Critical Amorphization Dose Research Articles

Nature of damage in diamond implanted at low temperatures

The most effective scheme for electrically activating ion implanted dopants in diamond involves implantation at low temperatures ( T i ≲ 300 K ) followed by rapid thermal annealing. For such implantations, all defects (both vacancies and interstitials) are believed to be “frozen in”, a fact which facilitates subsequent annealing. In the present work, the nature of the defects introduced into diamond by low temperature implantations is determined by combining channelling, electrical conductivity, swelling and Raman measurements on type IIa diamonds irradiated with 320 keV Xe ions at T i = 150 K over the dose range 1 × 10 13 –2 × 10 16 Xe cm −2 . The critical dose for amorphization was found to correspond to an energy deposited in the modified layer of 5.5 eV per C target atom. The carriers were determined to be holes for these cold implantations. The measurements suggest that isolated point defects in diamond behave as acceptors, whereas more complex agglomerated defects behave as donors.

On the Roles of Temperature and Interfaces in Irradiation and Thermally Induced Solid State Amorphization

ABSTRACTThe roles of irradiation temperature and interfaces (free surfaces and grain boundaries) in irradiation- and thermally- induced amorphization of ceramics (coesite, apatite, olivines and spinels) have been studied by transmission electron microscopy (TEM). The irradiations were performed with 1.5 MeV Kr+, 200 keV and 1 MeV electrons over a wide temperature range (20-700 K). The critical amorphization dose at which amorphization is complete, Dc, increased with increasing irradiation temperature for most materials except coesite (a high pressure polymorph of Si02) which showed a decreasing Dc with increasing temperature under 1 MeV electron irradiation. Although amorphization may occur directly within a displacement cascade or by cascade overlap, this study shows that free surfaces and grain boundaries are favorable sites for nucleation of amorphous volumes. Once the amorphous volume is formed at interfaces, it may grow rapidly under continued irradiation. Coesite which has a glass transition temperature higher than its melting temperature underwent spontaneous amorphization during thermal annealing at 1200 K. This thermally-induced amorphization also started at free surface and grain boundaries and propagated into the interior of the crystal. The interface-mediated amorphization is analogous to the process of thermodynamic melting.

Characterization of Collision Cascade Damage in Ca2La8(SiO4)6O2 by Hrtem

AbstractCa2La8(SiO4)6O2 thin crystals become amorphous under ion beam irradiation. The ion dose required for complete amorphization of the thin crystal (critical amorphization dose, Dc) increased with the increasing irradiation temperature and decreased with ion mass at elevated temperatures. Samples irradiated with 1-1.5 MeV Ar+, Kr+ and Xe+ ions to doses much lower than Dc, in the temperature range from 20 to 498 K were used for a detailed HRTEM investigation to study the amorphization process. The residual collision cascade damage after irradiation appeared as nanometer scale amorphous domains. The images of these domains are extremely sensitive to the sample thickness. Small domains of cascade size were found only at the very thin edge of the sample. In thicker regions, amorphous domains appear after higher doses as the result of cascade overlap in projection. At higher temperatures, the observed amorphous domains are smaller indicating thermal recovery at the amorphous/crystalline interface. The amorphous domains are also larger in size after irradiation with ions of higher mass at a fixed ion dose. These results are consistent with the Dc-temperature curves determined by in situ TEM with the HVEM-Tandem Facility at Argonne National Laboratory. The width of the amorphous rim along the edge of the specimen grew with increasing ion dose suggesting that amorphization also proceeds from the sample surface. Images of the collision cascade damage were compared to the cascade sizes calculated with the TRIM code. Some digitally acquired HRTEM images of the cascade damage were processed to reveal more detailed information.

Ion-Beam and Electron-Beam Induced Amorphization of Berlinite (AIPO4)

AbstractBerlinite (AIPO4) is isostructural with α-quartz. Like α-quartz, berlinite undergoes a pressure-induced amorphization at 15 ±3 GPa; however, upon release of the pressure, unlike α-quartz which remains amorphous, berlinite returns to the original crystalline structure of the single crystal. Berlinite was irradiated with 1.5 MeV Kr+ at temperatures ranging from 20 to 600K. The onset of amorphization was examined by monitoring the electron diffraction pattern by in situ transmission electron microscopy (TEM) at the HVEM-Tandem Facility at Argonne National Laboratory. The berlinite was easily amorphized at 20K at a relatively low dose of 4x1013 ions/cm2 or 0.05 dpa (displacements per atom). The critical amorphization dose increases with the sample temperature. These experiments also showed that the focused electron beam can locally amorphize the berlinite. After these irradiations, berlinite remained amorphous. At 500 °C, berlinite began to recrystallize: small areas of crystalline material appear in the aperiodic matrix. These results suggest that pressure-induced amorphization and ion-beam induced amorphization, in the case of berlinite, are different processes that result in two different aperiodic structural states.

Temperature Dependence of Amorphization for Zirconolite and Perovskite Irradiated with 1 Mev Krypton Ions

AbstractA transmission electron microscope investigation was made of zirconolites and perovskites irradiated to amorphization with 1 MeV krypton ions using the HVEM-Tandem Facility at Argonne National Laboratory. Three specimens were examined - a prototype zirconolite CaZrTi2O7, a gadolinium doped zirconolite Ca0.75Gd0.50Zr0.75Ti2O7and a uranium doped zirconolite Ca0.75U0.50Zr0.75Ti2O7. The critical amorphization dose Dc was determined at several temperatures between 20K to 675K. Dc was inversely proportional with temperature. For example, pure zirconolite requiring 10x the dose for amorphization at 475K compared with gadolinium zirconolite. Using an Arrhenius plot, the activation energy Ea for annealing in these compounds was found to be 0.129 eV and 0.067 eV respectively. The greater ease of amorphization for the gadolinium sample is probably a reflection of this element’s large cross section for interaction with heavy ions. Uranium zirconolite was very susceptible to damage and amorphised under 4 keV argon ions during the preparation of microscope specimens. In each sample, zirconolite coexisted with minor perovskite, reduced rutile (Magneli phases) and zirconia. These phases were more resistant to ion irradiation than zirconolite. Even for high gadolinium loadings, perovskite (Ca0.8Gd0.2TiO3) was 3-4 times more stable to ion irradiation than the surrounding zirconolite crystals.

Amortization And Dynamic Recovery Of A2BO4 Structure Types During 1.5 MeV Krypton Ion-Beam Irradiation

ABSTRACTThe temperature dependence of the critical amorphization dose, Dc, of four A2BO4 compositions, forsterite (Mg2SiO4), fayalite (Fe2SiO4), synthetic Mg2GeO4, and phenakite (Be2SiO4) was investigated by in situ TEM during 1.5 MeV Kr+ion beam irradiation at temperatures between 15 to 700 K. For the Mg- and Fe-compositions, the A-site is in octahedral coordination, and the structure is a derivative hep (Pbnm); for the Be-composition, the A- and B-sites are in tetrahedral coordination, forming corner-sharing hexagonal rings (R3). Although the Dc's were quite close at 15 K for all the four compositions (0.2–0.5 dpa), Dc increased with increasing irradiation temperature at different rates. The Dc-temperature curve is the result of competition between amorphization and dynamic recovery processes. The Dc rate of increase (highest to lowest) is: Be2SiO4, Mg2SiO4, Mg2GeO4, Fe2SiO4. At room temperature, Be2SiO4 amorphized at 1.55 dpa; Fe2SiO4, at only 0.22 dpa. Based on the Dc-temperature curves, the activation energy, Ea, of the dynamic recovery process and the critical temperature, Tc, above which complete amorphization does not occur are: 0.029, 0.047, 0.055 and 0.079 eV and 390, 550, 650 and 995 K for Be2SiO4, Mg2SiO4, Mg2GeO4 and Fe2SiO4, respectively. These results are explained in terms of the materials properties (e.g., bonding and thermodynamic stability) and cascade size which is a function of the density of the phases. Finally, we note the importance of increased amorphization cross-section, as a function of temperature (e.g., the low rate of increase of Dc with temperature for Fe2SiO4).

Amorphization and Dynamic Recovery of A2BO4 Structure Types During 1.5 MeV Krypton Ion-Beam Irradiation

ABSTRACTThe temperature dependence of the critical amorphization dose, Dc of four A2BO4 compositions, forsterite (Mg2SiO4), fayalite (Fe2SiO4), synthetic Mg2GeO4, and phenakite (Be2SiO4) was investigated by in situ TEM during 1.5 MeV Kr+ ion beam irradiation at temperatures between 15 to 700 K. For the Mg- and Fe-compositions, the A-site is in octahedral coordination, and the structure is a derivative hcp (Pbnm); for the Be-composition, the A- and B-sites are in tetrahedral coordination, forming corner-sharing hexagonal rings (R3). Although the Dc's were quite close at 15 K for all the four compositions (0.2–0.5 dpa), Dc increased with increasing irradiation temperature at different rates. The Dc-temperature curve is the result of competition between amorphization and dynamic recovery processes. The Dc rate of increase (highest to lowest) is: Be2SiO4, Mg2SiO4, Mg2GeO4, Fe2SiO4. At room temperature, Be2SiO4 amorphized at 1.55 dpa; Fe2SiO4, at only 0.22 dpa. Based on the Dc-temperature curves, the activation energy, Ea, of the dynamic recovery process and the critical temperature, Tc, above which complete amorphization does not occur are: 0.029, 0.047, 0.055 and 0.079 eV and 390, 550, 650 and 995 K for Be2SiO4, Mg2SiO4, Mg2GeO4 and Fe2SiO4, respectively. These results are explained in terms of the materials properties (e.g., bonding and thermodynamic stability) and cascade size which is a function of the density of the phases. Finally, we note the importance of increased amorphization cross-section, as a function of temperature (e.g., the low rate of increase of Dc with temperature for Fe2SiO4).

The amorphization of complex silicates by ion-beam irradiation

Twenty-five silicates were irradiated at ambient temperature conditions with 1.5 MeV Kr+. Critical doses of amorphization were monitored in situ with transmission electron microscopy. The doses required for amorphization are compared with the structures, bond-types, compositions, and physical properties of the silicates using simple correlation methods and more complex multivariate statistical analysis. These analyses were made in order to determine which properties most affect the critical amorphization dose. Simple two-variable correlations indicate that melting point, efficiency of atomic packing, the dimensionality of SiO4 polymerization (DOSP), and bond ionicity have a relationship with critical amorphization dose. However, these relationships are evident only in selected portions of the data set; that is, for silicate phases with a common structure type. A clearer relationship between the silicate properties and critical amorphization dose was determined for the entire data set with multiple linear regression. Several regression models are proposed which describe the variation in amorphization dose. All regression models contain the following properties: (i) melting point; (ii) a structural variable (DOSP, elastic modulus, and/or atomic packing); and (iii) the proportion of Si–O bonding (instead of bond ionicity). The regression models are equivalent, because they represent combinations of similar properties. Notably, density and atomic mass are not controlling properties for the critical amorphization dose. Melting and amorphization by ion irradiation are apparently related processes. Neither melting point nor critical amorphization dose can be predicted by considering only the structure, composition, or bonding of a particular phase. The Si–O bond is the most covalent bond in silicates, and is the “weak link” in the structure with respect to amorphization. Thus, DOSP is also an important property, as the topology of these “weak links” influences a structure's ability to accumulate amorphous regions. The efficiency of atomic packing is related to the process of defect self-recombination during amorphization. The bulk modulus and shear modulus are important variables within the regression models because of their direct relationship to atomic packing.

Amorphization of PLZT Material by 1.5 MeV Krypton Ion Irradiation with In Situ TEM Observation

ABSTRACTPLZT 9/65/35 single crystals were irradiated with 1.5 MeV krypton ions at 25–450°C in the HVEM-Tandem Facility at Argonne National Laboratory. In-situ TEM was performed during irradiation in order to determine the critical amorphization dose. At room temperature, the material was completely amorphized after a dose of only 1.9×1014 ions/cm2, less than one fifth of the critical amorphization dose for silicon (1×1015 ions/cm2). The critical amorphization dose for the PLZT material increased with increasing irradiation temperature. At 450°C, amorphization was not observed after a dose of 1.1×10 15ions/cm2.

Temperature and Ion-Mass Dependence of Amorphization Dose for Ion Beam Irradiated Zircon (ZrSiO4)

ABSTRACTThe temperature dependence of amorphization dose for zircon under 1.5 MeV Kr ion irradiation has been investigated using the HVEM-Tandem Facility at Argonne National Laboratory. Three regimes were observed in the amorphization dose-temperature curve. In the first regime (15 to 300 K), the critical amorphization dose increased from 3.06 to 4.5 ions/nm2. In the second regime (300 to 473 K), there is little change in the amorphization dose. In the third regime (> 473 K), the amorphization dose increased exponentially to 8.3 ions/nm2 at 913 K. This temperature dependence of amorphization dose can be described by two processes with different activation energies (0.018 and 0.31 eV respectively) which are attributed to close pair recombination in the cascades at low temperatures and radiation-enhanced epitaxial recrystallization at higher temperatures. The upper temperature limit for amorphization of zircon is estimated to be 1100 K. The ion-mass dependence of the amorphization dose (in dpa) has also been discussed in terms of the energy to recoils based on data obtained from He, Ne, Ar, Kr, Xe irradiations and a 238Pu-doped sample.

The orientation effect on amorphization in CoTi under 1 MeV electron irradiation

Since the first report of electron irradiation induced amorphization in 1982, this phenomenon has been characterized in many aspects. The effects of the dose and temperature, the mass of the incident beam, the deviation from stoichiometry and the electron flux, have been studied. There is, however, no systematic study has been reported on the crystallographic orientation effects. This paper will report the orientation effect on amorphization of intermetallic compound CoTi irradiated by 1 MeV electrons.An alloy button of Co-45 at.% Ti was prepared by arc-melting and subsequently annealed at 1100°C for ten days. The HVEM samples were spark-cut from the button and then thinned by double jetpolishing in the solution of 15%HCLO4and methanol. The irradiation was carried out with fully focused 1 MeV electron beam in a high voltage electron microscope. The critical electron dose for complete amorphization and its temperature dependence have been determined for <111>, <110> and <001> orientations.

In situ TEM study of ion-beam-induced amorphization of complex silicate structures

The in situ transmission electron microscopy (TEM) with ion-irradiation technique has been used for the first time to study the radiation-induced amorphization (metamictization) process of naturally occurring silicates: neptunite [Na 2KLi(Fe,Mn) 2Ti 2(SiO 3) 8], titanite (CaTiSiO 5), gadolinite (REE 2FeBe 2Si 2O 10), zircon (ZrSiO 4) and olivine [(Mg,Fe) 2SiO 4]. These phases were irradi 1.5 MeV Kr + ions in the Argonne HVEM-Tandem facility at room temperature with the electron diffraction pattern monitored in situ. The critical doses required for amorphization of the electron transparent thickness of neptunite, titanite, gadolinite, zircon and olivine have been determined to be 1.7, 2.0, 2.3, 4.8 and 6.0 × 10 14 ions/cm 2, respectively. The results show a correlation between amorphization dose and the chemical and structural complexity of these five phases. The most complex structure (e.g. neptunite) becomes amorphous at the lowest critical dose. The critical amorphization dose also increases with the increasing melting temperature of the minerals.

Radiation-induced amorphization of ordered intermetallic compounds CuTi, CuTi2, and Cu4Ti3: A molecular-dynamics study.

Solid-state amorphization resulting from the introduction of chemical disorder and point defects in the ordered intermetallic compounds CuTi, ${\mathrm{CuTi}}_{2}$, and ${\mathrm{Cu}}_{4}$${\mathrm{Ti}}_{3}$ was investigated, with use of the isobaric-isothermal molecular-dynamics method in conjunction with embedded-atom potentials. Antisite defects were produced by randomly exchanging Cu and Ti atoms, and vacancies and interstitials were created by removing atoms at random from their normal sites and inserting atoms at random positions in the lattice, respectively. The potential energy, volume expansion, and pair-correlation function were calculated as functions of the numbers of atom exchanges and point defects. The results indicated that, although both chemical disordering and point-defect introduction increased the system energy and volume, the presence of point defects was essential to trigger the crystalline-to-amorphous transition. By comparing the pair-correlation function calculated after the introduction of point defects with that of the quenched liquid alloy, the critical damage dose (in dpa, displacements per atom) for amorphization was estimated for each compound: \ensuremath{\sim}0.7 dpa for CuTi, \ensuremath{\sim}0.5 dpa for ${\mathrm{CuTi}}_{2}$, and \ensuremath{\sim}0.6 dpa for ${\mathrm{Cu}}_{4}$${\mathrm{Ti}}_{3}$. At the onset of amorphization, the volume expansions were found to be \ensuremath{\sim}1.9%, \ensuremath{\sim}3.7%, and \ensuremath{\sim}1.7% for these respective compounds. In general, the results obtained in the present work are in good agreement with experimental observations.

Ion Beam-Induced Amorphization of (Mg, Fe)2SiO4 Olivine Series: An In Situ Transmission Electron Microscopy Study

ABSTRACTEffects of ion beam irradiation of five members of the (Mg, Fe)2SiO4 olivine series, from synthetic pure fayalite (Fe2SiO4) to naturally occurring (Mg0.88Fe0.12)2SiO4, have been studied by in situ transmission electron microscopy (TEM). Under 1.5 MeV Kr+ ion room temperature irradiations, all of the samples have been amorphized. The critical amorphization dose or the total collision energy loss required for amorphization increased rapidly with the increasing Mg:Fe ratio which coincides with an increasing melting temperature (bond strength) and an increasing average bond ionicity. A 400 keV He+ ion irradiation of (Mg0.88Fe0.12)2-SiO4, which mainly results in ionization energy loss in the sample, did not cause amorphization even at a much higher dose rate and a much higher final dose. This indicates nuclear interactions (collisions) are primarily responsible for ion beam induced amorphization. Also, high resolution electron microscopy (HREM) images of the defect structure at a low ion dose have been obtained and compared with the displacement cascade structure generated by computer modelling.

Damage distribution and annealing behaviour of high-energy 115In+ implanted into Si(100)

Damage distribution and secondary-defect formation have been studied in 0.95 MeV 115In+ ion-implanted Si(100) by means of Rutherford backscattering spectrometry and cross-section transmission electron microscopy. The types of defect structures resulting after conventional thermal treatment have been classified as a function of the implantation dose. For low-dose implantation, 5 ×1013 cm−2, we found the formation of “subthreshold” or category I defects at the depth of the projected range, Rp = 4100 rA. This has never been observed before for heavy-mass ion implantation at low energies. A critical dose for amorphization of 1 × 1014cm−2 has been found. For an implantation dose of (1–3) × 10 14 cm−2 a buried amorphous layer is formed. After solid-phase epitaxial regrowth of a buried layer both category II and IV defects were observed. Rutherford backscattering analysis shows that segregation of indium atoms occurs at the depth where the two moving amorphous/crystalline interfaces meet during regrowth of the buried amorphous layer.

Proton-irradiation-induced crystalline to amorphous transition in a NiTi alloy

The crystalline to amorphous (C-A) transition induced by 2 MeV proton irradiation of a NiTi alloy containing 50.95 Ni was investigated at − 45°C and − 153°C using transmission electron microscopy and scanning electron fractography. The fractographic studies indicate that the irradiated region contains two layers, the one closer to the free surface consisting of a mixture of amorphous and crystalline phases, and the other having transformed completely to the amorphous phase. The progress of the C-A transition was dependent on both dose and temperature. The critical dose for complete amorphization was estimated as 0.25 displacements per atom (dpa) at − 153°C and 0.32 dpa at − 45°C, as determined from measurements of the distance from the surface of the sample to the interface between the two layers in the irradiated region. Amorphization commenced well before the crystalline matrix was completely disordered, and the amorphous phase was generally observed to nucleate homogeneously throughout the crystalline matrix. The features of the C-A transition induced by proton irradiation more closely resemble those of ion irradiation than electron irradiation. The spatially nonuniform buildup of point defects during proton and heavy-ion irradiation is invoked to explain the different responses of intermetallic compounds to ion and electron irradiation.

Regrowth of radiation-damaged layers in natural diamond

Abstract The regrowth of radiation-damaged layers created by carbon ion implantation in natural diamond was investigated by the Rutherford backscattering/channeling technique and by optical absorption. We present the first results of rapid thermal annealing of the implanted samples directly from the 77 K implantation temperature to 1100° C as well as data for isochronal annealing. We found that isochronal annealing up to 900° C was more effective than rapid thermal annealing for amorphized samples. The critical dose for amorphization of diamond was between 1.65 × 1015 and 3 × 1015 cm−2 for 200 keV carbon ion implantation at 77 K.

Dose rate and temperature dependence of the critical dose for amorphization of CuTi-irradiated by 1 MeV electrons

The dose rate and temperature dependence of critical dose for amorphization of CuTi under electron irradiation was investigated in a temperature range from 10 to 260K and in a dose rate range from 1.0 × 10−4 to 1.5 × 10−3 dpa/sec, using the Argonne HVEM and a helium coding specimen stage. An alloy button of Cu-54at%Ti was prepared by arc-melting and subsequently annealed at 1173K for two days. HVEM samples were spark-cut and thinned by jet polishing. The irradiation was carried out in HVEM with a fully focused beam. The Gaussian flux distribution of the beam was utilized to study the dose rate dependence of amorphization.Fig. 1 shows a few example photographs taken during a sequence of irradiation. The irradiation was always carried out on a low index bend contour. An interruption in the bend contour appears at the beam center where the dose rate is highest, as the irradiation proceeds. With further irradiation, the interruption grows outward into regions of lower dose rate. The critical dose for amorphization was calculated from each micrograph by multiplying the irradiation time with the predetermined dose rate. The length of the interruption in the bend contour was taken as the diameter of a completely amorphized volume at the accumulated dose. About ten micrographs were usually taken during a sequence of irradiation.

Temperature and irradiating species effects on the critical amorphization dose in NiAl 3

Thin film samples of NiAl 3 have been used to examine the effects of sample temperature and mass of the irradiating species on the crystalline to amorphous transformation. Irradiations were carried out at 100 K and 300 K using 300 keV Xe, 60 keV Ne, and 1 MeV electron. At 100 K the NiAl 3 phase was completely transformed into an amorphous solution between = 0.30 and 0.40 displacements per atom (dpa) for Xe, Ne, and electrons. At 300 K only Xe irradiation produced a complete transformation to the amorphous state between 0.40 and 0.50 dpa; Ne irradiations only partially amorphized the NiAl 3 phase while electron irradiated NiAl 3 remained crystalline and ordered. These results suggest that the critical damage dose for amorphization is independent of the irradiating species at low temperature and that the critical amorphization temperature is irradiating species dependent. There is reasonable agreement between the experimental amorphization dose and the dose predicted by a cascade model suggesting that a direct transformation mechanism may be operating during low temperature ion irradiation.

Temperature Dependence of Amorphization above 10K in the CuTi Intermetallic Compound Under Electron Irradiation

AbstractThe critical dose required to amorphize the crystalline compound CuTi during irradiation with 1 MeV electrons has been investigated from 10 to 288 K. The results show that above a critical temperature (Tc) of about 185 K, CuTi remains crystalline and only defect clusters are formed. Below Tc, amorphization occurs with no observable cluster formation. The critical dose for amorphization was found to be temperature dependent below Tc: as the irradiation temperature increases, a higher dose is required to induce amorphization. This observation supports the concept that Tc corresponds to the vacancy migration temperature. Below Tc, interstitial migration may contribute to the observed reduction in the amorphization rate with increasing temperature.