X-ray photoelectron spectroscopy study of the growth kinetics of biomimetically grown hydroxyapatite thin-film coatings

Hydroxyapatite (HA) thin-film coatings grown biomimetically using simulated body fluid (SBF) are desirable for a range of applications such as improved fixation of fine- and complex-shaped orthopedic and dental implants, tissue engineering scaffolds and localized and sustained drug delivery. There is a dearth of knowledge on two key aspects of SBF-grown HA coatings: (i) the growth kinetics over short deposition periods, hours rather than weeks; and (ii) possible difference between the coatings deposited with and without periodic SBF replenishment. A study centred on these aspects is reported. X-ray photoelectron spectroscopy (XPS) has been used to study the growth kinetics of SBF-grown HA coatings for deposition periods ranging from 0.5 h to 21 days. The coatings were deposited with and without periodic replenishment of SBF. The XPS studies revealed that: (i) a continuous, stable HA coating fully covered the titanium substrate after a growth period of 13 h without SBF replenishment; (ii) thicker HA coatings about 1 μm in thickness resulted after a growth period of 21 days, both with and without SBF replenishment; and (iii) the Ca/P ratio at the surface of the HA coating was significantly lower than that in its bulk. No significant difference between HA grown with and without periodic replenishment of SBF was found. The coatings were determined to be carbonated, a characteristic desirable for improved implant fixation. The atomic force and scanning electron microscopies results suggested that heterogeneous nucleation and growth are the primary deposition mode for these coatings. Primary osteoblast cell studies demonstrated the biocompatibility of these coatings, i.e., osteoblast colony coverage of approximately 80%, similar to the control substrate (tissue culture polystyrene).     

Non-destructive quantification of pharmaceutical tablet coatings using terahertz pulsed imaging and optical coherence tomography

Optical coherence tomography (OCT) and terahertz pulsed imaging (TPI) are two powerful techniques allowing high quality cross-sectional images from within scattering media to be obtained non-destructively. In this paper, we report experimental results of using OCT and TPI for quantitatively characterizing pharmaceutical tablet coatings in the thickness range of 10-140 μm. We found that the spectral OCT system developed in-house has an axial resolution of 0.9 μm, and is capable of quantifying very thin coatings in the range of 10-60 μm. The upper limit of 60 μm within the tablet coating and core is owed to the strong scattering of OCT light, which has relatively short wavelengths in the range of 0.5-1.0 μm. On the other hand, TPI utilizes terahertz radiation that has substantially long wavelengths in the range of hundreds of microns, and thus is less prone to the scattering problem. Consequently TPI has been demonstrated to be able to quantify thicker coatings in the range of 40-140 μm and beyond. We concluded that OCT and TPI are two complementary analytical techniques for non-destructive and quantitative characterization of pharmaceutical tablet coatings.     

Preparation and in vitro characterization of aerosol-deposited hydroxyapatite coatings with different surface roughnesses

Hydroxyapatite (HA) coatings with different surface roughnesses were deposited on a Ti substrate via aerosol deposition (AD). The effect of the surface roughness on the cellular response to the coating was investigated. The surface roughness was controlled by manipulating the particle size distribution of the raw powder used for deposition and by varying the coating thickness. The coatings obtained from the 1100 °C-heated powder exhibited relatively smooth surfaces, whereas those fabricated using the 1050 °C-heated powder had network-structured rough surfaces with large surface areas and were superior in terms of their adhesion strengths and in vitro cell responses. The surface roughness (R_a) values of the coatings fabricated using the 1050 °C-heated powder increased from approximately 0.65 to 1.03 μm as the coating thickness increased to 10 μm. The coatings with a rough surface had good adhesion to the Ti substrate, exhibiting high adhesion strengths ranging from 37.6 to 29.5 MPa, depending on the coating thickness. The optimum biological performance was observed for the 5 μm-thick HA coating with an intermediate surface roughness value of 0.82 μm.     

Fabrication of xenogeneic bone-derived hydroxyapatite thin film by aerosol deposition method

Xenogeneic bone-derived hydroxyapatite (HA) was coated on Ti-6Al-4V substrate using aerosol deposition (AD) system. HA precursor powder was derived from bovine bone for the deposition. In aerosol system, submicron particles of HA were mixed with a carrier gas to form an aerosol flow in the aerosol chamber. The aerosol flow was through a tube to a nozzle, and then ejected into a deposition chamber. The effect of the beam incident angle on the HA film formation was investigated. The incident angle of the beam was changed from 0° to 60°. Homogeneous HA film with the thickness of 1-2 μm was fabricated by flattering of particles shape for the incident angle of 60°.     

Passive Q-switching of short-length Tm-doped silica fiber lasers by polycrystalline Cr:ZnSe microchips

We demonstrate passive Q-switching of short-length double-clad Tm³⁺-doped silica fiber lasers near 2 μm pumped by a laser diode array (LDA) at 790 nm. Polycrystalline Cr²⁺:ZnSe microchips with thickness from 0.3 to 1 mm are adopted as the Q-switching elements. Pulse duration of 120 ns, pulse energy over 14 μJ and repetition rate of 53 kHz are obtained from a 5-cm long fiber laser. As high as 530 kHz repetition rate is achieved from a 50-cm long fiber laser at ∼10-W pump power. The performance of the Q-switched fiber lasers as a function of fiber length is also analyzed.     

Effect of microarc oxidation coating on fatigue performance of Ti-Al-Zr alloy

Ceramic coatings of different thickness were fabricated on Ti6Al2Zr1Mo1V alloy by microarc oxidation (MAO), and the effect of the coating on fatigue life was evaluated by 810 Material Test System. The microstructure, phase and chemical composition of the coatings were determined by SEM, XRD and EDS techniques. The coating mainly consists of rutile and a small amount of anatase TiO₂. With oxidation time ranging from 10 to 30 min, the coating thickness increases from 13 to 25 μm, while the interface between coating and substrate becomes more zigzag, characterized by increasing overgrowth regions of coating into substrate. Under the same cyclic stress of 750 MPa, the fatigue life decreases from 2.08 × 10⁶ cycles for uncoated specimen to about 3 × 10⁴ cycles for microarc oxidized specimen. Under the cyclic stress, the thicker the coating, the more cracks initiate in the overgrowth regions of coating into substrate near the interface, which are considered as the notch sites of stress concentration to induce the crack initiation, also is the key factor to cause the facture.     

Synthesis of ZnO nanowires by pulsed laser deposition in furnace

ZnO nanowires were fabricated on Au coated (0 0 0 1) sapphire substrates by using a pulsed Nd:YAG laser with a ZnO target in furnace. ZnO nanowires have various sizes and shapes with a different substrate position inside a furnace. The length and the diameter of these ZnO nanowires were around 3-4 μm and 120-200 nm, respectively, confirmed by scanning electron microscopy (SEM). The diameter control of the nanowires was achieved by varying the position of substrates. The ultraviolet emission of nanowires from the near band-edge emission (NBE) was observed at room temperature. The formation mechanism and the effect of different position of substrates on the structural and optical properties of ZnO nanowires are discussed.     

Optical properties of hydroxyapatite obtained by mechanical alloying

Calcium phosphate based bioceramics, mainly in the form of hydroxyapatite (HA), have been in use in medicine and dentistry for the last 20 years. Applications include coatings of orthopaedic and dental implants, alveolar ridge augmentation, maxillofacial surgery, otolaryngology, and scaffolds for bone growth and as powders in total hip and knee surgery. These materials exhibit several problems of handling and fabrication, which can be overcome by mixing with a suitable binder. In this paper, mechanical alloying has been used successfully to produce nanocrystalline powders of HA using five different experimental procedures. The milled HA were studied by X-ray powder diffraction, infrared and Raman scattering spectroscopy. For four different procedures, HA was obtained after a couple of hours of milling (on an average, 20 h of milling depending on the reaction procedure). The XRD patterns indicate that the grain size is within the range of 29-103 nm. This milling process, used to produce HA, presents the advantage that melting is not necessary and the powder obtained is nanocrystalline with extraordinary mechanical properties. The material can be compacted and transformed in solid ceramic samples. The high efficiency of the process opens a way to produce commercial amount of nanocrystalline HA. Due to the nanocrystalline character of this powder, their mechanical properties have changed and for this reason a pressure of 1 GPa is enough to shape the sample into any geometry.     

Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) study of melt-spun Fe85Ga15 ribbons

The local structure in melt-spun Fe₈₅Ga₁₅ ribbons with a width ∼3 mm and thickness ∼60 μm produced in argon atmosphere was studied by analyzing EXAFS and XANES data. The following results were obtained: Ga–Ga bonds were not detected excluding the tendency to form clusters of Ga atoms; Ga substitutes Fe creating a local strain of about +1% on the first shell Fe–Ga bond, whereas on the second Fe–Ga shell strain quickly relaxes down to +0.3%; XANES spectra are compatible with a random substitution of Fe atoms by Ga atoms in the A2 structure. From the AFM investigation, we observed that at the surface (free side) of the ribbon the particles are elongated along the ribbon (∼2 μm×∼5 μm) and each particle is formed by small grains of average size of 200 nm.     

Effect of temperature on residual stress and mechanical properties of Ti films prepared by both ion implantation and ion beam assisted deposition

Ti films with a thickness of 1.6 μm (group A) and 4.6 μm (group B) were prepared on surface of silicon crystal by metal vapor vacuum arc (MEVVA) ion implantation combined with ion beam assisted deposition (IBAD). Different anneal temperatures ranging from 100 to 500 °C were used to investigate effect of temperature on residual stress and mechanical properties of the Ti films. X-ray diffraction (XRD) was used to measure residual stress of the Ti films. The morphology, depth profile, roughness, nanohardness, and modulus of the Ti films were measured by scanning electron microscopy (SEM), scanning Auger nanoprobe (SAN), atomic force microscopy (AFM), and nanoindentation, respectively. The experimental results suggest that residual stress was sensitive to film thickness and anneal temperature. The critical temperatures of the sample groups A and B that residual stress changed from compressive to tensile were 404 and 428 °C, respectively. The mean surface roughness and grain size of the annealed Ti films increased with increasing anneal temperature. The values of nanohardness and modulus of the Ti films reached their maximum values near the surface, then, reached corresponding values with increasing depth of the indentation. The mechanism of stress relaxation of the Ti films is discussed in terms of re-crystallization and difference of coefficient of thermal expansion between Ti film and Si substrate.     

The study of mechanical behavior on the interface between calcar-defect femur and restorations by means of finite element analysis

The mechanical behaviors of calcar-defected femur and restorations under physiological load are the key factors that will greatly influence the success of femur calcar defect repairing, especially the stress distribution on the bone-restoration interface. 3D finite elements analysis (FEA) was used to analyze the mechanical characters on the interfaces between femoral calcar defects and bone cement or HA restorations. Under the load of two times of a human weight (1436.03 N) and with the increase of the defect dimension from 6 mm to 12 mm, the maximal stresses on the surface of restorations are from 7.06 MPa to 11.89 MPa for bone cement and 2.97-9 MPa for HA separately. In this condition, HA restoration will probably be broken on the bone-restoration interface when the defect diameter is beyond 8 mm. Furthermore, under the load of 1.5 times of a human weight, HA restoration would not be safe unless the defect dimension is smaller than 10 mm, because the maximal stress (4.62 MPa) on the restoration is only a little lower than compressive strength of HA, otherwise the bone fixation device should be applied to ensure the safety. It is relatively safe for all restorations under all the tested defect sizes when the load is just the weight of a human body.     

Low infrared emissivity of polyurethane/Cu composite coatings

Polyurethane/Cu composite coatings with low infrared emissivity near to 0.10 at the wavelength of 8-14 μm were prepared by a simple and convenient process. The influences of the content of Cu powder, surface roughness, coating thickness and temperature on infrared emissivity of the coatings were systematically investigated. The results indicated that the emissivity decreases significantly with increasing content of Cu powder and coating thickness. The coatings with smooth surface exhibit lower emissivity values than those with rough coatings. Moreover, we found the relationship between the emissivity of coatings and temperature presents a “U” type, and the emissivity reaches to the minimum at about 380 K. The mechanisms of low emissivity were proposed by optical theories, which are found to be in a good agreement with the experimental results.     

The structure and optical properties of evaporated Samarium fluoride films

Samarium fluoride (SmF₃) films have been deposited on quartz, silicon and germanium substrates by vacuum evaporation method. The crystal structure of the films deposited on silicon substrate is examined by X-ray diffraction (XRD). The films deposited at 100 °C, 150 °C and 250 °C have the (1 1 1) preferred growth orientation, but the film deposited at 200 °C has (3 6 0) growth orientation. The surface morphology evolution of the films with different thickness is investigated with optical microscopy. It is shown that the microcrack density and orientation of thin film is different from that of thick film. The transmission spectrum of SmF₃ films is measured from 200 nm to 20 μm. It is found that this material has good transparency from deep violet to far infrared. The optical constants of SmF₃ films from 200 nm to 12 μm are calculated by fitting the transmission spectrum of the films using Lorentz oscillator model.     

Preparation of dielectric mirrors from high-refractive index contrast amorphous chalcogenide films

We report the preparation of planar 15-layer dielectric mirrors by a thermal evaporation of alternating high refractive index contrast amorphous chalcogenide Sb-Se and Ge-S layers, exhibiting a high-reflection band around 1.55 μm. The layer deposition quality and the thickness accuracy of such prepared chalcogenide multilayers were then checked using transmission electron microscopy. The layer thickness deviation of chalcogenide layers did not exceed ∼7 nm in comparison with the desired thicknesses. The width of Sb-Se/Ge-S layer boundary was approximately ∼3 nm, which is in good agreement with the surface roughness values of thermally evaporated Sb-Se and Ge-S single layers. The optical properties of the prepared 15-layer dielectric mirrors were consistent in temperature range of 20-120 °C; however, at higher temperatures there started apparent structural changes of Sb-Se films, which were followed by their crystallization. Excellent optical properties of chalcogenide materials in the infrared range make them interesting for applications, e.g., in optics and photonics.     

A new solution of reducing polymer optical fiber losses

Polymethyl methacrylate (PMMA) is one of the most commonly used optical materials. However, the application of it in the area of optical communication is strongly limited by the intrinsic absorption loss of carbon-hydrogen stretching vibration. In this paper, we present a method to solve the problem by adopting the hollow-core fibers with cobweb cladding structure. The fibers use a single dielectric material and may solve the problem of structural support. Thus the feasibility of the “OmniGuide” fibers is improved, while a series of advantages of the “OmniGuide” hollow-core fiber are retained. It is promising that a fiber with low transmission loss, high bandwidth, large-core, and low costs can be designed and fabricated using PMMA. At the same time, a very broad range of the wavelengths (from visible to near infrared region, for instance, wavelengths at 0.65-1.12 μm, and even 1.30 μm, 1.54 μm and their neighbors) may be adopted for signal wavelength.     

Fabrication and characterization of rod-like nano-hydroxyapatite on MAO coating supported on Mg-Zn-Ca alloy

The poor corrosion resistance of magnesium alloys is a dominant problem that limits their clinical application. In order to solve this challenge, micro-arc oxidation (MAO) was used to fabricate a porous coating on magnesium alloys and then electrochemical deposition (ED) was done to fabricate rod-like nano-hydroxyapatite (RNHA) on MAO coating. The cross-section morphology of the composite coatings and its corresponding energy dispersion spectroscopy (EDS) surficial scanning map of calcium revealed that HA rods were successfully deposited into the pores. The three dimensional morphology and scanning electron microscopy (SEM) image of the composite coatings showed that the distribution of the HA rods was dense and uniform. Atomic force microscope (AFM) observation of the composite coatings showed that the diameters of HA rods varied from 95 nm to 116 nm and the root mean square roughness (RMS) of the composite coatings was about 42 nm, which were favorable for cellular survival. The bonding strength between the HA film and MAO coating increased to 12.3 MPa, almost two times higher than that of the direct electrochemical deposition coating (6.3 MPa). Compared with that of the substrate, the corrosion potential of Mg-Zn-Ca alloy with composite coatings increased by 161 mV and its corrosion current density decreased from 3.36 × 10⁻⁴ A/cm² to 2.40 × 10⁻⁷ A/cm² which was due to the enhancement of bonding strength and the deposition of RNHA in the MAO pores. Immersion tests were carried out at 36.5 ± 0.5 °C in simulated body fluid (SBF). It was found that RNHA can induce the rapid precipitation of calcium orthophosphates in comparison with conventional HA coatings. Thus magnesium alloy coated with the composite coatings is a promising candidate as biodegradable bone implants.     

Dependence of surface distribution of self-assembled InSb nanodots on surface morphology and spacer layer thickness

Self-assembled InSb nanodots (NDs) were grown on a GaSb (1 0 0) substrate using metal-organic vapour phase epitaxy (MOVPE). The effects of etching depth of the substrate and thickness of the GaSb buffer layer on the density and size distribution of single and double layer dots were studied for detector applications. The etch depth of the substrate was varied up to 30 μm. In this particular study, the dots were grown at 450 °C and the GaSb spacer thickness was varied between 50 nm and 200 nm. The optimum substrate etch depth was found to be 30 μm while the best spacer thickness was found to be 200 nm.     

Low-pump-threshold tunable optical parametric oscillator using periodically poled MgO:LiNbO3

We fabricated and characterized periodically poled MgO:LiNbO₃ device with five gratings in 0.5 μm increments from 29 μm to 31 μm for optical parametric oscillator (OPO). The OPO operation threshold is 30 μJ using this device with a 50 mm effective length. At 560 mW input pump power, we have achieved 300 mW of the total output power, and the conversion efficiency is 54%. Multi-periods and temperatures tuning of the OPO yields a signal wavelength range from 1.45 to 1.72 μm and an idler wavelength range from 2.8 to 4.05 μm in the mid infrared.     

Ceramic membrane by tape casting and sol-gel coating for microfiltration and ultrafiltration application

Alumina membrane filters in the form of thin (0.3-0.8 mm) discs of 25-30 mm diameter suitable for microfiltration application have been fabricated by tape-casting technique. Further using this microfiltration membrane as substrate, boehmite sol coating was applied on it and ultrafiltration membrane with very small thickness was formed. The pore size of the microfiltration membrane could be varied in the range of 0.1-0.7 μm through optimisation of experimental parameter. In addition, each membrane shows a very narrow pore size distribution. The most important factor, which determines the pore size of the membrane, is the initial particle size and its distribution of the ceramic powder. The top thin ultrafiltration, boehmite layer was prepared by sol-gel method, with a thickness of 0.5 μm. Particle size of the sol was approximately 30-40 nm. The structure and formation of the layer was analysed through TEM. At 550 °C formation of the top layer was completed. The pore size of the ultrafiltration membrane measured from TEM micrograph was almost 10 nm. Results of microbial (Escherichia coli—smallest-sized water-borne bacteria) test confirm the possibility of separation through this membrane     

Stress impedance effect of FeCoSiB/Cu/FeCoSiB sandwich layers on flexible substrate

FeCoSiB/Cu/FeCoSiB sandwich layers were deposited on flexible substrate to develop flexible stress/strain sensors. The influence of stress on the impedance of the multilayers is reported. The results show that the variation of the impedance increases with the increase in deflection of the free end of the cantilever. A relative change in impedance of 6.4% is obtained in the FeCoSiB(1.5 μm)/Cu(0.25 μm)/FeCoSiB(1.5 μm) sandwich layers at 1 MHz with deflection of 2 mm. The stress impedance effects are sensitive to the frequency of the current and the thickness of both FeCoSiB and Cu layers. The stress impedance effect increases with the increase in the thickness of FeCoSiB or Cu layers. The stress impedance effect increases slightly with the increase in frequency and decreases with the further increase in frequency, which can be understood by the stress and frequency-dependent permeability of magnetic films.