Methods for forming tunnel barrier layers are provided, including a method comprising exposing a surface of a material, the surface free of oxygen, to an initial water pulse for a pulse time and at a pulse temperature, the pulse time and pulse temperature selected to maximize hydroxylation of the surface; and exposing the hydroxylated surface to alternating, separated pulses of precursors under conditions to induce reactions between the hydroxylated surface and the precursors to form a tunnel barrier layer on the surface of the material via atomic layer deposition (ALD), the tunnel barrier layer having an average thickness of no more than 1 nm and being formed without an intervening interfacial layer between the tunnel barrier layer and the surface of the material.