Research

In this project, our group aims to develop a large-area intrinsically stretchable electronic system comprising monolithically integrated sensors and display elements, fabricated entirely using a low-cost printing process. Such a system can be considered as a smart fabric, which is extremely lightweight, can be stretched by at least 50% to allow conformable coverage of curved surfaces, and capable of displaying information and sensing various stimuli such as pressure, strain, temperature, light, etc. Such a system could find a wide range of applications in consumer electronic devices such as stretchable display, wearable electronics for health monitoring, biomedical devices, and soft robotics areas.

Key Publications:

• L. Cai, S. Zhang, Y. Zhang, J. Li, J. Miao, Q. Wang, Z. Yu, C. Wang, “Direct Printing for Additive Patterning of Silver Nanowires for Stretchable Sensor and Display Applications“, Advanced Materials Technologies, Vol. 3, 1700232, 2018.
• S. Bade, X. Shan, P. Hoang, J. Li, T. Geske, L. Cai, Q. Pei, C. Wang, Z. Yu, “Stretchable Light-Emitting Diodes with Organometal Halide Perovskite-Polymer Composite Emitters“, Advanced Materials, Vol. 29, 1607053, 2017.
• S. Zhang, L. Cai, W. Li, J. Miao, T. Wang, J. Yeom, N. Sepulveda, C. Wang, “Fully-Printed Silver Nanoparticle Based Strain Gauges with Record High Sensitivity“, Advanced Electronic Materials, Vol. 3, 1700067, 2017.
• L. Cai, S. Zhang, J. Miao, Z. Yu, C. Wang, “Fully-Printed Stretchable Thin-Film Transistors and Integrated Logic Circuits“, ACS Nano, Vol. 10, 11459–11468, 2016. 
• L. Cai, C. Wang, “Carbon Nanotube Flexible and Stretchable Electronics“, Nanoscale Research Letters, Vol. 10, 320, 2015. (Review Paper)

We develop various types of electronic inks in-house for scalable fabrication of electronic devices and circuits on both elastic and plastic substrates.

Key Publications:

• L. Cai, S. Zhang, Y. Zhang, J. Li, J. Miao, Q. Wang, Z. Yu, C. Wang, “Direct Printing for Additive Patterning of Silver Nanowires for Stretchable Sensor and Display Applications“, Advanced Materials Technologies, Vol. 3, 1700232, 2018.
• S. Zhang, L. Cai, W. Li, J. Miao, T. Wang, J. Yeom, N. Sepulveda, C. Wang, “Fully-Printed Silver Nanoparticle Based Strain Gauges with Record High Sensitivity“, Advanced Electronic Materials, Vol. 3, 1700067, 2017.
• S. Zhang, L. Cai, T. Wang, J. Miao, N. Sepulveda, C. Wang, “Fully Printed Flexible Carbon Nanotube Photodetector“, Applied Physics Letters, Vol. 110, 123105, 2017.
• L. Cai, S. Zhang, J. Miao, Z. Yu, C. Wang, “Fully-Printed Stretchable Thin-Film Transistors and Integrated Logic Circuits“, ACS Nano, Vol. 10, 11459–11468, 2016. 
• L. Cai, S. Zhang, J. Miao, Z. Yu, C. Wang, “Fully-Printed Foldable Integrated Logic Gates with Tunable Performance Using Semiconducting Carbon Nanotubes“, Advanced Functional Materials, Vol. 25, 5698–5705, 2015.
• P. H. Lau, K. Takei, C. Wang, Y. Ju, J. Kim, Z. Yu, T. Takahashi, G. Cho, A. Javey, “Fully-Printed, High Performance Carbon Nanotube Thin-film Transistors on Flexible Substrates“, Nano Letters, Vol. 13, 3864–3869, 2013.
• P. Chen, Y. Fu, R. Aminirad, C. Wang, J. Zhang, K. Wang, K. Galatsis, C. Zhou, “Fully Printed Separated Carbon Nanotube Thin Film Transistor Circuits and Its Application in Organic Light Emitting Diode Control“, Nano Letters, Vol. 11, 5301–5308, 2011.

Our group studies a variety of 2-dimensional semiconductors such as black phosphorous and transition metal dichalcogenides that are atomically-thin. We explore their electronic and optoelectronic applications as high-performance transistors, sensors, photodetectors, infrared imagers, and so on.

Key Publications:

• J. Miao, B. Song, Z. Xu, L. Cai, S. Zhang, L. Dong, C. Wang, “Single Pixel Black Phosphorus Photodetector for Near-Infrared Imaging“, Small, Vol. 14, 1702082, 2018.
• J. Miao, Z. Xu, Q. Li, A. Bowman, S. Zhang, W. Hu, Z. Zhou, C. Wang, “Vertically Stacked and Self-Encapsulated van der Waals Heterojunction Diodes Using Two-Dimensional Layered Semiconductors“, ACS Nano, Vol. 11, 10472–10479, 2017.
• J. Miao, B. Song, Q. Li, L. Cai, S. Zhang, W. Hu, L. Dong, C. Wang, “Photothermal Effect Induced Negative Photoconductivity and High Responsivity in Flexible Black Phosphorus Transistors“, ACS Nano, Vol. 11, 6048–6056, 2017.
• J. Miao, L. Cai, S. Zhang, J. Nah, J. Yeom, C. Wang, “Air-Stable Humidity Sensor Using Few-Layer Black Phosphorus“, ACS Applied Materials & Interfaces, Vol. 9, 10019-10026, 2017.
• J. Miao, S. Zhang, L. Cai, C. Wang, “Black Phosphorus Schottky Diodes: Channel Length Scaling and Application as Photodetectors“, Advanced Electronic Materials, Vol. 2, Article 1500346, 2016.
• J. Miao, S. Zhang, L. Cai, M. Scherr, C. Wang, “Ultrashort Channel Length Black Phosphorus Field-Effect Transistors“, ACS Nano, Vol. 9, 9236–9243, 2015.

In collaboration with Nelson Sepulveda at Michigan State University, we have demonstrated that it is possible to combine smart materials with complementary advantages to achieve close-to-ideal photothermal actuators (devices that convert energy from light into mechanical work) with high efficiency, fast response, and high energy density. In addition, we also study devices that can realize bi-directional conversion between mechanical energy and electrical energy. Examples include a flexible thin patch that can be used as a nanogenerator to harvest energy from human motion, as well as being operated in the opposite direction as a flexible thin-film loudspeaker when electrical signals are applied. The above energy conversion devices may find applications in wearable devices or as a propulsion mechanism for micro-sized robots.

Key Publications:

• W. Li, D. Torres, R. Diaz, Z. Wang, C. Wang, Z. Wang, N. Sepulveda, “Nanogenerator-based dual-functional and self-powered loudspeaker/microphone thin patch for flexible electronics“, Nature Communications, Vol. 8, 15310, 2017.
• W. Li, D. Torres, T. Wang, C. Wang, N. Sepulveda, “A Flexible and Biocompatible Polypropylene Ferroelectret Nanogenerator (FENG): on the path toward wearable devices powered by human motion“, Nano Energy, Vol. 30, 649–657, 2016.
• T. Wang, D. Torres, F. E. Fernandez, C. Wang, N. Sepulveda, “Maximizing the Performance of Photothermal Actuators by Combining Smart Materials with Supplementary Advantages“, Science Advances, Vol. 3, e1602697, 2017.
• T. Wang, D. Torres, F. E. Fernandez, A. J. Green, C. Wang, N. Sepulveda, “Increasing Efficiency, Speed, and Responsivity of Vanadium Dioxide Based Photothermally Driven Actuators Using Single-Wall Carbon Nanotube Thin-Films“, ACS Nano, Vol. 9, 4371–4378, 2015.
• X. Zhang, Z. Yu, C. Wang, D. Zarrouk, J.-W. T. Seo, J. C. Cheng, A. D. Buchan, K. Takei, Y. Zhao, J. W. Ager, J. Zhang, M. Hettick, M. C. Hersam, A. P. Pisano, R. S. Fearing, A. Javey, “Photoactuators and motors based on carbon nanotubes with selective chirality distributions“, Nature Communications, Vol. 5, 2983, 2014.

Two review papers about our early work on carbon nanotube electronics: 

• C. Wang, K. Takei, T. Takahashi, A. Javey, “Carbon Nanotube Electronics – Moving Forward“, Chemical Society Reviews, Vol. 42, 2592–2609, 2013.
• B. Liu, C. Wang, J. Liu, Y. Che, C. Zhou, “Aligned carbon nanotubes: from controlled synthesis to electronic applications“, Nanoscale, Vol. 5, 9483–9502, 2013.

We have demonstrated heterogeneous integration of various types of nanomaterials-based electronic devices for “system-on-plastic” applications. Examples include user-interactive electronic skin, full-color AMOLED display, integrated circuits, and high speed (ft >100 GHz) transistors built on ultrathin flexible substrates.

Key Publications: 

• C. Wang, D. Hwang, Z. Yu, K. Takei, J. Park, T. Chen, B. Ma, A. Javey, “User-interactive electronic-skin for instantaneous pressure visualization“, Nature Materials, Vol. 12, 899–904, 2013.
• T. Takahashi, Z. Yu, K. Chen, D. Kiriya, C. Wang, K. Takei, H. Shiraki, T. Chen, B. Ma, A. Javey, “Carbon Nanotube Active-Matrix Backplanes for Mechanically Flexible, Visible Light and X-Ray Imagers“, Nano Letters, Vol. 13, 5425–5430, 2013.
• C. Wang, J.-C. Chien, H. Fang, K. Takei, J. Nah, E. Plis, S. Krishna, A. M. Niknejad, A. Javey, “Self-Aligned, Extremely High Frequency III-V Metal-Oxide-Semiconductor Field-Effect Transistors on Rigid and Flexible Substrates“, Nano Letters, Vol. 12, 4140–4145, 2012.
• C. Wang, J.-C. Chien, K. Takei, T. Takahashi, J. Nah, A. M. Niknejad, A. Javey, “Extremely Bendable, High-Performance Integrated Circuits Using Semiconducting Carbon Nanotube Networks for Digital, Analog, and Radio-Frequency Applications“, Nano Letters, Vol. 12, 1527–1533, 2012.

We have developed a self-aligned T-gate platform for fabricating high-performance short channel RF transistors with minimized parasitic capacitance using carbon nanotubes, graphene, and 2D III-V nanomembranes.

Key Publications: 

• C. Wang, J.-C. Chien, H. Fang, K. Takei, J. Nah, E. Plis, S. Krishna, A. M. Niknejad, A. Javey, “Self-Aligned, Extremely High Frequency III-V Metal-Oxide-Semiconductor Field-Effect Transistors on Rigid and Flexible Substrates“, Nano Letters, Vol. 12, 4140–4145, 2012.
• Y. Che, A. Badmaev, A. Jooyaie, T. Wu, J. Zhang, C. Wang, K. Galatsis, H. A. Enaya, C. Zhou, “Self-Aligned T-gate High-Purity Semiconducting Carbon Nanotube RF Transistors Operated in Quasi ballistic Transport and Quantum Capacitance Regime“, ACS Nano, Vol. 6, 6936–6943, 2012.
• A. Badmaev, Y. Che, Z. Li, C. Wang, C. Zhou, “Self-Aligned Fabrication of Graphene RF Transistors with T-Shaped Gate“, ACS Nano, Vol. 6, 3371–3376, 2012.
• C. Wang, A. Badmaev, A. Jooyaie, M. Bao, K. L. Wang, K. Galatsis, C. Zhou, “Radio Frequency and Linearity Performance of Transistors Using High-Purity Semiconducting Carbon Nanotubes“, ACS Nano, Vol. 5, 4169–4176, 2011.

We were one of the first to report a highly-scalable, low-cost, and solution-based platform for wafer-scale deposition of high purity semiconducting carbo nanotube thin film back in 2009. This material platform was subsequently used in numerous device applications including both p-type and n-type thin-film transistors, CMOS integrated circuits, RF electronics, display electronics, transparent electronics, flexible electronics, and printed electronics. 

Key Publications: 

• C. Wang, J.-C. Chien, K. Takei, T. Takahashi, J. Nah, A. M. Niknejad, A. Javey, “Extremely Bendable, High-Performance Integrated Circuits Using Semiconducting Carbon Nanotube Networks for Digital, Analog, and Radio-Frequency Applications“, Nano Letters, Vol. 12, 1527–1533, 2012.
• J. Zhang, C. Wang, C. Zhou, “Rigid / Flexible Transparent Electronics Based on Separated Carbon Nanotube Thin-film Transistors and their Application in Display Electronics“, ACS Nano, Vol. 6, 7412–7419, 2012.
• J. Zhang†, Y. Fu†, C. Wang†, P. Chen, Z. Liu, W. Wei, C. Wu, M. Thompson, C. Zhou, “Separated Carbon Nanotube Macroelectronics for Active Matrix Organic Light-Emitting Diode Displays“, Nano Letters, Vol. 11, 4852–4858, 2011. († Equal contribution)
• J. Zhang†, C. Wang†, Y. Fu, Y. Che, C. Zhou, “Air-Stable Conversion of Separated Carbon Nanotube Thin-Film Transistors from P-type to N-type using Atomic Layer Deposition of High-κ Oxide and Its Application in CMOS Digital Circuits“, ACS Nano, Vol. 5, 3284–3292, 2011. († Equal contribution)
• C. Wang, J. Zhang, C. Zhou, “Macroelectronic Integrated Circuits Using High-Performance Separated Carbon Nanotube Thin-Film Transistors“, ACS Nano, Vol. 4, 7123–7132, 2010.
• C. Wang, J. Zhang, K. Ryu, A. Badmaev, L. Gomez, C. Zhou, “Wafer-Scale Fabrication of Separated Carbon Nanotube Thin-Film Transistors for Display Applications“, Nano Letters, Vol. 9, 4285–4291, 2009.

CVD growth of aligned carbon nanotubes with well-defined electronic type (metallic vs. semiconducting) and chirality was achieved. 

Key Publications: 

• J. Liu†, C. Wang†, X. Tu, B. Liu, L. Chen, M. Zheng, C. Zhou, “Chirality-Controlled Synthesis of Single-Wall Carbon Nanotubes Using Vapour-Phase Epitaxy“, Nature Communications, Vol. 3, 1199, 2012. († Equal contribution)
• Y. Che†, C. Wang†, J. Liu, B. Liu, X. Lin, J. Parker, C. Beasley, H.-S. P. Wong, C. Zhou, “Selective Synthesis and Device Applications of Semiconducting Single-Walled Carbon Nanotubes Using Isopropanol as Feedstock“, ACS Nano, Vol. 6, 7454–7462, 2012. († Equal contribution)

In this project, we have demonstrated wafer-scale CVD growth and transfer of high density aligned carbon nanotubes for high-performance field-effect transistors and CMOS integrated circuits.

Key Publications: 

• C. Wang, K. Ryu, A. Badmaev, J. Zhang, C. Zhou, “Metal Contact Engineering and Registration-Free Fabrication of CMOS Integrated Circuits Using Aligned Carbon Nanotubes“, ACS Nano, Vol. 5, 1147–1153, 2011.
• C. Wang, K. Ryu, L. Gomez, A. Badmaev, J. Zhang, X. Lin, Y. Che, C. Zhou, “Synthesis and Device Applications of High-Density Aligned Carbon Nanotubes Using Low-Pressure Chemical Vapor Deposition and Stacked Multiple Transfer“, Nano Research, Vol. 3, 831–842, 2010.
• K. Ryu†, A. Badmaev†, C. Wang†, A. Lin, N. Patil, L. Gomez, A. Kumar, S. Mitra, H.-S. P. Wong, C. Zhou, “CMOS-analogous wafer-scale nanotube-on-insulator approach for submicron devices and integrated circuits using aligned nanotubes“, Nano Letters, Vol. 9, 189–197, 2009. († Equal contribution)
• C. Wang, K. Ryu, A. Badmaev, N. Patil, A. Lin, S. Mitra, H.-S. P. Wong, C. Zhou, “Device Study, Chemical Doping and Logic Circuits Based on Transferred Aligned Single-Walled Carbon Nanotubes“, Applied Physics Letters, Vol. 93, 033101, 2008.