Writing and Low-Temperature Characterization of Oxide Nanostructures

In this video, we will demonstrate the steps necessary to create and to measure conductive nanostructures at Lengthen illuminate strontium TITANATE, or L-A-O-S-T-O interfaces. The first step is to obtain the samples. Each sample consists of five millimeters by one millimeter thick strontium titanate with 3.4 unit cells of Lome illuminate or LAO.

The next step is photo lithographic processing of the samples begin by spinning photoresist onto the samples at 600 RPM for five seconds, and at 4, 000 RPM for 30 seconds, apply the mask to expose desired areas of the photo. Resist irradiate the samples with 320 nanometer light for 100 seconds. Develop the photo resist and AZ 400 K developer for one minute ion mill the sample with an argon ion mill at 500 volts, 10 milliamps for 25 minutes.

To produce a milling depth of 15 nanometers, begin the DC sputtering process. Deposit four nanometers of titanium and 25 nanometers of gold onto the samples so that the gold makes electrical contact with the exposed STO layer. For the specific spattering procedures used here, please refer to the manuscript.

The next step is liftoff. Use ultrasonic wash to remove photoresist from the surface of the samples. The first layer is now complete after processing.

The sample should ideally look like this to create the second layer. Repeat steps one through six with the exception of step four ion milling. Finish processing the samples through plasma cleaning.

The next step is to wire bond a canvas to prepare for nano writing. For transport experiments. The canvas must be wire bonded to a chip carrier.

Electrical connections are made between bonding pads on the sample and the chip carrier. A ball bonder is used to attach a one mill gold wire between the electrical contacts and the chip carrier. After the sample has been mounted onto the chip carrier and wire bonded.

It should look like this. The next step is to write nanostructures to use the samples in an experiment. A design for the nano structure is sketched informally.

So what type of device should we write today? Okay, so let's schedule our device on the whiteboard. How about we start with some virtual electrodes to make a good contact to the interface?

Okay, so here are six virtual electrodes. I just draw, What about the main channel? Okay.We can draw a main channel vertically across the whole canvas, As well as a couple sensing leads.

Yes, we can also put a cavity with the two cuts And maybe a side gate to Capacitively couple to the main channel. Yes, that's a good idea. The precise design is created using Inkscape, an open source scalable vector graphics editor.

The path and voltages for the conductive A FM tip are encoded in the SVG bezier curves and solid shapes. The Inkscape file in the image of the sample surface are then specified in the lab view. A FM lithography software.

The program is executed and lithography commands are sent to the atomic forest microscope. Progress is tracked using a 3D visualization tool that emulates the lithography procedure. Green curves represent conductive paths written with positive voltage.

Red lines represent paths in which the insulating phase is locally restored. In this case, a one micron cavity is being created along a nanowire. The next step is to cool the device and take measurements.

After the nanostructures have been written, the sample is extracted from the A FM system. Red filters and or lighting should be used during the step to avoid photo excitation of carriers, the sample is mounted onto the dilution unit. The dilution unit is carefully inserted into the cryostat to ensure no damage is done to the cryostat.

During cool down, the resistance is monitored to ensure that the sample remains conducting. Once the sample has reached base temperature of 50 millikelvin, its resistance and transport can be measured. In this device, there is a crossover from Kula blockade behavior to Cooper pair tunneling to full superconductivity.

The differential conductance here is obtained from the full current voltage trace after numerical differentiation. After watching this video, you should have a comprehensive understanding of the essential steps necessary for producing conductive nanostructures at L-A-O-S-T-O interfaces.