| Although the birth of nanotechnology experienced only a short period of twenty years, the dramatic change in human society was brought by nanotechnology. Due to the surface effect, quantum size effect etc., the performances of the nanostructure (NS) of many materials could show some special properties which are very different from the bulk ones and favored people highly. Nowadays, nanomaterials have been closely linked with people’s lives and successfully used in many fields, including biomedicine, environmental monitoring, manufacturing, energy, optical, defense and so on. As the organic material with the advantages of easy processing, easy doping comparing with inorganic materials, and the excellent optical and electrical properties of the organic nanostructures (NS) have great values in the fabrication of the organic light-emitting diodes (OLEDs), organic field effect transistor (OFET), sensors, which makes the NS of the organic material to be particularly concerned. In this article, the preparation, the formation mechanism and the optical properties of the organic NS of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) were systematically investigated; the modulation of the morphologies and optical performance of PTCDA NS were carefully studied also. The contents above should be of great significance for the preparation and application of organic nanomaterials.In the introduction part, which is the first chapter, the progress made in the preparation and performance of organic nanomaterials in recent years are introduced; the second chapter concerns the main experiment techniques and the measurement methods; the third to the sixth chapters, which regard to the investigations on the NS of PTCDA, the concrete contents are as follows:Anodic alumina oxides (AAO) were used as the substrates to form the NS of PTCDA, so the preparation process of AAO was investigated firstly. In this work, the AAO with the characteristic of hexagonal nanohole arrays were prepared from the high purity Al foils in the electrolyte of the oxalic acid and the sulfur acid. Take the electrolyte of oxalic acid for example, the preparation processes of AAO were introduced detailedly; the influences of preparation conditions, including the oxidation voltage, oxidation times, the reiterations of oxidation, the types of electrolyte, etc., on the morphologies of the AAO were discussed clearly. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) were employed to the measurements of the morphologies of the surface, the cross-section, the barriers layer of the AAO as prepared in oxalic acid solution and the holes enlarged by phosphoric acid. The results of the above experiments indicate, the AAO with different pore dimension could be prepared by the changing of the oxidation voltage and the electrolyte, and the voltage is the main parameter affecting the AAO structures. The pore diameter could be varied in the range of20-40run, the density of the pore amount could be modified in the range of102～6×102in1нm2and the thickness of AAO could be controlled by the time of oxidation. The structural models of AAO were reviewed, the formation mechanism of AAO was discussed, that is the formation of AAO will be influenced by the cooperation of the chemical and physical factors.Different substrate temperature (Ts) were selected for the formation of the PTCDA NS with different characters, furthermore the PL intensities of AAO were significant influenced by the annealing temperature (Ta), how to confirm the unanimous properties of AAO is one critical task for the later experiments, so it is necessary to deeply learn the relationships between the AAO properties and the Ta. Anodic alumina oxides (AAO) prepared in oxalic acid (H2C2O4) solution at a constant voltage of40V were investigated systematically by the techniques of temperature programmed desorption combined mass spectrograph (TPD-MS), thermogravimetric analysis (TGA), differential thermal analysis (DTA) and photoluminescence (PL). The results of TGA indicate that the desorption of H2O, CO and CO2and the decomposition of H2C2O4doped in AAO occurred below402.2℃and led to the weight loss of AAOs samples, while the water desorption was the main weight loss reason. In the temperature range of402.2～866.7℃, a small quantity of aluminum oxalate (Al2(C2O4)3) decomposed and gave birth to CO and CO2, CO became the major product during this process. Under the influence of the collapses of crystal lattices of AAO, the drastic decompositions of aluminum carbonate (Al2(CO3)3) and Al2(C2O4)3took place and release a large amount of CO2during the range of866.7五1022.9℃. The amount of (C2O4)2-embedded in bulk AAOs was calculated versus the total weight of AAOs film; the PL intensity of AAOs, the doping of oxalic acid radical and the concentration of oxygen vacancies (F+) was correlated to the Ta; the PL mechanism of AAO was analysed. The above results provide the reliable testimony of the treating condition of AAO during the preparing processes of PTCDA nanotstructures. Different types of NS of an organic dye compound of PTCDA, were prepared on anodic alumina oxide (AAO) at different Ts by a facile organic molecule beam deposition (OMBD) method in molecular beam epitaxy (MBE) system; the techniques including SEM, transmission electron microscopy (TEM) and selected area electron diffraction (SAED) were applied to the systematical characterization of the NS of PTCDA. The SEM results indicates that the PTCDA nanofibers, nanoneedles, nanobelts, and nanorods were produced at330℃Ts, the high Ts leads to the lower formation rate of crystal nucleuses and the small nucleus number, but the fast growth velocity and the larger volume of PTCDA NS; Only nanorods are formed at280℃,230℃, and180℃, and the lengths of them get short as Ts decreases, the lower Ts leads to the faster formation rate of nucleus and the large number of nucleuses, but the lower growth velocity and the smaller volume of NS; the continuous films are obtained on50℃AAOs substrates. The HRTEM and the SAED results show that the nanoneedle and nanorods are single crystal; the PTCDA molecules array along the grown orientation of PTCDA nanoneedle the layer by layer. The "site selective" effect is protruded at the higher Ts, only the areas with smaller curvature radius provide the preferred nucleation centers for the PTCDA vapor. The formation mechanisms of PTCDA NS are proposed which should be mainly affected by the surface curvature and the Ts.In the sixth chapter, the modulation of the morphologies and the optical properties of PTCDA NS were investigated carefully by the SEM, TEM, SAED, PL, and ultraviolet-visible absorption spectroscopy (UV-vis) measurements. The SEM results indicate different types of NS of PTCDA could be generated at different Ts; the morphologies and amount of the NS could be influenced by the Ts and evaporation time (te). The TEM and SEAD results would be of great help to understand the relations between the structure and the performance of PTCDA NS. In the absorption spectra, only two apparent bands with the stronger absorbance at484nm were observed for the sample prepared at Ts=330℃; five bands located at357nm,373nm,475nm,500nm, and556nm appeared for the other samples and the centers of those bands except for the475nm one are rarely affected by Ts. Also five emission bands were observed in the PL spectra of the samples prepared at50～280℃Ts; the intensity of696nm one is the strongest in each single PL spectrum line and increased first and then decreased as Ts is increased; the PL spectrum of the sample prepared at Ts=330℃is very different from the others in the emission wavelength and intensity. For the second group sample prepared at Ts=280℃, the PL properties were modulated by the te significantly, namely, the main emission peak position shows the obvious red shift as the te was increasing. The different types of de-excitation processes inducing the sample luminescence were depicted. The results above indicate that the optical properties could be modulated easily and should be of great significances for the fabrication of organic functional devices. |
