Microstructural changes of surfaces during ion implantation have been investigated on the atomic level by molecular dynamics computer simulations. Unlike past surface studies, which have been focused on the problem of sputtering, the current work examines the effects of collective materials response on surface topography. Collective behavior has been noted for the crystal interior in the context of thermal spikes, but we show here that it can lead to far more dramatic consequences at the surface. The investigation includes implantation in several metals, but emphasizing Pt, Si and Ge. In addition, the study includes the first simulations of implantations of a metallic glass, CuTi, and amorphous Si.

New insight into damage formation in Si(100) during self-ion irradiation is gained from processing under extreme conditions. Dislocations form in the near-surface as a result of lattice relaxation in response to strain produced by precursor defects which are shown to be vacancy-type by positron analysis. A model to account for these defects and their distribution is presented. A novel technique is demonstrated which utilizes a subsequent implantation as a depth specific probe to manipulate the vacancy-type defects. Aspects of damage growth which emerge from the probe results are discussed.

Ejection properties of particles emitted from a keV-atom-bombarded Ag{100} surface are calculated using classical dynamics to model the energy dissipation process. The ejection behavior of the sputtered particles depends strongly on the time interval between the instant of the primary impact on the surface and the moment when the emitting surface atom passes the cutoff boundary of the interaction potential. Both the sputtered neutrals and ions have a similar collision-time distribution. Most particles eject from the surface within 350 fsec after the primary impact. The sputter intensity maximized at around 145 fsec. For particles leaving the surface after -100 fsec of the primary impact, the preferred azimuths of ejection are not sensitive to the collision time. The angular distribution of sputtered particles is less dependent of the collision time than of the ejection energy. The angular anisotropy is also significantly enhanced at high collision times. The results find applications in the characterization and imaging of material surfaces.

A 2-D model for boron implantation into (100) silicon through overlying oxide layers has been developed and implemented into the process simulator FLOOPS. This model is both accurate and computationally efficient and shows explicit dependencies on all of the key implant parameters: energy, dose, tilt and rotation angles, oxide layer thickness, mask height, mask edge orientation, and rotation of the wafer during implantation.

Tight-binding molecular dynamics (TBMD) simulations are performed (i) to evaluate the formation and binding energies of point defects and defect clusters, (ii) to compute the diffusivity of self-interstitial and vacancy in crystalline silicon, and (iii) to characterize the diffusion path and mechanism at the atomistic level. In addition, the interaction between individual defects and their clustering is investigated.

We performed molecular dynamics simulations to investigate the process of defect production in pure vanadium. The interaction of atoms was described by the EAM interatomic potential modified at short range to merge smoothly with the universal potential for description of the high energy recoils in cascades. The melting point of this EAM model of vanadium was found to be consistent with the experimental melting temperature. The threshold energies of displacement events in the model system are also consistent with experimental minimum threshold in vanadium, and its average was found to be 44 eV. We evaluated the efficiencies of defect production in the displacement events initiated by recoils with kinetic energy up to 5 keV, and found that the probability of cluster formation is smaller than that of simulated events in fee metals reported in the literature.

We present results of multiple-time-scale simulations of 5, 10 and 15 keV low temperature ion implantation of arsenic on silicon (100), followed by high temperature anneals. The simulations start with a molecular dynamics (MD) calculation of the primary state of damage after l0ps. The results are then coupled to a kinetic Monte Carlo (MC) simulation of bulk defect diffusion and clustering. Dose accumulation is achieved considering that at low temperatures the damage produced in the lattice is stable. After the desired dose is accumulated, the system is annealed at 800 °C for several seconds. The results provide information on the evolution for the damage microstructure over macroscopic length and time scales and affords direct comparison to experimental results. We discuss the database of inputs to the MC model and how it affects the diffusion process.

Secondary ion mass spectrometry (SIMS) is used to produce depth profiles of ion-implanted phosphorus in silicon. The implant energies are 250, 500, and 750 keV, and there is a 0.06-μm thick oxide on the silicon. The experimental profiles are compared with predictions from a variety of simulation programs, most of which give larger projected ranges than the data. The silicon crystal structure needs to be included in the calculations to produce projected ranges and depth profiles that agree with the present experimental data and with data from the literature.

The effects of 75-keV Ne+ and 300-keV Ni+ bombardment on electron radiation-induced segregation (RIS) in a Ni-9at%Al alloy were investigated in-situ using the HVEM (high voltage electron microscope)/Tandem accelerator facility at Argonne National Laboratory. The radial component of defect fluxes generated by a highly-focused 900-keV electron beam was used to induce segregation of Al atoms towards the center of the electron irradiated area via the inverse-Kirkendall effect. The radial segregation rate was monitored by measuring the increase in the diameter of the Al enriched zone within which γ'-νi3αl precipitates form during irradiation. Both dual electron-ion and pre-implanted ion-electron irradiations were performed in an attempt to separate the contributions of energetic displacement cascades and implanted ions acting as defect trapping sites to RIS suppression. It was found that 75-keV Ne implantation has a retarding effect on RIS.

A procedure of deflection of backscattered neutral atoms with low energy E° = (250÷3000) eV based on neutral ionization by electron impact has been developed. The ionization degrees η+of Ar atoms single scattered at the angle θ=138° from V and VI period metal polycrystal surfaces as well inelastic energy losses Q have been measured. It has been found that both η+ and Q changed nonmonotonically within each period. It has been shown that for the elements of the same group under otherwise equal conditions η+ at the scattering from V period elements appeared to be always higher than those for the VI period. It has been established that at scattering from MoRe alloy surface η+ in peaks of single scattering from Mo and Re the metal target values coincided with corresponding values measured for pure Mo and Re metal targets. Using the results obtained one could draw some conclusions about the dependence of the charge state on the target structure.

Six binary metal systems were selected to study the possibility of forming amorphous alloys by ion mixing or thermal annealing in multilayered Films, i.e. the Ta-Cu, Zr-Nb, Zr-Ta, Y-Zr, Y-Mo and Y-Ta systems, featuring positive heats of formation (ΔHf) ranging from +3 to +40 kJ/mol. Firstly, the interfacial free energy consisting of a chemical and an elastic terms was calculated and added to the energetic state of the multilayers. It was found that the excess interfacial free energy increased with increasing the fraction of the interfacial atoms in the multilayers, and could raise the multilayers to an energy level intersecting with or being higher than thai of the amorphous phase possessing a typical convex shape. It is therefore possible to produce amorphous alloys in such systems, if the multilayered filins included enough fraction of the interfacial atoms. The multilayered samples were then designed and prepared accordingly and both ion mixing and thermal annealing under appropriate conditions resulted in the formation of a number of new amorphous alloys, confirming the above prediction based on the interfacial free energy concern. It is noted that the success of synthesising amorphous alloys by solid-state reaction in the immiscible systems develops a new glass forming technique, namely interface-generated spontaneous amorphization, which has a great potential to produce new and relatively thick amorphous films, e.g. a Ta72Cu28 amorphous film of 800 nm thick was obtained.

Ion beam mixing involving insulator substrates is reviewed with an emphasis on thermochemical considerations. Studies generally have employed the bi-layer geometry for metal/insulator or oxide/oxide combinations. There is little evidence for long-range material transport in crystalline substrates.

Recoil mixing has been detected for both metal and oxide films deposited on sapphire and irradiated at room temperature. Agglomeration of non-wetting metal films suggests that surface diffusion is induced by the ion beam. Evidence has been reported for the occurrence of chemical reactions and perhaps thermally-induced migration in amorphous aluminum oxide substrates.

Ballistic mixing is also indicated for metal films on SiC, Si3N4 and SiO2. Ion beam-induced reactions have been observed at the interfaces for systems in which the enthalpy of reaction is favorable. Chemical effects in the cascade mixing regime may determine the phases present in the mixed zone after the composition changes caused by ballistic processes.

We have used 200 keV carbon ions to enhance the adhesion of 240-nm thick Be films to polished, vitreous carbon substrates. Adhesion of the as-deposited films was below that necessary to pass the scotch-tape test, but carbon ion fluences less than 1.6xl014 C/cm2 were sufficient to ensure the passage of the tape test without affecting the optical properties of the films. Adhesion failure of the as-deposited film was attributed to an inner oxide layer between the Be and the carbon. Because this oxide (-5 nm of BeO) was not measurably changed by the irradiation process, these results are consistent with adhesion enhancement occurring on the atomic scale at the interface between the inner oxide and the carbon substrate, and this conclusion was supported by Rutherford backscattering (RBS) data. Potential adhesion mechanisms are discussed with consideration of relative contributions from electronic and nuclear stopping.

Thin sputtered ceramic films deposited on ceramic substrates were subjected to either Kr+ or Xe+ ion bombardment for ion beam mixing studies in ceramic-ceramic systems. The amount of mixing if any was evaluated from Rutherford backscattering and Auger electron spectroscopy. In some instances ceramic films were deposited on epitaxial films or single crystal substrates for ion channeling analysis. No significant mixing was observed in any of the systems with ZrC. However, analysis of the interface in Si3N4/ SiC system indicates appreciable mixing and ion beam induced damage to the substrate. The mixing appears to be dose dependent for heavier ions.

Interfacial roughening during ion irradiation of an immiscible system is investigated by Monte Carlo computer simulation and by an x-ray diffraction technique called crystal truncation rod (CTR) analysis. In the simulations, ion flux and sample temperature are varied, and the system is allowed to evolve under irradiation until it reaches a steady state behavior. The observed behaviors are then sought experimentally in the Cu/Nb system implanted with 2 MeV Kr+ ions at different sample temperatures. Analysis of the roughness at the Cu interface is based upon the existence of a crystal truncation rod, which contains information on exactly how the crystal is terminated, or, in other words, the interfacial roughness. Rutherford backscattering spectrometry (RBS) is also used to study the intermixing of the Cu and Nb layers.

Thermal and irradiation induced intermixing of uranium suicide reactor fuels with the aluminum cladding is an important consideration in understanding their fission gas and fuel swelling behavior. We have used Rutherford backscattering to follow the behavior of an Al thin film on U3Si and U3Si2 during 1.5 MeV Kr ion irradiation at temperatures of 30 and 350°C. After an initial dose during which no intermixing occurs, the Al mixes quickly into U3Si. The threshold dose is believed to be associated with an oxide layer between the Al and the uranium suicide. At 300°C and doses greater than threshold, rates of mixing and aluminide phase growth are extracted.

Transmission electron microscopy was used to study the effect of nitrogen-ion irradiation on the microstructure of ion-plasma TiN coating deposited on a substrate of austenitic stainless steel. The principal peculiarities of the changes in the fine structure at the substrate-coating interface and in the bulk of the coatings having a thickness of several micrometers have been revealed for the conditions of ion-beam-assisted deposition and plasma-assisted deposition. Possible mechanisms for the effect of ion irradiation on the microstructure of the substrate-coating composition are discussed.

Defect creation in refractory oxides known to be unsensitive to radiolysis, was shown to take place by high level electronic excitations induced by swift heavy ions or energetic cluster bombardments. Depending on the oxide a threshold in electronic energy loss for damage production was observed : MgO 22 keV/nm, AI2O3 20 keV/nm and LiNbO3 6 keV/nm. A very strong dependence on the energy deposited for the defect production was evidenced above the threshold. In MgO, both point and extended defects were created whereas in AI2O3 only extended defects were observed and in LiNbO3 amorphization in the ion track was evidenced.

Atomic displacements due to the giant electronic excitations can be revealed at metal-oxide interfaces in the case of Na nanoprecipitates embedded in MgO single crystals.

In-situ stress measurements on single crystal MgO and A1203 have been performed during ion irradiation. A cantilevered beam sample arrangement was used, with the stress in the implanted layer determined from the deflection of the sample as measured by the change in capacitance between the free end of the sample and a reference electrode. Point defect concentrations are obtained by dividing the volume strain by the defect relaxation volume, with saturation values of 0.8 to 1.2% obtained for 1.0 MeV Ne, Ar and Kr irradiations. Defect production is sublinear with dose, with an efficiency of less than 25% compared to Kinchin-Pease predictions. Ionization induced annealing is evaluated with 1.0 MeV He and 1.0 MeV H irradiations following heavy ion irradiation.

We have measured surface roughening kinetics during low energy Xe ion sputtering of Ge (001) surfaces. The results are interpreted in terms of an instability theory developed by Bradley and Harper [1]. Although the calculated magnitude of the roughening rate does not agree with the measured value, the variation of the rate with ion flux and energy is in agreement with the theory.