Technology Transfer Center

The operating principle of the AFM technique is based on the physical, mechanical interaction between a very sharp AFM tip, made of silicon or silicon nitride, and the surface of the sample to be studied, the tip having a radius of curvature of several nanometers. The AFM tip is attached to the end of a cantilever. There are three main versions of the AFM technique: AFM contact, AFM noncontact, AFM tapping mode.

In contact AFM mode, the cantilever presses the AFM tip against the surface to be studied. As the AFM tip scans the sample surface, the sample will also be moved vertically to keep the position of the laser beam spot reflecting off the cantilever tip constant. This means that the AFM tip’s pressing force on the surface will be constant, thus the topography of the sample will be recorded as a multitude of linear profiles forming a three-dimensional image.

In noncontact AFM mode, the cantilever is placed in a vibrating state in the immediate vicinity of its resonant frequency. The AFM tip, as it is brought into the vicinity of the surface to be scanned, will sense an interaction with the sample surface, which will cause the cantilever’s resonant frequency to change. Thus a difference will occur between the excitation frequency of the cantilever and the resonant frequency of the cantilever, and if this difference is kept constant during the scan, the interaction between the tip and the surface is constant, which means that the AFM tip will faithfully scan the surface relief.

The multitude of linear scan profiles thus recorded will form a three-dimensional image of the topography under investigation. The noncontact AFM mode is used when there is an adhesion force between the AFM tip and the surface to be studied, which would make it difficult to scan in contact AFM mode due to the high friction forces between the tip and the sample.

Areas of application: R&D in electronics, biology, medicine, materials science

Systems: Ultra-high vacuum scanning probe microscopy is mainly used for samples that have been fabricated under such conditions, avoiding taking them out into the ambient atmosphere to avoid contamination. There may also be situations where the sample of interest has been manufactured in ambient atmosphere and, for microscopy measurements, needs to be introduced into the ultra-high vacuum facility to benefit from a preliminary surface decontamination process by thermal degassing.

Industries: STM and AFM microscopy allows the confirmation of the required surface quality, in terms of topography correlated with physico-chemical properties, for devices finding applications in the microelectronics and optoelectronics industry.

 Particularly good resolution: the image obtained can have a resolution about 1000 times better than that characteristic of optical microscopy, where light diffraction limits the resolution to a value comparable with the wavelength of the optical radiation used.

 Nanolithography method: AFM and STM microscopy can be used to create small structures on the sample surface, either by indentation of the surface (contact AFM) or by local melting (STM).

 Preserves sample purity: ultra-high vacuum scanning probe microscopy protects the surface under study from potential contaminants in the ambient atmosphere.

 Easy access to auxiliary manufacturing equipment: the ultra-high vacuum scanning probe microscopy facility is coupled to an Molecular Beam Epitaxy thin films deposition facility with argon ion beam sample treatment facilities and facilities for coating the sample with a thin protective layer of a suitable material of choice.