Meetings & Events

fall 1997 logo1997 MRS Fall Meeting & Exhibit

December 1 - 5, 1997 | Boston
Meeting Chairs:
 Harry A. Atwater, Peter F. Green, Dean W. Face, A. Lindsay Greer 
 

Symposium KK—Atomistic Mechanisms in Beam Synthesis and Irradiation of Materials

-MRS-

Chairs

J. Charles Barbour Daryush Ila, Sandia National Laboratories Alabama A&M Univ
Sjoerd Roorda Masanori Tsujioka, Univ of Montreal Dept of Inorganic Matls Res

Symposium Support 

  • Alabama A&M University, Center for Irradiation of Material 
  • High Voltage Engineering Europa B.V.
  • National Electrostatics Corp.
  • Sumitomo Electric Industries Ltd.

1997 Fall Exhibitor

Proceedings published as Volume 504 
of the Materials Research Society 
Symposium Proceedings Series.

* Invited paper

SESSION KK1: DEFECTS AND MODELING 
Chairs: Barend J. Thijsse and Michael O. Thompson 
Monday Morning, December 1, 1997 
Essex West (W)

8:30 AM *KK1.1 
DEFECT EVOLUTION IN ION IMPLANTED Si: FROM POINT TO EXTENDED DEFECTS. Sebania Libertino, INFM and Dipartimento di Fisica, Universite di Catania, Catania, ITALY; Janet L. Benton, Bell Labs, Lucent Technologies, Murray Hill, NJ; Salvo Coffa, CNR-IMETEM, Catania, ITALY; Lourdes Pelaz, Dave J. Eaglesham, Bell Labs, Lucent Technologies, Murray Hill, NJ.

Ion implantation is widely used in the processing of VLSI Si devices. However, ion beam damage is responsible of several phenomena, such as transient enhanced diffusion (TED) and extended defects formation, which severely hamper our ability to fabricate sub-micron devices. In order to understand and model these processes, the question of how the interstitial-vacancy (I-V) pairs produced by the beam evolves into defect clusters and extended defects has to be properly answered. In this talk I will review recent experiments elucidating the role of impurities (C, O), dopants (B, P) and extra implanted ion on defect evolution. Deep level transient spectroscopy analyses were used to monitor the defect structure of either ion implanted or electron irradiated Si samples annealed at 100-800 ƒC. In both cases the room temperature defect structure consists of I- and V-type point defect pairs, such as divacancies and carbon-oxygen complexes, storing an equal number of I and V. Thermal processes produce a concomitant annealing of I- and V-type complexes demonstrating that defect annihilation occurs preferentially in the bulk. At temperature above 300 ƒC, when all V-type defects have been annealed out, ion implanted samples present a residual I-type damage, storing 2-3 I per implanted ion. This unbalance between V and I, not observed in electron irradiated samples, is a direct consequence of the extra implanted ion. In the fluence and annealing temperature range where extended defects are not formed, the residual damage is dominated by Si interstitial clusters in which 40 to 125 Si self-interstitials are stored. The dissolution of these clusters has been correlated with TED phenomena occuring in the absence of extended defects. Finally, at higher implantation fluence, signatures of extended defects are observed and associated to the presence of 311 defects detected by transmission electron microscopy analyses. These results will be compared with the predictions of atomistic and kinetic Monte Carlo simulations and the implications on our current understanding of defect evolution in Si will be discussed.

9:00 AM KK1.2 
SPATIAL ISOLATION OF VACANCY SUPERSATURATIONS PRODUCED BY MeV IMPLANTATION USING THIN, SELF-SUPPORTING MEMBRANES. V.C. Venezia, T.E. Haynes, A. Agarwal, Oak Ridge National Laboratory, Oak Ridge, TN; H.-J. Gossmann, S.B. Herner, D. J. Eaglesham, Bell Laboratories, Lucent Technologies, Mrray Hill, NJ; L. Riciputi, Oak Ridge National Laboratory, Oak Ridge, TN.

Defects induced by ion implantation play an important role in materials modification. Distributions of interstitials and vacancies are created as ions collide with lattice atoms. For high-energy ion implantation (MeV) the spatial separation between these distributions becomes large enough that a net point defect imbalance is created as a function of depth within the sample. The imbalance consists of interstitial and interstitial clusters near the ion's projected range and vacancy and vacancy clusters in the near surface region. Experimental evidence for the vacancy-rich region produced by MeV implantation in silicon includes annihilation of interstitial clusters (311's and dislocation loops) and detection of open volume defects by positron annihilation spectroscopy. Although the interstitial and vacancy clusters are spatially separated, they are not completely independent of each other. For instance, experiments have shown that interstitials may be released from the deep clusters during annealing and recombine with vacancies in the near surface region, thereby lowering the vacancy supersaturation. Isolation of the vacancy rich from the interstitial rich region would permit more controlled studies of defect-defect and impurity-defect interactions, especially those involving vacancies. In this work, isolation of the vacancy-rich near surface region was accomplished by implanting MeV ions through thin, self-supporting silicon membranes prepared by selective chemical etching. The membranes were made from molecular-beam epitaxially grown silicon containing both Sb and B diffusion markers. Sb and B were chosen because of their complementary sensitivity during diffusion to vacancies and interstitials, respectively. Diffusion profiles of these markers following MeV implantation and annealing were then analyzed to monitor vacancy and interstitial fluxes as functions of implantation dose and temperature and of annealing temperature and time. These results will be discussed in terms of the dynamics of vacancy cluster dissolution in the presence and absence of interstitial sources.

9:15 AM KK1.3 
IN-SITU DLTS MEASUREMENT OF METASTABLE COUPLING BETWEEN PROTON-INDUCED DEFECTS AND IMPURITIES IN n-Si. K. Kono, N. Kishimoto, H. Amekura, National Research Institute for Metals, Tsukuba, Ibaraki, JAPAN.

Deep level transient spectroscopy has been conducted to reveal electronic states of defects in n-Si, under 17 MeV-proton irradiation. The DLTS device was installed into a beam line of the accelerator. The in-situ experiment was concentrated on, to trace dynamical evolution and effects of irradiation temperature on the deep centers. In order to study the interaction between defects and various impurities, FZ-Si of a low oxygen concentration was compared to CZ-Si. Samples were fabricated from n-Si wafers. Resistivity of the CZ and FZ wafers was about 10 and 3-5 cm, respectively. A Schottky barrier was formed by vacuum evaporation of gold. The samples were irradiated with 17 MeV protons. The total fluence was varied between 5.61012 ion/cm7.21013 ion/cm2. After the irradiation, isochronal (30 min) or isothermal (250 K) annealing was conducted. Measurement was carried out right after the irradiation or after the annealing, without exposing to room temperature. After the irradiation, deep levels of V-O, V-V and P-V were observed both in FZ- and CZ-Si. However, the FZ-Si showed a much weaker V-O signal than the CZ-Si, reflecting the lower oxygen concentration. Also, carbon-related levels, such as Cs- Sii, Ci or Cs-Ci, were detected. Intensity of those levels varied depending on irradiation/annealing conditions and the sample type; FZ or CZ. The variations indicate metastable coupling between impurities and proton-induced defects and that they change the population even below room temperature. The evolution of the deep levels will be discussed at the conference.

10:00 AM KK1.4 
INTRIGUING MICROSTRUCTURAL CHANGES IN ULTRA-HIGH DOSE Si IMPLANTATION INTO CRYSTALLINE AND AMORPHOUS SILICON. X.F. Zhu and J.S. Williams, Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, Australian National University, Canberra, AUSTRALIA.

In this study high dose Si implants to doses 1Ol8cm-2 into both crystalline and amorphous Si at temperatures up to 250C have revealed extremely large structural differences depending on implantation conditions. The implanted Si has been examined by time resolved reflectivity (TRR) to measure the crystallization kinetics, ion channeling (RBS) to measure disorder distributions and sputter rates, and transmission electron microscopy to measure microstructural changes. For high dose implantation into amorphous silicon, the epitaxial regrowth rates were ``normal'' (i.e. comparable with lower dose implants) under some conditions but very stow and often totally interrupted growth under other conditions (usually elevated temperature implantation). In crystalline Si, for implantation at and below room temperature, amorphous layers were formed which usually exhibited normal recrystallisation behaviour, whereas elevated temperature implantation conditions could generate complex amorphous and highly dislocated structures which exhibited odd behaviour on annealing. In a narrow temperature band, intriguing porous-like structures are generated which may be similar to those previously observed in implanted Ge. The observed behaviour is discussed in terms of defect-mediated processes during bombardment, beam-induced densification and flow, and formation of open volume defects, depending on the implantation conditions.

10:15 AM KK1.5 
NUMERICAL MODELING AND MODEL VERIFICATION DURING PULSED ION BEAM SURFACE TREATMENT. Michael O. Thompson, Cornell University, Dept. of Materials Science, Ithaca, NY; Timothy J. Renk, Sandia National Laboratories, Albuquerque, NM.

Pulsed ion beams with fluences of a few J/cm2 delivered over several hundred nanoseconds provide an efficient mechanism for rapid melt and solidification processing of metal alloys. In contrast to laser processing, the energy deposition for ions depends on the specific ions and the temporal voltage profiles, varying from near surface only using Xe ions to nearly uniform heating over 3-10 m with protons. One dimensional heat flow simulations, routinely used to model the melt behavior, are constrained by poor knowledge of high temperature thermal properties, further limiting our ability to quantitatively model the critical phase transformations. Bright and dark field in-situ optical measurements of metals, alloys, and semiconductors have been used to calibrate and verify 1-D numerical models. Bulk Si, with well known thermal properties, was used to examine the role of incident ion species on the melt and to provide overall verification of the numerical models with no free parameters. Diffusion of impurities in Si show that even for melts of 3 s, the melt puddles are quiescent and convective mixing is not significant. Using the onset of ablation, the thermal conductivity of liquid Si was also estimated. Measurements on Ti and Fe-based alloys show significant dependence of the solidification behavior on the thermal conductivity of the substrate alloys. Because of the relatively low enthalpy of melting for metallic alloys, these variations result in substantial changes in the quench rate and solidification velocities, and consequently in the final microstructure.

10:30 AM KK1.6 
MODELING COLLISION CASCADE STRUCTURE OF SiO2, Si3N4, AND SiC USING LOCAL TOPOLOGICAL APPROACHES. C. Esther Jesurum, Linn W. Hobbs, Vinay Pulim, Bonnie Berger, Massachusetts Institute of Technology, Departments of Mathematics, Materials Science & Engineering, and Laboratory of Computer Science, Cambridge, MA.

Many crystalline ceramics can be amorphized within high-energy collision cascades whose overlap leads to global structural amorphization. Because the structural rearrangements amount to topological disordering, we have chosen to model these rearrangements using a topological modeling tool as an alternative to molecular dynamics simulations. We focus on the tetrahedral network compounds SiO2, Si3N4, and SiC, each compound comprising corner-sharing tetrahedral units, because they represent increasingly topologically constrained structures. SiO2 and SiC are easily amorphized experimentally, whereas Si3N4 proves very difficult to amorphize. In this model, we consider the tetrahedron as the base unit, whose identity is largely retained throughout. In a collision cascade, all bonds in the neighborhood of a designated tetrahedron are broken, and we reform bonds in this region according to a set of local rules appropriate to crystalline assembly, each tetrahedron coordinating with available neighboring tetrahedra (insofar as is possible) in accordance with these rules. We generate fairly well connected amorphized structures for SiO2, but run into underconnected networks for Si3N4 and SiC which are irreparable without rebreaking and reforming primary tetrahedral bonds. The resulting structures are analyzed for ring content, bond angle distributions and radial density function for comparison to the crystalline precursors.

10:45 AM KK1.7 
ATOMISTIC SIMULATION OF DEFECT PRODUCTION IN -SiC. R. Devanathan and W.J. Weber, Pacific Northwest National Laboratory, Richland, WA; T. Diaz de la Rubia, Lawrence Livermore National Laboratory, Livermore, CA.

Silicon carbide (SiC) has potential applications as a structural material in fusion reactors and as a wide band-gap semiconductor in electronic and electro optic devices. Atomic displacement by nuclear radiation or by energetic ion beams used in device processing will result in the formation of lattice defects. The evolution of these non-equilibrium defects determines the performance of the materials and devices. In the present work, the displacement threshold energy surface and defect formation energies in -SiC have been calculated using molecular dynamics simulations with periodic cells containing 8000 atoms. The interactions of the atoms were modeled by a modified form of the Tersoff potential1 combined with an ab initio repulsive potential2. The results indicate that the threshold energy surface in -SiC is highly anisotropic. For instance, the energy for Si displacements is 36 eV along [001] but 113 eV along [111]. These results will be discussed in light of previous experimental studies of point defect production in SiC.

11:00 AM KK1.8 
THE INFLUENCE OF STRESS DURING ION BEAM MIXING. M. Nastasi, Y.-C. Lu, H. Kung, Material Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM; S. Fayeulle, Laboratoire Materiaux-Mecanique Physique, UMR CNRS, Ecully, FRANCE; P. Torri, University of Helsinki, FINLAND; J.P. Hirvonen, Joint Research Center, Institute For Advanced Materials, Petten, NETHERLANDS.

It is well established that thermodynamic forces influence ion mixing. Systems with a negative enthalpy of formation experience enhance ion mixing while systems with a positive enthalpy of formation experience no mixing or even ``de-mixing''. Recent experimental result have suggested that intrinsic stresses should be considered when evaluating the thermodynamic driving forces that influence ion mixing. We have studied the effects of thermal annealing and Ar ion irradiation on the structure and stability of multilayered DC sputtered thin films of TiN/B-C-N. These samples are in a state of bi-axial compression in their as-deposited form. Following thermal annealing, to temperatures as high as 1000C for 1 hr. it is observed that the intrinsic stresses are rapidly relieved and no interdiffusion or break down of the layered structure takes place. However, when samples are ion irradiated, we do observe intermixing and at the highest dose (5x106 ions/cm2) the multilayered structure partly disappears. The rate of intermixing is well correlated with the magnitude of compressive stress as a function of dose. We believe that the observed ion mixing, in this otherwise immiscible system, is being controlled by stress derived thermodynamic forces.

11:15 AM KK1.9 
EFFECTS OF HEAVY ION CASCADE ENVIRONMENTS ON THE SUPPRESSION OF RADIATION-INDUCED SEGREGATION IN ALLOYS. M.J. Giacobbe, L.E. Rehn, N.Q. Lam, P.R. Okamoto, L. Funk, and P. Baldo, Materials Science Division, Argonne National Laboratory, Argonne, IL; and J.F. Stubbins, Department of Nuclear Engineering, University of Illinois, Urbana, IL.

Previous Rutherford backscattering (RBS) investigations have demonstrated that near-surface Au depletion in a Cu-1at.% Au alloy during 1.5-MeV He ion irradiation is suppressed by concurrent heavy-ion bombardment. The dual irradiation effect suggests that short-lived cascade remnants from heavy-ion irradiations act as recombination centers for freely migrating defects (FMDs), reducing radiation-induced segregation (RIS). The suppression effect of heavy-ion bombardment increases with increasing heavy-ion damage rate (the He damage rate being held constant) until a critical value is obtained at which the concurrent ion irradiation produces the same depletion rate as the heavy-ion beam alone. We present a simple analysis which indicates that this critical value represents the dose rate at which resultant cascades fill the fraction of the irradiation volume necessary to annihilate all FMDs produced by light ions. To test this interpretation, we are conducting further RBS and in situ TEM studies employing various heavy ions, including Ti, Cu, Ni, and Ag.

11:30 AM KK1.10 
INFLUENCE OF 85 MeV OXYGEN ION IRRADIATION ON THE MAGNETIC PROPERTIES OF NANO-SIZED AND MICRO-SIZED POWDERS OF STRONTIUM FERRITE. S.I. Patil, S.R. Shinde, S.K. Date and S.B. Ogale, Department of Physics, University of Pune, pune, INDIA; G. Mehta, Nuclear Science Centre, New Delhi, INDIA; G. Marest, Institut de Physique Nucleaire de Lyon, CNRS-IN2P3, Universite Claude Bernard, Villeurbanne, FRANCE.

Strontium Ferrite powders having an average particle diameter of 40 nm, 100 nm and 1-2 microns were irradiated with 85 MeV 16O ions at a nominal dose of 1014 ions/cm2. The 40 nm powder had a coercive field of about 6665 Oe close to the theoretical value for single domain particles; this value being a factor of five larger than the coercive field observed for the multidomain particles with average size between 1-2 microns. It was observed that the magnetic properties viz. retentivity, coercivity, the shape of the hysterisis loop and the permeability are significantly modified after irradiation in the case of the multidomain large particles while no change occurs in the case of the nanosizced particles. Those data are explained in terms of the defect-domain wall interaction and directional ordering of Weiss domains. The stability of nanosized powders upon irradiation suggests that either the defects are not stable in small systems or that they are dynamically annealed out due to localiation of thermal energy. The observed changes in the case of micron-sized powders can be explained on the basis of thermal spike model, and points to the possibility of grain refinement.

11:45 AM KK1.11 
ION BEAM MIXING AND DEMIXING OF CO/CU MULTILAYERS PROBED BY X-RAY AND MAGNETOTRANSPORT MEASUREMENTS. M. Cai, T. Veres, R.W. Cochrane, S. Roorda, Dept. de physique, Univ. de Montreal, Montreal, CANADA; R. Abdouche, M. Sutton, Dept. of Physics, McGill Univ., Montreal, CANADA.

X-ray and magnetotransport properties of Cu/Co multilayers following ion beam mixing and thermal annealing show that both the giant magnetoresistance and the ion beam mixing in this system are dominated by an extremely thin interface layer. A series of (Co 17 /Cu 22 ) multilayers, repeated 30 times, was deposited by Ar sputtering onto glass substrates. This choice of Cu thickness resulted in room temperature giant magnetoresistances between 15 and 18 % in the as-deposited films. Grazing angle x-ray reflectivity, magnetization and magnetoresistance were measured before and after irradiation with 1 MeV Si ions at 77 K and also after thermal annealing in vacuum. Ion doses ranged from 1013 to 1015 cm-2 and anneal temperatures from 100 to 350 circC. X-ray reflectivity reveals that ion bombardment produces a blurring of the interface; this modification is accompanied by a systematic suppression in the interlayer antiferromagnetic coupling and the magnetoresistance. For ion doses not exceeding 5 x 1014 cm-2, both the higher order reflectivity peaks and the magnetoresistance can be restored by annealing this strongly immiscible system at temperatures up to 300 circC. Two main conclusions can be drawn: ion beam mixing under these circumstances does not exceed half the interlayer thickness (5 to 7 ) and such a small amount of intermixing is enough to destroy the interlayer antiferromagnetic coupling and the giant magnetoresistance.

SESSION KK2: MATERIAL FLOW, CERAMIC MATERIALS, AND CLUSTER-BEAM DEPOSITION 
Chairs: Carmine A. Carosella and Edwin Snoeks 
Monday Afternoon, December 1, 1997 
Essex West (W)

1:30 PM *KK2.1 
DOES THE LATENT TRACK APPEARANCE IN AMORPHOUS MATERIALS RESULT FROM A TRANSIENT THERMAL PROCESS? Marcel Toulemonde+, Ch. Dufouro, and E. Paumier+o, +CIRIL (CEA,CNRS), Caen, FRANCE; OLERMAT-ISMRA (upresa 6004 CNRS), Caen, FRANCE.

Heavy ion irradiations in the electron stopping power regime have been performed in amorphous materials [1,2]. Latent track radii have been observed in amorphous semi-conductors (a-Ge, a-Si) and have been deduced from a phenomenological analysis in amorphous metallic alloys and in vitreous silica. A transient thermal model is developed including energy diffusion on the electron gas, on the atomic lattice and the energy exchange between the two systems. According to Fick's law, the classical equations of heat flow on the two subsystems (electrons and atoms) are numerically [3] solved in a cylindrical geometry taking into account the evolution of all the parameters versus the temperature. Assuming that the latent track results from the quench of a molten phase, the radii of these latent tracks are reproduced in the amorphous semi-conductors with the same value of the electron-phonon coupling despite their large differences in the lattice thermodynamical parameters. Such a modelisation will be applied to amorphous metallic alloys and vitreous silica.

2:00 PM KK2.2 
MECHANISMS OF ENERGY TRANSFER IN SOLIDS IRRADIATED WITH SWIFT HEAVY IONS. G. Szenes, Institute for General Physics, Eötvös University, Budapest, HUNGARY.

The efficiency of energy deposition in the thermal spike g is deduced from the available experimental data on amorphous track formation. A model is applied which provides for insulators an analytical description and scaling without fitting parameters. The g value varies with the ion velocity from g=0.17 for high velocity irradiation (E7.6 MeV/nucleon) up to g=0.36 for low velocity irradiations [l]. This increase of g is the consequence of the change in contributions to the energy deposition. Various ionic and thermal spike mechanisms of energy deposition proposed so far are critically examined. Our analysis suggests that mechanisms related to the ion density in the track region may have significant contributions. However, the thermal energy of the spike is much higher than the electrostatic energy of the ionic spike and the short lifetime of the ionic spike is also a limiting factor.

2:15 PM KK2.3 
TEMPERATURE DEPENDENCE OF STRUCTURAL CHANGES, PLASTIC FLOW, DEFORMATION AND DEFECT KINETICS DURING MeV ION IRRADIATION OF SILICA. M.L. Brongersma, E. Snoeks, D. Peters, J.H.R. dos Santos and A. Polman, FOM-Institute for Atomic and Molecular Physics, Amsterdam, NETHERLANDS.

In-situ wafer curvature measurements were performed to determine the mechanical stress in thermally grown SiO2 films on Si during 4 MeV ion irradiation at various temperatures in the range of 95 K - 575 K. It is demonstrated that radiation induced structural changes in these films result in a stress change without a density change for a fluence of roughly 10l3 Xe/cm2. Furthermore, it is explained how radiation induced viscous flow leads to a densification of the SiO2 film that is different from what is found for bulk silica glass. This densification is temperature dependent and decreases from 2.6% to 1.0% between 95 K and 575 K. An anisotropic stress generating effect is measured and decreases roughly linearly from (2.5O.4)10-17cm2/ion at 95 K to (-0.90.7)^-17cm^2/ion at 575 K. The order of magnitude of this effect and its temperature dependence are in agreement with a thermal spike model. Finally, by measuring the stress decay kinetics after the ion beam was switched off we were able to estimate the activation energy spectrum for the annihilation of a steady state defect population during ion irradiation: it ranges from>0.23 eV at 90 K to> 0.63 eV at 255 K, respectively. These ion irradiation induced phenomena have important consequences for the understanding of ion induced nucleation of semiconductor and metallic nanoclusters in silica and sodalime glass, as will be shown.

2:30 PM KK2.4 
METASTABLE AMORPHOUS SiO2 CREATED BY ION IMPLANTATION. Koichi Awazu, Sjoerd Roorda, and John L. Brebner, Groupe de Recherche en Physique et Technologie des Couches Minces (GCM), Département de Physique, Université de Montréal, Montreál, Québec, CANADA.

Structural change in amorphous SiO2 (a-SiO2) by ion implantation was examined with FT-IR, ESR and XPS. H+, He+, Li+, C+, Si6+ were accelerated at 10,15,2,4,30MeV, respectively, with dosage of 1012-1016cm-2 and using the Université de Montréal 6MV Tandem accelerator. The IR peak at 1072cm-1, which is assigned to the Si-O stretching vibration mode, shifts towards lower frequency with increase of dosage, the contour of spectrum as well as the peak position were not changed after the peak position attained its final value of 1042cm-1. Normal a-SiO2 is composed of 5-7 membered rings of tetrahedral SiO4. The shift implies that following: implantation these 5-7 membered rings are turned into 3-4 membered rings in the meta-stabic a-SiO2 (hereafter called silica M). ESR and XPS data give some circumstantial evidence to support our model. The E' center can be seen in ESR, which is a hole centered on a silicon atom bonded with three oxygen atoms. Our ESR measurement show that the E' center concentration increased with dosage in the region of the transition from the normal a-SiO2 to silica M. In contrast, E' concentration decreased with dosage in the high dosage region. The 5-7 membered rings in a-SiO2 have split in two or more groups with ion implantation to create E' centers and oxygen deficient centers. The groups combine together to create 3-4 membered rings in the large dosage region. Stoichiometry was determined using XPS measurements. The x value in SIOx decreased in the transition region from the normal a-SiO2 to silica M whereas the x exceeds 2 with a large dosage. The oxygen excess must be a phantom oxygen excess and can be explained by the creation OH bonds near the surface. These phenomena are independent of ion species and ion energy.

3:15 PM *KK2.5 
PLASTIC FLOW IN FCC METALS INDUCED BY SINGLE-ION IMPACTS. Robert C. Birtcher, Materials Science Division, Argonne National Laboratory, Argonne, IL; and S. E. Donnelly, Joule Physics Laboratory, Science Research Institute, University of Salford, Salford, UNITED KINGDOM.

Irradiation of metal foils with 200 keV Xe ions at temperatures between 30 and 450 K has been monitored using in-situ transmission electron microscopy. Single ion impacts give rise to surface craters on the irradiated surface with sizes as large as 12 nm. Approximately 2 - 5 % of impinging ions produce craters. Temporal details of crater formation and annihilation has been recorded on video with a time-resolution of 33 milliseconds. Craters annihilate in discrete steps due to subsequent ion impacts or anneal in a continuous manner due to surface diffusion. Craters production (those persisting for one or more video-frames) as a function of temperature indicates that the surface diffusion process responsible for thermal annealing of craters has an activation energy of 0.76 eV in Au and 0.66 eV in Pb. Crater creation results from plastic flow associated with near surface cascades. Crater annihilation in discrete steps results from plastic flow induced by ion impacts, including those that do not themselves produce a crater. Additional examples of ion-induced plastic flow will be discussed.

3:45 PM KK2.6 
SIMILARITIES AND DIFFERENCES BETWEEN RADIATION INDUCED VISCOUS FLOW AND DIFFUSION. E. Snoeks, K.S. Boutros, J. Barone, Philips Laboratories, Briarcliff Manor, NY.

The concept of ion-beam induced viscous flow has been demonstrated in a variety of materials. Stress driven flow, which relieves stress in thin films, has conveniently been quantified by means of radiation-induced viscosity. We show that intrinsic tensile stress in plasma-enhanced chemical vapor deposited polycrystalline tungsten (W) films on SiO2 substrates can be relaxed at room temperature using ion irradiation. By measuring the relaxation rate under varying irradiation conditions, the radiation-induced viscosity is shown to scale reciprocally with the nuclear stopping. This agrees with the fact that the relaxation occurs via a ballistic process. No anisotropic hammering phenomenon is observed. We investigated the possible relation between radiation-induced viscous flow and the well quantified process of beam-induced diffusion. To experimentally assess this, we performed transmission electron microscopy on the W films before and after ion irradiation. Small 2-3 nm sized crystalline inclusions, which are observed before irradiation, have increased in size by about 1-2 nm during irradiation with 2.5x1014/cm2 400 keV P ions. The size increase is very close to the typical beam-induced self-diffusion length of W (1.4 nm) for these irradiation conditions, as can be extracted from local spike models. No structural changes were observed on larger length scales, notwithstanding the fact that the intrinsic tensile stress macroscopically relaxed. By comparison of relaxation rates of various metallic and covalent materials, we also found that the elastic constant is a scaling factor in the viscosity while it is not in the beam-induced diffusivity. This must be considered to understand and describe radiation-induced stress relaxation in terms of beam-induced diffusion and mixing.

4:00 PM KK2.7 
RADIATION EFFECT ON THE VISCOSITY OF GLASSES. A. Barbu and G. Jaskierowicz, Laboratoire des Solides Irradiés, CEA-DSM-DRECAM, Ecole Polytechnique, Palaiseau, FRANCE.

The creep velocity of B2O3 glass fibers under low flux 2.5 MeV electron irradiations (5 1013 e-cm-2s-1) has been studied versus temperature. As under very high energy heavy ions (1.6 GeV argon), the viscosity is drastically reduced below 300ƒC. An important difference is the occurrence of a compaction phenomena at the beginning of electron irradiation experiments. These results can be rationalised by assuming two totally different mechanisms with both kinds of particles : a relaxation driven by a melting along the path of the ions for very high energy heavy ions irradiations and a relaxation driven by radiation induced points defects similar to vacancies and interstitials for high energy electron irradiations.

4:15 PM *KK2.8 
ADVANCES IN ION AND LASER BEAM TECHNOLOGY: ACHIEVEMENTS OF JAPANESE GOVERNMENT AND UNIVERSITY PROJECTS. Isao Yamada, Ion Beam Engineering Experimental Laboratory, Kyoto University, Sakyo, Kyoto, JAPAN.

Technological advancement is strongly related to equipment development. During the last several years, extensive development related to advanced ion/Iaser beam equipment and associated processing technologies has been carried out under Japanese government sponsorships. A large-scale national project known as AMMTRA (Advanced Material-Processing and Machining Technology Research Association) has made a great contribution to industrial applications of beam processing by developing high density ion and laser beam equipment. A subsequent program, the ACTA (Advanced Chemical Processing Technology Research Association) project has conducted. The ACTA project involves development of multi-beam deposition systems for metal and dielectric materials formation including several systems which combine ion and laser beams, ion beams with CVD and plasma and laser beams with sputtering. Nano-composite films exhibiting tough and hard materials characteristics, highly adherent very thick metal oxide films which are durable at very high temperatures and ferroelectric thin films which are deposited at low temperatures etc. have been demonstrated. Since the discovery and subsequent development of ion beam processing, beams of either atomic or molecular ions have been used. The author has proposed Œ¹gas cluster ion beam processing¹¹. R&D involving gas cluster ion beams is being carried out under one of the projects sponsored by the Japan Science and Technology Corporation (JST). In cluster ion beam technology, non-linear collisions during the impact of accelerated cluster ions upon substrate surfaces produce fundamentally low energy bombarding effects at very high density. These bombarding characteristics have been applied for making 0.1 m PMOS junctions by shallow ion implantation, for creating high yield sputtering and smoothing effects on Si, diamond and SiC substrates, for producing low damage surface cleaning and for low temperature thin film formation. Cluster ion beam procedures will be discussed in comparison with traditional ion beam processing methods which are presently limited by available atomic and molecular ion beams.

4:45 PM KK2.9 
MOLECULAR DYNAMICS SIMULATION OF SURFACE MODIFICATION PROCESS BY CLUSTER ION IMPACT. Takaaki Aoki, Toshio Seki, Jiro Matsuo, Zinetulla Insepov and Isao Yamada, Ion Beam Engineering Experimental Laboratory, Kyoto University, Sakyo, Kyoto, JAPAN.

A cluster consists of from ten to thousands of atoms and a cluster ion impact causes multiple collision effects on solid surfaces. Cluster ion beams, which have properties different from those of monomer ion beams, are very useful for surface modification processes. We have examined cluster ion multiple collision effects by means of Molecular Dynamics simulations. Molecular Dynamics simulations of cluster ions consisting of Ar or carbon atoms, impacting on solid surfaces have been performed. The kinetic energy of an impacting cluster disperses isotropically through many collisions between cluster and surface atoms. The cluster ion deposits kinetic energy in to a shallow surface volume and a hemispherical damaged region is formed. If the energy of the cluster is high, a cylindrical damage region is created because of the proximity effect of each cluster atom. Once the cluster has disintegrated, cascade damage is formed as in the case of monomer ions.

5:00 PM KK2.10 
STRENGTHENING OF SINGLE-CRYSTAL SAPPHIRE BY HIGH TEMPERATURE ION IMPLANTATION. J.D. Demaree, J.D. Kleinmeyer, Weapons & Materials Research Directorate, U. S. Army Research Laboratory, APG, MD; D. Ila, Center for Irradiation of Materials, Alabama A&M University, Normal, AL; D.B. Poker, D.K. Hensley, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN.

Single-crystal c-axis sapphire was implanted with Cr+, Ti+, and Si+ ions at both room temperature and at 800C in order to induce surface compressive stresses and increase the shatter resistance of the material. The implanted sapphire was examined with Rutherford backscattering spectrometry and ion beam channeling to assess the composition and crystallinity of the implanted material. The optical transmittance of the sapphire was examined using visible spectrum transmission and Fourier Transform Infrared Spectroscopy to ensure that the material remained suitable for optical applications. The effect of implantation on the surface roughness was examined using photon tunneling and atomic force microscopy. Finally, the effects of implantation on the mechanical properties of the material were measured by indentation techniques, including nanoindentation. The effects of both ion implantation and and post-implantation annealing on the stress state and mechanical durability of the sapphire will be discussed.

SESSION KK3: POSTER SESSION: 
MECHANISMS IN IRRADIATION AND BEAM SYNTHESIS OF MATERIALS I 
Chairs: John D. Demaree and Jan van der Kuur 
Monday Evening, December 1, 1997 
8:00 P.M. 
America Ballroom (W)

KK3.1 
MECHANISM OF ENHANCED DIFFUSION DURING HIGH-TEMPERATURE ALUMINUM ION IMPLANTATION TO 6H-SiC. Igor O.Usov, Alexandra A. Suvorova, Ioffe Physical Technical Institute, St. Petersburg, RUSSIA; Alexander V. Suvorov, Cree Research Inc., Durham, NC.

The diffusion of Al in 6H-SiC during high-temperature Al ion implantation studied using secondary ion mass spectrometry. A 6H-SiC wafer implanted with 50 keV Al ions to a dose I .5e 16 cm-2 in the temperature range 1300-1800C and at room temperature. The Al distribution profile divided on two different regions. The first, high Al concentration region, where profile has Gaussian shape and is independent of implantation temperature. It is believed that Al precipitation can be the diffusion limiting process The second, low Al concentration region, where radiation enhanced diffusion leads to deeply penetrating tails in Al profile. The observed tails start at the order-disorder interface between inner host crystal and near surface damage layer. It is proposed that excess interstitials cause the enhanced diffusion in the crystalline area of the sample. The source of interstitials is believed to be provided by thermal dissolution of end of range defects that are formed by the implantation process. The radiation enhanced diffusion coefficients of Al obtained in the tail region about two orders of magnitude higher than the thermally activated diffusion coefficients.

KK3.2 
THE PULSED ELECTRON BEAM IRRADIATION OF SiC WITH N DOPING. Sergey Korenev, New Jersey Institute of Technology, Newark, NJ; Jozef Huran, Institute of Electrical Engineering of SAS, Bratislava, SLOVAK REPUBLIK; Alexander Kalmykov, Joint Institute for Nuclear Research, Dubna, RUSSIA.

The experimental results of pulsed electron beam irradiations of SiC structures with N doping are presented in the this paper. The pulsed electron beams with kinetic energy 150 keV, and current density 10 - 250 A/cm2 and pulse duration 300 nsec are used in the experiments. An absorbing Ti foils are used for decrease of depth of penetration for electron beam to SiC. The date from RBS, SEM and electrical characteristics of these structures are considered. Applications of SiC are discussed.

KK3.3 
DEFECT-IMPURITY INTERACTIONS IN SILICON AND SILICON-ON-INSULATOR. E. G. Roth and O. W. Holland, Oak Ridge National Laboratory, Oak Ridge, TN .

The understanding of defect-defect and defect-impurity interactions have become critical in ion-implanting processes for IC manufacturing. These defect-impurity interactions will be shown to be dependent upon the starting material; such as FZ- and CZ-silicon and silicon-on-insulator (SOI). The intrinsic impurities within these materials will be shown to have a marked effect upon the behavior of ion-implanted profiles. The synergism between the ion-induced defects, and the intrinsic and implanted impurities can cause substantial redistribution of the dopant profiles even during implantation near ambient temperatures. The specific mechanism of defect-impurity interactions driving this redistribution of the dopant profile will be discussed.

KK3.4 
DIRECT OXIDATION AND NITRIDATION OF SILICON INDUCED BY ION BOMBARDMENT. M. Petravic, J.S. Williams and M. Conway, Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, Australian National University, Canberra, AUSTRALIA.

It is well known that silicon dioxide and nitride layers can be synthesized by ion implantation followed by subsequent thermal annealing. It has also been reported that such phases can be synthesized directly during bombardment but few details are available on the atomistic processes and thermodynamic driving forces which lead to phase formation during bombardment. In this study we have used low energy (15 keV) oxygen and nitrogen bombardment of silicon to induce oxidation and nitridation. The composition (stoichiometry) has been studied by RBS and SIMS and structural modifications selectively examined by ion channeling and TEM. For oxygen bombardment, near-stoichiometric SiO2 can be formed even at liquid nitrogen temperatures, whereas considerable over-stoichiometry occurs following nitridation leading in some cases to generation of gas bubbles. These effects have been studied as a function of dose, bombardment temperature and angle of incidence. These quite large differences in the formation processes for oxides and nitrides are accompanied by similar differences in the segregation behavior of metals during beam-induced phase formation. The mechanisms for such phase formation, differences between oxidation and nitridation and segregation behavior are discussed in terms of differences in beam-induced atomic transport in amorphous silicon, oxides and nitrides and also thermo-dynamic driving forces occurring during bombardment.

KK3.5 
RDF ANALYSIS OF ION-AMORPHISED SI02 AND SIC USING POST SPECIMEN SCANNING IN FIELD EMISSION SCANNING TRANSMISSION ELECTRON MICROSCOPE. David C. Bell, Anthony J. Garratt-Reed and Linn W. Hobbs, Massachusetts Institute of Technology, Cambridge, MA.

Radial distribution function (RDF) information obtained from amorphised SiO2 and SiC can provide important near and medium range structure information, determination of this information has important consequences for the encapsulation and the long term stability of nuclear waste material. RDF data has been obtained from samples of ion-beam amorphised SiO2 and SiC. This data was obtained using a Vacuum Generators HB603 Field Emission Scanning Electron Microscope, equipped with a GATAN Digi-PEELS. Post specimen scanning was employed to minimize the effect of spherical aberration that is present in the incident beam rocking mode. Previous data obtained used the main-scan coils and rocking the incident beam on the specimen, diffraction information was collected from out to 16 nm-1. The intensity of the information falls of rapidly as the inverse forth power of the scattering angle, out to the point where the signal to noise of the detector becomes unity. This point is limited by the sensitivity of the detector and the spherical aberration of the objective lens which limits the ultimate collection angle, regardless of the sensitivity of the detection system. Utilizing this system, data collection of the angular elastic scattering distribution from amorphous glasses has been enhanced and the increased signal intensity and angular range, RDF information can now be identified past an angular range of 30 nm-1.

KK3.6 
SWELLING EFFECTS IN INSULATORS IRRADIATED WITH HEAVY IONS IN THE ELECTRONIC STOPPING POWER REGIME. C. Trautmann1, K. Schwartz1, A. Meftah2 and M. Toulemonde2, 1 Gesellschaft für Schwerionenforschung (GSI), Darmstadt, GERMANY; 2 CIRIL, laboratoire mixte du CEA et CNRS, Caen, FRANCE.

A pronounced swelling effect occurs when irradiating SiO2 quartz with heavy ions (Te, Ta, and Pb) in the electronic stopping power regime. The out-of-plane swelling was measured by means of a profilometer scanning over the border line between an irradiated and a virgin area of the sample surface. The step height varied between 20 and 450 nm depending on the fluence, the electronic stopping power and the range of the ions. Including earlier observations of dimensional growth of quartz samples perpendicular to the ion beam [1], leads to the conclusion that a volume increase is induced. Such a result is in agreement with earlier measurements of ion induced swelling in Al2O3 [2] and LiNbO3 where a volume increase of about 4 was found [3]. By comparing ion induced effects in various insulators, a possible universal swelling behaviour will be discussed.

KK3.7 
CHARACTERIZATION OF VACANCY-TYPE DEFECTS IN ION IMPLANTED AND ANNEALED SiC BY POSITRON ANNIHILATION SPECTROSCOPY. Wolfgang Anwand, Gerhard Brauer, Wolfgang Skorupa, Institut fuer Ionenstrahlphysik und Materialforschung, Dresden, GERMANY; Paul G. Coleman, University of East Anglia, Norwich, UNITED KINGDOM.

Positron annihilation spectroscopy is the most sensitive technique to assess vacancy-type defects formed due to doping of materials by ion implantation. Knowledge about this damage and its development due to annealing is essential for any device technology based on ion implantation. Deep effects well beyond the ion range in SiC for implantation of different species (Ge, In, Al) and ion beam synthesis (AlN) will be reviewed and examples how to identify these defects will be presented.

KK3.8 
RADIATION DAMAGE IN MO AND SI: SOME ATOMISTIC MECHANISMS. Bent Nielsen, Department of Applied Science, Brookhaven National Laboratory.

Defect formation and defect impurity interactions have been studied in Mo and Si using Positron Annihilation Spectroscopy. Emphasis will be given to information that reveal and/or suggest a specific atomistic mechanism. This includes binding of nitrogen to interstitials and vacancies in Mo. The stability of these pairs. The breakup process. And the rather dramatic effect these interactions have on the evolution of radiation damage in a N doped Mo crystal. Further a two step migration of F in Si is suggested.

KK3.9 
INFLUENCE OF FLUENCE AND FLUENCE-RATE ON THE FORMATION OF ELECTRON IRRADIATION DEFECTS IN Si. Fengmei Wu, Qiji Lai, Dept of Physics, Nanjing University, Nanjing, CHINA; Ling Gong, Nanjing Ericsson Communication Company Ltd., Nanjing, CHINA.

The influence of fluence and fluence-rate on the formation of 10 MeV electron irradiation defects in Si has been investigated. Under high fluence or fluence-rate irradiation, the efficiency of the formation of the oxygen-vacancy and the divacancy E2(V_2)^-%%) defects reduces obviously. The decrease of the density of the oxygen-vacancy is attributable to the decay and reconstruction of the irradiation defects. High fluence electron irradiation gives rise to higher generation rates for Frankel pair components and the increasing of the defects of a more complex nature, such as O+V2 or O+V3. The theory relevant to these results is also analysed.

KK3.10 
GIANT MAGNETORESISTANCE IN IRON IMPLANTED SILVER THIN FILMS. C.M. de Jesus, J.G. Marques and J.C. Soares, CFNUL, Lisboa, PORTUGAL; L.M. Redondo and M.F. da Silva, ITN, Sacaveém, PORTUGAL; M.M. Pereira de Azevedo, J.A. Mendes, M.S. Rogalski and J.B. Sousa, Dept Physics, Univ Porto, Porto, PORTUGAL.

In this work we report on the observation of magnetoresistive behavior in thin Ag films with granular Fe structure obtained by ion implantation. Ag thin films (2000 3000 Å) were deposited by pulsed laser ablation or evaporation and implanted with 56Fe ions at doses up to 1017at/cm2 and 150-180 keV energies. Rutherford Backscattering Spectroscopy (RBS) was used to control the thicknesses of the films and the profile of the implanted Fe. Moessbauer spectroscopy was used in some films implanted with 57Fe and has shown the formation of large and small Fe clusters, coexisting with isolated Fe atoms. Magnetization data reveals dominant paramagnetic behavior of the clusters at low implantation doses and an increasing ferromagnetic contribution as the Fe dose increases. A detailed study of the magnetoresistance from 4.5 K up to 300 K was made using magnetic fields up to 16 T. An increase in the GMR effect associated with the enhancement of the implantation dose was observed. The magnetoresistive behavior is consistently discussed in terms of structural RBS and Moessbauer data, combined with the magnetic properties of the granular films.

KK3.11 
MAGNETOSTRICTION RELATED EFFECTS IN PULSED LASER IRRADIATION OF AMORPHOUS MAGNETS. Monica Sorescu, Duquesne University, Department of Physics, Pittsburgh, PA; S.A. Schafer, Oklahoma State University, Department of Chemistry, Stillwater, OK.

Our previous results on the kinetics of laser induced phase transformations in metallic glasses were continued by considering pulsed alexandrite laser (=750 nm, =60 s, =2-5 J/cm2) irradiation effects in several Fe-, FeNi-, FeCo-, and FeCr-based amorphous ferromagnetic alloys with magnetostriction constants ranging from 0 to 35 ppm. irradiation-induced structural and property modifications were characterized using transmission and conversion electron Mossbauer spectroscopy. Complementary information was obtained from hysteresis loop measurements recorded at liquid helium temperatures in an applied magnetic field of 10 kOe. The coexistence of laser induced crystallization and oxidation effects depends on the values of the fluence employed. For the same values of the irradiation parameters, the onset of irradiation-driven phase transformations is determined by the magnetostriction constant of the material. Laser-induced crystallization was not observed in the zero magnetostrictive sample. The experimental data obtained in this work demonstrates the key role played by in explaining the mechanism of irradiation induced phase transformations in amorphous magnets.

KK3.12 
RADIATION DAMAGE EFFECTS IN FERROELECTRIC LiTaO3 SINGLE CRYSTALS. Christopher J. Wetteland, Venkatraman Gopalan, Jeremy N. Mitchell, Kurt E. Sickafus, Michael Nastasi, Carl J. Maggiore, Joseph R. Tesmer, Terence E. Mitchell, Thomas Hartmann, Los Alamos National Laboratory, Materials Science and Technology, Los Alamos, NM.

We report here on experimental results concerning the irradiation damage response of z-cut lithium tantalate (LiTaO3) ferroelectric single crystals, irradiated with 200 kV Ar++ ions. LiTaO3 possesses a structure that is a derivative of the corundum (Al2O3) crystal structure. A systematic study of the damage accumulation rate as a function of ion dose was performed using a combination of ion-beam channeling experiments and transmission electron microscopy. An ion fluence of 2.5ï1018 Ar++ ions/m2 was sufficient to amorphize the irradiated volume of a LiTaO3 crystal at an irradiation temperature of 120K. This represents a rather exceptional susceptibility to ion-induced amorphization, which may be related to a highly disparate rate of knock-on of constituent lattice ions, due to the large mass difference between the Li and Ta cations. We also observed that the C- end of the ferroelectric polarization exhibits slightly higher ion dechanneling along with a greater susceptibility to radiation damage, as compared to the C+ end of the polarization. Models will be presented to explain this difference based on a modification of the local atomic potential as viewed by an incident ion traveling parallel or anti-parallel to the ferroelectric polarization in the crystal.

KK3.13 
STRUCTURAL TRANSFORMATIONS IN PARTIALLY STABILIZED ZIRCONIA INDUCED BY ION IRRADIATION. Kurt E. Sickafus, Christopher J. Wetteland, Thomas Hartmann, and Michael Nastasi, Los Alamos National Laboratory, Materials Science and TechnologyLos Alamos, NM.

Partially-stabilized zirconia (PSZ) (i.e., zirconium oxide, ZrO2, stabilized with approximately 6 mole % yttrium oxide, Y2O3) powders were irradiated at 120K with 370 kV Xe++ ions to ion fluences ranging from 1ï1018 - 1ï1020 Xe++/m2. The starting PSZ powders consisted of heterogeneous mixtures of three crystalline phases of zirconia: monoclinic, tetragonal, and cubic. At the maximum Xe ion fluence tested, the monoclinic zirconia phase was observed to completely transform either to the tetragonal or the cubic phase. No evidence was found for amorphization of any of the zirconia phases at the maximum ion fluence, which corresponds to a peak dose of about 25 displacements per atom (dpa). Interestingly, this monoclinic to tetragonal (or cubic) phase transformation is accompanied by a volume contraction, so that the PSZ material apparently densifies during ion irradiation. An issue concerns whether this irradiation-induced phase transition is an intra-cascade transformation phenomenon, or is due to bulk point defect accumulation beyond a critical concentration. To distinguish between these two transformation mechanisms, results will be presented from Ne ion irradiations of PSZ powders, where bulk damage is achieved via ion cascades with low nuclear energy densities, compared to the Xe ion cascades.

KK3.14 
A GENERAL MODEL ON THE IRRADIATION-INDUCED AMORPHIZATION. S. X. Wang, L. M. Wang, R. C. Ewing, Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI.

We present a model describing the ion irradiation-induced amorphization process. The model is based on the disordering and recrystallization within a displacement cascade. The amorphous-in-growth is affected by the sample temperature, cascade size, and material parameters. In application to experimental data, the model gives a satisfying description of amorphous accumulation with ion dose at different temperatures. The temperature factor is given in two forms: one is based on the cascade cooling process; one is based on the activation energy controlled annealing process. Both the two forms of temperature factor are successful in addressing the temperature effects on the irradiation-induced amorphization. The effects of other factors, such as ion mass, ion energy, dose rate, and material, can be evaluated using the model. The effects of ion-mass and ion-energy on the amorphization process are on the cascade size and the number of cascades per incident ion. The general trends shown in the model are that increasing cascade size will result in a higher critical temperature, and a larger cascade size and/or more cascades per ion lowers the required amorphization dose. The dose rate effect is a result of cascade overlap. With increasing dose rate, the probability of cascade overlap increases. When overlap occurs, this, in effect, increases the cascade size, thus raising the critical temperature and lowering the amorphization dose.

KK3.15 
DAMAGE CALCULATION IN FUSION CERAMICS - COMPARISON BETWEEN NEUTRONS AND LIGHT IONS. Yu. Lizunov, A. Ryazanov, P.V. Vladimirov, RRC Kurchatov Institute 123182 Moscow RUSSIA; A. Moslang*, FZK Research Centre Karlsruhe, Institute of Materials Research, P.O. Box 3640, 76021 Karlsruhe, GERMANY.

The paper presents results on displacement damage calculations in fusion ceramics irradiated by various nurtron sources and light ion accelerators. The method used is based on solution of Boltzmnn transport equations, and in contrast to other codes, this novel method is especially suitable for materials with significant differences in atomic weight and threshold energies. It treats both types of irradiation in terms of unique physical and numerical models. For protons <40 MeV and alpha-particles <100 MeV as well as for several neutron environments (e.g. ITER, HEIR, FFTF), sublattice specific primary recoil spectra and damage cross sections have been calculated for Al203, AIN, BeO, MgO, MgAI204, and SiC. The results show, that damage rates in different sublattices neither follow the stoichiometric ratios of the elemental composition nor the ratio of the threshold energies. Although the primary recoil spectra can vary widely with the irradiation type, the relative sublattice specific damage rates are the same within 15% for all considered environments and materials.

KK3.16 
DEFECT PRODUCTION AND ANNEALING IN HIGH-Tc SUPERCONDUCTOR EuBa2Cu3Oy IRRADIATED WITH ENERGETIC IONS AT LOW-TEMPERATURE. Norito Ishikawa, Yasuhiro Chimi, Akihiro Iwase, Japan Atomic Energy Research Institute, Advanced Science Research Center, Tokai-mura, Ibaraki-ken, JAPAN; Koji Tsuru, NTT Basic Research Laboratories, Device Physics Research Laboratory, Tokai-mura, Ibaraki-ken, JAPAN; Osamu Michikami, Iwate Univ., Faculty of Engineering, Morioka-shi, Iwate-ken, JAPAN.

In this study ion-irradiation at 100K and in-situ measurement of electrical resistivity change at 100K as a function of ion-fluence were performed in EuBa2Cu3Oy (EBCO) irradiated with low energy (1-2MeV) ions and with high energy (80-200MeV) ions. Since the thickness of the sample was thin enough (300nm) for the incident ions to pass through the sample, defects are expected to be created uniformly along sample thickness. For low energy ion irradiations, the initial increase rate of resistivity against fluence, which corresponds to defect production rate, was found to increase linearly as a function of nuclear stopping power, Sn. This means for low energy ion irradiations defect production due to elastic displacement of atoms is a dominant defect production process. For high energy ion irradiation, the initial increase rate of resistivity against ion-fluence was much larger than that expected from the function of Sn obtained by low energy ion irradiation. This suggests electronic excitation may play an important role for the defect production in EBCO irradiated with high energy (80-200MeV) ions. After the irradiations, the samples were annealed to 300K, and the defect recovery due to annealing were observed at 100K for all of the irradiations. The fraction of resistivity-recovery observed for EBCO irradiated with high energy ions was greater than that observed for EBCO irradiated with low energy ions, suggesting that defects created via electronic excitation are less stable against thermal energy than those created via elastic displacement.

KK3.17 
IMPROVEMENT OF THE CRITICAL CURRENT DENSITY IN YBCO SINGLE CRYSTAL BY O+ ION IMPLANTATION. Hai-Yu Nan and Yunosuke Makita, Electrotechnical Laboratory, Ibaraki, JAPAN.

batch X46We have for the first time demonstrated that the critical current density of YBCO single crystals can be increased by O+ ion implantation technique. In this experiment as-grown single crystal of c-axis oriented YBCO sample was cut into a plate 1mm in thickness and low temperature annealed at 500 for 168 h in flowing O2 gas. This oxygenated sample showed the Tc of 93K. The annealed sample was implanted with 120 keV O+ ions/cm2 which made the surface layer amorphous. The thickness of the amorphous layer was estimated to be approximately 200 nm since the project range Rp and straggling range Rp were estimated to be 132 nm and 44 nm respectively. After ion implantation the sample was annealed at 500C for 80 h then cooled at a rate 0.8C /min in flowing O2 gas. DC magnetic susceptibility measurements were carried out at 77 K using a SQUID magnetometer for Tc and Jc determinations. For Jc measurements the magnetic field was applied up to 5 T along the c-axis of the sample. Recovery of the sample crystallinity was examined by X-ray diffraction using Cu-K radiation and micro-Raman scattenng spectroscopic measurements using an Ar-ion laser with a wavelength of 514.5 nm and an irradiation power of 0.5 mW. The critical current density of single crystal YBCO sample increased by about 100% as a result of ion implantation. The crystallinity almost perfectly recovered as it was before ion implantation by post annealing and exhibited Tc of 90 K.

KK3.18 
IMPROVING GRAIN CONNECTIVITY AND CRITICAL CURRENT BY 18 MeV PROTON IRRADIATION OF YBCO CERAMICS. Elvira Ibragimova, Eldar Gasanov, Anatoly Nebesny, Inst of Nuclear Physics, Tashkent, UZBEKISTAN; Marquis Kirk, Material Science Div, ANL, Argonne, IL.

As the range of 18 MeV protons in YBaCuO is about 1.2 mm and they produce less radioactivity than neutrons, it might be an advanced way for structure modification of superconducting material aimed to increase the critical current density. Ceramic samples of 0.5 - 2 mm thickness were exposed to fluences from 1013 to 1015cm-2 at 330 K and currents of 20 and 100 nA. The superconducting transition scanned from 80 to 300 K and current - voltage dependences were measured at 80 K using Ag contacts evaporated both on the exposed and back surfaces of the samples. The measurements along the exposed surface showed a decrease in Tc by 1 - 1.5 K and in a resistivity at T>Tc by an order of magnitude with a fluence growth. The transition, measured along the proton beam, moved to a higher temperatures and widened. The current-voltage curves showed a decrease in a slope (differential resistivity). X-ray diffraction pattern of the exposed side displayed a significant lowering of a background level and an increase in (OOL) peaks.

8:30 AM *KK4.1 
ENERGETIC PARTICLE SYNTHESIS OF METASTABLE LAYERS FOR SUPERIOR MECHANICAL PROPERTIES. D. M. Follstaedt, J.A. Knapp, S.M. Myers, M.T. Dugger, T.A. Friedmann, J.P. Sullivan, and T. Christenson, Sandia National Laboratories*, Albuquerque, NM; O.R. Monteiro, J.W. Ager and I.G. Brown, Lawrence Berkeley National Laboratory, Berkeley, CA.

Energetic particle methods have been used for controlled synthesis of two metastable phases. High-energy, overlapping implantations of Ti and C (180 and 45 keV, respectively) were used to form amorphous alloy layers on Ni at concentrations >15 at.% each. Nanoindentation was used to probe mechanical properties of the layer, which were evaluated with finite element modeling developed for indenter force versus depth. Cross-section TEM was used to identify microstructure boundaries in the implanted layer for accurate modeling. The yield stress evaluated for the amorphous phase, 4.7 GPa, greatly exceeds that of even hardened bearing steels. The intrinsic hardness, 14 GPa, exceeds that of other metalloid-stabilized amorphous metals due to Ti-C pairing interactions. This hard layer adheres less to steel pins during sliding contact, exhibiting no stick-slip adhesion and greatly reducing wear. Amorphous, tetrahedral diamond-like carbon (DLC) layers were formed by both vacuum-arc deposition and pulsed-laser deposition (PLD), and evaluated with indentation plus modeling. A pulsed bias of 2000V during vacuum arc deposition of C ions produces relatively soft DLC (27.5 GPa), whereas 100 V gives much greater hardness, 68 GPa. PLD coupled with controlled annealing to relieve compressive stress produced layers up to 1 µm thick with very high hardness, 88 GPa. The key to obtaining hardness approaching that of crystalline diamond (100 GPa) for both processes is deposition of C at energies 100 eV, which leads to sub-plantation below the growing surface and a high fraction of sp3 bonds. We have successfully produced adherent DLC layers on Ni with low coefficients of friction, 0.15-0.2. The properties of both amorphous Ni(Ti,C) and DLC/Ni appear favorable for treating micro-electromechanical system components made of electro-formed Ni.

9:00 AM KK4.2 
ION-BEAM MODIFICATION OF AMORPHOUS CARBON. Hyukjae Lee and Byungwoo Park, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA; David B. Poker, Oak Ridge National Laboratory, Oak Ridge, TN.

In our previous study [1,2], nitrogen implanted amorphous carbon showed higher surface hardness and elastic modulus than those of the unimplanted amorphous carbon. The apparent surface hardness and elastic modulus using 100 keV N+ at 5 A and dose of N+/cm2 showed an optimum value of and GPa, respectively, at implantation temperatures lower than 30C, while those of the unimplanted substrate are and GPa, respectively. The maximum hardness and modulus were well correlated with the asymmetric diffuse peak around 1,500 cm-1 in Raman spectroscopy. The enhanced strenghts were explained by the increased ratio of the sp3 versus sp2 bonds of carbon which was verified by EELS. Boron implantation into the amorphous carbon has been investigated at various implantation parameters such as temperature, dose and dose rate. Nanoindentation, Raman spectroscopy and EELS were employed to investigate the effects of boron, and compare with nitrogen implanted amorphous carbon.

9:15 AM KK4.3 
CHARACTERIZATION OF DIAMOND LIKE CARBON FILM FABRICATED BY ECR PLASMA CVD AT ROOM TEMPERATURE. K. Kuramoto, Y. Domoto, H. Hirano, H. Tarui and S. Kiyama, New Materials, R.C., Sanyo Electric Co., Ltd, Osaka, JAPAN.

Low temperature (<70C) fabrication of Diamond Like Carbon (DLC) films with a high hardness (>3000Hv) and a high resistivity (>10cm) was successfully achieved by applying a low substrate bias voltage in ECR plasma CVD. For advanced coating of the DLC films, control of the hydrogen concentration and sp2/sp3 configuration without substrate heating was desired. By utilizing low-energy ions with enough kinetic energy to dissociate the C-H atomic bonds, graphitization due to an excessive energy would be avoided. The ion energy and impingement were effectively controlled for high-quality DLC films by using ECR plasma CVD, which were difficult by popular conventional plasma CVD methods. In an experiment, the bias voltage was varied from 0 to -I50V, total pressure of Ar and CH4 was about 2.0xlO-1Pa. The hydrogen concentration measured by FT-IR drastically decreased as the bias voltage was increased. Film hardness increased above 3OOOHv by applying a bias voltage of -50V, and then became almost constant with increasing bias voltage to -I50V. The deposition temperature was confirmed to be less than 70C at a bias voltage of -50V. This result suggests that ion impingement promoted by the bias voltage plays an important role in effectively decreasing C-H atomic bonds and generating sp3C=C and nongraphitized sp2C=C atomic bonds. On the other hand, a high resistivity of more than 10cm was obtained at a bias voltage less than -50V, and it subsequently decreased with increasing bias voltage. Raman spectra indicated an increasing sp2 configuration when the bias voltage was increased from -50 to -150V, indicating that an increasing sp2 configuration is conceivably more sensitive to film resistivity and not so sensitive to film hardness. Accordingly, high-quality DLC films could be fabricated by controlling the hydrogen concentration and sp2/sp3 configuration in ECR plasma CVD.

9:30 AM KK4.4 
INVESTIGATION OF THE MICROSTRUCTURE OF CARBON IMPLANTED HIGH SPEED STEEL BY MEANS OF GIXRD AND MÖSSBAUER SPECTROSCOPY. D.M. Rueck, Gesellschaft für Schwerionenforschung mbH, Darmstadt, GERMANY; F. Jahrling, H. Fuess, Fachbereich Materialwissenschaft, TH-Darmstadt, GERMANY; G. Walter, Institut für Kernphysik, TH-Darmstadt, GERMANY.

The tribological behaviour of high speed steel, a widely used material for tools with high performance in forming industry, was improved by implantation of carbon ions. The used energy was 100 keV and the ion fluences between 5e17 and 3e18 ions/cm2. The formation of metastable -carbide Fe2+xC was investigated as function of the ion fluence by means of GIXRD and M{ossbauerspectroscopy. The formation mechanism of -Fe2+xC was related to the appearance of an x-ray amorphous phase, to the defect density and radiation enhanced diffusion. The x-ray amorphous phase was discussed to be related to -carbide particles with a grain size smaller than 5 nm. Complementary results were obtained by Conversion Electron M{ossbauerspectroscopy. Correlation between the phase formation (-Fe2+xC- and a graphitic carbon phase) in the implanted layer with the tribological behaviour is discussed. The tribological behaviour was tested using a pin-on-disc tester.

10:15 AM *KK4.5 
ENERGETIC DEPOSITION AS A UNIQUE TOOL FOR PRODUCTION OF METASTABLE MATERIALS. G.K. Hubler, C.M. Cotell, C.A. Carosella, Naval Research Laboratory, Washington, DC; and S. Schiestel, Deutsche Forschungsgemeinschaft Fellow at NRL.

The collision cascade, the fundamental event in ion-solid interactions, is responsible for the beneficial effects on thin films deposited by low energy ion beam assisted deposition (IBAD) or by energetic ion assisted deposition processes in general. However, the fundamental implications of the marriage of collision cascades and film growth processes have yet to be fully realized. The first half of this paper reviews the effects of ion bombardment on film growth and reaches some new conclusions: that IBAD processing drives material synthesis parameter phase space into new regimes in the time-temperature-flux continuum, and, that this attribute of IBAD processing can lead to microstructures far from equilibrium that are unattainable by other materials synthesis methods such as ion implantation, splat quenching and physical vapor deposition. The possibility for the production of unique metastable materials, a major strength of IBAD, has not been a focus of research to date, yet some success is evident (i.e., c-BN, B1-MoN, Cu5O4). The second half of this paper describes an example that uses the unique ion-solid interactions that occur during IBAD to control the kinetics of phase transformations that are thermodynamically favored but kinetically inhibited. We call this process beam assisted phase separation, or BAPS. A different method for preparation of metastable nanocomposites emerges from this work.

10:45 AM KK4.6 
BIAXIAL ALIGNMENT IN YSZ THIN FILMS PRODUCED BY ION BEAM ASSISTED DEPOSITION: THE EFFECT OF OXYGEN STOICHIOMETRY. Todd S. Stefanik, Kevin G. Ressler, Neville Sonnenberg, Michael J. Cima, Massachusetts Institute of Technology, Ceramics Processing Research Laboratory, Cambridge, MA.

The mechanism of biaxial alignment in yttria stabilized zirconia (YSZ) thin films produced by dual ion beam assisted deposition is examined with emphasis on the role of oxygen stoichiometry during film growth. Films produced under appropriate deposition conditions exhibit (200) out-of-plane alignment and in-plane alignment such that (111) planes face the assisting ion beam. The proposed mechanism of biaxial alignment is anisotropic damage tolerance on different crystallographic planes. Oxygen defects introduced during ion beam bombardment accumulate on planes with low damage tolerance, allowing the formation of low angle grain boundaries which result in a change of growth direction such that damage tolerant planes face the assisting ion beam. Computer simulations show that in the fluorite structure, (111) planes are most resistant to oxygen defect formation. The effects of r value (ratio of ions:formula units YSZ arriving at the film surface), ion energy, ion beam gas composition, ion bombardment angle, angle of deposition flux incidence, and substrate temperature on the alignment and stoichiometry of the resulting films are discussed. Films are characterized using X-ray /2 scans, X-ray pole figures, optical thickness and absorption measurements, and RBS.

11:00 AM KK4.7 
TEXTURE IN THIN FILMS BY ION BOMBARDMENT DURING VAPOR DEPOSITION. Hong Ji, ZhenQiang Ma and Gary S. Was, University of Michigan, Ann Arbor, MI.

Energetic ion bombardment during film deposition can be used to control both in-plane and out-of-plane texture in films and coatings. Desired texture in the films can be established by carefully choosing the ion beam incident direction with respect to the substrate normal. The mechanism of texture control by IBAD (ion energy < several keV) is the difference in sputtering rate for different crystallographic orientations due to ion channeling, resulting in preferential growth for certain grain orientations. The same mechanism also controls the surface morphology evolution of the films. In this work, we focused on the study of texture and surface morphology of polycrystalline Nb and Al films. Films were synthesized by ion beam assisted deposition (IBAD) at various ion energies and ion-to-atom arrival rate (R) ratios. Besides a 110 fiber texture, an in-plane texture was created in Nb films by proper orientation of the ion beam with respect to the substrate. In Al films, the fiber was controlled by ion channeling in a direction normal to the substrate. The dependence of in-plane and fiber texture on the ion energy and R ratio was established by x-ray pole figures. The surface morphology and roughness were characterized by SEM and AFM. A model for texture and surface morphology evolution was established to explain both types of texture development.

11:15 AM KK4.8 
CRACK NUCLEATION IN ION BEAM IRRADIATED MAGNESIUM OXIDE AND SAPPHIRE CRYSTALS. Val Gurarie, David Jamieson, Roland Szymanski, Alex Orlov, School of Physics, MARC, University of Melbourne, Melbourne, AUSTRALIA; Jim Williams, Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, ANU, Canberra, AUSTRALIA.

Monocrystals of magnesium oxide and sapphire have been subjected to ion implantation with 70 KeV Si- and Cr+ ions to a maximum dose to 5x1016 cm-2 and with 3 MeV H+ ions to a dose of 4x1017cm-2 prior to thermal stress testing in plasma. Fracture and deformation characteristics of the surface layer are measured in ion implanted and unimplanted samples using optical and scanning electron microscopy Implantation-induced near-surface damage is analyzed by ion channeling using 2 Me V He+ ions. Ion implantation is shown to modify the near-surface structure of samples by introducing damage, which makes crack nucleation easier under the applied stress. High energy ion implantation of sapphire crystals with 3 MeV H+ ions produces two kinds of crack nucleating defects: large-scale defects, which initiate fracture under a lower stress, and small-scale defects which require higher stresses for fracture initiation. The crack density measurements are used to evaluate the density of crack nucleating defects which is shown to be dependent on the irradiation dose, ion species and energy, The results indicate that the stress required for crack nucleation is strongly dependent on the ion range. Fracture mechanics principles are applied to evaluate the critical microcrack size which is shown to be comparable with the ion range in the crystals tested. Possible atomistic mechanisms involved in the formation of crack nucleating defects are discussed.

11:30 AM KK4.9 
SIMULATION OF INTERSTITIAL CLUSTER MOBILITY AND CLUSTER MEDIATED SURFACE TOPOLOGIES. Brian D. Wirth, G. Robert Odette, Dept of Mechanical and Environmental Engineering, Dimitrios Maroudas and Glenn E. Lucas, Dept of Chemical Engineering, University of California, Santa Barbara, Santa Barbara, CA.

Embedded atom method (EAM) atomistic simulations have shown that self-interstitial atoms produced by neutron or charged particle beam irradiations form tightly bound clusters in bcc-iron. The clusters are composed of <111> crowdions with interstitial binding energies in excess of 1 eV. The clusters can be described as perfect (b=a/2<111>) prismatic dislocation loops; however, core region is extended compared to an isolated edge dislocation. As the loops grow, interstitials occupy successive hexagonal shells, with minimum energy cusps found at magic numbers corresponding to filled shells. The clusters are highly mobile, undergoing rapid one-dimensional diffusion on their glide prism. The activation energy for glide diffusion is less than approximately 0.3 eV and the corresponding mechanism appears to be the intrinsic presence or easy formation of kinks. Kinks, which are preferentially observed on the hexagonal corners, propagate around the loop periphery, resulting in stochastic increments of glide. Image drift forces bias cluster motion near free surfaces and the consequential annihilation of clusters at the surface produces islands bounded by hexagonal ledges, that are jogged at non magic number sizes. While these simulations are specific to iron, similar behavior is expected for other cubic alloys. The potential effect of islands in promoting epitaxial growth is discussed.

11:45 AM KK4.10 
DEFECT PRODUCTION DURING ION-ASSISTED DEPOSITION OF MOLYBDENUM FILMS, STUDIED BY MOLECULAR DYNAMICS. Peter Klaver and Barend J. Thijsee, Delft University of Technology, Laboratory of Materials Science, Delft, NETHERLANDS.

We report recent results from molecular dynamics simulations of low energy (250 eV) argon-ion assisted deposition of molybdenum films up to 80 Åthick. It is found that argon ions at the higher end of the energy range can produce sub-surface vacancies or clusters of 2-4 vacancies, driving away molybdenum atoms to interstitial positions or via replacement collisions- to adatom positions Argon may get trapped substitutionally in the film (7% probability for 250 eV ions), either in existing vacancies or in vacancies just produced, but it may also be de trapped by subsequent ion impacts. At the lower end of the energy range (25 eV), argon ions have little more effect than a few extra atomic hops on the surface. The occurrence of vacancies and vacancy clusters in films deposited without ion assistance is also discussed. Various atomic transport and disordering processes are reviewed. Also, the effect of argon assistance during deposition on the defect state of the film is compared with experimental evidence from thermal helium desorption spectrometry and other techniques.

SESSION KK5: OPTICAL MATERIALS, NANOCLUSTERS, CERAMICS, AND POLYMERS 
Chairs: George W. Arnold and Robert L. Zimmerman 
Tuesday Afternoon, December 2, 1997 
Essex West (W)

1:30 PM *KK5.1 
MESOSCALE ENGINEERING OF NANOCOMPOSITE NONLINEAR OPTICAL MATERIALS. R.F. Haglund, Jr., L.C. Feldman, R.H. Magruder III, D.H. Osborne Jr., Vanderbilt University, Nashville, TN; C.N. Afonso, J. Solis, Instituto de Optica, CSIC, Madrid, SPAIN; F. Gonella, P. Mazzoldi, INFM, Universite di Padova, Padova, ITALY; R.A. Zuhr, Oak Ridge National Laboratory, Oak Ridge, TN.

Complex nonlinear optical materials comprising elemental, compound or alloy quantum dots embedded in appropriate dielectric or semiconducting hosts are attracting substantial attention for potential deployment in photonic devices. Ion implantation, ion exchange followed by ion implantation, and pulsed laser deposition have all been used to synthesize these materials. However, the correlation between the parameters of energetic-beam synthesis and the nonlinear optical properties is still very rudimentary when one starts to ask what is happening at nanoscale dimensions. Integration of complex nonlinear optical materials into device structures will demand that the nanoscale materials science issues in nonlinear optics be well understood. We discuss the effects of beam energy and energy density on quantum-dot size and spatial distribution, thermal conductivity, quantum-dot composition, crystallinity and defects ó and, in turn, on the third-order optical susceptibility of the composite material. Examples from recent work in our laboratories will be used to illustrate these effects. Research at Vanderbilt University is supported by the Army Research Office (Contract DAAH04-93-G-0123) and the Natural Sciences Council of Vanderbilt University. The Instituta de Optica is partially supported by CICYT (Spain) under contract TIC96-0467. Work at the Universit· di Padova is supported by the Institute for Materials Physics of the Italian National Research Council. Oak Ridge National Laboratory is supported by the U. S. Department of Energy under contract DE-AC05-84OR21400 with Lockheed-Martin Energy Systems, Inc.

2:00 PM KK5.2 
SILVER NANOCLUSTER FORMATION IN IMPLANTED SILICA. Fernando L. Freire Jr., PUC-Rio, Depto de Fisica, Rio de Janeiro, BRAZIL; Gino Mariotto, Universita di Trento, Dip di Fisica, Trento, ITALY.

Silica glass samples were implanted at room temperature with 300 keV-Ag+. The ion dose ranged from 0.8 to 13.5 1016 ions/cm2 and the current density was 1 A/cm2. The silver precipitates were characterized by a multitechnique approach including Rutherford backscattering spectrometry (RBS), optical absorption, Raman scattering, and X-ray diffraction technique (XRD). RBS measurements were used to determine the depth-profile of the implanted ions. The Ag-profile obtained from samples implanted with doses higher than 6 1016 ions/cm2 show a bimodal distribution, with the appearance of a second peak at the depth where occurs the maximum deposition of energy by the incident ions. Optical absorption has been used to characterize the effects of the ion dose on the optical properties of the metal clusters in the UV-Vis region. The broad band at around 400 nm due to the surface plasmon resonance increases in intensity with the ion dose. For doses higher than 6 1016 ions/cm2, a second broad band evolves at higher wavelength, up to 620 nm. These results are discussed in terms of the Mie scattering theory, and can be tentatively attributed to the formation of silver nanocluster with different shapes: spherical, responsible for the band at 400 nm, and spheroids, responsible for the second band at higher wavelength. Low-frequency Raman scattering measurements were also performed and a strong scattering from acoustic vibrations localized at the surface of the silver clusters is observed. XRD measurements confirm the formation of Ag clusters. The discrepancies on the cluster sizes derived from XRD and Raman measurements are discussed on the light of the optical absorption results.

2:15 PM KK5.3 
OPTICAL PROPERTIES OF ION-IMPLANTED SELENIUM NANOCRYSTALS. M.H. Wu, J.L. Chen, A. Ueda, R. Mu, Y.S. Tung and D.O. Henderson, Chemical Physics Laboratory, Department of Physics, Fisk University, Nashville, TN; C.W. White, R.A. Zuhr and J.D. Budai, Oak Ridge National Laboratory, Oak Ridge, TN.

Nanocrystals formed by ion implantation of selenium have been studied by static and time resolved photoluminescence (PL). The observed PL was critically dependent on both the substrate material and the annealing conditions. Strong PL peaked near 570 nm, was observed in annealed samples implanted with sapphire hosts, while almost no detectable PL was observed in as-implanted samples. Neither annealed nor as-implanted samples with fused silica substrates exhibited measurable PL. Substantial variations in the PL of samples implanted at dosage levels ranging from 1016 to 10-17 ions/cm2 and annealed under different conditions have also been observed. Transmission electron microscopy and x-ray diffraction studies were performed to correlate these changes in the optical properties of selenium nanocrystals to changes in size, shape or structure caused by differences in implantation and annealing conditions.

2:30 PM KK5.4 
FORMATION OF NANOCLUSTERS COLLOIDS OF TIN, GOLD, and COPPER IN MAGNESIUM OXIDE BY MeV ION IMPLANTATION*. R. L. Zimmerman, D. Ila, E. K. Williams, and S. Sarkisov, Center for Irradiation of Materials, Dept of Natural and Physical Sciences, Alabama A&M University, Normal, AL; D. B. Poker and D. K. Hensley, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN.

We have implanted ions of Sn, Au, and Cu at energies between 1.5 to 2.0 MeV into single crystals of MgO(100) at room temperature. The formation of nanoclusters was confirmed using optical absorption spectrophotometry, in combination with Mie's theory, which was indirect but non-destructive and by using Transmission Electron Microscopy (TEM), a direct but destructive method. Using Doyle's theory as well as Rutherford Backscattering Spectrometry (RBS), we correlated the full width half maximum (FWHM) of the absorption bands to the estimated size of the metallic nanoclusters between 1-10 nm. These clusters were formed by both over-implantation and by a combination of threshold fluence of the implanted species and post thermal annealing. The changes in the estimated size of the nanoclusters, after annealing at temperatures ranging from 500C to 1150C, were observed using optical absorption spectrophotometry.

2:45 PM KK5.5 
MECHANISMS OF FORMATION OF NONLINEAR OPTICAL LIGHT GUIDE STRUCTURES IN METAL CLUSTER COMPOSITES PRODUCED BY ION BEAM IMPLANTATION. S. Sarkisov, E. K. Williams, C.C. Smith, D. Ila, and Putcha Venkateswarlu, Center for Irradiation of Materials, Alabama A&M University, Department of Natural and Physical Sciences, Normal, AL; D.B. Poker, D.K. Hensley, Oak Ridge National Laboratory, Solid State Division, Oak Ridge, TN.

Composites of metal nanoclusters and dielectric hosts produced by ion beam implantation are of great importance as efficient optical nonlinear materials. High third order nonlinear susceptibility of these materials results from the dramatic enhancement of the local optical field in the vicinity of the metal nanoparticles at the wavelength of surface plasmon resonance. The next step in obtaining useful devices will be fabrication of light confinement structures such as optical waveguides based on these composites. Fortunately, the nuclear damage region produced by bombardment of some dielectric hosts with MeV metal ions can be used as an optical isolation barrier with low refractive index defining the light guiding structure. In this case, a light guiding structure and composite material can be produced simultaneously by the same ion beam. However, optimal characteristics of such composite waveguides have not been achieved yet mostly because the atomistic mechanisms of their formation are not clear yet. We will present the results of the analysis of microstructural and optical properties of various composite nonlinear optical waveguides made by ion implantation of optically transparent amorphous (silica, suprasil) and crystalline (MgO, LiNbO3) dielectrics with MeV ions of such metals as Ag, Au, Cu, and Sn. Special attention will be given to the influence of a host (especially crystalline) on the crystallinity and orientation of metal nanoclusters and also of heat treatment on the size of the clusters and subsequently on the third order susceptibility and characteristics of the optical isolation barrier.

3:30 PM KK5.6 
VANDIUM OXIDE PRECIPITATION IN ALPHA-ALUMINA FORMED BY ION IMPLANTATION. Hiroaki Abe, Hiroshi Naramoto and Shunya Yamamoto, Department of Materials Development, Japan Atomic Energy Reserach Institute-Takasaki, Takasai, Gunma, JAPAN.

Some of vanadium undergo phase transformation attributable for large variations in optical and electronic properties. In this work, we report the precipitation process of vanadium oxides and their structure during ion implantation at high temperature. Implantation of 300 keV V+ ions in c-plane sapphire at high temperature was performed in a transmission electron microscope interfaced with an ion accelerator. Evolution process of radiation damage and precipitates has been observed simultaneously. At implantation fluence of 2x1021 ions/m2 at temperature of 1000K, dot and plate contrast was observed in addition to radiation damage. Electron diffraction analysis reveals hexagonal V2O3 and monoclinic VO2 precipitates. Crystallographic relationship between matrix and precipitates are as follows: 
Al203 (0001) // V203 (h) (1 02), 
Al203 [ 030] // V203 (h) [20] 
Al203 [ (0001) // VO2 (305), 
Al203 [ 20] //VO2[040] The evolution process of precipitates and microstructural observations will be discussed.

3:45 PM KK5.7 
ION BEAM SYNTHESIS OF CdS, Zns, and PbS COMPOUND SEMICONDUCTOR NANOCRYSTALS. C.W. White, J.D. Budai, J.G. Zhu, S.P. Withrow, R.A. Zuhr, E. Sonder, A. Puretzky, and D.B. Geohegan, Oak Ridge National Laboratory, Oak Ridge, TN; D.O. Henderson, Fisk University, Nashville, TN.

We have used sequential ion implantation followed by thermal annealing to synthesize a wide range of compound semiconductor nanocrystals and quantum dots and to encapsulate them at high concentrations in the near surface region of several host matrices. Compounds are formed by sequential implantation of various combinations of ions at energies chosen to give an overlap of the profile. Here we discuss the formation and properties of CdS, ZnS, and PbS nanocrystals produced by this method in matrices of SiO2 and -Al2O3. In SiO2, nanocrystals are nearly spherical and randomly oriented, whereas in -Al2O3 nanocrystals are crystallographically oriented with respect to the matrix. In Al2O3, the PbS nanocrystals have a cubic structure, the CdS is mostly in the hexagonal structure, and the ZnS exhibits a mixture of hexagonal and cubic structures following implantation at elevated temperature. Strong optical absorption is observed for all of these nanocrystals in both matrices, and in some cases, evidence for bandgap shifts up to several eV resulting from quantum confinement are inferred for those systems where the nanocrystal size is considerably smaller than the exciton diameter (PbS). Several of these systems show strong optical phtoluminescence which will be discussed also.

4:00 PM KK5.8 
ION BEAM EFFECTS ON THE FORMATION OF SEMICONDUCTOR NANOCLUSTERS. S. Schiestel, U. of Heidelberg, Phys. Chem. Inst., Heidelberg, GERMANY; C.A. Carosella, C.M. Cotell, K.S.Grabowski and S. Guha, US Naval Research Laboratory, Washington, DC.

We have produced nanoclusters of semiconductors (Si or Ge) in silica films by the method of ion beam assisted deposition. The process parameters can control, for example, the visible photoluminescence from nanoclusters of Si in silica. In this contribution we describe the effects of an argon ion beam on the nanocluster formation resulting from the coevaporation of Si or Ge and silica. Material analyses with nuclear scattering techniques indicate the presence of hydrogen in the Si-silica films prepared without bombardment. Argon-bombarded films have much less hydrogen; they also have less oxygen than predicted from atomic arrival rates. The Si to silica ratios are correlated to changes in index of refraction and shifts in an asymmetric stretching mode ir-absorption. Photoluminescence between 550 and 650 nm is observed for Si-SiO2-films prepared with and without ion beam treatment, which is attributed to SiO2 defects. After annealing, this photoluminescence peak shifts to 750 nm and increases in intensity, indicating the formation of silicon nanoclusters. The micro structure of these films were investigated with TEM. We will present details of the dependence of photoluminescence and micro structure on the process parameters.

4:15 PM KK5.9 
CHEMICAL REACTIONS ON SURFACES IRRADIATED BY ION BEAM AND SYNCHROTRON LIGHT. Jiun-Chan Yang, Hsin-Yen Hwang, Che-Chen Chang, National Taiwan University, Taipei, TAIWAN; Wei-Hsiu Hung, Synchrotron Radiation Research Center, Hsinchu, TAIWAN.

We report on the effect of ion bombardment and synchrotron radiation on the chemical reactions occurring on the surface. The chemical reactivity of metal and semiconductor surfaces with chlorine and carbon monoxide is enhanced under particle bombardment The degree of the reactivity perturbation may be controlled by subjecting surfaces of different temperature to particle beams of different energy, irradiation time, and flux. Isotopic studies reveal that the change of the surface reactivity is caused not only by the alteration of the surface structure but also by the formation of new surface states. Synchrotron-radiation-induced core-level spectroscopy and temperature-programmed desorption studies show that the binding energy of molecules on the new states may be governed by the electronic distribution of the particle-perturbed surface and by the electron-donating or -accepting characteristics of the adsorbing molecules. Molecular dynamics calculations are used to understand the atomistic mechanism of the surface reaction affected by ion irradiation.

4:30 PM KK5.10 
ION ASSISTED REACTION IN POLYMER AND CERAMICS. Seok-Keun Koh, Sung-Chang Choi, Young Soo Yoon, Hyung-Jin Jung, Thin Films Technology Reserach Center, Korea Institute of Science and Technology, Cheongryang, Seoul, SOUTH KOREA.

Ion assisted reaction(IAR), in which energetic ions are irradiated on materials with blowing reactive gases near the irradiating surface, has been described for the surface modifications of polymer and ceramics. The energies of ions are varied from 0.5 to 1.5 keV, doses 1014 to 1017 ions/cm2, and blowing rate of oxygen 08 ml/min. Hydrophilic surfaces of polymers (advanced wetting angle10 and surface energy60 - 70 erg/cm2) have been accomplished by the reaction, and the improvements of wettability and surface energy are mainly due to the polar force and hydrophilic functional groups such as C=O, (C+O)-O, C-O, etc., without surface damage. The IAR was also applied on aluminum nitride in an O2 environment and on aluminum oxide in a N2 environment , and AlON on AlN and AlN on Al2O3 are formed by the Ar+ irradiation, respectively. The improvement of bond strength of Cu films on the AlN surface resulted from the interface bonds between Cu and the surface layers. The bending strength of polycrystalline Al2O3 irradiated by Ar+ ions in N2 gas environments was also increased and the formation of nitride layer on the Alumina was confirmed. Comparisons between the conventional surface treatments and the IAR are described in term of physical bombardment, surface damage, functional group, and chain mobility in polymer.

4:45 PM KK5.11 
STUDY OF THE EFFECTS OF MeV IONS ON PS AND PES. A. L. Evelyn, D. Ila, R. L. Zimmerman, and K. Bhat, Center for Irradiation of Materials, Department of Natural and Physical Sciences, Alabama A&M University, Normal, AL; D. B. Poker and D. K. Hensley, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN.

The electronic and nuclear stopping effects produced by MeV ion bombardment in polyethylene (PE) and polyvinylidene chloride (PVDC) have been previously studied and reported. We have subsequently selected polystyrene (PS) and polyethersulfone (PES), two other insulators which contain sulfur as a cross linking agent, and irradiated them with MeV alpha particles. The electronic and nuclear effects of the incident ions were separated by stacking thin films of the polymers. A layered system was selected such that the first layers experienced most of the effects of the electronic energy deposited and the last layers received most of the effects of the nuclear stopping. The electrical conductance and the changes in the chemical structure were measured by direct resistivity measurements, Raman microprobe analysis, RBS and FTIR. The post-irradiation characterization resolved the effects of the stopping powers on the PS and PES and the results were compared with those from PE and PVDC.

SESSION KK6: POSTER SESSION: 
MECHANISMS IN IRRADIATION AND BEAM SYNTHESIS OF MATERIALS II 
Chairs: Paula Provencio and Kurt E. Sickafus 
Tuesday Evening, December 2, 1997 
8:00 P.M. 
America Ballroom (W)

KK6.1 
TRIBOLOGICAL PROPERTIES OF Si-DLC COATINGS SYNTHESIZED BY ION BEAM ASSISTED DEPOSITION WITH NITROGEN, NITROGEN PLUS ARGON, OR ARGON ION BEAMS. C.G. Fountzoulas, L.C. Sengupta, J.D. Demaree, and J.K. Hirvonen, U.S. Army Research Laboratory, Materials Division, APG, MD; D. Dimitrov, Dept. of Physics and Astronomy, University of Delaware, Newark, DE.

Lubricous, silicon-containing diamond-like carbon coatings (Si-DLC), were synthesized on silicon and sapphire substrates (for Raman purposes only) at room temperature by the ion beam assisted deposition (IBAD) process, using energetic (N+ plus N2+), 50%(N+ plus N2+)/50%Ar+ or Ar+ ions with diffusion pump oil (tetraphenyl-tetramethyl-trisiloxane) as a precursor material. The ion acceleration voltage (40 kV), the ion beam current density (62 mA/m2) and the oil evaporation temperature (145C) were kept constant for all three kinds of ion beams. Optical microscopy showed that the nitrogen and nitrogen plus argon ion beam synthesized Si-DLC coatings (N/Si-DLC and (N+Ar)/Si-DLC respectively) were practically pin-hole free, while there were pin holes in the argon ion beam synthesized coatings (Ar/Si-DLC). The surfaces of the N and (N+Ar) assisted coatings were stain-free and more reflective than the surface of the Ar assisted coatings. The average growth rate of the 50%(N+ plus N2+)/50%Ar+ coating was 15% higher than the growth of the (N+ plus N2+) and Ar+ assisted coatings. The room temperature unlubricated ball-on-disk friction coefficient, , (at 0.5 N load) of all three different synthesized coatings was 0.1. The average Knoop microhardness of the (N+Ar)/Si DLC coatings was 40% more than that of the (Ar/Si-DLC) coatings. X-ray diffraction analysis showed that all films were amorphous with some differences detected from the FTIR and Raman spectra of the films. These differences were most pronounced with the FTIR of the (N+Ar)/Si-FLC coating. Results of the aforementioned areas and the elemental composition of these coatings, investigated by Rutherford Back Scattering (RBS) technique, will be presented and discussed in detail.

KK6.2 
INTERFACE ANALYSIS OF PLASMA-IMMERSION TRIBOLOGICAL COATINGS. M.A. Otooni1, I.G. Brown2, S. Sanders2 and Z. Wang2, US Army Armament Research, Development and Engineering Center1; and Lawrence Berkeley Laboratory, University of California, CA2.

Analysis of fired rails from electromagnetic railguns indicates that severe damage occurs due to high arcing and tribological mismatch. We have prepared and studied properties of several nanoscale multilayered gradient materials as a possible route to improve the thermomechanical properties of copper rail and aluminum armature components. Plasma-immersion ion implantation (PIII) and ion beam surface modification techniques for multilayer coatings were used. These methods utilize vacuum arc plasma as a metal plasma generator. The metal plasma so formed is used either in an ion source to form an energetic beam of metal ions for ion implantation, or in a filtered plasma deposition configuration for thin film synthesis. The nanoscale multilayer structures investigated include: (i) ZrN on Ti-Co alloy on TaN on dlc (diamond-like carbon) on copper; (ii) ZrN on Ti-Co alloy on TaN on dlc on aluminum. The coating thicknesses were in the range of 400A-7 microns. These interfaces were characterized by using high resolution electron microscopy of cross-sectional specimens, scanning electron microscopy, reflection high energy electron diffraction, arc erosion, scratch tests and adhesion tests. These results clearly show strong atomic bonding at the interfaces indicating marked improvement in adhesion and arc resistance of all multilayered structures prepared.

KK6.3 
SURFACE ALLOYING BY HIGH POWER ION BEAMS TO IMPROVE HARDNESS AND CORROSION RESISTANCE IN Al-, Ti-, AND Fe- BASED METALS. T.J. Renk, R.G. Buchheit, N.R. Sorensen, and D. Cowell Senft, Sandia National Laboratories, Albuquerque, NM; M.O. Thompson, Cornell University, Ithaca, NY; and K.S. Grabowski, Naval Research Laboratory, Washington, DC.

Intense ion beams with incident fluences up to 10 J/cm2 and cooling rates of 108-109 K/sec have been used to induce rapid melt and resolidification (RMR) of metal alloy surfaces. The RMR cycle leads to non-equilibrium structures and compositions, with attendant improvements in surface properties. Incident ions include H, He, C, N, Ar, and Xe generated by the MAP (Magnetically confined Anode Plasma) ion source operated on the 800 kV RHEPP-1 accelerator at Sandia National Laboratories. Binary surface alloys have been produced using the ion beam to intermix 0.1 - 4 m-thick sputter-deposited layers with Al, Ti, and Fe substrates. The overcoats were chosen to enhance surface hardness or corrosion resistance. Treated samples were tested for hardness/corrosion improvement, characterized for microstructural changes by x-ray diffraction and scanning electron microscopy (SEM), and analyzed for compositional changes by Rutherford Backscattering Spectrometry (RBS). Post-treatment RBS measurements indicate mixing was achieved to estimated depths up to 13 m, at surface concentrations as high as 30 at% (for 160 nm Pt on Ti). This is consistent with predictions from thermal modeling. Among the most promising results, the corrosion resistance measured for Al6061 with Hf overcoat significantly exceeds that of both 99.999% pure Al, and Hf overcoat without beam treatment. Mixing of Nb and Pt into Ti-5 has led to three times improved surface hardness and increased durability. Work is ongoing to better understand the microstructural basis for these performance improvements.

KK6.4 
PREPARATION OF HARD COATINGS ON POLYCARBONATE SUBSTRATE BY HIGH FREQUENCY ION BEAM DEPOSITION USING ARGON/METHANE/HYDROGEN/OXYGEN/SILOXANE. Sung R. Kim, Jun-Seob Song, Young-Jun Choi, Sam Yang R&D Center, Taejon, KOREA.

Polycarbonate is one of the most widely used engineering plastics because of its transparency and high impact strength. The poor wear and anti-scratch properties of polycarbonate have limited its application in many fields. In order to improve the tribological properties we have used a ion beam technique. The high frequency ion gun was used with argon, methane, oxygen, hydrogen and siloxane gases in this study. The effects of gas composition, ion energy(50 1000eV), vacuum pressure, gas flow rate and deposition rate on the final coating properties including wear and hardness behavior were characterized using Tabor type abrasion tester, XPS and FTIR.

KK6.5 
SYNTHESIS OF HARD NITRIDE COATINGS BY ION BEAM ASSISTED DEPOSITION. J.D. Demaree, C.G. Fountzoulas, C.W. Hubbard, U.S. Army Research Laboratory, APG, MD; M.E. Monserrat, G.P. Halada, State University of New York at Stony Brook, Stony Brook, NY.

Ion beam assisted deposition (IBAD) has been used to deposit chromium nitride coatings using 1200 eV nitrogen ions from an RF-type ion source and thermally evaporated chromium. The ion/atom arrival ratio was varied to modify the coating composition, microstructure, growth rate and stress state in order to optimize the properties of the material for use as a possible substitute for electroplated chromium in a number of anti-corrosion and tribological applications. The coatings were examined using Rutherford backscattering spectrometry and both and x-ray photoelectron spectroscopy. The microstructure of the coatings was determined by transmission electron microscopy and selected area electron diffraction. The corrosion behavior was examined with standard electrochemical techniques, and the tribological behavior of the coatings was examined using an automated scratch testing, pin-on-disc sliding wear evaluation, and nanoindentation. The optimization of IBAD deposition parameters for selected applications of these coatings will be discussed.

KK6.6 
A DEPTH SELECTIVE M{OSSBAUER STUDY OF ION IMPLANTED STAINLESS STEEL. G. Walter, B. Stahl, R. Nagel, R. Gellert, G. Klingelhofer, E. Kankeleit, Inst of Nucl Physics, TH-Darmstadt, GERMANY; D.M. Ruck, GSI Darmstadt, GERMANY; M. Soltani-Farshi, H. Baumann, Inst for Nucl Physics, University Frankfurt/Main, GERMANY.

To study the dynamics of the process of ion implantation, high austenitic stainless steel of composition Fe62Ni20Cr18 was implanted with 400 keV Eu ions of different fluences (3e16-12e16 ions/cm2). With Depth Selective Conversion Electron M{ossbauer Spectroscopy (DCEMS) the depth profile of phases in the implanted layer was analysed. Using an orange-type magnetic spectrometer a set of M{ossbauer spectra, containing the phase information, was measured at different electron energy settings. The energy loss of the conversion electrons in the sample reflects the depth information. The depth profile of the implanted ions was analysed by Rutherford Backscattering Spectroscopy (RBS). The originally high austenitic stainless steel shows an ion induced martensitic transformation, the depth profile of this martensitic transformed region coincides well with the depth profile of the implanted Eu ions. The dynamics of this implantation induced phase transformation as function of the ion fluence is discussed in detail. Furthermore, a new implantation setup is presented, containing an on-line M{ossbauer spectrometer which is installed at the 300 kV implanter at GSI.

KK6.7 
BORON NITRIDES FORMATION IN IRON SURFACE LAYERS DURING NITROGEN ION TREATMENT. V.V. Uglov, J.A. Fedotova, V.V. Khodasevich, Department of Solid State Physics, University of Belarus, Minsk, BELARUS.

Phase transformations of metastable amorphous Fe-B system after nitrogen implantation were investigated in this paper. Thin iron films (80 nm) were firstly amorphized by boron implantation and subsequently irradiated with nitrogen ions in dose range 1*1017-2*1017 ions/cm2. Energy and current density of implantation were 20 keV and 1.5 A/cm2 respectively. Elemental and phase composition of films was investigated by means of Conversion Electron Mossbayer spectroscopy (CEMS) and Auger electron spectroscopy (AES). CEMS investigations of samples after successive boron and nitrogen implantation indicated partial decomposition of amorphous -(Fe-B) phase and increase of crystalline -Fe relative abundance in comparison with monoelemental boron implantation. However, formation of iron nitrides was not observed. Analysis of differential AES line shape of boron displayed that chemical surrounding of boron after nitrogen incorporation into amorphous -(Fe-B) phase differs noticeably from boron AES line in -(Fe-B) phase. A comparison between differential AES boron line in -(Fe-B) modified by nitrogen implantation and boron line in boron nitride testifies that subsequent nitrogen implantation could lead to boron nitride formation at a sacrifice of amorphous phase decomposition.

KK6.8 
PROPERTIES OF CN FILM PREPARED BY MASS-SELECTED, HYPER-THERMAL CARBON AND NITROGEN IONS. Nobuteru Tsubouchi, Burkhard Enders, Akiyoshi Chayahara, Atsushi Kinomura, Yuji Horino, Dept of Material Physics, Osaka National Research Institute, AIST, Osaka, JAPAN.

CN films were prepared at PANDA (Positive And Negative ions Deposition Apparatus) using hyper-thermal(50-400eV) ion spieces such as C-, C2-, N+, N2+, CN- . Positive and negative ion beams are simultaneously irradiated on a substrate. We investigated the relation between a various energy combination of positive and negative ions and film properties such as bonding state, optical constants, film structure, etc. These films were evaluated by Rutherford Backscattering Spectrometry (RBS), Fourier Transform Infrared absorption spectrometry (FT-IR) and Raman scattering.

KK6.9 
FIELD ION MICROSCOPY OF PHASE TRANSFORMATIONS AND DEEP-EFFECTS IN ION-IRRADIATED METALS AND ALLOYS. Alexander Bunkin, Vladimir Ivchenko, Inst. of Electrophysics, Urals Division of Russian Academy of Sciences, Ekaterinburg, RUSSIA FEDERATION.

Phase and structural changes in Cu3Au, PdOuAg and pure iridium tip specimens have been studied. The samples were bombarded by Ar+ ions at the energy of 20 keV, total dose 1012 - 1018 ions/cm2 and fluence-rate varying from 6 1014 to 1.8 1015 ions/cm2 s. Irradiation was found to stimulate the processes of ordering in the disordered Cu3Au alloy and precipitation break-up in the supersaturated PdOuAg solid solution at temperatures lower than the temperatures of transformation, according to the phase diagrams. On the other hand it caused disordering of the surface layers of the ordered Cu3Au alloy up to the depth several times exceeding the projective range of Ar+ ions. A lot of point, linear and three-dimensional defects born as the result of ionbombardment have been revealed and examined at atomic scale in all three types of materials. Separate dislocations and dislocation arrays, pores and disordered regions have been found in pure iridium as well as in Cu3Au and PdCuAg solid solution. The zone saturated with these defects protrudes up to the distance more than 10-4 cm from the surface. The origin of deep effect of ion irradiation on the structural changes in metals and alloys is discussed.

KK6.10 
ELECTRONIC EXCITATION EFFECT ON RADIATION ANNEALING IN Fe IRRADIATED AT 80K WITH ENERGETIC IONS. Yasuhiro Chimi, Akihiro Iwase, Norito Ishikawa, Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki-ken, JAPAN.

Defect production and annihilation behavior in Fe irradiated with energetic ions has been studied. High-energy (100MeV) and low-energy (1MeV) ion irradiation experiments were performed at 80K. Specimens were Fe thin films about 200nm thick deposited on -Al2O3 single crystal substrates by using rf magnetron sputtering. Defect production curves, i.e. the changes in resistivity of the specimens, which correspond to the defect concentration, were measured as a function of the ion fluence. Cross-sections for defect production and defect annihilation were derived from the defect production curves. The defect annihilation cross-sections for high-energy ion irradiations are much larger than those for low-energy ion irradiations at the same nuclear stopping power. It indicates that in the case of high-energy ion irradiations the defect annihilation during irradiation (what is called radiation annealing) is caused by the electronic excitations as well as the elastic interactions. Besides, the result of the defect production cross-sections suggests that the defect production is also caused by the electronic excitations.

KK6.11 
THE FIRST FEW HUNDRED ANGSTROMS OF IBAD-DEPOSITED MOLYBDENUM FILMS. Jan van der Kuur, Jacqueline van der Linden, Bas Korevaar, Martin Pols, and Barend Thijsse, Delft University of Technology, Laboratory of Materials Science, Delft, NETHERLANDS.

Moly-on-moly films of 5 Å to 1000 Å thickness, e-beam evaporated with and without argon ion assistance ( eV), were implanted with 100 eV helium to serve as probe atoms for defects. Alternatively such films were grown on a thin base layer already implanted with helium. Upon heating a film, the helium atoms and the IBAD-incorporated argon atoms dissociate from their traps at specific temperatures. The desorption signals versus temperature (argon and helium are measured simultaneously) are then used to reconstruct quantitatively the defect state of the film and the changes therein as the temperature increases. The detection limit of defect concentrations is on the order of 10-6. Since the films are probed from the top and from the bottom, there is in principle no thickness limitation. We have looked at a great number of deposition conditions and film thicknesses. For evaporated films we find that the film starts out with full substrate coverage and that in the first 100 Åat least one change in growth mode takes place. The effect of argon ions in IBAD layers is a reduction of the thickness at which this change occurs. Moreover IBAD films contain up to ten times as many point defects as evaporated layers (). The argon incorporation is not uniform throughout the film, and the different types of vacancy clusters vary with thickness as well. Larger voids, grain boundaries, and the dynamics of such defects are also discussed in the paper. Recently we have observed considerable differences between (100) and (110) films.

KK6.12 
DEPOSITION OF IN-PLANE TEXTURED MgO ON AMORPHOUS Si3N4 SUBSTRATES BY ION-BEAM-ASSISTED DEPOSITION (IBAD) AND COMPARISONS WITH IBAD YSZ. Connie P. Wang, Khiem B. Do, Robert H. Hammond, Malcolm R. Beasley, and Theodore H. Geballe, Ginzton Lab, Stanford Univ, Stanford, CA.

We report the growth of in-plane textured (100) MgO film on amorphous Si3N4 substrates by ion beam assisted deposition (IBAD) to be used as a structural template for the subsequent epitaxial thin film deposition. The result is compared with in-plane textured IBAD (100) and (111) YSZ. Based on the TEM and in-situ RHEED characterization, the MgO texturing mechanism is a nucleation process and the alignment is found to be a function of nuclei size and density. This differs greatly from IBAD (100) YSZ's evolutionary-type texturing process. Consequently, we are able to obtain a in-plane aligned MgO films at while the IBAD (100) YSZ needs to be thicker than to achieve in-plane alignment better than . This result has important implications for the economical applications to a number of potential produces, including high temperature superconductor (i.e. YBCO) coated conductors, photovoltaics, magnetic thin films and semiconductor devices.

KK6.13 
EFFECT OF ION ENERGY ON STRUCTURE AND CHEMICAL PROPERTIES OF TIN OXIDE FILM IN REACTIVE ION-ASSISTED DEPOSITION(R-IAD). Jun-Sik Cho*, Won-Kook Choi, Ki Hyun Yoon*, J. Cho, Hyung-Jin Jung and Seok-Keun Koh, Thin Film Technology Research Center, Korea Institute of Science and Technology, Cheongryang, Seoul, SOUTH KOREA; *Department of Ceramic Engineering, Yonsei University, Sudaemoon Ku, Shincheon Dong, Seoul, SOUTH KOREA.

Composition, chemical state, crystallinity, and surface roughness of tin oxide films, fabricated by ion-assisted deposition (R-LAD) were investigated as a function of assisted oxygen ion energy and substrate temperature. Neutral tin atoms were evaporated with assisting ionized oxygen at a pressure of 1x10-4 Torr in order to fabricate tin oxide films deposited on Si and glass substrate at various substrate temperatures. Oxygen gas was ionized and accelerated by cold-hollow-cathode type ion gun at oxygen flow rate of 2.5 ml/min and acceleration energy (Vi) of oxygen ion was changed from 50 eV to 500 eV at fixed current density of ionized oxygen. The film (Vi=500 eV) deposited at room temperature showed amorphous structure and the grain size of the film was below a few tenths Å. XPS analysis showed that the atomic state of Sn in the film was Sn4+ and the composition (No/NSn was 1.91. In case of in situ substrate heating at 400C, XRD results showed that the film (Vi=500 eV) possessed the characteristic SnO2 peaks at 26.8, 34.1 and 51.8 corresponding to (110), (101) and (211) planes and the film was perfectly oxidized into SnO2. The grain size increased to 100-200 Å due to the increase of substrate temperature. In order to study the effect of oxygen ion energy on chemical state and surface roughness of the tin oxide films, SEM, AFM and AES surface analysis were carried out, respectively.

KK6.14 
HRTEM AND EELS STUDIES OF REACTED MATERIALS FROM CaF2 BY ELECTRON BEAM IRRADIATION. Toshihiro Kogure, Koichiro Saiki, the University of Tokyo, Graduate School of Science, Tokyo, JAPAN; Mitsuru Konno, Takeo Kamino, Hitachi Instruments Engineering Co., Ltd., Ibaraki, JAPAN.

Surface modifications of calcium fluoride (CaF2) by photon or electron beam irradiation are being investigated for potential applications to semiconductor processes. Among these works, several groups reported metallization of CaF2 surfaces by irradiation by relatively low-energy (1 keV) electrons. We have investigated this phenomenon by in situ HRTEM observation, EDS and EELS analyses in a field-emission TEM using 200 keV primary electrons. HRTEM images showed amorphization of CaF2 from thinner edges of the crystal and new nanocrystallites, which are identified as CaO by lattice images and EDS analyses, were formed in the amorphous material during observation. There is no epitaxial relation between these CaO crystallites and the CaF2 crystal. In the similar radiation condition, EELS spectrum changed with radiation time. It showed the decrease of the core-loss peak (685 eV) of fluorine and the formation of new two peaks (about 3.5 eV and 9 eV) around the low energy loss region, which correspond to surface and volume plasmon excitations of Ca metal respectively. These plasmon peaks extinguished upon further irradiation. From these analyses and observations it is supposed that the amorphous material observed in HRTEM is amorphous Ca metal. Other alkaline-earth halides and alkali halides are being investigated to reveal whether such amorphous metals are formed with the desorption of halogen elements by electron beam irradiation.

KK6.15 
THERMAL STABILITY OF THE OPTICAL CHANNELS IN PLANAR GaAS/AlGaAs WAVEGUIDES PRODUCED BY MeV IONS*. T. Taylor, D. Ila, R. L. Zimmerman, J. C. Cochrane, Center for Irradiation of Materials, Alabama A&M University, Department of Natural and Physical Sciences, Normal, AL; P. R. Ashley, Weapons Sciences Directorate, Research, Development and Engineering Center, U.S. Army Missile Command, Redstone Arsenal, AL; D. B. Poker and D. K. Hensley, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN.

In this work we have studied the thermal stability of the in-house fabricated optical channels in planar GaAs/AlGaAs waveguides. The waveguides were fabricated taking the advantage of the electronic energy deposited by MeV ions in its track. We have used both MeV oxygen ions as well as MeV carbon ions in fabricating these optical channels. Implantation at different temperatures as well as post annealing appear to have a direct effect on the extracted propagation mode losses. Single-mode operation is observed from all the fabricated optical channels at a wavelength of 1.3 mm. The optical characterization results provide insight as to which ion beam parameters are best suited to optimize this fabrication process.