We report, in this paper, three different ways of producing amorphous alloys in the Al-Yb system, (i) Al80Yb20multilayered films were readily amorphized by 180 keV xenon ion mixing at room temperature(RT) to a dose of 3×1015 Xe/cm2. (ii) When the dose went up to 1×1016 Xe/cm2 or higher, a metastable phase of hcp structure was formed. Interestingly, the hcp phase turned into amorphous after annealing at 500°C for about 10 minutes. (iii) Amorphous alloys were also formed by steady state thermal annealing of the Al-Yb multilayered films at about 450 °C for 20 minutes. The optimum amorphization range was found out by experiments to be 17 to 30 Yb at%, i.e., within this composition range, the multilayered films could entirely be amorphized by solid state reaction.

The recrystallization behavior of the amorphous alloys formed by different methods was also studied and the difference in this aspect was thought to relate to the structures resulting from different processing methods.

Possible explanation of the observed sequence of phase transition is also discussed.

Radiation enhanced diffusion in the intermetallic alloy Cu3Au was measured directly for the first time. Ni and Pd tracer impurities were used to probe the diffusion of atoms occupying Cu and Au sublattice site's, respectively. Measurements were performed temperatures both above and below the ordering temperature, of TC =390°C The ability to grow high quality Cu3Au films by MBE with buried marker layers in the form of either (Cu2Ni)Au or Cu3(AuPd), made these measurements possible. Under irradiation with 0.75MeV Ar+ ions, the diffusion of Ni is approximately equal to that of Pd above Tc, but smaller below Tc. In the absence of irradiation, the thermal diffusion coefficients reveal a similar trend. Activation energies for RED for the two species are similar both above and below Tc whereas, in absence of irradiation, the activation enthalpies below Tc are different. These results are interpreted on the basis of lattice order.

The properties of low-energy (≤500 eV) displacement cascades in the ordered intermetallic compound CuTi have been investigated by molecular dynamics simulations in conjunction with recently-developed embedded-atom potentials. Various aspects of the time evolution of cascades produced by Cu and Ti primary knock-on atoms have been considered, including the dynamics of Frenkel-pair production, generation of ‘pure’ replacements and anti-site defects, and the anisotropy of the threshold energy for displacement. The spatial distributions of Frenkel defects and the damage function have been analyzed, based on information obtained from various simulated events corresponding to different recoil directions.

We present the results of a molecular dynamics simulation of the crystalline-to-amorphous transformation in the ordered intermetallic compound NiZr, using embedded-atom potentials. It is found that NiZr can be amorphized by random atom exchanges as well as by the introduction of Frenkel pairs. In both cases, the shear elastic constants C44 and C decreased drastically and eventually became equal. The average shear elastic constant fell to about 40% of its original value. These results are in general agreement with experimental observations.

The effect of Al ion irradiation on the mobility of Xe gas bubbles in Al thin films was investigated. Transmission electron microscopy was used to determine bubble diffusivities in films irradiated and/or annealed at 673K, 723K and 773K. Irradiation increased bubble diffusivity by a factor of 2–9 over that due to thermal annealing alone. The Arrehnius behavior and dose rate dependence of bubble diffusivity are consistent with a radiation enhanced diffusion phenomenon affecting a volume diffusion mechanism of bubble transport.

An investigation of the phase transformations experienced by the decagonal and icosahedral phases in two different quaternary -alloys is carried out. The transformation in the decagonal phase of Al-Cu-Co-Si alloy is induced by the electron radiation in a transmission electron microscope. However, in the icosahedral phase of Al-Cu-Co-Fe alloy this transformation is induced by annealing. Electron diffraction patterns obtained from both phases suggest that the deformation mechanism involved in these kind of transitions is related with twinning

Ion irradiation and annealing experiments have been conducted on Au/Cu bilayer films to evaluate the effect of irradiation on diffusion-induced grain boundary migration (DIGM). The Au films were prepared with a large-grained microstructure with grain boundaries perpendicular to the film surface and extending through the film thickness. Irradiations were conducted with 1.5 MeV Kr at 228°C. Rutherford backscattering spectrometry of the samples revealed that interdiffusion was substantially enhanced in the irradiated area relative to the unirradiated area. Both irradiated and annealed-only areas were characterized by a nearly uniform composition of 14 at.% and 7 at.% Cu respectively through the entire thickness of the underlying Au film. Small probe X-ray energy dispersive spectroscopy showed significant lateral compositional homogeneities in both irradiated and annealed areas. These two results are consistent with previous observations of DIGM in the Au/Cu system, suggesting that this previously unexamined interdiffusion mechanism contributes to ion beam mixing.

The relation between the ion irradiation induced grain growth in bilayer system and the basic parameters involved in ion beam mixing process was studied. TEM micrographs showed that a significant grain growth has been induced by Ar+ irradiation at room temperature. The grain size increases rapidly in low dose region, while it approaches a saturated value in high dose region, and it has close relationship with thermodynamic properties such as cohesive energy ( ΔHc ) and heat of mixing( ΔHm ). The experimental results are in good agreement with the model for the grain growth based on the thermal spike induced atomic migration.

Ion irradiation induced grain growth size distributions in Pd are examined at low temperatures. Two features are observed: 1) A majority of the grains saturate in size. 2) Some grains achieve sizes much larger than the average grain size and continue to grow with ion dose. However, by careful choice of ion mass and ion dose, it is possible to produce a sample possessing a monomodal grain size. This process will have applications in producing thin films of nanocrystalline materials.

Direct ion implantation of radioactive isotopes, such as 7Be or 22Na, has recently been of interest as a means of surface layer activation for purposes of wear-rate measurement in material systems for which activation by conventional proton irradiation is ineffective. Though direct implantation doses anticipated for adequate wear measurement sensitivity are expected to be quite low (∼1012 cm−2), the potential for alteration of wear properties by ion damage cannot be ignored. The present work was designed to simulate 22Na implantation with non-radioactive 20Ne irradiations into specimens of 17–4PH stainless steel which had been deliberately heat treated to contain 98 vol% metastable martensite. Specimens were subjected to doses of 2×1012, 2×1013 and 2×1014 cm−2 of 20Ne2+, applied at a total energy of 50 MeV, giving a projected ion range (determined by TRIM-91 computations) of approximately 10 μm. Nanoindentation surface hardness traverses were conducted to detect any material softening which may have resulted from ion-solid interactions within the projected range. Though doses of > 1014 cm−2 produced a detectable softening (apparent as a dip in the hardness level corresponding to locations near the end of the ion range) the maximum dose for a negligible effect on nanoindentation hardness was found to be approximately 1013 cm−2, well above the doses anticipated for use in wear studies employing direct ion implantation of radioisotopes.

Copper films sputter deposited on mechanically polished (optical finish) and on annealed substrates were laser-irradiated at various energy densities. The effect of the substrate condition on both the evaporation threshold and the morphology of the laser-irradiated metallic films was investigated. The energy density threshold for laser-induced evaporation of the copper films was studied using energy dispersive x-ray spectroscopy (EDS) in a scanning electron microscope (SEM). It was found that for annealed substrates the energy density threshold decreases relative to the threshold for the as-polished condition. These results are compared with predictions of a mathematical model that assumes that the near surface region of the as-polished ceramic is a highly damaged region and, thus, constitutes a thermal barrier. The film remains intact and with almost no change in morphology after laser irradiation at energy densities lower than 0.80 J/cm2 if the substrate has been previously annealed. On the other hand, copper films deposited on as-polished substrates break up during laser processing forming copper islands.

Repeated laser pulses at a single point on an aluminum thin film can reduce the power needed to melt or damage the surface as compared with CW application. This multi-pulse effect was found to depend on metal thickness and number of pulses, while being weakly dependent on the pulse length. This behavior appears to result from cumulative mechanical fatigue due to cyclic thermal stress in excess of the aluminum yield stress. This principle has been applied to cutting metal wires in microelectronic applications for deletive redundancy. The results suggest a significant advantage over CW laser application since the power needed to cut a metal wire is reduced by more than 70%, and 87% as compared to a single pulse.

Atomic-scale observations by STM and TEM of the early stages of film growth and recent studies of the detailed composition of beams from ICB sources have led to new understandings of origins of some of the extraordinary properties of thin films deposited by ICB methods. The presence of a small fraction of atoms in the form of large clusters initiates a novel sequence of film growth steps starting with the immediate formation of stable islands for film growth. The growth of films from cluster-initiated islands leads to fundamentally altered film properties (compared to atomic beam, MBE, deposition) such as the epitaxial alignment of metal/semiconductor/ceramic multilayers grown near room temperature.

The collision dynamics of Cu, Ni or Al clusters containing 92 atoms with substrates of these same metals were studied using molecular dynamics computer simulations. For energies of 1.0 keV or 326 eV, diverse behavior was observed, depending sensitively on the relative properties of the cluster and substrate. For Cu clusters impacting Cu substrates, the cluster plastically deforms the substrate and creates a deep crater with substrate atoms forming a ridge at the periphery of the crater. In contrast, Al clusters do not much deform Ni substrates, but rather tend to spread epitaxially over the surface. Several Al atoms dissociate from the cluster, and either reflect into the vacuum or scatter over the surface. 326 eV Ni clusters embed themselves almost completely within Al substrates and form localized amorphous zones.

An ionized cluster beam (ICB) source has been developed for high rate deposition, and its possible application to ultra large scale integrated circuit (ULSI) metallization was investigated. Aluminum films were deposited onto oxidized silicon wafers using the ICB source. It was shown that an electrical resistivity was almost the same as the value for bulk aluminum, and the surface morphology of deposited films was improved by controlling the ionization and acceleration conditions of the cluster beam. It was confirmed that the ICB method showed an excellent coverage profile in contact holes when compared with the conventional sputtering method. Using the directivity of cluster beams, contact holes of 1.5 in aspect ratio were successfully metallized. From these results, it became evident that the ICB source is a favorable method for ULSI metallization.

ABSTRACT:Epitaxial Al films have been grown on heavily doped Si(100) by neutral cluster beam deposition. The Al films were evaluated by RBS, RHEED, optical interference roughness maps and STM imaging. The results were consistent with the formation of epitaxial Al (110) bi-crystals similar to films grown by ionized cluster beam deposition on lightly-doped Si

The ionized cluster beam deposition (ICBD) technique has been employed to fabricate high-purity polyimide (PI) films. The pyromellitic dianhydride (PMDA) and oxydianiline (ODA) were deposited using dual ionized cluster beam (ICB) sources. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoemission spectroscopy (XPS) studies show that the bulk and surface chemical properties are very sensitive to the ICBD conditions such as cluster ion acceleration voltage and ionization voltage. At optimum ICBD conditions, the PI films have a maximum imidization and negligible impurities(∼;1% isoimide) probably due to the high surface migration energy and surface cleaning effect.

Electron-beam induced damage of some oxide superconductors is examined by high-resolution transmission electron microscopy (HRTEM), using both 1 MV high-voltage machine and conventional 200kV one. By 1 MV electron beam, both YBa2Cu4Oy and Y2Ba4Cu7Oy suffer from amorphization due to knock-on effects which is initiated at (CuO)2 double-chain sites. By 200kV beam, some of the double-chains decompose into the single-chains and precipitation of CuO crystal is induced, due to thermal heating effects. Both Bi- and Pb-based superconductors, on the other hand, suffer from amorphizations at both 1MV and 200kV. The materials relating to La2CuO4, for instance the T*-type of superconductor (Nd, Sr, Ce)2CuO4, never amorphize even by irradiations of 1000kV electron beam. These results suggest that it is possible to introduce defects or precipitates to control the microstructures of superconductors by means of electron beam irradiations.

Up to 25 times enhancement of magnetic critical current density has been observed at 70 K and 2500 O for 3% 6Li-doped sintered YBCO sample irradiated with thermal neutrons at a dose of 1 × 1018 n/cm2. High energy reaction product of 6Li and thermal neutron, the 2.73 MeV 3H and 2.05 MeV 4He produced uniform damage throughout the bulk sample. The strong field dependence of the Jc enhancement points to the weak center nature of the radiation defects. The upper critical field of this weak center decreases with temperature, and is about 800, 300, 150 Oe at 30, 50, 70 K respectively.

The existence of effective pinning in single T1-layer 1223 superconductors has been reported [1–3], as opposed to lower values in T1- and Bi-double layer systems, which is intimately related to their crystal structures. In order to investigate the possibility of T1–1223 being applied as a practical superconductor, tape shaped wires of the chemical composition (T10.5Pb0.51 (Sr0.8Ba0.2Ca2Cu3O9were prepared. Transport Jc of T1–1223 was measured to be 1.8 × 104 A/cm2 at 77K in the absence of a magnetic field. These results seem to imply that T1–1223 has, not only effective pinning because of having a more 3-dimensional vortex line lattice like YBa2Cu3O7, but also better grain boundary weak-link performance than YBa2Cu3O7. PresenT1y it appears that T1–1223 may be a superior choice to make better superconducting wire, because of these considerations and of the higher Tc of 120K.

(T10.5Pb0.5)1Sr2CaCu2O7 (T1–1212) also seems to have effective pinning, as well as T1–1223, supporting the idea that shorter Cu-O plane spacing, or absence of thicker insulating region such as T12O2 or Bi2O2 double layer, are beneficial for effective pinning through facilitating a better 3D-like vortex line lattice [4, 5]. Our “1212” and “1223” samples are good counter examples to the 2D pancake-like vortex theory [6, 7].