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Thesis defense of Carl Arne Thomann

Begin: End: Location: AV-Raum + ZOOM
Event type:
  • Defense

Spectroscopic analysis of structural and chemical properties of solid thin film lubricants

There is a variety of solid thin film available to tailor surface properties for a given lubrication application; two common classes are amorphous carbons (a C) and molybdenum disulfide ( MoS 2 ). Upon tribological loading in a given working condition, especially at elevated temperatures or in humidity, chemical transitions and structural processes are known to take place in a C and MoS 2 thin films and to critically limit their performance. To ac commodate those restrictions and to suit thin film properties for a specific application, a selection of element modifications are regularly applied. Their impact on structure and chemistry are commonly studied by different spectroscopic methods in publica tions. This work aims to subsume such measurements in one concise method and to advance to a robust analysis framework for goal based manufacturing of a C and MoS 2 thin films. The concept allow s for spatially resolved studies and for resolving enmeshed str uctural and chemical transitions. The understanding of those transitions is a prerequisite for the scientific conception around tribo film formation, which is identified as critical part of the tribological system and as tribological benefit. For this, Ram an microscopy is augmented by an additional setup for optical temperature tuning via a nano second pulsed laser For a C, the following properties are (indirectly) measurable: internal stress, sp3 content, silicon content, and degree of graphitisation. In studies of optical temperature tuning in a C, two ordering mechanisms are found, which are affected by element modification. As initial reaction upon heating, graphitic clusters within an amorphous matrix increase in number and, subsequently, in size upon further heating. This allows for a spectra based definition of onset temperatures for solid to solid transition from a C to defected nano crystalline graphite. A Five Stage model of structural relaxation in a C is proposed. For MoS 2 , it is found that the f ormation of tribo films is strongly dependent on the working environment, the tribo film gains temperature resistance over untouched thin film material and tribo film formation is affected by element modification. In studies of optical temperature tuning in MoS 2 , an initial ordering process of amorphous MoS 2 and subsequent chemical reaction to distinct oxides of molybdenum were detected. The occurrence of such oxides with deviating hardness values in an otherwise intact MoS 2 thin film hints to a possible st ructure and chemistry based wear mechanism. A Five Phase model upon heating in MoS 2 is proposed.