Measurement of 4He-p recoil cross sections

The recoil cross sections of protons induced by ⁴He⁺ particles were experimentally determined in an energy range of 1.3–2.1 MeV at recoil angles of 20° and 30 ° . The angular dependence of the recoil cross section at 2.0 MeV was also measured. By using the principle of detailed balance, a calculation of ⁴He-p recoil cross sections were calculated from p-⁴He phase shift data. Good agreement between the experimental data and theoretical values was found. The results show that recoil cross sections at low energies are non-Rutherford and are larger than the Rutherford value by approximately a factor of 2 at 2.0 MeV.     

The calculation of the differential cross sections for recoil protons in 4He-p Scattering

The equation relating phase shift to energy given by the effective range theory for charged particle reactions and the effective range parameters which can well fit the experimental data of P-⁴He elastic scattering have been used to obtain the phase shifts and differential cross sections of protons in p-⁴He elastic scattering. Thereafter the differential cross section of recoil protons in ⁴He-p elastic scattering are calculated through the principle of detailed balance and compared with the experimental data and Rutherford cross sections. Better consistency between experimental and theoretical values than in previous work is achieved.     

Deuterium depth profiling in polymers using heavy ion elastic recoil detection

We have used ²⁰Ne and ⁴⁰Ar beams with energies between 3 and 8 MeV for elastic recoil detection (ERD) analysis of hydrogen isotopes in polymer samples and have also studied the depth resolution and the radiation damage. For the investigation of polymer mixtures it was possible to improve the depth resolution of ERD down to 8 nm FWHM with-out changing the experimental setup of conventional ERD, due to the higher energy loss factor of heavier ions and a reduced stopper foil thickness. For an improved surface depth resolution heavier ions are suitable, whereas lighter elements have a larger profiling depth. We found a ²⁰Ne beam with an energy between 4 and 6 MeV to have a maximum analysing depth of 380 nm with a near surface depth resolution of 9 nm; however, for high resolution ⁴⁰Ar-ERD measurements this maximum profiling depth is reduced to 90 nm. Due to the larger Rutherford scattering cross-section of heavier ions the measuring time decreases with increasing ion mass. We have investigated the ion beam radiation damage in polymer samples and introduced beam current density limits related to polystyrene samples. These results are supported by model calculations which give approximated values of the radiation damage.     

Depth profiling of hydrogen by detection of recoiled protons

The elastic recoil detection technique (ERD) using a 2.5 MeV ⁴He beam for depth profiling of hydrogen in the near-surface regions of solids is described. The optimization of the experimental conditions such as scattering geometry and analyzing beam energy is discussed. The factors limiting the depth resolution of the method have been evaluated showing that a depth resolution of the order of 20 nm can be obtained. Also presented are typical applications for hydrogen profiling in a silicon matrix.     

Rutherford backscattering spectroscopy and elastic recoil detection analysis with lithium ions – The better alternative to helium?

Rutherford backscattering spectroscopy (RBS) and elastic recoil detection analysis (ERDA) with lithium ions are compared to using helium ions. The availability and accuracy of backscattering cross-section and stopping power data for incident Li ions are reviewed, and energy broadening contributions due to detector resolution and energy loss straggling are discussed. Theoretical calculations of the depth resolution are compared with experimental data for RBS from Nb/Co multilayers and foil-ERDA from amorphous hydrogenated carbon multilayers. In RBS about the same or better depth resolution with Li than with He is achieved, while in ERDA for the detection of hydrogen isotopes the depth resolution is increased by a factor of about 1.5 compared to incident He.     

Development of a non-destructive micro-analytical method for stable carbon isotope analysis of transmission electron microscope (TEM) samples

The biogenicity of ancient morphological microfossil-like objects can be established by linking morphological (e.g. cell remnants and extracellular polymeric matrix) and chemical (e.g. isotopes, biomarkers and biominerals) evidence indicative of microorganisms or microbial activity. We have developed a non-destructive micro-analytical ion beam system capable of measuring with high spatial resolution the stable carbon isotope ratios of thin samples used for transmission electron microscopy. The technique is based on elastic scattering of alpha particles with an energy of 2.751 MeV. At this energy the ¹³C cross section is enhanced relative to the pure Rutherford cross section for ¹³C, whereas the ¹²C cross section is reduced relative to its pure Rutherford cross section. Here we report the initial results of this experimental approach used to characterize ultramicrotomed sections of sulfur-embedded graphite and microbial cells.     

Reliability,detection limit and depth resolution of the elastic recoil measurement of hydrogen

Reliability, detection limit and depth resolution were studied in the elastic recoil measurement of hydrogen mainly in silicon compounds by bombardment with argon ions accelerated up to 50 MeV. For the quantitative determination of hydrogen, recoil silicon atoms proved to serve satisfactorily as an internal monitor. The detection limit was shown to be about 1 to 2×10¹² (atoms/cm² for hydrogen on surface and about 1 wt. ppm for hydrogen in bulk. The depth resolution was found to be about 50 nm in most silicon compounds.     

3D hydrogen profiling by elastic recoil detection analysis in transmission geometry

An analytical procedure and a simulation-optimization algorithm are described for hydrogen determination based on elastic recoil detection induced by low-energy ⁴He ions ( 3 MeV) using transmission geometry. Hydrogen concentration depth profiles can be derived from the experimental recoil spectra for a depth range of up to 6 μm with a resolution better than 40 nm at the surface. The method is applied to thin polyimide films irradiated by high-energy heavy ions. The 3D hydrogen distribution is determined with a ⁴He⁺ mubeam. A high-hydrogen-concentration zone below the surface is shown. The hydrogen distribution is seen to evolve during the ⁴He⁺ irradiation.     

Depth profiling of lithium by use of the nuclear reaction 7Li(p, α)4He

The nuclear reaction ⁷Li(p, α)⁴He induced by a primary beam of 1.5 MeV protons was used for measuring depth profiles of Li in Al. From the experiments with a detection angle of 90° a detection sensitivity of about 400 ppm was obtainable for a proton incidence at 30° from the surface. The best depth resolution was about 0.1 μm at 85° incidence. The sampling depth was over 17 μm at 50° incidence. These results are in good agreement with theoretical predictions. After the measurement of the reaction cross section, the applicability of the method to analyzing Li behaviour in solids was experimentally demonstrated on an AlLi (3.53 at.%) alloy.     

Cross Section Measurement for 199Hg(n,n′)199m Hg Reaction from 0.78 to 6.3 MeV

Cross sections for the ¹⁹⁹Hg(n, n′)^199m Hg reaction have been measured at 10 energy points from 0.78 to 6.3 MeV by the activation method. Monoenergetic neutrons below 2 MeV were produced by the ⁷Li (p, n)⁷Be reaction and those above 2 MeV were produced by the D(d, n)³He reaction using a 5.5 MV Van de Graaff accelerator. The neutron flux was determined with a proton recoil telescope counter and In-foils. The measured cross sections were expressed by an empirical formula. The fission spectrum averaged cross section calculated with this formula is 238.3 mb for the Watt-type fission spectrum, and is about 14% smaller than that recently measured by three of the authors.     

Energy Dependence of MeV He+ Ion-Induced Re-Emission of Hydrogen Isotopes Implanted into Graphite

The energy dependence of MeV He⁺ ion-induced re-emission of hydrogen isotopes (H and D) implanted into graphite has been measured by means of the elastic recoil detection (ERD) technique in order to clarify the collision process for the ion-induced detrapping. The experimental re-emission profiles have been analyzed by solving the mass balance equations, in which the ion-induced detrapping cross section σ _d and the rate constants of the retrapping Σ ^T and local molecular recombination K between an activated hydrogen atom and a trapped one are taken into account. The values of σ _d and K/Σ _T have been determined from the best-fit analytical solution to the experimental re-emission profiles. It has been found that the average values of σ _d and K/Σ _T for H are twice as large as those for D, which is the so-called isotope effect.

It has been shown that the experimental values of σ _d and their energy dependence agree well with the theoretical ones, which are calculated using the power-law approximations for Thomas-Fermi potential, on the assumption that the ion-induced detrapping of hydrogen isotopes takes place due to elastic displacement collisions with energetic carbon recoils produced by incident MeV He⁺ ions.     

Coincident Rutherford Backscattering Spectrometry: A novel technique for measuring charge state distributions in violent ion-atom collisions

Charge-state distributions in violent ion-atom collisions were investigated using a novel combination of traditional Rutherford backscattering spectrometry (RBS), time-of-flight (TOF) coincidence, and position-imaging techniques. The combination is termed Coincident Rutherford Backscattering Spectrometry (CRBS). A special apparatus was built in which the backscattered and recoil ions are time and charge state correlated. CRBS measurements for 0.5 and 0.6 MeV He⁺-Ar collisions are presented. From the recoil ion-projectile ion coincidence measurements of the charge state distributions, it was observed that backscattered projectile ions of the same charge state correlate with different recoil ion charge states and vice versa, indicating that any particular charge state may result from different reaction channels. Moreover, the Ar recoil-ion and He projectile-ion correlation exhibits a strong dependence on the projectile beam energy. An energy deposition model was attempted to account for some of the recoil ion charge state distributions. The model qualitatively accounts for the distributions and confirms that energy loss of a backscattered projectile due to its interaction with the target electrons is very small compared to that due to its interaction with the target nucleus.     

Ionization of He,Ne and Ar atoms by 1.05 MeVamuCq+(q = 2–6) and Arq+(q = 4–14) ion impact

Total “apparent” ionization cross sections and partial cross section of the production of highly ionized recoil ions of He, Ne and Ar in 1.05 MeV/amu highly charged C^q+(q = 2–6) and Ar^q+(q = 4,6,10–14) ion impact have been measured and compared with theoretical prediction and other experimental data. The total ionization cross sections have been found to scale as the square of the effective charge of projectile ions $\text{q}{}^1$, as predicted by theories.     

Hydrogen depth profiling using the 6.46 MeV 1H(19F, αγ)16O resonance by detection of alpha particles

We have utilized the detection of α-particles from the 6.46 MeV ¹⁹F resonance nuclear reaction ¹H(¹⁹F, αγ)¹⁶O instead of measuring the γ-yield to profile the hydrogen concentration versus depth in hydrogen containing materials. A special particle filter was prepared to make the α-particle energy monoenergetic and to eliminate the recoiled particles and the scattered particles. The depth resolution and sensitivity were evaluated from the analyses of a polyester film and H-implanted silicon. Advantages of this method include: (1) the small space required for the detector arrangement, (2) easy utilization of a satisfactory current of highly-charged ¹⁹F ions from a small electrostatic tandem accelerator, (3) a good sensitivity useful for hydrogen depth profiling, even though this cross section is one-fifth that of the ¹⁹F 16.5 MeV resonance for ¹H(¹⁹F, αγ)¹⁶O and one-third that of the ¹⁵N 6.44 MeV resonance for ¹H(¹⁵N, αγ)¹²C, and (4) a maximum probing depth deep enough to be useful.     

DEPTH PROFILING OF ~1H AND/OR ~4He IN SOLIDS BY ERD WITH ~(19)F IONS

1H or 4He depth profiling in 1H or 4He implanted silicon samples was performed by elastic recoil detection (ERD) with multicharged 19F ions at a small accelerator. Optimization of the experimental parameters such as incident ions energy and scattering geometry were calculated by computer simulation. Depth resolution of about 20-30nm at depth of 400nm for 1H and at depth of 300nm for 4He can be obtained, respectively.     

ELASTIC RECOIL DETECTION ANALYSIS OF LIGHT ELEMENTS IN THIN FILMS USING 35 MeV~(35) Cl~(6+) BEAM

In this paper, an elastic recoil detection analysis method is described using 35 MeV ~(35)Cl as incident ions. This method can determine and profile simultaneously H, D, He, C and O or in the other case, H, C, N and O. The depth resolution for the elements heavier than He is better than 20 nm. It has been applied to study the Co/Si and TiN thin films, and the depth profiles of He implanted in monocrystal silicon.     

Measurement of He and H depth profiles in tungsten using ERDA with medium heavy ion beams

Elastic recoil detection analysis method (ERDA) with medium heavy analyzing ion beam and its application for the simultaneous measurement of light elements in a very heavy substrate is presented. The availability of cross section data and the method of cross section calculation for recoiled particles are discussed. Different ion species for analyzing beam are discussed with respect to the cross-section data availability, sensitivity of the method, and the depth resolution. Calculations of depth resolution for each element and maximum depth of analysis for tungsten substrate are presented. The influence of the detector geometry and multiple scattering effects on the depth resolution is discussed. An example spectrum measured on tungsten implanted with He seeded D plasma is shown.     

Stopping power measurements of 20–180 keV 1H and 4He in indium phosphide using thick target backscattering

The stopping power of InP for 20–180 keV ¹H and ⁴He was determined by measuring the absolute backscattering yield of thick InP targets. Several nonideal aspects of surface barrier detectors were observed which should be accounted for when making low to medium energy backscattering yield measurements. These are: non-Gaussian detector resolution, nonlinear detector energy calibration, and ion reflection in the detector Au window. The present ¹H in InP stopping cross section measurements are in good agreement with those recently obtained by Khodyrev et al. using a relative, bulk yield, single spectrum approach. The ⁴He in InP stopping cross section measurements were found to be velocity proportional below 30 keV/amu. The estimated standard error of the measurements is ±7% at 20 keV and ± 4% at 180 keV.     

Development of enhanced depth-resolution technique for shallow dopant profiles

A rapid shrinkage in the minimum feature size of integrated circuits requires analysis of dopants in their shallow source–drain and their extensions with an enhanced depth resolution. Rutherford backscattering spectroscopy (RBS) combining a medium-energy He ion beam with a detector of improved energy resolution should meet the requirement of a depth resolution better than 5 nm at a depth of 10–20 nm in the next 10 years. A toroidal electrostatic analyzer of 4×10⁻³ energy resolution has been used to detect the scattered ions of a medium-energy He ion beam. Five keV As⁺ implanted Si or SiO₂ samples were measured. Depth profiling results using the above technique are compared with those of glancing-angle RBS by MeV energy He ions. Limitations in the energy resolution due to various energy-spread contributions have been clarified.