Deposition of c-axis orientation aluminum nitride films on flexible polymer substrates by reactive direct-current magnetron sputtering

Aluminum nitride (AlN) piezoelectric thin films with c-axis crystal orientation on polymer substrates can potentially be used for development of flexible electronics and lab-on-chip systems. In this study, we investigated the effects of deposition parameters on the crystal structure of AlN thin films on polymer substrates deposited by reactive direct-current magnetron sputtering. The results show that low sputtering pressure as well as optimized N 2/Ar flow ratio and sputtering power is beneficial for AlN (002) orientation and can produce a highly (002) oriented columnar structure on polymer substrates. High sputtering power and low N 2/Ar flow ratio increase the deposition rate. In addition, the thickness of Al underlayer also has a strong influence on the film crystallography. The optimal deposition parameters in our experiments are: deposition pressure 0.38 Pa, N 2/Ar flow ratio 2:3, sputtering power 414 W, and thickness of Al underlayer less than 100 nm. © 2012 Elsevier B.V. All rights reserved.

Analysis of asphalt concrete permeability data using representative pore size

The permeability of asphalt concrete has been the subject of much study by pavement engineers over the last decade. The work undertaken has tended to focus on high air voids as the primary indicator of permeable asphalt concrete. This paper presents a simple approach for understanding the parameters that affect permeability. Principles explained by Taylor in 1956 in channel theory work for soils are used to derive a new parameter-representative pore size. Representative pore size is related to the air voids in the compacted mix and the D75 of the asphalt mix grading curve. Collected Superpave permeability data from published literature and data collected by the writers at the Queensland Department of Transport and Main Roads is shown to be better correlated with representative pore size than air voids, reducing the scatter considerably. Using the database of collected field and laboratory permeability values an equation is proposed that pavement engineers can use to estimate the permeability of in-place pavements. © 2011 ASCE.