In exemplary implementations of this invention, hydrothermal synthesis of zinc oxide nanowires is morphologically controlled. Metal complex ions are used to suppress growth in a face-selective manner, by electrostatic crystal growth inhibition. This permits the aspect ratio (height/diameter) of the nanowires to be dynamically tuned over a wide range, from needle-like nanowires that are efficient field emitters to flattened nanowires with a platelet-like shape. The nanowire synthesis is all inorganic and occurs at low temperatures (e.g.,