Does an AFM need to be have a technician responsible for it?  Or a senior scientist who can train others to use it? In many research labs, the answer seems to be “no”. Or at least, there is no-one fully responsible for the AFM, who can advise on experiment design, sample preparation, and train users, or even just run users’ samples. In this blog post, I’ll talk about why this situation exists, and what should be done about it.  

 


Image of dsDNA captured by a student on one of our courses. Such images can be challenging to acquire without adequate training.

In research labs in academia, (and, to a lesser extent, also in industry), there are often two kinds of facilities, those that are operated by individual researchers, in their own projects, and those that are run either ONLY by technicians /senior scientists, or only by fully qualified researchers under the close supervision of an expert. For example, in chemistry, a common instrument that is usually left to researchers (such as students) to run by themselves, is a UV/visible spectrometer. This is a pretty simple instrument, that is kind of a “black box”, which requires minimal training to use correctly.This is not to say that some things cannot go wrong, but an occasional prod in the right direction is all that’s required. Typically, if any-one is responsible for the instrument, they often just change the bulb now and again. More complex instruments are often run the same way, up to optical microscopes. But this is not the same for nanometre-resolution microscope, right?

 

Electron microscopes are *rarely* solely user-operated. They nearly always have a technician responsible, who might be the only one to use the microscope at all. When I began to use electron microscopes, it was clear that I was not going to get my hands on the instrument, until after a very thorough training lasting several weeks, and costing a lot of money. After this, I used the instrument for a long period of supervised operation, before finally being considered independent. This makes sense, for several reasons:

  • Electron microscopes are complex, with many controls you need to learn

  • They are easy to misalign, or even damage

  • They usually need careful sample preparation

  • The data from them can need careful interpretation

  • Electron microscopes are (usually) big and expensive instruments

 

So, what about the AFM? Doesn’t all this hold true for an AFM?

 

Surprisingly, there are many many cases where AFM instruments do not have a responsible user, let alone a technician. In the AFM training course I teach, something like 50% of the people who need training say there’s an AFM in the lab and no-one knows how to use it.

 

There are many AFM instruments sitting in lab corners, barely if ever used, or used only by un-trained students.

 

So, why is this? All those bullets points up there kinda hold true for AFM, don’t they? I think they mostly do, but I think the difference is in the last part.

 

An AFM can be a low-cost instrument! And an AFM might be very small indeed...which will often lead to the erroneous idea that it’s a simple instrument to use. Is AFM more difficult than electron microscopy? I don’t think so, but most electron microscopists seem to think so. Then again, perhaps this is because they’ve never been trained properly in use of an AFM.

Let’s look at cost; here’s a rough idea of what it costs to get an instrument with 1 nm resolution:  

 

TEM

SEM

AFM

around 1,000,000 USD

around 400,000 USD

40,000 to 100,000 USD

NOTE: These are “typical purchase costs”, and any of them might costs more or less than this, but not by an order of magnitude….

 

Now, these 3 instruments would not be the same, and I am not saying a 40,000 dollar AFM can do everything a million dollar electron microscope can do, but with these three instruments, you can achieve around 1 nm resolution. To explain what you can really do with them could make another looong blog post...

 

But, wow, it’s a big difference, isn’t it? Add to this the fact that a TEM takes up an entire room to itself, and may even need the ceilings raised to fit in (and it usually won’t fit through your door, either!), and you can start to see why sometimes people take the TEM or SEM more “seriously”...If you have to raise a million dollars in funding to buy a microscope, you are going to make damn well sure that a: It’s not broken by incompetent users, and b), that you get some money back to keep it going by selling services.

 

So there we have our poor little AFM, it’s the new kid on the block, electron microscopists don’t understand it, and no-one ever gets properly trained. Some AFMs are actually installed by technicians who don’t know how to used it.

 

So what can you do?

  • TRAIN your USERS!

  • MAINTAIN the KNOWLEDGE!

  • keep GOOD staff!

 

All of these are difficult, but check out our training courses here: http://afmhelp.com/course

 

I would be interested to hear what other people think about this, it’s something I’ve been telling people a long time, and no-one has contradicted me (audibly) yet! Do people out there who can use  AFMs and EMs think one is more difficult than the other? Modern electron microscopes are also highly automated, partially due to more mature technology, and partly, I guess, to justify their high costs!
What do you think?

 

Incidentally, if you need an AFM expert in your lab after reading this, I am looking for a job! Check out my CV here! ;-)

 

Pete.

 

 

Every year in our AFM training course, we hold a little competition among the students to produce and process an AFM image. The prize is always a liquid product from the city of Porto!

This year, the overall prize was won by this nice treatment of human red blood cells sent in by Akmaral.

 

 
Human erythrocytes, processed and submitted by Akmaral Suleimenova
 
     

 

Thanks to Christie for donating the blood!

 

In addition, this year, we have a special prize for “outstanding image processing”, which goes to Tobias for this unusual image presentation: I can only show you a photo of the image, as he 3D-printed the AFM image of 90nm nanoparticles. Great one, Tobias!

 

          
3D printed image of Nanoparticles from Tobias Burger
 
     

Congratulations to Akmaral and Tobias, your prizes and certificates will be with you soon!

 

Thanks to everyone who entered the competition this year. Hope to see you again!

One of the most important components of an AFM is the probe. AFM probes are made of a chip or substrate, a cantilever, and a tip. Usually, these are manufactured in one piece of silicon (or silicon nitride, Si3N4), by MEMS manufacturing techniques. In this way a wafer (with 400 or more probes) is manufactured at one time, with reasonable reproducibility of probe characteristics across the probes.

 Probe showing the Cantilever susbtrate and tip

 

Design of typical AFM probe, showing the substrate, cantilever and tip (probe).

 

Importantly, nearly all probes are interchangeable, so it’s possible to use probes from different manufacturers in your instrument. Thus, there is a fairly competitive market in AFM probes, and you can find a variety of probes from value to high-cost offerings, and an enormous range of probes, with different coatings, and physical properties, suitable for a wide range of applications. There are so many different probes here, that it’s not worth listing them all, so this page just links to the manufacturers of probes that I know of. Some companies resell probes from other manufacturers,such distributors are listed on this page. But here I list only the manufacturers. The manufacturers are listed in no particular order.

 

AFM Probe Manufacturers

Bruker

www.brukerafmprobes.com

Bruker (until recently Veeco) manufacture a huge range of probes, as well as reselling probes from various other producers. They have many representatives, as well as selling direct in the U.S.

Applied NanoStructures

www.appnano.com

AppNano manufacture a wide range of standard and speciality probes- they are resold by various companies, and also sell direct

Nanoworld

www.nanoworld.com

Nanoworld manufacture a very large range of standard and speciality probes - resold by various companies. Also branded as nanosensors

Mikromasch

www.spmtips.com

Mikromasch manufacture a very wide range of probes, both standard and speciality. They sell direct and are re-sold

NT-MDT

www.ntmdt-tips.com
NT-MDT manufacture many standard and specialty probes, including with a wide range of coatings

Olympus

probe.olympus-global.com 

Olympus manufacture many “standard” and novel probes, including the biolever-often used for force spectroscopy. They do not sell their own probes, but they are sold by a large number of companies

Artech Carbon

SCDProbes.com

Artech Carbon make single-crystal diamond porbes, which are very sharp and wear-resistant. 

Team Nanotec

www.team-nanotec.de

Team Nanotec make a variety of specialist AFM probes, including metrology tips, high-aspect ratio probes, MFM probes, etc. They both sell direct and are re-sold

Asylum Research

www.asylumresearch.com

Asylum make various speciality probes of their own design, as well as reselling various other brands. Asylum are now part of Oxford Instruments

Micro2Nano

www.micro2nano.com
Korean company, Micro2Nano manufacture tetra brand probes which are resold, and offer a custom probe service

Budget Sensors

budgetsensors.com
Budget Sensors manufacture a wide range of probes, including mix-and-match boxes. They have an online shop, and are resold

sQube

sqube.de

sQube manufacture a range of colloidal probe cantilevers, check their webpage for link to distributor

Kelvin Nanotechnologies

www.kelvinnanotechnology.com
Based on the campus of Glasgow University, Kelvin Nanotechnologies manufacture scanning thermal probes

NaugaNeedles

nauganeedles.com

Nauganeedles produce specialised probes with semiconductor nanowires grown from the end, useful for metrology and electrical applications

NuNano

www.nunano.com

Nunano is a Bristol (UK)-based startup specialising in SPM probe manufacture. Offer custom probe design.

Carbon Design Innovations

carbondesigninnovations.com

CDI manufacture AFM probes modified with carbon nanotubes on the tip

Smart Tip

www.smarttip.nl
Based in the Netherlands, Smart Tip make specialised probes, such as magnetic MFM probes

Novascan

www.novascan.com

Company that specialises in colloid probes and chemically modified probes

SCL-Sensor Tech.

www.sclsensortech.com

Company that specialises in self-sensing and self-actuating probes

 

Once again, distributors can be found here.

If I any have missed any manufacturers ,or made any other errors, please feel free to make suggestions, via the contact page.

Atomic Force Microscopy (AFM) is a high resolution technique to measure the topography of samples. However, in order for such measurements to be accurate, the AFM must be calibrated, so that the results can be trusted. The commercial materials listed here are suitable for making such calibrations of AFM instruments.
This information on AFM standards is extracted from my forthcoming book "Atomic Force Microscopy".
Please get in touch if any information is inaccurate or you know of another standard or supplier.

See appendix B of Atomic Force Microscopy for calibration procedures.

 

X-Y Standards

These are standards to calibrate or check linearity in the X-Y axis in SPMs.

Source

Standard

VLSI standards

www.vlsistandards.com

many in µm range (silicon, 2D) 100 to 1000 nm (silicon, 1D)

Ted Pella

www.tedpella.com

144 nm (aluminium on Silicon)

300 nm (titanium on silicon)

MikroMasch

www.spmtips.com

3 and 10 µm, HOPG

SPI Supplies

www.2spi.com

300 or 700 nm (metal-coated silicon)

Electron Microscopy Sciences

www.emsdiasum.com

300 or 700 nm (metal-coated silicon)

Applied NanoStructures

www.appnano.com

Various in micrometer range (metal-coated silicon). I personally tried use these standards.

Bruker

www.brukerafmprobes.com

1, 2, 10, 15 µm (silicon)

NT-MDT

www.ntmdt-tips.com

278 nm (aluminium on glass, 1D)

3 µm (silicon, 2D)

Asylum Research

www.asylumresearch.com

10 and 20 µm pitch (metal on silicon)

Nanosensors

www.nanosensors.com

100, 200 or 300 nm (silicon)

4, 8 and 16 µm (silicon

BudgetSensors

budgetsensors.com

500 nm, 5 and 10 µm - SiO2 on silicon.

Team Nanotech

www.team-nanotech.de

Pitch and feature width standards

Geller Micro

gellermicro.com

Geller sell references and standards (including traceable ones), suitable for AFM as well as EM.

Z standards

Here are standards to calibrate the z scale. Sometimes these can be the same ones as used for the x-y axis calibration, but often they are separate samples.

Source

Z calibration standard

VLSI standards

www.vlsistandards.com

various silicon and quartz

MikroMasch

www.spmtips.com

Various in silicon, HOPG

NTT AT

www.ntt-at.com

Silicon monatomic steps (0.31 nm)

Ted Pella

www.tedpella.com

20, 100 and 500nm (Silicon)

Applied NanoStructures

www.appnano.com

10nm, 1µm

BudgetSensors

budgetsensors.com

10, 100 and 500 nm steps - SiO2 on silicon

Veeco

www.veecoprobes.com

2, 100, or 200 nm (silicon)

NT-MDT

www.ntmdt-tips.com

Various steps in silicon and atomic steps in Silicon (0.31 nm)

Asylum Research

www.asylumresearch.com

200 nm (metal on silicon)

Nanosensors

www.nanosensors.com

8nm (silicon)

Silios Technologies

www.silios.com

2, 5 and 10 nm (silicon)

1 nm "in development"

Other standard materials include ultraflat samples - mica and HOPG, available from various suppliers, and quartz ultraflat sample from nanosensors.

Particle Standards

Particle samples are also useful both to calibrate the tip and as height references.

Supplier

Particle sample

Tedpella

www.tedpella.com

Gold colloids in 5, 15, or 15 nm diameter

Edmund Optics

www.thermo.com

Polystyrene nanospheres in a range from 20 to 900 nm

Evident Technology

www.evidenttech.com

Quantum dots ranging from 2.2 to 5.8 nm

Electron Microscopy Sciences

www.emsdiasum.com

Colliodal gold in 0.8 to 25 nm diameter

LFM Standards

Samples for calibrating LFM , with fixed angle slopes are:

Supplier

LFM sample

Mikromasch

www.spmtips.com

Triangles (silicon), top angle 70 °

Steps with sloped edges (silicon), slopes 54 °

Edmund Optics

www.edmundoptics.com

Ruled diffraction gratings, with various angles

Phase References

Samples for calibrating phase are available from Asylum Research and EMS. Both are polymer samples with regions of different hardness.

 

Probe Shape Calibration Samples

These are samples you can image with the AFM in order to get an in situ measurement of the radius and shape of the probe tip.

Supplier

Sample

Aurora NanoDevices

www.aurorand.com

Tip check sample (100 nm z-scale). Nioprobe tipcheck sample ( 10 nm z scale)

Mikromasch

www.spmtips.com

Porous aluminium

NT-MDT

www.nt-mdt.com

Silicon spikes

BudgetSensors

budgetsensors.com

Thin film on silicon wafer, with sharp pyramidal spikes. I have used this sample, and it can be used in contact or oscillating modes to characterise probe tip shape.

Feel free to get in touch with any updates / corrections.

This page has a list of corrections to the book "Atomic Force Microscopy".  If you notice any more mistakes, please let me know here. That way I can correct them in the next edition!

 

Important Note: All these errors will be corrected in the upcoming paperback edition. If you know of any more, let me know! 

Errors

  • Page 30 - Equation 2.6: Verr is used in place of Zerr in the first term.

 

  • Page 38 - The last paragraph erroneously refers to equations 2.5, 2.6 and 2.7, where it should be 2.7, 2.8 and 2.9, respectively.

 

  • page 53 - referring to the figure shown below:
Figure 3.4 - Canitlever and photodetector

In this figure, vertical bending is detected as "(A+B)-(C+D)", i.e. the difference of the top two and bottom two segments. On page 53 the book erroneously says "(A+B)-(C-D)".

 

  • Page 56 - Figure 3.6 Should read: "B-intermittent contact oscillation (large)".

 

  • Page 66 - Legend refers to colours in the image where there are none.

 

  • Page 114 - Section 5.2.4: Three-dimensional views. Should read: "...special glasses to differentiate the left eye's and right eye's views...".

 

  • Page 116 - Table 5.2. The Formula for skewness is incorect. The exponents should be 3, not 4. i.e., as shown below

Skewness formula

 

  • Page 164 - Misspelling of "fimbriae" as "fibriae".

 

Thanks very much to everyone who informed me of these errors!

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