White paper by Prof. Mike Zach, University of Wisconsin‐Stevens Point, MZach@uwsp.edu, 715/346‐3179 Electroplate and Lift Lithography Techniques The Electroplate and Lift Lithography technique is a simple and easy to understand nanomanufacturing method. Metals or other materials for making wires are deposited in the same way as a jeweler electroplates a ring. The design of the electrode allows the metal to form only at the edge of the holes of the electrode surface, which is made from diamond. The wires can be “grabbed” by using a sticky polymer (plastic) film that is painted on, similar to how nail polish is applied. Alternatively, it is easy to remove the wires using standard office tape. The images below (Figure 1) show platinum wires being lifted away from the diamond template. To get a sense of scale, more than 16 of these stars or circles would fit within the cross section of a single human hair. While the wires appear fractured in these images, it is due only to the extreme stretching of the polymer film necessary to obtain the dramatic images shown. Normal methods for lifting away wires leave the wires intact. The templates are also reusable. Once wires are removed, the template is immediately ready to have the same or a different metal deposited and the sequence of “electroplate and lift” can be repeated indefinitely. USES A new development that can impact the manufacture of smart electronic devices is building complexity into the way wires self‐assemble. Experiments are being developed to increase the complexity further to make a full range of electronic components including diodes, transistors, capacitors, antennae, sensors and actuators. Figure 2 shows a single wire that starts out as pure nickel and ends as pure copper. Two Figure 1 – Images of platinum dissimilar metals that meet at a single point create an electronic sensor called a wires being lifted off of the thermocouple. The same structure made from semiconductor materials is a diode. diamond electrode. Sample and images by UWSP Increasing the complexity further will allow even more useful devices to be made. undergraduate student, Daniel Dissing) Ni
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Figure 2 – SEM image and elemental map of a single wire that is about 1/10th the diameter of a human hair. Sample by UWSP undergraduate student Morgan O’Connell and images by postdoc Lori Lepak A crossed bar array made from nickel and copper wires can be seen in Figure 3 on next page. A crossed bar array allows electronic materials to be addressed individually as unique points. The image on the left is part of an array that contains over 2100 individual junctions with only one out of alignment wire. There are plans for this structure to be tested with piezoelectric materials to provide memory to a device or electroluminescent to make a light emitting display. 1 White paper by Prof. Mike Zach, University of Wisconsin‐Stevens Point, MZach@uwsp.edu, 715/346‐3179 COST EFFICIENCY AND SCALABILITY While the size of these particular devices is not extraordinary, the impressive feat is that these structures were made using simple electrodes on an ordinary laboratory bench top and standard transparent adhesive tape. A significant cost savings compared to university researchers who use expensive clean rooms to perform similar research. As our facilities and techniques are further improved one of the goals is to make very high density arrays that would rival commercially made devices for a small fraction of what the commercial devices cost. The process is easily scalable by making larger electrodes or using multiple parallel electrodes. Figure 3 – Optical microscope image and an elemental map of crossed bar arrays that are made from nickel (blue) and copper (red) wires on carbon tape (yellow). Sample by undergraduate student Julia Weber and images by Julia Weber and Mike Zach MASS PRODUCTION EFFORTS The permanent, non‐sacrificial diamond template allows wires of a wide variety of materials to be electroplated and lifted off without losing all of the tedious work for making micro and nanopatterned electrodes. This ability is unique among all known methods for making patterned nanowires. To fully utilize the Electroplate and Lift Lithography method, a new instrument is being produced that will perform automated harvesting of micro and nanowires. As the first proof of concept of this instrument, the goal is to produce gram quantities of patterned nanowires and single microwires greater than one kilometer long. These will establish new world records for the quantity of nanowires produced and length of continuous extremely thin wire. These new capabilities will provide nanostructures for making bulk materials with vastly improved properties. The ability to make huge quantities of patterned wires creates many new opportunities. The development of nanotechnology promises to affect nearly all sectors of the economy. Manufacturing for that future is particularly challenging if it is to be done cheaply. Eventually this technology will be spun off to create a company with products of the nanowires, electrode templates and the instruments for making more complex nanowire circuitry. Figure 4 – An engineer’s drawing for an automated nanowire harvesting instrument. Solidworks technical drawing from Marten Machining It is important to note that because of its simplicity and durability, Electroplate and Lift Lithography is a technology that’s amenable for Main Street nanomanufacturing. 2