON: I haven't worked through the night in some time. I daresay not too many of the rest of us have. Have you?

REDHEAD: Not for a long time.

HOBSON: [Laughs] At any rate, by the morning, I knew that that diagram in Brunauer's book was dead wrong. That in fact, the isotherm went out - he had drawn it as if it hit Henry's Law at about 10-3 or  -4. In fact, I knew that the isotherm went way out to much lower levels than that. That is the essential reason why cryopumps work; that the isotherm is very flat on a log coverage - log pressure scale. The picture in Brunauer's book was as if the isotherm was a linear isotherm, and it clearly was not. That was experimentally obvious.

REDHEAD: Brunauer's curve was theoretical, was it?

HOBSON: No, it had measurements, but only done down to the limit of McLeod gauges. I think there were points all down there, but McLeod gauges become less and less reliable as you push the pressure down. You know, it wasn't poor measurement. It was just that the instruments weren't up to this kind of a measurement, I think. That was my interpretation. 

The next question was, if indeed the linear isotherm did not apply, what did apply? I recall that you suggested to me - I don't know where you found these references, but you had a knack and still do of finding these references. You produced a reference somewhere and said, "Just look at this one." Do you remember that?

REDHEAD: No, I don't remember it.

HOBSON: Well, that's what you did. So I went and looked at that one. It was a paper describing an isotherm called Dubinin and Raduskevich by a couple of Russians. Dubinin was a senior scientist. He was a member of the USSR Academy of Sciences. I don't know who Raduskevich was; he was probably his student. Was it in Russian? I think it might easily have been. I'm not certain of that. 

REDHEAD: I think it was. I have a vague memory of getting it translated. Anyway, I may be wrong. 

HOBSON: It might easily have been in Russian. But in those days, that was slightly post-Sputnik, and the learning of Russian had suddenly risen high on scientists' priorities. I remember taking some courses in Russian. Did you ever take those?

REDHEAD: No. [Laughs]

HOBSON: They weren't much use in translating. 

REDHEAD: I had enough trouble with French without bothering about Russian.

HOBSON: [Laughs] At any rate, when this isotherm was applied to my data, it fitted almost exactly. It had all the right sorts of logarithmic dependencies.

REDHEAD: What sort of pressure range were you measuring at? How many decades?

HOBSON: Probably about six. It was done with a Bayard-Alpert gauge, so it was running from something like 10-3 Torr to something like 10-9 or -10. There was a nice broad pressure range, so you could test a logarithmic dependence. This was very successful. I remember publishing this; I think it was in the Canadian Journal of Physics, where we previously published the paper on the inverted magnetron. 

Then I guess I didn't foresee what that curve meant to the cryopump situation fully at that time. The next move was then to repeat that very experiment with helium on Pyrex glass, which was done. There was nothing difficult in the principle. And once again, the isotherm was extremely flat. And once again, the Dubinin-Raduskevich equation fitted. Then the next thing was to test the temperature dependence. We did a lot. It was tough experimental work because you had to be very careful. But indeed, over a whole series of measurements, the thing was really a very elegant fit. 

It was quite clear you could produce extremely low pressures with these two cryopumps. It wasn't really till a lot later - I guess 15 years or something like that - where the refrigerator was added to the cryopump, the electric refrigerator.

REDHEAD: I have a vague memory that some time around it, you actually immersed a complete system in liquid helium.

HOBSON: No, that's not true. I immersed a complete system in liquid nitrogen. And curiously enough, the motivating reason for that particular experiment was to decide did an ion gauge really measure density, or did it measure pressure? We filled an ion gauge with helium gas and immersed it in liquid nitrogen. 

REDHEAD: This was sealed-off gauge?

HOBSON: Sealed-off gauge. By that time, I knew approximately the amount of helium that would adsorb at liquid nitrogen temperatures. Indeed, the experiment was pretty dramatic. The gauge reading hardly moved. Everybody says, of course, that these gauges respond to density, not pressure. But I had to do that experiment before I really believed that statement. 

The history of cryopumps, of course, is now very well established. It was the electric refrigerator that has now became a very useful and convenient tool.

REDHEAD: So through all this period, the systems were presumably almost entirely in glass, with a limited amount of metal, as far as I recall.

HOBSON: That's right. They were whatever you needed to make a gauge. 

REDHEAD: Do you recall the great problem that we had with the mercury diffusion pumps about that time?

HOBSON: I don't want to really emphasize this because it hardly can go down as history of science or vacuum.

REDHEAD: History of non-science, perhaps.

HOBSON: Yes. It was an accident that tends to determine things in the laboratory. We were using glass vertical mercury diffusion pumps. On one occasion after a repair, as I recall, we left the thing running over the weekend, and it cracked right above the mercury reservoir. The whole reservoir just dropped down about an inch taking its cup heater with it. And the heater went on working. It spent the weekend depositing mercury vapor in the laboratory, so that when we came back on Monday, there was no mercury left in the reservoir and the whole lab - I mean, the whole lab! - was covered with mercury. It was your problem to organize the-- 

REDHEAD: As far as I remember, I told you to organize it.

HOBSON: No, that's not correct. I think you…

REDHEAD I certainly recall a fairly hectic week. I do recall finding the catastrophe on a Sunday afternoon.

HOBSON: Oh? You didn't come back on Monday.

REDHEAD: I came in for something on Sunday, looked in through the glass panel on the door, fortunately before opening it, and the whole room looked gray, and I wondered what the hell was going on. So I didn't open the door, of course. Went and got a gas mask, and then opened the door. I remember breaking the windows of the lab with an axe because the rooms, if you remember, were air-conditioned and the windows didn't open. I remember breaking the windows with a fire axe. But the following week, the cleanup was quite an operation. I suspect we were one of the few laboratories in the world that succeeded in recovering from a major mercury evaporation of that sort without killing anybody - as far as we know of. 

HOBSON: It's supposed to produce long-term mental symptoms, is it not? I'm not about to say that they are not here! 

REDHEAD: So basically, that led to an understanding of some of the features of cryopumping at very low pressures. Where did you pursue the ultra-high vacuum techniques after that? Or where did you apply them, perhaps would be a better way of saying it. 

HOBSON: Well, the first experiment had given us the idea that putting together cryopumping and UHV gauges gave us a means of calibrating gauges. We had created that concept. So I then developed the fairly simple job of developing a calibration system so that we could go back to the first experiment and actually plot the points. And indeed, the inverted magnetron gauge-- It wasn't quite linear. There was a bit of a break in it. But it was certainly still responding to the pressure. It had not snuffed out, and we repeated that. It was a very simple and very elegant-- 

REDHEAD: And presumably, if memory serves me right, you repeated it with the magnetron gauge. 

HOBSON: Yes. Then I went on to - You see, when you do a physical adsorption measurement with the gauge at room temperature and the adsorbing taking place at a much lower temperature, there is a thermotranspiration correction - always, every time you plot a point. There was something - and I don't really recall what - that disturbed me. There was an inconsistency in the normal application of the pressure ratio as going against the square root of the temperature, which I took seriously and did some measurements, particularly with Terry Edmonds, who had come over from England as a postdoctoral fellow. I said to him, "Look, Terry. There's something wrong with this classic equation that's in the literature."

REDHEAD: My recollection is that back in the '50s, part of the motivation for getting involved in ultra-high vacuum work was because it was of interest in surface work. Your work on low-energy electron diffraction. So let's go forward, then, to after this establishment of cryopumping techniques and the general techniques of getting pressures down to the order of 10-11 Torr or less. Where did this technology then get applied to that?

HOBSON: In our laboratory, as you know, we realized that we had in our hands the tools to make measurements of all sorts of phenomena over pressure ranges that had been just not available up to that time. We branched out, yourself and Ernie Kornelsen and myself, to do various physical measurements. In my case, my first thrust was toward this cryopump work that I described to you. You took up chemisorption work, flash filament desorption. And Ernie took on ion bombardment of metal surfaces and the subsequent thermal desorption. We were very conscious. We had grasped by then, which was probably now about the early ‘60s, that there was a synergistic relationship between ultra-high vacuum and surface science; that to do surface science properly, you had to have the technology of ultra-high vacuum. And on the other hand, if you were to understand the instruments you were using, both to create and measure ultra-high vacuum, you'd better know a bit about surface science as well. We had grasped that. We set out to do these back and forth types of measurements. You discovered electron-induced desorption, EID, and so forth. There was a whole series of investigations. 

REDHEAD: I guess the point I was getting at, that many of these more fundamental investigations were, in a sense, technology-driven. The work on electron impact desorption, for instance, came about because of observations of peculiar behavior of the Bayard-Alpert gauge in the system that I was using to study the adsorption of oxygen on tungsten. Remember that? And for some weeks, we couldn't understand these weird results we were getting on the Bayard-Alpert gauges. And it was only, if I remember now, that it happened that the gauge was a modulated Bayard-Alpert gauge, which we had developed along the way, that allowed us, quite fortuitously, to separate the surface ions from the gas phase ions. I think this sort of interconnection of technology and science was one of the key elements to all this work. 

HOBSON: That's right. We demanded, and fairly tenaciously hung on to, things we didn't understand that were qualitatively - We didn't know what was going on, and we did not put those aside. We would pursue them until we found at least some general explanation. That, I think, was a philosophy of the laboratory in those years, which now extends up into the middle '60s. It was very productive. Somewhere in the middle of all that, we started to write the book, The Physical Basis of Ultra-High Vacuum. By the time that was published, we had done work in just about every field described in that book. Somewhere in the lab, we could bring our own experience to bear even though we were commenting on work we'd done elsewhere.

REDHEAD: I guess the point worth making is that over that whole period, the availability of suitable commercial equipment for ultra-high vacuum work was very close to zero, with the exception of ultra-high vacuum valves. Good ultra-high vacuum valves were available, but that was about all. And that was true, I guess, in most labs around the world; they had to make their own equipment, more or less. 

HOBSON: That's true. The Bills valve was a tremendous technological advance. These were reliable valves. Before that, the Westinghouse valve was, I felt, a little less reliable, but it was also the pioneering valve. Of course, we would attach these to glass systems and every now and again closing these valves we would strain the system and lose it. 

REDHEAD: Do you have any final comments you might make to wrap this up?

HOBSON: Well, it was a very exciting period. I think it might be said to have lasted 15 years or something, from the middle '50s right through to about the beginning of the '70s. In our book, we mention Auger electron spectroscopy; Harris's fundamental paper was published in 1968, when the book was published. And it received mention in the book, but that is all. It was essentially that period that was the real beginning of surface science and all these elegant instruments that are available today. I think the fundamental work in ultra-high vacuum technology was also in place so that vacuum companies could start to really put on the market reliable UHV equipment, which is the essence of the situation today. 

REDHEAD: I think there's one final comment I'd like to make, if I may. Over that period of 15 years or so, we were able - I think you'll agree, and in fact you mentioned it yourself - to study problems that turned up that appeared to have some fundamental interest, we could go off and pursue them without having to persuade our management. We had really quite extraordinary intellectual freedom. That's not to say we ever had enough money to do what we wanted to do. But as far as I recall, we never had any interference in choice of scientific direction.

HOBSON: I perhaps wouldn't agree. I never felt financially limited. I felt my imagination was more limiting than the finances available.

REDHEAD: I entirely agree. 

HOBSON: But it is true, and in a sense it's a little hard to justify from the National Research Council's point of view, the fact that we had such elegant freedom. 

REDHEAD: I don't know. This is an ancient problem. 

HOBSON: One point I would like to make, which isn't strictly on the basis of science and technology, but it was just at the end of this period that the American Vacuum Society posed itself a question. It had become aware that surface science might be very important and very closely related to ultra-high vacuum. I think it was certainly you and Jim Lafferty - you followed each other, did you not, as President of the Society? '68 and '69?

REDHEAD: Is that right, Jim? Do you remember? I was President in '68.

LAFFERTY: No. I followed Bill Lange, from Westinghouse.

REDHEAD: So Bill Lange followed you?

LAFFERTY: Or did Bill Lange follow me? [Laughs] Which one was it?

HOBSON: Anyway, it was you that gave me the formal instruction to go ahead. I think - perhaps it was you, Paul - that gave me the instruction to find out the situation.

REDHEAD: Jim was Secretary at the time.

LAFFERTY: I guess I followed you, Paul, and Bill Lange followed me. I guess that's the way it went.

HOBSON: You had told me, "Go find out whether the surface science community would be interested in joining the American Vacuum Society in some form or another." There were perhaps 50 people in surface science at that time. I called them all, any that I knew. They were nearly all in North America, the ones that I called. The vote was very close. It was roughly 52% to 48%. I remember going to Jim Lafferty, who was President at that time, and saying, "It's a close call. What do you want me to do?" And he gave me the authorization - with Board approval, of course - to go form a Surface Science Division, and we'll see what happens.

REDHEAD: Interesting period. I recall a sort of, at the time, a degree of snobbishness in the community. The thought of joining up with this greasy-fingered bunch of engineers in the American Vacuum Society didn't please a lot of arrogant gentlemen. 

HOBSON: I think that's correct. That feeling was present. My sales pitch to those people was essentially, here is an organization, the American Vacuum Society, which knows how to run conferences. All you have to do is become a division, and you get all that for free. You can talk about what you like in your sessions. You don't have to go set up all that organization yourselves. And the equipment these people know how to make is important to you. That was my sales pitch. 

I do recall this, that the first Surface Science Division program was held in Seattle in 1969. I think it was all invited speakers. I went to the site in Seattle on Sunday night, the night before the conference was to open, and I was appalled. They had set the Surface Science Division off in some little room on the other side of the World Fair campus. Basically, all the arguments I had given for the surface science people to join the AVS were nullified by that. They were off in a corner, there would be no interaction, and they really wouldn't get a synergistic conference of any kind out of it! 

I went to the local organizer, and I said, "You've got to change the location of this program." I sort of issued the order. I really didn't know whether they would abide by it or not. I spent one of the worst nights of my life before that session was to open, wondering whether they would move that room. Which they did. I could hardly believe it when I walked in the door the following day in Seattle. All the chairs were where I wanted them. I was the program chairman for that thing, and the program was really quite successful. And that really - it took off after that. The rest is really history.

Notes:
1. D. K. C. McDonald
2. Lothar Meyer was the sole author

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