Characterising Nanostructures with a Hybrid AFM-SEM System

ZEISS GEMINI SEMs and DME's AFM module have been designed to work together, to allow simultaneous analysis by both microscopy techniques. This is of huge benefit to advanced applications in nanostructure characterization in research and industry.

Laser Deflection AFM

AFM images are generated by the mechanical motion of a fine tip in close proximity to a sample surface. Charge density, physical topography, magnetic field and other surface properties interact with the tip to deflect the cantilever.

The most accurate and flexible method to identify this deflection is to focus a laser on the back of the cantilever, and reflect the light onto a position detector.

Only ZEISS FESEM, based on the robust, flexible, provem GEMINI technology and the advanced on-axis SE and BSE detection system, allows seamless and rapid integration with the novel high-end AFM system designed by DME.

The key features of the AFM are:

• SEM guided positioning of AFM tip at ROI
• Laser deflection based cantilever readout
• Electrical contacts to cantilever and sample holders
• Tip and sample loading via Airlock Seamless hardware and software integration
• Compatible with all commercial cantilevers
• All AFM modes available (also EFM, SSRM, KPFM etc.)
• 5mm SEM working distance

Figure 1. Schematic Diagram of cantilever deflection, AFM setup as realized in the AFM option

Integrated SEM/FEM Combination

The AFM module from DME is developed in such a way to optimize the experience of operating both AFM and SEM within a single instrument.

The AFM is mounted to a specially designed stage enabling vertical and rotational movement. This stage forms part of the main door of the SEM. The overall construction includes a full door module with 7 axis stage to position SEM, AFM and region of interest (ROI) with respect to each other.

Figure 2. Tip and sample exchange via airlock

Characterize Electrical Properties Quantitatively

A common task for microscopists in both research and industry is the characterization of nano- and microstructured electrical devices. Modern electronic components are rapidly becoming smaller and smaller, necessitating the use of advanced microscopy techniques to accurately measure their features.

The AFM/SEM instrument from DME and ZEISS offers the necessary functionality to identify and characterize the electrical properties at specific material interfaces and structures in such devices.

In the following example, the potential distribution along a SMD capacitor’s electrodes has been studied. The key aims of the experiment are:

• Comparison of topography by SEM and AFM (elimination of artifacts)
• SEM material contrast
• Voltage contrast by SEM
• Characterizing surface potential quantitatively by AFM
• Evaluation of potential distribution graphs

Figure 3. Quantitative analysis from AFM data

Manipulate Samples with the AFM Tip

The interest in 2D materials and graphene has grown over the years. The combination of AFM and SEM offers a number of impressive capabilities to understand the extraordinary properties of these novel materials. Key features are:

• SEM guided positioning of AFM tip at ROI
• AFM based nano indentation reveals elastic properties and rupture toughness.
• Imaging of supported and suspended graphene
• Topography shows atomic steps wrinkles and folding

Figure 4. Force vs z travel shows elastic behavior and rupture toughness

Preparing and Studying Samples in a FIB-SEM-AFM System

Characterizing heterogenic structures is critical for developing nano-sized devices and functional structures in semiconductor, energy storage and sustainable energy applications.

DME's AFM option for SEMs is developed such that the AFM tip is always in the vicinity of the crossbeam point, the intersection of SEM and FIB beam. Hence, the target area can immediately after preparation be investigated by the AFM. Also, air exposure after FIB cutting is avoided.

In this example, the AFM module has been installed in a ZEISS CROSSBEAM™ system to study an organic solar cell’s potential distribution.

• In situ FIB modification of sample and AFM tip
• Localisation of interfaces critical for potential distribution for device optimization
• Avoiding contamination of FIB prepared surface by exposure to air
• Sub surface characterization of electrical properties by AFM

Figure 5. Topography - surface potential overlay (3D topography, colouring = surface potential)

This information has been sourced, reviewed and adapted from materials provided by DME Nanotechnologie GmbH.

For more information on this source, please visit DME Nanotechnologie GmbH.