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Traffic congestion is ubiquitous in major cities around the world. Congestion is associated with a slew of negative effects, including delays and local air pollution. Because of the negative effects of congestion, governments invest billions of dollars into the highway system to try to reduce congestion and accommodate peak-hour automobile travel demand. The COVID-19 pandemic presented a significant disruption to transportation systems globally. One impact was a drastic reduction in travel, leading to free-flowing traffic conditions in many previously-congested cities. As lockdowns eased, traffic volumes returned to near-normal levels. However, the temporal pattern of demand may differ, due to increased remote work or other factors. In this article, we examine the temporal distribution of highway demand in California, using data from over 3,500 traffic sensors. We find that peak-hour automobile travel is spreading in the post-lockdown period. In addition to decreased traffic congestion, this finding also has implications for infrastructure investment. Roadways are generally sized based on peak-hour demand. As the peaks spread, some highway construction project may prove unnecessary. It may be possible to reallocate road space to other uses with fewer tradeoffs in terms of traffic congestion. [ABSTRACT FROM AUTHOR]

Traditionally, scientists have placed more emphasis on communicating inferential uncertainty (i.e., the precision of statistical estimates) compared to outcome variability (i.e., the predictability of individual outcomes). Here, we show that this can lead to sizable misperceptions about the implications of scientific results. Specifically, we present three preregistered, randomized experiments where participants saw the same scientific findings visualized as showing only inferential uncertainty, only outcome variability, or both and answered questions about the size and importance of findings they were shown. Our results, composed of responses from medical professionals, professional data scientists, and tenure-track faculty, show that the prevalent form of visualizing only inferential uncertainty can lead to significant overestimates of treatment effects, even among highly trained experts. In contrast, we find that depicting both inferential uncertainty and outcome variability leads to more accurate perceptions of results while appearing to leave other subjective impressions of the results unchanged, on average. [ABSTRACT FROM AUTHOR]

The metal bipolar plates which play a crucial role in proton exchange membrane fuel cells (PEMFCs) are applied extensively due to their excellent property. However, the degraded corrosion resistance by corrosive ion and the increased interfacial contact resistance by passivation layer under acidic operating environment will affect the efficiency of PEMFCs. Metal nitride can solve that problem in some extent, however, the effect of nitrogen flow rates on the metal nitride formation during coating deposition is unclear. To solve these, NbN coatings with different N 2 flow rates were applied to the bare Ti substrate via magnetron sputtering and thereafter studied. Compared with bare Ti substrate, outstanding anticorrosion performance is exhibited for the coated sample, whose corrosion current decreased three orders of magnitude (∼10−8 A/cm2) in simulated PEMFC cathode environment and the interfacial contact resistance decreased to tenth of that bare Ti substrate (∼5 mΩ cm2). • Enhanced corrosion resistance and electrical conductivity of bare Ti is obtained through surface modification method. • Mechanism of anti-corrosive behaviors of NbN coatings are explored. • The structure transition of (NbN x) with different N 2 flow rates are explored. [ABSTRACT FROM AUTHOR]

Silicon nanocrystals are synthesized by reactive magnetron sputtering to distribute throughout the gate oxide layer. Electroluminescence (EL) from amorphous silicon dioxide (a-SiO2) film embedded with Si nanocrystals (nc-Si) has been studied under various gate voltages. Both the integrated EL intensity and the gate current first increase and then decrease with increasing gate voltage. The decrease in EL intensity is ascribed to the charging up of the nc-Si associated trapping centers. The EL intensity can be partially recovered by application of positive electric stress to release part of the trapped charges. [ABSTRACT FROM AUTHOR]

Abstract Titanium nitride (TiNx) films were deposited on 304 stainless steel and silicon (100) wafers by ion source assisted magnetron sputtering. The effect of substrate bias voltage on the preparation and properties of TiNx films was investigated. The results show that as the substrate bias voltage increases from 0 V to −400 V, the deposition rate of TiNx film decreases significantly and the density increases, which can be attributed to the re-sputtering effect at high ion bombardment. The texture of TiNx films varies gradually from (111) to (200) with the increase of energy delivered into the growing film. The hardness of the film deposited under −200 V bias voltage reaches the maximum value, 12.9 GPa. Meanwhile, the toughness and corrosion resistance of the film reach a maximum at a bias voltage of −400 V. In conclusion, the density, hardness, toughness and corrosion resistance of TiNx films can be increased by changing the substrate bias voltage. Highlights • TiNx films were prepared by ion source assisted magnetron sputtering. • Re -sputtering effect enhanced with increasing substrate bias voltage. • Both hardness and toughness of TiNx films were studied. • Tafel curve and EIS were measured to identify the corrosion resistance. • A corrosion model was provided for the explanation of corrosion mechanism. [ABSTRACT FROM AUTHOR]

In recent years, transition metal dichalcogenides (TMDs) have been widely used for gas sensors. Here, three-dimensional (3D) WSe 2 nanosheet arrays were surface treated by microwave plasma. Based on the original 3D structure, a 1T/2H hybrid phase structure was constructed by phase modulation, and Se vacancies were introduced to effectively improve its gas sensing performance. After only 60 s of treatment, the response (52.24 %), response/recovery time of the sample for 1 ppm NO 2 were significantly improved with excellent stability and selectivity at room temperature. The intrinsic mechanism of its performance enhancement was elicited through various characterizations and molecular model construction. It is demonstrated that microwave plasma is a promising treatment method to improve the gas-sensitive performance of TMDs. [Display omitted] • A facile Microwave plasma method for surface treatment of 3D-WSe 2. • Effectively construct 1T/2H hybrid phase structure and introduce se vacancies. • Effectively improve the response and reaction kinetics of 3D-WSe 2 to NO 2. • Demonstrate performance improvement mechanisms through molecular models. • Proving microwave plasma is a potential material processing treatment. [ABSTRACT FROM AUTHOR]

Synthesizing structural color coatings on magnesium alloys remains challenging. As inspired by the interference effect of visible light, this work sputtered a layer of Si on the Al bonding layer as the reflection layer followed by the deposition of AlN layer as the refraction layer. The influence of the Si interlayer on the morphology, structure, composition, color, corrosion resistance, and hardness of the AlN/Si/Al coatings was investigated systematically. With the introduction of the Si interlayer, the average grain size of AlN decreased from 19.3 to 16.7 nm, the surface roughness in R q reduced from 13.6 to 11.2 nm, and the color of the coatings changed from silvery white to yellowish. The AlN/Si/Al-coated Mg alloys respectively displayed purple, indigo, blue, green, yellow, orange and red colors as the AlN surface layer thickness increased from 165 to 180, 200, 220, 250, 270 and 290 nm. Meanwhile, introducing the Si interlayer significantly improved the corrosion resistance and hardness of the coatings. The corrosion current density decreased from 1.5 × 10−5 to 2.43 × 10−6 A/cm2, and the hardness doubled from 4.3 to 9.2 GPa. The mechanisms for color-tunning, corrosion resistance, and hardness enhancement were discussed in detail. • The color of AlN/Al-coated AZ31B Mg alloy could be tuned by introducing Si interlayer. • The AlN/Si/Al coating could display different color via changing the AlN layer thickness. • The AlN/Si/Al-coated AZ31B Mg alloy exhibits excellent corrosion resistance and hardness. [ABSTRACT FROM AUTHOR]

As an alternative to single crystal silicon photovoltaics, thin film solar cells have been extensively explored for miniaturized cost-effective photovoltaic systems. Though the fight to gain efficiency has been severely engaged over the years, the battle is not yet over. In this review, we comb the fields to elucidate the strategies towards high efficiency thin films solar cells and provide pointers for further development. Starting from the photoelectron generation, we look into the fundamental issues in photoelectric conversion processes, including light harvesting and charge handling (separations, transportations and collections). The emerging organic-inorganic halide perovskite systems, as well as the rapidly developed polycrystalline inorganic systems, organic photovoltaics and amorphous silicon cells are discussed in details. The biggest bottleneck for the cost-effective polycrystalline inorganic cells is the composition sensitivity and deep defects; for amorphous silicon cells, it is the quantum of the dangling bonds; for organic cells, it is the low charge carrier mobility and high exciton binding energy; and for perovskite cells, it is the environmental degradation and the controversial mechanisms of generation of I-V hysteresis. Strategies of light harvesting and charge handling as well as directions to break the bottlenecks are pointed out. [ABSTRACT FROM AUTHOR]

Graphene has been used to enhance conversion efficiency in dye-sensitized solar cell (DSSC) through increased electronic transportation. Introduction of graphene into DSSC is realized through reduction of graphene oxide (GO) to reduced graphene or RGO in TiO 2 nanoparticles in solution. Chemical and hydrothermal reactions are two commonly used avenues. In the chemical route, toxic hydrazine and its derivatives are the typical reducing agent. Hydrothermal process is not toxic but requires prolonged heating. In this study, we mix flakes of GO with TiO 2 nanoparticles and use vitamin C to realize the reduction at room temperature. The RGO–TiO 2 composite films are then used as photoanode in DSSC. A conversion efficiency of 30% increase (to 7.89%) is obtained as compared to that of the pure TiO 2 photoanode. [ABSTRACT FROM AUTHOR]

CrAlSiN coatings are of high hardness, excellent wear and oxidation resistance but lack of lubriciousness. Vanadium nitride (VN) is easily oxidized to form vanadium oxides and becomes lubricious under stress. Incorporating VN into CrAlSiN to form CrAlSiVN coating renders both hardness and self-lubrication in dry machining. This study investigates the effect of vanadium content on hard yet self-lubricious coating’s mechanical and tribological properties. The coatings are deposited on cemented tungsten carbide and Si wafer (1 0 0) substrates in an in-line magnetron sputtering system. Grazing incidence X-ray diffractometer, scanning electron microscopy, transmission electron microscopy, electron probe micro-analyzer, X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy are employed to characterize the microstructures and chemistry. Nanoindentation and ball-on-disc tribo-tester are used in characterization of the mechanical and tribological properties. The coatings demonstrate lubriciousness of coefficient of friction with tungsten carbide from 0.55 down to 0.39 with acceptable loss of hardness (from ∼35 GPa down to ∼30 GPa). [ABSTRACT FROM AUTHOR]

Over the past decades, hard and super hard ceramic coatings have been developed and widely used in various industrial applications. Meanwhile, an increasing number of studies have realized that the toughness is just as crucial, if not more, than hardness especially for ceramic coatings. However, hardness and toughness do not go naturally hand in hand. In other words, hard coatings usually are brittle and less durable while toughened coatings are of lower strength. For practical engineering applications, it is more desirable to have coatings with high hardness without sacrificing toughness too much. In this article, a review is presented on continuous progress to realize hard-yet-tough ceramic coatings from an angle of hardening as well as toughening. [ABSTRACT FROM AUTHOR]

Growth orientation of silicon (Si) nanowires is the key in tailoring the optical and electrical characteristics of semiconductor devices. To date, however, the distribution and dictator are still unclear. In this work, Si nanowires are grown via thermal annealing of nickel (Ni) coated Si wafers. The morphology, growth orientation and the relation to the seeding Ni catalyst particles are examined via high resolution transmission electron microscopy and selected area electron diffraction pattern. Statistical results show that Si nanowires prefer to be along the <112> orientation, followed by the ones in the <110>, <111>, <001>, <113> and <133> orientations. Besides surface energy that is commonly believed to control the nanowire׳s growth, this work found that the nanowire׳s growth follows certain structure-sensitive principle at the wire/catalyst interface to minimize the mismatch in lattice spacing and dihedral angle. [ABSTRACT FROM AUTHOR]

Abstract: Silicon (Si) nanoparticles that are precipitated through the disproportionation of SiO have been regarded as the seeds to the growth of Si nanowires during thermal evaporation of Si-containing powders in quartz or alumina tube without any supply of metallic catalyst. However, compositional scrutiny of the quartz tube after high temperature dwelling reveals traces of metallic aluminum and copper, which are perfect catalysts for Si nanowire seeding and growth. With all due respect, this study prompts rethinking of the seeding and growth mechanism of Si nanowires grown via thermal evaporation of Si-containing powders. [Copyright &y& Elsevier]

Highlights: [•] Closed magnetic circuit FeGa/BaTiO3/FeGa structure was assembled to improve magnetoelectricity. [•] The ratio of strain over magnetic field is five times better than that of the rod. [•] At the resonance frequency (68kHz) a maximum = 1.88V/cmOe was observed. [•] Closed magnetic circuit design improved the ME voltage by avoiding the demagnetizing field. [ABSTRACT FROM AUTHOR]

Abstract: Crystalline silicon (Si) nanowire could be directly grown from Si wafer upon thermal annealing in the presence of catalyst such as gold (Au). However, the role of the catalyst layer thickness is yet elucidated. In this work, 10nm, 20nm, and 40nm Au layers were respectively sputtered on Si wafer substrates, followed by 2min thermal annealing at 1000°C under Ar atmosphere, to find the relationship between the catalyst layer thickness and formation of the nanowire. Results show that in the case of thin layer of catalyst, crystalline-Si/amorphous-SiO x coaxial nanowires grew. But with thicker layers of catalyst, no wires were found but crystalline Au particles capsulated with amorphous SiO x . The catalyst and nanowire morphologies and structures were carefully examined through a scanning electron microscope, X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy and selected area diffraction. A model is developed to explain the formation mechanism of the Si/SiO x and Au/SiO x core–shell nanostructures. [Copyright &y& Elsevier]

Abstract: To improve the magnetoelectric (ME) property of piezoelectric thin film systems, Ni and FeCoV magnetic films are respectively used to sandwich piezoelectric foil Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) in the middle. The ME voltages and coefficients have been characterized in the longitudinally magnetized and transversely polarized mode. The measurement was conducted under a static magnetic field superimposed with an alternating magnetic field. The influences of the static and the alternating field strength are discussed. The peak ME coefficient obtained in the FeCoV film-sandwiched structure reached 27.4×10−3 mV/cm•A/m, which is about five times greater than the Ni film-sandwiched counterpart. A linear relationship is observed between the magnetoelectric voltage and the alternating field strength under a static field of 31.8kA/m for both structures. As FeCoV is also oxidation-resistant and low in cost, the FeCoV film-sandwiched structure (i.e., FeCoV/PMN–PT/FeCoV) makes a good candidate in miniature ME device applications. [Copyright &y& Elsevier]

Abstract: A set of CrAlSiN coatings was synthesized in homogenous and graded composition via magnetron sputtering in mixed Ar and N2 ambient. The microstructures are investigated using glancing angle X-ray diffractometry, field emission scanning electron microscopy and transmission electron microscopy. With compositional grading, CrAlSiN coatings exhibit much improved scratch adhesion strength and better crack propagation resistance at a little expense of hardness. [Copyright &y& Elsevier]

Abstract: To improve the tribological performance of CrN coating, VN was introduced to form the CrN/VN multilayer structure via magnetron sputtering. The CrN/VN multilayer coatings with bilayer periods of 7, 13 and 27nm were investigated on the mechanical and tribological properties. The coatings were deposited on SUS420 and Si wafers (100) via in-line magnetron sputtering system. X-ray diffractometer, scanning electron microscopy, transmission electron microscopy and electron probe micro-analyzer were used to characterize the microstructures and chemical contents. Ball-on-disc wear test was used for tribological studies. The wear debris was analyzed by X-ray photoelectron spectroscopy. A hardness of 25.2GPa and coefficient of friction of 0.21 were achieved for multilayered coating in contrast to 16.7GPa in hardness and 0.4 in coefficient of friction for CrN coating. [Copyright &y& Elsevier]

Highlights: [•] CrAlN/VN multilayer coatings are found self-lubricating at room temperature. [•] Vanadium nitride is tribo-oxidized into VO x acting as lubricant. [•] Period thickness of 20nm provides CrAlN/VN multilayer coating the best mechanical performance. [Copyright &y& Elsevier]

Abstract: Growth of crystalline silicon nanowire of controllable diameter directly from Si wafer opens up another avenue for its application in solar cells and optical sensing. Crystalline Si nanowire can be directly grown from Si wafer upon rapid thermal annealing in the presence of the catalyst such as nickel (Ni). However, the accompanying oxidation immediately changes the crystalline Si nanowire to amorphous SiOx. In this study, amorphous carbon layer was sputtered to on top of the catalyst Ni layer to retard the oxidation. Scanning electron microscope, transmission electron microscope, Raman spectroscopy and X-ray photoelectron spectroscopy were employed to characterize the wires and oxidation process. A model was developed to explain the growth and oxidation process of the crystalline Si nanowire. [Copyright &y& Elsevier]

Abstract: To combat the brittleness of hard nc-CrAlN/a-SiN x nanocomposite (nc-: nanocrystalline, a-: X-ray amorphous), different Ni content (from 0 to 39.8at.%) is doped via magnetron sputtering. Glancing Angle X-ray Diffractometry, X-ray photoelectron spectroscopy, Field Emission Scanning Electron Microscopy and Transmission Electron Microscopy are employed to investigate the microstructural evolution. With increased Ni, the grain size decreases accompanied with morphology change, from dense glassy to coarse columns. With 4.2at.% Ni, scratch toughness of nc-CrAlN/a-SiN x hard nanocomposite (28GPa) is improved by around 200% at expense of only 18% hardness. [Copyright &y& Elsevier]

Abstract: Chromium aluminum nitride (CrAlN) coatings were prepared via magnetron sputtering in a mixed Ar and N2 ambient. The effect of negative bias voltage (Vb) on the microstructure was investigated using a spectrum of characterizing techniques in terms of Glancing Angle X-ray Diffractometry, Field Emission Scanning Electron Microscopy and Transmission Electron Microscopy. As Vb increased from 50 to 260V, hardness was improved from 10 to 26GPa. Toughness grew at the same time and maximized at around 2MPa·m1/2 when Vb =210V. Simultaneous improvements in hardness and toughness were attributed to the densified microstructure with refined grains and increased compressive stress. [Copyright &y& Elsevier]

Abstract: The “step” in the load–displacement curves during nanoindentation of hard coatings has been regarded as a representation of the energy dissipated during fracture of the coating thus is used in measuring the fracture toughness of this coating. This paper scrutinizes the “step” and finds that the “step” is a gap artificially bridged up with a straight line and that the “step” size corresponds with the thickness of the coating in testing. It is realized that the gap is formed due to loss of contact of the indenter with the sample. Upon catastrophic fracture of the coating, the indenter undergoes a freefall of a distance about the thickness of the coating. The size of such a “step” has no logic relationship with the energy dissipation that fractures the coating before the freefall of the indenter takes place. [Copyright &y& Elsevier]

Abstract: Enormous progress has been achieved over the past decade in evaluating the toughness of hard coatings and thin films. This paper reviews methodologies developed based on indentation, bending, and microtensile testing. In addition, we discuss a recent development in fracture toughness measurement which involves the application of macrotension to a substrate in order to induce microtension in a patterned thin film. [Copyright &y& Elsevier]

Abstract: To combat the high residual stress problem in monolayer diamond-like carbon coatings, this paper fabricated multilayer diamond-like carbon coatings with alternate soft and hard layers via alternating bias during magnetron sputtering. The surface, cross sectional morphology, bonding structures and mechanical properties are investigated. The atomic force microscopy images indicate low bias results in rougher surface with large graphite clusters and voids suggesting low coating density. The multilayered coatings demonstrate relatively smooth surface stemming from higher bias. The cross sectional images from field emission scanning electron microscopy indicate coating thickness decreases as substrate bias increases and confirm that higher bias results in denser coating. Delamination is observed in monolayer coatings due to high residual stress. The trend of sp3/sp2 fraction estimated by X-ray photoelectron spectroscopy is consistent with that of ID/IG ratios from Raman spectra, indicating the change of bonding structure with change of substrate bias. Hardness of multilayer diamond-like carbon coating is comparable to the coatings deposited at low constant bias but the adhesion strength and toughness are significantly improved. Alternately biased sputtering deposition provides an alternative when combination of hardness, toughness and adhesion strength is needed in an all diamond-like carbon coating. [Copyright &y& Elsevier]

Abstract: High-aspect-ratio TiO2 nanotubes with small diameter are favored in dye-sensitized solar cells for large dye loading provided by high surface areas. However, long TiO2 nanotubes with small diameter are difficult to grow under usual anodizing conditions due to unavoidable chemical dissolution of the top portion of the as-fashioned tubes. In the present work, two kinds of double-layered TiO2 nanotube arrays were prepared by changing voltage from high to low (i.e., from 30V to 15V) or from low to high (i.e., from 15V to 30V). It is found that the top layer can serve as a sacrificial layer to protect the continuous growth of the bottom layer from chemical dissolution. Accordingly, the two-step anodization from high voltage to low voltage is proposed to produce high-aspect-ratio TiO2 nanotubes with small diameter underneath a sacrificial top layer. [Copyright &y& Elsevier]

Abstract: Magnesium-containing fluoridated hydroxyapatite (Mg x FHA) coatings have been developed to improve the biological performances of fluoridated hydroxyapatite (FHA) coatings. The coatings are deposited on Ti6Al4V substrates via a sol–gel process. The interface between the coating and substrate is characterized by scanning electron microscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy for coating thickness, elemental distribution and chemical states. Pull-off test is used to evaluate the adhesion strength. The results show that the interdiffusion of elements happens at the coating/substrate interface. The incorporation of Mg ions into FHA coatings enhances the pull-off adhesion strength between the coating and the substrate, but no significant difference is observed with different Mg concentrations. [Copyright &y& Elsevier]

Abstract: Si-rich oxide films (SiOx, 0

Abstract: For application in dye-sensitized solar cells, anodic titania nanotube arrays must have high-aspect-ratio configuration to load more dyes thus result in higher conversion efficiency. Although geometry of the nanotubes is reported to be affected by a variety of anodizing parameters, electric field strength is the essential factor in determining the tube features (length, pore diameter, wall thickness, etc.). In the present work, electric field strength was varied by changing applied potential and working distance. Effect of the field strength on tube length was studied under selected field strengths for prolonged anodizing durations. An Ion Flux Model, in consideration of F− and H+ concentration profiles within a single tube, is proposed to interpret the influence of the field strength on nanotube growth rate. The results indicate what essentially affects the tube length is the field strength which influences ion migration in electrolyte and ion transport in anodic barrier layer. [Copyright &y& Elsevier]

Abstract: Magnesium (Mg) is a trace element in natural bone, its existence plays an important role in cell adhesion and bone formation. To improve the biological properties, Mg and fluorine (F) are simultaneously incorporated in hydroxyapatite (HA) to form Mg x FHA coating on titanium alloy via sol–gel process. In vitro bioactivity of the coating is evaluated by examination of apatite precipitation on surface of the coatings during immersion in simulated body fluid. The chemical states of Mg and F in the coating are examined by X-ray photoelectron spectroscopy. Grazing incidence X-ray diffraction and scanning electron microscopy are employed for phase identification and surface morphology changes are compared after soaking in the SBF solutions for 7 to 28 days. The results show that both Mg and F ions are indeed incorporated into the HA crystal structure. The presence of F promotes Mg incorporation into the HA crystal structure. The presence of Mg makes the coatings more bioactive in promoting bone formation. However, at high Mg concentration, formation of β-TCMP (Mg substituted β-TCP) takes place. [Copyright &y& Elsevier]

Abstract: Amorphous hydrogenated carbon films were prepared by hot filament Plasma Enhanced Chemical Vapor Deposition using acetylene as precursor. NiP-coated Al substrate was sputtered with thin layer of ruthenium film prior to carbon deposition for its impact on carbon film growth. Film thickness measured and fitted using X-ray Reflectometry showed carbon film growth is an exothermic reaction with apparent activation energy of 914.6 J mol−1 in the temperature range studied. Carbon film density and surface roughness changed with substrate temperature, more profound when substrate is pre-heated at 300 °C and above, in sync with abrupt I D/I G increase at temperature higher than 300 °C. Substrate temperature higher than 200 °C and below 300 °C is preferred for hard and dense structure. Higher deposition rate and porosity were observed at higher C2H2 flow rate due to more H incorporation. Film surface morphology studied by Atomic Force Microscope showed Root Mean Square roughness increased at higher C2H2 flow rate due to less energetic ion peening effect. Atomic bonding structure with sp2 and sp3 contents in the films deposited at varied temperature and C2H2 flow was analyzed using XPS. [Copyright &y& Elsevier]

Abstract: Nd-doped SrBi2Ta2O9 films were sputtered on Pt/Ta/SiO2/Si substrates under various substrate biases. The radio frequency bias results in the reduction of the Aurivillius phase crystallization temperature. At 48 W, the crystallization temperature of film is lowered at a magnitude of about 80 °C. When the bias further increases, Aurivillius phase formation is suppressed due to too deficient Bi in film. The film deposited at 48 W after annealing at 670 °C shows ferroelectric characteristics. The remnant polarization of the films increases as the annealing temperature is increased. [Copyright &y& Elsevier]

Abstract: Si nanocrystals (nc-Si) were synthesized by rapid thermal annealing of magnetron-sputtered amorphous SiO x films. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were employed to study the evolution of chemical structures and the rapid growth of nc-Si. XPS results reveal five chemical structures of Si in the as-deposited films corresponding to silicon oxidation states: Si n+ (n=0, 1, 2, 3 and 4). Their bonding structures are found to be inhomogeneous, and far from that predicted by the random-bonding model. XPS and Raman spectra suggest that the formation of amorphous Si nanoclusters had already taken place in the as-deposited samples. Formation of nc-Si was realized through a combination of thermal decomposition and the diffusion process. Upon thermal annealing, Si suboxides (Si2O, SiO and Si2O3) decompose into Si and SiO2, resulting in the rapid growth of nc-Si. [Copyright &y& Elsevier]

Abstract: Magnesium is one of the most important bivalent ions associated with biological apatite. A series of magnesium-substituted calcium apatite coatings (Ca10−x Mg x )(PO4)6(OH)2, where x =0, 0.50, 1.00, 1.50 and 2.00, are synthesized onto Ti6Al4V substrate by sol–gel dip-coating method to determine how magnesium influences the synthesis and the resulting structural and biological properties. X-ray diffraction (XRD) analysis shows that the incorporation of magnesium helps formation of Mg-containing β-TCP (β-TCMP) phase. X-ray photoelectron spectroscopy (XPS) is used to study the chemical composition and the results show that the apatite structure can only host magnesium less than ∼2.4wt.% beyond which magnesium aggregates on the surfaces. The incorporation of magnesium slows down the dissolution of Ca2+ from the coating. The in vitro behavior of the coatings is evaluated with human osteosarcoma MG63 cells for cell morphology and proliferation. Similar cell morphologies are observed on all coatings. The cell proliferation results show that the incorporation of magnesium up to x =2 has no adverse effect on cell growth. [Copyright &y& Elsevier]

Abstract: In advanced drug delivery systems, drug permeation rate is the key parameter that governs performance. Among the factors that influence the permeation rate, partition effect is presently given less attention. In the first part of this study [L. Shang, S. Zhang, H. Du, S S. Venkatraman, A novel approach for the control of drug release rate through hydrogel membrane. I. Effect of drug immobilization on drug release rate by copolymerization method. Eur. J. Pharm. Biopharm. 68 (2008) 715–723], a scheme was proposed to alter the drug release rate through controlling the partition behavior by immobilizing drug molecules in the membrane. It was hypothesized that the immobilized drug contributes to the total chemical potential of all drug molecules, resulting in a reduction in the partition coefficient. In this paper, the working mechanism of the control scheme is studied through thermodynamic modeling on the assumption that substances in the system are dependent upon one another (rather than independent as they are usually treated). Experimental results provide satisfactory verification of the model. With this model, drug permeation rate can be quantitatively tailored. [Copyright &y& Elsevier]

Abstract: Nanocrystalline titanium carbide (TiC) thin films were prepared by magnetron sputtering deposition at 473 K. The effect of substrate bias on microstructure and mechanical properties was studied in details using X-ray photoelectron spectroscopy, X-ray diffraction, field emission scanning electron microscopy, indentation and scanning microscratch. The TiC films exhibit a (111) preferential orientation. Substrate bias decreases grain size and deposition rate of the TiC films. The TiC films have columnar structure which becomes finer at high substrate bias. Nanoindentation hardness, Young''s modulus, and toughness of the films are increased as the substrate bias goes up. However, the adhesion peaks at substrate bias of −100 V and drops when bias is increased further. [Copyright &y& Elsevier]

Abstract: Nd-doped SrBi2Ta2O9 thin films are magnetron-sputtered on Pt/Ta/SiO2/Si substrates. The effect of heating rate on crystallization behavior is investigated with conventional furnace annealing (CFA) and rapid thermal annealing (RTA). Grazing incidence X-ray diffraction and field emission scanning electron microscopy reveal that the crystallization goes through three stages (phases): amorphous, fluorite and finally Aurivillius. Under RTA, the fluorite-to-Aurivillius transformation starts around 100 °C lower than that under CFA. The reasons behind the transformation temperature drop are also discussed. [Copyright &y& Elsevier]

Abstract: Magnesium-containing apatite coatings were prepared on Ti6Al4V substrates by sol–gel dip coating method. Standard simulated body fluid (SBF) was used to evaluate the bioactivity of the coatings. A series of the coatings according to the composition (Ca10−x Mg x )(PO4)6(OH)2, where x =0 to 2, is synthesized and immersed in the standard SBF for periods of 7 to 35 days for direct deposition of apatite layer from the SBF solution. Scanning electron microscopy (SEM) was used to examine the morphology changes of the SBF apatite layer that occurred during in vitro immersion. X-ray diffractometry, Fourier Transformation Infra-Red Spectroscopy and X-ray Photoelectron Spectroscopy were used to analyse the phases, chemical groups and composition of the sol–gel coating. Results show that as the sol–gel coating contains magnesium, this promotes deposition of apatite layer from SBF. As x ≤1, SBF immersion gives rise to a dense apatite layer. However, as x ≫1, selected dissolution of the deposited layer takes place, which results in serious pitting on the surface. Also, Mg ions from the dissolution of the sol–gel coating during immersion in the SBF apparently played a role in the subsequent deposition of apatite o the coating, evidence of Mg was found in the apatite layer. [Copyright &y& Elsevier]

Abstract: Magnesium apatite coatings on Ti6Al4V substrate were synthesized by the sol–gel dip-coating method. Magnesium was incorporated in the coating according to the formula (Ca10−x Mg x )(PO4)6(OH)2, where x =0, 0.50, 1.00, 1.50 and 2.00. Approximately 2-μm-thick apatite coatings were derived after five cycles of dip–drawing–drying–firing process. A transitional region (R t) was formed between substrate and coating during the firing process. Adhesion tests show that the adhesion strength between substrate and apatite coating is enhanced by the incorporation of magnesium in the coating. The quantity of magnesium incorporated appeared to correspond to the Mg–Ti–O chemical bonds formed in the transitional region, which contributed to the adhesion strength of the coatings. [Copyright &y& Elsevier]

Abstract: Amorphous carbon has been studied for its biological properties. Doping can alter the film structure to achieve certain desirable properties, like lowering of stress. The incorporation of a secondary element however also alters the film surface properties, which in turn, the biological response. We have investigated the response of fibroblast and osteoblast-like cells on amorphous carbon and amorphous carbon containing silicon. The amorphous carbon with the highest silicon concentration exhibits higher surface energy, with higher polar component. Both cell types adhered, spread and proliferated well on all films, especially on the one with the highest silicon content. [Copyright &y& Elsevier]

Abstract: During magnetron sputtering deposition of SrBi2Ta2O9 thin films, oxygen gas is introduced in the deposition chamber to compensate the oxygen loss during sputtering. In this paper, the influence of oxygen partial pressure is systematically investigated in sputtering of Sr0.8Nd0.3Bi2.5Ta2O9+x thin films, using X-ray diffraction, X-ray photoelectron spectroscopy and field emission scanning electron microscopy. The studies confirm that at various oxygen partial pressure Nd3+ ions substitute into the bismuth layered perovskite structure, preferentially at the Sr2+ site. The deposition rate, composition, microstructure and polarization properties of the films highly depend on the oxygen partial pressure. [Copyright &y& Elsevier]

Abstract: β-tricalcium phosphate (β-TCP) powders are embedded in a fluoridated hydroxyapatite (FHA) matrix to form β-TCP-FHA composites via colloidal-sol gel method. This composite layer is deposited on top of a FHA layer to form a β-TCP-FHA/FHA biphasic coating. The effect of the nanosized powder on the residual stress is characterized through the X-ray diffraction peak shift. The powder incorporation increases the residual stress, while a large amount of β-TCP (Capowder/Casol ratio is higher than 1/2) results in less gel shrinkage that partially compensates the mismatch of thermal expansion coefficient and thus the residual stress. Despite the elevated residual stress as more powders are embedded, the coating adhesion strength remains virtually constant: around 430 mN–500 mN in scanning scratch test. [Copyright &y& Elsevier]

Abstract: Precise control of drug release rate in hydrogel drug delivery systems to better mimic physiological condition is a challenging research topic in development of Advanced Drug Delivery Systems. One of the major issues with bioresponsive drug delivery systems is the excessive ‘leakage’ of drug while the system is in the ‘off’ state, which leads to shortening of the device life-time and potential overdose problem for the patient. In the present study, a new approach, based on partition effects, termed drug immobilization via copolymerization, is proposed to control the drug release rate of membrane-based drug delivery systems. In this method, a certain level of drug is pre-immobilized in the membrane through copolymerization. The immobilized drug contributes to the overall chemical potential of drug molecules in the membrane but their mobility is restricted, hence will not be released. At equilibrium, the amount of drug from donor that dissolved in the membrane is reduced due to contribution of immobilized drug, resulting in an effective reduction in partition coefficient and hence the release rate. The testing of the method by bovine serum albumin (BSA) as a model drug confirmed the controllability of the method: almost 35% reduction of the drug leakage in the ‘off-state’ was observed when 20mg BSA was immobilized in the pH-sensitive hydrogel membrane. The mathematical model of the drug partition in the membrane was modified to describe the new partition phenomenon (mobile drug and immobilized drug in the membrane) in this study. [Copyright &y& Elsevier]

Abstract: Amorphous carbon (a-C) has good blood compatibility and has been proposed as a coating material for blood contacting devices such as heart pumps and stents. In this study, unhydrogenated a-C films with different silicon concentrations were synthesized by magnetron sputtering, and the corresponding evolution of the surface energy and compatibility with blood were analysed. The incorporation of silicon not only decreased the sp2-hybridized carbon bonding configurations, but the static evaluation of the films incubated in human platelet-rich plasma also showed a decrease in platelet adhesion. Bonding structure and surface energy were determined to be factors contributing to the improved haemocompatibility. [Copyright &y& Elsevier]

Bonding evolution of amorphous carbon incorporated with Si or a-C(Si) in a thermal process has not been studied. Unhydrogenated a-C(Si) films were deposited by magnetron sputtering to undergo two different thermal processes: i) sputter deposition at substrate temperatures from 100 to 500 °C; ii) room temperature deposition followed by annealing at 200 to 1000 °C. The hardness of the films deposited at high temperature exhibits a monotonic decrease whereas the films deposited at room temperature maintained their hardness until 600 °C. X-ray photoelectron spectroscopy and Raman spectroscopy were used to analyze the composition and bonding structures. It was established that the change in the mechanical property is closely related to the atomic bonding structures, their relative fractions and the evolution (conversion from C–C sp3 → CᆖC sp2 or CᆖC sp2 → C–Si sp3) as well as clustering of sp2 structures. [Copyright &y& Elsevier]

Abstract: Nd-substituted SrBi2Ta2O9 (SNBT) thin films are sputtered on Pt/Ta/SiO2/Si substrates. X-ray diffraction and x-ray photoelectron spectroscopy studies indicate that Nd3+ is substituted into the bismuth layered perovskite structure, preferentially at the Sr2+ site. The annealed thin film is polycrystalline with plate/needle-like grain microstructure. Secondary ion mass spectrometry results show that elements in SNBT thin film homogeneously distribute along film depth and interfacial diffusion takes place during post annealing. The Nd substitution leads to enhanced remnant polarization (2P r =18 μC/cm2) and reduced coercivity (2E c =64 kV/cm) at 180 kV/cm measured at 25 °C. After 1010 switching cycles, around 9% remnant polarization is decreased. [Copyright &y& Elsevier]

Abstract: Unhydrogenated amorphous carbon films with different silicon concentrations were synthesized by magnetron sputtering, and the corresponding evolution of inter-atomic bonding configurations, surface roughness and mechanical properties like hardness, modulus and stress was analyzed. Introducing silicon into amorphous carbon not only reduced the sp2-hybridized carbon bonding, it also helped to reduce residual stress. Both the hardness and elastic modulus suffered degradation when the silicon concentration was low. But these properties recovered when silicon dosage increased. Surface roughness increased when silicon concentration was low, but decreased when the silicon dosage increased. Such changes in the mechanical properties were closely related to the carbon and silicon inter-atomic interaction. The amorphous carbon network was modified by silicon, and affected by deposition kinetics. The mismatch in the atomic size and bond length, and the alteration of the carbon hybridization were determined to be the basis for the changes in the mechanical properties. [Copyright &y& Elsevier]

Abstract: β-tricalcium phosphate/fluoridated hydroxyapatite (β-TCP/FHA) biphasic coatings were prepared on titanium alloy substrate by means of sol–gel method. The coatings combine the initial dissolution of β-TCP with the long-term stability of FHA to create a high quality bioactive coating. Ca(NO3)2, P2O5 and HPF6 were dissolved in ethanol respectively and mixed in designed sequence and Ca:P:F ratios to form a sol. After the sol was refluxed for 24 h, the as-refluxed sol was used for FHA coating. β-TCP powders were dispersed into the sols to form colloidal sols for β-TCP/FHA biphasic coatings. The as-refluxed sols with different Ca:P:F ratios only resulted in apatite coatings with low F content. Biphasic coatings were prepared with the colloidal sols. The β-TCP contents of the coatings could be tailored by varying the amount of the powders in the colloidal sols. The surface morphology of the coatings becomes rougher with increasing amount of the powders, which favors cell attachment. However, excessive amount of powders results in powder agglomeration, leading to more cracks in the coatings. Fine powders and good dispersion are essential factors for good biphasic coatings. [Copyright &y& Elsevier]

Abstract: In this paper, we study the effects of film thickness on phase transformation of constrained Ti50.2Ni49.8 films deposited onto silicon substrates. When the film is too thin, surface oxide and interfacial diffusion layers exert dominant constraining effect that renders high residual stress and low recovery capabilities in the film. The surface oxide and inter-diffusion layer restricts the phase transformation, alters stoichiometry of the remaining TiNi film, and reduces volume of the material available for phase transformation. As a result, a lower thickness boundary (about 100 nm) exists for TiNi films to remain “shape remembering”. Results indicate that a maximum recovery stress and actuation speed can be realized with a thickness of about 800 nm. Based on the curvature measurement results, the relationship between the relative stress and strain of the films (during phase transformation with change of temperature) can be derived. [Copyright &y& Elsevier]

Abstract: Although silicon doping of amorphous carbon films can lower the intrinsic compressive stress, doping alone cannot ensure a stress free state. An additional thermal processing is needed for complete stress relaxation. This additional process can, however, alter the surface properties of the film and its relative haemocompatibility. In this study, unhydrogenated amorphous carbon film incorporated with silicon was synthesized by magnetron sputtering and annealed to relieve stress. The evolution of the bonding structure and compatibility with blood were investigated. The results showed that the clustering of the sp2-bonded carbon was retarded, and the amorphous network disordering was increased when annealing temperature increased to 600 °C. Surface thrombogenesis of the films were evaluated using in-vitro platelet adhesion assay. The static evaluation of the films incubated in human platelet-rich-plasma showed an increase in the number of adherent platelets, but with lower activation percentage. [Copyright &y& Elsevier]