Materials that confer antimicrobial activity, be that by innate property, leaching of biocides or design features (e.g., non-adhesive materials) continue to gain popularity to combat the increasing and varied threats from microorganisms, e.g., replacing inert surfaces in hospitals with copper. To understand how efficacious these materials are at controlling microorganisms, data is usually collected via a standardised test method. However, standardised test methods vary, and often the characteristics and methodological choices can make it difficult to infer that any perceived antimicrobial activity demonstrated in the laboratory can be confidently assumed to an end-use setting. This review provides a critical analysis of standardised methodology used in academia and industry, and demonstrates how many key methodological choices (e.g., temperature, humidity/moisture, airflow, surface topography) may impact efficacy assessment, highlighting the need to carefully consider intended antimicrobial end-use of any product.

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Substrate curvature measurements were used to study stress changes during thermal cycling and isothermal tensile stress relaxation in 800 nm Al-0.5 wt% Cu and Al-1 wt% Si-0.5 wt% Cu films. For both compositions dislocation glide can describe the relaxation data well for temperatures up to 120 ± C for Al-Si-Cu and up to 100 ± C for Al-Cu. The average activation energy for Al-Si-Cu and Al-Cu is 1.7 6 0.2 eV and 3.0 6 0.3 eV, respectively. The athermal flow stress is the same for both and equal to 600 6 200 MPa. This result is consistent with the obstacles for glide being Al 2 Cu precipitates, which, in the case of Al-Si-Cu, are fine and can be cut by the dislocations, and, in the case of Al-Cu, are strong and provide Orowan strengthening. Also, the stress changes during thermal cycling in the Al-Cu films are different from those in the Al-Si-Cu films. For Al -Cu films, the room temperature stress decreases after each thermal cycle, while for Al-Si-Cu stress changes during thermal cycling are stable from the second cycle on. These observations are supported by thorough transmission electron microscopy (TEM) studies.

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