Nanostructured surfaces

About the features of the interaction of a liquid metal drop generated by an arc of a vacuum discharge with a substrate under the conditions of the CVD synthesis of carbon nanotubes
Panarin V.E., Svavilny N.E., Khominich A.I., Shkola A.A.
Alloys Technology Laboratory, G.V. Kurdyumov Institute for Metal Physics of the N.A.S. of Ukraine. Academician Vernadsky Boulevard, 36, Kyiv-03142, Ukraine. E-mail: svavil@imp.kiev.ua

The catalytic centers (CCs) were formed by annealing thin Fe, Ni films that were deposited on the substrate by vacuum evaporation of cathodes from these materials during the CVD synthesis of carbon nanotubes (CNTs) with the addition of a plasma component [1]. The microdrop phase is always present in the plasma flow of the cathode material [2].
Such microdrops, deposited on the substrate, show good physical processes that occur both on the droplets themselves and around them when they cool on a substrate.  The experiments were carried out on an installation detailed in [1]. 
 The droplets generated by the vacuum arc, when flying to the substrate, are in the plasma vapor stream of solid phase material used as a catalyst for CVD synthesis and are overheated to different temperatures by ions during the flight. Sometimes the degree of overheating is so strong that the drop evaporates during the flight, i.e. a "coat" of vapor of the drop material is formed around it.  A typical view of an overheated droplet that has flown along a tangential trajectory to the substrate is shown in Fig. 1.
  
Fig.1 The view of Fe drop on SiO2 substrate  Fig.2. Distribution of Fe in the cross					   section of a drop

It can be seen that around the drop was a liquid metal layer solidified after the drop falling, and in this layer the drop moved along the surface of the substrate in the direction of its flight. The areas of superheating of a substrate with various degree of degradation of a material around a drop are also visible. But very often around the droplet there is an increased content of the droplet material, as follows from the data in Fig. 2, which can only be understood as the presence of a "coat" of material vapor around the droplet. The joint role of the catalyst material vapor distribution and the surface state transformation when it overheats demonstrate the optimum conditions for the formation of a CCs in the synthesis of CNTs around such a drop:

Fig.3. CNTs synthesized on SiO2 around a Ni-drop on a CCs of different sizes formed from catalyst material film of different initial thickness

1.	Panarin V.Ye., Svavil’ny N.Ye., Khominich A.I. The behavior dynamics of a droplet phase in vacuum arc discharge plasma in chemically active gas nitrogen // Journal of Materials Research and Technology. – 2017. – 6,  N 3. – P. 284-288.
2.	Devis W.D., Miller H.C. Analysis of the electrode products emitted by dc arcs in a vacuum ambient // J Appl Phys. – 1969. – 40, N 5. – P. 2212-2222.