Three-dimensional depth profiles of boron ions implanted in SiO2

Silicon dioxide films were implanted at room temperature with boron ions at 7° and 35°. Implantation energies ranged from 20 to 250 keV and the dose was 5×10¹⁴ ions/cm². The depth profiles of ion-implanted boron in SiO₂ were measured using secondary ion mass spectrometry and least-squares fitted to a Pearson distribution. The results demonstrated that the measured depth profiles are well approximated by Pearson distributions, while the experimentally determined range parameters correspond fairly well to the theoretical predictions yielded by the SRIM (stopping and range of ions in matter) Monte Carlo simulation code. The overall differences between the measured and calculated values are 4%, 7%, 15%, 22% and 10%, for projected range, longitudinal range straggling, skewness, kurtosis and transversal range straggling, respectively. Rapid thermal annealing (1050°C for 30 s) of the as-implanted specimens revealed that radiation-enhanced diffusion tends to increase projected range, longitudinal range straggling and transversal range straggling, but decrease (in absolute values) skewness and kurtosis. Notably, the increase in transversal range straggling is smaller than that of longitudinal range straggling.     

Enhancement of luminescence from encapsulated Si nanocrystals in SiO2 with rapid thermal anneals

Potentialities of rapid thermal annealing to enhance the photoluminescence emission of Si nanocrystals in SiO₂ have been investigated. Ion implantation was used to synthesize specimens of SiO₂ containing excess Si with different concentrations. Si precipitation to form nanocrystals in implanted samples takes place with a conventional furnace anneal. The photoluminescence intensity and the peak energy of emission from Si nanocrystals depend on implanted ion fluence. Moreover, the luminescence intensity is strongly enhanced with a rapid thermal anneal prior to a conventional furnace anneal. The luminescence intensity, however, decreases with a rapid thermal anneal following a conventional furnace anneal. It is found that the order of heat treatment is an important factor in intensities of the luminescence. Moreover, the luminescence peak energy is found to be dependent, but a little, on thermal history of specimens. Based on our experimental results, we discuss about the mechanism of an enhancement of the photoluminescence, together with the mechanism of photoemission from encapsulated Si nanocrystals produced in a SiO₂ matrix by ion implantation and annealing.     

Ion beam induced desorption from thin films: SiO2 single layers and SiO2/Si multilayers

The occurrence of O₂ molecular loss from the bulk of SiO₂ single layers and SiO₂/Si multilayers as a result of 50 MeV Cu⁹⁺ irradiation has been investigated. This process did not take place with a significant rate, if it occurs at all. Instead both Si and O are removed from the SiO₂ surface region, releasing molecular O₂. If an elemental Si layer is on top in a multilayer, removal of Si and O with an appreciable rate is not observed. The irradiation creates bubbles in the SiO₂/Si multilayers, which contain O₂. The distinct SiO₂ sublayers remain chemically intact. The bubbles deteriorate the depth resolution in elastic recoil detection.     

Visible photoluminescence of SiO2 implanted with carbon and silicon

The structures formed after sequential implantation of silicon plus carbon in amorphous SiO₂ and annealing presented strong photoluminescence bands in the deep red (1.4–1.6 eV) and green (2.0–2.2 eV) regions of the visible spectrum. The energy and intensity of the bands depended strongly on the temperature and duration of annealing. Different behaviours with post-processing were encountered for the red and green bands, including deexcitation kinetics and structural origin. The FTIR, Raman and HRTEM measurements showed that silicon crystallites were reponsible for the red emitting band while carbon aggregates were probably the origin of the green one.     

A study of the blue photoluminescence emission from thermally-grown, Si-implanted SiO2 films after short-time annealing

Thermal SiO₂ films have been implanted with Si⁺ ions using double-energy implants (200 + 100 keV) at a substrate temperature of about −20°C to total doses in the range 1.6 × 10¹⁶−1.6 × 10¹⁷ cm⁻² followed by short-time thermal processing, in order to form a Si nanostructure capable of yielding blue photoluminescence (PL). The intensity and the peak position of the PL band have been investigated as a function of ion dose, manner of heat treatment, anneal time and anneal temperature. For the formation of blue PL emitting centres, optimum processing conditions in terms of excess Si concentration and overall thermal budget are mandatory. The nature of the observed blue emission is discussed.     

Effects of MeV Si ions bombardment on the thermoelectric generator from SiO2/SiO2 + Cu and SiO2/SiO2 + Au nanolayered multilayer films

The defects and disorder in the thin films caused by MeV ions bombardment and the grain boundaries of these nanoscale clusters increase phonon scattering and increase the chance of an inelastic interaction and phonon annihilation. We prepared the thermoelectric generator devices from 100 alternating layers of SiO₂/SiO₂ + Cu multi-nano layered superlattice films at the total thickness of 382 nm and 50 alternating layers of SiO₂/SiO₂ + Au multi-nano layered superlattice films at the total thickness of 147 nm using the physical vapor deposition (PVD). Rutherford Backscattering Spectrometry (RBS) and RUMP simulation have been used to determine the stoichiometry of the elements of SiO₂, Cu and Au in the multilayer films and the thickness of the grown multi-layer films. The 5 MeV Si ions bombardments have been performed using the AAMU-Center for Irradiation of Materials (CIM) Pelletron ion beam accelerator to make quantum (nano) dots and/or quantum (quantum) clusters in the multilayered superlattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric generator devices before and after Si ion bombardments we have measured Seebeck coefficient, cross-plane electrical conductivity, and thermal conductivity in the cross-plane geometry for different fluences.     

Radiation effect on the photoluminescence properties of Si/SiO2 thin films

Silicon ions were implanted into SiO₂ thin films with various doses and energies. For the films implanted with various ion doses the photoluminescence (PL) intensity of 470 nm firstly increased with the increase of Si ion dose, which is similar to the variation trend of displacement per atom (DPA) number during ion radiation. Further increasing Si ion dose the PL intensity of 470 nm decreased gradually since the neutral oxygen vacancy centers were destroyed. For the samples implanted with different energy the variation trend of PL intensity for 470 nm peak is similar to the result of DPA under different radiation energy according to SRIM2006 simulation. With the increase of radiation energy a new PL peak at 550 nm appeared because of the variation of defect type. Combining with the simulation results and PL spectra the radiation effect on Si/SiO₂ thin films were proposed.     

CeO_2/SiO_2吸附剂的制备及其对碘酸根的吸附

以多孔二氧化硅为载体、六水合硝酸铈为原料,采用真空灌注法制备了CeO_2/SiO_2吸附剂,并利用扫描电镜(SEM)、X射线衍射(XRD)、红外光谱(IR)等方法对其进行表征。同时,通过静态和动态吸附实验探究了CeO_2/SiO_2对碘酸根的吸附和脱附行为,考察了pH、反应时间、碘酸根浓度以及共存阴离子等因素对CeO_2/SiO_2吸附性能的影响。研究结果表明:CeO_2/SiO_2在较广的pH值范围内对碘酸根有较高的吸附率,吸附过程符合准二级动力学模型以及Langmuir和Redlich-Peterson模型;共存阴离子对吸附的影响大小为NO_3~-SO_4~(2-)HCO_3~-H_2PO_4~-≈PO_4~(3-);动态吸附实验的柱利用率高达90.96%,且穿透曲线符合Thomas模型;通过IR谱图分析推测CeO_2/SiO_2的吸附机理为阴离子交换。     

Influence of annealing temperatures and time on the photoluminescence properties of Si nanocrystals embedded in SiO2

We report on the effects of annealing conditions on the photoluminescence from Si nanocrystal composites fabricated by implantation of Si ions into a SiO₂ matrix, followed by thermal treatment in a nitrogen atmosphere. The evolution of the photoluminescence under different annealing temperatures (900–1100 °C) and annealing time (0.5 up to 5 h) were systematically studied for the implanted samples. After annealing the spectra presented two photoluminescence bands: one centered at 610 nm and another around 800 nm. Combined with transmission electron microscopy, we conclude that the photoluminescence behavior of the two bands suggests different origins for their emissions. The 610 nm band has its origin related to matrix defects, while the 800 nm band can be explained by a model involving recombination via quantum confinement effects of excitons in the Si nanocrystals and the interfacial states recombination process confined in the interfacial region between nanocrystals and SiO₂ matrix.     

Plasma nitridation of thin SiO2 films: AES, ELS and IR study

Auger electron spectroscopy, low-energy electron loss spectroscopy and infrared spectroscopy are used to investigate the nitridation of thin (10–22 nm) thermal SiO₂ in RF soft NH₃ plasma. It is found that plasma action at a substrate temperature of 573 K can completely nitridate the thermal oxide to an oxynitride layer. The layers obtained are macroscopic mixtures of two phases SiO₂ and Si₃N₄, rather than amorphous polymers of Si, O and N.     

Effect of Si implantation on the microstructure of silicon nanocrystals and surrounding SiO2 layer

Si nanocrystals (Si-nc) embedded in a SiO₂ layer have been characterized by means of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). For local Si concentration in excess  8 × 10²¹ Si⁺/cm³, the size of the Si-nc was found to be 3 nm and comparatively homogeneous throughout the whole implanted layer. For local Si concentration in excess of 2.4 × 10²² Si⁺/cm³, the Si-nc diameter ranges from 2 to 12 nm in the sample, the Si-nc in the middle region of the implanted layer being bigger than those near the surface and the bottom of the layer. Also, Si-nc are visible deeper than the implanted depth. Characterization by XPS shows that a large quantity of oxygen was depleted from the first 25 nm in this sample (also visible on TEM image) and most of the SiO₂ bonds have been replaced by Si–O bonds. Experimental and simulation results suggest that a local Si concentration in excess of 3 × 10²¹ Si/cm³ is required for the production of Si-nc.     

添加Al2O3和SiO2的大晶粒UO2芯块制备研究

研究了Al2O3和SiO2添加剂对UO2芯块晶粒尺寸的影响.结果表明加入少量的Al2O3和SiO2,可有效促进烧结过程中UO2芯块的晶粒度长大,过量加入则会阻碍烧结过程中UO2芯块的致密化;在添加量一定的情况下,添加不同比例的Al2O3和SiO2,对芯块晶粒尺寸有较大影响,只添加SiO2,对芯块晶粒尺寸影响不大,Al2O3添加量增加,芯块晶粒尺寸随之增加;添加Al2O3和SiO2促进UO2芯块晶粒长大的机制是在烧结期间发生了液相烧结.     

Formation processes of nickel oxide nanoparticles in SiO2 by metal-ion implantation combined with thermal oxidation

Formation processes of nickel oxide (NiO) nanoparticles (NPs) in silica glass (SiO₂) by implantation of 60 keV Ni⁻ ions combined with thermal oxidation are studied using cross-sectional transmission electron microscopy (XTEM) and Rutherford backscattering spectrometry. In as-implanted state, Ni metallic NPs form within the surface layer of 80 nm thick. The mean depth z and the standard deviation (Δz)^21/2 of Ni atom distribution determined by XTEM were 43 and 15 nm, respectively. After the oxidation at 800 °C for 1 h, z and (Δz)^21/2 became 47 nm and 20 nm, respectively, i.e. the distribution was almost the same except a small diffusional shift to the deeper region. Mean volume of Ni- and NiO-NPs after heat treatments at 800 °C were 27 and 43 nm³, respectively. The larger mean volume of NiO-NPs is explained from the fact that NiO-NPs include both Ni and O atoms, i.e. approximately 2N atoms, while Ni-NPs include Ni atoms only, i.e. N atoms. Both the Ni- and NiO-NPs include 2.4 × 10³ Ni atoms per NP in average. These results indicate that NiO-NPs are formed by oxidation of Ni-NPs without pronounced redistribution of Ni atoms.     

Defect- and strain-enhanced cavity formation and Au precipitation at nano-crystalline ZrO2/SiO2/Si interfaces

Defect- and strain-enhanced cavity formation and Au precipitation at the interfaces of a nano-crystalline ZrO₂/SiO₂/Si multilayer structure resulting from 2 MeV Au⁺ irradiation at temperatures of 160 and 400 K have been studied. Under irradiation, loss of oxygen is observed, and the nano-crystalline grains in the ZrO₂ layer increase in size. In addition, small cavities are observed at the ZrO₂/SiO₂ interface with the morphology of the cavities being dependent on the damage state of the underlying Si lattice. Elongated cavities are formed when crystallinity is still retained in the heavily-damaged Si substrate; however, the morphology of the cavities becomes spherical when the substrate is amorphized. With further irradiation, the cavities appear to become stabilized and begin to act as gettering sites for the Au. As the cavities become fully saturated with Au, the ZrO₂/SiO₂ interface then acts as a gettering site for the Au. Analysis of the results suggests that oxygen diffusion along the grain boundaries contributes to the growth of cavities and that oxygen within the cavities may affect the gettering of Au. Mechanisms of defect- and strain-enhanced cavity formation and Au precipitation at the interfaces will be discussed with focus on oxygen diffusion and vacancy accumulation, the role of the lattice strain on the morphology of the cavities, and the effect of the binding free energy of the cavities on the Au precipitation.     

Investigation of films of YBa2Cu3O7 using Rutherford backscattering spectrometry

Rutherford backscattering spectrometry (RBS) has been applied to films of the high-temperature superconductor YBa₂Cu₃O₇. The films were prepared by rf and dc sputtering and silk-screen printing onto substrates of alumina, sapphire and magnesia. Some of the samples were exposed to various heat treatments in order to promote the superconducting phase. A 2 MeV beam of He⁺ particles from the 3 MV Dynamitron accelerator at Birmingham University's School of Physics and Space Research was employed for the RBS measurements. The composition and the depth profile of the elements in the films were determined by simulating the observed RBS spectra with a simulation software package. The simulations show that the heat treatment causes marked interdiffusion of the film and substrate. The experimental results and the computer simulations shown in this paper illustrate the advantages of using RBS to characterise films of the new superconducting materials.     

Er site in Er + Au-implanted SiO2: Effect of annealing in reducing atmosphere

The Er site in Er + Au-implanted silica has been investigated by x-ray absorption spectroscopy, in particular after annealing in reducing atmosphere (H₂(4%):N₂(95%)) at temperature ranging from 100 to 800 °C. The EXAFS analysis shows that Er ions are surrounded by a first shell of O atoms, while the absence of signal from further coordination shell indicates a disordered site. The Er-O distance is lower than that of the Er₂O₃; it is suggested that the annealing in reducing atmosphere leads to a significant reduction of the first shell coordination number. Correspondingly, in the XANES region of the spectrum, it is observed a decrease in the white line intensity for annealing temperature higher than 400 °C; similar annealing treatments in inert atmosphere did not result in significant changes of the near-edge region of the X-ray absorption spectrum. These results enlighten that the annealing procedure, normally used to tailor the size distribution of the metal clusters present in the matrix and/or to modify the matrix structure, can also have an effect on the site of the Er ions, and possibly on the rare-earth optical properties.     

Positron annihilation on the surfaces of SiO2 films thermally grown on single crystal of Cz-Si

Two-detector coincidence system and mono-energetic slow positron beam has been applied to measure the Doppler broadening spectra for single crystals of SiO₂, SiO₂ films with different thickness thermally grown on single crystal of Cz-Si, and single crystal of Si without oxide film. Oxygen is recognized as a peak at about 11.85 × 10⁻³m₀c on the ratio curves. The S parameters decrease with the increase of positron implantation energy for the single crystal of SiO₂ and Si without oxide film. However, for the thermally grown SiO₂-Si sample, the S parameters in near surface of the sample increase with positron implantation energy. It is due to the formation of silicon oxide at the surface, which lead to lower S value. S and W parameters vary with positron implantation depth indicate that the SiO₂-Si system consist of a surface layer, a SiO₂ layer, a SiO₂-Si interface layer and a semi-infinite Si substrate.     

Structural studies of Ge nanocrystals embedded in SiO2 matrix

Germanium nanoparticles embedded in SiO₂ matrix were prepared by atom beam sputtering on a p-type Si substrate. The as-deposited films were annealed at temperatures of 973 and 1073 K under Ar + H₂ atmosphere. The as-deposited and annealed films were characterized by Raman, X-ray diffraction and Fourier transform infrared spectroscopy (FTIR). Rutherford backscattering spectrometry was used to quantify the concentration of Ge in the SiO₂ matrix of the composite thin films. The formation of Ge nanoparticles were observed from the enhanced intensity of the Ge mode in the Raman spectra as a function of annealing, the appearance of Ge(3 1 1) peaks in the X-ray diffraction data and the Ge vibrational mode in the FTIR spectra. We have irradiated the films using 100 MeV Au⁸⁺ ions with a fluence of 1 × 10¹³ ions/cm² and subsequently studied them by Raman and FTIR. The results are compared with the ones obtained by annealing.