Alpha Particle Backscattering Research Articles

A comparison between the codes SRIM and AlfaMC in the Monte Carlo simulation of alpha-particle backscattering

The well-known code Stopping and Range of Ions in Matter (SRIM) and the more recent code AlfaMC were used in this work to evaluate the backscattering corrections required in the measurement of alpha particle sources. The differences found in the energy and angular distribution of backscattered particles for point sources mounted on backings of aluminum, silver, and platinum, were analyzed taking into account the models of multiple scattering included in each code. The lateral dispersion of alpha particles and the backscattering coefficients obtained with SRIM were in all the cases some greater than those derived with AlfaMC.

TEM Analysis of Deformation Zones in FIB-Prepared Samples of Microploughed Gold (100) and (111) Surfaces

To improve the understanding of the mechanical deformation mechanisms associated with friction, wear, and precision machining processes, a detailed set of microploughing experiments were performed on gold single crystal surfaces. Large single crystals that had an edge length of 1.5 mm and a thickness of 1 mm were used for this work. Since the microplough depths ranged from 100 nm to 1600 nm, it was important that the material be damage free at the surface. This condition was verified by alpha particle backscattering. A stand-alone STM head, having a singlecrystal diamond tip, was used in conjunction with a Digital Instruments Nanoscope Ilia controller to generate the 13 μm long microploughs. The vertical ploughing force was measured using a Mettler AE130 semi-microbalance.After generating the microploughs and measuring their geometry with an AFM, some of the microploughs were cross sectioned for TEM observation.

Photochemical transformation of C 60 and C 70 films

Thin solid films of C 60 and C 70 have been found to be sensitive to UV-visible light. In the absence of oxygen, which acts as a triplet state quencher, C 60 and C 70 have been observed to phototransform from a toluene-soluble to a toluene-insoluble state. This phototransformation has been studied via Raman and FTIR spectroscopies, UV-visible transmission spectroscopy and laser desorption mass spectroscopy. The results of these experiments have been interpreted as evidence for a phototransformation from a van der Waals solid to one in which the fullerenes are linked by covalent bonds. For C 60, it is proposed that a transformation to a polymeric solid has occurred, whereas a similar flux of UV-visible light applied to C 70 is proposed to lead to a random dimerization of the lattice and a much smaller population of higher oligomers. For both phototransformed C 60 and C 70, the covalent bonds between fullerenes can be broken thermally and the phototransformed material returns to the pristine, toluene-soluble state. UV-visible light can also be used to photochemically assist the diffusion of dioxygen into the interstitial voids in the solid C 60 and C 70 lattices. For C 60, a photochemical enhancement of the O 2 diffusion rate by a factor of ~ 10 is observed by alpha particle backscattering, leading to a stoichiometry of ~ C 60O 2. Similar to C 60-polyfullerene, C 60(O 2) x is also toluene insoluble. As a result, these C 60-based films might find photolithographic applications.

Characterization of thin Si1On surface layers on Si by proton and alpha particle backscattering

The stoichiometry and the oxygen areal density of Si1On (n = 0.1–2.0) polycrystalline films prepared on Si backing by deposition from the gaseous phase were determined using proton and 4He ion backscattering. Different methods of film stoichiometry and oxygen areal density determination are compared and the respective oxygen detection limits are discussed.

Analysis of Superconducting Oxide by 7 MeV Alpha Particle Backscattering Analysis

ABSTRACTHigh energy Ion backscattering analysis in combination with recently-developed resonance scattering analysis Is described, with a stress on precise and quantitative oxygen analysis and its successful application to the characterization and quality estimation of high Tc oxide superconductors. Particularly, the present status of high energy ion backscattering analysis, the review of analytical results for YBa2Cu3O7−x, the estimation of composition and crystalline quality of (La1−xSrx)2CuO4 by 7 MeV alpha particle backscattering analysis are described.

Nuclear analysis of zirconium nitride thin films

As part of a development programme for the production of zirconium nitride coatings by radio-frequency sputtering of red-hot zirconium rod targets in a nitrogen atmosphere, a series of thickness and stoichiometry measurements has been performed. A variety of nuclear analysis techniques have been used in the characterisation of the coatings. Concentration depth profiles were obtained using both alpha particle and deuteron backscattering. Nitrogen depth profiles were obtained independently using the 14N(d, α)12C and 14N(d, p)15N nuclear reactions. The results of this investigation confirmed correspondence to stoichiometric ZrN and revealed the compositional uniformity of the deposited layers.

Computer simulation programs for nuclear reaction analysis

Two FORTRAN computer programs have been written to simulate the experimental data obtained in prompt radiation techniques. The first of these programs calculates the emitted particle energy spectrum from the ion beam bombardment of any given target. This program is able to deal with both nuclear reactions and Rutherford scattering and with any experimental geometry. Particular examples cited relate to the use of the 12C(d.p) 13C and 16O(d, α) 14N nuclear reactions and also to alpha particle backscattering. The second program deals with the case of proton induced resonant gamma emission, producing a graph of gamma yield versus incident proton energy, and may be applied to any reaction involving a Breit-Wigner resonance. Examples given are of profiling using the 27Al(p, γ) 28Si resonance at 992 keV and the wider 19F(p, αγ) 16O resonance at 872 keV.

Retention of ion-implanted-xenon in olivine: Dependence on implantation dose

The diffusion of Xe in olivine, a major mineral in both meteorites and lunar samples, was studied. Xe ions were implanted at 200 keV into single-crystal synthetic-forsterite targets and the depth profiles were measured by alpha particle backscattering before and after annealing for 1 hour at temperatures up to 1500°C. The fraction of implanted Xe retained following annealing was strongly dependent on the implantation dose. Maximum retention of 100% occurred for an implantion dose of 3 × 10 15 Xe ions/cm 2. Retention was less at lower doses, with ≥ 50% loss at 1 × 10 14 Xe ions/cm 2. Taking the diffusion coefficient at this dose as a lower limit, the minimum activation energy necessary for Xe retention in a 10 μm layer for 10 7 years was calculated as a function of metamorphic temperature. For example, an activation energy of 50 kcal/mole implies Xe retention may be possible for metamorphic temperatures below 500°C.

Electrical and back-scattering studies of thermally annealed gallium implanted silicon

Abstract Dopant distribution, electrical activity and damage annealing of high-dose (∼5 × 1015 cm2) Ga-implanted silicon samples annealed by conventional thermal annealing have been studied by alpha particle back-scattering, differential Hall effect and ellipsometry measurements. Back-scattering spectra show that there is no long tail of Ga atoms in the as-implanted samples. Upon annealing these samples the damaged amorphous layer recrystallizes at about 570°C by solid phase epitaxy. During the epitaxial regrowth the dopant atom distribution seems to be modified. Further, very high levels of electrical activaton of Ga-atoms (∼3 × 1020 cm−3), much higher than the maximum solubility limit of Ga in Si (4.5 × 1019 cm−3), is achieved by thermal annealing of the sample at ∼570°C. This is comparable to the doping achieved by laser annealing of the Ga implanted Si. All the above three measurements show that there is residual damage in the high dose (≳1015cm−2) implanted samples after the recrystallization at abou...

Thermal annealing and electrical activation of high dose gallium imp lanted silicon

Samples of silicon single crystals implanted with 3 × 1014/ cm2, 1 × 1015/cm2 and 6 × 1015/cm2 Ga ions have been investigated by alpha particle back-scattering before and after annealing, differential Hall effect and ellipsometry measurements. The impurity depth profiles as obtained from the analysis of the back-scattering spectra do not show any long tail of Ga atoms even in the high dose as-implanted samples. Upon annealing, the dopant atom distributions are seen to be modified during recrystallization. High levels of electrical activation of Ga atoms (~3 × 1020 cm-3), exceeding the maximum solid solubility limit of Ga in Si (4.5 × 1019 cm-3) and comparable to those obtained by laser annealing have been achieved by conventional thermal annealing. The above three measurements have clearly shown that there is 20% residual damage in the high dose (6 × 1015 cm2) implanted sample after the recrystallization at about 570°C. This may be related to strain in the lattice at the high concentrations of metastable substitutional Ga atoms. Annealing at higher temperatures reduces the electrical activity of Ga atoms, possibly by driving out the metastable high substitutional concentrations of Ga atoms into electrically inactive clusters or precipitates.

Ion implantation phenomena related to hard bubble suppression in magnetic bubble YIG

Some aspects of the hard bubble suppression mechanism have been investigated in LPE grown magnetic bubble garnets, (Y1.65Sm0.18Lu0.21Ca0.96) (Fe0.96Ge4.04) O12. Following implantation of neon ions at a standard suppression dose of 5*1014 cm-2 collapse field measurements indicate effective hard bubble suppression. For this dose however, 57Fe Mossbauer spectra indicate the pressure of a non-magnetic surface layer while X-ray diffraction traces and alpha particle backscattering measurements indicate that the layer is structurally disordered. These observations are inconsistent with the capping layer model of hard bubble suppression. Implantation of nitrogen ions resulted in similar hard bubble suppression but produced a totally different form of radiation damage. Axial channelling of 800 keV nitrogen ions along the (111) direction is observed.

The study of the curing of lacquer films on tinplate by alpha-particle backscattering

The backscattering of4He+ ions of a few MeV has been used to measure the state of cure of oleo-resinous lacquer films on timplate. The elemental ratio of carbon to oxygen was studied as a function of curing temperature and duration of curing. This parameter could be determined rapidly enough to be used for process control and the precision of the method allowed stoving temperatures to be measured within manufacturing tolerance.

The use of alpha particle back-scattering for the study of printed and coated layers

A 1.8 MeV He-beam from a Van de Graaff accelerator has been used to demonstrate that back-scattering techniques can be usefully applied to study certain problems related to the interaction between coatings and paper substrates and between printing inks and coated or uncoated paper or plastic substrates. In particular, information on distribution profiles of various components can be obtained. The technique and some of its practical aspects are briefly described.

Thin film thickness determination by alpha particle backscattering

A method of determining the thickness of thin films deposited on thick, high mass backing materials by measuring the energy loss of alpha particles backscattered from the backing is described. Film thicknesses from 20 to 500 μg/cm 2 can quickly and easily be determined to an accuracy of 8 percent.

Surveyor 7 Lunar Mission

The spacecraft Surveyor 7 landed on the outer rim of the crater Tycho on January 10, 1968. The landing area was selected to provide contrast with the mare sites of previous Surveyor landings. The surface at this highland site, associated with a major crater, was expected to consist of material that came from depth in relatively recent times. Surveyor 7 carried an alpha-particle backscattering instrument, a soil mechanics surface sampler, a television camera, and auxiliary mirrors and magnets. Data were obtained on the following properties of the lunar surface: topography and geology of the site; character, variety, density, size, distribution, and erosion of rocks; photometry and optical polarization associated with rock surfaces; nature and depth of the surface layer of fine particles; density, bearing capacity, bearing load-penetration relations, cohesion, adhesion, photometry and optical polarization of the fine particulate material; elemental composition and magnetic behavior of fine material and rocks; infrared brightness temperature; thermal inertia; microwave reflectivity. Microwave Doppler measurements were made of the motion of the landing site relative to earth. Pictures were taken of earth through polarizing filters, of lasers on earth, and of the solar corona.

Surveyor 6 Lunar Mission

The spacecraft Surveyor 6 landed near a mare ridge in Sinus Medii November 7, 1967. It carried an alpha-particle backscattering instrument and a television camera. Data were obtained on the following properties of the lunar surface: topography, chemical composition, content of magnetic material, radar reflectivity, density, bearing capacity, modulus of rigidity, adhesion, albedo, photometric function, optical polarization, temperature, and thermal inertia. In general, the surface was strikingly similar to the mare sites where earlier Surveyors had landed. The surface layer of weakly cohesive particles is, however, probably deeper than in Oceanus Procellarum or Mare Tranquillitatus. A number of measurements were made of the velocity of the landing site relative to earth. Observations of the sun showed that the F corona extends out at least 30 solar radii.

Backscattering of alpha particles from thick metal backings as a function of atomic weight

Alpha-particle backscattering from thick metal backings has been studied using two separate counters with geometries of 2 π and approximately 1 π steradians.

Mesh size effects in alpha-particle backscattering

Alpha-particle backscattering is a familiar technique for determining the elemental composition of surfaces. In the present work, the effect of the surface structure of the sample is investigated. It is found that the spectrum of the backscattered α particles depends on the surface structure; hence, the ability to resolve different nuclear species in the sample by this method depends on the nature of the surface. If the linear dimension of the surface structure is of the same order of magnitude as the α-particle range in the material, a significant change in the spectrum of backscattered α particles is observed. For surface structures much larger or much smaller than the α-particle range, normal spectrums are observed.