Name: Analysis of Contact Interfaces for Single GaN Nanowire Devices (Video) | JoVE Journal
Uploaded: 2013-11-15T17:00:00.000+00:00
Duration: 11 min 13 s
Description: Learn a technique for removing Ni/Au contacts from GaN nanowire devices using carbon tape to examine contact interfaces. This method enables detailed SEM analysis of void formation at semiconductor nanowire interfaces.

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5 minutes

The Authors would like to acknowledge the individuals in the Quantum Electronics and Photonics Division of the National Institute of Standards and Technology in Boulder, CO&#160;for their assistance.

The GaN NWs used in these experiments were grown by catalyst-free molecular beam epitaxy (MBE) on Si(111) substrates9. The general procedure for preparing the NW suspension from the substrate with the as-grown NWs is illustrated in Figure 1.
1. Nanowire Suspension Preparation
<ol>
	<li>Cleave a small (&#60;5 mm x&#160;5 mm) piece of the as-grown NWs on the substrate.</li>
	<li>Fill a small capped vial with about 1 ml of isopropanol (IPA).</li>
	<li>Place the cleaved piece into the vial, close the cap and sonicate for about 30 sec in order to remove the NWs from the substrate. Once prepared, the NW suspension remains viable for an extended period of time.</li>
</ol>
2. Substrate Preparation
The substrates used are heavily-doped (&#961; ~0.001-0.005 &#937;-cm) 3-inch Si wafers with 200 nm of thermally-grown SiO2 on both sides.
<ol>
	<li>If electrical contact to the silicon substrate is desired, etch off the oxide from the backside of the wafer using an RIE etcher with the following conditions, O2 flow = 20 sccm, CHF3 flow = 50 sccm, -240 V bias, 120 W for 20 min. This step also helps avoid charging of the specimen during electron microscopy.</li>
	<li>After oxide etch, clean wafer by submersing it face down using a tripod holder into a 1,000 ml beaker with ~100 ml of acetone for 5 min.</li>
	<li>Remove wafer from acetone and immediately rinse off both sides of the wafer using a squirt bottle of IPA over an empty 1,000 ml beaker, which will be used for solvent waste.</li>
	<li>Repeat step 2 using IPA.</li>
	<li>Repeat step 3 rinsing the wafer with deionized H2O over the solvent waste beaker.</li>
	<li>Repeat step 2 using deionized H2O.</li>
	<li>Blow wafer dry using compressed dry N2.</li>
</ol>
3. Nanowire Dispersal
<ol>
	<li>Cleave the clean wafer into 4 equal quarters. Each quarter will have 3 contact patterns deposited on it in the general areas shown in Figures 2A and B.</li>
	<li>Sonicate the vial of NW suspension prior to dispensing in order to get a uniform NW concentration in the suspension.</li>
	<li>Set the micropipette to the desired drop size (3-30 &#956;l) and draw the NW suspension from the vial.</li>
	<li>Take substrate piece (&#188; wafer) that will be used for dispersal and ensure that it is level so that the NW suspension does not migrate away to the edges.</li>
	<li>Dispense the NW suspension onto the (oxidized) front surface of the Si substrate in the general area where the contact pattern will be deposited. If desired, deposit additional drops of the NW suspension in the same area, after the solvent from the previous drop has completely evaporated.</li>
	<li>Repeat step 3.4 for the other 2 areas where a contact pattern will be. Do not dispense the NW suspension from more than 1 growth run on a single substrate piece (&#188; wafer) in order to avoid cross contamination. The dispersal of the NW suspension onto the substrate is illustrated in Figures 2C and D.</li>
	<li>After the final drop of NW suspension has evaporated, place the sample face down in a tripod holder and gently dip in successive baths of acetone and isopropanol to remove unwanted impurities. Rinse in deionized H2O, and blow dry in N2. Do not use squirt bottles or sonicate the solvent during this cleaning process to avoid excess removal of NWs from the surface.</li>
</ol>
4. Photolithography of Contact Pattern
Use standard photolithographic techniques to create the contact pattern in a clean room with ambient conditions of ~20 &#176;C and ~40% relative humidity. Mask aligner intensity (step&#160;4.6), exposure time (step 4.8) and develop time (step 4.9) will be equipment-dependent and should be adjusted to produce maximum pattern definition with a lift-off-resist (LOR) undercut of about 0.5 &#956;m.
<ol>
	<li>Spin lift-off resist onto sample using a two step recipe of (1) 300 rpm for 10 sec (2) 2,000 rpm for 45 sec.</li>
	<li>Place sample on a hot plate to bake for 5 min at 150-170 &#176;C.</li>
	<li>Remove sample and allow to cool for 30 sec and then spin on photoresist using a two step recipe of (1) 1,000 rpm for 3 sec (2) at 5,000 rpm for 45 sec.</li>
	<li>Place sample on a hot plate to bake for 1 min at 115 &#176;C.</li>
	<li>Allow sample to cool for 1 min.</li>
	<li>Calibrate mask aligner to a light intensity of ~1.90 mW/cm2.</li>
	<li>Load sample into mask aligner, with the proper mask for the contact pattern installed.</li>
	<li>Bring sample into contact with mask and expose the sample for 24 sec.</li>
	<li>Develop photoresist by swirling sample in a beaker of developer for 21 sec.</li>
	<li>Rinse with deionized H2O and blow dry with N2.</li>
</ol>
5. Sample Pretreatment Prior to Metal Deposition
Prior to loading the samples into the electron-beam evaporator for metal deposition, give the patterned wafer a UV ozone treatment and a HCl:H2O bath.
<ol>
	<li>Load samples into UV Ozone generator for 10 min with an ultra-high-purity O2 flow rate of 80 sccm.</li>
	<li>After UV ozone treatment, place samples in a HCl:H2O (1:10) solution for 1 min at room temperature.</li>
	<li>Rinse samples with deionized H2O and blow dry gently with N2.</li>
</ol>
6. Electron-beam Evaporation of Contact Metals
<ol>
	<li>Immediately after pretreatment, mount the samples to the platen using screws and clips and secure platen in the e-beam evaporator. Make sure that sufficient Ni and Au are available for deposition.</li>
	<li>Pump down chamber until the pressure is below 1.3 x 10-3 Pa (1 &#956;Torr) (may require to pump overnight).</li>
	<li>Set high voltage to 10 kV and begin rotation of samples at 5 rpm. Make sure shutter is closed.</li>
	<li>Select the Ni crucible and enter parameters for Ni into the crystal rate monitor. Deposit 50 nm (500 &#8491;) of Ni at a deposition rate of ~0.1 nm/s.</li>
	<li>Once Ni source has sufficiently cooled down (~15 min), switch to Au crucible, change the parameters to those for Au, and deposit 100 nm (1,000 &#8491;) of Au at a deposition rate of ~0.1 nm/sec.</li>
	<li>Once Au crucible has cooled down (~10 min), vent chamber and unload sample platen. If unsure of metal thickness, use a profilometer to determine the Ni/Au thickness.</li>
</ol>
7. Contact Metal Lift-off
<ol>
	<li>Remove samples from platen and place in a photoresist stripper bath at room temperature for a few hours to lift off the metal deposited on the photoresist. If desired, elevate the bath temperature to around 50-60 &#176;C to accelerate lift-off.</li>
	<li>If the metal does not come off completely, use a squirt bottle of Remover PG to forcefully remove the remaining undesired metal from the surface. Do not sonicate the sample because this can cause the nanowires to break free from the metal.</li>
	<li>Rinse off the Remover PG from sample with IPA into a solvent waste beaker and place sample into a beaker of clean IPA.</li>
	<li>Repeat step 7.3 using deionized H2O and then blow the sample dry using N2.</li>
</ol>
8. Contact Anneal
Test devices before the contact anneal in order to compare these with annealed devices. Perform the contact anneal of the Ni/Au films using a rapid thermal annealer (RTA) with ultra-high-purity N2/O2 (3:1) as the process gas.
<ol>
	<li>Wait at least 24 hr after removal of contact metal before annealing samples, to ensure the metal contacts have reached equilibrium after deposition.</li>
	<li>Purge the RTA by running the N2/O2 at a temperature of 650 &#176;C for 5 min without any samples.</li>
	<li>Load samples and adjust flow rate of N2/O2 to 1.4 SLPM.</li>
	<li>Anneal samples at 550 &#176;C for 10 min. The temperature ramp rate was ~500 &#176;C/min.</li>
</ol>
9. Ni/Au Film Removal
Since removal of the Ni/Au film is a destructive process, devices are typically imaged and tested before this step. The procedure for the Ni/Au film removal is illustrated in Figure 3.
<ol>
	<li>Wait at least 24 hr after contact anneal before removing the Ni/Au film.</li>
	<li>Cleave a piece of the sample from the area of interest. Make sure size of sample is large enough in order to grab the edges with tweezers without touching the area of interest.</li>
	<li>Secure a SEM pin stub mount in a holder such that the mount can be easily moved or taken out.</li>
	<li>Place a piece of conductive carbon tape flat onto the mount surface. The piece of carbon tape should be larger than the area of the film that is to be removed. A conductive carbon tab that is the precise size of the mount surface works very well for this application. Apply the carbon tape or tab to the mount surface slowly and carefully to ensure that the surface is as smooth as possible.</li>
	<li>Before removing the backing of the tape, using a finger, press hard on the tape so that it is firmly adhering to the mount surface. This is very important so that the tape does not come off with the sample.</li>
	<li>Take a cleaved sample piece and gently lay the area of interest directly onto the carbon tape along the edge of the mount such that the area of the sample that was used for handling with tweezers is hanging off the edge (Figure 3A). Once sample has been placed onto tape, do not remove it for repositioning in order to avoid destroying the Ni/Au film.</li>
	<li>Press firmly down onto the back of the sample using forceps (Figure 3B). Take care not to press too hard on the sample around the mount edges because this can cause the sample to break.</li>
	<li>To remove the substrate, take a clean razor blade or scalpel and gently nudge it in between the substrate and the tape along the edges of the sample (Figure 3C). Carefully repeat this process, nudging the razor blade a little further each time until the substrate can easily be peeled off by grabbing it with tweezers. Using too much force can break the sample. To keep the tape from coming off with substrate, place a pair of forceps or a probe onto the area of the tape that is adjacent to the substrate when prying the substrate off (Figure 3C). The annealed Ni/Au film should remain adhered to the tape (Figure 3D). On average, this step will take about 1 min to complete.</li>
	<li>Image the newly removed Ni/Au film using SEM as soon as possible so as to observe the newly exposed interface of the film before it becomes contaminated.</li>
</ol>

<ol><li>Lu, W., Lieber, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Semiconductor+nanowires%5BTitle%5D)+AND+%22J.+Phys.+D%3A+Appl.+Phys%22%5BJournal%5D)">Semiconductor nanowires.</a> J. Phys. D: Appl. Phys. 39, R387-R406 (2006).</li>
<li>Mater Res, A. nnuR. ev 34, 83-122 (2004).</li>
<li>Pettersen, S. V., Grande, A. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Formation+and+electronic+properties+of+oxygen+annealed+Au%2FNi+and+Pt%2FNi+contacts+to+p-type%5BTitle%5D)+AND+%22%22%5BJournal%5D)">Formation and electronic properties of oxygen annealed Au/Ni and Pt/Ni contacts to p-type.</a> 22, 186-193 (2007).</li>
<li>Chen, L. C., Ho, J. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+Effect+of+Heat+Treatment+on+Ni%2FAu+Ohmic+Contacts+to+p-Type%5BTitle%5D)+AND+%22%22%5BJournal%5D)">The Effect of Heat Treatment on Ni/Au Ohmic Contacts to p-Type.</a> 176, 773-777 (1999).</li>
<li>Liday, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Investigation+of+NiOx-based+contacts+on+p-GaN%5BTitle%5D)+AND+%22J.+Mater.+Sci.+Mater.+Electron%22%5BJournal%5D)">Investigation of NiOx-based contacts on p-GaN.</a> J. Mater. Sci. Mater. Electron. 19, 855-862 (2008).</li>
<li>Narayan, J., Wang, H., Oh, T. H., Choi, H. K., Fan, J. C. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Formation+of+epitaxial+Au%2FNi%2FAu+ohmic+contacts+to+p-GaN%5BTitle%5D)+AND+%22Appl.+Phys.+Lett%22%5BJournal%5D)">Formation of epitaxial Au/Ni/Au ohmic contacts to p-GaN.</a> Appl. Phys. Lett. 81 (21), 3978-3980 (2002).</li>
<li>Ho, J. K., Jong, C. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Low-resistance+ohmic+contacts+to+p-type+GaN+achieved+by+the+oxidation+of+Ni%2FAu+films%5BTitle%5D)+AND+%22J.+Appl.+Phys.+Lett%22%5BJournal%5D)">Low-resistance ohmic contacts to p-type GaN achieved by the oxidation of Ni/Au films.</a> J. Appl. Phys. Lett. 86 (8), 4491-4497 (1999).</li>
<li>Herrero, A. M., Blanchard, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Microstructure+evolution+and+development+of+annealed+Ni%2FAu+contacts+to+GaN+nanowires%5BTitle%5D)+AND+%22Nanotechnology%22%5BJournal%5D)">Microstructure evolution and development of annealed Ni/Au contacts to GaN nanowires.</a> Nanotechnology. 23 (36), 5203.1-5203.10 (2012).</li>
<li>Bertness, K. A., Roshko, A., Sanford, N. A., Barker, J. M., Davydov, A. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Spontaneously+grown+GaN+and+AlGaN+nanowires%5BTitle%5D)+AND+%22J.+Crystal+Growth%22%5BJournal%5D)">Spontaneously grown GaN and AlGaN nanowires.</a> J. Crystal Growth. 287, 522-527 (2006).</li>
<li>Herrero, A. M., Bertness, K. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Optimization+of+Dispersion+and+Surface+Pretreatment+for+Single+GaN+Nanowire+Devices%5BTitle%5D)+AND+%22J.+Vac.+Sci.+Tech.+B%22%5BJournal%5D)">Optimization of Dispersion and Surface Pretreatment for Single GaN Nanowire Devices.</a> J. Vac. Sci. Tech. B. 30 (6), 2201.1-2201.5 (2012).</li>
</ol>

No conflicts of interest declared.

The technique presented allows for analysis of the contact/substrate and contact/NW microstructure of single NW devices. The main advantages of this technique are its low cost and simplicity. It allows for qualitative and quantitative analysis of the contact interface on a large scale with the substrate as well as on a submicrometer scale with individual NWs. The use of carbon tape for the film removal and SEM pin stubs for sample mounting make it possible for analysis using characterization techniques that require clean...

Single-NW devices are made by dispersing a NW suspension onto an insulating substrate and forming contact pads on the substrate via conventional photolithography and metal deposition, which results in randomly formed two-terminal devices. A thick SiO2 film on a Si wafer is typically used as an insulating substrate1,2. For metals deposited on a SiO2 surface, a common problem resulting from heat treatment is the occurrence of void formation at the metal/SiO2 interface. In addition to cracking and delamination of the metal film, this void formation can negatively affect device performance from an increase in resistance caused by a reduction of the contact area. Ni/Au contacts oxidized in N2/O2 atmospheres are the predominant contact scheme applied to p-GaN3-7. During heat treatment in a N2/O2, the Ni diffuses to the surface to form NiO and the Au diffuses down to the substrate surface.
In this work, excessive void formation at the contact/NW and contact/SiO2 interfaces was shown to occur during annealing of Ni/Au contacts to NWs on SiO28. The surface morphology of the annealed Ni/Au film, however, does not indicate the existence of voids or the degree to which void formation has occurred. To address this problem, we developed a technique for the removal of Ni/Au contacts and GaN NWs from SiO2/Si substrates in order to analyze the interface of the contact with the substrate and NWs. This technique can be used for the removal of any contact structure that has poor adhesion to the substrate. The Ni/Au films with GaN NWs embedded in them are removed from the SiO2 substrate with carbon tape. The carbon tape is adhered to a standard pin mount for characterization by use of scanning electron microscopy (SEM) along with several other tools. The detailed procedure for the fabrication of single GaN NW devices and analysis of their contact interface morphology are described.

<table><tbody><tr><td colspan="4">&lt;strong&gt;REAGENTS and MATERIALS&lt;/strong&gt;</td></tr><tr><td>Lift-off resist</td><td>MicroChem</td><td>LOR 5A</td><td>Varies according to application</td></tr><tr><td>Photoresist</td><td>Shipley</td><td>1813</td><td>Varies according to application</td></tr><tr><td>Developer</td><td>Rohm and Haas Electronic Materials</td><td>MF CD-26</td><td>Varies according to application</td></tr><tr><td>Photoresist stripper</td><td>MicroChem</td><td>Nano Remover PG</td><td>Varies according to application</td></tr><tr><td>Ni source</td><td>International Advanced Materials</td><td>99.999% purity</td><td></td></tr><tr><td>Au source</td><td>International Advanced Materials</td><td>99.999% purity</td><td></td></tr><tr><td>SiO&lt;sub&gt;2&lt;/sub&gt;/Si wafers</td><td>Silicon Valley Microelectronics</td><td>3-inch &amp;lt;100&gt; N/As 0.001-0.005 ohm-cm, 200 nm thermal oxide</td><td></td></tr><tr><td>Carbon tape</td><td>SPI Supplies</td><td>5072, 8 mm wide</td><td></td></tr><tr><td colspan="4">Solvents are standard semiconductor or research grade. Vendor is not important for the experimental outcome.</td></tr><tr><td colspan="4">Reactive ion etch gases and thermal annealing gases are high purity grade. Vendor is not important for the experimental outcome.</td></tr><tr><td colspan="4">&lt;strong&gt;EQUIPMENT&lt;/strong&gt;</td></tr><tr><td>Ultrasonic cleaner</td><td>Cole-Palmer</td><td>EW-08849-00</td><td>Low power</td></tr><tr><td>Micropipette</td><td>Rainin</td><td>PR-200</td><td>Metered, disposal tips</td></tr><tr><td>Reactive ion etcher</td><td>SemiGroup</td><td>RIE 1000 TP</td><td>Other vendors also used with different process parameters</td></tr><tr><td>Mask aligner</td><td>Karl Suss</td><td>MJB3</td><td>Other vendors also used with different process parameters</td></tr><tr><td>UV ozone cleaner</td><td>Jelight</td><td>Model 42</td><td>Other vendors also used with different process parameters</td></tr><tr><td>E-beam evaporator</td><td>CVC</td><td>SC-6000</td><td>Other vendors also used with different process parameters</td></tr><tr><td colspan="4">* Manufacturers and product names are given solely for completeness. These specific citations neither constitute an endorsement of the product by NIST nor imply that similar products from other companies would be less suitable.</td></tr></tbody></table>

analysis of contact interfaces for single gan nanowire devices

Analysis of Contact Interfaces for Single GaN Nanowire Devices

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit a strong degradation after annealing due to the occurrence of void formation at the contact/SiO2 interface. This void formation can cause cracking and delamination of the metal film, which can increase the resistance or lead to a complete failure of the NW device. In order to address issues associated with void formation, a technique was developed that removes Ni/Au contact metal films from the substrates to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN NW devices. This procedure determines the degree of adhesion of the contact films to the substrate and NWs and allows for the characterization of the morphology and composition of the contact interface with the substrate and nanowires. This technique is also useful for assessing the amount of residual contamination that remains from the NW suspension and from photolithographic processes on the NW-SiO2 surface prior to metal deposition. The detailed steps of this procedure are presented for the removal of annealed Ni/Au contacts to Mg-doped GaN NWs on a SiO2 substrate.

An example of SEM analysis on annealed Ni/Au films removed from the SiO2 substrate using carbon tape is shown in Figure 4. The surface of a Ni/Au contact prior to removal is shown in Figure 4A. The underside of the same area of that particular Ni/Au film after removal is shown in Figure 4B. Comparison of the surface and underside morphology can help determine if there is a relationship between the two. For example, when the two images are compared, it can be s...

A technique was developed that removes Ni/Au contact metal films from their substrate to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN nanowire devices.

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit  a strong degradation after annealing due to the  occurrence of void formation at the ...

The overall goal of this procedure is to allow for the examination and characterization of the contact substrate and contact nanowire interfaces for single gallium nitride nanowire devices. This is accomplished by first preparing a nanowire suspension and dispersing it onto a substrate. The second step is to deposit the nickel gold contacts on the nanowires and then a kneel the sample.The final step is to remove the anal to nickel gold contacts from the substrate by adhering them to carbon tape. Ultimately, a scanning electron microscope is used to examine the contact interfaces for void formation. This method can help answer questions about how to process semiconductor nanowires.In particular, it gives us a way to assess how well the metal contacts are sticking to the nano wires into the surrounding substrate. Visual demonstration of this method is important because the nanowire dispersal and film transfer techniques can be difficult to learn as the small details of handling and placement can have a large effect on the yield. I was looking at the sample with an SEM when I noticed an area of the metal contact had start lifting up away from the substrate.When I looked at it closer, I noticed the underside of the contact had this very unusual morphology. So in order to get a better look at that, the underside morphology, I developed this technique I To begin cleave a small piece of the as grown gallium nitride nanowires on a 1 1 1 silicon substrate and place it into a small vial with one milliliter of isopropanol. Sonicate the vial for 30 seconds in order to remove the nano wires from their anchoring substrate.Then clean a silicon wafer by submersing it face down in acetone using a tripod holder. After five minutes, remove the wafer from the acetone and rinse off both sides of the wafer using a squirt bottle of isopropanol. Next, submerge the wafer into a beaker with 100 milliliters of isopropanol.After five minutes, remove the wafer and rinse it with deionized water before placing it into yet another beaker with deionized water. After five minutes in the water, remove the wafer and dry it with a stream of nitrogen. Again, sonicate the vial of nano wires for 30 seconds.Then pipette 30 microliters of the solution onto each of the three regions on the oxidized surface of a clean quarter wafer, make sure that the wafer is level so that the nanowire suspension does not migrate away to the edges. After the final drop of the nano wire suspension has evaporated. Place the sample in successive baths of acetone and isopropanol to remove unwanted impurities.Then rinse the quarter wafer in deionized water and dry with nitrogen. Do not use squirt bottles or sonicate the solvent during the cleaning process. To avoid excess removal of nanowires from the surface, add a layer of LOR five A liftoff.Resist onto the silicon wafer with the dispersed nanowires by adding one to two milliliters of the resist on top of the nanowires spin coat the sample at a rate of 300 RPM for 10 seconds, followed by 2000 RPM for 45 seconds. After spinning, remove LOR five A remnants from the edges of the sample by swabbing it with micro chem nano EBR pg. Then transfer the sample onto a hot plate and bake it 150 to 170 degrees Celsius.After five minutes, remove the sample from the hot plate and allow it to cool for 30 seconds. Once cooled, place the sample back into the spin coder and add one to two milliliters of mega deposit SPR 6 61 0.0. Photo resist to cover the surface spin, coat the sample for 35 seconds at 3000 RPM.Then transfer the sample onto a hot plate and bake it for one minute at 95 degrees Celsius. Next, load the mask and then the sample into the mask aligner. Expose the sample with a dose of 240 millijoules per square centimeter.Then develop the photo resist by swirling the sample in a beaker of micro posit MF 26, a developer for about 60 seconds or until fully developed. Once developed, rinse the sample in deionized water and then dry it with a stream of nitrogen. Load the samples into a UV ozone generator and expose them to ozone for 10 minutes while flowing an ultra high purity oxygen at a flow rate of 80 standard cubic centimeters per minute through the device.After OZ zone treatment, place the samples in a 10%hydrochloric acid mixture for one minute at room temperature. Then remove the samples and rinse them with deionized water and dry them with a stream of nitrogen. Mount the dry samples to the electron beam evaporator by securing it to the platin using screws and clips.Then attach the platin into the e-beam evaporator and load the nickel and gold crucibles into the device. Pump down the chamber until the pressure is below one micro tour. Depending on pump strength, this may take a few hours to overnight.Then set the high voltage to 10 kilovolts, ensure the shutter is closed and begin to rotate samples at five RPM. Next, select the nickel crucible and set the deposition rate to 0.1 nanometers per second and deposit 500 nanometers of nickel onto the samples. When finished, allow the source to cool down for 15 minutes and then switch to the gold crucible.Set the gold deposition rate at 0.1 nanometers per second and deposit 100 nanometers onto the samples. Once deposition is finished, wait 10 minutes for the gold crucible to cool down, and then vent the chamber and unload the sample Platin. Remove the samples from the PLA and place them into a bath of photo reist.Stripper at room temperature for a few hours to lift off the metal deposited on the photo, resist if desired, elevate the bath temperature to around 50 to 60 degrees Celsius to accelerate. Lift off after a few hours. Check to see if the metal separated from the photo resist.Use a pipette or a squirt bottle of the photo. Resist stripper to forcefully remove any remaining undesired metal from the surface. Then rinse the entire sample with isopropanol, followed by deionized water, and then dry the samples with nitrogen following removal with at least 24 hours before annealing the samples.Then purge the rapid thermal annealer with three parts nitrogen to one part oxygen at a flow rate of 1.4 liters per minute at 650 degrees Celsius for five minutes without any samples in it. Next, reduce the temperature to 550 degrees Celsius. Load the samples and anal them for 10 minutes.Begin by carefully placing a piece of carbon tape on an SEM pin stub mount so that the tape is as smooth as possible. Before removing the backing of the tape, use a finger to press hard on the tape so that it is firmly adhering to the mount. Take the sample and gently lay the area of interest directly onto the carbon tape along the edge of the mount, such that the area of the sample that was used for handling with tweezers is hanging off the edge.Once sample has been placed onto the tape, do not remove it for repositioning. In order to avoid destroying the film, press firmly down onto the back of the sample using forceps. Take care not to press too hard around the mount edges because this can cause the sample to break.Then take a clean razor blade or scalpel and gently nudge it in between the substrate and the tape along the edges of the sample until the substrate can easily be peeled off by grabbing it with tweezers. Using too much force can break the sample to keep the tape from coming off with the substrate. Place a pair of tweezers onto the area of the tape that is adjacent to the substrate.When prying it off, the ailed nickel gold film should remain adhered to the tape image, the newly removed nickel gold film using SEM as as possible so as to observe the newly exposed interface of the film before it becomes contaminated. Shown here are SEM images of the Al Nickel gold film before and after being removed from the silicon dioxide substrate using carbon tape. The sample on the right received no cleaning prior to the metal deposition and the residual contamination produced non-uniform void distribution, and large macro voids that resemble blisters.One important application of this technique is analyzing the contact nano wire interface morphology as CM images of the underside of a kneeled nickel gold films that had been deposited onto nano wires dispersed onto silicon dioxide. Silicon substrates are shown here. High magnification images like those seen on the right hand side allows for the examination of the contact nano nanowire interface.The SCM image on the bottom right is missing the nanowire, allowing for the interface between the contact and the missing wire to be more easily studied. The presence of this residual contamination can cause a significant increase in the number of voids observed at the contact substrate interface. By quantifying the degree of void formation at the contact substrate interface, the effectiveness of different cleaning methods can be evaluated.These experiments focused on the effectiveness of the various cleaning methods prior to deposition of the nickel gold onto the silicon dioxide for the removal of residual contamination. This points out the obvious advantage of using UVO Zone and HCL cleaning prior to the deposition of the metals. After watching this video, you should have a good idea of how to disperse nano wires onto a new substrate deposit, into kneel metal contacts to the nanowires, and remove the metal contacts to examine the nanowire contact interface Using this procedure.Additional techniques like energy dispersive x-ray spectroscopy can be done in order to answer additional questions like layer composition.

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JoVE Journal

Engineering

We describe the device fabrication and measurement protocol for carbon nanotube based high frequency biosensors. The high frequency sensing technique mitigates the fundamental ionic (Debye) screening effect and allows nanotube biosensor to be operated in high ionic strength solutions where conventional electronic biosensors fail. Our technology provides a unique platform for point-of-care (POC) electronic biosensors operating in physiologically relevant conditions.

Fabrication of Carbon Nanotube High-Frequency Nanoelectronic Biosensor for Sensing in High Ionic Strength Solutions

This paper presents a detailed fabrication protocol for gate-defined semiconductor lateral quantum dots on gallium arsenide heterostructures. These nanoscale devices are used to trap few electrons for use as quantum bits in quantum information processing or for other mesoscopic experiments such as coherent conductance measurements.

Nanofabrication of Gate-defined GaAs/AlGaAs Lateral Quantum Dots

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Silver nanowires can simultaneously transport electrons and optical information in the form of surface plasmons. A procedure is described here to realize such a shared circuitry and the limitations at propagating both information carriers are evaluated.

Evaluating Plasmonic Transport in Current-carrying Silver Nanowires

We describe the approaches for the device fabrication and electrical characterization of molybdenum diselenide (MoSe2) layer semiconductor nanostructures with different thicknesses. In addition, the fabrication of ohmic contacts for MoSe2-layer nanocrystals by the focused-ion beam deposition method using platinum (Pt) as a contact metal is described.

Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

A method for the growth of low temperature vertically-aligned carbon nanotubes, and the subsequent fabrication of vertical interconnect electrical test structures using semiconductor fabrication is presented.

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

We describe key steps for biosensing by using polysilicon nanowire field-effect transistors, including the preparation of the device and the immobilization and confirmation of a DNA molecular probe on the nanowire surface, as well as conditions for DNA sensing.

Preparation of Silicon Nanowire Field-effect Transistor for Chemical and Biosensing Applications

In this paper, flow assisted dielectrophoresis is demonstrated for the self-assembly of nanowire devices. The fabrication of a silicon nanowire field effect transistor is shown as an example.

Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices

Here, we present a protocol to control the carrier number in solids by using the electrolyte.

Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating

Here, we present a protocol for fabrication of a closed-type wireless nanopore electrode and subsequent electrochemical measurement of single nanoparticle collisions.

A Closed-Type Wireless Nanopore Electrode for Analyzing Single Nanoparticles

This protocol describes the use of silicon nanowires for intracellular optical bio-modulation of cell in a simple and easy to perform method. The technique is highly adaptable to diverse cell types and can be used for in vitro as well as in vivo applications.

Silicon Nanowires and Optical Stimulation for Investigations of Intra- and Intercellular Electrical Coupling

Learn a technique for removing Ni/Au contacts from GaN nanowire devices using carbon tape to examine contact interfaces. This method enables detailed SEM analysis of void formation at semiconductor nanowire interfaces.

Analysis of Contact Interfaces for Single GaN Nanowire Devices

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