# The Effect of Local Doping of the Polymer-Polymer Interface Using Cu\({}_{2}\)O Particles
## 2 Materials and Methods
The next stage was the deposition of metal electrodes to the surface of the polymer layer via the thermal vacuum evaporation of Cu (99.99%, Sigma-Aldrich) at 10\({}^{-6}\) Pa through shadow masks. The gap between the electrodes was 30 \(\upmu\)m, thickness \(\sim\)100 nm and width 4 mm. The thickness of the deposited metal layer was calculated according to the formula  
\[d=\frac{m}{4\pi\,r^{2}\rho} \tag{1}\]  
where \(m\) is the deposited metal mass, \(\rho\) is the density and \(r\) is the distance from the sample surface to the evaporator. In the case of the second type of the structure, the EI layer was formed before metal electrodes deposition. The procedure consisted of the deposition of an island layer of copper with a thickness of \(\sim\)5 nm on the polymer surface, followed by its oxidation to Cu\({}_{2}\)O. The thickness of 5 nm was the maximum thickness when the surface conductivity of the copper film had an activation character typical of island films. Oxidation was carried out in an oxygen atmosphere at 200 \({}^{\circ}\)C for 40 min. This method is sufficient for complete oxidation of the copper film to single-phase Cu\({}_{2}\)O [16; 17; 18; 19]. The second polymer layer was formed on the surface of the first film with deposited electrodes. Polymer solution of 5 wt.% in cyclohexanone were used according to a similar procedure for the first polymer layer. The surface morphology and thickness films at all stages of the production of the multilayer structure were controlled using an atomic force microscope NTEGRA II (NT-MDT Spectrum Instruments, Moscow, Russia) adopting an Au-coated silicon probe with a nominal 35-nm tip curvature radius and a typical force constant of 0.1 N. The AFM images were obtained in contact mode. Before and after each measurement the noise level was 0.01 nm. The quality of the manufactured layers was estimated according to two criteria: root-mean-square (RMS) surface roughness and thickness. The numerical value of RMS was obtained from a series of AFM images from different parts of the sample surface with the same dimensions of 5 \(\times\) 5 \(\upmu\)m. The thickness was estimated using the height difference between the layers. In the case of a Cu\({}_{2}\)O layer and copper electrodes, the transition boundary was created using a tightly pressed shadow mask. For polymer films, a stump was formed using a copper cutter, since the layers were made via the method of centrifugation over the entire surface of the sample from a PDPh solution. The morphology of the surface of each layer is shown in Figure 2. The surfaces of the polymer films are smooth and flat (Figure 2a,d). The RMS surface roughness deduced from the AFM topography images is \(\sim\)1 nm. Figure 2e,f shows the topography of the surface and a 3D image of the lower polymer layer with a slice section. The film is homogeneous in thickness except for the small section along the cut. This indicates good film-forming properties of PDPh. This fact has been repeatedly confirmed in our previous works [8; 9; 10; 28]. Cu\({}_{2}\)O has a granular structure with a surface roughness of about 4 nm. This corresponds to approximately 80% of the nominal thickness of the oxide layer. A high surface roughness value indicates the presence of isolated islands instead of solid films. The surface of the copper electrodes has a structure with large grains with a surface roughness of 10 nm. The formation of grains, apparently, is a consequence of the pro  
Figure 2: AFM image of the surface of (**a**) the lower PDPh layer; (**b**) the Cu\({}_{2}\)O oxide layer; (**c**) the copper electrode; (**d**) the upper PDPh layer; (**e**,**f**) the surface topography and 3D image of the lower polymer layer with a slice section. cesses of recrystallization and agglomeration during the deposition of copper atoms on the substrate. The study of the electronic properties of Cu\({}_{2}\)O films was carried out via optical methods using a Shimadzu UV-1800 spectrophotometer (Shimadzu Corporation, Kyoto, Japan).