  We report on how to grow and control self-organized TiO2 nanotube arrays that
show defined and regular gaps between individual nanotubes. For this we use
electrochemical anodization of titanium in fluoride containing di-ethylene
glycol (DEG) electrolytes, with variations in voltage and water content in the
electrolyte. In these specific electrolytes, such nanotubes show a true
spacing, i.e. nanotubes are spaced both at top and at bottom in regular
intervals, this in contrast to classic nanotubes obtained in other organic
electrolytes showing a close-packed organization. We identify critical
parameters, that define the region of existence i.e. under which condition tube
spacing occurs as well as the intertube distance, to be the voltage and the
water content. Using these findings allows to grow tubes where diameter and
spacing can even be independently controlled.
