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51.
The effect of silicon ion implantation on the optical reflection of bulk polymethylmethacrylate (PMMA) was examined in the visible and near UV. A low-energy (30 and 50 keV) Si+ beam at fluences in the range from 1013 to 1017 cm−2 was used for ion implantation of PMMA. The results show that a significant enhancement of the reflectivity from Si+-implanted PMMA occurs at appropriate implantation energy and fluence. The structural modifications of PMMA by the silicon ion implantation were characterized by means of photoluminescence and Raman spectroscopy. Formation of hydrogenated amorphous carbon (HAC) layer beneath the surface of the samples was established and the corresponding HAC domain size was estimated. 相似文献
52.
Conducting polymer polydimethylsiloxane (PDMS) is studied for the high performance electrode of organic electroluminescence devices. A method to prepare the electrode consisting of a SiC thin film and PDMS is investigated. By using ultra thin SiC films with different thicknesses, the organic electroluminescence devices are obtained in an ultra vacuum system with the model device PDMS/SiC/PPV/Alq3, where PPV is poly para-phenylene vinylene and Alq3 is tris(S-hydroxyquinoline) aluminium. The capacitance voltage (C - V), capacitance-frequency (C - F), current-voltage (I - V), radiation intensity-voltage (R - V) and luminance eFficiency-voltage (E - V) measurements are systematically studied to investigate the conductivity, Fermi alignment and devices properties in organic semiconductors. Scanning Kelvin probe measurement shows that the work function of PDMS/SiC anode with a 2.5-nm SiC over layer can be increased by as much as 0.28eV, compared to the conventional ITO anode. The result is attributed to the charge transfer effect and ohmic contacts at the interface. 相似文献
53.
O. Yaroshchuk A.D. Kiselev Yu. Zakrevskyy J. Stumpe J. Lindau 《The European physical journal. E, Soft matter》2001,6(1):57-67
The photoinduced 3D orientational structures in films of a liquid crystalline polyester, containing azobenzene side groups,
are studied both experimentally and theoretically. By using the null ellipsometry and the UV/Vis absorption spectroscopy,
the preferential in-plane alignment of the azobenzene fragments and in-plane reorientation under irradiation with linearly
polarized UV light are established. The uniaxial and biaxial orientational order of the azobenzene chromophores are detected.
The biaxiality is observed in the intermediate stages of irradiation, whereas the uniaxial structure is maintained in the
photosaturated state of the photo-orientation process. The components of the order parameter tensor of the azobenzene fragments
are estimated for the initial state and after different doses of irradiation. The proposed theory takes into account biaxiality
of the induced structures. Numerical analysis of the master equations for the order parameter tensor is found to yield the
results that are in good agreement with the experimental dependencies of the order parameter components on the illumination
time.
Received 23 April 2001 and Received in final form 1 August 2001 相似文献
54.
D. Basko G.C. La Rocca F. Bassani V.M. Agranovich 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):353-362
We predict an efficient electronic energy transfer from an excited semiconductor quantum well to optically active organic
molecules of the nearby medium (substrate and/or overlayer). The energy transfer mechanism is of the F?rster type and, at
semiconductor-organic distances of about 50 ?, can easily be as fast as 10-100 ps, which is about an order of magnitude shorter
than the effective exciton lifetime in an isolated quantum well. In such conditions, the Wannier-Mott exciton luminescence
is quenched and the organic luminescence is efficiently turned on. We consider both free as well as localized quantum well
excitons discussing the dependence of the energy transfer rate on temperature and localization length. A similar mechanism
for the non-radiative energy transfer to the organic overlayer molecules from unbound electron-hole pairs excited in the 2D
continuum is shown to be much less competitive with respect to other relaxation channels inside the inorganic quantum well
(in particular, 2D exciton formation).
Received 20 July 1998 相似文献
55.
The C 1s, F 1s, and O 1s electron spectra for polymethyl methacrylate (PMMA) and polytetrafluoroethylene (PTFE) irradiated by KrF excimer laser with 248 nm wavelength were analyzed by the X-ray photoelectron spectroscopy (XPS) method. The results show that, after irradiation by the laser, the percentage of the carbon atoms of C-C bond decreases and the percentage of CO bond increases for PMMA, while for PTFE percentages of both C-C bond and CF2 group decrease drastically, respectively. Moreover, it was found that C-O bond and other complex carbon-oxygen groups appeared for PTFE. The photon-chemical processes associated with the energy level transitions, energy diversion, and dissociation of bonds in the interaction were theoretically analyzed based on the chemical structures of PTFE and PMMA. Our analyses can successfully explain that PMMA can be effectively etched by KrF excimer laser with 248 nm wavelength can efficiently etch the PMMA, but the surface of PTFE can only be modified by it. 相似文献
56.
H. M. Phillips D. Sarkar N. J. Halas R. H. Hauge R. Sauerbrey 《Applied Physics A: Materials Science & Processing》1993,57(1):105-107
The electrical conductivity of thin-film C60 has been changed by more than seven orders of magnitude with KrF (248nm) excimer-laser irradiation. Specific conductivities of 1 –1 · cm–1 have been obtained. The onset of conductivity is consistent with a laser-induced metal-insulator phase transition. The threshold for KrF-laser ablation of C60 has been determined to be 20±2 mJ/cm2. This laser-induced process generates an all-carbon semiconductor-metallic junction which may have important technological applications. 相似文献
57.
The steady current-voltage characteristics of single layer organic devices based on MEH-PPV and N,N′-diphenyl-N,N′-bis(4′-[N,N-bis(naphth-1-yl)-amino]-biphenyl-4-yl)-benzidine (TPTE) blend with different TPTE concentrations was investigated. The thickness dependence of the current-voltage relationship clearly demonstrates that the current at low voltage and at high voltage are all space charge limited. The current density-electric field characteristic proves the blend polymer LEDs to operate in the tunneling-controlled model. The effective hole mobility is directly determined by space charge limited current at high voltage and increases with increasing TPTE content in the blend. The EL efficiency shows concentration dependence, which is attributed to the change of the transport of holes in the blend film. 相似文献
58.
Optical and electrical measurements on green and blue organic light-emitting devices (OLEDs) with and without hole-blocking layers (HBLs) were performed, and the luminescence mechanisms of green and blue OLEDs utilizing HBLs were investigated by using energy band diagrams and carrier density distributions. The dependence of the electroluminescence efficiencies on the existence of HBLs was described on the basis of a luminescence mechanism. The density distributions of the electrons and the holes in OLEDs under applied electric fields were estimated from the energy band diagrams, taking into account the electronic parameters and the layer thicknesses. The luminescence efficiencies and the color chromaticities were significantly affected by the existence of the HBLs. These analyses can help improve understanding of the luminescence mechanisms at play in and the electroluminescence efficiencies of green and blue OLEDs with HBLs, and the present results provide important information on the optical properties for enhancing the efficiencies of OLEDs operating in the green and the blue regions of the spectra. 相似文献
59.
Dendrimers are highly branched molecules, which are expected to be useful, for example, as efficient artificial light harvesting systems, in nano-technological or in medical applications. There are two different classes of dendrimers: compact dendrimers with constant distance between neighboring branching points throughout the macromolecule and extended dendrimers, where this distance increases from the system periphery to the center. We investigate the linear optical absorption spectra of these dendrimer types using the Frenkel exciton concept. The electron-phonon interaction is taken into account by introducing a heat bath that interacts with the exciton in a stochastic manner. We discuss compact dendrimers with equal excitation energies at all molecules, dendrimers with a functionalized core as well as with a whole branch functionalized. Furthermore the line shape of a compact dendrimer is discussed when neighboring molecules at the periphery interact and when all molecules have randomly distributed excitation energies due to disorder. Finally, we discuss two models for extended dendrimers. 相似文献
60.
The nonlinear optical (NLO) properties of a novel cluster Polymer {WS4Cu4I2(bpe)3}n solution are studied by using Z-scan technique with laser pulses of 4.5 ns pulse-width at a wavelength of 532 nm. The results show that the cluster solution possesses strong nonlinear absorption and refraction. Nonlinear refraction of the cluster is composed of third-order nonlinear refraction and transient thermal effect. The thermal effect is mainly due to the strong nonlinear absorption. Numerical simulations obtained by solving simultaneously photo-acoustic and electromagnetic wave equations, agrees basically with experimental results. 相似文献