http://experimentationlab.berkeley.edu/sites/default/files/AFMImages/butt_AFM.pdf

Force measurements with the atomic force microscope: Technique, interpretation and applications

Effects of various fillers on the sliding wear of polymer composites

As the size of electronic and mechanical devices shrinks to the nanometre regime, performance begins to be dominated by surface forces. For example, friction, wear and adhesion are known to be central challenges in the design of reliable micro- and nano-electromechanical systems (MEMS/NEMS). Because of the complexity of the physical and chemical mechanisms underlying atomic-level tribology, it is still not possible to accurately and reliably predict the response when two surfaces come into contact at the nanoscale. Fundamental scientific studies are the means by which these insights may be gained. We review recent advances in the experimental, theoretical and computational studies of nanotribology. In particular, we focus on the latest developments in atomic force microscopy and molecular dynamics simulations and their application to the study of single-asperity contact.

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Recent advances in single-asperity nanotribology

This article reports the results of 2 studies conducted to examine the ability of the Situational Outlook Questionnaire(tm) (SOQ) to effectively discern climates that either encourage or discourage creativity and the ability to initiate change. The purpose of the studies is to examine the concurrent criterion-related validity of the SOQ. The climate for creativity and change is defined, and the context for the use of the measure in organizational settings is established through the development of a model for organizational change. The article presents the history of the SOQ's development and gives a description of the SOQ. The methodology and results of both studies, including 3 groups, are reported. The results of both studies show that when individuals complete the SOQ based on their recollection of a best- and worst-case work experience, the measure is able to consistently and significantly discriminate between the 2 types of experiences. Conclusions, implications, and areas for future research to furt...

Perceptions of the Best and Worst Climates for Creativity: Preliminary Validation Evidence for the Situational Outlook Questionnaire

Conventional pressure sensitive adhesives (PSAs) are fabricated from soft viscoelastic materials that satisfy Dahlquist's criterion for tack with a Young's modulus (E) of 100 kPa or less at room temperature and 1 Hz. In contrast, the adhesive on the toes of geckos is made of beta-keratin, a stiff material with E at least four orders of magnitude greater than the upper limit of Dahlquist's criterion. Therefore, one would not expect a beta-keratin structure to function as a PSA by deforming readily to make intimate molecular contact with a variety of surface profiles. However, since the gecko adhesive is a microstructure in the form of an array of millions of high aspect ratio shafts (setae), the effective elastic modulus (E(eff)) is much lower than E of bulk beta-keratin. In the first test of the E(eff) of a gecko setal adhesive, we measured the forces resulting from deformation of isolated arrays of tokay gecko (Gekko gecko) setae during vertical compression, and during tangential compression at angles of +45 degrees and -45 degrees . We tested the hypothesis that E(eff) of gecko setae falls within Dahlquist's criterion for tack, and evaluated the validity of a model of setae as cantilever beams. Highly linear forces of deformation under all compression conditions support the cantilever model. E(eff) of setal arrays during vertical and +45 degrees compression (along the natural path of drag of the setae) were 83+/-4.0 kPa and 86+/-4.4 kPa (means +/- s.e.m.), respectively. Consistent with the predictions of the cantilever model, setae became significantly stiffer when compressed against the natural path of drag: E(eff) during -45 degrees compression was 110+/-4.7 kPa. Unlike synthetic PSAs, setal arrays act as Hookean elastic solids; setal arrays function as a bed of springs with a directional stiffness, assisting alignment of the adhesive spatular tips with the contact surface during shear loading.

/pdf/effective-elastic-modulus-of-isolated-gecko-setal-arrays-349ymnqlpp.pdf

Effective elastic modulus of isolated gecko setal arrays

Tribological behaviour of materials at cryogenic temperatures

Adhesion measurements are presented which were carried out with an atomic force microscope between polymer balls attached to a cantilever and a silicon wafer under ultra high vacuum conditions. In using a silicon surface with a defined structure a correlation between adhesion force and contact area was found. This correlation could partly be explained by the Johnson-Kendall-Roberts model, if a change of the surface energy is assumed as a result of the structuring. For a constant geometric contact area an additional structuring leads to a decrease of the adhesion force.

T. Schneider

Papers

Tribological behaviour of materials at cryogenic temperatures

The influence of surface roughness on the adhesion force

The influence of roughness on friction: Part I: The influence of a single step

The influence of roughness on friction. Part II. The influence of multiple steps

Low temperature tribometers and the behaviour of ADLC coatings in cryogenic environment