This work was supported by the Aircraft Equipment Reliability and Maintainability Improvement Program and the Patuxent Partnership. Townsend was supported by an ONR Faculty Research Fellowship. The authors also acknowledge the general support of the SMCM Chemistry and Biochemistry Department faculty and students, including support from the SMCM football team.

1. Preparing coating salts
CAUTION: Nickel salts and boric acid are toxic and should be handled with proper personal protective equipment including nitrile gloves, goggles and a lab coat. Strong acids and bases should be handled in the fume hood, and all waste chemicals should be disposed of as hazardous waste.
<ol>
	<li>Using a balance, weigh out the following powders in these ratios: 10.000 g of NiSO4&#183;6H2O, 2.120 g of NiCl2&#183;6H2O, 1.600 g of H3BO3 and combine in a vial together. See Table 1 for concentrations.</li>
	<li>Weigh out 1.800 g of SrAl2O4:Eu2+, Dy3+ phosphor or alternative phosphors including europium doped yttrium oxide, europium doped barium magnesium aluminate, or replace with alternative oxide, metal, or organic composite material depending on the desired effect. 
	NOTE: The amount added here may vary based on the properties of the composite material and the desired qualities of the metal-composite film.</li>
	<li>Using a porcelain mortar and pestle, grind the composite powder for approximately 10 minutes until it becomes a fine powder. 
	NOTE: This does not change the particle size, but does separate aggregated particles.</li>
	<li>Likewise, grind the salt mixture from step 1.1 in batches until it becomes a fine powder.</li>
	<li>Combine the ground phosphor with the ground salt mixture in a container for storage.</li>
	<li>Weigh out 0.188 grams of the mixture per cm2 of coating area, as prepared in step 1.5 and add to a container with an open top that is easy to access.</li>
	<li>To this, add 40 &#181;L of water per cm2 of coating area, and stir to partially dissolve the salts forming a thick paste. Set this aside. 
	NOTE: The protocol can be paused here.</li>
</ol>
2. Preparing the electrodes
<ol>
	<li>Using scissors, cut the anode to the size and shape that matches the object to be plated. In this example, we prepare a 4 cm2 nickel foil to be coated, and a 4 cm2 nickel anode is cut to match this. 
	NOTE: Other objects can be coated including large objects. In this case, select the area on the object to be coated, and cut out the anode to match the coating area.</li>
	<li>Using a cotton swab or a cloth, clean the surface of the anode foil and the cathode (coating object surface) with concentrated (10 M) potassium hydroxide or sodium hydroxide base to remove organic material. Next, rinse the surfaces with water to remove excess base.</li>
	<li>Using a cotton swab or a cloth, activate the object surface with concentrated acid. In the case of nickel, 37% vol/vol HCl is used, although for steel, 10% by volume aqueous HCl may be more appropriate. Please refer to the recommendations for activating metal surfaces provided elsewhere to determine the appropriate method for activating specific metals or alloys23,24. 
	NOTE: After this step, the metal surface is reactive and the surface will start to react with oxygen in the air to form an oxide layer. This will cause the surface to be inactive, so the following steps (2.4 &#8211; 3.5) should be performed in the next 5 minutes; otherwise, step 2.3 should be repeated before continuing. 
	CAUTION: This step should be performed in a fume hood to avoid exposure to HCl vapors.</li>
	<li>Quickly, deposit the coating paste onto the cathode object. In this case, the cathode is a 4 cm2 nickel foil on the benchtop. Cover the object area to be plated evenly and try to avoid gaps in the paste. 
	NOTE: In this example, we are painting on this paste with two scoopulas, however, other options may include spraying, dipping or doctor blading to increase the speed and efficiency of this step.</li>
	<li>Using a cotton swab or a cloth, activate the anode with concentrated acid by dipping the swab in the acid and gently rubbing the cathode surface. In the case of nickel, 70% vol/vol HNO3 can be used. 
	NOTE: However, other acids may be more appropriate for specific metals and alloys. Please refer to the recommendations provided elsewhere for the appropriate reagent to activate specific anode surfaces23,24. 
	CAUTION: This step should be performed in a fume hood to avoid exposure to NO2, a toxic brown gas that is formed during the reaction. Continue treating the surface until the surface becomes grey and textured. After this step, the metal surface is reactive and the surface will start to react with oxygen in the air to form an oxide layer, so the following steps should be performed quickly to avoid inactivation of the anode.</li>
	<li>If calculating the current efficiency is desired, use an analytical balance to record the mass of the anode and the cathode.</li>
</ol>
3. Assembly and coating
<ol>
	<li>Pre-set a power supply to the desired current in constant current mode or voltage, if constant voltage mode is desired. In this example, constant current mode is used with a current of 0.1 Amperes (0.1 A per 4 cm2 = 0.025 A/cm2). 
	NOTE: For larger or irregularly shaped objects, the coating area can be predetermined with a grid or using a photo with scale bar and an imaging software like ImageJ. The applied current can be scaled to deliver the same current density required for the coating area.</li>
	<li>Cut a piece of nylon sheet (or alternative hydrophilic membrane) to a size larger than the anode so that the anode does not make direct contact with the cathode object.
	<ol>
		<li>Place the nylon sheet on top of the coating paste, and then add a small amount of paste to this.</li>
	</ol>
	</li>
	<li>Next, add 1-2 drops of water from a pipette to allow the salt to partially dissolve. Steps 3.2.1 &#8211; 3.3 make the nylon sheet conductive and allow for the mass transport of ions through the electrolyte, which is necessary to balance charge in the coating reaction.</li>
	<li>Finally, add the activated anode on top and attach the negative lead to the cathode object and the positive lead to the anode. 
	NOTE: It might be helpful to tape down these leads so that the setup remains stationary, especially if the experiment involves small pieces of metal foil. This is less important for large objects.</li>
	<li>Cover the system with plastic or seal to help retain water, and apply moderate pressure (~100 g per cm2 area), turn on the power supply and continue coating for the desired duration.</li>
	<li>Turn off the power supply and expose the system.</li>
	<li>Disconnect the leads, separate the electrodes and rinse the cathode object with water into a waste container.
	<ol>
		<li>Soak the other items in water to remove salts and dispose of this aqueous solution in the properly labeled hazardous waste container</li>
		<li>Wearing gloves, gently rub the cathode object by hand to remove any uncoated composite particles. The coating is complete and ready for characterization.</li>
		<li>Using an analytical balance, record the mass of the anode and the cathode and find the difference between these values and their original mass.</li>
		<li>Use Faraday&#8217;s Laws of electrolysis to calculate the current efficiency. The theoretical moles of metal coating can be determined using Equation 1. 
		<img alt="Equation 1" src="/files/ftp_upload/61484/61484equ01.jpg" />&#160; &#160; Equation 1 
		where n is the amount of metal deposited (units: mol), I is the applied current, t is the coating time, F is Faraday&#8217;s constant (96485 coulombs per mole) and z is the charge of the metal ion. Calculate this value based on the experimental parameters.</li>
		<li>Divide the experimentally determined deposit mass obtained from the masses of the cathode or anode (Steps 2.6 and 3.7.3) by the theoretical mass lost (anode) or gained (cathode) to calculate the current efficiency using Equation 2. 
		<img alt="Equation 2" src="/files/ftp_upload/61484/61484equ02.jpg" />&#160; &#160; Equation 2 
		[NOTE: At a current efficiency of 100%, under constant voltage, a theoretical deposit mass is expected of approximately 1.095 g of nickel or 12.3 &#181;m of nickel per hour, given 0.04 A and 4 cm2 area. Likewise, under constant current, approximately 614.6 &#181;m nickel would theoretically deposit per unit of 1 A&#8729;cm-2 after 30 min.]</li>
	</ol>
	</li>
</ol>
4. Characterization with electrochemistry
<ol>
	<li>Use chronopotentiometry to monitor changes in voltage under constant current, and chronoamperometry to monitor changes in current under constant voltage.
	<ol>
		<li>Turn on the potentiostat and designate the duration and the applied current or voltage.</li>
		<li>Repeat steps 3.2 &#8211; 3.5 to prepare the coating.</li>
		<li>Use a calibrated 3-electrode system to normalize the voltage to a reference standard.
		<ol>
			<li>Place a platinum wire pseudo reference electrode between on top of the nylon sheet and below the anode. In order to ensure that the reference electrode does not make direct contact with the anode, use a separate nylon sheet (or alternative membrane) placed on top of the reference followed by a few drops of water, a small amount of coating paste (repeat steps 3.2 &#8211; 3.3) and then the anode.</li>
		</ol>
		</li>
		<li>Connect the leads to the electrodes, seal, press, begin coating and monitor changes in voltage or current.</li>
	</ol>
	</li>
</ol>
5. Characterization with quantum yield fluorescence spectroscopy
<ol>
	<li>If the coating contains fluorescent composite particles, use a fluorometer equipped with an integrating sphere to obtain absolute quantum yield measurements.
	<ol>
		<li>Place the coating into the fluorimeter stage with the fluorescent coating facing 45&#176; from the excitation source and 315&#176; from the detector.</li>
		<li>Record the fluorescence spectra starting at a wavelength below the excitation wavelength to record the areas of the excitation peak and the fluorescence peak.</li>
		<li>Remove the sample from the fluorometer, and repeat step 5.1.2 to record the blank excitation peak. Calculate the quantum yield (QY) from the ratios of the areas of the excitation and emission peaks (Equation 3 and Figure 3B). 
		<img alt="Equation 3" src="/files/ftp_upload/61484/61484equ03.jpg" />&#160; &#160; Equation 3 
		where Aem, Aex and Ao are the peak areas at the emission wavelength of the sample, the excitation wavelength of the sample and the excitation wavelength of the blank, respectively.</li>
	</ol>
	</li>
</ol>
6. Characterization with optical microscopy
<ol>
	<li>Place the sample on the stage of a calibrated optical microscope with the coating side facing the lenses and bring the surface into focus.</li>
	<li>Record surface images at the desired magnifications and surface sample sites.</li>
	<li>Using image analysis software (ex. ImageJ (IJ 1.46r)), calculate and plot the surface coverage and average composite particle size.</li>
	<li>To determine coating thickness and cross-section features, cut the cathode foil with scissors. Set the coating on the side and re-adjust the focus. Repeat steps 6.2 &#8211; 6.3.</li>
</ol>

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The authors have nothing to disclose.

Critical steps of electrostamping. Bathless electrostamping shares many of the same critical steps with traditional bath electroplating. These include proper cleaning of the electrodes, mixing metal ions into the electrolyte and applying and external or chemical (electroless plating) potential to cause reduction of metal onto the cathode. In addition, the oxidation of the anode and cathode should be avoided after acid activation by quickly rinsing with water and adding these electrodes to the setup.
Electrostamping compared to traditional bath plating. A few metal-composite fluorescent metal films have been reported from bath plating16,17,28. However, in order to overcome the low physisorption of the composite to the cathode, some inventive methods have been demonstrated. These include removing the water and using dry organic solvents17, decorating the composite particles with charged surfactants to disrupt the hydration shell16 or only attempting the process with non-hygroscopic particles22,28,29. However, these methods continue to be limited to low surface coverages, small particle sizes from nanometers to a few micrometers12, and the potential for organic material incorporation. In contrast, the electrostamping method introduced in this report traps the composite particles in a stagnant electrolyte paste during coating, which forces the composite particles to remain near the cathode long enough to become embedded into the nickel matrix as it grows around them. Table 1 compares the recipes of both bath plating and electrostamping and highlights the effect of removing the majority of the water from the solution. For a 4 cm2 coating, the volume of the paste is approximately 0.5 mL. Without a liquid bath, the coating paste can physically contain the composite particles to allow for larger composites to be coated and also at higher loading amounts. It should be noted that even though the concentrations are expressed in grams per liter of solution, electrostamping does not require a liquid bath.
Interestingly, the power consumption required for plating is also comparable to bath plating. For example, in a typical bath, 0.02 &#8211; 0.07 A&#8729;cm-2 current densities are employed, which is a range that contains the 0.025 A&#8729;cm-2 current found to be optimal for bathless electrostamping. The resistivity of the electrolyte also plays a role, where lower resistance values lead to lower voltage requirements as a result of Ohm&#8217;s Law. In bath plating, the electrolyte solution is often heated (80 &#8211; 90 &#176;C) to decrease the resistance, which is also a source of power consumption. In contrast, for bathless coating, the concentration of metal salts in the electrolyte is significantly higher (Table 1), which leads to a low electrolyte resistance20 (14-35 &#937; for the samples here), even at room temperature. This results in power requirements of 2.0 V, 0.025 A&#8729;cm-2 and 50 mW&#8729;cm-2 for electrostamping of the metal-composites (Figure 3A). Without the presence of composites, we would expect the power demand to be lower than traditional bath plating as a result of the lower resistivity of the concentrated electrolyte. However, since this method is used to deposit high levels (up to 80%) of uncharged particles in the metal matrix, their presence in the film inherently increases the resistivity of the cathode. This effect may explain the lower than expected thicknesses as the ceramic particles occupy more of the nickel surface, decreasing the available sites for nickel reduction and film growth.
Limitations of electrostamping. A limitation of this method includes the potential for non-uniform coating if the electrolyte paste does not reach the crevices of complex surfaces. Whereas bath electroplating can be used to deposit a uniform coating over the entire surface of an object, electrostamping provides a localized deposition. This may lead to an uneven thickness and roughness distribution. For some applications were dimensions are critical, this method may need additional adjustments (sanding, polishing etc.) after deposition to account for discrepancies in thickness. Additionally, as a result of bringing the plating system out of the bath, surface coverages of up to 80 &#177; 12% are possible20, even with large (87 &#177; 30 &#181;m) hygroscopic composite particles and without organic reagents. However, at high loadings, a compromise must be made between durability and functionality. As the percentage of composite material increases, the film properties begin to deviate away from the original metal matrix toward the properties of the composite material, which is often a brittle powder. As a result, high coverages above 50% may not be practical for many applications that require durable metal films.
Electrostamping compared to localized jet and brush plating. Bath plating can be used to selectively etch/plate specific areas on conductive objects by protecting the rest of the object with masking tape as the cathode is submerged. However, like electrostamping, jet plating and brush plating can deposit metal onto localized areas without a bath. In jet plating, an electrical potential is established between the cathode (object to be coated) and a stream of jetting electrolyte as it passes from the anode nozzle30. A plating potential is established through the jet, and the metal salts can be reduced at the surface. Likewise, the surface can also be etched under reversed polarity. This method has applications in electronic fabrication where small deposits can be jet-printed onto a circuit board. Similarly, brush plating also involves a flow of electrolyte out of an anode covered in an absorbent cloth31. The anode brush holds the flowing electrolyte and when it contacts the cathode object, the metal salts are reduced at the surface to produce a highly controllable thickness. This method is used for repair of large metal parts and these parts are often spinning during plating to increase the uniformity of the coating.
Both jet and brush plating involve a flowing liquid electrolyte. For this reason, they are amenable to pure and alloy metal plating. However, these methods would not be ideal for composite-metal plating. The challenges facing embedding composite particles into the cathode film in a bath are also present with these methods, especially for large and hygroscopic particles. In order to promote the capture of these particles within the growing metal film, the solution flow should be stagnant. Electrostamping is a new technique that addresses this problem by coating metal and composites with no solution flow. For this reason, electrostamping stands out as a unique method for coating in general, which may become a more commonly accepted method for locally depositing pure metal as well as metal composites.
Troubleshooting electrostamping. Potential troubleshooting of absent or inconsistent coatings can be addressed by checking the following. 1) The metal electrodes may not be cleaned effectively with base so that a hydrophobic organic material barrier prevents plating. 2) The metal electrodes are not effectively activated with acid, or have been exposed to air for more than 5 min so that a less conductive metal oxide layer barrier forms and prevents plating. 3) The paste is not viscous enough and does not trap the composite particles or is too dry and causes a high resistance through the electrolyte.
Future applications of electrostamping. For many objects, electrostamping could be advantageous over traditional bath plating. For example, if the object to be coated is large, cumbersome, delicate or sensitive to corrosion, then a selected area can be &#8220;stamped&#8221; onto the side of the object. Examples may include the sides of appliances, road signs, metal fences, sides of buildings, covert messages onto walls, laptop computers, metal hand tools, or automobile and aircraft components. In addition to the potential versatility of this method to coat objects that were previously considered not possible, this method opens the door to future investigation of other metal-composite combinations, at higher surface loadings and with larger or hygroscopic particles. Here, we demonstrate this method for metal oxide composite/nickel metal matrix coatings; however, this method may motivate the investigation of multiple different metals and alloys, with a variety of composite particles that have not yet been realized.

Traditional electroplating is widely used to deposit thin films of a variety of metals, alloys, and metal-composites onto conductive surfaces to functionalize them for the intended application1,2,3,4,5,6,7,8,9,10,11,12. This method adds a metal finish to parts used in the manufacturing of aerospace, automotive, military, medical, and electronic equipment. &#173;&#173;&#173;&#173;The object to be plated, the cathode, is submerged in an aqueous bath containing metal salt precursors, which are reduced to metal at the surface of the object by the application of a chemical or electrical potential. Non-charged composite particles can be incorporated into the metal film by adding these to the bath during coating to enhance the film properties for increased hardness in the case of metal oxides and carbides, smoothness with polymers or lubrication with liquid oils12,13. However, because these particles lack an inherent attraction to the cathode, the ratio of composite that is incorporated into the metal remains low for bath plating13,14,15. This is especially problematic for large particles that do not adsorb to the cathode long enough to be embedded by the growing metal film. Additionally, hygroscopic particles solvate in aqueous solutions and their hydration shell acts as a physical barrier impeding contact with the cathode16.
Some promising methods have been shown to mitigate this effect by using dry non-polar solvents to remove the hydration barrier completely17, or by decorating the composite particles with charged surfactant molecules16 that disrupt the hydration shell to allow contact between the particle and the cathode. However, because these methods involve organic materials, carbon contamination is possible in the film and breakdown of these organic materials could occur at the electrodes. For example, the organic solvents used (DMSO2 and acetamide) are heated to 130 &#176;C in an inert atmosphere for air-free coating; however, we found them to be unstable during coating in air. Due to resistive heating at the electrodes, redox reactions with organic materials may result in impurities or sites for heterogeneous nucleation and growth of metal nanoparticles18. As a result, there is a need for an organic-free aqueous electroplating method that addresses the long-standing challenge of particle-cathode adsorption. So far, metal-composite bath coating has been shown to embed particles up to a few micrometers in diameter19 and as high as 15 % loading16,17.
In response to this, we describe an inorganic bathless electrostamping method that forces composite particles to become embedded into the film at high surface coverages despite their large size and hygroscopic nature20. By removing the bath, the process does not involve containers of hazardous coating liquids and the object to be plated does not need to be submerged. Therefore, large, cumbersome or otherwise corrosion- or water-sensitive objects, can be plated or &#8220;stamped&#8221; in select areas with the composite material. In addition, the removal of excess water requires less clean-up of liquid hazardous waste.
Here, we demonstrate this method to produce bright fluorescent metal films by co-depositing non-toxic and air-stable europium and dysprosium doped, strontium aluminate (87 &#177; 30 &#181;m) with nickel at high loadings (up to 80%). This comes in contrast to previous examples that were plated in a bath and therefore were limited to small (nanometers to a few micrometers) phosphors12. In addition, previously reported electrodeposited films fluoresce only under short-wave UV-light, with the exception of a recent report that grew 1 &#8211; 5 &#181;m luminescent strontium aluminate crystals in an alumina film with plasma electrolyte oxidation21. Fluorescent metal films could have far-reaching applications in many industries involving dim-light environments including road sign illumination21, aircraft maintenance equipment location and identification20, automobile and toy decorations, invisible messages, product authentication22, safety lighting, mechanochromic stress identification10 and tribological wear visual inspection12,16. Despite these potential uses for glowing metal surfaces, this method could also be expanded to include additional large and/or hygroscopic composite particles to produce a new variety of metal-composite functional coatings that were previously not possible via electroplating.

<table><tbody><tr><td>37% M Hydrochloric Acid (aq)</td><td>SigmaAldrich</td><td>320331-500ML</td><td>corrosive - handle in fume hood</td></tr><tr><td>70% Nitric Acid (aq)</td><td>SigmaAldrich</td><td>438073-500ML</td><td>corrosive - handle in fume hood</td></tr><tr><td>Barium magnesium aluminate, europium doped (s)</td><td>SigmaAldrich</td><td>756512-25G</td><td>fine powder</td></tr><tr><td>Boric Acid (s)</td><td>SigmaAldrich</td><td>B6768-500G</td><td>toxic</td></tr><tr><td>Cotton Swab</td><td>Q-tips</td><td>Q-tips Cotton Swabs</td><td></td></tr><tr><td>ImageJ</td><td>National Institutes of Health</td><td>IJ 1.46r</td><td>free software</td></tr><tr><td>Nickel (II) chloride hexahydrate (s)</td><td>SigmaAldrich</td><td>223387-500G</td><td>toxic</td></tr><tr><td>Nickel (II) sulfate hexahydrate (s)</td><td>SigmaAldrich</td><td>227676-500G</td><td>toxic</td></tr><tr><td>Nickel foil (s)</td><td>AliExpress</td><td>Ni99.999</td><td></td></tr><tr><td>Nitrile gloves</td><td>Fisher Scientific</td><td>19-149-863B</td><td></td></tr><tr><td>nylon membrane (s)</td><td>Tisch Scientific</td><td>RS10133</td><td></td></tr><tr><td>Optical Microscope equipped with FTIC filter (470 &amp;plusmn; 20 nm)</td><td>Nikon</td><td>Eclipse 80i</td><td></td></tr><tr><td>Plastic Wrap</td><td>Fisher Scientific</td><td>22-305654</td><td></td></tr><tr><td>Porcelain Mortar</td><td>Fisher Scientific</td><td>FB961A</td><td></td></tr><tr><td>Porcelain Pestle</td><td>Fisher Scientific</td><td>FB961K</td><td></td></tr><tr><td>Potassium Hydroxide (s)</td><td>SigmaAldrich</td><td>221473-25G</td><td>corrosive</td></tr><tr><td>Potentiostat with platinum wire</td><td>Gamry Instruments</td><td>1000E</td><td></td></tr><tr><td>Scoopula</td><td>Fisher Scientific</td><td>14-357Q</td><td></td></tr><tr><td>Spectrofluorometer</td><td>Photon Technology International</td><td>QM-40</td><td></td></tr><tr><td>Strontium aluminate, europium and dysprosium doped (s)</td><td>GloNation</td><td>756539-25G</td><td>powder</td></tr><tr><td>Variable linear DC power supply</td><td>Tekpower</td><td>TP3005T</td><td></td></tr><tr><td>Yttrium oxide, europium doped (s)</td><td>SigmaAldrich</td><td>756490-25G</td><td>fine powder</td></tr></tbody></table>

localized bathless metal-composite plating via electrostamping

Composite plating with particles embedded into the metal matrix can enhance the properties of the metal coating to make it more or less conductive, hard, durable, lubricated or fluorescent. However, it can be more challenging than metal plating, because the composite particles are either 1) not charged so they do not have a strong electrostatic attraction to the cathode, 2) are hygroscopic and are blocked by a hydration shell, or 3) too large to remain stagnate at the cathode while stirring. Here, we describe the details of a bathless plating method that involves anode and cathode nickel plates sandwiching an aqueous concentrated electrolyte paste containing large hygroscopic phosphorescent particles and a hydrophilic membrane. After applying a potential, the nickel metal is deposited around the stagnant phosphor particles, trapping them in the film. The composite coatings are characterized by optical microscopy for film roughness, thickness and composite surface loading. In addition, fluorescence spectroscopy can be used to quantify the illumination brightness of these films to assess the effects of various current densities, coating duration and phosphor loading.

After following this protocol, a thin coating of metal should become plated onto the cathode surface and contain the composite particles that were added to the coating paste. Fluorescent or colored particle incorporation can be observed by visual inspection as a result of a change in appearance compared to the uncoated surface (Figure 1A1-A3). To investigate the percent surface coverage of the composite particles and to observe the surface morphology of the coating, optical microscopy can be used (Figure 1). Samples can be observed top-down (Figure 1B1-B3 and 1C1-C3) or cut to reveal the cross-section (Figure 1D1-D3). This works for observing microscale composite particles and microscale features in the metal coating. However, nanoscale composite particles and nanoscale morphological features should be observed with a scanning electron microscope19,25,26,27. Imaging software can be used to calculate the sizes and surface coverage of the composite particles by including data from images of several areas over the coated surface.
The results of this analysis can be plotted to show the effects of applied current and/or coating duration on the amount of particle loading (Figure 2A). In general, particle surface coverage increases with time and with current density. For coatings under constant voltage, the surface coverage increases steadily up to 80% after 18 h at a rate of 0.066% per min. For constant current deposition, the particle surface coverage increases rapidly at low currents and then levels off at current densities above 0.025 A&#8729;cm-2. The reason for this is likely due to the observation that coatings at 0.25 A&#8729;cm-2 were rough (Figure 1A1) and a nonuniform coating corresponded to a runaway voltage due to increased resistance (Figure 2A). Therefore, an optimized current density was identified at 0.025 A&#8729;cm-2 for nickel and strontium aluminate phosphor particles, but this parameter may need to be re-determined when changing the metal salt or the composite material.
The thickness of the films increases with time and current density as well, and interestingly the surface coverage is also correlated with thickness (Figure 2B). This is expected because as the film thickness increases, it has the capacity to contain more particles. Coating parameters like these can be monitored by electrochemistry under constant current with chronopotentiometry and under constant voltage with chronoamperometry (Figure 3A). Under constant voltage, the resistance increases steadily and, as a result of Ohm&#8217;s law, the current density decreases. Fluctuations in the current can be explained by periodic plating of layers rich in composite particles (high resistance) alternating with layers of metal atoms (low resistance). Under constant current, the resistance stays steady for about 30 minutes; however, at some point, the resistance increases rapidly and the coating becomes unstable. This can be observed in the optical microscope (Figure 1A1) where high currents can lead to inconsistent and rough coatings. Likewise, low currents also produce inconsistent coatings with low composite loading as a result of the low driving force to deposit (Figure 1A3). In contrast, optimized current densities are required for uniform coatings (Figure 1A2). Under optimized conditions, the current efficiencies remain high (85-95%) as calculated from Equations 1 and 2. However, at either high current densities (&#62; 0.025 A&#8729;cm-2) or long durations (&#62; 1 h), we observed a decrease in coating efficiency as the particle loading increases. For example, the film thickness of this metal composite does not increase as would be expected for pure nickel despite higher applied currents (Figure 1D1-D3).
For fluorescent or phosphorescent metal-composite coatings, fluorescence spectroscopy can be used to quantify the brightness and the luminescence quantum yield (Figure 3B). An integrating sphere encloses the sample in a reflective dome and allows light to travel through two openings separated by 90&#176;. The excitation light that travels to the blank sample (no coating) will have minimal absorbance and maximum reflection. Light reflects off of the sample, scatters around the integrating sphere and escapes through the opening behind the sample. The coating surface is angled at 45&#176; from the excitation light and 315&#176; from the detector. When the spectrum is repeated with a fluorescent sample, the excitation peak diminishes as a result of absorbance, and the emission peak appears. The shape of the emission peak(s) and the wavelength is recorded. In addition, the ratios of the peaks can be used to calculate the luminescence quantum yield following the equation given in Figure 3B. In general, the phosphorescence brightness of the film increases linearly with particle surface loading (Figure 1A1-A3), which is controlled by film thickness (Figure 2B). The quantum yield was found to correlate proportionally to the particle surface coverage by Gerwitz et al., and this reference includes more discussion on this topic20.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Reagent / Parameter</td>
			<td>Watt&#8217;s Bath Plating23</td>
			<td>Electrostamping20</td>
		</tr>
		<tr>
			<td>NiSO4.6 H2O (g/L)</td>
			<td>270</td>
			<td>1325</td>
		</tr>
		<tr>
			<td>NiCl2.6 H2O (g/L)</td>
			<td>60</td>
			<td>238</td>
		</tr>
		<tr>
			<td>H3BO3 (g/L)</td>
			<td>38</td>
			<td>212</td>
		</tr>
		<tr>
			<td>Composite (SrAl2O4:Eu2+, Dy3+) (g/L)</td>
			<td>---</td>
			<td>238</td>
		</tr>
		<tr>
			<td>H2O (g/L)</td>
			<td>812</td>
			<td>21</td>
		</tr>
		<tr>
			<td>Cathode Current Density (A cm-2)</td>
			<td>0.045</td>
			<td>0.025</td>
		</tr>
		<tr>
			<td>Composite Size Range (&#181;m)</td>
			<td>0 &#8211; 11</td>
			<td>0 &#8211; 100</td>
		</tr>
		<tr>
			<td>Composite Loading (%)</td>
			<td>0 &#8211; 40</td>
			<td>0 &#8211; 90</td>
		</tr>
	</tbody>
</table>
Table 1: Recipes for Traditional Bath Plating and Electrostamping. These are based on Watts&#8217;s nickel bath plating solution and corresponding electrostamping methods where the relative amounts of dry reagents are the same for each. However, the amount of added water is significantly different which increases the concentrations (g/L solution). Also included are typical current densities (A&#8729;cm-2), possible composite particle sizes (&#181;m) and loading amounts (%).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61484/61484fig01.jpg" /> 
Figure 1: Representative images of composite coatings.&#160;This includes photos of 4 cm2 films in the dark 5 seconds after excitation with visible light &#62; 400 nm was removed (A), top-view optical microscope images in the dark under an FTIC filter and continuous 470 &#177; 20 nm excitation (B), and under brightfield light conditions (C), including cross-section images (D), after coating for 30 minutes with applied current of 1.0 A (0.25 A&#8729;cm&#8722;2) (1), 0.1 A (0.025 A&#8729;cm&#8722;2) (2), and 0.01 A (2.5 &#215; 10&#8722;3 A&#8729;cm&#8722;2) (3). This figure has been modified from Gerwitz et al.20 <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61484/61484fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61484/61484fig02.jpg" /> 
Figure 2: Representative analysis of microscopy images.&#160;This includes the composite surface coverage (%) as a function of time for chronoamperometry (blue) and as a function of current density (A&#8729;cm-2) for chronopotentiometry (red) during coating of a 4 cm2 nickel foil sample after 30 min (A). Additionally, the surface coverage can be plotted with the film thickness as measured from the cross-section (B). This figure has been modified from Gerwitz et al.20 <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61484/61484fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61484/61484fig03.jpg" /> 
Figure 3: Representative electrochemical analysis during the coating process and fluorescence quantum yield measurements.&#160;This includes chronoamperometry (blue) and chronopotentiometry (red) during coating of a 4 cm2 nickel foil sample over time (A). Solid state stage fluorescence spectra of a 4 cm2 nickel foil sample coated for 30 min at 0.025 A&#8729;cm&#8722;2 under constant current, plotted with the spectra from the blank metal film (B). The ratios of the peak areas are used to calculate photoluminescence quantum yield using the equation provided where Aem, Aex and Ao are the peak areas at the emission wavelength of the sample, the excitation wavelength of the sample and the excitation wavelength of the blank, respectively. This figure has been modified from Gerwitz et al.20 <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61484/61484fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Localized Bathless Metal-Composite Plating via Electrostamping at JoVE.com

Localized Bathless Metal-Composite Plating via Electrostamping

Presented here is a protocol of bathless electroplating, where a stagnant metal salt paste containing composite particles are reduced to form metal composites at high loading. This method addresses the challenges faced by other common forms of electroplating (jet, brush, bath) of embedding composites particles into the metal matrix.

Composite plating with particles embedded into the metal matrix can enhance the properties of the metal coating to make it more or less conductive, hard, ...

localized-bathless-metal-composite-plating-via-electrostamping

Nanyang Technological University

Research

JoVE Journal

Chemistry

4.1K Views.  St. Mary's College of Maryland. Elektrostempelen werken door composietdeeltjes in het elektrolyt te vangen, waardoor ze met het metaal moeten worden afgenomen. Met deze nieuwe techniek zijn hoge composiet deeltjesbelastingen mogelijk, zelfs op watergevoelige objecten. In tegenstelling tot typische elektroplating, vereist deze techniek niet het onderdompelen van het voorwerp in een vloeibaar bad.Elk geleidend object, ongeacht de grootte of vorm. Kan worden bekleed met functionele materialen. Fluorescerende metalen com...

Video: Localized Bathless Metal-Composite Plating via Electrostamping

Nanomoulding of Functional Materials, a Versatile Complementary Pattern Replication Method to Nanoimprinting

We describe a nanomoulding technique which allows low-cost nanoscale patterning of functional materials, materials stacks and full devices. Nanomoulding combined with layer transfer enables the replication of arbitrary surface patterns from a master structure onto the functional material. Nanomoulding can be performed on any nanoimprinting setup and can be applied to a wide range of materials and deposition processes. In particular we demonstrate the fabrication of patterned transparent zinc oxide electrodes for light trapping applications in solar cells.

We describe a nanomoulding technique which allows low-cost nanoscale patterning of functional materials, materials stacks and full devices. Nanomoulding can be performed on any nanoimprinting setup and can be applied to a wide range of materials and deposition processes.

We describe a nanomoulding technique which  allows low-cost nanoscale patterning of functional materials, materials stacks  and full devices. Nanomoulding ...

Engineering

Creating Two-Dimensional Patterned Substrates for Protein and Cell Confinement

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1 While microcontact printing can be employed to directly print a large number of molecules, including proteins,2 DNA,3 and silanes,4 the formation of self-assembled monolayers (SAMs) from long chain alkane thiols on gold provides a simple way to confine proteins and cells to specific patterns containing adhesive and resistant regions. This confinement can be used to control cell morphology and is useful for examining a variety of questions in protein and cell biology. Here, we describe a general method for the creation of well-defined protein patterns for cellular studies.5 This process involves three steps: the production of a patterned master using photolithography, the creation of a PDMS stamp, and microcontact printing of a gold-coated substrate. Once patterned, these cell culture substrates are capable of confining proteins and/or cells (primary cells or cell lines) to the pattern.
The use of self-assembled monolayer chemistry allows for precise control over the patterned protein/cell adhesive regions and non-adhesive regions; this cannot be achieved using direct protein stamping. Hexadecanethiol, the long chain alkane thiol used in the microcontact printing step, produces a hydrophobic surface that readily adsorbs protein from solution. The glycol-terminated thiol, used for backfilling the non-printed regions of the substrate, creates a monolayer that is resistant to protein adsorption and therefore cell growth.6 These thiol monomers produce highly structured monolayers that precisely define regions of the substrate that can support protein adsorption and cell growth. As a result, these substrates are useful for a wide variety of applications from the study of intercellular behavior7 to the creation of microelectronics.8
While other types of monolayer chemistry have been used for cell culture studies, including work from our group using trichlorosilanes to create patterns directly on glass substrates,9 patterned monolayers formed from alkane thiols on gold are straight-forward to prepare. Moreover, the monomers used for monolayer preparation are commercially available, stable, and do not require storage or handling under inert atmosphere. Patterned substrates prepared from alkane thiols can also be recycled and reused several times, maintaining cell confinement.10

Self-assembled monolayers (SAMs) formed from long chain alkane thiols on gold provide well-defined substrates for the formation of protein patterns and cell confinement. Microcontact printing of hexadecanethiol using a polydimethylsiloxane (PDMS) stamp followed by backfilling with a glycol-terminated alkane thiol monomer produces a pattern where protein and cells adsorb only to the stamped hexadecanethiol region.

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1  While microcontact printing ...

Bioengineering

Real-Time DC-dynamic Biasing Method for Switching Time Improvement in Severely Underdamped Fringing-field Electrostatic MEMS Actuators

Mechanically underdamped electrostatic fringing-field MEMS actuators are well known for their fast switching operation in response to a unit step input bias voltage. However, the tradeoff for the improved switching performance is a relatively long settling time to reach each gap height in response to various applied voltages. Transient applied bias waveforms are employed to facilitate reduced switching times for electrostatic fringing-field MEMS actuators with high mechanical quality factors. Removing the underlying substrate of the fringing-field actuator creates the low mechanical damping environment necessary to effectively test the concept. The removal of the underlying substrate also a has substantial improvement on the reliability performance of the device in regards to failure due to stiction. Although DC-dynamic biasing is useful in improving settling time, the required slew rates for typical MEMS devices may place aggressive requirements on the charge pumps for fully-integrated on-chip designs. Additionally, there may be challenges integrating the substrate removal step into the back-end-of-line commercial CMOS processing steps. Experimental validation of fabricated actuators demonstrates an improvement of 50x in switching time when compared to conventional step biasing results. Compared to theoretical calculations, the experimental results are in good agreement.

The robust device design of fringing-field electrostatic MEMS actuators results in inherently low squeeze-film damping conditions and long settling times when performing switching operations using conventional step biasing. Real-time switching time improvement with DC-dynamic waveforms reduces the settling time of fringing-field MEMS actuators when transitioning between up-to-down and down-to-up states.

Mechanically underdamped electrostatic fringing-field MEMS actuators are well known for their fast switching operation in response to a unit step input ...

Experimental Implementation of a New Composite Fabrication Method: Exposing Bare Fibers on the Composite Surface by the Soft Layer Method

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional component that should have high electrical conductivity, high mechanical properties, and high productivity.
In this regard, a carbon fiber/epoxy resin composite can be an ideal material to replace the conventional graphite bipolar plate, which often leads to the catastrophic failure of the entire system because of its inherent brittleness. Though the carbon/epoxy composite has high mechanical properties and is easy to manufacture, the electrical conductivity in the through-thickness direction is poor because of the resin-rich layer that forms on its surface. Therefore, an expanded graphite coating was adopted to solve the electrical conductivity issue. However, the expanded graphite coating not only increases the manufacturing costs but also has poor mechanical properties.
In this study, a method to expose fibers on the composite surface is demonstrated. There are currently many methods that can expose fibers by surface treatment after the fabrication of the composite. This new method, however, does not require surface treatment because the fibers are exposed during the manufacture of the composite. By exposing bare carbon fibers on the surface, the electrical conductivity and mechanical strength of the composite are increased drastically.

A protocol to expose bare fibers on the composite surface by eliminating resin rich area is presented. The fibers are exposed during fabrication of the composites, not by the post surface treatment. The exposed carbon composites exhibit high electrical conductivity in the through-thickness direction and high mechanical property.

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional ...

Scalable Solution-processed Fabrication Strategy for High-performance, Flexible, Transparent Electrodes with Embedded Metal Mesh

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a polymer film. This paper also presents a low-cost, vacuum-free fabrication method for this novel TE; the approach combines lithography, electroplating, and imprint transfer (LEIT) processing. The embedded nature of the EMTEs offers many advantages, such as high surface smoothness, which is essential for organic electronic device production; superior mechanical stability during bending; favorable resistance to chemicals and moisture; and strong adhesion with plastic film. LEIT fabrication features an electroplating process for vacuum-free metal deposition and is favorable for industrial mass production. Furthermore, LEIT allows for the fabrication of metal mesh with a high aspect ratio (i.e., thickness to linewidth), significantly enhancing its electrical conductance without adversely losing optical transmittance. We demonstrate several prototypes of flexible EMTEs, with sheet resistances lower than 1 &#937;/sq and transmittances greater than 90%, resulting in very high figures of merit (FoM) &#8211; up to 1.5 x 104 &#8211; which are amongst the best values in the published literature.

This protocol describes a solution-based fabrication strategy for high-performance, flexible, transparent electrodes with fully-embedded, thick metal mesh. Flexible transparent electrodes fabricated by this process demonstrate among the highest reported performances, including ultra-low sheet resistance, high optical transmittance, mechanical stability under bending, strong substrate adhesion, surface smoothness, and environmental stability.

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a ...

Fabricating Complex Culture Substrates Using Robotic Microcontact Printing (R-&#181;CP) and Sequential Nucleophilic Substitution

In tissue engineering, it is desirable to exhibit spatial control of tissue morphology and cell fate in culture on the micron scale. Culture substrates presenting grafted poly(ethylene glycol) (PEG) brushes can be used to achieve this task by creating microscale, non-fouling and cell adhesion resistant regions as well as regions where cells participate in biospecific interactions with covalently tethered ligands. To engineer complex tissues using such substrates, it will be necessary to sequentially pattern multiple PEG brushes functionalized to confer differential bioactivities and aligned in microscale orientations that mimic in vivo niches. Microcontact printing (&#956;CP) is a versatile technique to pattern such grafted PEG brushes, but manual &#956;CP cannot be performed with microscale precision. Thus, we combined advanced robotics with soft-lithography techniques and emerging surface chemistry reactions to develop a robotic microcontact printing (R-&#956;CP)-assisted method for fabricating culture substrates with complex, microscale, and highly ordered patterns of PEG brushes presenting orthogonal &#8216;click&#8217; chemistries. Here, we describe in detail the workflow to manufacture such substrates.

Fabricating Complex Culture Substrates Using Robotic Microcontact Printing R- &#181;CP and Sequential Nucleophilic Substitution

Cell culture substrates functionalized with microscale patterns of biological ligands have immense utility in the field of tissue engineering. Here, we demonstrate the versatile and automated manufacture of tissue culture substrates with multiple, micropatterned poly(ethylene glycol) brushes presenting orthogonal chemistries that enable spatially precise and site-specific immobilization of biological ligands.

In tissue engineering, it is desirable to exhibit spatial control of tissue morphology and cell fate in culture on the micron scale. Culture substrates ...

Fabricating Reactive Surfaces with Brush-like and Crosslinked Films of Azlactone-Functionalized Block Co-Polymers

In this paper, fabrication methods that generate novel surfaces using the azlactone-based block co-polymer, poly (glycidyl methacrylate)-block-poly (vinyl dimethyl azlactone) (PGMA-b-PVDMA), are presented. Due to the high reactivity of azlactone groups towards amine, thiol, and hydroxyl groups, PGMA-b-PVDMA surfaces can be modified with secondary molecules to create chemically or biologically functionalized interfaces for a variety of applications. Previous reports of patterned PGMA-b-PVDMA interfaces have used traditional top-down patterning techniques that generate non-uniform films and poorly controlled background chemistries. Here, we describe customized patterning techniques that enable precise deposition of highly uniform PGMA-b-PVDMA films in backgrounds that are chemically inert or that have biomolecule-repellent properties. Importantly, these methods are designed to deposit PGMA-b-PVDMA films in a manner that completely preserves azlactone functionality through each processing step. Patterned films show well-controlled thicknesses that correspond to polymer brushes (~90 nm) or to highly crosslinked structures (~1-10 &#956;m). Brush patterns are generated using either the parylene lift-off or interface directed assembly methods described and are useful for precise modulation of overall chemical surface reactivity by adjusting either the PGMA-b-PVDMA pattern density or the length of the VDMA block. In contrast, the thick, crosslinked PGMA-b-PVDMA patterns are obtained using a customized micro-contact printing technique and offer the benefit of higher loading or capture of secondary material due to higher surface area to volume ratios. Detailed experimental steps, critical film characterizations, and trouble-shooting guides for each fabrication method are discussed.

Surface fabrication methods for patterned deposition of nanometer thick brushes or micron thick, crosslinked films of an azlactone block co-polymer are reported. Critical experimental steps, representative results, and limitations of each method are discussed. These methods are useful for creating functional interfaces with tailored physical features and tunable surface reactivity.

In this paper, fabrication methods that generate novel surfaces using the azlactone-based block co-polymer, poly (glycidyl methacrylate)-block-poly (vinyl ...

Scalable Stamp Printing and Fabrication of Hemiwicking Surfaces

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. This wetting phenomenon is important in many technical fields ranging from physiology to aerospace engineering. Currently, several different techniques exist for fabricating hemiwicking structures. These conventional methods, however, are often time consuming and are difficult to scale-up for large areas or are difficult to customize for specific, nonhomogeneous patterning geometries. The presented protocol provides researchers with a simple, scalable, and cost-effective method for fabricating micro-patterned hemiwicking surfaces. The method fabricates wicking structures through the use of stamp printing, polydimethylsiloxane (PDMS) molding, and thin-film surface coatings. The protocol is demonstrated for hemiwicking with ethanol on PDMS micropillar arrays coated with a 70 nm thick aluminum thin-film.

A simple protocol is provided for the fabrication of hemiwicking structures of varying sizes, shapes, and materials. The protocol uses a combination of physical stamping, PDMS molding, and thin-film surface modifications via common materials deposition techniques.

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. ...

Metal-Assisted Electrochemical Nanoimprinting of Porous and Solid Silicon Wafers

Metal-assisted electrochemical imprinting (Mac-Imprint) is a combination of metal-assisted chemical etching (MACE) and nanoimprint lithography that is capable of direct patterning 3D micro- and nanoscale features in monocrystalline group IV (e.g., Si) and III-V (e.g., GaAs) semiconductors without the need of sacrificial templates and lithographical steps. During this process, a reusable stamp coated with a noble metal catalyst is brought in contact with a Si wafer in the presence of a hydrofluoric acid (HF) and hydrogen peroxide (H2O2) mixture, which leads to the selective etching of Si at the metal-semiconductor contact interface. In this protocol, we discuss the stamp and substrate preparation methods applied in two Mac-Imprint configurations: (1) Porous Si Mac-Imprint with a solid catalyst; and (2) Solid Si Mac-Imprint with a porous catalyst. This process is high throughput and is capable of centimeter-scale parallel patterning with sub-20 nm resolution. It also provides low defect density and large area patterning in a single operation and bypasses the need for dry etching such as deep reactive ion etching (DRIE).

A protocol for metal-assisted chemical imprinting of 3D microscale features with sub-20 nm shape accuracy into solid and porous silicon wafers is presented.

Metal-assisted electrochemical imprinting (Mac-Imprint) is a combination of metal-assisted chemical etching (MACE) and nanoimprint lithography that is ...

Direct-Contact Co-culture of Astrocytes and Glioblastoma Cells Patterned using Polyelectrolyte Multilayer Templates

Glioblastoma Multiforme (GBM) is the most abundant and fatal malignant brain cancer. There are more than 13,000 cases projected in the United States in 2020 and 2021. GBM tumors most often arise from astrocytes and are characterized by their invasive nature, often recruiting healthy tissues into tumor tissue. Understanding communication between astrocytes and glioblastoma cells is vital for the molecular understanding of tumor progression. This protocol demonstrates a novel patterned co-culture method to investigate contact-mediated effects of astrocytes on GBM employing layer-by-layer assembly and micro-capillary-force driven patterning. Advantages include a protein-free cell culture environment and precise control of cellular interaction dictated by the pattern dimensions. This technique provides a versatile, economical, reproducible protocol for mimicking cellular interaction between glioma and astrocytes in glioma tumors. This model can further be used to tease apart changes in GBM molecular biology due to physical contact with astrocytes or with non-contact mediated soluble cofactor communication.

This protocol describes a patterned direct contact glioma-astrocyte co-culture utilizing micro-contact printing on polyelectrolyte multilayers (PEMs) to pattern U87 or A172 GBM cells and primary astrocytes.

Glioblastoma Multiforme (GBM) is the most abundant and fatal malignant brain cancer. There are more than 13,000 cases projected in the United States in ...

Localized Bathless Metal-Composite Plating via Electrostamping

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