Organizational Unit:
School of Materials Science and Engineering
School of Materials Science and Engineering
Permanent Link
Research Organization Registry ID
Description
Previous Names
Parent Organization
Parent Organization
Organizational Unit
Includes Organization(s)
ArchiveSpace Name Record
Publication Search Results
Now showing
1 - 5 of 5
-
ItemAntimony doped p-type zinc oxide for piezotronics and optoelectronics(Georgia Institute of Technology, 2015-11-04) Pradel, Ken CharlesZinc oxide is a semiconducting material that has received lot of attention due to its numerous proeprties such as wide direct band gap, piezoelectricity, and numerous low cost and robust methods of synthesizing nanomaterials. Its piezoelectric properties have been harnessed for use in energy production through nanogenerators, and to tune carrier transport, birthing a field known as piezotronics. However, one weakness of ZnO is that it is notoriously difficult to dope p-type. Antimony was investigated as a p-type dopant for ZnO, and found to have a stability of up to 3 years, which is completely unprecedented in the literature. Furthermore, a variety of zinc oxide structures ranging from ultra-long nanowires to thin films were produced and their piezotronic properties were demonstrated. By making p-n homojunctions using doped and undoped ZnO, enhanced nanogenerators were produced which could see application in gesture recognition. As a proof of concept, a simple photodetector was also derived from a core-shell nanowire structure. Finally, the ability to integrate this material with other semiconductors was demonstrated by growing a heterojunction with silicon nanowires, and investigating its electrical properties. All this work together lays the foundation for a fundamentally new material that could see application in future electronics, optoelectronics, and human-machine interfacing.
-
ItemPatterned thin-film triboelectric generator for harvesting micro-meso scale ambient energy for kinematic sensing(Georgia Institute of Technology, 2015-07-20) Jing, QingshenHarnessing random micro-meso scale ambient energy (M2SAE), which is widely available in human motions, wind driven vibrations, water surface fluctuations, etc., is not only clean and sustainable, but it also enables self-powered sensors and devices to be realized. In my research, I have fabricated a case-encapsulated triboelectric generator (cTENG) based on the principles of sliding electrification for harvesting M2SAE from reciprocating motions. Patterned with multiple sets of grating electrodes and lubricated with polytetrafluoroethylene (PTFE) nanoparticles, cTENG generated an average effective output power of 12.2 mW over a 140 kΩ external load and a power density of 1.36 W/m2 at a sliding speed of 1 m/s. The cTENG can also be triggered by direct-applied forces, as well as, inertia forces to effectively capture ambient energy from vibrations of large amplitudes and low frequencies such as those arising in human motions and water surface fluctuations. Based on the success of the patterned cTENG, I have built a self-powered velocity sensor for either rectified linear or rotary motion by sourcing the energy from the triboelectric generator. Employing alternating Kapton-copper strips arranged in a spiral configuration wrapped on the inner and outer surfaces of two concentric cylinders, voltage assays for linear and rotary motions can be measured without the need for an external power source. The triboelectric generated output signals when integrated with a digital circuit and a microcontroller unit can be directly processed into remarkably stable, macro-scale output signals for measurements of (0.1-0.6) ms-1 +_ 0.5% for linear velocities and (300-700) rpm +_ 0.9% for rotary velocities. I have also fabricated a self-powered, thin-film motion direction sensor by harvesting the operational energy from a close-proximity triboelectrification of two surfaces in relative reciprocation. The mover made by coating a thin polytetrafluoroethylene film with a 2-column, specially arranged array of copper electrodes and the stator is made by coating the top and bottom surfaces of a thin polyimide film with a 2-column aligned array of copper electrodes placed in an alternating pattern. As the mover traverses over the stator, the electrodes in the mover actively generate electric signals of ±5 V to attain a peak power density of ≥ 65 mW/m2 at speeds of 0.3 ms-1. The prototype can be extend for 2-D motion direction sensing. The highly pliable sensor can be easily bent to spread over curved and uneven surfaces. Finally, I have demonstrated a quasi-static angular positioning sensor based on 4-channel encoded pattern on the electrification surface. The sensor consists of a rotator designed with 4-channel coding Cu foil material and a stator including electrodes covered with FEP (fluorinated ethylene propylene) film. Due to coupling effect of triboelectrification and electrostatic induction, the sensor generates electric output signals in response to mechanical rotating motion of an object mounted with the sensor. The sensor can read and remember the absolute angular position regardless being continuously monitored or segmented monitored. Velocity and acceleration can be calculated as well. Under a rotation speed of 100 rad min-1, the output voltage of the sensor reaches as high as 60 V. Angular resolution of 22.5° is achieved and can be further improved by increasing the number of channels. Triggered by the output voltage signal, the rotating characteristics of the steering wheel can be real-time monitored and mapped by being mounted to the sensor. My work represents the first successful attempt in harvesting M2SAE using a patterned triboelectric generator and then, using the harvested ambient energy to drive a kinematic sensor that is integrated with a commercial digital circuit for a dual-mode speed and direction sensing. I believe my pioneering demonstration of the applied triboelectric technology will have a huge impact in the industrial commercialization of self-powered devices and sensors.
-
ItemNanogenerators for mechanical energy harvesting and self-powered sensor networks(Georgia Institute of Technology, 2015-06-26) Lin, LongEnergy crisis and internet of things have attracted long term interests due to rapid development of modern society. In this regard, the invention of nanogenerators provide us new insights on scavenging wasted mechanical energy from the ambient environment, and convert kinetic agitations into electricity for powering electronic devices. Piezoelectric nanogenerators are based on the piezoelectric property of semiconductor nanowires. Vertical integration, proper selection of materials, and surface modifications have been applied to enhance its output performance. Triboelectric nanogenerators (TENG), on the other hand, work on the basis of contact electrification and electrostatic induction. Four fundamental working modes have been developed to accommodate different types of mechanical motions. A high output power density of 35.6 W/m2, an excellent energy conversion efficiency of up to 55%, and terrific output stability of over 300,000 cycles have been accomplished with the state-of-art TENG devices. The niche applications of the TENGs have been demonstrated for powering portable electronics toward the goal of fully-integrated self-powered system. Since the nanogenerators are enabled to convert mechanical input into electrical output signals, the information of mechanical stimuli (amplitude and frequency) can be retrieved through analyzing the output performance of the nanogenerators. In this way, nanogenerators were employed as self-powered/active sensors without an external power supply, and multiple functions could be achieved including pressure detection and motion sensing. Both static and dynamic pressure sensing was realized using the open-circuit voltage and short-circuit current from the TENG, respectively. A high sensitivity of 0.31 kPa-1 and a low detection limit of 2.1 Pa were also fulfilled. The integration of pressure sensor array for tactile imaging was further demonstrated for its potential application in electronic skin, human-machine interface, and security monitoring.
-
ItemPiezotronics as an electromechanical interfacing technology for electronic and optoelectronic applications(Georgia Institute of Technology, 2015-04-14) Wen, XiaonanInnovation on human-machine interfacing technologies is critical for the development of smart, multifunctional and efficient electronic/optoelectronic systems. The effect of piezotronics is a newly started field of study, which utilizes piezoelectric polarization that is mechanically induced inside a piezoelectric semiconductor to regulate electron transport across electronic contact interfaces. With the concept coined in 2006, many efforts have been contributed to studying the underlying physical mechanism of this effect as well as demonstrating various applications based on single nanowire piezotronic devices. This thesis selects ZnO as the material foundation and was started by firstly studying flexible, controllable and scalable synthesis methods for ZnO nanowires array and thin film. By replacing the use of random, individual nanowires with these materials, novel piezotronic and piezophototronic devices were designed, fabricated and tested to achieve the function of strain sensing, tactile imaging, piezo-enhanced photodetection and solar energy harvesting. The adoption of nanowires array and thin film materials over single nanowires leads to significant advantages in terms of scalable fabrication, industrial compatibility and broader functionality. By consistently going down this route, we believe that the field of piezotronics will eventually make revolutionary impact on MEMS, optoelectronics, multifunctional sensor networks, human-machine interfacing and so on.
-
ItemScanning probe microscopic study of piezotronics and triboelectrification for their applications in mechanical sensing(Georgia Institute of Technology, 2015-01-09) Zhou, YushengScanning probe microscopy was employed to characterize the piezotronic effect in both longitudinal and transverse force sensing modes in CdSe, and GaN nanowires, respectively. Both experimental results show exponential response of their conductivity change to applied forces. Theoretical models are also presented to explain this mechanism and quantify the relationship, where strain induced piezoelectric polarization changes the metal-semiconductor Schottky barrier height. An in-situ method based on SPM is developed to characterize the triboelectric process, including tribo-charge intensity, multi-cycle friction effect, as well as its surface diffusion. Beyond that, effect of external electric field was investigated as an approach to manipulate the polarization and intensity. Finally, a concept of self-powered motion sensing technology is developed and demonstrated experimentally with nanometer resolution, long working distance as well as high robustness. It provides a promising solution for application areas that need ultra-low power consumption devices.