PhD - Leuven | About a week ago
Transition metals are becoming increasingly important in the field of spintronics. The technology is recognized as a new paradigm that can replace and be adopted in conventional electronic devices for semiconductor, storage, biomedical, and automobile applications. Moreover, spintronic devices are finding further utilization for the internet of things (IoT) and the wireless industry owing to the remarkable performance characteristics such as nonvolatility, low power consumption, high-speed read and write operation, and cost benefit in terms of productivity.
For spintronic device fabrication, patterning of stacked metal layers is a critical step. Various nanofabrication techniques have been investigated of which ion beam etching has proven successful. However, this dry etching technique can cause shorting across a tunnel barrier due to redeposition of metal atoms because of the formation of nonvolatile etching products. An ion beam impinging on the sample at a tilted angle can be used to remove these atomic residues, but this technique does not scale well with the ever-increasing density of device structures. Halogen plasmas have also been investigated, and they are known to yield high etch rates. However, the etched metal byproducts produced by the plasma tend to be also nonvolatile at low temperatures, which degrades device performance. By contrast, wet atomic layer etching (wet-ALE) offers a simple and attractive solution which can avoid these problems. Atomic layer etching processes are typically based on a two-step mechanism where self-limiting surface oxidation and oxide product dissolution are time-separated. Depending on the surface oxide chemistry, also a 1-step mechanism can be used to achieve wet-ALE conditions. The proposed PhD work will explore new wet-ALE approaches for the etching of various metallic elements and alloys. The target materials will be at start pure elements such as Ru, Ni, Co, Fe and will be then extended to metal alloys such as RuAl and Ni3Al. Of special interest is the use of solvent-based chelating chemistries. Fundamental insights in the surface chemistry of metals are key to achieve the requirement of wet-ALE: the ability to selectively control oxidation and dissolution rates with atomic-scale resolution.
As a PhD student, you will learn to work in a highly dynamic and multicultural environment and be exposed to a large variety of analytical techniques and experimental methods. Inductively coupled plasma mass spectrometry (ICP-MS) in combination with electrochemical measurements will be used to study the metal/electrolyte interface in the parameter space. Based on these results, basic insights can be obtained on atomic-scale oxidation/dissolution kinetics and predict galvanic effects between metals in a stack. Surface chemistry and physics will be studied both ex situ and post operando by x-ray photoelectron spectroscopy (XPS) and high-resolution synchrotron radiation photoemission spectroscopy (SRPES). Other complementary physical characterization techniques like elastic recoil detection analysis (ERDA), electrical measurements, atomic force microscopy (AFM), scanning and transmission electron microscopy (SEM, TEM) are available to support your mechanistic studies on wet-ALE processing.
We are looking for an enthusiastic and results-driven PhD candidate with a strong background and interest in the chemistry and physics of materials.
Required background: Chemistry, Physics or Materials Science
Type of work: 60% experimental work, 25% data interpretation, 15% literature study and writing
Supervisor: Stefan De Gendt
Daily advisor: Dennis van Dorp, Harold Philipsen, Jean-Francois de Marneffe
The reference code for this position is 2021-026. Mention this reference code on your application form.