This work was supported by a grant from the RGC-NSFC Joint Fund sponsored by the Research Grants Council of Hong Kong (Project No. N_HKUST615/14). We would like to acknowledge Nanosystem Fabrication Facility (NFF) of HKUST for the device / system fabrication.

1. Fabrication of a Cr/Au adhesion layer using liftoff
<ol>
	<li>Spincoat HPR504 positive photoresist of 1.2 &#181;m thickness onto a quartz wafer using a spread speed of 1,000 rpm for 5 s and a spin speed of 4,000 rpm for 30 s.</li>
	<li>Softbake the photoresist on the quartz wafer at 110 &#176;C for 5 min on a hot plate.</li>
	<li>Using a mask aligner, expose the wafer such that locations for Cr/Au deposition are exposed with ultraviolet (UV) light. The exposure power density and time is 16 mW/cm2 and 7.5 s respectively (exposure energy density = 120 mJ/cm2).</li>
	<li>Develop the wafer by submersing it in positive resist developer FHD-5 for 1 min. Rinse the wafer with deionized (DI) water after the development process.</li>
	<li>Dry the wafer using a nitrogen (N2) gun. Put the wafer in an oven for 5 min at 120 &#176;C.</li>
	<li>Using electron beam (e-beam) evaporation, deposit a 5 nm Cr layer, followed by a 50 nm Au layer on the wafer. The deposition rates are 1 &#197;/s and 2 &#197;/s, respectively.</li>
	<li>Place the e-beam evaporated wafer into a container. Pour copious amount of acetone inside.</li>
	<li>Close the container using a lid. Place the lidded container in an ultrasonic cleaner for 10 min or until the liftoff process has completed.</li>
	<li>Flush the wafer using isopropanol (IPA) followed by DI water. Dry it using N2 gun and oven afterwards. 
	NOTE: The protocol can be paused here.</li>
</ol>
2. Fabrication of thin film Ag electrodes on the adhesion layer using liftoff
<ol>
	<li>Spincoat AZ P4620 positive photoresist of 7 &#181;m thickness onto the wafer using a spread speed of 1,000 rpm for 5 s and a spin speed of 4,000 rpm for 30 s.</li>
	<li>Softbake the photoresist on the wafer at 90 &#176;C for 450 s on a hot plate.</li>
	<li>Using a mask aligner, expose the wafer such that locations for Ag deposition are exposed with UV. The exposure power density and time is 16 mW/cm2 and 45 s respectively (exposure energy density = 720 mJ/cm2).</li>
	<li>Develop the wafer by submersing it in FHD-5 for 2 min. Rinse the wafer with DI water after the development process.</li>
	<li>Dry the wafer using a N2 gun. Put the wafer in an oven for 5 min at 120 &#176;C.</li>
	<li>Sputter a 1 &#181;m Ag layer on the wafer. The sputtering rate is ~86 nm/min.</li>
	<li>Place the sputtered wafer into a container. Pour copious amount of acetone inside.</li>
	<li>Close the container using a lid. Place the lidded container in an ultrasonic cleaner for 10 min or until the liftoff process has completed.</li>
	<li>Flush the wafer using IPA followed by DI water. Dry it using N2 gun and oven afterwards.</li>
</ol>
3. Passivation of the wafer to expose only the electrodes and contact pads
<ol>
	<li>Passivate the whole wafer surface with a 2 &#181;m silicon dioxide (SiO2) layer using plasma enhanced chemical vapor deposition (PECVD).
	<ol>
		<li>Passivate a small silicon dummy sample (a silicon wafer fragment) together the wafer simultaneously.</li>
		<li>Measure the thickness of the oxide layer of the dummy sample. 
		NOTE: The protocol can be paused here.</li>
	</ol>
	</li>
	<li>Spincoat AZ 5214E dual tone photoresist of 1.4 &#181;m thickness onto the wafer using a spread speed of 1000 rpm for 5 s and a spin speed of 3000 rpm for 30 s.</li>
	<li>Softbake the photoresist on the wafer at 90 &#176;C for 150 s on a hot plate.</li>
	<li>Using a mask aligner, expose the wafer such that the locations for pad opening are exposed with UV. The exposure power density and time is 16 mW/cm2 and 2.25 s respectively (exposure energy density = 36 mJ/cm2).</li>
	<li>Develop the wafer by submersing it in FHD-5 for 75 s. Rinse the wafer with DI water after the development process.</li>
	<li>After briefly drying the wafer using N2 gun, further dry and hard bake the wafer in an oven for 15 min at 120 &#176;C.</li>
	<li>Perform descum of photoresist on the wafer for 1 min using a plasma asher to ensure complete removal of unwanted photoresist.</li>
	<li>Perform reactive ion etching on the wafer and the dummy sample to expose the thin film electrodes and contact pads.
	<ol>
		<li>After performing the etching process for a short period of time (e.g., 5-10 min), stop the operation and take out the dummy sample.</li>
		<li>Measure the thickness of the oxide layer on top of the dummy sample. Compare it with the result obtained in step 3.1.2.</li>
		<li>Calculate the rate of SiO2 etching of the machine to fine tune the etching duration in order to achieve a 10% overetch.</li>
		<li>Continue the etching process without the dummy sample.</li>
	</ol>
	</li>
	<li>Resist strip the etched wafer by plasma ashing for 30 min, followed by a positive photoresist stripper MS2001 bath at 70 &#176;C for 5 min.</li>
	<li>Flush the wafer using DI water. Dry the wafer using N2 gun and oven. 
	NOTE: The protocol can be paused here.</li>
</ol>
4. Preparation for the fabrication of thin film Ag/AgCl electrodes (chip)
<ol>
	<li>Dice cut the wafer to obtain different testing chips.</li>
	<li>Polish the electrode surfaces on the chips using fine sandpaper.</li>
	<li>Bond the contact pads on the chip to an external printed circuit board for interfacing purposes in further steps.</li>
	<li>3D-print an acrylic hollow rectangular container to hold the electrolyte on the thin film electrodes. The dimensions of the rectangular container should allow placement of a wire and a pipette inside the void comfortably.</li>
	<li>Mix a small amount of polydimethylsiloxane (PDMS) prepolymer and its curing agent thoroughly. The ratio should be 10:1. 
	NOTE: It is very common to degas the PDMS mixture to obtain high quality PDMS devices; however, it is not needed in this case as the mixture is only used as an adhesive.</li>
	<li>Place the acrylic container on the diced chip in a fashion such that all the silver electrodes are inside the cavity of the container.
	<ol>
		<li>Using a toothpick or a fine rod, smear the uncured PDMS mixture on the outer edge where the container and the chip touch each other.</li>
		<li>Carefully place the chip on a flat hot plate and cure the PDMS for 2 h at 80 &#176;C or until the container is securely affixed onto the chip.</li>
	</ol>
	</li>
</ol>
5. Preparation for the fabrication of thin film Ag/AgCl electrodes (reagents)
<ol>
	<li>Using DI water and concentrated hydrochloric acid (HCl), obtain 0.01 M HCl solution.</li>
	<li>Using DI water and potassium chloride (KCl) powder, obtain 3.5 M KCl solution and 0.1 M KCl solution. 
	NOTE: The protocol can be paused here.</li>
</ol>
6. Preparation for the fabrication of thin film Ag/AgCl electrodes (macro electrodes)
<ol>
	<li>Cut some silver wires.</li>
	<li>Polish the surface of the silver wires with fine sandpaper.</li>
	<li>Submerse 80% of the silver wires into household bleach for 1 h. 
	NOTE: The color of the wire will change from silvery to dark purple. This shows the formation of AgCl on the surface of the silver wire.</li>
	<li>Flush the Ag/AgCl wire with DI water.</li>
	<li>Make an Ag/AgCl reference electrode using one of the Ag/AgCl wires referencing to Hassel et al. with modifications15. 
	NOTE: The modifications are using a pipette instead of a glass capillary, using 3.5 M KCl as the electrolyte, ditching the polymer block and the gold-plated connector and replace it with parafilm.</li>
	<li>Store the Ag/AgCl electrodes by submersing them in 3.5 M KCl solution. Make sure the silver part does not come in contact with the solution.
	<ol>
		<li>Cut several pieces of Ag/AgCl wires and put them into the KCl solutions mentioned in step 5.2. 
		NOTE: The protocol can be paused here.</li>
	</ol>
	</li>
</ol>
7. Cathodic cleaning of the micro Ag electrodes
NOTE: All of the following processes use the CHI660D electrochemical analyzer/workstation and its accompanying software.
<ol>
	<li>Flush the chip using IPA followed by DI water.</li>
	<li>Pour 0.01 M HCl solution into the acrylic container.</li>
	<li>Wipe dry the macro Ag/AgCl reference electrode&#39;s pipette exterior (fabricated in step 6.5) and a macro Ag/AgCl electrode (fabricated in step 6.3) using laboratory clean wipes.</li>
	<li>Connect the chip and the macro electrodes to the analyzer such that a thin film Ag electrode on the chip is defined as the working electrode, the macro Ag/AgCl reference electrode is defined as the reference electrode, and the bare macro Ag/AgCl electrode is defined as the counter electrode.</li>
	<li>Place the macro electrodes into the container. Use blu-tack as the lid of the container to anchor the macro electrodes.</li>
	<li>Place the setup into a Faraday cage.</li>
	<li>In the CHI660D software, click on the Setup tab at the top left corner of the window. Then click Technique | Amperometric i-t Curve | OK to perform cathodic cleaning of the electrodes.</li>
	<li>In the pop-up menu, modify the parameters for cathodic cleaning.
	<ol>
		<li>Set the Init E (V) as -1.5.</li>
		<li>Set the Sample Interval (sec) as 0.1 (Default).</li>
		<li>Set the Run Time (sec) as 900.</li>
		<li>Set the Quiet Time (sec) to be 0 (Default).</li>
		<li>Set the Scales during Run as 1 (Default).</li>
		<li>Set the Sensitivity (A/V) appropriately. For an 80 &#181;m x 80 &#181;m electrode, set it as 1e-006.</li>
	</ol>
	</li>
	<li>Press OK. Start the process by pressing the Start icon under the menu bar.</li>
	<li>Let the experiment run and finish.</li>
	<li>Open the Faraday cage.</li>
	<li>Remove the macro reference and counter electrode. Wipe dry their surfaces.</li>
	<li>Pour the used electrolyte in a waste container. Flush the acrylic container using DI water.</li>
</ol>
8. Fabrication of single layer AgCl on top of the thin film Ag electrodes
<ol>
	<li>Pour 0.1 M KCl solution into the acrylic container.</li>
	<li>Connect the chip and the macro electrodes to the analyzer such that the cleaned thin film Ag electrode on the chip is defined as the working electrode, the macro Ag/AgCl reference electrode is defined as the reference electrode, and the bare macro Ag/AgCl electrode is defined as the counter electrode.</li>
	<li>Place the macro electrodes into the container. Use blu-tack as the lid of the container to anchor the macro electrodes.</li>
	<li>Place the setup into a Faraday cage.</li>
	<li>In the CHI660D software, click on the Setup tab at the top left corner of the window, then click Technique | Chronopotentiometry | OK to perform galvanostatic fabrication of single layer AgCl on silver electrodes.</li>
	<li>In the pop-up menu, modify the parameters for such process.
	<ol>
		<li>Set the Cathodic Current (A) as 0 (Default).</li>
		<li>Set the Anodic Current (A) such that the current density applied to the thin film electrode is 0.5 mA/cm2.</li>
		<li>Keep the High and Low E limit and Hold Time as default.</li>
		<li>Set the Cathodic Time (sec) as 10 (Default).</li>
		<li>Set the Anodic Time (sec) correspondingly to achieve the degree of AgCl coverage needed. 
		NOTE: With reference to Faradays Law of Electrolysis, the time needed for 100% coverage is 262 s. The time needed varies linearly with the coverage percentage.</li>
		<li>Set the Initial Polarity as Anodic.</li>
		<li>Set the Data Storage Intvl (sec) as 0.1 (Default).</li>
		<li>Set the Number of Segments as 1 (Default).</li>
		<li>Set the Current Switching Priority as Time.</li>
		<li>Uncheck the Auxiliary Signal Recording When Sample Interval &#62; = 0.0005s (Default).</li>
	</ol>
	</li>
	<li>Press OK. Start the process by pressing the Start icon under the menu bar.</li>
	<li>Let the experiment run and finish.</li>
	<li>Open the Faraday cage.</li>
	<li>Remove the macro reference and counter electrode. Wipe dry their surfaces.</li>
	<li>Submerse the macro electrodes in 3.5 M KCl solution for storage.</li>
	<li>Pour the used electrolyte in a waste container. Flush the container using DI water.</li>
	<li>Cover the opening of the acrylic container using parafilm for further processing.</li>
</ol>

<ol>
	<li>Bakker, E., Telting-Diaz, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrochemical+sensors.">Electrochemical sensors.</a> Analytical Chemistry. 74 (12), 2781-2800 (2002).</li><li>Jobst, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thin-Film+Microbiosensors+for+Glucose-Lactate+Monitoring.">Thin-Film Microbiosensors for Glucose-Lactate Monitoring.</a> Analytical Chemistry. 68 (18), 3173-3179 (1996).</li><li>Matsumoto, T., Ohashi, A., Ito, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+a+micro-planar+Ag/AgCl+quasi-reference+electrode+with+long-term+stability+for+an+amperometric+glucose+sensor.">Development of a micro-planar Ag/AgCl quasi-reference electrode with long-term stability for an amperometric glucose sensor.</a> Analytica Chimica Acta. 462 (2), 253-259 (2002).</li><li>Suzuki, H., Hirakawa, T., Sasaki, S., Karube, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+integrated+three-electrode+system+with+a+micromachined+liquid-junction+Ag/AgCl+liquid-junction+Ag/AgCl+reference+electrode.">An integrated three-electrode system with a micromachined liquid-junction Ag/AgCl liquid-junction Ag/AgCl reference electrode.</a> Analytica Chimica Acta. 387 (1), 103-112 (1999).</li><li>Ives, D. J. G., Janz, G. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Reference Electrodes - theory and practice. , (1961).</li><li>Huynh, T. M., Nguyen, T. S., Doan, T. C., Dang, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+thin+film+Ag/AgCl+reference+electrode+by+electron+beam+evaporation+method+for+potential+measurements.">Fabrication of thin film Ag/AgCl reference electrode by electron beam evaporation method for potential measurements.</a> Advances in Natural Sciences: Nanoscience and Nanotechnology. 10 (1), 015006 (2019).</li><li>Katan, T., Szpak, S., Bennion, D. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silver/silver+chloride+electrode:+Reaction+paths+on+discharge.">Silver/silver chloride electrode: Reaction paths on discharge.</a> Journal of The Electrochemical Society. 120 (7), 883-888 (1973).</li><li>Katan, T., Szpak, S., Bennion, D. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silver/silver+chloride+electrodes:+Surface+morphology+on+charging+and+discharging.">Silver/silver chloride electrodes: Surface morphology on charging and discharging.</a> Journal of The Electrochemical Society. 121 (6), 757-764 (1974).</li><li>Polk, B. J., Stelzenmuller, A., Mijares, G., MacCrehan, W., Gaitan, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ag/AgCl+microelectrodes+with+improved+stability+for+microfluidics.">Ag/AgCl microelectrodes with improved stability for microfluidics.</a> Sensors and Actuators B: Chemical. 114 (1), 239-247 (2006).</li><li>Mechaour, S. S., Derardja, A., Oulmi, K., Deen, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+the+wire+diameter+on+the+stability+of+micro-scale+Ag/AgCl+reference+electrode.">Effect of the wire diameter on the stability of micro-scale Ag/AgCl reference electrode.</a> Journal of The Electrochemical Society. 164 (14), E560-E564 (2017).</li><li>Brewer, P. J., Leese, R. J., Brown, R. J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+improved+approach+for+fabricating+Ag/AgCl+reference+electrodes.">An improved approach for fabricating Ag/AgCl reference electrodes.</a> Electrochimica Acta. 71, 252-257 (2012).</li><li>Safari, S., Selvaganapathy, P. R., Derardja, A., Deen, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrochemical+growth+of+high-aspect+ratio+nanostructured+silver+chloride+on+silver+and+its+application+to+miniaturized+reference+electrodes.">Electrochemical growth of high-aspect ratio nanostructured silver chloride on silver and its application to miniaturized reference electrodes.</a> Nanotechnology. 22 (31), 315601 (2001).</li><li>Tjon, K. C. E., Yuan, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impedance+characterization+of+silver/silver+chloride+micro-electrodes+for+bio-sensing+applications.">Impedance characterization of silver/silver chloride micro-electrodes for bio-sensing applications.</a> Electrochimica Acta. 320, 134638 (2019).</li><li>Pargar, F., Kolev, H., Koleva, D. A., van Breugel, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microstructure,+surface+chemistry+and+electrochemical+response+of+Ag+|+AgCl+sensors+in+alkaline+media.">Microstructure, surface chemistry and electrochemical response of Ag | AgCl sensors in alkaline media.</a> Journal of Materials Science. 53 (10), 7527-7550 (2018).</li><li>Hassel, A. W., Fushimi, K., Seo, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+agar-based+silver+|+silver+chloride+reference+electrode+for+use+in+micro-electrochemistry.">An agar-based silver | silver chloride reference electrode for use in micro-electrochemistry.</a> Electrochemistry communications. 1 (5), 180-183 (1999).</li></ol>

The authors have nothing to disclose.

The physical properties of an Ag/AgCl electrode is controlled by the morphology and the structure of the AgCl deposited on the electrode. In this paper, we presented a protocol to precisely control the coverage of a single layer of AgCl on the surface of the silver electrode. An integral part of the protocol is a modified form of the Faraday&#39;s Law of Electrolysis, which is used to control the degree of AgCl on the thin film silver electrodes. It can be written as:
<img alt="Equation" src="...

The Ag/AgCl electrode is one of the most used electrodes in the field of electrochemistry. It is most commonly used as the reference electrode in electrochemical systems due to its ease of fabrication, non-toxic property and stable electrode potential1,2,3,4,5,6.
Researchers have attempted to understand the mechanism of Ag/AgCl electrodes. The layer of chloride salt on the electrode has been found to be a fundamental material in the characteristic redox reaction of the Ag/AgCl electrode in a chloride containing electrolyte. For the oxidation path, the silver at the imperfection sites on the surface of the electrode combines with the chloride ions in the solution to form soluble AgCl complexes, in which they diffuse to the edges of the AgCl deposited on the surface of the electrode for precipitation in the form of AgCl. The reduction path involves the formation of soluble AgCl complexes using the AgCl on the electrode. The complexes diffuse to the silver surface and reduces back to elemental silver7,8.
The morphology of the AgCl layer is a pivotal influence in the physical property of Ag/AgCl electrodes. Various works showed that the large surface area is key to form reference Ag/AgCl electrodes with highly reproducible and stable electrode potentials9,10,11,12. Therefore, researchers have investigated methods to create Ag/AgCl electrodes with a large surface area. Brewer et al. discovered that using constant voltage instead of constant current to fabricate Ag/AgCl electrodes would result in a highly porous AgCl structure, increasing the surface area of the AgCl layer11. Safari et al. took advantage of the mass transport limitation effect during AgCl formation on the surface of silver electrodes to form AgCl nanosheets on top of them, increasing the surface area of the AgCl layer significantly12.
There is a rising trend to design AgCl electrode for sensing applications. A low contact impedance is crucial for sensing electrodes. Thus, it is important to understand how the surface coating of AgCl would affect its impedance property. Our previous research showed that the degree of AgCl coverage on the silver electrode has a pivotal influence on the impedance characteristic of the electrode/electrolyte interface13. However, to correctly estimate the contact impedance of thin film Ag/AgCl electrodes, the AgCl layer formed must be smooth and have well-controlled coverage. Therefore, a method to form smooth AgCl layers with designated degrees of AgCl coverage is needed. Works have been done to address this need partially. Brewer et al. and Pargar et al. discussed that a smooth AgCl can be achieved using a gentle constant current, fabricating the AgCl layer on top of the silver electrode11,14. Katan et al. formed a single layer of AgCl on their silver samples and observed the size of individual AgCl particles8. Their research found that the thickness of a single layer of AgCl is around 350 nm. The aim of this work is to develop a protocol to form fine and well-controlled films of AgCl with predicted impedance properties on top of silver electrodes.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>AST Peva-600EI E-Beam Evaporation System</td>
			<td>Advanced System Technology</td>
			<td></td>
			<td>For Cr/Au Deposition</td>
		</tr>
		<tr>
			<td>AZ 5214 E Photoresist</td>
			<td>MicroChemicals</td>
			<td></td>
			<td>Photoresist for pad opening</td>
		</tr>
		<tr>
			<td>AZ P4620 Photoresist</td>
			<td>AZ Electronic Materials</td>
			<td></td>
			<td>Photoresist for Ag liftoff</td>
		</tr>
		<tr>
			<td>Branson/IPC 3000 Plasma Asher</td>
			<td>Branson/IPC</td>
			<td></td>
			<td>Ashing</td>
		</tr>
		<tr>
			<td>Branson 5510R-MT Ultrasonic Cleaner</td>
			<td>Branson Ultrasonics</td>
			<td></td>
			<td>Liftoff</td>
		</tr>
		<tr>
			<td>CHI660D</td>
			<td>CH Instruments, Inc</td>
			<td></td>
			<td>Electrochemical Analyser</td>
		</tr>
		<tr>
			<td>Denton Explorer 14 RF/DC Sputter</td>
			<td>Denton Vacuum</td>
			<td></td>
			<td>For Ag Sputtering</td>
		</tr>
		<tr>
			<td>FHD-5</td>
			<td>Fujifilm</td>
			<td>800768</td>
			<td>Photoresist Development</td>
		</tr>
		<tr>
			<td>HPR 504 Photoresist</td>
			<td>OCG Microelectronic Materials NV</td>
			<td></td>
			<td>Photoresist for Cr/Au liftoff</td>
		</tr>
		<tr>
			<td>Hydrochloric acid fuming 37%</td>
			<td>VMR</td>
			<td>20252.420</td>
			<td>Making diluted HCl for cathodic cleaning</td>
		</tr>
		<tr>
			<td>J.A. Woollam M-2000VI Spectroscopic Elipsometer</td>
			<td>J.A. Woollam</td>
			<td></td>
			<td>Measurement of silicon dioxide passivation layer thickness on dummy</td>
		</tr>
		<tr>
			<td>Multiplex CVD</td>
			<td>Surface Technology Systems</td>
			<td></td>
			<td>Silicon dioxide passivation</td>
		</tr>
		<tr>
			<td>Oxford RIE Etcher</td>
			<td>Oxford Instruments</td>
			<td></td>
			<td>For Pad opening</td>
		</tr>
		<tr>
			<td>Potassium Chloride</td>
			<td>Sigma-Aldrich</td>
			<td>7447-40-7</td>
			<td>Making KCl solutions</td>
		</tr>
		<tr>
			<td>SOLITEC 5110-C/PD Manual Single-Head Coater</td>
			<td>Solitec Wafer Processing, Inc.</td>
			<td></td>
			<td>For spincoating of photoresist</td>
		</tr>
		<tr>
			<td>SUSS MA6</td>
			<td>SUSS MicroTec</td>
			<td></td>
			<td>Mask Aligner</td>
		</tr>
		<tr>
			<td>Sylgard 184 Silicone Elastomer Kit</td>
			<td>Dow Corning</td>
			<td></td>
			<td>Adhesive for container on chip</td>
		</tr>
	</tbody>
</table>

fabrication of thin film silver/silver chloride electrodes with finely controlled single layer silver chloride

This paper aims to present a protocol to form smooth and well-controlled films of silver/silver chloride (Ag/AgCl) with designated coverage on top of thin film silver electrodes. Thin film silver electrodes sized 80 &#181;m x 80 &#181;m and 160 &#181;m x 160 &#181;m were sputtered on quartz wafers with a chromium/gold (Cr/Au) layer for adhesion. After passivation, polishing and cathodic cleaning processes, the electrodes underwent galvanostatic oxidation with consideration of Faraday&#39;s Law of Electrolysis to form smooth layers of AgCl with a designated degree of coverage on top of the silver electrode. This protocol is validated by inspection of scanning electron microscope (SEM) images of the surface of the fabricated Ag/AgCl thin film electrodes, which highlights the functionality and performance of the protocol. Sub-optimally fabricated electrodes are fabricated as well for comparison. This protocol can be widely used to fabricate Ag/AgCl electrodes with specific impedance requirements (e.g., probing electrodes for impedance sensing applications like impedance flow cytometry and interdigitated electrode arrays).

Figure 1 shows an 80 &#181;m x 80 &#181;m Ag/AgCl electrode with a designed AgCl coverage of 50% fabricated following this protocol. By observation, the area of the AgCl patch is around 68 &#181;m x 52 &#181;m, which corresponds to around 55% of AgCl coverage. This shows that the protocol can finely control the amount of AgCl coverage on the thin film Ag electrodes. The AgCl layer fabricated is also very smooth, as evident by the clumping of adjacent AgCl par...

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Fabrication of Thin Film Silver/Silver Chloride Electrodes with Finely Controlled Single Layer Silver Chloride

This paper aims to present a method to form smooth and well-controlled films of silver chloride (AgCl) with designated coverage on top of thin film silver electrodes.

This paper aims to present a protocol to form smooth and well-controlled films of silver/silver chloride (Ag/AgCl) with designated coverage on top of thin ...

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13.9K Views.  The Hong Kong University of Science and Technology. This paper aims to present a method to form smooth and well-controlled films of silver chloride (AgCl) with designated coverage on top of thin film silver electrodes.

Video: Fabrication of Thin Film Silver/Silver Chloride Electrodes with Finely Controlled Single Layer Silver Chloride

Profiling the Triacylglyceride Contents in Bat Integumentary Lipids by Preparative Thin Layer Chromatography and MALDI-TOF Mass Spectrometry

The mammalian integument includes sebaceous glands that secrete an oily material onto the skin surface. Sebum production is part of the innate immune system that is protective against pathogenic microbes. Abnormal sebum production and chemical composition are also a clinical symptom of specific skin diseases. Sebum contains a complex mixture of lipids, including triacylglycerides, which is species-specific. The broad chemical properties exhibited by diverse lipid classes hinder the specific determination of sebum composition. Analytical techniques for lipids typically require chemical derivatizations that are labor-intensive and increase sample preparation costs. This paper describes how to extract lipids from mammalian integument, separate broad lipid classes by thin-layer chromatography, and profile the triacylglyceride contents using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. This robust method enables a direct determination of the triacylglyceride profiles among species and individuals, and it can be readily applied to any taxonomic group of mammals.

Mammalian integument contains solvent-extractable lipids that can provide chemical compositions characteristic of individual species. This paper presents a routine method for separating broad lipid classes isolated from integumentary tissues using thin layer chromatography and determining the triacylglyceride profile by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

The mammalian integument includes sebaceous glands that secrete an oily material onto the skin surface. Sebum production is part of the innate immune ...

Thin-layer Chromatographic (TLC) Separations and Bioassays of Plant Extracts to Identify Antimicrobial Compounds

A common screen for plant antimicrobial compounds consists of separating plant extracts by paper or thin-layer chromatography (PC or TLC), exposing the chromatograms to microbial suspensions (e.g. fungi or bacteria in broth or agar), allowing time for the microbes to grow in a humid environment, and visualizing zones with no microbial growth.&#160;The effectiveness of this screening method, known as bioautography, depends on both the quality of the chromatographic separation and the care taken with microbial culture conditions.&#160;This paper describes standard protocols for TLC and contact bioautography&#160;with a novel application to amino acid-fermenting bacteria. The extract is separated on flexible (aluminum-backed) silica TLC plates, and bands are visualized under ultraviolet (UV) light.&#160;Zones are cut out and incubated face down onto agar inoculated with the test microorganism.&#160;Inhibitory bands are visualized by staining the agar plates with tetrazolium red.&#160;The method is applied to the separation of red clover (Trifolium pratense cv. Kenland) phenolic compounds and their screening for activity against Clostridium sticklandii, a hyper ammonia-producing bacterium (HAB) that is native to the bovine rumen.&#160;The TLC methods apply to many types of plant extracts&#160;and other bacterial species (aerobic or anaerobic), as well as fungi, can be used as test organisms if culture conditions are modified to fit the growth requirements of the species.

Thin-layer Chromatographic TLC Separations and Bioassays of Plant Extracts to Identify Antimicrobial Compounds

Methods are described for thin-layer chromatographic (TLC) separation of plant extracts and contact bioautography to identify antibacterial metabolites. The methods are applied to the screening of red clover phenolic compounds inhibiting hyper&#160;ammonia-producing bacteria (HAB) native to the bovine rumen.

A common screen for plant antimicrobial compounds consists of separating plant extracts by paper or thin-layer chromatography (PC or TLC), exposing the ...

Dynamic Electrochemical Measurement of Chloride Ions

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver chloride electrode is used extensively for potentiometric measurement of chloride ions concentration in electrolyte. In this measurement, long-term and continuous monitoring is limited due to the inherent drift and the requirement of a stable reference electrode. We utilized the chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode. A galvanostatic pulse is applied to an Ag/AgCl electrode which initiates a faradic reaction depleting the Cl&#713; ions near the electrode surface. The transition time, which is the time to completely deplete the ions near the electrode surface, is a function of the ion concentration, given by the Nernst equation. The square root of the transition time is in linear relation to the chloride ion concentration. Drift of the response over two weeks is negligible (59 &#181;M/day) when measuring 1 mM [Cl&#713;]using a current pulse of 10 Am-2. This is a dynamic measurement where the moment of transition time determines the response and thus is independent of the absolute potential. Any metal wire can be used as a pseudo-reference electrode, making this approach feasible for long-term measurement inside concrete structures.

Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver ...

Layer-by-layer Synthesis and Transfer of Freestanding Conjugated Microporous Polymer Nanomembranes

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in combination with their outstanding thermal and chemical stability, and low densities. However, their insoluble nature causes problems in their processing since usually applied techniques such as spin coating are not available. Especially for membrane applications, where the processing of CMP as thin films is desirable, the processing problems have hindered their commercial application.
Here we describe the interfacial synthesis of CMP thin films on functionalized substrates via molecular layer-by-layer (l-b-l) synthesis. This process allows the preparation of films with desired thickness and composition and even desired composition gradients.
The use of sacrificial supports allows the preparation of freestanding membranes by dissolution of the support after the synthesis. To handle such ultra-thin freestanding membranes the protection with sacrificial coatings showed great promise, to avoid rupture of the nanomembranes. To transfer the nanomembranes to the desired substrate, the coated membranes are upfloated at the air-liquid interface and then transferred via dip coating.

In this paper we describe the interfacial synthesis of conjugated microporous polymers (CMP) on sacrificial substrates, and the dissolution of the substrate for the preparation of freestanding CMP nanomembranes. In addition, we will describe how the fragile nanomembranes can be transferred to other substrates.

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in ...

Influence of Hybrid Perovskite Fabrication Methods on Film Formation, Electronic Structure, and Solar Cell Performance

Hybrid organic/inorganic halide perovskites have lately been a topic of great interest in the field of solar cell applications, with the potential to achieve device efficiencies exceeding other thin film device technologies. Yet, large variations in device efficiency and basic physical properties are reported. This is due to unintentional variations during film processing, which have not been sufficiently investigated so far. We therefore conducted an extensive study of the morphology and electronic structure of a large number of CH3NH3PbI3 perovskite where we show how the preparation method as well as the mixing ratio of educts methylammonium iodide and lead(II) iodide impact properties like film formation, crystal structure, density of states, energy levels, and ultimately the solar cell performance.

We present an extensive study on the effects of different fabrication methods for organic/inorganic perovskite thin films by comparing crystal structures, density of states, energy levels, and ultimately the solar cell performance.

Hybrid organic/inorganic halide perovskites have lately been a topic of great interest in the field of solar cell applications, with the potential to ...

Fabrication and Testing of Photonic Thermometers

In recent years, a push for developing novel silicon photonic devices for telecommunications has generated a vast knowledge base that is now being leveraged for developing sophisticated photonic sensors. Silicon photonic sensors seek to exploit the strong confinement of light in nano-waveguides to transduce changes in physical state to changes in resonance frequency. In the case of thermometry, the thermo-optic coefficient, i.e., changes in refractive index due to temperature, causes the resonant frequency of the photonic device such as a Bragg grating to drift with temperature. We are developing a suite of photonic devices that leverage recent advances in telecom compatible light sources to fabricate cost-effective photonic temperature sensors, which can be deployed in a wide variety of settings ranging from controlled laboratory conditions, to the noisy environment of a factory floor or a residence. In this manuscript, we detail our protocol for the fabrication and testing of photonic thermometers.

We describe the process of fabrication and testing of photonic thermometers.

In recent years, a push for developing novel silicon photonic devices for telecommunications has generated a vast knowledge base that is now being ...

Chemical Synthesis of Porous Barium Titanate Thin Film and Thermal Stabilization of Ferroelectric Phase by Porosity-Induced Strain

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its well-balanced ferroelectricity, piezoelectricity, and dielectric constant. In addition, BT does not contain any toxic elements. Therefore, it is considered to be an eco-friendly material, which has attracted considerable interest as a replacement for lead zirconate titanate (PZT). However, bulk BT loses its ferroelectricity at approximately 130 &#176;C, thus, it cannot be used at high temperatures. Because of the growing demand for high-temperature ferroelectric materials, it is important to enhance the thermal stability of ferroelectricity in BT. In previous studies, strain originating from the lattice mismatch at hetero-interfaces has been used. However, the sample preparation in this approach requires complicated and expensive physical processes, which are undesirable for practical applications.
In this study, we propose a chemical synthesis of a porous material as an alternative means of introducing strain. We synthesized a porous BT thin film using a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles were used as an organic template. Through a series of studies, we clarified that the introduction of pores had a similar effect on distorting the BT crystal lattice, to that of a hetero-interface, leading to the enhancement and stabilization of ferroelectricity. Owing to its simplicity and cost effectiveness, this fabrication process has considerable advantages over conventional methods.

Here, we present a protocol for the synthesis of porous barium titanate (BaTiO3) thin film by a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles are used as an organic template.

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its ...

The Effect of Ultraviolet Radiation on the Chemical Bath Deposition of Bis(thiourea) Cadmium Chloride Crystals and the Subsequent CdS Obtention

In this work, the effects on the preparation of bis(thiourea) cadmium chloride crystals when illuminated with ultraviolet (UV) light at a wavelength of 367 nm using the chemical bath deposition technique are studied comparatively. Two experiments are performed to make a comparison: one without UV light and the other with the aid of UV light. Both experiments are performed under equal conditions, at a temperature of 343 K and with a pH of 3.2. The precursors used are cadmium chloride (CdCl2) and thiourea [CS(NH2)2], which are dissolved in 50 mL of deionized water with an acidic pH. In this experiment, the interaction of electromagnetic radiation is sought at the moment the chemical reaction is carried out. The results demonstrate the existence of an interaction between the crystals and the UV light; the UV light assistance causes crystal growths in an acicular shape. Also, the final product obtained is cadmium sulfide and shows no evident difference when synthesized with or without the use of UV light.

The Effect of Ultraviolet Radiation on the Chemical Bath Deposition of Bisthiourea Cadmium Chloride Crystals and the Subsequent CdS Obtention

This article presents a protocol for the synthesis of bis(thiourea) cadmium chloride crystals by chemical bath deposition. Two experiments are described: one aided by ultraviolet light compared to one without ultraviolet light.

In this work, the effects on the preparation of bis(thiourea) cadmium chloride crystals when illuminated with ultraviolet (UV) light at a wavelength of ...

Solution-Processed "Silver-Bismuth-Iodine" Ternary Thin Films for Lead-Free Photovoltaic Absorbers

Bismuth-based hybrid perovskites are regarded as promising photo-active semiconductors for environment-friendly and air-stable solar cell applications. However, poor surface morphologies and relatively high bandgap energies have limited their potential. Silver-bismuth-iodine (Ag-Bi-I) is a promising semiconductor for optoelectronic devices. Therefore, we demonstrate the fabrication of Ag-Bi-I ternary thin films using material solution processing. The resulting thin films exhibit controlled surface morphologies and optical bandgaps according to their thermal annealing temperatures. In addition, it has been reported that Ag-Bi-I ternary systems crystallize to AgBi2I7, Ag2BiI5, etc. according to the ratio of the precursor chemicals. The solution-processed AgBi2I7 thin films exhibit a cubic-phase crystal structure, dense, pinhole-free surface morphologies with grains ranging in size from 200 to 800 nm, and an indirect bandgap of 1.87 eV. The resultant AgBi2I7 thin films show good air stability and energy band diagrams, as well as surface morphologies and optical bandgaps suitable for lead-free and air-stable single-junction solar cells. Very recently, a solar cell with 4.3% power conversion efficiency was obtained by optimizing the Ag-Bi-I crystal compositions and solar cell device architectures.

Herein, we present detailed protocols for solution-processed silver-bismuth-iodine (Ag-Bi-I) ternary semiconductor thin films fabricated on TiO2-coated transparent electrodes and their potential application as air-stable and lead-free optoelectronic devices.

Bismuth-based hybrid perovskites are regarded as promising photo-active semiconductors for environment-friendly and air-stable solar cell applications. ...

Bio-inspired Polydopamine Surface Modification of Nanodiamonds and Its Reduction of Silver Nanoparticles

Surface functionalization of nanodiamonds (NDs) is still challenging due to the diversity of functional groups on the ND surfaces. Here, we demonstrate a simple protocol for the multifunctional surface modification of NDs by using mussel-inspired polydopamine (PDA) coating. In addition, the functional layer of PDA on NDs could serve as a reducing agent to synthesize and stabilize metal nanoparticles. Dopamine (DA) can self-polymerize and spontaneously form PDA layers on ND surfaces if the NDs and dopamine are simply mixed together. The thickness of a PDA layer is controlled by varying the concentration of DA. A typical result shows that a thickness of ~5 to ~15 nm of the PDA layer can be reached by adding 50 to 100 &#181;g/mL of DA to 100 nm ND suspensions. Furthermore, the PDA-NDs are used as a substrate to reduce metal ions, such as Ag[(NH3)2]+, to silver nanoparticles (AgNPs). The sizes of the AgNPs rely on the initial concentrations of Ag[(NH3)2]+. Along with an increase in the concentration of Ag[(NH3)2]+, the number of NPs increases, as well as the diameters of the NPs. In summary, this study not only presents a facile method for modifying the surfaces of NDs with PDA, but also demonstrates the enhanced functionality of NDs by anchoring various species of interest (such as AgNPs) for advanced applications.

A facile protocol is presented to functionalize the surfaces of nanodiamonds with polydopamine.

Surface functionalization of nanodiamonds (NDs) is still challenging due to the diversity of functional groups on the ND surfaces. Here, we demonstrate a ...