As the interface between materials and their environment, surfaces are of great importance when it comes to a component’s properties and functions. The specific alteration of a surface can improve the surface properties, for example resistance to mechanical or chemical stress, microstructuring of the surface can make it fitter for complex applications.
The characteristics of material surfaces can be changed through the application of pulsed lasers. The ILM has a broad range of laser systems at its disposal that can be used for the following purposes:
A Q-switched Nd:YAG laser enables powerful (1J) laser pulses with a duration of about 10 ns to be generated. Frequency multiplication enables the fundamental wavelength of 1064 nm to be reached as well as wavelengths of 532 and 353 nm. An optical parametric oscillator (OPO) extends this spectrum to a range of 355 to 2600 nm.
An ultrashort pulse Ti:sapphire laser system in the 100 fs range, supplemented by the amplification with an optical parametric amplifier (OPA), enables the ablative or sub-ablative treatment of any materials over a broad range of wavelengths (300 nm to 3 μm).
A broad range of test methods has been established for the characterisation of surfaces and their modification.
Tribometers are used to determine the friction and the wear on surfaces. The sample to be investigated is moved towards a reference surface (by adding a fluid friction medium if required), giving a relative friction value. The tracking force can be adjusted.
Differently shaped sample bodies (Vickers; Rockwell; Brinell) are pressed into a sample with a defined force. The impressions are subsequently (automatically) measured under the microscope, giving the hardness of the material.
Tactile: A diamond tip of an exactly defined shape scans the surface under investigation in the micrometer range. The measurement values enable standard roughness parameters to be determined.
Optical: A white light beam, focused on the surface through a special lens with strong chromatic aberration, scans the sample surface. The reflected light is detected confocally. A certain object area is sharply displayed in one of a number of given colours, which provides information about its distance in the submicrometre range.
Scanning force microscopy
The scanning force microscope scans the surface under investigation in a contact mode using a defined measurement tip. This is similar to the tactile profilometry method. In the non-contact mode, the measurement tip swings across the surface. Both methods enable the representation of the scanned surfaces in the nanometre range and the calculation of roughness values.