Automated AFM Probe Calibration with GetReal™ from Asylum Research

By AZoNano.com Staff Writers

Topics Covered

Introduction
The Best Way to Calibrate AFM Probes
Real Calibration – From the Force Experts
Simplicity of Use
Specifications
Method of Working
GetReal is free with all Asylum AFMs
References
About Asylum Research

Introduction

You would never say that you are “2.5 Volts tall” or that you “gained 1.5 Volts on holiday.” The Volt is the wrong unit to measure height and weight. It’s difficult to interpret until converted to real, physical units.

Yet in the world of atomic force microscopy (AFM), many of us are accustomed to seeing the cantilever deflection, amplitude, and force measured in Volts. That’s because the conventional process to calibrate the cantilever is not trivial, requires a stiff sample, and poses some risk of damage to the tip.

Asylum Research’s GetReal automated probe calibration feature, exclusive to our MFP-3D™ and Cypher™ families of AFMs, makes this calibration simple, safe, and accurate. So don’t settle for Volts. GetReal!

The Best Way to Calibrate AFM Probes

GetReal makes probe calibration as easy as choosing a probe and clicking one button. The tip never touches the sample, so there’s no risk of damage or contamination.

The inverse optical lever sensitivity (InvOLS) and spring constant (k) are both calibrated in one step, with accuracy comparable to conventional methods.

GetReal enables more consistent, accurate results by making probe calibration effortless and therefore a routine part of AFM measurements.

Real Calibration – From the Force Experts

Asylum Research pioneered force measurements and spring constant calibration, including some of the earliest calibration techniques,1 the first commercial use of the thermal noise method, and later refinements to the thermal method.2

GetReal continues that legacy, providing a one-step, no-touch calibration that is just as accurate as conventional calibration methods (Figure 1), but much faster and easier. Other AFM companies have approached the issue by using nominal values of k and InvOLS tabulated in a “probe database.”

This eliminates the Volt and replaces it with values that appear deceptively accurate, but are in fact really no less arbitrary than the original value in Volts. Both k and InvOLS vary significantly among individual probes and AFM setups, making nominal values almost worthless.

Figure 1. GetReal works with a wide range of our most commonly used probes sold at www.AsylumResearch.com/ProbeStore. Here, the InvOLS was calibrated for 100 probes (four each of 25 different types) using both GetReal and a conventional force curve. Except for a few obvious outliers, the two methods match very closely. Note that the GetReal InvOLS calibration uses the k first calibrated by the Sader method, so this correlation is strong evidence that both values are accurately calibrated.

Simplicity of Use

The simplicity of GetReal makes it an easy choice to calibrate your cantilever every time you use your AFM, whether it’s for imaging or force measurements. You will quickly find that using calibrated, known imaging setpoints improves the consistency of your results, especially when switching among different probe types.

Once you have used GetReal, you will never be tempted to go back to Volts again! GetReal eliminates the hassle and risk of tip damage from calibrating InvOLS with a force curve on a hard surface. This is especially useful on samples like polymers and biological materials that are too soft to calibrate InvOLS accurately.

Specifications

The specifications of GetReal are:

  • Compatible with a wide range of probe models, including those with rectangular, arrow-shaped, and V-shaped cantilevers (see Figure 1 for the current list).

  • Included with all new MFP-3D and Cypher family AFMs

  • No cost software upgrade to existing MFP-3D and Cypher family AFMs (some may require a paid IGOR Pro upgrade).

Figure 2. The GetReal algorithm was developed by Asylum scientists in collaboration with scientists from the University of Dublin and the University of Melbourne.5 It combines the Sader method and the thermal noise method in a novel way to obtain both InvOLS and k. The user simply selects the probe type and clicks a button. The rest is fully automated and, a few moments later, returns a fully calibrated probe.

Method of Working

Asylum’s GetReal automated probe calibration feature is based on two well-established spring constant calibration techniques, the thermal noise method3 and the Sader method.4 Though typically used independently to calibrate only the spring constant, we recognized that the two methods could be used together to solve for both k and InvOLS, thereby eliminating the need to calibrate InvOLS with a force curve on a hard surface.5

Initially this approach was limited to rectangular levers, but recent work has generalized the Sader method to other lever shapes.6 This enables GetReal to work on a full range of probe models. You simply select the cantilever type and then click one button to start the calibration. The rest of the calibration is completely automated as shown in Figure 2.

GetReal is free with all Asylum AFMs

GetReal is included with all new Asylum Research AFMs. It’s also available for all existing MFP-3D and Cypher AFMs. The feature is enabled with a no-cost software upgrade (some systems will require a paid upgrade to IGOR Pro). The software can be downloaded from the Asylum Research support forums.

References

  1. J.P. Cleveland,* S. Manne, D. Bocek,* and P.K. Hansma, Rev. Sci. Instrum., 64, 403 (1993).
  2. R. Proksch,* T.E. Schäffer, J.P. Cleveland,* R.C. Callahan* and M.B. Viani,* Nanotechnology, 15, 1344 (2004).
  3. J.L. Hutter and J. Bechhoefer, Rev. Sci. Instrum., 64, 1868 (1993).
  4. J.E. Sader, J.W.M. Chon and P. Mulvaney, Rev. Sci. Instrum., 70, 3967 (1999).
  5. M.J. Higgins, R. Proksch,* J.E. Sader, M. Polcik, S. McEndoo, J.P. Cleveland,* and S.P. Jarvis, Rev. Sci. Instrum., 77, 013701 (2006).
  6. J.E. Sader, J.A. Sanelli, B.D. Adamson, J.P. Monty, X. Wei, S.A. Crawford, J.R. Friend, I. Marusic, P. Mulvaney, E.J. Bieske, Rev. Sci. Instrum., 83, 103705 (2012).

*Denotes Asylum Research scientist

About Asylum Research

Asylum Research is the technology leader in atomic force probe microscopy (AFM) for both materials and bioscience applications. Founded in 1999,we are dedicated to innovative instrumentation for nanoscience and nanotechnology, with over 300 years combined AFM/SPM experience among our staff.

Our instruments are used for a variety of nanoscience applications in material science, physics, data storage and semiconductors, polymers, chemistry, biomaterials, and bioscience, including single molecule mechanical experiments on DNA, protein unfolding and polymer elasticity, as well as force measurements for biomaterials, chemical sensing, polymers, colloidal forces, adhesion, and more.

This information has been sourced, reviewed and adapted from materials provided by Asylum Research - An Oxford Instruments Company.

For more information on this source, please visit Asylum Research - An Oxford Instruments Company.

Date Added: Nov 26, 2013 | Updated: May 7, 2014
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