Effects of annealing temperature and method on structural and optical properties of TiO2 films prepared by RF magnetron sputtering at room temperature

TiO₂ thin film was deposited on non-heated Si(1 0 0) substrate by RF magnetron sputtering. The as-deposited films were annealed by a conventional thermal annealing (CTA) and rapid thermal annealing (RTA) at 700 and 800 °C, and the effects of annealing temperature and method on optical properties of studied films were investigated by measuring the optical band gaps and FT-IR spectra. And we also compared the XRD patterns of the studied samples. The as-deposited film showed a mixed structure of anatase and brookite. Only rutile structures were found in samples annealed above 800 °C by CTA, while there are no special peaks except the weak brookite B(2 3 2) peak for the sample annealed at (or above) 800 °C by RTA. FT-IR spectra show the broad peaks due to Ti-O vibration mode in the range of 590-620 cm⁻¹ for the as-deposited film as well as samples annealed by both annealing methods at 700 °C. The studied samples all had the peaks from Si-O vibration mode, which seemed to be due to the reaction between TiO₂ and Si substrate, and the intensities of these peaks increased with increasing of annealing temperature. The optical band gap of the as-deposited film was 3.29 eV but it varied from 3.39 to 3.43 eV as the annealing temperature increased from 700 to 800 °C in the samples annealed by CTA. However, it varied from 3.38 to 3.32 eV as the annealing temperature increased from 700 to 800 °C by RTA.     

CdTe aggregates in KBr crystalline matrix

In this work, we report the experimental results on the fabrication and optical characterization of Czochralski (Cz) grown KBr single crystals doped with CdTe crystallites. The results of the optical absorption have shown two bands, the first one located at 250 nm demonstrates the incorporation of cadmium atoms in the KBr host followed by a partial chemical decomposition of CdTe, the second band located at 585 nm shows an optical response of CdTe aggregates. Photoluminescence spectra at room temperature before annealing showed a band located at 520 nm (2.38 eV), with a blue shift from the bulk gap of 0.82 eV (E_g (CdTe)=1.56 eV). While the photoluminescence spectra after annealing at 600 °C showed a band situated at 640 nm (1.93 eV), these bands are due to band-to-band transitions of CdTe nanocrystals with a blue shift from the bulk gap at 0.38 eV. Blue shift in optical absorption and photoluminescence spectra confirm nanometric size of dopant. X-ray diffraction (XRD) spectra have shown the incorporation of CdTe aggregates in KBr.     

Structural and optical properties of Au-implanted ZnO films

The structural and luminescence related optical behaviours of Au ion implanted ZnO films grown by magnetic sputtering and their post implantation annealing behaviours in the temperature range of 100-700 °C have been investigated. Optical absorption and transmittance spectra of the films indicate that band edge of Au-implanted ZnO has shifted to high energy range and optical band gap has increased, because the sharp difference of thermal expansion induces the lattice mismatch between ZnO and SiO₂. PL spectra reveal that UV and visible luminescence bands of ZnO films can be improved after thermal annealing due to recovery of defects and Au ions incorporation. Importantly, green luminescence band of 530 nm has been only observed in the Au-implanted and subsequently annealed ZnO films and it enhances with the increasing annealing temperature, which can be related to Au atoms or clusters in ZnO films. Furthermore, X-ray photoelectron spectroscopy measurements reveal that the Au⁰ is dominant state in Au implanted and annealed ZnO films. Possible mechanisms, such as optical transitions of Au atoms or clusters and deep level luminescence of ZnO, have been proposed for green emission.     

Blue-cathodoluminescent layers synthesis by high-dose N, C and B SiO2 implantation

Thermal silicon oxide layers have been implanted at 600 °C with N⁺+C⁺, N⁺+B⁺ and N⁺+C⁺+B⁺ ions. Two different implantation doses have been chosen in order to introduce peak concentrations at the projected range comparable to the SiO₂ density. Some pieces of the samples have been annealed in conventional furnace at 1200 °C for 3 h. After annealing, cathodoluminescence measurements show in all cases a main broad band centered at 460 nm (2.7 eV). High doses of C implantation give rise to an intensity attenuation. Phases formed in the oxides have been investigated by Fourier transform infrared spectroscopy before and after annealing. The spectra suggest that N incorporates as BN and probably as a ternary BCN phase in the triply implanted samples, while C seems to bond mainly with B. Boron is also bonded to O in B-O-Si configuration. Depth structure and quantitative composition of the films were deduced from fittings of the spectroscopic ellipsometry measurements.     

Preparation and luminescent characteristic of Li3NbO4 nanophosphor

Synthesis and luminescence properties of Li₃NbO₄ oxides by the sol-gel process were investigated. The products were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy and absorption spectra. The PL spectra excited at 247 nm have a broad and strong blue emission band maximum at 376 nm, corresponding to the self-activated luminescence of the niobate octahedra group [NbO₆]⁷⁻. The optical absorption spectra of the samples sintered at temperatures of 600 and 700 °C exhibited the band-gap energies of 4.0 and 4.08 eV.     

Thermal stability of CdZnO thin films grown by molecular-beam epitaxy

CdZnO thin films with near-band-edge (NBE) photoluminescence (PL) emission from 2.39 eV to 2.74 eV were grown by plasma-assisted molecular-beam epitaxy on c-plane sapphire substrates with 800 °C in situ annealing. CdZnO thin films evolve from pure wurtzite (wz) structure, to mixture of wz and rock-salt (rs) structures confirmed by X-ray diffraction studies. Rapid-thermo-annealing (RTA) was performed on in situ annealed CdZnO samples. Pure wz CdZnO shows insignificant NBE PL peak shift after RTA, while mixture structure CdZnO shows evident blue shifts due to phase change after annealing, indicating the rs phase CdZnO changes to wz phase CdZnO during RTA process.     

Influence of CH3COO on the room temperature photoluminescence of ZnO films prepared by CVD

ZnO films with strong c-axis-preferred orientation have been prepared by a single source chemical vapor deposition technique using zinc acetate as source material at the growth temperature of 230 °C. The strong UV and blue emissions were observed in the photoluminescence spectra of as-grown films. A small quantity of residual zinc acetate was reserved on the surface of as-grown ZnO films and the emission mechanism of blue luminescence was nearly related to the CH₃COO^- of unidentate type. The blue emission disappeared and the green emission appeared after annealing treatment. The green emission is related to the singly ionized oxygen vacancies.     

Photoluminescence from Er-doped silicon rich oxide thin films

 Photoluminescence (PL) properties of Er-doped silicon rich oxide thin films deposited on Si substrate by co-evaporation of silicon monoxide and Er under different atmospheres are investigated. The samples exhibit luminescence peak at 1.54 μm which could be assigned to the recombination in intra-4f Er³⁺ transition. PL shows that this transition is highest when ammonia atmosphere is used during deposition followed by an annealing temperature at 850 °C in 95% N₂+5% H₂ gas (forming gas). In fact, we believe that the presence of the N atoms around Er ions increases the intensity of the 1.54 μm luminescence.     

Improvement of photoluminescence mechanism of CTA-treated Si-implanted SiO2 films by using RTA

In this paper, a shift in the photoluminescence (PL) peak from blue to near-infrared region was observed in the Si⁺-implanted 400-nm-thick SiO₂ films with the rapid thermal annealing (RTA) method only. As the Si⁺-fluence was 1×10¹⁶ ions/cm², a blue band was observed in the films after RTA at 1050 °C for 5 s in dry-N₂ atmosphere; then, the band shifted from blue to orange upon increasing the holding temperature of RTA to 1250 °C in the films after the isochronal RTA in dry N₂. Furthermore, while the fluence was increased to 3×110¹⁶ ions/cm² and the holding temperature was at the same range between 1050 and 1250 °C, the PL peak occurred between red and near-infrared regions. Although the RTA and conventional thermal annealing (CTA) methods produce a similar mechanism, the CTA method needs a much longer annealing-time and a higher Si⁺-implanted dose than the RTA method for producing the same shift and intensity of PL peak from the as-implanted sample. Therefore, the RTA method can produce the mechanism in the Si⁺-implanted sample with the PL energy between blue and near-infrared band in place of the CTA method.     

Annealing effect on planar waveguides in LiNbO3 produced by oxygen ion implantation

We reported on planar waveguides in stoichiometric lithium niobate fabricated by 4.5 MeV oxygen ion implantation with a dose of 6 × 10¹⁴ ions/cm² at room temperature. After ion implantation, these samples were annealed at 240 °C, 260 °C, and 300 °C for 30 min. We investigated annealing effect on the guiding modes and near-field images in the waveguides by prism-coupling method and end-face coupling method respectively. We found that for the extraordinary refractive index a positive alternation occurred in the near-surface region while a negative alternation happened at the end of ion track. Moreover, we measured the transmission spectra for the pure sample and implanted samples before and after annealed at different temperatures, and we observed an absorption peak at ∼480 nm (2.6 eV) in all of these SLN samples.     

Analysis of the effect of annealing on the photoluminescence spectra of Cu ion implanted ZnS nanoparticles

In the present study, we report the photoluminescence (PL) study of nanoparticles of ZnS implanted with Cu⁺ ions at the doses of 5×10¹⁴, 1×10¹⁵ and 5×10¹⁵ ions/cm² and annealed at 200 and 300 °C. The photoluminescence spectra of the samples implanted at lower doses of 5×10¹⁴ and 1×10¹⁵ ions/cm² and annealed at 200 and 300 °C showed peaks at around 406, 418 and 485 nm. The PL emission peak at 485 nm was attributed to the transition of electrons from conduction band of ZnS to the impurity level formed by the implanted Cu⁺ ions. In the PL spectrum of the sample implanted at the highest dose of 5×10¹⁵ ions/cm², in addition to the emission peaks observed in the PL spectra of the samples implanted at lower doses, a peak at around 525 nm, the intensity of which decreased with increase in the annealing temperature, was observed. The emission peak at 525 nm was attributed to the transitions between sulfur and zinc vacancy levels. The full width at half maximum (FWHM) of the emission peak at 406 nm was observed to decrease with increase in annealing temperature, indicating lattice reconstruction. The observation of copper ion impurity related peak at 485 nm in the PL spectra of samples of the present study indicated that the doping of copper ions into the ZnS lattice is achievable by implanting Cu⁺ ions followed by annealing.     

Structure and luminescent properties of LaNbO4 synthesized by sol-gel process

The luminescence properties of LaNbO₄ synthesized by the citric gel process were investigated. The crystallized orthorhombic and monoclinic biphasic structure forms at temperatures below 1100 °C and well-crystallized monoclinic LaNbO₄ is obtained by heat treatment at a temperature of 1200 °C for 3 h. All of LaNbO₄ phosphors derived from the citric gel method exhibit red-shifted excitation spectra as the calcining temperature increased from 700 to 1200 °C. The effect of the heat treatment conditions on the peak shape and the peak positions of the photoluminescence (PL) emission are undetectable, and the PL spectra excited at 260 nm have a blue emission band maximum at 408 nm, corresponding to the self-activated luminescence center of LaNbO₄. The sample heat treated at 1100 °C for 3 h showed the highest absorption and fluorescence intensities among the prepared samples.     

Microstructural evolution upon annealing in Ar-implanted Si

The annealing effects of crystalline silicon (Si) implanted with argon (Ar) ions at a dose of 2 × 10¹⁶ Ar⁺/cm² at room temperature and subsequently annealed at 400-1100 °C for 30 min were investigated. The samples were analyzed by transmission electron microscopy and Raman spectroscopy. Before and after annealing up to 600 °C, an amorphous layer is formed but Ar bubbles are not observed in the damage layer. After annealing at 800 °C, argon bubbles are observed together with extended defects. The damage layer evolves into a polycrystalline structure. After annealing at 1100 °C; exfoliation occurs on the sample surface, and microtwin lamellas form in the damage layer. Raman scattering revealed that a strong recrystallization occurs from 600 °C to 800 °C. The results were compared with the case of helium implantation, with particular focus on bubble formation mechanisms.     

Oxygen contaminants affecting on the electronic structures of the carbon nano tubes grown by rapid thermal chemical vapor deposition

Oxygen-related electronic structures of CNTs (carbon nanotubes) grown by rapid thermal chemical vapor deposition (RT-CVD) have been investigated by using partial electron yield near edge X-ray absorption spectroscopy (PEY-NEXAFS) and X-ray photoelectron spectroscopy (XPS). On the CNT surface with increased oxygen resulting from e-beam irradiation under the O₂ gas environment, C k-edge NEXAFS spectra showed an increase of the oxygen-related resonance peaks ranging from 287 to 289 eV whereas the sp² related peak at 285.4 eV was nearly unchanged. After the complete removal process of the oxygen atom on the surface by annealing the sample at 500 °C for 30 min, C K-edge spectra showed an abrupt decrease of the oxygen-related resonance peaks in 287-289 eV and an increase of the sp² related peak at 285.4 eV, indicating that the degree of crystallinity in the CNT sample was improved.     

Effects of neutron irradiation and subsequent annealing on the optical characteristics of sapphire

In this paper, the effect of neutron irradiation on sapphire single crystal with fast neutron of 1.0×10¹⁸ and 1.0×10¹⁹ neutrons/cm² has been investigated along with the effect of annealing temperature. It is found that the colorless transparent sapphire single crystals were turned yellow after 10 MeV fast neutron irradiation at room temperature. There are peaks at 206, 230, 258, 305, 358 and 452 nm after neutron irradiation. And the intensity of optical absorption bands decrease with wavelength and annealing temperature. A new absorption peak at 452 nm was found after isothermal annealing at 400 °C for 10 min, which was ascribed to F₂⁺ color center. Because of the recombination of interstitial ions and vacancies, color centers were almost removed after annealing at 1000 °C. The TL peaks were found to shift to higher temperature after neutron irradiation. And a higher fluence of the neutron irradiation would result in deep traps revealed as the new TL peaks at 176 and 227 °C.     

Intense red upconversion fluorescence emission in NIR-excited erbium-ytterbium doped laponite-derived phosphor

In this report the optical properties and energy-transfer frequency upconversion luminescence of Er³⁺/Yb³⁺-codoped laponite-derived powders under 975 nm infrared excitation is investigated. The 75%(laponite):25%(PbF₂) samples doped with erbium and ytterbium ions, generated high intensity red emission around 660 nm and lower intensity green emission around 525, and 545 nm. The observed emission signals were examined as a function of the excitation power and annealing temperature. The results indicate that energy-transfer, and excited-state absorption are the major upconversion excitation mechanism for the erbium excited-state red emitting level. The precursor glass samples were also heat treated at annealing temperatures of 300 °C, 400 °C, 500 °C, and 600 °C, for a 2 h period. The dependence of the visible upconversion luminescence emission upon the annealing temperature indicated the existence of an optimum temperature which leads to the generation of the most intense and spectrally pure red emission signal.     

Photoluminescence properties of SiNx/Si amorphous multilayer structures grown by plasma-enhanced chemical vapor deposition

Very thin (nanometric) silicon layers were grown in between silicon nitride barriers by SiH₂Cl₂/H₂/NH₃ plasma-enhanced chemical vapor deposition (PECVD). The multilayer structures were deposited onto fused silica and silicon substrates. Deposition conditions were selected to favor Si cluster formation of different sizes in between the barriers of silicon nitride. The samples were thermally treated in an inert atmosphere for 1 h at 500 °C for dehydrogenation. Room-temperature photoluminescence (RT-PL) and optical transmission in different ranges were used to evaluate the optical properties of the structures. UV-VIS absorption spectra present two band edges. These band edges are well fitted by the Tauc model typically used for amorphous materials. RT-PL spectra are characterized by strong broad bands, which have a blue shift as a function of the deposition time of the silicon layer, even for as-grown samples. The broad luminescence could be associated with the confinement effect in the silicon clusters. After annealing of the samples, the PL bands red shift. This is probably due to the thermal decomposition of N-H bonds with further effusion of hydrogen and better nitrogen passivation of the nc-Si/SiN_x interfaces.     

Effects of annealing temperature on structure and magnetic properties of CoAl0.2Fe1.8O4/SiO2 nanocomposites

CoAl_0.2Fe_1.8O₄/SiO₂ nanocomposites were prepared by sol–gel method. The effects of annealing temperature on the structure and magnetic properties of the samples were studied by X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer and Mössbauer spectroscopy. The results show that the CoAl_0.2Fe_1.8O₄ in the samples exhibits a spinel structure after being annealed. As annealing temperature increases from 800 to 1200 °C, the average grain size of CoAl_0.2Fe_1.8O₄ in the nanocomposites increases from 5 to 41 nm while the lattice constant decreases from 0.8397 to 0.8391 nm, the saturation magnetization increases from 21.96 to 41.53 emu/g. Coercivity reaches a maximum of 1082 Oe for the sample annealed at 1100 °C, and thereafter decreases with further increasing annealing temperature. Mössbauer spectra show that the isomer shift decreases, hyperfine field increases and the samples transfer from mixed state of superparamagnetic and magnetic order to the completely magnetic order with annealing temperature increasing from 800 to 1200 °C.     

X-ray photoemission and X-ray absorption studies of Hf-silicate dielectric layers

Photoelectron spectroscopy and X-ray absorption spectroscopy (XAS) measurements have been performed on HfSi_xO_y and HfSi_xO_yN_z dielectric layers, which are potential candidates as high-k transistor gate dielectrics. The hafnium silicate layers, 3-4 nm thick, were formed by codepositing HfO₂ and SiO₂ (50%:50%) by MOCVD at 485 °C on a silicon substrate following an IMEC clean. Annealing the HfSi_xO_y layer in a nitrogen atmosphere at 1000 °C resulted in an increase in the Si⁴⁺ chemical shift from 3.5 to 3.9 eV with respect to the Si⁰ peak. Annealing the hafnium silicate layer in a NH₃ atmosphere at 800 °C resulted in the incorporation of 10% nitrogen and the decrease in the chemical shift between the Si⁴⁺ and the Si⁰ to 3.3 eV. The results suggest that the inclusion of nitrogen in the silicate layer restricts the tendency of the HfO₂ and the SiO₂ to segregate into separate phases during the annealing step. Synchrotron radiation valence band photoemission studies determined that the valence band offsets were of the order of 3 eV. X-ray absorption measurements show that the band gap of these layers is 4.6 eV and that the magnitude of the conduction band offset is as little as 0.5 eV.     

Slow positron beam study of nitrogen implanted CZ-Si subjected to rapid thermal processing

In this experiment, nitrogen ions were implanted into CZ-silicon wafer at 100 keV at room temperature with the fluence of 5 × 10¹⁵ N₂⁺/cm², followed by rapid thermal processing (RTP) at different temperatures. The single detector Doppler broadening and coincidence Doppler broadening measurements on slow positron beam were carried out to characterize the defects in the as-implanted silicon and RTP-treated samples. It is found that both nitrogen-vacancy complexes (N-Vsi) and oxygen-vacancy complexes (O-Vsi) produced by nitrogen implantation diffuse back to the sample surface upon annealing. But the N-Vsi and the O-Vsi complete with each other and give a summed effect on positron annihilation characteristics. It is shown that the N-Vsi win out the O-Vsi in as-implanted sample and by RTP at 650 °C, 750 °C, which make the S-parameter increase; O-Vsi plays a dominant role after annealing above 850 °C, which makes the S parameter decrease.