RESUMO
vacuum sublimation method was used to purify the homegrown 3,4,9,10 perylenetetracarboxylic dianhydride(PTCDA)powder with a purity of 98% in its sublimation point of 450 â. With Bill's law and ultraviolet-visible spectrophotometer testing analysis, its purity reached to 99.8%. Meanwhile, the contents of C and H elements in the pre-and post-purified molecules were also measured by using elemental analyzer. The measured results indicate that the contents of C and H elements in the post-purified the molecules are very close to the theoretical value. H element in the molecular structure was investigated with nuclear magnetic resonance (NMR) spectroscopy and the results demonstrated that there are an equal number of H atoms in two different chemical environments and it can only be located on the aromatic ring. By discussing the chemical bond formation of PTCDA molecules, the C, H and O atoms in high purity PTCDA molecules are mainly covalent bonds. The crystalline state and crystal structure of this organic material were tested and analyzed by X-ray diffractometer. The results suggest that the post-purified PTCDA power existed α-PTCDA and ß-PTCDA two phases, in which α-PTCDA phase is major component while ß-PTCDA phase accounts for about one five of the total ingredients. Besides, the crystal cell belonged to bottom-centered monoclinal structure. Meanwhile, the crystal state, grain size and band structure of PTCDA single crystal thin films formed on the surface of p-type silicon in its sublimation point are investigated in detail. During the high-purity α-PTCDA forming organic single thin film on the surface of p-type single silicon, the π-electron cloud covered on the top, bottom and two sides of its thin film's molecular layer plane. Due to the formation of delocalized bond that attributed to the overlap of the outermost valence electron orbital of C, H, O atom, the valence electrons generate co-movement and the energy level splitting for the band. The energy difference between valence band and the first tight binding is 2.2 eV which lead to this organic material possessing the properties of semiconductor conduction. In addition, this organic material with the intrinsic carrier concentration for 1014 cm-3 belong to weak p-type organic semiconductor material. This organic material combines with the surface of p-type silicon to form hetehomo-type heterojunction which is provided with excellent response for visible light to near infrared wavelengths of light.
RESUMO
The organic semiconductor 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA) with the purity of 97.5% was purified by sublimation to 99.9%. The high-purity PTCDA material was measured by mass spectra, infrared spectrum and X-ray photoelectron spectroscopy (XPS). Detailed analysis revealed its molecular structure, the forming of chemical bond, the vibration modes of atoms in equilibrium lattice position, electronic configuration and the shift of binding energy of atoms. Based on the infrared spectrum analysis, the molecular structure of PTCDA is consisting of perylene core group with five C rings and two anhydrides located at both ends of perylene core, which is mainly bonded with covalent bond. The stretching vibration of C atoms in the crystal lattice dominates in their equilibrium positions. The PTCDA molecules have a large number of π electrons which can move freely; the intermolecular delocalized π bond overlap determines the conductivity of PTCDA. Based on XPS analysis, it can be found that there exist two kinds of C atoms with different binding energy: 285.3 and 288.7 eV, respectively, corresponding to the C atoms in the perylene ring and anhydride. In addition, there are two kinds of O atoms, i. e. C==0 and C--O--C, whose bonding energy is 531.3 and 533.1 eV, respectively.
RESUMO
Polycrystalline silicon (poly-Si) thin-films were made on planar and textured glass substrates by aluminum-induced crystallization (AIC) of in situ amorphous silicon (a-Si) deposited by DC-magnetron. The poly-Si films were characterized by Raman spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). A narrow and symmetrical Ranman peak at the wave number of about 521 cm(-1) was observed for all samples, indicating that the films were fully crystallized. XRD results show that the crystallites in the authors' AIC poly-Si films were preferably (111) oriented. The measurement of full width at half maximum (FWHW) of (111) XRD peaks showed that the quality of the films was affected by the a-Si deposition temperature and the surface morphology of the glass substrates. It is likely that an a-Si deposition temperature of 200 degrees C seems to be ideal for the preparation of poly-Si films by AIC.
RESUMO
X-ray photoelectron spectroscopy (XPS) of surface and interface of PTCDA/ITO in PTCDA/p-Si organic-on-inorganic photoelectric detector was investigated. From C1s fine spectrum we found that the binding energy of C atoms in perylene rings was 284.6 eV; and the binding energy of C atoms in acid radical was 288.7 eV; moreover, some C atoms were oxidized by O atoms from ITO. The binding energy of O atoms in C=O bonds and C-O-C bonds was 531.5 and 533.4 eV, respectively. At the interface, the peak of high binding energy in C1s spectrum disappeared, and the main peak shifted toward lower binding energy.
RESUMO
It is demonstrated that a new solid-state cathodoluminescence device based on accelerated electron in SiO2 can be fabricated using organic light emitting materials as a fluorescent film. This device (the device of sandwiched structure) is composed of a glass substrate, an ITO layer, a double SiO2 films, and an organic fluorescent film. When a bias voltage is applied to the devices, they can uniformly emit red, green, and blue light. To some extent, when the voltage is low, the red (green) emission is obtained; and when the voltage is high, the blue emission is acquired. These emissions belong to the solid-state cathodoluminescence, they originate from the accelerated electrons in SiO2, which bombard the organic layers. Their devices have achieved full color (RGB) lighting and improved blue emitting.
RESUMO
Indium-tin-oxide (ITO) coated glass has been widely used as a hole injection electrode for organic light-emitting devices (OLEDs), but the work function of ITO film usually mismatches the highest occupied molecular orbital (HOMO) of the hole transport materials. Copper phthalocyanine (CuPc) has been used as a hole injection buffer to enhance the hole injection from ITO to the hole transport layer. A thin CuPc layer was thermally evaporated onto the ITO-coated glass substrate, and the surface and interface electron states of the CuPc/ITO close contact were measured and analyzed by X-ray photoelectron spectroscopy (XPS) technology. Results show that, in CuPc molecule, copper atom has a valence of +2 and interacts with nitrogen atoms through coordinate bonds. There are two kinds of carbon atoms: eight carbon atoms bonding with two nitrogen atoms and other 24 carbon atoms with an aromatic hydrocarbon character. The nitrogen atoms are also in two kinds of chemical environment: four nitrogen atoms only bond with two carbon atoms forming C-N=C bonds, and other four nitrogen atoms not only bond with carbon atoms but also bond with copper atom through coordinate bonds. Argon ion beam sputtering was used to study the interface characteristics of the CuPc/ITO contact. As sputtering time increases, the peaks of C 1s and N 1s spectra gradually become weaker, the peaks of Cu 2p, O 1s, In 3d and Sn 3d spectra get stronger. The core-levels of C 1s, N 1s, O 1s, In 3d and Sn 3d spectra all have chemical shifts towards higher or lower binding energy, but their behavior are different.