Atomic Layer Deposi0on on Jonathan ChenŦ , Griffith Allen+, Steven Letourneau Δ, Michael F. Hurley Δ,* (Mentor), Elton Graugnard Δ,** ( Mentor) Magnesium Alloys to Inhibit Corrosion to Inhibit Corrosion ŦCharles W. Davidson College of Engineering, San Jose State University, San Jose, CA 95192 USA. 2.2: Atomic Layer Deposi0on +Department of Mechanical Engineering, Boise State University, Boise, ID 83725 USA. ΔDepartment of Materials Science Engineering, Boise State University, Boise, ID 83725 USA. (*email: mikehurley@boisestate.edu), (**email: eltongraugnard@boisestate.edu) 1: Introduc'on Magnesium Background Strength to Weight ra'os of Common Metals1,2,3,4 Atomic Layer Deposi'on Background •  Atomic layer deposi0on (ALD) is a thin film deposi0on technique that involves binary self limi0ng surface reac0ons resul0ng in a highly conformal, pinhole free, monolayer coa0ng on the substrate. •  ALD gives precise control over the growth of each atomic layer regardless of surface roughness or geometric complexity. •  Magnesium alloys are some of the lightest structural metals used in aerospace, automo0ve, and electronics, where a lightweight but also strong metal is needed. •  Magnesium alloys have a higher strength-­‐to-­‐
weight ra0o than most structural metals. Corrosion •  Corrosion is the undesirable breakdown of metals. •  Pipng corrosion is oren called “Invisible Corrosion” due to its small size but large effects on structural integrity. •  Pinholes in coa0ngs decrease their effec0veness. •  Atomic layer deposi0on provides a conformal, pinhole free coa0ng. •  Layers of alumina were deposited by pulsing trimethylaluminum (TMA) and then H2O, both in the vapor phase. •  The TMA bonded with available hydroxyl groups on the surface. The H2O reacted with TMA to form alumina. Nitrogen was used to purge the chamber between each gas pulse so reac0ons occurred only on the surface. Corrosion Cell: 2: Materials and Methods Atomic Force Microscopy (AFM) Diagram8: 400 grit 800 grit 1200 grit 2. 3. Clean Samples Acetone Ethanol ~1x1cm samples All coa0ngs applied at 120!C. 225 Cycles, 25nm TMA/H2O Clean Samples 5 Minute Acetone Sonica0on for Si chips to remove photoresist 425 Cycles, 50nm TMA/H2O 675 Cycles, 75nm TMA/H2O 900 Cycles, 100nm TMA/H2O 1μm Tes0ng Reference Electrode 0.6 M NaCl Solu0on Pla0num Counter Electrode 1.  Scratch back of sample to expose bare AZ31 2.  Apply Conduc0ve Silver Grease 3.  Agach copper back plate Open Circuit Voltage (10 Minutes) Linear Polariza0on -­‐150mV to 400mV vs OCV at 1mV/s Less Likely to Corrode Corrodes Less S0r Bar Coa0ng thickness measured on Si samples with Atomic Force Microscopy 1. The back of the sample is scratched to ensure a good electrical contact with the bare substrate. 2. Conduc0ve silver grease is applied between the sample and the copper plate to ensure minimum electrical resistance. 3. The copper back plate allows the tes0ng apparatus to connect to the sample without deforming it. The sample is ler to sit for 10 minutes while the voltage is recorded. This is done, so when tes0ng begins the sample is at equilibrium. This technique tests the corrosion of magnesium by applying a voltage and recording the current. Less Likely to Corrode Corrodes More Less Likely to Corrode Corrodes Less A ultra fine 0pped probe connected to a can0lever is brought within a few nanometers of the surface. Tip-­‐surface interac0ons exert a force on the 0p that can be detected and used to track surface features as the 0p is rastered across the surface. AFM provided informa0on on coa0ng thickness and roughness. Photoresist Si Chips D.I. Water 1. Copper Back Plate Sample GemStar™ Benchtop ALD 5 Minute sonica0on 3: Tes'ng •  Coated and non-­‐coated samples were tested in the pictured corrosion cell. •  Sodium Chloride 0.6 Molar electrolyte was suspended between the test sample and the Pla0num coated mesh anode. 2.2: Sample Prepara0on •  The coa0ngs were verified for thickness as shown in the AFM images on the ler. Coa0ng thickness per ALD cycle were determined to be ~0.11nm. •  Below, the graphs from linear polariza0on tes0ng are organized by sample surface roughness and show the results of the various coa0ng thicknesses. •  The orange notes and arrows on the graphs describe the trends that current and voltage cause in corrosion propensity. •  The ALD system was used to grow amorphous aluminum oxide (alumina) coa0ngs . Preven'on Coa'ng Verifica'on (AFM) Corrosion Poten'al ALD Applica'on •  Magnesium is the fourth most abundant element on earth •  Processing magnesium alloys requires significantly less energy than crea0ng aluminum alloys. AZ-­‐31 Magnesium alloy (98% Mg/3% Al/1% Zn) 4: Results Corrodes Less Corrodes More Less Likely to Corrode Corrodes More Corrodes Less 5: Summary •  400 grit surface prepara0on showed higher rates of corrosion. •  800 and 1200 showed slower rates of corrosion than 400 grit, and pipng concentra0on occurred at the boundaries of the sample-­‐cell interface. •  1μm had a greater rate of corrosion in a single concentrated area. •  Based on the LP measurements 75nm of Al2O3 appears to be the most effec0ve coa0ng thickness for 800, 1200, and 1μm surface prepara0on. Corrodes More 400 grit 50nm 1200 grit 75nm 1cm 5mm 1200 Grit 100nm 1 μm 50nm 1cm 1cm 6: Cita'ons 1.  Materials Proper0es Handbook: Titanium Alloys, R. Boyer, G. Welsch, and E. W. Collings, eds. ASM Interna0onal, Materials Park, OH, 1994. 2.  Metals Handbook, Vol.2 -­‐ Proper0es and Selec0on: Nonferrous Alloys and Special-­‐Purpose Materials, ASM Interna0onal 10th Ed. 1990. 3.  Metals Handbook, Vol. 3, Proper0es and Selec0on: Stainless Steels, Tool Materials and Special-­‐Purpose Metals, Ninth Edi0on, ASM Handbook Commigee., American Society for Metals, Materials Park, OH, 1980. 4.  Structural Alloys Handbook, 1996 edi0on, John M. (Tim) Holt, Technical Ed; C. Y. Ho, Ed., CINDAS/Purdue University, West Lafayege, IN, 1996. 5.  ATLAS TECH NOTE No.7, August 2010 6.  What is Atomic Layer Deposi0on? By Yuichi Harada hgp://www.brl.ng.co.jp/people/yharada/res_pro/projects/ald.html 7.  Avedesian, M. M., and Hugh Baker. Magnesium and Magnesium Alloys. Materials Park, OH: ASM Interna0onal, 1999. Print. 8.  Atomic Force Microscopy -­‐ What is it? By Keysight Technologies hgp://www.keysight.com/main/editorial.jspx?ckey=1774141&id=1774141&nid=-­‐33986.0&lc=spa&cc=VE 9.  Pipng Corrosion, hgps://www.nace.org/Pipng-­‐Corrosion/. Web. July 2015. 7: Acknowledgments Special thanks to: Drew Lysne and Rick Ubic. This Project is supported by Boise State University Department of Materials Science and Engineering and the Na0onal Science Founda0on Research Experience for Undergraduates in Materials and Sustainability (grant number DMR 1359344).