RESUMEN
CeO2/Tb4O7 superlattices were deposited on P type Si wafers by e-beam evaporation technology. Four typical photoluminescence peaks of Tb3+ ions which located around 488, 544, 588 and 623 nm were obtained after the superlattices annealing in weak reducing atmosphere at high temperature. It was indicated that CeO2 films transferred to amorphous state as the valence transition of Ce4+ --> Ce3+ which was induced by thermal annealing, the energy transfer occurred between Ce3+ ions and Tb3+ ions, and the Tb3+ ions emition could be detected after obtaining the energy from Ce3+ ions. A study about the effect of Tb4O7 thickness on the superlattices photoluminescence showed that the maximum PL intensity as thickness of Tb4 O7 films were about 0.5 nm, the concentration quenching might occur because of the energy transfer among the Tb3+ ions. The annealing conditions research demonstrated that the maximum PL intensity could be obtained as the superlattices annealed at 1 200 degrees C for 2 hour. Further investigation inferred that the concentration of Ce3+ ions, Oxygen vacancy defects and the distance between Ce3+ ions and Tb3+ ions play an important role in the annealing process.
RESUMEN
In the present paper, SiO/SiO2 superlattices samples were prepared on Si substrates by electron beam evaporation. The samples were annealed in nitrogen atmosphere at high temperature subsequently. And then, Ce3+ ions with a dose of 2.0 x 10(14) and 2.0 x 10(15) cm(-2) respectively were implanted into these samples with formed Si nanocrystals. The photoluminescence (PL) spectra showed that the PL intensities of samples with Ce3+ implanting dropped sharply compared with the samples without Ce3+ implanting. The PL intensity increased gradually with increasing re-annealing temperature, but dropped again when the temperature exceeded 600 degrees C. The PL intensity even could be higher than that of samples without Ce3+ implanting if only the dose of Ce3+ was 2.0 x 10(14) cm(-2). When the dose of Ce3+ was 2.0 x 10(15) cm(-2), the PL intensity couldn't exceed that of samples without Ce3+ implanting even when the re-annealing temperature was 600 degrees C. Further investigations showed that the varieties of the PL intensities were mainly dependent on the re-annealing temperature, which had the best point at 600 degrees C, and the dose of Ce3+ had the right value. Furthermore, the experiment results proved that there was energy transfer from Ce3+ to Si nanocrystals in this kind of structure.
RESUMEN
SiO/SiO2 superlattices with different thickness of SiO and SiO2 films were deposited on the Si substrates at 200 degrees C by thermo-evaporation technology. The photoluminescence (PL) spectrum centers of the samples shifted from 400 nm to 600 nm with the increase in SiO films thickness. Similar phenomena were also found when increasing the thickness of SiO2 film but forming SiO film. It was found that the PL was attributed to the defects located at the interfaces between SiO and SiO2 films. The deconvolution of the PL spectra showed that the WOB(O3[triple bond]Si--O--O*), NOV(O3[triple bone]Si--Si[triple bond]O3), the E'center(O[triple bond]Si*) and NBOHC (O3[triple bond]Si--O*) defects contributed to the PL spectra. A mass of Si-O dangling bonds formed on the interfaces of the SiO and SiO2 during the deposition process, could provide many free O atoms and intrinsic defects. When the SiO film was thin (such as 1 nm), most of the Si6 rings were broken, and more WOB defects (415 nm) would be formed because of the combination of the intrinsic NBOHC defects and the diffusing O atoms on the interfaces. With the increase in the SiO film thickness, more Si6 rings were formed in the SiO films, that is the number of the Si-O dangling bonds decreased, less of WOB defects could be formed as both of the free O atoms and intrinsic defects decreased, but the NOV defects (470 nm) increased because of more E' center defects would be combined in pairs. With increasing of the SiO film thickness, the combination of the intrinsic defects became more difficult, so the E'center defects (520 nm) and NBOHC defects (630 nm) would dominate the PL of the SiO/SiO2 superlattices in turn. In conclusion, the evolution of the defects located at the interfaces induced the red shift of the PL
RESUMEN
Amorphous SiNx films were deposited on p-type Si(100)substrates by magnetron sputtering technology. The samples were then detected by a Bruker Tennsor 27 Fourier transform spectrometer. One intense absorption band of the SiNx films (from 812 to 892 cm(-1)) which was assigned to the stretching vibration mode of Si--N--Si bond was detected by Fourier transform infrared (FTIR) spectroscopy. Obviously, it was showed that a red shift of the absorption peak occurred in the FTIR spectrum with the sputtering power increasing; nevertheless, a blue shift of the absorption peak occurred after annealing with the temperature increasing. In the present paper, the deposition process and inner structures of the SiNx films were studied according to RBM (random bonding model)and CFM (central force model). With the increase in the ratio of N(Si)to N(N), the angle of the Si--N--Si changed and the different structures were formed correspondingly. Therefore the Si--Ny--Si(4-y) (0 < or = y < or = 4) models were set up to explain the inner structure of the SiNx films. The investigation showed that Si--N4 tetrahedron, Si--N--Si3, Si--N2--Si2, Si--N3--Si and Si--Si modes were formed accordingly in the SiNx films with the sputtering power increasing. And five models in total were formed during the deposition process. Different stretching vibration modes of Si--N--Si bond were corresponding to the different inner structures of thin films prepared by different sputtering power. With the temperature increasing, the activity of atoms increased which would let the angle of the Si--N--Si go to identical. As a result, Si3N4 and Si nanocrystals were formed with the phase separation of SiNx films during the annealing process with higher temperature, which would result in a blue shift to 870 cm(-1) (the standard absorption peak of Si3N4).
RESUMEN
Four organic solar cells with the different structures were fabricated. The structures are Device1 ITO/LiF/PEDOT: PSS/MEH-PPV/C60/Al, Device 2 ITO/PEDOT : PSS/MEH-PPV/C60/Al, Device 3 ITO/LiF/PEDOT : PSS/MEH-PPV : C60/C60/Al and Device 4 ITO/PEDOT : PSS/MEH-PPV : C60/C60/Al. Then we compared the current-voltage (I-V) characteristics of these devices and found that the insertion of a thin LiF layer between the ITO electrode and the PEDOT : PSS layer resulted in much improved device performance. The short-circuit current density (J(sc)) and fill factor (FF) of Device 1 were enhanced by 74% and 31%, respectively as compared to those of Device 2. The short-circuit current density (J(sc)) of Device 3 is about 1.4 times as large as that of Device 4. The increased solar cell performance mostly can be attributed to the fact that the hole transport to the anode can be effectively suppressed by a thin LiF layer, and the thin LiF layer between the ITO electrode and the PEDOT: PSS layer can form better interface properties. Hence, such change in structure of solar cells improves the performance of the organic solar cells effectively.
RESUMEN
SiO/SiO2 superlattices samples were prepared on Si substrates by reactive evaporation of SiO powder in vacuum or an oxygen atmosphere. The samples were annealed in nitrogen atmosphere at high temperature subsequently. And then, H+ with a dose of 3.0 x 10(14) x cm(-2) and 3.0 x 10(15) x cm(-2) respectively was implanted into these samples with formed Si nanocrystals at 20 keV. The PL spectra showed that the PL intensities of samples with H+ implanting dropped sharply compared with the samples without H+ implanting. The PL intensity increased gradually with increasing re-annealing temperature; and it even could exceed that of samples without H+ implanting if the dose of H+ was enough. Our further investigations showed that the varieties of the PL intensities were mainly dependent on the area density of the defects formed in the samples, and also the area density of the defects was influenced by the dose of H+ and the further re-annealing temperatures.
RESUMEN
Amorphous SiOx films were deposited on Si substrates by magnetron sputtering technology. Three absorption bands of the SiOx films were detected by Fourier transform infrared spectroscopy. The authors' investigation shows that Si-Oy-Si(4-y) (0 < y < or =4), Si6 rings, and non-bridging oxygen hole center defects were formed in the films with the sputtering power increasing. The appearance of the three absorption bands was due to the stretching and asymmetric stretching vibration of Si--O--Si bond and the vibration of O--Si--O bond corresponding to the above mentioned structures in the SiOx films.
RESUMEN
Three different inorganic-organic hetero-junctions (A: ITO/SiO2/Alq3/Al, B: ITO/Alq3/SiO2/Al and C: ITO/SiO2/Alq3/SiO2/Al) were fabricated. The emission can be observed only under positive bias in devices A and B, but under both biases in device C according to their brightness waveforms. With increasing voltage, the increase in blue emission in devices B and C is faster than that in green emission. This is because that the recombination of hot electrons and holes, i.e., electron-hole pairs, produced blue emission in devices B and C, and the recombination of electrons injected from Al with the accumulated holes, which are excited by hot electrons, produced green emission in device A. Hence, the emissions of the devices are attributed to not only the recombination of electrons and accumulated holes, but also the cathodoluminescence-like (CL-like) emission.