Selected Publications
Terahertz-field-induced insulator-to-metal transition in vanadium dioxide metamaterial

Terahertz-field-induced insulator-to-metal transition in vanadium dioxide metamaterial

  • Here we report the observation of an insulator–metal transition in vanadium dioxide induced by a terahertz electric field. This is achieved using metamaterial-enhanced picosecond, high-field terahertz pulses to reduce the Coulomb-induced potential barrier for carrier transport. A nonlinear metamaterial response is observed through the phase transition, demonstrating that high-field terahertz pulses provide alternative pathways to induce collective electronic and structural rearrangements. The metamaterial resonators play a dual role, providing sub-wavelength field enhancement that locally drives the nonlinear response, and global sensitivity to the local changes, thereby enabling macroscopic observation of the dynamics. This methodology provides a powerful platform to investigate low-energy dynamics in condensed matter and, further, demonstrates that integration of metamaterials with complex matter is a viable pathway to realize functional nonlinear electro- magnetic composites.

  • Mengkun Liu, Harold Y Hwang, Hu Tao, Andrew C Strikwerda, Kebin Fan, George R Keiser, Aaron J Sternbach, Kevin G West, Salinporn Kittiwatanakul, Jiwei Lu, Stuart A Wolf, Fiorenzo G Omenetto, Xin Zhang, Keith A Nelson, Richard D Averitt, “Terahertz-field-induced insulator-to-metal transition in vanadium dioxide metamaterial”, Nature 487, 345–348 (19 July 2012).-pdf

A physically transient form of silicon electronics

A physically transient form of silicon electronics

  • A remarkable feature of modern silicon electronics is its ability to remain physically invariant, almost indefinitely for practical purposes. Although this characteristic is a hallmark of applications of integrated circuits that exist today, there might be opportunities for systems that offer the opposite behavior, such as implantable devices that function for medically useful time frames but then completely disappear via resorption by the body. We report a set of materials, manufacturing schemes, device components, and theoretical design tools for a silicon-based complementary metal oxide semiconductor (CMOS) technology that has this type of transient behavior, together with integrated sensors, actuators, power supply systems, and wireless control strategies. An implantable transient device that acts as a programmable nonantibiotic bacteriocide provides a system-level example.

  • Suk-Won Hwang, Hu Tao, Dae-Hyeong Kim, Huanyu Cheng, Jun-Kyul Song, Elliott Rill, Mark A Brenckle, Bruce Panilaitis, Sang Min Won, Yun-Soung Kim, Young Min Song, Ki Jun Yu, Abid Ameen, Rui Li, Yewang Su, Miaomiao Yang, David L Kaplan, Mitchell R Zakin, Marvin J Slepian, Yonggang Huang, Fiorenzo G Omenetto, John A Rogers, “A physically transient form of silicon electronics”, Science 337 (6102), 1640-1644, 2012. -pdf

Metamaterials on Paper as a sensing platform

Metamaterials on paper as a sensing platform

  • A paper-based metamaterial (MM) device, which can potentially be utilized for quantitative analysis in biochemical sensing applications is introduced. Proof-of-concept demonstrations are accomplished by patterning micrometer-sized MM reson¬ators on paper substrates and monitoring the resonance shift induced by placing different concentrations of glucose solution on the paper MM.

  • Hu Tao, Logan R Chieffo, Mark A Brenckle, Sean M Siebert, Mengkun Liu, Andrew C Strikwerda, Kebin Fan, David L Kaplan, Xin Zhang, Richard D Averitt, Fiorenzo G Omenetto, “Metamaterials on paper as a sensing platform”, Advanced Materials, 23: 3197–3201, 2011.-pdf

Microwave and Terahertz wave sensing with metamaterials

Microwave and terahertz wave sensing with metamaterials

  • We have designed, fabricated, and characterized metamaterial enhanced bimaterial cantilever pixels for far-infrared detection. Local heating due to absorption from split ring resonators (SRRs) incorporated directly onto the cantilever pixels leads to mechanical deflection which is readily detected with visible light. Highly responsive pixels have been fabricated for detection at 95 GHz and 693 GHz, demonstrating the frequency agility of our technique. We have obtained single pixel responsivities as high as 16,500 V/W and noise equivalent powers of 10−8 W/Hz1/2 with these first-generation devices.

  • Hu Tao, Emil A Kadlec, Andrew C Strikwerda, Kebin Fan, Willie J Padilla, Richard D Averitt, Eric A Shaner, X Zhang, “Microwave and terahertz wave sensing with metamaterials”, Optics Express Vol. 19, Issue 22, pp. 21620-21626 (2011). -pdf

Reconfigurable terahertz metamaterials

Reconfigurable terahertz metamaterials

  • We demonstrate reconfigurable anisotropic metamaterials at terahertz frequencies where artificial “atoms” reorient within unit cells in response to an external stimulus. This is accomplished by fabricating planar arrays of split ring resonators on bimaterial cantilevers designed to bend out of plane in response to a thermal stimulus. We observe a marked tunability of the electric and magnetic response as the split ring resonators reorient within their unit cells. Our results demonstrate that adaptive metamaterials offer significant potential to realize novel electromagnetic functionality ranging from thermal detection to reconfigurable cloaks or absorbers.

  • Hu Tao, AC Strikwerda, K Fan, WJ Padilla, X Zhang, RD Averitt, “Reconfigurable terahertz metamaterials”, Physical Review Letters. 103, 147401, 2009.-pdf

A metamaterial absorber for the terahertz regime

A metamaterial absorber for the terahertz regime: Design, fabrication and characterizatio

  • We present a metamaterial that acts as a strongly resonant absorber at terahertz frequencies. Our design consists of a bilayer unit cell which allows for maximization of the absorption through independent tuning of the electrical permittivity and magnetic permeability. An experimental absorptivity of 70% at 1.3 terahertz is demonstrated. We utilize only a single unit cell in the propagation direction, thus achieving an absorption coefficient α=2000 cm-1. These metamaterials are promising candidates as absorbing elements for thermally based THz imaging, due to their relatively low volume, low density, and narrow band response.

  • Hu Tao, Nathan I Landy, Christopher M Bingham, Xin Zhang, Richard D Averitt, Willie J Padilla, “A metamaterial absorber for the terahertz regime: Design, fabrication and characterization”, Optics Express 16, 7181-7188 (2008).-pdf