Apparatus and methods are disclosed to provide arrays of substantially oxide-free structures, such as titanium nanotubes or microwells. In one aspect, a hot wire chemical vapor deposition (HWCVD) chamber includes a metal chamber liner manufactured from one or more of aluminum (Al), lithium (Li), magnesium (Mg), calcium (Ca), zirconium (Zr), strontium (Sr), cerium (Ce), barium (Ba), beryllium (Be), lanthanum (La), thorium (Th), and alloys thereof. In one aspect, a method includes positioning a substrate having an array of titanium oxide structures with an oxide layer on surfaces thereof in the HWCVD chamber having the metal chamber liner, exposing the titanium oxide structures with the oxide layer on surfaces thereof to hydrogen (H) radicals, and removing the oxide layer to form well-ordered titanium structures.