Controlling the Size of Nanoparticles

Depositing nanoparticles using the NL50 is now simpler than ever with the pre-loaded optimized recipes for a variety of frequently used materials, including Au, Ag, Pt and Cu.

These optimized recipes generate high-quality nano-coatings with premium deposition rates for each material. Moreover, the NL50 also enables the user to vary the size distribution of the deposited nanoparticles by changing two simple parameters – the argon gas flow and the magnetron current (power).

Both the argon gas flow and the magnetron current influence the thermodynamics within the vacuum chamber. Modifying these parameters can either encourage or hinder nanoparticle growth, thus changing the range of nanoparticle sizes produced.

General trend for nanoparticle size with increasing magnetron power or gas flow.

Figure 1. General trend for nanoparticle size with increasing magnetron power or gas flow. Image Credit: Nikalyte Ltd

The Effect of Magnetron Current (Power)

When increasing the magnetron current, the magnetron power also rises, which in turn sputters more material from the target. This subsequent increase in the material made available will generally increase the number of nanoparticles generated (increase the deposition rate) as well as enhancing the size of the nanoparticles produced.

The Effect of Changing the Ar Gas Flow

The effect of modifying the Ar gas flow is a bit more complicated. A rise in the flow of argon will increase the amount of sputtered material ready to form nanoparticles.

However, as the gas flow and pressure rise, the argon ions progressively cool (thermalize) the nanoparticles through inelastic collisions, thus inhibiting nanoparticle growth.

Therefore, it is not unusual to see both an increase and decrease in nanoparticle size with argon gas flow. While the change in behavior is dependent on the material, users are advised to experiment with the process conditions to identify the optimum gas flow and magnetron current for their specific material requirements.

Changing the Nanoparticle Size with the NL50

To adjust the process conditions, the user simply alters the gas flow or current in STEP 4 on the setup Wizard, as displayed in Figure 2. The result of changing the current or the gas flow on the nanoparticle size distribution is also shown for nickel in Figure 2.

Figure 2. User Interface of NL50 indicating current and gas flow control options (top), Effect of Magnetron current on nanoparticle size distribution for Ni (bottom left) and Effect of Argon gas flow on nanoparticle size distribution (bottom right). Image Credit: Nikalyte Ltd

Figure 2 exhibits a change in the nickel nanoparticle distribution to larger sizes with increasing current, as anticipated in Figure 1.

The decline in signal witnessed at 300mA occurs when the plasma temperature produced at high magnetron currents is too great for maximum nickel nanoparticle growth, demonstrating that it may be necessary to make a choice between deposition rate and nanoparticle size.

The result of changing the Ar gas flow for nickel neatly demonstrates the competing processes of the increased formation of sputtered material for nanoparticle creation as Ar ions increasingly suppress nanoparticle growth.

Figure 2 displays the shift to smaller nickel nanoparticle sizes as the Ar gas flow is increased. Initially, the number of nanoparticles rises as the gas flow is increased, demonstrating that additional smaller nanoparticles are produced with the peak deposition rate taking place at 40sccm.

Continuing to increase the gas flow results in a decrease in both the size and number of nanoparticles as thermalization of the nanoparticles becomes more dominant.

Figure 3 displays nanoparticle peak position of the measured trends for various current and gas flows, signifying the extensive range of different sizes that can be acheived through the manipulation of just two process variables.

Figure 3. Nickel nanoparticle peak size with argon flow for 3 different magnetron currents. Image Credit: Nikalyte Ltd

This information has been sourced, reviewed and adapted from materials provided by Nikalyte Ltd.

For more information on this source, please visit Nikalyte Ltd.

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