- Post Doctoral
MIT Unit Affiliation:
- Electrical Engineering & Computer Science
Post Doc Sponsor / Advisor:
Date PhD Completed:
Top 3 Areas of Expertise:
I am currently a postdoctoral associate working at MIT for institute professor Mildred S. Dresselhaus. I received my Ph. D. from the University of Illinois at Urbana-Champaign in Electrical and Computer Engineering under professor Eric Pop (now at Stanford). My main interests lie in studying energy dissipation and harvesting in nano-materials. This includes one-dimensional materials such as carbon nanotubes, two-dimensional materials such as graphene, or composite materials made from nano-materials such as carbon nanotube networks. While my Ph.D. work was focused on studying carbon allotropes, I have branched out during my postdocotoral experience to work with other two-dimensional materials and films such as Bismuth thin films and layered Black Phosphourous.
Expected End Date of Post Doctoral Position:
Electronic, thermal, and thermoelectric properties of thin film Bismuth and Bismuth Antimony.
Carbon nanotube network based non-volatile memory devices.
Energy dissipation in one and two dimensional material systems.
Electron-phonon interactions in low dimensional systems.
We use breakdown thermometry to study carbon nanotube (CNT) devices and graphene nanoribbons (GNRs) on SiO2 substrates. Experiments and modeling find the CNT-substrate thermal coupling scales proportionally to CNT diameter. Diffuse mismatch modeling (DMM) reveals the upper limit of thermal coupling ~0.7 WK‑1m‑1 for the largest diameter (3-4 nm) CNTs. Similarly, we extracted the GNR thermal conductivity (TC), ~80 (130) Wm‑1K‑1 at 20 (600) oC across our samples, dominated by phonons, with estimated <10% electronic contribution. The TC of GNRs is an order of magnitude lower than that of micron-sized graphene on SiO2, suggesting strong roles of edge and defect scattering, and the importance of thermal dissipation in small GNR devices.
We also compare the peak current density of metallic single-walled CNTs with GNRs. We find that as the “footprint” (width) between such a device and the underlying substrate decreases, heat dissipation becomes more efficient (for a given width), allowing for higher current densities. Because of their smaller dimensions and lack of edges, CNTs can carry larger current densities than GNRs, up to ~16 mA/μm for an m-SWNT with a diameter of ~0.7 nm versus ~3 mA/μm for a GNR having a width of ~15 nm. Such current densities are the highest possible in any diffusive conductor, to our knowledge.
We also study semiconducting and metallic single-walled CNTs under vacuum. Semiconducting single-wall CNTs under high electric field stress (~10 V/µm) display a remarkable current increase due to avalanche generation of free electrons and holes. Unlike in other materials, the avalanche process in such 1D quantum wires involves access to the third subband and is insensitive to temperature, but strongly dependent on diameter ~exp(‑1/d 2). Comparison with a theoretical model yields a novel approach to obtain the inelastic optical phonon emission length, λOP,ems ≈ 15d nm.
We find that current in metallic single-walled CNTs does not typically saturate, unlike previous observations which suggested a maximum current of ~25 μA. In fact, at very high fields (>10 V/μm) the current continues to increase with a slope ~0.5–1 μA/V, allowing m-CNTs to reach currents well in excess of 25 μA. Subsequent modeling suggests that carriers tunnel from the contacts into higher subbands. This allows currents to reach ~30–35 μA, which correspond to a current density of ~9 mA/μm for diameters of ~1.2 nm.
Top 5 Awards and honors (name of award, date received):
5 Recent Papers:
A. D. Liao, M. Yao, F. Katmis, M. Li, S. Tang, J. S. Moodera, C. Opeil, M. S. Dresselhaus, "Induced Electronic Anisotropy in Bismuth Thin Films," Appl. Phys. Lett. 105, 063144 (2014) link
F. Xiong, M.-H. Bae, Y. Dai, A. D. Liao, A. Behnam, E. A. Carrion, S. Hong, D. Ielmini, E. Pop, "Self-Aligned Nanotube-Nanowire Phase Change Memory," Nano Letters 13, 464-469 (2013) link
A. D. Liao, J. Wu, X. Wang, K. Tahy, D. Jena, H. Dai, E. Pop, "Thermally-Limited Current Carrying Ability of Graphene Nanoribbons," Phys. Rev. Lett. 106, 256801 (2011) link
A. Liao, R. Alizadegan, Z.-Y. Ong, S. Dutta, K.J. Hsia, E. Pop, "Thermal Dissipation and Variability in Electrical Breakdown of Carbon Nanotube Devices," Phys. Rev. B 82, 205406 (2010) link