Near-equiatomic porous nickel-titanium shape memory alloys (NiTi SMAs) are becoming one of the most promising biomaterials in bone implants because of their unique advantages over currently used biomaterials. For example, they have good mechanical properties and lower Young�s modulus relative to dense NiTi, Ti, and Ti-based alloys. Porous NiTi SMAs are relatively easy to machine compared to porous ceramics such as hydroxyapatite and calcium phosphate that tend to exhibit brittle failure. The porous structure with interconnecting open pores can also allow tissue in-growth and favors bone osseointegration. In addition, porous NiTi alloys remain exhibiting good shape memory effect (SME) and superelasticity (SE) similar to dense NiTi alloys. To optimize porous NiTi SMAs in bone implant applications, the current research focuses on the fabrication methods and surface modification techniques in order to obtain adjustable bone-like structures with good mechanical properties, excellent superelasticity, as well as bioactive passivation on the entire exposed surface areas to block nickel ion leaching and enhance the surface biological activity. This invited paper describes progress in the fabrication of the porous materials and our recent work on surface nanorization of porous NiTi scaffolds in bone grafts applications.

Amorphous Si/SiOx multi-layered films and nanostructures were deposited on Si substrates by the glancing angle deposition technique using Ar ion beam sputtering of a Si sputter target in an intermittent oxygen atmosphere at room temperature. The chemical composition of the samples was characterized by time-of-flight secondary ion mass spectrometry, as well as - for quantifying these first results - by elastic recoil detection analysis using a 200 MeV Au ion beam. The latter method was found to lead to a significant alteration of the sample morphology, resulting in the formation of complex nanometric structures within the layer stacks. In order to investigate these swift heavy ion irradiation induced effects in more detail, a series of experiments was conducted to determine the dominating influences. For this purpose, specific glancing angle deposited multilayered films and nanostructures were irradiated to constant ion fluence with the same 200 MeV Au ion beam at different incidence angles. Scanning electron microscopy of the stacks before and after swift Au ion irradiation revealed considerable changes in film morphology and density as a function of the ion incidence angle, such as an increased porosity of the silicon layers, accompanied by a layer swelling. In contrast, the SiOx layers did not show such effects, but exhibited clearly visible swift heavy ion tracks. The observed effects became stronger with decreasing ion incidence angle.

Ripple formation and smoothing of pre-patterned fused silica surfaces by low-energy ion beam erosion have been investigated. As pre-pattern ripple surfaces produced by low-energy Ar+ ion beam erosion were used. In addition to the enhanced ripple formation on the pre-patterned surfaces also the smoothing characteristics of surface is changed. Due to the anisotropic surface roughness of the ripple pattern the irradiation direction with respect to the pre-pattern becomes important. It is suggested that all of these effects are related to surface gradient dependent sputtering and therefore it is an important mechanisms also in the low-energy ion beam erosion of fused silica surfaces.

Using quantum mechanical and classical molecular dynamics computer simulations, we study the full three-dimensional threshold displacement energy surface in Si. We show that the SIESTA density-functional theory method gives a minimum threshold energy of 13 eV that agrees very well with experiments, and predicts an average threshold displacement energy of 36 eV. Using the quantum mechanical result as a baseline, we discuss the reliability of the classical potentials with respect to their description of the threshold energies. We also examine the threshold energies for sputtering in a nanowire, and find that this threshold depends surprisingly strongly on which layer the atom is in.

MeV-ion beam has long been applied to biology research and applications for many decades as highly energetic ions are undoubtedly able to interact directly with biology molecules to cause changes in biology. However, low-energy ion beam at tens of keV and even lower has also been found to have significant biological effects on living materials. The finding has led to applications of ion-beam induced mutation and gene transfer. From the theoretical point of view, the low-energy ion beam effects on biology are difficult to understand since the ion range is so short that the ions can hardly directly interact with the key biological molecules for the changes. This talk introduces interesting aspects of low-energy ion beam biology, including basis of ion beam biotechnology and recent developments achieved in Chiang Mai University in relevant applications such as mutation and gene transfer and investigations on mechanisms involved in the low-energy ion interaction with biological matter such as eV-keV ion beam bombardments of naked DNA and the cell envelopes.

Effective thermoelectric materials have a low thermal conductivity and a high electrical conductivity. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2sσ/ KTC, σ is the electrical conductivity T/KTC, where S is the Seebeck coefficient, T is the absolute temperature and KTC is the thermal conductivity. In this study we have prepared the thermoelectric generator device of Si/Si+Ge multi-layer superlattice films using the ion beam assisted deposition (IBAD). To determine the stoichiometry of the elements of Si and Ge in the grown multilayer films and the thickness of the grown multi-layer films Rutherford Backscattering Spectrometry (RBS) and RUMP simulation software package were used. The 5 MeV Si ion bombardments were performed to make quantum clusters in the multi-layer superlattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity.

Keywords: Ion bombardment, thermoelectric properties, multi-nanolayers, Figure of merit.

The use of an ion beam assist during the concurrent deposition of cubic materials can result in the growth of crystallographically oriented thin films. A model system, magnesium oxide (MgO), has been successfully used as a biaxially textured template film and develops texture in a different manner from that of other well-studied materials, like yttria-stablized zirconia. Here, we present data on the initial nucleation of biaxial texture in this model system using a novel in-situ quartz crystal microbalance (QCM) substrate combined with in-situ reflected high-energy electron diffraction (RHEED). Temporal correlation of mass uptake with the RHEED images of the growing surface can be used to elucidate the mechanism of texture development in these films. Experimental data shows that the initially polycrystalline MgO film develops biaxial crystallographic texture at a thickness of ˜2 nm, regardless of the ion-to-molecule ratio. RHEED images show the onset of texture occurs quickly and is somewhat analogous to a solid phase re-crystallization process with crystallite sizes of ˜3 to 4 nm. Imaging with transmission electron microscopy has corroborated these observations. Changes in the ion-to-molecule ratio can influence the crystallite size and affect the nucleation density of these films. Growth of these films on various substrates changes the sticking coefficient of the MgO and influences the nucleation density and film growth mode as well. This opens the possibility of using MgO and other materials to develop biaxially textured crystallites with a narrow, specified size distribution for nanoscale applications.

We report the magnetoresistance (MR) measurements in a nanoconstriction fabricated by focused-ion-beam (FIB) in the tunneling regime of conductance. The resistance of the contact was controlled during the fabrication process, being stable in the metallic regime, near the conductance quantum, and under high vacuum conditions. The metallic contact was deteriorated when exposed to atmosphere, resulting in a conduction mechanism by tunneling. The TMR was found to be of 3% at 24 K. The anisotropic tunneling magnetoresistance (TAMR) was around 2% for low temperatures, with a field angle dependence more abrupt than in bulk Fe. This preliminary result is promising for the application of this technique to fabricate stable ferromagnetic constrictions near the atomic regime of conductance, where high MR values are expected.

We present a novel fabrication method to create controlled 3-dimensional silicon nanostructures with the lateral dimensions that are less than 50 nm as a result of a rapid clean room compatible process. We also demonstrate periodic and nonperiodic lattices of nanopillars in predetermined positions with the minimum pitch of 100 nm. One of the uses of this process is to fabricate suspended silicon nanowhiskers.

Ion-beam induced etching and deposition rates are proportional to the flux of recoils reaching the surface. Based on this finding we propose an improved algorithm for etching and deposition simulations. In this algorithm the recoil flux at each point on the surface is calculated by summing up the recoil fluxes originating from ions impinging on any other surface point. The latter are determined by interpolation in tables calculated by binary collision simulations. For concave surfaces a correction to this algorithm is proposed. Fluxes calculated by this model are in good agreement with binary collision simulations of collision cascades in the same 2-d structure. Consistent with experimental findings, the model predicts that deposited pillars are broader than the ion beam, while etched trenches do not show such broadening. The pillar broadening is related to the lateral straggling of the recoils.

A novel technique to form periodically nanostructured Si surface morphologies based on nanosphere lithography (NSL) and He ion implantation induced swelling is studied in detail. It is shown that by implantation of keV He ions through the nanometric openings of NSL masks regular arrays of hillocks and rings can be created on silicon surfaces. The shape and size of these surface features can be easily controlled by adjusting the ion dose and energy as well as the mask size. Feature heights of more than 100 nm can be obtained, while feature distances are typically 1.15 or 2 (hillock or ring) nanosphere radii, which are chosen to be between 100 and 500 nm in this study. Atomic force and scanning electron microscopy measurements of the surface morphology are supplemented by cross-sectional transmission electron microscopy, revealing the inner structure of hillocks to consist of a central cavity surrounded by a hierarchical arrangement of smaller voids. The surface morphologies developed here have the potential to be useful for fixing and separating nano-objects on a silicon surface.

A key process in a successful treatment of patients with a great variety of musculoskeletal implants requires a fast, reliable and consistent osseointegration. Among the parameters that affect this process, it is widely admitted that implant surface topography, surface energy and composition play an important role.

Different surface modification techniques to improve osseointegration have been proposed and tested to date, but most focus on microscale features, and few control surface modifications at nanoscale. On the other hand, ion implantation modifies the outermost surface properties in relation to the nanotopography, chemical and physical characteristics at nanoscale. The meta-stable surface that results from the treatment, affects the adsorption of bio-molecules in the very first stages of the implant placement, and thus the signaling pathway that promotes the differentiation and apposition of osteoblast cells.

This study aimed at assessing the performance, in terms of osseointegration levels and speed, of ion implanted titanium made implants. The study included several in vitro and in vivo tests. The latter, comprised different insertion periods and both experimental and commercial implants as comparative surfaces. The final stage of the study included clinical trials in human patients.

In each and every case, bone integration improvement of tested materials/implants was achieved for the CO ion implanted samples. Furthermore, contact osteogenesis was observed in the ion implanted samples, unlike the Ti control samples, where only distance osteogenesis occurred, being this potentially one of the reasons for their faster healing and osseointegration process.

Finally, the use of ion implantation as a surface modification tool that allows for evaluating the effects of nanotopography and composition changes independently is presented.

One of the new applications of focused Ga ion beam (Ga FIB) techniques to fabricate micro fluid channels on plate glass was demonstrated. After discussing features of the FIB etched patterns, narrow channel or Y-shaped channels were fabricated by FIB etching on a patterned plate glass which was prepared by photo-lithography and wet etching processes. Micro fluid devices were then constructed using polydimethylsiloxane (PDMS) sheet and silicone rubber tubes and the water (or ink) flow in the devices was observed under a microscope using a syringe pump. Although no discussion based on fluid mechanics has done at present, the present results indicate a possibility of applying FIB techniques to fabricate micro fluid devices which can be used in bio- and/or chemical-related fields.

The TRISO fuel that is intended to be used for the generation IV nuclear reactor design consists of a fuel kernel of Uranium Oxide (UOx) coated in several layers of materials with different functions. One consideration for some of these layers is Silicon Carbide (SiC) [1]. The design, manufacture and fabrication of SiC are done at the Center for Irradiation of Materials (CIM). This light weight material can maintain dimensional and chemical stability in adverse environments and very high temperatures. The characterization of the elemental makeup of the SiC material used is done using X-ray photoelectron spectroscopy (XPS). Nano-indentation is used to determine the hardness, stiffness and Young's Modulus of the material. Raman Spectroscopy is used to characterize the chemical bonding for different sample preparation temperatures.

Ion beam synthesis of nanoclusters is studied via both kinetic Monte Carlo simulations and the self-consistent mean-field solution to a set of coupled rate equations. Both approaches predict a steady-state shape for the cluster size distribution that depends only on a characteristic length determined by the ratio of the effective diffusion coefficient times the effective solubility to the ion flux. The average cluster size in the steady state regime is determined by the implanted species/matrix interface energy.

High fluences of low energy Ge+ ions were implanted into Si matrix. We have also deposited Ge and SiO2 composite films by using the Atom beam sputtering (ABS). The as implanted/as-deposited films were irradiated by Swift Heavy Ions (SHI) with various energies and fluences. These pristine and irradiated samples were subsequently characterized by XRD and Raman to understand the crystallization behavior. Raman studies of the films indicate the formation of Ge crystallites as a result of SHI irradiation. Glancing angle X-ray diffraction results also confirm the presence of Ge crystallites in the irradiated samples. Moreover, the crystalline nature of Ge improves with an increase in fluence. Rutherford back scattering was used to quantify the concentration of Ge in SiO2 matrix and the film thickness. These detailed results have been discussed and compared with the ones available in literature. The basic mechanism for crystallization induced by SHI in these films will be presented.

The efficiency of the thermoelectric devices is limited by the properties of n- and p-type semiconductors. Effective thermoelectric materials have a low thermal conductivity and a high electrical conductivity. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and K is the thermal conductivity. In this study we prepared the thermoelectric generator device of SiO2/SiO2+Au multi-layer super-lattice films using the ion beam assisted deposition (IBAD). In order to determine the stoichiometry of the elements of SiO2 and Au in the grown multilayer films and the thickness of the grown multi-layer films Rutherford Backscattering Spectrometry (RBS) and RUMP simulation software package was used. The 5 MeV Si ion bombardments was performed to make quantum clusters in the multi-layer super-lattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric generator devices before and after Si ion bombardments we measured the cross-plane Seebeck coefficient, the cross-plane electrical conductivity, and the cross-plane thermal conductivity for different fluences.

We experimentally demonstrate a simple and efficient approach for silicon oxide nanowire growth by implanting Fe+ ions into thermally grown SiO2 layers on Si wafers and subsequently annealing in argon and hydrogen to nucleate silicon oxide nanowires. We study the effect of implantation dose and energy, growth temperature, and H2 gas flow on the SiOx nanowire growth. We find that sufficiently high implant dose, high growth temperature, and the presence of H2 gas flow are crucial parameters for silicon oxide nanowire growth. We also demonstrate the patterned growth of silicon oxide nanowires in localized areas by lithographic patterning and etching of the implanted SiO2 substrates before growth. This works opens up the possibility of growing silicon oxide nanowires directly from solid substrates, controlling the location of nanowires at the submicron scale, and integrating them into nonplanar three-dimensional nanoscale device structures.

The low energy ion beam erosion of solid surfaces is a simple bottom-up approach for the generation of nanostructures. For certain sputtering conditions caused by self-organization processes well ordered nanostructures on the surface like one-dimensional ripples or regular arrays of dots can be formed [1]. Using broad beam sources, the low energy ion beam erosion can be a cost-efficient method to produce large-area nanostructured surfaces in a one-step process.

The processes involved have been studied in the last decades and the pattern formation is attributed to the competition of curvature dependant sputtering and various relaxation mechanisms. It is also well known that the ion beam incidence angle (the angle between the sample surface normal and the axis of the beam source) is one critical parameter that determines the surface topography. However, inherent to all broad beam sources, the ion beam exhibits a certain divergence, i.e. the ion trajectories are not parallel to each other. This generates a spread of the local incidence angle with respect to the geometrically defined beam incidence angle.

Recent studies showed that the divergence angle and angular distribution of the ions, here called internal beam parameters, also affect the surface topography [2].

The angular distribution can be controlled by the total voltage applied on the geometrical defined ion optical system of the broad beam ion source. For the given multi-aperture two-grid ion optical system the total voltage is the sum of the voltages applied to the first (screen) and second (accelerator) grid. This total voltage, together with the geometrical characteristics of the used grid systems, including the shape of the plasma sheath boundary at the screen grid, define the overall ion-optical parameters of the source, i. e. the divergence angle and angular distribution of the ions within the beam.

In this contribution a first approach of the effect of the internal beam parameters on the surface topography is presented. It was analyzed the effect on the topography on Si surfaces of some experimental parameters that affect the internal beam parameters by changing the ion-optical parameters and the shape of the plasma sheath boundary. Explicitly, the influence of the discharge voltage, the operation time and the distance between the screen and accelerator grid is shown.

[1] B. Ziberi, M. Cornejo, F. Frost, B. Rauschenbach, J. Phys.: Condens. Matter (submitted).[2] B. Ziberi, F. Frost, M. Tartz, H. Neumann, B. Rauschenbach, Appl. Phys. Lett. 92, 063102 (2008)

We present result following localized ion implantation of rutile titanium dioxide (TiO2) using anodic porous alumina as a mask. The implantation were performed with 100 keV 56Fe+ ions using a fluence of 1.3·1016 ions/cm2. The surface modifications where studied by means of SEM, AFM/MFM and XRD. A well-defined hexagonal pattern of modified material in the near surface structure is observed. Local examination of the implanted areas revealed no clear magnetic signal. However, a variation in mechanical and electrostatic behavior between implanted and non-implanted zones is inferred from the variation in AFM signals.