Thin Gold Wires Research Articles

Multi-Reference Electrode Lithium-Ion Pouch Cell Design for Spatially Resolved Half-Cell Potential and Impedance Measurements

Reliable experimental methods for measuring local potentials in lithium-ion battery cells are challenging but vital for a deep understanding of internal processes at the individual electrode level, and to parameterize and validate electrochemical models. Different three-electrode setups and reference electrodes (REs) have been developed in recent years. Some are based on custom laboratory setups or are small, e.g. coin cell sized. This work addresses internal potentials and half-cell impedances in the widely used single-layer pouch (SLP) cell format and proposes a novel multi-reference electrode cell design, enabling spatially resolved measurements. For the first time, it is shown how multiple 25 μm and 50 μm thin gold wire REs, together with a larger LTO-RE, can be used to study occurring inhomogeneities, considering the geometrical anode overhang. Special attention is given to the subtleties of the measurements and their interpretation. Multiple REs allow plausibility checks and confirm stability for both types during a continuous measurement period of more than 7,500 h (>10 months), demonstrating suitability, e.g. for long-term cycling measurements. Results from electrochemical impedance spectroscopy (EIS) and half-cell potential measurements at low currents of C/100 and during fast charging at up to 3C highlight the versatility of the easily reproducible cell design.

Error factors in precise thermal conductivity measurement using 3ω method for wire samples

In designing thermoelectric and heat transfer devices on the micrometer scale, the accurate thermal conductivity measurement is very important, and a variety of measurement methods have been developed so far. Among them, the 3ω method is one of the best for conductive wires because it can directly measure thermal conductivity without measuring density or specific heat, and also in the same direction as electrical or thermoelectric property. However, previous studies have not sufficiently considered the effects of ambient pressure and the conductive adhesive used to attach the sample to the electrode, which may hinder accurate measurement. In this study, using a thin gold wire as a test sample, the influence of ambient pressure and the length of conductive adhesive along the sample has been investigated quantitatively as major factors of systematic errors in the 3ω method. When the pressure was increased in the transition flow region, the measured apparent thermal conductivity increased. An analytical model for the low-pressure gas heat conduction is proposed to quantitatively explain the pressure dependence. The measured value also increased when the length of the conductive adhesive exceeded 20% of the sample length. This work has revealed that the ambient should be evacuated to the molecular flow region and the length of conductive adhesive be less than 20% of the sample length. The guidelines proposed here will help researchers in various fields to more accurately determine the thermal conductivity of micrometer-scale wires.

Measuring In Situ Interfacial Contact Resistance in a Proton Exchange Membrane Fuel Cell

Interfacial contact resistance (ICR) is one of the remaining hurdles for successful implementation of stainless steel bipolar plates in PEM fuel cells. We have developed a reliable method, using thin gold wires, to measure the interfacial contact resistance between the bipolar plate material and the porous transport layer during fuel cell operation. The ICR values were found to be in the same range as the ICR values measured ex situ after fuel cell operation. Local ex situ ICR measurements on tested plates indicate uneven current distribution during fuel cell operation. Consequently, an average between three measuring points was used for the in situ measurements, which enabled consistent monitoring of the ICR development alongside fuel cell performance. For almost all of the tests, the largest ICR changes took place within the first two hours of operation, showing the importance of early ICR measurements. Non-coated stainless steel and titanium-coated steel BPPs experienced a higher ICR compared to the gold coated stainless steel.

A Novel Reference Electrode for Potential and Impedance Measurements of Individual Electrodes in Lithium-Ion Full-Cells

The lifetime of lithium-ion batteries strongly depends on the properties of the interface between each electrode and the electrolyte. Electrochemical impedance spectroscopy is a simple and non-destructive method to investigate the electrode/electrolyte interfaces and the effect of electrolyte additives. As impedance measurements of full-cells always reflect the sum of both electrodes, it is difficult to deconvolute the contributions of the cathode and anode interface. Therefore, numerous reference electrode designs for impedance measurements have been suggested.1–6 However, if the reference electrode is not placed centrally between cathode and anode, which is the case for commonly used Swagelok T-cells, the measurement can easily be biased.2,7,8 Starting from the conventional T-cell design, we developed a novel micro-reference electrode which is placed centrally between both electrodes and two 200 µm thick glass fiber separators. The reference electrode consists of a thin gold wire. Due to the small wire diameter compared to the electrode separation, a distortion of the potential field between the electrodes is thus minimized. Similar as proposed by Abraham et al.6 for a tin-coated wire, we achieve a stable potential of the gold wire by electrochemical alloying with lithium. We show that the potential of this lithiated gold wire reference electrode (GWRE) is stable for several weeks, even under elevated temperatures. With this lithiated GWRE, we are able to record the potential of both electrodes in LFP/graphite full cells for more than 150 cycles. Further, we evaluate the capabilities of the lithiated GWRE to accurately measure the impedance of individual electrodes. We verify the impedance measurements of individual electrodes in full-cells with the lithiated GWRE by comparison with symmetrical cell measurements, which are commonly used for accurate electrode impedance analysis.9 Besides the electrolyte/electrode interface resistances, the lithiated GWRE is also suitable to probe electronic contact resistances of the electrodes. Using symmetrical cells, Burns et al.10 have shown that the charge transfer of a graphite anode depends almost linearly on the concentration of vinylene carbonate (VC) in the electrolyte. As a proof of concept, we conducted a similar study in LFP/graphite full cells with lithiated GWRE and different VC concentrations in the electrolyte. We can reproduce the findings by Burns et al.10 and further demonstrate that the total amount of VC per anode surface, rather than its concentration, is the key parameter for the electrolyte/anode interface resistance (s. Fig. 1). This result is important when electrolyte additives are tested in laboratory cells, as these cells typically have a higher electrolyte to active material ratio than commercial lithium-ion cells. Figure 1: Charge transfer resistance of graphite and LFP electrodes in full-cells with different amounts of VC added to the electrolyte (1M LiPF6 in EC:EMC 3:7). The impedance spectra were measured at 25 °C in LFP/graphite full-cells with a lithiated GWRE after 1 formation cycle at C/10 at 40 °C and a subsequent charge to 50% SOC.

Low-cost bump-bonding processes for high energy physics pixel detectors

In the next generation of collider experiments detectors will be challenged by unprecedented particle fluxes. Thus large detector arrays of highly pixelated detectors with minimal dead area will be required at reasonable costs. Bump-bonding of pixel detectors has been shown to be a major cost-driver. KIT is one of five production centers of the CMS barrel pixel detector for the Phase I Upgrade. In this contribution the SnPb bump-bonding process and the production yield is reported. In parallel to the production of the new CMS pixel detector, several alternatives to the expensive photolithography electroplating/electroless metal deposition technologies are developing. Recent progress and challenges faced in the development of bump-bonding technology based on gold-stud bonding by thin (15 μm) gold wire is presented. This technique allows producing metal bumps with diameters down to 30 μm without using photolithography processes, which are typically required to provide suitable under bump metallization. The short setup time for the bumping process makes gold-stud bump-bonding highly attractive (and affordable) for the flip-chipping of single prototype ICs, which is the main limitation of the current photolithography processes.

Comparative Study of Experimental Enhancement in Free Radical Generation against Monte Carlo Modeled Enhancement in Radiation Dose Deposition Due to the Presence of High Z Materials during Irradiation of Aqueous Media

Purpose: To investigate conflicting results demonstrating higher cell-kill by irradiated high atomic number (Z) material, gold (Au) in tumor compared to Monte Carlo (MC) modeled enhancement in radiation dose deposition, and to compare the difference between radiosensitizing effects of gold and platinum. Methods and Materials: Since a majority of cell kill due to radiation is mediated by free radicals, evaluation of radicals generated from radiolysis of an aqueous medium can provide some insight into cell-kill. Here, free radicals generated due to the radiolysis of water by a clinical Iridium-192 (Ir-192) brachytherapy source in the presence and absence of thin and pure gold or platinum wires were quantified with electron paramagnetic/spin resonance (EPR/ESR) spectrometry and enhancements in free radical generation due to the presence of the wires during radiolysis were calculated. Those enhancements were compared against MC modeled enhancement in radiation dose deposition obtained from the geometry replicating the experimental setup. Results: Enhancements in free radical generation due to 100 and 127 μm diameter gold wires, and 127 μm diameter platinum wire were more than two times higher than the corresponding MC modeled enhancements in radiation dose deposition. Enhancement in hydroxyl free radical (OH?) generation due to thicker wires of gold and platinum were close to the enhancements in radiation dose deposition. The effects were similar for gold and platinum wires of equal diameter. Conclusions: Higher enhancement in radical generation compared to MC modeled enhancement in radiation dose deposition due to micron-size pure gold and platinum wires demonstrates that the surfaces of high Z materials in aqueous media become a secondary source of radicals under radiation field. High surface-to-volume ratio of nanoparticles can make this effect more pronounced, leading to higher cell kill than the predictions based on pure dose enhancement.

Hall–Petch effect and strain gradient effect in the torsion of thin gold wires

Gold wires with diameters of 20 and 50 μm were annealed in the temperature range 330–750 °C to obtain different grain sizes. Torsion and tension experiments on these wires confirm that the Hall–Petch effect is stronger than the strain gradient effect in the small grain size region (below 5 μm). With the grain size becomes larger, the strain gradient effect is evident. We find that these two mechanisms are synergistic, and this interaction strongly depends upon the grain size.

SU-E-T-341: Experimental Evaluation of Free Radical Generation in Nanoparticle-Aided Radiation Therapy

Purpose: Use of gold nanoparticles (NPs) in radiation therapy has been found promising due to the possibility of selective radiation dose enhancement within a tumor, and favorable biological compatibility. Recent studies demonstrated that the biological effect exceeds the expectations based on the physical energy deposition solely, thus pointing toward biochemical factors. Since free radicals are responsible for the majority of the biological damage, evaluation of their radiation induced free radicals near the gold-tissue interface offers a more relevant estimate of the biological damage in NP-aided radiation treatments. Methods: Samples in the capillaries were irradiated with clinical Ir-192 HDR source. Since free radicals are very short-lived (∼nanoseconds), we used a spin trap agent, high purity DMPO dissolved in water, to trap hydroxyl radicals generated by radiolysis of water. The formed spin adducts retain spin properties of free radicals for a prolonged time (∼hours), especially at low temperatures. Radicals were detected via electron spin resonance (ESR) spectrometry technique. Quantification of free radicals generated in water and in the presence of a thin gold wire was done by double integration of the obtained spectra. Results: Our Monte Carlo simulations demonstrated that the dose enhancement region is limited to a close vicinity (less than 1mm) of the gold-tissue interface still suitable for free radical measurement with ESR spectroscopy. We have established a protocol for quantitative ESR measurements. The radical generation was found to be proportional to the radiation dose, and strongly enhanced by the presence of gold. Conclusions: Free radicals generated by radiolysis of water can be measured quantitatively with ESR technique. Our evaluation of radiation induced free radical generation in water with nanoparticles sheds some light on the effects of NPs in biological systems. This project is supported through an NRC grant for faculty development. It is grant number NRC-HQ-12-G-38-0042.

Fabrication of nanogaps by a progressive electromigration technique using wires of various thicknesses

The authors report the fabrication of nanogaps formed by electromigration from gold wires of various widths (25–80 nm). This technique is a reliable and consistent method to create quality gaps without the need of very thin gold wires. The gaps are fabricated at room temperature and ambient atmosphere in contrast to the method of performing electromigration at liquid helium temperatures and in high vacuum environments. The authors observed that every nanogap formed using this technique was free of residual particles left over from the electromigration process.

Absence of a self-induced decay effect in 198Au

We report the results of an improved experiment aimed at determining whether the half-life ($T_{1/2}$) of $^{198}$Au depends on the shape of the source. In this experiment, the half-lives of a gold sphere and a thin gold wire were measured after each had been irradiated in the NIST Center for Neutron Research. In comparison to an earlier version of this experiment, both the specific activities of the samples and their relative surface/volume ratios have been increased, leading to an improved test for the hypothesized self-induced decay (SID) effect. We find T_1/2(sphere)/T_1/2(wire) = 0.9993+/-0.0002, which is compatible with no SID effect.

Which Frequency is Best for Wirebonding?

In industrial practice, frequencies from 40 kHz up to 160 kHz are currently employed for wire-bonding while for experimental purposes, lower and higher frequencies from around 25 kHz up to 300 kHz are discussed. Typically, heavy aluminium wire or ribbon is preferably bonded at lower frequencies between 40 and 80 kHz, while thin aluminium or gold wires are wedge- or ball-bonded at frequencies between 100 and 140 kHz. We present a discussion of the pros and cons of different ultrasonic frequencies by looking at the mechanics during the bonding process. Higher frequencies allow shorter bonding times and permit bonding on more sensitive surfaces, but suffer from a narrower parameter window. This is mainly due to the smaller vibration amplitudes at the tool tip which can be employed for higher frequencies. The major benefit for many applications is that higher bond quality is possible even at lower wire deformation which additionally creates a healthier bond heel. Lower frequencies, on the other hand, seem to have advantages for rougher surfaces where some planarizing and smoothing is required before bonding can begin to take place, while running a higher risk of damaging the bond after forming it. Resonance effects can seriously damage bond formation, and ways are discussed on how to deal with this problem.

Electrochemical impedance immunosensor for the detection of cardiac biomarker Myogobin (Mb) in aqueous solution

A label-free, electrochemical impedance immunosensor based on surface modified thin flat gold wire electrode is reported for the quantitative detection of cardiac biomarker Myoglobin in aqueous solution. The protein antibody, ab-Mb, was covalently immobilized through a self assembled monolayer of 11-mercaptoundecanoic acid (MUA) and 3-mercapto propionic acid (MPA) via carbodiimide coupling reaction using N-(3-dimethylaminopropyl)-N′-ethyl carbodiimide hydrochloride (EDC) and N-Hydroxy Succinamide (NHS). The immunosensor (ab-Mb/MUA-MPA/Au) was characterized by electrochemical techniques. The electrochemical performance of the immunosensor was studied by electrochemical impedance spectroscopy. The immunosensor showed an increased electrontransfer resistance on coupling with biomarker protein antigen, ag-Mb, in the presence of a redox probe [Fe (CN) 6] 3−/4−. The modified Au electrode immunosensor exhibits an electrochemical impedance response to antigen, ag-Mb concentrations in a linear range from 10 ng to 650 ng mL −1 with a lowest detection limit of 5.2 ng mL −1.

Dynamic Analysis on Underlay Microstructure for Cu/Low-k Wafer during Wire Bonding

Two major analyses were conducted in this paper. In the first, experimental procedures are accomplished to measure the tensile mechanical properties of ultra thin gold wire (=1mil) before/after electric flame-off (EFO). Characteristics of free air ball (FAB), heat affected zone (HAZ) and as-drawn wire have been carefully investigated by nanoindentation, microhardness and self-design pull test fixture. Secondary, with the obtained experimental material data, a comprehensive finite element model using software ANSYS/LS-DYNA is successfully developed to simulate the wirebonding. Dynamic analysis is performed to evaluate the overall stress distributions on the underlay microstructure of Cu/low-k wafer. Special emphasizes are focused on the Copper via and the intermetal dielectric (IMD)/undoped silica glass (USG) dielectric microstructure.

Laser-produced energetic electron transport in overdense plasmas by wire guiding

Laser-driven energetic electron transport in a two-layered (Au and DT) ultrahigh density plasma is investigated. It is shown that the jump in the resistivity at the interface of the two plasmas plays an important role in the slowing down of the energetic beam electrons and heating of the plasmas. Furthermore, a thin gold wire in the DT plasma can further slow down the beam electrons and absorb a part of the beam energy.

PFabrication of gold tips by chemical etching in aqua regia

We present a method to produce sharp gold tips for applications in apertureless near-field optical microscopy and spectroscopy. Thin gold wires are tapered by chemical etching in aqua regia, covered by an isooctane protective layer. Tips with apical radii of curvature of <50 nm are obtained with a 40% yield. The tip performances have been checked by shear-force imaging of amyloid fibrils samples and compared to optical fiber probes. The analysis of the tip morphology, carried out by scanning electron microscopy, shows the existence of two different etching processes occurring in bulk and at the liquid-liquid interface. A simple analytical model is presented to describe the dynamics of the tip formation at the liquid-liquid meniscus interface that fits remarkably well the experimental results in terms of tip shape and length.

Effect of wire diameter on the thermosonic bond reliability

Thermosonic bonding process is a viable method to make reliable interconnections between die bond pads and leads using thin gold and copper wires. This paper investigates interface morphology and metallurgical behavior of the bond formed between wire and bond pad metallization for different design and process conditions such as varying wire size and thermal aging periods. Under thermal aging, the fine pitch gold wire ball bonds (0.6 mil and 0.8 mil diameter wires) shows formation of voids apart from intermetallic compound growth. While, with 1-mil and 2-mil diameter gold wire bonds the void growth is less significant and reveal fine voids. Studies also showed void formation is absent in the case of thicker 3 mil wire bonds. Similar tests on copper ball bonds shows good diffusional bonding without any intermetallic phase formation (or with considerable slow growth) as well as any voids on the microscopic scale and thus exhibits to be a better design alternative for elevated temperature conditions.

Nanometre gaps in gold wires are formed by thermal migration

The formation of gold wires separated by a few nanometres is reported. Suchnanometre-separated gaps are formed by ramping, at ambient conditions, a bias voltageacross a thin gold wire until the wire breaks or fails. Externally heating the wire does notresult in a lowering of the mean bias or current conditions required for creatingthe break, although electromigration-based models predict rapid decreases inthe current required to cause the break. Based on measurements of changes inresistance during the voltage ramp, we determine that the temperature reachedin the wires is very large and can approach the melting point of gold. To avoiddeleterious effects of such large temperatures on molecules, we recommend herean alternate procedure for utilizing the break protocol in molecular electronics.

Effect of wire size on the formation of intermetallics and Kirkendall voids on thermal aging of thermosonic wire bonds

Thermosonic bonding process is a viable method to make reliable interconnections between die bond pads and leads using thin gold and copper wires. This paper investigates interface morphology and metallurgical behavior of the bond formed between wire and bond pad metallization for different design and process conditions such as varying wire size and thermal aging periods. Under thermal aging, the fine pitch gold wire ball bonds (0.6- and 0.8-mil-diameter wires) show formation of Kirkendall voids apart from intermetallic compound growth. With 1- and 2-mil-diameter gold wire bonds, the void growth is less significant and reveals fine voids. Studies also showed that void formation is absent in the case of thicker 3-mil wire bonds. Similar tests on copper ball bonds show good diffusional bonding without any intermetallic phase formation (or with considerable slow growth) as well as no voids on the microscopic scale and thus promises to be a better design alternative for elevated temperature conditions.

Development of MCP-based photon diagnostics at the TESLA Test Facility at DESY

A nondestructive radiation detector unit is under construction at the TESLA Test Facility at DESY providing monitoring of the radiation (pulse energy, transverse intensity distribution, and statistical properties). The concept of the detector design is based on experience obtained during operation of TTF FEL, Phase 1. Key element of the detector is a wide dynamic range micro-channel plate (MCP) which detects scattered radiation from a thin gold wire crossing photon beam. Operating wavelength range of the detector is from 6 to 100 nm . An important feature of the MCP-based detector is that it is capable to cover all dynamic range of the radiation intensity, from the level of spontaneous emission up to the saturation level of SASE FEL.

A new microcell or microreactor for material surface investigations at large current densities

The capillary-based droplet cell is well established in microelectrochemical surface analysis down to the μm range. The potentiostatic 3-electrode arrangement allows all common techniques like cyclovoltammetry, impedance spectroscopy and current transients of potential steps. A limiting factor was the immobile electrolyte, which meant an accumulation of products or depletion of educts, especially at larger current densities. Reaction products like gases (bubbles of O 2 or H 2) or precipitates blocked the capillary. Processes at larger current densities require a moving electrolyte. Examples are pulse deposition of metals, local corrosion and electrochemical machining (ECM), which means an anodic dissolution at current densities up to 100 A/cm 2. A new concept was developed, based on capillaries made of glass tubes with a partition. Accordingly, we employed two separated channels, one channel is used as an electrolyte inlet, the other as the outlet. One of the channels includes a thin gold wire as a counter electrode. A special gear pump moves the electrolyte with velocities up to 70 m/s in the mouth of the capillary. Current densities >100 A/cm 2 become possible under these conditions. Dissolution processes like ECM normally require an identification of the products, which became possible by adding a flow-through micro cuvette of an UV-Vis spectrometer at the electrolyte outlet.