The Origins and Development of Scanning Probe Microscopy

Interview conducted by Will SoutterDec 8 2014

In this interview, Dr Curt Sander, founder and CEO of SPM/AFM developer DME, talks to AZoNano about the origins of SPM technology, the beginnings of his company, and the future of the technique.

You have been involved in the SPM industry for a long time - can you tell us how you first got involved in the technology?

Yes, I am certainly one of the "old-timers" in SPM technology. I was involved from the very beginnings, in the 1980s, and I know most of the people that were the instigators of the technology - Binnig, Rohrer, Gerber, Ruska, and so on. We were also involved in the very early stages with some of the people at Aarhus University - we collaborated with Besenbacher and his team there.

DME at that stage was basically a software company. The 80s was the period where many people switched from using fixed wire electronics, to using programmable electronics and software. We were involved with helping a lot of people with that transition, to understanding the importance of software in electronics.

Just to give you a little background, we were involved in building the first mobile digital electronic system in the world, for Motorola. Around that time, Motorola bought a Danish company called Storno, who made radio equipment, and we were one of their biggest suppliers of software and digital electronics.

So that was our background at the time. From there, through our collaborations with the research groups I mentioned, we helped to build some of the forerunners to the commercial SPM instruments, which were really scientific projects at that time.

DME's SEM-integrated AFM, in use in the lab with a Carl Zeiss AURIGA^® Crossbeam system.

How have SPM instruments developed since the early days?

The main thing that has changed, apart from the increase in resolution, from micrometers down to nanometers or even picometers, is that anyone can now use an SPM.

Back in the 90's, and certainly in the 80's, it was only the professor, the really experienced researchers, who would be able to use the instrument, and get good results from it.

Now, with the modern instruments, you can use the instrument to gain good information about a surface, without needing to know the details of how it actually works, of what is going on in the mechanics of the interaction.

One of the most interesting things about SPM is that the fundamental principle is very straightforward - it is a sharp tip which interacts with the surface. Whilst it can be more complicated than that, in most cases it really is that straightforward.

This opens up some interesting possiblities, which are not possible with electron microscopy, for example. We can make the tip conductive, and do electrical characterization at the same time. We can make the tip an optical fiber, and observe what is taking place at the surface optically or chemically. These are all interesting additions to the core SPM technology, which no other technique can support.

What do you think has been the single biggest change during SPM's history?

There is no simple answer to that question. I don't think there have really been any big step changes in the technology. It is more of an evolutionary field, much like the microprocessor industry in the 60's and 70's.

It has really been a process of development in terms of the new modes and the extension into other scientific fields like biology and chemistry, along with gradually understanding more and more about the technology, and it's limitations. So it's a very evolutionary process.

How have the changes in SPM and AFM technology affected users of the instruments?

I think there is  a much broader range of questions that can be answered with AFM now. We probably have quite a unique take on this question, because of the way we approach our products.

Many of the standard things that people want to know about a surface can now be solved quite simply - you can buy an AFM, set it up, push a button on the PC, and you have your data. This accessibility and usability is great, as I said, and we have instruments that fit this kind of use.

However, since we have 25 years of working with AFMs and SPMs, our approach is to see what else we can do with the technology, by putting the users' needs first.

If scientists or researchers have a surface characterization problem that falls outside the limitations of standard AFMs, we ask them to ignore those limitations, and formulate the problem as an AFM problem. Then, with our knowledge, we see if we can deliver an instrument that can solve that problem.

Some of the ways DME's products can be used to characterize graphene

Can you tell us a bit more about the history of DME - how did you move from software and electronics into manufacturing full SPMs?

We were working on building the scientific prototypes at Aarhus, as I said, and we really saw the commercial potential of the technology. Unfortunately, at that time, SPM technology just wasn’t ready, from an industrial point of view. We can see that now with the benefit of hindsight, of course.

I think this happens in a lot of areas though. If you start any company around a forward-thinking technology, the chances are, if you look back, you would think you shouldn’t have started it so soon.

For that reason, we are keen to keep looking forward, not back.

What is unique about DME's SPM/AFM products?

I think the way we approach all of our product lines, from tabletop research and teaching instruments to in-line process monitoring setups, is quite unique, and it stems from the fact that we have so many years of experience. Basically, when we are putting a new instrument together, we will look for parts of the instrument that we already know how to make, so that we don’t reinvent the wheel.

Then, in a very modular way, we will put the separate building blocks together to create new capabilities, or solve new problems. This is a very effective way of using our accumulated knowledge of SPM.

Has the range of applications your users use your products for changed over the years, and how do you think it will evolve in the future?

There are new areas which are using SPM, but really the technology is relevant whenever surface characterization is involved. We are seeing AFMs and SPMs being used in a lot of cutting-edge technology, like nanowires, novel battery electrodes, etc., but fundamentally the instruments are solving the same kind of problems, with topography and surface roughness measurements, and things like that.

One area that I think will expand is the combination of AFM with other techniques. By using optical microscopy and spectroscopy techniques simultaneously with a tip scanning the surface, we can correlate chemical information with topographical information, and that is going to potentially open up a whole range of new applications for SPM.

A Carl Zeiss MERLIN FE-SEM with integrated AFM from DME investigates the properties of graphene

Are there any major challenges facing SPM manufacturers, which need to be overcome to help these application areas grow?

The main, long-standing issue that SPM has—which is the same for any technology that looks at a surface on such a small scale—is navigation. If you find a feature at the micrometer scale, then zoom into to nanoscale resolution to examine it, and then move your sample, you will probably never find that same area again.

We have built an instrument which works around this problem – a combined scanning electron microscope and AFM. This solution has been talked about for a while now, and it allows much simpler investigation of things like microchips, as well as complex materials.

The SEM is a very nice tool, because it can zoom from the micron scale down to nanometers, in some cases, and give you a really good idea of where everything is on your surface. However, it cannot give you 3D images at the lower end of the scale. By combining it with the AFM, which gives you 3D topography of the surface at very high resolution, you can very easily build up a detailed picture of the surface you are looking at.

Additional to topography it has turned out that the characterisation of local electrical properties of microelectronics, Li ion materials, and nanostrcures like nanorods, quantum dots and CNTs is possible.

This combination also allows certain applications that were not possible. For example, if you have a powder of a grainsize above your Z scanner's ability, and you want to inspect nanostructures on the grain with an AFM. With an AFM alone this is not  possible at all – if you don’t get the AFM tip on top of the grain, it will simply break. If you can use the SEM image to position the AFM tip, then this situation does not present any problem. This fact can directly be transferred to other samples structure wafers (memory) etc.

There are plenty of problems like this which will arise as surface technology advances, so I am sure that the SEM/AFM combination will be one of the major areas as the field progresses in the future.

About Curt Sander

Dr. Curt Sander is the President and CEO of Danish Micro Engineering A/S, which he founded in 1979. He has been a member of various Danish governmental R&D bodies, chairman of the research & education committee of the Association of Danish Electronics Industries, and Board member of the Association of Danish Electronics Industries, amongst other activities.

Dr. Sander was awarded the title of Knight of the Order of Dannebrog by Her Majesty Queen Margrethe II of Denmark in 1997.