Tip

It is a small silicon pyramid or silicon nitride with a typical height of about 20 μm and a base of about 10 μm on the side. The radius of curvature at the tip of the tip is generally between 2 and 20 nm.Its function is to limit the area of interaction with the sample to the few atoms that make up its apex in order to probe the local properties of the <<contact>> sample.

cantilever

It is a prismatic or triangular flexible lever made of silicon or silicon nitride that supports the AFM tip at its end. Typical dimensions are a few tens of micrometers in width, a thickness less than 10 μm and a length between 70 μm and 500 μm. The levers are placed on its chips to facilitate their handling and assembly on the AFM Its function is to support the AFM peak. It acts as a force sensor (a mechanical stiffness spring that converts an interaction force (F) between the AFM tip and the surface of the sample into a vertical deflection motion of amplitude δz. The AFM is thus a force sensor from which it is possible to trace the topography of the scanned sample:

For lever stiffeners typically between 0.001 N/m and several hundred N/m, and a vertical movement of the lever of the picoNewton order

The cantilever deflection of detection system

It is a device for measuring the oscillating movements (flexion and torsion) of the lever when it is subjected to the variable effects of the forces of interaction with the surface of the scanned sample. Its function is to convert the deflection measurement of the lever (mainly) into an electrical signal which will then be used in the control loop. As the deflection of the lever is proportional to the force of interaction between the tip and the sample, then it also represents the variations of the force field on the

Tip. It is therefore used to measure changes in the conditions of interaction between the tip and the surface of the sample. This is why it is used in the control loop to keep them constant. Many methods exist: using a STM, using resistive, capacitive levers, integrating strain gauges or measuring lever deflections by interferometry… however, the most common system uses the so-called optical lever method, consisting of a laser diode in the beam is reflected on the back of the lever and returned to a four-quadrant photodiode.

Usually, it is possible to detect on a four quadrant photodiode a minimum displacement of the order of the hundred nanometer, which corresponds to a vertical sensitivity on the measurement of deflections of the lever of the order of 0.1 nm

The XY scanning stage

Its function is to generate a relative displacement in the horizontal plane between the tip and the sample in order to probe the local properties of the latter at several points. This refers to the scanning of the sample surface by the AFM tip.

It is a set of actuators (piezoelectric, magnetic bearings, etc.) that is generally guided in translation-by flexible blades for example-to improve the rectitude of the displacements produced. The races available are generally between a few micrometers and several hundred micrometers.

The Z-Scanner

The control system

It is generally a multi-axis PID that controls and controls the position of the tip relative to the sample along three or six axes. In the vertical direction, its purpose is to keep the interaction conditions between the AFM tip and the sample below constant. In the horizontal plane, his goal is to pilot the sweep. Depending on the imaging mode used, there are several control modes, for example <<constant amplitude>>, <<constant deflection>> or <<constant altitude>> which each define a particular condition on the interaction between the tip and the sample.