Factors that influence the surface potential decay on a thin film of polyethylene terephthalate (PET)

The initial potential at the surface of the sample, as well as the temperature and the relative humidity of the ambient air are known to influence the surface-potential decay characteristics of corona-charged thin insulating films. The aim of the present work is to demonstrate the effectiveness of the Experimental Design methodology for evaluating the effects of these factors. Thus, a full factorial experimental design was carried out on a thin film of polyethylene terephthalate (thickness: 0.5 mm; surface: 50 mm × 50 mm). A negative corona discharge produced in a needle–grid–plate electrode system was employed to charge the surface of the film samples. The variation domains for the three factors were respectively: ?1000 V to ?1800 V; 25 to 55 °C; 50% to 80%. The surface-potential decay process was characterized by two output variables: the time needed for the potential to reduce to respectively 50% and 10% of the initial value. It was found that the former is more affected by the temperature, while the latter is more sensitive to the variation of the relative humidity.     

In situ electrochemical STM study of platinum nanodot arrays on highly oriented pyrolythic graphite prepared by electron beam lithography

Model electrodes consisting of platinum dots with a mean diameter of (30 ± 5) nm and heights of 3–5 nm upon highly oriented pyrolytic graphite (HOPG) were prepared by electron beam lithography and subsequent sputtering. The Pt nanodot arrays were stable during scanning tunnelling microscopy (STM) measurements in air and in sulphuric acid electrolyte, indicating the presence of “anchors”, immobilising the dots on the HOPG surface.Electrochemical STM was used to visualise potential induced Pt, carbon and Pt-influenced carbon corrosion in situ in 0.5 M sulphuric acid under ambient conditions. Potentiostatic hold experiments show that the Pt dots start to disappear at electrode potentials of E > 1.4 V vs. SHE. With increasing time and potential a hole pattern congruent to the original dot pattern appears on the HOPG basal planes. Corrosion and peeling of the HOPG substrate could also be followed in situ.Dissolution of Pt dots appears to be accelerated for potential cycling experiments compared to the potential hold statistics.     

Measurements and analysis of the acoustic signals produced by partial discharges in insulation oil

This paper focuses on the frequency analysis of acoustic signals produced by partial discharges (PDs) in insulation oil and the positioning of the PD occurrence for application in the diagnosis of oil-insulated transformers. Three types of electrode systems; the needle–plane, the plane–plane, and the wire–wire structures were assembled to simulate the partial discharge in insulation oil. A low-noise amplifier and a de-coupler were designed to detect the acoustic signal with high-sensitivity. The frequency ranges of the acoustic signal were 60–270 kHz in the needle–plane electrode system, 45–250 kHz in the plane–plane electrode system, and 50–180 kHz in the wire–wire electrode system. Their peak frequencies were 145 kHz, 118 kHz and 121 kHz, respectively.The position of the PD occurrence was calculated from the time difference of arrival (TOA) using three acoustic emission (AE) sensors. The position was found within a 1% error in the experimental set-up.     

2-D corona field computation in configurations with ionising and non-ionising electrodes

An efficient method is proposed for the computation of the electric field strength and of the space-charge density in configurations of at least three ionising and non-ionising electrodes. The physical model is derived under the assumptions commonly accepted for the study of corona fields. The mathematical model makes use of a conformal mapping that converts the actual boundary-free field zone into a rectangular domain with well-defined boundary conditions. The finite-difference method is then used for solving the differential equations that describe the ionic space-charge and electric field distribution. The computational procedure was employed for studying the simple case of the drift zone of the corona discharge generated between a so-called dual electrode and a grounded plate. The dual electrode consisted of an ionising wire (diameter 0.22 mm) located at 20 mm from a tubular metallic support (diameter 25 mm). The computed current–voltage characteristic and current density distribution at the surface of the collector plate were in good agreement with the experimental data obtained for this combined corona–electrostatics electrode arrangement.     

Comparison of characterization methods in high frequency sonochemical reactors of differing configurations

The aim of this study was to compare different characterization methods in order to evaluate the sonochemical efficiency of a cavitational reactor. The selected characterization methods were calorimetry and dosimetry based on potassium iodide oxidation or nitrite and nitrate ion formation. The effects of experimental parameters on physical and chemical effects of ultrasound were quantified with two transducers at a frequency of 366 kHz. The studied factors comprised temperature (16–28 °C), acoustic power (6–38 W), power density (4–61 W L^?1) and reactor configuration (D_{reactor 1} = 65 mm, D_{reactor 2} = 102 mm). Spectrophotometry was compared to ionic chromatography as a method to quantify nitrite and nitrate ions. Spectrometry was shown to be as representative as ionic chromatography. The reaction system based on the formation of both nitrite and nitrate ions was demonstrated to be as reliable as a potassium iodide dosimeter. The representativity of calorimetry was limited since part of acoustic energy was assumed to be used in the chemical reactions observed by dosimetry. Similar sonochemical efficiencies resulted from an increase of sonified surface (D_{reactor 1} = 65 mm vs. D_{reactor 2} = 102 mm) coupled to a 2-time decrease in power density at a constant emitting surface. The effect of emitting-to-sonified surface area ratio on the acoustic field was apparently limited by the height of the liquid.     

A STM point-probe method for measuring sheet resistance of ultrathin metallic films on semiconducting silicon

We report a novel approach for distinguishing surface, bulk and space–charge layer conductivities of metalized semiconductor surfaces. The method employs current injection from the tip of a scanning tunneling microscope and a spring-contact electrode placed on the surface in situ in UHV. The current–voltage behavior is sensitive to polarity in a way that distinguishes the surface contribution. The method is illustrated for the Si(1 1 1) 7 × 7 metallized surface and dependence of the conductivity with changing thickness of silver overlayers.     

Formation of reactive species in gliding arc discharges with liquid water

The effects of gas composition on gliding arc (glidarc) electrical discharge reactors with pure water have been studied. The glidarc reactors utilized AC electrical discharges with two different electrode configurations. In one case a set of two stainless steel electrodes connected to a single power supply was placed in the gas phase over the liquid surface (power=250–300 W, maximum voltage=12 kV). The second experimental arrangement utilized a reactor with a set of three stainless steel electrodes supplied by two identical high-voltage transformers, where the electrodes were placed over the water surface or with the water sprayed directly in the plasma formed between the electrodes (power=500–600 W, maximum voltage=12 kV). The variation of pH and conductivity and the formation of hydrogen peroxide, ozone, nitrate, and hydrogen were measured. The effects of the type of gas, including pure oxygen, pure nitrogen, and dry air, were determined.     

Application of indium tin oxide (ITO) thin film as a low emissivity film on Ni-based alloy at high temperature

Indium tin oxide (ITO) films as the low emissivity coatings of Ni-based alloy at high temperature were studies. ITO films were deposited on the polished surface of alloy K424 by direct current magnetron sputtering. These ITO-coated samples were heat-treated in air at 600–900 °C for 150 h to explore the effect of high temperature environment on the emissivity. The samples were analyzed by X-ray diffraction (XRD), SEM and EDS. The results show that the surface of sample is integrity after heat processing at 700 °C and below it. A small amount of fine crack is observed on the surface of sample heated at 800 °C and Ti oxide appears. There are lots of fine cracks on the sample annealed at 900 °C and a large number of various oxides are detected. The average infrared emissivities at 3–5 μm and 8–14 μm wavebands were tested by an infrared emissivity measurement instrument. The results show the emissivity of the sample after annealed at 600 and 700 °C is still kept at a low value as the sample before annealed. The ITO film can be used as a low emissivity coating of super alloy K424 up to 700 °C.     

Combined XPS,electrochemical and Kelvin probe measurements of NaY zeolite

In the present study X-ray Photoelectron Spectroscopy (XPS) combined with in situ electrochemical and Kelvin probe measurements was used in order to get a deeper insight on the mechanism of the cation transport through NaY zeolite and the charge transfer through the Au electrode/zeolite interface. It is shown that by imposing a potential gradient across the NaY powder which is sandwiched between two electrodes, Na⁺ ions can be electrically transferred to or from the Au working electrode area, following the direction of the applied potential between the two electrodes. Two peaks corresponding to sodium species were detected by means of in situ XPS investigation during potential application. The first peak of Na1s photoelectrons with binding energy at 1072.2 ± 0.2 eV is attributed to Na adsorbed on the grounded Au electrode with its coverage remaining unchanged upon potential imposition. The second peak is directly associated with Na present in the zeolite and upon potential application its binding energy varies proportionally with the variation of the surface potential measured by Kelvin probe. Upon varying the potential from − 4 to + 4 V between the working and counter electrode, the Na⁺ concentration decreases by ca30% at the Au/zeolite interface. However the invariant amount of Na on the Au electrode under vacuum shows that the variation in Na⁺ concentration is not due to ionic transfer onto the Au surface but instead Na⁺ accumulation can be assumed at the Au/zeolite interface. On the other hand, current or potential application under O₂ atmosphere promotes the electrocatalytic reaction of Na⁺ towards the formation of Na₂O on the Au electrode surface.     

Critical conditions of hydrogen-air detonation in partially confined geometry

This work presents the results of the large scale experiments with detonation propagating in hydrogen–air mixtures in partially confined geometries. The main aim of the work was to find the critical conditions for detonation propagation in semi-confined geometries with uniform and non-uniform hydrogen–air mixtures. The experimental facility consisted of rectangular 9 × 3 × 0.6 m channel open from the bottom, acceleration section and test section, safety vessel, gas injection and data acquisition system. Sooted plates technique was used as a witness of the detonation. The rectangular channel was placed in a 100 m³ safety vessel. For uniform hydrogen–air mixtures experiments with four different channel heights h were performed: 8, 5, 3 and 2 cm. The critical hydrogen–air mixture height h* for which the detonation may propagate in a layer is close to the 3 cm which corresponds to approximately three detonation cell sizes. For non-uniform hydrogen–air mixture with hydrogen concentration slope equal approximately ?1.1%H₂/cm the critical hydrogen concentration at the top of the layer is approximately equal 26% and the mean detonation layer height is close to the 8.5 cm corresponding to the hydrogen concentration at the bottom of the layer approximately equal 16–17%.     

Atomic and nanostructures of monolayer c(2 × 2)NiN on Cu(0 0 1)

Structures of monolayer nickel nitride (NiN) on Cu(0 0 1) surface are studied by X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Formations of Ni–N chemical bonds and NiN monolayer at the surface are confirmed by XPS on the N-adsorbed Cu(0 0 1) surfaces after Ni deposition and subsequent annealing to 670 K. A c(2 × 2) structure is always observed in the LEED patterns, which is a quite contrast to the (2 × 2)p4g structure observed usually at the N-adsorbed Ni(0 0 1) surface. Atomic images by STM indicate the mixture of Ni–N and Cu–N structures at the surface. Density of the trenches on the N-saturated surface decreases and the grid pattern on partially N-covered surfaces becomes disordered with increasing the Ni coverage. These results are attributed to the decrease of the surface compressive stress at the N-adsorbed Cu surface by mixing Ni atoms.     

Investigation of optimum condition in oxygen gas-assisted laser cutting

Laser cutting characteristics including power level and cutting gas pressure are investigated in order to obtain an optimum kerf width. The kerf width is investigated for a laser power range of 50–170 W and a gas pressure of 1–6 bar for steel and mild steel materials. Variation of sample thickness, material type, gas pressure and laser power on the average cut width and slot quality are investigated. Optimum conditions for the steel and mild steel materials with a thickness range of 1–2 mm are obtained. The optimum condition for the steel cutting results in a minimum average kerf width of 0.2 mm at a laser power of 67 W, cutting rate of 7.1 mm/s and an oxygen pressure of 4 bar. A similar investigation for the mild steel cutting results in a minimum average kerf width of 0.3 mm at the same laser power of 67 W, cutting rate of 9.5 mm/s, and an oxygen pressure of 1 bar. The experimental average kerf is about 0.3 mm, which is approximately equal to the estimated focused beam diameter of 0.27 mm for our focusing lens (f=4 cm and 100 W power). This beam size leads to a laser intensity of about 1.74×10⁹ W/m² at the workpiece surface. The estimated cutting rate from theoretical calculation is about 8.07 mm/s (1.0 mm thickness and 100 W power), which agrees with the experimental results that is 7.1 mm/s for 1.0 mm thickness of mild steel at the laser power of 88 W.     

Ultrasound-aided synthesis of gold-loaded boron-doped graphene quantum dots interface towards simultaneous electrochemical determination of guanine and adenine biomolecules

To acquire substantial electrochemical signals of guanine-GUA and adenine-ADE present in deoxyribonucleic acid-DNA, it is critical to investigate innovative electrode materials and their interfaces. In this study, gold-loaded boron-doped graphene quantum dots (Au@B-GQDs) interface was prepared via ultrasound-aided reduction method for monitoring GUA and ADE electrochemically. Transmission electron microscopy-TEM, Ultraviolet–Visible spectroscopy-UV–Vis, Raman spectroscopy, X-ray photoelectron spectroscopy-XPS, cyclic voltammetry-CV, and differential pulse voltammetry-DPV were used to examine the microstructure of the fabricated interface and demonstrate its electrochemical characteristics. The sensor was constructed by depositing the as-prepared Au@B-GQDs as a thin layer on a glassy carbon-GC electrode by the drop-casting method and carried out the electrochemical studies. The resulting sensor exhibited a good response with a wide linear range (GUA = 0.5–20 μM, ADE = 0.1–20 μM), a low detection limit-LOD (GUA = 1.71 μM, ADE = 1.84 μM), excellent sensitivity (GUA = 0.0820 µAµM⁻¹, ADE = 0.1561 µAµM⁻¹) and selectivity with common interferents results from biological matrixes. Furthermore, it seems to have prominent selectivity, reproducibility, repeatability, and long-lasting stability. The results demonstrate that the fabricated Au@B-GQDs/GC electrode is a simple and effective sensing platform for detecting GUA and ADE in neutral media at low potential as it exhibited prominent synergistic impact and outstanding electrocatalytic activity corresponding to individual AuNPs and B-GQDs modified electrodes.     

Non-adiabaticity in surface chemical reactions

Chemical reactions at surface may dissipate energy exciting electron-hole pairs in the metal substrate. Direct detection of the chemically induced hot charge carriers may be achieved by measuring the tunnel current in Ta–TaOx–Au tunnel junctions when the Au top electrode is exposed to an atomic hydrogen beam. A current of 1 nA cm^?2 was observed during a hydrogen exposure with a flux of 0.1 ML s^?1. The transient is related to the reaction kinetics and allows us to identify the elementary reaction steps causing the electronic excitations which are monitored by the observed current. Using Pt as top electrode material a markedly different transient is observed. Applying a bias voltage to the sensor allows spectroscopy of the electronic excitations. The experiments provide detailed insights into the non-adiabaticity of various reaction steps at a surface.     

Underwater current distribution induced by spark discharge on a water surface

Discharge current distributions generated underwater by spark discharges from the atmosphere to free water surfaces with conductivities in the range 0.07–10.0 S/m were investigated using a laboratory-scale electrode system consists of a discharge electrode and nine underwater grounding electrodes. Discharge emission on the water surface, which shows significant change with slight increase in conductivity, affects the current distribution in the water. The electric potential of the water surface also changes significantly with slight increase in conductivity. Results of numerical calculations of the underwater discharge current based on the water surface potential agree with the experimental results.     

Accuracy and efficiency of an infrared based positioning and tracking system for patient set-up and monitoring in image guided radiotherapy

An infrared based positioning and tracking (IPT) system was introduced and its accuracy and efficiency for patient setup and monitoring were tested for daily radiotherapy treatment. The IPT system consists of a pair of floor mounted infrared stereoscopic cameras, passive infrared markers and tools used for acquiring localization information as well as a custom controlled software which can perform the positioning and tracking functions. The evaluation of IPT system characteristics was conducted based on the AAPM 147 task report. Experiments on spatial drift and reproducibility as well as static and dynamic localization accuracy were carried out to test the efficiency of the IPT system. Measurements of known translational (up to 55.0 mm) set-up errors in three dimensions have been performed on a calibration phantom. The accuracy of positioning was evaluated on an anthropomorphic phantom with five markers attached to the surface; the precision of the tracking ability was investigated through a sinusoidal motion platform. For the monitoring of the respiration, three volunteers contributed to the breathing testing in real time. The spatial drift of the IPT system was 0.65 mm within 60 min to be stable. The reproducibility of position variations were between 0.01 and 0.04 mm. The standard deviation of static marker localization was 0.26 mm. The repositioning accuracy was 0.19 mm, 0.29 mm, and 0.53 mm in the left/right (L/R), superior/inferior (S/I) and anterior/posterior (A/P) directions, respectively. The measured dynamic accuracy was 0.57 mm and discrepancies measured for the respiratory motion tracking was better than 1 mm. The overall positioning accuracy of the IPT system was within 2 mm. In conclusion, the IPT system is an accurate and effective tool for assisting patient positioning in the treatment room. The characteristics of the IPT system can successfully meet the needs for real time external marker tracking and patient positioning as well as respiration monitoring during image guided radiotherapy treatments.     

A simple dye-sensitized solar cell sealing technique using a CO2 laser beam excited by 60 Hz AC discharges

Dye-sensitized solar cells (DSSCs) use two glass substrates (photo electrode and counter electrode) coated with fluorine-doped tin oxide (FTO) to harvest light into the cell and to collect electrons. The space between the photo electrode and the counter electrode are filled with a liquid type electrolyte for electron transfer into the cell. Therefore, an appropriate sealing method is required to prevent the liquid electrolyte leaking out. In this paper, a simple CO₂ laser beam with TEM₀₀ mode excited by a 60 Hz AC discharge was used to seal two glass substrates coated with FTO for the fabrication of DSSCs. The sealing technique improved the durability and stability of the DSSCs. The optimal conditions for the sealing of the DSSCs are related to the pin-hole diameter, the discharge current and the moving velocity of the target. Especially, the CO₂ laser beam is used as a heat source that is precisely controlled by the pin-hole, which plays an important role in adjusting its spot size. From these results, the maximum laser power was found to be 40 W at 18 Torr and 35 mA. In order to achieve the best sealing quality, the following parameters are required: a pin-hole diameter of 4 mm, input voltage of 10.73 kV, discharge current of 9.31 mA, moving velocity of 1 mm/s and distance from the target surface of 26.5 cm. Scanning electron microscope images show that the sealing quality obtained using the CO₂ laser beam is superior to that obtained using a hot press or soldering iron.     

Use of thermal imaging to characterize laser light reflection from thermoplastics as a function of thickness,laser incidence angle and surface roughness

Laser light reflection during the laser transmission welding (LTW) of thermoplastics has the potential to overheat and/or cause unintentional welding of adjacent features of the part being welded. For this reason, and in order to assess how much light is being absorbed by the transparent part (after measurement of the light transmitted through the transparent part), it is important to be able to quantify the magnitude and distribution of reflected light. The magnitude and distribution of the reflected light depends on the total laser input power as well as its distribution, the laser incidence angle (angle between the normal to the transparent part surface and the laser beam), the laser light polarization as well as the surface and optical properties of the transparent part. A novel technique based on thermal imaging of the reflected light was previously developed by the authors. It is used in this study to characterize the magnitude and distribution of reflected light from thermoplastics as a function of thickness (1–3.1 mm), laser incidence angle (20–40°) and surface roughness (0.04–1.04 μm). Results from reflection tests on nearly polished nylon 6 (surface roughness between 0.04 and 0.05 μm) have shown that, for the various thicknesses tested (1–3.1 mm), the total reflection was larger than the specular top surface reflection predicted via the Fresnel relation. From these observations, it is conjectured that, in addition to top surface reflection, the bulk and/or bottom surface also contribute to the total reflection. The results also showed that reflection decreased slightly with increasing thickness. As expected, for the p-polarized light used in this study, the reflection decreased with increasing angle of incidence for the range of angles studied. It was also found that when the surface roughness was close to zero and when it was close to the wavelength of the input laser beam (i.e. 940 nm), the reflectance values were close and reached a minimum between these two roughness values.     

Rechargeability improvement of δ-type chemical manganese dioxide with the co-doping of Bi and Ni in alkaline electrolyte

δ-MnO₂ with the doping of Ni and Bi was prepared through a simple chemical precipitation/oxidation method. Its structure was confirmed by the X-ray diffraction tests. The results of cyclic voltammetry and galvanostatic charge–discharge tests showed that both the doping of Bi and Ni benefited the electrochemical activity of the MnO₂ electrode. Compared to the un-doped electrode, the Bi-doped one showed larger discharge capacity and the Ni-doped one showed higher discharge potential and better cycleability. With the co-doping of 5 wt% Bi and 10 wt% Ni, the discharge capacity of the MnO₂ electrode reached 252 mA h g^?1 at a 0.2C rate and 116 mA h g^?1 at a 1C rate, respectively. Its capacity remained in 105 mA h g^?1 after 50 cycles at a 1C rate, but the capacity of a commercial electrolytic MnO₂ electrode was only 37 mA h g^?1.     

Microhardness of a dental restorative composite resin containing nanoparticles polymerized with argon ion laser

The objective of this study was to compare the microhardness of two resin composites (microhybrid and nanoparticles). Light activation was performed with argon ion laser 1.56 J (L) and halogen light 2.6 J (H) was used as control. Measurements were taken on the irradiated surfaces and those opposite them, at thicknesses of 1, 2 and 3 mm. To evaluate the quality of polymerization, the percentages of maximum hardness were calculated (PMH). For statistical analysis the ANOVA and Tukey tests were used (p ≤ 0.05). To microhybrid was shown that the hardness with laser was inferior to the hardness achieved with halogen light, for both the 1 mm and 2 mm. The nanoparticles polymerized with laser, presented lower hardness even on the irradiated surface, than the same surface light activated with halogen light. The microhybrid attained a minimum PMH of 80% up to the thickness of 2 mm with halogen light, and with laser, only up to 1 mm. The nanoparticles attained a minimum PMH of 80% up to 3 mm thickness with halogen light and with laser this minimum was not obtained at any thickness. Based on these results, it could be concluded that light activation with argon ion laser is contra-indicated for the studied nanoparticles.