Search

Modifying implant surfaces to improve their biocompatibility by enhancing osteoblast activation, growth, differentiation, and induction of greater bone formation with stronger attachments should result in improved outcomes for total joint replacement surgeries. This study tested the hypothesis that nano-structured surfaces, produced by the ion beam-assisted deposition method, enhance osteoblast adhesion, growth, differentiation, bone formation, and maturation. The ion beam-assisted deposition technique was employed to deposit zirconium oxide films on glass substrates. The effects of the ion beam-assisted deposition technique on cellular functions were investigated by comparing adhesion, proliferation, differentiation, and apoptosis of the human osteosarcoma cell line SAOS-2 on coated versus uncoated surfaces. Ion beam-assisted deposition nano-coatings enhanced initial cell adhesion assessed by the number of 4′,6-diamidino-2-phenylindole–stained nuclei on zirconium oxide nano-coated surfaces compared to glass surfaces. This nano-modification also increased cell proliferation as measured by mitochondrial dehydrogenase activity. Moreover, the ion beam-assisted deposition technique improved cell differentiation as determined by the formation of mineralized bone nodules and by the rate of calcium deposition, both of which are in vitro indicators of the successful bone formation. However, programmed cell death assessed by Annexin V staining and flow cytometry was not statistically significantly different between nano-surfaces and glass surfaces. Overall, the results indicate that nano-crystalline zirconium oxide surfaces produced by the ion beam-assisted deposition technique are superior to uncoated surfaces in supporting bone cell adhesion, proliferation, and differentiation. Thus, surface properties altered by the ion beam-assisted deposition technique enhanced bone formation and may increase the biocompatibility of bone cell–associated surfaces.

The rationale behind novel surface engineering and coating technologies for implant articular surfaces is described especially for the significant number of metal-sensitive patients with total hip replacement. We list the important coating characteristics, and emphasize adhesion as the most challenging. We report on 2 large scale experimental hip wear simulator studies we conducted on samples of 2 such coating technologies implemented by external experts in their respective fields. One was a titanium nitride ceramic coating on a metal-on-metal total hip replacement, which aimed at wear reduction and a barrier against metal-ion diffusion. The other was a nanocrystalline homometallic surface treatment where same element metals were vapor-deposited in a novel ion-beam-assisted deposition process onto CoCr alloy femoral heads in CoCr metal on ultra high molecular weight polyethylene (UHMWPE) hips. The gradual reduction in crystal size toward the surface into nano size aimed at increasing hardness and reducing wear. Both test series were conducted on an AMTI hip simulator for 5 million cycles under the 14242-1 ISO standard, simulating walking gait, without any deliberate edge-loading or harsh conditions, and using uncoated specimens of identical design and materials as controls in each test. Both tests resulted in some of the coating eventually rubbing away (separating) to various levels on all specimens. The wear rate of the coated specimens was generally higher not lower than the uncoated controls, but not multiply so. Our discussion compares and contrasts our results with others, and we speculate whether a metal-sensitive arthritic patient who badly needs a hip replacement may still benefit from a coated implant despite the risk.

Ever increasing energy needs have raised the demands for advanced fuels and cladding materials that withstand the extreme radiation environments with improved accident tolerance over a long period of time. Ceria (CeO2) is a well known ionic conductor that is isostructural with urania and plutonia-based nuclear fuels. In the context of nuclear fuels, immobilization and transmutation of actinides, CeO2 is a model system for radiation effect studies. Covalent silicon carbide (SiC) is a candidate for use as structural material in fusion, cladding material for fission reactors, and an inert matrix for the transmutation of plutonium and other radioactive actinides. Understanding microstructural change of these ionic-covalent materials to irradiation is important for advanced nuclear energy systems. While displacements from nuclear energy loss may be the primary contribution to damage accumulation in a crystalline matrix and a driving force for the grain boundary evolution in nanostructured materials, local non-equilibrium disorder and excitation through electronic While displacements from nuclear energy loss may be the primary contribution to damage accumulation in a crystalline matrix and a driving force for the grain boundary evolution in nanostructured materials, local non-equilibrium disorder and excitation through electronic energy loss may, however, produce additional damage or anneal pre-existing defect.more » At intermediate transit energies where electronic and nuclear energy losses are both significant, synergistic, additive or competitive processes may evolve that affect the dynamic response of materials to irradiation. The response of crystalline and nanostructured CeO2 and SiC to ion irradiation are studied under different nuclear and electronic stopping powers to describe some general material response in this transit energy regime. Although fast radiation-induced grain growth in CeO2 is evident with no phase transformation, different fluence and dose dependence on the growth rate is observed under Si and Au irradiations. While grain shrinkage and amorphization are observed in the nano-engineered 3C SiC with a high-density of stacking faults embedded in nanosize columnar grains, significantly enhanced radiation resistance is attributed to stacking faults that promote efficient point defect annihilation. Moreover, competing effects of electronic and nuclear energy loss on the damage accumulation and annihilation are observed in crystalline 4H-SiC. Systematic experiments and simulation effort are needed to understand the competitive or synergistic effects. energy loss may, however, produce additional damage or anneal pre-existing defect. At intermediate transit energies where electronic and nuclear energy losses are both significant, synergistic, additive or competitive processes may evolve that affect the dynamic response of materials to irradiation. The response of crystalline and nanostructured CeO2 and SiC to ion irradiation are studied under different nuclear and electronic stopping powers to describe some general material response in this transit energy regime. Although fast radiation-induced grain growth in CeO2 is evident with no phase transformation, different fluence and dose dependence on the growth rate is observed under Si and Au irradiations. While grain shrinkage and amorphization are observed in the nano-engineered 3C SiC with a high-density of stacking faults embedded in nanosize columnar grains, significantly enhanced radiation resistance is attributed to stacking faults that promote efficient point defect annihilation. Moreover, competing effects of electronic and nuclear energy loss on the damage accumulation and annihilation are observed in crystalline 4H-SiC. Systematic experiments and simulation effort are needed to understand the competitive or synergistic effects.« less

Grain growth of nanocrystalline materials is generally thermally activated, but can also be driven by irradiation at much lower temperature. In nanocrystalline ceria and zirconia, energetic ions deposit their energy to both atomic nuclei and electrons. Our experimental results have shown that irradiation-induced grain growth is dependent on the total energy deposited, where electronic energy loss and elastic collisions between atomic nuclei both contribute to the production of disorder and grain growth. Our atomistic simulations reveal that a high density of disorder near grain boundaries leads to locally rapid grain movement. The additive effect from both electronic excitation and atomic collision cascades on grain growth demonstrated in this work opens up new possibilities for controlling grain sizes to improve functionality of nanocrystalline materials.

The goal of the experiment outlined in this article is to improve upon noncemented methods of arthroplasty for clinical application in elderly patients. This was done by determining whether titanium implants with a novel nanostructured zirconia surface, which was created by ion beam–assisted deposition, would prevent impaired osseointegration of intramedullary implants in 1-year-old rats receiving a protein-deficient diet. Specifically, we asked whether the implant with the nanostructured zirconia surface would increase expression of markers of bone maturation within the remodeling of peri-implant woven bone. The control implants, which were made of commercially pure titanium, had a polished surface ex vivo but are known to acquire a microstructured titania surface in vivo. Ten 1-year-old rats received experimental implant (group A) and 10 had control (group B) implants. Ten 3-month-old rats received normal protein diet and the control implant (group C). Animals were euthanized 8 weeks after implantation, and transverse sections of femur-implant samples were used for histology, micro-computed tomography and immunohistochemical evaluations. In group B, the expression of α2β1 and α5β1 integrins, which are known to mediate osteoblast adhesion, glycosaminoglycans, heparan sulfate and chondroitin sulfate, was less than half of that in group C. Important to this study, the zirconia surface used in group A prevented these deficiencies. Therefore, these results indicate that nanostructured zirconia surface created on clinical implants by ion beam–assisted deposition may prevent impaired osseointegration in elderly patients by promoting quicker maturation of peri-implant woven bone.

Thin films of nanocrystalline ceria deposited onto a silicon substrate have been irradiated with 3 MeV Au+ ions to a total dose of 34 displacements per atom to examine the film/substrate interfacial response upon displacement damage. Under irradiation, a band of contrast is observed to form that grows under further irradiation. Scanning and high-resolution transmission electron microscopy imaging and analysis suggest that this band of contrast is a cerium silicate phase with an approximate Ce:Si:O composition ratio of 1:1:3 in an amorphous nature. The slightly nonstoichiometric composition arises due to the loss of mobile oxygen within the cerium silicate phase under the current irradiation condition. This nonequilibrium phase is formed as a direct result of ion-beam-induced chemical mixing caused by ballistic collisions between the incoming ion and the lattice atoms. This may hold promise in ion beam engineering of cerium silicates for microelectronic applications e.g., the fabrication of blue LEDs.

Thin films of nanocrystalline ceria on a Si substrate have been irradiated with 3 MeV Au+ ions to fluences of up to 1x1016 ions cm-2, at temperatures ranging between 160 to 400 K. During the irradiation, a band of contrast is observed to form at the thin film/substrate interface. Analysis by scanning transmission electron microscopy in conjunction with energy dispersive and electron energy loss spectroscopy techniques revealed that this band of contrast was a cerium silicate amorphous phase, with an approximate Ce:Si:O ratio of 1:1:3.

The rapid development of nanoscience and nanotechnology has raised many fundamental questions that significantly impede progress in these fields. In particular, understanding the physicochemical processes at the interface in aqueous solvents requires the development and application of efficient and accurate methods. In the present work we evaluate the electrostatic contribution to the energy of model protein-ceramic complex formation in an aqueous solvent. We apply a non-local (NL) electrostatic approach that accounts for the effects of the short-range structure of the solvent on the electrostatic interactions of the interfacial systems. In this approach the aqueous solvent is considered as a non-ionic liquid, with the rigid and strongly correlated dipoles of the water molecules. We have found that an ordered interfacial aqueous solvent layer at the protein- and ceramic-solvent interfaces reduces the charging energy of both the ceramic and the protein in the solvent, and significantly increases the electrostatic contribution to their association into a complex. This contribution in the presented NL approach was found to be significantly shifted with respect to the classical model at any dielectric constant value of the ceramics. This implies a significant increase of the adsorption energy in the protein-ceramic complex formation for any ceramic material. We show that for several biocompatible ceramics (for example HfO2, ZrO2, and Ta2O5) the above effect predicts electrostatically induced protein-ceramic complex formation. However, in the framework of the classical continuum electrostatic model (the aqueous solvent as a uniform dielectric medium with a high dielectric constant ∼80) the above ceramics cannot be considered as suitable for electrostatically induced complex formation. Our results also show that the protein-ceramic electrostatic interactions can be strong enough to compensate for the unfavorable desolvation effect in the process of protein-ceramic complex formation.

Zirconium nitride films were deposited on Si substrates by an ion beam assisted deposition (IBAD) approach. The response of nanocrystalline ZrN/Si films upon intense ion irradiations was investigated with the focus on new phase formation. Zirconium silicide (ZrSi) forms at the ZrN/Si interface under intense irradiations of 300 keV Ne + and 1 MeV Kr 2+ in the elastic stopping regime. The strong ballistic effects may cause atom mixing at the ZrN/Si interface, leading to the precipitation of ZrSi. Interface mixing and the formation of ZrSi also occur with swift heavy ion irradiation (1.465 GeV Xe). Thermal spikes in the nano-scale latent tracks and transient high temperature may lead to the atom mixing across the ZrN/Si interface and subsequent ZrSi formation following thermal spikes.

With a wide variety of applications in numerous industries, ranging from biomedical to nuclear, ceramics such as ceria are key engineering materials. It is possible to significantly alter the materials functionality and therefore its applications by reducing the grain size to the nanometer size regime, at which point the unique varieties of grain boundaries and associated interfaces begin to dominate the material properties. Nanocrystalline films of cubic ceria deposited onto Si substrates have been irradiated with 3 MeV Au + ions at temperatures of 300 and 400 K to evaluate their response to irradiation. It was observed that the films remained phase stable. Following a slight stress relief stage at low damage levels, the overall lattice is extremely stable up to high irradiation dose of � 34 displacements per atom. The grains were also observed to undergo a temperature-dependent grain growth process upon ion irradiation. This is attributed to a defect-driven mechanism in which the diffusion of defects from the collision cascade is critical. Formation of dislocations that terminate and stabilize at symmetric grain boundaries may be the limiting factor in the grain growth and overall energy reduction of the system. Utilizing ion modification, possible improvement of the adhesion of thin films and reduction of the probability of detrimental effects of stress-induced problems are discussed.

The response of nanocrystalline, stabilizer-free cubic zirconia thin films on a Si substrate to electron beam irradiation with energies of 4, 110 and 200 keV and fluences up to ∼1.5 × 10 22 e m −2 has been studied to determine the displacement energies. The 110 and 200 keV irradiations were performed in situ using a transmission electron microscope; the 4 keV irradiations were performed ex situ using an electron gun. In all three irradiations, no structural modification of the zirconia was observed, despite the high fluxes and fluences. However the Si substrate on which the zirconia film was deposited was amorphized under the 200 keV electron irradiation. Examination of the electron–solid interactions reveals that the kinetic energy transfer from the 200 keV electrons to the silicon lattice is sufficient to cause atomic displacements, resulting in amorphization. The kinetic energy transfer from the 200 keV electrons to the oxygen sub-lattice of the zirconia may be sufficient to induce defect production, however, no evidence of defect production was observed. The displacement cross-section value of Zr was found to be ∼400 times greater than that of O indicating that the O atoms are effectively screened from the electrons by the Zr atoms, and, therefore, the displacement of O is inefficient.

The influence of high-k dielectric bioceramics with poly(amino acid) multilayer coatings on the adhesion behavior of Escherichia coli (E. coli) was studied by evaluating the density of bacteria coverage on the surfaces of these materials. A biofilm forming K-12 strain (PHL628), a wild-type strain (JM109), and an engineered strain (XL1-Blue) of E. coli were examined for their adherence to zirconium oxide (ZrO(2)) and tantalum oxide (Ta(2)O(5)) surfaces functionalized with single and multiple layers of poly(amino acid) polyelectrolytes made by the layer-by-layer (LBL) deposition. Two poly(amino acids), poly(l-arginine) (PARG) and poly(l-aspartic acid) (PASP), were chosen for the functionalization schemes. All three strains were found to grow and preferentially adhere to bare bioceramic film surfaces over bare glass slides. The bioceramic and glass surfaces functionalized with positively charged poly(amino acid) top layers were observed to enhance the adhesion of these bacteria by up to 4-fold in terms of bacteria surface coverage. Minimal bacteria coverage was detected on surfaces functionalized with negatively charged poly(amino acid) top layers. The effect of different poly(amino acid) coatings to promote or minimize bacterial adhesion was observed to be drastically enhanced with the bioceramic substrates than with glass. Such observed enhancements were postulated to be attributed to the formation of higher density of poly(amino acids) coatings enabled by the high dielectric strength (k) of these bioceramics. The multilayer poly(amino acid) functionalization scheme was successfully applied to utilize this finding for micropatterning E. coli on bioceramic thin films.

Among three TiO2 polymorphs, rutile is thermodynamically unstable as compared with anatase and brookite when the crystal size is ∼10 nm. In this study, nanocrystalline rutile with an average grain size of ∼6 nm was synthesized in a thin film geometry by ion beam-assisted deposition (IBAD) with an amorphous TiO2 interlayer between the rutile film and Si-substrate. Nonstoichiometry produced by high-intensity ion bombardment during deposition may have stabilized the metastable rutile phase on the nanoscale. The phase stability of nanosized rutile was investigated by irradiation using 1 MeV Kr2+ combined with thermal annealing. In situ transmission electron microscopy (TEM) results indicate that partial amorphization occurred in nanocrystalline rutile when irradiated at room temperature, whereas the nanocrystals remained stable upon irradiation at 573 K. Ion beam-induced recrystallization occurred in the amorphous TiO2 at a 573 K, significantly lower than the temperature for thermally induced recrystallizatio...

The oxygen ion conductivity, attributed to an oxygen vacancy mechanism, of yttria-stabilized zirconia membranes used in solid oxide fuel cells is restricted due to trapping limitations. In this work, a high concentration of oxygen vacancies has been deliberately introduced into nanocrystalline stabilizer-free zirconia through ion-irradiation. Oxygen vacancies with different charge states can be produced by varying irradiation temperatures. Due to the reduced trapping sites and high oxygen vacancy concentration, this work suggests that the efficiency of solid oxide fuel cells can be improved.

The phase stability and microstructure evolution of zirconia nanofilms on Si substrates prepared by ion beam assisted deposition (IBAD) upon thermal annealing and intensive radiation have been stud...

Defect- and strain-enhanced cavity formation and Au precipitation at the interfaces of a nano-crystalline ZrO 2 /SiO 2 /Si multilayer structure resulting from 2 MeV Au + irradiation at temperatures of 160 and 400 K have been studied. Under irradiation, loss of oxygen is observed, and the nano-crystalline grains in the ZrO 2 layer increase in size. In addition, small cavities are observed at the ZrO 2 /SiO 2 interface with the morphology of the cavities being dependent on the damage state of the underlying Si lattice. Elongated cavities are formed when crystallinity is still retained in the heavily-damaged Si substrate; however, the morphology of the cavities becomes spherical when the substrate is amorphized. With further irradiation, the cavities appear to become stabilized and begin to act as gettering sites for the Au. As the cavities become fully saturated with Au, the ZrO 2 /SiO 2 interface then acts as a gettering site for the Au. Analysis of the results suggests that oxygen diffusion along the grain boundaries contributes to the growth of cavities and that oxygen within the cavities may affect the gettering of Au. Mechanisms of defect- and strain-enhanced cavity formation and Au precipitation at the interfaces will be discussed with focus on oxygen diffusion and vacancy accumulation, the role of the lattice strain on the morphology of the cavities, and the effect of the binding free energy of the cavities on the Au precipitation.

Patterned micro- and nanostructured surfaces have received increasing attention because of their ability to tune the hydrophobicity and hydrophilicity of their surfaces. However, the mechanical properties of these studied surfaces are not sufficiently robust for load-bearing applications. Here we report transparent nanocrystalline ZrO 2 films possessing combined properties of hardness and complete wetting behavior, which are expected to benefit tribology, wear reduction, and biomedical applications where ultrahydrophilic surfaces are required. This ultrahydrophilic behavior may be explained by the Wenzel model.

The temperature dependence of the optical excitation cross section of Er implanted n-type GaN was studied using photoluminescence excitation spectroscopy. Due to the large 3.4 eV band gap of GaN, it was possible to probe two Er absorption lines using a tunable Ti:sapphire laser in the 770–1010 nm range. Photoluminescence excitation spectra exhibiting several Stark splittings revealed a complex dependence upon temperature. The largest excitation cross section in the third excited state was 1.65×10−20 cm2 at an excitation wavelength of 809.4 nm when measured at 77 K. This value is roughly three times larger than the cross section in the second excited state at 4.8×10−21 cm2 when pumping at 983.0 nm. The Er-related photoluminescence was reduced between 1.5 and 4.8 times when going from 77 K to room temperature, except when pumping around 998 nm. At this excitation wavelength the room temperature photoluminescence was stronger by a factor of 1.26 compared to that at 77 K.

Efficient Er-related photo-, cathodo-, and electroluminescence at 1539 nm was detected from Er and O co-implanted n -type GaN on sapphire substrates. Several combinations of Er and O implants and postimplant annealing conditions were studied. The Er doses were in the range (0.01–5)×10 15 ions/cm 2 and O doses (0.1–1)×10 16 ions/cm 2 . GaN films implanted with 2×10 15 Er 2+ /cm 2 at 350 keV and co-implanted with 10 16 O + /cm 2 at 80 keV yielded the strongest photoluminescence intensity at 1539 nm. The annealing condition yielding the strongest Er-related photoluminescence intensity was a single anneal at 800 °C (45 min) or at 900 °C (30 min) in flowing NH 3 . The optimum O:Er ratio was found to be between 5:1 and 10:1. Co-implanting the GaN:Er films with F was also found to optically activate the Er, with slightly (20%) less photoluminescence intensity at 1539 nm compared to equivalent GaN:Er,O films. The Er-related luminescence lifetime at 1539 nm was found to depend on the excitation mechanism. Luminescence lifetimes as long as 2.95±0.15 ms were measured at 77 K under direct excitation with an InGaAs laser diode at 983 nm. At room temperature the luminescence lifetimes were 2.35±0.12, 2.15±0.11, and 1.74±0.08 ms using below-band-gap excitation, above-band-gap excitation, and impact excitation (reverse biased light emitting diode), respectively. The cross sections for Er in GaN were estimated to be 4.8×10 −21 cm 2 for direct optical excitation at 983 nm and 4.8×10 −16 cm 2 for impact excitation. The cross-section values are believed to be within a factor of 2–4.

We have investigated the time evolution of the 1.54 μm Er3+ photoluminescence (PL) intensity of Er-implanted porous silicon in the temperature range from 15 to 375 K. Er was implanted into porous silicon with a dose of 1 × 1015 Er/cm2 at 380 keV and annealed at 605 °C for 30 min. Upon optical excitation at 488 nm, erbium ions are excited by photo-generated carriers and an intense 1.54 μm PL is observed at room temperature. We have compared the time evolution of the 4 I 13 2 → 4 I 15 2 transition of Er3+ to a double-exponential decay. The analysis suggests the existence of two classes of Er sites in porous silicon. This is supported by a study of the Er3+ PL decay time as a function of excitation pulse width. The characteristic Er3+ lifetimes in the two sites are 145 μs and 1.37 ms, respectively. In the temperature range from 15 to 150 K, the back transfer of energy from the excited erbium level 4 I 13 2 to the host plays the dominant role in the thermal quenching of the Er3+ luminescence. At temperatures above 150 K, the reduction in Er3+ PL can mainly be ascribed to thermalization of bound electrons to the conduction band. We have compared the observed Er3+ PL intensity with the result from a theoretical model and a good agreement is obtained.

Electrical impedance of aging porous silicon layers (PS) was studied applying the regime of temperature cycling (from -50 to +150°C) in a range of alternating current (a.c.) frequencies 0.2 to 10 5 Hz (amplitude 1 V). Freshly obtained PS exhibits changes of electrical properties at temperatures above 50°C, presumably associated with the escape of electrolyte from the pores. A.C. electrical conductivity of PS is very sensitive to its postanodizing treatments (heat-treatment, pore filling by inert electrolyte, evacuation at increased temperatures, annealing in nitrogen). Activation energy for the electrical conduction ranges from 0.1 to 0.23 eV depending on a.c. frequency and postanodizing treatments. An electric equivalent circuit was designed to fit the experimental data acquired at differently treated PS samples. The components of the equivalent circuit were assigned to physical elements of PS (a surface phase on top of PS and a layer of underlying bulk material). Based on the measurements of the electrical impedance and chemical composition of PS films the mechanism of electrical conduction is assumed to be a charge carrier migration through the localized states associated with the surface impurities (hydrides and/or oxides of silicon). The obtained impedance data show the strong influence of residuals of the electrolyte inside the pores of freshly prepared PS on its aging stability.

This paper explores the challenges faced in developing efficient room temperature porous Si-based light emitting diodes. We experimentally demonstrate that porous Si is an excellent host material for erbium ions to emit strong, room temperature, sharp-line luminescence at 1.54 μm. A comparison of photoluminescence data for erbium implanted samples of bulk Si, porous Si, and quartz indicate that quantum confinement likely enhances the erbium IR luminescence efficiency. Due to the 650 to 850°C annealing, it is unlikely that the environment of erbium in our samples is amorphous Si.

This paper addresses the application of engineered nanocrystalline ultrahydrophilic titanium oxide films to artificial orthopaedic implants. Titanium (Ti) is the material of choice for orthopaedic applications and has been used for over fifty years because of its known bio-compatibility. Recently it was shown that biocompatibility of Ti metal is due to the presence of a thin native sub-stoichiometric titanium oxide layer [1] which enhances the adsorption of mediating proteins on the surface thus enhancing cell adhesion and growth [2,3,4]. Improving the quality of surface oxide, i.e. fabricating stoichiometric oxides as well as nanoengineering the surface topology that matches the dimensions of adhesive proteins, is crucial for the increase of protein adsorption [2] and, as a result, the biocompatibility of Ti implant materials. We have fabricated ultrahydrophilic nano-crystalline transparent films of anatase phase of titania (TiO2) by ion beam assisted deposition (IBAD) processes in an ultrahigh vacuum system. Source material was 99.9% pure rutile TiO2. Various ion beam conditions were used to produce these coatings with different grain sizes (4 to 70 nm) that affect the wettability, roughness, and the mechanical and optical properties of the coating [5]. Our biological experiments have shown that biocompatibility of these ultrahydrophilic nanoengineered TiO2 coatings are superior to commonly used orthopaedic titanium and even hydroxyapatite.

Bulk ZrO(2) polymorphs generally have an extremely high amorphization tolerance upon low energy ion and swift heavy ion irradiation in which ballistic interaction and ionization radiation dominate the ion-solid interaction, respectively. However, under very high-energy irradiation by 1.33 GeV U-238, nanocrystalline (40-50 nm) monoclinic ZrO(2) can be amorphized. A computational simulation based on a thermal spike model reveals that the strong ionizing radiation from swift heavy ions with a very high electronic energy loss of 52.2 keV nm(-1) can induce transient zones with temperatures well above the ZrO(2) melting point. The extreme electronic energy loss, coupled with the high energy state of the nanostructured materials and a high thermal confinement due to the less effective heat transport within the transient hot zone, may eventually be responsible for the ionizing radiation-induced amorphization without transforming to the tetragonal polymorph. The amorphization of nanocrystalline zirconia was also confirmed by 1.69 GeV Au ion irradiation with the electronic energy loss of 40 keV nm(-1). These results suggest that highly radiation tolerant materials in bulk forms, such as ZrO(2), may be radiation sensitive with the reduced length scale down to the nano-metered regime upon irradiation above a threshold value of electronic energy loss.

Grain growth and phase stability of nanocrystalline ceria are investigated under ion irradiation at different temperatures. Irradiations at temperatures of 300 and 400 K result in uniform grain growth throughout the film. Anomalous grain growth is observed in thin films of nanocrystalline ceria under 3-MeV Au${}^{+}$ irradiation at 160 K. At this low temperature, significant grain growth is observed within 100 nm from the surface, and no obvious growth is detected in the rest of the films. While the grain growth is attributed to a defect-stimulated mechanism at room temperature and above, a defect diffusion-limited mechanism is significant at low temperatures with the primary defect responsible being the oxygen vacancy. The nanocrystalline grains remain in the cubic phase regardless of defect kinetics.

We designed and produced pure cubic zirconia (ZrO2) ceramic1 coatings by an ion beam assisted deposition (IBAD) with nanostructures comparable to the size of proteins. Our ceramic coatings exhibit high hardness and a zero contact angle with serum. In contrast to hydroxyapatite (HA), nano-engineered zirconia films possess excellent adhesion to all orthopaedic materials. Cell adhesion and proliferation experiments were performed with a bona fide mesenchymal stromal cell line (OMA-AD). Our experimental results indicate that the nano-engineered cubic zirconia is superior in supporting growth, adhesion, and proliferation. Since cell attachment is mediated by adhesive proteins such as fibronectin (FN), to elucidate why cells attach more effectively to our nanostructures, we performed a comparative analysis of adsorption energies of FN fragment using quantum mechanical calculations and Monte Carlo (MC) simulation both on smooth and nanostructured surfaces. We have found that a FN fragment adsorbs significantly stronger on the nanostructured surface than on the smooth surface2.

Thin films nano-crystalline zirconia of ~ 300 nm thick were deposited on Si substrate, and the samples were irradiated with 2 MeV Au+ ions at temperatures of 160 and 400 K, up to fluences of 35 displacements per atom. The films were then studied using glancing incidence x-ray diffraction, Rutherford backscattering, secondary ion mass spectroscopy and transmission electron microscopy. During the irradiation, cavities were observed to form at the zirconia/silicon interface. The morphology of the cavities was found to be related to the damage state of the underlying Si substrate. Elongated cavities were observed when the substrate is heavily damaged but not amorphized; however, when the substrate is rendered amorphous, the cavities become spherical. As the ion dose increases, the cavities then act as efficient gettering sites for the Au. The concentration of oxygen within the cavities determines the order in which the cavities getter. Following complete filling of the cavities, the interface acts as the secondary gettering site for the Au. The Au precipitates are determined to be elemental in nature due to the high binding free energy for the formation of Au-silicides.

Room temperature Raman spectra are reported of Si 1-x Ge x epitaxial layers on Si substrates (for 0.08≤x≤0.2). The samples were grown using atmospheric pressure chemical vapor deposition techniques. Layer thicknesses varied from 0.03–10 μm. The relative frequency shift of the Si-Si phonon mode for the SiGe strained epilayers from an incommensurate pseudo-alloy of the same composition is used as a quantitative measure of the lattice relaxation factor. For thicknesses below a critical value the Raman data indicate that the films are highly strained and the growth is commensurate with the substrate whereas thicker films are partially or fully relaxed.

Grain growth, oxygen stoichiometry, and phase stability of nanostructurally stabilized cubic zirconia (NSZ) are investigated under 2 MeV Au-ion bombardment at 160 and 400 K to doses up to 35 displacements per atom (dpa). The NSZ films are produced by ion-beam-assisted deposition technique at room temperature with an average grain size of 7.7 nm. The grain size increases with irradiation dose to $\ensuremath{\sim}30\text{ }\text{nm}$ at $\ensuremath{\sim}35\text{ }\text{dpa}$. Slower grain growth is observed under 400 K irradiations, as compared to 160 K irradiations, indicating that the grain growth is not thermally activated and irradiation-induced grain growth is the dominating mechanism. While the cubic structure is retained and no new phases are identified after the high-dose irradiations, oxygen reduction in the irradiated NSZ films is detected. The ratio of O to Zr decreases from $\ensuremath{\sim}2.0$ for the as-deposited films to $\ensuremath{\sim}1.65$ after irradiation to $\ensuremath{\sim}35\text{ }\text{dpa}$. The loss of oxygen suggests a significant increase in oxygen vacancies in nanocrystalline zirconia under ion irradiation. The oxygen deficiency may be essential in stabilizing the cubic phase to larger grain sizes.

Motivated by experimentally observed biocompatibility enhancement of nanoengineered cubic zirconia ZrO2 coatings to mesenchymal stromal cells, we have carried out computational analysis of the initial immobilization of one of known structural fragment of the adhesive protein (fibronectin) on the corresponding surface. We constructed an atomistic model of the zirconia nano-hillock of 3-fold symmetry based on AFM and TEM images. First-principle quantum-mechanical calculations show a substantial variation of electrostatic potential at the hillock due to the presence of surface features such as edges and vertexes. Using an implemented Monte Carlo simulated annealing method we found the orientation of the immobilized protein on the zirconia surface (both flat and nanostructured) and contribution of the each amino acid residue from the protein sequence to the adsorption energy. Accounting for the variation of the dielectric permittivity at the protein-implant interface we use a model distance-dependent dielectric function to describe the inter-atom electrostatic (Coulomb) interactions in the adsorption potential. We find that the initial immobilization of the rigid protein fragment on the nanostructured pyramidal ZrO2 surface is achieved with magnitude of adsorption energy larger than the one for the protein on the smooth (flat) surface. The strong attractive electrostatic interactions are a major factor in the enhanced adsorption at nanostructured surface that is absent in the case of adsorption on the flat uncharged surface. We show that the best electrostatic and steric fit of the protein to the inorganic surface corresponds to a minimum of the adsorption energy determined by the non-covalent interactions., 13 pages, 10 figures

Electrical impedance of aging porous silicon layers (PS) was studied applying the regime of temperature cycling (from -50 to +150°C) in a range of alternating current (a.c.) frequencies 0.2 to 10 5 Hz (amplitude 1 V). Freshly obtained PS exhibits changes of electrical properties at temperatures above 50°C, presumably associated with the escape of electrolyte from the pores. A.C. electrical conductivity of PS is very sensitive to its postanodizing treatments (heat-treatment, pore filling by inert electrolyte, evacuation at increased temperatures, annealing in nitrogen). Activation energy for the electrical conduction ranges from 0.1 to 0.23 eV depending on a.c. frequency and postanodizing treatments. An electric equivalent circuit was designed to fit the experimental data acquired at differently treated PS samples. The components of the equivalent circuit were assigned to physical elements of PS (a surface phase on top of PS and a layer of underlying bulk material). Based on the measurements of the electrical impedance and chemical composition of PS films the mechanism of electrical conduction is assumed to be a charge carrier migration through the localized states associated with the surface impurities (hydrides and/or oxides of silicon). The obtained impedance data show the strong influence of residuals of the electrolyte inside the pores of freshly prepared PS on its aging stability.

Using a nonlocal electrostatic approach that incorporates the short-range structure of the contacting media, we evaluated the electrostatic contribution to the energy of the complex formation of two model proteins. In this study, we have demonstrated that the existence of an ordered interfacial water layer at the protein-solvent interface reduces the charging energy of the proteins in the aqueous solvent, and consequently increases the electrostatic contribution to the protein binding (change in free energy upon the complex formation of two proteins). This is in contrast with the finding of the continuum electrostatic model, which suggests that electrostatic interactions are not strong enough to compensate for the unfavorable desolvation effects.

Si1−xGex layers grown using atmospheric pressure chemical vapor deposition have been characterized using both room temperature spectroscopic ellipsometry (SE) and low-temperature photoluminescence (PL). Single layers of Si0.9Ge0.1, 30, 100, 1000, and 2000 nm thick on p+ Si(100) wafers were investigated to determine the effect of strain on the indirect and direct optical transitions. The thinner two layers were pseudomorphic and the thicker ones relaxed. The samples were examined by spectroscopic ellipsometry, which allowed the optical constants to be determined from the ultraviolet to near infrared (3.5–1.8 eV). Using optical constants available from the literature for cubic Si1−xGex, the thicknesses of the alloy layers were verified. From our optical constants and the published calibration curves for normal incidence reflectivity at 633 nm and for the energy of the E1 transition (both a function of x), we found that the average germanium concentration appeared to be significantly below the nominal 10% for these samples. Phonon-resolved PL spectra were observed at 2 K for the thicker three samples with the transition from strained to unstrained layers clearly visible in the shift of the Si1−xGex band gap as seen from the energy of the no-phonon line. Dislocation lines appeared only for the relaxed material and the no-phonon line widths were ~4 times smaller for the strained Si1−xGex material., 6th Canadian Semiconductor Technology Conference, 11-13 August 1992, Ottawa, Canada

Nanocrystalline zirconia has recently attracted extensive research interest due to its unique mechanical, thermal and electrical properties as compared with bulk zirconia counterparts, and it is of particular importance for controlling the phase stability of different polymorphs (amorphous, cubic, tetragonal and monoclinic phases) in different size regimes. In this work, we performed ion beam bombardments on bilayers (amorphous and cubic) of nano-zirconia using 1 MeV Kr2+ irradiation. Transmission electron microscopy (TEM) analysis reveals that amorphous zirconia transforms to a tetragonal structure under irradiation at room temperature, suggesting that the tetragonal phase is more energetically favorable under these conditions. The final grain size of the tetragonal zirconia can be controlled by irradiation conditions. A slower kinetics in the grain growth from cubic nanocrystalline zirconia was found as compared with that for the tetragonal grains recrystallized from the amorphous layer. The radiation-induced nanograins of tetragonal ZrO2 are stable at ambient conditions and maintain their physical integrity over a long period of time after irradiation. These results demonstrated that ion beam methods provide the means to control the phase stability and structure of zirconia polymorphs.

Nano-crystalline films of pure cubic ZrO2 have been produced by ion beam assisted deposition (IBAD) processes which combine physical vapor deposition with the concurrent ion beam bombardment in a high vacuum environment and exhibit superior properties and strong adhesion to the substrate. Oxygen and argon gases are used as source materials to generate energetic ions to produce these coatings with differential nanoscale (7 to 70 nm grain size) characteristics that affect the wettability, roughness, mechanical and optical properties of the coating. The nanostructurally stabilized chemically pure cubic phase has been shown to possess hardness as high as 16 GPa and a bulk modulus of 235 GPa. We examine the mechanical properties and the phase stability in zirconia nanoparticles using first principle electronic structure method. The elastic constants of the bulk systems were calculated for monoclinic, tetragonal and cubic phases. We find that calculated bulk modulus of cubic phase (237GPa) agrees well with the measured values, while that of monoclinic (189GPa) or tetragonal (155GPa) are considerably lower. We observe considerable relaxation of lattice in the monoclinic phase near the surface. This effect combined with surface tension and possibly vacancies in nanostructures are sources of stability of cubic zirconia at nanoscale.

We have studied two temperature-related effects in the fabrication of high quality SIMOX materials: 1) the large ion beam induced rise in sample temperature during oxygen implantation, and 2) the time dependence of the high temperature annealing required after implantation. Oxygen ions were implanted at 160 keV into (100) Si wafers to a total dose of 4 × 10 17 O + cm 2 with current densities from 10 to 60 μA/cm2. The samples were annealed at 1300°C for 0 to 6 h. The microstructures were examined using cross-sectional transmission electron microscopy. With a current density of 60 μA/cm2, permanent damage occurred in the top Si layer. No effects were observed after post-implantation annealing for samples implanted with 10–50 μA/cm2 current densities. Oxygen precipitates were found to grow and coarsen with increasing anneal time, finally becoming a non-uniform buried oxide layer. Oxide layer formation is an oxygen diffusion controlled process.

Ion channeling has been used in a detailed study of 3C–SiC films grown by chemical vapor deposition on a Si/SiO2/Si substrate. For a 160-nm-thick 〈100〉-oriented SiC film, the results show a minimum yield (χmin) of ∼28% at the SiC–Si interface, while a SiC film with a thickness of ∼2.4 μm, grown under identical conditions, was almost defect free (χmin=5.3%) in the surface region. Angular scans around the 〈110〉 axis revealed the existence of a superlattice structure at the SiC–Si interface. The strain-induced angular shift was determined to be 0.16°±0.05°, indicating a kink between the SiC and Si layers along the inclined 〈110〉 axis. A modified model is suggested to interpret the experimental observations.

The application of titanium dioxide (TiO(2)) films as surgical implant coatings for antibiotic attachment depends crucially on their available surface area and thus their surface morphology and crystallinity. Here, we report our fabrication of high Wenzel ratio TiO(2) films targeted to increase the film surface area using the ion beam-assisted deposition (IBAD) technique at high-deposition temperatures (approximately 610 degrees C). The modulation of the films' surface morphology was accomplished by varying the chemical identity of the concurrent ion beams bombarded on the films during the e-beam evaporation process. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were employed to investigate the surface morphology of the as-deposited films. X-ray diffractometry (XRD) revealed that these nanocrystalline films primarily consist of anatase phase TiO(2). Wenzel ratio, the ratio of the actual surface area to the projected area, of IBAD films prepared with argon, oxygen, and nitrogen ion beams was measured to be 1.52, 1.31 and 1.49, respectively. The effect of the differences in chemical reactivity and ion size of these three type ion beams are discussed to explain the present results.

There is a great need to develop methods to regulate cellular growth in order to enhance or prevent cell proliferation as needed, to either improve health or prevent disease. In this work we evaluated the adhesion, survival and growth of bone marrow stromal cells on the surface of several new ion beam engineered nano-crystals of ceramic hard coatings such as zirconium, titanium, tantalum and cerium oxides. Cell adhesion and growth on the ceramic coatings were compared to adhesion and growth on a nano-crystalline silver coating which is known to possess antibacterial properties. The initial results of a study to determine the effect of nanocrystalline titanium and silver coating onstaphylococcus aureusbiofilm growth is also discussed.

Room temperature operation of erbium and oxygen coimplanted GaN m‐i‐n (metal–insulator–n‐type) diodes is demonstrated. Erbium related electroluminescence at λ=1.54 μm was detected under reverse bias after a postimplant anneal at 800°C for 45 min in flowing NH3. The integrated light emission intensity showed a linear dependence on applied reverse drive current.

A photoluminescence excitation (PLE) study was performed of Er‐implanted porous Si with two different porosities. Erbium was implanted at a dose of 1×1015 cm−2 at 380 keV and the samples were annealed for 30 min at temperatures from 650 to 850 °C. We observed that PLE spectra from Er3+ at 1.54 μm are nearly identical to those from the visible‐emitting porous Si layers. Our results provide the first direct experimental evidence that infrared photoluminescence at 1.54 μm arises from Er3+ ions in porous Si and that ions are excited through the recombination of excess carriers spatially confined in Si nanograms.

We report a spectroscopic study on the photoluminescence (PL) of erbium implanted into porous silicon (Er:PSi). Two different porous Si samples were implanted with a dose of 1015 Er/cm2 at 380 keV and annealed at 650 °C for 30 min under identical conditions. Both samples exhibited Er3+ luminescence at 1.54 μm, which was quenched by less than a factor of two between 15 K and room temperature. Visible PL studies of Er implanted and annealed porous Si samples showed broad spectra which peaked at ∼700 nm for sample A and peaked at ∼660 nm for sample B. Sample A showed a four times stronger Er3+ luminescence than that observed from sample B. In contrast, temperature quenching of the Er3+ luminescence was found to be similar or slightly weaker from sample B than from sample A. The spectroscopic data will be discussed in terms of the excitation mechanisms of Er3+ in porous Si nanostructures.

This communication demonstrates a strong, room‐temperature (RT), infrared (IR) (1.54 μm) emission from Er‐implanted red‐emitting (peaked at 1.9 eV) porous silicon (Er:PSi). Erbium was implanted into porous Si, bulk Si, and quartz with a dose of 1015/cm2 at 190 keV and annealed for 30 minutes in N2 at temperatures ranging from 500 °C to 900 °C under identical conditions. No RT IR emission was observed from Er implanted quartz and silicon after annealing at 650 °C (although after annealing at 900 °C very weak emission was observed from quartz at 9 K). The highest RT emission intensity at 1.54 μm was from Er:PSi with a peak concentration of 1.5×1020/cm3 and annealed at 650 °C. Even the luminescence intensity from Er:PSi annealed at 500 °C was 26 times higher than that observed from Er‐implanted quartz at 400 keV and annealed at 900 °C. A reduction in photoluminescence (PL) intensity of about a factor of two from Er:PSi over the 9 to 300 K temperature range was observed which is consistent with Er in wide ban...

The cathodoluminescence(CL) of erbium and oxygen coimplanted GaN(GaN:Er:O) and sapphire (sapphire:Er:O) was studied as a function of temperature. Following annealing, the 1.54 μm intra‐4f‐shell emission line was observed in the temperature range of 6–380 K. As the temperature increased from 6 K to room temperature, the integrated intensity of the infrared peak decreased by less than 5% for GaN:Er:O, while it decreased by 18% for sapphire:Er:O. The observation of minimal thermal quenching by CL suggests that Er and O dopedGaN is a promising material for electrically pumped room‐temperature optical devices emitting at 1.54 μm.

We have created thin buried films of low resistivity CoSi2 in silicon by ion implantation, and used them to provide intercell ohmic contacts for monolithically stacked multijunction photovoltaic energy converters. We have grown epitaxial silicon pn junction diodes by chemical vapor deposition onto the thin film of crystalline silicon formed over the CoSi2 layer after post‐implantation annealing. A single junction photovoltaic device with two CoSi2 contacts displayed an open circuit voltage of 0.60 V and a fill factor of 0.80, while a double junction tandem cell with three CoSi2 interconnects generated 1.2 V, under identical conditions of illumination with a Nd:YAG laser. These results indicate very low defect levels in the deposited silicon epitaxial layers, and excellent functioning of the CoSi2 interconnects.

A systematic study to determine the effect of dose and dose rate on implanting oxygen at 80 and 160 keV is reported. Samples were produced by implanting oxygen into p-type Si

Improvement of the crystalline quality of epitaxial silicon grown on separation by implantation of oxygen (SIMOX) material was investigated by confining the threading dislocations in the silicon top layer with a GeSi strained layer. The standard SIMOX used was produced by implantation of 1.6*10/sup 18/ O+/cm/sup 2/ at 160 keV, followed by annealing for 6 h at 1300 degrees C in N/sub 2/. Thin Si/GeSi/Si epitaxial structures were grown on the SIMOX and on Si substrates by chemical vapor deposition (CVD). The material was evaluated using a variety of methods, including cross-sectional transmission electron microscopy (XTEM), plane view TEM, and Rutherford backscattering spectroscopy (RBS)/channeling. The GeSi strained layer grown by CVD appears to be high quality, and no misfit dislocations were observed for Si/GeSi/Si structures grown at the same time on bulk silicon. CVD may also be a simple and economical method for growing Si/GeSi/Si structures for device applications such as heterojunction bipolar transistors. >

Formation of ultra-thin SOI material using the SIMOX process is addressed. Research has been carried out to determine the effect of total dose, dose step, dose rate, implantation temperature, and energy on the formation of ultra-thin SIMOX material. Attempts were made to determine the lowest energy possible for the implantation of oxygen which results in the formation of high quality, thin SIMOX material. All samples were annealed at 1300 degrees C for 6 h in N/sub 2/ and analyzed using a variety of techniques, including TEM. The electrical properties of the LES samples were characterized and compared with those of standard SIMOX samples. An empirical curve of voltage breakdown versus oxide thickness for both LES and standard SIMOX samples was developed. The results show the formation of high quality SOI structures by oxygen implantation at 20-80 keV. >