| In recent years, the organic semiconductor devices have attracted great interests and developed rapidly since them possess a lot of advantages that the conventional inorganic semiconductor devices don’t possess. Moreover, the organic semiconductor devices are used in the fields of organic photovoltaic solar cells, organic field effect transistors, organic spin valve and so on. Thus how to improve the performance of the organic semiconductor devices is a core issue of concern to researchers. The semiconductor organic molecules usually have specific spatial geometry and their stacking in different ways tend to form distinct surface morphology. It thereby largely affect the performance of the organic photovoltaic devices. The research of modulating method for the organic molecular orientation and stacking thus becomes critical, which can give a useful guide in optimizing the performance of devices. One of the useful ways to modulating organic molecular orientation is to introduce the role of magnetic fields in the molecular growth process. But considering the current researchs in this area far from complete, there is a great need for further research and exploration.In this paper, thin iron phthalocyanine(FePc) films were grown by organic molecular beam deposition on Si and Cu substrates in a high magnetic field (8.5T) perpendicular to the substrates. The influence on the molecular orientation and the morphology of FePc thin films by the magnetic field was investigated by means of X-ray diffraction(XRD), angle dependent near-edge X-ray absorption fine structure(NEXAFS), Raman spectroscopy and atomic force microscopy(AFM). The main conclusions are as follows:Firstly, the XRD results show that the FePc films prepared on Si(111) substrate in the absence of external magnetic field and in the presence of the external magnetic were both ordered a-phase FePc in (200) plane orientation. The thin film grown in magnetic field had higher crystallinity and crystalline quality. The stacking spacing between the molecules decreased under the influence by the magnetic field so that the molecular arrangement was more closely. As it is observed from the AFM images, the grains of the film deposited in the magnetic field were distributed more orderly and uniformly on the substrate, and the surface is more smooth. The synchrotron radiation NEXAFS spectra and Raman spectra show that, FePc molecules stood on the substrate surface, which have a greater tilted angle relative to the substrate, under the influence by the magnetic field. The Semi-quantitative polarized Raman spectroscopy results show that the angle of the molecular plane with respect to the substrate increased from 63.6° to 67.1° after the magnetic field applied.Secondly, we prepared the FePc films on Cu substrate. The XRD and AFM results show that, the FePc molecules presented an edge-on configuration relative to the substrate and formed α-phase thin films, the crystallinity of which was enhanced in magnetic field. The grains of the film deposited in magnetic field were distributed on the substrate more orderly and uniformly. What’s moreover, continues magnetization after the deposition can reduced roughness. Angle dependent NEXAFS spectra and Raman spectra show that, the angle of the molecular plane with respect to the substrate decreased in the magnetic field, and it continues to decreased by magnetization after deposition. The Semi-quantitative polarized Raman spectroscopy results show that, the angles of the three samples grown without the magnetic field, grown in the magnetic field for 1h and grown in the magnetic field for 1h with 23h-magnetization after growth were respectively 66.25°, 64.20° and 62.05°. Compared to the results of Si substrate, the tilted angle of molecular plane with respect to the Cu substrate decreased under the influence by the magnetic field, but the tilted angle of molecular plane with respect to the Si substrate increased, indicating that the effect of the magnetic field is different on the different substrates. |
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