Electrically active defects in BF2+ implanted and germanium preamorphized silicon

Ultra-shallow p⁺-n junctions have been formed using 15 keV/10¹⁵ cm⁻² BF₂⁺ implantation into both Ge⁺-preamorphized and crystalline 〈1 0 0〉 silicon substrates. Rapid thermal annealing (RTA) for 15 s at 950°C was used for dopant electrical activation and implantation damage gettering. The electrically active defects present in these samples were characterized using Deep Level Transient Spectroscopy (DLTS) and isothermal transient capacitance (ΔC(t, T)). Two electron traps were detected in the upper half of the band gap at, respectively, E_c - 0.20 eV and E_c - 0.45 eV. They are shown to be related to Ge⁺ implantation-induced damage. On the other hand, BF₂⁺ implantation along with RTA give rise to a depth distributed energy continuum which lies within the forbidden gap between E_c - 0.13 eV and E_c - 0.36 eV. From isothermal transient capacitance (ΔC(t, T)), reliable damage concentration profiles were derived. They revealed that preamorphization induces not only defects in the regrown silicon layer but also a relatively high concentration of electrically active defects as deep as 3.5 μm into the bulk.     

Stopping power and energy straggling for small and large energy losses of MeV protons transmitted through polyester films

The stopping power S(E) and the energy straggling $\text{Ω}{}^2\text{(E}{}_{\mathrm{<mtext>i</mtext>}}\text{,}\text{ΔE}\text{)}$ of 0.5 MeV to 2 MeV proton beams in polyester (C₁₀H₈O₄) have been measured in transmission geometry. S(E) is found to be 2% to 4% lower than the Andersen and Ziegler tabulations, assuming the Bragg's additivity rule. The energy straggling $\text{Ω}{}^2\text{(E}{}_{\mathrm{<mtext>i</mtext>}}\text{,}\text{ΔE}\text{)}$ was measured at various beam energies E_i, mean energy losses$\text{ΔE}$ and target thicknesses (from 5.6 μm to 47 μm). The ratio $\text{Ω}\text{Ω}{}_{\mathrm{<mtext>B</mtext>}}$, (where $\text{Ω}{}_{\mathrm{<mtext>B</mtext>}}$ refers to the free electron model in the small energ approximation) of the order of 1.07 for small energy losses ($\text{ΔE}\text{E}{}_{\mathrm{<mtext>i</mtext>}}\text{, ≈ 0.05}$), increases to about 1.5 to 2 for large energy losses $\text{(}\text{ΔE}\text{/E}{}_{\mathrm{<mtext>i</mtext>}}\text{≈ 0.75)}$. For not too small beam energies (E_i?700 keV) and for our targets, a nearly universal curve $\text{Ω(E}{}_{\mathrm{<mtext>i</mtext>}}\text{,}\text{ΔE}\text{)}\text{Ω}{}_{\mathrm{<mtext>B</mtext>}}$ is obtained as a function of the mean relative energy loss $\text{ΔE}\text{E}{}_{\mathrm{<mtext>i</mtext>}}$. For $\text{ΔE}\text{E}{}_{\mathrm{<mtext>i</mtext>}}\text{?0.7}$, the beam energy sp Gaussian, were compared to theoretical predictions $\text{Ω}{}_{\mathrm{T}}$, valid for nearly symmetrical energy loss spectra. Our experimental results Ω are from 0 to 7% larger than the theoretical values $\text{Ω}{}_{\mathrm{<mtext>T</mtext>}}$ up to $\text{ΔE}\text{E}{}_{\mathrm{<mtext>i</mtext>}}\text{≈ 0.8}$. The surface roughness of the targets was ch influence on the experimental results was generally between 1% and 5%, depending on the targets and on E_i.     

Charge exchange observations and analysis in the dite tokamak

Measurements of the enhancement of line intensities from oxygen and carbon ions during beam injection of hydrogen atoms into the DITE tokamak have been made for neutral energies of 25 keV and beam powers up to 2 MW. Observations of the spectrum from O encompass the Lyman series in the XUV region (1s?np, n < 9) and Δn = 1 transitions in the VUV and visible regions. The different selection rules for these transitions allow a differentiation between C/X and electron impact excitation of the different (n,l) states. Using theoretical cross-sections and a cascade model for C/X recombination in to hydrogenic ions, the concentrations of impurity nuclei (eg: O⁸⁺) are determined from the Δn = 1 VUV lines. This analysis is unsuitable for the Lyman series which lack the C/X signature. Their intensity is determined primarily by the ionisation balance, and the excitation from ground state hydrogenic ion. l state mixing is considered. No indication of statistical repopulation of the sublevels is observed for n < 7.     

Irradiation creep of previously irradiated 304 stainless steel in a fast flux environment

Results of a fast flux neutron irradiation experiment designed to investigate the effects of high levels of prior irradiation (to 10²³ n/cm², E > 0.1 MeV) on the irradiation creep of type 304 stainless steel at 700 K (800°F) are reported. The steady state creep coefficient is found to increase by a factor of 7 as the specimen fluence increases from 3 to 10 × 10²²n/cm², (E > 0.1 MeV). A non-linear dependence of strain on stress is exhibited. The results of this study are compared with previously reported stress relaxation data and with predictions of a swelling enhanced irradiation creep model.     

Influence of implantation parameters on the poly(paraphenylene) electrical conductivity

We have studied the influence of implantation parameters (energy E, beam current density j, fluence D) on the transport properties of an electroactive polymer: poly(paraphenylene)PPP. Under appropriate mild conditions (E ≈ 50 keV; j ≈ 0.75 μA, D ≈ 10¹⁶ions/cm²) and with particular ions one can get an electronic conductivity — n-type with alkali ions and p-type wit ions. But with larger parameters the final conductivity is p type and seems to be accounted for by defects.     

Energy distributions of neutral atoms sputtered by very low energy heavy ions

Polycrystalline Cu was sputtered by normally incident, very low energy Ar⁺ ions (E₀ = 40–1000 eV). The kinetic energy (E) distributions of the neutral Cu atoms sputtered normally from the Cu surface were measured, using secondary neutral mass spectrometry. For values of E₀ above approximately 600 eV, the observed energy distributions agreed closely with the Thompson-Sigmund theory. For values of E₀ less than about 600 eV the distributions fell off faster than predicted by the Thompson-Sigmund theory, and the peak value of the distribution shifted to somewhat lower energies. Both these effects were exaggerated as E₀ was further lowered. The average kinetic energy of the sputtered neutral Cu atoms increased with increasing E₀. The rate of this increase was less at higher values of E₀.     

Single- and multiple-electron loss cross-sections for fast heavy ions colliding with neutrals: Semi-classical calculations

Extensive calculations of single, multiple and total electron-loss cross-sections of fast heavy ions in collisions with neutral atoms are performed in the semi-classical approximation using the DEPOSIT code based on the energy deposition model and statistical distributions for ionization probabilities. The results are presented for Ar¹⁺, Ar²⁺, Kr⁷⁺, Xe³⁺, Xe¹⁸⁺, Pb²⁵⁺ and U^q+ (q = 10, 28, 39, 62) ions colliding with H, N, Ne, Ar, Kr, Xe and U atoms at energies E > 1 MeV/u and compared with available experimental data and the n-particle classical-trajectory Monte Carlo (nCTMC) calculations. The results show that the present semi-classical model can be applied for estimation of multiple and total electron-loss cross-sections within accuracies of a factor of 2.From calculated data for the total electron-loss cross-sections σ_tot, their dependencies on relative velocity v, the first ionization potential I₁ of the projectile and the target atomic number Z_A are found and a semi-empirical formula for σ_tot is suggested. The velocity range, where the semi-classical approximation can be used, is discussed.     

Isobaric identification techniques of AMS at CIAE

Some long-lived nuclides, such as ³⁶Cl, ⁴¹Ca, ⁵³Mn, ⁷⁹Se, etc., are very interested in life science, environment science, geo- and cosmo-sciences, nuclear wastes management, and other fields. Taking the advantages in high sensitivity and the strong ability to reduce the interferences from molecular ions and isobars, AMS has been one of the most promising methods for the measurement of these nuclides. However, the sensitivity of AMS is often unsatisfactory due to the interferences of stable isobars especially for medium and heavy radioisotopes. Gas-filled time of flight (GF-TOF), Gas-filled Magnet with a time of flight (GFM-TOF), Bragg Curve detector and energy loss (ΔE) combined with a Q3D magnetic spectrometer (ΔE-Q3D) are among the techniques used or being developed in AMS lab of China Institute of Atomic Energy, in an attempt to further reduce the interferences from isobars. These techniques will be tested in our AMS measurement of ⁵³Mn, ⁷⁹Se, ⁹³Zr, ⁹⁹Tc, etc., for identifying isobaric interferences.     

Effect of fast-neutron irradiation on mechanical properties of stainless steels: AISI types 304, 316 and 347

The effect of low-temperature (< 100° C) fast-neutron irradiation on the room-temperature tensile and hardness properties of stainless steels, AISI Types 304, 316, and 347, was investigated up to a fluence of 1.43 × 10²⁰ n/cm² (E > 1 MeV). Several methods were used for analysis of results and the approach using the irradiation-induced increase in yield stress, Δσ = σ ? σ, where σ_i and σ are the yield stresses of irradiated and unirradiated specimens, respectively, proved to be the best for describing irradiation-hardening. Below saturation fluence, ≈ 4?5 X 10¹⁹n/cm² (E > 1 MeV), it was shown that $\text{Δσ ∝(øt)}\text{1}\text{2}$ in agreement with Seeger's model. Yield points were observed at a fluence of _{1.3 × 10¹⁹ n/cm²} (E > 1 MeV) and above. The results are discussed in relation to transmission electron microscopy results of irradiated materials. The relation between irradiation-induced changes in yield stress and Vickers hardness was described by ΔH = KΔσ, where K = 2.82 for AISI Type 304, and 3 for both AISI Type 316 and AISI Type 347.     

New local model for electronic energy loss and its application to computer simulations of channeling

We used the average of the Thomas-Fermi (TF) electron distribution instead of that of Hartree-Fock (HF) electron distribution as the screening length of an isolated atom. Based on the Firsov theory, we proposed a new Firsov formula of the electronic energy loss which has a simple form ΔE_e(E, b) ∞ S_e(E) exp(γb)/(1 + βb)⁶, where S_e(E) is the electronic stopping cross section, b = p/a, p and a are the impact parameter and the screening length, respectively, and β and γ are the fitting parameters. Using the present screening lengths with the shell effect and the new Firsov formula, the depth distributions of channeling were simulated by the ACOCT code for 20 keV B⁺ ions impinging along the [1 1 0] channel direction of silicon (1 1 0) surface. The ACOCT depth profiles of channeling using the new Firsov (solid) local model for the AMLJ potential are in good agreement with the experimental ones.     

Implantation profiles and sputtering studied by detecting the optical radiation from sputtered particles during ion bombardment

A method of sputter-etching and simultaneous registration of the emitted light is used to obtain depth profiles of implanted Li atoms. Measured mean penetration depths (R_p) and straggling values (ΔR_p) for implanted Li into Ag, V, Si and Al are reported. We find e.g. for 10 keV Li⁺ into $\text{V: R}{}_{\mathrm{n}}\text{= 400 ± 30}\text{A}\text{?}$ and $\text{ΔR}{}_{\mathrm{p}}\text{= 250 ± 30}\text{A}\text{?}$. Known implanted profiles are used as a scale of depth to determine sputtering yields of keV He⁺ ions. With this new method the sputtering yield of 40 keV He⁺ ions bombarding Ag was found to be 0.095 ± 0.020. Sputtering through a thin film is also used to determine sputtering yields. A remarkable increase in the light intensity from excited Ag I atoms is observed during sputtering through the interface between an Ag film and the underlying Al substrate. This is found to be due to a change in the excitation mechanism. Continuous features in the observed emission spectrum have in a few cases been identified as originating from deexcitation radiation of molecules formed in the sputtering process.     

Effect of Stress Ratio on Crack Extension Rate of Fine-Grained Isotropic Nuclear Graphite

Effect of stress ratio on the crack extension rate da/dN was examined for an iso-tropic nuclear graphite IG-11, using tapered double cantilever beam specimens. Loads were applied to the specimens cyclically at a loading rate of 251 N/s in the load range where the stress ratio R range of 0～0.8. Here R is defined as the ratio of the minimum stress intensity factor K _min to the maximum stress intensity factor K _max. The rate da/dN was measured optically using a comparator. Conclusions derived as 1. For a given value of R, crack extension rate da/dN can be expressed as da/dN = C(ΔK)ⁿ. here, ΔK is a stress intensity factor range, i.e. ΔK = K_max ? K_min , and C and n are constants and strongly dependent on R value respectively.

2. Threshold stress intensity factor range ΔK_th which was defined as the point below which no crack extension more than 10 μm was observed after loadings of 10⁵ cycles was related with R-values as ΔK_th /ΔK_tho = (1 ? R)^0.89, (ΔK_tho = ΔK_th at R = 0).

     

Neutron dosimetry and damage calculations for the TRIGA MARK-II reactor in Vienna

In order to improve the source characterization of the reactor, especially for recent irradiation experiments in the central irradiation thimble, neutron activation experiments were made on 16 nuclides and the neutron flux spectrum was adjusted using the computer code STAY'SL. The results for the total, thermal and fast neutron flux density at a reactor power of 250 kW are as follows: 2.1 × 10¹⁷, 6.1 × 10¹⁶ (E < 0.55 eV), 7.6 × 10¹⁶ (E > 0.1 MeV) and 4.0 × 10¹⁶ (E > 1 MeV) m⁻² s⁻¹. respectively. Calculated damage energy cross sections and gas production rates are presented for selected elements.     

The (He, tf) as a surrogate reaction to determine (n, f) cross sections in the 10-20 MeV energy range

The surrogate reaction ²³⁸U(³He, tf) is used to determine the ²³⁷Np(n, f) cross section indirectly over an equivalent neutron energy range from 10 to 20 MeV. A self-supporting ∼761 μg/cm² metallic ²³⁸U foil was bombarded with a 42 MeV ³He²⁺ beam from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory (LBNL). Outgoing charged particles and fission fragments were identified using the Silicon Telescope Array for Reaction Studies (STARS) consisted of two 140 μm and one 1000 μm Micron S2 type silicon detectors. The ²³⁷Np(n, f) cross sections, determined indirectly, were compared with the ²³⁷Np(n, f) cross section data from direct measurements, the Evaluated Nuclear Data File (ENDF/B-VII.0), and the Japanese Evaluated Nuclear Data Library (JENDL 3.3) and found to closely follow those datasets. Use of the (³He, tf) reaction as a surrogate to extract (n, f) cross sections in the 10-20 MeV equivalent neutron energy range is found to be suitable.     

Refractive index tailoring in congruent Lithium Niobate by ion implantation

Refractive index profiles of ion-implanted Lithium Niobate waveguides are investigated. Z⁺ and z⁻ congruent Lithium Niobate samples have been implanted with C³⁺ ions at a fluence of 4 × 10¹⁴ ions/cm². Dark m-lines measurements have been performed on ordinary (n_o) and extraordinary (n_e) indexes for three different wavelengths (532 nm, 632.8 nm, 818 nm) before and after the annealing process. A reconstruction of refractive index profiles by Reflectivity Calculation Method (RCM) is presented and commented. The literature data for nuclear damage regime have been collected and critically examined. n_o and n_e curves as function of the density of energy released in nuclear collisions, E_d, describing the effects of ion implantation on LN refractive indexes has been obtained on the basis of literature data. n_o depth profile, predicted according to n_o(E_d) curve, is in good agreement with the RCM reconstructed one. In the case of n_e, a satisfactory agreement has been reached only slightly modifying the n_e(E_d) curve and considering an alternative RCM profile structure.     

A UHV-compatible ΔE−E gas telescope for depth profiling and surface analysis of light elements

We have developed a compact ΔE−E gas telescope that can easily be incorporated into a standard ultrahigh vacuum ion scattering chamber. If energetic, heavy ions are available as a primary beam, the gas telescope can be used to detect light elastic recoils scattered from the surface region of a sample. The detector consists of a gas ionization chamber in front of a surface-barrier detector. The energy loss signal in the gas (ΔE) is taken in coincidence with the energy signal in the surface-barrier detector (E) to identify both the atomic number and the total energy of the elastic recoil. The design parameters of the detector have been chosen to allow detection of elements from H to O with good depth resolution ( < 100 Å) and submonolayer sensitivity. The mass resolution is adequate to easily separate all elements from H to O.     

Range profiles of medium and heavy ions implanted into SiO2

As, Cs, Xe, Eu and Yb have been implanted into SiO₂ in a typically 10–200 keV energy range. The implanted profiles were analysed using the Rutherford backscattering technique. The obtained projected ranges (R)_p) and projected range stragglings (ΔR_p) are compared with recent predictions due to Ziegler, Biersack and Littmark. While good agreement is obtained between the theoretical and experimental values of R_p, significant deviations are found for ΔR_p.     

Stopping of 0.3-1.2 MeV/u protons and alpha particles in Si

The stopping cross sections ε(E) of silicon for protons and alpha particles have been measured over the velocity range 0.3-1.2 MeV/u from a Si//SiO₂//Si (SIMOX) target using the Rutherford backscattering spectrometry (RBS) with special emphasis put on experimental aspects. A detection geometry coupling simultaneously two solid-state Si detectors placed at 165° and 150° relative to each side of the incident beam direction was used to measure the energies of the scattered ions and determine their energy losses within the stopping medium. In this way, the basic energy parameter, E_x, at the Si/SiO₂ interface for a given incident energy E₀ is the same for ions backscattered in the two directions off both the Si and O target elements, and systematic uncertainties in the ε(E) data mainly originating from the target thickness are significantly minimized. A powerful computer code has been elaborated for extracting the relevant ε(E) experimental data and the associated overall uncertainty that amounts to less than 3%. The measured ε(E) data sets were found to be in fair agreement with Paul’s compilation and with values calculated by the SRIM 06 computer code. In the case of ⁴He⁺ ions, experimental data for the γ effective charge parameter have been deduced by scaling the measured stopping cross sections to those of protons crossing the same target with the same velocity, and compared to the predictions of the SRIM 06 computer code. It is found that the γ-parameter values generated by the latter code slightly deviate from experiment over the velocity region around the stopping cross section maximum where strong charge exchanges usually occur.     

Elastic electron scattering by silver atom

The experimental and theoretical studies of elastic electron scattering by silver atom have been carried out. The experimental investigation was based on crossed beam technique with effusive atomic beam being perpendicularly crossed by electron beam. The measurements were performed at electron-impact energies (E₀) of 10, 20, 40, 60, 80 and 100 eV and for a range of scattering angles (θ) from 10° up to 150°. The absolute differential cross sections (DCSs) have been obtained from the elastic-to-inelastic (the unresolved silver resonant lines 4d¹⁰5p²P_{1/2, 3/2}) intensity ratio at θ = 10° at each E₀. Calculations have been performed using the parameter-free complex optical potential (OP) with the inclusion of spin-orbit interaction for the same E₀. Comparison between present experiment and theory has been made.     

Populations of np terms in deuterium atoms emergent from carbon foils bombarded with D+, D2+ and D3+ ions

We have measured relative beam-foil populations of 2p, 3p, and 4p terms in D⁰ as a function of the projectile energy $\text{(20 ?}\text{E}\text{M}\text{? 500}\text{keV}\text{amu}\text{)}$ for D⁺, D₂⁺, and D₃⁺ ions impinging on carbon foils of various thicknesses (? 2–20 $\text{μg}\text{cm}{}^2$).With D⁺ projectiles, the np populations reach their equilibrium values even in the thinnest foils used. We compare the dependence on energy of these populations to the equilibrium neutral fraction variation for hydrogen (deuterium) beams emerging from a carbon foil and deduce some information concerning beam-foil populations.When molecular projectiles pass through very thin foils, well known molecular effects appear which depend on the dwell time, t, i.e., the time spent by the projectile in the foil. In this work we consider only the long-dwell-time region t > 2 × 10^?15s. We study the variation of R_α = I^molec/I^atom (I^molec and I^atom are the Ly-α intensities per incident deuteron (proton) observed with molecular and atomic projectiles of the same velocity, respectively) with the projectile energy per nucleon ($\text{E}\text{M}$) and the thickness (T) of the foil. For a foil of given thickness, R_α increases with $\text{E}\text{M>}$ and reaches a saturation value R_∞ which decreases when T increases. These results, in agreement with our previous measurements using hydrogen projectiles, indicate that t is not the only parameter relevant to molecular effects. Comparisons are reported between $\text{R>}{}_{\mathrm{\alpha }}\text{(E}\text{M>}$) values obtained (a) with H₂⁺ and D₂⁺ projectiles and (b) with D₂⁺ and D₃⁺ projectiles, using foils of various given thicknesses. Ratios $\text{R}{}_{\mathrm{\beta }}\text{(E}\text{M}$) and $\text{R}{}_{\mathrm{\gamma }}\text{(E}\text{M}$) are also measured using Ly-β and Ly-γ radiations and compared to $\text{R}{}_{\mathrm{\alpha }}\text{(E}\text{M}$) values. An interpretation for some of our results is proposed.