Depth Distribution Profiles Research Articles

Bragg-Case Synchrotron Section Topography of Silicon Implanted with High-Energy Protons and α Particles

Back-reflection section topography using white-beam synchrotron radiation has been applied for the investigation of silicon implanted with 1 and 1.6 MeV protons and 4.8 MeV α particles. The beam width was limited to 5 μm, and a series of spots in the vicinity of a centrally adjusted reflection were indexed and analysed. The back-reflection section pattern of implanted crystals usually exhibits fringes corresponding to the reflection from the surface and a series of fringes corresponding to the rear region of the shot-through layer, the destroyed layer and the bulk. The patterns were used for direct evaluation of ion ranges and thicknesses of the shot-through layer. The overall characteristics of the obtained patterns were successfully reproduced in simulations based on numerical integration of the Takagi–Taupin equations. The agreement between the simulation and experiment proves that the lattice-parameter depth-distribution profiles can be assumed to be proportional to interstitial-vacancy distributions obtained using the Monte Carlo method from the Biersack–Ziegler theory. The simulation also reproduced interference tails observed in some section patterns. It was found that these tails are caused by the ion-dose change along the beam and they were probably formed due to the interference between the radiation reflected from the bulk and those rays reflected by the rear region of the shot-through layer.

Quantitative analysis of nitride phases determined from CEMS spectra on N + implanted Fe samples

A deconvolution procedure for Conversion Electron Mössbauer Spectroscopy ICEMS) data allowing the quantitative analysis of phase concentration and a visualization of phase depth distribution profiles in nitrogen implanted iron (FeN) is described. An experimental verification and application of this procedure to high dose nitrogen implanted bulk iron are presented. The method permits to demonstrate that the phase transformation in the FeN system is incomplete (i.e. a pure α-Fe phase remains in the surface layer) notwithstanding that the saturation of nitrogen is observed.

Sources of Biogenic Methane to Form Marine Gas Hydrates In Situ Production or Upward Migration?a

Potential sources of biogenic methane in the Carolina Continental Rise -- Blake Ridge sediments have been examined. Two models were used to estimate the potential for biogenic methane production: (1) construction of sedimentary organic carbon budgets, and (2) depth extrapolation of modern microbial production rates. While closed-system estimates predict some gas hydrate formation, it is unlikely that >3% of the sediment volume could be filled by hydrate from methane produced in situ. Formation of greater amounts requires migration of methane from the underlying continental rise sediment prism. Methane may be recycled from below the base of the gas hydrate stability zone by gas hydrate decomposition, upward migration of the methane gas, and recrystallization of gas hydrate within the overlying stability zone. Methane bubbles may also form in the sediment column below the depth of gas hydrate stability because the methane saturation concentration of the pore fluids decreases with increasing depth. Upward migration of methane bubbles from these deeper sediments can add methane to the hydrate stability zone. From these models it appears that recycling and upward migration of methane is essential in forming significant gas hydrate concentrations. In addition, the depth distribution profiles of methane hydrate will differ if the more » majority of the methane has migrated upward rather than having been produced in situ. « less

Codoping effects of As and Xe on ion-beam-induced epitaxial crystallization of Si

We report properties of ice-beam-induced epitaxial crystallization of thin amorphous Si layers, which were made by successive implantations of As and Xe at room temperature into Si(100), as well as by single implantations of As or Xe. The crystallizations were induced by 400 keV Ar irradiations at 350°C. After the crystallization was completed we observed a redistribution of Xe atoms towards the surface, whereas this did not occur when As atoms were codoped with Xe atoms in the initial amorphous Si layer. The velocity of the amorphous-crystal interface motion was substantially enhanced by As atoms in comparison with the Xe-single-doped case. We suggest that because the interface velocity was raised in the As and Xe codoped Si in comparison with the Xe-single-doped Si by the presence of As atoms, the diffusion of Xe atoms towards the amorphous Si layer could not follow the interface moving as the crystallization proceeded. Xe atoms remained in the regrown crystal Si layer and the depth distribution profile did not change.

Diffusion of implanted nickel in diamond

Natural diamonds implanted with 160 keV, 340 keV and 69 MeV nickel ions were annealed at temperatures up to 2200 C and studied by cathodoluminescence. The depth distribution profiles of the implanted nickel and radiation defects were investigated. It was shown that high temperature diffusion strongly influences the distribution both of nickel and of radiation defects. The vacancy-enhanced mechanism of diffusion was supposed for nickel in ion implanted diamond.

Evidence of chemical effects in niobium implanted oxides

We have investigated the influence of chemical bonding and structure of different oxides on niobium implantation effects. For this purpose, single crystals of α-Al 2O 3, TiO 2, MgO and amorphous SiO 2 have been implanted with 150 keV Nb + ions and fluences ranging from 10 16 up to 10 17 ionscm −2. Two different behaviours have been observed depending on ionicity of the studied materials. For more covalent oxides such as α-Al 2O 3, TiO 2 and SiO 2 implanted with low fluences, the implantation profiles are in good agreement with theoretical predictions (TRIM). For high doses (> 5 × 10 16ions/cm −2) the formation of an amorphous layer has been observed in sapphire and rutile. For a typical ionic oxide such as MgO an anomalous depth distribution profile of implanted particles is observed and the major part of implanted niobium is in substitutional sites. The amorphization is not observed even for the highest implantation doses. These results suggest that different chemical effects occur and they could be correlated with the ability to deform octahedral sites in these oxides and space charge effects.

Contouring of SIMOX profiles by oxygen ion energy change

The objective of this work was to determine if, by changing the ion energy during the implant, depth distribution profiles could be contoured to produce improved SIMOX material. In the SIMOX process, oxygen ions are implanted into bare silicon or into silicon through a silicon dioxide capping layer. During the course of the implant, the incoming fast ions sputter silicon atoms from the surface. Through this mechanism, by the end of the implant, the apparent depth of penetration with respect to the original surface will have increased. However, a competing action is at work: oxygen ions retained by the formation of the buried oxide layer will cause swelling. Detailed calculations have been performed, which show that the sputtering effect is approximately compensated by the swelling. Experimentally, by increasing the oxygen beam energy during the implant, improved SIMOX material was formed without the silicon islands normally observed.

Point paramagnetic defects in diamond irradiated by high-energy ions

The spectra of paramagnetic centers (PC) O1 and R5 are observed in natural diamond samples irradiated by high-energy (> 1 MeV/a.m.u) ions. Both PC are the prevailing paramagnetic point centers in the annealing temperature range of 600 to 1100°C. It is shown that the paramagnetic centers O1 are produced practically completely due to inelastic ion collisions. It is found that the spin-Hamiltonian parameters of the paramagnetic centers O1 and R5 depend on the annealing temperature. The dependence is probably related to the modification of the crystal local strains as a result of the annealing. In the cathodoluminescence spectra of the investigated samples the narrow zero-phonon lines (ZPL) ≈︁511.5 and ≈︁509 nm are observed. The annealing kinetics and the depth distribution profiles of their intensities are similar to those of the PC O1 ones. It is suggested, that one of these lines is the optical analogue of PC O1. The 〈100〉 Frenkel pair (Ci + V) is proposed as the model of PC O1. The epuilibrium geometry of the Ci + V center in the neutral charge state is theoretically calculated by the CNDO/2 method using the cluster approximation. Relaxation of the atoms of the first coordination sphere is taken into account. The localisation of the C1 atom along the 〈100〉 axes is found to be more energy profitable than that along the 〈111〉 axes. The distance between the vacancy center and the interstitial atom position in the equilibrium configuration of the defect is about 0.02 nm. [Russian Text Ignored].

Experimental study of point-defect creation in high-energy heavy-ion tracks.

Thin platelets of LiF crystals have been bombarded on the side with Ne (40 MeV/amu), Ar (60 MeV/amu), Kr (42 MeV/amu), and Xe (27 MeV/amu) ions at room temperature in the dose range from ${10}^{8}$ to ${10}^{13}$ ions ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$. Taking into account the large penetration depths of these high-energy ions (\ensuremath{\simeq}1.4, 1.8, 0.6, and 0.2 mm for Ne, Ar, Kr, and Xe, respectively), it was possible to measure the depth distribution profiles of primary point defects (F centers) and aggregated defects (${\mathit{F}}_{2}$ centers) using a microspectrophotometric technique. These defects are localized in tracks surrounding the ion trajectories in which the energy is deposited by the \ensuremath{\delta} rays emitted. Concerning the creation of primary defects, it has been shown that each individual track is saturated with F centers (\ensuremath{\simeq}4\ifmmode\times\else\texttimes\fi{}${10}^{18}$ F centers/${\mathrm{cm}}^{3}$). From the evolution of the F center depth profiles as a function of the ion doses, using a model of saturated tracks, it has been possible to determine the radii of the tracks all along the ion trajectories.These radii, which are of the order of 7.5, 8, 14, and 32 nm at the entrance in the crystals for Ne, Ar, Kr, and Xe, respectively, increase continuously up to the values of 12, 16, 20, and 44 nm during the slowing down of the ions up to the end of the trajectories. In the wide range of energy deposition into electronic processes studied (from 0.2 to 20 MeV \ensuremath{\mu}${\mathrm{m}}^{\mathrm{\ensuremath{-}}1}$), a continuous behavior of the primary-defect creation is observed. This seems to indicate that the same excitonic mechanism is responsible of the primary-Frenkel-pair creation in the volume of the track irradiated by the secondary electrons and other mechanisms such as Coulomb explosion or melting, which could take place in the tracks above a certain dissipated-energy threshold, must be ruled out. Finally, the specificity of damaging with ions compared with other irradiation modes (electrons or electromagnetic radiation) is mainly observed with aggregated defects. Due to the high energy density dissipated in the tracks and saturation with isolated primary defects, a great number of other primary defects are stabilized in the form of various aggregate centers in the anionic and cationic sublattices. With such a complex damage microstructure, the recombination, aggregation, and annealing mechanisms observed are nonconventional. For example, it is shown that the aggregation of F centers into ${\mathit{F}}_{2}$ centers is markedly influenced by the nature and energy of the projectile.

Influence of dose effects on depth distribution of implanted particles

The influence of irradiation dose effects on the depth distribution of implanted atoms for 120 keV gold ion implantation into silicon was investigated. A dynamic computer code DYNA based on the binary collision approximation was used to describe the implantation process. Simulation results were analyzed and compared with the pertinent experimental data and results, which were obtained in the framework of the LSS model. Conclusions related to the substantial influence of dose effects such as range shortening and ballistic mixing on the shape of the depth distribution profile are drawn.

Weathering and Migration of Chernobyl Fall-out in Sweden

In situ gamma spectrometer measurements of the Chernobyl fall-out in Sweden have been made in the Gävle and Studsvik areas. The main objective of the measurements was to study the weathering effects on typical urban surfaces and migration on permeable surfaces. Measurements were made in May, July and September 1986 and in May 1987. The average remaining fraction after 12 months is about 0.4 (excluding decay). No significant differences between typical urban surfaces were found, except for paving stones, which showed a remaining fraction of 0.8. The depth distribution profiles in soil showed a half-value depth of a few centimetres. Activity was found below 20 cm, which indicated other transport mechanisms than pure diffusion. A similar behaviour of all nuclides with respect to both weathering and migration, indicates that the main part of the activity is bound to carrier particles.

Variations in atmospheric trace element deposition studied by INAA of peat cores from ombrotrophic bogs

In the present work INAA is used to determine as many elements as possible in peat samples from ombrotrophic bogs. Results for depth distribution profiles of some elements of particular interest are presented for selected bogs from areas with highly different input from long-range atmospheric transport of pollutants. In addition to information on air pollution, the data provide knowledge about contribution from natural processes to the airborne supply of some elements, such as in the case of selenium.

Decrease in Electrical Resistivity of W Films on GaAs Substrates after High-Temperature Annealing

A specific decrease in the electrical resistivity of W films on GaAs substrates was found after annealing above 800°C in Ar. A decrease in the concentration of oxygen in sputter-deposited W films (0.2 µm thick) with a diffusion of Ga and As atoms from GaAs substrates into the films was also observed after annealing using AES and SIMS measurements. The decrease in the resistivity could be explained by a remarkable W grain growth by applying the Mayadas and Shatzkes grain boundary scattering theory. The grain growth was accompanied by the release of oxygen from the films. Depth-distribution profiles of Ga, As, and O in W/GaAs structures suggest two processes for the release. One is a pile-up of the oxygen which forms Ga-oxide on a W film surface. The other is the evaporation of oxygen from the surface in the form of As-oxide.

A positron annihilation spectroscopy determination of defect depth distribution profiles in electron irradiated Zr and Ti

Abstract Doppler-broadening measurements of the positron annihilation characteristics of both well-annealed and electron irradiated Zr and Ti have been made. Data obtained with the use of both a “hard” (68Ge) and a “soft” (22Na) positron-emitting source were used to yield information about the defect depth distributions of the irradiated materials. Good agreement between these results and theoretical defect profiles, based on electron energy loss calculations, were found for one set of irradiated samples. A striking disagreement between experimental and theoretical defect depth profiles for another set of samples, irradiated under different conditions, was resolved when a hitherto unsuspected H− component of the electron beam was taken into account.

Range and range straggling of 15 to 350 keV 69Ga in amorphous silicon

Abstract Depth distribution profiles of 15 to 350 keV 69Ga+ implanted at room temperature in amorphized silicon have been measured by 4He ion Rutherford backscattering. The measured projected ranges and range stragglings are in excellent agreement with the predictions calculated via realistic Monte Carlo simulations, TRIM code.

Vertical and horizontal distribution of meiofauna in mangrove sediments in Transkei, southern Africa

The depth-distribution profiles of meiofauna in four transects in the Mngazana River, Transkei were studied during summer 1980. Highest densities [±1000(100 cm 3) −1] were encountered within the top 10 cm of the sediment. Nematodes dominated (80%) and the remainder was made up of ciliates, oligochaetes, gastrotrichs, and low numbers of polychaetes, copepods, kinorhynchs and various crustacean larvae. Among chemical parameters Eh correlated most consistantly with distribution, particularly at the lower tidal levels. Temperature and pH appeared to be of lesser importance. The maximum estimated depth of penetration was on average 72 cm at the HW levels; 32 at MW and 23 at LW. The mean dry biomass was estimated at 1073 mg m −2; 941 mg m −2 and 196 mg m −2 at these tidal levels respectively. The importance of preliminary studies designed to estimate the depth distribution of meiofauna is discussed.

Silicon amorphization by ion beam with radiation heating

A study is made of the depth distribution of the amorphous phase and paramagnetic centers in silicon bombarded by P+ and Ar+ ions with energy E = 40 to 50 keV, average current densities j = 0.2 to 15 μA/cm2, and doses Θ= 1015 to 2 × 1016 ions/cm2. Increase in current density and, hence, in sample temperature, results in a smaller thickness of the amorphous layer. In Si layers bombarded by P+ ions with dose Φ ≧ 5 ± 1015 ions/cm2 the depth distribution profile of paramagnetic centers has a dip in the region 0 < x < Rp whose width increases with j. Variations in the depth distribution o f the amorphous phase are calculated using the model of Morehead and Crowder including the dependence of the amorphous cluster radius on the coordinate x along the ion projected range. Assuming the VV-center-impurity interaction to obey a diffusion-controlled mechanism in layers bombarded with P+ ions it is concluded from the theoretical analysis that the diffusion coefficient of phosphorus in the layer is strongly dependent on x. [Russian Text Ignored].

Mechanical and Microstructural Properties of Boron Implanted Beryllium

ABSTRACTHigh dose boron implantation into instrument grade 1–400 beryllium has been found to produce a substantial increase of its wear resistance. A comparison of the friction and wear behavior resulting from two shapes of the boron depth distribution is made. The wear resistance provided by a boron layer of constant (flat) concentration was found to be superior to that of a gradually decreasing (graded) profile. Rutherford backscattering was used to determine the boron depth distribution profiles and transmission electron microscopy was used to examine the microstructure. Electron diffraction pattern analysis provides evidence for the formation of beryllium borides.

Depth distribution profiles of colour centers produced in alkali halides by electron irradiation

Depth distributions of colour centers produced in 〈100〉 KCl crystals by irradiation with 1.0 and 2.0 MeV electrons were measured. A distinct anisotropy in the depth distributions of the optical colouration density as well in the F- and M-center density was observed.

Interdiffusion effects of heat treatment on Ga x In 1-x Sb diodes metallised with gold

A thick gold deposition has been used for metallic contact to GaxIn1-xSb. On a diode arrangement, the interdiffusion of these elements has been studied with heat treatment at 200°C. Only Ga and In diffuse out of the initial interface into the gold top layer, where they form stable compounds. The depth distribution profiles show that the microalloying takes the form of a layered structure of fixed intermetallic phases.