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Atomic force microscopy

Researcher: Diana Bogdan

Keywords: atomic force microscopy, AFM, surface characterization, nanomaterials, nanoparticles, thin films, polymers, electrochemical sensors

Description

Atomic Force Microscopy (AFM) is part of the Scanning Probe Microscopy (SPM) family of techniques for the investigation of surfaces by scanning with a very sharp tip.

The AFM image is obtained by monitoring the position of a probe (scanning probe) attached to a microcantilever as it scans the sample surface.

The AFM topography has nanometer resolution in the xy-plane and sub-nanometer resolution in the z-direction and can be obtained in two common modes: contact and intermittent contact/tapping. A 3D image of the surface is obtained by recording the height at each scanning point. In tapping mode, the microcantilever oscillates at a frequency close to its resonant frequency and the amplitude of the oscillation is monitored. During scanning, the cantilever vibrates so that the AFM tip periodically touches the sample surface, the friction between the tip and the surface, present in the contact mode, being avoided, preventing damage of the sample.

 Applications

Areas of application: As an investigation technique, AFM microscopy is suitable for all types of surfaces. The applications are practically unlimited, AFM microscopy being used in all fields:

  • research: nanotechnology, life sciences, nanoparticles, polymers
  • industry: manufacturing process control, corrosion analysis, morphology of coatings, glass, ceramics, metals
  • medicine and dentistry: implants, filling materials, endodontic sealants
  • education: undergraduate and postgraduate level

Systems: nanomaterials, biomaterials, nanoparticles, polymers and polymer blends, electrochemical sensors, metals, life science samples (cells, bacteria), medical devices (implants)

Industries:

  • Automotive industry: development of new materials, quality control of surfaces nanoscale analysis and measurement. The automotive industry is continuously developing advanced materials to keep pace with the challenges it faces in making cars more efficient. The use of nanotechnology can bring much needed advances in materials used in many automotive components, from metals to polymers
  • Industrial process control: surface evaluation of samples for process development and/or manufacturing process control.
  • Photonics: 3D measurement of structures. AFM images are independent of optical properties and do not require conductive coating of samples, provide excellent contrast for optically smooth samples, glass surfaces, diffraction gratings, etc.
  • Medicine, biology: nanoscale imaging of biomaterials, cell surfaces, implants, etc.

 Infrastructure

INCDTIM Cluj-Napoca provides the infrastructure for the study of surfaces by AFM:

  1. Ntegra Spectra AFM platform (NT-MDT). Maximum scanning area: 100 μm × 100 μm, zmax 10 μm, equipped with Olympus IX71 microscope, configurations: direct, 100X objective (NA 0.7), inverted 100X objective with oil immersion (NA 1.3), optimized for samples on transparent substrate. Most AFM modes are available. Data acquisition and image processing: Nova software.
  2. AFM Cypher S microscope (Asylum Research – Oxford Instruments). Maximum scanning area: 30 μm × 30 μm, zmax 5 μm. Equipped with integrated videomicroscope with software-controlled optical zoom, optical resolution < 1 μm; NA 0.45; 3 Mpx color CMOS camera, field of view 650 μm × 900 μm. Deflection sensing optical system noise < 7 pm (cantilever not in contact with sample); < 15 pm (cantilever on surface); Z sensor noise < 50 pm; XY (closed-loop) sensor noise < 60 pm. Data acquisition and software AR processing with Igor Pro SPM modules. Sample dimensions: Ømax = 2 cm, h = 0.7 cm.

Advantages

 Any type of material, soft or hard, conductive, semiconducting or insulating, can be analyzed, the only requirements are related to the size of the sample (Ømax sample 2 cm, hmax = 0.7 cm) and the roughness of the sample surface (hmax 5 μm) (seen with the naked eye, the sample appears smooth).

 Complementary to other imaging techniques, such as electron microscopy, which provides high-resolution images but provides a 2D image of the samples, AFM microscopy additionally provides a 3D topographic image of surfaces.

Estimated costs

The total cost of AFM characterization involves machine operating time, labor and consumables, sample preparation operations, data processing, image analysis and preparation of the report:

 Preliminary tests: 350 lei/day (30 € consumables)

 Complex analysis: 700 lei/day

 Outputs: topographic images for maximum areas of 30 × 30 μm2, surface morphology down to nanometer scale, roughness evaluation, cross-section profiles, comparative analysis for samples subjected to different processes, thin coating layers, etc.