Advances in the synthesis of group IV metal oxide nanocrystals

If you want to know the names of some of the world’s up-and-coming scientific talent, the Malvern Panalytical Scientific Award shortlist is a good place to start. The winner of the 2023 edition was Rohan Pokratath, who used an Empyrean Nano for part of his research on synthesis of zirconium and hafnium nanoparticles.^[1] On September 26, 2024, Rohan will be sharing more about his research and answering audience questions in a special Ask an Expert webinar. Read on to catch up on his research and prepare for this exciting event!

The task: Finding alternatives to silicon oxide

As semiconductor technology advances and transistor sizes continue to shrink, the limitations of SiO₂ (silicon dioxide) as a gate insulator have become more apparent, particularly due to increasing leakage currents in ultra-thin layers. “Because of their high dielectric constant,”¹ Rohan wrote, “zirconium dioxide (ZrO₂) and hafnium dioxide (HfO₂) are considered a potential replacement for SiO₂ (gate insulators) in field-effect transistors.”¹ With a significantly higher dielectric constant, ZrO₂ allows for thicker insulating layers that maintain the necessary capacitance while reducing leakage, thereby enabling further scaling of transistors. Additionally, ZrO₂ offers excellent thermal stability, making it suitable for the high-temperature processes in semiconductor manufacturing. Despite challenges such as integration complexity and potential defect densities, the shift to ZrO₂ represents a critical step in overcoming the limitations of traditional SiO₂, paving the way for more efficient and powerful electronic devices.

The challenge: Identifying the underlying synthesis mechanisms

Understanding the mechanisms behind the synthesis and behavior of Group IV oxide nanoparticles, such as TiO₂, ZrO₂, and HfO₂, presents several significant challenges. One of the primary difficulties lies in the complexity of nucleation and growth processes, where controlling the size, shape, and uniformity of nanoparticles is crucial yet difficult to achieve. This complexity makes it difficult to fully understand and optimize the synthesis of Group IV oxide nanoparticles, which are critical for applications. Rohan’s work would pave the way to produce ZrO₂ and HfO₂ at commercial scale. The challenge is that this procedure requires a good understanding of the interactions between precursor compounds. Achieving this understanding was therefore the focus of Rohan’s research.

Finding the solution…

Rohan’s first step was to investigate the speciation of the zirconium and hafnium precursors – in other words, the distribution of various elements in the system – and their reaction with the coordinating solvent, which brings the precursors together to form the synthetic material. He did this by gradually adding solvent to the precursor materials and monitoring the reaction using nuclear magnetic resonance (NMR).

This allowed Rohan to determine zirconium’s and hafnium’s stoichiometry: the proportion of elements necessary to initiate the desired reactions. From this information, Rohan was able to identify each species directly involved in the synthesis, validating the results using X-ray total scattering and pair distribution function analysis with the Empyrean Nano.

… And putting it into practice!

With deeper insights into the precursor chemistry, the question that remained was whether this could indeed enable more efficient synthesis of hafnium and zirconium nanocrystals. To test this, Rohan used a seeded growth approach, where precursor atoms deposit onto nanoparticle ‘seeds’  and grow into the desired nanocrystals.

The experiment was a success: Rohan introduced “a valid pathway to gain control over nanocrystal size.”¹ This is a great achievement, as such control is particularly challenging for group 4 and 5 metal oxides like hafnium and zirconium. These insights, Rohan continues, “will enable the formation of even more complex oxide nanocrystals, which will serve as valuable building blocks in material science.”¹

Exciting prospects for medicine and advanced materials

Rohan’s research enables greater colloidal stability and control over nanocrystal size for hafnium and zirconium. This is particularly exciting, as group 4 oxides have many prospective applications, including computed tomography, superconducting and optical nanocomposites, dentistry, catalysis, and coatings.

We’re thrilled that the Empyrean Nano served a crucial role in Rohan’s research, helping him to explore the atomic-scale structural evolution of the synthesis and estimate particle concentrations. We’re looking forward to hearing more about Rohan’s research and the Empyrean Nano’s role on September 26 – see you there!

Don’t miss out – register for the Ask an Expert webinar now.

[1] Rohan Pokratath et al., “Mechanistic Insight into the Precursor Chemistry of ZrO2 and HfO2 Nanocrystals; towards Size-Tunable Syntheses”, JACS Au 2022 2 (4), 827-838.