Analysis of sapphire implanted with different elements using artificial neural networks

Five elements (Ti, Fe, Co, Er and Au) were implanted in sapphire to fluences between 8×10¹³ and 5×10¹⁷ at/cm², and energies between 200 and 800 keV. We used Rutherford backscattering to determine the dose and depth of the implanted elements. The data analysis is performed using an artificial neural network (ANN). Here we report a generalisation of previous works where ANNs were successfully applied for specific implantations such as Er in sapphire and Ge in Si. We have now developed a code that it is able to analyse data from implantations of any element with Z between 18 and 83 into sapphire. Although this problem is considerably more complex than single-system ANNs, the ANN developed produced excellent results when applied to experimental data. We discuss the reliability of the ANN and its applicability to the analysis of large batches of implanted samples.     

Study on preventing segregation of erbium atoms to a silicon surface by annealing in oxygen atmosphere at high temperature

The damage produced by implantation of Er ions of 400 keV at a fluence of 5 × 10¹⁵ ions/cm² in silicon was investigated by Rutherford backscattering spectrometry with 2.1 MeV He²⁺ ions with multiple scattering models. It was found that the damage around the Si surface was almost removed after annealing in oxygen and nitrogen atmospheres successively at 1000 °C, and only a small portion of the Er atoms segregated to the silicon surface. Most of the Er atoms diffused to deeper depths because of the affinity of Er for oxygen.     

The range distribution and annealing behavior of Er ions implanted in silicon-on-insulator

The range distribution for energetic 400 keV Er ions implanted in silicon-on-insulator (SOI) at room temperature were measured by means of Rutherford backscattering followed by spectrum analysis. The damage distribution and annealing behavior of implanted Er ions in SOI at the energy of 400 keV with dose of 5 × 10¹⁵ cm⁻² were obtained by Rutherford backscattering technique. It has been found that the damage around the SOI surface had been almost removed after annealed in nitrogen atmosphere at 900 °C, and a lot of Er atoms segregate to the surface of sample with the recrystallization of surface Si of SOI sample after annealing at 900 °C.     

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.     

Influence of UV irradiation and RTA process on optical properties of Si implanted SiO2

Si ion implantation was widely used to synthesize specimens of SiO₂ containing supersaturated Si and subsequent high temperature annealing induces the formation of embedded luminescent Si nanocrystals. In this work, the potentialities of excimer UV-light (172 nm, 7.2 eV) irradiation and rapid thermal annealing (RTA) to enhance the photoluminescence and to achieve low temperature formation of Si nanocrystals have been investigated. The Si ions were introduced at acceleration energy of 180 keV to fluence of 7.5 × 10¹⁶ ions/cm². The implanted samples were subsequently irradiated with an excimer-UV lamp. After the process, the samples were rapidly thermal annealed before furnace annealing (FA). Photoluminescence spectra were measured at various stages at the process. We found that the luminescence intensity is strongly enhanced with excimer-UV irradiation and RTA. Moreover, effective visible photoluminescence which is not observed with a simple FA treatment, is found to be observed even after FA at 900 °C, only for specimens treated with excimer-UV lamp and RTA. Based on our experimental results, we discuss the effects of excimer-UV lamp irradiation and RTA process on Si nanocrystals related photoluminescence.     

Study of doping uniformity of a 200 kV ion implanter by RBS and sheet resistance measurements

The ion implantation uniformity is of vital importance for an ion implanter.In this paper,we report the,uniformity measurement for a large current ion implanter(LC-16 type) by implanting of 190-keV Ar ions into Si to 3×1016 atoms/cm2,followed by Rutherford backscattering spectroscopy(RBS) and sheet resistance measurement providing quantitative information on spatial distribution of dopants.The implant doses obtained from RBS at selected points of the sample give a spatial uniformity of 5%,which are confirmed by the sheet resistance measurement.While sheet resistance is an indirect method for dose evaluation of ion-implanted samples,RBS provides a competent technique for calibration of the ion implantation system.And both measurements show that good uniformity can be achieved for the ion implanter by tuning of the scanning process.     

Release of cesium from zirconia inert matrix

The release upon annealing or irradiation at high temperature of fission products (Cs) from zirconia, a candidate for inert matrix, is studied by Rutherford backscattering experiments. The work is focused on the understanding of the influence of various parameters (mainly the atomic concentration of foreign species and the damage created by an external irradiation) on the diffusion and release of Cs. The results reveal that the Cs mobility is strongly enhanced when the impurity concentration exceeds a threshold of the order of a few atomic per cent. Irradiation with medium-energy heavy ions is shown to cause a further increase of the Cs mobility.     

The property of Si/SiGe/Si heterostructure during thermal budget characterized by HRXRD

Si/SiGe/Si heterostructures grown by ultra-high-vacuum chemical vapor deposition (UHVCVD) were characterized by Rutherford backscattering/Channeling (RBS/C) together with high resolution X ray diffraction (HRXRD). High quality SiGe base layer was obtained. The Si/SiGe/Si heterostructures were subject to conventional furnace annealing and rapid thermal annealing with temperature between 750℃ and 910℃. Both strain and its relaxation degree in SiGe layer are calculated by HRXRD combined with elastic theory, which are never reported in other literatures. The rapid thermal annealing at elevated temperature between 880℃ and 910℃ for very short time had almost no influence on the strain in Si0.84Ge0.16 epilayer. However, high temperature (900℃@) furnace annealing for 1h prompted the strain in Si0.84Ge0.16 layer to relax.     

Atomistic modeling of the effects of dose and implant temperature on dopant diffusion and amorphization in Si

We discuss atomistic simulations of ion implantation and annealing of Si over a wide range of ion dose and substrate temperatures. The DADOS Monte Carlo model has been extended to include the formation of amorphous regions, and this allows simulations of dopant diffusion at high doses. As the dose of ions increases, the amorphous regions formed by cascades eventually overlap, and a continuous amorphous layer is formed. In that case, most of the excess interstitials generated by the implantation are swept to the surface as the amorphous layer regrows, and do not diffuse in the crystalline region. This process reduces the amount of transient enhanced diffusion (TED) during annealing. This model also reproduces the dynamic annealing during high temperature implants. In this case, the local amorphous regions regrow as the implant proceeds, without the formation of a continuous amorphous layer. For sufficiently high temperatures, each cascade is annealed out independently; interstitials and vacancies can escape from the cascade and thus increase dopant diffusion.     

Radiation damage induced by 5 keV Si ion implantation in strained-Si/Si0.8Ge0.2

The damage distributions induced by ultra low energy ion implantation (5 keV Si⁺) in both strained-Si/Si_0.8Ge_0.2 and normal Si are measured using high-resolution RBS/channeling with a depth resolution better than 1 nm. Ion implantation was performed at room temperature over the fluence range from 2 × 10¹³ to 1 × 10¹⁵ ions/cm². Our HRBS results show that the radiation damage induced in the strained Si is slightly larger than that in the normal Si at fluences from 1 × 10¹⁴ to 4 × 10¹⁴ ions/cm² while the amorphous width is almost the same in both strained and normal Si.     

Si related defects in the VUV in silicon multi-energy implanted Type III silica

Some effects on the vacuum ultraviolet optical bands (6-8 eV) produced by implanted Si, using multi-energies ranging from 320 to 35 keV energies to produce a layer of constant concentration in (Type III) silica, approximately 600 nm thick, have been measured. Based on two methods of analyzing the spectra as a function of implanted layer concentration; first, by subtracting the spectrum of an un-implanted sample from each spectrum of the implanted samples and second, subtracting the spectrum of one concentration from the spectrum of the next largest concentration, we have identified band maxima. In the case of the first subtraction the maxima are at ∼7.54, 7.7, and 7.92 eV. In the case of the second subtraction the maxima are at ∼7.5, 7.85, and 7.95 eV. These difference spectra show that the various states have differing rates of increase with increase in Si concentration. The absorption between 6 and 7 eV increases with increasing Si concentration indicating that there is/are a band or bands in this region of the spectra. Because all of the bands that are resolved increase with increasing Si concentration we attribute these bands to Si related electronic states. An estimate of the oscillator strengths of these bands is made by comparison of their peak absorption with that of the E′ optical band at 5.83 eV, f = 0.14 ± 0.05, in the same samples. This comparison shows that all of the resolved bands between 6 and 8 eV have oscillator strengths equal to or larger than the E′ state, consistent with our assignment of the bands to Si related states. By comparing to the spectra from the Si implanted samples, the bands produced by radiation damage in an Ar implanted sample are between 7.3 and 8 eV bands are attributed to Si related states.     

110keV56Fe^1^＋离子注入麦胚中的能量沉积分布

测量１１０ＫＥｖ５６Ｆｅ＾１＾＋离子注入麦胚中的射程为２５７．１ｎｍ。根据测得的＾５＾６Ｆｅ＾１＾＋离子相对浓度随深度的分布和注入离子的总面密度，求得了＾５＾６Ｆｅ＾１＾＋离子绝对浓度随深度的分布。采用ＴＲＩＭ８８程序计算得到了不同浓度上注入离子的阻止本领，从而求得了随深度的能量沉积分布。并讨论了细胞损伤的可能机理。     

Rapid-relocation model for describing high-fluence retention of rare gases implanted in solids

It has been known for a long time that the maximum areal density of inert gases that can be retained in solids after ion implantation is significantly lower than expected if sputter erosion were the only limiting factor. The difference can be explained in terms of the idea that the trapped gas atoms migrate towards the surface in a series of detrapping–trapping events so that reemission takes place well before the receding surface has advanced to the original depth of implantation. Here it is shown that the fluence dependent shift and shape of implantation profiles, previously determined by Rutherford backscattering spectrometry (RBS), can be reproduced surprisingly well by extending a simple retention model originally developed to account only for the effect of surface recession by sputtering (‘sputter approximation’). The additional migration of inert gas atoms is formally included by introducing an effective shift parameter Y_eff as the sum of the sputtering yield Y and a relocation efficiency Ψ_rel. The approach is discussed in detail for 145 keV Xe⁺ implanted in Si at normal incidence. Y_eff was found to increase with increasing fluence, to arrive at a maximum equivalent to about twice the sputtering yield. At the surface one needs to account for Xe depletion and the limited depth resolution of RBS. The (high-fluence) effect of implanted Xe on the range distributions is discussed on the basis of SRIM calculations for different definitions of the mean target density, including the case of volume expansion (swelling). To identify a ‘range shortening’ effect, the implanted gas atoms must be excluded from the definition of the depth scale. The impact-energy dependence of the relocation efficiency was derived from measured stationary Xe concentrations. Above some characteristic energy (20 keV for Ar, 200 keV for Xe), Y exceeds Ψ_rel. With decreasing energy, however, Ψ_rel increases rapidly. Below 2–3 keV more than 90% of the reemission of Ar and Xe is estimated to be due to bombardment induced relocation and reemission, only the remaining 10% (or less) can be attributed to sputter erosion. The relocation efficiency is interpreted as the ‘speed’ of radiation enhanced diffusion towards the surface. The directionality of diffusion is attributed to the gradient of the defect density on the large-depth side of the damage distribution where most of the implanted rare gas atoms come to rest. Based on SRIM calculations, two representative parameters are defined, the peak number of lattice displacements, N_d,m, and the spacing, z_r,d, between the peaks of the range and the damage distributions. Support in favour of rapid rare gas relocation by radiation enhanced diffusion is provided by the finding that the relocation efficiencies for Ar and Xe, which vary by up to one order of magnitude, scale as Ψ_rel=kN_d,m/Δz_r,d, independent to the implantation energy (10–80 keV Ar, 10–500 keV Xe), within an error margin of only ± 15%. The parameter k contains the properties of the implanted rare gas atoms. A recently described computer simulation model, which assumed that the pressure established by the implanted gas drives reemission, is shown to reproduce measured Xe profiles quite well, but only at that energy at which the fitting parameter of the model was determined (140 keV). Using the same parameter at other energies, deviations by up to a factor of four are observed.     

Formation of Si/SiC multilayers by low-energy ion implantation and thermal annealing

Si/SiC multilayer systems for XUV reflection optics with a periodicity of 10-20 nm were produced by sequential deposition of Si and implantation of 1 keV ions. Only about 3% of the implanted carbon was transferred into the SiC, with a thin, 0.5-1 nm, buried SiC layer being formed. We investigated the effect of thermal annealing on further completion of the carbide layer. For the annealing we used a vacuum furnace, a rapid thermal annealing system in argon atmosphere, and a scanning e-beam, for different temperatures, heating rates, and annealing durations. Annealing to a temperature as low as 600 °C resulted in the formation of a 4.5 nm smooth, amorphous carbide layer in the carbon-implanted region. However, annealing at a higher temperature, 1000 °C, lead to the formation of a rough poly-crystalline carbide layer. The multilayers were characterized by grazing incidence X-ray reflectometry and cross section TEM.     

X射线衍射法研究刚玉注入层的结构

用Ｘ射线衍射法和ＰＯＷＤ１２理论计算程序探讨了多晶刚玉Ｆｅ离子注入层的结构变化。     

Trace element quantification in high-resolution Rutherford backscattering spectrometry

The potential of high resolution Rutherford Backscattering (RBS) for identification and quantification of trace elements in thin films was investigated. A beam of 250 keV d⁺ ions from the AN700 van de Graaff accelerator in Linz was used to characterize the composition of an organic multi-element compound, i.e. a thin film of dried human blood on a carbon substrate. It was possible to identify more than 10 chemical elements with high accuracy, in the absence of any matrix effects. For instance, the Fe concentration was determined with a relative error <3% (400 ± 10 ppm), in perfect agreement with standard blood test values. The detection limit of heavy elements with atomic number higher than Fe was found to be below 50 ppm.     

Study of defects in implanted silica glass by depth profiling Positron Annihilation Spectroscopy

Positron Annihilation Spectroscopy (PAS) performed with continuous and pulsed positron beams allows to characterize the size of the intrinsic nano-voids in silica glass, their in depth modification after ion implantation and their decoration by implanted ions. Three complementary PAS techniques, lifetime spectroscopy (LS), Doppler broadening spectroscopy (DBS) and coincidence Doppler broadening spectroscopy (CDBS) will be illustrated by presenting, as a case study, measurements obtained on virgin and gold implanted silica glass.     

Enhancement of ferromagnetism in Ni-implanted HfO2 dielectric thin films

We report thermal annealing and 100 MeV Si⁸⁺ swift heavy ion irradiation effects on the structural and magnetic properties of Ni-implanted HfO₂ thin films. At low Ni doping concentration (∼1%), HfO₂ thin films show ferromagnetic behavior. We clearly demonstrate the cluster free nature of our film using cross-sectional high resolution transmission microscopy and magnetization vs. temperature data. Rutherford backscattering spectrometry is used to estimate the film thickness and to establish that Ni-ions are placed in the HfO₂ matrix. By comparing the results for the annealed and swift heavy ion irradiated samples, it is concluded that the enhancement in magnetic signal is closely related to the dispersion/diffusion of implanted Ni and defect creation such as oxygen vacancies. The results of magnetic force microscopy supported the observation of room temperature ferromagnetism in Ni-implanted HfO₂ films.     

Effect of the annealing atmosphere on the Au site in Er + Au-implanted silica

The Au site in Er + Au-implanted silica has been investigated by X-ray absorption spectroscopy, after annealing at 600 °C in either neutral N₂ or reducing H₂ (4%):N₂ (95%) atmosphere. High-resolution X-ray fluorescence spectra collected near the Au L_III-edge indicate the presence of oxidized Au atoms in the N₂-annealed sample. Correspondingly, the EXAFS analysis shows a weak Au-O coordination only for the sample annealed in neutral atmosphere. For both cases, the EXAFS results evidence the presence of sub-nanometer metallic Au clusters: the cluster size, always below 1 nm, is smaller for the sample annealed in reducing atmosphere. The Au clusters embedded in the Er-doped layer promote a strong enhancement of the Er photoluminescence emission at 1.5 μm.