Shear-force microscopy investigation of roughness and shape of micro-fabricated holes

•Specifically conceived SPM overcoming some limitations of conventional AFMs.•Analysis of surface roughness, with nanosized accuracy, of complex shape samples.•High resolution topography maps across the edge of a nozzles drilled by different techniques.•High grade comparison of nozzles drilled by different techniques. The paper reports the analysis of roughness and shape of micro-machined workpieces carried out with a specifically conceived scanning probe microscope using the shear-force established between a vibrating tungsten tip and the surface under investigation. Samples, fuel injector nozzles, were prepared by different drilling techniques using either electro-discharge or laser-based machining techniques. Owing to its operation in true non-contact mode and the ability to analyse recessed surfaces, the microscope enables comparing the performance of the drilling processes through the determination of roughness parameters of the hole inner surface and the reconstruction of the shape at its edge. Both finishing and morphological details, expected to be involved in determining the fluid dynamics occurring inside the nozzle, can be captured by the developed diagnostics. The findings reveal that the use of ultrafast laser machining can lead to significantly improve the quality of fuel injector nozzles with respect to the present technology standard.