Incubation Dose for Ion Beam Induced Anisotropic Growth of Amorphous Alloys: Insight into Amorphous State Modifications

Abstract

Under energetic ion bombardment, amorphous materials deform plastically in the form of anisotropic growth. At medium electronic stopping power (5 to 30 keV͞nm) this phenomenon starts only after a certain incubation dose depending on values of the electronic stopping power and temperature. This delay is modeled on the basis of the assumption of a drastic irradiation induced viscosity reduction, resulting from accumulation of atomic displacements in the matrix and local material heating in the heavy ion track. A simple analytical expression is derived which is in a good agreement with experimental data for the amorphous alloy Fe 85 B 15 . PACS numbers: 61.80.Jh In the amorphous (or glassy) state, solid materials are far from equilibrium. An important aspect of this nonequilibrium solid state is that it may be realized, at least within short time periods, in a broad spectrum of metastable states with different degrees of relative stability, relaxation times, and activation barriers for these relaxations [1].There are several techniques to amorphize crystalline and to treat amorphous materials, but bombardment with heavy ions is certainly the method where the most extreme conditions can be realized due to the deposited energy being extremely localized and having a high density. Thus, displacement cascades and electronic excitations along the ion trajectory induce rapid heating and cooling in sub-ns time scales and at rates of up to 10 15 K͞s. Under such conditions, an amorphous material may be investigated at temperatures where it would recrystallize within the time scales of "classical" methods. Bombardment of amorphous materials with heavy ions can also considerably influence the relaxation kinetics of the metastable states and may be considered to provide a deeper understanding of the dynamics of the amorphous state.Energetic heavy ions penetrating a solid lose their energy by quasielastic collisions with the target atoms and by electronic excitations characterized, respectively, by "nuclear" and "electronic" stopping powers, S n and S e . We are interested here in ion energies above 1 MeV͞amu where S e dominates the stopping power. In this energy range, heavy ions with sufficiently high electronic stopping power (S e . 5 keV͞nm) induce in amorphous materials at low temperatures (T irr # 200-300 K) two striking deformation phenomena: (i) anisotropic expansion ("growth") of unstressed amorphous foil samples perpendicular to the ion-beam direction [2-8] and (ii) creep of stressed amorphous samples with creep or stress relaxation rates [7][8][9][10][11][12][13] which are larger by orders of magnitude than those in crystalline or polycrystalline materials.At medium electronic stopping power (5-30 keV͞nm) the occurrence of both deformation phenomena, i.e., (i) and (ii), requires some incubation fluence (dose) f c which depends on the electronic and nuclear stopping powers, irradiation temperature, and amorphous material properties [2,3,5,6].Recently, ion-beam induced anisotropic growth [14-17] and creep (or stress ...

External irradiation with heavy ions of neodymium silicate apatite ceramics and glass-ceramics

“…Indeed, it is known that under energetic ion bombardment, due to viscosity reduction resulting from the accumulation of atomic displacements and local heating, amorphous materials (oxides, metals) may exhibit plastic deformation (expansion) in the plane perpendicular to the ion beam, i.e. hammering effect [88,89,90]. We propose that it could be the impediment by the crystals of the residual glass creep in the direction perpendicular to the ion beam that would explain the apparent crystals sinking on the glass-ceramic surface (under irradiation the glass of reduced viscosity would rise on the edge of the crystals).…”

“…Literature [89,92] indicates that creep phenomena under heavy ion beams occurs in glassy materials only if the electronic stopping power Se of the ions is high enough and starts only after an incubation dose related to Se. This suggests that in our experiments the electronic stopping power of the 995 MeV Xe ions (Se = 17.5 keV/nm, Table 2) was probably too high and the fluence (2×10 13 ions/cm 2 ) was probably higher than the incubation one.…”

Elastic recoil detection (ERD) analysis of GeOx thin films

“…The energy stored in the electronic system is then transferred to the lattice, resulting in a large temperature rise for short duration ($10 À9 s) along the ion path. The maximum temperature increase in the system attained by this heating process depends on the deposited energy, S e , and on the width of its distribution (R T (s ea )), reached at a time of the order of s ea [17]. It is calculated by using relation…”

High electronic excitation-induced crystallization in Fe73.5Cu1Nb3Si13.5B9amorphous alloy: II. Carbon cluster irradiation

“…In the thermal spike model based on electron-atom interaction, the temperature increase does not lead to a local melting of the sample. In this case, the diffusion coefficient has to be calculated in a solid phase, and the characteristic time t will correspond to the complete electronic relaxation, 10 −9 s [42]. In this case, the calculated diffusion coefficient is D ∼ 10 −8 m 2 s −1 .…”