SECM imaging of latent fingerprints developed by deposition of Al-doped ZnO thin film

A novel vacuum metal deposition (VMD) based technique has been efficiently employed for the visualization of latent fingerprints on glass and plastic substrates. Al-doped ZnO thin film (ZAO) was deposited on the bare surface and the valleys between the fingerprint ridges by direct current magnetron sputtering with the oblique target, which yielded normal development of latent fingerprints. The enhanced results of latent fingerprints have been photographed with good contrast by a conventional digital camera. Additionally, an electrochemical method, scanning electrochemical microscopy (SECM), has also been successfully applied to the image acquisition of a latent fingerprint developed on the glass surface due to its superb sensitivity toward the small variation of the conductivities at the substrate surface. The SECM image of a latent fingerprint on glass substrate provided good contrast between valleys and ridges and micrometer-scale resolution images of fingerprints under wet conditions by using ferrocene methanol as a redox mediator to detect the topology of the fingerprint deposits in constant-height feedback mode.