While we have proven that the localized Cu deposition process studied here is electrochemically driven, we find a particularly intriguing critical dependence of deposition on the contact time. Namely, the longer the contact time the more material is deposited. This is rather counter-intuitive as we suspect the tip to be in electrical contact with the substrate during the time in contact (see supplementary file SI-5 for more details), and therefore suspend electrochemical growth.