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In this work, three dimensional self-supported Co3O4@Ni3S2 nanowire arrays on nickel foam substrates are prepared by a multi-step method. The as-synthesized product harvests the advantages of the high electrical conductivity of the Co3O4 nanowire arrays, large surface area provided by the Ni3S2 nanosheets, and the efficient ion diffusion pathway offered by the self-supported structure. The sample is subsequently used as the electrode material for supercapacitors, at a current density of 2 mA cm−2 a charge storage capability of 2.41C cm−2 (5.5 F cm−2) was achieved. When the sample is charged and discharged at 50 mA cm−2 for 10000 cycles, a stable capacity of 0.86C cm−2 (1.5 F cm−2) can still be maintained at the end of the test. Such a performance is better than those values reported in the literature obtained with similar systems even at a lower current density. We also assemble an asymmetric supercapacitor by pairing the Co3O4@Ni3S2 nanoarrays with activated carbon, and it shows good cyclability over 10000 cycles. The device yields energy densities of 65 and 32.3 Wh kg−1 at power densities of 361 and 9090 W kg−1, respectively. Furthermore, it is able to light up 12 red light-emitting diodes, showing promising potential for practical applications.

Many previous simulations of the plastic deformation in metallic glasses showed that shear banding is the dominant mode accompanied by Voronoi volume continuous generation and softening. In the present work, we report a contrary phenomenon where Voronoi volume recovery is dominant during plastic deformation in CuZr metallic glasses under tension. By creating a notched geometry, the deformation mode of notched samples transits from shear banding to necking due to the introduction of triaxial stress state. With the suppressing of shear banding, a notch strengthening and structure ordering phenomenon together with the recovery of Cu-centered full-icosahedra fraction are also observed. The present work enriches our understanding on the mechanical behavior and deformation mechanism of metallic glasses.

Nanocrystalline and amorphous nickel-tungsten alloy with relatively high tungsten contents of up to 34 at.% were produced by electrodeposition. The Hall-Petch relationship and breakdown was studied in this alloy, with grain sizes ranging from 25 nm to fully amorphous. In this higher tungsten content alloy, evidence of solid-solution strengthening was found, which was previously absent in alloys with

As the emergence of SARS-CoV-2 variants brings the global pandemic to new levels, the performance of current rapid antigen tests against variants of concern and interest (VOC/I) is of significant public health concern. Here, we report assessment of the Abbot BinaxNOW COVID-19 Antigen Self-Test. Using genetically sequenced remnant clinical samples collected from individuals positive for SARS-CoV-2, we assessed the performance of BinaxNOW against the variants that currently pose public health threats. We measured the limit of detection of BinaxNOW against various VOC/I in a blinded manner. BinaxNOW successfully detected the Omicron (B.1.1.529), Mu (B.1.621), Delta (B.1.617.2), Lambda (C.37), Gamma (P.1), Alpha (B.1.1.7), Beta (B.1.351), Eta (B.1.525), and P.2 variants and at low viral concentrations. BinaxNOW also detected the Omicron variant in individual remnant clinical samples. Overall, these data indicate that this inexpensive and simple-to-use, FDA-authorized and broadly distributed rapid test can reliably detect Omicron, Delta, and other VOC/I.

Positively charged nanodiamond (ND) is used to decorate negatively charged graphene oxide (GO) to form a GO-ND hybrid nanomaterial by electrostatic force. Structural studies results showed that after the decoration, the aggregation of GO sheets is extensively hindered in both at the powder and dispersion states, with a clear reduction in the layer numbers in the latter. The mechanical properties of epoxy/GO, epoxy/ND and epoxy/GO-ND were investigated and compared. The results showed that the GO increased the ductility of epoxy, while the ND increased the rigidity. The best mechanical performance was found for the epoxy/GO-ND nanocomposites, at a GO:ND ratio of 1:5. The reinforcement mechanism of the nanophases was further illustrated by the fracture surface of SEM/optical images and TGA analysis. In addition, the anti-corrosion property of the thus developed epoxy nanocomposite coatings was revealed by electrochemical impedance spectroscopy (EIS), and the results demonstrated that the epoxy/GO-ND coatings exhibited better anti-corrosion property.

The role of biogenic H 2 S in the microbiologically influenced corrosion (MIC) of carbon steel was investigated. Desulfovibrio vulgaris (ATCC 7757), a sulfate reducing bacterium, was tested against C1018 carbon steel in anaerobic vials with three different sizes, each filled with 40 mL of ATCC 1249 culture medium, providing headspace volumes of 10 mL, 85 mL and 160 mL, respectively for H 2 S to escape. Results showed that a larger headspace led to a lower H 2 S concentration in the culture medium, and this increased the sessile cell count and made the iron sulfide film thinner, resulting in increased MIC.

The micro-galvanic interactions between Cu-Fe-Mn-Li-containing aluminides and the alloy matrix of aluminium alloy AA2099 during chloride-induced corrosion were investigated in-situ with real-time monitoring of the local contact potential difference (VCPD) using the scanning Kelvin probe force microscopy (SKPFM) at controlled relative humidities. The aluminides showed noble potentials and were able to ennoble their neighbouring matrix sites when a cluster of aluminides surrounded the matrix. The matrix, hence, adopted a more positive VCPD, towards that of the aluminides. The anode-to-cathode ratio changed throughout the corrosion exposure and was seen to show a dynamic character. Much higher local VCPD activities were recorded during the earliest stages of corrosion, when the Al-Li AA2099 surface was first exposed to high humidities, than in later RH cycles; a phenomenon not seen in other aluminium alloys.

Biofouling induced corrosion of stainless steels grades UNS S31603 and UNS S31254 was investigated at three sites off Singapore for 30 months. No corrosion was observed on grade UNS S31254, while the propensity for corrosion by shellfish of UNS S31603 is ranked as oyster >> barnacles >> green mussels. Oysters caused extensive localised corrosion, penetrating 2 mm thick plates with 12 months with tracks of corrosion several centimetres long. Shallow crevice corrosion was observed under dead barnacles, with an explanation presented for why corrosion is more severe under dead barnacles than live ones. Green mussels did not cause any corrosion.

Investigations in microbiological-influenced corrosion in recent years have suggested a positive correlation in steel corrosion with methanogens. However, many cases reported in the literature were performed in medium containing Na2S·9H2O or l -cysteine, from which the methanogens can produce H2S that in itself is corrosive. Here it is demonstrated that if all sources of H2S are removed, the methanogenic strain Methanosarcina barkeri only cause accelerated corrosion when deprived of traditional energy sources for methanogenesis, such as methanol and H2. Possible mechanisms for this phenomenon of starvation conditions triggering accelerated corrosion are discussed.

To improve the corrosion resistance of the steel matrix, 1% and 3% Cr and 1% Al are added to ordinary carbon steel for the design of a corrosion-resistant alloying composition. And based on the principle of electrochemical tests, a method for determining the depassivation of Cr and Al alloy steel bars in coral aggregate concrete (CAC) is established. The equivalent circuit model was used based on the electrochemical impedance spectroscopy (EIS) results to characterise the corrosion behaviour of the Cr and Al alloy steel bars and determine their corrosion resistance and the protective effect of the steel bar passivation film. The corrosion resistance of the Cr1 reinforcement to chloride increases by 37.67%, that of the CrAl reinforcement increases by 64.08%, and that of the Cr3 reinforcement increases by 171.82% with respect to that of the HPB 400 bar. The polarisation curves of the alloy steel bars with different Cr and Al contents in CAC were recorded by linear polarisation resistance (LPR), and the time variations of the corrosion potential and corrosion current in the low-alloy steel bars containing Cr and Al were analysed. In addition, the free chloride ion concentration and pH value of the CAC were measured while the Cr and Al alloy steel bars were rusting. The chloride threshold values (% by weight of concrete) of the HPB 400, Cr1, CrAl, and Cr3 steel bars are 0.515%, 0.718%, 0.950%, and 1.084%, and the chloride thresholds (Cl−/OH− ratio) are 0.288, 0.382, 0.502, and 0.693, respectively. Initial-corrosion condition behavior of the Cr and Al alloy steel bars in CAC was obtained. There is considerable scientific value and application significance attainable from the examination of the corrosion mechanism and behavior of corrosion-resistant steel bars in a harsh marine environment.

In this work, self-supported Ni 3 S 2 nanorod arrays on nickel foam substrate are prepared by a facile one-pot hydrothermal method. These phase-pure nanorods possess an interesting secondary structure: the surface is covered with ultrathin Ni 3 S 2 nanosheets. Such an integration of one-dimensional nanorod array with two-dimensional nanosheets combines the advantages of the two components, demonstrating enhanced pseudocapactive performance with a high and very stable areal capacitance over prolonged charge-discharge tests. When the as-prepared material is incorporated as the cathode in an asymmetric supercapacitor, where activated carbon is selected as the anode, the device exhibits highly reversible capacitance with insignificant decay over 3000 cycles. Excellent energy densities of 115 and 102 Wh kg −1 are achieved at power densities of 506 and 1094 W kg −1 , respectively. Such a performance can be attributed to the unique sheet-on-rod nanoarray on the nickel foam substrate.

Grades 2, 5 and Grade 7 were investigated in near anaerobic (

The structural stability of the electrode material is very important to achieve a long cycle life of a supercapacitor. In this work, we demonstrate a multi-step preparation of metal organic framework (MOF)-reinforced Co9S8 self-supported nanowire arrays for high-performance supercapacitor with very high durability. Co-based nanowires with a composition of Co2(OH)2(CO3)2 are first synthesized on the nickel foam substrate by a facile hydrothermal method. After converting them into Co3O4 nanowires by calcination, leaf-like Co-based MOF (Co-MOF) has been deposited on the surface of the oxide nanoarrays (NAs), forming Co3O4 NAs@Co-MOF core-shell structure. Co9S8 nanoarrays are finally obtained by an in-situ hydrothermal sulfurization, and this process not only realizes the chemical transformation, but also changes the morphology of the Co-MOF from leaf-like microplatelets into nanosheets wrapping around the one-dimensional (1D) nanowires. When this sample has been applied for supercapacitor, it exhibits a 4.48 F cm−2 at a current density of 2 mA cm−2. The long-term cycling test is conducted at 25 mA cm−2, and the sample can maintain a high and stable capacitance of 1.6 F cm−2 after 100k cycles. This gives rise to a capacitance loss of only 5.1 × 10−4% per cycle, demonstrating an exceptional cycling stability. Furthermore, an asymmetric supercapacitor is assembled by pairing the Co9S8 nanoarrays with activated carbon, and the device delivers excellent cycle stability with a reversible capacitance of 416 mF cm−2 after 100k cycles, leading to a capacitance loss of 2.8 × 10−4% per cycle. Furthermore, a quasi-solid-state asymmetric supercapacitor is able to light up 16 red LEDs, demonstrating great potential for practical application with excellent cycle stability and mechanical flexibility.

Compared to graphene, graphene oxides (GO) have also been applied in many areas due to their unique structures and properties, such as tunable and functionalized surfaces, great processing and competition for scalable production. In this review, GO reinforced epoxy resins are systematically looked into, where they can be classified into two broad groups: epoxy/GO nanocomposites and epoxy/GO coatings, depending on the application types. In the epoxy/GO nanocomposites, the GO reinforcement on the different properties of epoxy matrices are described in details, like mechanical, toughness, thermal conductivity and so on. As for the epoxy/GO coatings, the GO effect on the anti-corrosion properties is one of the main concerns. For both of them, GO modification methods and dispersing routes in the respective epoxy matrices are among the most important considerations. There are some remaining unsolved issues, which will be highlighted together with the future perspectives of the GO reinforced epoxy resins.

Titanium is being considered as a candidate material for high-level nuclear waste container due to its superior corrosion resistance. However, problems may arise when titanium comes in contact with hydrogen-bearing environments, as it is vulnerable to hydrogen embrittlement. To assess the lifetime of titanium container, hydrogen content and hydrogen permeation efficiency were estimated in infiltrated water through bentonite prepared with simulated groundwater of Beishan, the preselected area in China, by electrochemical and metallurgical analysis. It is concluded that the absorbed hydrogen due to general corrosion will not be sufficient for hydrogen embrittlement to occur in titanium for at least 10,000 years after deep geological disposal. This represents more than 300 and 5,000 half-lives of Cs137 and Cs134 respectively; cesium being the most likely element to escape a repository due to its high solubility in groundwaters.

The mechanism of corrosion protection of steel substrate by a 96 wt% zinc primer that was damaged by scratch was simulated. The primer was approximated to pure zinc layer due to high percentage of zinc. Results show that while the middle of scratch is protected by sacrificial protection, at the corners of scratch a local cathodic inhibition results in barrier protection due to variations in the dissolved oxygen concentration. Moving boundary simulation allowed to predict the changes to the geometry of the corroding electrodes. Finally, taking into account zinc electrodes consumption, the period of sacrificial protection was predicted by simulations.

This work describes a versatile hydrothermal approach to synthesize different types of hierarchical structures composed of single crystalline β-Ni(OH) 2 nanosheets. We use the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride (BmimCl) as a structure directing agent, which allows the formation of films consisting of β-Ni(OH) 2 nanosheets on the nickel foam substrate. It is found that the IL not only controls the formation of the sheet-like structure, but also promotes the growth of the nanosheets on the substrate, building an intimate contact between the active hydroxide film and the conducting metal foam. This IL agent is so effective that such a hierarchical film can also be obtained with different thickness and organization if different nickel salt precursor is used. When these film samples were applied as the electrode materials for pseudocapacitor, they exhibited promising capacitive properties with a high capacitance of about 700 F g ⿿1 even at a high charge-discharge current rate of 5 A g ⿿1 for prolonged cycling.

The critical chloride threshold concentration and the polarizability of the barrier layer/outer layer (as defined by the Point Defect Model) have been determined for AISI 1020 carbon steel in simulated concrete pore solutions of pH 9, 10, 11 and 12.5 with varying chloride and bicarbonate/carbonate concentrations. It was found that bicarbonate/carbonate ions have a beneficial effect on the charge transfer resistance, the critical chloride threshold concentration and the pitting potential. When the critical chloride threshold concentration for pitting is exceeded, the inhibitive effectiveness of bicarbonate/carbonate against pitting corrosion is around one order of magnitude lower compared to hydroxide.

The corrosion performance of commercial hard disk media which was subjected to bi-level surface modification has been reported. The surface treatment was carried out by bombarding the surface of the magnetic media with C+ ions at 350 eV followed by 90 eV using filtered cathodic vacuum arc (FCVA). The energy and embedment depth of the impinging C+ ions were adjusted by applying an optimized bias to the substrate and simulated by a Stopping and Range of Ions in Matter (SRIM) code which predicted the formation of a graded atomically mixed layer at the carbon-media interface. Cross-section transmission electron microscopy (TEM) revealed the formation of a 1.8 nm dense nano-layered carbon overcoat structure on the surface of the media. Despite an ~ 33% reduction in the thickness, the bi-level surface modified disk showed corrosion performance similar to that of a commercially manufactured disk with a thicker carbon overcoat of 2.7 nm. This improvement in the corrosion/oxidation resistance per unit thickness can be attributed to the formation of a dense and highly sp3 bonded carbon layer, as revealed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. This study demonstrates the effectiveness of the bi-level surface modification technique in forming an ultra-thin yet protective overcoat for future hard disks with high areal densities.

In this paper, the degradation of Acid Orange 7 (AO7), by persulfate activated from in situ electrochemically generated Cu+ (EC-Cu-PDS) was studied. The influence of key parameters such as pH, current density, copper concentration and electrode size were investigated, with the optimal operation condition being pH 2 with cathode to anode area of 4:1. The degradation efficiency of the EC-Cu-PDS after 30 min was compared to the efficiency of other electrocatalysis system using iron, cobalt or silver. The proposed EC-Cu-PDS process has a higher degradation efficiency of 70%, as compare to 56% of the EC-Fe-PDS process. Although the EC-Cu-PDS process has a lower degradation efficiency compared to 100% of Co-PMS and 80% of the EC-Ag-PDS processes, the EC-Cu-PDS process would be cheaper and safer to operate than the latter processes. The estimated electrical energy consumption of the EC-Cu-PDS processes was significantly lower than other electrocatalysis processes, ranging from 0.008 to 2.42 kW h m−3. The degradation of AO7 by the EC-Cu-PDS process was via oxidization of AO7 by both hydroxyl radicals generated at the anode and sulfate radicals generated by both electrochemically at the anode and Cu+ activation of PDS.

A sensor device is demonstrated based on changes in the impedance within a layer of porous silicon on exposure to the target analyte. Selectivity can be obtained by attaching functional organic groups onto the porous silicon. If the target molecules do not interact with the attached functional groups, then the sensor's response varies linearly with concentration. In the event however, when strong hydrogen-bonding occurs a much larger response is recorded on exposure to low concentrations than would be expected. The hydrogen-bonding either causes increased penetration of the solvent into the porous matrix or reduces the potential drop across the solvent/porous silicon interface, i.e. reduces magnitude of the space charge capacitance in the silicon nanorods.

The electropolishing of p-type silicon has been investigated over a wide range of wafer conductivities (p− to p++) and HF concentrations (0.01–15 wt%) by potentiodynamic polarization. The rate of oxide dissolution was determined from the plateau current density observed in the electropolishing region of the IV curve; i.e. where the growth and dissolution rates of the anodic oxide film are equal. The IV curves of silicon are reminiscent of a corrosion process control by the dissolution of a salt film in which the rate of reaction is controlled by the removal of dissolved products away from the surface rather than reactants to the surface as previously proposed. For the silicon anodic oxide films this can be by either mass transport or further chemical reaction with HF species in solution. It is shown that this means the dissolution rate should be described by: Dissolution rate = D K sp [ HF ] 2 δ + k A K sp [ HF ] 6 This relationship is shown to hold for the whole concentration range investigated. Because hydrofluoric acid is a weak acid this rate equation converts to a cubic equation when written in terms of the total HF concentration as opposed to only the HF species, but in this form the connection with the dissolution mechanism is lost.

A DC magnetron is used to sputter highly conductive ITO on the surface of porous silicon to form LEDs that not only emit the usual red-orange light in one bias direction, but stable white light when biased in the opposite direction. The direction of the bias required for white light emission depends on whether p- or n-type silicon is used. The white light is clearly visible to the naked eye and stable for >2 h of continuous operation. The likely source of the white light emission is from the intra- or inter-band transitions of hot carriers generated in an avalanche process.

The electrodeposition of ZnO nanowire arrays from nitrate-based solutions was systematically studied as a function of electrodeposition parameters such as the concentration of zinc and nitrate ion precursors, applied current and charge. A model based on the local concentrations of Zn2+ and OH−, generated from the electrochemical reduction of NO3−, is proposed to explain the growth mechanism of ZnO nanowires. The ratio between OH− production and Zn2+ diffusion rates is identified as a crucial parameter, determining the nanowire growth regime and therefore the nanowire dimensions. As a result of the model and using NaNO3 as an additional source of NO3−, the versatility of ZnO deposition was enhanced in comparison with the deposition from sole Zn(NO3)2 solutions. Arrays of large aspect ratio (∼450) ZnO nanowires were successfully obtained at growth rates compatibles with large-scale production. The obtained ZnO nanowire arrays were characterized and analyzed by field emission scanning and transmission electron microscopies, X-ray diffraction, X-ray photoemission and optical spectroscopies.

AISI 416 is a high sulphur martensitic stainless steel with elliptical shaped sulphide inclusions over 2 μm in length. After laser melting the sulphide inclusions became spherical and reduced in size to below 0.5 μm in diameter. SEM investigations showed that the total number of inclusions increased dramatically and it was calculated that the total volume of sulphur in the stainless steel had not changed during the laser treatment. The pitting potential was increased by over 200 mV with an inverse linear dependency on the average inclusion size. The frequency of metastable pitting events decreased by a factor of 100.

The effects of fluoride concentration, anodization temperature, and anodization applied potential difference on the formation and dimensions of the titania nanotubes in ethylene glycol/water systems were investigated. It was found that fluoride concentration and anodization temperature were the two critical parameters for controlling the nanotube formation whilst anodization applied potential difference mainly contributes to tuning the dimension of the nanotubes. Electrolytes containing a low fluoride concentration are beneficial for initiating nanotube formation, whilst a higher anodization temperature is helpful to the rapid growth of the nanotubes. It is shown that the current–time curve obtained during the anodization can be used as an effective tool to predict the morphology of titania nanotubes. A model based on the competition between electrochemical oxidation of the titanium and chemical dissolution by fluoride ions is developed to explain the experimental observations.

Surface plasmon resonance from noble metal nanoparticles is a promising way to improve the efficiencies of silicon based photodiodes and solar cells. Electroless plating is an extremely simple technique for producing such metallic nanoparticles. It is found that the deposition of gold on Si photodiodes occurs as chains that drastically reduce the photodiodes conversion efficiency. However, silver deposits as nano-islands that are efficient SPR centers, which improve the performance of Si photodiodes in the visible region; as measured by both IPCE and I–V curves. The greatest improvement observed was a 3.5% increase in Jsc under solar irradiation. Although this improvement is lost upon annealing it can be regained by a further treatment in acidified HAuCl4. Possible explanations for these latter two behaviors are proposed.

Calcium phosphate coatings, in particular synthetic hydroxyapatite, are applied to the surfaces of titanium and its alloys so as to improve the biocompatibility and biological performance. Currently, plasma spraying is the clinically accepted technique for the deposition of calcium phosphate onto titanium. Electrochemical cathodic deposition is emerging as an alternative technique due to it being a nonline-of-sight technique. In this present study, it is demonstrated that increased thickness, crystallinity and adhesion of calcium phosphate coating on titanium is achieved by periodic pulsed low current densities compared to a constant current deposition method. It is believed that the “off” part of the AC deposition cycle gives the calcium and phosphate ions in the bulk solution sufficient time to diffuse to the titanium's surface maintaining more favourable conditions for HA growth. Unfortunately, although pulsed deposition at high current densities is able to produce thick coatings it cannot avoid problems associated with hydrogen bubbles and thus both AC and DC films deposited at high current densities have low crystallinity and poor adhesion.

To improve on the biological performance of titanium and its alloys hydroxyapatite coatings are applied to the surface. Although plasma spraying is currently the clinically accepted deposition technique, it has drawbacks including being a line-of-site method which greatly limits its uses for coating either irregular-shapes or the low elastic moduli porous materials and metallic sponges now being developed for implants. Electrochemical cathodic deposition is an alternative technique but this also has disadvantages, mainly the crystallinity of the deposited hydroxyapatite and its adhesion to the substrate. In the present study it is demonstrated that increased adhesion and crystallinity are obtained by either pre-treating the Ti substrate with NaOH followed by a heat treatment at 600 °C or the addition of H 2 O 2 to the electrolyte. The increased adhesion is believed to result in the former case from the development of a titanate binding layer. In the latter case the local alkaline conditions required for deposition are obtained from the reduction of the peroxide, thereby negating the need to evolve hydrogen that can damage the film. Rotating the substrate at low revolutions is also beneficial for adhesion however; at high rotation rates bulk precipitation is favoured over film formation.

The role that applied potential has in controlling the properties of porous silicon formed on highly conductive p-type silicon in diluted HF has been investigated by studying the photoluminescence characteristics along the current–voltage curve and using high resolution transmission electron microscopy (HRTEM) evidence to support the conclusions drawn. A dramatic decrease in the average nanocrystal size was found to take place after the etching current density switched from an exponential dependence on the applied potential to a linear relationship. Importantly this event occurred prior to reaching the Ups potential (usually consider the onset of electropolishing). This rapid decrease in particle sizes has been explained in terms of the partial formation of an oxide film. The presence of oxygen terminated porous silicon allows a trapped exciton states model to be invoked, which removes the quantum confinement restrictions on the minimum particle size. Support for the presence of a partial oxide prior to Ups comes from both FTIR measurements and previous literature related to the location of the flat-band potential. © 2008 Elsevier Ltd. All rights reserved.

Combined ion beam irradiation and electrochemical etching of silicon has been used to pattern light emitting porous silicon. A highly focused beam of helium ions is made to scan across a 4 Ω cm resistivity silicon in a predefined manner. As the ion beam penetrates the sample, it induces lattice damage and increases the local resistivity of the material. This slows down the rate of porous silicon formation, so that a thinner porous layer is formed at the irradiated regions. In this work, the photoluminescence properties of the irradiated porous silicon are studied as a function of dose. The porous silicon is then removed to reveal the underlying irradiated structure. The decrease in thickness of porous silicon with dose is correlated with the observed change in photoluminescence properties.

By employing microcavity (MC) techniques, the broad spectral band and wide emission angle of photoluminescence from porous silicon (PSi) can be narrowed, directed and tuned in PSi microcavities. The microcavity structure is formed with a porous silicon active layer sandwiched between two Bragg reflectors. We have characterised the optical properties of the porous silicon multilayer structures. A number of Bragg reflectors and Fabry–Perot optical microcavities are fabricated with tuning of emission wavelengths over a wide range in heavily doped p-type silicon. The optical properties of these microstructures were investigated using reflectivity and photoluminescence measurements at different temperatures. This paper reports the ability of focussed 2 MeV proton beam irradiation to controllably blue shift the resonant wavelength of porous silicon microcavities in heavily doped p-type wafers. Using this process wafers are patterned on a micrometer lateral scale with microcavities tuned to different resonant wavelengths, giving rise to high-resolution full-colour reflection images over the full visible spectrum. � 2007 Elsevier B.V. All rights reserved.

It has long been accepted that manganese sulphide favours pitting on stainless steels. However, there are different standpoints on the most important mechanism for pit initiation; due to dissolution of sulphide inclusions, chromium depletion around the inclusion or mechanical rupture of the passive film by metal chlorides. Analysing the pitting potential and metastable pitting rates on different grades of stainless steels has rationalised the effect of sulphide content on pitting corrosion resistance. In situ atomic force microscopy (AFM) has been used in conjunction with conventional electrochemical techniques for imaging real time pit initiation events.

The formation and breakdown of the passive films on stainless steels are mainly controlled by ionic and electronic transport processes. Both these processes are in part controlled by the electronic properties of the oxide film. Consequently, it is vital to gain a detailed perception of the electronic properties of the passive films together with structural and compositional information for a comprehensive understanding of mechanisms behind passivity and localised corrosion. As a step towards this goal the passive films formed on two main austenitic stainless steels AISI 316L and AISI 304L in borate solution were characterised by in situ Raman spectroscopy and photocurrent spectroscopy coupled with electrochemical measurements. This revealed the formation of an Fe-Cr spinel as the dominant constituent in the passive films with more Cr enrichment in the oxide film on 316L than that of 304L. Bandgap readings and semiconductivities of the two stainless steels suggested that three different applied potential regions existed; 800 mV(SCE) to 300 mV(SCE), 200 mV(SCE) to −300 mV(SCE) and below −500 mV(SCE).

The influence of dissolved oxygen on titanium oxide film growth at various sweep rates was explored for both pure titanium and a titanium alloy. The results showed that the dissolved oxygen becomes only significant when the sweep rate is sufficiently low, but which can be neglected in the case of enough high sweep rates. It reasonably assumes that there is no adequate time for oxygen to move to the anodic surface when the sweep rate is sufficiently high so that the role of oxygen becomes insignificant. However, the situation was found to be different when the anodic oxide film was growing at a sufficiently low sweep rate dynamically. This is because the reduction of dissolved oxygen in the solution occurs and produces an additional current, which opposes the oxide growth current produced by adsorption and subsequent charge reaction.

The nature of the anodic oxide film that forms on titanium on titanium in 0.9% NaCl has been investigated using a wide range of techniques. A linear relationship was found between the critical current density required for passivation of titanium in 0.9% NaCl and the sweep rate. Anodic oxide films formed on titanium in 0.9% NaCl appear to consist of two layers, an inner compact layer, the growth of which continues to follow a high field growth law, and a porous less protective outer porous layer. XPS and XRD indicated that passive films on titanium consist mainly of TiO2. However, hydroxides and lower oxides are also present, especially in rapidly grown films. XRD data indicated that in 0.9% NaCl the anodic oxide film is formed through the preferential removal atoms in the plane of (0 0 2) in the course of electrochemical reaction. A model based analysis XPS spectra was proposed to explain the growth rate dependence of the degree of protection offered by anodic oxide films on titanium. XPS clearly demonstrated the present of Ti(III) and Ti(II) cations in the passive film. This is strong evidence that cation migration more likely dominates over anion migration in the growth mechanism of anodic oxide film. XPS data also revealed that the concentrations of Ti(III) and Ti(II) species within the oxide films increased as the oxide/metal interface was approached.

This report describes how proton beam writing can be used to produce direct write, high resolution three dimensional structures on the nano and micron scales in semiconductor materials such as p-type (1 0 0) bulk silicon and gallium arsenide. The lattice damage caused by the proton irradiation increases the electrical resistance of the semiconductors resulting in a raised structure of the scanned area after an electrochemical etch. Advances in this field over the past few years and its relevance to future technology mean that it is now a powerful contender for direct write technology for future nodes 45 nm and below.

The ability to directly pattern the surface of semiconductor wafers using very accurately controlled fluences of finely focused high-energy ion beams has opened up new research directions for the fabrication of a variety of high-aspect ratio, multi-level microstructures in silicon. A beam of hydrogen or helium ions, focused to 50–100 nm in a nuclear microprobe, is used to selectively damage the semiconductor lattice in the irradiated regions. A higher beam fluence at any region produces a higher damage concentration, so by pausing the focused beam for different times at different locations, any pattern of localized damage can be built up in the material. This damage acts as an electrical barrier during subsequent formation of porous silicon by electrochemical etching. This enables local modification and control of the properties of the porous silicon formed by ion irradiation, resulting in patterned porous silicon. If the etched sample is immersed in potassium hydroxide, the unirradiated regions are preferentially removed, leaving a copy of the patterned area as a micromachined three-dimensional structure. The fundamental mechanisms involved in the creation of such porous and silicon microstructures are discussed here.

We describe a novel technique for silicon microfabrication based on energetic mega-electron-volt (MeV) helium irradiation and subsequent electrochemical etching. The ion-induced damage in the irradiated regions slows down the porous silicon formation during electrochemical etching, producing a raised microstructure after cleaning in diluted potassium hydroxide solution. The thickness of the porous silicon layer formed depends on the accumulated fluence at each scan point. A relationship between the irradiated fluence and feature height is investigated on a p-type [1 0 0] silicon with a resistivity of 0.03 Ω cm using focused 2 MeV helium beam. We use this relationship to micromachine multilevel structures with a single focused helium beam energy.

The temperature at which silicon is electrochemically etched has been found to influence the structure and photoluminescence properties of porous silicon. Decreasing the temperature increased both the current efficiency of the dissolution process and the porosity of the resulting porous layer. Furthermore, a blue-shift was observed in the photoluminescence indicating that the decreased temperature allowed smaller nanocrystals to be formed. An analysis of temperature dependence of the pore initiation and propagation models currently available in the literature failed to yield a satisfactory explanation for the decrease in the average size of the nanocrystals indicated by the results presented in the present paper. Therefore it was proposed that at lower temperature smaller nanocrystals are stabilized due to a combination of their reduced solubility and the increased viscosity of the diffusion layer that leads to a higher localized concentration of silicon ions, thereby allowing smaller nanocrystals to be in equilibrium with their surroundings. The fact that previous authors did not observe blue-shifting highlights the importance of the composition of the etching solution in controlling the quality of the porous silicon produced.

Porous titanium has mechanical advantages over its solid counterpart, especially for use in surgical implants, however, its corrosion resistance is not as good. The relative stability of various oxide films on both porous and solid titanium was thus investigates. The point of initial failure of the oxide films on porous titanium was found to be within the depths of the pores. It is also postulated that galvanic coupling to the outer surface, via a mechanism akin to crevice corrosion, may promote the rapid dissolution in the pores. Preliminary, results suggest that thermal oxides offer better corrosion protection to porous titanium than anodic oxides.

The corrosion behaviour of melt-spun amorphous Mg 82 Ni 18 and Mg 79 Cu 21 ribbons have been investigated using hydrogen evolution testing in 3% (0.51 M) solution and electrochemical techniques in 0.01 M NaCl. Open circuit potential measurements showed that the as-spun alloys were more electrochemically noble than that of pure Mg. Dissolution rate measurements showed that the corrosion rates of the partially crystallised samples were lower than that of the fully amorphous samples. Potentiodynamic polarisation results showed that although there was ennoblement in the corrosion potential E corr , the corrosion current density i corr was higher for the melt-spun alloy than for pure Mg. Comparison of the polarisation responses for the partially crystallised samples in 0.01 M NaCl showed that the passivation current density i p was lower than for the as-spun amorphous sample. With prolonged heat treatment duration, fully crystallised samples exhibit a marked deterioration of corrosion resistance. The corrosion results have been discussed and correlated with the progress of crystallisation processes by means of XRD and TEM.

The commercial application of rare earth magnets has been in part held back by their poor corrosion resistance. As part of e!orts to overcome this problem two types of nickel coatings were electroplated on the surface of Nd 2 Fe 14 B substrates, one from an acidic plating solution and the other from an alkaline solution. The corrosion characteristics of both coatings were evaluated both by electrochemical potentiodynamic polarisation and by physical exposure to high-humidity environments. The results showed that both coatings enhanced the corrosion resistance of substrate. However, both the degree of protection a!orded by the coating and the strength of its adhesion to the substrate strongly depended on the chemical composition of the original plating solution. The coating plated from the acidic solution provided a high degree of protection against both aqueous and atmospheric corrosion, whilst that plated from the alkaline solution behaved only marginally better than the bare substrate. It was postulated that the poor performance of the coatings plated from the alkaline bath could have been due to the spontaneous formation of a passive oxide "lm between the Nd 2 Fe 14 B substrate and the nickel coating. ( 2001 Elsevier Science B.V. All rights reserved.

UV–VIS spectroscopy, electron spin resonance spectroscopy (ESR) and conductivity measurements have been used to characterise the interactions between methanol vapour and polyaniline. The data indicates that the methanol hydrogen bonds to two locations on the emeraldine base such that it is able to form a bridge between the polymer chains causing twisting. This prevents the few remaining polarons from moving beyond a few monomer units, effectively localising them, giving rise to a decrease in conductivity and an increase in absorption at ca. 1.6 eV. However, in the case of the emeraldine salt protonation of the quinoid moieties’ nitrogen restricts the number of potential hydrogen bonding sites, preventing the methanol from forming a bridge between two polymer chains. At the same time, the high conductivity of the emeraldine salt allows the charge that is transfer to the polyaniline, as a result of the hydrogen bonding to the methanol, to be distributed along the conjugated chain in the form of polarons and bipolarons.

Both potentiostatically and galvanostatically controlled electrochemical impedance spectroscopy were used to show that the impedance obtained from passivated titanium electrodes is dominated by the capacitance of the space-charge layer. As a result neither the thickness of the oxide layer nor its rate of thinning can be readily determined from impedance measurements. Furthermore, it appears that the corrosion rates of passive metals determined by EIS may significantly overestimate the true rate of dissolution. No significant differences were observed between the impedance data obtained from the galvanostatic and the potentiostatic measurements.

The electrochemical behavior of two kinds of Cu–Al–O coatings prepared by CVD at different temperatures was monitored anodically and cathodically in a solution of 0.1M NaCl. The results show that the coating achieved at 700°C has lower resistance against anodic polarization than the coating achieved at 800°C. Alternatively, the former exhibits rather higher susceptibility to hydrogen evolution than the latter. The atomic hydrogen evolves at the surface of the coating and penetrates deeply into the coating resulting in initiation of hydrogen bubbles. With the increase of hydrogen pressure in bubbles, they grow continuously leading to hydrogen-induced cracking ultimately at the moment when the hydrogen pressure reaches a critical value. Essentially, the susceptibility of hydrogen-induced cracking for coatings should be attributed to the temperature that prevailed during CVD. Higher temperature can evidently enhance the resistance against hydrogen-induced cracking.

Porous titanium is a popular surgical implant material. Its low elastic modulus encourages regular bone growth, whilst its porosity enables bone in-growth. Unfortunately, porous titanium has poor friction and wear properties. The addition of graphite, to lower the friction coefficient and titanium carbide to increase wear resistance, could produce a multi-component material that overcomes these disadvantages. However, polarisation measurements revealed that the graphite causes an increase in the titanium’s corrosion rate. Therefore, the extent that graphite can be used in porous titanium biomaterials will be a compromise between the benefits of improved friction properties against the disadvantage of increased corrosion.

The effect of heat treatment on the corrosion resistance of rapidly solidified amorphous Mg 82 Ni 18 ribbons has been studied by hydrogen evolution testing in 3% NaCl solution and potentiodynamic scanning in 0.01 M NaCl solution. The results show that the dissolution rate for the partially crystallised sample obtained after 4 min heat treatment at 160°C, was lower in comparison to the fully crystalline or fully amorphous samples. Comparison of the polarisation responses of the samples showed that, for the partially crystallised samples, passivation current density was lower than that of the fully amorphous sample, although passivation behaviour was weaker. With prolonged heat treatment duration, fully crystallised samples exhibited a marked deterioration of corrosion resistance. The corrosion results were discussed and correlated with the progress of crystallisation processes by means of XRD, DSC, TEM and SEM.

The mechanisms involved in the (photo)dissolution of silicon in fluoride solutions are discussed. Several methods, including intensity modulated photocurrent spectroscopy, in situ ir spectroscopy, rotating ring disc voltammetry and ellipsometry, have been used to examine the anodic dissolution process. The valence state of the dissolving silicon has been determined under different conditions, and the optical properties of the surface have also been characterized. The generation of hydrogen has been linked in the case of n-Si to intensity dependent photocurrent multiplication, and in the case of p-Si it has been related to different etching regimes. The current oscillations observed during the anodic dissolution of p-Si are also discussed.