Metal Spikes Research Articles

Degradation characteristics of insulation near aluminium foil edges inside dry‐type bushing cores under electrothermal compound stress

Insulation breakdown of dry-type valve-side bushing cores under electrothermal compound stress has become a key factor limiting the safe and stable operation of the converter transformer. Based on slices of the real bushing core, it is observed for the first time that fold, peeling off, and fracture defects exist near the aluminium (Al) foil edge, accompanied by many metal spikes with a curvature radius <4 μm. Coupled with a capacitor screen thickness of ∼2 mm, an electrical tree model is designed to simulate insulation defects near aluminium foil edges inside dry-type bushing cores, whose insulation degradation characteristics under electrothermal compound stress are investigated accordingly. The results show that high temperature significantly increases the dielectric loss heat energy density and Joule heat energy density, accelerating the insulation degradation near Al foil edges. The parallel crepe paper interface significantly accelerates the growth of electrical trees under AC-superimposed positive DC voltage, while this effect is not significant under AC voltage. As the crepe paper consists of wooden fibres of 10 μm diameter, the electrical trees tend to grow along interfaces between fibres and epoxy resin to form “feathery” electrical trees in epoxy resin-impregnated paper samples.

Economic and GHG emissions changes of aeration and gypsum application

Alternative pasture management strategies are needed to ensure long-term ecological and economical use of abundantly available poultry litter as a source of valuable nitrogen (N), phosphorus (P) and potassium (K). In combination with the common practice of broadcasting poultry litter and soil compaction from equipment and livestock traffic, pasture aeration offers the potential for added soil water penetration and reduced nutrient runoff by creating soil perforations ranging length from 5 to 15 cm using metal spikes that penetrate the soil to 15 cm depth. Also, the addition of gypsum can further reduce P runoff. We evaluate different pasture management scenarios that included gypsum application, spreading poultry litter, pasture aeration, or combinations thereof, to assess relative profitability, greenhouse gas (GHG) emission and nutrient runoff effects. Specifically, default values for nutrient runoff along with an evaluation framework as provided in decision support software, as attached, assist with the selection of field activities to perform to either enhance profitability by way of forage yield improvement or to estimate the cost of mitigating nutrient runoff or GHG emissions. Using Excel®’s VBA programming we develop a decision aid that collects relevant user-specific farm parameters and literature-based default values on nutrient runoff changes with the implementation of various practices to allow the user to conduct sensitivity analyses. A basic consequential life cycle assessment offers insight on expected greenhouse gas (GHG) mitigation potential by applying published GHG emission estimates associated with fuel and fertilizer use changes that were not calibrated in the field. A survey of producers that employed pasture aeration over a two year time period of free access to equipment was also conducted to at least capture some producer feedback. Results indicate that pasture aeration using rented equipment requires relatively little yield improvement (< 5%) to offer greater profit while reducing runoff. Given that pasture aeration is a time-intensive production practice, survey results are mixed in terms of producer willingness to adopt the practice. The tool lends itself to estimating operation-specific subsidies needed to encourage pasture aeration with the intent to reduce nutrient runoff, enhance forage yield, and thereby the feasibility of poultry litter application.

Late-Holocene diatom community response to climate driven chemical changes in a small, subarctic lake, Northwest Territories, Canada

The paleolimnological record of diatoms and climate, spanning the last 2800 years, was investigated in a small subarctic lake (Pocket Lake) that from AD 1948 to 2004 was contaminated by gold smelting waste. An age-depth model was constructed using a combination of 210Pb, 14C, and tephra to determine a 2800 year history of lake ontogeny (natural aging), biological diversity, and regional climate variability. Diatoms form six strong paleoecological assemblages over time in response to changes in local hydrological and sedimentological conditions (including metals). Selected environmental variables explained 28.8% of the variance in the diatom assemblages, with Fe, Ca, and sediment end member distribution being important indicators. The diatom assemblages correlated to the Iron Age Cold Epoch (2800–2300 cal BP), Roman Warm Period (2250–1610 cal BP), Dark Age Cold Period (1500–1050 cal BP), Medieval Climate Anomaly (ca. 1100–800 cal BP), and the Little Ice Age (800–200 cal BP). The disappearance of Staurosira venter highlights the change from the Iron Age Cold Epoch to the Roman Warm Period. After deposition of the White River Ash (833–850 CE; 1117–1100 cal BP), transition to circumneutral conditions was followed in tandem by a transition to planktic influenced communities. Ten discrete peaks of Cu, Pb, and Zn were observed and attributed to soluble mobility from catchment soils through enhanced seepage and spring snowmelt. The prominent metal spikes were aligned with increases in Brachysira neoexilis. Downward mobilization of arsenic and antimony from contaminated surficial sediments highlight the problem of post depositional industrial contamination of paleosediments. Results demonstrate that paleoclimatic changes in the region, modulated by solar radiation, impacted temperature and precipitation in the lake catchment, influencing temporal shifts in diatom ecology. Changes in diatom taxa richness provided valuable information on the relative influence of water quality (planktic taxa) and sediment input (benthic taxa). The diatom assemblage succession also provides evidence that natural aging over time has played a role in the ecological evolution of the lake.

Defensive Architecture Mapping: a case study in the city of Curitiba, Paraná, Brazil

Defensive Architecture Mapping: a case study in the city of Curitiba, Paraná, Brazil

Li Dendrite Nucleation from First Principles Perspective

Given the demands of modern society, current chemical energy storage needs significant improvement. Advanced battery technology research has focused on the use of Lithium metal anodes to increase performance for Li-ion, Li-sulfur and Li- air batteries. Unfortunately, the use of these anodes causes several problems for battery operation such as the formation of dendrites. In the cycling of lithium anodes, the lithium will be deposited in a way that lithium metal tendrils or spikes grow on the surface of the electrode. These dendrites can cause the short circuiting and other mechanical problems that hurt performance and can even lead to significant safety concerns. Researchers have been focusing counteracting dendrite growth and formation from an experimental and practical approach but there has been a lack in fundamental understanding of how lithium dendrites form and grow. We used first principles simulations to study the nucleation, growth and properties of lithium clusters to determine the basic principles that govern dendrites. By exploring the reduction chemistry with small clusters, general principles can be derived that will help intelligently guide experimental and other modeling research to better battery design. We found that the reduction of Li ions is highly favorable regardless of position on the nucleating cluster which indicates that other factors are more important to the direction of cluster growth like the electrostatic potential that corresponds to a given electronic density distribution. With this information, the evolution of lithium clusters was investigated to connect clusters to dendrites as well as the influence of a copper substrate and SEI species. These models provide a methodology that gives a base for further study of dendrite fundamentals that can be easily extended to engineer high performance battery technology.

Atomic-resolution Raman spectroscopy

By combining scanning probe microscopy, laser spectroscopy, and surface science, researchers have sharpened the spatial resolution of microspectroscopy to the angstrom level. The study demonstrates a way to record vibrational spectra from select regions within a single molecule and a technique for capturing images of that molecule’s modes of vibration (Nature 2019, DOI: 10.1038/s41586-019-1059-9). Raman spectroscopy is a powerful tool for probing molecular vibrations. It’s used commercially for quality and process control and in research settings to study molecular phenomena. But the Raman signal, produced by sample molecules interacting with light—often visible light from lasers—is weak, limiting the method’s sensitivity. Over 40 years ago, researchers discovered that Raman signals could be boosted by a factor greater than 1 million by adsorbing analyte molecules on rough metal surfaces, such as silver, patterned with microscopically sharp points. The metal spikes acted like antennas, amplifying the elec...

A Simple Electrostatic Device for Eliminating Tobacco Sidestream Smoke to Prevent Passive Smoking

An electrostatic apparatus was constructed to capture tobacco sidestream smoke. This apparatus consisted of a perforated polypropylene plate with metal spikes and a grounded metal net arrayed in parallel at a defined interval. Spikes were negatively charged to positively polarize the net and an electric field was formed between the opposite charges of the spike tips and the grounded net. Discharge from the spike tips occurred, which depended on the pole distance and the voltage applied to the spikes. At lower voltages (&lt;12.1 kV) that do not cause arc discharge from the tips, a corona discharge occurred with the generation of an ionic wind from the spiked plate to the net. This discharge increased in direct proportion to the applied voltage and relative humidity, while a larger corona discharge generated a stronger ionic wind. The ionic wind involved negative ions and the number of negative ions in the wind increased with increasing applied voltage. The optimal voltage (10 kV) generated sufficient negative ions to ionize smoke particles in the electric field, before the ionized smoke particles were successfully captured by the oppositely charged metal net. Thus, this study provides an experimental basis for the practical application of an electrostatic-based method to prevent the production of tobacco sidestream smoke that leads to passive smoking by non-smokers.

Formation of Ag-Al Alloy in context of PERC solar cell metallization

The Ag-Al spike formation at the transition between silver pad and aluminum metallization of the rear side of industrial PERC solar cells was investigated. Silver and aluminum layers were deposited by thermal evaporation on top of silicon nitride layers forming a system of reduced complexity. The absence of glass frit and other usual components of metallization paste leads to a focused study on interaction between the metal alloy and passivation layer. The samples were tempered stepwise from 400°C to 1000°C using a rapid thermal processing tool. X-ray diffraction measurement reveals the expected formation of Ag2Al phase, starting at 400°C. Furthermore, silicon was detected which is accompanied with the occurrence of square shaped indentations in the metal layer, which are the base area of pyramidal metal spikes penetrating the silicon. The formation of these spikes occur for anneal temperatures above 700°C, whereas the silicon nitride shows a high resistance against the molten alloy. The silicon nitride has to contain pinholes to enable a contact between metal and silicon substrate to form these spikes. Electrical characterization of these unintended contacts show an ohmic behavior, similar to the Al-Si system. In combination with the previous observations, a model for the spike formation at the rear side of industrial solar cells is presented.

Contacting BBr3-based Boron Emitters with Aluminium-free Screen-printing Paste

For n-type solar cell concepts, B emitters are commonly diffused in a BBr3-based process. However, the metallization of these p+ layers is challenging. Up to now, low contact resistances on B emitters were only reported to be possible using Al-containing Ag screen-printing pastes. A drawback of the addition of Al to the paste is that, facilitated by the Al, deep metal spikes grow into the Si surface. As these spikes are deep enough to penetrate the emitter and affect the space charge region, they are made responsible for low Voc values that limit solar cell efficiency. However, in 2015 Engelhardt et al. reported specific contact resistances around 1 mΩcm2 of Al-free Ag screen-printed contacts on B emitters diffused by inductively coupled plasma plasma enhanced chemical vapour deposited SiOx:B layers. In their process the doping layer remained on the wafer serving as surface passivation layer. The low contact resistances were attributed to the presence of the doping layer. In this work we use two Al-free Ag screen-printing pastes for contacting a BBr3-based B emitter. Specific contact resistances well below 10 mΩcm2 are reached on alkaline textured wafers with dielectric layer. It is shown that with the use of Al-free Ag screen-printing pastes deep spiking can be avoided and therefore a wider window of firing parameters is available. These results allow the use of the same screen-printing paste on both sides of the solar cell. Additionally it is shown, that with an old generation Al-free Ag paste low specific contact resistances can only be achieved in a narrow firing window at low temperatures. The addition of Te to the old generation paste shifts and broadens the temperature range for which low specific contact resistances are reached to higher firing temperatures.

Contacting boron emitters on n-type silicon solar cells with aluminium-free silver screen-printing pastes

In the production of n-type Si solar cells, B diffusion is commonly applied to form the p+ emitter. Up to now, Ag screen-printing pastes, generally used to contact P emitters, had been incapable of reliably contact B emitters. Therefore, a small amount of Al is generally added to Ag pastes to allow for reasonable contact resistances. The addition of Al, however, results in deep metal spikes growing into the Si surface that can penetrate the emitter. Losses in open-circuit voltage are attributed to these deep metal spikes. In this investigation we demonstrate, that state-of-the-art Al-free Ag screen-printing pastes are capable to contact BBr3-based B emitters covered with different dielectric layers and reach specific contact resistances <1 mΩ cm2. Bifacial n-type solar cells with Al-free Ag pastes on both sides show efficiencies of up to 18.3% and series resistances <0.5 Ω cm2. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Результаты изучения металлических находок с поселения Колыванское-I (северо-западные предгорья Алтая)

The article is devoted to the characterization of metal products, found during the excavations of the Kolyvan-I settlement. The monument is located in the north-western foothills of Altai near the Savvushki village (Zmeinogorsky District of the Altai Territory). Over three decades of the field study excavation was carried out of about 2,500 square meters, the area where investigation was performed of the variety of objects relating to the economic activities of the people living there (the fire-places, facilities, production facilities, pits, etc.). Archaeological material includes a collection of pottery fragments, stone, bone and metal tools, as well as findings related to the bronze casting (slag, pieces of ore, metal spikes). Early complex of Kolyvan-I settlement is dated mainly 21-19th&nbsp;centuries, BC and refers to Elunino Archaeological Culture. The collection of products is represented by a series of metal needles, rings and fragments of knives. Spectral analysis of metal, carried out with the help of X-ray fluorescence spectrometer ALPHA SERIES ™ (Model Alpha 2000), showed that the products are made of tin bronze (needles, knives) and lead (rings). Perspective is the study of toxins detected.

Crystalline Nature of Metal Spikes and Silicon Inclusions in Ag/Al Screen-Printing Metallization

For contacting boron emitters by screen-printing metal pastes, up to now, it has been necessary to add a small amount of Al to the Ag paste to facilitate a reasonable contact resistivity. With the addition of Al to the Ag paste, deep Ag/Al spikes appear, which can be deep enough to penetrate the emitter and, therefore, affect the emitter and space charge region, and, finally, affect the performance of the solar cell. In this paper, a transmission electron microscopy (TEM) analysis of these Ag/Al spikes is presented. The crystalline nature of the Ag/Al spikes is revealed for different surface structures of the crystalline Si wafer and different Al contents in the screen-printing paste. This result is confirmed by X-ray diffraction measurements of etched-back contacts. Additionally, TEM energy-dispersive X-ray spectroscopy facilitates the examination of the Si-rich inclusions found in the Ag/Al spikes. They prove to be multicrystalline Si precipitates with at least 99 at% Si. The observations help to understand the contact formation process of Al containing Ag screen-printing pastes and support the previously presented model.

Towards understanding the characteristics of Ag–Al spiking on boron-doped silicon for solar cells

With this work, we introduce numeric three-dimensional simulation of metal spiking into highly boron-doped surfaces of n-type silicon solar cells, which is moreover performed with a simulation of the quasi-steady-state photoconductance technique. This setup serves as a virtual experiment to simulate the dark saturation current density j0,met of metallized boron-doped emitters with respect to metal spikes originating from the silver–aluminum (Ag–Al) contact. With the results obtained from this simulation model we approach quality and quantity of increased j0,met and give detailed insight to which degree a solar cell’s performance is possibly harmed by this effect. We show that metal spikes penetrating into boron-doped emitters are of harmless nature concerning j0,met until their tips reach depths where boron doping concentration is lower than approximately 1018cm−3. Deeper spikes then lead to an exponential increase in j0,met as more and more carriers from emitter and also the base are able to diffuse to its tip and recombine there. With the help of j0-results obtained experimentally in combination with the simulation results, we discuss the influence of spikes on emitter recombination, the benefits that can be achieved with deeper emitter doping profiles, and suggestions for the further development of pastes to contact boron-doped surfaces.

Efficient and Flexible Supercapacitors Assembled on Metal Spikes

AbstractLavender‐like, lightweight, and flexible supercapacitive electrodes with high specific capacitance have been fabricated for the first time by assembling petal‐like nano‐nickel oxides on nickel spikes that are grown by using a simple non‐templated method. Compared with traditional fiber‐shaped electrodes, the specific capacitance of these electrodes increases six‐fold to 4.47 F cm−2. For a 1 cm‐long spike electrode, the capacitance reaches over 1.4 F, and no evident drop is observed at a bending angle of 180°. Both the mechanical strength and large current discharging property are unexpectedly good. The spike structure makes the apparent mass density of the electrode as light as carbon fiber, and exhibits considerable potential for use in future portable energy‐storage devices.

Preservation of Si Surface Structure by Ag/Al Contact Spots – An Explanatory Model

Abstract In the past years, the contact formation of Ag screen-printing pastes to n+ emitters has been profoundly investigated and at least in parts explained. However, p+ emitters cannot be contacted well with standard Ag pastes. It has been shown that adding Al to Ag screen printing pastes leads to lower contact resistances. Therefore different mechanisms must play a role in the contact formation process. The role of Al and the exact mechanism of contact formation of these Al containing Ag screen-printing pastes have not been well understood up to now. A drawback of Al containing pastes is that metal spikes growing into the Si wafer can be deep enough to corrupt the space charge region and contact the base thus shunting the pn-junction. A better understanding of the contact formation process is necessary to enable the development of improved screen-printing pastes with a reduced probability of shunting. In this work the influence of differently structured Si surfaces on the contact formation to a BBr3 based boron emitter is investigated. The Ag/Al contact spots that grow into the Si surface show the same surface structure as the surrounding Si. It is concluded, that the SiNx:H layer acts as a mould of the Si surface for the growth of the contact spots. The presented observations are then explained by a recently introduced model for the contact formation of Al containing Ag screen-printing pastes to p+ emitters through a SiNx:H layer.

Coulomb explosion during the early stages of the reaction of alkali metals with water.

Alkali metals can react explosively with water and it is textbook knowledge that this vigorous behaviour results from heat release, steam formation and ignition of the hydrogen gas that is produced. Here we suggest that the initial process enabling the alkali metal explosion in water is, however, of a completely different nature. High-speed camera imaging of liquid drops of a sodium/potassium alloy in water reveals submillisecond formation of metal spikes that protrude from the surface of the drop. Molecular dynamics simulations demonstrate that on immersion in water there is an almost immediate release of electrons from the metal surface. The system thus quickly reaches the Rayleigh instability limit, which leads to a 'coulomb explosion' of the alkali metal drop. Consequently, a new metal surface in contact with water is formed, which explains why the reaction does not become self-quenched by its products, but can rather lead to explosive behaviour.

Schottky-Contact Technology in InAlN/GaN HEMTs for Breakdown Voltage Improvement

In this paper, we demonstrate a 253% improvement in the off-state breakdown voltage (BV) of the lattice-matched In0.17Al0.83 N/GaN high-electron-mobility transistors (HEMTs) by using a new Schottky-contact technology. Based on this concept, the Schottky-source/drain and Schottky-source (SS) InAlN/GaN HEMTs are proposed. The proposed InAlN/GaN HEMTs with an LGD of 15 μm showed a three-terminal BV of more than 600 V, while the conventional InAlN/GaN HEMTs of the same geometry showed a maximum BV of 184 V. Without using any field plate, the BV of 650 V was measured in the SS InAlN/GaN HEMTs with LGD = 15 μm, which is the highest BV ever achieved on InAlN/GaN HEMT. The corresponding specific on-resistance (Rsp, on) is as low as 3.4 mΩ·cm2. A BV of 118 V was also obtained in SS InAlN/GaN HEMTs with LGD = 1 μm, which is the highest BV in GaN-based HEMTs featuring such a short LGD with GaN buffer. The improvement of the BV relies on the effective suppression of source carrier injection into the GaN buffer under the SS due to the smooth metal morphology and elimination of metal spikes in the Schottky metallization.

Effects of metal spikes on leakage current of high-voltage GaN Schottky barrier diode

We have investigated effects of metal spikes on the leakage current of high-voltage GaN Schottky barrier diodes (SBDs) on Si substrate. The metal spikes are formed underneath Ohmic contacts during a thermal annealing. The diffusion of Ti/Al/Mo/Au into GaN is analyzed by measuring Auger electron spectroscopy (AES). Ti/Al/Mo/Au on GaN is stripped by a wet etchant and its surface is observed to verify metal spikes by scanning electron microscope (SEM) and atomic force microscopy (AFM). The annealing temperature of the Ohmic contact is proportional to the diffusion depth of the metal spikes and the leakage current. The reverse current of GaN SBD with an Ohmic alloy at 700°C is 0.37A/cm2 at −100V while that of GaN SBD with the Ohmic alloy at 800°C is 13.45A/cm2 at −100V. The metal spikes in GaN power devices should be suppressed for the low power loss and the high breakdown voltage. The reverse current of GaN SBD is further decreased by a recessed Schottky contact because the Schottky contact is closer to unintentionally-doped (UID) GaN buffer and the depletion is increased. The reverse current of GaN SBD with the recessed Schottky contact is finally decreased to 0.05A/cm2 at −100V. When an anode–cathode distance (DAC) is 5μm, the measured on-resistance, breakdown voltage and figure-of-merit (BV2/Ron,sp) are 3.15mΩcm2, 320V, and 32.5MW/cm2, respectively. When DAC is increased to 20μm, fabricated devices show the breakdown voltage of 450V and good device-to-device uniformity.

1000 Consecutive Venous Anastomoses Using the Microvascular Anastomotic Coupler in Breast Reconstruction

Sir: We read with great interest the article entitled “1000 Consecutive Venous Anastomoses Using the Microvascular Anastomotic Coupler in Breast Reconstruction” by Jandali et al. (Plast Reconstr Surg. 2010;125:792–798). As the coupling device is also routinely used at our department, we would like to contribute a technical detail that might be helpful for comfortable and safe use. After pulling the vessel end through the ring, a special forceps should be used to pin the vessel wall onto the metal spikes. Unfortunately, the instrument provided for this purpose is subject to trouble. The tips tend not to meet properly, thereby not forming the hole needed to push the vessel wall onto the spike. In rare cases, besides being just an annoyance, the endothelium exposed to blood flow might be injured. We have modified this maneuver by using a microsurgical sponge to dab blood out of vessel ends. After cutting the tip, use of these sponges is a gentle means of pressing the vessel wall over the spike. This saves time and is also much faster than targeting the spike by using the forceps. As these microsurgical sponges are used routinely for preparation of the arterial vessel ends, this might be a low-cost improvement of the coupling technique. Heinrich M. Schubert, M.D. Thomas Schoeller, M.D., M.Sc. Gottfried Wechselberger, M.D., M.Sc. Department of Plastic and Reconstructive Surgery Krankenhaus der Barmherzigen Brüder Salzburg Paracelsus Medical University Salzburg, Austria

Schottky-Drain Technology for AlGaN/GaN High-Electron Mobility Transistors

In this letter, we demonstrate 27% improvement in the buffer breakdown voltage of AlGaN/GaN high-electron mobility transistors (HEMTs) grown on Si substrate by using a new Schottky-drain contact technology. Schottky-drain AlGaN/GaN HEMTs with a total 2-?m-thick GaN buffer showed a three-terminal breakdown voltage of more than 700 V, while conventional AlGaN/GaN HEMTs of the same geometry showed a maximum breakdown voltage below 600 V. The improvement of the breakdown voltage has been associated with the planar contact morphology and lack of metal spikes in the Schottky-drain metallization.