Syntheses, Analyses and Applications of 2D Materials and Their Heterostructures

There has been a growing interest in two dimensional (2D) crystals beyond graphene, facilitating novel electronic and optoelectronic devices. We demonstrate the growth of TMD homobilayers with well-ordered stacking angles by controlling edge structures of the underlying TMD layer. We work on the valleytronic properties of CVD-grown WS2 bilayers that maintain the spin-valley locking in AB-stacked WS2 bilayers and inversion symmetric AA' bilayers. In addition, we demonstrate direct in-situ growth of metal-atom doped TMDs, toward a new class of room-temperature van der Waals ferromagnets at a priori large-scale. Other related projects include modeling to prevent the anomalies encountered in topographic images of TMD monolayers in dynamic atomic force microscopy, and elucidating the effect of TMD surfaces and their geometric arrangements on cellular morphology and adhesion. If our growth and nanofabrication strategy could be developed to be highly reliable and high fidelity, it could have a large impact on the future research and commercialization of TMD-based devices..


Tunable Wetting and Oil Separation using Smart Surfaces

We investigate and utilize smart polymer functional surfaces using dodecylbenzenesulfonate-doped polypyrrole (PPy(DBS)). We demonstrate a novel in situ control of droplet pinning on the polymer surface, enabling the control of droplet adhesion from strongly pinned to extremely slippery (and vice versa). The pinning of organic droplets on the surfaces is dramatically controlled in situ, presenting great potential for manipulation and control of liquid droplets for various applications, including oil separation, water treatment, and anti-bacterial surfaces. In addition, we demonstrate controlled lateral actuation of organic droplets on PPy(DBS) electrodes in an aqueous environment. The adhesion of the organic droplets on the surfaces dramatically switches in situ (i.e., without the removal of liquid droplets), presenting great potential for in situ manipulation and control of liquid droplets for various applications, including lab-on-chip technologies, oil separation, and water treatment.


Flexible and Stretchy Electrodes

Skin-attachable electronic devices can be subjected to various lateral strains via stretching, bending, and distortion, while the devices must provide reliable outputs under pressure orthogonally applied to the surface. Our facile technique enables the partial-embedding of vertically aligned carbon nanotubes in polydimethylsiloxane, which are stable under both stretching and bending (flexibility) for long-cyclic testing. The devices (e.g., pressure sensors) made using this process are insensitive to these lateral strains induced by mechanical deformation (such as stretching, bending, twisting, and wrinkling). Stretchable electrodes will have applications in the fields of wearable electronics, flexible photovoltaics (e.g., rolled-up displays), self-powered wearable optoelectronics, and electronic skins.

Representative Invited Presentation slides

Functional Nanomaterials Conference (Hangzhou, China) 2018

MSE Colloquium, Columbia University, 2014

NASA Goddard Space Flight Center, 2013

SPIE Conference (Baltimore, MD) (2009)

Keynote at InterPACK Conference (Vancouver, Canada) 2007

Funded Projects

2D Material-based Heterostructures (Funded by US Army): This project is to develop 2D materials for sensing elements using graphene toward developing matter wave interferometers.

Carbon Nanotube-based Sensors for Munition (Funded by US Army): This project is to develop stretchable strain gauges fabricated via a partial-embedding of vertically aligned carbon nanotubes in polydimethylsiloxane. This stretchable device can be used for several applications including wearables and electronic skins.

Rejuvenating Conjugated Polymer Membranes for Oily Water Treatment (Funded by ACS PRF): This project is to investigate self-cleaning of surfactant-doped conjugated polymer membranes and the relationship between the interface and permeation dynamics in several types of membranes.

Graphene Microstructures for Photodetectors (Funded by NSF and AFOSR): This project is to investigate the graphene microribbon arrays for applications in infrared detectors. We demonstrated fully-suspended CVD-grown graphene microribbon arrays that are dominated by photoelectric effect.

Tunable Wetting on Smart Polymers for Microfluidics (Funded by NSF): The goal of this research is to achieve controlled manipulation of liquid droplets on PPy electrodes for ultra-low voltage lab-on-a-chip devices. This investigation represents a pathfinder study aimed at future research and development in the areas of bio and energy applications.

Nanotechnology Exposure for Undergraduate Students (NUE-NEXUS) (Funded by NSF): The primary goal of this program is to create a nexus between nanotechnology and undergraduate engineering education at Stevens to expand understanding of nanotechnology and its applications to a broad undergraduate student population.

Atomic Lattice Imaging of Graphitic Materials for Advanced Nanoelectronics and Nanosensing Systems (Funded by AFOSR): This project funds the purchase of a high-resolution scanning probe microscope (SPM), capable of imaging in ambient conditions, to directly support the needs of current federally funded research programs.

Nanoimprint Lithography for Nanoscience Research and Education based on Low-Dimensional Materials (Funded by NSF): This grant funds the acquisition of a Nanoimprint Lithography System, a whole-wafer nanoimprinter for thermoplastic resins that has high-resolution and high-throughput capabilities.

Carbon-based Electron Wave Interferometer for Chip-Scale Gyroscopes for Guided Gun Launched Munitions and Missiles (US Army ARDEC): This project is to explore a chip-scale inertial gyroscope technology based on nanoscale processing and characterization techniques that meet the requirements of guided projectile and missile applications.

Ultra-Low Leak Rate Piezoelectrically actuated Microvalves for Controlled Sampling by Mass Spectrometers (NASA GSFC IRAD) (PI: Balvin, NASA Goddard Space Flight Cener): This project is to develop piezoelectrically actuated microvalves for controlled sampling by mass spectrometers for NASA applications.

Graphene as Transparent Conductive Electrodes for High Density Focal Plane Assemblies (NASA GSFC IRAD) (PI: Li, NASA Goddard Space Flight Center): This project is to develop graphene growth technology and help GSFC to build the CVD system to grow graphene.

Micromachined Piezoelectric Multi-layer Actuators for Cryogenic Adaptive Optics (NASA SBIR Phase I and II) (PI: Jiang, TRS Technologies): This project is to develop micromachined piezoelectric actuators for cryogenic Adaptive Optics toward NASA applications.

Single Electronic Memory Devices based on Carbon Nanotube Quantum Dots (Funded by AFOSR: This project is to investigate carbon-based transistor devices. Quantum dot-based electron transistor devices were successfully fabricated and demonstrated.

EH Yang Research at JPL (1999-2006) (Presentation Slides)

  • Inchworm microactuator (Funding: National Reconnaissance Office, NASA): 2001~2005
  • MEMS Adaptive optics (Funding: Center for Adaptive Optics, JPL Director's Research and Development Fund, DARPA/LASSO): 1999~2006
  • Actuated membrane development (Funding: National Reconnaissance Office): 2003~2004
  • Piezoelectric microvalve (Funding: NASA Code R Enabling Technology Thrust): 2001~2004 (Market Analysis)