Zinc Oxide is a wide band gap semiconductor with a relatively large exciton energy of 60 meV, and longitudinal optical phonon energy of 72 meV. ZnO can be grown in any nanostructure such as nanoribbons, nanowires, nanorods, films, core-shell, among others, to be implemented in a variety of applications improving the current state of the art. In our group, we have grown under metal-organic chemical vapor deposition (MOCVD), films, nanowires, nanorods and heterostructures with extraordinary crystal and optical quality. For instance, by adding Mg to ZnO, the energy band separation increases and shift to a lower wavelength. We have pushed the ZnO energy band gap to 4.17 eV by adding up to 30% of Mg, which makes it suitable for UV detection/laser. In addition to the optoelectronic applications, we have also used ZnMgO to growth ZnMgO/ZnO co-axial core-shell structures enhancing the gas sensing properties by inducing native defects at the ZnMgO-ZnO junction. As the lattice mismatch increase upon Mg mole fraction, for a core less than the critical layer, native defects raise from the built in-strain. The native defects work as donors that are released upon in contact with the gas.

At lower temperature, we have used hydrothermal synthesis to growth ZnO nanorods (NRs) in p-Si, SiO2, GaN and a flexible substrate. The flexible substrate is of high interest as it brings down cost and provides a platform for different application, especially when it comes to energy harvesting. For this matter, we fabricated a device using two flexible substrates with the NR sides facing each. As ZnO is a piezoelectric material, meaning that it can convert mechanical vibration into an electric potential, using a load of 0.17 kg/cm2 the device produced a maximum open-circuit voltage of 1.4 V (peak). The output voltage can be used to self-powered sensors such as gas and vibrations. It can also be used to recover energy from noisy environments.

The growth of vertically aligned nanorods at low temperature is very straightforward. However, when it comes to horizontally aligned nanowires (NWs) most reported horizontal NWs/NRs are grown by confining the growth along the surface using patterns, dislocations, and catalyst. A novel process has been developed by our group to grow horizontal nanowires using controlled hydrothermal synthesis. It is to be noted that unlike the standard practice of growing vertical NRs followed by pick-and-place technique to obtain horizontal nanostructures or by confining the growth along the surface using patterns, dislocations, and catalyst, the present technology allows the direct growth of horizontal nanowires. These nanowires are single crystals with high crystal quality and are used for ZnO memristors.

ZnO NWs

ZnMgO-ZnO Core-Shell

ZnO Nanorods

ZnO NRs via Sonochemistry

ZnO Memristor Crossbar

ZnO NWs-solar blind detector

Energy Harvesting

 

Publications:

• Abdiel Rivera, Anas Mazady and Mehdi Anwar, ZnMg/ZnO Core-Shell Structures for Gas Sensing, J. Hi. Spe. Ele. Syst. 24, 1550010 (2015)
• Abdiel Rivera, Anas Mazady and Mehdi Anwar, “Energy Harvesting Leveraging Piezoelectric Property of ZnO Nanorods”, J. Hi. Spe. Ele. Syst. 24, 1520013 (2015)
• Abdiel Rivera, Anas Mazady and Mehdi Anwar, “Optimized Growth of ZnO Nanowires and Nanorods Using MOCVD”, J. Hi. Spe. Ele. Syst. 24, 1520014 (2015)
• Anas Mazady, Abdiel Rivera, Kiarash Ahi and Mehdi Anwar, "Optical Parameters of ZnMgO/ZnO Core-Shell Structures in THz Regime", SPIE, Terahertz Physics, Devices and Systems IX: Advanced Applications in Industry and Defense, Baltimore, MD, April 20-24, 2015.
• Abdiel Rivera, Anas Mazady and Mehdi Anwar, “Co-axial Core-Shell ZnMgO/ZnO NWs”, Solid State Electronics, Vol. 104, pp.126-130, February 2015.
• Abdiel Rivera, John Zeller, Ashok Sood, and Mehdi Anwar, “A Comparison of ZnO Nanowires and Nanorods Grown Using MOCVD and Hydrothermal Processes”, Electron. Mater., Vol. 42, No. 5, pp. 894-900, May 1, 2013.
• Anas Mazady, Abdiel Rivera, and Mehdi Anwar, “Optical Parameter of Zn_1-xMg_xO Nanowires in THz Regime” Solid State Electronics, vol. 101, pp. 8-12, November 2014.
• Abdiel Rivera, Anas Mazady, Kiarash Ahi and Mehdi Anwar, "Variation of ZnMgO Properties upon Growth Technique in THz Spectrum",SPIE, Terahertz Physics, Devices and Systems IX: Advanced Applications in Industry and Defense, Baltimore, MD, April 20-24, 2015.
• Anas Mazady, Abdiel Rivera and Mehdi Anwar, “Optimization of Annealing Conditions for ZnO-based Thin Films Grown Using MOCVD”, MRS Proceedings, Vol 1675, 2014.
• Abdiel Rivera, Anas Mazady and Mehdi Anwar, “Low Temperature Growth of Horizontal ZnO Nanorods, MRS Proceedings, Vol. 1707, 2014
• Anas Mazady, Abdiel Rivera and Mehdi Anwar, “Effect of Annealing on Structural and Optical Properties of ZnO Nanowires”, MRS Proceedings, Vol 1675, 2014.
• Mehdi F. Anwar, Abdiel Rivera, Anas Mazady, Hung Chi Chou, John W. Zeller, and Ashok K. Sood, "ZnMgO Solar Blind Detectors: from Material to Systems", Proc. SPIE 8868, Infrared Sensors, Devices, and Applications III, 88680B, September 19, 2013.
• Abdiel Rivera,M Anas Mazady, John Zeller, Mehdi Anwar, Tariq Manzur, and Ashok Sood, "ZnO Nanowire Growth and Characterization for UV Detection and Imaging Applications",  SPIE 8711, Sensors, and Command, Control, Communications, and Intelligence (C3I) Technologies for Homeland Security and Homeland Defense XII, 871116, June 6, 2013.
• Abdiel Rivera, Mehdi Anwar, John W. Zeller, Tariq Manzur, Ashok K. Sood, "ZnO nanowire UV detector technology for marine boundary layer", SPIE Defense, Security, and Sensing, May 1, 2013, Baltimore, Maryland
• Abdiel Rivera, Anas Mazady, John Zeller, Mehdi Anwar, Tariq Manzur, and Ashok Sood, "MOCVD Growth of ZnO Nanowire Arrays for Advanced UV Detectors",  Soc. Optics Photonics,86260B-86260B-7, March 18, 2013.
• Abdiel Rivera, Anas Mazady, Mehdi Anwar, John W. Zeller, Tariq Manzur, Ashok K. Sood, " MOCVD growth of ZnO nanowires arrays for advanced UV detectors ", SPIE Photonic West, Conference Volume 8626, Feb 02, 2013 San Francisco, CA
• Abdiel Rivera; Aurora Edington; John Zeller; Mehdi Anwar, "Energy scavenging using ZnO nanorods grown on flexible substrates," Lester Eastman Conference on High Performance Devices (LEC), 2012 , vol., no., pp.1,4, 7-9 Aug. 2012, doi: 10.1109/lec.2012.6410973