the present invention relates to a data storage device comprising : a polymer layer for storing data in the form of topographic features ; a substrate comprising a conductor , a first surface of the polymer layer being provided on the substrate ; and at least one probe which , when the device is in use , interacts with a second surface of the polymer layer , wherein , when in use , the data storage device is operable to apply a first electrical potential to the at least one probe relative to the substrate , thereby to cause a protrusion to be formed on the second surface of the polymer layer .