Xu et al. Nanoscale Research Letters 2011, 6:525 http://www.nanoscalereslett.com/content/6/1/525 patterns (both Cu and Ag) were fabricated on glass sub- strates, using the procedure shown in Figure 2. Electro- deposition had selectively taken place on the exposed metal area (which act as pads), initially defined by the lithography, due to the insulation of photoresist. After dissolving of AAM in KOH solution and stripping off the photoresist, patterned nanowire array pads on the Au/Ti-coated glass substrate were achieved. Figure 4a shows a representative image of the Ag nanowire pat- terns with different pad sizes. Homogeneous deposition on pad sizes from 200 × 200 to 50 × 50 μm2 was achieved, while smaller features are also feasible. There is a reduction of the length of nanowires around the edge of the pads (Figure 4b), which showed similar results as the low aspect ratio nanowire array pads made by other template-based methods [9]. The specific reason for this phenomenon is unknown. Figure 4c shows a higher magnification image of a single pad where aligned nanowires and the intermediate Ag layer are visible. The bonding integrity between nanowire/interlayer film and the Si wafer was characterised by a tensile tes- ter. The adhesion strength between them is 38.4 MPa (3.84 kN/cm2) which is regarded as strong bonding [26]. Although it is not recommended that the value reported here be compared directly with those obtained by differ- ent testing methods, this interface is still much stronger than the strongest bonding of CNT arrays on Si sub- strate, which showed a strength of 30 to 110 N/cm2 by a compression shear test [27,28]. Also, the sample was fractured at the interface of Au/Ti thin film and Si wafer (see Figure S1b in Additional file 1), suggesting comparatively stronger bonding between the nanowires and Au/Ti film than that of between Au/Ti film and Si wafer. This strong bonding between nanowires and the substrate is another big advantage for the Z-axis inter- connects application. The bonding between Ag nano- wire pads and the glass substrate were further characterised by SAM technique using a SONIX HSl000 Page 5 of 7 (SONIX, Inc., Springfield, VA, USA). SAM is a non- destructive technique used extensively throughout the microelectronics industry to inspect a bonded interface for the visualisation of delamination and cracking. Fig- ure 5a shows the optical image of Ag nanowire pads (dark area) on glass substrate, the white colour shows the empty AAM without nanowires. The related SAM image in the C-scan mode for the same sample of pat- terned nanowire array pads on glass substrate is shown in Figure 5b. Almost all of the nanowire pads are clearly distinguishable and appear greyish in colour, whereas the empty AAM area without Ag nanowires shows black colour, which is the typical delaminating image. Further to this, two typical oscilloscope traces are shown in Figure 5c. The traces show that about 69% and 70% waves were captured, suggesting a good adhe- sion between the glass substrate and all of the nanowire pads. Uniform length with firm electrical connection of these nanowires on a large surface area is another important factor to be considered for applications such as Z-axis interconnects. Thus, the electrical connection between the mechanically polished Cu nanowire arrays and the bottom Si substrate (for the sample in Figure 3d) was further characterised using a Dimension D3100 scanning probe microscope (Veeco, Plainview, NY, USA) in conductive atomic force microscopy mode (C-AFM). The topographic and the correspond- ing conductive scanning images (current image) of these nanowires are shown in Figure 6. Figure 6a, b shows the topographic image for 10 × 10-μm2 scan area and the corresponding current map image. Nearly 95% of the nanowires were conductive, suggesting good electrical connection between the tip of the nanowires and the bottom substrate. Different areas of the sample, from middle to the edge were scanned and a similar percentage of conductive nanowires were obtained, suggesting a large area of uniformity among these nanowires. Figure 4 Silver nanowire array patterns. (a) Silver nanowire array patterns on glass substrate with different feature sizes; (b) one nanowire array pattern with size of about 60 × 60 μm; (c) high magnification of image (b) (45° tilt view).