(84c) Scaling of the Adhesion between Particles and Surfaces from Micron-Scale to the Nanometer Scale

Particulate contaminants adhering to surfaces are of great concern in many applications, ranging from microelectronics and pharmaceutical production to remediation of dirty bomb contamination. These applications require a detailed understanding of particle adhesion, including the nature of the scaling of adhesion forces as particle sizes scale down from the micron to the nanometer scale. This work employed micron-scale model particles to determine adhesion forces to model surfaces. Force measurements were obtained in both air and liquid environments using particles of interest to the microelectronics industry. Particles were mounted onto tipless AFM cantilevers and the pull-off force of each was measured in contact with model surfaces. A distribution of adhesion forces was observed in each case, resulting from particle and surface roughness and geometry variations. Particle and surface morphologies and mechanical properties were considered in modeling the measured adhesion force distributions, using adhesion models which have been previously validated. The predicted force distributions showed good agreement with the experimental data. In order to demonstrate the viability of scaling adhesion forces between the micron- and nano-scales, AFM cantilevers ranging from 8 nm - 60 nm, composed of the same materials as the micron-scale particles were used and the interaction forces with the same model surfaces were measured. Two tip sizes were used in each case, to provide two data points at the nanometer scale. As observed with the micron-scale particles, a distribution of adhesion forces was obtained in each case. The geometry of the cantilevers and the morphology of the surfaces were inputs to the model. The composition specific components of the electrostatic and van der Waals force models (the surface potentials and Hamaker constants) from the micron-scale studies were used as inputs to describe nano-scale behavior. The modeled force distributions showed good qualitative and quantitative agreement with the measured forces. The above study provides an understanding of the magnitude of adhesion forces that can be expected when nanometer size particles adhere to surfaces, allowing the design of improved cleaning protocols using the adhesion models developed. It also demonstrates the utility of model systems at the micron-scale, which are comparatively easy to manipulate, to describe nano-scale phenomena.