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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.
Titanium (Ti) is the material of choice for orthopaedic applications because it is biocompatible and encourages osteoblast ingrowth. It was shown that the biocompatibility of Ti metal is due to the presence of a thin native sub-stoichiometric titanium oxide layer which enhances the adsorption of mediating proteins on the surface . The present studies were devised to evaluate the adhesion, survival, and growth of cells on the surface of new engineered nano-crystal films of titanium and titanium oxides and compare them with orthopaedic-grade titanium with microcrystals. The engineered nano-crystal films with hydrophilic properties are produced by employing an ion beam assisted deposition (IBAD) technique. IBAD combines physical vapor deposition with concurrent ion beam bombardment in a high vacuum environment to produce films (with 3 to 70 nm grain size) with superior properties. These films are “stitched” to the artificial orthopaedic implant materials with characteristics that affect the wettability and mechanical properties of the coatings.
To characterize the biocompatibility of these nano-engineered surfaces, we have studied osteoblast function including cell adhesion, growth, and differentiation on different nanostructured samples. Cell responses to surfaces were examined using SAOS-2 osteoblast-like cells. We also studied a correlation between the surface nanostructures and the cell growth by characterizing the SAOS-2 cells with immunofluorescence and measuring the amount alizarin red concentration produced after 7 and 14 days. The number of adherent cells was determined by means of nuclei quantification on the nanocrystalline Ti, TiO2, and microcrystalline Ti and analysis was performed with Image J. Our experimental results indicated that nanocrystalline TiO2 is superior to both nano and microcrystalline Ti in supporting growth, adhesion, and proliferation. Improving the quality of surface oxide, i.e. fabricating stoichiometric oxides as well as nanoengineering the surface topology, is crucial for increasing the biocompatibility of Ti implant materials.
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  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  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 . Our biological experiments have shown that biocompatibility of these ultrahydrophilic nanoengineered TiO2 coatings are superior to commonly used orthopaedic titanium and even hydroxyapatite.
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
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.
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.
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 on staphylococcus aureus biofilm growth is also discussed.
A systematic study of photoluminescence (PL) of Er and O ion implanted and annealed n-type GaN grown on R-plane sapphire (A12O3) was performed. The Er implants ranged from 2 × 1013 to 1 × 1015 Er++/cm2, and the O co-implants ranged from 1014 to 1016 O+/cm2. The resulting nine different combinations of GaN:Er,O were annealed at 600 °C (4 hrs. in N2), 700 °C (1.5 hrs. in N2), 800 °C (0.75 hr. in NH3), and 900 °C (0.5 hr. in NH3) Following each annealing step, the Er3 -related PL at 1.54 μm was measured from each sample at 77K, when pumped directly with 135 mW of power at 980 nm. The three samples with the highest dose of Er (1 × 1015 Er++/ cm 2), regardless of O co-dopant dose, yielded the strongest PL peak intensity at 1.54 μm after all the anneals. The integrated PL from 1.52 to 1.58 μm was reduced by 62 % when going from 77 K to room temperature (RT).
We have demonstrated a strong, room-temperature, 1.54 μm emission from erbium-implanted at 190 keV into red-emitting porous silicon. Luminescence data showed that the intensity of infrared (IR) emission from Er implanted porous Si annealed at ≤ 650°C, was a few orders of magnitude stronger than Er implanted quartz produced under identical conditions, and was almost comparable to IR emission from In0.53Ga0.47As material which is used for commercial IR light-emitting diodes (LEDs).
The strong IR emission (much higher than Er in quartz) and the weak temperature dependency of Er in porous Si, which is similar to Er3+ in wide-bandgap semiconductors, suggests that Er is not in SiO2 or Si with bulk properties but, may be confined in Si light-emitting nanostructures. Porous Si is a good substrate for rare earth elements because: 1) a high concentration of optically active Er3+ can be obtained by implanting at about 200 keV, 2) porous Si and bulk Si are transparent to 1.54 μm emission therefore, device fabrication is simplified, and 3) although the external quantum efficiency of visible light from porous Si is compromised because of self-absorption, it can be used to pump Er3+.
Arsenic precipitates can be formed in GaAs using arsenic implantation and annealing, thereby producing very high resistivity (surface or buried) GaAs layers. Arsenic-implanted materials are similar to low-temperature (LT) GaAs:As buffer layers grown by molecular beam epitaxy (MBE) which are used for eliminating side- and backgating problems in GaAs circuits. Arsenic implantation is not only a simple and economical technique for device isolation but also can improve the quality of individual devices. Through surface passivation, arsenic implantation can reduce gate-to-drain leakage in and enhance the breakdown voltage of GaAs-based metal semiconductor field-effect transistors (MESFETs) and high electron mobility transistors (HEMTs). High resistivity thin surface layers may be used as gate insulators for GaAs-based metal insulator semiconductor (MIS) FETs, leading to the development of a novel GaAs-based complementary metal insulator semiconductor (CMIS) technology like advanced Si-based complementary metal oxide semiconductor (CMOS) technology but with higher radiation hardness and operational speed.
We have investigated the application of ion implantation technique for introducing activator and co-activator ions into host materials such as ZnS and Zn2SiO4, and have produced phosphors with differing emission peaks throughout the visible range. A number of different ions including, Mn+, Al+ and rare-earth metals have been implanted. Zn2SiO4:Mn showed bright yellow cathodoluminescence. We have demonstrated that by varying the parameters for ion implantation and annealing, a single ZnS sample with emission peaks ranging from violet to yellow can be produced; i.e, chromaticity engineering. In one case, our results indicated that photoluminescence (PL) spectrum of ZnS phosphors shifts from blue to green by increasing the dose of implanted A+ ions. The Al+-implanted ZnS samples showed emission peaks shifting from 440 to 510 nm when the aluminum dose was raised from 1 × 1015 to 1 × 1017 A1+/cm2. Therefore, by activating color centers in thin film phosphors using ion implantation, efficient and low-cost full-color field emission displays can be fabricated on a single layer of host material.
High resolution cross-sectional electron microscopy and electron diffraction of an np heterojunction porous Si device, capable of emitting light at visible wavelengths, clearly indicates the presence of Si nanostructures within the quantum size regime. These results indicate that the quantum confinement effect is at least partially responsible for photoluminescence at visible wavelengths.
The objective of this research was to demonstrate heteroepitaxial growth of yttria stabilized cubic zirconia on single crystal silicon substrates by chemical vapor deposition (CVD) using metalorganic source materials. We succeeded in depositing extremely smooth, well aligned films of zirconia on silicon substrates, both the <100> and <111> orientations, without an oxide interfacial layer. Experimental variables investigated included varying zirconia source materials, substrate temperatures, oxygen concentration, gas flow rates, yttria doping, substrate orientation, and cobalt-silicide as an oxygen diffusion barrier. ZrO2 films were predominantly tetragonal when deposited in the absence of oxygen while cubic phase material could be put down at 750°C with oxygen background. Films deposited from TMHD zirconium contained no measurable carbon contamination. Deposits from trifluoro-acetylacetonate Zr contained small amounts of fluorine, even in the presence of water vapor, and some carbon when hydrogen was used as a diluent gas.
Silicon-on-insulator (SOI) materials made by standard energy (150 to 200 keV) separation by implantation of oxygen (SIMOX) processes have shown great promise for meeting the needs of radiation-hard microelectronics. Since much smaller doses are required, low energy SIMOX (LES) reduces cost, improves radiation hardness, and increases the throughput of any ion implanter. The process can also produce high quality thin SIMOX structures that are of particular interest for fully depleted and submicron device structures. In this paper, we address the formation as well as the material and electrical characterization of LES wafers and compare them with standard SIMOX wafers.
We have investigated the dependence of electrical and material properties of buried CoSi2 layers on Co+ implantation and annealing conditions. The results indicated that the electrical resistivity and crystalline quality of the implanted buried CoSi2 layers depend strongly on the implantation temperature. CoSi2 layers with the lowest resistivity and best crystalline quality (Xmin as low as 3.6%) were obtained from samples implanted at 300°C-400°C. Implantation at higher temperatures (e.g., 580°C) produced cobalt disilicide layers with significantly higher electrical resistivity and a Xmin of about 10.7%.
Although silicon-on-insulator (SOI) materials made by standard energy (150–200 keV) SIMOX processes have shown great promise for meeting the needs of radiation hard microelectronics, there are still problems relating to the radiation hardness and economic viability of standard SIMOX. A low energy SIMOX (LES) process reduces cost and improves radiation hardness and increased throughput of any implanter because much smaller doses are required. In addition, the process is uniquely able to produce high quality thin SIMOX structures that are of particular interest for fully depleted device structures. In this paper, we address the formation of high quality ultrathin SIMOX structures by low energy implantation.
The creation of SIMOX material by multiple step substoichiometry oxygen ion implantation of silicon wafers followed by high temperature annealing has already been demonstrated by different groups [1-4] This paper reports on the formation of SIMOX wafers at temperatures well below the critical temperature (500-550°C) specified for oxygen implantation of the SIMOX process. A multiple step procedure has been devised, each step consisting of oxygen ion implantation at doses of 2.5 and 3 x 1017 O+/cm2 followed by solid phase epitaxy at a temperature of 950°C for two hours. Non-destructive optical analysis and XTEM investigation of the wafers indicates the formation of a continuous buried oxide with good quality single crystal silicon on the surface after accumulated dose of 1.1x1018 O+/cm2 following high temperature annealing at 1300°C for six hours.
The processing of SIMOX material at a lower temperature will enable the utilization of a wide variety of ion implanters, will simplify the design of the end station of the new generation high current ion implanters, and will have an impact on the availability and economics of SIMOX wafers.
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