Damage Threshold Energy Research Articles

Effect of MeV beams on the interface structure of metal(adlayer)-silicon (crystal substrate) systems

The influence of MeV ion beams on the measured intensity of the surface peak (SP) in channeling studies has been examined for Ag and/or Au covered Si(111), and Pd covered Si(111) systems with film thicknesses up to several monolayers. A simple phenomenological model is introduced to analyse the observed increase in atomic displacements induced by probing He ions of 1 MeV. For the Ag and Pd cases, effects attributable to the deposited metal was small while for Au an appreciable enhancement of the beam sensitivity was observed which increases with increasing Au thickness for beam doses of ⩽ 3.1 × 10 16 ions/cm 2. The observe differences cannot be explained by the difference in mass and atomic number of the overlayer atoms. The model suggests that the chemical nature of atomic bonds near the interface affects the damage threshold energy.

106-μm laser damage of optical coatings: regression analyses of round-robin test results

The laser-induced damage thresholds of four different coating designs obtained with three to six samples each at eight laboratories involved in a round-robin experiment were evaluated by means of multiple regression analyses for the two main independent parameters: pulse width τ and beam diameter d [ K. H. Guenther , Appl. Opt.23, 3743 ( 1984).] The analyses show that the F vs τ1/2 relationship, with F being the damage threshold energy density (J/cm2) known from other experiments also holds for this one. The F vs d−m scaling law, however, yields only rather weak powers of m = 0.015–0.2 for Fmin(D) (the minimal energy density threshold causing damage) and m = 0.06–0.5 for Fmix(ND) (the maximum energy density threshold for which no damage is observed). This is in contrast to the previously established scaling laws of d−1 or d−2. The results are discussed in terms of defect density, which was checked for a number of samples with distribution plots taken from optical micrographs of undestroyed portions of the coating.

Laser-induced damage to transparent conducting SnO2 films at 1062 nm

Transparent conducting SnO2 films prepared by chemical vapor deposition were damage tested at 1062 nm using an electro-optically (EO) Q-switched Nd:glass laser emitting 15-ns pulses. The damage threshold energy densities for films of thickness 151.0 and 140.9 nm were found to be 18.2±1.3 and 15.9±1.1 J/cm2, respectively. These films find application in large aperture Pockels cells and other EO modulators for pulse shaping and gating purposes in high power laser amplifiers.

Radiation damage in MgAl2O4

Exposure of single crystals of Mg${\mathrm{Al}}_{2}$${\mathrm{O}}_{4}$ to fast neutrons and to Van de Graaff electrons with energies in excess of 0.35 MeV introduces an optical-absorption band at 5.3 eV with a 1-eV half-width. This band can be partially bleached at temperatures as low as 40 K and a shoulder at 4.75 eV develops concurrently. This bleaching treatment also partially destroys a previously reported $V$-type absorption centered at 3.2 eV. Subsequent exposure to ionizing radiation destroys the 4.75-eV band and restores both the 5.3- and 3.2-eV bands to their original intensities. Since this behavior is analogous to the interconversion of $F$ to ${F}^{+}$ centers in ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, it is concluded that the 5.3-eV band is the principal optical transition of the $F$ center (two electrons trapped at an oxide-ion vacancy) and the 4.75-eV band is attributed to absorption by the ${F}^{+}$ center (one electron trapped at an oxide-ion vacancy). In electron-irradiated crystals the 5.3-eV absorption begins to anneal near 110\ifmmode^\circ\else\textdegree\fi{}C and is about 90% destroyed upon isochronal annealing (10-min pulses) up to 355\ifmmode^\circ\else\textdegree\fi{}C. Neutron-irradiated crystals behave similarly. Measurement of the threshold energy for damage by electrons at 77 K yields a displacement energy for the creation of ${\mathrm{O}}^{2\ensuremath{-}}$ interstitial-vacancy pairs of 59 eV. The defect yield drops off substantially with increasing temperature, and at room temperature the apparent ${\mathrm{O}}^{2\ensuremath{-}}$ displacement energy is 130 eV. Possible reasons for this strong temperature effect are discussed.

Influence of optical absorption on the laser damage threshold of glasses

It was shown experimentally that the bulk damage threshold of K8 optical glasses containing color centers is proportional to α–0.5 (α is the absorption coefficient). This result may be attributed to nonlinearity of α. A consequence of this assumption is the dependence (Wth is the damage threshold energy density and τp is the radiation pulse duration).

Radiation damage of α-Al 2O 3 in the HVEM : I. Temperature dependence of the displacement threshold

The temperature dependence of the apparent displacement threshold energy has been measured for single crystal α-Al 2O 3 in a high voltage electron microscope, over the temperature range 320–1120 K. Below 570 K the threshold energy for observable damage remains constant at 390 ± 10 keV, then rises to a peak of 440 ± 20 keV at 695 K followed by a rapid fall to ~200 keV at 870 K and above. Measurement of the displacement threshold energy, using the optical absorption and luminescence of oxygen and aluminium electron irradiation induced vacancies at several temperatures, gives a value of 440 ± 25 keV for the oxygen ion and 175 ± 25 keV for the aluminium ion. These results show that oxygen and aluminium ions have widely different displacement energies, E d , of ~75 and 18 eV respectively.

Tunnel Diode Amplifier SGEMP Response

An X-band tunnel diode amplifier (TDA) has been studied for SGEMP response. This study has involved analytical modeling and predictions, tunnel diode electrical pulsing to develop damage statistics, and experimental measurements in an 800 kvp flash X-ray environment. In contrast to photocurrent limited TREE response, significant SGEMP replacement currents can flow through the tunnel diode. This response is associated with mechanical design, the use of gold-plated conductors facing aluminum surfaces within a cavity with corresponding photoemission differences and the differences in fore and back emission between the tunnel diode amplifier and the evacuated test chamber walls. The SGEMP current is independent of bias circuit design. The modeling and prediction effort included SGEMP current determination, electrical circuit modeling and computerized transient radiation circuit analysis. The experimental SGEMP tests were performed in vacuum using the BLACK-JACK 3 (BJ3) facility at Maxwell Laboratories, Inc., in San Diego, California. Measurements are reported for the current responses of the tunnel diode and the circulator. Eight tunnel diodes were damaged due to SGEMP and their damage threshold energies were calculated, using tunnel diode characteristics, radiation dose and SGEMP currents. Damage frequency data for the BJ3 tests correlates with separate electrical pulse data and supports the conclusion that the SGEMP response of TDA's is predictable using the model developed in this study.

The threshold energy for electron irradiation damage in single-crystal graphite

Abstract A high-voltage electron microscope has been used to study displacement damage at 600°C in graphite. Small defect clusters were observed for incident electron energies above 150 keV, indicating a threshold energy of 34 ± 2eV for atomic displacement along the c-axis.

Sputtering Thresholds and Displacement Energies

A spectroscopic method for the measurement of small numbers of atoms sputtered at low energies was developed; a strong emission line of the target material is monitored by a monochromator and measured by a photomultiplier detector. The plot of spectral line intensity vs. bombarding ion energy in most cases closely matches the yield plot obtained by absolute methods. The sensitivity of this method is 10/sup -4/ or more atoms per ion for many metals. Measurement of yields was made for about 20 metals sputtered by Ar/sup +/ and Hg/ sup +/ ions; one such yield curve is given for chromium. The results indicate that yields at very low ion energies (<50 ev) become sensitive to the anode voltage above a critical value and decrease with decreasing ion energy more rapidly than previous estimates. The threshold energy for sputtering appears to be 15 to 45 ev, with 25 ev as the approximate value for Ar/sup +/ ions; this is on the same order as the displacement threshold energy for radiation damage. (D. L.C.)

Radioactive and Photoelectric p-n Junction Power Sources

An electrical power source can be made by exposing a p-n junction to radioactivity or light, so that the junction field separates electron-hole pairs produced by the radiation. Expressions for maximum power, optimum load resistance, and efficiency are derived from an equivalent circuit and rectification theory. Power and efficiency increase with source current Ig of separated charges and zero-bias junction resistance. Ig increases with energy and intensity of radiation, but is limited by self-absorption in the radioactive isotopes. Estimates of attainable power and efficiency for silicon cells are 3·10−3 watt cm−2 and 15 percent for solar radiation, averaged, allowing for night, weather, and varying angle of incidence; and 3·10−4 watt cm−2 and 8 percent, for beta radiation from Sr90–Y90 of activity 32 Curie/g. However, lattice defects produced by Sr90–Y90 beta radiation impair cell performance by increasing electron-hole recombination. A theoretical estimate of threshold energy for radiation damage in silicon is about 0.3 Mev, about half the experimental value reported for germanium. Avoiding radiation damage by annealing, by absorbers, and by use of less energetic isotopes is discussed. The Y90 beta spectrum is given; it is used in estimating damage rates in germanium, which are high, and efficiencies obtainable with absorbers, which are low. Theory and experiment are compared for Sr90–Y90 cells of silicon and of germanium.