Our protocol provides a technique to customize nanoparticle distribution, fabricated on a substrate, with changing the dewetting dynamics, without changing the material thickness. Our technique is simple, yet still provides a range of particle sizes. Other techniques out there require extensive lithographic steps to provide the particle control.
Our control of particle distribution provides a technique for nanoparticle fabrication that benefits research focused on solar energy conversion, creating photonic devices, and increasing density of data storage. Pay close attention to the deposition thicknesses at each step. Our technique is extremely sensitive to layer thicknesses.
Seeing the experiment performed provides a level of detail that can't be conveyed in print. Seeing examples moving throughout the process is essential. First, clean a 100 nanometer silicon dioxide on silicon substrate, using an acetone rinse, followed by an isopropyl alcohol rinse.
Dry the substrate using a stream of nitrogen gas. Load the substrate into a thermal evaporator system and evacuate the chamber to reach the desired pressure for the deposition of the metal film. Ensure that the chamber is evacuated to a pressure on the order of 10 to the minus six torr for the removal of air and water vapor in the chamber.
Using the thermal evaporator system, deposit the gold film at the desired thickness, which is five nanometers in this experiment. At the second deposition stages, the argon pressure is one to five millitorr, and the range is given as different pressures are chosen to calibrate for the deposition rate. Our technique is extremely sensitive to film thicknesses, as shown in our results.
It is critical to calibrate the deposition rates prior to depositing the films, to ensure appropriate thicknesses. Following deposition, vent the chamber and remove the substrate, with the deposited metal film, from the thermal evaporator system. Next, load the substrate, with a deposited metal film, into a direct current magnetron sputter deposition system and evacuate to reach the desired pressure for deposition of the capping film.
To locate the sample in the system, put the sample in the load lock. And the device transfers the sample to the main deposition chamber to ensure a sufficient level of vacuum. Now, deposit the capping layer of the desired material and thickness, following a similar procedure and condition as the gold layer deposition.
With variable thickness Illumina, in this case. Following deposition, vent the chamber and remove the prepared sample from the sputter deposition system. Place the five nanometer gold film, capped with Illumina, onto a pre-heated hot plate at 300 degrees Celsius, and allow the sample to dewet for one hour.
Etch the Illumina, while leaving the gold and underlying substrate with an aqueous solution of ammonium hydroxide and hydrogen peroxide at 80 degrees Celsius for one hour. For characterization, prepare the sample to be vacuum-compatible by rinsing with acetone and isopropyl alcohol. Then, dry the sample using a stream of nitrogen gas.
Image the nanoparticle films using scanning electron microscopy under high vacuum and at high magnification. Perform image analysis to obtain information on nanoparticle size and spacing distributions. The protocol described here has been used for multiple metals and has shown the ability to produce nanoparticles on a substrate over large area, with controllable size and spacing.
Representative results are shown here, and highlight the ability to control the fabricated nanoparticle size and spacing. The size and spacing distributions of the fabricated nanoparticle film will be dependent upon the metal, the substrate, the capping layer material, the metal thickness, and the capping layer thickness. As an example, the five nanometer gold film on silicon dioxide, with aluminum oxide capping layer thickness of zero, five, 10, and 20 nanometers result in an average nanoparticle radii of 14.2, 18.4, 17.3, and 15.6 nanometers respectively.
And an average nonoparticle spacing of 36.9, 56.9, 51.3, and 47.2 nanometers respectively. For the desired particle distribution, accurate control of the deposition layer thicknesses is critical. Depending on the application of your nanoparticle films, more characterization may be required.
This would include application-based measurements, like light absorption and magnetic properties. Studies of nanoparticle films in application can be performed using this technique, to control their particle size and distribution. Appropriate personal protective equipments should be worn.
Especially do not come into contact with the etchings. Avoid contact with the hot plate.
