# The Effect of Local Doping of the Polymer-Polymer Interface Using Cu\({}_{2}\)O Particles
## 2 Materials and Methods  
A polymer with polar side functional groups, polydiphenylenphthalide, was chosen as an organic dielectric [4; 8; 9]. Anomalous electronic properties of the interface between two dielectric polymer films were previously observed in poly-N-phenyldiphenylenphthalimide, polydiphenyleneoxidepthhalide, polydiphenylenesulfidephthalide and polytherphenylenphthalide [8]. Additionally, it was shown in [13] that similar properties can be observed along the interface of the well-known commercial organic dielectric polymethylmethacrylate. Historically, the first report of the abnormally high conductivity of the polymer-polymer interface was made using the example of the polydiphenylentalide/polydiphenyltalide interface. Various studies of the electronic properties of the interface between two polymer dielectrics were carried out on such a structure and numerous experimental results were accumulated. In this regard, polydiphenylenphthalide was chosen as the object of research. The structural formula of PDPh is shown in Figure 1a. The synthesis of this polymer is described in detail in the work of [PERSON] et al. [14]. PDPh is distinguished by high chemical and heat resistance. The temperature of the beginning of softening in air is \(\sim\)420 \({}^{\circ}\)C, the temperature of the beginning of decomposition \(\geq\) 440 \({}^{\circ}\)C. It is soluble in traditional organic solvents: chloroform, methylene dichloride, cyclohexanone, etc. In the normal state, PDPh is a dielectric and is characterized by the following parameters: a band gap width of \(\sim\)4.3 eV, electron affinity of \(\sim\)2 eV and first ionization potential of \(\sim\)6.2 eV [15]. An island film of copper oxide (I) was chosen as the EI. Among the thin films of oxide semiconductors, copper oxide can be produced by the simplest, inexpensive and fastest method of thermal evaporation of Cu and annealing in air [16; 17; 18; 19]. Metallic copper is easily oxidized at relatively low temperatures (\(\geq\)200 \({}^{\circ}\)C). Cu\({}_{2}\)O is a p-type semiconductor with a band gap of 2.04-2.71 eV [20; 21]. Cu\({}_{2}\)O is an oxide with fully filled d-orbitals. These oxides are usually semiconductors due to the gap between the d-band and the next largest energy band (usually obtained from the s-orbitals of the metal). These oxides tend to behave like their own p-type semiconductors, where the Fermi level is closer to the valence band than to the conduction band; however, the mobility of holes for these materials is quite low [20; 22; 23; 24; 25; 26; 27]. The character of the Cu\({}_{2}\)O p-type is explained by the presence of negatively charged copper vacancies, which introduce an acceptor level approximately 0.3 eV above the valence band [27]. In the work samples were 2 types: a pure polymer-polymer interface (Figure 1b) and an interface with an embedded thin layer of EI (Figure 1c). The samples of the first type were a two-layer PDPh-PDPh polymer film with electrodes embedded in the interface. The samples of the second type were with an island Cu\({}_{2}\)O film placed along the polymer-polymer interface. Slide glasses with a size of 15 \(\times\) 15 mm were used as substrates. The substrates were cleaned in an ultrasonic bath. Cleaning was carried out sequentially in acetone, ethanol, deionized water, followed by drying at a temperature of 100 \({}^{\circ}\)C. Each stage of cleaning was carried out for at least 10 min. The first polymer layer was deposited to the cleaned substrate via centrifugation of 5 wt.% polymer solution in cyclohexanone at 3000 rpm for 1 min. Then, the samples were dried for 45 min in air at room temperature. To remove solvent residues, the sample was annealed under pre-vacuum conditions at a temperature of 150 \({}^{\circ}\)C for 1 h. It is known that PDPh films produced by this technology are continuous and homogeneous up to thicknesses of several nanometers [28].