Blood triggered corrosion of magnesium alloys

Intravascular stents manufactured out of bioabsorbable magnesium (Mg) or Mg-alloys are considered as auspicious candidates for the next stent generation. However, before clinical application numerous physical and biological tests, especially to predict the clinically highly important degradation kinetics in vivo, have to be performed. In a Chandler-Loop model, the initial degradation of eight different magnesium alloys during 6 h in contact with human whole blood was investigated. The magnesium release varied between 0.91 ± 0.33 mg/cm² (MgAl9Zn1) and 2.57 ± 0.38 mg/cm² (MgZn1). No correlation could be found with Mg release data obtained after immersion in simulated body fluid (SBF). This pilot study showed that Mg corrosion is highly influenced by the biological test environment (SBF or blood, etc.) and that a modified Chandler-Loop model with human whole blood may be superior to predict corrosion of Mg alloys under clinical conditions than the SBF models presently used.     

Evaluation of thin film passivation using inorganic Mg-Zn-F heterointerface for polymer light emitting diode

In this study, we manufactured Mg-Zn-F targets using magnesium fluoride (MgF₂) and zinc (Zn). The passivation films were deposited on a poly-ethylenenaphthalate (PEN) substrate using a radio-frequency magnetron sputter. The thickness of the manufactured passivation film was 120 nm. Among the three targets tested, the 4:6 weight target of MgF₂ to Zn resulted in films with the highest Zn content that would increase the packing density of the thin film. The water vapor transmission rate of a 120 nm Mg-Zn-F film prepared from this target and inserted between two 40 nm MgF₂ interlayers on PEN was 2.9 × 10^− 2 g/(m² day) at a relative humidity of 90% and a temperature 38 °C. Its optical transmittance was approximately 80%.     

Void formation in silica glass induced by thermal oxidation after Zn ion implantation

Thermal annealing effects on Zn⁺ ion-implanted silica glass (a-SiO₂) have been studied in order to control void formation. Void formation in a-SiO₂ with Zn⁺ ion implantation and subsequent oxidation has been observed using transmission electron microscopy (TEM). Zn⁺ ions of 60 keV were implanted into a-SiO₂ to a fluence of 1.0 × 10¹⁷ ions/cm². After the implantation, thermal annealing at 600 or 700 °C for 1 h in oxygen gas was conducted. In as-implanted state, metal Zn nanoparticles (NPs) of 10-15 nm in diameter are formed in the depth region around the projected range. The size of the Zn nanoparticles increases after the annealing at 600 °C in oxygen gas. Annealing in oxygen gas at 700 °C for 1 h caused two processes: (1) the migration of Zn atoms which formed Zn NPs in as-implanted state to the surface of the a-SiO₂ substrate and (2) the transformation to the oxide phase on the substrate. The transportation of Zn NPs to the surface leaves voids of 10-25 nm in diameter inside the a-SiO₂. These results indicate that the oxidation at 700 °C for 1 h causes the migration of Zn atoms to the surface without diffusion and recombination of vacancies which form the voids.     

Concentration profiles of Zn ions implanted with 60 keV for nanoparticle formation in silica glass

Surface recession due to sputtering under low-energy and high-fluence heavy-ion implantation makes shallower and broader depth profile of implanted ions than those calculated by conventional ion-range simulation-codes such as SRIM. Depth profiles of Zn atoms in silica glasses (SiO₂) implanted with Zn⁺ ions of 60 keV up to 1.0×10¹⁷ ions/cm² were evaluated using both experimental methods as Rutherford backscattering spectrometry (RBS), sputtering depth-profiling by X-ray photoelectron spectroscopy (XPS), and an advanced numerical simulation code TRIDYN, which includes the sputtering loss effects. The TRIDYN code predicts the shallowing of the projectile range from ∼46 to ∼27 nm with increasing the fluence up to 1×10¹⁷ ions/cm², and very high-concentration (∼20 at%) of Zn atoms close to the surface. However, RBS and XPS results exclude such high concentration close to the surface. These results suggest remarkable redistribution of Zn atoms from the nearer surface to the deeper region during the implantation. In fact, Zn-atom concentration near the surface and that near the projectile range are, respectively, lower and higher than those by the SRIM code predictions.     

Synthesis and characterization of a new layered magnesium zinc phosphate hydrate

A new layered magnesium zinc phosphate hydrate, MgZn(HPO₄)₂·H₂O, with a zinc phosphate framework isostructural with the one of Na₂Zn(HPO₄)₂·4H₂O, was prepared by the direct ambient pressure and temperature reaction between zinc 2,4-pentanedionate, phosphoric acid and hexahydrated magnesium chloride. The as-prepared sample is monoclinic (a = 8.780(7) Å, b = 13.240(7) Å, c = 11.123(0) Å and β = 116.21(2)°). The prepared solid undergoes two thermal transformations when it is heated from 110 to 600 °C. The first transformation is due to the release of intercalated water molecules and the second one is due to the HPO₄²⁻ → P₂O₇⁴⁻ transition.     

In vitro degradation,hemolysis and MC3T3-E1 cell adhesion of biodegradable Mg–Zn alloy

In this study a kind of patent binary Mg–6 wt.%Zn magnesium alloy was investigated as degradable biomedical material. The results of in vitro degradation including electrochemical measurements and immersion tests in simulated body fluid (SBF) revealed that zinc could elevate both the corrosion potential and Faraday charge transfer resistance of magnesium and thus improve the corrosion resistance. XRD and EDS analysis proved that the corrosion products on the surface of Mg–Zn contained hydroxyapatite (HA), Mg(OH)₂ and other Mg/Ca phosphates, which could reduce the degradation rate. The degradation process of magnesium alloy and the mechanism of corrosion layer formation were also discussed in this work, i.e. the byproducts of degradation of magnesium, Mg²⁺ and OH^?, reacted with the phosphate and Ca²⁺ in the SBF, thus the corrosion layer containing HA, Mg(OH)₂ and other magnesium-substituted apatite precipitated in corrosion pits and covered the surface of magnesium alloy.The hemolysis test found that the hemolysis rate of Mg–Zn was 3.4%, which is lower than the safe value of 5% according to ISO 10993-4. For the cell culture experiments, after 2 h incubation the pre-osteoblastic cell MC3T3-E1 was able to adhere and spread on the corrosion layer of Mg–Zn alloy, indicating that despite the fluctuation of pH value of DMEM culture solution, Mg–Zn alloy could still support the earlier adhesion of pre-osteoblastic cells on the surface. Hemolysis and adhesion of cells display good biocompatibility of Mg–Zn alloy in vitro.     

Structure and luminescence of (Zn,Mg)O:Zn nanophosphor films

A versatile homogeneous solution growth method is developed for depositing (Zn,Mg)O:Zn²⁺ nanophosphor films from aqueous solutions of zinc, magnesium and triethanolamine. The effect of pH on the structural and morphology of (Zn,Mg)O:Zn²⁺ nanophosphor films was studied and the optimum deposition conditions have been outlined. The deposition rate of nanophosphor film at neutral pH condition was comparatively larger than in basic conditions. The as-deposited films exhibit good crystallinity with hexagonal wurtzite crystalline structure and preferably oriented along (0 0 2) plane. With time, the nanophosphor films appeared dense on the glass substrate comprising of particle sizes of 30-50 nm. Upon excitation at 326 nm, photoluminescence (PL) spectrum corresponding to deep level impurities (∼ 410-530 nm) was completely masked by the strong blue-green emission at ∼ 456 nm. The ratio of Mg to Zn was optimized for maximum PL brightness whereas the optical transmittance of the nanophosphor film decreased with increasing thickness.     

Photocatalytic degradation of paraoxon-ethyl in aqueous solution using titania nanoparticulate film

Photocatalytic degradation of paraoxon-ethyl (o,o-diethyl o-(4-nitrophenyl) phosphate), a well known surrogate of chemical warfare agents, in aqueous solution was studied by using titania nanoparticulate film. Reaction followed pseudo first order behaviour. Photolytic degradation reaction of paraoxon-ethyl demonstrated relatively low rate with a value of rate constant of 2.5 × 10^− 3 min^− 1. Whereas, degradation reaction in the presence of titania nanoparticulate film and UV light displayed enhanced rate with a value of rate constant of 6.9 × 10^− 3 min^− 1 due to photocatalysis. Gas chromatography-mass spectrometry analysis showed the formation of p-nitrophenol, o,o-diethyl phosphonic acid, o-ethyl, diphosphonic acid, phosphoric acid, dimerized product of o,o-diethyl phosphonic acid, acetaldehyde, and carbon dioxide due to photocatalytic degradation of paraoxon-ethyl. It indicates that, photocatalytic degradation reaction begins with destruction of P-O-C bonds. Subsequently, P, C atoms were found to be oxidized gradually, and contributed to its photocatalytic degradation.     

Effect of oxide additives on the low-temperature sintering of dielectrics (Zn,Mg)TiO3

The effect of oxide additives on the low-temperature sintering and dielectric properties of microwave dielectrics (Zn,Mg)TiO₃ have been investigated. The study showed that a small amount of V₂O₅ accelerated the densification rate of (Zn,Mg)TiO₃ dielectrics as compared with the other oxide additives. In addition to lower sintering temperature of zinc titanate dielectrics, the addition of V₂O₅ decreased the decomposition temperature of (Zn,Mg)TiO₃. Additionally, the increased amount of magnesium raised both the sintering temperature and the decomposition temperature of (Zn,Mg)TiO₃. Relative permittivity of (Zn,Mg)TiO₃ dielectrics decreased accompanied with increase of Q × f as the amount of magnesium content increased. The temperature coefficient of resonant frequency of (Zn,Mg)TiO₃ shifted to more negative values as the amount of magnesium increased.     

Correlation between surface damage and micro-defects in Si covered with insulating layer by implantation of He and H ions

Cz n-type Si (100) wafers covered with a 220 nm SiO₂ layer or a 170 nm Si₃N₄ layer were singly implanted with 160 keV He ions at a dose of 5 × 10¹⁶/cm² or successively implanted with 160 keV He ions at a dose of 5 × 10¹⁶/cm² and 110 keV H ions at a dose of 1 × 10¹⁶/cm². Surface morphologies together with defect microstructures have been studied by means of several techniques, including optical microscopy, atomic force microscopy, and cross-sectional transmission electron microscopy (XTEM). Only surface blistering has been observed for He and H sequentially implanted SiO₂/Si samples after annealing in temperature range up to 1000 °C. However, as for the He and H implanted Si₃N₄/Si samples, surface features including blistering and the localized exfoliation of both the top Si₃N₄ layer and the implanted Si layer have been well demonstrated during subsequent annealing. XTEM observations reveal quite different defect morphologies in two kinds of materials under the same implantation and annealing conditions. The possible mechanisms of surface damage in two kinds of materials have been discussed and presented based on the XTEM results.     

Influence of aluminum ions implanted on oxidation behavior of ZIRLO alloy at 500 °C

The beneficial effect of aluminum ion implantation on the oxidation behavior of ZIRLO alloy at 500 °C has been studied. ZIRLO alloy specimens were implanted with aluminum ions with fluence range from 1×10¹⁶ to 1×10¹⁸ ion/cm², using a MEVVA source at an extraction voltage of 40 kV at maximum temperature of 380 °C. The weight gain curves were measured after being oxidized in the air at 500 °C for 120 min, which showed that a significant improvement was achieved in the oxidation behavior of ZIRLO alloy implanted with aluminum compared with that of the virgin ZIRLO alloy. It has been obviously found that when the fluence is 1×10¹⁸ ion/cm², the oxidization of the implanted ZIRLO alloy is reduced into 30% of the virgin ZIRLO alloy.     

Annealing behavior of single mode planar waveguide in YVO4 produced by He ion implantation

We report, for the first time to our knowledge, the formation of single mode planar waveguide in z-cut YVO₄ by 400 keV, 500 keV He ion implantation in fluence of 3 × 10¹⁶ ions/cm² at room temperature or at liquid nitrogen temperature (77 K). We investigated annealing behavior of the guiding mode and near-field image in the waveguide by prism-coupling method and end-face coupling method respectively. We found that the effective refractive index of the TE₀ mode was different before and after annealing for the samples implanted at room temperature, while, annealing had nearly no influence on the effective refractive index of the TE₀ mode of the samples implanted at liquid nitrogen temperature (77 K). After annealing at 600 K for 1 h, no guiding mode was observed in the sample implanted by 400 keV He ion in fluence of 3 × 10¹⁶ ions/cm² at room temperature. The Rutherford backscattering/channeling technique was used to investigate the damage reduction after annealing treatments. The minimum yield of the implanted, annealed sample was 5.43%. We reconstructed the refractive index profiles in the waveguide under different condition by applying intensity calculation method.     

Role of aluminum ion implantation on microstructure, microhardness and corrosion properties of titanium alloy

Ti-Al-Zr alloy was implanted with Al at cumulative doses between 1 × 10¹⁷ and 1 × 10¹⁸ ions/cm². The results indicate that the Al-implanted layers are ∼0.1 μm thick and are composed almost entirely of an amorphous layer. Implanted layer hardness is dose dependent and is increased by more than a factor of 4 for the high-dose implanted specimen when compared with that of the substrate material. The corrosion resistance of the sample was markedly improved after aluminum implantation.     

Ion-implanted resist removal using atomic hydrogen

We removed B-, P-, and As-ion-implanted positive-tone novolak resists with an implantation dose of 5 × 10¹² to 5 × 10¹⁵ atoms/cm² at 70 keV, using atomic hydrogen. Though the removal rate decreased with increase in the implantation dose, all of the ion-implanted resists were removed. The rates of thickness of the surface-hardened layer/all resist layer of B, P, and As implanted resists were 0.38, 0.26, and 0.16, respectively, by SEM observation. The removal rate decreased with increasing the rate of the surface-hardened layer. The energy supplied from the ions to the resist concentrated on the surface side in the increasing order of B-P-As.     

Degradation of alachlor in aqueous solution by using hydrodynamic cavitation

The degradation of alachlor aqueous solution by using hydrodynamic cavitation was systematically investigated. It was found that alachlor in aqueous solution can be deomposed with swirling jet-induced cavitation. The degradation can be described by a pseudo-first-order kinetics and the degradation rate was found to be 4.90 × 10⁻² min⁻¹. The effects of operating parameters such as fluid pressure, solution temperature, initial concentration of alachlor and medium pH on the degradation rates of alachlor were also discussed. The results showed that the degradation rates of alachlor increased with increasing pressure and decreased with increasing initial concentration. An optimum temperature of 40 °C existed for the degradation rate of alachlor and the degradation rate was also found to be slightly depend on medium pH. Many degradation products formed during the process, and some of them were qualitatively identified by GC–MS.     

Modification of polycarbonate surface by Ar ion implantation for various opto-electronic applications

The samples of polycarbonate were implanted to 100 keV Ar⁺ ions at fluences ranging from 1 × 10¹⁵ to 2 × 10¹⁶ ions/cm². The effect of ion implantation on DC conductivity and optical behaviour of this polymer has been investigated. The observed changes have been correlated with the induced structural changes in the implanted layer using Raman spectroscopy. The increase in electrical conductivity, decrease in UV-visible transmission and red shifting of the optical absorption edge may be due to the formation of a three dimensional carbonaceous structure having conjugated double bonds in the near surface layer of polycarbonate as a result of ion implantation. The shift in the conduction mechanism in the implanted layer from ohmic towards SCLC has been observed as a function of implantation dose. The novelty of the present study is to investigate the implantation induced electrical conduction mechanism in the implanted polycarbonate and to comprehend it with induced optical behaviour for its utilization as optically active material with conductive surface in various opto-electronic devices.     

Effects of Si-ion implantation on crystallization behavior of Ge2Sb2Te5 film

Crystallization and thermal stability of Ge₂Sb₂Te₅ (GST), the benchmark working material in phase-change non-volatile memory, were modified via Si-ion implantation. Through 5 × 10¹⁵ Si-ions/cm² ion-implantation, crystallization temperature increases from 165 °C to 177 °C. Furthermore, the activation energy of crystallization increases from 2.9 eV in the pristine film to 3.3 eV and 4.0 eV in films implanted with the doses of 5 × 10¹⁵ and 5 × 10¹⁶ Si-ions/cm², respectively. Temperatures corresponding to a 10-year failure-time increase from 83 °C in the pristine film to 96 °C and 107 °C in films implanted with 5 × 10¹⁵ and 5 × 10¹⁶ Si-ions/cm², respectively. Thermal stability of Si-ion implanted GST thus improves significantly. It was also found that grain growth is inhibited with higher implantation doses. In the case of the 5 × 10¹⁶ ion/cm² dose, the second-phase transition from face-centered cubic to hexagonal closed-packed structure of the GST is completely inhibited. However, crystallization time increases slightly due to Si-ion implantation.     

Analysis of the energy distribution of interface traps related to tunnel oxide degradation using charge pumping techniques for 3D NAND flash applications

The energy distribution and density of interface traps (D_it) are directly investigated from bulk-type and thin-film transistor (TFT)-type charge trap flash memory cells with tunnel oxide degradation, under program/erase (P/E) cycling using a charge pumping (CP) technique, in view of application in a 3-demension stackable NAND flash memory cell. After P/E cycling in bulk-type devices, the interface trap density gradually increased from 1.55 × 10¹² cm⁻² eV⁻¹ to 3.66 × 10¹³ cm⁻² eV⁻¹ due to tunnel oxide damage, which was consistent with the subthreshold swing and transconductance degradation after P/E cycling. Its distribution moved toward shallow energy levels with increasing cycling numbers, which coincided with the decay rate degradation with short-term retention time. The tendency extracted with the CP technique for D_it of the TFT-type cells was similar to those of bulk-type cells.     

Study of SHI induced recrystallization effects in SOI structures synthesized by nitrogen and oxygen ion implantation in silicon

Silicon oxynitride (Si_xO_yN_z) buried insulating layers were synthesized by implantation of nitrogen (¹⁴N⁺) and oxygen (¹⁶O⁺) ions sequentially in the ratio 1:1 at 150 keV to ion-fluences ranging from 1 × 10¹⁷ to 5 × 10¹⁷ cm⁻² to prepare silicon on insulator (SOI) structures. The as implanted samples were held at 270 °C and irradiated to total fluence of 1 × 10¹⁴ cm⁻² by 60 MeV Ni⁺⁵ to study the structural changes/recrystallization of SOI structures induced by swift heavy ion (SHI) irradiation. Fourier transform infrared (FTIR) measurements on the as implanted samples (≤1 × 10¹⁸ cm⁻²) show a single absorption band in the wavenumber range 1300-750 cm⁻¹ attributed to the formation of silicon oxynitride (Si-O-N) bonds in the implanted silicon. It is observed that a nitrogen rich silicon oxynitride structure is formed after SHI irradiation. The study of X-ray rocking curves on the samples show the formation of small silicon crystallites due to swift heavy ion irradiation.     

Dynamic degradation behavior of MgZn alloy in circulating m-SBF

A test platform was designed to mimic the conditions that an implanted coronary stent encounters in coronary arteries, and the degradation behavior of a biodegradable MgZn alloy in the circulating modified simulated body fluid (m-SBF) was investigated on the platform. Results indicated that the presence of circulating solution over the surface of the specimen increased its corrosion rate compared to that in static immersion test, and the diffusion of Mg²⁺ and other ions dominated the corrosion mechanism of the alloy. A corrosion layer with randomly scattering particles conglomerated to clusters on its surface was observed after 168 h of measurement. While the amount of Mg decreased from the matrix to the corrosion layer, the concentration ratio of Zn did not have a significant change. The concentrations of calcium and phosphor seemed to be gradually increased with the extension of distance from MgZn matrix to the degradation layer.