Dip-Pen illustration (Dip-Pen Lithography, 2008)
The tip of an Atomic Force Microscope is coated with a thin film of thiol molecules that are insoluble in water but react with a gold surface.
When the device is exposed to an atmosphere with high saturation of water vapour, then tiny water molecules will condense between the tip of the microscope and gold surface. Surface tension ensures there is a constant fixed distance between the tip and the surface, as the tip moves across the surface, a bridge is formed and the thiol molecules can move onto the gold surface, where they stay fixed due to a chemical reaction.
This technique is slow and cumbersome and can however create features a few nanometers across. So this device can even build smaller wires that are only one atom wide.