More SEM images of the nanotubes grown on plasma-treated membranes can be found in Additional file 1: Figure S3. It should be noted that SEM and TEM examinations reveal the open-end carbon nanotubes grown inside the channels and on the membrane top (see Figures 1, 4 and 5 in Additional file 1: Figures S2 and S3). Examination of many SEM images made

at different tilt angles shows that most of the nanotubes LBH589 manufacturer have open ends. This important finding could be explained by the specific mechanism of the nanotube nucleation and growth on the nanoporous membranes. We believe that the surface features of the membrane surface play a major role in nanotube nucleation and sustaining the growth (a similar mechanism was described for the silicon surface with mechanically written features [32]). In this particular case, channel walls nucleate open selleck chemical nanotubes and sustain their growth with open ends. It should be also noted that the diameter of the channel-nucleated and grown nanotubes corresponds to the channel diameters (20 to 50 nm, Figure 5), whereas the diameters of the nanotubes nucleated on the membrane top can reach 70 to 80 nm (Figure 4).

The number of atomic carbon layers composing the nanotube walls is also larger for the case of nanotubes nucleated on the membrane top. Thus, the plasma posttreatment of the alumina membranes before the nanotube growth radically changes the outcomes. Indeed, nucleation of the nanotubes inside long channels becomes possible. Here, we should stress that we did not use any special catalyst applied into the channels (directly at the bottom), as it was demonstrated by other authors [33]. In contrast, we used a rather simple technique of depositing cheap and commonly used S1813 photoresist and a thin Fe layer onto the upper surface of the membrane. Most probably, the plasma posttreatment changes the

energy state of the alumina membrane and promotes deep penetration of the photoresist (which serves as a carbon precursor) into the channels. HAS1 As a result, nucleation and efficient growth of carbon nanotubes in the pores become possible. To decide if the ion flux extracted from the plasma can penetrate into the channels in the alumina membrane and affect the surface state of the material, one should compare the thickness of the sheath between the plasma and the surface with the diameter of a typical channel (i.e. of about 50 nm) and estimate the typical ion energy colliding with the surface. For a floating surface, the surface potential U S can be estimated [18, 34] (1) where T e is the electron temperature, k is the Boltzmann’s constant, e is the electron charge, m e is the electron mass and M i is the ion mass. For typical low-temperature plasma parameters (T e  ≈ 2 to 3 eV), the surface potential is U s  = (5 to 7) × T e = 10.20 eV.