Showing papers on "Fluence published in 1971"

Ionization, thermal, and flux dependences of implantation disorder in silicon

Abstract: Proton channeling effect measurements were used to study the implantation lattice disorder in silicon as a function of ion flux (dose-rate), fluence, implant temperature, ion mass, and the presence of ionizing radiation. For both O+ and Sb+ implantation at 87°K the lattice disorder production is the same for equal total energy into atomic processes/cm3 at a fixed rate of energy into atomic processes/cm3-sec. The disorder production for both light (O+)and heavy (Sb+) ions exhibits a flux dependence at low temperatures and at room temperature. At low temperatures an increase in disorder is observed for increasing flux at constant fluences; however, for low fluence Sb implantation at 300°K, lower disorder is observed with increasing flux. The lattice disorder increases for all ions with decreasing implant temperature from 300°K down to temperatures as low as 38°K, but the variation with temperature is greater for lighter ions. The stimulation of lattice disorder annealing (typically ≍ 10 per cent) b...

Void formation in irradiated Nickel 270

Abstract: Nickel 270 (99.98 per cent nominal purity) was irradiated in EBR-II to fluences ranging from 1 × 1018 to 1.5 × 1022 neutrons/cm2 at temperatures between 375 and 525°C. Voids were observed in all specimens in concentrations of 1 to 3 × 1014/cm3, independent of temperature and fluence. At low fluences the voids were non-homogeneously distributed. These observations are interpreted in terms of void nucleation on sites existing in the material prior to irradiation. The results are compared with other observations on nickel of comparable and higher purity. Large differences exist not only in the magnitude of void concentrations but also in temperature and fluence dependencies. These differences indicate that a single, void nucleation mechanism is not operative and that impurities play an important role in determining the nature and amount of damage produced by neutron irradiation at elevated temperatures.

Flux and fluence dependence of disorder produced during implantation of 11B in silicon

Abstract: The flux and fluence dependence of disorder produced in silicon during the implantation of 11B has been investigated at room temperature, -50°C. and -120°C. Implantations were carried out with 200 keV 11B ions using current densities in the range from 0.06μA/cm2 to 15μA/cm2, and the disorder monitored by measuring the energy spectra of backscattered protons which were incident on the sample at 450 keV parallel to a (110) axis. Significant differences in the dependence of the disorder on 11B flux and fluence were observed between the implantations performed at room temperature and those carried out at the two lower temperatures.

Simulation of high fluence fast neutron damage with heavy ion bombardment

Abstract: 316 stainless steel has been irradiated with 5 MeV Cu ions to a fluence of 2 × 1016 ions/cm2 at 500°C. Transmission electron microscopy of this sample reveals that 6 × 1015 voids/cm2 of average diameter equal to 180 A were produced. A method for correlating the fluence of ions with equivalent neutron fluences is described. This method predicts that the Cu bombardment in this study should produce a microstructure similar to that found in steel irradiated with 2–5 × 1122 neutrons/cm2. A comparison of the ion produced voids with those found after previous neutron irradiation experiments confirms this prediction.

RAMAN SCATTERING OF ION‐IMPLANTED GaAs

Abstract: We report measurements of Raman scattering in ion‐implanted semiconductors. The broadening of the phonon modes produced by lattice strains on Xe ion implantation is measured for GaAs. The measurements show pronounced effects on the linewidth at moderate fluence levels and demonstrate that Raman scattering can provide a sensitive technique for probing stresses introduced by ion implantation. At higher‐fluence levels where the material begins to transform from crystalline to amorphous, the linewidth is found to increase rapidly with fluence.

The effects of fast-neutron irradiation on tensile strengths of carbon fibers

Abstract: Two types of commercially available carbon fibers (high tensile strength, HTS, and high modulus, HMS) were irradiated in the Ground Test Reactor in environments of air and of liquid nitrogen (LN2). The tensile strength of HTS fibers irradiated in air increased sharply above a fast-neutron fluence of 6 × 1017 n/cm2 (E> 1 MeV) and was 17 per cent greater than the strength of unirradiated control fibers at a fluence of 8.5 × 1017 n/cm2, but then the strengrh began to decrease for additional neutron exposure in air and fell 25 per cent below the control strength at the highest fluence of 4.5 × 1018 n/cm2. However, when irradiated in LN2 where surface oxidation did not take place, the room-temperature strength of HTS fibers continued to increase beyond 8.5 × 1017 n/cm2 and became almost 30 per cent greater than the control strength for a fluence of 3 × 1018 n/cm2. The tensile strength of HMS fibers irradiated in air increased slowly but steadily with neutron exposure and was only 4 per cent greater th...

Annealing of Electron-Irradiated n-Type Silicon: Illumination and Fluence Dependence

Abstract: The effects of strong illumination and radiation fluence on the annealing behavior of the E center in electron‐irradiated phosphorus‐doped float‐zoned silicon were studied by Hall‐effect measurement Illumination of the sample during anneal increased the rate of recovery significantly Increasing the radiation fluence and, hence, the level of the induced‐carrier compensation, also increased the rate of anneal These results were found to be consistent with a previously proposed model in which the charge state of the defect was found to be a major determinant of the activation energy of recovery

Zn Displacement Threshold in ZnTe

Abstract: The energy required to displace Zn atoms in ZnTe by irradiation with energetic electrons has been measured. Above an electron beam energy of 185 keV, corresponding to a maximum recoil energy of 7.35 eV for Zn atoms, the near‐band‐edge cathodoluminescence is observed to increase in intensity with increasing fluence. This rate of increase is proportional to the square of the electron beam energy near the displacement threshold.

Charged-Particle Radiation Damage Observed as Dimpling of Thin Silicon Targets

Abstract: When thin uniform silicon targets are bombarded with energetic ions, macroscopic deformation of the target occurs in the irradiated region. This deformation, which is euphemistically termed a ``dimple'', may be interpreted as a radiation‐induced lattice expansion. Measurement of the amount of deformation allows lattice expansion to be determined with a sensitivity comparable to or better than the most sensitive existing methods. Measurements on silicon irradiated at room temperature by 1.8‐MeV He ions show that the lattice expansion at low flux increases essentially linearly with fluence below about 5×1016 He ion/cm−2, whereupon it increases more rapidly until saturation starts to occur at an order‐of‐magnitude higher fluence. Isochronal annealing results are discussed.

Irradiation-produced defects in austenitic stainless steel.

Abstract: The microstructure of annealed AISI Type 304 and type 316 stainless steels has been characterized by transmission electron microscopy as a function of fast reactor irradiation at fluence levels from 4×1021 to 7×1022 n per sq cm (E>0.1 mev) and at irradiation temperatures from 370° to 700°C. Several irradiation produced defect types where found: voids, Frank faulted loops, perfect loops, dislocation networks, and precipitates. Void number density obeys a power law relationship to fluence, wherein the exponent increases with increasing temperature from 0.8 to 1.4 over the irradiation temperatures investigated. The void size is nearly independent of fluence and increases with increasing temperature. The upper limit irradiation temperature for void formation is about 650° to 700°C. The density and size of Frank faulted loops followed trends similar to those found for voids to temperatures of ∼550°C where unfaulted loops, perfect loops, and dislocation networks coexist. These experimental results do not confirm predictions of recently acvanced models of void formation. The major deficiency of these models appears to be the nucleation rate. Accordingly, empirical nucleation rates were used to formulate a diffusion-controlled void growth model. This model was found to closely describe experimentally determined void growth kinetics.

Protons and Deuteron Irradiation Damage in Silicon Solar Cells

Abstract: Damages in n-on-p silicon solar cells by proton and deuteron irradiations are investigated in the energy region of 0.8~2.8 MeV as functions of the particle-mass, -energy, -fluence and also of the wave-length of the illuminating light. The damage rate due to deuteron irradiation is equivalent to that due to proton irradiation of about 1.8 times the fluence provided both particles have the same range in silicon. The most harmful proton energy to the degradation of short circuit current ISC shifts from the initial value of about 4 MeV down to about 3 MeV with increasing irradiation fluence. Under the illumination by near-infrared light, the degradation of Isc can be approximated by a formula (Isc/Isc0)-2=8.6×10-12E(MeV)1.5\varPhi+1 in the energy region below the most harmful proton energy as far as the degradation is not very significant, i.e., Isc/Isc0>0.7. These results can be interpreted satisfactorily by the analysis based on minority carrier diffusion equations in sub-divided multi-layers in the solar cell which take into account the non-uniformity of damages introduced by the irradiation.

Study of atomic displacements in He+ irradiated silicon and a silicon-germanium alloy, through rutherford scattering

Abstract: The disorder created by He+ ions of 275 keV and 1610 keV in Si and in a Si-Ge alloy (0.6 per cent atomic Ge) has been studied at 295 and 85°K through the use of channeling and back scattering of these ions. The disorder is measured through the relative yield of back-scatter for the beam incident in and directions. In both crystals, the disorder is not linear with fluence, and shows a tendency to saturate. In many cases the disorder measured along channels is larger than along channels, which indicates a prevalence of ‘interstitial-type’ defects. However, there is no indication of the structure of the defects. Part of the disorder could be attributed to slight displacements of atoms in the strain field of radiation defects. The low temperature irradiations create more disorder than room temperature irradiations, and this excess disorder does not fully anneal at 120°C. In Si(Ge), the number of Si or Ge scatterers is close to the concentration ratio even at high fluences. Thi...

Surface States Induced by Ion Implantation

Abstract: Surface states induced by N+-, K+, and Si+-ion implantation into SiO2-Si interfaces were measured under various conditions of ion energy, fluence, oxide thickness, etc.