Metal Field Research Articles

Triple-Cation-Based Perovskite Photocathodes with AZO Protective Layer for Hydrogen Production Applications.

Metal halide perovskites are actively pursued as photoelectrodes to drive solar fuel synthesis. However, currently, these photocathodes suffer from limited stability in water, which hampers their practical application. Here, we report a high-performance solution-processable photocathode composed of cesium formamidinium methylammonium triple-cation lead halide perovskite protected by an Al-doped ZnO (AZO) layer combined with a Field's metal encapsulation. Careful selection of charge transport layers resulted in an improvement in photocurrent, fill factor, device stabilityand reproducibility. The dead pixels count reduced from 25 to 6% for the devices with an AZO layer, and in photocathodes with an AZO layer the photocurrent density increased by almost 20% to 14.3 mA cm-2. In addition, we observed a 5-fold increase in the device lifetime for photocathodes with AZO, which reached up to 18 h before complete failure. Finally, the photocathodes are fabricated using low-cost and scalable methods, which have promise to become compatible with standard solution-based processes.

Integrated Field's metal microelectrodes based microfluidic impedance cytometry for cell-in-droplet quantification

Microfluidic impedance cytometry (MIC) provides a non-optical and label-free method for single cell detection and classification in microfluidics. However, the cleanroom intensive infrastructure required for MIC electrode fabrication limits its wide implementation in microfluidic analysis. To bypass the conventional metal (platinum) electrode fabrication protocol, we fabricated coplanar ‘in-contact’ Field's metal (icFM) microelectrodes in multilayer elastomer devices with a single photolithography step. Our icFM microelectrodes displayed excellent and comparable performance to the platinum electrodes for detection of single erythrocytes with a lock-in amplifier based MIC setup. We further characterized it for water-in-oil droplets generated in a T-junction microfluidic channel and found high sensitivity and long-term operational stability of these electrodes. Finally, to facilitate droplet based single cell analysis, we demonstrate detection and quantification of single cells entrapped in aqueous droplets.

Liquid metal core–shell structures functionalised via mechanical agitation: the example of Field's metal

Field's metal particles synthesised by mechanical agitation exhibit peculiar core–shell structure and functionality.

Directional Stiffness Control Through Geometric Patterning and Localized Heating of Field’s Metal Lattice Embedded in Silicone

This research explores a new realm of soft robotic materials where the stiffness magnitude, directionality, and spatial resolution may be precisely controlled. These materials mimic biological systems where localized muscle contractions and adjustment of tissue stiffness enables meticulous, intelligent movement. Here we propose the use of a low-melting-point (LMP) metal lattice structure as a rigid frame using localized heating to allow compliance about selectable axes along the lattice. The resulting shape of the lattice is modeled using product of exponentials kinematics to describe the serial chain of tunably compliant axes; this model is found to match the behavior of the physical test piece consisting of a Field’s metal (FM) lattice encased in silicone rubber. This concept could enable highly maneuverable robotic structures with significantly improved dexterity.

Organic solar cells based on graphene derivatives and eutectic alloys vacuum-free deposited as top electrodes

Here is presented the use of two graphene derivatives in organic solar cells (OSCs) based on PTB7:[70]PCBM active layer. Reduced graphene oxide (rGO) was used as hole transport layer (HTL). Also, solution-processable functionalized graphene (SPFG) was incorporated as a third component in the active layer. Furthermore, the top electrode was either Field’s metal (FM): Bi/In/Sn or BS: Bi/Sn, eutectic alloys that melt at 62 and 138 °C, respectively; they are vacuum-free deposited by drop coating under normal atmosphere conditions. For OSCs with rGO as HTL, thin films were prepared by reiterative spin-deposition and thermal reduction of GO after each deposition. The best results were achieved for 6-rGO with a PCE = 5.50%, similar to that reached in control devices, i.e., PEDOT:PSS as HTL. On the other hand, ternary active layers were prepared by blending SPFG, at different weight ratios: 0, 2, 4, and 6 wt. %, with PTB7:[70]PCBM. An increment in PCE (6.73%) for OSCs with 4 wt. % of SPFG was found, which is 22% larger than that of the reference devices. Finally, PCEs of 5.52% and 5.31% were reached in OSCs fabricated and tested under normal room conditions with FM and BS, respectively.

Stability study in organic solar cells based on PTB7:PC71BM and the scaling effect of the active layer

Performance and stability of organic photovoltaic cells (OPVs) based on the benchmark bulk heterojunction PTB7:PC71BM and the alloy Field’s metal (FM) as top-electrode deposited by doctor blade technique, are fully studied when the active area is scaled by a factor of 25. Power conversion efficiency (PCE) of small active area (0.09 cm2) devices resulted in 7.4 ± 0.8%, which is within the range of values commonly achieved for devices comprising Al as traditional, costly and nonstable top-electrode. However, PCE decreased 60% for scaled OPVs (2.25 cm2). Studies of stability as a function of the active area were performed in accordance with the ISOS-L1 (laboratory simulation of constant lighting) and ISOS-D1 (shelf storage) protocols for devices tested in air and without encapsulation. The time to reach 50% of the initial PCE (T50) is about 14 h and 2000 h under ISOS-L1 and ISOS-D1 protocols, respectively, with a tendency of stability improvement for scaled devices. A whole PV analysis through the single diode model, impedance spectroscopy, and light beam induced voltage (LBIV) measurements is presented. Our results are a good indication that FM top-electrode, of cheap and easy deposition under vacuum free conditions, provides an acceptable photovoltaic performance after scaling the active area.

Soft Multifunctional Composites and Emulsions with Liquid Metals.

Binary mixtures of liquid metal (LM) or low-melting-point alloy (LMPA) in an elastomeric or fluidic carrier medium can exhibit unique combinations of electrical, thermal, and mechanical properties. This emerging class of soft multifunctional composites have potential applications in wearable computing, bio-inspired robotics, and shape-programmable architectures. The dispersion phase can range from dilute droplets to connected networks that support electrical conductivity. In contrast to deterministically patterned LM microfluidics, LMPA- and LM-embedded elastomer (LMEE) composites are statistically homogenous and exhibit effective bulk properties. Eutectic Ga-In (EGaIn) and Ga-In-Sn (Galinstan) alloys are typically used due to their high conductivity, low viscosity, negligible nontoxicity, and ability to wet to nonmetallic materials. Because they are liquid-phase, these alloys can alter the electrical and thermal properties of the composite while preserving the mechanics of the surrounding medium. For composites with LMPA inclusions (e.g., Field's metal, Pb-based solder), mechanical rigidity can be actively tuned with external heating or electrical activation. This progress report, reviews recent experimental and theoretical studies of this emerging class of soft material architectures and identifies current technical challenges and opportunities for further advancement.

Luminance enhancement in quantum dot light-emitting diodes fabricated with Field’s metal as the cathode

This work reports the fabrication and characterization of blue–green quantum dot light-emitting diodes (QD-LEDs) by using core/shell/shell Cd1−xZnxSe/ZnSe/ZnS quantum dots. Poly [(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9–dioctylfluorene)] (PFN) was introduced in order to enhance the electron injection and also acted as a protecting layer during the deposition of the cathode (a Field’s metal sheet) on the organic/inorganic active layers at low temperature (63 °C). This procedure permitted us to eliminate the process of thermal evaporation for the deposition of metallic cathodes, which is typically used in the fabrication of OLEDs. The performance of devices made with an aluminum cathode was compared with that of devices which employed Field’s metal (FM) as the cathode. We found that the luminance and efficiency of devices with FM was ~70% higher with respect to those that employed aluminum as the cathode and their consumption of current was similar up to 13 V. We also demonstrated that the simultaneous presence of 1,2-ethanedethiol (EDT) and PFN enhanced the luminance in our devices and improved the current injection in QD-LEDs.Hence, the architecture for QD-LEDs presented in this work could be useful for the fabrication of low-cost luminescent devices.

PTB7:PC$_{\text{71}}$BM-Based Solar Cells Fabricated With the Eutectic Alloy Field's Metal as an Alternative Cathode and the Influence of an Electron Extraction Layer

In this work, we study the performance of organic photovoltaic (OPV) cells based on the PTB7:PC $_{\text{71}}$ BM blend and the use of an alternative metal cathode called field's metal (FM) (Bi/In/Sn: 32.5%, 51%, 16.5%), which can be easily deposited through a vacuum-free process at regular atmosphere and low temperature (90 °C). The charge extraction and losses involved with the use of FM, in combination with an electron extraction layer, in this case the widely used polymer PFN, were fully analyzed using equivalent circuit models for the architecture ITO/PEDOT:PSS/PTB7:PC $_{\text{71}}$ BM/PFN/FM. Power conversion efficiencies (PCEs) higher than 6% were reached with this architecture, which exhibited $J_{{\rm{sc}}}$ of 14.3 mA/cm2, $V_{{\rm{oc}}}$ of 0.76 V, and FF of 0.6. The single-diode equivalent circuit model demonstrates that devices comprising FM as counterelectrode are characterized by a low series resistance (1.0 Ω · cm2), large shunt resistance (1.1 × 10 5 Ω · cm2), and low saturation current (1.4 × 10−7 mA/cm2). Additional electrical characterization, through impedance spectroscopy, was also carried out. The obtained PV parameters are similar to those exhibited by devices comprising standard counterelectrodes, i.e., Al, deposited through a high-vacuum evaporation process. Thus, FM, as nonconventional and alternative counterelectrode, in combination with an electron extraction layer, can be used to fabricate OPVs cells with very acceptable performance through a vacuum-free process.

Semiconductor Polymer/Top Electrode Interface Generated by Two Deposition Methods and Its Influence on Organic Solar Cell Performance.

In this Research Article, the effect of two techniques for top-electrode deposition in organic photovoltaics (OPVs) cells with the configuration ITO/PEDOT:PSS/PTB7-Th:PC71BM/PFN/top-electrode is analyzed. One deposition was made by evaporation under high vacuum, meanwhile the other was carried out at normal room atmosphere; for the former, a double layer of Ca and the eutectic alloy Field's metal (FM) was thermally evaporated, while for the latter FM was deposited just by melting and dropping it on top of the delimited active area at temperatures about 90 °C. The average short-circuit photocurrent density, open circuit voltage and fill factor for devices with either Ca/FM (evaporated) or FM (by dripping) cathode, were very similar: around 13.20 mA/cm2, 840 mV, and 0.6, respectively. Average efficiency for devices with the mentioned evaporated cathode was of 6.4% (largest value 7.0%), meanwhile for devices with the cathode deposited by dripping, it was of 6.1% (largest value 6.5%). Morphological analysis, by atomic force microscopy on the surface of a FM electrode, detached from an OPV device, shows inhomogeneities and pinholes in its surface with an average roughness of 16 nm. OPV photocurrent was studied by means of laser beam induced current (LBIC), it showed that OPVs devices with FM top electrode exhibits an inhomogeneous response. An impedance analysis was also carried out and results were correlated with defects observed at the studied interface. In spite of the mentioned deficiencies at FM interface, overall PV performance of devices with this electrode highlights the convenience of using FM because of its easy, fast, and low-cost deposition (vacuum free) characteristics.

Formation of microbeads during vapor explosions of Field's metal in water.

We use high-speed video imaging to investigate vapor explosions during the impact of a molten Field's metal drop onto a pool of water. These explosions occur for temperatures above the Leidenfrost temperature and are observed to occur in up to three stages as the metal temperature is increased, with each explosion being more powerful that the preceding one. The Field's metal drop breaks up into numerous microbeads with an exponential size distribution, in contrast to tin droplets where the vapor explosion deforms the metal to form porous solid structures. We compare the characteristic bead size to the wavelength of the fastest growing mode of the Rayleigh-Taylor instability.

SU‐F‐T‐88: Field's Metal for Electron Beam Inserts and Blocks

Purpose:The aim of this work is to show that Field's metal can be used as a viable alternative material to lead‐based low‐melting temperature alloys (e.g., Cerrobend) for electron beam inserts and blocks. The goal is to eliminate exposure risks associated with lead and cadmium.Methods:Field's metal (51% Indium, 32.5% Bismuth, 16.5% Tin) is a low‐melting point eutectic alloy, and is proposed as a lead‐free replacement for Cadmium‐free alloy (52.5% Bismuth, 32% Lead, 15.5% Tin). The experiments were done using a Varian 21EX linac equipped with 6, 9, 12, and 16 MeV beams. The 10×10 cone was used with 1.8cm thick insert made of Fields metal, Cd‐Free alloy or open field. The transmitted radiation was measured using a diode at various depths in water. Block transmission factor (BTF) is determined as the ratio of maximum transmission radiation dose over the dose at dmax of the open field.Results:The data shows BTFs for both alloys are very similar, well below 5% for 6, 9, and 12 MeV beams. For 16 MeV, the BTF of the Fields metal is about 5.3%; the Cd‐free metal 4.2%. The peak dose of the transmitted radiation occurs less than 1 cm below the water surface, at a much shallower depth than the dmax of the electron beam in the open field. The beam profile shows the maximum block transmission is along the central axis of the beam.Conclusion:The present study shows that Fields metal can be used to make electron cutouts and blocks for 6, 9, 12, and 16 MeV beams. Because it has a similar density as other lead‐based alloys, the same thickness of Fields metal would be adequate for shielding the electron beams. This means that it can be used as a replacement without modification to the existing block holder.

Performance and stability of PTB7:PC71BM based polymer solar cells, with ECZ and/or PVK dopants, under the application of an external electric field

The effect on the J–V behavior of polymer solar cells (PSCs) based on the active layer PTB7:PC71BM under a previous application of an external electric field (Eext) is presented. The active layer is doped with 0.01–0.04 wt. ratio (with respect to PTB7) of poly(9-vinylcarbazole) (PVK) as a photoconductor, and/or 0.25–0.5 wt. ratio of 9-ethylcarbazole (ECZ) as plasticizer. The general PSC structure was Glass-ITO/PEDOT:PSS/PTB7:PC71BM:dopant/PFN/FM where dopant means PVK, ECZ or a mixture of them. Field’s metal (FM) is an eutectic alloy with a melting point above 62 °C, which is deposited in a vacuum free atmosphere. Electric fields of 5 or −70 V/μm (forward and reversed polarity, respectively) are applied. For PSCs doped with PVK, under forward polarity, it is observed a remarkable variation (36 %) on Jsc: from 7.7 to 4.9 mA/cm2, while Voc remains almost constant: ~0.76 V; whereas with the reversed polarity, a drastic variation of 95 % is observed on Voc: from 0.76 to 0.04 V; while Jsc value changes from 7.4 to 5.6 mA/cm2 (24 %). On the other hand, PSCs doped with the combination of ECZ and PVK, an increase of 10 % in Jsc is reached for reversed bias (Eext = −70 V); and without applying any field, and keep them under N2 atmosphere, a slower photovoltaic degradation, with respect to that one from all the other studied samples, is shown over 57 days of monitoring them: FF variation is of just 6 % and PCE decays only 21 %.

Melt-and-mold fabrication (MnM-Fab) of reconfigurable low-cost devices for use in resource-limited settings

Interest in low-cost analytical devices (especially for diagnostics) has recently increased; however, concomitant translation to the field has been slow, in part due to personnel and supply-chain challenges in resource-limited settings. Overcoming some of these challenges require the development of a method that takes advantage of locally available resources and/or skills. We report a Melt-and-mold fabrication (MnM Fab) approach to low-cost and simple devices that has the potential to be adapted locally since it requires a single material that is recyclable and simple skills to access multiple devices. We demonstrated this potential by fabricating entry level bio-analytical devices using an affordable low-melting metal alloy, Field's metal, with molds produced from known materials such as plastic (acrylonitrile–butadiene–styrene (ABS)), glass, and paper. We fabricated optical gratings then 4×4 well plates using the same recycled piece of metal. We then reconfigured the well plates into rapid prototype microfluidic devices with which we demonstrated laminar flow, droplet generation, and bubble formation from T-shaped channels. We conclude that this MnM-Fab method is capable of addressing some challenges typically encountered with device translation, such as technical know-how or material supply, and that it can be applied to other devices, as needed in the field, using a single moldable material.

Synthesis of liquid core-shell particles and solid patchy multicomponent particles by shearing liquids into complex particles (SLICE).

We report a simple method that uses (i) emulsion shearing with oxidation to make core-shell particles, and (ii) emulsion shearing with surface-tension driven phase segregation to synthesize particles with complex surface compositions and morphologies. Subjecting eutectic gallium-indium, a liquid metal, to shear in an acidic carrier fluid we synthesized smooth liquid core-shell particles 6.4 nm to over 10 μm in diameter. Aggregates of these liquid particles can be reconfigured into larger structures using a focused ion beam. Using Field's metal melts we synthesized homogeneous nanoparticles and solid microparticles with different surface roughness and/or composition through shearing and phase separation. This extension of droplet emulsion technique, SLICE, applies fluidic shear to create micro- and nanoparticles in a tunable, green, and low-cost approach.

Fusible core molding for the fabrication of branched, perfusable, three-dimensional microvessels for vascular tissue engineering.

A novel method for fabrication of branched, tubular, perfusable microvessels for use in vascular tissue engineering is reported. A tubular, elastomeric, biodegradable scaffold is first fabricated via a new, double fusible injection molding technique that uses a ternary alloy with a low melting temperature, Field's metal, and paraffin as sacrificial components. A cylindrical core metal of 500 μm or lower dia-meter with the target branching scaffold geometry is first constructed, then the metal structure is coated with paraffin and, finally, the metal-paraffin construct is embedded in polydimethylsiloxane (PDMS). The paraffin layer is then removed by heating and replaced by a biodegradable elastomeric pre-polymer that is subsequently UV-cured inside the PDMS. Next, the metal core is melted away and the PDMS is removed to attain the branched tubular elastomeric biodegradable scaffold. Finally, it is also demonstrated that human umbilical vein endothelial cells (HUVEC) were able to spread on the surface of the scaffold and form a confluent monolayer, confirming the potential of this new technique for making engineered blood vessels.

Fracture Resistance of Yttria‐Stabilized Zirconia Dental Implant Abutments

An in vitro study was performed to assess the effect of different degrees of clinical reduction of zirconia abutments on the failure load of clinical assemblies. Zirconia abutments (Y-TZP Ceramic Abutment, Astra Tech) were prepared with 0, 0.5, or 1 mm of external axial reduction starting 1 mm above the height-of-contour. Abutments (n = 10) were attached to implant analogs (25 Ncm torque) embedded in a stainless steel cylinder using Field's metal. Fracture loads (N) were determined when assemblies were loaded at 60 degrees off-axis until failure (Instron, CHS = 0.1 mm/min). Groups were statistically compared using ANOVA (p < 0.05). Fracture loads for all assemblies displayed large variations within groups. There were no statistically significant differences (p > 0.05) among different abutment groups with a mean fracture load of 429 N (+/-140) for the control group, 576 N (+/-120) for 0.5-mm margins, and 547 (+/-139) for 1.0-mm margins. All fractures occurred at the interface where the abutment was connected to the analog. In this in vitro study of simulated ultimate assembly strength, the preparation of zirconia abutments did not significantly impair the fracture resistance of simulated implant assemblies. All implant abutments fractured at rates higher than the maximum incisal forces (90-370 N) estimated to occur in the anterior region of the mouth.