Part of the Oxford Instruments Group

Atomic Force Microscopy

WITec AFM Principle

Atomic Force Microscopy (AFM) traces the topography of samples with extremely high - up to atomic - resolution by recording the interaction forces between the surface and a sharp tip mounted on a cantilever. AFM provides spatial information parallel and perpendicular to the surface. In addition to topographic high-resolution information, local material properties such as adhesion and stiffness can be investigated by analyzing tip-sample interaction forces.

WITec's Atomic Force Microscope

The WITec Atomic Force Microscope integrated into a research-grade optical microscope provides superior optical access, exact cantilever alignment and high-resolution sample survey. The sample is scanned under the tip using a piezo-driven scanning-stage and the results (e.g. topography etc.) are displayed as an image.

The optical mode combined with an advanced video camera system allows high-resolution sample survey and quick selection of the area-of-interest. Through the simultaneous sample and AFM-cantilever view, the measurement position can be easily identified and adjusted. Using additional illumination and detection techniques (e.g. bright-field, dark-field, polarization, fluorescence, etc.), the user can further determine the point-of-interest for the AFM measurement. By simply rotating the microscope turret, the user can switch between optical and AFM modes quickly and accurately, maintaining the look and feel of optical microscopy in the AFM mode.

WITec AFM Beam Path
Beam path
WITec AFM Sample Cantilever View
Simultaneous cantilever and sample view for easy identification and adjustment of the measurement position.

Digital Pulsed Force Mode

The Digital Pulsed Force Mode (DPFM) is a non-resonant, intermittent-contact mode. It avoids the surface damage that can result from operating in contact mode on soft samples and provides additional sample information.

When added to an AFM system, the DPFM extends the capabilities of the microscope beyond simply measuring topography to properties such as local stiffness, adhesion, viscosity, energy dissipation, contact time, long range forces etc. This can be done at normal scan rates, because the system works at up to several thousand pixels per second.

The electronics of the DPFM include a high speed data-acquisition system, a freely programmable modulation generator and a real-time data evaluation module. With the storage of the complete measurement, extensive post-processing data evaluation is performed.

The DPFM electronics introduces a sinusoidal modulation to the z-piezo of the AFM with an amplitude of 10-500 nm at a user-selectable frequency between 100 Hz and 2 kHz, far below the resonance frequency of the cantilever. A complete force-distance cycle is carried out at this repetition rate resulting in the shown force signal.
WITec DPFM curves

AFM in Combination With Other Microscopy Methods

The modular design of the WITec systems allows to combine various imaging techniques such as Raman imaging, fluorescence, luminescence, atomic force microscopy (AFM) and near-field microscopy (SNOM or NSOM) and in one single instrument for a more comprehensive, correlative sample analysis. Switching between the different modes is simply done by rotating the microscope turret.

Raman and AFM

By coupling confocal Raman imaging with AFM, the chemical properties of the sample can be easily correlated with its surface structure. These two complementary techniques are available in our combinatorial Raman-AFM microscope alpha300 RA for flexible and comprehensive sample characterization.

TERS (Tip-Enhanced Raman Spectroscopy) is a typical application for correlative Raman-AFM microscopes.

WITec Raman AFM polymer blend
Polymer blend imaged with Raman (left) and AFM (right) on the same sample area with a combined WITec Raman-AFM microscope.

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