## 3 Results and Discussion  
Figure 2 shows the SEM image and AFM image of PPy film. It can be seen from Figure 2a that the surface of the film is continuous and flat without any holes or wrinkles. Figure 1: Illustration of the process for preparation of PPy film. (�⃝1 represents an aqueous hydrochloric acid solution in which ammonium persulfate is dissolved and ⃝2 represents a chloroform solution in which pyrrole is dissolved.) The AFM image shown in Figure 2b shows that the surface of the film is very smooth with a root square roughness of 1 nm. Usually, when the PPy film is prepared by chemical method, the oxidant and the pyrrole monomer are dissolved in the same solvent. Therefore, the reaction process is random, and the PPy powder is generated and dispersed in the solution without forming a thin film. In this work, in order to control the progress of the reaction, the oxidant and the pyrrole monomer were dissolved in different immiscible solvents. Once the reactants are in contact at the interface, rapid and random nucleation of PPy was initiated in the interface of the two solutions. Due to the hydrophobic nature, the generated PPy was restricted to the interface to form a dense film [27,28]. By controlling the reaction speed, a film with a flat surface can be obtained. Figure 3a shows the XRD pattern of the PPy film. For solid materials, the crystal structure can be divided into crystalline and amorphous. For semiconductor materials, the crystalline state with long-range ordering of atoms can reduce the barrier effects on free carriers which were caused by grain boundaries, thus improving the conductivity of the materials. The crystallinity can be determined by the X-ray diffraction method. PPy is a common conductive polymer material. It has a conjugated long chain structure. The \(\pi\) electrons in the conjugated double bond (C=C) which are similar to the free electron in metals can move in the molecular chain to make it conductive. In addition, the \(\pi\) electrons can also transfer between adjacent chains. Therefore, the longer the molecular chain, the larger the number of \(\pi\) electrons, and the more regular the molecular chain is arranged, which  
Figure 3: (**a**) XRD pattern of PPy film. (**b**) Raman spectrum of PPy film. (**c**) FTIR spectrum of PPy film. (**d**) Molecular formula and molecular connection form of pyrrole monomer. Figure 2: (**a**) SEM and (**b**) AFM image of as-grown PPy film. is more conducive to the transmission of electrons. From the XRD pattern, three sharp diffraction peaks can be found. In order to facilitate the test, the PPy film is placed on the substrate. The substrate material is quartz glass and it has no diffraction peak. In order to determine whether the diffraction peaks belong to PPy, we referred to the related literature. However, the XRD results in the literature are broad bulges and no sharp diffraction peaks appear [9; 11; 29], indicating that this is the first time we have reported the diffraction peaks of PPy films. According to the molecular structure of the pyrrole monomer as shown in Figure 3d, it is known that there are two types of carbon atoms [30] (\(\alpha\)-C and \(\beta\)-C), indicating that there are three possible connection modes for polymerization process, namely \(\alpha\)-\(\alpha\) connection, \(\alpha\)-\(\beta\) connection and \(\beta\)-\(\beta\) connection, as shown in Figure 3d. The \(\alpha\)-\(\alpha\) connection can form an ordered planar structure, while other connections can cause disorder in the polymer chain. PPy belongs to conjugated polymer and its electrical conductivity is mainly affected by carrier concentration and carrier mobility. The carrier mobility is related to the chain spacing and the effective conjugation length of the molecular chain. High \(\alpha\)-\(\alpha\) connection ratio indicates a high degree of order, which is conducive to carrier migration.