For analyzing the depth distribution of DCF within the nanotubes a combined method of focused ion beam sputtering (FIB) and time of flight secondary ion mass spectrometry (TOF -SIMS) was used. FIB (DualBeam Helios NanoLab 600, FEI) was used to mill an inclined plane into the filled nanotubes from the top to the Zr substrate in an area of 50×100 mm² with adjustment to their thickness. The beam parameters were 16 kV acceleration voltage and 21 nA beam current. The milling was performed in three consecutive steps, each one increasing the depth successively by reducing the milled area (schematic for the ion milling shown in fig ). This was done to reduce the heating and fragmentation of the sample. The crater created at an incline, was analyzed in the negative polarity using secondary ion mass fragments (Cl -34.97 m/z; CHO 2 -45.017 m/z;), with respect to DCF and were recorded with TOF -SIMS (TOF -SIMS 4, ION -TOF GmbH). For imaging mode, Bi3 ions with an accelerated voltage of 25000 eV were used. The sample stage was tilted at 4 ͦ towards the primary ion beam to avoid shadowing effects and to increase the impact angle of the probe.