A method for sidewall spacer line doubling uses thermal atomic layer deposition (ALD) of a titanium oxide (TiOx) spacer layer. A hardmask layer is deposited on a suitable substrate. A mandrel layer of diamond-like carbon (DLC) is deposited on the hardmask layer and patterned into stripes with tops and sidewalls. A layer of TiOx is deposited, by thermal ALD without the assistance of plasma or ozone, on the tops and sidewalls of the mandrel stripes. Thermal ALD of the TiO2, without energy assistance by plasma or ozone, has been found to cause no damage to the DLC mandrel stripes. After removal of the TiOx from the tops of the mandrel stripes and removal of the mandrel stripes, stripes of TiO2 are left on the hardmask layer and may be used as an etch mask to transfer the pattern into the hardmask layer.