Session Q51: Industry Fellows

Distinguished Lectureship Award on the Applications of Physics: Induced polarization for subsurface characterization and energy industry experience

There has been substantial interest in applying induced polarization phenomena, including electrode and membrane polarization, to characterize organic contamination and biogeochemical environments. The presence of dispersed electronically conductive grains contributes to electrode polarization, which arises due to the capacitive charging of the Stern Layer at the conductor-electrolyte interface. On the other hand, the membrane polarization is driven by spatial inhomogeneity in the ionic transferences, i.e., the proportion of current carried by the cation vs. the anion. Several phenomenological models have been proposed to understand induced polarization. Here, we developed theoretical frameworks to quantitatively explain electrode and membrane polarization based on insights from experiments on model systems. We obtained quantitative agreement between experiment and theory, not just for characteristic frequencies and amplitudes but for the entire spectral shape of the phase angle between the electric field and current density.   

Spin-Transfer-Torque MRAM: the Next Revolution in Memory

   Spin-Transfer-Torque MRAM was invented at IBM by John Slonczewski in the early 1990s.  By using a spin-polarized current, instead of a magnetic field, to write a magnetic free layer in a magnetic tunnel junction, the required write current naturally decreases with area, providing attractive technology scaling.  The discovery of perpendicular magnetic anisotropy in thin CoFeB/MgO layers at IBM and independently by Tohoku University enabled a dramatic reduction in the switching current, and opened the way to practical perpendicular magnetic tunnel junctions for dense Spin-Transfer-Torque MRAM.  

    This talk will provide an overview of Spin-Transfer-Torque MRAM, including the two basic building blocks described above.  I’ll give an introduction to the physics of spin-transfer torque and applications of Spin-Transfer-Torque MRAM.  Then I will review why perpendicular magnetic anisotropy is advantageous for MRAM compared to in-plane anisotropy, and the materials challenges of perpendicular anisotropy.  I will discuss the research at IBM in 2009 that led to our discovery of perpendicular anisotropy in thin CoFeB/MgO layers, and our use of these layers to make the first practical perpendicular magnetic tunnel junctions and the first demonstration of reliable writing in Spin-Transfer-Torque MRAM.  Finally I will review our recent results on methods to lower the switching current of Spin-Transfer-Torque MRAM by using optimized magnetic materials and double magnetic tunnel junctions, including our recent demonstration of reliable 250 ps switching.

    

Plasmonic Terahertz Imaging and Spectroscopy Systems

Terahertz waves have unique specifications that enable unprecedented sensing functionalities for personal health monitoring, environmental monitoring, and security screening as well as pharmaceutical, industrial, and agricultural product quality control. This is because most molecules have unique spectral signatures in the terahertz frequency range and many optically opaque materials are relatively transparent to terahertz waves. Additionally, terahertz photons are sufficiently low energy that they don’t cause any damage or ionization especially for biomedical sensing applications. Although unique potentials of terahertz waves have been recognized for quite a while, the low efficiency, higher costs, and bulky nature of traditional terahertz systems has impeded their usage in practical applications. In this talk, I will give an overview of the unique applications of terahertz waves for chemical identification, material characterization, biomedical sensing and diagnostics and describe the state of the existing terahertz imaging and sensing technologies and their limitations. I will introduce a game changing technology that enables high performance, low cost, and compact terahertz spectroscopy and imaging systems for various applications. More specifically, I will introduce plasmonic terahertz imaging and spectroscopy systems, which offer several orders of magnitude higher signal-to-noise ratio levels compared to the state of the art.

    

The physics and applications of topologically complex light

This talk will describe the propagation, control and manipulation of light that manifests spatial complexity. In free space and bulk media, such higher order eigenstates of light possess intriguing characteristics such as the ability to carry spin and orbital angular momentum and the ability to self-heal. Upon confinement, either by focusing them, or by guiding them in fibers, even more exotic behaviour, akin to spin-orbit interactions of confined electrons in atomic and molecular systems, is observed – light's polarisation as well as phase and group velocities become dependent on the intrinsic as well as extrinsic geometric path that the light beam takes. Such attributes have spawned applications as diverse as super-resolution microscopy, deep-tissue imaging, DNA sorting, classical and quantum communications, remote sensing and directed-energy defence strategies. This talk will describe recent applications, after elucidating the fundamental phenomena that make singular light beams behave dramatically differently from commonly encountered, conventional, Gaussian-shaped beams of light.   

What Are 2D Materials Good For?

This talk will present my (biased!) perspective of what two-dimensional (2D) materials could be good for. For example, they may be good for applications where their ultrathin nature and lack of dangling bonds give them distinct advantages, such as flexible electronics [1] or DNA-sorting nanopores [2]. They may not be good where conventional materials work sufficiently well, like transistors thicker than a few nanometers. I will focus on 2D materials for 3D heterogeneous integration of electronics, which presents significant advantages for energy-efficient computing [3]. In this context, 2D materials could be monolayer transistors with ultralow leakage [4] (thanks to larger band gaps than silicon), used as access devices for high-density memory [5]. Recent results from our group have shown monolayer transistors with record performance [6,7], which cannot be achieved with sub-nanometer thin conventional semiconductors, and the 2D performance could be further boosted by strain [8]. I will also describe some unconventional applications, using 2D materials as good thermal insulators [9] and as thermal transistors [10]. These could enable control of heat in “thermal circuits” analogous with electrical circuits. Combined, these studies reveal fundamental limits and some unusual applications of 2D materials, which take advantage of their unique properties.

Refs: [1] A. Daus et al., Nature Elec. 4, 495 (2021). [2] J. Shim et al. Nanoscale 9, 14836 (2017). [3] M. Aly et al., Computer 48, 24 (2015). [4] C. Bailey et al., EMC (2019). [5] A. Khan et al. Science 373, 1243 (2021). [6] C. English et al., IEDM, Dec 2016. [7] C. McClellan et al. ACS Nano 15, 1587 (2021). [8] I Datye et al., Nano Lett. 22, 8052 (2022). [9] S. Vaziri et al., Science Adv. 5, eaax1325 (2019). [10] M. Chen et al., 2D Mater. 8, 035055 (2021).