Threshold Energy For Atomic Displacement Research Articles

A comparison between ion irradiation assisted- and electron irradiation assisted-oxygen plasma treatment on modification of nanostructured carbon films

Oxygen plasma treatment has been used for surface modification of carbon materials. However, the working mechanism is not well clarified. Here, the ion irradiation assisted- and electron irradiation assisted-oxygen plasma etching were proposed and realized in an electron cyclotron resonance plasma processing system. The effects of the ion assisted- and electron assisted-argon plasma and oxygen plasma etching on the surface morphology and nanostructure of graphene nanocrystallites embedded carbon film were compared. In the ion assisted plasma etching, compared with argon plasma, the oxygen introduction made the sp2/sp3 and ID/IG of the film upper layer further decrease. While in the electron assisted plasma etching, after O2 introduction, the sp2/sp3 and ID/IG in the film upper layer increased. Then the oxygen plasma treatment mechanism was proposed. In the ion assisted oxygen plasma treatment, the attracted oxygen positive ions took major effect, which would reduce the threshold energy for atom displacement and then implant more carbon or oxygen atoms into the film subsurface to make the film denser. In the electron assisted oxygen plasma treatment, the neutral oxygen took major effect, which would preferentially react with the more unstable amorphous carbon and then make the film equipped with more sp2 bonds.

Degradation fitting of irradiated solar cells using variable threshold energy for atomic displacement

AbstractCharacteristic degradation curves for proton and electron induced degradation of triple junction (3J) and isotype Ga0.5In0.5P/GaAs/Ge solar cells were obtained. The displacement damage dose methodology in combination with a varying effective threshold energy for atomic displacement Td,eff was used to analyze 3G28 and 3G30 3J cell data. The nonionizing energy loss (NIEL) was calculated analytically, and Td,eff was explicitly introduced as a fit parameter. Using the GaAs NIEL in fitting the 3J degradation data, a Td,eff of 21 eV was determined, whereas a Td,eff of 36 eV was found using the Ga0.5In0.5P NIEL. In GaAs and Ga0.5In0.5P single junction cells, the effective threshold energies for atomic displacement of 22 and 34 eV were determined. Copyright © 2017 John Wiley & Sons, Ltd.

Clusters of Radiation Defects in Silicon Crystals

While considerable progress has been achieved in radiation influence on the solid states, the quantitative assessment of defect production is very scarce. In this paper radiation defects studies in silicon crystals are briefly reviewed and comprehensively analyzed depending on irradiation energy and dose, paying special attention to electron irradiation in wide energy spectrum when crystal lattice disordered regions (clusters) occur. Electron irradiation, which is a simple way to introduce intrinsic defects, was used as one of the most powerful techniques to study point and cluster defects which affect properties of semiconductors depending on irradiation energy. Fundamental aspects of radiation induced defects are discussed and it is shown that they bring information on the threshold energy for atomic displacement, on the recombination of vacancy—interstitial pair and mainly, on radiation defects cluster formation which essentially influences on the irradiating material properties. The determination of the irradiation critical dose and energy for the formation of homogeneous disordered regions (clusters) are detailed.

Computer simulation of a 10 keV Si displacement cascade in SiC

The threshold energy for atomic displacement and the evolution of high-energy displacement cascades in β-SiC have been examined using molecular dynamics simulations. A modified form of the Tersoff potential was used in combination with a repulsive potential obtained from density functional theory to describe the interactions between the atoms. The evolution of lattice damage in a 10 keV Si cascade was studied for about 10 ps. The system size varied from 8000 atoms for the displacement energy calculations to 192,000 atoms for the cascade simulations. The results indicate that the minimum displacement energy is about 36 eV for Si and 28 eV for C. The cascade lifetime was found to be of the order of 0.1 ps, and the surviving C vacancies and interstitials outnumbered the corresponding Si defects by a factor of about 3. These results are discussed in light of previous theoretical and experimental studies of radiation damage in SiC.

Influence of vacancy clusters on the atomic arrangement and displacement threshold energies in Ni3Al

A lot of work has been done to investigate the influence of irradiation on the structure and properties of nuclear reactor materials in high irradiation for the safety and reliability. Although the point defect survival and micromechanism by irradiation are important issues, the evolution of such a region is difficult to follow experimentally, so many results are obtained from computer simulation experiments together with some purely theoretical work. Some work on the irradiation effect has been done through calculating the threshold energy for atomic displacement by computer simulation. If a displaced atom whose energy exceeds some critical or "threshold" value, Ed, causes a Frenkel pair to be produced, the displaced atom is called the primary knock-on atom (PKA) and the displacement threshold, Ed, characterizes importantly the damage irradiation. Ni3Al ordered alloy is of interest for its structure (LIZ) for threshold energy investigation and its excellent high-properties, so the threshold energy has been calculated by neutron irradiation'" 21. In this work, we adopt F-S potential modified by ~ao'~] for Ni3A1 to calculate threshold energies in typical directions, using molecular dynamics method. The results are shown in figs. 1 and 2, in which E * denotes the threshold energy without vacancy clusters. * To whom correspondence should be addressed.

Temperature Dependence of the Atom- Displacement Mechanism in fcc Metals

The experimentally determined threshold energy for atom displacement, E d , in fcc metals shows a particularly strong temperature dependence along the direction. This is discussed paying special attention to the propagation of replacement collision sequences. Taking into account thermal effects, molecular dynamics calculations of such collision sequences along , and are compared. Two mechanisms exhibiting a strong temperature dependence along are found: First, by increasing the temperature, the energy loss caused by the opening of atomic windows decreases more rapidly for sequences than for sequences along and

Defects production and annealing in self-implanted Si

230-keV 28Si ions were implantated into Si(100) at room temperature with doses from 1014 to 1015/cm2. The samples were analyzed by x-ray double crystal diffractometry and 2-MeV 4He ion channeling spectrometry. The implanted layer has a parallel lattice spacing equal to that of the unimplanted substrate. The perpendicular lattice spacing is larger than that of the unimplanted substrate and is proportional to the defect concentration extracted from the channeling measurement. Both the perpendicular lattice spacing and the defect concentration increase nonlinearly with ion dose. The defect concentration initially increases slowly with dose until a critical value (∼15%, at 4×1014/cm2), then rises rapidly, and finally a continuous amorphous layer forms. The initial sluggish increase of the damage is due to the considerable recombination of point defects at room temperature. The rapid growth of the defect concentration is attributed to the reduction of the threshold energy for atomic displacement in a predamaged crystal. The amorphization is envisioned as a cooperative process initiated by a spontaneous collapse of heavily damaged crystalline regions. The annealing behavior of the damaged layer reveals various stages of defect recovery, indicating that the damage consists of a hierarchy of various defect structures of vacancy and interstitial aggregates.

The threshold energy for atom displacement in fcc metals

Prolonged electron irradiation of metals at elevated temperatures usually leads to the formation of large interstitial-type dislocation loops. The growth rate of the loops is proportional to the total cross-section for atom displacement,which is implicitly connected with the threshold energy for atom displacement, Ed . Thus, by measuring the growth rate as a function of the electron energy and the orientation of the specimen with respect to the electron beam, the anisotropy of Ed can be determined rather precisely. We have performed such experiments in situ in high-voltage electron microscopes on Ag and Au at 473K as a function of the orientation and on Au as a function of temperature at several fixed orientations.Whereas in Ag minima of Ed are found close to <100>,<110>, and <210> (13-18eV), (Fig.1) atom displacement in Au requires least energy along <100>(15-19eV) (Fig.2). Au is thus the first fcc metal in which the absolute minimum of the threshold energy has been established not to lie in or close to the <110> direction.

The anisotropy of the threshold energy for atom displacement in silver and gold

Abstract The anisotropy of the threshold energy for atom displacement, E d, in Au and Ag at 473 K has been determined. Whereas in Ag, minima of E d are found close to the 〈100〉, 〈110〉 and 〈210〉 directions (E d = 13–18eV), atom displacement in Au requires least energy near 〈100〉 (15–19eV). So far Au is the only f.c.c. metal exhibiting a distinctly lower E d in the 〈100〉 than in the 〈110〉 direction. This is discussed in terms of the atomic processes controlling the propagation of replacement collision sequences.

The anisotropy and temperature dependence of the threshold for radiation damage in gold — comparison with other FCC metals

The growth behaviour of interstitial-type dislocation loops in Au as observed in a high-voltage electron microscope is used to determine the anisotropy and temperature dependence of the threshold energy for atom displacement, E d . At 473 K minima of E d are found in the 〈100〉 (17.5 eV) and the 〈110〉 (21 eV) directions. Au is thus the first fcc metal in which the absolute minimum of the threshold surface has been established not to lie in or close to the 〈110〉 direction. A comparison of the threshold-energy data of fcc metals leads to the conclusion that the reason for the “anomalous” behaviour of Au is to be found in the exceptionally large ratio of ionic radius to lattice parameter. In a discussion of the temperature dependence of E d it is shown that the rather strong reduction of the threshold energies in or near the 〈111〉 directions at elevated temperatures may be explained in terms of the “window-opening” mechanism.

Solid-phase epitaxy of amorphous silicon induced by electron irradiation at room temperature.

The technique of cross-sectional electron microscopy has been used to investigate the mechanism of electron-beam-induced solid-phase epitaxy of amorphous silicon at room temperature. Cross sections of samples with surface and buried amorphous layers were irradiated in a transmission electron microscope with electrons of energies higher than the threshold energy for atomic displacement and the induced recrystallization process was characterized. Evidence is given that the dominant mechanism of recrystallization is the diffusion to the amorphous-crystalline interface of the defects produced by elastic displacements both in the crystalline and in the amorphous region. The diffusion length of such defects results in the order of 25--30 nm and is approximatively the same in the crystalline and amorphous Si. Electron-beam irradiation is shown to induce room-temperature polycrystalline nucleation in the amorphous layer. Such a process becomes competitive with solid-phase epitaxy for a dose higher than 5\ifmmode\times\else\texttimes\fi{}${10}^{5}$ C/${\mathrm{cm}}^{2}$.

The Temperature Dependence of the Effective Threshold Energy for Atom Displacement in Tantalum

The Temperature Dependence of the Effective Threshold Energy for Atom Displacement in Tantalum

Temperature dependence of the threshold energy for atom displacement in irradiated molybdenum

The effective threshold energy for atom displacement is measured in molybdenum single crystals in a high-voltage electron microscope. Displacement is monitored at 70 K ≦ T ≦ 300 K by observing the nucleation of interstitial dislocation loops, and at 500 K ≦ T ≦ 800 K by measuring the growth rate of previously induced loops. By use of reference irradiations the results of both methods may be calibrated to allow comparison over the whole temperature range covered. At 70 K ≦ T ≦ 150 K the effective threshold energy for irradiation along a 〈100〉-direction is found to have a constant value of (34.5 ± 0.5) eV. Above this range the threshold energy decreases continuously with temperature to (26.5 ± 0.5) eV at 800 K. The role of subthreshold processes is discussed. It is found that such processes contribute little to the displacement cross section. The observed temperature dependence of the displacement threshold energy is explained in terms of the effect of thermal vibrations on the production of stable Frenkel pairs. Die effektive Schwellenenergie für Atomverlagerung wird an Molybdäneinkristallen im Hochspannungselektronenmikroskop gemessen. Zwischen 70 und 300 K dient als Kriterium für Verlagerung die Keimbildung von Zwischengitteratomversetzungsringen, bei Temperaturen von 500 bis 800 K wird das Wachstum von vorbestrahlten Ringen dieses Typs beobachtet. Durch Eichbestrahlungen können die Ergebnise beider Meßmethoden auf die gleiche Skala reduziert werden. Das erlaubt einen Vergleich der gewonnenen Werte über den gesamten untersuchten Temperaturbereich. Zwischen 70 und 150 K weist die effektive Schwellenenergie für Bestrahlungen parallel zu einer <100>-Gitterrichtung einen konstanten Wert von (34,5 ± 0,5) eV auf. Für höhere Temperaturen nimmt diese Größe kontinuierlich ab bis sie bei 800 K einen Wert von (26,5 ± 0,5) eV annimmt. Eine Untersuchung der Auswirkung unterschwelliger Verlagerungen zeigt, daß solche Ereignisse wenig zum Wirkungsquerschnitt für Atomverlagerung beitragen. Die beobachtete Temperaturabhängigkeit der Verlagerungsschwellenenergie wird durch den Einfluß thermischer Schwingungen auf die Erzeugung stabiler Frenkelpaare erklärt.

A review of neutron radiation damage on corundum crystals

The first neutron radiation damage studies were carried out on corundum (Al 2O 3) crystals nearly thirty years ago by Levy and Dienes and nearly twenty years ago Compton and Arnold measured the threshold energy for atomic displacement using energetic electrons. However, it was not until about five years ago that a series of optical studies of crystals bombarded with neutrons and with energetic ions laid the basis for identifying radiation-induced lattice defects. Since that time a variety of lattice defects have been identified through their optical absorption and emission characteristics. Some information on the spatial distribution of neutron damage has been obtained through a study of the effect of annealing on the luminescent efficiency which increases as the high local damage concentration in the displacement spike is annealed, thus decreasing concentration quenching of F centre luminescence. In this paper all of the recent developments related to the identification of lattice defects created by fast-neutron irradiation and the annealing of damage will be reviewed with particular attention to outstanding problems and areas needing addition work.

The threshold energy for atom displacement in irradiated copper studied by high-voltage electron microscopy

Abstract The dependence of atom displacement on irradiation direction and temperature has been studied in copper at low electron energies in a high-voltage electron microscope. The displacement was monitored by observing the nucleation and growth of interstitial dislocation loops. At 550 K a pronounced dependence of the displacement rate on irradiation direction was found. From this it can be concluded that the threshold energy surface exhibits ring-shaped ranges of minimum threshold energy around the 〈110〉 directions. The angular separation of them ranges from the respective 〈 110〉 directions is about 6° and the angular width about, 4°. The minimum threshold energy increases from 16.5 eV at 10 K to 17.5 CV at 70 K and then decreases continuously to 10.5 eV at 550 K. As the result of a sub-threshold process at suitably oriented stacking faults, displacement occurs already at energies that are about 1 eV lower. The observed dependence of atom displacement on knock-on direction and temperature can be explai...

On the temperature-dependence of the threshold energy for atomic displacement in copper

(1981). On the temperature-dependence of the threshold energy for atomic displacement in copper. Radiation Effects: Vol. 59, No. 1-2, pp. 103-104.

An investigation of the temperature dependence of the threshold energy for atom displacement in electron-irradiated copper

The temperature dependence of the threshold energy for atom displacement in copper has been determined by observing the formation of interstitial clusters as a function of electron energy and irradiation temperature in a high-voltage electron microscope. The threshold energy is found to be 17.5 eV at 70 K and decreases continuously to 10.5 eV at 550 K.

On the determination of the threshold energy for atomic displacement in semiconductors

Abstract The assumption made when the threshold energy is measured using secondary defect production is discussed and shown to lead to a value higher than the exact one.

Near-threshold displacements in tantalum single crystals

Tantalum single crystals of the four orientations (100), (110), (111), and (112) have been irradiated with electrons in the energy range 1.0-1.7 MeV. A special irradiation procedure has been used which enables us to distinguish between subthreshold and intrinsic defects. The threshold energy for atomic displacement is found to be the lowest in and around the $〈100〉$ direction. Moreover, the defect production in the $〈100〉$ direction is found to be governed by two slightly different threshold energies. An analysis based on a geometrical model for the threshold energy surface leads to the following results: ${T}_{d1}^{〈100〉}=33\ifmmode\pm\else\textpm\fi{}1$ eV, ${T}_{d2}^{〈100〉}=38\ifmmode\pm\else\textpm\fi{}1$ eV, and ${T}_{d}\ensuremath{\ge}55$ eV for all other crystallographic directions. Although several models can account for the observed defect production rates, these two different values for the threshold energy in the $〈100〉$ direction can best be interpreted as corresponding to different separation distances between the interstitial atom and its vacancy; for the closest distance, i.e., the lowest threshold energy, only one of the two possible configurations of the Frenkel pair (depending on the orientation of the split interstitial with respect to the pair axis) is stable at the irradiation temperature. A value of ${\ensuremath{\rho}}_{F}^{\mathrm{Ta}}=16\ifmmode\pm\else\textpm\fi{}3$ \ensuremath{\mu}\ensuremath{\Omega}cm per at.% is deduced for the Frenkel-pair resistivity in tantalum. An empirical interatomic potential of a Born-Mayer form is proposed in the range $1.4lrl2.7$ \AA{}. Finally, a tentative interpretation is given for the tantalum recovery spectrum between 7 and 20 K.

On a relation between threshold energy for atomic displacement in metals, bulk modulus, and interatomic potential

Abstract An empirical relation between the threshold energy for atomic displacement Td , bulk modulus B, and the interatomic distance r 1 is derived for metals Td = 0.0264 Br1 e 1.18r1 which gives the experimental Td values within a factor of 1.5 and is therefore more precise than a relation between Td and the sublimation energy. This relation is interpreted in terms of defect production by replacement collisions. Regarding only metals with regular fcc, hcp and bcc lattices, an agreement within about 20% would be obtained by Td = 0.022 Br1 e 1.18r1 Td (ev), B(1010Pa), r 1(10–10m).