Ni Microstructure Research Articles

Microstructure Evolution Analysis of Ni/YSZ Cermet Electrode using Cross-Sectional Model Cells

Abstract Degradation of solid oxide cells can be partially attributed to the microstructural changes in Ni/YSZ fuel electrodes owing to Ni migration. This study aims to evaluate the microstructural evolution of Ni/YSZ fuel electrodes as a function of the oxygen potential along the thickness direction. To this end, comb-shaped Ni-patterned electrodes were designed on the top layer of a YSZ thin film using two different systems: (a) a symmetrical Ni-patterned electrode and (b) an asymmetrical Ni–Pt electrode with a reference electrode. In the symmetrical electrode, one side of the Ni-patterned electrode operated at the fuel cell (FC) mode, exhibiting expansion that led to an increase in triple-phase boundary (TPB) length and a decrease in electrolyte width. Conversely, the Ni-patterned electrodes that operated in electrolysis (EC) mode showed a slight migration away from the electrolyte. Detailed microstructural changes in the EC mode were examined using the asymmetrical electrode, revealing a correlation between water vapor content and Ni morphology. The results suggest that the amount of water vapor adsorbed on the electrode surface causes the decrease of oxygen potential at TPB. This causes the decrease in the wettability that led to significant change of Ni microstructure across the electrode length.

Investigation of Electrochemical Parameters on Cost-Effective Zn/Ni-Based Electrocatalysts for Electrochemical CO2 Reduction Reaction to SYNGAS(H2+CO)

Electrochemical CO2 reduction reaction (CO2RR) has been studied in 0.1 M of KCl (pH of 6.96), NaHCO3 (pH of 8.3) and K2CO3 (pH of 11.36) cathodic solutions with various counter electrodes including graphite rod, SS316 rod and Pt mesh at different potential ranges on the Znx–Ni1-x bimetallic electrocatalysts. Among the Znx–Ni1-x electrocatalysts, the Zn–Ni electrode with a composition of 65 wt% Zn and 35 wt% Ni and cluster-like microstructure has the best performance for CO2RR by according to minimum coke formation and optimum CO and H2 faradaic efficiencies (CO FE% = 55% and H2 FE% = 45%). The cyclic voltammetry (CV) measurements and gas chromatography (GC) analysis for the CO2RR showed that KCl solution as the cathodic electrolyte with pH of 7 has the best performance and appropriate faradaic efficiency for H2(40%) and CO(30%) products in low potential value (−0.6 v) in this study. The best potential range for the CO2RR on the Zn-Ni bimetallic electrocatalyst in KCl solution with the scan rate (SR) 0.05 V. s−1 is between −0.3 V to −1 V vs Ag/AgCl. The use of stainless-steel electrode (SS316) as a counter electrode for electrochemical CO2RR is cost-effective and performs better than graphite electrode, but at high applied potential it oxidizes and dissolves in the electrolyte and then ions transfer to the Nafion membrane and poisons it.

Effect of Yttria-Stabilized Zirconia Concentration in an Electroless Bath on Microstructure and Composition of Ni/Yttria-Stabilized Zirconia Nanocomposite.

The effect of the yttria-stabilized zirconia (YSZ) nanoparticle loading in an electro-less bath was considered as one of the vital synthesis variables for control Ni content and microstructure of prepared nanocomposite particles, which are two crucial factors to achieving high-performance SOFC anode. Nanocomposite particles were prepared using a simple electroless method without any expensive pretreatment of sensitizing by Sn²+ ions as well as activating by Pd2+ ions that are usually used to apply nickel coating on the surface of a non-conductive substrate. The process was performed by adding YSZ nanoparticles into NaOH solution, separating them from the solution by the centrifugal method, then providing several water-based nanofluids with different concentrations of activated YSZ nanoparticles, mixing them with NiCI₂ solution, followed by adding the hydrazine and then NaOH solution. X-ray diffraction and scanning electron microscopy coupled with energy dispersive X-ray analysis were used to analyze the prepared nanocomposite particles. It is observed that after adding YSZ nanoparticles into the NaOH solution, the pH of the solution varied gradually from a starting pH of 10.2 to 9. Also, by increasing the YSZ nanoparticles loading in the electroless bath from 76 mg/l to 126 mg/l, the grain size of Ni deposits, the Ni content and the average size of the prepared nanocomposite particles decreased. The electrochemical mechanism previously proposed for the nickel ion reduction was modified, and a novel analytical model was proposed for variation of the efficiency of Ni deposition with YSZ nanoparticles loading.

Effect of the Microstructures on Vulcanized Rubber Frictions.

Vulcanized rubber is widely used in a wide range of applications because of its flexibility, durability, sealing properties, and high degree of friction. However, this high degree of friction can also become an issue, as it leads to the wearing and breakage of parts. In this report, we investigated the effects of the vulcanized rubber microstructures on friction force by using simple, anisotropic microstructures. The line and space master microstructures were prepared from a photoresist, and the structures were transferred to PDMS, PSt, and then Ni. After surface modification of the Ni microstructures by TEOS, the vulcanized rubber microstructures were fabricated by a simple hot press process with the TEOS-coated Ni microstructure molds. The structural parameters of the vulcanized rubber line and space microstructures were found to be successfully varied by elongation, and the structural deformations were also investigated by FEM simulations. Measurements of the frictional force of the vulcanized rubber microstructures revealed the friction coefficient was reduced by the surface microstructures and was affected by the directions of the contact because of the microstructure anisotropy. The reason for of these results can be explained by the changes in the contact area and hysteresis friction. These results suggest that the friction coefficients of vulcanized rubbers can be reduced by the simple surface microstructures that are applicable to a wide range of fields.

The Effect of Surface Nano and Microstructures on Hydrogen Gas Evolution Behavior on Ni Patterned Electrodes

Highly efficient water electrolysis process is one of the key technologies for hydrogen economy suppressing global warming. Now, alkaline water electrolysis (AWE) and Proton exchange membrane (PEM) electrolysis are regarded as the representative industrial process. The advanced electrode without precious metal or oxide catalysts for hydrogen evolution reaction (HER) in these processes plays an important role to design HER efficiently and economically. Tremendous efforts focusing to unique characteristic catalysts exploration have been engaged world-widely not only tediously and steadily but also with materials informatic-science utilization driven by AI technology. Roughly speaking based on electrochemical engineering aspects, the energy loss in water electrolysis is composed of electrode reaction kinetics governed by catalytic activity, concentration overpotential and ohmic drop in gas-liquid two phase dispersion layer. The concentration overpotential and ohmic resistance are sometimes result in significant energy loss in large scale industrial process. From the sustainable and economical views toward Hydrogen Economy Society, AWE with less precious catalysts is considered as hydrogen production candidate with cheaper cost and longer durability. Many papers on gas electrode behavior have focused on macroscopic observation, but more fundamental understanding on nucleation and growth behavior of gas bubbles is rather limited due to the experimental difficulties. It is believed that the electrode surface structure tailoring may also provide one of promising methods to improve the catalytic performance as well as advance catalytic HER activity. Especially, nano/micro-scale structures on the electrode surface are suggested to affect the catalyst performance by controlling the nucleation and growth behaviors of bubbles. However, the detailed mechanisms of the effect of surface nano/micro-scale structures on HER and bubble behaviors have not been elucidated. Therefore, to analyze the influence of microstructure and surface wettability of catalytic electrode on bubble behaviors and HER, this study focuses on bubble behaviors on the electrode surface using Ni micro-patterned electrode fabricated by electrodeposition and Pt single crystalline electrodes. Ni micro-patterned electrodes were electrodeposited in the electrolyte containing 0.05 mol dm-3 NiCl2∙6H2O (pH 2.5) on patterned Cu substrate. Pt and Ag/AgCl electrode were employed as CE and RE, respectively. Surface structures and wettability of prepared electrodes were evaluated by scanning electron microscopy (SEM) and contact angle measurement. Water electrolysis was performed in 1 M KOH and Pt mesh and Hg/HgO. The effect of surface roughness on bubble behaviors was additionally examined in 0.1 M H2SO4 with three electrode system; Pt single crystalline electrode prepared by the Clavier method as WE, carbon rod as CE, and reversible hydrogen electrode as RE, respectively. Microdot structures, cylinder-, semisphere- and square-like were prepared. Ni coverage ratio of Ni electrodeposited area to Cu substrate, was calculated to correlate surface wettability measured by sessile drop method and Ni microstructure. It was suggested that electrode surface wettability could be controllable by changing Ni coverage and each Ni microdot structure exhibited an apparent catalytic electrode by surface tailoring. The effect of microstructures and surface wettability on HER performance was then studied during galvanostatic electrolysis at -20 mA cm-2 for 30 min. Total overpotential measured from 200 s to 1800 s seemed to proceed water electrolysis stably. It increased with decreasing surface wettability. This may indicate lower surface wettability derived from Ni microarray structures increases overpotential by accumulating newly evolving H2 bubbles. To further analyze the phenomena, high-speed CCD camera cinematography was applied. The ratio of larger diameter bubble tended to increase with increasing the contact angle. It indicates lower surface wettability would enhance bubble growth behaviors on cathode surface. Moreover, larger diameter bubbles were generated on cylinder-like Ni microdots. These results suggest increasing contact area between bubbles and Ni micropatterned electrode would enhance bubble growth behaviors. The effect of Ni microdot height on bubble nucleation behaviors was also observed. It apparently demonstrated that taller Ni dot height rather increased the nucleation site of bubbles. In order to additionally investigate the effect of nano-scale roughness tailored by single crystalline growth technique on bubble behaviors, H2 bubble evolution behaviors on Pt single crystalline electrode were cinematographically recorded. No H2 bubbles were generated on smooth surface fabricated by Pt (111) microfacet, suggesting lower nano-scale surface roughness considerably suppressed bubble nucleation on Pt electrode surface. These results suggested micro and nano structures and surface wettability influenced on bubble nucleation and growth phenomena frequently encountered in industrial electrolysis. Further unknown room still remains to be challenged even in such a rather matured AWE. This work was partly carried out in Case Western Reserve University. Prof. Daniel Scherson’s supervisions are highly appreciated.

Challenges to model the role of heterogeneities on the shock response and spall failure of metallic materials at the mesoscales

The predictive modeling of the experimentally observed behavior of metallic materials under shock loading conditions (wave structures, spall strengths) is a critical challenge toward the design of next-generation structural materials. This challenge is due to the lack of computational methods that can predict microstructural evolution at the mesoscales under dynamic loading conditions. While classical molecular dynamics simulations have been able to provide atomic-scale insights in the defect and damage nucleation/evolution mechanisms, the capability to have a direct comparison with experimental data at the same time and length scales is still a challenge. The current computational approaches require that several approximations be made either for the loading conditions or for the micromechanisms related to defect evolution and interaction at the mesoscales. This viewpoint discusses the insights obtained from molecular dynamics simulations of shock deformation and spall failure of heterogeneous metallic microstructures. An example Al–Ni microstructure is used to identify the critical atomic-scale phenomena that need to be addressed by the mesoscale methods when considering shock deformation and failure (spallation) at the mesoscales.

Effects of Microstructure of Nickel Electrodeposits on the Growth of Tin-Nickel Intermetallic Compound and Joint Reliability

The mechanical breakage and electrical open failure of the flipchip bump interconnection are main issues that retarding the scale shrinkage of the 3D interconnections. In this study, the effects of the microstructure of the nickel electrodeposits on the growth of Sn-Ni intermetallic compound (IMC) and on the electro-migration (EM) reliability were investigatged. The crystal structure of the Ni diffusion barrier can be controlled by addition of additives in electroplating bath. When both coumarin and cis-2-butene-1,4-diol were contained in the bath, extremely fine grain Ni electrodeposits were deposited by the synergistic effects of the additives. The growth rate of Ni3Sn4 IMC formed on the interface between the extremely fine grain structured Ni layer and Sn solder is higher than that of the IMC formed on the interface between the large grain structured Ni layer and Sn solder. The EM failure stage corresponds to large void propagation at the Sn-Ni3Sn4 interface due to volume consumption of Sn for IMC formation. The results of STEM analysis in an early stage of the heat treatment of the solder demonstrated that substantial quantities of Ni atoms were dominantly dissolved into the liquid Sn layer. Ni3Sn4 IMC was mainly formed on the finely grained Ni layer due to the high dissolution of Ni atoms into the solute Sn during the reflow process. IMC growth was suppressed at the interface between the large and fine grain structured area. This study suggests a robust concept of the vertical structure of Ni diffusion barrier having a multi layered Ni microstructure, which can reinforce an adhesion property as well as diffusion barrier properties Figure 1

Microstructure, thickness and sheet resistivity of Cu/Ni thin film produced by electroplating technique on the variation of electrolyte temperature

In this research, it has been made Cu/Ni thin film produced with electroplating technique. The deposition process was done in the plating bath using Cu and Ni as cathode and anode respectively. The electrolyte solution was made from the mixture of HBrO3 (7.5g), NiSO4 (100g), NiCl2 (15g), and aquadest (250 ml). Electrolyte temperature was varied from 40°C up to 80°C, to make the Ni ions in the solution easy to move to Cu cathode. The deposition was done during 2 minutes on the potential of 1.5 volt. Many characterizations were done including the thickness of Ni film, microstructure, and sheet resistivity. The results showed that at all samples Ni had attacked on the Cu substrate to form Cu/Ni. The raising of electrolyte temperature affected the increasing of Ni thickness that is the Ni thickness increase with the increasing electrolyte temperature. From the EDS spectrum, it can be informed that samples already contain Ni and Cu elements and NiO and CuO compounds. Addition element and compound are found for sample Cu/Ni resulted from 70° electrolyte temperature of Ni deposition, that are Pt and PtO2. From XRD pattern, there are several phases which have crystal structure i.e. Cu, Ni, and NiO, while CuO and PtO2 have amorphous structure. The sheet resistivity linearly decreases with the increasing electrolyte temperature.

Effect of anode firing on the performance of lanthanum and nickel co-doped SrTiO3 (La0.2Sr0.8Ti0.9Ni0.1O3−δ) anode of solid oxide fuel cell

Perovskite oxides have potential for use as alternative anode materials in solid oxide fuel cells (SOFCs) due to stability in anode atmosphere; donor-doped SrTiO3 (e.g., La0.2Sr0.8TiO3−δ) is a good candidate for this purpose. Electro-catalytic nanoparticles can be produced in oxide anodes by the ex-solution method, e.g., by incorporating Ni into a perovskite oxide in air, then reducing the oxide in H2 atmosphere. In this study, we varied the temperature (1100, 1250 °C) and atmosphere (air, H2) of La0.2Sr0.8Ti0.9Ni0.1O3−δ (LSTN) anode firing to control the degree of Ni ex-solution and microstructure. LSTN fired at 1250 °C in H2 showed the best anodic performance for scandia-stabilized zirconia (ScSZ) electrolyte-supported cells in H2 and CH4 fuels due to the favorable microstructure and Ni ex-solution.

Highly Conductive and Low Cost Ni-PET Flexible Substrate for Efficient Dye-Sensitized Solar Cells

The highly conductive and flexible nickel-polyethylene terephthalate (Ni-PET) substrate was prepared by a facile way including electrodeposition and hot-press transferring. The effectiveness was demonstrated in the counter electrode of dye-sensitized solar cells (DSSCs). The Ni film electrodeposition mechanism, microstructure, and DSSC performance for the Ni-PET flexible substrate were investigated. The uniform and continuous Ni film was first fabricated by electroplating metallic Ni on fluorine-doped tin oxide (FTO) and then intactly transferred onto PET via hot-pressing using Surlyn as the joint adhesive. The obtained flexible Ni-PET substrate shows low sheet resistance of 0.18Ω/□ and good chemical stability for the I(-)/I(3-) electrolyte. A high light-to-electric energy conversion efficiency of 7.89% was demonstrated in DSSCs system based on this flexible electrode substrate due to its high conductivity, which presents an improvement of 10.4% as compared with the general ITO-PEN flexible substrate. This method paves a facile and cost-effective way to manufacture various metals on a plastic nonconducive substrate beneficial for the devices toward flexible and rollable.

Morphology change of galvanically displaced one-dimensional tellurium nanostructures via controlling the microstructure of sacrificial Ni thin films

One-dimensional Tellurium (Te) nanostructures with controlled dimensions and morphologies have been synthesized by the galvanic displacement reaction (GDR) of electrodeposited nickel (Ni) thin films. The effects of sacrificial Ni microstructure and HTeO2+ ion concentration on the resulting Te nanostructures were systematically investigated. The preferred crystal orientation of sacrificial Ni thin films was varied to synthesize Te nanostructures with various levels of distinctiveness. By adjusting the concentration of HTeO2+ ions in the galvanic displacement electrolyte, well-aligned one-dimensional (1-D) Te nanostructures such as conical and hexagonal pillars were prepared where the diameter ranged from ∼70 to ∼900nm and the length ranged from 1 to 3.6μm.

Ni/YSZ pattern anodes fabrication and their microstructure and electrochemical behavior changes in H2–H2O environments

An effective photolithographic process was investigated to fabricate Ni/YSZ pattern anodes using a bi-layer lift-off resist method. Suitable undercut size was found critical for successful pattern fabrication. Effects of Ni thickness, temperature and H2O content on Ni pattern microstructure were evaluated. Ni/YSZ pattern anodes with 0.5 μm thick Ni was tested in dry H2 at 550 °C without significantly changing the TPB line. Ni/YSZ pattern anodes with Ni thickness of 0.8 μm were tested at 550 °C under dry and humidified H2 (3–50% H2O) conditions without TPB line change. At 700 °C, and for 0.8 μm thick patterns, the TPB length showed pronounced change in H2 with 10–50% H2O. Significant increase in TPB length due to holes formation was observed at 800 °C with 3% and 10% H2O. Ni/YSZ pattern anodes with 1.0 μm thick Ni was stable in H2 with 3% H2O in the range 550–800 °C, with TPB line only slightly modified. However, distinct change of TPB line and Ni microstructure was observed with 10–70% H2O above 700 °C. Stabilization of the polarization resistance depends on temperature. To accelerate stabilization of the cell, pre-treatment of the cell in H2 with 3% H2O at 750 °C or 800 °C could be performed.

Impact of Reduction Parameters on the Initial Performance and Stability of Ni/(Sc)YSZ Cermet Anodes for SOFCs

In-situ reduction of Ni cermet anodes produces the porosity and influences the microstructure, performance and stability of the anodes. The impact on initial performance, stability and microstructure of two different reduction procedures currently in use at DTU Energy Conversion with reduction temperatures of 850 °C and 1000 °C was evaluated for tape-cast, thin electrolyte, Nickel/8 mol% Yttria-Stabilized Zirconia (Ni/8YSZ) or (Ni/10Sc1YSZ) symmetric cells. High temperature activation produced the lower Ohmic and polarization resistances related to Triple Phase Boundary (TPB) charge transfer processes for Ni/10Sc1YSZ cells. The Ni/8YSZ cells behaved oppositely with respect to reduction temperature. A hypothesis is proposed relating performance to variations in Ni microstructure, Ni/ceramic contacting and extent of TPB resulting from differences in reduction parameters. Further, the performance stability under high steam conditions was evaluated, and very stable performances and microstructures of the anode layers were observed.

Application of photo-etching of polytetrafluoroethylene induced by high energy synchrotron radiation to LIGA

Polytetrafluoroethylene (PTFE) microstructures’ processing characteristics using X-ray photo decomposition and desorption are studied in the highest energy region (2–12 keV). While the exposed surface states are seen melting and boiling from the remaining bubble structure of the irradiated surface, basic photochemistry of PTFE is also same as previous reports. Surface modification of PTFE from hydrophobic to hydrophilic was investigated in order to bond PTFE sheets to a brass substrate. Then, we have a successfully fabricated Ni microstructure by LIGA process using PTFE photo-etching using high energy X-ray. Proposed LIGA using SR-photo-etching of PTFE can simplify the total process, and it can ensure that dimensional errors remain small due to swelling in developer and electroplating bath.

Multilayered SOFC Anode Structure with Electroless Ni-YSZ for Enhancement of Cell Performance

High performance SOFC is fabricated using multilayer anode support with graded porosity. The graded anode fulfills the requirement of proper fuel oxidation at anode, effective electrochemical reaction at anode/electrolyte interface, thermal compatibility among cell components and long term stability. In such multilayer anode, conventional cermet (40 vol % Ni) helps in proper fuel diffusion and catalytic oxidation. Novel electroless anode (28-32 vol % Ni) is employed adjacent to YSZ electrolyte for effective electrochemical activity and thermal compatibility. Because of the presence of unique core (YSZ)-shell (Ni) microstructure, electroless anode is found to extend the anodic electrochemical reaction from electrolyte/anode interface to the bulk. Significant performance enhancement with current density of ~3.3 Acm-2 is observed for single cells fabricated with multilayer anode at 800degC, 0.7V. The multilayer anode is found to reduce the cell degradation from ~11 % (conventional anode) to ~1.6 % /1000 h during long term performance (~2000 h).

Electroforming of Ni mold for imprint lithography using high-aspect-ratio PMMA microstructures fabricated by proton beam writing

Proton beam writing (PBW) was applied for micromachining of a PMMA mother for Ni electroforming. Proton beam focused down to about 1μm at beam energy of 1.0–3.0MeV was used for PBW on a PMMA layer on Si or Cu substrate. Using modified techniques for developing of 15–30-μm thick resists exposed to PB and electroforming steps, fabrication of the Ni structures with aspect ratio up to 30 by electroforming with a 30-μm thick PMMA mother micromachined by PBW was successful. We also tried thermal imprint using a 15-μm thick Ni microstructure on Cu substrate with an aspect ratio of more than 4 on a PMMA film.

A kinetic study on the electrodeposition of nickel nanostructure and its electrocatalytic activity for hydrogen evolution reaction

The electrodeposition of nickel was studied using electrochemical techniques in different electrolytes and various agents. The voltammetry analysis clearly showed that the electrodeposition of nickel was a diffusion-controlled process associated with a typical nucleation process. The current transients represented instantaneous nucleation with a typical three-dimensional (3D) growth mechanism. Scharifker’s equations were derived for instantaneous and progressive nucleation of the 3D growth of the spherical centers under diffusion-controlled condition. The number of nucleation sites increased with the increment in overpotential and Ni2+ concentration. Atomic force microscopy was used to confirm the presumed model. Also, the electrocatalytic activities of the Ni films were investigated for hydrogen evolution reaction (HER). The electrocatalytic activity of the Ni nanostructure was three times higher than the 2D Ni microstructure when the overpotential of −1.2 V was applied. The HER current density at −1.4 V for Ni nanostructure (−20 mA cm−2) was considerable with respect to the Ni microstructure (−8.46 mA cm−2) too.

Influence of substrate microstructure on the high field dielectric properties of BaTiO3 films

The temperature dependence of the electrical leakage current density of chemical solution deposited BaTiO3 films on high purity Ni foils was investigated as function of the underlying Ni microstructure. Depending on the Ni heat treatment prior to BaTiO3 deposition, it was found that pores in the dielectric followed the profiles of the underlying Ni grain boundary grooves. The electrical properties were then characterized on capacitors with and without the presence of Ni grain boundaries. When a Ni grain boundary from the substrate was present in the capacitor used during the electrical measurements, the loss tangent of the capacitor rose rapidly for dc biases exceeding ∼25 kV/cm. The critical bias increases to ∼100 kV/cm when no substrate grain boundaries are included in the capacitor. In addition, the capacitance-voltage curves are much more symmetric when grain boundaries are absent. This disparity in the electrical behavior was analyzed in terms of the mechanisms of charge conduction across the Ni-dielectric interface. While a reverse biased Schottky emission mechanism dominates the current in areas free of Ni grain boundaries, the barrier at the cathode is ineffective when Ni grain boundaries are present in the substrate. This, in turn, leads to a larger leakage current dominated by the forward biased Schottky barrier at the anode. The results are important to both embedded and surface mount capacitors.

Development of Ni Grid Mask for Microfocus X-ray Inspection Apparatus

A Microfocus X-ray inspection apparatus requires a grid mask as a scale which gives an indication of distortion correction and magnification. In addition, a grid mask must be an X-ray absorber. A thick micro structure is available to an X-ray absorber. Ni which is a typical electroforming material has a vocation for a thick micro structure. In this study, we make use of Ni micro structure 40μm thick as X-ray absorber. We fabricated the Ni grid mask using LIGA-like process. When the X-ray tube voltage was 70kV, we could observe the plain gird through an IC chip. Additionally, the center distance of the grid was to within an average of ±1μm in both the lengthwise direction and crosswise direction. These results suggest a Ni micro-structure is available as the position indicator for a Microfocus X - ray Inspection Systems.

SEM morphology and XRD characterization of Ni microstructure arrays synthesized by dc electrodeposition in porous polycarbonate templates

SEM morphology and XRD characterization of Ni microstructure arrays synthesized by dc electrodeposition in porous polycarbonate templates