Automatic Atomic Force Microscopy (AFM) with the FX40
This article introduces the recently announced Park FX40, a revolutionary autonomous atomic force microscope, featuring innovative robotics, intelligent learning functions, safety functions, software and specialized add-ons. The Park FX40 Atomic Force Microscope is the first AFM to automate all initial setup and scanning processes, placing the intelligent Park FX40 in a revolutionary new class of atomic force microscope. The article includes analysis of samples using the new automated features of Park FX40.
Developing the crosstalk elimination design of AFM’s XE and NX series, FX40 further improves performance and productivity accessible to all. Through the use of the FX40, meaningful and high definition data can be acquired with just a few clicks.
From start to finish, this article explains the imaging process, along with examples demonstrating real-world applications.
Figure 1. Park FX40 Atomic Force Microscope. (a) FX40 main body, (b) multisample chuck showing kinematic mounting plates, (c) advanced cassette for automated tip exchange (ATX) and (d) new beam rebound diagram for measuring deflection of the overhang. Image Credit: Park systems
With an atomic force microscope (AFM), the user can reliably perform repeated measurements of the surface topography in three dimensions, with sub-nanometer resolution. Additional information such as magnetic, electrical, chemical or nanomechanical information can be recorded simultaneously, producing a large volume of information from a single instrument. Sample preparation, if required, is minimal and the cost of ownership is low compared to similar techniques.
Images can be obtained in controlled atmosphere, liquids and air, making AFMs indispensable tools in research and industrial applications. Before acquiring AFM data, the user should select an appropriate cantilever / tip (or probe), load it into the tool using tweezers, before aligning the optical detection system, and visualization optics. Only then can a sample be loaded and the areas to be imaged can be selected.
The user must then select a basic imaging mode, such as Tapping or Contactless, tune the system, and manually guide the AFM tip through the detection range of the surface. To acquire valid surface information, the operator must instruct the AFM on how to track the surface – often only on the basis of “visual” feedback.
Such complex procedures have prevented AFM from becoming widespread, as it usually requires experienced technicians to acquire reproducible data of a high level.
Park Systems AFMs, like the NX or XE series, have already solved some of the existing obstacles; a user-friendly interface that helps the operator select imaging parameters based on objective boundary conditions and the addition of pre-mounted tips. However, the FX40 goes one step further by automating the entire imaging process; this removes barriers, allowing for the quick and easy generation of consistent data. This essential breakthrough provides access to a wider audience and, subsequently, to the valuable nanometrology information that AFM can produce.
In addition to the automated imaging process, the new optomechanical design of the FX40 improves measurement accuracy and data quality. The low noise level allows the FX40 to easily perform precise nano-metrology on the most difficult samples. Although counterintuitive, a frequent challenge for AFM is the acquisition of precise data on large, flat samples.
Here, FX40 extends the experience gained using the elimination of crosstalk on the previous generation of AFM Park. The gross out-of-plane movement (OPM) before image correction is
Figure 2. Low noise levels for precise nano-metrology. a) Atomic terraces on sapphire, b) Linear profile of sapphire. Steps with signals of sub-nm characteristics are perfectly matched in forward (red) and reverse (green) scanning. Image Credit: Park systems
The following describes the process of purchasing topographic images using four different samples, while demonstrating the automation capability of Park FX40, including easy sample-to-sample navigation:
- The second sample, graphene on boron nitride, is a common 2D material system, currently being studied for its electronic properties (Figure 9).
- The third sample is a styrene-butadiene-styrene copolymer (Figure 10).
- The fourth sample is polytetrafluoroethylene (Teflon), a polymer with a wide variety of industrial applications (Figure 11).
As well as topographic data, FX40 can obtain further physical information about the sample, and correlate this with the topography. Four examples are given in Figure 3: nano-mechanical information including adhesion information or modulus (Figure 3a), magnetic information such as studying samples under controllable external magnetic fields (Figure 3b), nanolithography (3c), and measuring electrical properties with high spatial frequency (3d).
Figure 3. A small sample of FX40 Data acquisition modes. a) Young’s Modulus of block copolymers obtained by PinPointTM. b) Magnetic Vortex Cores in Cr/Ni/Mo alloy obtained by Magnetic Force Microscopy. c) Topography of divided graphene flakes. d) Surface Potential of Semifluorinated alkanes obtained by Sideband KPFM: Negative potential (yellow/blue section) identifies the alkanes relative to the substrate. Image Credit: Park Systems
From tip mounting to final imaging, the real-time operational process is executed in three simple steps, and described below in the following outline:
- “ATX” (Automatic Tip Exchanger) – the user selects the cantilever for the chosen imaging mode. Without any additional operator intervention, the FX40 automatically mounts the probe tip and then, using machine learning, aligns the beam bounce system for optimal cantilever detection.
- “Sample” – the operator selects the sample and the required initial imaging area using the two integrated high performance optical viewing systems. After selection, the AFM moves to the chosen zone, performs the required adjustment operations and automatically moves to the sample. The integrated optical autofocus system enables a peak sample approach in seconds.
- The automatic AFM scan and data acquisition starts.
This article splits the methodology into discrete steps, whilst explaining the mechanism behind each one.
Figure 4. Part of the SmartScanTM Interface for FX40. “ATX” button in the top left corner enables the automatic-tip exchange. Auto align button focuses the cantilever, aligns the SLD and the photo detector. Sample button enables the sample navigation camera, allowing the user to select the desired sample. Image Credit: Park Systems
Step 1: Auto Tip Mounting and Beam Alignment
By reading the QR-codes on the chip carriers in the probe cassette, the software can identify the probe type. After identification, the user may select their chosen probe, and FX40 automatically picks the corresponding probe from the cassette. Subsequently, the FX40 finds the super-luminescent diode (SLD) and cantilever and automatically performs the photodetector alignment.
The Park FX40 positions the SLD within the optical microscope; this inventive design guarantees that the SLD beam is focused at the center of the lens at all times. As a result of the fixed position of the SLD, centering the cantilever in the middle of the optics immediately aligns with the SLD.
To conclude beam-bounce alignment, embedded motors in the AFM head fine-tune the angle of the steering mirror, which automatizes the photodetector alignment process – all with one simple click. The automatization of this process eliminates human error and ensures faultless and consistent operation with every use.
Figure 5. Automatic tip exchanger (ATX). a) View of automatic tip exchange slots image with cantilevers. b) Magnified rendering of QR codes that allows the system to recognize the selected probe and automatically upload the cantilevers profile. c) Probe cassettes can easily be removed and exchanged. Image Credit: Park Systems
Figure 6. Optical cantilever alignment and laser beam detection. a) Park FX40 superluminescent diode beam path. b) Machine learning is used to center the cantilever. c) Centering the cantilever automatically aligns the beam-bounce system. Image Credit: Park Systems
Step 2: Auto Sample Positioning
FX40 uses a dedicated sample view camera to move the probe to the desired location. Depressing the “Sample” button (Figure 4) will open the positioning panel and activate the sample view camera. The sample view camera is situated above the sample chuck and can store a maximum of four samples.
After the desired initial imaging location has been selected, the system immediately navigates toward the area selected (Figure 7). After choosing the preferred imaging spot, FX40 performs a fully automated, fast tip-sample approach .
Figure 7. Example of navigation. a) Park FX40 main body with multisample chuck kinematically locating samples. bd) The sample panel activates and allows the user to select the desired location on the sample. The cantilever then moves to the location selected by the user and automatically approaches the location of the selected sample. Once the data acquisition is complete, the software secures the system by lifting the Z stage and turning off the SLD. The used probe returns to the ATX cassette if the operator does not plan to use it right away. Image Credit: Park systems
Step 3: Automatic imaging
SmartScan Auto Image Mode is selected to obtain topographic data. This function performs all required imaging operations and intelligently selects the optimum scanning speed and image quality. By selecting this mode, consistent data quality is guaranteed, regardless of capabilities and user experience.
Processes such as operation set point, cantilever frequency sweep, gain adjustment or sweep speed are part of the automated procedures. As a result, this level of automation dramatically reduces the amount of manual inputs and manipulations required by the operator, saving time.
Figure 8. Semi-fluorinated alkanes on Si. (A) Topographic image showing the spiral morphology of the sample (vertical scale range 0 to 12 nm) and (b) Phase image of F14H20 alkanes (vertical scale range of 0 to 6 degrees). The phase highlights additional details of the sample. Image Credit: Park systems
A testament to the automation capabilities of the FX40, the data in Figure 8 was obtained in minutes from start to finish. Figure 8 illustrates the high quality topographic data acquired using an NCHR cantilever in non-contact mode, which unambiguously represents the spiral superstructure of the F14H20 aggregates.
After imaging the first sample, the “Sample” button was activated, instructing the FX40 to switch to the next sample: graphene on h-BN. The same cantilever was used to generate the topographic data, capturing information about the moiré patterns of the sample (Figure 9).
Graph 9. Moiré pattern observed on graphene on h-BN. a) Topographic scan of graphene on h-BN, vertical scale 0 to 6 nm. b) Zoom in: Moiré clearly visible, vertical scale from 0 to 6 nm. Image Credit: Park systems
Figure 10. Styrene-butadiene-styrene (SBS) copolymer. a) Topography, vertical scale range 0 to 5 nm. b) Corresponding phase showing the organizational structure, vertical scale from 0 to 5 degrees. Image Credit: Park systems
Again, the same tip was used to image the third sample. The phase image of Figure 10 emphasizes the composition of the sample. For the fourth and final sample, the tip was replaced with a high frequency tip and positioned in the scan location on the multisample chuck. Figure 11 shows the molecular arrangement of the in-phase sample and topographic data.
Figure 11. High resolution image of PTFE (Teflon). a) High resolution topography. Vertical scale range 0 to 3 nm b) Corresponding phase image. Vertical scale range from 0 to 10 degrees. Image Credit: Park systems
This article demonstrates the advanced imaging capabilities, innovative design and ease of use of the new FX40 Park. This automatic AFM system can quickly generate high quality images using new techniques such as pattern recognition and machine learning, including fully automatic tip exchange and alignment and tip selection based on a QR code.
Finally, the FX40 can generate precise data thanks to its low signal-to-noise ratio and intuitive user interface. Park FX40 is a major development in metrology and nanotechnology that will facilitate innovation and discovery in the fields of engineering and nanoscience.
Material originally produced by Armando Melgarejo, Cathy Lee, Charles Kim, Ben Schoenek, Jiali Zhang, Byong Kim and Stefan Kaemmer of Park Systems Corporation.[if–>
- Park SmartScanMT: Park AFM operating software https://parksystems.com/products/operating-software/park-smartscan
- Park systems (2020). Probe store. California, United States: https://parksystems.com/service/probe-store
- Parc Systems Inc (2015). Park Systems’ revolutionary SmartScan system automates the atomic force microscope imaging process – high quality images at the click of a button. California, United States. https://parksystems.com/company/news/press-release/490-smartscan-automatizes-the-atomic-force-microscope-imaging-process
- Parc Systems Inc (2021). NCHR cantilever. Probe store. California, United States: https://parksystems.com/service/probe-store
This information was obtained, reviewed and adapted from documents provided by Park Systems.
For more information on this source, please visit Park systems.